Studies in Surface Science and Catalysis 98 ZEOLITE SCIENCE 1994: RECENT PROGRESS AND DISCUSSIONS
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S t u d i e s in S u r f a c e S c i e n c e a n d C a t a l y s i s Advisory Editors: B. Delmon and J.T. Yates Vol. 98
ZEOLITE SCIENCE 1994: RECENT PROGRESS AND DISCUSSIONS S u p p l e m e n t a r y Materials to the 10th International Zeolite Conference, Garmisch-Partenkirchen, Germany, J u l y 17-22, 1994
Editors H.G. Karge
Fritz Haber Institute of the Max Planck Society, Berlin, Germany
J. Weitkamp
University of Stuttgart, Stuttgart, Germany
1995 ELSEVIER
Amsterdam - - Lausanne-- New York-- Oxford ~ Shannon m Tokyo
ELSEVIER SCIENCE B.V. Sara Burgerhartstraat 25 P.O. Box 211, 1000 AE Amsterdam, The Netherlands
ISBN 0-444-82308-5 91995 Elsevier Science B.V. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher, Elsevier Science B.V., Copyright & Permissions Department, P.O. Box 521, 1000 AM Amsterdam, The Netherlands. Special regulations for readers in the U.S.A. - This publication has been registered with the Copyright Clearance Center Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923. Information can be obtained from the CCC about conditions under which photocopies of parts of this publication may be made in the U.S.A. All other copyright questions, including photocopying outside of the U.S.A., should be referred to the copyright owner, Elsevier Science B.V., unless otherwise specified. No responsibility is assumed by the publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. This book is printed on acid-free paper. Printed in The Netherlands
Table of Contents
Preface ................................................................................................................................
vii
List o f Sponsors .................................................................................................................
viii
Welcome Address .................................................................................................................
x ~
Breck Award 1994 .......................................................................................................
xvn
IZA Award 1994 ............................................................................................................
xviii
Election o f Professor R. M. Barrel F. R. S., as Honorary President of the Imemational Zeolite Association ...........................................................................................................
xix
After Dinner Speech given by C. T. O'Connor at the Congress Banquet .............................
xx
List o f Recent Research Reports .........................................................................................
xxv
Recent Research Reports ..................................................................................................... 1 Full-Length Paper "Alkylation of aniline with methanol on Beta and EMT zeolites exchanged with alkaline cations" by P. R. Had Prasad Rao, P. Massiani and D. Barthomeuf ............................................................................................................
287
Index of Authors of Recent Research Reports ..................................................................... 295 Index of Subjects of Recent Research Reports .................................................................... 300 Transcripts o f the Discussions .............................................................................................
304
List o f Participants of the 10th IZC ..................................................................................... 452
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vii
PREFACE
The 10th International Zeolite Conference was held from July 17 to 22, 1994 at Garmisch-Partenkirchen, Germany. The attendance was unexpectedly high and very encouraging with respect to the future perspective of the scientific field to which the conference was devoted. About 950 active and 50 accompanying attendees were welcomed by the Organising Committee. The Proceedings of the Conference were handed out at the beginning of the Conference. As far as one can judge from the immediate response to the presentations as well as from that to the Proceedings, the conference seemed to be a remarkable scientific success. We are now able to issue a supplementary volume which comprises in the first chapter various items, viz. (i) a list of the sponsors to whom the organisers are particularly grateful because of their significant support; (ii) the welcome address; the phrasings of the BRECK AWARD and the IZA AWARD which was first awarded at the 10th International Zeolite Conference; (iii) the address on the occasion of the appointment of the first Honorary President of the International Zeolite Association (IZA), Professor R. M. Barrer, and, finally, the marvellous after dinner speech by Professor Cyril O'Connor from the University of Cape Town. The larger part of the supplementary volume presents the full texts of the Recent Research Reports, which were presented as posters, and the Discussions of all the lectures and posters which were submitted to the editors. One full paper is also included, viz. the paper "Alkylation of aniline with methanol on Beta and EMT zeolites exchanged with alkaline cations" by P. R. Had Prasad Rao, Pascale Massiani and Denise Barthomeuf because, due to a regrettable error, one page was missing in the version published in the Proceedings. Finally, the supplementary volume also contains a complete list of the participants. The editors sincerely hope that not only the attendees of the 10th IZC, but also any colleagues interested in the field will enjoy reading the book and draw some benefit from it.
Berlin and Stuttgart, May 1995
Hellmut G. Karge
Jens Weitkamp
viii
10th International Zeolite Conference July 17- 22, 1994
List of Sponsors The Organizing Committee gratefully acknowledges support by the following institutions and companies: 1
Deutsche Forschungsgemeinschaft, Bonn, Germany
2
Max-Planck-Gesellschaft zur Fiirderung der Wissenschaften e. V.,
Mfmchen, Germany 3
Air Products and Chemicals, Inc., Allentown, PA, USA
4
Altamira Intruments, Incorporated, Pittsburgh, PA, USA
5
BASF Aktiengesellschaft, Ludwigshafen, Germany
6
Bayer AG, Leverkusen, Germany
7
Biosym Technologies GmbH, M~nchen, Germany
8
CEM GmbH, Kamp-Lintfort, Germany
9
Coulter Electronics GmbH, Krefeld, Germany
10
CU Chemie Uetikon AG, Uetikon, Switzerland
11
Degussa AG, Frankfurt am Main, Germany
12
DuPont Company, Wilmington, DE, USA
13
Elsevier Science Publishers B. V., Amsterdam, The Netherlands
14
Engeihard Corporation, lselin, NJ, USA
15
Exxon Chemical International, Brussels, Belgium
16
Fonds der Chemischen Industrie, Frankfurt am Main, Germany
17
Grace GmbH, Worms, Germany
18
Haldor Topme A/S, Lyngby, Denmark
19
Hemmer Repetitorium, Wftrzburg, Germany
20
Henkel KGaA, Di;tsseldorf, Germany
21
Hiden Analytical Limited, Warrington, England
22
Hoechst AG, Frankfurt am Main, Germany
List of Sponsors (continued) 23
Hills AG, Marl, Germany
24
Institut Frangais du P~trole, Rueil-Malmaison, France
25
Merck & Co., Inc., Whitehouse Station, NJ, USA
26
Molecular Simulations, Cambridge, England
27
Perkin-Elmer GmbH, Oberlingen, Germany
28
Quantachrome GmbH, Eurasburg, Germany
29
SKW Trostberg Aktiengeselischaft, Trostberg, Germany
30
Statoil Petrochemicals and Plastics, Stathelle, Norway
31
Siid-Chemie AG, Mfmchen, Germany
32
Texaco Incorporated, Beacon, NY, USA
33
The Dow Chemical Company, Midland, MI, USA
34
The PQ Corporation, Valley Forge, PA, USA
35
UOP Research and Development, Des Plaines, 1L, USA
36
VAW aluminium AG, Schwandorf, Germany
Welcome Address by Jens Weitkamp, Chairman of the Organizing Committee (held on July 18, 1994)
Dear Participants, Distinguished Guests, Friends,
Welcome to the 10th International Zeolite Conference! This is the day we have been looking forward to since the decision of the Council of the International Zeolite Association in early 1991, to have the 10th International Zeolite Conference held in this country, in the beautiful City of Garmisch-Partenkirchen. Our experience with the local authorities and people were so good that we felt a strong temptation to apply again for the 12th International Zeolite Conference, again with Garmisch-Partenkirchen as the venue.
In fact, as many of you will have recognized, this is a truly European rather than a German congress. Not only is our hosting city located fight in the heart of Europe, within walking
distance of Austria and within hiking distance of Italy; but the organization, which extended over years, was done by a team of European experts. Our deeply felt thanks go to a number of colleagues who - upon our request - spontaneously agreed to shoulder large parts of the burden of the organizational work:
Dr. Koos Jansen from Delft University of Technology, The Netherlands, and Dr. Michael StOcker from SINTEF in Oslo, Norway, organized the Summer School on Zeolites held last Thursday, Friday and Saturday in Wildbad Kreuth, some 60 km away from here, and as we understand from the participants, they did an excellent job. Professor Johannes Lercher, who recently moved from Vienna University of Technology in Austria to Twente University at Enschede, The Netherlands, took over the responsibility for the program offered to accompanying persons. And Professor Carmine Colella with his team from the University of Naples, Italy, organized the Post-Conference Field Trip to the Latium and Umbria Regions m Central Italy. Ladies and gentlemen, organizing large international congresses has lately become more difficult, at least in Europe, since both governmental institutions and industrial companies are getting increasingly reluctant to sponsor the flood of scientific conferences. The Organizing Committee appreciates the generous support by
xii -
-
the Max Planck Society, the German Science Foundation (Deutsche Forschungsgemeinschatt) and the State Government of Bavaria.
In addition, an impressive number of industrial companies from many countries were willing to support the 10th IZC, and we express our gratitude to these industrial sponsors whose names are given on posters displayed at various locations in this building and on a list handed out to every participant during registration. This Conference was organized in close contact with the International Zeolite Association, and IZA appointed Jan van Hooff as official IZA observer. We enjoyed very much the cooperation with Jan, and we thank him for his active support of this Conference. Let me now briefly address the scientific program and the procedures of paper selection. The Organizing Committee is grateful to a number of renowned experts from the international zeolite community who agreed to present plenary lectures on key issues of zeolite science and technology: Synthesis and structure analysis are becoming increasingly important and will be dealt with by Peter Jacobs and Lynne McCusker, respectively. The progress in diffusion inside microporous solids will be reviewed by Lovat Rees. And various aspects of the use of zeolites as catalysts ranging from ab-initio calculations to industrial and environmental catalysis will be covered by Werner Haag, Joachim Sauer, .loop Naber and Mazakazu Iwamoto. Ladies and gentlemen, I confess that there was much concern within the Organizing Committee about the repercussions of the IZA's decision to shorten the intervals between successive Conferences from three to two years. We had a number of worst case scenarios in our drawers, but fortunately, when the deadline for submission of papers approached in the 37th week of 1993, we could abandon all these scenarios. Not only was the response to our call for papers overwhelming, but - to our surprise - the authors were willing to meet the deadline.
xiii 100
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27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. Calendar week
Still more importantly, the originality and quality of many abstracts were outstanding, and our Sub-Committee for Paper Selection chaired by Dr. Ernst Ingo Leupold and Dr. Lothar Puppe had a very difficult task. The Organizing Committee is deeply indebted to the European experts who spent a huge amount of their precious time on ranking and selecting the submitted abstracts:
E.I. Leupold,
Hoechst AG, Frankfurt, Germany
L. Puppe,
Bayer AG, Leverkusen, Germany
C. Baerlocher,
ETH Zurich, Switzerland
G. Bellussi,
Eniricerche S.p.A., San Donato, Italy
E. Gallei,
BASF AG, Ludwigshafen, Germany
H. Kessler,
E.N.S.C.M., Mulhouse, France
P. Kleinschmit,
Degussa AG, Hanau, Germany
P. Krings,
Henkel KGaA, D0sseldorf, Germany
W. Mortier,
Exxon Chemical Int., Machelen, Belgium
M. StOcker,
SINTEF, Oslo, Norway
K.K. Unger,
University of Mainz, Germany
xiv
6oot
Conference
Papers
Recent Research Reports
- 300
527
243
5OO
- 200
400 139
300 200
- 100
100 0
Subm. Rej. Posters Oral
Subm. Rej.
Acc.
0
Our thanks furthermore go to all those who submitted a contribution. In fact, more than 500 Conference papers were submitted out of which we accepted ca. 100 for oral and ca. 180 for poster presentation. Let me emphasize here again that no quality difference exists between papers presented orally and those displayed as posters, and you will detect no difference at all in the Conference Proceedings you received here in Garmisch-Partenkirchen. In our opinion Elsevier Science Publishers did an excellent job, and we convey our thanks to Elsevier for their efficiency. Another flood of abstracts submitted for presentation as posters in the Recent Research Report Session this afternoon, reached us in March, April and May of this year, and we were able to accept slightly more than 50 % of these. Ladies and gentlemen, one of the very early and most important duties of an Organizing Committee is the selection of a good logo. We were, in fact, extremely lucky in this respect: An exciting new structure was discovered in Europe by our colleagues Lynne McCusker, Christian Baerlocher and Henri Kessler and their coworkers. Our Organizing Committee is grateful to these outstanding scientists not only for having made the discovery, but also for having made it at the fight time for our purposes and for giving us every support, together with Walter Meier, in translating the structure into a suitable logo.
As we believe, it teaches and reminds us of a number of different things, namely (i)
how aesthetic zeolitic structures are,
(ii)
that super- or ultra-large pore zeolites are certainly among the thrust areas of ou science,
Oil)
that, in the heart of our beloved science, considerable darkness continues to exist an, many questions are still obscure.
(iv)
Finally, it wiU accompany us during the whole Conference week with its four-leafe, clover.
xvi The Organizing Committee sincerely hopes that the four-leafed clover will contribute to make this Conference efficient, fi~itful and successful and wishes you a week fifll of luck and happiness. I declare the lOth International Zeolite Conference opened.
Jens Weitkamp
xvii
10th IZC
Garmisch- Partenkirchen, July 17- 22, 1994
Breck Award 1994 In 1992
C.T. Kresge M.E Leonowicz W.J. Roth J.C. Vartuli
and
J.S. Beck of the Mobil Research and Development Corporation reported a significant breakthrough in the synthesis of porous materials. The Mobil group successfully prepared the first ordered mesoporous silicate and aluminosilicate materials containing pores in the range of 16 to 100 A. This startling discovery was accomplished by using liquid crystal "templates". That is surfactant molecules that can self-assemble into ordered structures which interact with the inorganic species to form the final composite material. The Mobil work is the first to use organized organic species as "templates" rather than single molecules as is common in molecular sieve synthesis. The impact of the discovery of the Mobil is large since it: i)
created a new type of material
ii)
developed a new synthetic strategy
iii)
opened new areas of technology for catalysis, separation and guest-host chemistry.
and
The novelty and generality of these concepts provide research directions for years to come.
Thus the efforts of the Mobil group deserve the 1994 Breck Award.
xviii
IZA A W A R D 1994
A decision was made by the IZA Council to create an IZA Award that would be given to an individual who would serve as an ambassador for the IZA to the world zeolite community. This person will be responsible for educating other scientists about zeolite molecular sieves, and a grant will be given to assist them m this task. The mechanism for arranging visits by the Recipient wiLl be handled by a representive of the IZA Council. The individual chosen for this award is being honored by the IZA for long term committments and contributions to Zeolite Science.
At this 10th IZC, the first IZA Award will be presented to an individual, whose name is almost synonymous with zeolites and molecular sieves:
Edith M. Flanigen Edith's Synthesis Group has been called "The Discovery Group". They were adwarded the First Don Breck Award given at the 6th IZC for the discovery of the AIPO4 Molecular Sieve family of material and have gone on beyond that to SAPOs, MeAPOs, MeAPSOs, Sulfide materials and much, much more. She has enthusiastically led her group at Union Carbide and UOP, and we feel that she will be the ideal zeolite ambassador for the IZA to the world.
Hellmut G. Karge IZA President
Roland von Ballmoos IZA Secretary
xix
10th IZC
G a r m i s c h - Partenkirchen, July 17 - 22, 1994
Honorary President The IZA Council honours
Professor Richard Barrer for his outstanding contributions to zeolite science by awarding him the title of Honorary President of the IZA.
With great appreciation.
Hellmut G. Karge
Roland von Ballmoos
IZA President
IZA Secretary
XX
AFTER-DINNER SPEECH PRESENTED AT THE BANQUET OF THE 10TH INTERNATIONAL Z E O L I T E C O N F E R E N C E , G A R M I S C H - P A R T E N K I R C H E N , GERMANY, JULY 1994. by Cyril T. O'Connor Ladies and Gentlemen I hope that you will sympathise with me being requested to deliver an after dinner speech at the end of a long hard-working conference week. When Hellmut asked me to fulfil this duty he suggested that something light hearted would be appropriate. I suppose that after he and the Organising Committee had recovered from the fits of laughter they must have had when they read some of the hilarious contents of the abstracts I submitted they must have immediately concluded that here was an excellent candidate for an equally hilarious after dinner speech. Anyway, I suppose that one of the advantages of this conference slot compared the poor people who landed the early afternoon siesta or graveyard sessions is that my paper hasn't had to be refereed and there is no question time at the end. In preparing a few words for this evening it soon became apparent to me that one difficulty in trying to be humorous in front of such an international audience is that humour does not easily cross geographical boundaries. Each country does have their country bumpkin - in South Africa we call him van der Merwe, in Ireland he's called Paddy and so on. One species of the human race, however, which does lend itself at all times to being laughed at and about are politicians. Before I relate the following story let me remind you that many of you who know me well are very much aware of the fact that I am a great lover of Germany, German life and German hospitality. One distinctive feature of German hospitality is that it is most usually accompanied with excellent wine or beer. A visit to Germany is unfulfilled if one hasn't enjoyed the excellent white wines in particular or the wide variety of beer for which Germany is so famous. One of the most famous of these is, of course, Pils which originates from Czechoslovakia. Any newcomer to the wonders of a Pils soon finds out that it takes a long time to pour a pils. My story revolves around an invitation extended some years ago by a famous Indian Maharajah to President Ronald Reagan, Mrs Margaret Thatcher and Chancellor Helmut Kohl. It was an interesting palace except that the swimming pool was permanently empty. Upon being quizzed on this matter the Maharaja informed his illustrious guests that the distinguishing feature of the pool was that as one stood at the edge ready to dive in one could call out the name of any liquid which one fancied and the pool would immediately be filled with this. Margaret Thatcher, being the lady, was first to take the plunge and just before she jumped in she called out "Guinness Stout". Immediately the pool was filled with marvellous stout even including the froth and upon leaving the pool it promptly drained. President Reagan repeated the trick except that he preferred Jack Daniels. Chancellor Kohl was last in and he fancied a
xxi Pils. Upon leaping into the pool to his dismay no liquid appeared and he bashed his head, rather sorely, on the bottom of the empty pool. Upon protesting to the Indian Prince at this shoddy treatment he was promptly reminded: "Herr Kohl, you of all people should know that it takes 8 minutes to pour a Pils". One of the wonderful privileges we all enjoy as researchers is that we belong to a unique family of friends and I always cherish the opportunity which attending a Conference such as this affords us all to renew old acquaintances as well as to forge new friendships. We are indeed all fortunate to have this opportunity which is one of the great privileges of a research career. Attending conferences can also of course be a source of some considerable humour. How many of you during this week may have stood at a poster wondering what on earth the authors were trying to convey. This experience always reminds me of the story of the famous artist, Pablo Picasso who was visited one day by an old friend. Pablo had been pondering over a new painting of his for hours and when asked by his friend as to the source of his concern, the old artist replied that he was troubled with the look of the nose on the face of the figure in the painting. When his friend simply pointed that he could surely simply touch it up a bit, Picasso replied: "That's exactly what I have been intending to do for the last three hours but the trouble is that I can't find the nose". Writers of scientific papers may be among the greatest perpetrators of the euphemism. Isaac Newton is quoted as having said that "False facts are highly injurious to the progress of science for they often endure long but false views if supported by some evidence do little harm for everyone takes great pleasure in proving their falseness". Of course the history of science is fiddled with wonderful examples of famous men making, with hindsight, incredible statements. Some wonderful examples of these which I enjoy quoting are: 1. "We hope that Professor Langley will not put his substantial greatness as a scientist in further peril by continuing to waste his time and the money involved in further airship experiments. Life is too short, and he is capable of services to humanity incomparably greater than can be expected to result from trying to fly ... For students and investigators of the Langley type there are more useful employments." (New York Times, Dec.10, 1903, editorial page). 2. "My personal desire would be to prohibit entirely the use of alternating currents. They are as unnecessary as they are dangerous ... I can therefore see no justification for the introduction of a system which has no element of permanency and every element of danger to life and property." (Thomas A. Edison 1889). 3. "I would much prefer to have Goddard interested in real scientific development than to have him interested in more spectacular achievements which are of less real value." (Charles A. Lindbergh to the Guggenheim Foundation, 1936). 4. "The biggest fool thing that we have ever done. The bomb will never go off and I speak as an expert in explosives." (Adm William Leahy to President Truman 1945).
xxii Often of course what scientists say in a paper and what they mean can be light years apart. I am indebted to an extract from the same book as that quoted earlier, viz. "A Random Walk in Science" for the examples of this phenomenon peculiar to research scientists often under severe pressure to generate papers to justify next years funding. When scientists say "A surprising finding" they mean "We barely had time to revise the abstract. Of course we fired the technician." When they say "We have a tentative explanation" they mean " I picked this up in a bull session last night". When they say "We didn't carry out the long-term study" they mean " We like to go home at 5pm. What do you think we are, slaves?" When they say " It is hoped that this work will stimulate further work in the field" they mean "This paper isn't very good but neither are any of the others in this miserable subject". When they say " Thanks are due to Joe Glotz for assistance with the experiments and to John Doe for valuable discussions" they mean that Glotz did all the work and Doe explained what it
meant". Anyone who has organised an International Conference will know that one of the more onerous duties which I am sure must have given Jens and his organising committee not a few sleepless nights is the worry over whether the books will balance at the end of the conference. If there's a problem in this regard then I have some good advice to give Jens - hire an accountant. Usually they don't have such delicate consciences and have incredible abilities at being able to show a loss as an incredible profit. They are masters at the an of manipulating the mass - or in their case money - balance. I think maybe I am being unfairly harsh on accountants and to prove that they are not all scoundrels you may have heard the story of the accountant who passed away and arrived at the gates of heaven. Shortly before he died the Pope died and our accountant friend found himself immediately behind the Pope in queue. When the Pope's turn came for his interview with St. Peter the accountant was astonished to see how roughly the Pope was treated and what poor accommodation he was given. When the accountant's turn came he was understandably very concerned about what his fate would be, especially since he hadn't led the most exemplary life. To his amazement St. Peter gave him royal treatment, laying on a chauffeur, giving him one of the plushest houses high on a hill overlooking, among others, all the popes. When at last he had a chance to speak he turned to St. Peter and expressed his amazement at how well he had been treated compared to the shoddy treatment afforded to the great Pope. To which St. Peter replied: "You know that Pope - we've got many more than 200 of his type up here and so we're used to them. We decided to give you special treatment since we were a little concerned as to how to handle you - you see you're the first accountant we've ever had here!!" Ladies and Gentlemen you will all agree with me that the Organising Committee of this years Conference - Jens Weitkamp, Hellmut Karge, Harry Pfeifer and Wolfgang H61derich - as well
xxiii
as the organisers of the pre-conference summer school - Koos Jansen, Michael StOcker, Gianther Engelhardt and J/Srg Karger - have done a marvellous job and we are all greatly indebted to them for the wonderful arrangements, both scientific and social, which have characterised the 1994 IZC. It crossed my mind that we could have some fun dreaming up appropriate Christmas presents for them and this idea was sparked by an article in the New Scientist in December 1993 in which readers were invited to suggest appropriate Christmas presents for various famous scientists past and present. Some of the more interesting ideas of presents were : 1. For Erwin Schr~dinger
a plain-wrapped gitt box marked "Guess?"
2. For Einstein
a visit by his great great grandchildren and a travelling clock without hands
3. For Stephen Hawking
mints with holes in the middle
4. For Isaac Newton
a crash helmet and an Apple computer
5. For Leonardo da Vinci
the address of a good patent lawyer
6. For the Trojans
an airport luggage scanner
7. For Icarus
some superglue and Araldite
8. For Niccolo Machiavelli
Margaret Thatcher's autobiography
9. For the Xerox R&D team
a very large waste paper basket
10.For Werner Heisenberg
a tie - no - maybe socks -um, I'm not sure??
What about our world of zeolites ..... for the proponents of molecular traffic control a motorbike, a canary for the first man to propose the cage structure? Ladies and Gentlemen before I close I would like to remind you all of the wonders which all experience from time to time of paging through the older volumes of the journals and suddenly coming across forgotten pearls of wisdom. I'm sure that so many of you here tonight who have attended many more Internatiol Zeolite Conferences that most of us, could relate many stories reminding us that much of what we heard this week has been done before. So in closing may I remind you of the intellectual wonders of that wonderful old friend of ours, the dinosaur. This poem first appeared in the Chicago Tribune in about 1920 and was later reprinted in the Journal of the Optical Society of America in May 1964. It is called the Triumph of Reason and was written by Bert Liston Taylor: Behold the mighty dinosaur Famous in pre-historic lore, Not only for his weight and length But for his intellectual strength. You will observe by his remains The creature had two sets of brains One in his head (the usual place), The other at his spinal base.
xxiv Thus he could reason a priori As well as a posteriori. No problem bothered him a bit He made both head and tail of it. So wise was he, so wise and solemn, Each thought filled just a spinal column. If one brain found the pressure strong It passed a few ideas along. If something slipped his forward mind 'Twas rescued by the one behind. And if in error he was caught He had a saving afterthought. As he thought twice before he spoke He had no judgement to revoke. Thus he could think without congestion Upon both sides of every question. Oh, gaze upon this model beast Defunct ten million years at least.
XXV
List of Recent Research Reports I. Synthesis RPO01
Synthesis and Characterization of Zeolites LZ-276 and LZ-277 ............................ 3
M. Sears, G. W. Skeels, E. M. Flanigen, C. A. Bateman, N. McGuire and R. All. Kirchner RP002
Zeolite Nu-1 Prepared from Near-Neutral Fluoride Aluminosilicate Gels .............. 5
RP003
Synthesis and Characterization of Transition-Metal-Incorporated Beta-Zeolites .... 7
J. Patarin, P. Caullet, B. Marler, A. C. Faust and 3,. L. Guth S.-H. Chien, Y. K. Tseng, A&. C. Lin and J. C. Her RP004
Synthesis, Characterization and Structure of SAPO-56, a New Member of the ABC Double-Six Ring Family of Materials with Stacking Sequence AABBCCBB ........................................................................................................
9
S. T. Wilson, N. K. McGuire, C. S. Blackwell, C. A. Bateman and R. M. Kirchner RP005
Synthesis and Characterization of CoAPO / CoAPSO-44 and CoAPO-5 ............. 11
RP006
Synthesis and Sorption Properties of the Zirconium Aluminophosphate Molecular Sieves ZrAPO-5 .................................................................................
U. Lohse, E. L6ffler, B. Parlitz and E. Schreier 13
,I. Kornatowski, M. Rozwadowski, W. Lutz, M. Sychev, G. Pieper, G. Finger and W. H. Baur RP007
Molecular or Supramolecular Templating: Defining the Role of Surfactant Chemistry in the Formation of M41S and Zeolitic Molecular Sieves... 15
J. S. Beck, J. C. Vartuli, G. J. Kennedy, C. T. Kresge, W. J. Roth and S. E. Schramm RP008
Synthesis and Characterization of Boron Containing MCM-41 ............................ 17
U. Oberhagemann, 1. Topalovic, B. Marler and H. Gies RP009
Synthesis of V and Ti Modified MCM-41 Mesoporous Molecular Sieves ............ 19
A. Sayari, K. M. Red@ and1. Moudrakowski RP010
Synthesis of Titanium Molecular Sieve ETS- 10 and ETS-4 ................................. 22
A. Nastro, D. T. Hayhurst and S. M. Kuznicki RP011
Preparation by the Sol-Gel Method of Raw Materials for the Synthesis of Ti Containing Zeolites .............................................................................................
M. A. Uguina, G. Ovejero, R. van Grieken, D. P. Serrano and M. Camacho
24
xxvi RP012
The Synthesis and Structure of a New Layered Aluminium Phosphate [AIaP40~6]3" 3(CH3(CH2)3NH3) +. ......................................................................... 26
A. M. Chippindale, Q. Huo, R. H. Jones, .L. M. Thomas, R. Walton and R. Xu RP013
Synthesis and Characterization of (H3N-(CH2)6-NH3)4~ISP2062], a Dawson-Type Anion in a new Environment ..................................................... 28
M. HOlscher, U. Englert, B. Zibrowius and IV. F. HOlderich RP014
Growth of Zeolite A on Rutile, Sapphire and Quartz ........................................... 30
RP015
Preparation and Properties of Primary Leonhardite, (Na, K)-Exchanged Forms of Laumontite .......................................................................................... 32
RP016
Geoautoclave-Type Zeolitization in the Miocene Tufts, Meczek Mrs., SW-Hungary ......................................................................................................
A. Erdem-Senatalar, H. van Bekkum and j C. Jansen
A. Yamazaki, T. Shiraki, H. lshida and R. Otsuka 34
M. P61gari, 1. F6rizs, M. T6th, E. P~csi-Dondtth and Z. Mdtth~ RP017
The Synthesis of Zeolites from Dry Powders ...................................................... 36
R. Althoff, S. Reitmaier, B. Zibrowius, IE. Schmidt, K. K. Unger and F. Schftth RP018
Synthesis and Crystal Structures of the Decasils, A New Family of Porosils ........ 38
B. Marler, A. Grfmewald-Lftke and H. Gies RP019
New Templates for the Synthesis of Clathrasils ................................................... 40
G. van den Goor, C. Braunbarth, C. C. Freyhardt, J. Felsche and P. Behrens RP020
Synthesis of Zeolites in Anhydrous Glycol Systems ............................................. 42
N. B. Milestone, S. M. Hughesy, P. J. Stonestreet RP021
Synthesis of a Novel Microporous Crystal with Organic Group Covalently Bonded to the Skeleton ..................................................................... 44
K. Maeda, Y. Kiyozumiy, F. Mizukami RP022
Synthesis and Properties of Zeolite A with Salt-Containing Beta-Cages .............. 46
C. Gums, D. Reich, d. C. Buhl and W. Hoffmann
II. C h a r a c t e r i z a t i o n
RP023
Structural Characterization of SSZ-26 and SSZ-33 Molecular Sieves by High Resolution Electron Microscopy and Electron Diffraction .......................... 48
M. Pan and P. A. Crozier RP024
Electron Microscopic Study of Cloverite (CLO) ................................................. 50
0. Terasaki, T. Ohsuna, D. Watanabe, H. Kessler and C Schott-Darie RP025
HRM
Study of Pt-clusters on K-LTL Crystal Surfaces ..................................... 52
0. Terasaki, T. Ohsuna and D. Watanabe
~ XXVll
RP026
Location of Tb(III) Ions in Hydrated Y Zeolites by Luminescence Spectroscopy ......................................................................................................
54
J. S. Seo, C.-H. Pyun, C.-H. Kim, Y. S. Uh, W. S. Ahn and S. B. Hong RP027
Localization of Pt 2§ in NaX ................................................................................. 56
t~ Schnell, C Kirschhock and H. Fuess RP028
Characterization of SO2-Contaminated Cu-ZSM-5 Catalysts ............................... 58
C. L. Lengauer, E. Tillmanns and C. Plog RP029
Single Crystal Structure Analysis and Energy Minimizations of a HoZSM-5/p-Dichlorobenzene Complex at Low Sorbate Loading ...................... 61
H. van Koningsveld, J. C Jansen and A. J. M. de Man RP030
Single Crystal Structure Analysis of a High-Loaded Complex of H-ZSM-5 with p-Dichlorobenzene ...................................................................... 63
H. van Koningsveld and J. C. Jansen RP031
Characterization of Bimetallic Zeolite Supported Pt-Pd Catalyst by EXAFS, TEM and TPR ......................................................................................
65
T. Rades, M. Polisset-Thfom, J. Fraissard, R. Ryoo and C. Pak RP032
SIMS Investigation on Vanadium-Zeolite Interactions in Cracking Catalysts ....... 67
RP033
XPS and Adsorption of Dinitrogen Studies on Copper-Ion-Exchanged ZSM-5 and Y Zeolites ........................................................................................
K.-J. Chao, L.-H. Lin and L.-K Hon 69
G. Moretti, G. Minelli, P. Porta, P. Ciamelli and P. Corbo RP034
Model of adsorbed NO Molecules on Lewis Sites in Zeolites .............................. 71
A. Gutsze, M. Plato, F. Witzel and H. G. Karge RP035
A Combined EPR and NMR Study of Oxidation Sites in Dealuminated Mordenites .........................................................................................................
73
G. H. Estermannn, R. Crockett and E. Roduner RP036
Study ofNi-Containing SAPO-5 by ESR Spectroscopy and Hydrogenolysis of Thiophene ............................................................................. 75
A. Spojakina, N. Kostova and K Penchev RP037
Electron Spin Resonance and Electron Spin Echo Modulation in Spectroscopic Study of Pd(I) Location and Adsorbate Interactions in PdH-SAPO-34 Molecular Sieve .......................................................................... 77
RP038
Stability of the Co(II) Valence State in Aluminophosphate-5 Molecular Sieve to Calcination from Low Temperature Electron Spin Resonance ....................................................................................
J.-S. Yu, G.-H. Back, K Kurshev and L. Kevan
79
V. Kurshev, L. Kevan, D. Parillo and R. Gorte RP039
Characterization of Alkali Metal Cluster-Containing Faujasites by Thermal, IR, ESR, Multi-NMR and Test Reaction Studies .................................. 81
1. Hannus, 1. Kiricsi, A. Bdres, J. B. Nagy and H. FOrster
o~176 XXVlll
RP040
A Study of Cu-Y and Cu-Rho Zeolites by ~Z~ N-MR........................................ 83
A. G~d~on, J. Fraissard RP041
Direct Observation of Distributions of Mixed Clusters of Coadsorbed Species in Zeolite NaA ....................................................................................... 85
A. K. Jameson, C. J. Jameson, A. C. de Dios, E. Oldfield and R. E. Gerald H RP042
Studies on the Formation and Structure of the Molecular Cluster of (CdS)4 in Zeolite Y by in-situ IR and ~3Cd MAS NMR ..................................................... 87
RP043
NMR Studies of Hydrofluorocarbon-Zeolite Interactions .................................... 89
M. Qi, Z. Xue, Y. Zhang and Q. Li C. P. Grey and D. R. Corbm RP044
Aluminium-27 Double-Rotation NMR Investigations of SAPO-5 with Variable Silicon Content ................................................................................................... 91
M. Janicke, B. F. Chmelka, D. Demuth and F. Schflth RP045
29Si and 27A1MAS NMR Studies ofFaujasite / Gallium Oxide Catalysts ............. 93
Z. Olejniczak, S. Sagnowski, B. Sulikowski and J. Ptaszynski RP046
A New Assignment of the Signals in ~Na DOR NMR to Sodium Sites in Dehydrated NaY Zeolite .................................................................................... 95
H. A. M. Verhulst, W. J. J. Welters, G. Vorbeck, L. J. M. van de Ven, V. H. J. de Beer, R. A. van Santen and J. W. de Haan RP047
Study of Mordenite Acidity by 1H NMR Techniques: Broad-Line at 4K and High Resolution MAS at 300K. Comparison with HY. Bronsted Acidity Scale and Importance of Structure Defects ............................................. 97
L. Heeribout, V. Semmer, P. Batamack, C. Dor~mieux-Morin and J. Fraissard RP048
Spectroscopic Evaluation of the Relative Acidity of the Bridged Hydroxyl Species in Zeolites and the Isolated Hydroxyl Species in Amorphous Silica ............................................................................................... 99
E. Garrone, B. Onida, G. Spano, G. Spoto, P. Ugliengo and A. Zecchina RP049
One-Point Method for the Determination of Strength of Zeolite Acidity by Temperature Programmed Desorption of Ammonia Based on Trouton's Rule... 101
M. Niwa, N. Katada, M. Sawa and Y. Murakami RP050
Interaction of CO, H20, CH3OI-I, (CHH)20, CH3CN, H2S, (CH3)2CO, NH3 and Py with Brensted Acid Sites of H-ZSM-5" Comparison of the IR Manifestation .................................................................................................... 104
R. Buzzoni, S. Bordiga, G. Spoto, D. Scarano, G. Ricchiardi, C. Lamberti and A. Zecchina RP051
IR Characterization of Hydroxyl Groups in SAPO-40 ....................................... 106
E. Garrone, B. Onida, Z. Gabelica and E. G. Derouane
xxix RP052
FTIR Evidence ofPt Carbonyls Formation from Pt Metal Clusters in KL Zeolite ........................................................................................................
108
A. Yu. Stakheev, E. S. Shpiro, N. 1. Jaeger and G. Schulz-Ekloff RP053
IR Spectra of ~SO Exchanged HZSM-5 ............................................................. 110
F. Bauer, E. Geidel and Ch. Peuker RP054
Structure and Reactivity of Framework and Extraframework Iron in Fe-Silicalite as Investigated By Optical (IR, Ramart, DRS, UV-VIS) and EPR Spectroscopies .........................................................................................
112
F. Geobaldo, S. Bordiga, G. Spoto, D. Scarano, A. Zecchina, G. Petrini, G. Leofanti, G. Tozzola and M. Padovan RP055
Electrochemistry of Transition Metal Complexes Encapsulated into Zeolites ..... 114
C. A. Bessel and D. R. Rolison
I I I . Modification RP056
Structure and Properties of Active Species in Zinc Promoted H-ZSM-5 Catalysts ..........................................................................................
116
H. Berndt, G. Lietz, B. Lftcke and J. VOlter RP057
FT IR and FT Raman Studies of [B, Al]-Beta + Ga203 System ......................... 118
M. Derewinski, J. Krysciak, Z. Olejniczak, ,I. Ptaszynski and B. Sulikowski RP058
Faujasite-Hosted Nickel-Salen ..........................................................................
120
H. Meyer zu Altenschildesche and R. Nesper RP059
Modification of Aluminophosphate Molecular Sieves by Reaction with Organopalladium Complexes ............................................................................
122
K. M. Tearle and J. M. Corker RP060
Zeolite-Stabilized Rhodium Complexes with Molecular Nitrogen as Ligand ...... 124
H. Miessner RP061
Intrazeolitic Redox Chemistry of Manganese Prepared from Chemical Vapor Deposition of Mn2(CO)~0 on NaY .......................................................... 126
C. Dossi, S. Recchia, A. Fusi and R. Psaro RP062
Calcination of Pd(NH3)42§ and Reduction to Pd ~ in NaX and CsX Zeolites ........ 129
A. Sauvage, P. MassianL M. Briend, D. Barthomeuf and F. BozonVerduraz RP063
Ion Exchange in CoAPO-34 and CoAPO-44 ..................................................... 131
C. G. M. Jones, P~ Harjula and A. Dyer RP064
Characterization of ZSM-5 Samples Modified by Ions of Group IIIA ................ 133
L. Frunza, R. Russu, G. Catana, K Parvulescu, G. Gheorghe, F. Constantinescu and K 1. Parvulescu
XXX
RP065
Formation of Small Na and Na-M Alloys (M=Cs, Rb) Panicles in NaY Zeolite ...................................................................................................... 136
L. C. de M~norval, E. Trescos, F. Rachdi, F. Fajula, T. Nunes and G. Feio RP066
Attachment and Reactivity of Tin-Cobalt and Tin-Molybdenum Complexes in Y Zeolites and MCM-41 ............................................................................... 13 8
C. Huber, C. G. Wu, K. Moiler and T. Bein RP067
Simultaneous Exchange and Extrusion of Metal Exchanged Zeolites ................. 140
s N. Armor and T. S. Farris RP068
Modification of Layer Compounds for Molecular Recognition .......................... 142
T. Uematsu, M. lwai, N. lchilcuni and S. Shimazu
IV. Catalysis RP069
H-[B]-ZSM-5 as Catalyst for Methanol Reactions ............................................ 144
RP071
NOx Reduction with Ammonia over Cerium Exchanged Mordenite in the Presence of Oxygen. An IR Mechanistic Study ............................................ 146
E. Unneberg and S. Kolboe
E. Ito, E J. Mergler, B. E. Nieuwenhuys, P. M. Lugt, H. van Bekkum and C. 3/1. van den Bleek RP072
Catalytic Activity and Active Sites in Zeolite Catalysts for N20 Decomposition ................................................................................................. 148
E. B. Uvarova, S. A. Stakheev, L. M. Kustov and V. V. Brei RP073
Role of the Preparation and Nature of Zeolite on the Activity of Cu-Exchanged MFI for NO Conversion by Hydrocarbons and Oxygen ............. 150
G. Centi, S. Perathoner and L. Dall'Olio RP074
Selective Photooxidation of Abundant Hydrocarbons by 02 in Zeolites with Visible Light ..................................................................................................... 153
F. Blatter, H. Sun and H. Frei RP075
Applications of VAPO-5 in Liquid Phase Oxidation Reactions: Indications for the Presence of Different Vanadium Sites .................................................... 155
M. J. Haanepen and J.H. C. van Hooff RP076
Oxidation of Primary Amines over Titanium and Vanadium Silicates: Solvent Effect ................................................................................................... 157
d. S. Red@ and A. Sayari RP077
Room Temperature Oxidation of Methane to Methanol on FeZSM-5 Zeolite Surface ................................................................................................. 159
V. L Sobolev, A. S. Kharitonov, O. V. Parma and G. L Panov
xxxi
RP078
Oxidation and Ammoxidation of Picolines over VSAPO Molecular Sieves ........ 161
S. J. Kulkarni, R. Ramachandra Rao, M. S. Farsinavis, P. Kanta Rao and A. K Rama Rao RP079
Subrahmanyam,
Transition Metal Cations in Zeolites - a Catalyst for HDS Reactions ................. 163
R. Lugstein, O. E1Dusouqui, A. Jentys and H. Vinek RP080
A New Coupling Reaction Between ~-Pinene and Acetone Catalyzed by Beta Zeolites ................................................................................................ 165
J. Vital, J. C. van der Waal and H. van Bekkum RP081
Catalysis of a Liquid-Phase Diels-Alder-Reaction by Zeolites Y, A and Beta ..... 167
K. Bornholdt and H. Lechert RP082
Isomerization of n-Hexane over Platinum Loaded Zeolites ................................ 169
J.-K. Lee and H.-K. Rhee RP083
Benzene Alkylation with Ethanol over Shape Selective Zeolite Catalysts ........... 171
RP084
Effect of Aluminum Content at the External Surface of the ZSM-5 in the Disproportionation of Ethylbenzene .................................................................. 174
RP085
Methanol Conversion to Hydrocarbons over ZSM-5. Use of Isotopes for Mechanism Studies ........................................................................................... 176
RP086
Fischer-Tropsch Synthesis on Ruthenium Supported Titanium Silicate Catalysts .............................................................................................. 178
R. Ganti and S. Bhatia
M. J. B. Cardoso, E. L. Gomes and D. Cardoso
I. M. DaM, S. Kolboe and P. O. Ronning
R. Carli, C. L. Bianchi, R. Bernasconi, G. Frontini and K Ragami RP087
Synthesis and Catalytic Properties of Extra-Large Pore Crystalline Materials for n-Hexadecane Cracking ............................................................... 180
W. Reschetilowski, K. Roos, A. Liepold, M. StOcker, R. Schmidt, A. Karlsson, D. Akporiaye and E. MyhrvoM RP088
Conversion of Ethane into Aromatic Hydrocarbons on Zinc Containing ZSM-5 Zeolites - Role of Active Centers .......................................................... 182
A. Hagen and F. Roessner RP089
Conversion of n-Butane into Aromatic Hydrocarbons over H-ZSM-11 and Ga-ZSM-11 Zeolite Catalysts ................................................... 184
N. Kumar and L.-E. Lindfors RP090
Highly Dispersed Platinum Clusters in Zeolite Beta: Synthesis, Characterization and Catalysis in Liquid-Phase Hydrogenations ........................ 186
E. J. Creyghton, R. A. W. Grotenbreg, R. S. Downing and H. van Bekkum
xxxii RP091
The Effect of the Outer Surface Silylation on the Catalytic Properties ofFeZSM-11 .................................................................................................... 188
L. K Piryutko, 0. 0. Parenago, E. K Lunina, A. S. Kharitonov, L. G. Okkel and G. 1. Panov RP092
Hydrolysis of Disaccharides by Dealuminated Y-Zeolites .................................. 190
RP093
Adsorption and Catalysis Mechanism of CFC- 11 in NaX Zeolite ....................... 192
C. Buttersack and D. Laketic M. Hiraiwa, A. Yamazal#, R. Otsuka and T. Nagoya RP094
Effect of Basicity on the Catalytic Properties of Lead Containing Zeolites ......... 194
P. Kovacheva and N. Davidova RP095
Physico-Chemical and Catalytic Properties of Y Zeolites with High Modulus Obtained by Direct Synthesis. Preparation of Pilot Lot of NaY Zeolite with High Modulus ............................. 196
M. L Levinbuk, M. L. Pavlov, K B. Melnikov, B. K Romanovsky, Y. L Azimova and Y. A. Smorodinska
V. Adsorption and Diffusion RP096
Counter Diffusion of C8 Aromatics in Y Zeolite Pellets ..................................... 198
RP097
Motion of Cyclohexane in Compacted Zeolite NaX .......................................... 200
V. Moya Korchi and A. Methivier R. Stoclameyer
RP098
Mobility of Methane in Zeolite NaY: A Quasi-Elastic Neutron Scattering Study ............................................................................................... 202
H. Jobic and M. Bee RP099
Measurement of Diffusivity of Benzene in a Microporous Membrane by Quasi-Elastic Neutron Scattering and NMR Pulsed-Field Gradient Technique... 204
H. Jobic, M. Bee, J. Kdrger, C. Balzer and A. Julbe RP100
Zeolite MAP: A New Detergent Builder ........................................................... 206
C. J. Adams, A. Araya, S. I~. Carr, A. P. Chapple, P. Graham, A. R. Minihan and T. J. Osinga RP101
Use of Natural Zeolites for Liquid Radioactive Waste Treatment (Russian Experience) ........................................................................................ 208
N. F. Chelishchev RP102
Selectivity for Different Cations of Zeolite-Containing Hydrothermally Treated Fly Ash ................................................................................................ 211
K Berkgaut and A. Singer RP103
Experimental and Theoretical Studies of Water and Sulfur Dioxide Selective Adsorption in 3 A Zeolites .................................................................. 213
K. M. Shaw, M. Eic and R. Desai
xxxiii RP104
Permeation and Separation Behaviour of a Silicalite (MFI) Membrane .............. 215
F. Kapteijn, W. ,1. W. Bakker, G. Zheng, ,I. A. Moulijn and H. van Bekkum RP105
Adsorption and Polarization of Molecular Hydrogen and Light Paraffins on Cationic Forms ofZeolites: IR-Spectroscopic Study .................................... 217
L. A4. Kustov, V. B. Kazansky and A. Y. Khodakov RP106
Promising Air Purifications on Clinoptilolite ..................................................... 219
RP107
Mass Transfer Kinetics Measurements by Thermal Frequency Response Method ............................................................................................. 221
RP108
Study of Fast Diffusion in Zeolites Using Higher Harmonic Frequency Response Method ............................................................................ 223
R. W. Triebe, F. H. Tezel, A. Erdem-Senatalar and A. Sirkecioglu
V. Bourdin and Ph. Grenier
D. Shen and L. V. C. Rees RP109
Purification of Horseradish Peroxidase by the Use of Hydrophobic Zeolite Y .... 225
D. Klint, Z. Blum and H. Eriksson
VI. Theory and Modelling RPll0
Modelling Sorption in Zeolite NaA with Molecular Density Functional Theory ............................................................................................ 227
M. C. Mitchell, P. R. van Tassel, A. V. McCormick and H. T. Davis RPIll
Evaluation of Water Adsorption on Different Kinds of Zeolite through the Monte-Carlo Simulation ................................................................. 229
T. Inui, Y. Tanaka RPll2
Modelling Structural and Dynamical Properties of Silica Sodalites and Comparison to the Experiment ......................................................................... 232
RPll3
Computer Modelling of Iron-Containing Zeolites .............................................. 234
A. M. Schneider, J. Felsche and P. Behrens 17. G. Bell, D. W. Lewis and C. R. A. Catlow RPll4
Theoretical Investigation of the Thermal Decomposition of Neopentane near SIII Centers of Zeolite Y ........................................................................... 236
O. Zakharieva, M. Grodzicki and H. FOrster RPll5
Modelling of High Pressure Propene Oligomerisation Using Skeletal Groups ................................................................................................ 238
S. ,I. Seal),, D. M. Fraser and C. T. O'Connor RPll6
Investigation of the Dynamics of Benzene in Silicalite using Transition-State Theory .................................................................................... 240
R. Q. Snurr, A. T. Bell and D. N. Theodorou
xxxiv
RPII7
Ab Initio Study of the Interaction of Methanol with Bronsted Acid Sites of Zeolites ............................................................................................................ 242
RPll8
Ab Initio Derived Shell Model Potential for Modelling of Zeolites .................... 244
F. Haase and J. Sauer K.-P. Schrrder and J. Sauer RPll9
A Computer Simulation of Shape Selective Catalysis on Zeolites ...................... 246
E. Klemm, H. Seller and G. Emig RP120
Molecular Dynamic and Structural Studies of the Interactions of HFC-134 and CFC-13 with the Faujasite Framework ........................................ 248
J. P. Parise, L. Abrams, J. C. Calabrese, D. R. Corbin, J. M. Newsam, S. Levine and C. Freeman
VII. Structure RP121
The Framework Topology of Zeolite MCM-22 ................................................. 250
,I. A. Lawton, S. L. Lawton, M. E. Leonowicz and M. K. Rubin RP122
Optical Investigations of the Crystal Intergrowth Effects of the Zeolites ZSM-5 and ZSM-8 ........................................................................................... 252
C. Weidenthaler, R. X. Fischer, R. D. Shannon and O. Medenbach RP123
Is the VFI Topology Compatible with Tetrahedral AI? ...................................... 254
J. de Ohate, C. Baerlocher and L. McCusker RP124
Rietveld Refinement of the Tetragonal Variant of AIPO4-16 Prepared in Fluoride Medium ............................................................................ 256
J. Patarin, C. Schott-Darie, P. Y. Le Goff, H. Kessler and E. Benazzi RP125
Structure of the Microporous Titanosilicate ETS- 10 ......................................... 258
M. W. Anderson, O. Terasaki, T. Ohsuna, A. Philippou, S. P. MacKay, A. Ferreira, J. Rocha and S. Lidin RP126
Avoidance of 2 AI Atoms in a 5-Ring. A New Rule Complementing Loewenstein's Rule .............................................. 260
M. Kato, H. Araki and K. Itabashi RP127
The Crystal Structure of the New Boron Containing Zeolite RUB-13 ............... 262
S. Vortmann, B. Marler, P. Daniels, L Dierdorf and H. Gies RP128
Synthesis and Structure of a Novel Microporous Gallophosphate: Na2Gas(PO4)40(OH)3-4H20 ............................................................................. 264
M. P. Attfield, R. E. Morris, E. Gutierrez-Puebla, A. Monge-Bravo and A. K. Cheetham RP129
Structure Determination from Powder Diffraction Data of a New Clathrasil, TMA Silicate ................................................................................... 266
R. W. Broach, N. K. McGuire, C. C. Chao and R. M. Kirchner
XXXV
RP130
The Pore Structure of Alumina Pillared Clays Depending on the Kind of Intercalated Al-Cation ...................................................................................... 268
V. Seefeld, R. Trettin and W.. Gessner RP131
Synthesis and Structure Determination of a New Aluminophosphate from Fluoride Medium .............................................................................................. 270
N. Zabukovec, L. Golic and V. Kaucic RP132
04 Molecule in the Pore of Ca~-A Zeolite ......................................................... 272
T. Takaishi RP133
Structure and proper/ies of Cd4Se6+Nano Clusters Encapsulated in an Aluminate Framework .................................................................................. 274
E. Brenchley and3~1. T. Weller
VIII. New Materials RP134
A New One-Dimensional-Membrane: Aligned A1PO4-5 Molecular Sieve Crystals in a Nickel Foil ........................................................................... 276
M. Noack, P. K61sch, D. Venzke, P. Toussaint and J. Caro RP135
Synthesis of a Zeolite Membrane on the Mercury Surface ................................. 278
Y. KiyozumL K. Maeda and F. Mizukami RP136
Molecular Recognition in Zeolite Thin Film Sensors. Growth of Oriented Zeolite Films ...................................................................................... 281
S. Feng, Y. Yah and T. Bern RP137
Phase Formations in the Sinter Process of Cordierite / Mullite Ceramics from Mg-Exchanged Zeolites A, P and X ......................................................... 283
B. Rfldinger and R.X. Fischer RP138
Silicalite with Polycyanogene ............................................................................ 285
Y. Schumacher and R. Nesper
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Recent Research Reports
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1. Synthesis
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H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SYNTHESIS
M
9
Sears I !
~UOP,
G
AND
W
9
Tarrytown
2Dow C h e m i c a l 3Manhattan
9
CHARACTERIZATION
OF
ZEOLITES
Skeels I, E M Flanigen I C A and R.M. K i r c h n e r 3 9
Technical
Co.,
College,
1702
9
,
Center,
Building,
Department
9
Tarrytown, Midland,
MI
of Chemistry,
LZ-276
9
NY
AND
LZ-277
B a t e m a n I, N
.
M c G u i r e 2,
10591
48674 Bronx,
NY
ABSTRACT
A new zeolite, p o s s i b l y r e l a t e d to z e o l i t e Phi, has b e e n s y n t h e s i z e d in an o r g a n i c s y s t e m by m o d i f y i n g ~he p r o c e d u r e of J a c o b s and M a r t e n s for the s y n t h e s i s of z e o l i t e Phi. I, A more siliceous zeolite, d e s i g n a t e d LZ-276, can be p r o d u c e d from the same s y n t h e s i s gel by v a r y i n g c r y s t a l l i z a t i o n t e m p e r a t u r e 9 U l t i m a t e l y , a P h i - l i k e z e o l i t e was s y n t h e s i z e d in a t o t a l l y i n o r g a n i c s y s t e m w i t h p r o p e r t i e s ~ i m i l a r to LZ-276. This p r o d u c t was d e s i g n a t e d LZ-277. The c h e m i c a l and p h y s l c a i p r o p e r t i e s ~f LZ-276 ~nd LZ-277 are p r e s e n t e d and c o m p a r e d co the p r o d u c ~ d e s c r i b e d ~s z e o l i t e Phi by G r o s e and F l a n i g e n I and others. 2'3'4'5 INTRODUCTION
The f i r s t s y n t h e s i s of zeolite Phi u s e d a c i d - e x t r a c t e d , calcined c h a b a z i t e as the s i l i c a and a l u m i n a s o u r c e and t e t r a m e t h y l a m m o n i u m h y d r o x i d e as the o r g a n i c base. I The p r o d u c t was c h a r a c t e r i z e d as a l a r g e - p o r e z e o l i t e b a s e d on a d s o r p t i o n data b e c a u s e b o t h n e o p e n t a n e (6.2A radius) and p e r f l u o r o b u t y l a m i n e (10.2A) w e r e a d s o r b e d 9 The SiO2/Al203 r a t i o of the Phi p r o d u c t was 4.6. J a c o b s and M a r t e n s i n a d v e r t e n t l y m a d e Phi in t h e i r a t t e m p t to s y n t h e s i z e ZSM-20. 2 From c a t a l y t i c data, t h e y s u g g e s t e d t h a t t h e i r p r o d u c t was c o n s i s t e n t w i t h a l a r g e - p o r e m a t e r i a l 9 S y n t h e s i s of z e o l i t e Phi was also r e p o r t e d by Li et al. u s i n g t e t r a m e t h y l a m m o n i u m h y d r o x i d e and w a t e r g l a s s . 3 Franc. et al. s y n t h e s i z e d z e o l i t e Phi from a gel t h a t was s i m i l a r to that of J a c o b s and M a r t e n s but it a l s o c o n t a i n e d K§ 4 M. Davis et al. have also r e p r o d u c e d the J a c o b s and M a r t e n s and the F r a n c . et al. s y n t h e s e s of z e o l i t e Phi. 5 EXPERIMENTAL
The
synthesis 16.6SIO2
gel for LZ-276 is as follows: 9 A1203 : 7.8(TEA) 2~ : 1.3Na20
It d i f f e r s f r o m that 2 0 S i O 2 : AI203
: 465H2 O
s u g g e s t e d by J a c o b s and M a r t e n s , 9 9.3(TEA)2 9 : l.iNa20 : 558H20.
which
was:
The
gel
ratio
for LZ-277
is"
8SiO 2
9 AI203
: 1.6Na20
9 256H20
The LZ-276 gels were c r y s t a l l i z e d in T e f l o n - l i n e d s t a i n l e s s steel a u t o c l a v e s at both 100~ and" 125~ for from 1-21 days. The L Z - 2 7 7 gels were c r y s t a l l i z e d in Teflon bottles at 100~ for up to 45 days. A f t e r c r y s t a l l i z a t i o n , the samples were filtered, w a s h e d w i t h d e i o n i z e d water, and dried at room temperature. S y n c h r o t r o n X - r a y p o w d e r d i f f r a c t i o n and e l e c t r o n m i c r o s c o p y were used to c h a r a c t e r i z e the m a t e r i a l s . RESULTS
AND
DISCUSSION
W h e n c r y s t a l l i z e d at 100~ LZ-276 had a SIO2/A1203 r a t i o of 5.0. At 125~ the SIO2/A1203 ratio i n c r e a s e d to 7.7. W h e n c r y s t a l l i z e d at 100~ LZ-277 had a SiO2/AI203 ratio of 6.9. Adsorption measurements on both p r o d u c t s showed them to be small to m e d i u m p o r e m a t e r i a l s thal a d m i t t e d n - h y d r o c a r b o n s and r e j e c t e d the b r a n c h e d - c h a i n h y d r o c a r b o n s . The X - r a y p o w d e r d i f f r a c t i o n p a t t e r n s showed both b r o a d and sharp r e f l e c t i o n s for each synthesis product. R e l a t i v e i n t e n s i t i e s are quite d i f f e r e n t b e t w e e n the samples s y n t h e s i z e d at 100~ and 125~ and they are also d i f f e r e n t from the r e p o r t e d values of G r o s e and Flanigen, Li et al., and Franco et al. A l t h o u g h the X - r a y p o w d e r p a t t e r n s of all of the r e p o r t e d p r o d u c t s have many s i m i l a r d ( A ) spacings, they are not identical in size or shape. A d d i t i o n a l l y , the Franco et al. X-ray d i f f r a c t i o n p a t t e r n showed the p r e s e n c e of a second i m p u r i t y phase, a p o t a s s i u m a l u m i n o s i l i c a t e h a v i n g the X - C H A type structure. TEM-esuits 9n "Z-277 show the m a t e r i a l to be a x t r e m e l y faulted along c. A model for a highly faulted c h a b a z i t e ~as used in c o n j u n c t i o n w i t h the DIFFAX program. 6 A s i m u l a t e d p o w d e r d i f f r a c t i o n p a t t e r n u s i n g the DIFFAX program, c l o s e l y m a t c h e s the e x p e r i m e n t a l LZ276 and LZ-277 S y n c h r o t r o n data. CONCLUSIONS
A l t h o u g h a r e l a t i o n s h i p appears to exist b e t w e e n all of the m a t e r i a l s that are reviewed, there are d i s t i n c t i v e p r o p e r t y differences. Among these d i f f e r e n c e s are the t h e r m a l and h y d r o t h e r m a J stability, and the a d s o r p t i o n p r o p e r t i e s i n c l u d i n g pore size. However, it a p p e a r s that all of these m a t e r i a l s are v a r i a t i o n s of h i g h l y f a u l t e d chabazite. REFERENCES
I. Grose, R.W., and Flanigen, E . M . U . S . Pat. 4 124 686 (1978). 2. Jacobs, P.A., and Martens, J.A. Stud. Surf. Sci. Catal., 1987, 33, 15. 3. Li, H.Y., L i a n g J., Liu G.Y., and Ying M.L., Shiyou H u a q o n g ( P e t r o l e u m C h e m i c a l Engineering) 1990, 19, 148. 4. Franco, M.J., and P e r e z - P a r i e n t e , J. Zeolites 1991, ii, 349. 5. Davis, M.E., Lobo, R.F., and Annen, M . J . J . Chem. Soc. F a r a d a y Trans., 1992, 88(18), 2791. 6. Treacy, M.M.J., Deem, M.W., and Newsam, J.M., D I F F a X vi.76, (1991).
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
Zeolite Nu-1 prepared from near-neutral fluoride aluminosilicate gels J. Patarin, P. Caullet, B. Marler*, A.C. Faust and J.L. Guth Laboratoire de Mat6daux Min~raux URA-CNRS428 ENSCMU - UHA, 3, rue Alfred Werner, 68093 MULHOUSE Cedex, France * institut fQr Mineralogie, Ruhr Universit&t Bochum D-44780 Bochum, Germany SUMMARY The preparation of zeolite Nu-1 from near-neutral (pH ~8-10) fluoride-containing media was found to be only possible in a very narrow range of experimental conditions. The crystals display a pseudo-cubic morphology, with in some cases a size up to 40 I~m. The materials were characterized by conventional techniques. Three 19F nmr signals may be attributed to more or less mobile F- anions incorporated into the structure of Nu-1. INTRODUCTION This work deals with the synthesis and characterization of zeolite Nu-11 from nearneutral synthesis media containing F- ions. The organic templating agent is the usual Me4N + ion. The F- ions replace here the usual OH- ions as the mineralizing agents, according to the method developped in our laboratory 2. EXPERIMENTAL The starting mixture was prepared by first dissolving TMACI and NH4F in water. The combined or separated sources of alumina and silica were then added under stirring.After mixing, the reaction mixture (pH ~ 8-10) was transferred into a Teflon-lined stainless-steel autoclave and heated under static conditions at the desired temperature. After reaction (pH ~ 8-10), the products were filtered and washed with water and sometimes sonicated in order to separate the two main populations, i.e., MTN-type and Nu-1 crystals. After drying, the materials were checked by optical microscopy and powder X-ray diffraction before additional characterizations. RESULTS AND DISCUSSION
Influence of starting composition, temperature and heating time The preparation of pure zeolite Nu-l(experiment 1,Table 1) is only possible in a very narrow range of experimental conditions. Co-crystallisation of MTN-type clathrasil is most often observed.As previously seen for other phases synthesized from fluoride-containing media, the crystals(twinned) of zeolite Nu-l(Sample no.2) obtained here(Figure 1) are very large (20-501~m) in comparison to those prepared from alkaline fluoride-free gels (1-51~m).
Characterization of zeolite Nu- 1 A typical molar composition determined by chemical analysis is (Me4N+)1.25 (Me3NH+)o.29 (AIO2-) (SiO2)13.3.(F')o.41 .The organic species content was
determined from 1H liquid nmr spectroscopy after dissolution of the solid in HF. The presence of Me3NH + ions beside the Me4N + cations is clue to the hydrothermal decomposition of the latter. It appears that only part of the organic cations compensate the negative charges of the tetrahedrally coordinated aluminium atoms, the excess of cations being probably associated with the F- anions in ion-pairs. Table 1 : Description of the most representative syntheses (Starting molar ratio Me4NCI/SiO2=0.5 and NH4F/SiO2=I ) Exp. Mixture(molar ratios) T Time' Produ~s .... Crystal size (~ (d) (minor phases )* of Nu-1 (l~m) No. SIO2/AI203 H20/SiO2 1 16.7 9 170 5 Nu-1 20 2 16.7 9 170 42 MTN + (Nu-1)* 40 3 16.7 30 170 9 MTN + (Nu-1)* 20 4 16.7 9 200 1 MTN + / (NH4)3AIF6) ~ 5 16.7 9 200 3 FER + MTN / 6 _>25 9 170 6 MTN / The typical 19F nmr spectrum shown in Figure 2 (Sample no.2) displays several peaks. The broad signal located at about -140 ppm is attributed to the (NH4)3AIF6 impurity. not observed by XRD.The presence of such an impurity is confirmed by the corresponding 27AI MAS nmr spectrum ;indeed a very small signal at 0 ppm (hexacoordinated AI) is detected besides the main peak at 51 ppm (tetracoordinated AI). The other 19 F nmr signals at -116 (narrow), -73 (broad) and -58 (broad) ppm may be attributed to more or less mobile F- anions incorporated into the structure of Nu-l.Complete removal of the occluded organics is difficult to achieve by calcination. A partial collapse of the structure occurs after heating at 700~
-/,0
Figure 1. Micrograph of Nu-1
- 80
- 120
-
ppm / C FC 13
160
Figure 2. 19F nmr spectrum of Nu-1. 9side bands
REFERENCES
1 - Whittam, T.V. and Youll, B., US Pat. 4060590 (1977) assigned to ICI 2 - Guth, J.L. et al., in New Developments in Zeolite Science and Technology (Eds. Y. Murakami, A. lijima and J.W. Ward), Elsevier, Amsterdam, 1986, p. 121
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SYNTHESIS AND C H A R A C T E R I Z A T I O N OF TRANSITION-METALI N C O R P O R A T E D BETA-ZEOLITES Shu-Hua ChiCn*, Yung-Kuan Tseng, Maw-Chen Lin and Jen-Cheng Ho Institute of Chemistry, Academia Sinica, Taipei 11529, Taiwan, ROC. SUMMARY. The incorporation of transition-metal ions in Beta-zeolite was carried out by direct hydrothermal synthesis. The synthesized zeolites (H-, Ti- and V-Beta) were characterized by powder X-ray diffraction (XRD), scanning electron microscopy with x-ray energy dispersive analyzer (SEM/EDS), infrared (IR), UV-visible and electron paramagnetic resonance (EPR) spectroscopies. Both XRD and IR spectroscopic studies confirmed that the synthesized Ti-Beta carried out isomorphous substitution of Si by Ti in the Beta-zeolite framework. In case of V-Beta, the EPR studies evidenced the formation of VO 2+ species that seem to be located at the cation sites of the zeolites. INTRODUCTION.
The composite metal oxide-zeolite materials have attracted
attention because of their application as bifunctional catalysts. Due to their reducibility and notable catalytic properties, the zeolites with incorporated titanium and vanadium are of particular interest. The aims of the present study are to synthesize large pore titanium- and vanadium- containing Beta-zeolites by direct hydrothermal method, and to well characterize the synthesized materials for the promising catalytic selective oxidation reactions. EXPERIMENTAL. The transition-metal containing Beta-zeolites (V-Beta and TiBeta) were synthesized by direct hydrothermal method, using tetraethyl ammonium hydroxide (TEA-OH),
amorphous Aerosil silica, aluminum nitrate, and
tetrabutylorthotitanate or vanadium oxide. The procedures were as follows: an aqueous solution of tetrabutylorthotitanate (or vanadium oxide) was oxidized by hydrogen peroxide first, then added with the aqueous solution of TEA-OH, Aerosil silica and finally aluminum nitrate. The mixture was stirred in a water-bath at 80oc for 30 minutes before transferring to an autoclave, which was then heated in an oven at 140oc for 20 days. After cooling the autoclave, the sample was centrifuged at 10000 rpm, the solid was calcined at 550oc. The synthesized zeolites were well characterized by XRD, SEM/EDS, IR, Uv-vis and EPR spectroscopies. The atomic ratios in the three samples are as follows: A1/Si = 1/30 in H-Beta zeolites, Ti/AI/Si = 1/1/30 in Ti-Beta and V/AI/Si = 2/1/30 in V-Beta. RESULTS AND DISCUSSION.
We have successfully synthesized the H-form
(H-Beta), Ti- and V- containing Beta (Ti-Beta and V-Beta) zeolites
by direct
hydrothermal method with A1/Si atomic ratio = 1/30. The powder x-ray diffraction
patterns of the three samples show good crystalline structures in Beta-form zeolites. The SEM micrographs of the three samples exhibit almost the same morphologies of cubic shapes. The average particle sizes are about 0.6 lam, no visible differences among the three. For the synthesized Ti-Beta zeolite, there appears isomorphous substitution of Si by Ti in the zeolite Beta framework, which is confirmed by the increase in the interplanar d-spacing in Ti-Beta as compared to bare H-Beta zeolite. Estimation was taken from the most intense peak at 20 -- 22.60 of the powder x-ray diffraction pattern following the method given in Ref. [1]. The intense IR band at 960 cm "l also gives the evidence of the successful substitution. Besides, an X-ray microprobe examination demonstrated that the titanium is uniformly distributed within the crystal. The EPR spectrum (taken at 77 K) of the evacuated sample exhibits an intense symmetric signal at g = 2.0030 due to the F-center and the signals at gl = 2.025, gz = 2.010 and g3 = 2.0024 due to the presence of 02- in the orthohombic geometry. The typical EPR signals of 02 - were remarkably enhanced when contacting with low pressure oxygen. We have tried to reduce the sample in hydrogen at high temperature, but no visible Ti 3+ EPR signals were observed, while traces of 02- still appeared. The 02- is known to be responsible for the selective oxidation reaction. In the case of the synthesized V-Beta zeolite, it is surprising that no vanadium signal was detected by EDS. The vanadium ions might hide inside the zeolites. The powder XRD pattern of V-Beta is very similar to the H-Beta zeolite and the interplanar d-spacing shows only a subtle increase. The infrared spectrum is similar to that of H-Beta, gives no evidence on the formation of V=O bond or Si-O-V species. However, evacuation of the V-Beta sample at 500oc, it appeared a distinguished EPR spectrum at g~= 1.930 and gi = 1.989 with A~ = 201.1 G and A• = 84.4 G rising from 51V (I = 7/2), which is most likely to be due to VO 2§ in the cation sites [2]. The high temperature interaction between V205 and the zeolite must have taken place during calcination. Apparently, the incorporation of titanium ions into the framework of Beta zeolite is successful in the present hydrothermal synthesis, while vanadium ions seem to prefer to occupy the cation sites.
The consequential
performance may be due to the different electronic properties of both ions. We believe that the results are important and helpful in the catalytic processes occurring in these systems. References: 1. M. Taramasso, G. Perego and B. Notari, US pat. 4 410 501, 1983. 2. M. Petras and B. Wichterlova, J. Phys. Chem. 1992, 96, 1805.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SYNTHESIS, CHARACTERIZATION, AND STRUCTURE OF SAPO-56, A NEW MEMBER OF THE ABC DOUBLE-SIX RING FAMILY OF MATERIALS WITH STACKING SEQUENCE AABBCCBB. Stephen T. Wilson UOP Research and Development, 50 E. Algonquin Rd., Des Plaines, IL 60017 Nancy K. McGuire 1 Union Carbide Chemicals and Plastics Co., Inc., 777 Old Saw Mill River Rd., Tarrytown, NY 10591 C. Scott Blackwell and Charles A. Bateman UOP Research and Development, 777 Old Saw Mill River Rd., Tarrytown, NY 10591 Richard M. Kirchner Chemistry Department, Manhattan College, Bronx, NY 10471 SUMMARY
Three small pore (8-ring) structures have been synthesized using N,N,N',N'-tetramethyl-l,6-hexanediamine (TMHD) as the structure-directing agent, AIPO-17 or SAPO-17 (ERI), MAPSO-34 (CHA) and a new structure, designated SAPO-56. Synthesis conditions and gel composition influence the structure-type formed. SAPO-56 adsorbs oxygen, nitrogen, and normal paraffins but not isoparaffins, and has a pore volume comparable to SAPO-34 (CHA). Synchrotron x-ray powder diffraction, electron diffraction, and MAS-NMR were used in conjunction with model building to solve the structure. The SAPO-56 structure, a member of the ABC six-ring family, contains only D6R units (like CHA and AFT), arranged to give gmelinite cages (GME) and large cages (AFT) previously observed in AIPO-52. INTRODUCTION The use of novel amine templating agents in the synthesis of AIPO-based molecular sieves continues to produce novel structures. One class of such structures is characterized by parallel stacking of 6-rings, the ABC 6-dng family. The AIPO members of this family include structure-types ERI, SOD, CHA, LEV, AFT, and now SAPO-56. EXPERIMENTAL
SAPO-56 was prepared by heating a reaction mixture with the composition: 1.0 TMHD :0.6 SiO2 : AI203 : P20~ : 40 H20 at 200C for 96 hours. At low Si concentrations (< 0.2 SiO2) SAPO-17 or AIPO-17 is more commonly observed. The best synthesis conditions for the SAPO-56 appear to be: 1) higher Si concentrations, 2) a fumed silica source, and 3) higher TMHD concentrations. Mixtures of SAPO-17 and SAPO-56 are sometimes observed, particularly at intermediate Si synthesis levels. From a gel containing Mg and Si, a pure MAPSO-34 (chabazite framework) was prepared with TMHD. Synchrotron x-ray powder diffraction was used in conjunction with model building to solve the structure of the calcined, never-rehydrated form of SAPO-56. Solid state MAS 27AIand 31p NMR were measured on a similarly prepared sample. Adsorption capacities were measured gravimetrically. currently at Dow Chemical Co., Midland, MI
10
RESULTS AND DISCUSSION Adsorption characterization indicated that SAPO-56 was a small pore structure, most probably with an 8ring controlling sorption. Oxygen and n-butane were readily adsorbed and isobutane was excluded, and the sorption capacity was comparable to that of SAPO-34 (CHA). MAS-NMR was consistent with the presence of D6R units and the absence of S6R units. Electron diffraction produced a 13.8 x 13.8 x 19.9 ~, cell, consistent with one of the unit cells found by the indexing programs. Discussions with J.V. Smith led to a trial model drawn from the hypothetical enumeration of ABC 6-dng structures. 2 This model contains only double 6-rings, arranged to give gmelinite (GME) cages and another type of cage which has only been observed before in AIPO-52, and is referred to as the AFT cage. The stacking sequence of the 6-rings in the structure is AABBCCBB. The trigonal space group is P3barlc. Cell dimensions from a Rietveld refinement using GSAS are a = b = 13.7617(2) ~,, c = 19.9490(5) ~,, "= $ = 90 ~ , ( = 120 ~ . The synchrotron x-ray data and selected area diffraction patterns indicate faulting in the stacking sequence along the c-axis.
2J.V. Smith and J.M. Bennett, Amer. Mineral., 66, 777-788 (1981)
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
11
SYNTHESIS AND CHARACTERIZATION OF CoAPOICoAPSO-44 and CoAPO-5 U. Lohse 1, E. L6ffler 2, B. Parlitz 1 and E. Schreier a t Institute of Applied Chemistry Berlin-Adlershof, Berlin 12484, Germany 2 AUF GmbH, Rudower Chaussee 5, Berlin 12484, Germany 3 Humboldt University, Hessische Str.1, Berlin 10115 Summary It is shown that Co atoms occupy framework positions and create Br6nsted and Lewis acid sites. Introduction The incorporation of Co into the framework positions is studied for two structures (44 and 5). Special interest is devoted to the created acid sites. Experimental Section The composition of the reaction mixtures was the following: CoAPOICoAPSO-44: (0.8-1.0)AI203x (0.6-0.1) P2Osx (0-0.4) SiO2x (0.1-0.4) CoO x 1 CHA x 1HF x 60 H20 CoAPO-5:0.9 AI203 x 1P205 x 0.1 CoO x 1CHA x 190 H20 [CHA: cyclohexylamin]. The crystallization was performed in the common way (stainless steel vessel in an oven at 200~ 4-24h) or in microwave power system ( CEM corporation, 200 ~ 25-30 min). The samples were characterized by XRD, adsorption of N2, TPDA, IR spectroscopy, calorimetric measurement of NH3 sorption. Results and Discussion Characteristic changes of the color were observed after elimination of the template and after adsorption of H20, NH3, N2 (green, greybluelanthracite, blue). The results of the chemical analysis give evidence for the isomorphous substitution of AI atoms by Co (Co+AI=P). The Co content in the crystals is in the range of 2.0-8.7 wt% CoO. From our experience about synthesis it follows that the crystallization of pure CoAPO-44 needs a definite amount of Co in the gel. This confirms the conclusions already drawn for SAPO-44 that the building of the chabazite-like structure requires one negative charge per double-6-ring which may be realized by substitution of P by Si or of AI by Co. [cm3/g STP] 160-
Co
CoAPSO-44(0.2)
(O.Z)
;!
%
120-
.3677
1"3580
80
40
/
4-000
[P/Po] 10-5 10-3 i0-1 Adsorption isotherms of nitrogen at 77 K i
='
1
3500 3000 w o v e n u m b e r s / c m -1 9J
,
4
-
1
[R spectrtu~ of CoAPO--44
12 The X-ray difractograms and the adsorption isotherms demonstrate the full crystallinity of the samples. The pore volumes amount to 0.2 cm3/g for CoSAPO-44 and 0.13 cm3/g for CoAPO-5 and agree with those of the corresponding AIPO4/SAPO samples. The destabilization of the framework in dependence on the cobalt content is significant. The collapse of CoAPO-44 takes place at 600 ~ whereas SAPO-44 is stable up to 1000 ~ Furthermore, CoAPO-44 is attacked by water at low temperature. The loss of adsorption capacity (see isotherms) is due to a hydrolysis process. The heating of the water saturated sample (30 wt%) in air leeds to the total destruction of the lattice at about 250 ~ A higher stability is found for the CoAPSOs. 0.1
- SA~:)-44
21~
"J
-CoA.PO-44
~
15TorrCO
"~ P'~ " v ~ 73 9
$73
G73
z73
- - - - - - - 1" (K)
10~ Tort 5' 10~ ToK
" " - - - - - 1~ 10~ Tort
TPDA cun, es ~
of CO on CoAPO44
From the results of TPDA and calorimetric measurements it follows unambiguously that the total number of acid sites corresponds well with those of SAPO-44 (one acid site per double-6-ring), but the intensity of the low and high temperature peaks are reversed. In contrast to SAPO-44 the IR spectrum for CoAPO-44 shows no bands of isolated bridging hydroxyls. The character of the spectra (a broad band at 30003600 cm -1 with a maximum at 3580 cm-1 and POH groups at 3670 cm -1) is independent of the structure type and confirms the spectra of CoAPO-11 and CoAPO-5 known from the literature. The presence of adsorbed molecular water can be ruled out (no band at 5200 cm-1). It seems that the POH groups are connected with the Co atoms and have a higher acidity than those found in most aluminophosphate molecular sieves. We assign the broad band to interacting hydroxyls which are present beside isolated centers. In dependence on the probe molecule the Co atoms appear as Br5nsted (B) or Lewis (L) sites. 0 H 0 0 Co-- 0 ............... P 0 0 0
~
0 0 Co 0
0 HO P 0 0
B and L sites were detected by IR spectroscopy after adsorption of NH 3. The ratio of B and L sites (about 11) remains unchanged even after evacuation and heating of the sample. After CO adsorption a new band at 2196 cm -1 appear in the IR spectrum which can assign to a CO complex on the Co2+.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
13
SYNTHESIS AND SORPTION PROPERTIES OF THE ZIRCONIUM ALUMINOPHOSPHATE MOLECULAR SIEVES ZrAP0-5
J. Kornatowski 1,2 , M. Rozwadowski 2, W. Lutz 3, M. Sychev 4 , G. Pieper 1 G. Finger i, W. H. Baur 1 1 1 n s t i t u t fGr Kristallographie, Johann Wolfgang Goethe-Universit~t, 60054 Frankfurt/Main, Germany 2 Instytut Chemii, Uniwersytet Miko~aja Kopernika, 87-100 Torun, Poland 3 Institut fGrAngewandte Chemie, 12489 Berlin, Germany 4 Institute of Colloid and Water Chemistry, Ukrainian Academy of Sciences, 252680 Kiev, Ukraine
The sorption isotherms of the synthesized ZrAPO-5 samples indicate that their sorption capacities for water are higher while for benzene and nitrogene are lower than those of ALP04-5. The sorption studies might indicate a framework incorporation of the Zr ions.
INTRODUCTION
The first efforts to incorporate Zr ions into zeolitic materials applied to silicates of the MFI type 1,2. However characterization
of Zr-silicalite-1
the first studies on synthesis
and
have been published much later3.
The
materials have been found to be catalytically active in the synthesis
of
olefins from methanol 2 and in the hydroxylation of benzene 5. This indicates that the Zr materials have properties similar to their Ti analogues. While Ti containing aluminophosphates
have been known
already
since 19864 , the Zr
aluminophosphate derivatives have been first reported by us 5,6 in 1991. This paper presents the results of our syntheses of [Zr]AFI molecular sieves and some of their properties. EXPERIMENTAL The ZrAP0-5 materials were synthesized hydrothermally according to our well established procedure 7,8 for AFI type materials. As the source of zirconium, seven
different
Zr(0H)2C03,
Zr(IV)
compounds
Zr(ethoxide) 4,
were
used:
Zr(propoxide) 4
and
Zr02,
Zr0C12,
Zr(S04)2,
Zr(acetylacetonate) 4.
The
formal molar composition of the reaction gel (triethylamine=TEA as template) was: A1203
90,915P205 " 0,17Zr02
91,37TEA " 270H20.
The materials were characterized using XRD, sorption of H20, C6H 6 and N 2.
SEM,
EPM,
TGA techniques
and
14 RESULTS AND CONCLUSIONS
All batches except those using the last Zr compound yielded large crystalline phases of AFI type. The dimensions of the crystals in particular preparations reached 150 x 60 to 750 x 85 ,m and their colour was white to yellowish. The crystals had the typical shape of hexagonal prisms cavities
spread over
(EPM) with a number of
the surface 6. The content of Zr
(EPM) was
for all
prepartions within a range of 1,0 to 1,5 wt% except for the sample prepared from Zr(0H)2C03 where crystals.
the Zr ions were not found on the surface of the
The XRD patterns were
typical
for the AFI
type structure
and
indicated a good crystallinity of the materials. All samples showed a good sorption
capacity
for water within
a range
of 0,235
to 0,255
cmS/g
at
p/ps=0,95, i.e. higher than the reference AIP04-5 sample (-0,195 cmS/g). The sorption capacity for benzene was nearly independent on the source and amount of Zr and it reached -0,6 to 0,7 mmol/g at p/ps=0,85 except for the sample prepared from Zr0C12 (-0,27 mmol/g). The sorption of N 2 (77K) was different. At p/ps=0,8 the sorption amounted only to -0,35 (Zr0C12) to 2,4 [Zr(OH)2C03] N 2 molecules/unit cell . The sorption rose strongly when approaching p/ps=l,0 but it did not exceed 3 molecules/UC, i.e. it reached only about 1/3 to 1/2 of the experimental value typical for ALP04-5 preparations (about 6). As the sorption of water proves that the pore system is open, the significant discrepancies in sorption of N 2 can be explained by differences in the mutual interaction between the sorbate molecules and the heterocentres located on the Zr atoms. A possible mechanism could be the condensation of N 2 around the Zr
centres
which
could hinder
and
stop
a further
diffusion/sorption
of
nitrogen. Thus, it might indicate a framework incorporation of the Zr ions in all the investigated samples. Acknowledgments. The work was partially supported by the Bundesministerium ffir Forschung und Technik and the Polish Committee for Scientific Research (KBN). REFERENCES
I. B.A. Young, USPats. 3 329 480 and 3 329 481 (1967). 2. H. Baltes, H. Litterer, E.I. Leupold, F.Wunder, Eur.Pat. 77 523 (1983) and Ger.Offen.De 341 285 (1983). 3. M.K. Dongare, P. Singh, P.P. Moghe, P. Ratnasamy, Zeolites ii (1991), 690. 4. E.M. Flanigen, B.M. Lok, R.L. Patton, S.T. Wilson, Stud. Surf. Sci. Catal. 2_88 (1986), 103. 5. J. Kornatowski, M. Rozwadowski, G. Finger, Pol.Pat.Appl. 291.460 (1991). 6. J. Kornatowski, M. Sychev, G. Finger, W.H. Baur, M. Rozwadowski, B. Zibrowius, Proc. Polish-German Zeolite Colloquium, Torun, Apr. 23-24, 1992, ed. M. Rozwadowski, N. Copernicus University Press, Torun. i~J92, p.20. 7. J. Kornatowski, G. Finger, Bull. Soc. Chim. Belg. 99 (1990). 857 and refs. therein. 8. G. Finger, J. Kornatowski, Zeolites i_O0 (1990), 615.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
Molecular Or Supramolecular Templating: Defining The Role of Surfactant Chemistry In the Formation of M41S and Zeolitic Molecular Sieves J. S. Beck 1~ J. C. Vartuli 1, G. J. Kennedy 2, C. T. Kresge 2, W. J. Roth 2, and S. E. Schramm 1 Contribution from Mobil Research and Development Corporation Central Research Laboratory, Princeton, New Jersey 08543 and Paulsboro Research Laboratory, Pauisboro, New Jersey 08066 We have explored the ability of alkyltrimethylammonium surfactants of the type CnH2n+I(CH3)3NBr to serve as structure directing agents, or templates, for the formation of microporous or mesoporous molecular sieves frameworks. At equivalent gel compositions and reaction conditions, it was observed that the alkyl chain length of the surfactant molecule dictated the nature of the silicate product obtained as indicated by the X-ray diffraction patterns shown in Figure 1. Over the entire range of synthesis temperatures examined (100-200~ the shortest alkyl chain length surfactant (n=6), produced amorphous or microporous zeolitic materials, such as ZSM-5. The zeolite contained the intact surfactant cation consistent with a commonly observed molecular templating effect. At 100~ as the surfactant chain length was increased (n=8,10,12,14, and 16), the formation of mesoporous molecular sieves (MCM-41) was observed. In these cases, a combination of surfactant chain length and reaction conditions favor surfactant aggregation (micelles), and hence, the formation and utilization of supramolecular templates. At synthesis temperatures of 200~ zeolitic and dense phase products were obtained for even the higher alkyl chain lengths, suggesting that these supramolecular aggregates were disrupted and molecular structural direction dominated. 13C CP/MAS data of MCM-41 and zeolitic materials prepared with identical surfactants indicates that the role of the organic directing agent is different in the formation of these two classes of materials. MCM-41 materials have NMR spectra that suggest a micellar array of surfactant and the zeolite materials exhibit spectra that are indicative of a more rigid, isolated environment. The data are consistent with a hypothesis that single surfactant molecules serve to direct the formation of microporous materials whereas mesoporous molecular sieves, such as MCM-41, are formed by surfactant aggregates. These results reinforce the LCT (Liquid Crystal Templating) mechanism proposed for the formation of the mesoporous MCM-41 materials and further add to our understanding of the formation of inorganic porous materials. 1 Mobil Research and Development Corporation Central Research Laboratory 2 Mobil Research and Development Corporation Paulsboro Research Laboratory
15
16
rO
~0 0
04
oo ,1--=
(~ o
rO
0
oj rO
rO
0
o
rO
0
~
fq!sumul
rO
rO
~
rO
rO
o
0
00
r
'--
(P
0
_oi--
_0
--
o~I
c~
a
0
oi--
-
0 ',-
0
--
--
0
H.G. Karge and J. Weitkamp (Eds.)
17
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SYNTHESIS AND CHARACTERIZATION OF BORON CONTAINING MCM-41.
U. Oberhagemann, I. Topalovic, B. Marler, H. Gies Institut ih" Mineralogie, Ruhr-Universit/it Boehum, D-44780 Bochum, Germany Introduction MCM-41 is a novel mesoporous material first described by Kresge et al. in 1992 (1). MCM-41 has channel like pores of uniform size which are arranged in a regular hexagonal pattern. The pore diameters are in the range of 25 to 100 ./k depending on the type of detergent cation used as templates during the synthesis. So far, only the aluminosilicate and the pure silica forms of MCM-41 are largely characterized (e.g. 2,3). We report here on the synthesis and general characterization of the boron containing MCM-41 (B-MCM-41). Experimental B-MCM-41 was synthesized from aqueous silicate solutions in the system SiO2/B203//H20/Template. The reaction mixtures were sealed in silica glass tubes and heated at 95~176 for eight weeks. As templates five different n-alkyl-trimethylammonium cations, N(CH3)3-(CH2),-CH3 with n = 5, 9, 11, 13, 15 were used. The boron content of B-MCM-41 samples was determined using a PU7000 ICP spectrometer. X-ray powder data of various samples were collected on a Philips PW1050 diffractometer. 29Si, 13C and I*B MAS NMR spectra were recorded with Bruker MSL-400 or MSL-300 spectrometers using standard Broker MAS probes. Thermal properties of boron containing MCM-41 were investigated by TGA and DTA. Isotherme sorption and TPD experiments were made with n-Hexan and NH3 respectively. Results and Discussion The d-value of the fast X-ray reflexion of the different B-MCM-41 materials depends on the chain lenght of template molecule (see Tab. 1). This reflects the fact that the molecule lenght determines the pore diameter of the channels which is in the range of 27.0A (with hexyltrimethylammonium, n=5) to 42.3A, (with hexadecyltrimethylammonium, n=15). All X-ray powder diagrams can be indexed in the hexagonal symmetry (Fig. 1). 15000-
Template
molecule lenght
d,oo-values
n= n= n= n= n=
11.2A 16.2A, 18.7A, 21.2]k 23.7A
27.0]k 32.0A, 35.5A, 41.0/~ 42.3A
5 9 11 13 15
~oo
oo
0-~
2 ' ,i ' g ' ~ ' lb' 1'2' 1'4' 1%' 1'8 ' ~o 2-THETA
Tab. 1: dloo-values of various B-MCM-41 samples and chain lenghts of the N(CH3)3-(CH2)n-CH3template.
Fig. 1. X-ray powder diagram of B-MCM-41 synthesized with N(CI-I3)3-(CH2)16-CH3
Sorption experiments on various B-MCM-41 samples revealed an uptake of 24.5 to 37.6 weight percent n-hexane proving the high porosity of this material. The results mentioned in the following are obtained from a sample synthesized with tetradecyltrimethylammonium: The chemical analysis of the as synthesized sample revealed a ratio Si/B = 47. In the calcined material the boron content is slightly reduced to Si/B = 55. TGA measurements up to 1200~ revealed a total weight loss of 36 percent which occurs in three main steps. The first step (25-150~ -- 3 %) originates from molecular water, the second (150-500~ -- 25 %) is caused by the decomposition and expulsion of the guest molecule, the
18 third step (500-680"C, - 8 %) is a loss of water which originates from OH groups of the framework. DTA shows that the remaining material (= 64 %) transforms to cristobalite. The 295i M.AS NMR spectrum shows three broad signals (Fig. 2a). Neglecting the very low boron content, we assign these signals to SiO4 groups (with a chemical shift o f - 1 0 8 ppm), SiChOH groups (-101 ppm) and SiCh(OH)2 groups (-89 ppm). The broadness of the signals indicate a framework structure of very low order. The ~IB MAS NMR spectrum of the as synthesized material presents one sharp signal. The chemical shift of about -2 ppm, is typical for tetrahedraJly coordinated boron in the silicate framework (Fig. 2b).
-6o '~o -~o''~o '"'~bo -f~o - ~ " - i ' ~ " - ~ ppm |
|
'
!
!
Fig. 2. a) 29Si MAS NMR spectrum and
~ ' 6 '-h'-lo'-is'-~o pont b) nB MAS NMR spectrum of the as synth, sample. ~b'
The t~B spectrum of the calcined sample shows one strong, shar ~signal at ca. 19 ppm and a weak signal at ca. -2 ppm (Fig 3). The latter value reflects boron atoms which are still tetrahedrally coordinated within the silicate framework. In contrast, a chemical shift of about 19 ppm is typical for boron atoms trigonally coordinated by oxygen atoms in natural and synthetic borates (4). To our knowledge however, the very narrow linewidth of the ] signal is unique among calcined porous borosilicates. As a possible explanation, we assume that boron is removed from the sili4b ' 3b ' 2b ' l b ' 6 '-io'-~o care framework during the calcination process ppn by forming a separate borate phase. Fig. 3. nB MAS NMR spectrum of the calc. sample.
__9
The ~3C NMR spectrum shows a significant pattern of at least 8 signals which proves that the template tetradecylyltrimethylammortium in fact occupies the channels of B-MCM-41. Conclusion The properties of B-MCM-41 are very similar to those of their aluminosilicate and silica analogues. NMR spectroscopy proves that boron is part of the silicate framework in the as synthesized material introducing acid sites into the framework. Preliminary investigatins of the acidity of B-MCM-41 revealed that the material has only a very weak acidity, even lower than the aluminium containing MCM-41. References 1. C.T. Kresge et al, US Patent No. 5.098684 (1992); US Patent No 5.102643 (1992). 2. C. T. Kresge et al, Nature, Vol. 359, 710-712 (1992). 3. Cong-Yan Chen et al., Microporous Materials, 2 (1993), 17-26. 4. G. L. Turner et al, J. M ag;.Resonance 67,ff44Z5_50, (...__1.98_6)= We thank Dr. A.Ryfinska and Dr. C.A.Fyfe for providing the NMR facilities and for helpful advice.
I-I.G. l~arge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
19
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. SYNTHESIS OF V A N D Ti MODIFIED MCM-41 MESOPOROUS
MOLECULAR SIEVES Abdelhamid Sayari, Kondam Madhusudan Reddy and Igor Moudrakovski Universit~ Laval, Department of Chemical Engineering and CERPIC, Ste-Foy, Qc, CANADA GIK 7P4
SUMMARY V a n a d i u m and titanium modified MCM-41 mesoporous molecular sieves have been synthesized. Their physico-chemical and catalytic properties indicate a probable incorporation of the Ti(IV) and V(V) cations in the f r a m e w o r k of the molecular sieve.
INTRODUCTION Modification of zeolite frameworks by transition metal cations often leads, to new materials with remarkable catalytic properties. Several well documented Ti and V modified silicates were found to be excellent catalysts for partial oxidation of organic substrates under very mild conditions. Recently, a new family of mesoporous molecular sieves designated as MCM-41 has been discovered (1). These zeolite-like materials have uniform channels with adjustable dimensions from 15 to more than 100 ,~. Modification of MCM-41 by transition metal cations such as Ti and V may lead to new catalysts for redox reactions involving molecules too large to be accommodated in microporous structures. The objective of this communication was to report on the synthesis and characterization of both V and Ti modified MCM-41 molecular sieves. EXPERIMENTAL V-MCM-41 and Ti-MCM-41 were synthesized hydrothermally at 373 K for 6 to 7
days in Teflon lined autoclaves tumbled at 25 rpm. Fumed silica, NaOH, VOSO4, 2H20, dodecyltrimethyl ammonium bromide and water were used for the synthesis of V-MCM-41. Because the presence of Na ions in the synthesis gel is detrimental to the incorporation of Ti in zeolitic frameworks (2), dodecyltrimethyl a m m o n i u m hydroxide was used instead of the corresponding bromide, thus avoiding the use of NaOH. The other ingredients were tetraethylorthosilicate, Ti tetrabutoxide and deionized water. The resulting solids were filtered, washed and calcined at 823 K for 6 h. All samples were characterized by AAS, XRD, IR, UV-Vis., XPS, 51V N M R and nitrogen adsorption. The oxidation of phenol, naphthol and cyclododecane as
20 well as the epoxidafion of 1-hexene by diluted H202 were used to evaluate the catalytic properties of these new materials. Samples of the reaction mixtures were analyzed by GC using a 50 m capillary column (HP-1). RESULTS AND DISCUSSION XRD patterns of V and Ti modified MCM-41 matched well that of pure silica MCM-41. Chemical analysis showed that Ti and V contents in the final products were lower than in the synthesis gel. Nitrogen adsorption isotherms exhibited a step at P / P ~ of ca. 0.20 characteristic of the presence of a mesoporous system with a unique pore size (3). The BET areas were about 950 m2/g. 51V MAS NMR provided definite proof that all vanadium in calcined V-MCM-41 was in tetrahedral symmetry. Two isotropic peaks were observed: a major signal at-527 p p m (relative to VOCI3) with a shoulder at-506 p p m (4). Such features are characteristic of tetrahedral vanadium. No NMR peak with a chemical shift around-300 p p m was detected indicating, in agreement with Raman spectroscopy data, that no free V205 was present. UV-Vis. reflectance spectroscopy showed that Ti-MCM-41 exhibits a strong absorption band at 210 nm attributable to isolated Ti species in tetrahedral environment. Moreover, XPS analysis of Ti-MCM-41 showed that the Ti(2p) signal can be deconvoluted into two doublets the relative intensities of which were 85 and 15%. The strongest doublet corresponded to a Ti(2p3/2) binding energy of 459.9 eV and the weakest to a Ti(2p3/2) binding energy of 457.8 eV. Similar photoelectron transitions were assigned to tetrahedral and octahedral Ti, respectively (5). Pure silica MCM-41 had an IR absorption band at about 960 cm -1, probably due to silanol groups. Modification by Ti brought about an increase in the relative intensity of this band. As stated in the literature, this may be regarded as an indication of Si-O-Ti bonding. Our UV-Vis. and FTIR findings are in agreement with data published recently by Corma et al. (6). As far as catalytic properties are concerned, V-MCM-41 was found to be highly active and selective in the hydroxylafion of cyclododecane and naphthol (4) as well as the epoxidation of 1-hexene in the presence of 30 wt% H202. Based on all this information, it is concluded that V is incorporated in the framework of MCM-41 molecular sieve. Unlike V-MCM-41, the Ti-MCM-41 samples were active only in the epoxidafion reaction. No significant activity was found in the hydroxylation of phenol or nhexane. Similar observations were made concerning Ti-AI-~ (7) and Ti-ZSM-48 (8) zeolites. Moreover, the epoxidafion of olefins by diluted H202 is known to take place even in the presence of highly dispersed TiO2 on silica. To date, the
21 only Ti modified molecular sieves with significant activity in selective oxidation of alkanes and phenols are TS-1 and TS-2, with MFI and MEL structure, respectively. This is probably an indication that Ti in silicalite-1 and 2 has a unique local environment. REFERENCES
1. J.S. Beck et al., J. Am. Chem. Soc., 114 (1992) 10834. 2. B. Notari, Stud. Surf. Sci. Catal. 60 (1991) 343. 3. P.J. Branton, P.G. Hall and K.S.W. Sing, J.C.S., Chem. Commun., (1993) 1257. 4. K.M. Reddy, I. Moudrakovski and A. Sayari, J.C.S., Chem. Commun., (1994) in press. 5. A. Sayari et al., (a) J. Mol. Catal. 74 (1992) 233; (b) in Proc. 9th IZC, Butterworth-Heinemann, Stoneham, 1993, Vol. 1, p. 453. 6. A. Corma, M.T. Navarro and J. P(~rez Pariente, J.C.S., Chem. Commun., (1994) 147. 7. C.B. Khouw, C.B. Dartt, H.X. Li and M.E. Davis, Prepr., Div. Petrol. Chem., 1993, p. 769. 8. A. Sayari et al., Catal. Lett. 23 (1994) 175.
22
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SYNTHESIS OF TITANIUM MOLECULAR SIEVE ETS-10 AND ETS-4 Alfonso Nastro*, David T. Hayhurst** and Steven M. Kuznicki *)Dept of Chemistry, University of Calabria, Arcavacata di Rende, 87030 Rende (CS), Italy; **)College of Engineering, University of South Alabama, EGCB108, Mobile AL, 36688 USA; ***) Engelhard Corporation, 101 Wood Avenue, Iselin NJ, 08830-0770 USA. SUMMARY In this paper the crystallisation kinetics of the large and small pored crystalline titanium molecular sieve ETS-10 and ETS-4 are reported. These ETS materials have an open structure, both with tetrahedral and octahedral primary building units. The effect of varying the single components of the reaction mixture, as reported in the patent literature on the kinetic parameters, on the gel preparation and on the properties of the final products is discussed. INTRODUCTION In 1967 Young reported that the synthesis of charge bearing titanium silicates can be obtained under reaction conditions similar to aluminosilicate zeolite formation (1). In 1972 a naturally occurring alkaline titanosilicate identified as Zorite was discovered in the Siberian Tundra (2). While these materials were called titanium zeolites, no further reports on titanium silicates appeared in the open literature until 1983, when traces of tetrahedral Ti(IV) were reported in a ZSM-5 analogue (3). The object of this research is to report the synthesis of ETS-4 (4) and ETS-10 (5) crystalline titanium silicates molecular sieve, discussing the effect of the individual chemicals reported in the patents in the preparation of these crystalline materials. EXPERIMENTAL The general batch composition is xNa20-yTiO2-1.63HCI-!.49SiO2-39.5H20, where 0.44<x>2.26, 0.25
0.47. This composition was modified additioning potassium salts or replacing part of NaOH with KOH in the initial reaction mixture. The preparation of both ETS materials was carried out mixing an alkaline sodium silicate solution with a dilute Titanium Oxicloride solution without addition of seeds. The potassium salts, 0.69 moles of KF or KCI, were added alternatively to alkaline (procedure a) or to acidic mixture (procedure b). The relative crystallinity was defined from the intensities of the peaks of the XRD pattern. For use as standard samples of ETS-4 and ETS-10, these materials were synthesised following the procedures type b reported in the patents (4,5) without addition of seeds. RESULTS AND DISCUSSION The attached Figure shows the relative crystallinity versus the reaction time of the ETS-10, referred to procedure a and b. The third curve describes the course of
23 the relative crystallinity of the ETS-10 obtained from the batch without K. The addition of K salts to the batch composition for both ETS molecular sieves produces a negative effect on the nucleation and on the crystal growth. In particular, the combined action of the K and F added to the alkaline mixture, as reported in the patents, produces a modification on the prepolimerization of the titanium silicate gel. In addition, the presence of KF in the batch modifies the solubility of these building units. For these reasons the crystal size of the products obtained in presence of KF is smaller. The replacement of KF with KCI produces a reduction of the yield of the reaction, and the substitution of NaOH with KOH gives an amorphous product after 5 days of reaction time. The higher values of x and/or y in the batch composition produce ETS-4 with a kinetic and a crystallinity higher than the crystallinity obtained following the gel preparation procedures reported in the patent (4) 200
~ Z
160
<
120
~:
80
o
w
~_ I-.
5
w ft.
"
Procedure a 9 Procedure b 9 Procedure c
40 0
0
24
48 72 96 REACTION TIME, HOURS
120
Figure. Value of the relative crystallinity versus the reaction time CONCLUSIONS The titanium zeolites ETS-4 and ETS-10 may be considered as Sodium molecular sieves because the potassium play a negative role on their synthesis. The crystallisation of ETS-4 and ETS-10 is not considered an autocatalitic reaction because the relative crystallinity does not follow a sigmoid course, but, a straight line. The crystallisation domain of ETS-4 and ETS-10 is also function of the ratios Na/Si and Si/Ti in the initial batch composition and of the source of the chemicals.. REFERENCES 1) Young, US Patent, 3,329,481, 1967. 2) P.A. Sandomirskil and N.Y. Belov, Sov. Phys. Crystallogr., 24(6), 1979. 3) 3) G. Perego et al. Proc. 7th Int.Zeolite Conf. p.129, 1986 4) S.M. Kuznicki, US Patent, 4,938,939, 1990. 5) S.M. Kuznicki, US Patent, 4,853,202, 1989.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
24
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. PREPARATION BY THE SOL-GEL METHOD OF RAW MATERIALS FOR THE SYNTHESIS OF Ti CONTAINING ZEOLITES M.A. Uguina, G. Ovejero, R. Van Grieken, D. P. Serrano and M. Camacho Chemical Engineering Department, Faculty of Chemistry Complutense University of Madrid, 28040 Madrid, Spain.
SUMMARY Sol-gel methods have been applied for the preparation of amorphous SiO2-TiO2 solids having Si-O-Ti bonds, in order to get a suitable raw material to synthesize TS-1. The procedure involves the wetness impregnation of these solids with TPAOH solutions followed by crystallization under autogeneous pressure. This method seems to be also successful in the incorporation of other elements (A1) and the synthesis of other Ti containing zeolites (TS-2, Ti-Al-13). INTRODUCTION The conventional method of synthesis of Ti containing zeolites is based on the preparation of a liquid gel obtained by basic hydrolysis of Si and Ti alkoxides. Since Ti tends to precipitate as TiO2, the hydrolysis has to be performed under extremely careful conditions according to a laborious procedure (1). A completely different approach recently developed (2) is the TS-1 synthesis via wetness impregnation of a commercial SiO2-TiO2 coprecipitate with TPAOH solutions. We have found this way also successful when SiO2-TiO2 solids prepared by sol-gel methods are used as raw materials (3). The composition and physicochemical properties of the starting SiO2-TiO2 cogels can be adjusted and varied in a wide range through the different variables involved in the sol-gel process.
EXPERIMENTAL The starting SiO2-TiO2 solids were prepared by two step sol-gel processes: acid hydrolysis of the Si and Ti alkoxides and subsequent gelation by different procedures (addition of TPAOH or NH3 and heating at 80~
in the acid medium). TS-1 samples were synthesized by wetness
impregnation of dried SiO2-TiO2 cogels (Si/Ti= 30) with a 20% TPAOH solution followed by crystallization at 170~ for 1 day under autogeneous pressure. The samples obtained were characterized by XRF, XRD, IR and SEM. The catalytic properties were checked using the n-hexane oxidation with H202 (100~
1 h) as test reaction.
RESULTS AND DISCUSSION Figure 1 shows the IR and XRD spectra of a SiO2-TiO2 cogel and those of the corresponding TS-1 sample. No crystalline structure is detected in the cogel but the presence of the 960 cm 1 IR band indicates that Si-O-Ti bonds have been formed in the starting material. This band is also present in the TS-1 sample which denotes that Ti-O-Si linkages remain in the zeolite. In addition, its orthorhombic symmetry shows the effective Ti incorporation into the zeolite framework. Then, the sol-gel method allows Ti atoms to be stabilized previously to the synthesis step.
25
IR
XRD
I4100
-'~oo ,,
2O
,o~ Wavenumber
~
~o
,oo
( c m "1)
Figure 1. XtLD and IR spectra of a starting SiO2-TiO2eogel and the corresponding TS-1 sample.
Table 1 summarizes the major physicochemical and catalytic properties of several TS-1 samples synthesized from SiO2-TiOz cogels prepared by different gelation procedures. All TS-1 samples present orthorhombic symmetry, the typical 960 cm ~ IR band and exhibit high catalytic activity for n-hexane oxidation. However, some differences among them are observed in regards to the Ti content, crystal size and catalytic behaviour, showing how the properties of the starting SiO2TiO,. cogels influence those of the TS-1 samples. Table 1. Physicochemicalproperties of TS-I samplesprepared from different SiO,.-TiO2cogels.
Sample ~
Si/Ti (XRF)
Dp(SEM) (/~m)
I96o/Iso0 (IR)
n-hexane conv.( % )
H20 z conv.( % )
H20~ select.( % )b
TS-1 (1)
45.9
1.0
1.84
52.9
79.3
85.9
TS-1 (2)
40.1
3.5
1.87
33.6
84.4
46.2
TS-1 (3)
44.2
0.2-1.5
1.78
46.5
95.1
TS-1 (4)
49.9
4.0
1.88
38.0
81.7
58.6
...
56.9
aSamples I, 2 and 3 were synthesized from cogels prepared by addition of TPAOH (20%), 1.2 % NI-I3 and 21% NI-I3 respectively, duringthe gelation step. Gelation of cogel 4 was performed by heating at 80"C in acid medium. t'I-I.,O,,selectivity towards oxygenated products. We are also applying this method for the preparation of bifunctional catalysts having Ti and AI atoms in the framework. Thus, the wetness impregnation of a SiO2-TiOz-A1203 cogel leads to AI-TS-1, material with both acid and oxidation sites. Likewise, preliminary results show that other Ti containing zeolites, such as TS-2 and Ti-Al-g, can be obtained by wetness impregnation of solids prepared by the sol-gel method. REFERENCES 1. A.J.H.P. van der Pol and J.H.C. van Hoof, Appl. Catal. A, 1992, 92, 93. 2. ~I. Padovan. G. Leofanti and P. Roffia, Eur. Pat. Appl., 0311983, 1989. 3..XI.A. Uguina. G. Ovejero, R. Van Grieken. D. P. Serrano and M. Camacho, J. Ctzem. Soc., Ctzem. Commun., 1994, 1, 27.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
26
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
THE SYNTHESIS AND STRUCTURE ALUMINIUM PHOSPHATE
OF A NEW LAYERED
[ A L 3 P 4 0 1 6 ] 3- 3 ( C H 3 ( C H 2 ) 3 N H 3 ) +
A.M. Chippindalea,Q. Huo b, R. H. Jones c, J.M. Thomas d, R. Walton a, R. Xu b a b c d
Chemical Crystallography Laboratory, University of Oxford, 9 Parks Road, Oxford, OX1. 3PD, U.K. Department of Chemistry, Jilin University, Changchun, P.R.C. Department of Chemistry, Keele University, Staffordshire ST5 5BG U.K. Davy Faraday Research Laboratory, The Royal Institution of Great Britain, 21 Albemarle Street, London W1X 4BS U.K.
SUMMARY A new layered framework aluminium phosphate has been obtained by the reaction of aluminium isopropoxide and phosphoric acid in a non-aqueous medium using 1-butylamine as a templating agent. The structure was solved using single crystal X-ray diffractometry. The space group is P -3 with R = 0.107, Rw = 0.119. The structure consists of two-dimensional layers stacked in an AAAA manner. The individual layers containing large 12-membered rings The template molecules are located within the channels created by the stacking of these rings. INTRODUCTION The synthesis
of microporous aluminophosphates in 1982 [1] started
a major
research effort in this field. There has been less success in synthesising layered aluminophosphates, which can be thought of as aluminophosphate analogues of clays. We have recently synthesised and characterised several new layered aluminophosphates [2,3,4,5] having AI:P ratios which are not equal to 1:1. Other workers have also recently produced layered materials which also have non-unitary A1/P ratios. [6,7] EXPERIMENTAL PROCEDURE The title compound was synthesised under hydrothermal conditions. Typically, the starting material consisted of a mixture of phosphoric acid (0.63cm3; 85 wt%), aluminium isopropoxide (lg) with butan-1-ol as the solvent. The mixture was stirred until homogeneous followed by the addition of 1-butylamine as the template. The gel was heated under autogeneous pressure for 10 days at 180~
The product consisted of large single crystals
suitable for 4-circle diffractometry. Crystal data for A13P4016C12H36N3, M = 683.27, trigonal, space group P - 3 , a = 13.165 c = 9.774 .~, U = 1467.0 .~3, Z = 2, Dc = 1.547 g cm -3, ~. = 1.5418A, I.t(Cu-Ka) = 39.36 cm -1, 1929 unique reflections (0 < 20 < 144 ~ number observed 667 I > 3(~(I). The structure was solved by direct methods (SHELXS) and refined by full-matrix least-squares (CRYSTALS) to R = 0.107, Rw = 0.119. A total of 94 parameters were used in the refinement. The new material is illustrated in figures 1 and 2.
27
RESULTS AND DISCUSSION The structure consists of macroanionic layers of empirical formula [A13P4016] 3- with NH3(CH2)3CH3 cations situated between the layers. The individual layers contain a central 12-membered ring which is surrounded by 4 and 6 membered rings (figures 1 and 2). The 6membered tings are capped by PO4 groups, which alternate above and below the plain of the layer. The removal of these capping PO4 groups would leave a 4.6.12 net which we have previously observed [5]. The stacking of the layers in these two compounds is different. In the title compound the layers stack in an AAAA sequence whilst in the previously characterised material an ABAB stacking sequence was observed[5]. The control of the stacking is thus governed by hydrogen bonding to the amine templates. The template ions in the title compound are hydrogen bonded to the sides of the channels with the hydrophobic alkyl groups directed towards the centre of and blocking the channels.
i
I
~.
(
Figure 1 View normal to the plane of the sheet template omitted for clarity Legend
AI
P
O
Figure 2 View normal to the plane of the sheet template retained N
C
t
o
REFERENCES 1. S.T. Wilson, B. M. Lok, C. A. Messina, T. R. Cannan and E. M. Flannigen, J. Amer. Chem. Soc., 1982, 104, 1146. 2 R.H. Jones, A. M. Chippindale, S. Natarajan and J. M. Thomas,, J. Chem. Soc., Chem. Commun., 1994, 565. 3, A.M. Chippindale, A. V. Powell, L. M. Bull, R. H. Jones, A. K. Cheetham, J. M. Thomas and R. Xu, J. Solid State Chem., 1992, 96, 199. 4. R.H. Jones, J. M. Thomas, R. Xu, Q. Huo, A. K. Cheetham and A. V. Powell, J. Chem. Soc., Chem. Commun., 1991, 1266. 5. J.M. Thomas, R. H. Jones, R. Xu, J. Chen, A. M. Chippindale, S. Natarajan and A.K. Cheetham, J. Chem. Soc., Chem. Commun., 1992, 929. 6 B Kraushaar-Czarnetzki, W.J.H Stork, R.J. Dogterom, lnorg.Chem, 1993, 92, 5029. 7 A. Kuperman, S. Nadimi, S. Oliver, G. A. Ozin, J. M. Garcesand M. M. Olken, Nature, 1993, 365, 239.
H.G. Karge and J. Weitkamp (Eds.)
Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
S Y N T H E S I S AND C H A R A C T E R I Z A T I O N
OF
( H 3 N - ( C H 2 ) 6 - N H 3 ) 4 [W 18P2 O621, A D A W S O N - T Y P E A N I O N IN A N E W E N V I R O N M E N T
Markus Hflscherl, Ulli Englert2, Bodo Zibrowius 1 and Wolfgang F. Hflderichl lInstitut fiir Brennstoffchemie und physikalisch-chemische Verfahrenstechnik der RW771 Aachen, Worringerweg 1, 52074 Aachen, Germany 2Institut fftr Anorganische Chemie der RIJ~H Aachen, Prof. Pirlet-Str. 1, 52074 Aachen, Germany
INTRODUCTION One aspect of heterogeneous catalysis with microporous materials lies in the defined structure of the micropore volume, which allows a variety of organic reactions to proceed shape selectively l, 2. Heteropolyoxoanions have served as useful oxidation catalysts both in homogeneous and heterogeneous reactions 3, but to our knowledge they are not known as a part of a microporous material. In the course of our attempts to prepare such a catalyst we were successful in obtaining materials which could serve as catalysts of the above mentioned kind. For the first time we report on the synthesis and characterization of (H3N-(CH2)6-NH3)4[W18P2062] (1), an opened heteropolyoxometallate structure having a unidimensional microporous channel system.
EXPERIMENTAL Hydrothermal syntheses were carried out in stainless steel autoclaves fitted with 250 ml teflon beakers that contained a mixture of tungsten metal, ttmgstenoxide, phosphoric acid, 1,6-diammohexane and water. The reaction mixture was heated to 140 - 220~ After removing the mother liquor the remaining solid was air dried. The sample was characterized by means of X-ray powder diffraction, single-crystal X-ray analysis, FTIR, 13C and 31p MASNMR spectroscopy, TG/DSC, nitrogen and water adsorption, SEM and chemical analysis.
29 R E S U L T S AND DISCUSSION The product obtained from the synthesis yielded dark blue crystals of (1) in tetragonal shape with approximate dimensions of 0.5 x 0.5 x 0.5 ram. FTIR as well as 13C and 31p MASNMR spectroscopy showed, that the compound contained the organic molecule and phosphate. The X-ray powder diffraction pattern could be indexed orthorhombic with a = 19.838, b =18.682, c =12.605. The single crystal structure analysis of (1) showed the compound to consist of P2W18062-anions which are linked by the H3N+-groups of the 1,6diammohexane molecules (Fig. 1). The diamme works as a spacer that opens up the dense structure, in contrast to the known corresponding alkali salts 4.
Figure 1 View of the structure of (1) along the crystallographic c-axis The structure shows the compound to have a defined micropore volume, which we are studying at the present moment by means of adsorption. References: 1 W.F. H61derich and H. van Bekkum, Stud. Surf. Sei. Catal. 58 (1991) 631-727 2 S.M. Csicsery, Zeolites, _4(1984) 202-213 3 M. Misono, Catal. Rev.-Sci.-Eng. 29 (1987) 269-321 4 B. Dawson, Acta Cryst. _6(1953) 113-126
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
GROWTH OF ZEOLITE A ON RUTILE, SAPPHIRE AND QUARTZ A.Erdem-~enatalar*, H. van Bekkum* and J.C. Jansen* * Istanbul Technical University, Department of Chemical Engineering 80626 Maslak, Istanbul, Turkey. * Delft University of Technology, Laboratory for Organic Chemistry and Catalysis Julianalaan 136, 2628 BL, Delft, The Netherlands. SUMMARY Single crystals of zeolite A have been grown on essentially fiat single crystal surfaces of 001 futile and sapphire and on single crystals of quartz. Two events of nucleation were observed, one initially on the support surface directly from dilute solution, and the other from a gel layer which formed later on the surface, resulting in a bimodal size distribution. Type of the support was seen to influence both events as was reflected in the orientation of the crystals. Formation of a monolayer of randomly oriented crystals of A was followed by time experiments on quartz surfaces. INTRODUCTION Recently, thin films and coatings of zeolites have been prepared for catalysis, separation and sensor applications. In particular, continuous monolayers of silicalite-1 crystals were grown on silicon wafer as support, the orientation of the crystals being a function of the presence of a continuous gel layer preceeding the crystallization [1]. In the case of low SilAI zeolites, however, nonuniform multilayers of randomly oriented crystals were reported [2]. The purpose of this work is to gain more insight on whether a particular gel phase can be formed or excluded in order to prepare a monolayer of zeolite A crystals either from a precursor phase or directly on the support surface. For this purpose, we followed the growth of single crystals of zeolite A on essentially flat single crystal supports of rutile, sapphire and quartz, which have physical and/or chemical framework matching properties with the zeolite A crystals. EXPERIMENTAL Single crystal essentially flat 001 wafers of futile and sapphire and quartz single crystals were used as supports. Synthesis mixtures of different compositions were prepared using sodium aluminate, sodium hydroxide and sodium silicate solutions. PET bottles containing the supports, precleaned and placed in teflon inserts, were kept in a preheated oven at 65, 80 or 100 ~ for various periods. The surfaces, after being cooled and cleaned, were studied with optical microscopy, SEM and XRD. The 001 single crystal surfaces of the rutile and sapphire wafers were sampled for at least 100 single crystals of zeolite A, with SEM , using equal areas of I00 l~m2, selected randomly from different sections of the wafers.
3]
RESULTS AND DISCUSSION After the preliminary experiments with typical zeolite A synthesis mixture compositions, it was found to be necessary to strongly dilute the synthesis mixture in order to obtain a monolayer of zeolite A crystals. In a particular series of experiments from synthesis mixtures having a molar oxide composition of 10 Na20:0.2 AI203:1.0 SiO2:200 H20, growth of single crystals of zeolite A could be observed on the surfaces, much earlier than any crystal formation was observed in the bulk solution by conventional techniques. Two events of nucleation were indicated by the bimodal crystal size distribution of zeolite A, especially on rutUe and quartz surfaces. After the initial nucleation which started on the support surface in the dilute synthesis mixture resulting in relatively large crystals with enriched morphology, a continuous thin gel layer was formed on the surface initiating an explosion of small crystal formation. Type of the support surface was seen to influence both events. Of the large crystals born at an early stage on the support surface when still no gel phase was present, a substantial part (60 %) was edge oriented on futile whereas a fiat orientation was preferred on sapphire. No absolute orientation relation occurred though, despite the presence of local lattice matching units, for example in the case of 001 futile. The small crystals were mainly face oriented on futile. However, like the large crystals they were not alligned, which excludes epitaxy. It is therefore concluded that as soon as the crystallites growing in the gel layer touch the support surface, they become face oriented by electrical and surface tension forces, in this case. The absence of small crystals on the sapphire surface and the fact that their fiat orientation was not observed on quartz, indicate that the formation
and
physical/chemical nature of the gel layer are determined by the type of the support surface used. The formation of a monolayer, fiat on one side, of zeolite A crystals could be followed by time experiments at 65 ~
on quartz surfaces. The initial rate of nucleation is strongly
dependent on the surface topology and/or orientation of the support surface in the reaction mixture, as was seen from the markedly different larger crystal populations on different faces of the single quartz crystals. The growth rate, on the other hand, estimated to be 0.8 i~m/h for the initial crystals formed on the surface, was much higher than that for the second crop of smaller crystals growing from the gel, which was on the order of 0.3 l~m/h. REFERENCES 1. J.C.Jansen, W.Nugroho and H. van Bekkum, Proc. 9th. IZC, Montreal (1992), R. von Ballmoos, J.B.Higgins and M.M.J.Treacy (Eds.), 247. 2. M.W.Anderson, K.S.Pachis, J.Shi and S.W.Carr, J.Mater.Chem., 2(1992), 255.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
32
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved. PREPARATION AND PROPERTIES OF PRIMARY LEONHARDITE, (Na, K)-EXCHANGED FORMS OF LAUMONTITE Atsushi Yamazaki, Takahiro Shiraki, Hironori Ishida and Ryohei Otsuka Department of Mineral Resources Engineering, Waseda University, 3-4-10hkubo, Shinjuku-ku, Tokyo 169, Japan
SUMMARY (Na, K)-exchanged forms of laumontite, co-called "primary leonhardite", can be prepared under hydrothermal conditions. The products show two steps of dehydration at about 180 and 240~ on TG-DTA curves, the same as previous reports about primary leonhardite. XRD data recorded under controlled relative-humidity suggest that the synthetic "primary leonhardite" maintains a similar framework structure to the fully hydrated phase of laumontite between 0 and 100% RH at 25~ The number of water molecules varied from 13 to 17 per unit cell when replacing Ca by alkaline cations. The alkaline extra-framework cation sites of "primary leonhardite" are determined by Rietveld's method. INTRODUCTION Laumontite is a Ca-rich zeolite mineral, with the ideal chemical formula Ca4A18Si16048-16H20. It is well known that laumontite partially dehydrates to leonhardite under ordinary atmospheric conditions. This dehydration is normally reversible; if submerged in water, leonhardite reverts to laumontite. Fersman (1909) and Pipping (1966) reported an alkaline-rich laumontite "primary leonhardite", the atomic ratio (Na+K)/Ca was higher than 1.0, and suggested that this chemical character should be related to the impossibility of getting from the specimen the fully hydrated phase. However, mineralogical properties of the primary leonhardite have been scarcely defined because of its rare occurrences. In this study, (Na, K)-exchanged forms of laumontite were prepared from natural laumontite crystals under hydrothermal conditions. Crystallo-chemical properLies, and de- and re-hydration behaviour of the synthetic "primary leonhardite" were determined. EXPERIMENTAL The starting material was a high-temperature phase obtained from natural laumontite, from Hotokezaka, Yamagata Pref., Japan, preheated at 600~ for 1 hour. Hydrothermal experiments were performed with 3 mol dm-3 of (Na, K)C1 soluLions at 200~ using a Morey type bomb, containing a Teflon bottle - 10 ml in
33 volume. The products were characterized by thermal analysis (TG-DTA), hightemperature X-ray diffractometry and XRD measurement under the conditions of strictly controlled relative-humidity. The crystal structure of the products were refined by Rietveld's method. RESULTS AND DISCUSSION (Na, K)-exchanged forms of laumontite with higher (Na+K)/Ca ratio up to 6 were obtained under the above hydrothermal conditions. Assuming that the symmetry of the products was monoclinic, the chemical formula and unit-cell parameters obtained were Na6CaA18Si16048.17H20, a=14.794(8) ~, b=13.091(3) ./~, c=7.525(5) A and ]3=110.79(5) ~ for the sodium form; K4Ca2A18Si16048-13H20, a=14.718(8) A, b=13.182(4) A, c=7.570(5) ,/~ and ]J=110.64(5) ~ for the potassium form, respectively. The (Na, K)-forms dehydrate in two steps at about 180 and 240~ and show the same TG-DTA patterns as that of "primary leonhardite" reported by Pipping (1966). The XRD patterns of the products under ordinary atmospheric conditions were similar to that of natural laumontite (Ca-form) at 80 - 100% RH, and a discernible change of XRD pattern was not observed from 0 to 100% RH. These results suggest that the (Na, K)-forms of laumontite maintained a similar framework structure to the fully hydrated phase of laumontite at 25~ between 0 and 100% RH. The number of water molecules varied from 13 to 17 per unit cell when replacing Ca by alkaline ions, indicating a dependence on the composition of the extra-framework cations. The results of the crystal structure refinement by Rietveld's method suggest that the exchangeable alkaline cations were replaced and occupied only on Ca cation sites of laumontite. REFERENCES Gottardi, E. and Galli, E. (1985) "Natural Zeolites", Springer-Verlag, Berlin, p. 100. Pipping, F. (1966) Mineral. Soc. Indea IMA, Vol. 159. Yamazaki, A., et al. (1991) Clay Sci., 8, 79.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
34
G E O A U T ~ V E - ' r Y P E 71=OLmZATION IN THE MIOCENE "RJF::FS,MECSEK MTS., SW-HUNGARY M. Polg~r 1, h Fbrizs 1, M. Tbth 1, r Pdcsi-Don~th 1 and Z. M&the2 1 Laboratory for Geochemical Research, Hungarian Academy of Sciences, H-1502 Budapest, Pf 132 2 Mecsek Ore Mining Co., H-7633 P~cs, Eszt~g~r L. 0t 19, Hungary Summary Two types of zeolitization has been found in the Mecsek Mountains, Hungary. The economically important reserve was formed in closed system by the so called "geoautoclave" zeolitization. In~oduction Miocene rhyolite tufts and dacite tuft were studied in the Mecsek Mountains (SW-Hungary). The tufts and tuffaceous sediments occur in two horizons. The lower rhyolite tuff has two types, flood tuff and ash-fall tuff, the dacite tuff is ash-fall tuff. The lower rhyolite flood tuff appears among terrestrial and lake sediments, with a thickness of 1020 m. The dacite tuff of the upper horizon was accumulated under partly terrestrial, partly marine conditions, its thickness is less than 10 m (H~mor, 1970). The tufts of the two horizons were partly zeolitized, namely, the welded rhyolite tuff is rich in clinoptilolite (Ravasz-Baranyai, 1973), but at the same time the ash-fall type of the rhyolite tuff is not zeolitized, and some occurrences of the dacite tuff which were accumulated under marine conditions were partly zeolitized. The purpose of this paper is to characterize the main mineralogical characteristics in the frame of accumulation of the tufts and the degree of alteration processes, and to give a new model for zeolitization in the welded tuff. Materials and Methods Samples were collected from drill-cores from the W-Mecsek Mts. and from quarry faces of the M~.aTuff-Mine from the E-Mecsek Mts.. The samples consisted of fresh and more or less altered ash-fall, and welded tuft from the different horizons of Miocene tuff occurrences. 100 samples were investigated under microscope, scanning electron microscope for petrological and textural identification, by X-ray diffraction for mineralogical components, wet chemical and X-ray fluorescence methods, and electron microprobe studies for major and trace element association. Mineralogy According to X-ray diffraction data the welded rhyolite tuff contain 0-80% clinoptilolite, cristobalite, smectite (d < 14.5 ~), quartz, volcanic glass. The ash-fall type of rhyolite tuff and the dacite tuff contain mainly volcanic glass, and smectite (d > 14.5 ~). The main phenocrystals of the tufts are: plagioclase, biotite, quartz, and rarely, sanidine and hornblende. The clinoptilolite occurs in the Y shape caves of the dissolved volcanic glass, and in the matrix. Based on electron-microprobe study the clinoptilolite has three different compositional types. One
35
type is rich in alkali cations (Na and K) and the Ca content is low. The second one is Ca-(Ba)-rich, and the alkali cation content (Na and K) is low. The third one is transitional member between the previous two ones. Results and Discusdon Sporadic zeolitization can be found in the ash-fall dacite tuff accumulated in shallow marine conditions, it can be explained by the well known open system zeolitization. High scale zeolitization has been found in the welded rhyolite tuff. At the time of accumulation this type of tuff was characterized by high temperature, which is proved by the coal fragments, the assimilation of the underlying fluvial sediments, and the partial melting of the outer part of the pumice fragments. The local Ca-(Ba)-rich character of clinoptilolite can be explained by local assimilation of limestone fragments. The only zeolite mineral (clinoptilolite)is microcrystalline. The alteration process of the volcanic glass was similar to the general and well known steps of dissolution of the glass, and increasing alkalinity of the system, which finally created optimal conditions for zeolite precipitation. The associating minerals are smectite and K-rich gel-like glass. On the basis of the results the zeolitization in the Miocene welded type of rhyolite tuff can be explained by the "geoautoclave" model of zeolitization, which was described first by Lenzi and Passaglia (1974) and Aleksiev and Djourova (1975), and emphasized by Gottardi (1989). The main reason of zeolitization was the special accumulation of the tuff, namely the preserved high temperature and the impermeable crusts at the bottom and top of the tuff layer, which created similar conditions inside the ash-flow, what is characteristic in autoclaves. The high volatile pressure probably also influenced the process of zeolitization. The zeolitization in this closed system was very intensive and quick compared to the open system one. Conclusions The zeolitization in the Miocene tufts of the Mecsek Mts. has been described as an open system diagenetic process by Ravasz-Baranyai (1973). The authors has found that the ash-fall type rhyolite tuff zeolitized as was described by Ravasz-Baranyai (1973), but the welded rhyolite tuff zeolitized in a special closed system, in the so called geoautoclave. Probably the revision of "open system" diagenetic zeolitization of some welded tufts would lead to the application of the geoautoclave model. Acknowledgements This study was financially supported by the O'I'KA 4067 Project. References Aleksiev, B. and Djourova, E. G. (1975) C. R. Acad. Bu/g. Sci., 28, 517-520 .~a'va-Sbs, E., M~th~, Z. (1992) Acta Geologica Hungarica, 35(2):177-192 Gottardi, G. (1989) Eur. J. Mineral., 1,479-487. H~mor, G. (1970) Annals of theHungarian Geological Institute, 53, 1, 1-371. Lenzi, G. and Passaglia, E. (1974) Boll. Soc. Geol. Ital., 93, 623-645. Ravasz-Baranyai, L. (1973) Annals of the Hungarian Geological Institute, 53, 2, 1-741.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
36
THE SYNTHESIS OF ZEOLITES FROM DRY POWDERS R. Althoff, S. Reitmaier, W. Schmidt, B.Zibrowius', K.K. Unger, F. SchiJth Institut for A n o r g a n i s c h e C h e m i e und Analytische C h e m i e der J o h a n n e s G u t e n b e r g Universit~it Mainz Institut fQr B r e n n s t o f f c h e m i e und p h y s i k a l i s c h - c h e m i s c h e V e r f a h r e n s t e c h n i k der RWTH Aachen
Summary ZSM-5 was synthesized by different methods with a gradually decreasing water content ending in a reaction mixture with absolutely dry reagents in form of a powder in the complete absence of a solution phase. Amorphous precursors obtained by drying SiO=*AI=O3 gels at 650~ were transformed into zeolites in the presence of dried NH,F and TPABr. The reaction products were characterized by XRD, REM, TG/DTA, MAS NMR and Electron Micropobe. Pure ZSM-5 or Silicalite-1 was obtained in all cases. Some water is probably formed as a reaction product, but the maximum water pressure is appreciably below the saturation pressure at the given reaction conditions. To explain the formation of a zeolite, we suggest a vapor phase mass transfer process with SiF, as the mobile species between the solid phase which contains the amorphous Si/AI-precursor and the formed zeolite.
Introduction In the last 10 years some work has been invested in reducing the water content in zeolite syntheses. Some authors replaced the water by organic solvents, others increased the solid/liquid-ratio up to 3. Another way to form ZSM-5 with a small amount of water is the so called water-organic vapor transport, but in all cases the amount of water was high enough to formulate a classical crystallization mechanism, i.e. a mechanism which includes the presence of a solution phase with OH or F as mineralizer. We here introduce a procedure which leads to the formation of a zeolite without the presence of a liquid phase, starting from powdered reagents. This synthesis process strongly suggests that a vapor phase transport mechanism is possible.
Experimental The ZSM-5 was synthesized by the following three methods with gradually decreasing water content using a dried SVAI- precursor prepared from fumed silica and AI2(SO,)3"18H20. Synthesis A: The precursor was mixed with ammoniumfluoride, organic template (TPABr), and different amounts of water to obtain an overall composition of: 80 SiO 2 : 1 AI20 3 : 145 NH4F : 6 TPABr : 750-3000 H20 The reaction mixture was placed in a 50 ml teflon-lined stainless steel autoclave and sealed before heating it to the reaction temperature of 180"C for 60 hours. After quench cooling, the products were filtered, dried and kept for characterization.
37
Synthesis B: The precursor, the NH,F and TPABr were vacuum dried under a vacuum of 10"4 mbar for 6 hours to remove residual water. The dried reagents were transferred to a glove box, and all the following steps until the sealing of the autoclaves were carried out in the glove box in a dry argon atmosphere. The ammonium fluoride was added and all the reaction components were ground in a mortar for 5 minutes. The composition of the reaction mixture was : 80 SiO 2 : 1 AI20 3 : 6 TPABr : 55 NH4F. The synthesis and the post synthesis treatment were carried out as described above. Results and discussion XRD of the materials proved that pure ZSM-5 was formed in all cases from the amorphous precursor. The morphology of the ZSM-5 obtained from the non aqueous syntheses B is not very different from that observed for ZSM-5 synthesized in the aqueous systems. Bulk analysis of the aluminum content was carried out by X-ray fluorescence. In the dry reaction process there is no aluminum found in the samples, zgSi MAS NMR spectra of these samples showed 11 well resolved peaks which is indicative of an essentially aluminum free framework. The aluminum detected by =TAIMAS NMR could be identified as AIF3. The high SVAI -ratio would support the idea of a gas phase transport mechanism with SiF4 as the mobile species, since AIF3 has a very high melting and boiling point. To explain the formation of a zeolite in the absence of a solution phase as shown in synthesis B, we thus suggest a vapor phase mass transfer process with SiF 4 as the mobile species, based on the reaction SiO 2 + 4 NH4F --) SiF4 + 4 NH 3 + 2 H20 It can be seen that water is formed in this reaction. The maximum amount of water formed, however, is not sufficient to reach the saturation pressure under reaction conditions. Conclusions It was shown that by using a large amount of fluoride (in our case ammonium fluoride) as mineralizer ZSM-5 can be synthesized. The possibility of reducing the amount of additional water down to zero lead to a reaction system only based on powdered reactants. In this system the vapor pressure formed by the reaction of SiO 2 + 4NH4F was high enough to reach the saturation pressure under reaction conditions. Decreasing the amount of added ammonium fluoride lead to a system in which probably no liquid water phase is present under reaction conditions. Based on thermodynamic calculations we propose a gas phase transport process with SiF4 as the transport species.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
38
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SYNTHESIS AND CRYSTAL STRUCTURES OF THE DECASILS, A NEW FAMILY OF POROSILS.
B. Marler, A. G r i i n e w a l d - L t i k e , H. G i e s Institut ftir Mineralogie, Ruhr Universit~t Bochum, D-44780 Bochum, Germany Introduction The synthesis of porosil structure types having different pore geometries is strongly influenced by the nature of the template. The size and shape of the template molecules determine the size and shape of the pores and the dimensionality of the pore system. We report here on the synthesis and structure of two new porosils, RUB-3 and RUB-4, which belong to the "decasil" family. Experimental The decasils were synthesized under hydrothermal conditions from a reaction mixture of SiO2H20-Template, where aminonorbornane (ANB) and azabicyclononane (ABN) are the templates. The mixtures were heated in silica tubes at 160~ - 180~ for up to 6 months. Single crystal studies of the materials were performed on precession cameras. High resolution X-ray powder data were collected on a Siemens D5000 diffractometer with Cu K(xl-radiation. Results and Discussion Though the crystal structures of RUB-3 and RUB-4 are closely related RUB-4 is stabilized only by ABN, while RUB-3 is obtained only with ANB. The density of the as synthesized materials of RUB-3 and RUB-4 is 1.99g/cm 3. From thermogravimetry a weight loss of ca. 12% was determined leading in both cases to a framework density of 17.6 Tatoms/1000A 3. Comparing the X-ray powder diagrams (Fig. 1) it is evident that some reflections of the RUB-3 diagram appear as sharp maxima, whereas other reflections are considerably broadened in the pattern of RUB-4. This indicates structural disorder of the structure of RUB-4. The powder diagram of RUB-3 can be indexed in the monoclinic system with a=14.039A, b=13.602A, c=7.428]k and B=102.22 ~ in space group C2/m.
R U B - 3
(
a
s
-
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y
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)
2000-
1500-
1000-
500-
i , . A A . ..... 0
-
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-
,
12
-
-
9,
16
9
20
R U B - 4
24 2B 2 The'La
(
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.
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-
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32
.
)
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o
B
9
9.
l
-
12
.
-
, - .
16
9,
20
.
,
-'.'.
24 2 Theta
,
2B
9 ,
32
.
-
-
,
-
36
.-
,
40
Fig. 1. XRD diagrams of RUB-3 and RUB-4. Complicated intergrowth of the crystals prevented a conventional single crystal structure determination. Nevertheless, "single" crystal X-ray photographs of the hk0-1ayer of RUB-3 and RUB-4 crystals show identical diffraction pattems indicating that the (001) projections of both structures are identical. Higher level photographs of RUB-3 only give sharp diffraction maxima
39 on commensurate sites in reciprocal space. RUB-4, however, shows diffuse intensities extending parallel h01 and 01d and additional intensity maxima on incommensurate sites. RUB-3 and RUB4 are, therefore, two members of a new family of porous structures built from the same basic building units: RUB-3 as an ordered structure and RUB-4 as disordered in two dimensions. The structure of RUB-3 was solved from model building and simulation of X-ray powder diagrams. The structure model was subsequently optimised in a distance-least-sqares (DLS) refinement. The resulting atomic coordinates were used as a starting set for a preliminary Rietveld refinement which proves the correctness of the structure (RF---0.101, Rw--0.153, R,xp--0.059).
Description of the Structure of RUB-3 The fundamental unit of the structure is a cage-like decahedron composed of four 4MR, four 5MR and two 6MR, the [445462]-cage. Neighbouring cages are connected via common 4MR to form 1-dimensional infinite chains (the d e e ~ i l chain) (Fig. 2). Connecting the decasil chains as in RUB-3 leads to another polyhedral unit, the [46546682]-cage (V -- 300 A 3) which houses the ANB guest molecule. With the 8MR pore openings of the [4654668~]-cages a 1-dimensional channel system is formed (Fig. 3).
Fig. 2. The decasil chain
Fig. 3. Schematic representation of the framework of RUB-3.
The decasil chain is the basic building unit of a new family of porous structures, the decasils. By connecting the chains in different ways three simplest ordered structure types (A, B, C) are generated. All of these structure types possess a framework with cage-like voids which are interconnected via common 8MR pore openings to give a 1-dimensional channel system. Type A is represented by the structure of RUB-3; type B is monoclinic (P21/m) with a -- 9.7A, b = 19.6A, c = 7.4A, 13= 98.9 ~ type C is tetragonal (P4m2) with a -- 19.4A, c --- 7.4A.
Description of the Structure of RUB-4 RUB-4 is a disordered material belonging to the decasil family of structures. Diffuse X-ray diffraction intensites which extend along the h01 and 01d directions reveal 2-dimensional disorder indicating that the sequence of decasil chains in the a and b direction has no periodic ordering. From the type of disorder and from the structures of the ordered decasils (A, B, C) it can be concluded that even the disordered structure of RUB-4 has a 1-dim. channel system with 8MR pore openings which is not blocked by the stacking disorder. Therefore, all properties of RUB-4 which are dependent of the pore size and geometry are not effected by the stacking disorder.
H.G. Karge and J. Weitkamp (Eds.) 40
NEW
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
TEMPLATES
FOR THE
SYNTHESIS
OF CLATHRASII~S
G. van de Goor, C. Braunbarth, C.C. Freyhardt, J. Felsche and P. Behrens Fakult~t for Chemie, UniversiNt Konstanz, D-78434 Konstanz, Germany SUMMARY Three new templates for the synthesis of silica sodalites and three different clathrasil compounds synthesized with the first metal-organic template molecule are presented. INTRODUCTION The template mechanism in the synthesis of microporous solids is still not fully understood. Besides direct investigations of the crystallization process, it is worthwhile to study the action of new template molecules, which either (a) are derived from known templates by arguments of chemical and geometrical similarity, or which (b) open up new classes of (possible) template molecules. In this contribution, we illustrate point (a) by the judicious choice of templates for synthesis of silica sodalites; point (b) is exemplified by the use of a metal-organic complex as a template. In any case the host matrix is built up from pure silica, in order to simplify the synthesis system and to restrict host-template interactions to van der Waals forces. EXPERIMENTAL All syntheses were carried out in teflon-lined steel autoclaves. Typical data for the synthesis of silica sodalites are given in Table 1. As metal-organic template the cobalticinium cation [Co(C5H5)2] + =- Cocp~ was investigated in the system SiO 2 - N H 4 F - Cocp2PF 6 - H20. Three different clathrasil phases were obtained (Table 2). RESULTS AND DISCUSSION The choice of possible new templates for the synthesis of silica sodalites was guided by arguments of geometric and chemical similiarity to the known templates, namely ethylene glycol (EG) [1] and 1,3,5-trioxane (TR) [2]. The new template 1,3-dioxolane (DI) may be regarded as a hybrid structure between TR and one of the conformations of EG, which contains an intramolecular hydrogen bond and exhibits a five-membered ring structure [3]. Two further new templates for silica sodalite synthesis, namely ethanol amine (EA) and ethylene diamine (ED), are derived by step-wise substitution of the OH groups of EG by NH 2 groups. EA and ED are the first amines that direct the synthesis of silica sodalite [4]. With the Cocp~ cation as template, three different clathrasil phases with structure types nonasil (NON), octadecasil (AST) and dodecasil-lH (DOH) were obtained [5]. All exhibit the yellow colour typical of the cobalticinium cation. The formation of [Cocp~F-]-NON was also recently indicated by BALKUS & SHEPELEV [6]. The fact that also other clathrasil
41
compounds can be formed shows that templating with metal-organic molecules is a general approach for the synthesis of microporous solids. Table 1. Molar composition ratio of the synthesis mixture, crystallization conditions and yield for the synthesis of silica socialites M[SiO2]6. sodalite
SiO 2
M
Na20
H20
T (K)
time (d)
yidd
TRS-SOD
1
0.54
0.07 (Na2CO3)
8.9
443
3
95 %
DIS-SOD
1
2.55
0.20
51
423
6
86 %
EGS-SOD
1
1.60
0.05
-
443
35
90 %
EAS-SOD
1
1.25
0.025
-
443
61
90 %
EDS-SOD
1
1.25
0.025
-
443
33
88 %
Table 2: Molar composition ratio of the synthesis mixture and crystallization conditions for Cocp~-containing clathrasils. SiO 2
NH4F
[Cocp2] PF 6
H20
T (~
time (days)
product
formula
1.0
1.0
0.45
55.5
160
14-21
[Cocp~F-l-NON
[Co(C5H5)~F-I [SiO2122
5.5
5.5
0.45
55.5
170
7
ICocp~F-l-AST
[Co(C5H5)~F-I [SiOzll0
5.5
5.5
0.45
55.5
190
10
[Cocp~F-I-AST and =5% [Cocp~F-l-DOH
ICo(C5H5)~F-] [SiO2110 and [Co(C5H5)~F-] [SiO2134
[COCp~F-]-NON was characterized by a single-crystal x-ray diffraction analysis (Fig. 1) [5]. Surprisingly, the Cocp~ cation is entrapped in a well-ordered manner, with no signs of rotational or other disorder. Also of interest is the position of the F- ion compensating the charge of the Cocp~ cation: It occupies a site in one of the smaller cages of
Fig. 1. Structure of Cocp~-NON as determined by the nonasil structure and is loosely coordinated single crystal structural analysis. Note the alignment tO a Si atom of the framework (dsi_F: 1 84 ,/k) of the Cocp~ ions. The framework is indicated only 9 " by Si-Si connections. This work was supported by the DFG (Fe72/17-1, Be1664/1).
REFERENCES [1] D.M. Bibby, M.P. Dale, Nature 317 (1985) 157. J. Keijsper et al., in "Zeolites: Facts, Figures, Future", Elsevier 1989, p. 237. [2] G. van de Goor, P. Behrens, J. Felsche, Microporous Mater., in the press. [3] [4] C. Braunbarth, G. van de Goor, A.M. Schneider, J. Felsche, P. Behrens, in prep. G. van de Goor, C.C. Freyhardt, P. Behrens, subm. to Z. Anorg. Allg. Chemie. [5] [6] K.J. Balkus, S. Shepelev, Microporous Mat. 1 (1993) 383.1
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
42
SYNTHESIS OF ZEOLITES IN ANHYDROUS GLYCOL SYSTEMS N.B. Milestone', S.M. Hughes and P.J. Stonestreet Industrial Research Limited, PO Box 31-310, Lower Hutt, New Zealand Summary- Sodalite and cancrinite have been synthesized in non aqueous diol systems containing silica, aluminium isopropoxide and sodium hydroxide. Pure sodalite is formed only with 1,2-ethane-diol while other 1,3-diols form predominantly cancrinite. Introduction - Silica sodalite was first synthesized by Bibby and Dalela using a non aqueous route based on alkaline 1,2-ethane-dioi. Later worklb defined the region over which synthesis was possible. Attempts to prepare silica sodalite using other alcohols and diols have not proved successful. Laine et a/. 2 prepared a crystalline potassium trisdiolatosilicate salt in which the silicon was penta-coordinate. The structure of the monomeric sodium salt was determined by Gainsford et al. 3 This penta-coordinated silicon species was shown to be an intermediate in the synthesis route to silica sodalite by Carr eta/. 4 Attempts to prepare other trisdiolato salts directly from silica and alkaline diol solutions have not proved possible except for 1,2-ethane-and 1,2-propane-diol although Kemmitt and Milestone s were able to synthesize several of the other species by ligand exchange of tetraethoxysilane and determine their NMR spectra. Our work has shown that continued heating of the sodium trisdiolatosilicate salt in a minimum amount of 1,2-ethane-diol slowly converts to silica sodalite at temperatures over 150~
Addition of only
a trace of aluminium isopropoxide converts all the salt to sodalite with 24 hours.
Experimental - Pure silica (Aerosil) was heated at 170~ in sealed vessels in a range of anhydrous diols containing sodium hydroxide and varying concentrations of aluminium isopropoxide. The products were examined after 2.5 weeks heating.
Results and Discussion - Pure silica sodalite is formed only with both 1,2-ethane-dioi and 1,2-propanediol provided the Na:Si ratio exceeds 0.5 although Na2Si20s is also formed with the latter. Only a range of different forms of sodium silicates are found with the other diols tested. Additions of small amounts of aluminium as the isopropoxide allows the formation of crystalline aluminosilicates. While 1,2-ethanediol always gives sodalite, 1,3-propane-diol and 1,3-butane-diol consistently produce cancrinite for Si/Ai ratios of 2.5 to 15. At Si/AI ratios of 5 or greater, reactions in 1,2-propane-diol and 2,2-dimethyl-1,3propane-diol tend to produce sodalite while at lower ratios, cancrinite is formed. For all diols other than 1,2-ethane-diol, as the Si/AI is increased, various amounts and forms of sodium silicates are produced. The various crystalline products are presented in Table 1. In pure silica sodalite synthesized in 1,2ethane-diol, one glycol unit per sodalite cage is incorporated. The size of the cage is such that the larger
43
TABLE 1 Crystalline products formed with reactions of glycols with silica and aluminium isopropoxide Si/AI DioI
2.5
1,2-ethane 1,2-propane
sodalite sodalite
1,3-propane
cancrinite sodalite cancrinite sodalite sodalite cancrinite sodalite
1,3-butane 2,3-butane 1,4-butane 2,2-dimethyl 1,3-propane
5
sodalite sodalite cancrinite cancrinite sodalite cancrinite sodalite cancrinite sodalite
10
sodalite cancrinite ~ Na2Si205 sodalite cancrinite cancrinite Na2Si03
~ Na2Si20s
oo
sodalite sodalite ~ Na2Si2Os ,13Na2Si205 ~ Na2SiO3 Na2SiO3 Na2SiO3 J3Na2Si20s
Reaction mixture is 1.5g and SiO2 2.6g NaOH (dry pellet) mixed with lOg of diol and the appropriate amount of Al(OiPr)3 sealed in nitrogen and heated to 170~ for 2.5 weeks.
glycols are unable to pack into the space whereas in the cancrinite structure, the large channel can incorporate the glycol units. Thermogravimetry indicates approximately 1.5 diol per unit cell is retained for the cancrinite products. For the sodalite structures formed with the larger diols, thermogravimetry indicates there is only a small amount of diol present, possibly associated with faults.
It is not
incorporated in the sodalite cages. Only 1,2-ethane- and 1,2-propane-diols are able to initially dissolve the silica to form the penta-coordinated silicon precursor explaining sodalite formation with the pure silica mixtures. Addition of aluminium which readily forms diolato complexes6 is required to allow other glycols to form complexes to provide the nucleation needed for formation of aluminosilicate structures. Clearly the mechanism for formation of these species proceeds by a through solution mechanism via silicon and aluminium complexes. Diethylene and triethylene glycols are unable to form these complexes and do not form crystalline products. REFERENCES
la lb 2
D.M. Bibby and M. Dale, Nature (London) (1985), 37, 157. D.M. Bibby, N.I. Baxter, D. Grant-Taylor and L.M. Parker (1989), ACS Symp Series, p209. R.M. Laine, K.Y. Blohawiak, T.R. Robinson, M.L. Hoppe, P. Nardi, J. Kampf and J. Uhm, Nature (1991), 353, 642. G.J. Gainsford, T. Kemmitt and N.B. Milestone, submitted to Acta Cryst C. B. Heireros, S.W. Carr and J. Klinowski, submitted to Science. T. Kemmitt and N.B. Milestone, submitted to Aust J Chem Soc. T. Kemmitt, unpublished results.
H.G. Karge and J. Weitkamp (Eds.)
44
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SYNTHESIS OF A NOVEL MICROPOROUS CRYSTAL WITH ORGANIC GROUPS COVALENTLY BONDED TO THE SKELETON Kazuyuki Maeda, Yoschimichi Kiyozumi, and Fujio Mizukami National Institute of Materials and Chemical Research, Higashi 1-1, Tsukuba, Ibaraki 305, Japan
SUMMARY
A novel microporous aluminium methylphosphonate (A1MePO-J3) with an approximate composition of A12(CH3PO3)3 was synthesized by a hydrothermal procedure. MAS-NMR measurements revealed that the network structure consists of [A104], [A106], and [CH3PO3] units. The microporous structure of A1MePO-13 is supported by the Langmuir-type N2 adsorption isotherm. INTRODUCTION Microporous crystalline materials with various channel systems represented by zeolites and aluminophosphates were extensively studied. In conventional microporous crystals, however, the wall of the channel is generally composed only of oxygen atoms which are larger in size than aluminum and phosphorus atoms. Therefore, the character of the micropore is fundamentally determined by the arrangement of these oxygen atoms apart from the elements incorporated in the network structure. In this work we intended to construct a new aluminophosphonate network system and modify the character of the channel wall by introducing organic groups directly attached to the phosphorus atoms. Generally, the covalent P-C bond of alkylphosphonates is relatively thermostable towards cleavage. In this article we report the synthesis of a novel microporous crystalline a l u m i n u m methylphosphonate entitled AIMePO-~. EXPERIMENTAL SECTION The typical synthesis procedure was as follows: Pseudo-boehmite p o w d e r ( P U R A L | SCF, Condea Chemie; 74.4 wt.% A1203, 25.6 wt.% water) and methylphosphonic acid (Aldrich, 98 wt.%) were dispersed in water (Al : P : H 2 0 = 1 : 1.5 : 40) by stirring at ambient temperature for 1 hour. The mixture was hydrothermally treated in a Teflon| autoclave at 160~ for 48 hours under autogeneous pressure. The air-dried sample was characterized by ICP, SEM, XRD, and MAS-NMR. Nitrogen adsorption isotherms at 77 K on AIMePO-[5 evacuated at elevated temperatures were also measured.
45 RESULTS AND DISCUSSION The compound obtained (AIMePO-~) consists of well-grown needle-like crystals, as observed by SEM. The elemental analyses of as-synthesized AIMePO-~ gave C 10.5%, H 3.2%, A1 15.2%, and P 27.6%, from which the molar ratio P/A1 was calculated as 1.58. These values correspond with the calculated values; C 10.2%, H 3.1%, A1 15.2%, and P 26,3% for A12(CH3PO3)3- H20, the ideal composition of the neutral salt of aluminum methylphosphonate with water. The XRD of as-synthesized A1MePO-~ gave a complicated pattern with a strong diffraction peak at 7.2 ~ (Cu-K0~, d=12.3 ~). A tentative indexing can be made using a hexagonal lattice with a = 24.7 ,/~, c = 25.3 ~ at present. A1MePO-13 degassed at 500~ under vacuum for 6 h also gave a distinct and intrinsically identical diffraction pattern. The 27Al MAS-NMR spectra of as-synthesized A1MePO-13 gave two sharp signals at-17.6 and 41.2 p p m in the integral ratio of I : 3 attributed to 6- and 4-coordinated aluminum, respectively. These values are consistent with the reported 27A1 chemical shifts for aluminophosphates [1,2] whose aluminate units are surrounded only by phosphate units. The 31p MAS-NMR showed five sharp signals between 1 and 15 p p m and the 13C CP-MAS NMR showed overlapped signals in the region 11 - 14 ppm. As a reference, methylphosphonic acid gave a doublet centered at 11.3 ppm in 13C NMR and a 31p NMR signal at 37.6 ppm. Connection of phosphoric acid with four aluminate units generally gives rise to an up-field shift of 31p from -19 to -30 ppm [1]. The above results and comparisons confirmed that the methyl groups were still attached to the phosphorus atoms in the network structure. Furthermore, it is proposed that a [CH3PO3] unit is connected with two [AIO4] and one [AlO6] units and that all aluminate units are connected only with [CH3PO3] units. A detailed structural analysis is in progress. All of the N2 adsorption isotherms for A1MePO-[Ys degassed at 300-500~ for 6 h were of the Langmuir type (type 1 of the IUPAC classification) which is typical of microporous structures. Although the adsorbed amount of nitrogen remarkably increased from 300~ to 400~ there was no significant increase between 400~ and 500~ The micropore volume of the sample degassed at 400~ was calculated to be 0.117 cm3/g from the DR plot. REFERENCES
[1] C.S. BlackweU and R.L. Patton, J. Phys. Chem., 92 (1988) 3965. [2] D. Mfiller, I. Grunze, E. Hallas and G. Ladwig, Z. Anorg. AUg. Chem., 500 (1983) 80.
H.G. Karge and J. Weitkamp (F_,ds.) 46
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. SYNTHESIS AND PROPERTIES OF ZEOLITE A WITH SALT-CONTAINING [~-CAGES
Ch. Gurris, D. Reich, J.-Ch. Buhl and W. Hoffmann Institut f'tir Mineralogie, Universitfit Miinster Corrensstr. 24, D-48149 Mtinster Summary The enclathration of sodium salts (nitrite, borate, rhodanide) into the 13-cages of zeolite A has been studied. The gel-method combined with hydrothermal treatment proved to be the best way to a maximum degree of salt encapsulation. The products were investigated by X-ray powder diffraction, IR-spectroscopy and simultaneous thermal analysis (TG, DTG, DTA). Introduction The enclathration of stable salt molecules into the 13-cages of zeolites A, X or Y is expected to play an important role to modify the thermal stability, the sorption properties and the reactivity of these zeolites as already proposed by Barrer and co-workers many years ago [ 1-2]. More recently also the imbibition of thermally unstable salts into the polyhedral cages of tectosilicates has become of interest for the development of new materials [3]. In order to study the attainable alterations of zeolites we report here on the synthesis and characterization of zeolite A with salt-filled 13-cages. In this respect it seemed to be worthwile to prepare sodium rhodanide (NaSCN), sodium nitrite (NaNO2) and sodium boratehydrate (NaBO 2 9 4H20) containing zeolites A, because the thermochemical properties of sodalites could already be improved by the imbibition of these guest molecules [3-5]. Experimental Barter and ViUiger described the zeolite treatment with molten salts in order to fill their microporous structures with anions [2], but this method is not suitable here because of the limited thermal stability of the guest salts mentioned above. Therefore different other preparation procedures have been used to study the synthesis of salt-filled zeolite A: (1) The hydrothermal treatment of zeolite A (FLUKA 69836) at low temperatures and pressures (473 K and about 0,015 GPa) in a 4-molar salt solution. (2) The hydrothermal treatment at elevated temperatures and pressures (773K, 0.15 GPa). (3) Hydrothermal synthesis at 353 K using tetraethylorthosilicate as described by Kerr [6] but with an addition of the salts. (4) The gel-method: 15.6 g Na2SiO 3 - 9H20 + 19.7 g NaSCN + 125 ml H20 were added to a second mixture of 12.5 g NaA10 2 + 19.7 g NaSCN + 125 ml H20 and crystallized at 348 K in 50 ml teflon liners for two weeks. An equimolar batch composition is used in the case of nitrite- and borate-zeolite formation. All products were washed extensively in order to extract salt molecules from the s-cages of the zeolite A structure. The crystalline phases were characterized by X-ray powder diffraction, IR-spectroscopy, and simultaneous thermal analysis (TG, DTG, DTA).
Results and Discussion The preparation according to (1) led only to the incorporation of the salts into tx-cages of the zeolite and the enclathrated molecules could easily be removed by washing with water. Using route (2) the initial zeolites were transformed into sodalite phases in the form of small single crystals. Zeolite A with salt containing 13-cages could be observed using the procedures (3) and (4). Whereas (3) only yields a low salt content according to the co-crystallization of sodalite,
47 the gel-method (4) has proved to be the best way for the formation of zeolite A with a maximum degree of salt encapsulation. Obviously the salt is enclathrated into the I]-cages of the structure and therefore could not be removed during extensive extraction with water. IRspectroscopy produced evidence for the salt anions being part of the zeolite structure (see fig. la-c: nitrite absorption at 1260 cm "1, borate absorption in the range of 1150-1500 cm -1 and rhodanide absorption at 2060 cm-1). Boron is found in the 3-fold as well as in the 4-fold coordination. u}
b)
Fig. 1: IR-spectra of zeolites A containing salt molecules in the I]-cages: a) nitrite-zeolite A b) borate-zeolite A c) rhodanide-zeolite A
0
W a ~ ~ b e r (eta- l)
Compared with common zeolite A-hydrate X-ray powder diffraction indicates a slight reduction of the lattice constants in each case. Simultaneous thermal analyses of the new zeolite A species reveal differences in the thermal decomposition behaviour at elevated temperatures. The rhodanide containing zeolite decomposes according to exothermic signals at 1123 K and 1163 K. An additional exothermic reaction in air at lower temperatures indicates the decomposition of rhodanide in connection with the formation of thermally stable SO42-anions inside the [3-cages due to the uptake of oxygen from the atmosphere. The nitrite containing product shows endothermic decomposition at 1173 K and 1193 K respectively. High temperature X-ray powder diffraction shows the formation of carnegieite followed by a nepheline phase at elevated temperatures for both types of zeolites. In contrast to a slight enhancement of the thermal stability of rhodanide- and nitrite-zeolite A (the collapse of saltfree zeolite A-hydrate occurs at 1093 K and 1133 K) the borate containing phase exhibits a much lower stability.
References [1] [2] [3] [4] [5] [6]
R.M. Barrer and W. Meier: J. Chem. Soc. 58 (1958) 299. R.M. Barrer and H. Villiger: Z Krist. 128 (1966) 352. F. Hund: Z. allg. anorg. Chem. 511 (1984) 255. J.-Ch. Buhl: J. Solid State Chem. 94 (1991) 19. J.-Ch. Buhl: Mat. Res. Bull. 28 (1993) 1319. G.T. Kerr: J. Phys. Chem. 70 (1966) 1047.
II. Characterization
This Page Intentionally Left Blank
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
48
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
S T R U C T U R A L C H A R A C T E R I Z A T I O N OF SSZ-26 AND SSZ-33 M O L E C U L A R SIEVES BY H I G H R E S O L U T I O N E L E C T R O N M I C R O S C O P Y AND E L E C T R O N DIFFRACTION M. Pan and P.A. Crozier Center for Solid State Science, Arizona State University, Tempe, AZ 85287-1704, USA SUMMARY: Framework structures of SSZ-26 and SSZ-33 molecular sieves have been characterized in detail by using high resolution electron microscopy (HREM) and electron diffraction techniques. SSZ-26 and SSZ-33 have similar 3-D pore systems. They are the intergrowth of two end members which have intersecting 10- and 12-member rings. Direct evidence for the two polymorphs and stacking faults has been obtained. For the first time, the 2-D, 3-connected structural net for the projected framework structure has been successfully derived from experimental high resolution images. INTRODUCTION: Molecular sieves of SSZ-26 and SSZ-33 have been synthesized under hydrothermal conditions using the organic structure directing agents [ 1]. The sorption experiment indicates that they have a similar multidimensional pore system [ 1]. The synchrotron x-ray diffraction spectra showed sharp and broad lines indicating the presence of stacking disorder in the structures. In determining their framework structures, HREM and electron diffraction have provided a much deeper insight than x-ray diffraction technique due to the faultings in the structures. EXPERIMENTAL: We have demonstrated the possibilities of performing low-dose HREM on zeolites using a commercial slow-scan CCD camera, and the subsequent image processing procedures to extract the periodic structural information [2]. The same techniques have been used to characterize the framework structures of SSZ-26 and SSZ-33. RESULTS AND
DISCUSSION:
Electron diffraction patterns from single crystals of SSZ-33 frequently showed sharp spots and streakings for certain reflections. The sharp spots occurred at columns of k=3n and the streakings at columns of k=3n.+_+l (n=0,+l,+_2 .... ). Such a characteristic intensity distribution was indicative of layer stackings with frequent faults. The pattern was very similar to that of zeolite beta [3]. By analogy to beta, polymorph A (ABAB...stacking) had an orthorhombic unit cell, and polymorph B (ABCABC... stacking) had a monoclinic unit cell. From the systematic absence observed in electron diffraction patterns, the possible space groups can be obtained. HREM was carried out along the projection discussed above. The two polymorphs were easily seen in the corresponding high resolution images. The averaged unit cells for both polymorph A and B were obtained using the real space averaging techniques, and are shown in figs. 1a and 1b. The bright regions in these figures correspond to regions in the framework with less density, i.e. the pores. Under the approximation for thin crystals, which can be justified for
49 these images, the image intensity is linearly related to the number of T-atoms in a given region. Hence, if the image intensity is reversed, one would obtain a 2-D map representing the projected framework structure (fig.2). This map is identical to the well-known 2-D, 3-connected net in zeolite modeling. For example, the large bright dots in figs. 1a and lb actually correspond to the 10-member tings in the framework structure, and the surrounding 10 rings have been unambiguously identified as two 6-member rings and eight 5-member rings. HREM and electron diffraction have provided critical information in the complete determination of SSZ-26 and SSZ-33 molecular sieve framework structures [4]. CONCLUSIONS: Solving zeolite structures containing defects is generally difficult by using the conventional x-ray diffraction technique. HREM and electron diffraction have proved to be very powerful techniques capable of providing framework structural details at atomic scale (-2A). The 2-D map for the projected framework structure is extremely valuable for the determination of unknown zeolite structures, and has been derived successfully for the first time from experimental high resolution images. We believe that this break-through will contribute a great deal to solving many more zeolite structures in the future.
REFERENCES: [1] S.I. Zones, M.M. Olmstead, and D.S. Santilli, J. Am. Chem. Soc. 114 (1992) 4195. [2] M. Pan and P.A. Crozier, Ultramicroscopy 48 (1993) 322. [3] J.M. Newsam, M.M.J. Treacy, et al. Proc. R. Soc. London Ser. A 420 (1988) 375. [4] R.F. Lobo, M. Pan, et al. Science 262 (1993) 1543.
H.G. Karge and J. Weitkamp (Eds.) 50
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
Electron Microscopic Study of Cioverite(-CLO ) O. Terasaki 1), T.Ohsuna2), D.Watanabe2), H.Kessler 3) and C.Schott-Darie 3) 1) Department of Physics, Tohoku University, Sendai 990-77, Japan 2) Department of Materials Science, Iwaki Meisei University, Iwaki 970, Japan 3) Laboratoire de Materiaux Mineraux, URA du CNRS 428, Ecole Nationale Superieure de Chimie, F-68093 Mulhouse Cedex, France S ~ Y Single crystals of gallophosphate, cloverite(-CLO), were studied by scanning electron microscopy(SEM) and high resolution transmission electron microscopy(HRTEM). Both images revealed the existence of parallelepiped-shaped voids, surfaces of which are { 100 } planes inside the crystal. No discernible distortion of the framework structure was observed in lattice images by HRTEM. INTRODUCTION We are interested in zeolites not only from their characteristic structures 1) but also as containers for making new quantum confined materials, which will show physical properties different from those of the bulk crystal, in their spaces2). Recently Nozue et al. published an interesting property that alkali metal K-cluster in LTA shows ferromagnetism at low temperature 3) and this encourages us for making new materials in the spaces. From this view point, it has been always expected to have new zeolites with larger and tunable spaces and also to have high quality large single crystals. A new gallophosphate, cloverite(-CLO), has been synthesized4). From single crystalX-ray diffraction data, the crystal structure was solved. The crystal has the space group of Fm3c with a lattice constant a=51.712/~, and has a characteristic shape of pore opening of a four-leafed clover defined by a ring of 20 gallium and phosphorous atoms 5) . Based . on this structure analysis, the supercage of 29-30 A diameter is expected at the intersection of the channels running along the <100>. We are thus interested in the crystal as a new container for making new materials conf'med in the spaces and in having a large single crystal with high quality. EXPERIMENTAL The -CLO samples were synthesized in Mulhouse, France. The crystal morphology and surface fine structures were studied by using SEM with Field Emission Gun(FEG), Hitachi S-4100, in order to obtain high resolution images at low acc. voltage from as synthesized crystals without metal coating. For HRTEM study, JEOL 4000EX with Cs= 1.0 mm was operated at 400 kV and specimens were prepared by crushing the single crystals and dispersed on microgrids. RESULTS The size of single crystals of-CLO is approximately 80 ttm and the dominant external surfaces of the crystals are either the{ 100} or { 111 } surfaces as shown in Fig. 1. For all samples we have observed in the SEM images craters of rectangular parallelepiped shape on the { 100} or of trigonal pyramids on { 111 } as marked by the arrows in the figure. These craters were also observed in HRTEM images with [ 100] incidence as shown in Fig. 2, where low magnification and high resolution images are shown in (a) and (b), respectively. It is easier to observe contrast from the voids inside the crystal at lower magnification and their density is not small as observed in Fig.2a. The lattice image(Fig. 2b) shows regular structure without any distortion although there are voids inside the crystal. From the observed crystal morphology and the shape of craters, the crystal growth mechanism will be discussed. REFERENCES 1) O.Terasaki: Acta Chem. Scand.45(1991), 785. 2) O.Terasaki: J.Solid State Chemistry 106(1993), 190.
51 3) Y.Nozue, T.Kodaira, S.Ohwashi, T.Goto & O.Terasaki: Phys. Rev. B48(1993), 12253. 4) H.Kessler: Proc. MRS Meeting, Anaheim CA., USA, April 29-May 3, 1991. 5) M.Estermann, L.B.McCusker, C.Baerlocher, A.Merrouche & H.Kessler: Nature 352( 1991 ),320.
Fig. 1. SEM images of CLO without metal coating. Low(a) and high(b) magnifications.
Fig. 2. HRTEM images taken with [ 100] incidence by 400 kV EM. Low magnification(a) and high resolution(b).
H.G. Karge and J. Weitkamp (Eds.) 52
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. H R E M S t u d y o f Pt-clusters on K - L T L C r y s t a l S u r f a c e s Osamu Terasakil), Tetsu Ohsuna 2) & Denjiro Watanabe 2) 1) Department of Physics, Tohoku University, Sendai 980-77, JAPAN 2) Department of Materials Science, Iwaki Meisei University, Iwaki 970, JAPAN
Zeolites containing noble-metal particles have attracted attention as catalysts. The accurate characterization of particles is essential for the understanding of their chemical properties. Highresolution electron microscopy (HREM) is a powerful method for this purpose, but it is not easy to confirm that the particles are inside the channels of the zeolite. This is because that zeolites are electron-beam sensitive and that the strong contribution from the framework masks the contrast from the clusters, when electrons are incident with the direction of the channels. There are several ways to overcome this difficulty: image processing 1), HREM observation of serial ultrathin-sectioned specimens 2) and the Z-contrast method3). Normally, if we can not find the particles on the surface by looking at the direction perpendicular to the channel, we are able to say that the particles are inside. A question then arises, how small particles can be observed along this axis. Consider Pt / K-LTL as an example. The LTL sample ( Si/A1 = 2.4) was kindly supplied by Tosoh Coorp., Japan and Pt was evaporated onto the crystals by the sputtering method. The amount of Pt was controlled by changing the distance between the zeolite powder and the Ptplates, and by the duration of sputtering. HREM images were taken by 400 keV TEM along both the [001] and the <100> directions. The cylindrically shaped K-LTL crystals are electron beam sensitive and show characteristic morphology change ( e.g. to form a waist4)) under the electron beam, also at relatively small electron dose. With the electron beam parallel to the channels, we can observe a contrast from Pt-clusters which are on the (001) plane, if the particles are larger than approximately 30 A. It is however rather difficult to verify that this contrast is caused by the particles, unless the framework is destroyed by the beam. Pt-clusters, which are sticking to the side-wall of the crystals, i.e., { 100}, show a strong tendency to align along the channels facing to the surface (this is observed after morphology change in the beam). HREM images (Fig. 1) taken with the electron beam perpendicular to the channels show clearly where the Pt-particles are before (a) and after (b) a serious damage by the electrons. Pt-particles are stationary on the surface during the electron beam irradiation and this is different from the previous observation of metallic particles5). The Pt-particles, with a diameter larger than 10 ~, are situated on the (001) surface and in the projection shown in Fig.la they can be seen situated above the row of channel openings at the surface. It is clear from all observations that there is a spatial correlation between the channels and Pt-particles (three of them are shown by arrows in Fig 1.a). The shape and darkness of the contrast from the different rows of Pt-particles
53 indicates that the occupancy is not the same for each row and a slight off-set can be seen in some cases. In Fig. lb one can see the lattice fringes of Pt-particles, and it is quite clear from the images that the K-LTL crystal changes its morphology and the Pt-particles are migrated by the beam influence. Therefore one must be careful to discuss the particle size after the destruction of the framework, although it is easier to observe contrast from the particles in this way. REFERENCES 1) V.Alfredsson, O.Terasaki & J-O.Bovin: J.Solid State Chem.,105(1993), 223. 2) J-O.Bovin, V.Alfredsson, G.Karlsson, Z.Blum & O.Terasaki: Proc. MSA'94. 3) S.B.Roce, J.Y.Koo, M.M.Disco & M.M.J.Treacy: Ultramicroscopy 34(1990),108. 4) M.M.J.Treacy & J.M.Newsam: Ultramicroscopy 23(1987), 411. 5) R.Wallenberg, J-O.Bovin & D.J.Smith: Naturwiss. 72(1985), S.539.
Fig. 1 HREM images (a)before and (b)after a serious damage by the electrons.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
54
Location of Tb(lll) Ions in Hydrated Y Zeolites by Luminescence Spectroscopy Jeong Suk Seo, Chong-Hong Pyun, Chang-Hong Kim, Young Sun Uh, Wha Seung Ahn* and Suk Bong Hong Division of Chemistry, Korea Institute of Science and Technology, P.O.Box 131, Cheongryang, Seoul 130-650, Korea *Department of Chemical Engineering, Inha University, Inchon 160, Korea
Abstract Luminescence spectroscopy of the Tb 3§ ion is used to monitor the variation of the cation distribution in Tb, Na-Y zeolites which were fully rehydrated under ambient conditions after thermal treatments at different temperatures.
Introduction In view of zeolite catalysis, the detailed information on the distribution of rareearth ions in zeolites is important because both thermal stability and catalytic performance of zeolites are dramatically enhanced by ion-exchange with rare-earthions. 1 Rare-earth-ion exchanged zeolites are widely used as commercial fluid catalytic cracking catalysts. Luminescence methods have been used to study the effects of thermal or chemical treatments on the physicochemical properties of the rare-earth-ions in zeolites such as changes in coordination environment, oxidation states, or hydrolysis effects. However, no investigations into the distribution of rareearth-ions in zeolites only by luminescence spectroscopy have been reported. Here we report the results obtained from the excitation and emission spectra of Tb, Na-Y zeolites rehydrated after thermal treatments at different temperatures.
Experimental Na-Y (Si/A1=2.43) were obtained from Aldrich. Tb, Na-Y was prepared by ionexchange of Na-Y at room temperature in 0.05 M Tb(NO3)3 solutions for 24 h and followed by heating under the flowing N 2 at desired temperatures for 6 h. Finally, the Tb 3§ -exchanged zeolite powder were fully rehydrated over saturated NH4CI solution at room temperature for 2 days, before the luminescence spectra were taken. Thus, all the samples discuss iex;i in the work were studied in the hydrated state. Excitation and emission spectra were obtained at room temperature using a home-built instrument. A 150-W Xe arc lamp with an Oriel 1/8-meter monochrometer was used as an excitation source.
55
Results and Discussion The emission spectrum of the Tb, Na-Y dried at room temperature shows four emission bands at 491,547, 587 and 624 nm. These bands can be attributed to the transition between the SD and ~F levels of the Tb 3§ion. Their band positions are in agreement with the previous emission data on Tb, Na-Y reported by Tanguay and Suib. 2 Re-exchange of this Tb, Na-Y sample with Na shows significant decrease in their emission intensity, indicating that the Tb 3§ ions exchanged into Na-Y are located in the supercages. Two interesting results are obtained from the emission spectra of Tb, Na-Y samples treated at different temperatures. First, the intensities of the SD4 --> 7Fj transition bands remarkably increase with elevating treatment temperature. In particular, the SD4~ 7Fsemission band at 547 nm begins to split into two bands at 544 and 551 nm, respectively, from the temperatures higher than 423 K. Second, the intensity ratio of SD4 ~ ZFs to SD,~ ZF8 transition, which is 1.5 in the emission spectrum of unheated Tb, Na-Y, is changed to 3.0 in that of Tb, Na-Y heated at 423 K. This value does not vary even with heat treatments at higher temperatures up to 823 K. Also, no noticeable changes in the band shape and intensity are caused by re-exchange with Na. These observations indicate that the migration of Tb 3§ ions from supercages into the internal sites such as sodalite cages or hexagonal prisms of Na-Y begins from at least 423 K. Further evidence to support the conclusion drawn from emission spectra is given by the excitation data. Unheated Tb, Na-Y shows a strong broad band at 224 nm and numerous bands between 250-450 nm, which are due to the ~F ~ 7D transition of f-d level and the SD3---)7Fj transition bands of f-f levels, respectively. As observed in the emission spectra, the intensities of all the excitation bands of Tb, Na-Y increase with elevating the treatment temperature. However, the 7F~TD transition band at 224 nm shifts to 232 nm at the temperatures higher than 423 K, whereas the other bands due to the f-f transitions do not show changes in their band positions by heating up to 823 K. It is well-known that the f-d transition bands of rare-earth-ions doped into inorganic glasses or crystals are very sensitive to variations in the local environment, but the f-f transition bands are not. For example, Brixner et aL 3 show that the 7F ~ ~D transition band of Tb 3§ shifts from 250 to 262 nm when the host is changed from LaOCI to LuOCI. Therefore, it can be concluded from the observations presented here that the variation of the rare-earth-ion distribution in zeolites can be successfully monitored by luminescence technique.
References 1. S. Bhatia, Zeofite Catalysis: Principles and Applications, CRC, Boca Ranton (1990). 2. J. F. Tanguay and S. L. Suib, Catal. Rev.-Sci. Eng. 29, 1 (1987). 3. L. H. Brixner, J. F. Ackerman and C. M. Foris, J. Lumin. 26, 1 (1981).
56
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
LOCALIZATION OF PT2+ IN NAX R. Schnell, C Kirschhock, H. Fuess Fachgebiet Strukturforschung, Fachbereich Materialwissenschaft, Petersenstr. 20, D-64287 Darmstadt
SUMMARY The zeolite NaX was cation exchanged with [Pt(NH3)4] 2+ . The platinum cations were localized by powder X-ray diffraction. Temperature dependent measurements revealed the platinum-cluster formation in the partially reduced material. INTRODUCTION The reduction of transition metals in the cavities of zeolites yields highly dispersed metal particles. These systems are potential materials for catalytic applications. The present note reports results on NaX, partially ion exchanged with [Pt(NH3)4] 2+ [1]. Dispersed Pt-particles are obtained by heating this material. The resulting particle-size depends on the degree of exchange [2,3,4]. Although platinum is a classical catalyst the mechanisms of nucleation and growth of platinum clusters are not understood. To enhance knowledge on this system the [Pt(NH3)4]2+-complexes have been localized within the host for different Ioadings. Furthermore temperature dependent studies should reveal the process of cluster formation. E X P E R I M E N T A L SECTION The ion exchanged samples were prepared by the group of Schulz-Ekloff (Bremen)[1]. The metal content was analysed by AAS and energy-dispersive X-ray analysis. Samples with the following compositions were examined: Na72Pt6AI84Si1080384, Na54Pt15AI84Si1080384, Na40Pt22AI84Si1080384 equaling an Na + exchange degree of 13%, 35% and 52%. To remove the water, the zeolites were heated up to 393-403 K (4-10K/h) in vacuo (10 .4 mbar). The X-ray powder measurements were carried out on a Stoe STADIP powderdiffractometer. Experiments were performed at room temperature and several elevated temperatures ( 423 K, 443 K, 463 K, 483 K, 548 K, 623 K, 723 K ). The structural parameters of the frame and the guest molecules were refined with the program 'RIETAN' [5], the difference Fourier syntheses were calculated using the software package 'XTAL '.
57
RESULTS
AND
DISCUSSION degree of ion exchange were examined at roomtemperature. Depending on the pretreatment the Pt 2+ is distributed over one to three different positions within the supercage. A sample where all the platinumcations could be localized at the position V in the 12 ring window was examined under argon atmosphere as a function of temperature. From 298 K to 443 K all the Pt2+ ions remained at their position. From 463 K up to 543 K the occupation factor decreased while broad Pt-reflections characteristic for Pt metal occurred. No additional Pt 2+ positions were detected. At 543 K the reduction is completed and the Pt 2+ occupation factor is close to zero. At higher temperatures the platinum reflections do not change anymore. The behaviour of the occupation factor of Pt 2+ shows that up to the onset of reaction no extended diffusion takes place but the cations are fixed on their adsorption sites. This is an indication of an undisturbed coordination sphere of platinum cations up to 483 K. It clearly explains why no platinum is found in the small cavities as due to the size of [Pt(NH3)4]2+-complexes access through six ring Three samples with different
windows is excluded.
ACKNOWLEDGEMENT We thank the BMFT and the Max Buchner-Stiftung for financial support.
REFERENCES
[1] [2]
[3]
[4] [5]
Busch, F., Jaeger, N.I., Schulz-Ekloff, G.: in preparation Kleine, A., Ryder, P.L., Jaeger, N.I., Schulz-Ekloff, G.: Electron Microscopy of Pt, Pd, and Ni Particles in a NaX Zeolite Matrix. J. Chem. Soc., Faraday Trans. 1, 82, (1986), 205-212. Tonscheidt, A., Ryder, P.L., Jaeger, N.I., Schulz-Ekloff, G.: Orientation and morphology of iridium, rhodium and platinum nanocrystals in zeolite X. Surf. Sci. 281, (1993) 51-61. Gallezot, P., Bergeret, G.: Characterization of Metal Aggregates in Zeolites. Stud. Surf. Sci. Catal. 1982, 167. Izumi, F., Asano, H., Murata, H., Watanabe, N.: Rietveld Analysis of Powder Patterns. J. Appl. Crystallogr. 20 (1987) 411-418.
ft.(3, l~arge and J. Weitkamp (Eds.) 58
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
Characterization of SO2-contaminated Cu-ZSM-5 catalysts C. LLengauer l_, E. Tillmanns l C.Plog, 2 1 Inst. f. Mineralogie und Kristallographie, Universit~t Wien. Dr.Karl Lueger-Ring 1, A-10I0 Wien 2 Dornier GmbH, Deutsche Aerospace, D-7990 Friedrichshafen 1
The removal of nitrogen oxides (NOx), which are considered to play an active role in air pollution processes, is an important topic in the field of catalytic applications of ion exchanged molecular sieves. Beside other types of catalysts, like Y-Ba-Cu-oxides or Pt-coated A1203, copper exchanged zeolites show a high catalytic performance in the direct decomposition of NOx from emissions of diesel engines and industrial boilers. Because of their thermal stability up to 1000~ and their high activity in the oxidised state Cu2+/I+-ZSM-5 zeolites (1) are an important alternative to common noble metal or metal oxide catalysts. A SO2-content in the feeding gas, however, which is inevitable in real exhaust gases, 'poisons' the zeolite catalyst. This behaviour is also reported for Cu-MOR (2) and Cu-FAU (3). To depict the SO2 contamination of ZSM-5 three Na-ZSM-5 materials with Si/AI ratios of 27, 30 and 55 were treated with Cu-solutions and contaminated under a SO2 gas flow. 12 samples (3 Na-ZSM-5, 3 Cu-ZSM-5, 3 Na-SO2-ZSM-5, 3 Cu-SO~-ZSM-5) were investigated by X-ray powder diffraction (XRD) and thermal gravimetry (TG). The 6 copper exchanged zeolites were additionally heated in the range from 100-800~ with an increment of 100~ under reducing conditions (30%I-12, 70%N2). The line broadening of the Cu-111 peak was determined by interactive peak fitting and the mean particle size was calculated with the Scherrer formula (4). The XRD investigation of all 12 samples reveals that the incorporation of copper and SO2 affects the intensity of the low angular reflexions, thus confirming the occupation of distinct sites in the channel system. The lattice parameter of the zeolites do not change upon cation exchange. Only the thermal treatment leads to a slight contraction of the zeolite framework. The TG measurements indicate a clear interaction between Cu and SO2 within the zeolite pore system (Fig. 1). The Cu-ZSM-5 as well as the Na-ZSM-5 phases show a two step dehydration in the range of 50-250~ (Fig. I.A,B). The Na-SO2-ZSM-5 samples, however, are characterized by an additional distinct loss of the SO2 contamination at 300~ (Fig. I.C). The Cu-SO2-ZSM-5 zeolites reveal a completely different behaviour with a three step weight loss at 320~ 575~ and 625~ respectively (Fig. 1.D). The amount of absorbed SO2 decreases with increasing Si/AI ratio. The growth of the Cu-clusters under reducing conditions of the Cu-ZSM-5 samples starts at 200~ after the two dehydration steps. The first recognizable clusters have a mean diameter of 4006 0 0 ~ which is doubled at 300~ and continuosly increases to 1600-3000A at 800~ The final size increases with decreasing Si/AI ratio, i.e. with increasing amount of loaded copper. Simultaneously the amount of the metallic Cu-clusters increases linearly with temperature. The SOz poisoned samples, on the other hand, show a beginning of Cu-cluster growth at 300~ again a steep increase within the next 100~ and a continuous growth up to 800~ to a significantly bigger diameter in the range of 2500-6000A. In these samples the growth of Cu-clusters proceeds differently and is correlated to the gravimetric results (Fig.2). The intensity of the Cu-111 peak rises between 300500~ after the first SO 2 decontamination step, stays constant to 600~ and again increases until 700~ after the second and the third decontamination step. The results of the investigations lead to the assumption that SOz competes with NO• for the adsorption sites and prevents the catalytic reaction by blocking the channels, but is contrary to the interpretation that the deactivating agents are deposited on the surface of the catalyst. References: (1)IWAMOTO,M. et ai.; Jour.Chem.Soc. Faraday Trans.( 1981 ); 1,77,1692. (2)KHULBE, K.C.; MANN, KS.; MANOOGIAN, A.; J.Mol.Catal.(1988);48,365. (3)MIZUMOTO,M.; YAMAZOE, N.: SEIYAMA, T.; J.Catal.(1979)~59,319. (4)JENKINS,R.; DE VRIES,J.L.; Philips Technical Library (1970),Mac Millan.
59
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F i g . l Thermogravimetric measurements of ZSM-5 catalyst with Si/AI-27. A: Na-ZSM-5; B Cu-ZSM-5: C Na-ZSM-5+SO2: D: Cu-ZSM-5+SO2. The upper line represents the first derivative of the TG results.
~
60
-
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Cu-ZSM-5+S02 [counts]
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Fig.2: XRD pattern of the Cu(l I 1) peak of a SO2-contaminated Cu-ZSM-5 during thermal treatment under reducing atmosphere.
4~.5
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
61
SINGLE CRYSTAL STRUCTURE ANALYSIS AND ENERGY MINIMIZATIONS OF A H-ZSM-5/p-DICHLOROBENZENE COMPLEX AT LOW SORBATE LOADING H. van Koningsveld, J.C. Jansen and A.J.M. de Man Laboratories of Applied Physics and Organic Chemistry and Catalysis, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands Arbeitsgruppe
Quantenchemie
an
der
Humboldt-Universit&t
Max-Planck-
Gesellschaft, Jaegerstral3e 10/11, D-10117 Berlin, Germany SUMMARY. The crystal structure of a low-loaded complex of H-ZSM-5 with p-dichlorobenzene has been studied by single crystal X-ray diffraction. The controversy in the literature, concerning the location of the p-dichlorobenzene molecule, is explained by different interpretations of the difference electron density map representing the electron density of the adsorbed molecule. There are 2.56(2) p-dichlorobenzene molecules per unit cell. The adsorbed molecules very probably prefer the position at the intersection of channels. Energy calculations, using the BIOSYM Catalysis and Sorption Software, strongly support this interpretation. The unit-cell is orthorhombic Pnma, with a = 20.009(3), b = 19.909(4) and c = 13.366(2) A. The final R(Rw) is 0.044(0.048), w = 1/o2(F), for 5306 observed reflections with I > 2.0 a(I) measured at 293 K.
INTRODUCTION. The structure of the high-loaded complex of H-ZSM-5 with p-dichlorobenzene (8 pdcb mols/u.c.) has been studied by Mentzen (1) using X-ray powder diffraction data. The structure is in all details comparable to those observed in the H-ZSM-5/8 p-xylene complex (2). Conflicting results are reported on the location of pdcb on the low-loaded complex (< 4 mols pdcb/u.c.) with H-ZSM-5. Two possible locations are suggested differing by a shift of 1A b: one is at the intersection of channels (1) and the other is in between the intersections (3, 4). We prepared a low-loaded single crystal of H-ZSM-5 with 2.6 pdcb mois/u.c. This complex was studied by single crystal X-ray diffraction. In addition, preferred adsorption sites were looked for with energy minimizations using the BIOSYM Catalysis Software (5). EXPERIMENTAL. A calcined single crystal of H-ZSM-5 was evacuated at 353 K and
exposed to a vapour of pdcb. After 3 h the temperature was lowered to room temperature. X-ray data were collected on an CAD-4 diffractometer using Mo-K~ radiation. All X-ray calculations were performed using the XTAL-3.2 system of
62 programs (6). The energy calculations were done on a Silicon Graphics Iris Indigo Workstation.
~ E "~
~'
I' 9 ~
0
, ~
~0 /.I-
.....
~f
~a
!
!
Figure 1.
I Figure 2
RESULTS. Figure 1 shows, in two projections, the location of pdcb at the intersection of channels. Figure 2 gives the rotational energy curves for both models suggested in the literature. The benzene ring is rotated ~~ around the molecular CICI axis, using the CI atomic positions obtained from X-ray refinements. SE gives the guest-host and guest-guest interaction energy per unit cell. The XRD position of pdcb given in Figure 1, is indicated. Full minimizations were performed in the minima of the rotation curves. The results of these calculations will be presented. References: Available from the authors at the poster stand.
H.G. Karge and J. Weitkamp (l~ds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SINGLE
CRYSTAL
H-ZSM-5
WITH
STRUCTURE
ANALYSIS
63
OF
A
HIGH-LOADED
COMPLEX
OF
PARA-DICHLOROBENZENE
H. van Koningsveld and J.C. Jansen Laboratories of Applied Physics and Organic Chemistry and Catalysis, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands. SUMMARY. The structure of the H-ZSM-5/p-dichlorobenzene complex, containing 8 molecules pdcb/u.c, has been solved by single crystal X-ray diffraction. One of the two independent pdcb molecules lies at the intersection of channels with its long molecular axis nearly parallel to the straight channel axis. The second pdcb molecule is in the sinusoidal channel with its long molecular axis nearly parallel to [100]. The unit cell is orthorhombic, P212121, with a = 20.102, b = 19.797 and c = 13.436 A. All structural details in H-ZSM-5/8 pdcb are comparable with those in the H-ZSM-5/8 p-xylene complex. INTRODUCTION. The adsorption of p-xylene in H-ZMS-5, at high Ioadings, induces a symmetry change to P212121. The adsorption in the sinusoidal channels is accompanied by a cooperative deformation of the (100) pentasil layers (1). To see whether pdcb was able to induce the same symmetry change or not, a high-loaded complex of H-ZSM-5 with pdcb was prepared. A single crystals of this complex was used for X-ray analysis. EXPERIMENTAL. H-ZSM-5 single crystals of 30 x 50 x 110 #m were prepared according to a well established method. To obtain a high loaded complex the following procedure was used. H-ZSM-5 as well as pdcb crystals were placed in a 20 ml vessel. Excess of pdcb was stored in a connecting vessel of 40 ml. After evacuation of both vessels the temperature was kept fixed at 523 K for the first five hours. Subsequently, an alternating temperature profile, between 333 and 373 K with a heating and cooling rate of 2K/min was performed seven times. This procedure was adopted to achieve high Ioadings by making optimal use of the framework flexibility during the adsorption. Finally the crystals were cooled to room temperature. One of these crystals was chosen for the structure analysis. X-ray data were collected on a CAD-4 diffractometer using Mo-K~ radiation. All X-ray calculations were done using the XTAL-3.2 system of programs. The 4final R(Rw)=0.044 (0.040), w = 1/o2(F) for 5836 observed reflections with I > 2.0 o (I) at 293 K.
64 RESULTS. Figure 1 shows the structure of the H-ZSM-5/8 pdcb complex. For comparison the H-ZSM-5/8 p-xylene complex (Figure 2) is added. Both structures are en along the b-axis.
Figure 1
O~3
Figure 2
REFERENCE 1 H. van Koningsveld, F. Tuinstra, H. van Bekkum and J.C. Jansen, Acta Cryst. (1989), B45, 423-431.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
CHARACTERIZATION
65
OF BIMETALLIC
ZEOLITE SUPPORTED
Pt-Pd CATALYST BY EXAFS, TEM AND TPR T. Rades, M. Polisset-Thfoin, and J. Fraissard, (Laboratoire de Chimie des Surfaces, Universit~ Paris 6, France) and R. Ryoo, and C. Pak, (Department of Chemistry and Center for Molecular Science, Korea Advanced Institute of Science and Technology, Taeduk Science Town, Taejon, Korea)
SUMMARY Pd-Pt/NaY catalysts have been characterized by TEM, TPR and EXAFS. TEM was used to determine the particle size distribution and the dispersion, the latter decreasing with increasing Pd content. By TPR it was shown that mixed particles were formed. Intraparticulardistribution of the two metals was analysed and alloy-formation confirmed by EXAFS. EXAFS measurements showed that Pd and Pt are randomly mixed in metal particles. A sample with high Pt content, however, had a Pt core structure.
INTRODUCTION Petrochemistry is based on heterogenous catalysis using mainly zeolites and supported
metals as catalysts.
In hydrogenation
and dehydrogenation
of
hydrocarbons platinum- or palladium-based catalysts are the most widely used. The association of two metals may confer many advantages, such as improvement of activity or modification in selectivity for some kinds of reaction, these differences being mainly due to a mechanistic change. In the case of a Pt-Pd catalyst the Pd may increase the resistance of Pt to poisoning by sulphur or nitrogen compounds, larger amounts of which are present in the heavy petrol cuts [1]. A different surface state or a different dispersion of the metal may lead to synergetic effects. Catalyst characterization is very important in catalysis because it elucidates the chemical, structural and electronic properties of the system. The important information in heterogenous catalysis concerns surface properties (structure and composition) at the atomic scale, but, in the case of bimetallic catalysts, also metal distribution inside the clusters.
EXPERIMENTAL
Preparation:
SECTION Samples consist of small metal particles supported on an
industrial faujasite type NaY zeolite (0.6 mmol of metal per gram of raw zeolite) prepared by simultaneous cation exchange [2]. The sample is calcined in oxygen flow at T c = 300~ T c was chosen in order to obtain free M 2+ metal ions [3]. The sample is purged and then reduced at 300~
Sample Characterization:
under H 2 flow for 2h.
For EXAFS measurements, the powder sample is
reduced again in a Pyrex U-tube flow reactor connected to an EXAFS cell then
66 sealed off under H2 atmosphere. The EXAFS measurements are performed in the transmission mode at the Pt LIII and the Pd K edges at RT. 80nm thick sections of zeolite are analysed by Transmission
Electron
Microscopy. The direct picture of the supported metal particles obtained is used to determine the particle size distribution and then the metal dispersion.
Temperatureprogrammed Reduction is performed in a microflow reactor. After the calcination step the sample is reduced in a 7 ml/min Noxal flow (5% H2-95% Ar) with the temperature increasing linearly from RT up to 650~ at the rate of 600~ H 2 consumption is detected with a thermal conductivity detector.
RESULTS
AND
DISCUSSION
Extended X-Ray Absorption Fine Structure (EXAFS): Significantly large values of coordination numbers of Pt around Pd and Pd around Pt indicate the formation of bimetallic Pt-Pd clusters. The very similar values of the Pd and Pt coordination numbers mean that the two metals are randomly mixed. In the case of Pt75 (75% Pt), however, the coordination numbers are significantly different (Npd < Npt). This suggests that the cluster core is rich in Pt [4]. The size of bimetallic clusters seems to be less than 1.8 nm, but may be underestimated.
Transmission Electron Microscopy(TEM): Very small particles (<1 nm) are always blurred and may therefore not always be recognized. The number of very small clusters is therefore underestimated by TEM. The average diameter decreases with the increase of Pt content 5.8 A for 1% Pt and 1.5 A for 75% Pt.
Temperatureprogrammed Reduction (TPR):
Reduction
temperature
is
heavily dependent on the environment of the ion [5], reduction profiles are therefore like fingerprints of the sample. The bimetallic TPR profiles have one more peak than the monometallic ones. Additionally, we can observe a non-proportional decrease of the characteristic high temperature Pd peak with increasing Pt content. This is a very strong indication that mixed particles have been formed [6]. It seems likely that the reduction of Pd 2+ at unusually low temperatures is catalysed by the dissociation, and hence activation, of hydrogen on Pt 0.
REFERENCES M. Briend-Faure, D. Delafosse. J. Jeanjean, G. Rocherolles, and G. Spector, J. Chem. Phys. 83, 431- 439 (1986). P. Gallezot, A. Alarcon-Diaz, J.-A. Dalmon, A. J. Renouprez, and B. Imelik, J. Catal. 39,334-349 (1975). M. S. Tzou, B. K. Teo, W. M. H. Sachtler, J. Catal. 113, 220-235 (1988). G. H. Via, K. F. Drake, Jr, G. Meitzner, F. W. Lytle, and J. H. Sinfelt, Catal. Lett. 5, 25-34 (1990). S. T. Homeyer, and W. M. H. Sachtler, J. Catal. 117, 91-101 (1989). F. B. Noronha, M. Schmal, M. Primet, and R. Fr~ty, Appl. Catal. 78, 125-139 (1991).
H.G. Karge and J. Weitkarnp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SIMS I n v e s t i g a t i o n o n V a n a d i u m Cracking Catalysts
67
Zeolite Interactions
in
Kuei-Jung Chao, Long-Hui Lin and Liang-Yuan Hon
Department of Chemistry, National Tsinghua University, Hsinchu, Taiwan, Republic of China Summary. In this study, secondary ion mass spectrometry (SIMS) was employed to study the interaction between vanadium and zeolite in multicomponent cracking catalysts. Because of its ability to view elemental distribution with ~ 0.5 tLm spatial resolution at concentration in the p p m range, S I M S images of 51V+, 139La+ and 27A!+/28Si + distributions are quite suited to probe the location of rare earth exchanged Y and the interaction between Y zeolite and V on a cracking catalyst, which is deposited by V of several thousand p p m and contains Y zeolite of ~ 1 ~ m size embedded in amorphous silica-alumina matrix of diameter ~ 60 pm with or wthout Ca as vanadiumpassivator. The strong interaction between V and Ca compared with zeolite was also confn~ned by MAT (microactivity test).
Introduction. Vanadium has been recogonized as one of the major and poisonous m e t a l - c o n t a m i n a n t s found in typical cracking catalysts. The irreversible destruction of cracking activity by the interaction of vanadium with zeolite in cracking process has been well noted in the literature and application [1-3]. Minimization of the deleterious effect of v a n a d i u m deposition is very important, especially for heavy feedstock processing in current refiners. Using the solid phase to trap vanadium has been considered as the most promising way to reduce the reaction of vanadium with zeolite. Since the formation of vanadates by reacting alkali-earth with acidic H3VO4 was found to be favor thermodynamically at 700~ [4], SiO2" A1203 supported Ca was used as vanadium passivator in this study. The interaction between V and zeolite and the V passivation effect of Ca in cracking catalysts were examined by both MAT and SIMS measurements. E x p - ~ r i m e n t a i . V-loaded samples were prepared by i m p r e g n a t i o n of a cyclohexane solution of vanadyl n a p h t h e n a t e onto the commercial cracking catalysts with and without calcium. Equilibrium cracking catalysts and Vloaded samples were embedding in thermosetting epoxy, sliced using microtom and pressed on indium foil with copper grid for SIMS measurements. The SIMS analyses were performed with a CAMECA IMS-4f ion microscope using a 500 hA, 15 kV, mass filtered 0 2 + primary ion. The images were processed and analyzed with an IBM-compatible microcomputer run by using a home-built image analysis software. Catalytic evaluation was performed u s i n g a microactivity test (MAT). The conditions of the test were at 498~ and catalyst to oil ratio of 3.0. Liquid and gaseous products were analyzed with gas chromatography. R e s u l t s a n d D i s c u s s i o n . The equilibrium cracking catalyst contains 2000 ppm La in its active component, rare earth exchanged Y zeolite, which is
58 distributed on catalyst particles and can be identified by 139La+ ion image. The overlapping of 51V+ ion image with 139La+ ion image indicates that V is more concentrated in zeolite than in matrix. The relative concentrations of V on zeolite and matrix phases of equilibrium cracking catalyst can be estimated by analysizing the SIMS data [2], the RC value (the percentage of V on a phase divided by the area fraction of that phase) of 1.5 on zeolite greater than the average value of 1.0 for the whole particle indicates that V prefers to reside on the zeolite phase than on the matrix (RC -- 0.9) in equilibrium cracking catalyst. The effect of Ca on V passivation is shown in SIMS images of 40Ca+, 139La+ and 51V+ distributions on the cracking catalyst with adding Ca. Since the average Si/A1 molar ratio of Ca phase is greater than that on cracking catalyst determined by EDX, the location of Ca phase is expected to be revealed by both 40Ca+ and 28Si+/27A1 + ion images. For 3650 ppm V-loaded catalyst with adding calcium phase, V was found to be trapped in both zeolite and Ca phase with RC factors of 1.8 and 2.7 respectively. That reduces the RC factor on the matrix phase to 0~3. Adding Ca on cracking catalyst decreases the yield of coke and gas (C4") with increasing gasoline selectivity in MAT test as shown in Table 1. This result confirms that the poison of vanadium on cracking catalyst can be reduced by adding calcium. References 1. Shen, Y.F., Suib, S.L. and Occelli, M.L., ACS Sym. Ser., 517, 185(1993). 2. Leta, D.P., Lamberti, W.A., Disko, M.M., Kugler, E.L. and Varady, W.A., ACS Sym. Ser., 452, 269(1991). 3. Biswas, J. and Maxwell, I.E., Applied Catalysis, 63, 197(1990). 4. Wormsbecher, R.F., Peters, A.W. and Masell, J.M., J. Catal., 100, 130(1986).
Table 1 Microactivity cracking results of 2300 ppm Ni and 4500 ppm V deposited catalysts Catalyst
Coke (wt%)
Gas (wt%)
66.3
4.9
13.2
72.7
52.5
Cracking catalyst + 58.8 SiO2 9A1203 with Ca
2.9
10.5
77.2
52.0
Cracking catalyst
Gasoline Selectivity(%)
H2/Gas
Conversion (%)
(vol%)
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
XPS AND ADSORPTION OF DINITROGEN EXCHANGED ZSM-5 AND Y ZEOLITES
69
STUDIES ON COPPER-ION-
Giuliano Moretti (a), Giuliano Minelli (a), Piero Porta (a), Paolo Ciambelli (b) and Pasquale Corbo (c) (a)Centro di Studio del CNR "SACSO", Dipartimento di Chimica, Universit& "La Sapienza", Piazzale A. Moro 5, 00185 Roma, Italy. (b)Dipartimento di Ingegneria Chimica e Alimentare, Universit& di Salerno, 84084 Fisciano, Salerno, Italy. (c) Istituto Motori del CNR, Via G. Marconi 8, 80125 Napoli, Italy. SUMMARY By X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger spectroscopy (XAES) it is shown that Cu (11)ions exchanged in ZSM-5 and Y zeolites are easily reduced, in vacuum and under X-ray irradiation, to Cu (I). This process is faster for Cu (11) ions in ZSM-5. Dinitrogen adsorption measurements at 273 K have been performed after pretreatments of as prepared samples both in vacuum and in 02 at 788 K . Only on Cu-ZSM-5 zeolites with Cu exchange levels close to 100% we have measured a relatively strong and irreversible adsorption of dinitrogen. INTRODUCTION Copper-ion-exchanged Y and ZSM-5 zeolites are active catalysts for decomposition and for removing NOx from oxygen-rich exhaust gas [1].
NO In a
previous contribution we reported on the catalytic activity of Cu-ZSM-5 and Cu-Y zeolites for NO decomposition at 773 K [2]. It was clearly shown that the superior activity of the Cu-ZSM-5 catalysts can be related to a small fraction of Cu(ll) ions which are easily reduced to Cu (I). These special copper ions are introduced in the ZSM-5 zeolite only at the higher exchange levels [2]. In this report we present XPS, diffuse reflectance spectroscopy (DSR) and adsorption of N2 at 273 K data which help to understand the nature of the active sites in Cu-Y and Cu-ZSM-5 catalysts. EXPERIMENTAL The zeolites used as starting materials were NaY (Si/AI = 2.4, Union Carbide) and HZSM5 (Si/AI =17, Enichem Anic). Copper was introduced into the zeolites by the ion-exchange method. The samples and their main features are reported in Table 1. XPS and XAES spectra were obtained using Mg Ko~ radiation (hv = 1253.6 eV) with a Leybold-Heraeus LHS-10 spectrometer. DRS of fresh and thermal treated samples (10-5 torr, 788 K, 1 h) were recorded using a Cary 5 spectrometer. Dinitrogen adsorption measurements were performed in a vacuum line. The samples were degassed at 788 K under vacuum (10-5 torr) for 1 h, or treated in 350 torr of 02 at 788 K, and the adsorption of N2 was measured at 273 K in the range
?0 0- 100 torr. The reversible and irreversible adsorption were calculated. results obtained on samples pretreated in vacuum are reported in Table1.
The
RESULTS AND DISCUSSION DRS spectra of the as prepared samples show that the d-d transitions lie in the range expected for Cu2+ in octahedral environment of O-containing ligands (range 10000-15000 cm-1) [3]. In the case of Cu-Y and Cu-ZSM5 zeolites treated under vacuum at 788 K the intensity of d-d transitions is confused in the background indicating an almost complete reduction of Cu (11)to Cu (I). On the contrary Cu-Y and Cu-ZSM-5 zeolites pretreated first in oxygen and then in vacuum at 788 K presented a very limited reduction of Cu (11) ions. By a study of the Cu(2p) photoemission and Cu(LMM) Auger transition we conclude that Cu (11) ions are easily reduced, in vacuum and under X-ray irradiation, to Cu (I). This process, equivalent to the treatment in vacuum at 778 K of the as prepared samples, is faster for Cu (11) ions in ZSM-5, in agreement with the work reported by Jirka and Bosacek [4]. On Cu-Y zeolite no adsorption of N2 takes place. On the contrary on Cu-ZSM-5 zeolites with high copper Ioadings we have a relatively strong and irreversible adsorption of N2. The irreversible adsorption does not depend whether the samples were pretreated in vacuum or in 02. (The total amounts of adsorbed N2 on the contrary decreases after treatment in 02.) It appears that the last fraction of Cu(ll) ions exchanged in ZSM-5 zeolite has unique properties which are important both in the catalytic decomposition of NO at 773 K [2] and in the irreversible adsorption of N2 at low temperature. Table1. Samples and their main features. N2 adsorption is measured at 273 K on as prepared samples treated in vacuum at 778 K. Sample NaY Cu-NaY Cu-NaY HZSM5 Cu-HZSM5 Cu-HZSM5 Cu-HZSM5
Cu wt%
% of exchange
mol N2 (total) per mol Cu
mol N2 (irreversible) per mol Cu
5.06 9.38
50 94
0.00 0.00
0.00 0.00
0.73 1.85 3.33
25 65 117
0.14 0.27 0.32
0.03 0.04 0.12
REFERENCES [1] M. Iwamoto and H. Hamada, Catalysis Today 10 (1991) 57. [2] M. C. Campa, V. Indovina, G. Minelli, G. Moretti, I. Pettiti, P. Porta and A. Riccio, Catal. Lett. 23 (1994) 141. [3] R. A. Schoonheydt, Catal. Rev.-Sci. Eng. 35 (1993) 129. [4] i. Jirka and V. Bosacek, Zeolites 11 (1991) 77.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
71
Model of adsorbed NO molecules on Lewis sites in zeolites. A. Gutszel, 3, M. Plato 2, F. Witzel 1, H. G. Kargel 1 Fritz - Haber Institute of the Max Planck Society, Berlin, Germany 2 Physics Department, Free University Bedin, Germany
Results and Discussion
It has already been reported [1] that NO molecule which is a radical, is a very good probe to investigate Lewis acid sites in zeolites. This peculadty comes from the fact that the ground state of the NO molecule is degenerated and therefore the magnetic moment is equal to zero. To observe an ESR signal from NO one has to quench
the orbital mmomentum of the free
electron. This can be done by the electric field originating from an ion on which NO molecule is sorbed, for example from the Lewis site in a
Figure
1
zeolite.
10 mT
To adsorb the NO on this site and therefore to get an ESR spectra one has to cool the whole sample with the gas to the low temperature ( 77 K ). At that temperature one can see very nice ESR spectrum, which shows
the
hyperfine
x,
splitting
comming from the I"N nucleus and the superhyperfine 27AI nucleus.
splitting
from
The ESR spectrum of NO molecules adsorbed in the H-ZSM5zeolite at 277 K. A simulated spectrum which is (Takt =1075 K, p(NO)=50 Pa, Tad. =298 K, in very good agreement with the Xad.=l h.Tmeas" =77 K ) a) experimental b)simulated experimental one, was obtained by
the assumption that we have a symmetry close to axial, that means that the g - factors are equivalent gxx=gyy=l.997 and gzz =1.94 and the hyperfine splitting constant for AI: Axx = Ayy = 4.5 MHz ( Fig. 1 ) Cooling the probe to 10 K, the ESR spectra of NO adsorbed on Lewis sites changes. The superhyperfine splitting is two times smaller 3 Permament Adress: Medical Academy Bydgoszcz, Department of Biophysics, Poland
?2 To understand this change one has to go back to the Hamiltonian of the hyperfine interaction. This interaction is a sum of two parts, the contact and the dipole part. At 77 K the NO molecule adsorbed on a Lewis sites may still rotate around the AI-N axis, that means that the dipole part of the hyperfine interaction is averaged out. Therefore the superhyperfine splitting at 77 K is given by the contact interaction alone. At 10 K the NO molecule is rigidly bound to the Lewis site. The dipole part of the superhyperfine interaction is no longer averaged. Because of the smaller superhyperfine splitting at 10 K than at 77 K, the contact and the dipole
interactions
have
opposite
Figure 2
signs. It was possible for this model to simulate a spectrum which is in good agreement one
with
the
experimental
( Fig. 2 ). In this simulation the
distance between AI and N plays an important role. The best results are for the distance 0.1 nm, which is a resonable result. There
is
one
question
remainnig about the Lewis sites; what is the
charge
of AI in this
site,
because there are three posibilities:
AI 3*, AI 2., AI * ?
The ESR spectrum of NO molecules adsorbed in the H-ZSM5 zeolite at 10 K. (Takt =875 K, p(NO)=50 Pa, Tad . =298 K, Tmeas" =10 K ) a) experimental b) simulated
Figure 5
From these three posibilities,
one is impossible, namely AI 2.. This ion
is
paramagnetic
with a
large
o)
coupling constant and would influence the NO spectrum very strongly. AI 3. has
excatly
the
same
electronic
b)
configuration as the sodium ion (Na § ). For NO adsorbed on Na § ion ( Fig. 3 ) one does not see in the ESR spectra
The ESR spectrum of NO molecules adsorbed
in the Na-ZSM5 zeolite at 10 K. ('l'akt =875 K, p(NO)=50 Pa, Tad. =298 K, sodium nucleus ( 1=3/2 ). Therefore Tmeas" =10 K ) a) experimental b) simulated the most probable state of the AI of the superhyperine splitting from the
the Lewis site is AI *.
References:
1.Witzel, F., Karge, H., G., Gutsze, A., H~irtel, U., Chem. Ing. Tech. (1991), 63, 744
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
73
A COMBINED EPR AND NMR STUDY OF OXIDATION SITES IN DEALUMINATED MORDENITES. G. Harvey Estermann, Laboratorium f0r Technische Chemie, ETH-Zentrum, CH-8092 Z0rich. R. Crockett and E. Roduner, Physikalisch-chemisches Institut der Universit&t ZOrich, CH-8057 ZUrich
Summary The radical cation of 2,5-dimethyl-2,4-hexadiene (1) has been observed after adsorption of 2,5-dimethyl-3-hexene (2), and 2,5-dimethyl-l,5-hexadiene (3) onto dealuminated mordenites. The intensity of the EPR signal correlated with the presence of extra-framework aluminium as observed by 27AI MASNMR. When the extra-framework aluminium was removed by mineral acid leaching or chelation by oxalic acid, only a very weak EPR signal was detected. The conversion of alkenes (2) and (3) to diene (1) was also shown by G.C. analysis to be dependant on the type of mordenite. The generation of radical cations in these mordenites is dependant on the presence of Lewis acid sites located on extra-framework aluminium, although cationic reactions due to Bronsted acid sites often remain the major reaction pathway. Introduction EPR has often been used as a technique to identify intermediates in zeolite catalysis 1, although it remains unclear, which species within the zeolite is responsible for the generation of radical cations 2. One possibility is that the extra-framework aluminium, frequently present in dealuminated zeolites, forms Lewis acid sites, which act as electron acceptors 3. Experimental HM/NH, dV03: Na-mordenite (MOR) (PM-1, CU Chemie Uetikon AG) was exchanged
twice with 1M NH4NO3 and calcined at 700~ in air for ca. 15 h. HM/HN03: Na-MOR was treated first with 1M HCI and then with 6N HNO3 under reflux for 3h. The zeolite was calcined at 700~ for 1 h. The HNO3 treatment was repeated and finally the zeolite heated to 700~ for ca. 15 h. HM/OX: Na-MOR was exchanged with 1M NH4NO3 and then with 2M oxalic acid 3 times and calcined at 550~ for 8h. All zeolites were characterised by XRD and elemental analysis. For EPR and G.C. measurements HM/NH4NO3/A, HM/HNO3, and HM/OX were heated in air, and under vacuum, HM/NH4NO3/B, to 700~ for 15 h. EPR measurements were made at room temp. on a Bruker ESP 300 spectrometer. For G.C. the products were distilled off at room temp. and ca. 5x10-6 mbar. The 27AI, 29Si and 1H MASNMR measurements were recorded on a Bruker AMX400.
Results and Discussion HM/NHdNO3 Following adsorption of diene (3) onto HM/NH4NO3/A, the EPR spectrum of the radical cation of diene (1) was observed. The same signal was
?4
measured after adsorption of hexene (2), and the parent diene (1). In all cases the EPR signal was strong. No EPR signal could be detected after adsorption onto HM/NH4NO3/B. It was thus concluded that oxygen was required to generate the necessary oxidation sites. The Si:AI ratio only increased from 5.8 to 6.4 after treatment but the 27AI NMR spectrum showed that a large proportion of the AI was present as extra-framework species. 1H NMR of the dehydrated sample showed the presence of some Bronsted acid sites. G.C. analysis of the diene (1) showed that no reaction had taken place beyond the formation of a radical cation, the alkene (2) and diene (3) were converted to diene (1) to a small extent on both mordenites (table 1).
2
1
3
Table I Percentage of diene (11 formed after 30 min on mordenites.
diene (1) aikene (2) diene (3)
HM/NH4NO3/A
HM/NH4NO3/B
HM/HNO3
HM/OX
no reaction 0.5% 1%
no reaction <0.02% 4%
no reaction 0.2% 31%
43%
HM/HNO3 The intensity of the EPR spectrum obtained after adsorption of diene (1) onto HM/HNO3 was only 1.5% of that measured above. Acid leaching increased the Si:AI ratio to 63 and the 27AI NMR spectrum showed that the remaining aluminium was present both as framework and extra-framework species. 1H NMR showed that, as above, some Br~nsted acid sites were present. The alkene (2) underwent very little reaction (table 1). However, diene (3) reacted to (1) to a much greater extent. This is probably a Br~nsted acid catalysed reaction, and indicates that the acid sites are stronger or more numerous in the mordenite treated with HNO3. HM/OX This mordenite (Si:AI 51) gave similar results as HM/HNO3 indicating that the presence of extra-framework aluminium is important, and not the method of removal. Conclusion
These results indicate that the generation of radical cations is closely correlated with the presence of a large amount of extra-framework aluminium which has been previously treated at high temperature in air, resulting in the formation of Lewis acid sites. 1: R. Crockett and E. Roduner, J. Chem. Soc. Perkin Trans. 2, 1503, 1993. 2: S. Shih, J. Catal., 79, 390, 1983. 3: R.D. Shannon et al, J. Phys. Chem., 89, 4778, 1985.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
STUDY
OF N i - C O N T A I N I N G
75
SAPO-5
HYDROGENOLYSIS
A. Spoj a k i n a ,
I n s t i t u t e of K i n e t i c s * I n s t i t u t e of Organic
OF
BY E S R
SPECTROSCOPY
AND
THIOPHENE
N. K o s t o v a
a n d V. P e n c h e v *
and Catalysis, 1113 Sofia, B u l g a r i a Chemistry, 1113 Sofia, B u l g a r i a
SUMMARY
ESR m e a s u r e m e n t s and the t h i o p h e n e h y d r o g e n o l y s i s have b e e n carried out on the N i - c o n t a i n i n g (7 wt.% Ni) SAPO-5 s y n t h e s i z e d by i n t r o d u c t i o n of Ni0 and Ni a c e t a t e in the r e a c t i o n m i x t u r e and i m p r e g n a t i o n of SAPO with Ni nitrate. It has been s h o w n that the Ni r e d u c i b i l i t y and d i s p e r s i o n and a c t i v i t y of s a m p l e s in the t h i o p h e n e h y d r o g e n o l y s i s are c o n t r o l l e d by the Ni s t a t e introduced in SAPO-5. INTRODUCTION
Preliminary
perties
studies of N i - m o d i f i e d
of samples
rothermal
synthesis
with
connected
with
conversion.
EXPERIMENTAL
SAPO
5 was
were
(NiSAPO)
pared
Ni
or
by
200
after
by
Ni
the
D
All
acetate
to
calcined
were
at
in
the
flow
samples
and its
we
after
The
SAPO
calcined
a
zeolite
[i].
ESR m e a s u r e m e n t s conditions
The
results
Ni-modified
samples
sample 873
in h y d r o g e n
flow
(40 ml/min).
RESULTS
DISCUSSIONS
the
AND
The
catalytic
of
activities
addition
in
NiacSAPO>/ N i + S A P O
the
of
of
the
Ni
Ni+SAPO
aqueous K for
at
room
the
as NiO
was
pre-
6 h and
con-
solution
of
on a B r u k e r
catalytic
temperature test.
The
flow at a t m o s -
of 673 K, W H S V 0.6 h-1 of t h i o p h e n e .
of t h i o p h e n e
performance
role_in
were p e r f o r m e d
reactor
hyd-
the
addition
with
at
pro-
during
report
c o n v e r s i o n was c a r r i e d out in a h y d r o g e n temperature
to
in these
specific
in
paper
procedure
pheric pressure, Prior
this
(NiacSAPO).
spectrometer
pretreatment
thiophene
of
samples
7 wt.% Ni.
In
according
same
impregnation
nitrate.
tain about ESR
the Ni state
synthesized
prepared
indicated
the Ni i n t r o d u c e d
[1,2].
thiophene
SAPO-5
each
of N i - m o d i f i e d total
thiophene
sample
was
samples
gives
conversion
and that in the h y d r o g e n a t i o n
heated
the
1.5
order
NiSAPO
activity
h
NiSAPO
>>
>
76 NiacSAPO
>> Ni+SAPO.
The acid sites are r e s p o n s i b l e
c o n v e r s i o n but the formed b u t e n e s
No
signal
of nickel
was o b s e r v e d
localization
[3]. H e a t i n g
for t h i o p h e n e
are h y d r o g e n a t e d on m e t a l l i c in the
ESR
spectra
of
all
during
1.5
Ni
air-
c a l c i n e d samples 9 This could be the result of its high d i s p e r s i o n
or/and
to
appearance
The
decrease
of
in order NiacSAPO
overlapping
ESR
in hydrogen
signal
of Ni ~ w i t h
< NiSAPO < Ni+SAPO.
of the
parameters
in the
intensity
spectra
h
leads
increased
of N i S A P O
and two
signals in that of Ni+SAPO are revieled after sequen-
tial treatment
mixture 9 It NiSAPO
the
and
of samples
shows
Ni ~
a
at 673 K for 3 h by h y d r o g e n + t h i o p h e n e
formation
and
Ni
sulfide
of
more
fine
phases
particles
in
Ni+SAPO
due
[3]
in
to
a
c o m p e t i t i o n between sulfidation and reduction of Ni species 9 Note
that,
the
nickel
state
in N i S A P O
makes
easier
its
reduction 9 No
change in the ESR spectra of N i a c S A P O is observed 9
No ESR signals
are revealed
are pretreated
by
nickel
sulfides
of
NiSAPO
to
this
treatment appeared
probably
and
The
result,
in
Ni+SAPO
activity
No
samples
singlet
2. 3.
are
changes
revealed
the
nickel
show
the
during
sample
different
state
reducibility
is
hydrothermal
makes
is
easier
Ni-containing
nickel
observed
in
synthesis 9 The
reduced SAPO-5
and
the
these
spectra
sequantial
(g=2.25)
case H2S
and
of
in
after
nickel
In this
state
when
diamagnetic
mixture 9 A c o n t r a r y
ferromagnetic
REFERENCES 9
essential
of samples
of p r o b a b l y
More nickel is reduced and m i g r a t e s
nickel
of
of
i n c o r p o r a t e d during synthesis 9 1
spectra
spectra of NiacSAPO.
changes
results hard
formed.
Ni+SAPO
in the
introduced
in the
at 673 K because
by the reaction t h i o p h e n e + h y d r o g e n
redusibility.
The
are
H2S
the
samples
by
its
samples. with
impregnated
sulfided.
enhances
easier
to surface 9
in
is
adsorbtion
Hydrogenation Ni
species
V Penchev, H Lechert et al in "Zeolites for the Nineties" J Jansen et al. (Eds.), A m s t e r d a m , p . 2 4 7 , 1989 V. M a v r o d i n o v a , Ya. N e i n s k a , Ch. M i n c h e v , H. L e c h e r t , V. M i n k . v , V. P e n c h e v , S t u d . S u r f . Sci. Catal., 69 295 ( 1 9 9 1 ) . S. S u r i n e t a l . , D o k l . A k a d . N a u k SSSR, 2 4 2 , 649 ( 1 9 7 8 ) . 9
9
9
Ni
nickel
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
77
Electron Spin Resonance and Electron Spin Echo Modulation Spectroscopic Study of Pd(1) Location and Adsorbate Interactions in PdH-SAPO-34 Molecular Sieve Jong-Sung Yu, Gern-Ho Back +, Vadim Kurshev and Larry Kevan ++ Department of Chemistry, Han Nam University, Taejon, Chungnam, 300-791, Korea +Department of Chemistry, Changwon University, Changwon, Kyungnam, Korea ++Department of Chemistry, University of Houston, Houston, Texas 77204-5641,USA
ABSTRACT Electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopies have been used to monitor the location of P d ( I ) a n d its interaction with water, methanol, ethanol, ethylene, benzene, carbon monoxide and ammonia in silicoaluminophosphate type 34 (SAPO-34) molecular sieve containing Pd(II) by ion-exchange. After activation at 600 oC, three different Pd(I) species are observed: Al(g_L = 2.177), A2 (gj_ = 2.136) and A3(g_L = 2.070) with a common gll = 2.92. These correspond to three different site locations in the framework. A1 is assigned to the least accessible site HI in the center of a hexagonal prism, A3 to site I displaced from a six-ring into the ellipsoidal cage and A2 to the most accessible site IV near an eight-ring window based on adsorption of oxygen and hydrogen and 31p modulations from the SAPO framework observed by ESEM. Oxygen and water oxidize Pal(I) ions in an activated sample to Pd(II) ions complexed to O2" indicating water decomposition. Adsorption of methanol and ethanol causes a change in the ESR spectrum which indicates some relocation of Pd(I) to better coordinate with one molecule of the alcohol. Exposure to ethylene also changes the ESR spectrum indicating interaction of Pd(I) with ethylene. ESEM shows that the Pd(I) species coordinates to one ethylene. The adsorption of carbon monoxide results in a Pd(I) complex with three molecules of carbon monoxide based on resolved 13C superhyperfine splittings. Upon adsorption of ammonia, one molecule of ammonia coordinates to Pd(I) based on resolved nitrogen hyperfine coupling. Upon adsorption of big molecules such as benzene, however, no change of ESR spectrum is observed, and no deuterium modulation was detedcted on ESEM spectrum, indicating no detectable interaction between Pd(l) and benzene.
?8
INTRODUCTION In the last ten years the synthesis and characterization of the new group of aluminophosphate (AIPO4-n) and silicoaluminophosphate (SAPO-n) molecular sieves have been reported. These new molecular sieves have some frameworks isomorphous with aluminosilicate zeolites and other novel structures not found in zeolites. SAPO molecular sieves are particularly important because ion-exchange
these have
properties and can incorporate catalytically active ions.
Pal-loaded catalysts are widely used for various reactions. for ethylene dimerization
Pd(I) is active
and for the synthesis of methanol from CO and H2.
In this study Pd(II) is incorporated into H-SAPO-34 by solid state ion-exchange to form PdH-SAPO-34. SAPO-34 is a cage-type molecular sieve with a structure similar to the zeolite aluminosilicate called chabazite. ESR and ESEM spectroscopies
are
used to
monitor
adsorbates to determine the coordination structure of Pd(I).
Pd(I)
the ion
interactions locations
of
Pd(I)
and
with the
various
adsorbate
EXPERIMENTAL SECTION SAPO-34 was synthesized by a modification of the methods of Xu et al. as developed in our laboratory. Pd(II) was ion-exchanged into H-SAPO-34 using a solid-state reaction method. SAPO-34 samples after synthesis, Pdexchange and calcination were examined by powder X-ray diffraction (XRD) with a Philips PW 1840 diffractometer. PdH-SAPO-34 was first loaded into 3 mm o.d. by 2 mm i.d. Suprasil quartz tubes and evacuated at room temperature. Evacuation was continued by raising the temperature to 600 ~ over 8 h and then holding at 600 oC for 12 h. These samples were then heated in about 600 tort of dry o~jgeP, at 600 o c for !6 h and evacuated again at 600oc for about 16 h to give "activated" samples. The "activated" samples were exposed to liquid adsorbates (D20, CH3OD, CD3OH, C2H5OD) at their room temperature vapor pressure or to gaseous adsorbates (ND3, 15NH3,12CO, 13OO and 0204).
The sample tubes were sealed after exposure to adsorbates and
were stored in liquid nitrogen. ESR spectra were recorded at 77 K on a modified Varian E-4 spectrometer interfaced to a Tracor Northern TN-1710 signal averager. ESEM spectra were recorded with a Bruker ESP 380 pulsed ESR spectrometer. Three-pulse echoes were measured by employing a 90o-~:-90~ 90 ~ pulse sequence as a function of T.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
79
STABILITY OF THE Co(II) VALENCE STATE IN ALUMINOPHOSPHATE-5 MOLECULAR SIEVE TO CALCINATION FROM LOW TEMPERATURE ELECTRON SPIN RESONANCE
Vadim Kurshev and Larry Kevan Department of Chemistry, University of Houston Houston, TX 77204-5641 David Parillo and Ray Gorte Department of Chemical Engineering, Univ. of Pennsylvania Philadelphia, PN 19104-6393 SUMMARY As-synthesized CoAPO-5 is blue and it becomes yellow-green after calcination in oxygen. This was interpreted by several research groups as indicating a valence state change from Co(II) to Co(III); however, our electron spin resonance and temperature programmed desorption results provide no evidence for Co(HI) and are consistent with all the framework species existing as Co(II) both before and after calcination. INTRODUCTION Transition metal ion incorporation into aluminophosphate molecular sieve frameworks can increase the stability of the metal ion for catalytic reaction, prevents ion removal by reaction products, and controls the acidity of the molecular sieve. Insertion of a metal ion into a synthetic mixture does not guarantee metal ion incorporation into the framework and it is not easy to definitely verify framework incorporation. Electron spin resonance (ESR) and its temperature dependence can be sensitive to the local symmetry of a paramagnetic center. CoAPO-5 presumably has Co(II) incorporated into the framework of aluminophosphate-5. Upon calcination in flowing oxygen the color of CoAPO-5 changes from blue to yellow-green. This was previously interpreted as oxidation of Co(II) to Co(m). However, new ESR data from 7 to 35 K do not support this and indicate that no valence change occurs during calcination. EXPERIMENTAL SECTION CoAPO-5 was synthesized per literature measured with a Bruker ESR spectrometer.
procedures
and
ESR
was
RESULTS AND DISCUSSION Our ESR measurements verify a Co(N) ESR intensity decrease at 4 K, but show no chan0e at 20 K and higher temperatures. The absence of an ESR
80
signal intensity difference before and after calcination above 20 K indicates that all cobalt in calcined samples remained Co([I). The anomalous (non-Curie) ESR temperature dependence is due to changes in the population of the ESR active level. As follows from a group theory analysis, the ground level of high spin Co(II) ion in a crystal field of tetrahedral symmetry is degenerate and consists of two Kramers doublets with total electron spin projections Ms = __.3/2 and Ms =___1/2. The structure of the ground level has a normal temperature dependence of the ESR intensity (Curie behavior). In a crystal field of lower symmetry like dihedral, the degeneracy is lifted, and when the ESR active level lies at higher energy the ESR intensity can have a maximum at the temperature comparable to the zero field splitting between the two Kramers doublets. We can fit the experimental temperature dependence of the Co(II) ESR intensity in calcined CoAPO-5 for a zero field splitting parameter of 2D =-13 cm -1. The dependence of the Co(II) ESR intensity in as-synthesized Co-APO-5 shows Curie behavior. These facts indicate that Co(I]) has nearly tetrahedral symmetry in as-synthesized CoAPO-5 consistent with framework substitution and that the symmetry is distorted dihedral upon calcination. The absolute value of the zero field splitting parameter supports the distortion to dihedral (D'2h)symmetry. Temperature programmed desorption (TPD) experiments also support nonoxidation of framework Co(II) upon calcination. Since a framework Co(II)ion produces uncompensated framework charge, the number of Br/~nsted acid sites in calcined and "reduced" CoAPO-5 must be identical and equal to the number of Co(H) ions. This was confirmed by TPD measurements. The following experiment suggests distortion of the local symmetry of Co(II) by oxygen. As-synthesized blue CoAPO-5 was evacuated at slowly increasing temperature to remove the tetraethylammonium hydroxide synthesis template from the pores. At 500 oC CoAPO-5 remained blue, but it instantly changed to yellow-green after exposure to oxygen gas at 500 oC. CONCLUSIONS
The ESR temperature dependence indicates cobalt(H) incorporation into tetrahedral sites in the CoAPO-5 framework. Co(H) does not oxidize to Co(HI) upon calcination. The E SR intensity decrease at 4 K is due to distortion of the Co(II) local symmetry from near tetrahedral to a lower dihedral symmetry upon calcination.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
8]
CHARACTERIZATION OF ALKALI METAL CLUSTER-CONTAINING FAUJASITES BY THERMAL, IR, ESR, MULTI-NMR AND TEST REACTION STUDIES 11. Hannus, ~1. Kiricsi, 1A. B~res, 2J.B. Nagy and 3H. F6rster 1Applied Chemistry Department, J6zsef Attila University, H-6720 Szeged, Rerrich Bela ter 1, Hungary. 2Laboratoire de Catalyse, Facultes Universitaires Notre-Dame de la Paix. B-5000 Namur, 61 rue de Bruxelles, Belgium. 3Institute of Physical Chemistry, University of Hamburg, D-20146 Hamburg, Bundesstrasse 45, Germany Summary Characterization of alkali metal clusters in MY-FAU (M=Li§ Na § K§ Rb§ Cs§ by a combination of physical-chemical methods revealed the formation of both charged and neutral Na~ and My clusters upon heat treatment of NaN 3-loaded zeolites. They turned out to be efficient basic catalysts. Introduction Alkali metal clusters in the cavities of zeolites can be prepared via exposure to metal vapour [1]. A convenient method for in situ generation of sodium vapour
in the pore system of zeolites is the
decomposition of sodium azide [2]. The aim was the characterization of the so-formed clusters in alkali metal ion-exchanged faujasites by the concomitant application of thermal analysis, IR, ESR and multiNMR spectroscopy as well as 1-butene isomerization as test reaction. Experimental section NaN 3 was introduced into the Li § Na§ K§ Rb§ or Cs" ion-exchanged zeolite either as a solid material [2] or in methanol solution [3]. The thermal behaviour of the NaNVIVlY-FAU system was studied by thermal analysis. The decomposition of sodium azide was monitored by IR spectroscopy as well, using self-supporting wafers in a variable-temperature cell. The metal clusters formed were characterized by both ESR and MAS-multi-NMR (ZLi-, 23Na-, 87Rb- and l~Cs-) spectroscopies. Isomerization of 1butene was investigated in a recirculation reactor with GC analysis. Results and discussion Thermal analysis showed that decomposition of sodium azide took place in two partly overlapping or one unresolved stages at low and fast heating rates respectively. Similar observation was reported by Martens et al., who proved that the state of sodium formed was influenced by the heating rate and affected by the catalytic activity of the zeolites thus modified [3]. Upon evacuation with increasing temperature the broad band centered at 2080 cm ~ in the IR spectrum splits into two bands at 2060 and 2170 cm ~ which are the only bands present prior to NaN 3 decomposition and remain after heat treatment at 673 K for 12 h. Cooling down to room temperature resulted in absorptions at 2037, 2070, 2170, 2187 and 2205 cm1 assigned to azide species in different environment. From these spectral changes follows that in the zeolite cavities azide ions are stabilized even above the decomposition temperature of neat NaN 3 and distributes over different sites in the pores strongly influenced by temperature.
82 The ESR spectra of samples prepared by solid-solid mixture was changing as a function of time. The rather large clusters formed outside the zeolite crystallites were decreasing in favour of the intra zeolite particles, especially in cases of K, Rb and CsY-FAU. Samples prepared by methanol solution impregnation did not show any evolution with time. The 23Na-MAS-NMR spectra of all MY-FAU samples show the presence of neutral sodium clusters in the region characteristic of a Knight shift [4]. This proves unambigously, the formation of Nax clusters in presence of other alkali cations. The 133Cs-NMR spectra of the decomposed NaN3/CsY-FAU zeolites show in addition the presence of Cs containing metal particles. According to the catalytic activity measurements, the tested Li, Na, K, Rb and CsY-FAU zeolites and their modified varieties proved to be strong basic catalysts, as could be established from the product distribution of 1-butene isomerization as well as the appearance of a carbanion intermediate during isomerization of allyl cyanide. Conclusions NaN3 introduced into the zeolites does not decompose completely during heat treatment. A small portion is stabilized in the pore system as it can be concluded from thermal analysis and IR spectroscopic data. Its decomposition leads to generation of Nax and My clusters, the presence of which is proved by ESR and multi-NMR spectroscopies. Alkali metal ion-exchanged faujasites and their metal cluster-containing derivatives are catalytically active in 1-butene isomerization resulting in product distribution characteristic for basic catalysts. Formation of carbanionic intermediate from allyl cyamde proved to be probable in these basic zeolites. Acknowledgement Financial supports from National Research Foundation of Hungary (OTKA No. 1064), Deutsche Forschungsgemeinschaft and Belgian FNRS are gratefully acknowledged. References [1] J.A. Rabo, P.H. Kasai, Progr. Solid State Chem., 9,1 (1975) [2] P. Fejes, I. Hannus, I. Kiricsi, K. Varga, Acta Phys. Chem., Szeged, 24, 119 Kiricsi, I. Hannus, A. Kiss, P. Fejes, Zeolites, 2, 247 (1982) [3] L.R.M. Martens, P.J. Grobet, W.J.M. Vermieren, P.A. Jacobs, Stud. Surf. Sci. [4]
(1986)
(1978); ~
I.
28, g35
P.J. Grobet, G. van Gorp, L.R.M., P.A. Jacobs, Proc. 23rd Congr. Ampere (Rome, 1g86) p.356
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
83
A Study of Cu-Y and Cu-Rho zeolites by 129Xe NMR A. GEDEON and J. FRAISSARD Laboratoire de Chimie des Surfaces, associe au CNRS -URA 1428 Universite P. et M. Curie Casier 196, Tour 55 4, place Jussieu 75252 PARIS Cedex 05 - France
SUMMARY
The adsorption isotherms and 129Xe nuclear magnetic resonance (NMR) chemical shifts of xenon adsorbed on Cu(ll)-exchanged Y and Rho zeolites were measured. The location and the oxidation state of the copper ions as well as the nature of Xe-cation interactions were determined. INTRODUCTION 129Xe NMR spectroscopy is a useful tool for the determination of the void space, the structural and chemical properties of zeolites and the location and electrostatic effects of cations therein (1,2). In previous papers we observed that the chemical shift of xenon in AgY and Ag-X zeolites ( Ag+: [Kr] 4d 10) was less than that of Na-Y or Na-X and even less than that of the quasi-isolated xenon atom (3,4). We attributed this exceptional result to the formation of an unstable Ag+-Xe complex whose lifetime was however long enough for the instantaneous increase in the electron density, due to 4d10-5d0 transfer from Ag+ to xenon, to cause this variation of the chemical shift. Recently, we have shown that in dehydrated Cu-Y and Cu-X (5,6), the chemical shifts of adsorbed xenon are also lower than in Na-Y or Na-X. These results were attributed to the specific interaction with Cu + formed by the autoreduction of Cu2+ during the dehydration of the zeolites. We have also shown that after dehydration at 400~
many Cu2+ ions have
migrated towards sodalite cavities and prisms and that the Cu2+ ions remaining in the supercages have been autoreducted to Cu +. To confirm these hypotheses, we looked for a system where, even after dehydration, the Cu 2+ were still in supercages or cavities in contact with the xenon. We chose Cu(ll)-Rho zeolite.
EXPERIMENTAL SECTION Copper-exchanged Na-Y zeolite, Cu-Y was prepared conventionally by refluxing at 80~ the zeolite with a 0.1M aqueous copper nitrate solution for 12tl at pH 6. Starting from Cs-Rho zeolite, exchanged Cu(li)-Rho zeolite was also prepared with aqueous solutions of copper nitrate. The Cu2+ cations were quantitatively analyzed by atomic absorption spectroscopy. The samples prepared correspond to 95% cation exchange.
84 The zeolites were evacuated 12 h under 10-5 Torr vacuum at 26~ and then slowly heated to 400~
They were held at this temperature for 12 h and then brought back to ambient
temperature. The adsorption isotherms were measured volumetrically at 26~
129Xe NMR
spectra were recorded on a Bruker spectrometer, either a MSL 400 or CXP 100, at 110.642 and 24.905 MHz, respectively. RESULTS AND DISCUSSION Cu(ll)-Rho zeolite: The observed chemical shift ~)is much greater than that of Na-Y. The form
of the ~>versus N (xenon concentration) curve, in particular the presence of a minimum and the line broadening (about 100 kHz) prove that the xenon interacts with strong adsorption sites which can only be Cu2+ . Such variations due to the presence of paramagnetic ions have also been shown in the case of the Ni(II)-Y zeolite (7,8). in Cu(ll)-Rho zeolite, we attribute this large positive shift to the high polarization of xenon and the distortion of the xenon electron cloud by the strong electric fields created by the Cu2+ ions in contact with it. Cu-Y zeolite: The chemical shift ~>decreases monotonically with N and is always lower than that in NaY and Cu(ll)-Rho zeolites. That there is no minimum (low shifts and lines not wider than 200 Hz), indicates that there are no Cu2+ ions (paramagnetic centers) in the supercages. This suggests that during dehydration at 400~
many C u2+ have migrated
outside the supercages and the Cu2+ remaining in the supercages has been transformed by autoreduction to Cu +. In our opinion, xenon in contact with Cu + ions in special locations (Sill) exhibits unusually large displacements of the resonance line to low frequency via the dx -dTr back-donation mechanism. REFERENCES 1. J. Fraissard and T. Ito, Zeolites, 8 (1988) 350. 2. P. J. Barde, J. Kiinowsld, Progr. NMR Spect., 24 (1992) 91. 3. R. Grosse, R. Burmeister, B. Bocldenberg, A. Gedeon and J. FraJssard, J. Phys. Chem., 95 (1991) 2443. 4. A. Gecleon, R. Burmeister, R. Grosse, B. Boddenberg and J. Fraissard, Chem. Phys. Letters, 179 (1991) 191. 5. A. Gedeon, J. L. Bonardet, and J. FraJssard, J. Phys. Chem., 97 (1993) 4254. ~. A. Gedeon and J. FraJssard, Chem. Phys. Letters, 291 (1994) 440. 7. N. Bansal and C. Dybowsky, J. Phys. Chem., 92 (1988) 2333. 8. A. Gedeon, J. L. Bonardet, T. Ito and J. Fraissard, J. Phys. Chem., 93 (1989) 2563.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
DIRECT OBSERVATION OF DISTRIBUTIONS OF MIXED CLUSTERS OF COADSORBED SPECIES IN ZEOLITE NaA A. K. Jameson, % C. J. Jameson,* A. C. de Dios, @E. Oldfield, @and R. E. Gerald II* Departments of Chemistry, *University of IUinois at Chicago, Chicago IL 60607, %Loyola University, Chicago IL, 60626, and @University of Illinois at Urbana, Urbana, IL 61801 Summary We show for the first time that the individual peaks corresponding to Xe~ clusters inside the alpha cages of zeolite NaA can be narrowed under magic angle spinning. Under these high resolution conditions we observe the individual peaks corresponding to mixed dusters Xe,d~m inside the alpha cages, which allows the direct determination of the distribution of coadsorbates in a microporous solid for the first time. INTRODUCTION.
In our studies of molecular interactions and dynamics of sorbates in
microporous solids using NMR observables together with computer simulations, we have focussed on xenon clusters trapped in the regular array of cages in the NaA zeolite. ~-3 We have directly observed the fractions of alpha cages in zeolite NaA that have trapped from one to eight Xe atoms, ~ and measured the rate constants for migration of xenon atoms from one alpha cage to another, 3 as have the Pines group. 4'5 These direct determinations of adsorbate distribution as a function of loading and temperature provide detailed tests of computer simulations. Furthermore, the chemical shifts of the clusters measured as a function of temperature provides a test of the averaging amongst the large numbers of configurations of a particular cluster within an alpha cage. Thus we have elicited information on the structure of the Xe~ clusters through the simulations. 2 The origin of the width of the lines (about 10 ppm) of the Xe~ clusters has been a continual puzzle, 1 ppm-wide lines being rather commonplace for Xe in other zeolites. 6"s We have been able to "bum" a hole as narrow as 2 ppm in one of the lines in a typical spectrum by using a selective DANTE pulse sequence. Furthermore, T2 (CPMG) experiments in several different samples of Xe in zeolite NaA have yielded relaxation times from 15-40 ms, indicating limiting line-widths in the vicinity of 25 Hz. This information suggested that the broad lines might be narrowed under magic-angle spinning conditions. EXPERIMENTAL RESULTS AND DISCUSSION. A Gay-type spinner held the sealed 3-cm sample tube in a specially built MAS probe in a wide-bore 8.5 T magnet. A substantive improvement in signal/noise is obtained by the factor-of-10 narrower lines
85
86 achieved for the first time for Xe in NaA. The next MAS experiments involve determination of distributions of Xe atoms in the presence of coadsorbate molecules. We have observed the distribution of xenon atoms in the presence of coadsorbed molecules such as argon as a function of the average occupancy number (n)xc and (n)Ar, Ar being in fast exchange, moving freely from cage to cage during the observations. 9 There are however, many molecular species that, like Xe, have long mean residence times in the alpha cages. Because the chemical shift of mXe in the presence of another molecule is quite distinct from that in the presence of another Xe, as we have determined from the second virial coefficients of nuclear shielding in the gas phase, ~~ we expect the distinct 129Xe chemical shifts for those clusters corresponding to one Xe atom and various numbers of B molecules in the alpha cage to provide separate signals. If individually resolved, the peaks should be directly assignable on the basis of the known relative magnitudes of the shielding virial coefficients for Xe-Xe versus Xe-B. 1~ In samples of mixtures of xenon with krypton in zeolite NaA the individual lines overlap so badly that virtually no structure can be seen in the conventional static spectrum at 9.4 T. Under MAS conditions the multitude of 1 ppm-wide lines are well-resolved and are readily assigned to specific mixed clusters of Xe,Kr=. From the relative intensities of each line in the spectrum we can determine the fractions of the alpha cages containing specifically n Xe atoms and m Kr atoms. This is the first direct determination of the distribution of coadsorbates in a microporous solid. 1. C.J.Jameson, A.K.Jameson, R.Gerald II, A.C.deDios, J..Chem. Phys. 96,1676 (1992). 2. C.J.Jameson, A.K.Jameson, B.I.BaeUo, H.M.Lim, J. Chem. Phys. 100, xxx (1994). 3. A.K. Jameson, C. J. Jameson, and R. E. Gerald II, J. Chem. Phys. submitted. 4. B.F.Chmelka, D.Raftery, A.V.McCormick, L.C.deMenorval, R.D.Levine, A.Pines, Phys. Rex,. Lett. 66, 580 (1991); R.G.Larsen, J.Shore, K.Schmidt-Rohr, L.Emsley, H. Long, A.Pines, M.Janicke, B.F.Chmelka, Chem. Phys. Lett. 214, 220 (1993). 6. C.J.Jameson, A.K.Jameson, R.Gerald II, A.C.deDios, J. Chem. Phys. 96, 1690 (1992). 7. T.Ito, J.Fraissard, J. Chem. Phys. 76,5225 (1982); J.Fraissard, Zeits. Physik. Chemie 152, 417 (1987). 9. C.J.Jameson, A.K.Jameson, H.M.Lim, to be published. 10. A.K.Jameson, C.J.Jameson, H.S.Gutowsky, J. Chem. Phys. 53, 2310 (1970). 11. C.J.Jameson, A.K.Jameson, S.M.Cohen, J. Chem. Phys. 59, 4224 (1973). We are grateful to Gary Turner for lending us the special purpose probe used in this work. This work has been supported by the National Science Foundation and the Materials Research Laboratory at the University of Illinois Urbana-Champaign.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
87
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
STUDIES ON THE FORMATION AND STRUCTURE OF MOLECULAR CLUSTERS OF (CdS)4 IN ZEOLITE Y BY in-situ IR AND 113Cd MAS NMR Qi Ming 1, Xue Zhiyuan 1, Zhang Yongchao I and Li Quanzhi 2 1The Center of Analysis and Measurement, Fudan University, Shanghai, 200433, P.R. China 2The Department of Chemistry, Fudan University, Shanghai, 200433, P.R. China
SUMMARY The formation of molecular clusters of (CdS)4 in zeolite Y was studied by the changes of HF-OH and LF-OH bands of Y zeolite measured with in-situ FT-IR at different stages of preparation such as exchange, thermal treatment, sulphuration etc., and the coordination structure was evidenced by the results of 113Cd MAS NMR.
INTRODUCTION As is well known, molecular clusters of the semiconductor (CdS)x formed in zeolite Y can produce a blue shift of absorbed light relative to bulk CdS. The arrangement among atoms in molecular clusters is also different from bulk CdS with the structure of sphalerite, and its rock-salt structure has been suggested by the EXAFS technique [1]. However, the relationship between preparation conditions and formation of molecular clusters (CdS)x have not been studied in detail. In this work, the changes of hydroxyl groups of zeolite Y in each procedure of preparation of CdS were measured by in-situ FT-IR and from these results, the formation of CdS in Y zeolite cages will be discussed. The coordination structure of molecular clusters of (CdS)4 has also been evidenced by 113Cd MAS NMR. EXPERIMENTAL SECTION The (CdS)4 in zeolite Y was prepared by the following sequence NaY(Si/AI=2.3) --~ NH4Y --~ CdOH-HY--~ CdS-HY whose absorption in UV-Visible spectra is at 410nm (bulk CdS is at 520nm). The spectra of hydroxyl groups of various Y zeolites were measured by an in-situ Nicolet 5SXC FT-IR spectrometer and 113Cd MAS NMR spectra were recorded by a Bruker MAS-300 spectrometer. The chemical shifts are reported relative to Cd(NO3)2 solid.
88
RESULTS AND DISCUSSION The 113Cd MAS N M R results show that the chemical shift of hydrated Cd++-HY sample calcined at 400~
under an atmosphere of oxygen is at 115 p p m which
approximates to the chemical shift of 83.5 p p m for bulk CdO with the rock-salt structure in which the coordination n u m b e r of Cd ++ ions is six. Thus it can be inferred that the structure of Cd(OH) + in Cd(OH)-HY is the same as that of bulk CdO. For the CdS-HY sample, the chemical shift of 113Cd at 109 p p m approximates to that of Cd(OH)-HY, but it is quite different from the chemical shift of 583.9 p p m for bulk CdS with sphalerite structure. It means that the CdS in Y zeolite has the rock-salt structure, like Cd(OH)-HY in Y zeolite. The results of in-situ FT-IR show that w h e n the hydrated Cd++-HY zeolite was evacuated at 150~
the ratio of the strength I(LF)/I(HF) is greater than one. This
is related to the decomposition process of Cd(H20)x ++, i.e. Cd(H20)x ++ --~ Cd(OH) + + H +. Both Cd(H20)x ++ and Cd(OH) + ions located in the supercage bring about the decrease of strength of HF-OH. On evacuating at 200~ I(LF)/I(HF) < 1, it shows that Cd(OH) + ions located at site II near 0(2) in supercage move to site r near 0(3) in the sodalite cage [2], i.e. Cd[O(2)]H) + + O(3)H ~ Cd[O(3)]H) + + O(2)H. In this case, the Cd ++ ions are in site r and the OH-ions located at site Ir in the sodalite cage. Thus the ratio of I(LF)/(HF) decreases with the increase of exchange degree. W h e n the evacuation temperature was elevated to 250~ this ratio did not o b v i o u s l y change. It shows that the Cd(OH) + ions completely m o v e to the sodalite cage at 250~ Maybe there are four Cd ++ ions occupying site r arranged with tetrahedra in one sodalite cage in which the coordination n u m b e r is six and the other three 0(3) are in the six-membered ring of the hexagonal prism cage. Thus the structure of the cluster is Cd4(OH)40(3)12. After s u l p h u r a t i o n , the reaction Cd(OH) + + H2S ---) CdS + H 2 0 + H + occurs. When CdS-HY was evacuated above 150~
one found I(LF)/I(HF)>I, this result is opposite to that f o u n d before
sulphuration. It means that the H + released by s u l p h u r a t i o n r e m a i n s in the sodalite cage and increases the strength of LF-OH, and S2- ions replacing the OH" ions combined with Cd ++ ions to form the guest cluster of (CdS)4 whose structure is that of rock-salt. REFERENCES
[1] N. Herron et al., J. Am. Chem. Soc., 111 (1989) 503. [2]. M. CaUigaris et al., Zeolites 6 (1986) 439.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
NMR STUDIES
OF HYDROFLUOROCARBON-ZEOLITE C. P. Grey* and D. R. Corbin #
89
INTERACTIONS
#DuPont Cr&D, Wilmington, DE 19880-0262, USA (contribution number 6952) and *SUNY Stony Brook, Chemistry Department, NYl1794-3400, USA ABSTRACT A 19F and 27AI NMR study of the reaction of hydrofluorocarbon-134 with the zeolites NaX and NaY is reported. 134 decomposes on NaX at 250oc, and tetrahedral aluminum fluoride species are observed. On hydration, the tetrahedral aluminum fluoride species disappear and octahedral AI species become visible. At these temperatures, 134 does not react with the NaY framework. INTRODUCTION
W e are studying the interactions of HFCs 134 (CF2HCF2H) and 134a (CF3CFH2) with basic zeolites such as NaX and CsY. 134a is one of the new generation replacements for the refrigerant CFC-12. The syntheses of the new CFC alternatives are more complex than the syntheses of the old CFCs, involving many more steps I and unwanted HFC and HCFC isomers are often produced during the reactions. Consequently, the purification of the products remains a concern. We are investigating the differential binding of 134 and 134s to basic zeolites, in order to design methods to separate these two molecules. A correlation has been established between the separation factor of 134 and 134a and the Sanderson electronegativity of the zeolite: the greater the electronegativity, the poorer the separations 2. The NaX zeolite is sufficiently basic that decomposition of the 134 at 275oc was observed to occur in gas chromatography studies3. Only HFC-1123 (CF2CFH) elutes at this temperature. An NMR study was commenced, to investigate this decomposition reaction more fully. This study is reported below. EXPERIMENTAL
The zeolites were dehydrated by heating the samples under vacuum at 400oc. Quantitative amounts of 134 were then adsorbed, and the samples were heated at 250oc or 275oc. Rehydration was achieved by exposing the zeolite sample to a saline solution for 1 hour. The NMR samples were packed in a glove-bag. NMR spectra were acquired on CMX-120 and MSL-360 spectrometers. The HartmannHahn condition for 19F-27AI cross polarization (CP) was determined using AIF3.
90
RESULTS AND DISCUSSION 19F MAS NMR spectra of the 134/NaX system show that partial decomposition of the 134 occurs after heat treatment at 250oc. New peaks, in addition to the resonance from the 134, are observed in spectrum of a sample that has been heated for only 5 minutes. Resonances from the HFCs 134 & 1123 can be observed. In addition, resonances that result from rigid fluorine species are seen. These are assigned to fluorine coordinated to tetrahedral AI species (-203ppm), F- ions (189ppm) and F - N a + species (-255ppm). The intensities of these resonances increase, after heating for longer periods. On hydrating the samples, a resonance at -180ppm, from octahedral aluminum fluoride species, dominates the spectra. 27AI MAS NMR of the 134/NaX samples gave spectra that are similar to those of NaX. On hydration of these samples, however, a resonance at 1.3ppm and a much smaller peak at -36.4 ppm are observed. These resonances can be assigned to octahedral AI. 19F-27AI CP was also performed. A resonance was observed in the spectrum of the dehydrated sample at 47ppm. Since this resonance must arise from AI in close proximity to a fluorine atom, we assign this resonance to a tetrahedral aluminum fluoride species. This is consistent with the 19F spectra assignments. The 27AI CP spectrum of the hydrated sample shows two resonances in the octahedral region of the AI spectra, from AI(H20)6-xFx species. X-ray diffraction show that the crystallinity of NaX decreases considerably on treatment with 134 at 275oc, indicating that the zeolite framework is being destroyed. In contrast to NaX, the sample of 134 adsorbed on NaY shows very little 134 decomposition. Some 1123 is visible, but the only other observable resonance (at -254ppm) is from an F- Na + species. CONCLUSIONS 134 decomposes on NaX to liberate 1123, and tetrahedral aluminum species are observed in the 19F and 27AI NMR. A possible mechanism for the formation of such species involves protonation of a basic oxygen site in the zeolite, followed by an attack of the F- on the adjacent aluminum atom. Attack of the zeolite framework does not occur in the case of the less basic zeolite NaY, and only NaF-type species are formed. We have been able to observe selectively AI species that are in close proximity to fluoride ions, by using 19F-27AI CP. This has important implications for the study of other catalytic AI/F systems. 1. L.E.Manzer, Science, 249, 31 (1990). 2. D.R. Corbin, patent pending. 3. D.R.Corbin, unpublished results.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
91
ALUMINUM-27 DOUBLE-ROTATION NMR INVESTIGATIONS OF SAPO-5 WITH VARIABLE SILICON CONTENT Michael Janicke and Bradley F. Chmelka Department of Chemical and Nuclear Engineering, University of California, Santa Barbara, CA, 93106, USA Dirk Demuth and Ferdi Sch0th Institut fdr Anorganische und Analytische Chemie, Johannes Gutenberg-Universita't 55099 Mainz, Germany
Mainz,
SUMMARY Double-rotation NMR (DOR) studies of 27AI species in SAPO-5, a silicon aluminophosphate molecular sieve with a one dimensional channel system, have revealed a minimum of three aluminum sites resulting from the synthesis. The DOR technique was used specifically to increase the spectral resolution by removing the broadening influences from second-order quadrupolar interactions associated with the spin 5/2 27AI nuclei. The DOR investigations of SAPO-5 crystals with variable Si/AI ratios resulted in the identification of three aluminum species, two consistent with the reported isotropic shift values for ALP04-5; however, these t w o resonances are only observable when small quantities of silicon are added to the synthesis. Increased substitution of silicon into the AFI framework caused the two peaks in the NMR spectra to coalesce into one resolvable resonance. The third aluminum species, observable in syntheses with only small amounts of silicon, corresponds to a condensed aluminophosphate phase similar to cristobalite. INTRODUCTION Recent research into SAPO-5 molecular sieves has been focused on the synthesis of high quality, single crystals for use as optoelectronic materials 1. This requires that the resulting SAPO-5 crystals be sufficiently large such that they can be studied as single crystals, while being nearly defect free. Synthesis of material such as this has been optimized, resulting in optically perfect, single crystals of SAPO-5 2
Examination of the long-range order of these materials using
powder X-ray diffraction, scanning electron microscopy, and optical microscopy establish morphological differences among the samples, with a condensed phase appearing in the materials as the amount of silicon in the synthesis was decreased. To correlate these measurements with the local structure of the materials, 27AI DOR NMR was used to probe changes in aluminum sites associated with the addition of silicon into the AFI structure. EXPERIMENTAL The Silicoaluminophosphate molecular sieves SAPO-5 were synthesized from gels with a molar ratio of 1AI203, 1.03P205, xSi02, 1.55TEA, 750H20 and x = 0.0375 to 0.5 at 210~
for 70h
and an AIPO4-5 reference sample with a gel composition of 1 AI203, 1.03 P2Os, 1.55 TEA, 375 H20 at 195~
for 10h. Powder X-ray diffraction, scanning electron microscopy and optical
microscopy were used to characterize these materials prior to further investigations. Solid-state 27AI DOR NMR investigations of the aluminum species in the SAPO-5 samples were conducted on a Chemagnetics CMX-500 spectrometer at a magnetic field strength of 1 1.7 T. DOR removes the anisotropic broadening influences caused by the quadrupolar nature of the spin-5/2 27AI nuclei 3 and has provided high-resolution spectra for 27AI in other aluminophosphates, not containing silicon 4 .s.
92
RESULTS AND DISCUSSION Determination of the lattice constants and the unit cell volume with P6cc symmetry showed that the silicon incorporation up to a molar ratio of AI203/SIO2 = 0.25 followed the one phosphorus by one silicon replacement mechanism e. Higher silicon amounts showed deviations from the expected unit cell volume and probably followed a mechanism, where two silicons substituted an aluminium-phosphorus pair.
10
20 2 theta
30
75
50
25
0
-25
pprn
Figure la: XRD powder pattern for calcined SAPO-5 sample, molar ratio of AI203/Si02 in
synthesis 0.0375. Reflections 20 = 20.5 ~ 21.5 ~ and 21.8 ~ correspond to the condensed aluminophosphate phase. Figure Ib: 2~AI DOR NMR spectrum for the same SAPO-5 sample acquired at 1 1.7 T. The peak at 42 ppm (referenced to AIN03) corresponds to the condensed aluminophosphate phase, while the two peaks 38 and 36 ppm are similar to reported isotropic shift values for AIPO4-5 s. Based on the 27AI DOR NMR and XRD results, it is apparent that two phases result from the current syntheses for SAPO-5. One phase is the AFI structure and the second is an undesirable aluminophosphate byproduct similar to cristobalite which is formed for synthesis conditions with low amounts of silicon, Figure 1. As the amount of silicon in the synthesis was increased, substantially less of the condensed phase is formed; moreover, the t w o peaks in the 27AI DOR NMR spectra merge to one isotropic shift. Previous studies of the aluminophosphate analog AIPO4-5 suggest three aluminum sites are present in the structure, but not observable at this magnetic field strength 6. The DOR results for SAPO-5 suggest that silicon is substituting randomly into the AFI framework as it replaces the phosphorus. Had the silicon selected specific phosphorus sites, one would have expected a decrease in one peak with respect to the other. Thus, 27AI DOR NMR has provided a new means of observing silicon substitution into the SAPO5 molecular sieve structure and discovered indiscriminate replacement of phosphorus T-sites with silicon.
REFERENCES S.D. Co>~T.E. Gier, and G.D. Stucky, Chem. Mater., 2 (1990) 609. 2 F. ~ , D. Demur, B. Zibmvv~, J. Komatowski,and G. F~ger,J. Am. Chem. Soc., 116 (1994) 1090. 3 A. Samoson, E. Lippm~,andA. F n e s , ~ ~ , 6 5 ( 1 9 8 8 ) 1013;Y. Wu, B.Q. Sun, A. Frnes,A. Samoson, and E. ~ , J. Magn. Reson.,89 (1990) 297. 4 Y. Wu, B.F. ~ , A . Pines,M.E. Davis, PJ. Grobet, P.A.Jacobs, Nature, 346 (1990) 550; R. ~ B.F. Ctwel
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
93
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
29Si and 27A1 MAS NMR STUDIES OF FAUJASITE/GALLIUM
OXIDE CATALYSTS Z. Olejniczak, S. Sagnowski, B. Sulikowski*, J. Ptaszynski* Institute of Nuclear Physics, ul. Radzikowskiego 152, 31-342 Krak6w, Poland *Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 1, 30-239 Krak6w, Poland
SUMMARY 29Si and 27A1 NMR spectroscopy was used to study the changes in the faujasite matrix upon loading with gallium oxide followed by reduction with hydrogen. The gallium-containing faujasites were active catalysts in the oxidative dehydrogenation of propane to propene.
INTRODUCTION Gallium-containing zeolites are, due to their combined redox and acid properties, of considerable interest and are used in a Cyclar process, where low alkanes are dehydrocyclized to benzene and xylenes. Most research has been focused on GaMFI and Ga-MEL systems. Interaction of gallium oxide with other, especially wide pore zeolites, is less known. We studied zeolite Y, loaded with Ga203 and monitored the changes in the zeolite matrix by using solid-state NMR. EXPERIMENTAL
Ultrastable acid-washed zeolite Y was prepared by ion exchange with a m m o n i u m nitrate, followed by hydrothermal and acid treatment. The zeolite matrix had Si/A1=8.91 and Na/AI=0.003 by chemical analysis. Zeolite US-Y-ex was homogenized with spectroscopically pure gallium oxide (III), and the precursors containing 4.76 to 44.4 wt% of Ga203 were reduced in hydrogen at 473 to 873 K. Solid-state magic-angle-spinning (MAS) NMR spectra were recorded at 6.3 T (53.7 MHz for silicon and 70.4 for A1). 29Si MAS spectra were acquired with 7r/2 pulses and repetition time of 10 s. 27A1 MAS spectra were obtained using very short I ~ts with 25 kHz B1 amplitude pulses to ensure that they are quantitatively reliable. The recycle delays were 0.5 s. Typcially 2000 and 1000 transients were accumulated per silicon and aluminium spectra, respectively. The rotors were spun in air at 4kHz.
94 RESULTS AND DISCUSSION The Si/A1 ratio in the aluminosilicate framework can be calculated directly from the 29Si MAS NMR since all the framework sites in zeolite Y are crystallographically and magnetically equivalent. Additionally the siting of aluminium can be monitored by using 27A1 MAS NMR. By comparing (Si/A1)NMR with the results of chemical analysis (which gives bulk composition), the amount of extraframework aluminium can be calculated. Our starting material had well resolved signals with chemical shifts at-106.5, -101, -95.2 and -90.1 p p m from TMS, corresponding to Si (nAl) sites, where n = 0 to 3, respectively. The Si (4AI) signal was missing, as the sample was already quite siliceous. From this material with 55.6 Al/u.c., an ultrastable form with 33.2 A1/u.c. was obtained, which upon acid leaching gave US-Y-ex with 19.9 A1/u.c. The signals of the matrix were very well resolved, with chemical shifts at-95.1,-101.4,-108.1 and-114.7 ppm. The samples loaded with gallium oxide and reduced with hydrogen had a significantly changed spectrum, corresponding to a more siliceous framework. The amount of A1 was in the range 4.5 to 7 Al/u.c. We observed a strong signal corresponding to Si (0A1) groupings and a weak one from Si(1AI) sites. Also weak Si (1Ga) sites were found in the spectra. This confirms directly that gallium oxide, reduced in the presence of the zeolite and transported to faujasite cages as Ga20, is inserted into the defects of the matrix, in agreement with XRD, Laser Raman Spectroscopy and FT IR measurements. Moreover, catalytic studies revealed that propane was oxydehydrogenated to propene, without forming aromatic hydrocarbons [1]. This points to the fact that the siliceous matrix contained the Br~nsted acid sites of intermediate strengths, and hence aromatization of propene did not take place. To conclude, NMR spectroscopy is an indispensable tool and can give direct insights into the behaviour of gallium-containing faujasite catalysts subjected to various treatments. ACKNOWLEDGEMENT We are grateful to the Committee of Scientific Research (Warsaw) for support (project 2P.303.149.04 ). REFERENCES [1] B. Sulikowski, J. Krysciak, R.X. Valenzuela and V. Cortes Corber~n, Stud. Surf. Sci. Catal. (1994) - in press
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
95
A NEW ASSIGNMENT OF THE SIGNALS IN 23NA DOR NMR TO SODIUM SITES IN DEHYDRATED NaY Z E O L I T E Harry A.M. Verhulst ", Wim J.J. Welters, Gert Vorbeck, Leo J.M. van de Ven", Vincent H.J. de Beer, Rutger A. van Santen and Jan W. de Haan ~ Schuit Institute of Catalysis and Laboratory of Instrumental Analysis ~, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands SUMMARY A new assignment of the signals in the 23Na DOR NMR spectra to the different sodium sites in dehydrated NaY zeolite is presented. 23Na DOR- and MAS NMR measurements of dehydrated NaY, Ca 2§ exchanged NaY samples and NaY samples in which Mo(CO)6 is adsorbed are used for this purpose. INTRODUCTION Several 23Na NMR techniques have been used to probe the distribution of the sodium cations in zeolites. However, NMR spectra of quadrupolar nuclei, like 23Na, are limited in resolution, because of the second-order quadrupolar line broadening of the readily observable central +1/2 ~
-1/2
transition in these spectra. The double rotation NMR (DOR) technique is able to reduce this line broadening and thus gives a much better spectral resolution. Recently, Jelinek et al. 1"2 measured the 23Na DOR NMR spectrum of dehydrated NaY at 11.7 T. They found three different 23Na DOR NMR signals (centrebands). Subsequently, Hunger et al. 3 published a reassignment of the 23Na DOR and MAS spectra with only two distinguishable signals (7.0 and 9.4 T): one is assigned to sodium cations at site SI and the second signal to sodium cations at site SII and site SI'. Here, we present evidence that in fact four out of the possible five different sodium sites can be distinguished with 23Na DOR and MAS NMR, in combination with simulation procedures. The simulations were carried out with the program QNMR 4.
E X P E R I M E N T A L SECTION Dehydrated samples of zeolite NaY, zeolite NaY partly ion-exchanged with CaCI 2 solution and zeolite NaY fully saturated with Mo(CO)6 (gas phase deposition), were used for the measurements. 23Na DOR and MAS NMR measurements were carried out on a Bruker MSL 400 NMR spectrometer at 105.8 M H (9.4 T). DOR spinning speeds were approximately 5 kHz and 850 Hz for the inner and outer rotor respectively. Odd-numbered DOR sidebands were suppressed by synchronized pulsing. Chemical shifts were referred to a saturated NaCl solution as an external standard. The DOR and MAS simulations were performed using the program QNMR 4.
96
Far-IR spectra were recorded using a Bruker IFS 113v FT-IR spectrometer equipped with a heatable in situ cell connected to a vacuum system at 300 K.
RESULTS AND DISCUSSION Four distinct signals are needed to simulate satisfactory the 23Na DOR NMR spectra of dehydrated NaY zeolite at 9.4 T : the first signal, positioned at -6 ppm and a quadrupolar coupling constant PQ of 0.4 MHz, which is - in agreement with literature - assigned to sodium cations in hexagonal prisms (site SI). The second one, at -24 ppm and with a PQ value of 2.3 MHz, is assigned to Na § located in the sodalite cages (sites SI' and SII'). The third and the fourth signal, with chemical shifts of-43 and -46 ppm and PQ values of 4.2 and 4.7 MHz, respectively, are assigned to sodium cations in the supercages (sites SII and SIII) 5. Additional support for the changed and extended assignment of the signals found for the 23Na DOR NMR spectra of dehydrated NaY comes from measurements and simulations of the 23Na DOR NMR spectra (9.4 T) of a CalgNaI6Y zeolite sample. At this level of sodium exchange (70 %) most of the SI sites will be occupied by Ca 2§ after drying at 673 K in a He flow whereas the residual sodium will be mainly located in the supercages. This could be confirmed by additional Far-IR measurements of this sample. It easily explains the markedly lower intensity for the signal caused by Na § in SI positions in the corresponding 23Na DOR NMR spectra compared to that for NaY. For the complete simulation of the spectra again four different signals with PQ values of 0.4; 2-.3; 4.6 and 5.0 MHz are required. Interestingly, the latter two are enlarged compared to those for the dehydrated NaY, implying enhanced electric field gradients at sites SII and Sill. Most likely this is due to the influence of the calcium cations as well as to local changes in the framework geometry caused by these cations. Further evidence for our assignment was taken from the 23Na DOR NMR spectra of NaY, in which Mo(CO)6 has been adsorbed. Mo(CO)6 can interact only with Na § in the supercages (sites SII and Sill). Our results show that the quadrupolar interactions of the sodium cations have decreased considerably, due to a more symmetric surrounding of these cations upon Mo(CO)6 adsorption. On the other hand, the sodalite cage Na § (sites SI' and SII') are not affected, because neither the signal position nor the quadrupolar interaction did change significantly (PQ = 2.3).
REFERENCES 1. 2. 3. 4.
R. Jelinek, S. t3zkar, G.A. Ozin; J. Am. Chem. Soc. 114 (1992) 4907. R. Jelinek, S. t3zkar, H.O. Pastore, A. Malek, G.A. Ozin; J. Am. Chem. Soc. 115 (1993) 563. M. Hunger, G. Engelhardt, H. Koller, J. Weitkamp; Solid State Nucl. Magn. Res. 2 (1993) 111. Program for simulation of solid state NMR lineshapes QNMR, developed and supplied by the Institute of Chemical Physics and Biophysics, Tallinn, Estonia. 5. H.A.M. Verhulst, W.J.J. Welters, G. Vorbeck, L.J.M. van de Ven, V.H.J. de Beer, R.A. van Santen, J.W. de Haan; J. Phys. Chem. accepted for publication.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
97
STUDY OF MORDENITE ACIDITY BY 1H NMR TECHNIQUES: BROAD-LINE AT 4 K AND HIGH RESOLUTION MAS AT 300 K. COMPARISON WITH HY. BRONSTED ACIDITY SCALE AND IMPORTANCE OF STRUCTURE DEFECTS.
L. HEERIBOUT, V. SEMMER, P. BATAMACK, FRAISSARD
C. DOREMIEUX-MORIN
and J.
Laboratoire de Chimie des Surfaces, associ(~ au CNRS -URA 1428 Universite P. et M. Curie, Casier 196, Tour 55, 4, place Jussieu F 75252 PARIS Cedex 05 SUMMARY The interaction of water molecules with the acidic OH groups of decationized zeolites, giving H20...HO- and H30 +, is quantitatively studied using 1H NMR, broad-line at 4 K and MAS at 300 K. Results for industrial Y and mordenite samples are compared. The influence of Lewis acid sites is emphasized. INTRODUCTION
1H broad-line NMR at 4 K allows a quantitative measure of the concentration of hydroxonium ions formed by interaction of water molecules with bridging OH groups in zeolites, denoted Z O H. 1 A Br0~sted acidity scale for solids has been based on this measure. 2 Results previously obtained on a partially dealuminated HY zeolite (D HY) have shown the great influence of Lewis acid sites 1,3 (expressed, using 1H MAS NMR, by the number of water molecules that they bond)4 on the hydroxonium concentration for high loading of adsorbed water, in view of the great industrial interest of zeolite acid strength we propose to compare the concentrations of hydroxonium ions formed in H-mordenites containing different numbers of Lewis sites and to compare them to those known for D HY. 1 EXPERIMENTAL SECTION
Two industial mordenite samples, denoted A and B, were chosen for comparison. Only one of them, A, is a good catalyst for the conversion of toluene to xylenes. The Si/AI ratio measured by 29Si MAS NMR is 9.4 for A and 10.3 for B. All samples are "shallow bed" pretreated. Water adsorption, sample sealing and homogenization have been described previously. 1 The methods and especially the spin 112 magnetic configurations used to simulate the broad-line experimental spectra have also been described. 1 RESULTS AND DISCUSSION
Quantitative analyses of the samples obtained from MAS NMR experiments are summarized in Table 1. The main differences between mordenites A and B are the following: (i) the number of Lewis acid sites per Br0nsted site (sa), denoted m, is much larger for A (0.3) than for B (0.01); (ii) only A contains ZOH of two types (not distinguishable in Table 1), one being ZOH hydrogen-bonded to framework O atoms. 5 The number of hydroxonium ions per
98
Table 1 (1), (2) and (3) obtained using 1H MAS NMR on pretreated samples; (4) after adsorption of small amounts of water; (5) using 27AI MAS NMR on fully hydrated samples. Number of m: Number of Number of Number of Number of Sample extraLewis acid ZOH per uc AIOH per uc SiOH per uc framework AI (1) (2) (3) sites per Br0nsted site (5) 0 0.3L-H3.2 0.5:L-0.2
35~8&2 4.3L--H3.4 3.8_+0.3 , ,
DHY ],3 Mordenite A Mordenite B
1.5L+0.5 2.4_+0.2 3.3L+0.2
(4)
0.04 0.3 0.01
0
0.8_+0.2 0.8_+0.2
BrOnsted acid site (H30 +/sa), obtained from broad-line NMR spectrum simulations, versus the number of adsorbed water molecules per BrOnsted acid site (H20/sa) is shown in Fig. 1. For both mordenites, H30 +/sa is 0.33 when H20/sa is 1. The corresponding value for D HY is 0.2. When H20/sa increases H30 +/sa does not increase very greatly for B though it does for A, to 0.8 when H20/sa is 3.7, m being 0.3 (Table 1). For the same H20/sa value, H30 +/sa is about 0.4 for D HY, m being 0.04 (Table 1). Results obtained on D HY have been interpreted on the basis of a synergy between Lewis and Br0nsted sites which, for enhancing H30 + concentration, necessitates the formation of a network of hydrogen-bonded water molecules also bonded to the acid sites.-3 Lewis acid sites appear responsible for a marked enhancement of the hydroxonium concentration for high adsorbed water molecule concentrations. .o-~
-
mordenl[e
i
[
4{ .
o.s-~
06"i,
9
I
as
=
CONCLUSION
A
morctenite B
In the present state of our results, we
0
conclude that the order of H30 +/sa values
HY Br6nsted
acid
site
for H20/sa equal to 3.7 is to be related to the order of m, the number of Lewis acid
0 "l-
0,4i
9 I
i
sites per BrOnsted acid sites. This common order is: mordenite B < D HY < mordenite A.
I
!o
REFERENCES
1. P. Batamack, C. Doremieux-Morin and J. FraJssard, Catalysis Letters., 11 (1991) 119 and references therein. Fig. 1 H20/as 2. P. Batamack, C. Dor~'nieux-Modn, R. Vincent and J. Fraissard, J. Phys. Chem., 97 (1993) 9779 and references therein. 3. P. Batamack, C. Doremieux-Modn, R. Vincent and J. Fralssard, Microporous Materials, 2 (1994). 4. M. Hunger, D. Freude and H. Pfeifer, J. Chem. Soc., Faraday Trans., 87 (1991) 657. 5. E. Brunner, K. Beck, L. Heedbout, V. Semrner, H.G. Karge and M. Koch, Zeolites, submitted. 0
.
,
i
3
,
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
99
SPECTROSCOPIC EVALUATION OF THE RELATIVE ACIDITY OF THE BRIDGED HYDROXYL SPECIES IN ZEOLITES AND THE ISOLATED HYDROXYL SPECIES IN AMORPHOUS SILICA by E. Garrone, B. Onida, G. SpanS, G. Spoto, P. Ugliengo and A. Zecchina Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Materiali, Universit~ di Torino, via P. Giuria 7 10125 Torino Italy ABSTRACT The classical Bellamy-Hallam-William plot of the shifts in the OH stretching mode suffered by the two types of hydroxyls when H-bonded to a set of base molecules allows a measure of their relative acidity. INTRODUCTION One way to define the acid strength of a surface hydroxyl species is to measure the shift in the OH stretching mode Av(OH), brought about by the formation of H-bonded complexes with mildly basic compounds, like carbon monoxide (1, 2). For instance, the relative acidity of the Si(OH)AI species in various zeolites can be measured in this way (2). The Av(OH) values are usually relatedto either Proton Affinity of the base molecule B (3) or to the Pka value of the conjugated acid BH + (4): eventually, values for the proton donor ability or pka of the acidic hydroxyl are obtained. A different approach is assumed in the present work. The relative acidity of the Si(OH)AI species in zeolites and the Si(OH) hydroxyl groups in amorphous silica is determined via a procedure well known for species in solution (Bellamy-Hallam-William plot BHVV), consisting in the comparison of Av(OH) values in the two cases for the same set of basic molecules. EXPERIMENTAL Molecules considered were: nitrogen, carbon dioxide, nitrous oxide, carbon monoxide, acetylene, methylacetylene, benzene, ethylene, propene. The interaction spans from the very weak N2/SiOH case to the relatively strong cases of Si(OH)AI species interacting with methylacetylene, etc., when H-bonded species show up as short-lived intermediates in the process of PT. As a consequence, three versions of FTIR spectroscopy have been used: i) plain, room temperature; ii) plain, low-temperature; iii) room temperature, time-resolved. The silica sample was Areosil outgassed at 800~
the zeolite was HZSM-5 outgassed at 500~
RESULTS AND DISCUSSION Most Av(OH) data concerning SiOH have already been published (N2, CO2, N20, CO, C6H6, C2H2), as are those concerning CO, N2, N20, C6H6, C2H2 and CH3CCH with Si(OH)AI. All available data, including those measured for the present work, have been plotted one set against the other in a BHW
100
MeCCH 9
1,50 -
/ /
A VSiOH /cm-1
f
/
/
f
/
/
f
J
/
/
9 Me_CH=CH 2
/
HCCHe 100
J
/
/
/
f
/
/
/
/
t
/
2-- Ct.4 2
~/&CO
/
CC~/ //
50 /
t
/
/
AN20
.A'N2 -AVzeOH/cm-~ I
!
plot (4). Triangles refer to stable H-bonded complexes, and dots to short-lived intermediates. A very good linearity is observed: points nearly line up with the origin, though this is not stdctly required. Whithin this set of molecules, an upper limit value at = 350 cm-1 is observed for the Av(OH) in zeolites for H-bonded adducts not evolving to protonated species. The slope is = 3. Such a value may be related, on the one hand, to calorimetrically determined enthalpy of interaction of strong bases (5), with excellent agreement. On the other hand, it may be related to the pka of silica, also experimentally determined to be ~ 7: the indication is that Si(OH)AI is as strong as perchloric acid.
REFERENCES
(1) L. M. Kustov, V. B. Kazansky, S. Beran, L. Kubelkov~, and P. Jiru, J. Phys. Chem., (1987), 91, 5247. (2) E. Garrone, R. Chiappetta, G. Spoto, P. Ugliengo, A. Zecchina and F. Fajula, Proc. 9th International Zeolite Conference, Montreal...1.992, R. von Ballmoos et al., (1993), 267. (3) E. A. Paukshtis and E. N. Yurchenko, React. Kinet. Catal. Lett., (1981), 16, 131. (4) P. G. Rouxhet and R. E. Sempels, J. C. S. Faraday I, (1974), 70, 2021. (5) N. Cardona and J. A. Dumesic, J_..Catal., (1990), 125, 427.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
101
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
ONE-POINT METHOD FOR THE DETERMINATION OF STRENGTH OF ZEOLITE ACIDITY BY TEMPERATURE PROGRAMMED DESORPTION OF A M M O N I A BASED O N TROUTON'S RULE
Miki Niwa 1, Naonobu Katada 1, Masahiko Sawa 2 and Yuichi Murakami 2 1Department of Materials Science, Faculty of Engineering, Tottori University, Koyama-cho, Tottori 680, Japan 2Department of Applied Chemistry, School of Engineering, Furo-cho, Chiku-saku, Nagoya 464-01, Japan
SUMMARY
We propose a one-point method to measure the strength of zeolie acidity from temperature programmed deorption (TPD) of ammonia. Based on the assumption of constancy of AS, one can determine the AH from the theoretical equation describing the TPD of ammonia which was derived by the authors. The constancey of AS upon desorption of ammonia is in agreement with the Trouton's rule about the vaporization of liquids. INRODUCTION Temperature-programmed desorption (TPD) of ammonia has been used often to characterize zeolite acidity. However, the principle of the method is not simple. Previous investigations by the authors reported the identification of peaks and the freely occurring readsorption of ammonia1, and then derived the theoretical equation as shown below 2. l n T m _ In(AFW) = AH + In fl(1- Ore)2(AH- RTm) p0 exp(AS / R) RTm This equation shows that the temperature of the peak maximum (Tm) is influenced by not only the contact time of carrier gas (W/F), but also by the number of acid sites (Ao); therefore, the s~ength of zeolite acidity is not estimated from the Tm at all. The strength of zeolite acidity (AH) can be derived from this equation, since the second term of the right hand side is invariant under the experimental conditions, and a plot of the left hand side 1/Tm gives a straight line from which AH may be determined. The thus determined AH was in close agreement with the value measured by calorimetry, and the theoretical equation was thereby confirmed experimentally. The above method needs three to four experiments at least. Thus, a more simple method to measure the AH has been proposed. The parameters except for AS and
102 AH are measured from one experiment. However, AS calculated from the measured AH was almost constant on various zeolites, as shown in Table 1. Therefore, we will assume the constancy of AS (averaged value, 150 JK-lmol-1), and by using the AS, AH can be measured by only one experiment. This proposal is supported by following physical chemistry. (1) Trouton's rule claims that a wide range of liquids give approximately the same ASvap, although the AHvap and boiling points are different. Our hypothesis is exactly the same as this rule. (2) A value of AS of 150 JK-lmo1-1 is approximately equal to the change of entropy from solid ammonia to gaseous ammonia at 673 K. In other words, the entropy of adsorbed ammonia is similar to that of solid ammonia. It is natural that there is a similarity between the states of adsorbed ammonia and solid ammonia. Table 2 shows the values of AH thus measured for different weights of various zeolites. AH has only a small exprimental error within 1 kJmo1-1. Thus, a simple and easy method to determine the acid strength of a zeolite has been established. Nomenclature acid amount [mol kg-1] A0 flow rate of carrier gas [m3 s -1] F AH enthalpy change of desorption [Jmol-1] po pressure at standard conditions [1.013 x 105 Pa] gas constant [8.31 JK-lmol-1] R AS entropy change of desorption [JK-lmo1-1] T m temperature at peak maximum [K] zeolite weight [kg] W heating rate [Ks-1] Om surface coverage at peak maximum [-] Table I
AH and AS of measured zeolites
Zeolite
JRC-Z-HM15 JRC-Z-HM20 JRC-Z5-25H JRC-Z5-75H HF15
AH (kJmo1-1) 150 160 130 132 143
AS (JK-lmo1-1) 146 160 149 148 145
JRC-Z, reference catalyst supplied by the Catalysis Society of Japan. HM, mordenite; Z5, ZSM-5; HF, ferrierite
103 Table 2
AH measured by one-point method by using different amounts of zeolite
Zeolite
JRC-Z-HM10
JRC-Z-HM15
JRC-Z-HM20
JRC-Z5-25H
JRC-Z5-70H
HF15
W (g)
AH (kJmo1-1)
0.202 0.302 0.402 0.110 0.141 0.201 0.202 0.300 0.402 0.077 0.141 0.205 0.301 0.400 0.052 0.101 0.500 1.00 0.202 0.412 0.637 1.00 0.061 0.100 0.149 0.200 0.302
147 146 148 152 153 153 152 152 152 153 154 154 154 153 131 132 131 131 133 133 133 133 146 147 147 147 147
REFERENCES
(1) (2)
M. Niwa, M. Iwamoto and K. Segawa, Bull. Chem. Soc. Jpn., 59 (1986) 3735. M. Sawa, M. Niwa and Y. Murakami, Zeolites 10 (1990) 307.
H.G. Karge and J. Weitkamp (Eds.) 104
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
INTERACTION OF CO2, H20, CH3OH, (CH3)20, CH3N, H2S, (CH3)2CO, NH3 AND Py WITH BRONSTED ACID SITES OF H-ZSM-5: COMPARISON OF THE IR MANIFESTATION R. Buzzoni, S. Bordiga, G. Spoto, D. Scarano, G. Ricchiardi, C. Lamberti and A. Zecchina* Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Materiali, Universith di Torino, Via Pietro Giuria 7, 10125 Torino, Italy
Summary The object of this study is the interaction of HZSM-5 with probe molcules, characterized by different basicity by using IR spectroscopy. The formation of H-bonded species and the proton transfer are considered. Experimental results are compared with literature data (experimental and theoretical)
,Introduction The acidic properties of H-ZSM-5 zeolite arise mainly from bridged structural hdroxyls inside the channels. During the reaction pathway where protonation is involved these groups often give primarily H-bonded species. As FTIR is a rapid method for demonstrating the existence of H-bonding and for characterizing it, in this work we consider the interaction of Bronsted acid sites with probe molecules characterized by different basicity in order to obtain a complete set of results to be compared with literature data (experimental and theoretical).
Experimental H-ZSM-5 samples with Si/AI=14 were suplied by Enichem Laboratories (Bollate, Milano). Thin self-supporting wafers were activated in vacuum at 673 K for lhr, inside the IR cell. Infrared spectra were taken using a Bruker IFS 66 spectrometer operated at 2 cm ~ resolution and following an "in-situ" procedure.
Results and Discussion The interaction of Bronsted sites with basic molecules (X) such as NH3 and Py leads to a proton transfer reaction following the reaction scheme
H I
~si-O-A(- X-
H X+
Si /0-~ AI/
With molecules like CO at 77K, H2S, (CH3)2CO, CH3CN, proton transfer reactions are less probable. In this case the most plausible structure will be
X H Si
I /O~
/
AI
As far as }-120, CH3OH and CH3OCH3 are concerned, the situation is more controversial and the interpretation of experimental data is still debated. In particular, the problem of the formation of H30 § and of the associate vibrational manifestation have been object of several studies in the recent years by many researchers using spectroscopic [1 ] as well as theoretical
105 methods [2]. The presence of two bands at 2885 and 2465 cm"~ in the IR spectraa of H20 on H-ZSM-5 can be associated with the asymmetric and symmetric stretching modes of the hydroxonium ions formed inside the zeolite channels or can be due to pseudo-bands generated by Evans-holes in hydrogen bonded H20 (this transmission window is typical of medium or strong H-bonds and it is due to the Fermi resonance between overtone bending modes and the components of the broad band characteristic of H-bond absorbing at similar wavenumbers) [3,4]. The presence of two absorptions or a transmission window, very similar to those obtained for water, also in the cases of molecules which can give only one OH...X bond (CH3CN, (CH3)2CO, Py) is in favour of the second hypothesis. An example of the spectra obtained in this investigation is given in Figure 1 where IR spectra of dimethylether at increasing coverages are reported ( the arrow indicate the transmission window) 1.5
I
-.5
.3500
.3000
2500
cm-I
2000
1500
Figure 1: Difference spectra of (CH3)20 on HZSM-5 outgassed at 673 K (increasing coverage) The IR spectra of NH4+ and PyIT species formed by protoin transfer are also discussed in detail, because they represent prototype species when the proton is totally transferred. References
[1] [2] [3] [4]
A. Jentys, G. Earacka, M. Derewinski, J. A. Lercher; J. Phys. Chem. 1989, 93, 4837 J. Sauer, H. Horn, M. Haser, R. Ahlrichs; Chem. Phys. Lett. 1990, 173, 26 D. Hadzi, S. Bratos, in: The Hydrogen Bond. Eds. P. Schuster et al., North-Holland Publ. 1976, 576 S. Bratos, H. J. Ratajczak; J. Chem. Phys. 1982, 76, 77
106
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
IR CHARACTERIZATION OF HYDROXYL GROUPS IN SAPO-40 E. Garronel, B. Onidal,2, Z. Gabelica2 and E. G. Derouane2 Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Materiali, Universita di Torino, via P. Giuria 7, 10125 Torino Italy 2 Facult6s Universitaires N.-D. de la Paix, Laboratoire de Catalyse, rue de Bruxelles 61, B-5000 Namur, Belgium ABSTRACT Adsorption of NH3 and CO allow a thorough IR characterization of four types of Si(OH)AI hydroxyls, the only species present in SAPO-40. INTRODUCTION SAPO-40 is a silicoaluminophosphate recently synthesized in a pure form [1], showing two types of intersecting channels involving respectively 12-membered and 8-membered rings. So far, available data only concem the structure. The first IR investigation of such novel solid is reported in this work, wich deals with the type, number and acidity of hydroxyl species. This latter has been characterized by two methods, i.e. the propensity to transfer the proton to NH3 and to form week H-bonds with CO, N2, benzene and methyl-substituted benzenes. EXPERIMENTAL SECTION
The SAPO-40 samples were prepared according to ref. [1], slowly calcined up to 500~
during 5
hours, then oxidized in 02 at the same temperature for one additional hour. IR spectra were taken on a Perkin-Elmer 1720 and a Bruker IFS 66 FTIR instruments. RESULTS AND DISCUSSION
The figure shows the variation of the absorption pattem in the 3200-3700 cm-1 region of the IR spectrum during the desorption of adsorbed NH 3. The most intense spectrum at high frequencies is that of the naked sample, showing four peaks at 3637 cm-1 (A), 3625 cm-1 (B: shoulder) and 3550 cm-1 (C), 3528 cm-~ (D). Adsorption of NH3 results in the most intense spectrum in the low frequency region, which shows the depletion of the four hydroxyl species and the consequent formation of NH4+ species (bands at 3385 and 3320 cm-~). Both the extremely small population of POH species (tiny band at 3676 cm-~) and the absence of any SiOH species indicate negligible presence of inner structural defects as well as a limited external surface, in agreement with SEM pictures of the samples. The four main bands are all ascribed to bridged Si(OH)AI groups. As in the case of faujasite [2], the high frequency bands (A and B) are assumed to be due to hydroxyl species located in large cavities (here the 12-ring channels), whereas peaks C and D occuring at lower frequencies are most probably
107
.4
=o
..Q
.2
. . . . .
36'o0
. . . . . . . . .
34'oo'
Wavenumbers ( ' c m - 1 )
. . . . . . .
322o
related to hydroxyl species in smaller cavities (here 8-rings channels and "side pockets" in the 12-ring channels). Heat treatments lead to the decomposition of NH4+ species and the recovery of OH species (isosbestic point at 3440 cm-1). Bands A, C and D basically reappear together, thus suggesting a similar acidity in all cases, whereas the band B is the last to be recovered. Upon CO adsorption, species A and B readily form H-bonded complexes, the corresponding shift Z~v(OH) being 290 and 350 cm-1, respectively. Species C requires moderately high CO pressures to be involved in a H-type bond, the corresponding Z~v(OH) being however only of about 100 cm-l. Species D does not react with CO at all. As Av(OH) is directly related to acidity, the following inferences may be drawn: (i) species B appears to be the most acidic species; (ii) species C, which according to the NH 3 experiment has an acidity comparable to that of species A, is probably stedcally hindered in H-bonding with CO; (iii) species D is even more hindered, so that no interaction is seen. Interactions with other molecules (N2, benzene, etc. ) confirm this picture, on the basis of which attempts are being made to locate precisely species C and D in the 8-ring channels and/or "side pockets" by means of molecular graphics. REFERENCES
[1] N. Dumont, Z. Gabelica, E. G. Derouane and L. B. McCusker, Microporus Mat..e.rials, 1 (1993) 149. [2] P. A. Jacobs and J. B. Uytterhoeven, J. Chem. Soc. Faraday Trans. I, 69 (1973) 359.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
108
F T I R E V I D E N C E O F Pt C A R B O N Y L S F O R M A T I O N F R O M Pt M E T A L C L U S T E R S IN K L Z E O L I T E A.Yu. Stakheevl), E.S. Shpirol), N.I. Jaeger2), G. Schulz-Ekloff2) 1) N.D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Leninskii prospect 47, 117913 Moscow, Russia. 2) Institut far Angewandte und Physikalische Chemic, Universit~t Bremen, 2800 Bremen 33. SUMMARY FTIR spectroscopy revealed the reversible formation o f P t carbonyls upon adsorption at high CO pressure (~ 500 mbar). It is suggested that small Pt clusters located inside zeolite channels are transformed into (Zeol-O:) mPtx(CO)v spezies stabilized by the basic oxygen atoms of KL framework. The transformation is found to be readily reversible upon CO adsorption-desorption at room temperature (RT). INTRODUCTION Pt/KL zeolite exhibit unusual high catalytic activity and selectivity in n-hexane aromatization. These characteristics were ascribed to the effect of zeolite support on the properties of the Pt metal particles [1 ]. The aim of this paper is to study the reactivity of the small Pt clusters entrapped inside the zeolite channels toward CO. EXPERIMENTAL 1 % Pt/KL sample was prepared by incipient wetness impregnation o f KL zeolite with water solution of Pt(NH3)CI 2. The sample was calcined and reduced at 400 ~
FTIR spectra of
adsorbed CO were recorded on a BIO-RAD FT1R spectrometer with a resolution of 2 cm -l . R E S U L T S AND D I S C U S S I O N The CO adsorption on Pt/KL at RT and 1 mbar CO pressure results in the appearance of the very broad band (FWHH ~ 150 cm -l) in the region 2060 - 1910 cm -1, which can be ascribed to the linearly bonded CO molecules. The comparison of the IR spectra obtained upon CO adsorption at RT and desorption at elevated temperature reveal that the broad band consists of at least two distinctive bands. The first is found at 2050 - 2060 cm -1, and we tentatively ascribed it to the Pt particles which are located in the near surface region of the zeolite microcrystals or in voids of the lattice. CO adsorption on this particles is not strongly perturbed by the zeolite matrix. The second band has a frequency o f ~ 1980 - 1930 cm -1 and the extrapolation o f its frequency to the zero coverage gives the value o f 1920 cm -1. We suggest that such low value is related to the strong effect o f the zeolite matrix on the small Pt metal clusters encaged in the zeolite channels. After 30 min o f CO adsorption at 1 mbar the integral band intensity reaches its maximum and does not changed later on. We assume that the surface saturation with CO is achieved under these conditions. However, additional treatment in CO at elevated pressure ( ~. 500 mbar) results in the 5-fold increase of the intensity of the linearly bonded CO band, its narrowing and shift toward higher wavenumbers. Moreover, several sharp, well-defined bands appear at 2130, 2069, 2030 and 2008 cm -1 (Fig.). CO desorption at RT leads to the decrease o f their intensity
109
0.20-
e fl. I 5 o ,r b e'O.I 0 r~
___J ,,,
2256
_
2260
--
~
2150
2100
i
2~50
1
I
2~00 1950 Wav, nu~b,r
I
I
I
i
1
1900 s
1850
1800
1258
12~0
without change of their frequencies. The readsorption of CO at 500 mbar gives reversible spectrum. The observed behavior is similar to those reported by Sachtler et al. [2] for Pd/NaY system and Kubelkova et al. for Ni/NaY [3]. In these systems the formation of Pd and Ni carbonyl clusters was established. The comparison of the data allows us to suggest that the formation of the unknown Pt carbonyl species takes place in Pt/KL upon CO adsorption at high pressure. We presume that highly reactive Pt clusters located inside zeolite channels are converted into the Pt carbonyls of the possible structure: (Zeol-O:)mPtx(CO)y These carbonyls are stabilized by the oxygen atoms of KL framework, which exhibit strong basic properties and can act as 6"-donor ligands [4]. REFERENCES 1. C. Besoukhanova, J. Guidot, D. Barthomeuf, M. Breysse and J.R. Bernard, J. Chem. Soc., Faraday Trans. I, 77 (1981) 1595. 2. L.L. Sheu, H. Knoezinger and W.M.H. Sachtler, J. Am. Chem. Soc., 111 (1989) 8125. 3. L. Kubelkova, J. Novakova, N.I. Jaeger and G. Schulz-Ekloff, Appl. Catal. A., 95 (1993) 87. 4. F.R. Hartley, in: Comprehensive Organometallic Chemistry, Vol. 5, ed. G. Wilkinson (Pergamon Press, Oxford, 1978) 471.
110
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
IR SPECTRA OF 180 EXCHANGED HZSM-5
F.BAUER 1, E.GEIDEL 2, CH.PEUKER 3 1WIP Isotopenchemie, Permoserstr. 15, 04303 Leipzig, Germany 2 Universitat Hamburg, Institut ~ r Physikalische Chemie, Bundesstr. 45, 20146 Hamburg, Germany 3 Humboldt Universitat, FB Chemie, WIP, Rudower Chaussee 6, Geb. 19.5, 12489 Berlin, Germany
INTRODUCTION IR spectroscopy is widely used in zeolite research. Its successful application is depending on a well-founded assignment of the IR bands. Beside empirical assignments some theoretical investigations are published about vibrational spectra of zeolite frameworks. The aim of this study is to obtain more detailed information on the spectrum of HZSM-5 comparing the IR spectra of 180 exchanged HZSM-5 and of HZSM-5 in the framework vibration region and the OH vibration region as well as the combination tones of the framework and the hydroxyl groups of the two samples. The experimental framework spectra have been compared with frequencies calculated for various ditetrahedra (O3Si-O-SiO3) as one of the most simple framework model. EXPERIMENT The commercial, template-free synthesized NaZSM-5 zeolite (Chemiewerke Bad KOstritz GmbI-I, Germany) with a Si/AI ratio of 15 was threefold ion exchanged with aqueous solution ofNH4NO 3 and calcined 12 hours on air at a temperature up to 820 K for yielding the H-form. Hydrothermal route/1/or exchange with 1802 gas at elevated temperatures/2/can be used for the post- synthesis 180-labeUing of zeolites. The zeolite sample was exchanged with H 2180 (95.2% 180, Chemotrade, Germany) in a water/nitrogen stream at 700 K for 1 hour. This way of exchange was chosen because some dealumination of the sample was required for further kinetic studies. The IR measurements were performed on a spectrometer IFS 66 (Bruker). The Praying Mantis DRIFT attachment (Harrick) was connected with a heated vacuum cell (Harfick) to record diffuse reflectance spectra. The samples were measured at temperatures up to 873 K under a dynamical vacuum better than 10-5 mbar. The calculation of vibrations was carried out for various ditetrahedra (O3Si-O-SiO3) by using the method of normal coordinate analysis based on Wilson's GF matrix method/3/. Structural parameters were taken from a single crystal X-ray diffraction study of Olson et al./4/of an assynthesized ZSM-5 (Si/Al=86). According to Blackwell /5/ the so-called bond length scaled force field (BLSF-BR), without adjustment of force constants, was used as model force field.
111
RESULTS AND DISCUSSION The bands in the framework spectrum of the 180 exchanged HZSM-5 sample are shifted to lower wavenumbers (1062, 794, 537, 443 cm-1) compared with the HZSM-5 spectrum (1094, 797, 546, 450 cm-1). The calculation of the v~orational spectra of the ditetrahedra O3Sil-O16-Si403
and
O3Si2-O13-Si803 (Olson's indication) with 180 or with 160 atoms gave the following results. The vibration forms and the sequence of the vibrations remain with 180 exchange. All bands shif~ to lower wavenumbers due to 180 substitution. The highest difference of about 40 cm -1 was calculated between wavenumbers of the anti-symmetrical stretching vibrations of the Si-OSi bridge, which seems to be caused by the low coupling of this vibration with others. This value is in good agreement with the experimental one of 32 cm-1. Similar results concerning the band shifts due to 180 exchange were published for tridymite /6/ and quartz/7/. The DRIFT spectra of undiluted samples show shifts of the f~amework combination tone bands from 1988 cm-i to 1943 cmd and from 1874 cm-1 to 1833 cmd due to the 180 exchange, i.e. the combination tone bands shift 45 and 41 cm-1 to lower wavenumbers compared with 32 cm"1 for the band of the fundamental vibrations. The acid OH band shit, s from 3608 cm-1 to 3586 cm-1 due to the 180 exchange, the combination tone band from 4657 to 4625 cm-1. The appearance of a new band at 3657 cm -1 shows that dealumination takes place during 18O exchange. CONCLUSION Shifts of IR bands were proved due to 180 exchange for framework vibrations and for OH vibrations as well as for the combination tones. The calculated value for the shift of the antisymmetrical Si-O-Si stretching vibration is in good agreement with the experimental finding. The analysis of more extended models for the ZSM-5 fi'ameworlc, including periodic boundary conditions, will allow to compare the calculated band shifts due to 180 exchange with the experimental data for all of the framework bands. ACKNOWLEDGEMENT The authors want to thank the DFG for the support of this work. REFERENCES 1. R.von Ballmoos: The 1SO-exchange method in zeolite chemistry; Otto Salle Verlag, Frankfurt, 1981 2. S.Yang, K.D.Park, E.Oldfield; J.Am.Chem.Soc. 111 (1989) 7278 3. E.B.Wilson, Jr., J.C.Decius, P.C.Cross: Molecular Vibrations; McGraw-Hill Book Company, Inc., New York, 1955 4. D.H.Olson, G.T.Kokotailo, S.L.Lawton, W.M.Meier; J.Phys.Chem 85 (1981) 2238 5. C.S.Blackwell; J.Phys.Chem. 83 (1979) 3251; 83 (1979) 3257 6. A.M.Hofmeister et al.; J.Phys.Chem. 96 (1992) 10213 7. R.K.Sato, P.F.McMillan; J.Phys.Chem 91 (1987) 3494
H.G. Karge and J. Weitkamp (Eds.) 112
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
STRUCTURE AND REACTIVITY OF F R A M E W O R K AND E X T R A F R A M E W O R K IRON IN Fe-SILICALITE AS INVESTIGATED BY OPTICAL (IlL RAMAN, DRS UV-Vis) AND EPR SPECTROSCOPIF~S.
Geobaldo FI., BordigaSl., SpotoGl., Scarano DI., ZecchinaAla., PetriniG2., Leofanti G2., Tozzola G2., Padovan M 2. 1) Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Materiali, Universit/~ di Torino, Via P. Giuria 7 10125 TORINO ITALY 2) ENICHEM Centro Ricerche di BoRate, via S. Pietro 50 20021 BoUate (Mi) ITALY
Introduction Silicalites and Al-substituted Silicalites are characterised by substantially identical optical UVVis and EPR spectra. Substitution of Si with a variety of heteroatoms can cause dramatic changes in the spectroscopic properties of the zeolite. Fe-Silicalite has been studied by means of optical (DRS UV-Vis, IlL Raman) and EPR spectroscopies in order to characterise the coordination state of framework species and to identify the presence of extrafi'amework species (isolated and clustered). It is found that the ratio between framework and extraframework Fe species is strictly related to the sample calcination procedure. Probe molecules like CO, NO, NH 3, etc. prove their utility to characterise the properties of this material, through interaction with Brensted and Fe sites and formation of adducts having simple vibrational properties.
Experimental Fe-Silicalite was produced in the ENICHEM laboratory following a procedure described elsewhere (1 and references therein). Samples were calcined in air at 393 K, 823 K and 973 K; thermal treatments was done in suitable in situ cells at increasing temperature under dynamic vacuum.
Results and Discussion The IR and Raman spectra of Fe-Silicalite show the same general features of other substituted silicalites (1 and reference therein). The lattice modes and the Si.OH stetching band at 976 cm "1 (shoulder) associated with internal defective nests, can be easily detected. Beside this, a very prominent peak at 1020 cm" 1 in the Raman spectra is also observed. In the IR spectra an analogous adsorption at 1015 cm" 1 appears as a shoulder. These two peaks can be considered as finger print of framework iron in Fe-Silicalites. Immersion of Fe-Silicalite in a dilute NH 3 solution does not perturbs the iron sensitive Raman mode. This indicates a small propensity of framework iron to increase its coordination sphere. This conclusion is confirmed by CO and NO adsorption experiments from the gas phase, which are specially sensitive to extraframework Fe. The IR spectra of adsorbed CO and NO on FeSilicalite show dramatic changes when calcination and pretreatments conditions are changed, showing feature: ~:e to the presence of va,'i able amount of extraframework ye3+/Fe 2+ pairs,
113 T~-,e presence of extraframework iron can be easily monitored with DRS UV-Vis and EPR spectroscopies. In figure 1 the UV-Vis spectra of a Fe-Silicalite sample in air, after three different calcinations are reported. o
c
1
i
~
c
b
a ~ : o o . ~ o 7. . . .
~o
#,
o
~oooo ,
,,
40600 ,
,
~o6oo
Wavenumbers
zo6oo
(ore-- I)
10600 ,,1
Fig.1 DRS UV-Vis spectra of Fe-Silicalites calcined at a) 393 K, b) 823 K, c) 973 K for 24 h.
As clearly visible, calcination at high temperature, causes an enhancemem of the absorption at lower frequencies and a dramatic absorption decrease of the bands, in 30000-20000 cml range, which are due to forbidden d-d transition of Fe 3+ in tetrahedral coordination. On these samples, an indirect evidence of the formation of extraframework Fe upon calcination at high temperature, is given by IR spectra in the OH stetching region where a decrease of the absorption due to the Brensted acidic species is observed. Moreover EPR spectra show an intense band at g --- 2.00, due to the presence Fe 3+ in octahedral coordination. The intensity of this absorption increases when Fe-Silicalite is calcined at higher temperature (as expected). Conclusion
In as synthesised Fe-Silicalite, only a part of iron of reaction mixture is present in framework positions; DRS UV-Vis, IR and EPR results indicated that calcination at increasing temperature causes a partial iron extraction from the lattice and formation of very small clusters of iron oxides entrapped into the silicalite channels. Finally, when Fe-Silicalite is calcined at high temperature (973 K) no more evidence of structural iron is obtained by means of physical methods. References
1) Scarano D., Zecchina A., Bordiga S., Geobaldo F., Spoto G., Petrini G., Leofanti G., Vzdova 9M., and Tozzola G. Faraday Trans. in press.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
114
ELECTROCHEMISTRY OF TRANSITION METAL COMPLEXES ENCAPSULATED INTO ZEOLITES Carol A. Bessel and Debra R. Rolison* Surface Chemistry Branch (Code 6170), Naval Research Laboratory 4555 Overlook Avenue, SW, Washington, DC, 20375-5342, USA SUMMARY. The electrochemistry of transition metal complexes (Co(salen) and [Fe(bpy)3]2+ ) encapsulated into zeolites was studied using zeolite-modified electrodes (ZME). Grinding time, binding material, carbon source, electrolyte, solvent, scan rate, and the charge of the encapsulated complex all affect the cyclic and differential pulse voltammetry of these ZMEs. INTRODUCTION. Modification of electrode surfaces with zeolites is of current interest to both electrochemical and solid-state disciplines as the suggested applications include chemical sensing and electrocatalysis. 1-5
In order to demonstrate the utility of transition metal
complexes encapsulated into zeolites for electrosynthesgs, the reactivity of these materials [Z(ML)] at modified electrodes was investigated.
The use of Z(ML) for electrocatalysis
requires insight into the mechanism by which redox activity occurs in the zeolite lattice. Optimization of the variables associated with the synthesis of the modified zeolite and their preparation and use as zeolite-modified electrodes must first be investigated before such issues as changes in the redox reactivity due to interior versus exterior lattice sites, the steric strain to the encapsulated complex imposed by the zeolite and/or bonding of the complex to the zeolite, and electronic communication within the zeolite lattice itself can be addressed. Several fundamental studies to optimize the voltammetry of ZME were conducted using monograin films of Z(ML) applied to the working electrode surface to provide a uniform method for systematically studying the variables that arise in the production and use of 7MEs. EXPERIMENTAL SECTION. NaY (Strem Chemical) was equilibrated in an aq. 0.1 M NaCI for 24 h, dnsed free of CI', and then brought to constant weight over a saturated NH4CI solution. Co(salen)-Y was synthesized following published procedures.3, 6 [Fe(bpy)3]2+-Y was similarly synthesized.
The transition metal encapsulated zeolites were characterized by FT-IR and
diffuse reflectance UV-Vis spectroscopies and by cyclic and differential pulse voltammetry. Electrochemical measurements were conducted in a three-compartment cell containing a coiled Pt auxiliary electrode, a saturated sodium chlodde calomel reference (SSCE) and a zeolite-modified glassy carbon working electrode. The ZME was prepared using a variant of Li and Calzaferri's layered-monograin approach: 7 a MeOH suspension of ground Ultra Pure Carbon and modified zeolite was floated onto the electrode surface, dried, and then covered with a thin layer of polyacrylic acid (PAA, MWavg 450,000) from a methanolic solution.
115 RESULTS AND DISCUSSION. Figure 1 demonstrates one of the variables affecting the cyclic voltammetry of Z(ML)-modified electrodes.
This figure shows that as grinding time of the
zeolite plus carbon powder is increased, the resolution of the redox couple(s) improves and the concentration of the redox species increases.
Grinding the zeolite crystallites appears to
fracture the crystallites and with increased grinding time allows a greater extracrystalline surface area of the zeolite to be exposed to the electrolyte thereby enhancing electrochemical response.
the
This implies that the electrochemical response of the ZME is
caused by electron transfer to transition metal complex located on the exterior of the zeolite. Changes in scan rate, electrolyte, binding material, carbon source, solvent, and charge of the encapsulated complex will be discussed in terms of the cyclic and differential pulse voltammetry of zeolite-modified electrodes.
C
-210
,
;
Volts vs. SSCE
,
....
+2.0
Figure 1. Grinding Study. Cyclic voltammetry of [Fe(bpy)3]2+-encapsulated zeolite Y in 0.1 M LiCIO4/ CH3CN at 10 mV/s. 60 mg of carbon + 60 mg of modified zeolite were ground in a sapphire mortar and pestle for the specified period of time with 10 mg removed to prepare the ZME. A: unmodified glassy carbon electrode; B: ZME with 10 min grinding; C: ZME with 30 min grinding; and D: ZME with 60 rain grinding. The wave negative of-1.2 V is consistent with ligand-centered reduction and the couple positive of 0 V is consistent with Fell/Ill-centered redox for [Fe(bpy)3] 2+.
REFERENCES 1. Rolison, D. R.; Chem. Rev. 1990, 90, 867. 2. Li, Z.; Mallouk, T. E. J. Phys. Chem. 1987, 91,643. 3. Bedioui, F.; De Boysson, E.; Devynck, J. Balkus, K. J. Jr. J. Chem. Soc., Faraday Trans. 1991, 87(24), 3831. 4. Shaw, B. R.; Creasy, K. E.; Lanczycki, C. J.; Sargeant, J. A.; Tirhado, M. J. Electrochem. Soc. 1988, 135, 869. 5. Baker, M. D.; Senaratne, C.; Zhang, J. J. Phys. Chem. 1994, 98, 1668. 6. Herron, N. Inorg. Chem. 1986, 25, 4714. 7. Li, J.; Calzaferri, G. J. Chem. Soc., Chem. Commun. 1993, 1430.
III. Modification
This Page Intentionally Left Blank
H.G. Karge and J. Weitkamp (Eds.)
116
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
STRUCTURE
AND PROPERTIES
IN ZINC PROMOTED
OF ACTIVE SPECIES
H-ZSM-5 CATALYSTS
H. Berndt, G. Lietz, B. Lticke, and J. V61ter Institute for Applied Chemistry Berlin-Adlershofe.V., Rudower Chaussee 5, 12484 Berlin, Germany SUMMARY Different zinc promoted H-ZSM-5 samples were prepared using ion exchange and impregnation techniques. The samples were characterized by TPSK, TPDA and FTIR and catalytically tested in the conversion of propane to aromatics. Ion exchange generates catalysts with highest activity. TPSR-CO enables to determine the concentration of Lewis acidic [Zn(OH)] + ions and their concentration could be correlated with the catalytic activity. INTRODUCTION Zinc promoted H-ZSM-5 is a very active catalyst for the transformation of low alkanes into more valuable products. However, the best method of preparation, the nature of the active species and their location inside or outside the channels are still questionable [ 1-3]. Samples with different nature of zinc species were prepared. Their concentration should be determined using the TPSR with CO as probe molecule and correlations could be studied between the content of the different zinc species and their catalytic activity in the conversion of propane. EXPERIMENTAL H-ZSM-5 was promoted with zinc either by impregnation (Zni) or by ion exchange (Zne). Propane was converted in a flow reactor between 480 and 510 ~
TPSR-CO studies were
carried out using the equipment AMI-1 coupled with a QMS. The IR spectra in the OHstretching vibration region and the absorption bands of adsorbed pyridine and ammonia were recorded with a Bruker IFS 66 FTIR spectrometer. RESULTS AND DISCUSSION The catalytic experiments showed that Zn e was (z
much more active than Zni, whereas the selectivity for aromatics was nearly the same. Unpromoted H-ZSM-5 was very inselective. The activity of Zn i was increased by a factor of two after a H 2 treatment at 450 ~ C (sample Zni/a). TPSR-CO curves of different samples are shown in Figure 1. Only CO 2 is displayed, but H 2 is obtained in equivalent amounts, too. The peaks o~ and 13 indicate two types of zinc
Zne/l.l --
a
, 200
,.
, 400
0
t 600
.ti 650
T/*C
species.
The
portions
depend
on
the
Figure 1: TPSR-CO plots, zinc content
preparation method and the zinc content.
of the catalysts 1. I- 1.6 wt.-%
Moreover, there is a third type of species (7).
117 This one does not react with CO. Remarkably, the hydrogen activation causes a considerable increase of the a peak of the curve ofZni, a compared to Zn i. The acidity of the samples was studied by TPD of ammonia. On the one hand, the promotion with zinc decreased the high temperature peak (h.t.p.) caused by desorption from the Br/Snsted sites. On the other hand, the h.t.p, was shifted towards higher temperatures indicating the generation of strong acidic sites. The amount of these new sites increases in the sequence Zni, Zni, a and Zn e. FTIR spectroscopy confirmed the decrease of the concentration of Br6nsted sites and the generation of new acidic sites of the Lewis type. Fig. 2 shows the conversion of propane in dependence on the concentration
o~ 80 -~
of zinc
species in Zni, Zni/a, and two Zn e samples determined as i) the total amount of formed
/t/l.e f
CO 2 (a+13), ii) the partial amount (a) and iii)
60
o
9 ~
u~/,.s the total zinc content representing the sum of
40
(a+13+T).
20
a
ell.l
~.~
..... Zn species / pmol g--I
0 "r
I : c:+ 13
curve
based
on
(a+13)
activity. However, using only the a-peak area a 200
I00
The
demonstrates a nearly linear relation to the
A:
Figure 2: Correlation between activity and concentration of zinc species
linear
curve
is
established
crossing
approximately the origin. This finding enables the conclusion that i) the TPSR-CO data can be used for correlations with the activity and ii) only the a species are active. Because of the formation of CO 2 and H 2 by the reaction with CO, the a species contain O and H.
Therefore, we suggest that these are [Zn(OH)] + ions located in the zeolite channels. TPDA and FTIR data showed that Zn species generate strong acidic Lewis sites. These sites should promote the propane conversion by hydride abstraction according to the mechanism proposed by Ono [1]. We suggest that the high activity of the Zn e sample is due to these species in the channels, whereas the Zn i sample contains predominantly less active 13 species and inactive ~/ species (zinc oxide) located on the outer surface of the zeolite crystals. Consequently, the observed activation by hydrogen can be explained by transportation of zinc from outside into the channels enhancing the concentration of strong acidic Lewis sites. CONCLUSION Zinc species of different reactivity could be detected by TPSR-CO. Only the [Zn(OH)] + ions located on Bronsted sites in the channels activate the propane conversion. REFERENCES [1] Y.Ono, Catal. Rev.Sci. Eng., 34 (1992) 179 [2] Le van Mao, L. Dufresne and J. Yao, Appl. Catal., 65 (1990) 143 [3] M. S. Scurrel, Appl. Catal., 32 (1987) 1
118
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
FT IR AND FT RAMAN STUDIES OF [B,AI]-BETA + Ga=Os SYSTEM M. Derewifiski, J. Kn/~ciak, Z. Olejniczak *, J. Ptaszyflski, B. Sulikowski Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 1, 30-239 Krak6w, Poland. * Institute of Nuclear Physics, ul. Radzikowskiego 152, 31-342 KrakSw, Poland. Key words: [B,AI]-Beta zeolite, G~O3, H2 treatment, FT IR and FT Raman
INTRODUCTION Gallium can be readily incorporated into numerous zeolitic structures both directly during hydrothermal synthesis [1] and by post-synthesis modifications [2,3]. Such a substitution results in a new chemical properties which make Ga-containing materials useful for certain catalytic applications. Highly siliceous, large pore beta zeolite containing boron and aluminium was chosen for modification with Ga203. Boron is partially removed from tetrahedral framework sites during thermal treatment thus giving defect sites (sUanol nests) in the lattice [4]. The objective of this work is to study the interaction of Ga203 with defects-rich beta zeolite and to examine if Ga can reoccupy sites in the framework previously containing boron atoms. The effect of H2 / thermal treatment on the state of Ga in the [B,AI]-beta/Ga203 system was investigated by means of FT IR and FT Raman spectroscopies.
EXPERIMENTAL [B,AI]-Beta zeolite (Si/AI = 71, Si/B = 14) has been synthesized using tetraethylammonium (TEA) as a template. Calcined and ion-exchanged zeolite was mechanically mixed with 13-Ga203 (5 wt%) and subsequently calcined at 600 ~ under flow of H 2. FT IR and FT Raman measurements were carded out on a Nicolet 800 spectrometer.
RESULTS AND DISCUSSION For as-synthesized [B ,AI]- beta zeolite, boron incorporation into the framework is evidenced by a band at 899 cm-1 (Si-O-B asymmetric stretching vibrations) (Fig.lA). Calcination of zeolite at 500 ~ to remove organic template and subsequent ion-exchange procedure result in a deep deboronation and formation of the lattice defects, i.e. silanol nests, as indicated by formation of a new band at 948 cm ~ (Fig.1B). The decreased in intensity band of tetrahedral framework boron is seen as a shoulder on a band attributed to silanol nests. On the other hand, such a post-synthesis treatment does not result in aluminium extraction from the framework. The decrease of intensities of the structure sensitive bands at 1218, 626, 578, 532 and 428 cm 1 suggests the structural changes in the zeolite framework, no amorphisation could be however detected by XRD. Mechanical mixing of activated
119
[B,AI]-beta sample with
p-Ga~O~do
not modify IR spectra of zeolite (Fig.lC). Subsequent
calcination at 600 ~ under flow of H2 leads to significant changes in the IR spectra (Fig.1D). The band attributed to silanol nests is significantly reduced in intensity and the strongest stretching band is shifted to lower wavenumbers (1095 - 1093 cm 1) thus indicating healing of the framework by gallium. Simultaneously restored structure sensitive bands give rise to the spectrum characteristic for a highly ordered, defects-free beta zeolite as observed for as-synthesized material. Such a behaviour indicates insertion of Ga atoms into the sites previously occupied by boron. The parallel FT Raman studies confirm that bulk gallium oxide is absent in the spectrum of the reduced material. The appearance of bands in the reduced samples recall those found in faujasite/Ga203 system [3]. It can be therefore concluded that interaction of gallium oxide with various zeolitic structures proceeds similarly.
Fig.1. IR spectra of the samples: A - parent [B, AI] - beta zeolite , B - sample A calcined at 500 ~ and ion exchanged, C - sample B mechanically mixed with u
P- Ga203,
Z (12
D - sample C calcined at 600 ~ in the presence of H2.
5"z <12 P--
~
1~
.,
~oo
1500 ~6oo ~oo HAVENUMBER
,
4oo
ACKNOWLEDGEMENT We are grateful to the Committee of Scientific Research (Warsaw) for support (project no. 2P.303.149.04).
REFERENCES [1] J.M. Newsam, D.E.W. Vaughan, Stud.Surf.Sci.Catal., 28 (1986) 457 - and references therein. [2] J.M. Thomas, L. Xinsheng, J.Phys.Chem., 90 (1986) 4843. [3] B. Sulikowski, J. Kry~ciak, R.X. Valenzuela, V. Cortes Corber&n, Stud.Surf.Sci.Catal., (1994) -in the press. [4] M. Derewir~ski, F. Fajula, Appl.Catal., A 108 (1994) 53.
120
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
F A U J A S I T E - H O S T E D NICKEL-SALEN. H. Meyer zu Altenschildesche and R. Nesper, Laboratorium for Anorganische Chemie, ETH Zentrum, CH-8092 ZOrich, Switzerland
SUMMARY. [Ni(salen)] was prepared inside the supercages of NaY by the reaction of Ni-exchanged zeolite witli salen. The 2SNa NMR spectra of dehydrated NaY and (Ni,Na)Y (up to 33% Na+ exchanged) reveal that there is no preferential loss of Na+ from the double six-rings. Thus, the known preference of Ni2+ for this site does not lead to complete substitution of sodium. During reaction with salen, Ni2+-cations are able to migrate back to the supercage. Complex formation was proven by means of IR, diffuse reflectance UVNIS, and solid state 1H NMR spectroscopy. Rietveld refinement of powder X-ray diffraction data indicate a preference of [Ni(salen)] for positions where interaction between Na+ and the oxygen atoms of the guest molecule is favourable. INTRODUCTION. Neutral transition metal complexes of Schiff base ligands, e.g., salen (N,N'bis(salicylaldehyde)ethylenediimine), synthesized in the nanometer-sized voids of porous hosts have attracted much attention recently [1,2]. These materials possess promising properties like shape-selective catalytic reactivity and reversible oxygen binding behavior. In previous investigations the zeolite was assumed to stay essentially unchanged and no specific interactions between the host and guest molecules were discussed. However, transition metal complexes of salen are known to act as ligands towards alkali, alkaline earth and other cations [3]. This implies that interactions between Na+-cations and guest complexes are to be expected and may change structure, properties and accessibility of the guest species.
Structure of Ni[[(salen). EXPERIMENTAL. Zeolite NaY (Chemie Uetikon, Si/A! = 2.94) was partially ion-exchanged with dilute nickel-acetate solution. After washing with deionized water, the exchanged zeolite was calcined in air and dehydrated in vacuo at 723 K. The zeolite was mixed with an excess of salen in an inert-atmosphere glovebox and heated to 413 K for 4-5 hrs.
121
Unreacted ligand was extracted with dichloromethane. The solvent was then removed by evacuation at 473 K. Powder X-ray diffraction of [Ni(salen)]/NaY showed no loss of crystallinity. The dark-red products were investigated by IR, diffuse reflectance UVNIS, and 1H, 23Na, and 13C MAS NMR spectroscopy. Rietveld refinement was performed with the XRS-82 program package. RESULTS AND DISCUSSION. The 23Na MAS NMR spectra of dehydrated NaY and its partially nickel-exchanged derivative are very similar, showing no preferential loss of Na+ from the double sixrings. Therefore, the known preference of Ni2+ for this site does not lead to complete substitution, at least for exchange levels up to 33%. Previously published results indicating that not all double six-rings were occupied by Ni2+ can now be understood in terms of a mixed occupation by Na+ and Ni2+ [4]. Under the synthesis conditions applied, Ni2+-cations are able to migrate back to the supercage. The formation of [Ni(salen)] was proven by means of IR, diffuse reflectance UVNIS, and solid state 1H NMR spectroscopy. Elemental analysis reveals that complex formation is quantitative and adjacent supercages can be occupied, although the phenyl rings of [Ni(salen)] protrude through the 12-ring pore openings. The 2SNa MAS NMR spectrum of [Ni(salen)]/NaY is very different from that of the zeolite precursors. This results from the change in the environment of supercagehosted Na+-cations. A Rietveld refinement of powder X-ray diffraction data indicates a preference of the guest molecules for positions where interaction between Na§ and the oxygen atoms of the complex is favourable. Thus, the properties of uncharged transition metal complexes included in zeolites may depend on the number and type of charge-compensating cations or other coadsorbed molecules. This opens a way to materials which are tailor-made for specific applications.
REFERENCES. [1] N. Herron, Inorg. Chem. 25 (1986) 4714. [2] D. E. de Vos, F. Thibault-Starzyk, P. A. Jacobs, Angew. Chem. 106 (1994) 447. [3] N. Bresciani-Pahor, M. Calligaris, P. Delise, G. Nardin, L. Randaccio, E. Zotti, G. Fachinetti, C. Floriani, J. Chem. Soc., Dalton Trans. (1976) 2310. [4] P. Gallezot, B. Imelik, J. Phys. Chem. 77 (1973) 652.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
122
MODIFICATION OF ALUMINOPHOSPHATE MOLECULAR SIEVES BY REACTION WITH ORGANOPALLADlUM COMPLEXES. KATHRYN M. TEARLE AND JUDITH M. CORKER DEPARTMENT OF CHEMISTRY, UNIVERSITY OF SOUTHAMPTON, HIGHFIELD, SOUTHAMPTON, SO9 5NH, ENGLAND. SUMMARY Aluminophosphates, VPI-5 and AIPO4-5 were synthesisecl and characterised by powder x-ray diffraction. The AIPO4 materials were treated with Pd(TI3 -C3Hs)(TI~-CsHs). Direct structural evidence of the species formed was obtained using extended x-ray absorption fine structure (EXAFS). On reaction of VPI-5 with Pd(q 3 -C3H5)(~1~ -CsHs), the allyl ligand is lost but the cyciopentadienyl group remains attached to the palladium centre. INTRODUCTION Over the past few years there has been much interest in the development of new types of catalyst materials. The small uniform pores and large internal volumes characteristic of porous, microcrystalline aluminophosphate materials, 1 potentially make them ideally suited as shape-selective catalysts or supports. Most catalytic applications however require quite specific pore geometries or cut off diameters and these can not necessarily be achieved via direct synthesis of the microporous material itself. Efficient processes for structural modification post-synthesis are thus highly desirable. The incorporation of organometallic complexes in such materials is one post-synthesis modification route which has not been extensively investigated. 2 We
are developing
methods
of anchoring organopalladium
complexes within the
large-pore
aluminophosphates, VPI-5 and AIPO4-5. The interest in supporting organopalladium complexes stems oxidation catalysis: it is well known that Pd complexes in solution are capable of catalysing various alkene oxidation reactions, but examples of well-defined organopallaclium complexes on inorganic supports are few in number. One reaction which has been reported is that of Pd(TI3-C3Hs)2 with silica 3 which leads to the apparent formation of [Si]-O-Pd(~l 3-C3H5), but firm spectroscopic evidence is lacking. EXPERIMENTAL AIPO4-5 was synthesised following the method of Wilson et af =. VPI-5 was synthesisecl from an aluminophosphate gel of composition 0.2TMAOH:DPTA:AI203:P2Os:40H20, at 150"C for 20 hours. Pd(TI3 -C3Hs)(TIs-CsHs) was synthesised following the method of Tatsuno et af'. Treatment of VPI-5 and AIPO4-5 with Pd(TI3 -C3Hs)(~I~-CsHs) was carried out using metallo organic chemical vapour deposition (MOCVD) techniques.
123
RESULTS AND DISCUSSION Two carbon shells can be readily identified in the Pd K-edge EXAFS spectrum of Pd(TI3-C3Hs)(TIs-CsHs) at room temperature; the first shell at 2.11A due to 3 carbons of the allyl group and the second at 2.31A caused by the 5 cyclopentadienyl carbons. Physisorption of Pd013-C3Hs)(~-CsHs) onto VPI-5 is apparent initially on room temperature deposition of the organometallic complex in vacuo.
Reaction with the
support then occurs, and a pale yellow colouration is observed. The Pd K-edge EXAFS, recorded at room temperature under vacuum (2xl0Storr), shows a marked change in coordination; the EXAFS is best fitted by 1 shell of 5 carbons at 2.13A and by a more distant shell of cal-2 oxygens at 2.95A, suggesting that the allyl group is last in the reaction.
The distant shell at 2.95A could be attributed to a weak
interaction with the framework oxygens.
Decomposition of the AIPO4-supported organopalladium
complexes species to metallic Pd is observed above 250" C; EXAFS analysis indicates a first coordination sphere of ca6 Pd atoms at 2.75A, indicative of small metal particles.
P'WmlI[:II' N w W l u l l
k
~
POIIIIII ~
f~=~pom~tl
e,p,
Q,,, Lo,
,~,
L,
u
i,o
~
~.J
n,e
l_~
Q,I
a,a
~
L,
u
u
M
I.i
a,o
Figure 1 Pd K-edge EXAFS of VPI-5/Pd(TI3-C3Hs)(TIs-CsHs), at a) 25"C 2xl0~torr and b) after heating to 300" C under 2xl0Storr. REFERENCES 1. D.M.Poojary, J.O.Perez and A.Clearfield, J.Phys.Chem.,1992, 96, 7709. 2. G.Ozin and G.Gil, Chem.Rev., 1989, 89, 1749 3. "Catalysis by supported Complexes", Yu.I.Yermakov, B.N.Kaznetsov and V.A.Zakharov,Eds., Studies in Surface Science and Catalysis, Elsievier, Amsterdam, 1981, Chapter 2. 4. S.T.Wilson, B.M.Lok and E.M.Flanigen, US Patent,4,310,440, 1982. 5 Y.Tatsuno, T.Yoshida and Seiotsuka, Inorganic Synthesis, 1979, 19, 220.
H.G. Karge and J. ~eitkamp (l:xls.) 124
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
ZEOLITE-STABILISED RHODIUM MOLECULAR NITROGEN
COMPLEXES
WITH
AS L I G A N D
Hans Miessner* Zentrum ~ r Heterogene Katalyse, KAI e.V., Rudower Chaussee 5, 12484 Berlin, Germany
S ~ Y The surface complexes RhI(CO)fN2) + with v(CO)=2062 cm-1 and v(N2)=2252 cm-1 and RhI(N2)2 +, v(N2)=2242+2218 cm"1 , which are stable in flowing nitrogen up to 250~ have been synthesised from RhI(CO)2 + on highly dealuminated zeolite Y (DAY, US-Ex). INTRODUCTION Several transition metal complexes containing dinitrogen as ligands are known and attempts have been made to utilise these complexes as models to the nitrogen fixation 1 However, the interaction of molecular nitrogen with transition metals has been found to be weak and the adsorption of N 2 on supported metal catalysts has been observed, therefore, generally at low temperature and/or at high pressures.
The adsorption of N 2 on supported Rh at low
temperature 2,3 or at high pressures 4,5 have been studied ]R-spectroscopically. In previous work we could show that dealuminated Y zeolite (US-Ex, DAY) is a unique material to stabilise well-defined surface complexes of transition metals. Subcarbonyls of Rh 6-8, Ru and Ir 9 and mixed carbonyl-nitrosyls of Rh 8,10 could be identified and, due to the unusual sharpness of the infrared bands, structurally characterised. In the present work we will show that these well-defined surface species can be used as the starting material to surface chemistry, to the synthesis of other well-defined surface complexes. EXPERIMENTAL SECTION Rh/DAY and Rh/US-Ex (lwt% Rh) was prepared by impregnating the supports DAY (Si:Al > 100, kindly supplied by DEGUSSA, obtained by exchange of the Al atoms for Si by treating the NaY with SiC14 ) or US-Ex (Si:A1 -- 100, obtained by hydrotherrnal treatment of NH4Y ) with an appropriate amount of RhCl 3 in ethanolic solution and drying the sample at 120~ in air. The transmission ]R studies were performed with self-supported wafers using a special infrared cell made from stainless steel for in-situ measurements up to 400~
and 50 bar,
connected to a gas flowing system, which allows a fast variation of the feed gas. The spectra were recorded with an FT]R spectrometer (BIORAD FTS 60A) at 2 cm-1 resolution.
*Present Address:
ENIRICERCHE S.p.A., CATA, Via Maritano, 26 1-20097 SAN DONATO MILANESE, ITALY
125 RESULTS AND DISCUSSION In a first step, Rh dicarbonyl RhI(CO)2 + was formed on the cation positions of DAY by treating the sample in a flow of CO(5%)/Ar at 150~ In the IR spectra, strong bands at 2118 and 2053 cm -1 appear and, simultaneously, the intensity of the OH-bands at 3630 (HF) and 3567 cm -1 (LF) of the acid hydroxyls decreases 12 A subsequent treatment of the dicarbonyl in a flow of H2/N 2 at 200~ results in a partial decarbonylation as indicated by decreasing of the corresponding IR bands at 2118 and 2053 cm- 1 At the same time, a new carbonyl species is formed with a carbonyl stretching vibration at ca. 2090 cm-1 After switching the gas feed at 200~ fi,om H2/N 2 to pure nitrogen, the band at ca. 2090 cm-1 of the monocarbonyl decreases and new bands in the dinitrogen and carbonyl stretching region appear. The wavenumbers of these bands at r.t. are collected in Tab. 1. A correlation analysis of the integrated absorbances of the corresponding bands in a series of experiments suggests that there are at least two well-defined surface complexes with dinitrogen as ligands: a mixed dinitrogen-carbonyl complex with i.r. bands at 2252 and 2062 cm -1 and a complex with two nitrogen stretching bands at 2244 and 2218 cm -1, most probably a surface complex with two dinitrogen ligands.
The nitrogen complexes are stable in flowing nitrogen, but react
immediately with CO to give the Rh dicarbonyl. The assignment of the IR bands was verified by experiments using isotopic mixtures containing C 180 or 15N2. The two supports used have the same crystal structure and a similar Si:AI ratio, but differ significantly in the mesopore structure. Due to the different dealumination procedure, U S-Ex has a high amount of mesopores and, consequently, a higher amount of terminal silanol groups as compared with DAY 11
The formation and the properties of the well-defined surface
species described in the present work are, nevertheless, similar for both supports. This is an argument in favour of the formation of these species at the cation positions rather than on the outer surface or in the mesopores of the zeolite. REFERENCES 1 G.J. Leigh, Acc.Chem.Res., 1992, 25, 177. 2 Yu. G. Borod'ko and V. S. Lyutov, Kinet.Katal., 1971, 12, 238. 3 H.P. Wang and J. T. Yates, Jr., J.Phys.Chem., 1984, 88, 852. 4 J.P. Wey, H. D. Burkett, W. C. Neely and S. D. Worley, J.Am.Chem.Soc., 1991, 113, 2919. 5 J.P. Wey, W. C. Neely and S. D. Worley, J.Phys.Chem., 1991, 95, 8879. 6 I. Burkhardt, D. Gutschick, U. Lohse and H. Miessner, J.Chem.Soc., Chem.Commun., 1987, 291. 7 H. Miessner, I. Burkhardt, D. Gutschick, A. Zecchina, C. Morterra and G. Spoto, J.Chem.Soc., Faraday Trans., 1, 1989, 85, 2113. 8 H. Miessner, I. Burkhardt, D. Gutschick, A. Zecchina, C. Morterra and G. Spoto, J.Chem.Soc., Faraday Trans., 1990, 86, 2321. 9 H. Landmesser and H. Miessner, J.Phys.Chem., 1991, 95, 10544. 10 H. Miessner, I. Burkhardt and D. Gutschick, J.Chem.Soc., Faraday Trans., 1990, 86, 2329. 11 H. Stach, U. Lohse, H. Thamm and W. Schirmer, Zeolites 1986, 6, 74.
126
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
INTRAZEOLITIC REDOX CHEMISTRY OF MANGANESE PREPARED FROM CHEMICAL VAPOR DESPOSITION OF Mn2(CO)10 ON NaY Carlo Dossi, Sandro Recchia, AchiUe Fusi and *Rinaldo Psaro Dipartimento di Chimica Inorganica, Metallorganica e Analitica and *Centro C.N.R., Via Venezian, 21, 20133 Milano, Italy
ABSTRACT Intrazeolite redox chemistry of manganese has been exploited by the use of vapor-deposited Mn2(CO)10 complex onto NaY. INTRODUCTION Ion exchanged Mn 2+ ions inside Y-type zeolite have a very high stability, being virtually inert under both oxidizing and reducing conditions [1]. The use of neutral organometaUic molecules as metal precursors instead of the exchanged metal ion is supposed to possibly overcome the non-reducibility of several exchanged ions under gas-phase reduction conditions, or, if the reduction is succesful, the stoichiometric creation of protonic acidity [2]. In fact, the original distribution of positive charges inside the zeolite structure is left unaltered upon deposition of the neutral organometaUic precursor, and zerovalent metal atoms are simply obtained by thermal removal of ligands [3]. EXPERIMENTAL Mn2(CO)10 was sublimed inside dehydrated NaY zeolite (Linde LZY-52) at 105~ in flowing argon. Full details of sample preparation and thermoanalytical characterization are reported elsewhere [3]. Diffuse Reflectance Infrared (DRIFT) studies of CO chemisorption have been carried out in a specially designed, hightemperature flow cell. RESULTS AND DISCUSSION Mn2(CO)10 is easily deposited from the vapor phase inside the supercages of NaY zeolite without decomposition, as demonstrated by the similarity of the IR spectrum with that of the pure compound. Removal of CO ligands is then observed in flowing He to start at 120-130~ being complete below 250~ Analysis of the gas evolution during the thermal decomposition showed evolution of H2 paralleling that of CO. This unusual behavior can be rationalized on the basis of a twostep reaction:
127 (i) first, naked zerovalent Mn atoms are formed by removal of CO ligands Mn2(CO)10/NaY B >
2 Mn0/NaY
+
10 CO
(reaction 1)
(ii) these highly reactive monoatomic Mn sites are immediately re-oxidized by reacting with residual traces of water left in zeolite, with formation of small aggregates of MnO inside the supercages of NaY zeolite. Mn~
+
H20
m > MnO/NaY +
H2
(reaction 2)
Accordingly, the color of the sample changes from light yellow to white at the end of the TPRD experiment. Reaction 2 is extremely favored, and is completely shifted to the right even in H2-rich atmospheres, as demonstrated by theoretical predictions based on standard electrode potentials [4]. Reduction of NaY-entrapped manganese(II) oxide is instead feasible by using carbon monoxide as the reducing agent. CO has no action on Mn 2+ exchanged in NaY. On the contrary, a full set of carbonyl IR bands develops in the 22001800 cm -1 region by contacting CO with NaY-entrapped MnO. From the location of such bands, and by comparison with the infrared spectra of pure reference compounds, the presence of entrapped Mn(0) and Mn(I) carbonyls, much likely Mn2(CO)10 and [Mn(CO)3(O-Z)] (O-Z represents a framework oxygen ion) can be inferred. Carbon monoxide has the dual function to reduce MnO and, at the same time, to act as a ligand for the zerovalent Mn atoms forming intrazeolitic Mn carbonyls: (3O MnO/NaY + CO m > CO2 + Mn0/NaY m > [Mnx(CO)y]/NaY + [Mn(CO)3(O-Z)] The coordination of water molecules on metal centers, the first step in the redox chemistry leading to oxidized manganese, is thus prevented by the strong affinity of carbon monoxide for zerovalent transition metals. In further contrast with ion-exchanged Mn2+/NaY, entrapped MnO can be further oxidized in oxygen or air, giving a dark brown material. A Temperature Programmed Reduction (TPR) analysis shows a monoelectronic reduction step occurring around 300~ A reversible oxidation/reduction cycle between MnO and Mn203 is thus suggested, in contrast to the high stability of ion-exchanged Mn 2+ toward 02 oxidation at 500~ CONCLUSIONS The redox chemistry of intrazeolite manganese can only be exploited when it is prepared from neutral organomanganese complexes, such as Mn2(CO)10. In this
128 way, no stable Mn 2+ ions are formed, and the whole range of oxidation states from 0 to 3 can be observed. REFERENCES [1] A Jones and B. McNicol, "Temperature Programmed reduction for solid material characterization", Marcel Dekker, New York (1986). [2] T.T. Wong and W.M.H. Sachtler, ]. Catal., 141 (1993) 407. [3] C. Dossi, R. Psaro, A. Bartsch, E. Brivio, A. Galasco and P. Losi, Catal. Today, 17 (1993) 527. [4] T.P. Wilson, P.H. Kasai and P.C. EUgen, J. Catal., 69 (1981) 193.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
129
CALCINATION OF Pd(NH3)42+ AND REDUCTION TO Pd ~ IN NaX AND CsX ZEOLITES A. Sauvage, P. Massiani, M. Briend, D. Barthomeuf Laboratoire de R6activit6 de Surface, Universit6 Paris 6 (France) F. Bozon-Verduraz Laboratoire de Chimie des Mat6riaux Divis6s et Catalyse, Universit6 Paris 7 (France)
Summary The decomposition in 02 of Pd(NH3)42+ in NaX and CsX followed by TPO, UV-Visible and near IR occurs at lower temperature for PdCsX than for PdNaX. This is connected to different decomposition steps of Pd(NH3)x 2+. The reduction of Pd2+ to Pd ~ is easier in PdCsX than in PdNaX. Introduction The interaction of palladium tetrammine complexes with NaY has been extensively studied 1. It was observed in the case of Pt supported zeolites that the decomposition temperature of the ammine complex is different on PtNaX or PtCsX suggesting an influence of the framework chemical properties on the strength of interaction 2. The aim of the present work is to compare the decomposition of the Pd tetrammine complex and the reduction of Pd2+ on NaX and CsX to check the possible influence of the zeolite properties.
Experimental Pd7,4NaX and Pd8,oCs3oNaX (referred to as PdNaX and PdCsX) are prepared by exchange of the zeolite with a Pd(NH3)4CI2 solution at pH 10. The ion contents are expressed per unit cell. The decomposition, upon heating, of the complex is followed by TPO (thermoprogrammed oxidation) using thermal conductivity (TCD) or mass spectrometry (MS) and by UV-Visible and near infrared (NIR) spectroscopies. The reduction with H2 is studied by TPR (thermoprogrammed reduction) using TCD and by UV-Visible spectroscopy. The materials are heated at a rate of 7,5 K/rain in a flow of O2/He (oxidation) or H2/Ar (reduction). Results and Discussion Common features Figure 1 gives the TPO results (TCD analysis). For both samples a main peak is seen (585 K-PdCsX and 620 K-PdNaX). In addition smaller peaks are present at lower temperature, embedded in the big peak, or at higher temperature (around 610 K-PdCsX and 665 K-PdNaX). The detection of three peaks, comparable to the case of PdNaY, reveals the step-wise removal of NH3 from the supported complex 3. The decomposition of the desorbed phase followed by mass spectroscopy shows for both samples the removal at different temperatures of NH3 (505 K-PdCsX, 545 K-PdNaX) and of N2 (605 and 630 K-PdCsX, 630 and 680 K-PdNaX). As already observed for
130
PdNau 3, oxygen consumption mirrors N2 production. In addition our results show that NH3 is removed at temperature below the main TPO peaks of figure 1. A study using UV-Visible and near infrared spectroscopies shows that the ammine ligands are removed between 470 K and 700 K and replaced by framework oxygen as was reported for PdNaY 4. Simultaneously the NH3 peaks near 1525-1545 nm (NIR) decrease and disappear at about 650-680 K.
Comparison of PdNaX and PdCsX Figure 1, mass spectrometry, UV-Visible and NIR results show that the decomposition of the complex occurs a lower temperature in PdCsX than in PdNaX. The profile of temperature of decomposition steps are then not identical for the two zeolites. This probably arises from at least two parameters. At first the space available in the cavities is less in PdCsX than in PdNaX due to the cation size. This may modify the possibility of formation of specific Pd complexes like those proposed in PdNaY 4. Secondly the higher basic strength of framework oxygen in CsX compared to NaXS very likely influences
A
the energy of Pd2+-Ozeo bonds. The reduction to Pd ~ is followed by TPR and UV-Visible spectroscopy. The
J
maxima of the TPR peaks are near 395 K (PdCsX) and 435 K (PdNaX). The easier reduction of PdCsX is confirmed by UVVisible showing, for this sample,
an
Ta 450
550
650
Temperature(10
750
important disappearance of Pd 2+ ions Figure 1: TPO of PdNaX (a) and PdCsX (b) under an H2 flow at room temperature .. while PdNaX retains a large part of them. This behavior suggests the preferential location of Pd 2+ in the supercage for PdCsX and in the sodalite for PdNaX. In conclusion the zeolite characteristics influence both the decomposition of Pd(NH3)4 2+ and the further reduction of Pd 2+ to Pd metal. 1 W.M.H.Sachtler, Z. Zhang, Adv. Catal., 1993, 39, 129 2 A. de Mallmann, Thesis Paris 1989 A. de Mallmann, D. Barthomeuf,to be published 3 S.T. Homeyer, W.M.H. Sachtler, J. Catal., 1989, 117, 91 4 Z. Zhang, W.M.H. Sachtler, H. Chen, Zeolites, 1990, 10, 784 5 D. Barthomeuf, J. Phys. Chem., 1984, 88, 42
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
131
ION EXCHANGE IN CoAPO-34 AND CoAPO-44 C.G.M. Jones, Dr. R. Harjula*, Dr. A. Dyer University of S.alford, Salford, M5 4WT. U.K. *Department of Radiochemistrv. University of Helsinki, Finland SUMMARY A number of SAPOs, MeAPOs and MeAPSOs with the chabazite structure were synthesised. The uptake of uranium and thorium by these samples was measured by L.S.C. Many of the samples had high K D values. The ion exchange properties of CoAPO-34 and CoAPO-44 were studied further. It was found that these CoAPOs will remove actinides more efficiently when in the Na forms, or in alkaline solutions, than in the H forms, or in acid solutions. INTRODUCTION Zeolites are currently being used in the nuclear power industry in Britain to remove Cs-137 and Sr-90 from spent fuel pond water. When considering storage and final disposal of a waste ion exchanger, zeolites have significant advantages over organic exchangers - namely their low cost, resistance to radiation and compatibility with cements and glass materials. Several actinides, e.g. uranium, thorium, plutonium and americium appear as waste products of the fuel enrichment process and in spent fuel reprocessing. It is with the uptake of these elements by zeolites and zeotypes that this study is concerned. EXPERIMENTAL SECTION Several zeotypes were synthesised according to the patented[ 1-3] methods. Thermogravimetric analysis was used to look at the removal of the template from the structure. The samples were characterised by X-ray powder diffraction. Maintenance of the structure after calcination was also confirmed by X-ray powder diffraction. The distribution coefficients for the uptake of uranium and thorium were measured by liquid scintillation counting after equilibration of samples for 3 days. Many of the zeotypes had high K D values for uranium in these tests. CoAPO-34 and CoAPO-44 were selected for further study. The H-CoAPO forms were converted progressively to their Na forms by equilibration (3 days) with sodium nitrate/hydroxide mixtures (total normality 0.05 or 0.1N). The conversion to the Na form was calculated from the change in activity of Na-22 tracer added to the solutions.
132
RESULTS AND DISCUSSION
In the case of CoAPO-34 the sodium loading increased linearly with pH up to pH 9.5. Above this pH the loading decreased due to dissolution of cobalt from the framework, which was observed by the characteristic cobalt colour change.
The maximum loading was similar to the theoretical ion
exchange capacity which was calculated from electron probe analysis data. For CoAPO-44 the maximum loading was much lower than the theoretical capacity showing that the material was very selective for (H30+). Conversion will need to be repeated using higher sodium concentrations. From the data, the selectivity coefficient, KG, was calculated for CoAPO-34 (using the equation in reference [4]). Log K G increased linearly as a function of the equivalent fraction of H ions in the zeolite. Selectivity coefficients were high showing that the material is selective for H ions. The KD values were measured for the exchange of uranium, plutonium and americium into the H-CoAPOs in solutions of pH 2 to 5. The KDS for U and Am increased linearly with increasing pH. The KD values for U were also measured for the partially converted Na forms ([Na] 0.01 to 1M). The values were higher than in the pure H forms even at high concentrations of sodium. These results confirm that Na ions are less strongly bound than H ions. CONCLUSION
In conclusion, the results show that the CoAPO materials studied will remove actinides more efficiently when in the Na forms (alkaline solution) than in the H forms (acid solutions). REFERENCES [1] B.M. Lok, C.A. Messina, R.L. Patton, R.T. Gajek, T.R. Cannan, E.M. Flanigen, US 4440871 [2] S.T. Wilson, E.M. Flanigen, US 4567029 [3] B.M. Lok, L.D.Vail, E.M. Flanigen, H. Eggert, EP0158348A2, EP0158975A2 B.M. Lok, B.K. Marcus, E.M. Flanigen, EP0161489A1 [4] R. Harjula, A. Dyer, S.D. Pearson, R.P. Townsend, J. Chem. Soc. Faraday Trans. 1992 88 (11 ) 1591 - 1597
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
133
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. CHARACTERIZATION OF ZSM-5 SAMPLES MODIFIED BY IONS OF GROUP IIl A L. Frunza 1, R. Russu 2, G. Catana 1, V. Parvulescu 3, G. Gheorghe 2, F. Constantinescu 2 and V.I. Parvulescu 4 1Institute of Physics and Technology of Materials, Bucharest-Magurele, 2Research Institute of Petroleum Processing and Petrochernistry S.A., Ploiesti, 3Institute of Physical Chemistry, Bucharest, 4Faculty of Chemistry, University of Bucharest, Romania
SUMMARY Modification of ZSM-5 zeolites (Si/Al=25) by impregnation with Ga, In or TI salts is obtained. The interaction of Py molecules with the modified samples was spectroscopically studied: the components of IR peaks were ascribed to different adsorption sites, a m o n g which there are the modifier ions. On this basis, the location of modifier ions inside the zeolitic framework is discussed. A m m o n i a adsorption and textural measurements as well as recent electrochemical titration data [1] also s u p p o r t the differences regarding the deposition of the three modifiers.
INTRODUCrION Gallium containing zeolites have received considerable interest in recent years due to the remarkable improvement they brought to the alkane conversion to aromatics, as reviewed e.g. in [2]. There are many papers focuesed on Ga catalysts, but few regard the influence of In or T1 on the catalytic reactions. As a first step of such studies, this work deals with the sites appearing on the surface of some MFI zeolites modified by impregnation not only with Ga salts, but with In or T1 ones. The sites containing ionic T1 species were clearly identified; the other sites were indirectly evidenced. EXPERIMENTAL MFI laboratory samples with Si/Al=25 were synthesized using common patent literature. The H form was obtained either by calcination of the a m m o n i u m exchanged form or by HNO3 treatment of the Na form. The impregnation with a salt of the group IIIA modifier was carried out as it was elsewhere described [1], on the H or Na form of the parent zeolite, so to assure a final content of modifier oxide u p to 7 wt%. The sample structure was characterized by X-ray diffraction, IR spectroscopy in the lattice vibration range, BET surface area and pore size distribution. Acidic pro-
134 perties were investigated before any catalytic pretreatment by ammonia desorption and IR spectroscopy of adsorbed pyridine (Py). The IR peaks were deconvoluted in order to facilitate their attribution. Quantitative comparison of the samples was achieved commonly using the integrated absorbance per unit mass. RESULTS AND DISCUSSION studies showed highly crystalline materials with the ZSM-5 structure. The lines characteristic for Ga and Tl oxides were not observed in the corresponding samples, in contrast, In oxide appears, its lines growing in intensity as the concentration increases. Therefore we supposed Ga and Tl have high dispersion onto o u r samples. The surface area decreases with impregnation showing that the modifier deposition takes place mainly on the zeolite external surface. The pore volume decreases too; this behaviour as well as the observed changes of pore size distribution could be due to the narrowing of access windows by depositions at pore mouths. Ammonia adsorption decreases with impregnation, e.g. by ca. 15% for a temperature of 200~ following the sequence, but show a lower acidity for T1 samples than for Ga or In containing ones. Brensted sites are still present in modified samples, although in a smaller amount than in the parent zeolite: this indicates that neutralization was not complete, some modifier ions have to be present at exchange sites within the zeolite channels. However, there is no straightforward dependence between the concentrations of Brensted sites and of the modifier. Taking into account the Ga content compared to the framework Al, it was found that, under our impregnation conditions, Ga species enter the zeolite to a higher extent than that described in the literature for related samples. The Lewis acidity of Tl samples increases since Py which is coordinated to T1 species contributes to 19b peak. In addition, the 8a peak, appearing as for alkaline ion containing zeolites, can be used to identify TI in cationic positions. Some activation of Py adsorption could be due to TI migration, but it rather shows the presence of steric hindrance by modifier deposition. The contribution of Indium to the sample acidity is reduced because it is deposited as a distinct phase, onto the external surface. The assumption [1] that some new Brensted sites are generated by the modifier species cannot be entirely neglected; these new protons could then appear in connection with the hydroxyl groups coordinated to isolated trivalent ions of the modifier.
135
REFERENCES
[1] L. Frunza et al., Int. Symp. Zeol. Microporous Crystals, Nagoya, 1993, P120 [1] Y. Ono, Catal. Rev. Sci. Engn. 34, 179 (1992)
136
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
FORMATION OF SMALL Na AND Na-M ALLOY (M=Cs, Rb) PARTICLES IN NaY ZEOLITE; by L. C. de M6norval 1, E. Trescos 2, F. Rachdi 2, F. Fajula 1, T. Nunes 3, and G. Feio 3 1Laboratoire de Chimie Organique Physique et Cin6tique Chimique Appliqu6es, URA-418 CNRS, ENSCM, 8 rue de rEcole Normale, 34053 Montpellier C6dex 1, France. 2Groupe de D y n a m i q u e des Phases Condens6es URA-233 CNRS, USTL Place E. Bataillon, 34095 Montpellier C6dex 5, France. 3Instituto de Ciencia e Tecnologia de polimeros, av. Prof. Gama Pinto, 2, 1699 Lisboa, Portugal. Summary A dehydrated NaY zeolite has been reacted with sodium, rubidium or cesium metal vapor. Using 129Xe, 23Na, 87Rb and 133Cs Solid State NMR and ESR techniques, we have characterized the behavior of metal particles and Na-M bimetallic alloys (M=Rb, Cs) in the a NaY zeolite. Introduction Previous experiments(1-2) were focussed on studying the and some properties of alkali metal clusters in zeolite NaY. are still many different aspects to be understood. In this have used Solid State NMR (129Xe, 23Na, 87Rb, 133Cs) together
small Na cavities of
formation But there work we with ESR
techniques to elucidate some physical properties of these m o n o m e t a l l i c or bimetallic clusters, like q u a n t u m size effects, bimetallic alloy formation or physical state of the clusters (solid or liquid). Experimental Section NaY zeolite was evacuated at 750 K under vacuum (10 -2 Torr) overnight. The temperature was then lowered to 520 K and the zeolite was exposed to the alkali vapor. After a suitable reaction time, the sample was transferred to ESR or NMR tubes without exposing it to the atmosphere. ESR measurements were carried out on a Bruker ER 200D spectrometer, operating at 9 GHz (X-band). NMR measurements were performed on a Bruker CXP 200 MHz, using a home build probe head which allows magic angle spinning of the sample in a sealed tube, or with a Bruker AC 250L spectrometer for 129Xe NMR experiments.
137 Results and Discussion F i g . l a shows the temperature independence of the linewidth and a Curie type paramagnetic behavior of the inverse intensity of the ESR signal of the Na loaded metallic particles in the NaY sample. These results suggest the formation of small Na particles having quantum size effect. In Fig.2, the 129Xe-NMR spectra of adsorbed Xe is presented. This technique proves that the Na particles are small and are homogeneously distributed in the supercages. Fig.3 shows the 23Na-NMR spectrum. The fact that the observed line is not positioned at the expected Knight shift position, but near zero position, is a probe of the existence of even Na particles in the zeolite. The Na-Rb metallic alloy formation in the supercages for the NaY samples exposed to Rb. and the corresponding NMR spectra (23Na and 87Rb) as a function of the temperature, were also studied in this presentation. 17
~
16
-
15 -r m
~14
I
0
I
0
0
0
i
!
'"i
0
o
o
1
CO
o
0
o
tZVXc RMN l~: s~ T o f f s
0
oO
'
-
_i f ' , 'o~176
_
-1
Figure 2
,.,13
-r
11 -
o
oo
101-
I
I,,
0
50
100
i
!
so
I 150
I
1
i
1
Iso 2so TEMPEI~AT~JRE ( K ) 1 200
TEMPERATURE
1 250
250 I
300
200
150 I00 (ppttt)
50
20
35C
( K )
Figure 1 Figure 3 I 1000
L 0
~
-I000
Conclusions -~ The unique electronic properties of small alkali and bimetallic alkali alloy clusters encaged in NaY zeolites are well measured using ESR and Solid State (129Xe, 23Na, 87Rb and 133Cs) NMR. References 1) Harrison, M. R.; Edwards, P. P.; Klinowski, J.; Thomas, J. M.; Johnson, D. C. Page, C. J. J. Solid State Chem. 1984, 54, 330. 2) E. Trescos,; L. C. de M6norval,; and F. Rachdi. J. Phys. Chem. 1993, 97, 6943-6944.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
138
ATTACHMENT AND REACTIVITY OF TIN-COBALT AND TINMOLYBDENUM COMPLEXES IN Y ZEOLITES and MCM-41
Christian Huber, Chun-Guey Wu, Karin Moiler and Thomas Bein* Department of Chemistry, Purdue University, West Lafayette, IN 47907, U.S.A. FAX: 317-494-0239 SUMMARY Novel attachment techniques for bimetallic organometallic species in large-pore zeolites are described. The intrazeolite surface chemistry and thermal stability of M e 3 S n C o ( C O ) 4 in NaY and H6Y zeolite (H45NaloAI55Si1370384) were studied with X-ray absorption spectroscopy (Sn, Co edge EXAFS) and in-situ FTIRKPD-MS techniques. In the NaY host, the complex decomposes at about 160oc by loss of CO ligands and cleavage of the Sn-Co bond. Sn-Co bimetallic cluster species containing only a few atoms appear to form above that temperature. The acidic H6Y host can interact with the Me3Sn moiety of the bimetallic complex. IR and EXAFS data indicate attachment of the complex to the zeolite framework already at room temperature, while the Sn-Co bond seems to remain stable up to at least 90oc. These results are compared and contrasted with the reactions of Me3SnMo(CO)3Cp in the new mesoporous host MCM-41. Attachment of the latter complex to the MCM walls is observed, but due to the striking stability of this complex, cluster formation occurs after removal of the CO ligands only at very high temperature. INTRODUCTION The development of catalysts combining organometallic molecular species with a solid support structure (hybrid catalysts) continues to be of great interest. We have recently developed a novel concept for stabilizing Iow-valent
transition metal moieties in large-pore zeolites, by using bimetallic complexes such as CI2(THF)GeMo(CO)51 or Me3SnMn(CO)52 where the oxophilic maingroup element serves to attach the complex to the internal zeolite cage surface. In this contribution we discuss the surface chemistry and stability of M e 3 S n C o ( C O ) 4 in different forms of zeolite Y and compare it with Me3SnMo(CO)3Cp in MCM-41. EXPERIMENTAL
The precursor Me3SnCo(CO)4 was immobilized into zeolite Y containing different proton concentrations. MCM-413 was loaded with Me3SnMo(CO)3Cp. EXAFS samples were prepared by heating to between 90 and 300oc under vacuum. The temperature was ramped up at a heating rate of l oC/min to the desired temperature and kept constant for 6 h. EXAFS measurements were
139
carried out at NSLS (Brookhaven National Laboratories) at beamline X-11A with a stored energy of 2.5 GeV and ring currents between 100-200 mA.
RESULTS AND DISCUSSION Intrazeolite Chemistry of (Trimethylstannyl)tetracarbonylcobalt. EXAFS data analysis shows that the bimetallic complex remains intact when adsorbed into the dry sodium form NaY (Co-CO: 4.1 ligands at 1.79A; CoCO, 3.6 at 2.93A. On heating in vacuum, the complex is stable up to about 90oc, starts to release CO above 120oc, and fragments at about 160oc under evolution of methane. Beyond this temperature, EXAFS data show formation of extremely small cobalt/tin clusters. The reactivity of the SnCo complex in proton-containing zeolite H6Y is very different from that of NaY. Sleight CO evolution begins already at about 60oc, and IR studies indicate that the complex fragments completely above 120oc. No indication for metal clusters but attachment of cobalt to the zeolite framework is observed. Organometallics in Mesoporous Channel Hosts: Reactivity of Tricarb~176176 The bimetallic complex Me3SnMo(CO)3Cp was adsorbed into MCM host (3 nm channels) from hexane solution. The in situ infrared spectra show a weakly distorted CO coordination environment at room temperature, consistent with the absence of Na-ions in the channels of the host. This complex exhibits a striking thermal stability in MCM: the CO ligands are only removed on heating above 250oc. The stability of the Sn-Mo bond in this system, and the nature of the decomposition products determined from EXAFS data will be discussed. ACKNOWLEDGMENTS Funding from the U. S. Department of Energy (DE-FG04-90ER14158 and DE-FG02-92ER14281) for this work is gratefully acknowledged. REFERENCES 1 2 3
Borvornwattananont, A.; Moiler, K.; Bein, T., J. Phys. Chem., 1992, 96, 6713. Borvornwattananont, A.; Bein, T. J. Phys. Chem., 1992, 96, 9447. Beck, J. S., U. S. Patent 5,057,296, Oct. 15, 1991.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
140
SIMULTANEOUS EXCHANGE AND EXTRUSION OF METAL EXCHANGED ZEOLITES John N. Armor and Thomas S. Farris Air Products & Chemicals, Inc., 7201 Hamilton Blvd., Allentown, PA 18195 USA Summary: We wish to report that simple combination of an aqueous transition metal salt, alumina, and the ammonium form of the zeolite can be readily extruded, and upon calcination to 650~ the resulting extrudate as a catalyst behaves similarly to catalysts derived from more complex preparations of multiple, aqueous ion exchange followed by extrusion. Introduction In the course of our recent work to prepare cobalt exchanged zeolites for the removal of NOx by methane/oxygen or N20 by decomposition, we needed to prepare large batches of extruded material for scale up studies. This can be done by extending the traditional ion exchange preparation and then performing an extrusion of the resulting product. Traditionally, for cobalt ions multiple exchange is carded out in dilute, aqueous solutions of cobalt salts under reflux for 24 hours [1]. There are numerous reports of solid state exchange of cations into a variety of zeolites [2-4]. Similarly, there are several reports describing different recipes for extrusion of various zeolites [5,6]. Generally, this requires the addition of an alumina or clay binder and some dilute, aqueous acid to the zeolite to produce an extrudate in a commercial extruder. The binder is often set with some high temperature calcination. It occurred to us that one might be able to simplify the preparative procedure by carrying out both solid state exchange and calcination of the extrudates in one step. This brief report describes our success at producing a tough extrudate of cobalt-ZSM-5 with this simplified procedure. Experimental We attempted to use a slight excess of cobalt salt to achieve near 100% exchange. Ammonium exchange ZSM-5 [template-free synthesis mute] [40.0g] was purchased from VAW Aluminum AG [SM27] [Schwandorf, Germany] and dry mixed with 4.44 g of Vista Dispal alumina [Houston, TX] in a Naigene bottle for 15 minutes using a ball mill. Separately, 0.57 g of 70% HNO3 and 3.90 g of COCI2 were added to 21.5 g of deionized water. This latter solution was kneaded with the dry mixed ZSM-5/alumina powder while adding about 6 cc of water until an extrudable paste was obtained. This
141
paste was extruded in a bench top, 1 inch Bonnot extruder [Kent, OH]. The 1/8 inch extrudates were dried overnight in a purged oven at 110~ The binder was then set while simultaneously carrying out the cobalt ion exchange by slowly heating the extrudates at l~ to 650~ in flowing air and holding at this temperature for 6 hours. Results & Discussion
The resulting pale blue extrudates obtained above were quite hard, and upon breaking the extrudates in half, the blue color was uniform throughout the extrudate. [The above procedure may need to be modified as a function of the extruder, zeolite, and metal ion, but we believe this approach will work with a wide variety of cations and zeolites. It will depend on the thermal stability of the zeolite as well.] Analysis of the extrudate indicated we achieved 110% of the theoretical exchange level. We tested this catalyst for Ng.O decomposition at 450~ under conditions previously established for this reaction [7]. Compared to a catalyst prepared with three aqueous ion exchanges, followed by stepwise extrusion and calcination there was only a slight difference in activity between these two extrudates. We also established that using Na-ZSM-5 in place of NH4-ZSM-5 in the procedure describe above was ineffective for this same reaction. Conclusions
We have demonstrated that one can achieve solid state exchange of cobalt ions into ZSM-5 by first mixing the binder, cobalt salt, and the ammonium form of the zeolite, and then setting the binder and accomplishing ion exchange by calcination at 650~ The resulting catalyst performs similarly for Ng.O decomposition compared to one prepared using a more traditional, complex approach for preparing the catalyst. This new procedure greatly simplifies the preparation of larger quantities of extrudates. References
1. Y. Li and J. N. Armor, Appl. Catal. B, 1993, 3, L1. 2. J. A. Rabo, in Zeolite Chemistry and Catalysis; J. A. Rabo, Ed., ACS Monograph 171, Am. Chem. Soc., Washington, DC, 1976, p. 332. 3. H. K. Beyer, H. G. Karge, and G. Borbely, Zeolites 1988, 8, 79. 4. H. G. Karge, Y. Zhang, and H. K. Beyer, Catal. Lett., 1992, 12, 147. 5. W. H. Flank, W. P. Fethke, Jr., J Marte, US Patent 4818508 (1989). 6. S. Schwarz, M. Kojirna, and C. T. O'Connor, Appl. Catal., 1991,68, 81. 7. Y. Li and J. N. Armor, Appl. Catal. B, 1992, 1, L21.
H.G. Karge and J. Weitkamp (Eds.)
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Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
MODIFICATION OF LAYER COMPOUNDS FOR MOLECULAR RECOGNITION Takayoshi Uematsu, Makoto Iwai, Nobuyuki Ichikuni and Shogo Shimazu Department of Applied Chemistry, Faculty of Engineering, Chiba University, Yayoi-cho, Inage-ku, Chiba, 263, Japan
ABSTRACT Interlayers of Na-hectorite (HT) and zirconium phosphate (ZrP) were modified with "chirality tuning guests" to enhance enantio-selective adsorption. The modified interlayers were characterized by means of spectroscopic techniques. The enantio-selective entrapments of alkylamines were studied, and their mechanisms will be discussed in terms of chiral pair formation. Regio-selective hydrogenation of geraniol was also found over multiply modified HT. INTRODUCTION Clay minerals and zirconium phosphate are typical swellable ion-exchangers with layer structures, which provide very suitable layers to prepare a new class of inorganic host for molecular recognition. Using "tuning guests" we have been studying various modification methods to control shape-selective and stereo selective entrapment and catalysis [1,2]. The present report gives some results for molecular recognition by multiply modified inter-layer spaces, such as enantio selective adsorption and regio-selective catalysis over asymmetrically modified layers. EXPERIMENTAL Synthetic HT and ZrP were chirally modified by cation exchange with R- or Salkyl-ammonium ions (RA +) in aqueous solution at room temperature. Multiply modified HT's were prepared by the successive intercalation of tuning guests; firstly introducing organic cations (pyridinium ion, Py, or alkylammonium ions, (CnN)), followed by the interlayer polymerization of 3-aminopropyl-tri-methoxysilane (APMS). The catalytically active species of Pd(II) complexes were chemically anchored to the amino groups of polymerized APMS (PAPMS). The modified layer structures were characterized by means of spectroscopic measurements. Catalytic tests and adsorption measurements were carried out in static systems. RESULTS AND DISCUSSION The d001 spacings of these multiply modified HT's expanded according to the molecular size and amount of tuning guest intercalated. They were effective also
143 to control the hydrophobic and/or hydrophilic properties of interlayers, as well. Asymmetry recognition by chirally modified layers was exemplified by Fig. 1. The layer host modified with R-PEA + (R-PEA/HT) entrapped S-PEA predominantly from a racemic mixture of (R+S) PEA. The reverse was also true clearly for SPEA/HT. The recognition ability increased up to 75% enantio excess as a function of the extent of modification. The interlayer distances were larger for the heterochiral coupling structures (R-S; S-R) than those for the homo-coupling structures (R-R; S-S). The peak areas of the XRD intensities were much larger for the hetero pairs. Plausible host-guest complexation models (Fig. 2) were interpreted in terms of the orientation and interaction of CH3 groups between the modifiers and the guest molecules. The enantio-selectivity depended on the structures of the asymmetry modifiers of 1-arylethylammonium ions (aryl=phenyl, p-tolyl, p-nitrophenyl, phenylethyltrimethyl and 1-naphthyl) and decreased in the following order: PEA>TEA>NPEA>PETM>NEA. Similarly, S-PEA + modified ZrP (SPEA+/ZrP) showed effective enantio-selective adsorption of R-PEA. Regio-selective hydrogenation of geraniol over multiply modified HT is shown in Fig. 3. The selectivity is defined by the ratio of the reaction rates R1/R2 as a measure to recognize the inner C=C bond close to the OH group against the other C=C bond adjacent to the terminal CH3 group. The regio-selectivity was controlled by tuning guest of amines in the following order: 0.91 = [Pd(OAc)2]3(Homg) <
)i;)
. (R
I nln
b (,.) j
s)
| ~r~n
F i g . I E ~ _ n t i o selective a d s o r p t i o n a: S-PF_.A/I-1T b: R - I ~ A / H T
4
4O
~3 '-i 2 1
Fig. 2 Plausible m o d e l for ch/ral pair o f h o s t - g u e s t complex. S-PHNH 2 on R-PF-.A+/HT
05 10 doo~ b~m]
Fig. 3 Regio selective h y d r o g e n a t i o n o f geraniol. Selectivity R 1 / R 2 -citroneUol/3.7-d~nethyl-2-octen-l-ol T u n i n g G u e s t 1: CSN. 2: Py(1). 3: Py(5). 4: (C12)2N. 5: (C18)2N
REFERENCES
[1] M. Iwai, H. Shoji, S. Shimazu and T. Uematsu, Chem. Lett. (1993) 403. [2] M. Iwai, H. Shoji, S. Shimazu and T. Uematsu, Chem. Lett. (1993) 989.
IV. Catalysis
This Page Intentionally Left Blank
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
144
H-[B]-ZSM-5 AS CATALYST FOR METHANOL REACTIONS Erik UNNEBERG and Stein KOLBOE Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo, Norway SUMMARY
Several characterization techniques confirmed that boron is located in the framework of hydrothermally synthesized [B]-ZSM-5. In protonated form it catalyzes the alkylation of toluene with methanol and also the dehydration of methanol to hydrocarbons, though it was much less active than H-[AI]-ZSM-5 and showed markedly different selectivities. INTRODUCTION
The catalytic properties of borosilicates with the MFI structure ("[B]-ZSM-5") have been discussed by several authors. In order to give rise to Bronsted acidity in the [B]-ZSM-5 when protonated, the boron has to be in the catalyst framework. It has been stated that H-[B]-ZSM5, due to the weaker acid strength of the Si-OH-B sites compared to the Si-OH-AI sites, is neither active in the alkylation of toluene with methanol nor in the dehydration of methanol to hydrocarbons (1). Conflictingly, it has been claimed that the catalyst is active in both reactions (2). Derewi~ski et al., who used a pulse reactor, found a very small activity for transforming methanol to hydrocarbons, and a sizeable alkylation activity with high para selectivity from a methanol/toluene mixture (3). On this background we found it of interest to carry out a reinvestigation of the H-[B]-ZSM-5 system. EXPERIMENTAL
Silicalite-I, [AI]-, [AI,B]- and [B]-ZSM-5 were synthesized hydrothermally by various methods. In order to minimize Ai-contamination in the [B]-ZSM-5's, tetraetoxysilane was used as the silicon source, and the syntheses were carried out in teflon-lined stainless steel autoclaves. The synthesis products were characterized by SEM, IR, BET, XRD, NMR, ion exchange and elemental
(ICP) analyses. Catalytic reactions were performed in a continuous flow
microreactor using methanol and toluene + methanol as reactants. RESULTS AND DISCUSSION
The XRD patterns showed the "as synthesized" products to be pure and highly crystalline MFI's with orthorhombic symmetry, though some of the products became monoclinic upon calcination. Nitrogen adsorption (BET) and SEM confirmed the high crystallinity. XRD also showed the unit cell volumes of the [B]-ZSM-5's to be significantly lower than those of their
145
boron-free analogs, which indicated that boron is located at lattice positions. In addition, the H-[B]-ZSM-5's exhibited ion exchange properties, and the amount of acid sites found by those experiments correlated well with the ICP-determined boron content in the samples. It was found, however, that repeated ion exchange of the H-[B]-ZSM-5 led to loss of boron from the lattice. In the IR spectra O-H stretch frequencies appeared at 3700 cm 1 for H-[B]-ZSM-5 and at 3600 cm 1 for H-[AI]-ZSM-5, indicating weak and strong Bronsted acidity respectively (4). The IR and 11B-NMR spectra of H-[B]-ZSM-5 also showed boron to be located in tetrahedral positions. The reversible transition to trigonal boron (1) could be followed by NMR by heating the sample to 150~
in dry atmosphere. By cooling to 20~
in air tetrahedral boron
reappeared. H-[B|-ZSM-5 was able to convert methanol to hydrocarbons at temperatures above 250~ but the conversions were much smaller than those over H-[AI]- and H-[AI,B]-ZSM-5. Blank test runs gave no hydrocarbons. The hydrocarbon selectivities were markedly different. While mainly ethene and propene were formed over the AI-containing zeolites, methane was the dominating hydrocarbon over H-[B]-ZSM-5. The conversion of toluene in the alkylation reaction (435~
over H-[B]-ZSM-5 was also very
low compared to the conversion over H-[AI]-ZSM-5. Over the [B] catalyst no other alkylation products than xylenes, 1,2,4-trimethylbenzene and durene could be detected (a typical molar distribution was 85/12/3), while p-ethyltoluene was the predominant C9 component in the [AI] case, possibly due to alkylation of toluene with ethene (formed from methanol). While our H-[AI]-ZSM-5 catalyst was fairly para-selective, the typical o-/m-/p-xylene product distribution in the alkylation reaction over H-[B]-ZSM-5 was 38/25/37. This selectivity is in contrast to most literature results on catalysts with the MFI structure where o-xylene usually is much lower. However, in an other study on the H-[B]-ZSM-5 system, using a micro pulse reactor a m-xylene/o-xylene ratio less than unity is reported, but at the same time a high paraselectivity was observed (3). The relatively high o-xylene concentration in our product mixtures indicates that the ortho-para directing effect of the toluene methyl group is not canceled by steric restrictions in H-[B]-ZSM-5. Further discussion is given in the full report. REFERENCES 1. G. Coudurier, A. Auroux, J.C. V~drine, R.D. Farlee, L. Abrams and R.D. Shannon, J. Catal. 108, 1-14 (1987). 2. P. Ratnasamy, S.G. Hegde and A.J. Chandwadkar, J. Catal. 102, 467-470 (1986). 3. M. Derewiflski, S. D~,wigaj, J. Haber, R. Mostowicz and B. Sulikowski, Zeitschrift fQr Physikalische Chemie 171, 53-73 (1991). 4. M.B. Sayed, A. Auroux and J.C. V(~drine, J. Catal. 116, 1-10 (1989).
H.G. Karge and J. Weitkamp (Eds.)
146
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. NO x REDUCTION WITH AMMONIA OVER CERIUM EXCHANGED MORDENITE IN THE PRESENCE OF OXYGEN. AN IR MECHANISTIC STUDY. E. Ito a, Y.J. Mergler b, B.E. Nieuwenhuys b, P.M. Lugt a, H. van Bekkum a and C.M. van den Bleek a Delft University of Technology, Department of Chemical Technology and Material Sciences, lulianalaan 136, 2628 BL Delft (The Netherlands) University of Leiden, Gorlaeus Laboratoria, P.O. Box 9502, 2300 RA Leiden (The Netherlands)
SUMMARY An IR mechanistic study of NO reduction with ammonia in the presence of oxygen was performed over cerium-exchanged mordenite (CeNa-MOR) and compared with lanthanum-exchanged mordenite (LaNa-MOR), which does not possess redox properties. The formation of NO x (x - 2 or 3) species was observed upon NO adsorption, which was obviously enhanced in the presence of oxygen over both mordenites. These NO x species were found to be reactive towards ammonia over cerium already at 300 ~ while the same species remained unreacted over lanthanum. The importance of redox properties in this reaction is indicated. INTRODUCTION The removal of nitrogen oxides in oxygen rich atmosphere is an urgent environmental issue with respect to diesel exhaust cleaning and lean-burn operation of gasoline automobiles. We have found that cerium-exchanged zeolites are very promising catalysts for NO reduction with ammonia in the presence of oxygen providing high activity and selectivity towards nitrogen [1,2]. A reaction mechanism was examined using in-situ infrared spectroscopy and reported here.
EXPERIMENTAL The preparation of cerium and lanthanum exchanged mordenite has been described elsewhere [1]. A sample in the form of a self-supporting wafer was evacuated (10 .5 - 10.6 Tort) for 2.5 h at 330 - 350 ~
(FT-IR apparatus: Mattson galaxy 2020).
Background spectra of mordenite were taken at different temperatures and used for subtraction from the spectra taken in the presence of reactant gases (NO, 0 2 and NH3). RESULTS AND DISCUSSION N O / 0 2 adsorption and the subsequent N H 3 admission
NO was first admitted at room temperature at 1 - 5 Tort, and it turned out that CeNa-MOR and LaNa-MOR gave similar spectra exhibiting two sharp peaks (2248 c m l : N20 and 2163 cm-l: NO + or NO2 + [3]) and slowly growing broad peaks at 1300 - 1500 m
cm -1 (NO 2 or NO 3 ). This indicates disproportionation of NO to N20 and NO 2. The peaks observed at 1635 cm -1 and 3200 - 3700 cm -t are ascribed to water or nitrous acid.
147
At 100 ~
peaks at 1487 and 1337 cm 1 with a shoulder at 1510 cm 1 became evident.
These can be assigned to nitrato (1510, 1487 and 1337 crnq), or to the following three species; nitrato (1510 cmq), nitrito -ONO- (1487 cm 1) and free NO 2- ion (1337 c m l ) . Upon the subsequent admission of 0 2 (5 Torr) at 100 ~
the peak at 2163 cm -1 (NO +
or NO2 +), and the NO x (x = 2 or/and 3) peaks at 1487 and 1337 cm "1 were observed to be greatly enhanced over both rnordenites. NH 3 was then admitted (Figs. 1 and 2). The observed broad peaks at 2200 - 3500 cm "1 and the large peak at 1435 cm -1 were assigned to NH4 + / N H 3. It should be noted that the strong NO x- (x = 2 or/and 3) peak at 1487 cm -1 remained unchanged up to 200 ~ over both cerium and lanthanum. At 300 ~
the peaks assigned to NH3/NH4 + (2500 - 3500 cm "1 and 1435 cm "1) and NO x- (1350 -
1530 cm -1) disappeared simultaneously over cerium, indicating a reaction between these species. In contrast, these species remained unchanged over lanthanum even after 10 min at 300 ~
This demonstrated the important role of the redox property of CeNa-MOR
in high reactivity of these surface species: NH3/NH4 + and NO x (x - 2 or/and 3). 1.4
1.4
-..S t~
t~
0.8-
0.8-
0.6-
0 0.6-
_.j" 02_ . f / 0.4-
0,
4000
J
3500
3000
2500
2000
1500
Wavenumber / cm.1 Fig. 1 N O / O 2 / N H 3 adsorption over CeNa-MOR.
After N O / O 2 adsorption, NH 3 (5 Torr) was admitted and the temperature was subsequently raised. Spectra taken at (a) 100~ (b) 200~ (c) 300 ~ and (c) 300 *C after 10 rain.
4ooo' s~oo' s~oo' 2~oo' 2~oo' ,~oo Wavenumber/ cm-1 Fig. 2 NO/O2/NH 3 adsorption over LaNa-MOR. After N O / O 2 adsorption, NH 3 (5 Torr) was admitted and the temperature was subsequently raised. Spectra taken at (a) 100*C (b) 200 *C (c) 300 *C and (c) 300 *C after 10 rain.
REFERENCES 1. E. Ito, R.J. Hultermans, P.M. Lugt, M.H.W. Burgers, M.S. Rigutto, H. van Bekkum and C.M. van den Bleek, Appl. Catal. B, 4 (1994) 95. 2. E. Ito, R.J. Hultermans, P.M. Lugt, M.H.W. Burgers, H. van Bekkum and C.M. van den Bleek, Proc. of the Third International Congress on Catalysis and Automotive Pollution Control, Brussels (1994). A. Frennet and J-M. Bastin (Editors) Stud. Surf. Sci. Catal. (1995), in press. 3. C-C Chao and J. Ltmsford, J. Am. Chem. Soc., 93 (1971) 71.
H.G. Karge and J. Weitkamp (Eds.) 148
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
CATALYTIC ACTIVITY AND ACTIVE SITES IN ZEOLITE CATALYSTS F O R N20 DECOMPOSITION E.B. Uvarova, S.A. Stakheev, L.M. Kustov and V.V. Brei N.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, Russia
SUMMARY Catalytic activity of various modified zeolites and related materials in the reaction of nitrous oxide decomposition is studied. Active sites and mechanisms of this reaction are discussed. INTRODUCTION Modified zeolites are widely used as catalysts for reactions involving NOx oxides. Among them attention should be paid to selective reduction of NO with hydrocarbons, selective oxidation of aromatics with N20 and N20 decomposition as commercially attractive processes. Catalytic properties of zeolites in N20 decomposition have been studied in much detail, but the nature of active sites is not yet revealed. The goal of this work is to find some new zeolite and related catalysts for N20 decomposition and to study the nature of active sites using physicochemical methods, in particular diffuse-reflectance IR spectroscopy and XPS. RESULTS AND DISCUSSION The HZSM-5 pentasil type zeolite (Si/Al = 20) modified with copper and zinc oxides (1-5 wt %) were prepared by impregnation of the starting H-form with 1 M solutions of nitrates followed by calcination in air. Ti-silicalites of the TS-1 type were synthesized according to the known patent procedure. Amorphous Co-Cr-Cu/AI203, Fe-Cr-Cu/AI203, and TiO2/SiO 2 catalysts were prepared by impregnation of AI203 (S-~150 m2/g) and used as reference samples. Catalytic testing in N20 decomposition was carded out at 350 - 600 ~ and a N20 : He (1 : 1) flow rate of 40-50 ml/min, catalyst loading was 0.2 g. The results of testing show that Zn-containing catalysts are somewhat more active in N20 decomposition as compared with Cu/HZSM-5 systems and far more active than amorphous catalysts studied in this work. This effect was explained by a decisive role of strong Lewis sites connected with ZnO microparticles incapsulated in zeolite channels. These centers were revealed IR-spectroscopically by the low-temperature adsorption of molecular hydrogen (VH_H = 3970, 4010 cm-l). Surprisingly, Ti-silicalites revealed high activity in N20 decomposition, which at low temperatures (350 - 375 ~ exceeds the activity of the known Cu/HZSM-5 catalyst. The lower activity of Ti-silicalites passes a maximum at SFTi - 30 - 35. The lower activity of Ti-silicalites with a higher Ti content was explained by the formation of a separate TiO~ phase or coupled Ti-O-Ti fragments in the framework, which seem to be inactive in N20 decomposition. Isolated TiO 4 tetrahedra or titanyl groups (=Ti=O) were assumed to play the
149 role of active sites in this reaction. The state of titanium in Ti-containing systems is studied by XPS and the data obtained agree with the proposed nature of active sites. Adsorption and decomposition of N20 was also studied by diffuse-reflectance IRspectroscopy and an activated form of N20 was observed in ZnS-IZSM-5 zeolites (v3= 2275 cm-1), which is decomposed atter heating the sample at 250 - 300 ~ The mechanisms of N20 decomposition on strong Lewis acid sites and Ti-centers are discussed in detail.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
150
ROLE OF THE PREPARATION AND NATURE OF ZEOLITE ON THE ACTIVITY OF Cu-EXCHANGED MFI FOR NO CONVERSION BY HYDROCARBONS AND OXYGEN Gabriele Centi, Siglinda Perathoner, and Laura DalrOlio Department of Industrial Chemistry and Materials, V. le Risorgimento 4, 40136 Bologna, Italy
SUMMARY The effect of the Cu/A1 ratio for ZSM-5 zeolites with SIO2/A1203 ratios of 50 and 16, the influence of the procedure of copper addition and the role of the acidity of the zeolite are discussed. In particular, the higher activity that it is possible to obtain using a new preparation procedure by hot ion-exchange and the high activity shown by a Cu-Boralite sample with the MH structure are reported.
INTRODUCTION Lean-burn and diesel-engines have several advantages in terms of higher efficiency and lower CO2 emissions, but due to the presence of around 2 - 3% 02 in the exhaust gas, commercial three-way catalysts are not effective in the conv_ersion of NO. Metal-exchanged zeolites and Cu-ZSM-5, in particular, however, show a high activity in the reduction of NO in the presence of 02 and of hydrocarbons (propane, in particular). The further development of these catalysts requires, however, a better understanding of the dependence of their catalytic behavior on the preparation procedure and the nature of the zeolite, in order to obtain samples active at lower temperatures and stable for longer times. In this communication we will discuss the dependence of the activity on the Cu/A1 ratio for ZSM-5 samples with different SIO2/A1203 ratios and the influence of the method of introduction of the copper component into the zeolitic catalyst. The dependence of the activity upon the acidity of the zeolite will be investigated by comparing the activity of samples in the H- and Na-forms with the activity of a Cu-Boralite sample with the same structure of ZSM-5, but lower strength of acid sites due to the substitution of AI with B. EXPERIMENTAL Cu-ZSM-5 was prepared from the sodium of the parent zeolite by conventional ion-exchange at room temperature or under reflux (hot ion-exchange) using an aqueous solution of copper-acetate. The SIO2/A1203 ratio of the zeolites were 49, 52 or 16 and the Cu/A1 ratio was changed in the range 0-1.25 using repeated ion-
151 52 or 16 and the Cu/A1 ratio was changed in the range 0-1.25 using repeated ionexchanges. Cu-Boralite was prepared in the same way using a sample with the MFI structure and a SIO2/B203 ratio of 24. Catalytic tests were performed in a plug-flow-type reactor equipped with an online mass-quadrupole system for real-time analysis of all products. Tests were made using the following feed: [NO]---800 ppm, [C3H8]=2300 ppm, [02]=3.9 %, W/F-0.3 g . sec/cc. The reaction temperature was varied in the range 250-550~
g so ~
40
O
//;/ 7
20 0 200
.
I'.NO(Bora,. )
//
I V C3 (Borml.)
9" " 9 "" '
I I
300
i 400
9NO (ZSM5)
I I = C3 (ZSMS)
500
600
Temperature, "C
Figure I
Catalytic behavior in the selective reduction of NO by propane/O2 of Cu-ZSM-5 (dotted line) and Cu-Boralite (solid line) samples with the same MFI structure and copper content.
RESULTS AND DISCUSSION
Role of the Cu/Al ratio and Si02/A1203 ratio. The introduction of copper by ionexchange promotes the conversion of both NO to N2 and propane to CO2. The activity does not depend on the absolute amount of copper, but on the Cu/A1 ratio in the sample. For the same Cu/A1 exchange level, the zeolite with the higher SIO2/A1203 ratio shows better activity in both reactions with respect to the zeolite with SIO2/A1203 of 16. No significant differences were found, on the contrary, for the two ZSM-5 samples with similar SIO2/A1203 (49 and 52), but from different sources, suggesting that the activity depends weakly on the specific preparation of the parent zeolite, but mainly on the SIO2/A1203 ratio.
152
Role of the method of copper addition. The comparison of the catalytic behavior of three Cu-ZSM-5 samples with the same C u / A I and SIO2/A1203 ratio, but prepared using the conventional ion-exchange procedure, a wet impregnation or a new hot-ion-exchange method is reported. At 350~ the conversion of NO and propane over the sample prepared by conventional ion-exchange are 67.3% and 59 %, respectively. These values decrease to 24.5 % and 32.7 % for the sample prepared by wet impregnation, but increase to 95.5 % and 54.5 % for the hot-ionexchange method. These results show that the method of preparation greatly influences the reactivity, and also that the rates of propane and NO depletions are differently influenced by this factor.
Role of the acidity. At 350~
H-ZSM-5 (SIO2/A1203=16) is around 2-3 times more active both in propane and NO depletion when compared to the sodium form of the same sample, indicating the role of acid sites in both mechanisms. However, the comparison of the activity of Cu-ZSM-5 (SIO2/A1203=16) with that of a CuBoralite sample with similar structure (MFI), total number of active sites (SIO2/B203=24) and copper content (4% wt. as CuO), but lower acid strength due to substitution of A13+ by B3+, shows that a slightly better catalyst can be prepared (Fig. 1) indicating that the role of the acid sites on the mechanism of reaction or formation of active sites should be analyzed in more detail.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
153
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SELECTIVE PHOTOOXIDATION OF ABUNDANT HYDROCARBONS BY 0 2 IN ZEOLITES WITH VISIBLE LIGHT Fritz Blatter, Hai Sun, and Heinz Frei Lawrence Berkeley Laboratory, University of California Berkeley, CA 94720 SUMMARY Selective oxidation of small alkenes and of toluene by 02 has been accomplished by irradiation of the reactants in zeolite Y with visible light. Products are industrially important compounds like benzaldehyde (from toluene) and acrolein (from propylene). The key to these tightly controlled reactions is an unprecedented stabilization of hydrocarbonoO2 excited charge-transfer states by the ionic environment of the zeolite matrix cage. INTRODUCTION Selective oxidation of small abundant hydrocarbons is the mostimportant type of reaction in organic chemicals production. For example, essentially all building blocks for the manufacture of plastics and synthetic fibers are produced by oxidation of hydrocarbons. Among these, oxidations by molecular oxygen play a particularly important role. A key problem is the product specificity in hydrocarbon + 02 reactions, and here photoassisted processes hold special promise. They can typically be conducted at or around ambient temperature, thus minimizing the chance for loss of product control due to secondary thermal chemistry of the initial products. Inexpensive artificial light can be used if the reaction can be driven by visible or near-infrared light. All these are attractive ingredients for environmentally benign chemical synthesis. EXPERIMENTAL Hydrocarbon and 02 were loaded from the gas phase into self-supporting zeolite pellets mounted inside a miniature infrared cell. Reaction was induced with light from a cw dye laser (for wavelength dependence studies) or a filtered tungsten source. The chemistry was monitored in situ by FT-infrared spectroscopy. Visible spectra were recorded by diffuse reflectance spectroscopy. RESULTS AND DISCUSSION We have accomplished selective photooxygenation of small alkenes and aromatics by irradiating hydrocarbon.O2 collisional complexes in alkali and earth alkali exchanged zeolite Y with visible and near-infrared light. 1,2 Propylene, cis and trans-2-butene, and 2,3-dimethyl-2-butene (DMB) were oxidized to the corresponding alkene hydroperoxide with very high selectivity. These rearrange thermally at room temperature to a single carbonyl compound in each case, namely acrolein in the case of propylene + 02, methyl vinyl ketone in the case of 2-butene, and acetone when DMB + 0 2 was photolyzed. This is the first selective synthesis of these organic
154 compounds by direct alkeneoO2 photolysis in any phase. Reactions are rather efficient, with quantum yields ranging from 0.1 to 0.3. Diffuse reflectance spectra revealed a continuous visible absorption of alkene + 0 2 loaded zeolites 3 which coincided with the measured laser reaction excitation spectra. The onset of the band increased monotonically with the ionization potential of the alkene, indicating that the absorption originates from an alkeneoO2 charge-transfer transition. Red-shifts relative to corresponding alkeneoO2 charge-transfer bands in the 02 gas phase, O2-saturated solution, or solid oxygen are between 12,000 and 15,000 cm -1 (1.5 to 1.9 eV) depending on the hydrocarbon and the metal cation in the zeolite. This unprecedented stabilization of the excited chargetransfer state is attributed to the very high electrostatic fields (on the order of V/A) inside the charged cages of zeolite Y. The rather high reaction quantum yields imply that the primary elementary step of the excited alkene +02- charge-transfer state competes effectively with back electron transfer. The proposed initial step is deprotonation of the highly acidic alkene radical cation to generate an allyl radical and HO2". Re-combination of the radical cage pair yields the observed alkene hydroperoxide, which then rearranges thermally to the corresponding carbonyl compound. An exciting case is the selective photooxidation of toluene to benzaldehyde by 0 2 in earth alkali exchanged zeolite Y. Diffuse reflectance spectroscopy of toluene and 02 loaded zeolite CaY showed a continuous charge-transfer absorption in the visible region extending to 600 nm. This corresponds to a 10,000 cm" 1 red shift compared to the tolueneoO2 charge-transfer absorption in O2-saturated toluene solution. Irradiation at wavelengths as long as 590 nm led to reaction. In zeolite CaY, an intermediate was formed that reacted upon continued photolysis to yield benzaldehyde as the exclusive final oxidation product. In BaY, yields were lower, but the reaction gave benzaldehyde with complete selectivity as well. This work is supported by the Chemical Sciences Division of the U.S. Department of Energy. REFERENCES [1] [2] [3]
Blatter, F.; Frei, H. J. Am. Chem. Soc. 1993, 115, 7501. Blatter, F.; Frei, H. J. Am. Chem. Soc. 1994, 116, 1812-1820. Blatter, F.; Moreau, F.; Frei, H. Chem. Phys. Lett., submitted.
155
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
APPLICATION OF VAPO-5 IN LIQUID PHASE OXIDATION REACTIONS: INDICATIONS FOR THE PRESENCE OF DIFFERENT VANADIUMSITES
M.J. HAANEPEN and J.H.C. van HOOFF Schuit Institute of Catalysis, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands SUMMARY
VAPO-5's with different vanadium content (0.18 - 2.0 at%) have been used as catalyst for the liquid phase epoxidation of cinnamylalcohol (3-phenyl-2-propan-l-ol) by t-butylhydroperoxide ('I'BHP). It has been found that the activity, expressed as turnover frequency (TOF), increases with increasing vanadium content. Diffuse Reflectance UV VIS (DRUWIS) shows that in samples with a high vanadium content a second type of vanadium species is present that probably is responsible for the observed higher catalytic activity. INTRODUCTION
VAPO-5 has been reported as a potential catalyst for liquid phase oxidation reactions [1-3]. Until now very little is known about the influence of the vanadium content on the catalytic activity and the stability of these materials during the reactions. In this report the results of our investigations on the oxidation of cinnamylalcohol by TBHP catalyzed by VAPO-5 are reported.
~
0H
VAP0-5 .....
CH3CN, 50 oC TBHP
~
0H
EXPERIMENTAL
VAPO-5 samples with different vanadium content have been prepared hydrothermally (boehmite (Condea); phosphoric-acid, vanadylsulfate (Merck); Et3N or Pr3N (Janssen); 1.0-x AI20 3 : 1.0 P2Os : x V20 s : 44 H20 : 1.3 T (x = 0-0.05); cryst: 160~
48h).
Samples have been characterized by XRD, SEM, hAS, DRUWIS and butane sorption. Reactions have been performed in a thermostatted batch reactor at 50~ using 15 ml of a cinnamylalcohol (0.3 M) / TBHP (0.3 M) solution in dry acetonitrile. For a reaction 0.3-0.6 g VAPO has been used. Samples have been analyzed by gaschromatography.
156
RESULTS AND DISCUSSION XRD spectra and sorption data of all VAPO-5's studied indicate a highly crystalline AFI structure. The morphology of the samples is comparable (agglomerates of about 12 pm). In table 1 the performance of the samples in the liquid phase oxidation of cinnamylalcohol is described. A blanc reaction with AIPO4-5 did not show any significant conversion of the substrate. Table 1: Performance of VAPO-5 in the oxidation of cinnamylalcohol by TBHP" Catalyst a b c VO(acac)2
V (at%)
Amount (g)
Activity (mol.hl.I 1) at 30% conversion
TOF (mol.mol V'l.h ~) at 30% conversion
0.18 1.1 2.0
0.60 0.30 0.30
0.018 0.132 0.287
16 37 44
-
0.025
1.67
~ 250
" For reaction conditions see experimental section. The activity of VAPO-5 at 30% substrate conversion increases upon increasing vanadium content, although the activity always remains lower than the homogeneous catalyst VO(acac)2. The activity of different VAPO-5 samples increases more than can be expected from the increasing vanadium content alone. Leaching of vanadium from the lattice, thereby creating a highly active homogeneous vanadium species, seems not to be a likely reason for this increased activity. After three reaction cycles, the calcined VAPO-5's still had the same activity and the same vanadium content. From DRUWIS there is evidence that there are different vanadium species present. Samples with a low vanadium content show absorption between 200-300 nm. Upon increasing of the vanadium content an additional absorption appears between 350 450 nm. The latter species can be related to the more active species. REFERENCES [1] M.S. Rigutto and H. van Bekkum, J. Mol. Cat., 81 (1993) 77-98 [2] C. Marchal, A. Tuel and Y. Ben Taarit, Stud. Surf. Sci. and Cat., 78 (1993) 447-454 [3] M.J. Haanepen and J.H.C. van Hooff, Proceedings of the DGMK-conference 'Selective Oxidations in Petrochemistry', Goslar, (1992) 227-236
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
157
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. OXIDATION OF PRIMARY AMINES OVER TITANIUM A N D VANADIUM SILICALITES: SOLVENT EFFECT J. Sudhakar Reddy and A. Sayari Universit6 Laval, Department of Chemical Engineering and CERPIC, Ste-Foy, Qc, CANADA GIK 7P4
SUMMARY In the oxidation of primary amines over titanium (TS-1) and v a n a d i u m (VS-1) silicalites, the solvent plays a significant role in determining the conversion of amine as well as p r o d u c t selectivity. When v a n a d i u m silicalite was u s e d as a catalyst, the selectivity for oxime was low (20-40%) and one of the major p r o d u c t s was imine (30-55%). However, over titanium silicalite, imines were formed only in the presence of chloroform. Chloroform also favors the formation of nitroalkanes over both titanium and v a n a d i u m silicalites. INTRODUCrION Oxidation of various nitrogen containing c o m p o u n d s to the c o r r e s p o n d i n g oxygenated derivatives in the presence of peroxides is known to take place over_ a variety of catalysts. However, attempts to use zeolites as catalysts were not m a d e until recently / . This development is part of an emerging research area, the purpose of which is to use zeolites modified with transition metal cations such as Ti and V to catalyze organic synthesis reactions 2. In this respect, Ti silicalite (TS-1) was f o u n d to catalyze the oxidation of primary amines by diluted H 2 0 2 to the corresponding oximes lb. However, no detailed studies on this reaction are available. In addition, the use of vanadium silicalites as catalysts for the oxidation of primary amines has not been reported. The scope of this work was to investigate the influence of various solvents on the activity and selectivity of titanium a n d v a n a d i u m silicalites in the oxidation of aliphatic primary amines containing (z-hydrogen. EXPERIMENTAL Catalysts were prepared according to the procedures available in the literature3, 4. As-synthesized samples were calcined at 823 K before use. Reactions were carried out in a 100 ml r o u n d bottom flask placed in a heating mantle connected to a t e m p e r a t u r e controller. In a typical reaction, 70 mmol of substrate, 200 m g of catalyst, 15 ml of solvent and 35 mmol of H202 (35 wt.%) were mixed and stirred at 333 K. The products were analyzed using a GC equipped with a 50 m methylsilicon g u m column. Product identification was carried out with GCMS.
158
RESULTS AND DISCUSSION Oxidation of primary amines over TS-1 in the presence of ethanol as solvent led mainly to the corresponding oximes with about 85% selectivity. Similar results were reported by Reddy and Jacobs lb who used methanol and t-butanol as solvents. The present study shows however, that in the presence of chloroform, the major p r o d u c t is an imine (6), instead of oxime (4). In this case, significant amounts of nitroalkanes were also obtained. In the presence of alcohols, no nitroalkanes were formed. Conversely to TS-1, VS-1 favored the formation of imine in all the solvents tested. R-CH2-NO2 [0]/'~ 3 [o] R-CH2-NH2 -'~ R - C H 2 = N O 1 I " - ~ R-CH = NOH 4 R-CH = NOH 4
[0] IV
,'~
R-CH = O 5
R-CH2-NH2 ,'~ R - C H = N - C H 2 - R V 6
To investigate the various reaction pathways, we have carried out additional experiments using cyclohexanone oxime as substrate. Our experimental results are summarized in Table 1 based on the proposed reaction scheme.
Table I
Summary of experimental data
Solvent
Alcohol Alcohol Alcohol Chloroform Chloroform Chloroform
Catalyst TS-1 VS-1 None TS-1 VS-1 None
Reaction
I, HI I, III, IV, V V I, II, HI, IV, V I, II, HI, IV, V IV, V
REFERENCES
1.
2. 3. 4.
(a) S. Tonti, P. Roffia, A. Cesana, M.A. Mantagazza and M. Padovan, EP 0 314 147 5 1988; (b) J.S. Reddy and P.A. Jacobs, Perk. Trans. I, (1993) 2665; (c) J.S. Reddy and A. Sayari, Catal. Lett., (1994) submitted. W.F. H61derich and H. van Bekkum, Stud. Surf. Sci. Catal., 58 (1991) 631. G. Perego et al., Stud. Surf. Sci. Catal., 28 (1986) 129. M.S. Rigutto and H. van Bekkum, Appl. Catal., 68 (1991) L1.
H.G. Karge and J. Weitkamp (Eds.) Zeol#e Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
159
ROOM TEMPERATURE OXIDATION OF METHANE TO METHANOL ON FeZSM-5 ZEOLITE SURFACE V.I.
Sobolev, A . S . Kharitonov,
O.V. Panna and G.I. Panov
Boreskov Institute of Catalysis, Novosibirsk 6 3 0 0 9 0 ,
Russia
Summary A spel;ific surface oxygen form produced upon N20 decomposition on FeZSM5 zeolite was shown to oxidize selectively methane to methanol at room temperature.
Introduction Nitrous oxide decomposition on Fe-containing ZSM-5 zeolites is known to produce a specific surface oxygen form ((z-form) which cannot be produced by 02 adsorption
[1].
(z-Form exhibited remarkable reactivity. The most conspicuous
example is its 1:1 interaction with methane which readily proceeded at room temperature. But product of this reaction were not identified yet since sensitivities of spectroscopic
techniques
( I R , NMR)
proved
to
be
not
sufficient
while
thermodesorption procedure was followed by secondary processes resulting in CO and CO2 desorption into the gas phase. We have shown recently for the case of benzene [2] that surface products of (zoxygen reactions can be reliably identified chromatographically after their extraction from the zeolite. This procedure is applied now for (z-oxygen interaction with methane.
Experimental ZSM-5 zeolite containing 1.54 wt.% AI203 and 0.30 wt.% Fe203 was used as a catalyst. (z-Oxygen form was loaded by N20 decomposition at 240oc according to the following reaction: N20+(
)0c=(O)(z+N2
(1)
This reaction was carried out in vacuum static setup equipped with an on-line massspectrometer. Concentration of (z-oxygen was determined from N2 amount evolved in reaction (1) as well as using its isotope exchange with 02. Interaction with methane at starting pressure P(CH4) = 0.4 Torr was carried out after cooling the sample to room temperature. Then, the sample was taken from the reactor and subjected to extraction procedure. GH "ZWET-500" provided with FID was used for the product analysis.
Results and discussions The amount of methane reacted with (z-oxygen was equal to 6.5 #mol/g zeolite. Extraction wi'th water revealed methanol as the only reaction product, but its amount
160 did not exceed 10-15% of the methane consumption. A mixture of acetonitril with water proved to be more efficient extragent. The figure shows how methanol amount increases with increasing number of acetonitril extractions. One can see that after 4fold extraction the methanol amount _
~6 o
~5 o
~3 .
o ~2
anol e x t r a c t e d Methane reacted
1
0
~,
,,
i
Number
g
of e x t r a c t i o n s
4
is equal to 5 llmol/g which responsible for nearly 80% of methane consumption. In conclusion we discuss a similarity between (~-oxygen oxidation on FeZSM-5 and that by monooxygenases whose unique activity is also relates to iron. References 1. Panov G.I" Sobolev V.I. and Kharitonov A.S., J. Mol. Catal., 61 (1990) 85. 2. Sobolev V.I., Kharitonov A.S., Paukshtis E.A., Panov G.i., J. Mol. Catal., 84 (1993) 117.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
161
OXIDATION A N D AMMOXIDATION OF PICOLINES OVER VANADIUM-SILICOALUMINO-PHOSPHATE MOLECULAR SIEVES
S ] Kulkarni,
R Ramachandra
Rao,
M Subrahmanyam, S Farsinavis, P Kanta
Rao and A V R a m a Rao
Indian Institute of Chemical Technology, Hyderabad 500 007, India SUMMARY :
The oxidation and ammoxidation of 3- and 4-picolines over vanadium s i l i c o - a l u m ino-phosphate and vanadium-alumino-phosphate molecular sieves lead to corresponding 60-85% yields of aldehydes and nitriles. We report crystalline and microporous modified (V-) silico-alumino-phosphates as a new class of oxidation and ammoxidation c a t a l y t i c materials. INTRODUCTION :
The resulting nitriles in the ammoxidation of 3- and 4-picolines are important i n t e r m e d i a t e s in the p h a r m a c e u t i c a l s . We have c a r r i e d out various oxidation and ammoxidation heterocyclic (VSAPO),
reactions
compounds
of aliphatic
like picolines,
vanadium-alumino-phosphates
alcohols,
aromatics
over vanadium (VAPO)
and
like toluene
and
silico-alumino-phosphates silico-alumino-phosphates
(SAPO) molecular sieves. In this paper, we report the oxidation and a m m o x i d a tion of picolines over vanadium silico-alumino-phosphate (VSAPO) and vanadium alumino-phosphate (VAPO) particularly. EXPERIMENTAL :
The 41
type
sulphate,
crystalline, catalytic
microporous
materials
phosphoric
acid,
are
sodium
VSAPO,
VAPO
hydrothermally silicate,
vanadium
like t e t r a p r o p y l a m m o n i u m bromide at 200~
and
SAPO-5,
synthesized
11,
using
pentoxide
37,
40,
aluminium
and
templates
for 24-80 hrs at 20 a t m pressure.
The e x p e r i m e n t a l details are given e l s e w h e r e 1. RESULTS AND DISCUSSION :
The materials tion
was
carried
out
are highly crystalline. The physico-chemical using X-ray diffraction,
infra-red
characteriza-
spectroscopy,
electron
spin resonance spectroscopy, t h e r m a l analysis, e t c . techniques. In case of VSAPO and VAPO catalysts, ESR has shown well resolved hyperfine splitting corresponding to V 4§ cation bonded strongly to oxygen ions in the matrix. The gtt a r e 2.0221 and 2.0046 and ~
values
2.0440 and 2.0380 for VSAPO and VAPO c a t a l y s t s
r e s p e c t i v e l y . Compare to the l i t e r a t u r e , these values correspond to V~'+ bonded -! with oxygen atoms. The IR band at 1400-1460 cm represents V-N-(template) bonding in the catalysts. The e f f e c t of calcination t e m p e r a t u r e has been studied. The i n c r e a s e of vanadium amount varies the crystallographic s t r u c t u r e .
162 The ammoxidation of 4-picoline with ammonia, air and water at 420~ -I and 0.5 hr W.H.S.V. over VSAPO and VAPO leads to 79.3 and 60 wt % yield of
~-cyanopyridine respectively. The ammoxidation of 3-picoline at 420~ and -I W.H.S.V. over VSAPO and VAPO leads to 37.2 and 58.8 wt % yield
0.5 hr of
3-cyanopyridine.
various
reaction
velocity,
the
time
stream
on
The selectivities
parameters
picoline
like
to ammonia
were
studied
were
above
reaction ratio,
over
90% for
temperature,
picoline
various
to
best
catalyst.
weight
water
crystalline,
hourly
ratio
The space
in the feed,
microporous
VSAPO,
VAPO and SAPO catalysts. The oxidation
of 4-picoline
using air and water
at 420~
with
0.5 hr - I
W.H.S.V. over VSAPO and VAPO leads to 51.8 and 57.9 wt % of p y r i d i n e - 4 - c a r boxaldehyde 420~ to
respectively. The oxidation of 3-picoline using water and air at -I 0.5 hr W.H.S.V. over VSAPO, VAPO and Sb203-VSAPO leads
with
45.6,
15.0 and 83.3 wt
% of
pyridine-3-carboxaldehyde,
respectively.
The
reaction mechanism of ammoxidation over these catalysts has been investigated.
The
reaction
of
3-or
4-picoline
with
ammonia
and
of air has been carried out over VSAPO and VAPO at 420~
water
in absence
and 0.5 hr - I W.H.S.V.
But 3- or 4-picolylamine was not observed in the products. So scheme I, reactionroute through aldehyde formation
is recommended. The corresponding carboxylic
acid or amide was also not observed in the products. In case of VSAPO, t e t r a hedraI the
vanadium
substitution
-VO4- , V-O-P of
linkages
and
Bronsted
silicon in place of phosphorus
acidic
centres
are the active
due
centres
to and
the catalyst is bifunctional. It is worth to note here that SAPO-5, I I , 377 40 and 4I, w i t h o u t vanadium or titanium lysts
is a class of mild and selective oxidation and ammoxidation
showing
in one step
~98% via
formation
of
acetonitrile
from
ammoxidation I . Thus we report
ethanol
(SAPO-#0
and emphasize
novel class of oxidation and ammoxidation c a t a l y t i c
catatype)
the new and
materials namely vanadium
of titanium-silico-alumino-phosphate molecular sieves. REFERENCES
1.
:
S 3 Kulkarni, R Ramachandra
Rao,
M Subrahmanyam
Rao, 3 C h e m Soc Chem Commun, (1994) 273.
and
A V Rama
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
163
TRANSITION METAL CATIONS IN ZEOLITES - A CATALYST FOR HDS REACTIONS A. Lugstein, O. El Dusouqui, A. Jentys and H. Vinek lnstitut for Physikalische Chemie, TU Wien, Getreidemarkt 9, A-1060 Wien, Austria SUMMARY We describe the incorporation of Co 2§ cations into ZSM5 zeolites by direct synthesis and by ion exchange methods, carded out in liquid phase and as a solid state reaction. The influence of the preparation method on the density of the sites and the stoichiometry of the ion exchange reactions was investigated.
INTRODUCTION Hydrotreating catalysts usually consist of two components: one which catalyses hydrogenation and the other which catalyses carbon-heteroatom bond cleavage
(hydrogenolysis sites) (1). In
conventional hydrodesulfurization (HDS) catalysts, the active sites for hydrogenation are related to Co(Ni)/Mo(W) sulfide phases and those for hydrogenolysis to the alumina support (2). Zeolites containing transition metal sulfides were commercially introduced and offer interesting alternatives where
enhanced
hydrocracking
activity
is
combined
with
hydrodesulfurization
and
hydrodenitrogenation (1). In these materials, hydrogenation takes place on the metal sulfide sites, hydrogenolysis on the strong Bmnsted acid sites (3). EXPERIMENTAL
Cobalt containing ZSM5 zeoUtes were directly synthesised according to ref. (4). HZSM5 (Si/AI = 42) samples were ion exchanged by conventional liquid phase method with a 0.2 molar COCI2 solution at 353 K for 48 hours (5). Solid state ion exchange was carded out by grinding HZSM5 with CoCl2.6H20 and heating the mixture in He atmosphere at 773 K for 6 - 10 hours (6, 7). Following the ion exchange, the samples were washed with destilled water until no CI~ ions were detected. Ir and XAS spectra of the samples were measured after activating the samples at 673 K in an inert gas atmosphere. The number of acid sites was determined by temperature programmed desorption (t.p.d.) of NH3. the number of sites affiliated with the presence of Co 2§ ions by NO t.p.d. The degree of ion exchange was calculated from the difference in the number of strong Bmnsted acid sites present before and after ion exchange. The structure of the zeolites was vedfied by XRD experiments. RESULTS AND DISCUSSION
The solid state ion exchange was carried out at various C02*/AI 3* ratios. Considering the formal charges of the Co 2§ cations, two protons (from the SiOHAI group) can be exchanged with one Co 2* cation. Therefore, 100% exchange should be achieved at a molar ratio of C02*/AI 3. = 0.5 (stoichiometdc ratio). For samples prepared with an C02*/A! 3+ ratio higher than 1, the ir spectra revealed the complete removal of the strong Br~nsted acid sites. The XANES of the samples indicated that the Co 2§ is surrounded by CI~ ions rather than by 02. The t.pod, of NH3 carded out on these samples showed a new desorption maximum of NH3 at a temperature higher than that of NH3 desorbing from the strong Bmnsted acid sites. The formation of these new sites was also shown in
164 the t.p.d, of NO, where an additional desorption maximum was observed on samples containing Co 2§ cations. We assign these sites to (CoCl)* species with Lewis acid character, which remain within the lattice even after carefully washing the zeolite. The number of strong Br~nsted acid sites present after the ion exchange decreased with increasing Co2*/AI3. ratio and reached a value of zero at a Co2*/AI3. ratio of 1.2. This clearly shows that under our solid state ion exchange conditions only one proton from the SiOHAI group was exchanged for one Co cation. We propose that these cations are associated with c r ligands probably as (CoCI)§ groups. The presence of similar groups was already reported for solid state ion exchange of four and five valent cations into ZSM5 (8) and for Cu into ZSM5 (9). The ion exchange carried out in liquid phase did not lead to a complete removal of the strong Br~nsted acid sites. Moreover, by repeating the ion exchange procedure up to five times, an increase over the initial degree of ion exchange of about 30 % was not observed. The ir spectra and the t.p.d. experiments showed that dudng the ion exchange the number of acid sites decreased without causing the formation of new sites in the zeolite. In the CoZSM5 samples prepared by a direct synthesis, the Co was partially substituted into the lattice (substitution of S='), but was also found to be present in Co-oxide clusters. The XANES indicated that the Co atoms are surrounded by O atoms. Co neighbours at short distances were not observed in the EXAFS. The t.p.d, of NH3 and NO showed an additional desorption maximum, which in the case of NH3 was lower in temperature compared to that on the solid state exchanged samples. CONCLUSIONS
Co ions can be incorporated into ZSM5 zeolites by ion exchange methods and by direct synthesis. In the case of liquid phase ion exchange only a partial cation exchange (30%) is achieved even after multiple ion exchange treatments. When the ion exchange is carried out by a solid state reaction a complete exchange (200%) can be achieved at a Co2*/AI3. ratio above 1. The Co cations are associated with c r ligands, formig new sites with Lewis acid character with a stoichiometry of 1:1 between Co 2. and AI3.. The direct synthesis of CoZSM5 results in a lattice substitution of Si with Co and in the formation of small Co-oxide clusters. ACKNOWLEDGEMENTS The work was supported by the "Fonds zur F0rderung der Wissenschaftlichen Forschung" under project FWF P9167. Partial support of this work by the Christian Doppler Society is gratefully acknowledged. We are grateful to P. Ngan for the synthesis of the CoZSM5 samples. REFERENCES B. Delmon, Catal. Lett. 22, 1 (1993). C. T. Douwes and M. Hart, Erd61 und Kohle 21,202 (1968). C. W. Ward, Stud. Surf. Sci. Catal. 16, 587 (1983). J. A. Rossin, C. Saldarriaga and M. E. Davis, Zeolites 7, 295 (1987). H. S Sherry, Ion Exchange (ed. J. Marinsky), Chap. 3 (1969). H. G. Karge, H. K. Beyer and G. Bart~ly, Catalysis Today 3, 41 (1988). A. V. Kucherov and A. A. Slinldn, Zeolites 7, 43 (1987). A. V. Kucherov and A. A. Slinkin, Zeolites 7, 38 (1987). Z. Schay and L. Guczi, Catalysis Today 17, 175 (1993).
I-I.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. A
NEW
COUPLING
REACTION
BETWEEN
BY
CATALYSED
BETA
165
c~-PINENE
AND
ACETONE
ZEOLITES
J. V'ffal*, J. C. van der Waal and H. van Bekkum Laboratory of Organic Chemistry and Catalysis, Delft University of Technology, Julianalaan 136, 2628 BL, Delft, The Netherlands. Fax (31-15)-782655 Abstract
When pure ketones, like acetone, 2-butanone or cyclohexanone are used as solvents in the isomerization of a-pinene over zeolite beta, products of a coupling reaction between terpenes and the solvent, are formed.
They were identified by GCMS analysis, as a-terpinyi acetone, 1 - ( a -
terpinyl)-butan-2-one and 2-(a-terpinyl)-cyclohexanone, respectively. Introduction
The hydration and isomerization of a-pinene catalysed by diluted mineral acids yields complex mixtures of monoterpenes, alcohols and hydrocarbons. In the presence of some solvents, e. g. acetone, the medium is homogeneous and the main products are a-terpineol, limonene, and terpinolene. Minor amounts of camphene, a -
3
and -~-terpinene, a - and I~-fenchol, isobomeol, bomeol, 1,4- and 1,8-cineol, 13- and y-terpineol, p-cimene and tricyclene are also formed. In absence of water a new product is formed. 5
2
I 1
10 7
Experimental
11
The catalyst (0.50 g) was suspended into
8
9
=l
__
a).__=
_
b) I
110 i
I
I
I
I
20
I
i
I
I
Time (rain)
~'
30
I
I
i
I
the solvent and the mixture heated up to the reaction temperature u 56oc _ under N2. After
i
40
I
Figure 1 m Isomerization of a-pinene over zeolite beta (Si/AI - 40) at 56 ~ C, in the presence of: a) acetone; b) ethyl methyl ketone; c) cyclohexanone. Chromatograms of the reaction mixtures at high conversions of a pinene. 1 - a-pinene; 2 - camphene; 3 ~a-terpinene; 4 limonene; 5 - y-terpinene; 6 - terpinolene; 7 - 13-fenchol;
a delay of 30 minutes to allow temperature stabilization, the reaction was started by adding the terpene used as starting reagent (1.65 mmoles) to the reaction mixture. Samples were taken at regular intervals and analysed by GC using a 50 m X 0.53 mm CP Sil-5 CB capillary
8 - borneol; 9 - a-terpineol; 10 - a-terpinyl acetone; 11 - column. Peak identification was performed by 1-(a-terpinyl)-butan-2-one; 12 - 2-(a-terpinyl)cyclohexanone. GCMS analysis and co--injection of known compounds.
* Universidade Nova de Lisboa, 2825 Monte de Caparica, Portugal
166
179
100
Results and discussion
80
~
60 40
7911 ~s -
ss
20
s9
When (z-pinene isomerization is carried
121
out over zeolite beta, using acetone as solvent, a
I
new product is formed (peak n o 10 in figure 1).
107
The correspondent mass spectrum (figure 2)
161
._IL14g [
] "
194
allows us to identify this substance as a-terpinyl
acetone. .... 40 80 120 160 200 However, the new product is not formed Figure 2 - Mass spectrum corresponding to the peak ng if limonene, a-terpineol or bomeol are used as 10 in the gas chromatogram shown in figure 1. o
starting materials instead of cr
So, the
a-terpinyl acetone must be formed directly from a-pinene.
100 80
This result suggest that an intermediate carbocation is not involved in the formation of the
60
new product. The new product is assumed to be
40
formed
20
by
a concerted
mechanism
9This
hypothesis is supported by the behaviour of the value of the initial rate of formation of the new
~
179 121
L
165
79
/
107 ~ ~L, L. . . . . . . . .
~2
,
.~[19320e
0 "- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
80
120
160
200
240
product: it goes through a maximum when the Figure 3 - Mass spectrum corresponding to the peak n9 11 in figure 1, obtained by GCMS analysis of the product initial value of the mole fraction of a - p i n e n e of a-pinene isomerization over beta zeolites in the varies from 0 to 1. presence of ethyl methyl ketone, at 56~ C. When the a-pinene isomerization is carried out catalysed by sulfuric acid instead of beta zeolites, in the same conditions, 100
complete
conversion is achieved in about 1 h. However,
$0
products from reaction between terpenes and
80
the solvent are not found. When zeolite HX was
60
17s 191
used as catalyst no formation of new product was observed. These observations suggest that a terpinyl acetone is formed, if not only with beta
40
80
120
160
__| _2 .t 200
l 240
zeolites, at least only with high silica zeolites.
The reaction above described, can also Figure 4 - Mass spectrum corresponding to the peak ng 11 in figure 1, obtained by GCMS analysis of the product take place with other ketones besides acetone. of a-pinene isomerization over beta zeolites in the Experiments of a - p i n e n e isomerization were presence of cyclohexanone, at 56~ carried out using 2-butanone and cyclohexanone, respectively. In both cases the reaction product presents
new chromatographic
peaks (peaks 11 and 12 in figure 1). The respective mass spectra allow to identify these components as 1-(a-terpinyl)-butan-2-one and 2-(a-terpinyl)-cyclohexanone, respectively (figures 3 and 4).
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
167
CATALYSIS OF A UQUID-PHASE DIELS-ALDER-REACTIONBY ZEOUTES Y,EMT AND BETA K. Bomholdt and H.Lechert Institute of Physical Chemistry, University of Hamburg Bundesslr.45, 20146 Hamburg, Germany SUMMARY The liquid phase catalysis of a Diels-Alder-reaction by zeolites Y, EMT and Beta has been studied. The use of a silica binder has an effect on catalyst activity and selectivity, depending on catalyst pretreatment. EMT has similar performance as zeolite Y, Zeolite Beta exhibits a lower activity than zeolite Y. INTRODUCTION The Diels-Alder-reaction is one of the main routes to six-membered rings in organic chemistry. Though it is highly favourabie for e l ~ reasons, the reacSonoften needs high temperature or pressure to take place [1]. Since the conventionally used catalysts, e.g. Lewis-acids like tin tetrachloride have serious drawbacks (work-up of the reaction mixture, environmental problems) it is advantageous to utilize zeontes as catalysts. With zeolites the necessary temperature is lower and very often an increased selectivity for the endoisomer or the =para"-isomeris observed when cyclic dienes or acyclic dienes rest:mcSvelyare used [2,3]. In this paper we investigated the performance of the zeolites Y, EMT and Beta for the reaction of isoprene (1) with methylvinylketone (2) to 4Ac ety I-1 -methy I-1 -cy do hexen -F-
o (1)
(2)
(3)
(4)
(3) and 4-Acetyl-2-methyl-1cyclohexen (4). Furthermore it was attempted to use a silica sol as a binder in order to make particles easier to handle and with well defined sizes.
EXPERIMENTAL The Y-zeolites were commercial products whereas the samples of EMT and Beta were synthesized in our laboratory and calcined in flowing air at 823K. The ammonium forms of the catalysts were prepared by twofold ion-exchange with 2m NH4NO3 at 353K for 1hour. Afterwards the catalysts were washed with water and dried. When a binder was used the catalysts comptsed 40wt% of silica binder. All catalysts were activated at 673K for 5 hours under reduced pressure. For the reaction the catalysts were suspended in 5ml dry methylene chloride and 10mMole of each reactant in 2ml methylene chloride were added via two dropping funnels over 30 minutes. The reaction was carried out for further 2 hours at 273K under nitrogen atmosphere and rapid stirring. Afterwards the solvent and the reactants were evaporated and the product separated from the catalyst by extraction with pentane. Identification was carried out by 1H- and 13C-NMRand the purity and isomer ratio were checked by capillary column GC.
168
RESULTS AND DISCUSSION
Figure 1 shows the conversion for H-Y with binder. The activity of Y (Si/AI = 2.5) is high and the conversion can be further increased by longer reaction times. Zeolite Y with Si/AI = 100 is rather inactive indicating that the number of active, i.e. 100 acid, sites is crucial for catalytic activity. Experiments with non-exchanged zeolite Y with binder did not reveal any activity at all so it is evident that the amorphous silica i--.i rl D 8]binder is completely inactive without pre.C>
treatment. Experiments with Sodalite confirmed that the outer surface of a zeolite only 40plays a minor role. BET surface measure 9 HY, Si/A1100 merits gave neady the same specif'r surface area of 600m2/g for pure zeolite Y and zeolite Y with 40wt% of binder. or I I Obviously, the catalytic mechanism works o 05 1 via adsorption of the ketone at the active amount of catalyst [g] sites, decreasing of the frontier orbital Fig. 1" Activity of zeolite Y with Si/AI = 2.5 and 100 energy gap of the reactants. The activity of H-EMT is slightly lower than that of H-Y (Si/AI = 2.5) and halves for H-EMT with binder. But H-EMT with binder is submitted to an additional ion-exchange, the activity is even higher than that of H-EMT without binder. The selectivity (= (3)/(4)) was enhanced from 17 for H-Y and H-EMT to 20 for HE~
Si/AI 2.5
EMT with binder and up to 30 for H-{zeolite + binder}. This means that active sites are generated on the binder surface upon ion-exchange. The results of experiments with zeolite Beta are presented in the following table: ....
catalyst pretreatment none binder, ion exchancje binder, ion exchange
amount of catalyst 0.9279 0.67g 1.17
conversion 13% 410 650
Zeolite Beta is less active than Zeolite Y (Si/AI = 2.5) but more active than a zeolite Y with Si/AI = 5 although the number of active sites is lower. This implies that either the sites in Beta are more active or the framework structure of spacious intersecting channels offers advantages such as easier diffusion of reactants and products. REFERENCES
[1] [2]
Sauer,J., Sustmann, R., Angew. Chem., 92, 773, (1980) Ipaktschi,J., Z. Naturforsch., 41b, 496, (1986)
[3]
Hochgr~ber-Paetow, D., Lechert, H., Proc. of the 9th IZC, (von Ballmoos, R. et al.,eds), Butterworth-Heinemann, Stoneham (1993)
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved. ISOMERIZATION OVER
PLATINUM
OF
169
n-HEXANE
LOADED
ZEOLITES
J e o n g - K y u Lee and H y u n - K u Rhee Department of Chemical Engineering, Seoul National University K w a n a k - k u , Seoul 151-742, Korea SUMMARY The isomerization of n - h e x a n e w a s studied over bifunctional catalysts, P t - H M , P t - H Z S M - 5 , and P t - H Y , in a f i x e d - b e d flow reactor. In particular, the effects of the pretreatment conditions and the platinum content on the catalytic activity for the isomerization were investigated. T h e catalyst calcined and reduced at 300-350"C and 500~2, respectively, showed the g r e a t e s t activity. Appropriate metal/acid balance w a s achieved by adding as small amount of platinum as 0.2 wt%. With equivalent metal sites the activities and stabilities of the catalysts as well as the product distributions were governed by the acidity of zeolites and the pore size. In case of P t - H M c a t a l y s t the acidity increased with the Si/A1 ratio and there existed an optimum value of the Si/A1 ratio with respect to the stability of the c a t a l y s t and the selectivity of isomers. Based on the experimental results the isomerization of n - h e x a n e was found to proceed by a sequence of reversible reactions. INTRODUCTION Isomerization of n - p a r a f f i n s is an industrially important o c t a n e - u p g r a d i n g process. Thermodynamic consideration of isomerization reactions reveals that the lower the reaction temperature the greater the increase in the octane number[I] and t h u s chlorinated alumina base catalysts, which can be operated at low temperatures(383-453K), are regarded as the best bifunctional catalysts. However, t h e s e catalysts present corrosion problems and are sensitive to impurities, and hence their usage requires severe pretreatment of feedstocks. T h e noble metal loaded zeolite catalysts axe free from these d r a w b a c k s and can be operated at a relatively low temperature. In this study the catalytic activities of various platinum loaded zeolites for the isomerization of n - h e x a n e were examined, compared with one another, and then analyzed in connection with the results from characterization of the catalysts. We also investigated the effects of the p r e t r e a t m e n t conditions, the platinum content and the Si/A1 ratio on the catalytic activity. T h e reaction p a t h w a y s for the isomerization of n - h e x a n e w a s deduced by analyzing the experimental data. EXPERIMENTAL Platinum loaded zeolite catalysts, P t - H Z S M - 5 ( S i / A I = 2 6 . 0 ) , Pt-HM(Si/AI=5.0, 12.5, 22.5) and Pt-HY(Si/AI=2.8), were prepared by i o n - e x c h a n g e method [2] with Pt(NHa)4C12 in competition with NH4NO3. The calcination and reduction of the samples were carried out under various conditions. The acidic properties of the samples w e r e examined by T P D of ammonia and F T - I R spectroscopy of p y r i d i n e - a d s o r b e d c a t a l y s t s whereas T E M , H2 chemisorption and H2-O2 titration in a pulse s y s t e m were employed to characterize the metal site. T h e reaction experiments were conducted in a f i x e d - b e d flow reactor with H2/n-Ce molar ratio of 6.0. RESULTS AND DISCUSSION The pretreatment conditions appeared to have a significant influence upon the metal cluster distribution on the zeolites as well as the dispersion level and thereby upon the activities of bifunctional catalysts for the isomerization of n - h e x a n e . The catalyst
170
calcined and reduced at 3 0 0 - 3 5 0 ~ and 500~ respectively, showed the greatest activity. T h i s is consistent with the previous reports[3,4] which were concerned with the maximum hydrogenation activity and the dispersion value of platinum on P t - X , P t - Y and P t - H Z S M - 5 . The isomerizing activity over bifunctional catalyst was m a r k e d l y enhanced in comparison to that over pure zeolite catalyst. It is to be noted that appropriate metal/acid balance was achieved by addition of as small amount of platinum as 0.2 wt%. The temperature giving m a x i m u m yield of isomers was decreased HY > HM > HZSM-5. T h i s sequence turned out to be the same as acid site strength of zeolites obtained by T P D of ammonia and F T - I R p y r i d i n e - a d s o r b e d catalysts. Among the three different platinum Pt-HM
gave
rise
to
the
largest
yield
of isomers
and
the
in the order of the order of the spectroscopy of loaded zeolites,
highest
selectivity
to
dimethylbutanes(DMB's). Over P t - H Z S M - 5 catalyst, the formation of D M B ' s w a s considerably hindered by the medium sized pore although the conversion of n - h e x a n e w a s the largest. Due to the low acidity, the conversion of n - h e x a n e to isomers over P t - H Y c a t a l y s t s was limited by the thermodynamic equilibria. Both the P t - H Z S M - 5 and the P t - H M catalysts were found stable within the range of experimental conditions of this study whereas rapid deactivation by coking was observed at high reaction temperatures over P t - H Y catalsyt. In case of P t - H M catalyst, the acidity increased with the Si/A1 ratio and there existed an optimum value of the Si/A1 ratio with respect to the stability and activity of the catalyst as well as the product selectivities. Based on the experimental results, it was found that while m e t h y l p e n t a n e s ( M P ' s ) were the primary products formed directly from n - h e x a n e , 2,3-DMB was the s e c o n d a r y product formed from M P ' s and 2,2-DMB was the tertiary product formed f r o m 2,3-DMB. Therefore, it may be concluded that the reaction p a t h w a y s for the isomerization of n - h e x a n e would be represented as follows : n-C6 ~- MP's ~ 2,3-DMB 2,2-DMB. CONCLUSIONS P r e t r e a t m e n t conditions of platinum loaded bifunctional catalysts appeared to a s s u m e an important role for the isomerization of n - h e x a n e and should be carefully selected. Metal/acid balance was achieved by loading 0.2 wt% of platinum. Consideration of both the catalytic activities and the yield of D M B ' s revealed that zeolites with 12 or more membered oxygen ring would be favored and that the stability and the s t r e n g t h of the acid sites should be taken into account. It was found that M P ' s were the primary products, 2,3-DMB the secondary product and 2,2-DMB the tertiary product formed from 2,3-DMB. T h e isomerization of n - h e x a n e may be regarded to proceed by a sequence of reversible reactions.
REFFERENCES 1. A. P. Bolton, in Zeolite Chemistry and Catalysis edited by J. A. Rabo, ACS Monograph 171, Washington, D. C., 714(1976). 2. G. E. Giannettoe, G. R. Perot and M. R. Guisnet, Ind. Eng. Chem. Prod. Res. Dev., 25, 481(1986). 3. D. Exner, N. Jaeger, K. M~ller & G. Schulz-Ekloff, J. Chem. Soc., Farady Trans., 78(1), 3537 (1982). 4. G. Giannetto, G. Perot & M. Guisnet, in Catalysis by Acids and Bases edited by B. Imelik, C. Naccache, G. Coudurier, Y. Ben Taarit & J. C. Vedrine, Elsevier, Amsterdam, 265(1985).
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
171
BENZENE ALKYLATION WITH ETHANOL OVER SHAPE SELECTIVE ZEOLITE CATALYSTS Radhakrishna Ganti and Subash Bhatia Department of Chemical Engineering, Indian Institute of Technology, Kanpur-208016, India
SUMMARY Selective formation of ethylbenzene using benzene and ethanol over HZSM-5 has been studied in the temperature range of 548-648 K at atmospheric pressure. The activity and selectivity of the catalyst showed m a x i m u m conversion at a particular Si/AI ratio of the HZSM-5 catalyst. The experimental data were analyzed based on the p r o d u c t pattern using the L a n g m u i r - H i n s h e l w o o d Hougen-Watson approach. INTRODUCTION Synthesis of ethylbenzene, a raw material for styrene manufacture, in the one step alkylation of benzene with ethanol over shape selective high silica zeolite catalysts is of great commercial importance. Most of the studies reported on the alkylation of benzene have been to improve the selectivity of ethylbenzene ~-3, little is known to be reported on the kinetics of the reaction. This selectivity study was carried out with the following specific objectivities: 1. Kinetics of benzene alkylation with pure ethanol over HZSM-5 catalyst 2. To derive a kinetic model based on the reaction mechanism 3. To estimate the kinetic parameters of the model 4. Effects of important variables such as b e n z e n e / e t h a n o l molar ratio, silica/ alumina ratio of ZSM-5 and reaction t e m p e r a t u r e over selectivity and conversion. Alkylation was carried out in a fixed bed flow reactor at atmospheric pressure. The catalyst (about 2-3 gram) was placed in an electrically h ea t ed stainless steel reactor (1.8 cm i.d. x 7.5 cm length) and reduced in an atmosphere of hydrogen. The reactant mixture of benzene and ethanol was p u m p e d to the reactor through a preheater by a metering pump. Liquid samples were separated through a 1.6mm x 4 m long stainless steel column packed with 5% B e n t o n e - 3 4 and 5% diisodecylphthalate on 60 - 80 mesh chromosorb W using a CIC chromatograph. Experimental data were taken at t e m p e r a t u r e s in the range 5 4 8 - 648 K over HZSM-5 zeolite at W / F values between 30 and 80 g c a t / g m o l / h r at b e n z e n e / ethanol molar ratios of 3/1 to 6 / I . Conversion of benzene, selectivities of
172 ethylbenzene, diethylbenzene and the activity of the catalyst were calculated for each experimental run. The silica/alumina ratio of the HZSM-5 zeolites was varied from 30 - 280. The activity and selectivity of the catalyst showed maximum conversion at a particular silica/alumina ratio of the HZSM-5 catalyst. Both ethylbenzene and diethylbenzene selectivities were found to decrease with increasing temperature. At higher benzene/ethanol molar ratios, the selectivity towards ethylbenzene decreased. Benzene(A) and ethanol(B) react to form ethyl benzene(C) as the primary product and a mixture of diethylbenzenes (ortho, meta and para), considered as a single c o m p o u n d in the present study due to low yields. The overall reaction is represented as: Benzene
+
Ethanol
---> Ethylbenzene
+
Diethylbenzene (DEB) (1)
The surface reaction model which fitted the experimental data is given by equation (2) as: r=
ksKaKaPaPa (1 + KApa + Kap B + KcPc + Kop o)2
(2)
Table 1 gives the kinetic adsorption constants thus estimated by non-linear regression 4 using the Marquardt algorithm.
Table 1
Reaction parameters obtained using non-linear regression
Temperature
KA
K
KB
KC
KD
(arm -1)
ks
(gmol/hr/gca0
548
0.400
1.660
6.50
38.57
0.200
573
0.332
1.580
4.47
40.00
0.382
598
0.363
0.526
5.05
16.20
1.215
623
0.288
0.585
4.50
14.99
1.350
648
0.150
1.468
3.50
21.36
2.500
The above kinetic model (equation (2)) predicted the conversions and rates comparable with the experimental values. The deactivation of the catalyst was completely absent during 20 hours time on stream test.
173 REFERENCES
[1] F. Fajula, M. Lambert and F. Figueras, "Respective Influence of the geometric and chemical factors in the conversion of aromatics over acidic zeolites". In: International Symposium on Zeolites as Catalysts, Sorbents and Detergent Builders: applications and innovations, Wfirzburg, Elsevier Science Publications, Amsterdam, September 1988. [2] Z. Hwang, S. Yu and Y. Qui, Huagong Shiyou 17(8) (1988) 477-482 (Chinese). [3] P. Levesque and L.H. Dao, "Alkylafion of Benzene using an aqueous solution of ethanol", Appl. Catal. 53 (1989) 157-167. [4] J.I. Kuester and J.H. Mize, "Optimization Techniques with Fortran", McGraw Hill Book Co., New York, 1973, 240-250.
H.G. Karge and J. Weitkamp (Eds.) 174
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
E F F E C T O F T H E A L U M I N U M C O N T E N T AT T H E E X T E R N A L S U R F A C E O F T H E ZSM-5 IN THE D I S P R O P O R T I O N A T I O N O F E T H Y L B E N Z E N E M. J. B. Cardoso 2 , E. L. Gomes 1. D. Cardoso ~ 1 Chemical Engineering Department, Federal University S. Carlos, 13565 - S. Carlos - SP - Brazil 2 Petrobr~is/CENPES / Dicat - 21910 - R. Janeiro - RJ - Brazil INTRODUCTION One of the main properties of the ZSM-5 is the possibility to form preferentially paraalkylated compounds. These compounds, e.g., p-xylene, p-styrene, are industrially very important but their formations are thermodynamically unfavorable: about 20 to 25% among the other two less important meta and ortho-isomers. The para-selectivity of the ZSM-5 is due to the fact that the diameters of its pores are very close to the kinetic diameter of the benzene ring (about 5,5 A). In consequence, the difusivity of the less bulky para-isomer in this zeolite is about 1000 times faster [1]. Several authors have found that the para-selectivity increases using larger crystals of the ZSM-5. Two main explanations have been done for this behavior: i) the diffusion path increases with the crystal size, favoring the diffusion of the less bulky compound [1,2], ii) the larger crystals have less external surface area and therefore less acid sites at the external surface, which are not para-selective [3,4]. EXPERIMENTAL The aim of this work is to verify the influence of the external acid sites in the paraselectivity of the disproportionation of the ethylbenzene. The synthesis of the zeolite was carried out using a Si/Al = 50 or 75, n-butylamine as template agent and sodium trisilicate as silicium source. To obtain crystals with the same global composition and different sizes, the same gels were aged from l to 7 days at 40 o C and then, for the crystal formation, maintained 21 hours at 170 ~ C. The crystal were characterized by X-Ray diffraction, Scanning Electron Microscopy and X-Ray Photoelectron Spectroscopy. The catalytic disproportionation of ethylbenzene was carded out in a flow micro-reactor at 325 ~ C at conversions of ethylbenzene between 10 and 20%. RESULTS In all preparations, the crystals of the ZSM-5 presented well-formed hexagonal prisms with crystallinity higher than 90%. As found with other zeolites, the crystal sizes (c axis) diminished with the aging time (Fig. 1) due to the greater number of crystal germs. The aging time had no influence in the global composition of the crystals. The XPS analysis reveals, however, an enrichment of aluminum at the outer surface with the aging time, indicating that it is incorporated to the crystals at the latter steps of the synthesis. With respect of the catalytic properties, the formation of para-diethylbenzene increases with the crystal size, but for the same size, depends on its Si/A1 ratio. However, the formation of the para-diethylbenzene decreases with the number of aluminum at the external surface of the crystal, regardless of the global Si/A] ratio (Fig 2). This indicates that in this reaction the para-selectivity depends only on the number of acid sites at the external surface. These sites are responsible for non para-selective reactions, specially the isomerization of the para to metadiethylbenzene. The dependence of the para-selectivity on the crystal size is obviously considered in this proposition, as the larger crystals have a lower specific external surface, and thus, less external acid sites.
175
L e n g t h ( ~t m ) 20 ,\\ 15"
Si/AI = 75 " \\ e,
10" ~ ' , , , ,
I ' I ' I ' I ' T i m e (Days) 0 2 4 6 8 Fig. 1 Influence of the aging time in the size of the crystals of ZSM-5 % p-Diethylbenzene 80 0 Si/AI = 50 e Si/AI = 75 ....... Equilibrium
70 60 t
50
ft.----
40 0 ...................................................................................................................... I
0
'
I
1
'
I
'
2
I
'
3
I
4
External Sites/u. c.
Fig. 2: Influence of the number of aluminum external sites in the p-selectivity of ZSM-5 REFERENCES (1) (2)
N.Y. Chen, W. W. Kaeding, F. G. Dwyer, J. Am. Chem. Soc., 101, 6783, (1979) D.H. Olson, W. O. Haag, in "Relationship Between Structure and Reactivity", ACS, 248, (1984)
(3)
J. Kim, S. Namba, T. Yashima, Zeolites, I1, 59, (1991)
(4)
G. Paparatto, et alli, J. Catal., 105,227, (1987)
ACKNOWLEDGMENTS This work received financial support from "Fundagao de Amparo h Pesquisa do Estado de S. Paulo".
H.G. Karge and J. Weitkarnp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
176
METHANOL CONVERSION TO HYDROCARBONS OVER ZSM-5. USE O F I S O T O P E S FOR M E C H A N I S M S T U D I E S . Ivar M. Dahl 1, Stein Kolboe 2 and Per Ola Ronning 2 1) Department ~ H y ~ b o n Process Chemistry, SINTEF-OSLO P. O. Box 124, N-0314 Oslo, Norway. 2) Department of Chemistry, University of Oslo, P. O. Box 1033, N-0315 Oslo, Norway. SUMMARY Methanol conversion over H-ZSM-5 has been studied in a micro reactor using a mixture of 13C-methanol and propene (isopropanol). The products were analyzed with a GC-MS instrument allowing an isotopic analysis of the emerging reaction products. INTRODUCTION H-ZSM-5 is an efficient catalyst for converting methanol into hydrocarbons [1,2]. The reaction may also be carried out over a large number of other protonated zeolites or other zeo-type materials [3]. The reaction mechanism is still not clarified [2,4]. As a means of obtaining additional information on the methanol to hydrocarbons reaction over zeolites we have investigated the reaction between 13C labeled methanol and (12C) propene (made in situ from isopropanol) over H-ZSM-5. The isotopic composition of the reaction products was measured by GC-MS. From a simplistic view, there are two main mechanism types for olefine formation in the MTH reaction:
A: A consecutive build up type mechanism with one carbon from methanol adding in each step: CH3OH --> C2H4 --> C3H6 --> C4H8 --> 05H10--> ...... B: A "hydrocarbon pool" type mechanism which in a somewhat oversimplified form may be represented by scheme 1. We have tried to discriminate between the two mechanism types, A and B, by reacting isopropanoi (as a propene source) with 130 labeled MeOH. We have chosen to use the C2H4 molar ratio MeOH:iPrOH=3:4. 12C: 13C=4:1. If we then look at the isotopic composition of the butenes formed, we should expect from the type CH3OH-->(CH2) n ~ C3H6 A mechanism above to find only singly and quadruply labeled butene (primary product, scrambling leads to a more complex C4H8 pattern). Type B mechanisms might lead to a random distribution. Scheme 1
1L
1L
EXPERIMENTAL The reactions have been run at 400 ~ and 1 bar total pressure with 30 mg catalyst and a methanol equivalent WHSV of 27 h-1. Helium (99.99+ %), partial pressure 0.6 bar, was used as diluent. Methanol: 99 % 13C1-13OH (Cambridge Isotope Laboratories) or
177
ordinary reagent grade methanol (Merck). lsopropanol: water-free reagent grade. The ZSM-5 was prepared according to the literature. Elemental composition was determined by ICP; authenticity and crystalline purity was verified by X-ray powder diffraction. The experiments were performed using a high precision syringe pump (homemade) for feeding the liquid reactant mixture to an evaporator, and a Brooks Mass Flow Controller for the helium diluent. The water formed was condensed out (4 ~ and the products were analyzed with a Hewlett Packard GC/MS system, model 5890/5970 (equipped with a J&W Scientific DB1, 60m, 0.2mm column). RESULTS Gross product formation and the isotopic composition of selected products (ethene, propene, t-2-butene, 2-methyl-2-pentene, t-2-methyl-3-pentene, an unidentified branched hexene, and p-xylene) have been measured for several TOS. Reported here is TOS=2h. Important findings are: Propene emerges virtually un-reacted. Methanol may possibly methylate propene to a limited extent to form butenes, but this reaction is not a major reaction path for methanol. For propene the major reaction path appears to be dimerization to hexene isomers. (C6 contains little 13C.) The atomic ratio 120:130 in the feed is 4:1. In spite of this the ratio 12C:130 in xylene is only 1:2, showing that the aromatic compounds are not formed rapidly from alkenes by hydrocarbon interconversion reactions. Methanol conversion is much faster. Ethene is essentially a primary product from methanol. The isotopic composition (120=12C, 120=130, 130=130) iS at variance with a possible formation by cracking of higher aikenes. Like in previous works on methanol conversion over SAPO-34 [5] a consecutive mechanism where each alkene is formed by methylation of the next lower homologue is not tenable. A carbon pool mechanism is in agreement with the results. This carbon pool can, however, hardly consist simply of C 1 entities (methoxy groups) since all products also exhibit a very sizeable 120 content. TABLE 1 EFFLUENT COMPOSITION* mbar Carbon %
TABLE 2 ISOTOPE CONTENT OF PRODUCTS % C2 C3 C4 C5 C6 xylene
Ethene Propene DME MeOH+iC 4 rest C4 C5 C6 C7 Xylene
12C 13C
13.4 126.6 6.6 17.9 30.6 10.7 9.3 2.0 3.0
3.8 53.7 1.8 2.5 17.3 7.6 7.9 2.0 3.4
32 68
93 7
77 23
73 27
*Main components REFERENCES 1. C.D. Chang and A. J. Silvestri, J. Catalysis 47 (1977) 249. 2. C.D. Chang, Cata!. Rev.-Sci. Enq. 25 (1983) 1 and 26 (1984) 323. 3. S.W. Kaiser, Arab; J. Sci. En.q. 10 (1985) 361. 4. G.J. Hutchings and R. Hunter, Catalys!s Today 6 (1990) 279. 5. I.M. Dahl and S. Kolboe, Catalysis Letters 20 (1993) 329.
80 20
34 66
178
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
Fisher-Tropsch Synthesis on Ruthenium Supported Titanium Silicate Catalysts. R.Carli, C.L.Bianchi, R.Bernasconi, G.Frontini and V.Ragaini Department of Physical Chemistry and Electrochemistry, University of Milan, Via Golgi 19, 20133 Milan, Italy. Introduction
CO hydrogenation on classical Fisher-Tropsch ( F T ) catalysts leads to the formation of a wide distribution of products, according to Anderson-Schultz-Flory (ASF) chain-growth probability. Attempts in order to control the product selectivity have been made, involving molecular sieves as catalyst support for metals which are known to be active catalysts in FT synthesis [1-3]. Geometric or diffusional constrains on the product molecules coupled with strong acid functions greatly influenced the normal chain-growth process in FT synthesis. Among the many studies, a large variety of molecular sieves has been used, such as zeolites of FAU, MFI, MOR, LTL and ERI structure types in their acidic or alkaline forms [4 and ref. therein]. There have been a significant number of recent promising developments in FT catalyst technology based on zeolites, leading to a new class of zeolite-based multifunctional metal catalysts. In this work it has been proposed to combine the shape selectivity with the electronic properties of the well-known FT-catalyst support TiO 2, exploiting the unique characteristics of the titanium silicate, ETS-10, recently developed by Engelhard [5].
Materials [] Titanium Containing Molecular Sieves
Molecular sieves, containing titanium in framework position, have been synthesized with MFI [6-7] and MEL [8-9] structure types. These titanium-silicalites, named TS(1) and TS(2), show interesting catalytic activities in oxidation reactions probably due to titanium centers in tetrahedral coordination [10-11]. It is important to note that these materials have no acid sites, because of framework-titanium is present as Ti(IV). Consistently with these characteristics, no significant effects due to metalsupport electronic interactions have been pointed out on TS(1)-supported ruthenium FT-catalyst [12]. In order to allow a suitable interaction between Ti and Ru centers in the final catalyst, a new class of titanium-containing molecular sieves composed of tetrahedral and octahedral oxide polyhedra have been used as catalyst supports. Titanium silicates such as ETS-4 and ETS-10, recently synthesized by Engelhard [13,5] have all the properties of classical molecular sieves with small (ETS-4) or large (ETS-10) pore channel systems. In spite of a lack of strong acidic functions, ETS-10 has a pore diameter of about 8 A and a BET surface area of 300 m2/g. These important characteristics make ETS-10 molecular sieve a suitable catalyst support.
[] Catalyst Preparation
The final form of the catalyst were prepared by impregnation of NaY (LYZ-82, from UOP) and ETS-10 (from Engelhard) samples with a solution of Ru(AcAc)3 in ethanol (both from Fluka). The recovered powders, calcined at 4 5 0 ~ for 12 hr, were reduced in flowing hydrogen at 3 5 0 ~ for 4 hr. All the samples were characterized by means of ESCA measurements, H2-chemisorption, ICP-AES analyses. The content of Ruthenium for all the samples were 1% wt.
179
Results and Discussion The samples were tested in a bench scale reactor designed for FT-synthesis. The testing procedure was as follow: 1 g of fresh catalyst were packed in copper coated stainless steel reactor; the sample was activated in flowing H 2 (12 I/hr) at 3 5 0 ~ and 8 bar for 12 hr; the FT-reaction were carried out with a mixture of CO/H 2 (1:2, W H S V = 1 hr -1) at 235+300~ and 5 bar for 3 hr. The activity of the catalyst samples are summarized in Table 1.
Table 1: Catalytic Activities sample
Temp.~
Ru-NaY
275
7.1
72.6
3.2
24.1
0.5
Ru- ETS- 10 (Na form)
235 275 300
2.9 8.5 25.6
42.3 53.7 60.6
11.4 7.0 3.3
46.3 39.3 36.1
2.0 1.1 0.7
Ru-ETS-IO (K form)
235 275
3.7 11.3
33.5 43.4
36.0 33.5
30.5 23.1
1.8 3.3
CO Cony. % CH 4 % CO 2 % C2+ % C3=/C 3
As one can infer from the data reported in Table 1, it is very interesting to note the higher activity of ETS-catalysts toward olefins production, compared to the reported one for Ru-NaY. While the selectivity to C 1 products (CH4+CO 2) decreases, the selectivity to hydrocarbons C 2+ increases from Ru-NaY to Ru-ETS samples. These results are due to the particular interactions between ETS support and Ru centers.
References [1] R.Oukaci, A.Sayari and J.G.Goodwin, J.Catal., 102(1986)126 [2] R.Oukaci, A.Sayari and J.G.Goodwin, J.Catal., 107(1987)471 [3] R.Oukaci, A.Sayari and J.G.Goodwin, J.Catal., 110(1988)45 [4] C.H.Bartholornew, in "New Trends in CO activation", L.Guczi (ed.), Studies Surf.Sci. and Catal., Vo1.64, Elsevier, Amsterdam, 1991 [5] S.M.Kuznicki, US Pat.4,853,202, (1989) [6] M.Taramasso, G.Perego and B.Nortari, US Pat. 4,410,501, (1983) [7] A.Thangaraj, R.Kumar, S.P.Mirajkar and P.Ratnasamy, J.Catal., 1 31 (1991 ) 1 29 [8] G.Belussi, A.Carati, M.G.Clerici, A.Esposito, R.Millini and F.Buonomo, Belg.Pat. 1,001,038, (1989) [9] J.S.Reddy, R.Kumar and P.Ratnasamy, Appl.Catal., 58(1990)L1 [10] A.Thangaraj, R.Kumar, S.P.Mirajkar and P.Ratnasamy, J.Catal., 1 31 (1 991)294 [11] J.S.Reddy, R.Kumar and P.Ratnasamy, J.Catal., 130(1991)440 [12] R.Carli, unpublished results. [13] S.M.Kuznicki, US Pat.4,938,939, (1990)
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
180
Synthesis and Catalytic Properties of Extra-Large Pore Crystalline Materials for n-Hexadecane Cracking W. Reschetilowski, K. Roos, A. Liepold, Karl-Winnacker-lnstitut der DECHEMA e.V., Theodor-Heuss-Allee25, D-60486 Frankfurt, Germany M. StScker, R. Schmidt, A. Karlsson, D. Akporiaye, E.Myhrvoid, SlNTEF Oslo, Box 124 Blindem, N-0314 Oslo, Non~ay Introduction
9
The Fluid Catalytic Cracking process (FCC) is of paramount importance in petroleum refining [1]. At present, besides an active matrix, the active component of the cracking catalyst is zeolite Y and/or ZSM-5, both of which are limited in the processing of heavier oil fractions due to the restriction caused by their pore dimensions. The new zeotype/mesoporous materials VPI-5 [2], Cloverite [3] and MCM-41 [4] open up interesting perspectives for the conversion of heavier feedstocks because of the accessibility of long-chain and/or bulky molecules to the active centres. This paper presents the synthesis of and discusses the results obtained by using Si-VPI-5 and MCM-41 as catalysts in n-hexadecane cracking in comparison with a commercial FCC catalyst. Experimental " The commercial equilibrium standard catalyst based on zeolite Y was supplied by GRACE GmbH (A1203 42.2 wt.%; 56.2 wt. % SiO2) and the samples of Si-VPI-5 (Si/AIg~ = 0.4) and MCM-41 (Si/AI = 17.3) were prepared by hydrothermal crystallization. The samples were activated beforehand by heating a shallow bed of the catalyst in a crucible ( RT to 120"C, 5 ~ flowing nitrogen ; 120"C for 3 h, flowing nitrogen ; 120 to 590"C, 5 ~C/min, flowing nitrogen ; 590"C for 16 h, flowing synthetic air). MAT (Microactivity Test) equipment according to ASTM D 3907-92 was used to test several types of catalysts with n-hexadecane as feed. Conversion and selectivity investigations were carried out using GC-FID ( VEGA 6300-01, Carlo Erba ) with two different columns for the analysis of crack gas (PLOT, GS-AL 30 m x 0.53 i.d., Megabore) and syncrude (DB-1, 30 m x 0.53 i.d., Megabore). To ascertain the amount of coke on the catalyst an elemental analyser (1106, Carlo Erba) was used. For additional characterisation adsorption/desorption investigations were carried out. Results and Discussion
9
To standardize the MAT testing and to compare conversion and selectivity, a commercial equilibrium standard catalyst was used. The optimal performance of a cracking catalyst will predominantly be the production of syncrude (liquid phase) with a high octane number to get an optimum yield of transport fuels with less gas and coke. If a comparison is made between MCM-41 and Si-VPI-5, the conversion is found to be identical and the syncrude/gas yield almost identical (Fig. 1).
181 Furthermore, compared to the standard catalyst, it is evident that these initial results with the pure materials nearly attain the catalytic properties of the standard catalyst without any further modification. In addition, no activation decay was observed by cyclic regeneration and MAT testing of these extra-large pore materials. Comparison of the pore volume distribution of the zeotype/mesoporous materials used with that of the standard catalyst indicates (Fig. 2) a marked increase in the dimension of the pores inside these new materials. Proceeding from this insight into porosity properties, the cracking of longer or even bulkier molecules than n-hexadecane as the model feed is proposed.
0"0251 Si-VPI-5 .,..-.. .., .~
0.020-~ 0.015 .~ 0.010
!
i.""'.'" /Standab
/,
o oo i ...~.,/:;'
'.
"
","
.
o . o o o J ~ 0
Fig. 1:
Comparison of syncrude / gas and coke yields and conversion of the investigated materials
Fig. 2:
1
2 3 Pore Diameter X (nm)
4
Dubtnin-Stoeckll pore size dtstrtbuUon for standard catalyst. SI-VPI-5 and MCM-41
Conclusion " By optimizing their catalytic properties there is a great possibility of developing the new zeotype/mesoporous MCM-41 and Si-VPI-5 as cracking catalysts for more effective conversion of heavy gas oil. Acknow.ledgem enl;s 9 The authors gratefully acknowledge financial support from the Commission of the EC under the JOULE II Programme and the kind assistance of EURON S.p.A. and GRACE GmbH. References
[1] [2] [3]
[4]
Wojciechowski, B.W. and Corma, A., (1986), Catalytic Cracking : Catalysts, Chemistry and Kinetics, Marcel Dekker, New York. Davis, M.E., Saldarriaga, C., Montes, C., Games, J., Crowder, C., Nature, (1988), 331,698-699. Estermann, M., McCuster, L.B., Baelocher, C., Merrouche, A., Kessler, H., Nature, (1991 ), 352, 320-323. Kresge, C.T., Leonowicz, M.E., Roth, W.J., Vartuli, J.C., Beck, J.S., Nature, (1992), 359, 710-12.
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H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
CONVERSION OF ETHANE INTO AROMATIC HYDROCARBONS ON ZINC CONTAINING Z S M - 5
ZEOLITES - ROLE OF ACTIVE CENTERS A. Hagen, F. Roessner
University of Leipzig, Faculty of Chemistry and Mineralogy, Institute of Technical Chemistry, Linnestr. 3, D-04103 Leipzig, F.R.G. SUMMARY
Zinc ions located at cationic positions of ZSM-5 are effective centers for the activation of ethane and catalyze further reactions to aromatic compounds. However, the rate of aromatization of ethene is enhanced in the presence of Brmnsted acid sites. INTRODUCTION
Investigations concerning the conversion of lower paraffins into aromatic hydrocarbons have been forced during the last years. ZSM-5 zeolites modified with zinc are known to enhance the conversion on one hand and the selectivity for the formation of aromatics on the other. However, the mechanism of the complex aromatization process as well as the roles of active sites involved are still in discussion. In this work we investigate the aromatization of ethane on zinc containing ZSM-5. Results on mechanical mixtures of various components possessing different acid properties should contribute to the discussion about the role of active centers. EXPERIMENTS
H-ZSM-5 was synthesized without template (Si/AI=15, crystallinity nearly 100 %). Starting from this parent material a HNa-ZSM-5 was prepared by 3-fold ion exchange with NaNO 3 solution at 353 K. Zinc was incorporated by mechanical admixing of ZnO to zeolite or ion exchange with Zn(NO3)2 solution at 353 K, denoted as ZnO+Zeolite and Zn-Zeolite, respectively. Samples were in situ pretreated at 723 K in air flow for 2 h. Reactions were carried out in a plug flow microreactor at 773 K, atmospheric pressure and GHSV=600 v/vh (pure ethane). Products were analysed by on line GC. RESULTS AND DISCUSSION
Fig. 1 shows the results of ethane conversion on various mechanical mixtures of the following components: ZnO supported on SiO2 (ZnO/SiO=), Na-ZSM-5, H-ZSM-5
183
and ZnNa-ZSM-5. For comparison, theoretical product distribution determined by addition of yields on single components was added. A synergetic effect with respect to the yields on the single components can be observed on mechanical mixtures of ZnO and Na-ZSM-5 (ZnO+Na-ZSM-5)
and ZnO
Fig. 1 Product distribution on mechanical mixtures after 2 h time on stream at 773 K
supported on SiO 2 and H-ZSM-5 (ZnOISiOz+H-ZSM-5). However, experimental yields correspond to theoretical ones on ZnNa-ZSM-5+H-ZSM-5. Ethene is main product on ZnO+Na-ZSM-5 whereas aromatic hydrocarbons are formed to a large extend on ZnO/SiO2+H-ZSM-5. I.r. investigations reveal traces of Bronsted acid sites in Na-ZSM5 which are completely exchanged by zinc ions at 773 K via solid state ion exchange (SSIE) in ZnO+Na-ZSM-5 111. Furthermore, SSIE takes place in ZnO+H-ZSM-5 121. Consequently, zinc species at cationic positions of ZSM-5 are effective centers for the activation of ethane to form ethene. In the absence of Bronsted acid sites formation of aromatic hydrocarbons is possible on zinc species. However, the rate of further reaction of ethene to aromatics is enhanced by Bronsted acid sites. On the other hand, formation of methane increases. Due to the acid conditions during the introduction of zinc via ion exchange of Na-ZSM-5 in aqueous solution as well as to the PlankHirschler-mechanism also Bronsted acid sites were created in the so formed ZnNaZSM-5. An increase of concentration of these sites by addition of H-ZSM-5, however, does not enhance aromatization activity. Therefore, back spillover of hydrogen discussed in the literature for aromatization of lower paraffins 13/should be excluded in the studied system. REFERENCES 1 A. Hagen, F. Roessner, Proc. Int. Symp. on Zeolites and Microporous Crystals, Nagoya (1993)in press 2 F. Roessner, A. Hagen, U. Mroczek, H.G. Karge, K.-H. Steinberg, Stud. Surf. Sci. Catal., 75 (1993) 1707 3 R. Le Van Mao, L. Dufresne, J. Yao, Appl. Catal. 65 (1990) 143
H.G. Karge and J. Weitkamp (Eds.)
Zeolite Science 1994: Recent Progress and Discussions
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Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
CONVERSION OF n-BUTANE INTO AROMATIC HYDROCARBONS OVER H-ZSM11 AND G a - Z S M - I I Z E O L I T E CATALYSTS
Kumar, N., Lindfors, L..E., Abo Akademi University, Laboratory of Industrial Chemistry, Biskopsgatan 8, FIN-20500 ~BO, FINLAND. Telefax 358-21-654 479 SUMMARY Conversion of n-butane into aromatic hydrocarbons, mainly benzene, toluene and xylenes, over H-ZSM-11 and Ga-ZSM-11 zeolite catalysts was studied at 713 K,743 K, 773 K and 803 K at a constant WHSV. The effect of gallium was studied by preparing Ga-ZSM-11 zeolite catalysts with Ga contents between 0.5 to 2.5 wt%. The acidic properties of H-ZSM-11 and Ga-ZSM-11 having different Ga contents were studied by using TPD spectra of ammonia.
INTRODUCTION
Light alkanes can be converted into hydrogen and valuable aromatic hydrocarbons, using high silica zeolites of the pentasil family (1). Modification of the proton form of these zeolites by metals such as Ga, Zn and Pt increases the selectivity towards aromatic hydrocarbons. GaZSM-5, Zn-ZSM-5 and Pt-ZSM-5 zeolite catalysts have been studied extensively for the conversion of light alkanes into aromatic hydrocarbons (2,3). The aim of the present work was to study the conversion of n-butane over H-ZSM-11 and Ga-ZSM-11 zeolite catalysts.
EXPERIMENTAL
The zeolite Na-ZSM-11 was synthesized in the laboratory by using the method given in ref (4) with some modification. The XRD analysis of the prepared Na-ZSM-11 indicated that the zeolite was highly crystalline. Na-ZSM-11 was then ion-exchanged with 5 M NH4C1 solution for 24 hours at 300 K. The ion exchanged zeolite was washed free of C1- ions and dried at 353 K over night. The NH4-ZSM-11 was then calcined at 813 K for 8 hours to obtain HZSM-11. Gallium was introduced into H-ZSM-11 by ion exchange with an aqueous solution 0.1 M Ga(NO3)3.9H20 (Fluka; 99.999%) for 30 hours. The zeolite was then filtered and washed with distilled water. This process was repeated three times to complete the exchange of protons by a fixed amount of gallium. The gallium content in J-I-ZSM-11 was varied between 0.5 to 2.5 wt% and determined by X-ray fluorescence analysis (X-Met 800 Outokumpu). The acidity of the H-ZSM-11 and Ga-ZSM-11 zeolite was estimated by TPD
185 of ammonia. The catalytic reaction was carried out at atmospheric pressure in a micro fixedbed reactor consisting of a quartz tube with an inner diameter of 10 mm. The amount of catalyst used in the testing was 0.5 g and the temperature of the catalyst bed was monitored and controlled by a thermocouple. WHSV of n-butane was kept constant during the test reaction and the reaction temperatures selected were 713 K , 743 K, 773 K and 803 K. The reactant feed consisted of 20% butane and 80% nitrogen (99.999 vol% purity).The reaction product analysis was performed by using a Varian 3700 gas chromatograph equipped with a FID detector. Reaction product from the reactor was fed into the gas chromatograph via a short tubing and a control valve, both of which were heated so that all products remained in the gas phase.
RESULTS AND DISCUSSION
The conversion of n-butane over H-ZSM-11 and Ga-ZSM-11 increases with increasing temperature and the maximum conversion was obtained at 803 K. The selectivity towards aromatic hydrocarbons also depends upon the reaction temperature and it increases with increasing temperature. The main aromatic hydrocarbon products obtained were benzene, toluene and xylenes. Yields of the cracking products methane and ethane also increased with increasing temperature. H-ZSM-11 zeolite catalyst shows very low selectivity for aromatic hydrocarbon. Addition of gallium increases selectivity towards aromatic hydrocarbons and the yields of paraffins and olefins decreased with increasing gallium content. The role of gallium is dehydrogenation of alkanes to alkenes which are chemisorbed on the acid sites of the zeolite and undergoes oligomerization reaction to give unsaturated oligomers. The unsaturated oligomers are then quickly converted to aromatic hydrocarbons. There is a rapid deactivation of both H-ZSM-11 and Ga-ZSM-11 zeolite catalyst. The probable reason for deactivation could be the result of poisoning of the acid sites, coke deposition or from sintering of gallium particles.
REFERENCES 1.Oscar A.Anunziata and Liliana B.Pierella, Catalysis Letters 16(1992)437-441. 2.H.Kitagawa, Y.Sendoda and Y.Ono J.Catal. 101(1986)12. 3.T.Mole, J.R. Anderson and G.Creer, Appl.Catal.17(1985)141. 4.Pochen Chu, N.J.Woodbury, US 3,709,979 (1972).
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
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Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
HIGHLY DISPERSED PLATINUM CLUSTERS IN ZEOLITE BETA: SYNTHESIS, CHARACTERIZATION AND CATALYSIS IN LIQUID-PHASE HYDROGENATIONS
E.J. Creyghton, R.A.W. Grotenbreg, R.S. Downing and H. van Bekkum Laboratory of Organic Chemistry and Catalysis, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands
SUMMARY Platinum loaded zeolite Beta was synthesized and characterized by TEM. Homogeneously distributed clusters with an average size smaller than 15/~ were observed; reactivity experiments indicated that these clusters are located in the zeolite. Furthermore, its potential as catalyst in regioselective hydrogenations is indicated. INTRODUCTION Platinum loaded zeolites are important catalysts in various reactions [1] and of particular importance in hydroisomerization [2]. We have selected zeolite Beta for the preparation of a platinum containing catalyst as this material has a three-D structure and can be prepared in a wide range of Si/A1 ratios [3].
EXPERIMENTAL The zeolite catalysts were prepared as described elsewhere [4]. Pt-AI20 3 (5 wt%) was obtained from Janssen Chimica, Pt black from Drijfhout. Platinum dispersions were determined by CO adsorption or TEM. Hydrogenation of allyl 3,5-di-t-butylphenyl ether (2 mmol) was performed in 25 ml EtOAc at 295K and atmospheric pressure; 25 mg catalyst was used. Hydrogenations of 1-decene and trans-5-decene were performed in 25 ml EtOAc at 275K and atmospheric pressure; between 2 and 25 mg catalyst was used.
RESULTS AND DISCUSSION T E M measurements show that all platinum clusters have approximately the same size, less than 15~,, and are homogeneously distributed over the zeolite. To discriminate between platinum clusters on the outer surface and clusters occluded in the zeolite matrix the hydrogenation of the allylic function of allyl 3,5-di-t-butylphenyl ether was used as a probe reaction. The size of allyl 3,5-di-t-butylphenyl ether is approximately 11.0x10.8x5.8 ,~ which means that it cannot enter the pores of zeolite Beta. The hydrogenation results are shown in Table 1. From the large differences in initial rates
187 it is clear that the platinum clusters are almost exclusively located inside the zeolite. Table 1. Conversion of allyl 3,5-di-t-butylphenyl ether over Pt catalysts
a
Catalyst
Si/A1
Pt (wt%)
Dispersion
rinitiala
Pt-A120 3
-
5.0
0.3
25.2
Pt-Beta
11
1.6
0.85
0.02
Pt-Beta
39
2.0
0.85
0.43
initial rate (mol- h"l.g surface Pt-t) Hydrogenation of 1-decene and of trans-5-decene were also carried out over
different platinum catalysts. From the results shown in Table 2. it can be seen that the r l / r 2 ratios (rl: initial rate 1-decene, r2: initial rate trans-5-decene) are higher w h e n the reactions were carried out over platinum contained in the matrix of zeolite Beta. Reaction rates can be expressed using Langmuir-Hinshelwood kinetics, showing zero order behaviour in both alkenes up to conversions over 70%; this indicates a full coverage of available sites. Therefore an end-on approach of the 1-decene to the active site cannot be used here to explain the observed selectivity for hydrogenation of the terminal double bond [5]. We assume that the limited number of sites available for adsorption of trans-5-decene in the zeolite channels is the key factor to determine the observed increase in selectivity. Table 2. Hydrogenation of 1-decene and trans-5-decene over Pt catalysts
a
Catalyst
Pt(wt%)
1-decene (rl) a
trans-5-decene (rE) a
rl/r 2
Pt black
100
1.44
0.64
2.3
E U R O P T - 1 [6]
6.3
5.56
1.71
3.3
Pt-A120 3
5
1.54
0.30
5.1
Pt-Beta (Si/A1 = 11)
1.6
1.06
0.19
5.6
Pt-Beta (Si/A1 =39)
2.0
3.1
0.47
6.6
initial rate (mol-h'l-g Pt-1)
REFERENCES
[1] [2] [3] [4]
W.M.H. Sachtler, Acc. Chem. Res., 26, 1993, 383. R. de Ruiter, K. Pamin, A.M.P. Kentgens, J.C. Jansen and H. van Bekkum, Zeolites, 13, 1993, 611. I.E. Maxwell and W.H.J. Stork, Stud. Surf. Sci. Catal., 58, 1991, 571. E.J. Creyghton, M.H.W. Burgers and H. van Bekkum in Proc. DGMK Conf. "Selective Hydrogenations and Dehydrogenations", M. Baerns and J. Weitkamp, Eds.; Kassel, 1993, pp 247-254. [5] H. Kuno, M. Shibagaki, K. Takahashi I. Honda and H. Matsushita, Bull. Chem. Soc. Jpn., 65, 1992,1240. [6] G.C. Bond and Z. Pa~l, Appl. Catal., 86, 1992, 1.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
188
THE
EFFECT
OF
OUTER
SURFACE
SlLYLATION
ON
THE
CATALYTIC
PROPERTIES OF FeZSM-11 L. V. Piryutko, O.O. Parenago*, E . V . Lunina*, A.S. Kharitonov, L. G. Okkel and G.I. Panov. Boreskov Institute of Catalysis, Novosibirsk 6 3 0 0 9 0 , * M o s c o w State University, Moscow 117234, Russia
Russia
SUMMARY Silylation with polymethylsiloxane suppresses both the acidity of FeZSM-11 outer surface and its activity in mesitylene isomerization reaction, though it does not affect the reaction of benzene oxidation to phenol with dinitrogen monoxide.
INTRODUCTION Benzene oxidation to phenol with N20 belongs to new catalytic reactions arousing a remarkable interest among researchers. Fe-containing zeolites of pentasil type are the most efficient catalysts for this reaction which are much superior to other systems [1]. Their unique properties are related to specific Fe-containing active sites ((z-sites). To elucidate the location of (z-sites in a zeolite matrix (inside the channels or on the outer crystal surface),the silylation effect on FeZSM-11 catalytic activity was studied in this paper.
EXPERIMENTAL SECTION FeZSM-11
chemical
composition
corresponds to SiO2/AI203 = 59;
Fe203 -
0.12 wt.%; Na20 - 0.03 wt.%. Polymethylsiloxane (PMS) was used as a silylation agent for selective deactivation of the outer surface. 3, 10 and 15 wt.% SiO 2 samples were prepared. Texture characteristics were determined from nitrogen adsorption isotherms at 7"7 K. The outer-surface acidity was measured by the paramagnetic probe method upon recording ESR spectra of tanan nitroxyl radicals [2]. A flow reactor was used for catalytic measurements.
RESULTS AND DISCUSSION SiO 2 deposition does not affect the zeolite channel system, the micropore volume remains unchanged upon silylation within the experimental error (5-'7 %). But silylation deactivates the outer surface due to covering it with the inert SiO 2 layer. Thus, deposition
189
of 15 wt.% SiO 2 (this equals to 2.5 monolayer coverage with account of FeZSM-11 outer surface area) suppresses the outer acidity by 75-80 %. This brings about a remarkable deceleration of mesitylene isomerization reaction proceeding over the outer surface of the zeolite, mesitylene conversion drops from 12 % to 2 %.
A
loo
.,_,
90
o~ =
-
20
-
>0 15
-
0
O
o
,.,
,,
10
wt. % 8iO 2
0 - 0.0 (parent) 11-3 e-lO [3-15
m
O N9
m
Fig.
5
I 30
I I I 60 90 120 Time on stream,
I 150 rain
I 180
1. Silylation effect on the oxidation of benzene to phenol over FeZSM-11 at 350~
Fig. 1 shows a silylation effect on FeZSM-11 catalytic activity in benzene oxidation to phenol with N20. Deposited SiO 2 affects practicaly neither benzene conversion nor selectivity, thus indicating that at least the main portion of (z-sites (if not all of them) is located inside the microporous system of the zeolite. Coke deposition usually provides zeolite deactivation. This phenomenon occurs upon the oxidation of benzene. The activity of all FeZSM-11 samples decreases with time on stream (Fig.l), without showing a distinct dependence on the extent of silylation. It means that coke formation also proceeds mainly inside the zeolite channels. REFERENCES
[1]. [2].
G.l.Panov, A.S.Kharitonov and V.i.Sobolev, Appl.Catal.A, 98 (1993) 1. E.V.Lunina, O.E.Lebedeva and I.L.Aleksandrova, Zh. Fiz. Khim., 60 (1986) 183.
190
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
HYDROLYSIS OF DISACCHARIDES BY DEALUMINATED Y-ZEOLITES Christoph Buttersack and Daniela Laketic Sugar Institute, Technical University, P.O. Box 4636, D-38036 Braunschweig, Germany Hydrolysis of X-O-a-D-glucopyranosyI-D-fructoses w i t h X = 2 (sucrose), X = 5 (leucrose) and X = 6 (isomaltulose) by protonated Y-zeolites w a s s h o w n to be strongly accelerated by dealumination. T w o or less protons per unit cell provide a maximal proton related rate constant of the sucrose hydrolysis. The rate c o n s t a n t is the same compared to diluted homogeneous acid solution. Hydrophobic interactions essentially contribute to the adsorption of the sucrose molecule but not to the energy of the activated transition state. It w a s proven that the zeolite pores are able to include a sucrose molecule plus at least one w a t e r molecule interacting w i t h the glycosidic bond. Because of the limited space inside the zeolite pore a change of c o n f o r m a t i o n compared w i t h the state in solution is required. Introduction The acid catalyzed hydrolysis of sucrose is generally considered to follow an A1 mechanism in which a fast pre-equilibrium protonation is followed by a unimolecular, rate-determining heterolysis of the fructosyl-oxygen bond [1]. The reaction is established on industrial scale using acid ion-exchange resins [2]. In contrast to the polymeric acid system, which bears some problems concerning the microenvironment and swelling [3], acid zeolites are characterized by a fixed geometry. The precisely uniform pore size enables specific interactions, which are the basis for chromatographic separation of carbohydrates on zeolites [4]. To our knowledge nothing has been reported on the utilization of zeolites for the hydrolysis of saccharides. One is tempted to expect that the dimensions of disaccharide molecules are too big to enter even the relative large pores of Y-zeolites [4]. However, it was shown recently that the interaction of sucrose, leucrose and isomaltulose can be significantly enhanced by dealumination of the zeolites [5]. Therefore, we were encouraged to start investigations concerning their corresponding catalytic activities. Experimental section Dealuminated NaY-zeolites (Si/AI ratio: 26, 55, 110) produced by the SiCI4 method [6] and the original Y-zeolite (Si/AI = 2.4) were treated with NH, CI [7] and heated (110 ~ / 16 h plus slowly up to 450 ~ / 16 h). An EDX and AAS analysis revealed a reduction of Na § by more than 60%. Hydrolysis of the disaccharides was carried out in a thermostatted stirred solution of 100 g/L saccharide with 10 g/L zeolite. Results and Discussion A considerable hydrolysis of all three disaccharides was obtained with the highest dealuminated zeolite (Si/AI= 110). As expected, the reaction was found to obey a first order kinetics, and up to a conversion of 50% at 70 ~ no considerable amounts of side products were formed. The rate constant per mass of catalyst observed with a usual Y-zeolite (Si/AI = 2.4) was very low. For sucrose the factor of reduction was about 800. Assuming the ideal case that the process of dealumination by SiCI4 [6] replaces the AI of the original framework in a pure statistical manner, the unit cell of the highest dealuminated zeolite contains only 1.7 Ai-atoms. With reference to the generally accepted assumption that 58% of the quickly exchangeable cation positions are located inside the supercage [7] one can postulate that only one proton per unit cell (8 supercages) exists as an acid site for the catalysis. Table 1 shows the results obtained with Y-zeolites of varying degree of acid sites and different temperature. The rate of hydrolysis was related to the number of acid sites in the supercage nil§ (in mole/g). Thus, the kinetics should obey
. d c s = knH+ Ccat cs dt where cr and c= are the zeolite respective sucrose concentration in g/L. k represents an effective
191
rate constant composed of the actual value and the concentration of sucrose inside the pores n=. On deactivated zeolites (Na*-form) the adsorption was completed within some minutes, and the analysis of the corresponsing isotherm suggests that n, corresponds to the saturation value (about 170 mg/g) when no influence of pore diffusion occurs. The activation energies are 29.7 and 30.1 kcal mole 1 K~ for Si/AI = 110 and 26 resp. These values are very close to that for the homogeneous solution. For the hydrolysis with HCI a value of 2 5 . 9 + 0 . 7 kcal mole "1 K"~ [8] is published. Therefore, the activated transition complex of the sucrose inside the zeolite is very similar to that in the liquid phase with respect to the activation enthalpy. The concentration of the zeolite particles was always 10 g/L. In case of the zeolite with the ratio Si/AI = 110 the amount of protons (58% of the AI-content) is 0.867 mole/I of the reaction volume. Surprisingly, a corresponding diluted solution of HCI causes about the same rate constants (Table 1). Thus one is tempted to postulate that despite the high concentration of protons and sucrose molecules inside the zeolite volume the separation of the reaction centres by the zeolite lattice has the same effect as a dilution of a concentrated solution. In other words: no difference exists when the sucrose molecules are separated by many water molecules or by thin "walls" mainly consisting of SiO2. Literature 1 2 3 4 5 6 7 8
T.L. Mega and R. van Etten, J. Am. Chem. Soc. 110 (1988) 6372 G. Siegers and F. Martinola, Int. SugarJ. 87 (1985) 23 C. Buttersack, React. Polymers 10 (1989) 143 C. Buttersack, W. Wach and K. Buchholz, Stud. Surf. ScL Catal. (1994), this congress C. Buttersack, W. Wach and K. Buchholz, J. Phys. Chem. 97 (1993) 11861 H.K. Beyer and I. M. Belenykaja, Stud. Surf. Sci. CataL 5 (1980) 203 T.L.M. Maesen, H. van Bekkum, T. G. Verbourg, Z. I. Kolar and H. W. Kouwenhoven, J. Chem. Soc., Faraday Trans. 87 (1991) 787 K. Vukov, Int. Sugar J. 67 (1967) 172
Table 1 Rate constants k of the sucrose hydrolysis in Y-zeolites with different degrees of dealumination (The concentration of protons available for the sucrose molecule was assumed to be 58 % of the bulk aluminum content. Data for hydrolysis in acid solution was taken from literature [8]. The k-value for Si/AI=2.4 at 40"C was extrapolated assuming the same activation energy found for Si/AI=27). charge
A
C
Si/AI
2.43
per unit cell
[mmole /g]
32.5
0.171
27 55 110
4.1 2.0 1.0
0.340 0.171 0.0867
110
1.0
0.0867
0.57 M HCI
k [10"1 L mole-1 min"1]
H +
50 "C
60 "C
0.0072 0.536 0.566
0.024
0.096
0.128
0.625
2.46
10.5
0.157
0.622
2.22
7.59
30"C
40 "C [0.00042]
70 "C 0.029 0.505 52.12
23.7
,..
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
192
ADSORPTION AND CATALYSIS MECHANISM OF CFC-11 IN N a X ZEOLITE M.Hiraiwa, A.Yamazaki, R.Otsuka and T.Nagoya Department of Mineral Resources Engineering, Waseda University, 3-4-10hkubo, Shinjyuku-ku, Tokyo 169, Japan
SUMMARY Apply NaX zeolite to catch and decompose the molecules of Chlorofluorocarbons(CFCs) and determine the behaviour of CFC-11 molecules in zeolitic pores by using various methods; powder X-ray diffractometory, Rietveld analysis, Gas Chromatography, Ion Chromatography and Nuclear Magnetic Resonance measurement. Each step of the decomposition process of the CFC-11 molecules in the zeolitic pores were characterized.
INTRODUCTION The supply of Chlorofluorocarbons(CFCs) is decreasing because of its destruction of the stratospheric ozone layer. Using substitutes for CFCs, however, would have many problems of cost and ability, and would take a long time to be applied for practical use. In this situation, the best way not to release CFCs is to catch the gas at source and then to recycle or decompose it. In this study, the adsorption behavior and the catalytic ability of CFC-11 in the zeolitic pores of NaX zeolite were tested. To examine in detail the behaviour of CFC-11 in the zeolitic pores, crystal structures before and after adsorption were refined by using powder X-ray diffraction Magnetic Resonance (NMR) data.
and Nuclear
193 EXPERIMENTAL The catalyst used was NaX zeolite(ZEOSTAR NX-112S) provided by Nippon Chemical Industrial Co.,Ltd. The adsorption procedures were as follows: (1) sampling the adsorbent; (2) drying at 400~
for 1 hour; (3) after cooling in a desiccator, filling in a
flask; (4) exposing the sample to 100% CFC-11 gas in the flask. The catalytic procedure was as follows: (1) CFC-11 gas was prepared in order to obtain the required concentration; (2) heating the catalyst at 400 ~C; (3) the gas is in contact with the catalyst; (4) sampling and analizing the decomposed CFC-11 gas. The structure refinement procedures were as follows: the crystal structures of NaX zeolite before and after adsorption were refined by the Rietveld method (RIETAN, Izumi, 1990) using high-brightness powder X-ray diffraction data. RESULTS AND DISCUSSION The positions of the water and CFC-11 molecules in NaX zeolite were determined. Although water molecules occupied almost all the supercages, the CFC-11 molecules were located only in the 12-ring of the framework structure. Calculated from the results in the adsorption procedure, it was found that about 29.2 CFC-11 molecules were adsorbed per unit cell. On decompositon CFC-11 using the zeolite catalyst, the activity near ordinary temperature is recognized. This fact shows that the deomposition of CFCs at low temperature is possible. Adsorpton of CFC-11 on a zeolite surface is dependent upon not only physisorption but also chemisorption. On investigation of these phenomena, the steps of a decomposition process in zeolitic pores were determined. REFERENCES David H.Olson, The Journal of Physical Chemistry, 72, 2758 (1970). Fujio Izumi, Journal of The Crystallographic Society of Japan, 34, 76 (1992). Koichi Mizuno et al., Ind.eng.Chem.Res., 30, 2340 (1991).
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
194
EFFECT
OF B A S I C I T Y ON THE C A T A L Y T I C
CONTAINING
ZEOLITES
P. K o v a c h e v a Institute
Sciences,
PROPERTIES
OF LEAD
Bulgarian
Academy
and N. Davidova
of K i n e t i c s
Sofia
and Catalysis,
1113,
Bulgaria
of
SUMMARY The b a s i c i t y of lead c o n t a i n i n g X z e o l i t e s was s t u d i e d by m e a n s of t h e r m o p r o g r a m m e d d e s o r p t i o n (TPD) of CO 2. A good r e l a t i o n s h i p b e t w e e n the basicity, the c a t a l y t i c - a c t i v i t y and C 2 s e l e c t i v i t y in the r e a c t i o n of o x i d a t i v e c o n v e r s i o n of m e t h a n e was o b s e r v e d in the p r e s e n c e of the zeolite, c o n t a i n i n g about 3.3 wt.% lead. INTRODUCTION Less a t t e n t i o n
compared former
is paid to the b a s i c p r o p e r t i e s
to t h e i r acidic p r o p e r t i e s .
study,
w h e r e the role of the z e o l i t i c
the reaction of oxidative [i],
conversion
in the p r e s e n t work the b a s i c i t y
zeolites
is e x p e r i m e n t a l l y
EXPERIMENTAL
The catalysts loading.
TPD of CO 2 was c a r r i e d out in a quartz 50~
for 30 min.
heating
conductivity
Chemically
rate of 10~
The c a t a l y t i c
at a t m o s p h e r i c
RESULTS
AND D I S C U S S I O N
were
by m e a n s
of T P D of CO 2.
to give
3-12 wt.%
reactor
detector.
on z e o l i t e lead
of flow type,
CO 2 was
fed at
at a
conducted
in a f i x e d - b e d
temperature
of 750~
flow rate of 60 ml/min.
The TPD plots of CO 2 a d s o r b e d in Fig.l.
supposed
of lead c o n t a i n i n g
s o r b e d CO 2 was d e s o r b e d
pressure,
r a t i o of 4.5/1 and total
shown
in
and a r g o n rate of 20 ml/min.
experiments
reactor
was
as
of our
sites
study w e r e p r e p a r e d
N a X by i m p r e g n a t i o n with lead n i t r a t e
c o u p l e d to a thermal
basic
of m e t h a n e
determined
for the s c r e e n i n g
of zeolites,
As a c o n t i n u a t i o n
on the c a t a l y s t s
examined
flow CH4/O 2
are
195
~
6
~
Fig.l.
TPD profiles
of the samples: 1 - NaX; ~
2 - 3 3%Pb/NaX; 3 - 6.4%Pb/NaX
C
4 - 12.2%Pb/NaX
0
200
zOO
T, o c
------.
600
BOO
The starting NaX zeolite is c h a r a c t e r i z e d by two TPD signals I00-350~
and 600-800~
for the p r e s e n c e
with different After
(curve i). The signals give indication
of high amount of h e t e r o g e n e o u s
strength.
i m p r e g n a t i o n of NaX with 3.3 wt.%
heterogeneous
basic sites with d i f f e r e n t
middle temperature
range are observed,
(curve 2). The origin of these sites
lead-zeolite
interaction.
basic sites
lead a number of strength in the
w h i c h are absent in NaX
is u n d o u b t e d l y due to
This sample,
shows the best activity and s e l e c t i v i t y
oxidative
-
conversion of methane.
c o m p a r e d to the others, in the reaction of
The i m p r e g n a t i o n of NaX with more than 3.3 wt.% lead has as a result gradual
loss of TPD signals
(curves
3 and 4).
In the
m e a n t i m e the same samples show a c t i v i t y and selectivity close to that of 3.3%Pb/NaX, an important,
properties. REFERENCES
i. P. Kovacheva,
N. Davidova,
E x t e n d e d Abstracts 1992,
which fact implies that the b a s i c i t y
is
but not the only factor a f f e c t i n g the catalytic
RP 29.
A.H. Weiss.
of 9th Int.
Zeol.
In: Book of
Conf.,
Montreal,
H.G. Karge and J. Weitkamp (Eds.)
196
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. PHYSICO-CHEMICAL AND CATALYTIC PROPERTIES OF Y ZEOLITES WITH HIGH MODULUS OBTAINED BY DIRECT SYNTHESIS. PREPARATION OF PILOT LOT OF NaY ZEOLITE WITH HIGH MODULUS M.I. Levinbuk 1, M.L. Pavlov 2, V.B. Melnikov, 1 B.V. Romanovsky3, Y.I. Azimova3 and Y.A. Smorodinska 3 1Moscow Oil Academy, 2GrozNII, 3Moscow State University, Russia
SUMMARY
The catalytic cracking of gas oil, adsorptive and acidic properties have been investigated over catalysts containing Y, ultrastable zeolites Y (USY and LZ-210) and high modulus zeolite Y (HMY) obtained by direct synthesis. The catalyst with HMY give higher gasoline and coke selectivities compared with catalysts containing Y and ultrastable zeolites Y. INTRODUCI'ION Industrial preparation of Y zeolites is widely spread throughout the world. However, unlike the zeolites of the pentasil (ZSM) series, their catalytic activity and selectivity are controlled by the molar ratio (modulus) SIO2/A1203, which is often varied by methods of post synthesis modification and not by direct synthesis. Zeolites obtained in such a way (hydrothermal - USY or chemical treatments LZ-210) with the modulus above 5.5 are called ultrastable ones. The disadvantages of ultrastable zeolites are the partial distortion of the crystalline framework, the appearance of extra-framework aluminium and the higher cost of the zeolite product due to construction and operating charges. These additional expenses are due to the necessity of special blocks for modification of NaY zeolite with modulus 4.5 - 5.0 synthesized by the traditional method. Scientists at GrozNII, Moscow Oil and Gas Academy and Moscow State University have modified the method of direct synthesis of NaY zeolites with modulus 5,8 - 6,0 by the silicate method without reconstruction of the existing equipment of zeolite production on the basis of chemical composition of crystallisation. EXPERIMENTAL SECTION Physico-chemical properties of Y zeolite with modulus 4.5, of ultrastable zeolite (LZ-210) with modulus 9.0 and HMY with modulus 5.95 were compared by adsorption of nitrogen, water and n-hexane and X-ray analysis. The acidity was studied by thermal desorption of ammonia chemisorbed at room temperature. The catalytic properties of the moving-bed catalysts (TCC-catalyst) prepared on the basis of the above said Y zeolites (sample-I, sample-2) and commercial catalysts
197 Emcat-Extra (Engelhard, containing USY) Zeokar-2 (GrozNII, containing Y) were examined in a laboratory unit in the cracking of vacuum gas oil at 460~ catalyst/feed ratio 2.2, space velocity 1.5 r -1. Properties of the vacuum gas oil: density- 0.915 g/cc, sulfur - 1.52 wt%, conradson carbon- 0.52 wt%, IBP 321~ FBP 518~ Catalyst pretreatment 750~ 6h, 100% steam. RESULTS AND DISCUSSION Table
Products produced upon testing of vacuum gas oil cracking over spherical catalysts Emcat-Extra Engelhard (USA)
Y type zeolites in catalysts (modulus in brackets) Zeolite content, wt% Product yield, wt% gasoline LC~ gas HC~ coke Conversion, wt% Gasoline / conversion ratio
Re USY (12.0) 10-12
Zeokar-2 GrozNII (Russia) Re Y (4.,5) 10
Sample-1
Sample-2
Re LZ-210 (9.0) 10
Re HMY (6.0) 10
30.1 28.,3 10.7 27.2 3.7 44.5
29.0 27.7 7.7 31.4 4.2 40.9
33.5 32.6 7.9 21,7 4,3 45.7
37.5 28.9 9.8 20.0 3.5 50.8
0.68
0.70
0.73
0.74
It is obvious from the table, that the catalyst containing HMY differed from the other samples by higher selectivity to gasoline and by the lower coke yield. Physico-chemical characterization of the Y zeolites showed that the high gasoline selectivity on HMY is due to the absence of non-framework alumina and defects of zeolite crystalline structure. CONCLUSIONS On the basis of the obtained results, the pilot lot (1 ton zeolite = 2,1 ton bead cracking catalyst) of Y zeolite with a high modulus (M 5.85) was prepared at the catalyst factory of the Anisimov refinery in Grozny and Ufa refinery (Russia). Laboratory tests of the pilot lot confirmed its catalytic properties of high efficiency.
V. Adsorption and Diffusion
This Page Intentionally Left Blank
198
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
COUNTER DIFFUSION OF C8 AROMATICS IN Y ZEOLITE PELLETS V.MOYA KORCHI, A.METHIVIER Institut Francais du Petrole, Applied Physico-Chemistry and Analysis Department, 1 & 4 avenue du Bois Prdau, 92506 Rueii-Malmaison FRANCE SUMMARY: A kinetic study of the counter diffusion of paraxylene and orthoxylene in Y zeolite pellets has been performed at low temperature. This study has shown a change in the rate limiting step for adsorption from micropore diffusion at 293 K to macropore diffusion at 323 K. INTRODUCTION:
The separation process of xylene isomers by adsorption on X or Y exchanged zeolites is well known in chemical engineering [1]. The process which usually operates in liquid phase involves a simulated moving bed adsorption unit whose design requires a deep understanding of mass transfer inside the adsorbent. The adsorbent which consists of small microporous crystals of Y zeolite formed into a macroporous pellet offers two distinct diffusionnal resistances to mass transfer: the micropore resistance of the crystals and the macropore resistance of the pellets [2]. The rate limiting step for the adsorption may be due either to the micropore or the macropore resistance depending on experimental conditions. EXPERIMENTALS:
In order to determine which step is rate limiting for liquid adsorption and to derive corresponding diffusivities, an experimental study of the counter diffusion of paraxylene, orthoxylene and isooctane is performed in a temperature range of 293 to 323 K and for different pellet sizes (0.3 to 0.9 mm). The experiments are conducted in a perfectly stirred thermostated cell. Prior to the experiment, the zeolite is dehydrated at 673 K for 10h in a nitrogen flow and then introduced in the vessel with a known quantity of isooctane or a solution of orthoxylene and isooctane. The experiments consist in injecting a small amount of xylene in the liquid phase and following the subsequent concentration change as a function of time. The uptake can be derived from these measurements. Depending on initial conditions, two kinds of experiments are carried out in order to study either the counter diffusion of isooctane and one xylene or the counter diffusion of the two xylenes. MODELLING AND DISCUSSION:
Figure 1 and 2 show typical examples of results obtained for the counter diffusion of paraxylene and orthoxylene at 293 and 323 K for different pellet sizes.
199
0,030
A Q
C O
xr
0,025
o.o26
~= 0,02o
I
t
0,020
I
0,015
'
t
o
9 0.56 m m 9 0.45 m m 9 026 rnm
I
,
0,005 o,ooo
0
N,
= 0.71 m m
"6 o,olo o.
i
A
1
2000
t 4000
6000
|
~" 0.010 o
"
t
J I,
8000
0.015
10000
12000
tlme (s) Figure 1 : Uptake of paraxylene as a function of time at 293 K and for various pellet sizes
0,000
YE i 0
50
100
150
200
250 time ( s )
l
0.71 m m 9 0.56 m m 9 025 m . . .m .
! I
300
350
400
Figure 2 : Uptake of paraxylene as a function of time at 323 K and for various pellet sizes
It appears that the kinetic at 293 K is independent of the pellet size while at 323 K, it exhibits a dependence on this factor. These results clearly show that in this case, there is a change in the rate limiting step for adsorption between 293 and 323 K from a micropore diffusion control to a macropore diffusion control. All the experiments which have been performed are modellised either by a macropore diffusion model or by a micropore diffusion model with the assumption of a constant diffusivity at saturation. Adsorption isotherms are highly non linear so that the diffusion equations had to be solved numerically. At 323 K the macropore diffusion model allows to fit all the results with a rather good agreement by the adjustment of an effective diffusivity De whose expression is: De = F,p Dm/~ where, F..p is the porosity of the pellet, Dm is the molecular diffusivity of the xylenes and ~ is the tortuosity of the pellet. The porosity can be measured by mercury intrusion and the diffusivity calculated by a Wilke and Cheng correlation [3.]so that the only parameter to adjust is the tortuosity ~ which has been found to be equal to 5. At 293 K the micropore diffusion model is used to fit the results with diffusion coefficients in good agreement with those found in the litterature [4] BIBLIOGRAPHY: [1] G.Hotier, B.Balannec, p301 In Preparative and production scale chromatography, G.Ganestos, P.E.Barker, New York, Basel, Hong Kong (1992) [2] D.M.Ruthven, Principles of adsorption and adsorption processes, Wiley, New York (1984) [3] R.C.Reid, J.M.Prausnitz, T.K.Sherwood, p567 in Properties of gas and liquids, Mc Gray Hill 3rd ed, ( 1 9 7 7 ) [4] D.M.Ruthven, M.Eic, E.Richard, Zeolites, 11,647 (1991)
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
200
MOTION OF CYCLOHEXANE IN COMPACTED ZEOLITE NaX Rolf Stockmeyer Institut fOr FestkSrperforschung, Forschungszentrum D-52425 JLilich SUMMARY The motion of a liquid/gas boundary of cyclohexane has been observed in a compacted sample of zeolite by scattering of slow neutrons. Comparing the experimental data with solutions of a nonlinear dispersion/diffusion equation we got the parameters of the tranport process. The capillary drift with a velocity V o = 2 . 1 0 -6 m s-1 is the dominant part of the mass transport. INTRODUCTION The density distribution C(x,t) of fluids in Zeolite NaX bodies has been observed by neutron transmission I l l on a length scale of x < 120 mm with a resolution of dx =2 mm and on a time scale t < 3 days with a resolution of dt = 43 s. Generally the experimental data can be understood as solutions of a nonlinear dispersion/diffusion equation with a drift term. In this report we present data on the transport of cyclohexane in zeolite NaX. EXPERIMENTAL A sediment of zeolite NaX has been compacted to a body of size (X = 200 mm) (Y 9 = 60 mm) (Z 9 = 6 mm) with a density of 1.5 g/ml. The sample is kept under pressure between aluminum plates and a teflon sealing. The sample has been dried and filled with nitrogen gas. Neutron transmission experiments/2/have been done with a beam ( 2 . 1 0 mm) from the port $2 at the FMRB, PTB Braunschweig. The beam crossed the sample along the Z-direction. The sample has been moved stepwise through the neutron beam along the X-direction and the neutron intensity was monitored before and behind the sample. Having taken neutron data with the dried sample a stock of cyclohexane has been connected with one end of the zeolite body and the motion of the fluid has been studied along the X-direction. Fig.1 shows the relative density of cyclohexane (symbols) as derived from neutron transmission data. DISCUSSION We discuss the measured relative density distribution, C(x,t), of cyclohexane in the compacted sediment of zeolite NaX in terms of the equation of mass transport
aC(x,t) = i[D(C).aC/ax]+ ~gt
<3x
~. ac / ax
with C(x,0)= 0 and C(0,t) = 1 and D ( C ) = D O. e x p { C ( x , t ) . In A } with D O= O ( O ) a n d A = O ( 1 ) / D ( O )
(1)
(2)
The velocity V(t) = ~ in eq.(1) describes the motion of a steep front of humidity which is driven by an external pressure or by a capillary pressur e. According to capillary models g=Dk/2.s
s2=Dk.t
(3)
with a diffusion-like coefficient Dk[m2s'l ]. For the fit of our data we assume a constant velocity V o at the beginning of the migration of the liquid through the sample during an interval of time 0 < t < DT. At t > DT we let the velocity of migration relax as V ( t ) = 4 D T / t = O. 5. ~/Dk / t with D k = 4. D T . Vo2
(4)
201
Fig.1 shows (drawn curves) numerical solutions of eq.(1) with Vo = 2 . 4 - 1 0 --6rns-'(DT = 2.55 104 s),D k = 6-lO-Tm2s-',Do = 2 . 4 - l O - " m 2 s - ' , A = 100. For comparison of the neutron data with results from NMR one may look at tel. 131. At the poster presentation we shall also refer to recent models of advective mass transport in porous solids 14,51.
REFERENCES
I l l R.Stockmeyer Microporous Materials, Vol 1 (1993) pp.373-381
/2/R.Stockmeyer J01-2699 (1992), ISSN 0366-0885 /3/M.Krus K.KieSI IBP Mitteilung Nr.175, Neue Forschungsergebnisse Vo1.16 (1989) Fraunhofer Institut fLir Bauphysik, Stuttgart u. Holzkirchen /4/M.M.R.Williams Ann. Nucl. Energy, Vo1.19 (1992) pp. 791-814 /5/M.M.R.Williams Radioactive Waste Management and the Nuclear Fuel Cycle, V01. 16 (1991) pp.101-117 1.0
0.8 E-, r.D Z r~
0.6
~>. 0.4
0.2
0.0
I
10 INDEX
I
20
I
30
I
40
I 50
OF POSITION
Fig. 1 The relative density of cyclohexane in zeolite NaX is plotted over the index of position n which characterizes the coordinate x(n) = 60 mm + 0.157. n [mm] and the time t(n) at which C(x,t) was measured. The circles (first curve from the left side) represent the experimental data taken at time of permeation t(n) = tl + 43.3 n9 [sec], tl = 4.2 [hours], n=l ..... 50. The following experimental curves have been taken at the corresponding times with t2 = 5.4, t3 = 6.6, t4 = 7.8 [hours]. The drawn curves are numerical solutions of the nonlinear dispersion/diffusion equation including a drift term, which have been computed using the parameters Do = 2- 10-11 m2s-1, A = 100, V o = 2 . 4 . 1 0 -6ms -1 (DT=2.55.104s),D k = 6 . 1 0 -7m2s -1.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
202
MOBILITY OF METHANE IN ZEOLITE NaY: A QUASI-ELASTIC NEUTRON
SCATTERING STUDY H. JOBIC 1 and M. BEE2 1 Institut de Recherches sur la Catalyse, 2 Ave. A. Einstein, 69626 Villeurbanne, France 2 Laboratoire de Spectromdtrie Physique, Universitd Joseph Fourier, 38402 St Martin d'H~res, France SUMMARY
The translational and rotational dynamics of methane in NaY zeolite have been studied by quasi-elastic neutron scattering (QENS). The progressive delocalization of the molecules with increasing temperature, as predicted by theoretical methods, is nicely followed. The self-diffusion coefficients determined by QENS are in excellent agreement with the NMR results and, to a lesser extent, with molecular dynamics simulations. INTRODUCTION The dynamics of methane in zeolites of various structures have been investigated
by several experimental
and theoretical
methods.
The siting,
energetics, and mobility of methane in NaY have recently been studied by Monte Carlo and molecular dynamics (MD) simulations techniques [1,2]. We have
used
quasi-elastic
neutron
scattering
(QENS)
to
characterize
the
translational and rotational dynamics of methane in NaY zeolite, at different temperatures and Ioadings. EXPERIMENTAL
Neutron experiments were carried out at the Institut Laue-Langevin, Grenoble, on the time-of-flight spectrometer IN5. After scattering by the sample, neutrons are analysed as a function of flight-time and angle. The zeolite was contained in a slab-shaped aluminium container of circular geometry. The cell was connected to a gas inlet system allowing loading of the samples in situ at different pressures and temperatures. RESULTS AND DISCUSSION
For the system under study, only incoherent scattering need to be considered because of the large incoherent cross section of hydrogen. The intensity scattered by the sample is proportional to the incoherent scattering function, Sinc(Q,o~), which is the space and time Fourier transform of the self-
203
correlation function Gs(r,t). The incoherent scattering function is the convolution of the individual scattering functions corresponding to the different molecular motions. The measured QENS spectra can be conveniently divided into two parts: (i) a central peak which is either purely elastic or broadened by long-range diffusion, and (ii) a broader contribution which is related to rotational motions. The temperature dependence of the QENS results was found to be much more pronounced than the concentration dependence. At 100 K, t w o different types
of
methane molecules can
be
observed
on the time-scale
of
the
experiment. Firstly there are molecules having a fixed center-of-mass but freely rotating (88%). Secondly there is a small proportion of molecules diffusing locally within the supercages (12%). No elastic broadening resulted from the fits of the data at this temperature, which corresponds to molecules spending more than 35 ps in a supercage. This value is a factor two larger than the cage residence time calculated from MD simulations. At 150 K, there are no fixed molecules, 44% of methane molecules are diffusing between the cages, while performing rotational diffusion. The remaining 56% are diffusing locally in the supercages. The presence of two distinct methane species (on the time-scale of the experiment) is justified by the residual purely elastic intensity which is a clear indication of a local motion. Therefore, at low temperature, a molecule can be trapped in a supercage, during its migration from cage to cage. We conclude that the transition between local and long-range mobility occurs between 100 and 150 K. As the temperature increases, the proportion of mobile molecules increases. At 200 K, 70% of the molecules migrate between the supercages, rising to 82% at 250 K. At room temperature, all the molecules are expected to be highly mobile, in agreement with theoretical methods. The self-diffusion coefficients determined by QENS for methane in NaY are in excellent agreement with the values obtained for methane in NaX by the pulsedfield gradient NMR technique. This indicates that the long-range diffusion of methane is similar in NaX and NaY zeolites. There is also agreement with the MD simulations at 300 K, but a discrepancy is observed at lower temperatures because of the relatively short run lengths. The activation energy for the selfdiffusion of methane is larger in the faujasite structure, 6.3 kJ mo1-1 , than in the silicalite structure, 4.7 kJ tool -1, which accounts for the different dynamics measured for methane in the two zeolites.
REFERENCES 1. S. Yashonath, J. M. Thomas, A. K. Nowak and A. K. Cheetham, Nature 331, 601 (1993). 2. S. Yashonath, P. Demontis and M. L. Klein, J. Phys. Chem. 95, 5881 (1991).
204
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
MEASUREMENT OF THE DIFFUSIVITY OF BENZENE IN A MICROPOROUS MEMBRANE BY QUASI-ELASTIC NEUTRON SCATTERING AND NMR PULSED-FIELD GRADIENT TECHNIQUE H. JOBIC 1, M. BEE2, J. KARGER3, C. BALZER 4 and A. JULBE4 1 Institut de Recherches sur la Catalyse, 2 Ave. A. Einstein, 69626 Villeurbanne, France 2 Laboratoire de Spectrom~trie Physique, Universit~ Joseph Fourier, 38402 St Martin d'H~res, France 3 Fachbereich Physik, Universit&t Leipzig, Linn~str.5, D-04103 Leipzig, Germany 4 Laboratoire de Physico-Chimie des Mat~riaux, ENSCM, 8 rue de I'Ecole Normale, 34053 Montpellier, France SUMMARY
The diffusivity of benzene in a silica membrane has been measured by neu.t[on_scattering and NMR techniques. Self-diffusion coefficients of the order of 10-1U m2 s"1are found at 300 K by both techniques so that the model of Knudsen diffusion is not valid for this microporous material. Due to the presence of small pores the diffusion of benzene in the membrane approaches the diffusion regime usually observed in zeolites. Furtl2er, the diffusivity follows an Arrhenius law with an activation energy of 11 kJ moI-L INTRODUCTION The experimental determination of diffusion coefficients is essential to model the fundamental transport properties of membranes to be used as catalytic reactors. However, the measurement of diffusion coefficients in microporous materials is not straightforward, in the field of zeolites, reported diffusion coefficients for a given molecule in similar structures may differ by several orders of magnitude according to different techniques [1]. We have applied quasi-elastic neutron scattering (QENS) and pulsed-field gradient NMR (PFG NMR) methods to study the diffusivity of benzene in a microporous silica membrane, at different Ioadings and temperatures. EXPERIMENTAL The silica membrane was prepared by the sol-gel process. After drying, the film is calcined under flowing oxygen at 720 K. A sharp pore size distribution has been determined by small-angle X-ray scattering, the mean diameter being 1.8 nm. The neutron experiments were performed at the Rutherford Appleton Laboratory, UK, using the spectrometer IRIS. The NMR measurements were made
205
on the spectrometer FEGRIS at the Department of Physics of the University of Leipzig. The benzene ioadings were the same for the NMR and for the neutron experiments: E)1 corresponds to 0.09 g of benzene per g of membrane and E)2 to 0.14 g/g, which is close to the saturation. RESULTS AND DISCUSSION For the QENS experiments, only incoherent scattering has to be considered because of the large incoherent cross section of hydrogen. The scattered intensity is related to self-motions of the hydrogen atoms under the effect of the different molecular motions. The measured QENS spectra have been fitted with a scattering function for translation convoluted with the uniaxial rotation around the C6 axis of benzene and with the instrumental resolution. With the experimental conditions used, molecular displacements of benzene in the membrane are followed over a few nm. At 300 K, the self-diffusion coefficient which is derived is 1.3x10-10 m2 s"1 for E)I and 10-10 m2 s'l for e 2. Only two temperatures could be studied, from which an estimate of the activation energy was obtained: 15 kJ mo1-1. Hydrogen containing molecules are also the best choice for PFG NMR because of the large value of the gyromagnetic ratio of the proton. It has been checked that the mean square displacement varied linearly with the observation time, over diffusion paths ranging from 1 to 10/~m. The self-diffusion coefficient obtained at 300 K for E)1 is 9.5x10 "11 m2 s-1 and 5.7x10 "11 m2 s"1 for E)2. The experimental error is = 15% compared to 50% for the QENS results, the accuracy of the PFG NMR measurements is thus better in this study. Varying the temperature between 223 and 453 K, an Arrhenius dependence was observed with an activation energy of 11 kJ mo1-1, identical for the 2 Ioadings. In conclusion, the self-diffusion coefficients which are obtained by QENS and PFG NMR for benzene in the silica membrane are in good agreement. The observed decrease of the diffusion coefficient with increasing concentration may be explained by the mutual hindrance of the molecules. The diffusion in this microporous membrane is found to be activated, the activation energy being 11 kJ mo1-1. The model of Knudsen diffusion usually applied for mesoporous materials is not valid, this model would yield diffusion coefficients of 2x10 -7 m2 s -1 for a pore diameter of 2 nm. Therefore, the diffusion of benzene in the silica membrane is comparable to the diffusion in zeolites, because of the presence of small pores. REFERENCE 1. J. Caro, M. BDIow, H. Jobic, J. K&rger and B. Zibrowius, Adv. Catal. 39, 351 (1993).
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
206
ZEOLITE MAP: A NEW D E T E R G E N T BUILDER
Christopher J. Adams 1", Abraham Araya ~, Stuart W. Carr ~, Andrew P. Chapple ~, Peter Graham 1, Alan R. Minihan 1 and Theo J. Osinga2. Unilever Research, Port Sunlight Laboratory, Quarry Road East, Bebington, Wirral, Merseyside, L63 3JW, United Kingdom 2 Crosfield Chemie B.V., Eijsden, Netherlands SUMMARY
A new detergent zeolite, zeolite MAP, has been developed by the Crosfield Group (a Unilever Company) under the tradename Doucil A24. We report here the technical properties which make the new material superior to zeolite 4A in modern detergent products. These properties - of calcium exchange selectivity and kinetics, water adsorption/mobility and controllable particle size/porosity - lead to superior building, bleach stability and liquid surfactant carrying in fabric washing powders. MAPs characteristics derive from the novel particle engineering which has produced the framework structure, primary crystallites of selected size and tailored particle size. This new zeolite is the cornerstone of Lever's new range of detergent powders. INTRODUCTION The first detergent zeolite, 4A, was introduced in 1977 in response to concerns in the USA over phosphate levels in surface waters.
4A was selected from a candidate group of over
30 natural and 90 synthetic zeolites, on the grounds of ease of synthesis, high ion-exchange capacity resulting from the maximum aluminium framework, accaptable ion-exchange kinetics and cost 1. In this report, we present the technical background to zeolite MAP, the new detergent zeolite which has been commercialised by the Crosfield Group and is central to the 1994 launch of high performance detergent products by Lever Europe. R E S U L T S & DISCUSSION
As the name MAP (Maximum Aluminium P) suggests, the new product has the zeolite P (gismondine) structure, with
a Si:AI ratio of 1.0. The structure is described 2 as doubly
connecting crankshaft chains composed of 4-membered rings, giving a 2-dimensional array of channnels with a pore size of 3.6 x 3.8 A. MAP crystallises from the Na~O.SiO2.AI203.H20 system and can be made under a range of conditions with or without seeds. It can be manufactured at costs comparable with those of 4A and is commercially manufactured by Crosfield under the trade name Doucil A24.
207
The particular properties of MAP derive from its engineered hierarchical structure; the primary crystallites are platelets of appproximate dimensions 20 x 300 A, which are agglomerated into mesoporous spheroids, the size of which can be controlled in the range 0.5-5 micron by adjusting the manufacturing conditions. MAP exhibits a high intrinsic thermodynamic selectivity for calcium over sodium. High flexibility of the framework leads to co-operative calcium binding, so that, at Ca Ioadings typical of wash conditions, MAP reduces water hardness far more effectively than does 4A. Very fast ion-exchange kinetics result from the combination of small crystallite size and significant mesoporosity. Another result of high framework flexibility is the unusual water adsorption/desorption behaviour, which exhibits massive hysteresis at low humidities. The material is thus easily prepared & stored at high (>95%) solids content.
With low water mobility within the
framework, this results in significant enhancement in stability of reactive bleaches in detergent formulations.
Acknowledgements: The authors would like to thank D Aldcroft, G T Brown, A Bell, P Knight, A L Lovell, M J Partington, E G Smith and A T Steel for their contributions to the success of this project.
REFERENCES 1) R A Llendado, Proceedings 6th Int. Zeolite Conf., Butterworth, 1986 2) Atlas of Zeolite Structure Types, W M Maier and D H Oslan, Butterworth (3rd Edition), 1992
H.G. Karge and J. Weitkamp (Eds.) 208
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
USE OF NATURAL ZEOLITES FOR LIQUID RADIOACTIVE WASTES TREATMENT (RUSSIAN EXPERIENCE) N.F. Chelishchev Institute of Mineralogy, Geochemistry and Crystallchemistry of Rare Elements, Moscow, 121357, Veresaeva St. 15, Russia
SUMMARY Substitution of clinoptilolite for ion exchange resins increases the volume of purified low-level radioactive sewage water up to 5-10 times. Substitution of clinoptilolite for quartz sand in rapid waterworks and individual filters permits the reduction of specific radioactivity down to n.10-9 cu/1. Use of zeolite filtration permits the reduction of specific radioactivity of milk from n-10-8 to n.10 -9 cu/l. Use of clinoptilolite permits the concentration of 137Cs on the solid phase by a factor of 1000 and much more.
INTRODUCTION Over thirty years ago, Ames showed that clinoptilolite is an excellent ionexchanger of radioactive cesium (Ames, 1959). The studied detail of the ion exchange properties of natural zeolites from Russian tuffaceous sedimentary deposits reveals some general regularities that are significant for the utilization of zeolites as selective ionites for radionucleides (Chelishchev, Volodin, Krukov, 1988). Due to the Chernobyl accident, the problems related to exploitation of nuclear power stations and elimination of nuclear weapons, it is expedient to discuss the experience of the usage of natural zeolites for removal or exchange of radionucleides. MATERIALS AND METHODS Particular attention was given to the determination of exchange capacity, mobility of exchange ions and ion exchange selectivity of natural zeolites from Russian zeolite deposits (Shyvirtuy, Holinskoe, Sokirniza, Tedsamy). The abovementioned spheres of application of zeolites in connection with Chernobyl and Chelyabinsk problem were studied with different degrees of detail. There is a problem with secrecy too. That is why it is hard to assess the real d e m a n d of natural zeolites for radioactive waste treatment in Russia.
209 RESULTS AND DISCUSSION Purification of low-level radioactive sewage waters with subsequent disposal of the zeolite exchangers is well developed (Zajtsev, Kulakov, Chelishchev, 1984). Substitution of clinoptilolite for ion exchange resins increases the volume of purified water up to 5-10 times. Selective sorption of 137Cs and 90Sr on clinoptilolite is possible in the presence of considerable concentrations of other metals. The zeolite filters for purification of potable water were tested under industrial conditions. Substitution of clinoptilolite for quartz sand in rapid waterworks and individual filters reduces specific radioactivity down to n-10-9 cu/1. There are several versions of installations for purification of potable water for individual consumers. Field tests have been conducted to deactivate liquid dairy products. The use of zeolite filtration reduces the specific radioactivity of milk from n-10-8 to n.10 -9 cu/l. A special zeolitic sorbent preserves high quality of milk. Clinoptilolite is the best material for solidification of low-level liquid radioactive wastes. The use of clinoptilolite concentrates 137Csin the solid phase by a factor of 1000 and much more. Specially-made zeolitic blocks may be disposed and saved in shallow ground for a long time. Safety assessment of zeolitic barriers has been conducted in Chernobyl. Removal and industrial treatment of radioactive soil to obtain clean soil and to concentrate radionucleides from the wash water on clinoptilolite was performed. The method of electrodialyses allows the cleaning of local strips and the concentration of radionucleides from irrigation water on zeolitic electrodes. CONCLUSION Due to organizing difficulties and engineering errors, a series of problems were left without answers. The quantitative parameters of the capacity of zeolite dams to hold radionucleides have not yet been obtained. Along with the Chernobyl problem, a hazard of productive units for treatment of exhausted fuel of nuclear power plants also exists in Russia. The character of radioactive pollution should be taken into account when determining the possibilities for the use of natural zeolites. For example, the main pollutant of the Chernobyl territories is 137Cs, but in the Chelyabinsk region it is 90Sr, which contributed most to the pollution. Evidently, the possibilities to use zeolites for environment protection will differ greatly for these two cases. Thus, there is a need for the comprehensive scientific foundation for the usage of natural zeolites in areas polluted with radionucleides.
210 REFERENCES
Ames L.L. (1959) Zeolific extraction of cesium aqueous solutions. US Atomic Energy Comm. Un class. Rept. HY-62607, 23. Chelishchev N.F., Volodin V.F., Krukov V.L. (1988) Ion exchange properties of natural high-silica zeolites. Nauka, Moscow, 1-129. Zajtsev B.A., Kulakov S.L., Chelishchev N.F. (1984) Use of clinoptilolite for NPS low-level radioactive sewage water treatment. Waste Management research. Abstract No. 15. International Atomic Energy Agency, Vienna, 294-295.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
211
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. SELECTIVITY FOR DIFFERENT CATIONS OF ZEOLITE-CONTAINING HYDROTHERMALLY TREATED FLY ASH Vadim Berkgaut and Arieh Singer Seagram Centre for Soil and Water Science, Hebrew University of Jerusalem, P.O.B.12, Rehovot 76100, Israel. Summary. Fly ash derived from the combustion of Colombian coal in a power plant was treated for 24 h in 3.5 M NaOH at 100oc. --40% of fly ash was converted to zeolite P with the cation exchange capacity (CEC) of resulting product reaching 1.9 meq/g. Treated fly ash displayed high selectivity for pb2+>Sr2+>Cu2+>Cd2+>Zn2+>Cs§ in competition with Na § especially at low concentrations of these cations. It was not selective for Ni 2§ and UO~+. In a column test 160 bed volumes of NH;-contaminated fish-pond water were filtered through treated fly ash until NH; breakthrough occurred. Introduetiom
Huge quantifies of fly ash are produced as a waste-product from the
combustion of coal in power plants, presenting a formidable ecological problem. Only a small proportion is used in the building materials industry; other applications are hindered by toxic concentratiom of certain elements, principally B, Mo and Se. The main constituents of fly ash are aluminosilicate glass, mullite and quartz; the glass accounts for 50-70% of fly ash and makes a readily available source of Si and A1 for zeolite synthesis. Henmi (1) and Catalfamo et al (2) reported conversion of a significant fraction of fly ash to different zeolites as a result of hydrothermal treatment in NaOH medium. The objective of this work was to study cationexchange properties of products resulting from such treatment. Experimental Section. Fly ash derived from the combustion of Colombian coal in the Hadera power plant, Israel, was heated at 100oc at constant stirring in 3.5 M NaOH with 6:1 (v/w) solution/solid ratio for 2-48 hours in a closed polypropylene vessel, then washed free of NaOH with deionized water and dried. XRD patterns of the resulting products revealed that zeolite P gradually formed during the treatment, while quartz slowly dissolved and multite remained stable. The yield of zeolite P did not change after 24 hours of treatment. Treated for 24 hours fly ash was additionally washed with 0.5 M Na acetate - acetic acid buffer solutions (pH 5) to remove traces of calcite, then with water and isopropanoL XRD revealed that this procedure completely removed calcite without affecting zeolite P. This material was used in further experiments. Its CEC determined by replacing Na + for NH 4 comprised 186+5 meq/100 g air-dry ash. Cation exchange isotherms were obtained at pH 5 to avoid precipitation of heavy metals. 30 ml of solutions containing Na acetate-acetic acid buffer and a soluble salt of respective cation were added to 50 mg of fly ash and equilibrated for 12 hours at constant shaking. The total concentration of cations in the initial solutions was in all cases 0.01 N, and the equivalent fraction of a cation competing with Na varied between 1/15 and 1/3. The pH of solutions after interaction with fly ash did not change more than 0.3 units. NH~ was measured with an ionselective electrode, Cs by AAS, other elements by ICP-AES. The column filtration
212 experiment was carried out with a fish-pond water containing 8.3 mg/1 NH]-N passed through 0.45 ~tm filter and a 7 ml column packed with treated fly ash; flow rate was maintained at 2 ml/min by a peristaltic pump. Ammonium in the effluent was determined colorimetrically by the indophenol blue method and B, Mo and Se by ICP/AES. Results and ]Discussion. From Figure 1 it can be seen that zeolite P-containing fly ash was extremely selective for Pb 2., less selective for Sr2+, Cu 2*, Cd2*, Zn2+ and Cs* (but still very selective at low concentrations), slightly selective for NH; and not at all selective for Ni 2+ and UO~*. Hg was completely excluded from zeolitic framework; this can be attributed to the very low degree of dissociation of the used salt (HgC12). Cation exchange occurred without side reactions, since the sum of cations in solutions was found unchanged within analytical error upon their interaction with fly ash.
1 pb + +
r es
/
"9_
Figure 1. Cation exchange isotherms Sr ++ Cu ++
of NH;
zeolite
P
containing
hydrothermally treated coal fly ash with Na as competing cation. Total
e-
C,s +
"~" 0.5
concentration of cations in solution 0.01 N.
Ni ++
0~
-"
,
~-
~
~
,
++
o Hg~', '2'"
equivalent fraction in solution
0.5
Although selectivity of treated fly ash for NH~ was relatively low under static conditions, in the column test it was found that 160 bed volumes of NH4-contaminated fish-pond water could be filtered through a cohmm in Na-form until a 10% breakthrough occurred. Concentrations of B, Se and Mo in the effluent were below ICP/AES limits of detection. Therefore, these toxic elements can not be considered environmental hazards in waters interacting with treated fly ash. From these results hydrothermally treated fly ash seems to be a promising exchanger for the purification of waters with low concentrations of heavy metals or radioisotopes of Sr and Cs. Its application to activated sludge process could probably enhance biological nitrification and improve sludge feasibility as fertilizer.
References. (1) Henmi, T. Clay Sci., 1987, 6,277-282; (2) Catalfamo, P.; Corigliano, F.; Primerano, P. et al.J. Chem. Soc. Faraday Trans., 1993, 89, 171-175.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
EXPERIMENTAL. SULFUR
DIOXIDE
AND
THEORETICAL.
SELECTIVE
213
STUDIES
ADSORPTION
IN
OF 3A
WATER
AND
ZEOL.ITES
I
Kathryn M. Shaw, Mladen Eic and Rajendra Desai Department of Chemical Engineering, University of New Brunswick, P.O. Box 4400, Fredericton, N.B., Canada E3B 5A3 INTRODUCTION. Fragile environmental conditions require accurate monitoring of sulfur dioxide content in flue gas from fossil fuel combustion processes. The current methods of on-line analyzing require that the sample of flue gas have the water vapor content removed. The present study investigated an alternative way making use of zeolite 3A to selectively remove water without adversely affecting SO2 composition in a carrier gas. Three different samples of zeolite A were used to measure breakthrough curves of SO 2 and water vapor in N2 as a carrier gas. Limited information using synthetic flue gas (15 vol% CO2) was also obtained. An ion exchange solution consisting of KCI, KOH and EDTA with pH of 9 was used to convert binderless Grace Davison 5A sieve to binderless 3A. A procedure involved continuous flow of the solution through a column packed with original sample at 70-80~ About 80% of ion exchange was achieved. Another EXPERIMENTAL..
modification involved addition of boric acid in Linde 3A zeolites according to the procedure given by Vansant 1. Breakthrough measurements were carried out with the treated samples described above and samples of Linde 3A. All samples were crushed to 8-16 mesh and packed in 10 cm column (ID = 2.54 cm). The carrier gas was saturated with water (5 vol%). Sulfur dioxide was fed by using mass flow controller at a flow rate corresponding to about 2,000 ppmv in the carrier gas stream. The breakthrough experiments were run with a column temperature of approximately 60~ RESULTS AND .DISCUSSION. Breakthrough measurements using binderless 3A and modified 3A samples showed virtually no SO 2 adsorption. Water vapor adsorption varied greatly depending on the regeneration conditions used. Effects of regeneration on the adsorptive properties of water in these samples are still under investigation.
214
Breakthrough curves for sulfur dioxide on Linde 3A zeolite (about 20% binder) in the presence and in absence of water vapor showed almost instantaneous break of SO 2 followed by spreading of the curves. The results were interpreted using a model based on the second moment analysis for a biporous adsorbent. 2 Assuming that spreading of the sulfur dioxide mass transfer zone is only attributed to the axial dispersion in the packed bed, one can extract the experimental value of the axial dispersion using the model (all other mass transfer resistances are neglected). This can be compared with the predicted value of axial dispersion based on the semiempirical correlation developed by Edwards and Richardson. 3 The close agreement of both experimental and predicted values proved that the spreading of mass transfer zone for SO2 on 3A zeolite was entirely due to the axial dispersion. 4 Breakthrough curves for water vapor adsorption can be analyzed using linear driving force model for a non-isothermal and axially dispersed plug flow 5. In addition Langmuir model for adsorption equilibrium was employed. A comparison of the breakthrough curves obtained experimentally to those obtained with the model showed very good agreement. A set of breakthrough curves were also developed using synthetic flue gas as a carrier gas. Results of these experiments showed no significant differences with those obtained using nitrogen as a carrier gas. 4 Linde 3A proved to be selective for SO2/H20 adsorption. Further studies are required to address the problem of SO2 delayed response that is associated with the spreading of its mass transfer zone. REFERENCES o
.
.
4. 5.
E.F. Vansant, Pore Size Engineering in Zeolites, Chapter 2, J. Wiley and Sons, New York, 1990. J. K~rger and D. M. Ruthven, Difffusion in Zeolites and Other Microporous Solids, p. 299, J. Wiley and Sons, New York, 1992. M. F. Edwards and J. F. Richardson, Chem. Eng. Sci. 23, 109 (1968). K. M. Shaw, M. Sc. Thesis, University of New Brunswick, Canada, 1993. D. M. Ruthven, Principles of Adsorption and Adsorption Processes, pages 270270, J. Wiley and Sons, New York, 1984.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
215
Permeation and separation behaviour of a silicalite (MFI) membrane F. Kaptei~, W.J.W. Bakker, G. Zheng, J.A. Moulijn and H. van Bekkum "~ Department of Chemical Engineering and Organic Chemistry .) Delft University of Technology Julianalaan 136, 2628 BL Delft, The Netherlands
Introduction Combining catalytic conversion processes with membrane permeation in-situ, i.e. in the reactor configuration, offers in principle many new opportunities such as increased yields of equilibrium limited reactions, increased selectivities in complex reaction networks and coupling of catalytic reactions by mass and/or heat exchange. This requires controlled addition of reactants or separation of products under reaction conditions. Hence, knowledge of permeation and separation characteristics are indispensable for the design and process control of this emerging new type of reactors. The behaviour of membranes operating in the molecular- and Knudsen type diffusion region can be predicted on the basis of established theories. If the membrane pores approach the size of molecular dimensions, however, and the socalled configurational diffusion and molecular sieving are operative, hardly any theory and data are available to predict permeation and separation properties. This is mainly due to the fact that up to now these zeolite type of membranes are hardly available. Recently, we succeeded to prepare a silicalite (MFl-type) membrane [1], which turned out to possess high permeabilities and interesting and surprising separation properties [2], on which we report here further with new insights and results.
Experimental The RVS supported membrane, of thickness 40#m and area 3 crn:, was tested in a WickeKallenbach type cel, using helium as a purge gas and mass spectrometric gas analysis. The total pressure could be varied between 0 and 10 bar and the temperature between 200 to 700 K. In general the permeation and separation behaviour was measured at constant gas phase conditions while cycling the temperature at 1-2 K/min. Additionally, gas adsorption measurements with silicalite crystals have been performed in a thermobalance at corresponding conditions. Results and Discussion The membrane turned out too be very thermostable. After one year of operation it did not show any sign of changing properties, which is promising for reactor applications at elevated pressures and temperatures. Figure 1 shows the permeation behaviour as a function of the temperature of a 1:1 mixture of H~ and n-butane at 1 bar total pressure. At low temperatures nbutane completely blocks the hydrogen permeation, which only becomes appreciable above 400 K, when the permeation flux goes through its maximum. This occurs around the critical temperature
,
20
E
is
o
/
300
400
f
500
i
600
T e m p e r a t u r e (K)
Figure 1 Separation behaviour of a H: / n-butPne mixture (1:1) as a function of temperature by a silicalite membrane at 100 kPa
216 of n-butane. Around 600 K the n-butane flux starts to increase again, while hydrogen increased monotonically over the whole range. As reference the n-butane uptake by silicalite at 0.5 bar is given in figure 2 as a function of the temperature. From this it is evident that the amount of adsorbed n-butane changes markedly just in the region where the permeation flux goes through its maximum. From this adsorption data values of -95 J/mol.K and -40.4 kJ/mol were calculated for the entropy and enthalpy of adsorption of nbutane, in agreement with literature. These type of results can be observed for all lower alkanes and alkenes. The temperature dependency can be completely ascribed to the occupancy and mobility of the molecules that dominates the flux, resulting in the maximum occurring around the critical temperature and where the coverage changes most. If corrected for this occupancy a monotonically increasing curve is obtained with an apparent activation energy for n-butane diffusion of 34.6 kJ/mol. In general weakly adsorbing species do not hinder each other and separation is proportional to the ratio of the adsorption equilibrium constants. Strongly adsorbing species completely block weakly adsorbing ones, while the separation behaviour of two strongly adsorbing species is not yet clear. Multicomponent adsorption data are needed to this purpose.
'~
2
t,.. 0 "10 <
0
m
" 300
400
500
600
Temperature (K)
Figure 2 n-Butane adsorption at silicalite at 50 kPa as a function of temperature.
5.0 "(~ 4.0
_~3.0 ~2.0
i-Butane
x ~ 1.0
, -'.~---
0.0 300
400
500
600
Temperature (K)
Figure 3 Single component permeation of isobutane (50 kPa) as a function of temperature.
Figure 3 shows the activated permeation of iso-butane at 0.5 bar, which clearly indicates that for this molecule the molecular sieving effect becomes manifest. An apparent activation energy for permeation of 25 kJ/mol was observed in this case, resulting in a diffusion activation energy estimation of 64 kJ/mol after correction for the surface coverage variation. At the workshop more detailed results for alkanes and alkenes will be presented. Further developments that will be undertaken are, among other things, the incorporation of catalytic activities in the membrane and the preparation of other zeolitic type of membranes. References .
2.
E.R. Geus, Ph.D. Thesis, Delft University of Technology, 1993. W.J.W. Bakker, G. Zheng, F. Kapteijn. M. Makkee, J.A. Moulijn, E.R. Geus and H. van Bekkum. in M.P.C. Weijnen and A.H.H. Drinkenburg (eds.) Precision Process Technology Kluwer: Dordrecht. 1993, p.425-436.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
ADSORPTION RAFFINS
AND
POLARIZATION
ON C A T I O N I C
L.M.KUSTOV,
Institute
Moscow,
OF M O L E C U L A R
OF ZEOLITES:
V.B.KAZANSKY,
N.D.Zelinsky Sciences,
FORMS
217
HYDROGEN
AND
LIGHT
IR-SPECTROSCOPIC
STUDY
PA-
and A.Yu. K H O D A K O V
of O r g a n i c
Leninsky
prosp.
Chemistry,
Russian
47,
Russia
117334
Academy
of
Summary - A d s o r p t i o n and p o l a r i z a t i o n of molecular hydrogen and light p a r a f f i n s on c a t i o n i c forms of various zeolites is s t u d i e d by d i f f u s e r e f l e c t a n c e IR s p e c t r o s c o p y . The extent of p o l a r i z a t i o n c h a r a c t e r i z e d by the s t r e t c h i n g f r e q u e n c y is found to be s t r o n g l y d e p e n d e n t on the n a t u r e of c a t i o n (electrostatic field, p r e s e n c e of d - e l e c t r o n s ) and z e o l i t e f r a m e w o r k ( l o c a l i z a tion sites, b a s i c i t y of oxygen). Introduction tal
Various
simple
cations
molecules
in zeolites.
a re the m o s t
efficient
used
purpose.
accepting
properties
for this
one-point rather sible
states of the zation
quate
narrow
However, even
zeolite
These the
in the
to d i s t i n g u i s h of c a t i o n s
to test
their
the
correlations
range
case
of the n e i g h b o r i n g
in the
activation
shown
that m o l e c u l a r
probe
for a c i d - b a s e
and
real
in zeolites,
electron-accepting
the n e i g h b o r i n g catalytic
test-molecules
hydrogen pairs
basic
substrates, that
of
and
that
can be
Light also
can be p o l a r i z e d
by
pos-
is
the m e c h a n i s m
of p o l a r i -
and
to
take
of a c a t i o n
oxygen
both
sites
derive
characteristics
should
used
include
oxygen.
not
shifts
in d i f f e r e n t
substrate.
m a y be
this
different
catalytic
framework
via
of
to
localized
one
also
cations
it is u s u a l l y
corresponding
ability
a
with
are
a measure
frequency
molecules
the
properties involved
ions
being
for me-
monoxide
electron:
and p y r i d i n e
the
of CO,
nitrogen
interact
To u n d e r s t a n d
of c a t i o n s
only the
and
of
of v a r i o u s
between
accessibility
and
Ammonia
molecules
properties not
both
complexes
structure.
probes
IR f r e q u e n c y
or to m e t a l
and a c t i v a t i o n
as m o l e c u l a r
monoxide
of cations.
mechanism,
interaction.
are u s e d
Carbon
into but
that m a y Recently
as
a
the
Lewis
paraffins, used
as
cations.
and
account
also
the
be
also
we
have
universal acid
which
ade-
are
effective
IR site
the IR
218 Results
and D i s c u s s i o n
Adsorption,
polarization,
gen and light p a r a f f i n s olites was
alkaline
and a c t i v a t i o n of m o l e c u l a r
(CH4,C2H6,CF3H)
on cationic
studied by d i f f u s e reflectance
forms of A, X, Y, MOR,
IR
and ZSM-5
zeolites,
the spectral
ra of H 2 on Y zeolites,
three types of complexes
alkaline
cations
located
guished.
The extent
SI',
ZSM-5
chanism of H 2 a d s o r p t i o n
and a n e i g h b o r i n g
cationic
forms,
charge,
reasonable d e p e n d e n c e For H 2 a d s o r p t i o n
leads to a d e c r e a s e
on
of c a t i o n s . T h e
zeolites
cations
zeolites,
with
with
the
rather low t e m p e r a t u r e s
yielding
des and surface OH groups.
For instance,
cm
cm 1
c o m p l e x c h a r a c t e r i z e d by
shifted by 210
en-
following me-
a cation for
ad-
decreases
and a c c e s s i b i -
we
take
same
of the
(200-400K)
to
observed
a
of cations.
transition-metal
and H 2 may
dissociation
to
distin-
hydrolysis
of cations,
ions,
place,
which
electrostatic
field
of the strength of the H-H bond,
In m a n y cases,
(77K)
the
of the frequency on the radius
with n o n - t r a n s i t i o n metals
the m o l e c u l a r
found
in
the ionicity of the pair,
chemical b o n d i n g b e t w e e n
(e/r).
attributed
the spectral p a t t e r n
O n l y for h i g h - s i l i c a
adsor-
confirms a t w o - p o i n t
the e l e c t r o n - a c c e p t i n g p r o p e r t i e s
lity of cations.
IR spect-
on an acid-base pair i n c l u d i n g
sorbed H 2 is c o m p l i c a t e d by hydrolysis
their e f f e c t i v e
In the
oxygen of the framework.
For p o l y v a l e n t
weakens
relation
of H-H bond p o l a r i z a t i o n was
< M O R < Y < X < A. This
For
a
and SII sites w e r e
hance w i t h i n c r e a s i n g b a s i c i t y of the lattice sequence:
of ze-
features of h y d r o g e n
sites distribution.
in SI,
forms
spectroscopy.
was e s t a b l i s h e d b e t w e e n
bed at 77K and l o c a l i z a t i o n
hydro-
H-H
as c o m p a r e d
bond
occurs
corresponding
for
the
dissociates
ZnZSM-5
frequency upon
at
hydri-
zeolite,
of
warming
3950
the
sample up to 300K. Simultaneously, Zn-H m o i e t i e s (nznH=1610, 1589cm -I ) and b r i d g i n g OH groups (nOH=3610cm -I) appear. IR s p e c t r a of methane,
forms of zeolites
sorbed hydrogen.
revealed
and CF3H a d s o r b e d
In some
further t r a n s f o r m a t i o n s
(T~500-600K).
light p a r a f f i n m o l e c u l e s
on
cationic
the same trends as the s p e c t r a
Strongly polarized
band are observed. conditions
ethane,
cases
species with a
(ZnZSM-5),
of a d s o r b e d m e t h a n e
Two-point mechanism is proposed.
of ad-
shifted
n as
dissociation
and
occur at r a t h e r m i l d of
activation
of
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
219
PROMISING AIR PURIFICATIONS ON CLINOPTILOLITE by Robert W. Triebe, F. Handan Tezel, Ayse Erdem - Senatalar*, and Ahmet Sirkecioglu* Department of Chemical Engineering, University of Ottawa, Ottawa, Ontario, K1N 6N5, CANADA *Department of Chemical Engineering, Technical University of Istanbul, Istanbul, TURKEY
SUMMARY A natural clinoptilolite from Turkey [1] has been tested for a variety of potential air purification / separations. Henry's law constants for adsorption of CO=, CO, NO, and N= were measured on clinoptilolite, 4A and 5A zeolites, and H - Mordenite over various temperature ranges between 243 and 473 K. Equilibrium separation factors were calculated for COIN z and NO/N= systems on the various zeolites. Low concentration separation factors for the COIN= and NO/N2 systems ranged from 5 to 20 for clinoptilolite. Pure component adsorption isotherms were determined for N= and CO= on clinoptilolite at 303 K and up to 1 atmosphere. Binary adsorption isotherms for the CO=/N=/clinoptilolite system were predicted using the extended Langmuir equation, the Ideal Adsorbed Solution Theory (lAST), and the Fiory- Huggins and Wilson forms of the Vacancy Solution Theory (FH-VST and W-VST, respectively).
INTRODUCTION Clinoptilolite, the most abundant natural zeolite, has been shown to be a versatile sorbent for gas ~parations and deserves further examination [2]. The objective of this study was to determine the otential of a natural clinoptilolite for a variety of common gas separations and purifications. The gas ;hromatographic method [3, 4] was used to determine Henry's law constants over various temperature 'anges between 243 and 473 K. Pure component isotherms were determined for CO= and N= on clinoptilolite under possible separation conditions.
EXPERIMENTAL A Varian 3400 gas chromatograph equipped with FID and TCD detectors was used for all Henry's Law experiments. A 10 cm column containing approximately 2 grams of 20 - 42 mesh sorbent was fully contained in the GC oven for accurate temperature control. Sampling and data acquisition were done automatically using an Akran 486-33 computer fitted with National Instrument's VIEWDAC data acquisition system. For determination of Henry's law constants, ultra high purity He carrier (99.999%) was used to transport the .25 cc gas sample through the column, and all flows were metered with digital flow controllers. For determination of the pure N= isotherm carrier gases were mixed using rotameters, and the carrier composition was verified with a Gow Mac TCD cell, a Gow Mac Power Supply Control Unit and a chart recorder. The CO= isotherm at 303 K was determined volumetrically up to 1 atmosphere. The
220
zeolites used were a natural Turkish clinoptilolite [1], Linde 4A and 5A zeolites, and Zeolon 900H H-Mordenite.
RESULTS AND DISCUSSIONS Henry's law constants for CO adsorption on 4A and 5A zeolite agreed well with those in literature. Henry's law constants and heats of adsorption for CO, N z, and NO on clinoptilolite between 323 and 473 K were higher than those on all other sorbents examined. Subjecting the clinoptilolite column to a CO 2 pulse produced no interpretable response peak, likely due to the strong retention of CO z in the clinoptilolite pores. Clinoptilolite produced the highest separation factors over the entire temperature range examined for separation of NO/N2 and COIN z, as shown in figures 1 and 2. Pure gas isotherms for CO= and N 2 adsorption on clinoptilolite at 303 K and up to 1 atmosphere were measured and found to be quite rectangular. Experimental pure isotherms and binary adsorption equilibria predicted through the extended Langmuir equation, the lAST, the FH-VST and the W-VST show promise for the CO2/N2 separation under ambient conditions.
Figure # 1 NO / Nitrogen Separation Factors
,,_. 100
100
z
Z El
E1
o
o z
~.
-
.f.
f..
El
10
U_
!
5^
.o_
/
03 i,.
L_ ....
CL
El
0J 03
\
I0
CL
v I.. O O G~ LL r
Figure #2 CO / Nitrogen Separation Factors
1
2.;
2.4
2.6
2.8
3
3.2
Thousandths
3.4
~
..
3.6
3.8
1 / Temperature (l/K)
0.1
4
2.2
2.4
2.6
2.g
3
3.2
Thousandths
:3.4
3.6
3.8
1 / Temperature (l/K)
References 1 - Sirkecioglu, A., Altay, Y., and Erdem - Senatalar, A., in preparation. 2 - Ackley, M.W., Giese, R.F., and Yang, R.T., Clinoptilolite: Untapped Potential for Kinetic Gas Separations, Zeolites (1992), 12, 780. 3 - Haynes, H.W., and Sarma, P.N., A Model for the Application of Gas Chromatography to Measurements of Diffusion in Bidisperse Structured Catalysts, AIChE J.(1973), 19, 1043. 4 - Shah, D.B., and Ruthven, D.M., Measurements of Zeolitic Diffusivities and Equilibrium Isotherms by Chromatography, AIChE J.(1977), 23, 804.
4
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
221
MASS TRANSFER KINETICS MEASUREMENTS BY THERMAL FREQUENCY RESPONSE METHOD V.Bourdin and Ph.Grenier LIMSI-CNRS B.P. 133 F91403 Orsay, France SUMMARY A frequency response method based on the temperature measurement of a sample by I.R. emission is described. The possibilities of this thermal method, are shown by some results obtained on the NaX-water system which has very fast kinetics. Precise determination of the Fickian diffusion coefficient and the surface barrier are obtained even for such a fast system. The results agree well with N.M.R. results obtained for the same crystals. INTRODUCTION In recent years the frequency response method (currently pressure response to a volume modulation) has attracted more and more attention to determine mass transfer kinetics in adsorbents. [ 1-3]. This development is due to the following advantages: -The method transforms a transient system to a quasi-stationnary one. This allows very precise measurements. - The phase lag of output signal (e.g. pressure) relative to input signal (e.g. volume) is directly related to transfer characteristic times, independent of most thermodynamic parameters. - The response is sensitive to nature of transport mechanisms (surface barrier or Fickian diffusion). Nevertheless, when only the pressure and volume are measured, it is difficult to take into account the thermal effects which always occur during adsorption and may alter significantly the response curve.J4-5] The new method consists of measuring the temperature of the adsorbent sample submitted to volume modulation, as well as the pressure in the chamber. EXPERIMENTAL The experimental set up consists of a chamber with a bellows which may be moved as a sinusoidal function of time at various frequencies between 10-4 and 20 Hz. The pressure is recorded through a fast (x =1 ms) Baratron gauge and the temperature obtained by the IR emission of the sample.The amplitudes and phases of p and T with respect to the volume modulation are numerically determined by the Fourier Transform method. RESULTS AND DISCUSSION The figure shows one set of temperature curves obtained with the NaX-water pair on a sample of mass 50 rag.The curves ITIcosr and ITIsinr are plotted taking the measured pressure p as reference for amplitude and phase; this allows the elimination of the wall adsorption effect. The theoretical curves are obtained with a non isothermal diffusion model which takes into account surface barriers ( characteristic time: xs) as well as Fickian diffusion (Xd)- [6]
222
It c a n
be seen that the model fits the experimental data well and a raw diffusion coefficient
close from 10"9m2 s -1 may be identified, as well as a very small surface barrier effect. After applying the Darken correction, the diffusivity ( D0=7 10 "11m2 s "1 ) agrees quite well with the results obtained by K i r g e r ( D0=1.4 10"1~ 2 s-1 ) using the P F G - N M R technique on crystals of the same origin. [7] 0.20 NaX
(100
/~m
crystals)
154 Pa
-
water
31~
0.15 I ~D 0.10
L
[--
0.05
o.oo Model * results --- ITI sin~o Model 9 * * * * ITI sin~o Exp. results ITI
ooooo
-0.05
, ,, ....m
0.001
ITl
cosy cos~
........ J 0.01
Exp.
........ , 0.I
*'v
*',, "* *,
, , , .....l " , 1
. t., -- --. tr~**~ ....... I
Frequency (Hz)
10
, T
C O N C L U S I O N With the thermal frequency response method it is possible to determine very fast mass transfer kinetics on a very small sample, avoiding spurious effects like wall adsorption and bed effects. Moreover, it is easy to distinguish between surface mass transfer resistance and intracrystalline diffusional resistance. REFERENCES 1-Betemps, M., Mange, lV[, Scavarda, S. and Jutard, A., 1977, Problems raised by application of the usual methods of process identification to the determination of diffusion coe~cient of gases in molecular sieves. Phys. 1)." appL Phys.lO, 697-715. 2-Yasuda,Y.,1982, Determination of vapor diffusion coefficient in zeolite by the frequency response method. J. Phys. Chem. 86, 1913-1917. &-Van-Den-Begin, N.G. and Rees, L.V.C.,1989, in Zeolites: Facts, Figures, Future (Eds. P.A. Jacobs and ltA. Van Santen) Elsevier, Amsterdam, p. 915. 4-Sun, L.M., Meunier, F., Grenier, P. and Ruthven, D.M.,1994, Frequency response for nonisothermal adsorption in biporous pellets.Chem. Eng. Sci. 49-3, 373-381. 5-Sun, L.M. and Bourdin, V.,1993, Measurement of inuacryst~Uine diffusion by the frequency response method: analysis and interpretation ofbimodal response curves.Chem. Eng. Sci. 48-22, 3783-3793 6-Sun, L.M., Meunier, F. and K~ger, J.,1993, On heat effect in measurements of sorption kinetics by the frequency response method Chem. Eng. Sci. 48-4, 715-722 7-.Karger, J.and Pfeifer, H.,1987, N.M.lt self-diflh~ion studies in zeolite science and technology. Zeolites, 7, 90-107.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
223
Study o f Fast Diffusion in Zeolites Using Higher Harmonic Frequency R e s p o n s e Method Dongrnin Shen and Lovat V.C. Rees Department of Chemistry, University of Edinburgh, King's Buildings, West Mains Road, Edinburgh EH9 3JJ, UK
ABSTRACT The high harmonic frequency response method has been applied for the first time to measure fast diffusion processes in zeolites, e.g. carbon dioxide/Silicalite-1, n-hexane/Beta and n-hexane/NaX. The frequency range can be increased up to 100 Hz when the ninth harmonic is taken in the Fourier transformation of the square-wave signals, as shown in Figure 1. These higher harmonic Fourier transforms widen the dynamic time scales that can be followed by the FR method from 0.1-1000 seconds to 0.01-1000 seconds. 10-Ring Channel
Structures: Theta-1 (l) 0.3.-
(b)
and Silicalite-I r KSin Figure 2 shows that the diffusivities O of carbon dioxide in Silicalite-1 measured ~ o2. by this frequency response method are in a good agreement with the corresponding values determined by PFG NMR. The ~o--o.1 activation energy of 9i-_l kJ/mol for K~out diffusion of CO 2 in silicalite-1 was nearly u. 0.0 the same as that in theta-1, but the 0.01 0.1 1 10 100 diffusivities of CO 2 in theta-l were about Frequency / Hz one order of magnitude slower than in silicalite-1, although both zeolites are 10ring channel frameworks. The difference in Figure 1. Frequency response curves of CO 2 diffusivity between these two 10-ring diffusion in silicalite-1 at 273K and 2.0 Ton'. zeolites may be explained by their different ([], ~), the first, (@, O), third; ( , , r fifth; (V, frameworks. Firstly, although both of V), seventh and (k, A), ninth harmonic them-1 and silicalite-1 have 10-ring pore frequency response data fitted by the theoretical channels, the pore size of theta-1 (0.44x0.55 rim) is smaller than those of model (lines). silicalite-1 (0.51x0.55 and 0.53x0.56 nm). Secondly, theta-1 has one-unidimensional channels, whereas silicalite-1 has two sets of intersecting channels which form a three dimensional network. The diffusion mechanisms in these two types of networks are different from the microscopic point of view. In the three dimensional silicalite-1, the diffusion mechanism can be well described by the random jump model, i.e. the Einstein equation: =6Dt with D denotes the self-diffusivity. In contrast to this type of diffusion, in the case of the unidimensional theta-1, a molecule's jump will take place only if there is an empty site available in the jumping direction, since the kinetic diameter of the carbon dioxide molecule (0.46 nm) is close to the channel diameter oftheta-1 and it is impossible for the carbon dioxide molecules to
224
pass each other within the channels. Therefore, the diffusion mechanism in theta-1 may be described by the single file diffusion model. In the macroscopic uptake measurements, e.g. the FR method, in which the diffusion kinetics are followed by changing concentration gradients, this single file diffusion may become particularly important because a blockage of pore openings and a mutual interaction of diffusing molecules will lead to a significant reduction of the uptake rates. These blockage phenomena have been observed in FR 10 -8 . studies of N2, CO and CO 2 diffusion in theta-1. "T, r r
E
o 10"9" 12-Ring Channel and Window D Structures: Beta and N aX The diffusivity of 4x101~ m2s"1 at 323K for n-hexane in Beta was able to be 10-1 determined when the higher harmonics were ~,'5 ' 31o 3'5 41o 4;~ applied. The diffusion coefficient of IO00K/T 1.Sxl 011 m2s-] for 2,2,4-tfimethylpentane in Beta at 298K was obtained from the Figure 2. Temperature dependenceofCO 2 fundamental frequency response method as diffusion in silicalite-1 (12): FR at 2.0 Ton-; (O) expected. The diffusivity of 2,2,4- PFG NMR and theta-1 (A) FR at 2.0 Torr trimethylpentane in Beta is about one order of magnitude slower than that of n-hexane. The diffusion coefficient of n-hexane in NaX of 4.7x109 m2s-1 at 323K as determined by the high harmonic FR method is in a reasonable agreement with the corresponding value of 2-~3x109 m2s-1 at 323K by PFG NMR, since the diffusion coefficient from the FR measurements has not been corrected by the Darken equation. These diffusion coefficients are about two orders of magnitude larger than those of n-alkanes in NaX obtained by the membrane and ZLC methods. The diffusivity of n-hexane in NaX is about one order of magnitude larger than in Beta , which are measured by the FR method. The slower diffusivity in Beta may be caused by the narrower 12-ring channels, compared with those in NaX. Secondly, in the case of NaX molecules diffuse through 12-ring windows (0.74 rim) into supercages (1.2 nm), while in the case of Beta molecules diffuse along two linear 12-ring channels (0.64x0.76 nm) and one nonlinear 12-ring channel (0.55x0.55 run).
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
225
P U R I F I C A T I O N OF H O R S E R A D I S H PEROXIDASE BY THE USE OF H Y D R O P H O B I C ZEOLITE Y Daniel Klint and Zoltan Blum, D e p a r t m e n t of Inorganic Chemistry 2, Chemical Center, Lund University, P.O.B. 124, S-221 00 Lund, Sweden and H~kan Eriksson, D e p a r t m e n t of Tumor Immunology, The Wallenberg Laboratory, Lund University, P.O.B. 7031, S-220 07 Lund, Sweden. SUMMARY Proteins can be adsorbed on solids i n order to achieve purification and]or concentration. Undesired proteins can thus be removed or proteins can be adsorbed and subsequently eluted. Removal of undesired proteins is exemplified by the purification of horseradish peroxidase from a crude extract by the use of hydrophobic zeolite Y. The zeolite procedure enhanced the specific activity 5 times and provided a yield similar to t h a t which was obtained by the use of s t a n d a r d procedures, (NH4)2SO4 fractionation and ion-exchange chromatography. INTRODUCTION In the purification of proteins from crude extracts, fractionation by precipitation techniques and chromatographic methods are commonly combined. After the initial precipitation, the purification procedure is often continued by chromatographic separation. C h r o m a t o g r a p h i c s e p a r a t i o n methods are divided into gel exclusion chromatography, ion exchange chromatography, affinity chromatography and hydrophobic chromatography. Here we present a much less time consuming procedure by the use of sintered zeolite (1). EXPERIMENTAL SECTION Weighed a m o u n t s of hydrophobic zeolite Y and 20 % binder were blended into a s l u r r y with distilled water. After thorough mixing the slurry was allowed to dry. The solid was then pressed into wafers before it was fired at 800 "C for approximately 48 h. The sintered material was then grinded and sieved, and the 63-125 pan fraction was collected. Purification of horseradish peroxidase (HRP) by the use of zeolites was performed by incubating sintered zeolite, 31.25 mg ml "1, and crude HRP extract (2 mg protein ml "1) on a rocking table at 20 ~
Prior to use the zeolite was degassed and washed with either 10 mM
NaAc pH 4.4, 10 mM NaAc 150 mM NaC1 pH 4.4 or PBS. S i n t e r e d zeolite was removed by pouring the incubation mixture in a column and collecting the filtrate. To compare the results from the purification of peroxidase using zeolite, HRP was purified essentially according to Shannon et al (2). RESULTS AND DISCUSSION Zeolite Y crystallites are about 0.1 - 2 ~m in size which makes column chromatography almost impossible due to the build-up of a high back pressure. Sintered zeolite fractionated between 63 and 125 tim greatly increased the flow properties in column chromatography and separation in batch experiments was simply achieved by filtration. In column chromatography flow rates of at least 3 1 h -1 was obtained using columns with a bed volume of 60 ml. According to powder diffraction analyses the sintering procedure seems to have little or no effect on the crystallinity of the material. Due to size considerations, adsorption of proteins can only take place on the zeolite surface and the SEM images of the sintered particles show very irregular surfaces, having a lot of
226
cavities (Fig. 1). It is clearly seen in fig. 1A that the small crystallites are agglomerated, forming larger particles, although not mechanically stable. Figure 1C shows sintered crystaUites at high magnification, the binder holding them together conveying sufficient mechanical stability to the particles. A result equal to the purification of HRP by ion exchange chromatography was obtained when the crude extract was incubated with zeolite at low pH and low ionic strength. The same result was achieved with both sintered and non-sintered zeolites. The non-sintered material was much faster, 15 minutes compared to 2 h, however, centrifugation is needed in order to remove the zeolite. Non-sintered zeolite can be used on a laboratory scale but when larger volumes are to be processed, the sintered form of the zeolite is preferred since its removal only requres filtration. The low pH and ionic strenght may also induce the formation of aggregates in the crude extract which are to small to be removed by the centrifugation force at 13,000 x g. The sintered zeolite Y, being i n h e r e n t l y micro porous, also displays meso- a n d macroporous structure. These pore structures may fit in size with the protein micro aggregates, which are to small to be pelletated by centrifugation unless ultra centrifugation is used, or the pore s t r u c t u r e may even trigger and increase the formation of these aggregates. F u r t h e r investigations will show if this is the mechanism behind the purification of peroxidase. If this m e c h a n i s m holds true, t h e n a new purification concept can be utilized where sub-optimal precipitation conditions and hydrophobic zeolite Y are combined.
Fig. 1. SEM images of micro-crystalline and sintered zeolite Y. (A) Non-sintered zeolite at low magnification. (B) Sintered zeolite particles fractionated between 63-125 ttm. (C) Fraction of a sintered particle at high magnification.
REFERENCES 1. Klint, D., Arvidsson, P., Blum, Z., and Eriksson, H. Purification of proteins by the use of hydrophobic zeolite Y. Submitted. 2. Shannon, L.M, Kay, E. and Lew, J.Y. (1966) Peroxidase isoenzymes from horseradish roots I. Isolation and physical properties. J. Biol. Chem., 241, 2166 - 2172.
VI. Theory and Modelling
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H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
227
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
MODELLING SORPTION IN ZEOITE NaA WITH M O L E C U L A R DENSITY FUNCTIONAL THEORY Martha C. Mitchell. Paul R. Van Tassel, Alon V. McCormick, and H. Ted Davis Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455
SUMMARY We have used molecular theory and simulation techniques to help elucidate the fundamental physics of adsorption of xenon in zeolite NaA. We have used the simulations to guide development of an approximate density functional theory of this system. INTRODUCTION Fluids confined to pores of molecular dimensions cannot be treated by standard bulk fluid theories. With the introduction of powerful computers, simulations (both Monte Carlo and molecular dynamics) have provided insights into molecular-level events that are occuring in zeolitic systems. However, an area that has received less attention for adsorption in zeolites is that of basic theory. A natural theoretical tool for zeolitic systems, which are strongly inhomogeneous, is density functional theory. In the past molecular density functional theory has focused primarily on systems where there is a one-dimensional symmetry (spheres, cylinders, or planar slit pores). In this paper we apply density functional theory to model a pure fluid confined to zeolitic micropore. First, we discuss grand canonical Monte Carlo simulations of adsorption in zeolite NaA and then we show the results of applying three-dimensional molecular density functional theory to predict adsorption of xenon in NaA. EXPERIMENTAL SECTION Density functional theory is one method for predicting adsorption in threedimensional, confined fluid systems [Percus, 1988]. This approach can be less timeconsuming than experiments. The basic idea is to construct an expression for the free energy of the system. Different forms of density functional theory are distinguished by their treatment of repulsive interactions. Here we apply the Tarazona model of density functional theory [Tarazona and Evans, 1984] to predict adsorption of xenon in the alpha cage of NaA. The Tarazona model has been shown to work well for a pure fluid in a planar slit pore [Vanderlick et al., 1989]. Because of the importance of zeolite-sorbate interactions and the imprtance of the geometry of the zeolite structure in determining these interactions in the xenon/NaA system, we modeled the alpha cage of NaA as a fully three-dimensional system, instead of approximating the alpha cage as a sphere (which would have a one-dimensional symmetry).
228 RESULTS AND DISCUSSION We have used the discoveries of a Monte Carlo simulation study of adsorption of xenon in zeolite NaA to guide our development of a molecular density functional theory model, namely, the recognition of the twelve-site structure of adsorption in the alpha cage at low loadings. We have used this, along with a zeolite-sorbent interaction that is the same as that used for the Monte Carlo simulations, in the construction of a free energy expression for this system. We then minimized this free energy to determine the density distribution for xenon atoms. We have compared our results from the density functional theory model to the results from the simulations. REFERENCES Percus, J.K. (1988) Journal of Statistical Physics, 52, 1157-1178. Tarazona, P.; Evans, R. (1984) Molecular Physics, 52, 847-857. Vanderlick, T.K.; Scriven, L.E.; Davis, H.T. (1989) Journal of Chemical Physics, 90, 24222436.
1-1.~. Karge ancl J. Weitlcamp (Eels.) Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
229
EVALUATION OF WATER ADSORFFION ON DIFFERENT KINDS OF ZEOLITE
T H R O U G H THE MONTE CARLO SIMULATION T. Inui and Y. Tanaka Division of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Sakyo-ku, Kyoto 606-01, Japan
SUMMARY Adsorption of water molecules on various zeolites was simulated by the Monte Carlo (MC) method. Water molecules were adsorbed surrounding the counter metal cation in zeolites such as Na-ZSM-5 and Fe-ZSM-5 even at a low H 2 0 pressure, while acid sites of protonated zeolites such as H-ZSM-5 and H-Fesilicate were scarcely covered with H 2 0 molecules. These results are consistent with the high tolerance of metaUosilicate catalysts to water vapor such as H-Cosilicate in the N O conversion reaction.
INTRODUCTION Removal of NO in exhaust gases from diesel engines and other lean-burn combustion facilities has been one of the most important but difficult subjects in catalytic chemistry, because 02 in the exhaust gas strongly interferes with N O conversion on the catalyst. In our previous study, it was found that Cu-incorporated zeolite [1] showed a high performance for NO decomposition in the absence of water vapor. However, under practical conditions, the catalyst must have durability against water vapor. For this purpose, H-Co-silicate [2] was adopted and it exerted a high performance in NO conversion even in the presence of a high concentration (10%) of water vapor. Water adsorption properties of zeolitic catalysts are usually m e a s u r e d by an infrared analysis or a nuclear magnetic resonance method; however, the details of the microscopic states of water molecules adsorbed has remained ambiguous. In this study, the microstructure of water molecules was simulated by computational chemistry methods to understand the water resisting property of metallosilicates. EXPERIMENTAL METHOD
Four kinds of MFI-type silicates and NaA zeolites were treated for calculation. Four silicon atoms of the T12 sites in the unit cell of MFI-type silicate, which are the most probable for the evaluation of lowest potential, were replaced by A1 or Fe atoms. Counterpart Na cations for substituted elements in those MFI-type
230 metaUosilicates were exchanged by H, or Fe. In the case of NaA zeolite, half of the silicon atoms were replaced by AI. The positions of exchanged ions were optimized by energy minimization. The charges of the zeolites and H20 molecules were calculated with the charge equilibration method before simulation of H20 adsorption on zeolites. The Monte Carlo simulation [3] was carried out for the five zeolites, Na-ZSM-5, Fe-ZSM-5, H-ZSM-5, H-Fe-silicate and NaA using CERIUS software which is a computational instrument for material research offered by Molecular Simulation Inc.. One cycle of a fixed pressure (grand canonical) algorithm consisted of creation, removal, translation and rotation of a molecule. The amount of H 2 0 adsorbed was counted after this cycle, and the cycle was repeated 250,000 times, under a condition of 300 K and a pressure range from 0.1k to 20kPa by means of graphics super computer TITAN750V (Stardent Inc.). RESULTS AND DISCUSSION Figure 1 shows the geometric distribution of H20 molecules adsorbed in the unit cell of Na-ZSM-5 under 0.1kPa depicted as A-C coordinate, and areas composed of the dots are proportional to the number of adsorbed H20 molecules. In this case, H20 molecules adsorbed surrounding the Na cations. Each ion was covered by two or three H20 molecules. In the case of Fe-ZSM-5, the result was quite similar although the total amount of adsorbed H20 molecules was smaller than that on Na-ZSM-5. The adsorbed amounts of water on H-ZSM-5 (i.e. H-Al-silicate) and H-Fe-silicate were much smaller than those on Na-ZSM-5 and Fe-ZSM-5, and the acid sites on those protonated metallosilicates were not covered by H 2 0 molecules. Such metaUosilicates, in which transition metal elements are stabilized by incorporation in the framework of the silicate, have high durability against H 2 0 vapor as demonstrated by H-Co-silicate [2]. Figure 2 shows the adsorption isotherms of H20 on NaY, Na-ZSM-5, and H-ZSM5. The isotherms of H20 for NaA and Na-ZSM-5 were of the Freundlich type. On the other hand, the isotherm on H-ZSM-5 obeyed the B.E.T. type. This is rationally understood since the interaction between H20 and protons is weaker than the mutual interaction between water molecules, which would occur in NaZSM-5. At higher water pressure, the adsorbed amount increased due to the condensation of water molecules.
231
] ~176 A
1 =<1
0.25 f
O t~
Q.P
._r
8
(3
0 2 4 6 8 10 12 14 16 18 20 A coordinate (A) Figure 1 Distribution of H20 molecules adsorbed on Na-ZSM-5 at 3 0 0 K under 0.1 kPa. o:the position of AI in the framework .,:the position of counter cation (Na+)
~0
0. 5i
0"10f
E E 0"05t~ tO 0 4)~ G~"
:=:
I
,
,
,
0 2 4 6 8 10 12 14 16 18 20 Pressure (kPa) Figure 2 Adsorption isotherms of H20 molecules at 300K on NaA(o), Na-ZSM-5(=). and H-ZSM-5(=).
REFERENCES [1] T. Inui, S. Kojo, M. Shibata, T. Yoshida and S. Iwamoto, Stud. Surf. 5ci. Catal., 69, 355 (1991). [2] T. Inui, T. Hirabayashi and 5. Iwamoto, Catal. Left., under contribution. [3] T. Inui, T. Tanaka, K. Matsuba, N. Goto, Y. Nakazaki and M. Inoue, Preprints 9th Annual Meeting of Zeolite Association of Japan, 1993, p. 52.
H.G. Karge and J. Weitkarnp (Eds.) 232
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
MODELLING STRUCTURAL AND DYNAMICAL PROPERTIES OF SILICA SODALITES AND COMPARISON TO THE EXPERIMENT Andreas M. Schneider, Jtirgen Felsche and Peter Behrens Fakult~t fOr Chemie, Universit~t Konstanz, D-78434 Konstanz, Germany SUMMARY The structures of known and of one hypothetical silica sodalite were minimized and the dynamics of the molecular motion of the guest species were investigated. INTRODUCTION The interaction of organic and inorganic matter is of great importance not only to catalytic processes on heteregeneous catalysts as zeolites, but also to the cooperative structuring of both components leading to the formation of well-ordered micro- and mesoporous solids and biominerals. In two aspects, silica sodalites serve as model substances for the study of this interaction: Ionic interactions between the SiO 2 host framework and the organic guest molecules M are excluded, as both are neutral, and the sodalite structure is a simple structure type built up from only one kind of cage, the sodalite cage. Five different molecules M are known to template the crystallization of silica sodalites M2[SiO6] 2. These are 1,3,5-trioxane (TR) [1], 1,2-dioxolane (DI) [2], ethylene glycol (EG) [3], ethanole amine (EA) [4] and ethylene diamine (ED) [4]. Although these molecules are embedded in the same silica matrix with sodalite structure, their structural and dynamical properties differ greatly. Molecular Modelling and Molecular Dynamics methods were used to study the structural and dynamical behaviour of the different sodalites. Here, we present our results for TR silica sodalite (TRS-SOD) and EA silica sodalite (EAS-SOD). Furthermore, the minimum energy conformation of tetrahydrofurane silica sodalite (THFS-SOD), an unknown compound, was calculated. EXPERIMENTAL Calculations were performed on a Silicon Graphics Iris Indigo Powder Station using the BIOSYM Catalysis and Sorption Software and the DISCOVER cff91_czeo forcefield. Starting models were created from one sodalite cage (representing the framework geometry as determined by structure refinements and with the dangling Si-O bonds saturated by H atoms) and the molecule under investigation, and were then minimized. To calculate the dynamical behaviour of TRS-SOD and EAS-SOD, their lowest energy structures were extended to infinite P1 structures. Dynamic calculations were performed over a time period of 10000 fs.
233 RESULTS AND DISCUSSION The minimization of TRS-SOD in space group l;*3m revealed eight local minima with rather small energy differences. The lowest minimum corresponds to the structure as found by single-crystal x-ray and powder neutron diffraction [5]. It features specific interactions between the trioxane molecule and the silica host which let this compound appear as a prototype system for molecular recognition in solid-state compounds [5]. The trajectory of EAS-SOD shows more minima than Fig. 1: Lowest energy conformation for that of TRS-SOD, although the minimization was perfor- ethanol amine in a sodalite cage with an intramolecular O-H--NH2hydrogenbond. med in space group Im3m, a supergroup of l;~3m. This result is not surprising, as EA has more nearly equivalent conformations than the TR molecule. Correspondingly, the energy difference between neighbouring minima is smaller than in the case of TRS-SOD. This, together with the fact that these minima differ strongly in atomic positions, explains the difficulties in locating the template molecule in a Rietveld refinement of x-ray diffraction data [4]. The minimum energy structure of EA in silica sodalite is similar to that calculated for EA in the gas phase [6], featuring in both cases a gauche conformation of the substituents at the C atoms, thus allowing for an intramolecular hydrogen bond (Fig. 1). Minimization of THF in a sodalite cage shows that the hypothetical THFS-SOD in principle is as stable as the other silica sodalites. In hydrothermal syntheses, however, THF directs the formation of the dodecasil-3C structure. Molecular dynamics calculations show that the TR molecule possesses four preferred orientations in a sodalite cage which it occupies for comparably long times. These results are in line with the results of diffraction and NMR studies [5]. The EA molecule, on the contrary, possesses more preferred orientations and moves more frequently from one orientation to another than the TR molecule does. Part of this work was performed during a stay of A.M.S. (sponsored by Fonds der Chemischen Industrie) and P.B. (sponsored by the DFG, Be1664/1-1) at the University of California, Santa Barbara, in the group of Galen Stucky. We thank him and his group for their kind hospitality and the possibility to use their computer equipment. This work was also supported by the DFG (Fe72/17-1). REFERENCES [11 J. Keijsper et al., in "Zeolites: Facts, Figures, Future", Elsevier 1989, p. 237. [21 G. van de Goor, P. Behrens, J. Felsche, Microporous Mater., in the press. [31 D.M. Bibby, M.P. Dale, Nature 317 (1985) 157; D.M. Bibby et al., in MZeolite Synthesis", ACS Symposium Series 1989, p. 209. [4] C. Braunbarth, G. van de Goor, A.M. Schneider, J. Felsche, P. Behrens, in prep. [51 P. Behrens et al., VIIIth Int. Symp. on Inclusion and Molec. Recogn., Ottawa 1994. [61 A.-M. Kelterer, M. Ramek, J. Molec. Str. (Theochem) 232 (1991) 189.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
234
COMPUTER MODELLING OF IRON-CONTAINING ZEOLITES R.G. Bell, D.W. Lewis, and C.R.A. Catlow Davy Faraday Research Laboratory, The Royal Institution of Great Britain, 21 Albemarle Street, London W l X 4BS, UK.
SUMMARY The substitution of Fe(lll) onto tetrahedral sites in silicalite to form Fe-ZSM-5 has been investigated by computer simulation techniques. At low iron content, the incorporation energies of Fe(lll) were found to be endothermic and there is an associated increase in unit cell volume. There was no evidence of strong interaction between different Fe sites and it is concluded that the maximum framework iron content is determined by the entropically-driven solution limit.
INTRODUCTION Fe-ZSM-5, an isomorph of silicalite, is one of the best-documented Fe(lll)-substituted zeolites, and has been shown to be an active catalyst for the methanol and hydrocarbon transformation reaction and for various oxidative reactions, such as the dehydrogenation of propane1. From numerous characterisation studies on Fe-ZSM-5 it is generally accepted that there is a maximum amount of Fe which may be included in the zeolite framework at T-atom sites, this maximum occurring at roughly the composition Si/Fe=25 (i.e. circa 4 irons per 96 T-atom unit cell). Any attempt to incorporate further iron during synthesis is believed to result in the formation of extraframework iron oxide species and of iron oxide particles on the zeolite surface. As part of our general interest in iron-containing zeolites we are carrying out a computer simulation study of the incorporation of Fe 3+ into the framework of silicalite, initially to determine whether there is any thermodynamic basis for the observed maximum Fe content.
METHODOLOGY Lattice energy minimisation calculation were carried out using the program THBREL, which permits the optimisation of all atomic positions and cell dimensions of a periodic system to a minimum energy configuration, using an ionic model with Borntype interatomic potentials. (Fe,Si)-ZSM-5 was modelled by introducing increasing amounts of Fe 3+ into the siliceous framework, all iron being substituted for silicon on tetrahedral sites. The electrical neutrality of the unit cell was maintained by protonating a framework oxygen adjacent to each Fe site, thus simulating an acidic ZSM-5-type zeolite which corresponds to a calcined and evacuated sample. At each composition random distributions of Fe, with a neighbouring OH, were generated, with the constraint that irons should not occupy neighbouring tetrahedral sites (i.e. LSwenstein's rule is obeyed).
235
RESULTS AND DISCUSSION
A range of Fe/Si compositions was studied. For low Fe concentrations (up to 6 atoms per unit cell), energies of solution of iron into the framework have been calculated and are given in table 1. Table 1. Solution Energies of Fe 3+ in the ZSM-5 framework Reaction 95/96Si960192 94/95Si950191(FeOH) 93/94Si940190(FeOH)2 92/93Si930189(FeOH)3 91/92Si920188(FeOH)4 90/91Si~)lO1~7(FeOH) 5
AE/kJmol-1 + 48/96Fe203 + 48/96H20 + 48/95Fe20 3 + 48/95H20 + 48/94Fe20 3 + 48/94H20 + 48/93Fe20 3 + 48/93H20 + 48/92Fe20 3 + 48/92H20 + 48/91Fe20:~ + 48/91H20
Si950191(FeOH ) Si940190(FeOH)2 --~ Si930189(FeOH)3 Si920188(FeOH)4 ---> Si910187(FeOH)5 SigoO 186(FeO H).~
+28 +14 +47 +82 +18 + 56
The local geometry of the Fe sites was examined in a selection of the minimised structures. Fe-O(H) bond distances were found to lie in the range 1.98-2.09A, with the other Fe-O(non-protonated) distances being in the range 1.74-1.80A. The average Fe-O distance was 1.83A, which corresponds closely with experiment 2. FeSi distances were also in good agreement with observed values. Unit cell volume was found to increase roughly uniformly with Fe content. It may be seen from table 1 that the solution energies are endothermic, but without any marked non-linear variation with Fe concentration. Moreover, further calculations, up to an Fe 3+ content of 32 per unit cell, revealed similar behaviour, it is therefore apparent that the Fe sites do not interact with one another, even at quite high concentrations. The fact that the incorporation process is always endothermic, however, suggests that a solution limit will be reached. ACKNOWLEDGEMENT We thank the Gas Research Institute for support, and Dr R.W. Grimes for helpful
discussions. REFERENCES
[1 ]. P. Ratnasami & R. Kumar, Catalysis Today (1991 ), 9, 329, and references therein. [2]. S.A. Axon, K.K. Fox, S.W. Carr & J. Klinowski, Chem. Phys. Lett. (1992), 189, 1.
Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
THEORETICAL INVESTIGATION OF THE THERMAL DECOMPOSITION OF NEOPENTANE NEAR Sill CENTERS OF ZEOLITE Y O. Zakharieva 1 , M. Grodzicki 2 and H. FOrster3 1University of Sofia, Physical Faculty, Sofia 1126, Bulgaria 2Medical University of Ls Institute of Physics, 23538 LObeck, Germany 3University of Hamburg, Institute of Physical Chemistry, 20146 Hamburg, Germany Summary
Model calculations have been performed for the thermal decomposition of neopentane near the Sill center of zeolite Y. Assuming a specific reaction coordinate, the reaction dynamics has been explored. Introduction The reaction pathway is interpreted in the literature mostly qualitatively, calculations of potential surfaces as a funtion of all internal degrees of freedom are often on a semiempirical level. Using the local density approximation results for calculated energy barriers are comparable to those of ab initio calculations and simultaneously the computer time is 2 to 4 orders of magnitude lower. In the present calculations the reaction of neopentane conversion on Br~nsted acid sites of zeolite Y is investigated using the SCC-Xc~ method, based on the local density approximation. Procedure The cluster modeling the Sill center of zeolite Y contains 24 atoms. It consists of the atoms of the 4-ring at the top of Fig.1 indicated by numbers, i.e. sites 10, 11 and 17 occupied by Si, site 16 by AI, sites 69 and 72 by 0(3) and sites 73 and 76 by 0(4), as well as the O(1) and 0(2) atoms, lying outside the ring. In order to improve convergency the cluster was terminated by H atoms. The center of the coordinate system is H25 (Fig. 2), placed at the position of the cation center on Sill and connected with 0(4) on site 73. This proton simulates the Br~nsted acid center. As can be taken from Fig. 2 the neopentane molecule approaches the cluster in the direction of the Cl-C 2 bond. Geometries for the gasphase analogue H+-CMe4 have been optimized for this reaction coordinate by ab initio methods with STO-3G and 3-21G basis sets. The potential surface including the zeolite cluster has been computed applying the SCC-Xo~ method. Results and Discussion Charges of the atoms: (i) The largest changes of effective atomic charges take place with 0(4) on site 73, where the Brensted acid center is simulated. This is also re-
237
flected in the diminishing of the positive charges of the adjacent Si and AI atoms on sites 17 and 16 in the direction of the transition complex. (ii) A small weakening of the negative charges of the other oxygens in the ring is obtained. (iii) The positive charge of H25 is reduced. This charge is grasped from C 1 of the neopentane. The charge of C1 in the direction of the transition complex approaches the charge of the carbon in the final reaction product tert-butyl ion. A part from the positive H25 charge is also accepted from the geometrically favourably orientated H atoms (Hlo, H12, H15) of neopentane. (iv) The negative charge of C2 increases and comes close to that of the carbon in the final product methane. Bond order matrix: (i) Approaching the transition state we obtain a strong diminishing of the bond order between 0(4) on site 73 and H25. Simultaneously the bonds of this oxygen with AI and Si on sites 16 and17 are strengthened. (ii) The Ai atom also interacts with H25. With the approach of H25 to neopentane this attractive interaction gradually diminishes. (iii) The changes are strongest in the H25-C2 bond. The electron density increases from 0.0 to 0.196 in the transition state. (iv) With decreasing distance between neopentane and the cluster a small attractive interaction is obtained between H25 and the H6, H7 and H 8 atoms of the attacked methyl group. With approaching the transition state the corresponding changes in the HOMO and LUMO are obtained. Conclusions A first insight into the reaction dynamics of the thermal decomposition of neopentane near the Sill center of zeolite Y has been obtained. The changes of the molecular charge density at different points of the reaction pathway are presented. These calculations are of interest as being a first quantitative investigation of the reaction dynamics for complex surface reactions. H9
\ '~
..'7 / 1425
Fig. 1. Numbering of atomic sites of the cubooctahedron.
A4
I-I14/
H6 H7
Fig. 2. Reaction coordinate of the system H§ + neopentane.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
238
MODELLING OF HIGH PRESSURE PROPENE OLIGOMERISATION USING SKELETAL GROUPS Sarah J Sealy, Duncan M Fraser, Cyril T O'Connor Catalysis Research Unit, University of Cape Town, Private Bag, Rondebosch, 7700, South Africa
SUMMARY This recent research report presents a preliminary model for propene oligomerisation using skeletal groups. The use of skeletal groups is justified because even at low conversions equilibrium with respect to the double bonds within each group is reached. This model is based on hydrocarbon mechanisms, proposed by Jacobs and Martens, which use protonated cylopropane intermediates. INTRODUCTION Oligomerisation reactions are highly complex and the identification of all individual reaction products is extremely difficult. For example, there are 17 Ce olefin isomers and over 100 C8 olefin isomers. Therefore the models developed to date are fairly simple and involve lumping all product isomers of the same carbon number together. Cracking reactions are generally ignored. The aim of this study is to develop a model for propene oligomerisation. At present, only oligomerisation
reactions
are being
considered.
Other
reactions
such
as
cracking
and
disproportionation may subsequently be included.
EXPERIMENTAL Pure propene was oligomerised in a tubular, packed bed reactor at 5 MPa and 250~
and two
levels of conversion namely, 5% and 50%. H-ZSM-5 with a Si/AI ratio of 35 was used as a catalyst.
The skeletal structures of the reaction products were determined using a gas
chromatograph with online hydrogenation.
RESULTS AND DISCUSSION Equilibrium concentrations for the hexene isomers were predicted using data from various sources. Comparisons between low and high conversion results with equilibrium predictions indicate that at low conversion the hexene isomers are not at equilibrium with respect to their skeletal structure, but that they were at equilibrium with respect to double bond isomerisation within each skeletal structure. At 50% conversion the hexene isomers were at equilibrium with respect to their skeletal structure. (Sealy et al) Because the product spectrum from propene oligomerisation is complex, all the individual reaction steps cannot be included in the model and hence some degree of simplification is required. Based on the above conclusions regarding the product spectrum of propene oligomerisation, all isomers of the same carbon skeleton can be lumped together into five groups. This is an improvement on previous models which lumped according to carbon number only. Table 1 shows the relative amounts of the hexene carbon skeletons at 5 and 50% conversion are presented as well as their approach to equilibrium at 5% conversion. Because detailed information regarding the C6 dimer product spectrum has already been obtained, a preliminary mechanism for the dimerisation step can therefore be formulated. This mechanism is based on the substituted protonated cyclopropane mechanism of Jacobs and Martens (1990). In
239 this mechanism it is proposed that the different hexene isomers interconvert via protonated cyicopropane intermediates. The formation of the dimers can thus be summarised in the diagram below. Table 1
Carbon Skeleton
50% Cony. (Equilibrium)
5% Cony.
Approach to Equilibrium - 5% Conv.
3,3-dimethyl-Butane
-
-
-
2,3-dimethyI-Butane
15.4
7.97
52 %
2-methyI-Pentane
42.2
59.6
141%
31.7
24.3
76%
10.7
8.16
76%
3-methyI-Pentane
.
Hexane
.
.
.
3- methyl-pentane group
T~ Cs- + Cs-
~
2-methyl-pentane group ~ 2,3-dimethyl- or 3,3-dimethyl-butane T~ group group hexane group
The primary product is thus proposed to be the 2-methyl-pentane group. This primary product then isomerises to the other isomer groups. Both the 3-methyl-pentane group and hexane group have the same cyicopropane intermediate. However, the 3-methyl-pentane group appears to form about three times faster than the hexane group. This can be seen from the table above where at both conversion levels the amount of 3-methyl-pentane is always triple that of hexane. The above mechanism is in the process of being verified by separately feeding two of the hexene isomers namely, 4-methyl-l-pentene and 1-hexene. These isomers are then allowed to isomerise at the same reaction conditions as the propene oligomerisation. Preliminary experimental data appear to confirm the above mechanism. The mechanism for the trimerisation step is currently also being studied. The C~ skeletal structures observed at 5% conversion are the following : 3-methyl-octane, 4-methyl-octane, 2methyl-octane, 2,5-dimethyl-heptane, 2,4-dimethyl-heptane, 2,3-dimethyl-heptane, 3,4-dimethylheptane and nonane. The nonene isomers are clearly influenced by shape selectivity since the more bulky isomers do not appear in the product spectrum. The model that is being developed will have to take into account this shape selective effect. REFERENCES Martens, J.A. and Jacobs, P.A., 1990, in "Theoretical Aspects of Heterogeneous Catalysis" (J.B.Moffat, Ed), pp 52-109. Van Nostrand Reinhold Catalysis Series Sealy, S.J., MSIler, K.P., Fraser, D.M., O'Connor, C,T, "Equilibrium Considerations in the Modelling of'Propene Oligomerisation", accepted for publication, Chem. Eng. Sci.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
240
INVESTIGATION OF THE DYNAMICS TRANSITION-STATE THEORY
OF BENZENE
IN SILICALITE
USING
Randall Q. Snurr, Alexis T. Bell, and Doros N. Theodorou Department of Chemical Engineering and Center for Advanced Materials, Lawrence Berkeley Laboratory University of California, Berkeley, CA 94720 USA SUMMARY Transition-state theory has been applied to predict the self-diffusivity of benzene in silicalite. Starting with an atomistic model of the system, adsorption sites were identified and rate constants were calculated for transitions between the sites. The rate constants were used in a dynamic Monte Carlo simulation to obtain the selfdiffusivity. Details of the molecular motion were investigated.
INTRODUCTION There is much interest in understanding and predicting the transport mechanisms of aromatics in ZSM-5 zeolites, such as silicalite, due to the shape-selectivity displayed by various catalytic processes involving such systems. Molecular modeling techniques that are firmly based on statistical mechanics and validated against existing experimental measurements may be useful in elucidating the details of diffusion in zeolites and can be used as a predictive tool. Molecular dynamics (MD) simulation is a common technique for studying the diffusion of small molecules in zeolites. For the case of aromatics in silicalite, however, MD is unable to predict the diffusivity because it cannot access the long time scales that characterize diffusive motion in these systems. A more appropriate technique is transition-state theory (TST).
A variety of experimental and
simulation evidence indicate that aromatics in silicalite are localized in well-defined adsorption sites and that they diffuse by infrequent hops from site to site. The rates of these hops are amenable to TST analysis. CALCULATIONS
The atomistic model used here is exactly the same as in our
calculations of adsorption thermodynamics of benzene in silicalite. 1 Atomic sites interact via a Lennard-Jones plus Coulomb potential. In the TST picture, molecules hop from one potential energy minimum to another following a diffusion path that goes over the saddle point (or transition state).
All minima and saddle points of the potential energy
241
hypersurface are identified. The intrinsic reaction coordinate approach of Fukui 2 is then used to construct the diffusion paths between minima. Note that each such path is in 6 dimensions, including both translational and rotational motion of the benzene molecule. First-order rate constants for the hops are computed using the harmonic approximation. The rate constants of hops at a given temperature are found to span many orders of magnitude. States separated by low energy barriers (and therefore mutually accessible by "fast" motions) are lumped together to form macrostates, and effective rate constants for the slower motions between macrostates are then calculated. Using the macrostate picture, the diffusivity is computed from a dynamic Monte Carlo simulation. 3 RESULTS AND DISCUSSION The minima in a unit cell are found to group together naturally into 12 macrostates: 4 straight channel states, 4 sinusoidal channel states, and 4 channel intersection states. Transitions between minima within a macrostate are orders of magnitude faster than transitions between macrostates, allowing the minima within a given macrostate to be viewed as being in equilibrium with one another. The fastest motions are found to be relatively insensitive to temperature, while the rate constants for transitions
between
macrostates are strongly temperature
dependent.
These
observations agree with experimental studies of this system. 4 Low-occupancy diffusion was studied between 200 and 500K. Benzene is seen to diffuse most readily in the straight channels, but diffusion in the sinusoidal channels is not negligible. An activation energy of 36.7 kJ/mol was calculated. This is significantly higher than the experimental value of about 27 kJ/mol 4 and leads to predicted diffusivities that are 1 to 2 orders of magnitude smaller than the experimental values. The high activation energy is most likely due to our assumption of a rigid zeolite structure. Future work should incorporate zeolite flexibility into the model. Visualizations of the diffusion paths will be presented. REFERENCES 1 Snurr, R.Q.; Bell, A.To; Theodorou, D.N.J.Phys.Chem. 1993, 97, 13742-13752. 2 Fukui, K. Acc.Chem.Res. 1981, 14, 363-368. a June, R.L.; Bell, A.T.; Theodorou, D.N.J.Phys.Chem. 1991, 95, 8866-8878. 4 K&rger, J.; Ruthven, D.M. Diffusion in Zeolites and Other Microporous Solid~, WileyInterscience: New York, 1992.
242
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 r 1995 Elsevier Science B.V. All rights reserved.
AB INITIO STUDY OF THE INTERACTION OF METHANOL WITH BRONSTED ACID SITES OF ZEOLITES Frank Haase and Joachim Sauer Max-Planck-Gesellschaft, Quantum Chemistry Group at the Humboldt University Berlin Js 10/11, D - 10117 Berlin, Germany SUMMARY The adsorption of methanol on cluster models of Brcnsted acid sites of zeolite catalysts has been investigated by ab initio quantum chemical methods. It is found that the ion-pair complex is not a minimum structure, but a transition structure. Its energy, however, is only a few kJ/mol above that of the neutral complex. Based on the predicted 1H MAS-NMR chemical shifts the formation of the ion-pair structure is unlikely. The calculated vibrational frequencies support neither an ion-pair adsorption complex nor the interpretation in terms of an A-B-C triplet of pseudobands for the neutral complex. INTRODUCTION The adsorption of methanol on Brcnsted sites of zeolites was the objective of a variety of theoretical and experimental studies of the last years. Our previous calculations suggested two possible structures of the adsorption complex which is formed upon loading the zeolite with methanol: a neutral hydrogen-bonded complex (NC) of the methanol molecule with the bridging hydroxyl group and an ion-pair complex (IP) which consists of a methoxonium ion coordinated via two protons onto the negatively charged framework site. Though IR and MAS NMR spectroscopy have frequently been used in studying such interactions an unambigous assignment of vibrational bands or NMR signals proved difficult. In particular, it has not become clear which of these two possible adsorption structures is representative of the real adsorption complex or whether both structures are present. The present ab-initio study aims at providing further theoretical evidence to facilitate the interpretation of experimentally measured IR and 1H MAS-NMK spectra. We present a systematic investigation of the adsorption structures of methanol with zeolite clusters of increasing size. The structures of all model complexes were fully optimized not only on the SCF level but also including correlation effects by the second order Mr perturbation theory (MP2). These equilibrium structures were then used to evaluate the binding energies, the vibrational spectra in harmonic approximation, and the 1H NMR chemical shifts. MODELS AND CALCULATIONS All SCF and MP2 structure optimizations, the evaluation of the harmonic force constants, and calculation of the nuclear shielding constants were performed with the TURBOMOLE program package. Three models of increasing size were adopted for the bridging hydroxyl site. The first and smallest- HO(H)Al(OH)3 1 - consist simply of a A104 tetrahedron saturated with hydrogen atoms and the bridging hydroxyl proton. In the second cluster- H3Si0(H)AI(OH)20SiH3 2 - the two oxygen atoms acting as adsorption sites are bound to Sill3 groups, i.e. there is a partial (half) second coordination sphere. Finally, the third cluster- H3Si0(H)AI(OSiH3)3 3- contains a complete second coordination sphere of four silicon atoms. In Addition to clusters 1 - 3 which are not specific for a particular framework site we designed a cluster which shows structural elements typical of the faujasite lattice. It consists of four condensed rings of T-atoms. Two 4-rings belong
243 to the hexagonal prism and, one 4-ring and one 6-ring belong to the sodalite cage. The aluminum as the central atom is part of all four rings. The dangling bonds of the silicon atoms are saturated with hydrogen atoms. RESULTS AND DISCUSSION Starting from the equilibrium structure of the ion-pair complex with Cs symmetry no further minimum with C1 symmetry was found. The proton was detracted from the methoxonium ion and was transferred to the bridging oxygen of the zeolite cluster yielding the neutral H-bonded complex. This was also the case for the complex with the large faujasite cluster. As result of the inclusion of the correlation energy the H-bonds between the adsorbed molecule and the zeolite model become shorter. For methanol adsorbed on H-rho a shift in the range of 10 to 12 ppm was measured for a loading of one methanol molecule per acid site. While the calculated chemical shifts of the SCF optimized structures of the IP complexes exceed the observed shifts by about 7-5 ppm the values obtained for the N C complexs are too small by about the same amount. In the present study the calculation of the xH chemical shifts was also performed for MP2 optimized adsorption structures. For both types of complexes a considerable increase of the chemical shift is observed. This is the result of the higher deshielding of the protons in the intermolecular H-bonds which are significantly shorter in the MP2 optimized structures. In contrast to the data of our recent study which were not conclusive the 1H NMR shifts of the MP2 optimized structures now rule out the ion-pair complex. Furthermore the best available value of 10.75 ppm for the neutral complex fits well in range of the observed shift of methanol adsorbed on H-rho. The IR bands of adsorbed methanol observed at 3545, 2900, 2440 and 1670 cm -1 are subject of conflicting interpretations. The first assignment assumes the formation of a methoxonium ion and assignes the bands at 2900 and 2440 cm -1 to the antisymmetric and symmetric OH stretching vibrations and the band at 1670 cm -1 to the HOH bending vibration of the oxonium group. The interpretation of the band at 3545 cm -~ is so far not clear. Our calculations of the harmonic vibrational frequencies (Cs point group) shows that the ion-pair structure is not a local minimum but a transition structure (1 imaginary frequency for clusters 1 and 2) or a saddle point of higher order (2 imaginary frequencies for cluster 3). From the predicted vibrational frequencies the following points arise: (i) Even for the largest cluster the frequencies of the symmetric and asymmetric stretching vibrations of the OH + moiety are too small. (ii) The observed band at 1687 cm -~ fits the calculated band at 1670 cm -1 of the HOH deformation of the OH + group of the methoxonium ion. (iii) No vibrations are calculated to lie in the region of about 3500 cm -1 to explain the band observed at 3545 cm -1 . The basis of the second interpretation is a neutral surface complex. The neutral complexes of all clusters posses no imaginary frequencies and hence represent local minima on the potential energy surface. From the calculated SCF vibrational frequencies two conclusions can be drawn: (i) The calculated shifts of the OH stretching vibrations of the adsorption complex compared to the free hydroxyl groups are by far too small to support the recent interpretation in terms of an A-B-C triplet of pseudo-bands. (ii) The band observed at 3545 cm -1 can be assigned to the OH stretch of methanol weakly interacting with a lattice oxygen atom.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
244
AB INITIO DERIVED SHELL MODEL POTENTIAL FOR MODELLING OF ZEOLITES K.-P. Schr•der and J. Sauer Max Planck Society, Quantum Chemistry Group at the Humboldt University, J~igerstr. 10/11, D-10117 Berlin, Germany SUMMARY A new parametrization of the classical shell model potential for the simulation of alumimumofree zeolite structures are presented. The parameters have been derived from ab initio calculations on molecular models. Observed and calculated structures of dense and microporous silica are in close agreement. INTRODUCTION A complete structural model of an acidic zeolite catalyst including details of the active site cannot be derived from observed data. Theoretical structure determination using periodic quantum chemical techniques is not feasible because of the enormous size of zeolite unit cells. The use of lattice energy minimizations employing classical potential functions is limited by the lack of reliable potential function parameters [1]. A known way out of this dilemma is deriving the potential parameters from ab initio calculations on relatively small molecules and to adjust only very few scaling factors to experimental results, e.g. [2]. There are two competing potential expressions that can be used for this purpose: (1) molecular mechanics force fields describing the interaction of the atoms in terms of bond distances, bond angles, torsion angles etc. and (2) ionic pair potentials as a combination of long range electrostatic and short-range repulsive contributions. In a preceding work [3] a potential of type (1) was successfully derived. Here we report on an ionic pair potential with parameters adjusted to the same quantum chemical data base. Thus, we are able to study the influence of the form of the potential on the quality of the structure predictions. As a first step pure silica modifications are considered. CALCULATIONS Quantum chemical calculations on typical structure elements of zeolites like four, five, and six membered rings were performed using a DZP/TZP basis set (see ref. [3] for details). The minimum structures and force constants were fitted to a shell model potential, which includes a term that accounts for polarizability of oxygen ions. In addition, the need of a O-Si-O bond angle term was tested. RESULTS AND DISCUSSION Already a simple potential representation, which consists only of the electrostatic (full charges), the oxygen core-shell (two adjusted parameters) and an exponential Si-O repulsion term (two adjusted parameters), shows a very good agreement with observed structures of dense and microporous SiO2 with an averaged deviation in unit cell lengths of about 0.5 % (Tables 1 and 2). The shell model potential seems to describe silica structures more realistically than the molecular mechanics potential, although the number of its adjustable parameters is clearly smaller. Work on a potential for aluminosilicates including Bronsted sites is in progress.
245 Table 1: Cell parameters of microporous and dense SiO2 modifications (in pm and degrees) modification
Jackson & Catlow [4]
van Beest [5]
Hill [3]
this work
obsd.
faujasite
A=B=C
2423
2478
2470
2421
2426
sodalite
A=B=C
882
899
903
879
883
theta-1
A B C
1382 1739 500
1392 1756 510
1428 1797 528
1388 1746 505
1386 1742 504
mordenite
A B C
1802 2004 743
1846 2049 760
1849 2068 762
1798 2013 745
1810 2038 749
A B C o~
1998 1974 1332 90.8
2037 2033 1368 90
2059 2048 1373 90
2006 1984 1340 90
2011 1988 1337
rho
A=B=C
1477
1511
1509
1475
1485
o~-quartz
A=B C
484 540
494 545
.a
494 544
491 540
A=B C
497 701
492 660
.a
502 713
498 695
A B C 13
703 1229 712 122.5
712 1249 727 120.5
729 1273 746 120.6
713 1232 715 121.1
714 1237 7t7 120.3-
ZSM-5
(x-cristobalite
coesite
90.7
a the high-temperature ~phases are obtained
Table 2" Bond lengths and bond angles in aluminum-free faujasite (in pm and degrees) rs~o(1) rs~2) rs~o(3) rs~o(4)
Hill [3] 162.6 161.7 162.0 162.1
this work 161.7 159.7 160.6 160.9
obsd.[6] 160.7 159.7 160.4 161.4
<SiO(1)Si <SiO(2)Si <SiO(3)Si <SiO(4)Si
Hill [3] 138 157 153 144
this work 137 149 147 140
obsd.[6] 138 149 146 141
ACKNOWLEDGMENT
This
work
has
been
supported
by the
Deutsche
Forschungsgemeinschaft
and
Volkswagenstiftung. REFERENCES [1] [2] [3] [4] [5] [6]
K.-P. Schr0der, J. Sauer, M. Leslie, C. R .A. Catlow, and J. M. Thomas, Chem. Phys. Letters 188 (1992) 320. G.J. Kramer, A. J. M. de Man, and R. A. van Santen, J. Amer. Chem. Soc., 113 (1991) 6435. J.-R. Hill and J. Sauer, J. Phys. Chem., 98 (1994) 98. R.A. Jackson and C.R.A. Catlow, Mol. Simul., 1 (1988) 207. B.W.H. van Beest, G.J. Kramer, and R.A. van Santen, Phys. Rev. Lett. 61 (1990) 1955. J.A. Hriljac, M. M. Eddy, A. K. Cheetham, J. A. Donohue, and G. J. Ray, J. Solid State Chem., 106 (1993) 66.
the
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
246
A COMPUTER SIMULATION OF SHAPE SELECTIVE CATALYSIS ON ZEOLITES E. Klemm, H. Seller and G. Emig Institute of Technical Chemistry I Egerlandstr. 3, 91058 Erlangen (Germany)
SUMMARY A numerical computer model was developed to simulate shape selective catalysis on zeolites in a gradientless, isothermic recycle reactor. The reaction scheme consists of two consecutive reactions. A primary product distribution of ortho-, m e t a - and para-dialkylbenzenes is formed by disproportionation or alkylation in the micropores of the zeolite. Restricted transition state shape selectivity may occur. Subsequent isomerization and diffusion of the isomers may cause product shape selectivity or nonselective equilibration. The influence of mass transport on the observable product distribution and the combination of the above mentioned shape selective effects were studied by computer simulation. INTRODUCTION Catalysis on microporous solids like zeolites is a means to control the product distribution of a complex reaction. This distribution will be affected by shape selective, selective and nonselective steps of the overall reaction. A numerical computer simulation has been developed to study the behaviour of such a complex system. The simulation is based on a gradientless, isothermic recycle reactor. A general reaction scheme is considered to consist of two consecutive reactions: A + B ~ (o,m,p)pr + C (o,m,p)pr k , (o, rn, p),er Disproportionation or alkylation of monoalkylbenzenes lead to a primary distribution of dialkylbenzenes (ortho,meta,para)pr in the micropores. Steric constraints may favour the formation of the para-isomer (restricted transition state shape selectivity). Subsequent isomerization yields a thermodynamic equilibrium mixture of the isomers. The observable product distribution (o,m,p)~r can be affected significantly by diffusional limitations in the micropores concerning species A/B in disproportionation/alkylation and the dialkylbenzenes in isomerization (product shape selectivity). Nonselective reactions at the outer surface of the cristallites have been neglected.
NUMERICAL MODEL The situation described in the INTRODUCTION is considered in our numerical model. Some further assumptions have been made. Provided that the disproportionation/alkylation is an irreversible reaction of first order the rate of primary formaRF,i(r) = Yv,',i" k f " CA(r) . Varytion of isomer i can be depicted as follows: ing Yp,,i allows to model restricted transition state shape selectivity and cA(r) reflects a possible diffusional limitation concerning species A ( r = radial coordinate). Describing isomerization we employed a kinetic model which was proposed by Wei [1]: 3 RI,i = k1 - ~k=l(Ti,k" ck) i,k = o,m,p. The mass balance for each isomer i on the differential shell of a spherical cristallite results in a system of three coupled ordinary differential equations: "\a,,
+
;" a,;
+ Rf, i ( r ) +
Rz,i(cl(r),c2(r),c3(r))=
0
247 Boundary conditions are the symmetry of the concentration distribution at the centre of the cristallite and a linear adsorption isotherm at the outer surface. The finite volume technique applied to that boundary value problem results in a set of simultaneous linear equations A . c = b, with A being a real band matrix. The linear system is solved by complete lower-upper decomposition of matrix A.
RESULTS In order to use suitable and realistic parameters for the simulation, disproportionation of ethylbenzene on modified zeolites Y was chosen. Adsorption and diffusion coefficients were measured by a chromatographic method [2] and catalysis experiments have been done in a recycle apparatus [3]. A parameter estimation of rate constants kF and ki as well as a determination of transport parameters under reaction conditions are our current research topics.
~'100 ~-~ i
i
$
.
.
.
~bution ortho/meta/para
pri,malT.
90.
----7 /. 63 /. -~-:.-.-=-:-10 /. 50 Z
10 Z 40 Z ====~ 10 ] . . 3 0 Z
80. ~
.~..~--- 10 /. 20 /.
r162
"~ :~ 70. ~ - - - - - - , ~ , - - ~ o li
60
.
10 /. 10 /.
r162162 0 9
0 /
30 40 50 60 70 80
100
equnibHum va, ue
,-,
I "~
..~
o., =o
,o-
,o-
,o:,
'
isomerization activity k~ fig. 1: Effect of activity on para-isomer selectivity
Product shape selectivity would be the only significant step, if the primary product distribution yp,,, was equal to thermodynamic equilibrium ( o / m / p = 7% / 63% / 30%) and RF,, ~ f(r). A further presupposition is D~a > DCf = D ~ . In this case the effect of activity k~ on the observable para-selectivity y .... papa is represented by a distinct maximum curve (see fig. 1) 9 The height of the maximum depends on the ratio I") e~/l) err,~ .-.p i~.-o which amounts to 100 in fig. 1. By increasing transition state shape selectivity, i.e. increasing value of Yp~,pa~a in our model, a higher para-selectivity ys~c,p~ is observed with the m a x i m u m becoming smaller and smaller until it disappears entirely. In this case there is no contribution of product shape selectivity on the observed increasing para selectivity. Additional simulations have been carried out concerning the influence on the observable product distribution by diffusion limitation in the primary formation of the isomers, the ratio D~fr/DCofr and the radius of the cristallites [4]. REFERENCES (1) Wei, J.: J. Catal. 76 (1982)pp.433. Hilgert, W.: Ph.D. thesis, University of Erlangen-Niirnberg, 1991. (2) Klemm, E.; Sasse, F.; Eraig, G.: Book of Abstracts, ZMPC'93, Nagoya 1993. (3) Klemra, E.; Seller, H.; Emig, G.: submitted to Chem.-Ing.-Tech. (4)
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
248
MOLECULAR DYNAMIC AND STRUCTURAL STUDIES OF THE INTERACTIONS OF HFC-134 AND CFC-13 WITH THE FAUJASITE FRAMEWORK. J. B. Parise #, L. Abrams*, J. C. Calabrese*, D. R. Corbin*, J. M. Newsamw S. Levinew and C. Freemanw #Earth and Space Sciences, SUNY, Stony Brook, NY 11794-2100, USA, *DuPont Central Research and Development, Wilmington, DE 19880-0262, USA, w
Corporation, 9685 Scranton Rd., San Diego, CA 92121, USA
SUMMARY Molecular simulation and structural studies based upon single crystal and powder x-ray diffraction data have been used to explore the interactions of CFC-13 (CF3CI) and HFC-134 (CF2HCF2H) with the Na-exchanged faujasite framework. Calculations of the isotherm for the adsorption of CFC-13 on zeolite Y match the observed isotherm closely, especially at low pressures. This result suggests simulation will be an efficient and cost effective aid in screening potentially useful molecular sieves for separations applications. The on-going structural investigations suggest that although the sorbed molecules are partially disordered within the pore space, there is evidence for preferred sorption to the Na-sites. INTRODUCTION Chlorofluorocarbons (CFC's) have been linked I to ozone depletion. As a result, industry has identified several hydrofluorocarbons (HFC's) as possible substitutes. 2 These materials are reasonable compromises in terms of physical properties, flammability, cost, environmental impact and toxicity. Unlike the CFC's, which can be made in a single step, these alternatives are generally synthesized 2 via multiple-step processes. Separations technologies will play an increasingly important role in obtaining desired products, which in some cases are produced at 3 - 20% yield. 2. Zeolite molecular sieves have been proposed for this purpose. 3. In processes leading to products with similar boiling points 4 separations based upon distillation are precluded, and make the use of molecular sieves desirable, if not imperative. While activated carbons hasve been proposed in some patents, the shape selective properties of aluminosilicate molecular sieves offer many advantages. 5. A key factor in the screening of potentially useful molecular sieves for CFC/HFC-separations is the careful determination of experimental absorption isotherms and their comparison with those derived by theoretical methods. The successful prediction of isotherms would bolster efforts to rapidly survey a variety of ion-exchanged compounds for their potential utility in separations processes. We have begun these investigations and-, ,as a complement to these studies, have also begun structural investigations of HFC-134 sorbed in faujasite-frameworks using single crystal and synchrotron x-ray powder diffraction. RESULTS AND DISCUSSION The isotherm for CFC-13 on zeolite Na-Y was measured using a volumetric isothermal static adsorption mode at 298 K. Each datum point was taken from samples equilibrated for 3-24 hrs. and the pressure was monitored by a capacitance manometer. The sorption isotherm was calculated using the
249
9
I
I
I
I ~
Monte Carlo techniques within the Catalysis
40
and Sorption program suite (Fig. 1).
The
Monte Carlo approach to calculating isosteric
o
:~30
heats assumes that there is a fixed number of
L O r "O
m,
~20 d
o calculated experimental
0
~10
molecules within the zeolite host during the Monte Carlo simulation; typically only one sorbate molecule is studied.
In order to
simulate the number of molecules taken up by 0
0.0
0.2
I I I 0.4 0.6 0.8 Pressure (atm)
Fig 1. Observed and calculated isotherms for the absorption of CFC13 (CF3CI) on zeolite Na-Y.
t1.0
the sorbent at a defined sorbate partial pressure, the Grand Canonical ensemble must be used. In this case, each Monte Carlo step includes the rotation and repositioning of a sorbate molecule together with the possible creation or destruction of a molecular species.
The creation-destruction probability is computed from the defined sorbate partial pressure.
The
simulation is then run analogously to that for the isosteric heat case and repeated for a series of sorbate partial pressures. At each simulated pressure, the average number of molecules adsorbed is computed (together with the average sorption heat) and this is then plotted against partial pressure to give the simulated sorption isotherm (Fig. 1). This fit to the observed data is reasonable, especially at lower pressures. Following validation of the simulation approach and the interatomic potentials used, the sorption isotherms can then be extended to other CFC/HFC molecules and to other zeolite structure types or compositions. Single crystal x-ray diffraction data were collected on an octahedrally shaped crystal of Na-X, 201~m on edge, dehydrated under vacuum, exposed to an atmosphere of HFC-134, and mounted on a RigakuR-axis imaging plate system. Data were collected at 125 K. Fourier difference techniques were used to locate scattering in two positions close to Na-sites; one consists of a cluster of partially occupied sites within the sodalite cage close to Na at (x, x, x); x = -0.0613(5). These features may represent products from the breakdown of HFC-134. A second set of partially occupied sites is close to a Na-site associated with the 4-ring at (0.115(2), 7/8, 7/8). In both cases the absorbed species appear to be disordered with three partially occupied sites within 2.3A of the Na-sites. These are presumed to be F-atoms. The final discrepancy indices for the refinement were R = 4.21%, Rw = 3.76%, s = 2.21.
REFERENCES: (1) Molina, M. J.; Rowland, F. S. Nature 1974, 249, 810-812. (2) Manzer, L. E. Science 1990, 249, 31-35. (3) Corbin, D. R.; Mahler, B. A. WO 94/02440 (February 3, 1994). (4) Edwards, D. W. European Patent App/ication 92301574.7. (5) Corbin, D. R.; Femandez, R. E.; Mahler, B. A. WO 93/17988 (September 16, 1993).
VII. Structure
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H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
250
THE FRAMEWORK TOPOLOGY OF ZEOLITE MCM-22 Jeffrey A. Lawton*, Stephen L. Lawton, Michael E. Leonowicz, and Mae K. Rubin Mobil Research and Development Corporation, P. O. Box 480, Paulsboro, NJ 08066 USA
SUMMARY The framework topology of the molecular sieve MCM-22 has been determined from high resolution electron micrographs and refined with synchrotron X-ray diffraction powder data. MCM-22 crystallizes as very thin sheets. The borosilicate form of this material, having unit cell framework composition (AIo.4Bs.lSis6.5)O144, may be indexed on a hexagonal lattice in space group P6/mmm (D16h, No. 191). The refined unit cell parameters are a = 14.1145(8) and c = 24.8822(18) A. The MCM-22 structure contains hexagonal sheets constructed by interconnecting modified DOH cages through shared 4-ring faces in a manner analogous to that found in DOH. This modified cage has a TO 3 cap on top (forming a small [43] unit) and a -T-O-T- chain passing through its center. The MCM-22 sheets bond together in two ways m one side involving an oxygen bridge between TO 3 caps and the other side through double 6rings. The net effect is to produce two different, independent pore systems with 10-ring apertures. One of these pore systems is defined by two-dimensional, sinusoidal channels. The other consists of large superca~es whose inner free diameter, 7.1 A, is defined by 12rings and whose inner height is 18.2 A
INTRODUCTION Molecular sieves are being synthesized in increasing number with the use of an organic directing agent.
These directing agents, if present in the reaction gel, may be used to
influence the formation and geometry of the internal pores.
MCM-22 is believed to be an
example of a material that may be synthesized in this manner. By using hexamethyleneimine as a directing agent, a molecular sieve with a unique pore system is formed. This pore system may provide for a variety of useful applications.
EXPERIMENTAL The MCM-22 sample used in this study was hydrothermally synthesized by a procedure described elsewhere 1 using HiSil~ precipitated silica (87% SiO2), hexamethyleneimine (HMI), triethanolamine (TEA), boric acid (H3BO3), and sodium hydroxide.
The mixture was
crystallized under static conditions at 120~ for 230 days. The product was water washed and dried at 120~
then calcined in air at 540~ for 16 hours.
* Present address: Program in Cell and Molecular Biology, One Baylor Plaza, Room S-101, Houston, TX 77030 USA
251
RESULTS AND DISCUSSION Topologically, the framework connectivities in MCM-22 are remarkably similar in some respects to those in dodecasil-lH (DOH). The DOH structure contains hexagonal sheets of [435663] cages (Figure l a), joined together by sharing 4-ring faces.
In MCM-22, the DOH
[435663] cage is modified by reversing the orientation of the two tetrahedral T atoms that reside on the 3-fold axis and joining them together inside the cage through a shared oxygen atom. This unusual coordination inside the cage is completed by the placement of a TO 3 cap on top of the cage, thereby forming a small [43] unit. The new {435663143]} cage, with the bridge inside, is shown in Figure lb. The T atom located at the top of the [43] unit serves as the link that joins two identical layers together through an oxygen atom. This linkage forms 10-ring apertures to large supercages. The supercages stack one above the other through double 6rings, an arrangement that forms two-dimensional, sinusoidal channels with 10-ring apertures. There is no communication between the supercage and the sinusoidal channel.
(a)
(b)
Figure 1. (a) [435663] cage in dodecasil-1H, with idealized D3h symmetry. (b) {435663[43]} cage in MCM-22, with idealized C3v symmetry. Resident within the framework is a T-O-[43]-O-[43]-O-T chain parallel with the unit cell caxis. The T-O-[43] - segment is part of the {435863[43]} cage and the central oxygen atom in the -[43]-0-[43] - segment is the bridge that links two MCM-22 layers together.
Within this
chain, TOT angles involving atoms that are situated on the 3-fold axis are constrained to be linear in space group P6/mmm. Since stereochemical bonding considerations predict that TOT angles are not linear in their local environment, P6/mmm probably represents only an average symmetry.
An energy minimization study proposes that reduction of this space group to
orthorhombic Cmmm (D192h, No. 65) will permit more reasonable TOT angles to be achieved. This has been confirmed by a DLS refinement.
REFERENCE 1. Rubin, M. K. and Chu, P., U. S. Pat. 4,954,325 (1990).
H.G. Karge and J. Weitkamp (Exts.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
252
O P T I C A L I N V E S T I G A T I O N S OF T H E C R Y S T A L I N T E R G R O W T H OF T H E Z E O L I T E S Z S M - 5 A N D Z S M - 8
EFFECTS
C . W e i d e n t h a l e r 1, R.X.Fischer 1, R.D.Shannon 1 & O. M e d e n b a c h 2 l l n s t i t u t fiJr G e o w i s s e n s c h a f t e n der Universit~it, D - 5 5 0 9 9 Mainz, G e r m a n y 21nstitut for Mineralogie der Universit&t, D - 4 4 7 8 0 B o c h u m , G e r m a n y ABSTRACT
X-ray precession photographs and optical investigations of TPA-ZSM-5 (silicalite) and TEA-ZSM-8 reveal that ZSM-8 shows intergrowth effects similarly to ZSM-5. Both zeolites consist of t w o interpenetrating species rotated by 90 ~ round their crystallographic c-axes. The intergrowth species are differently shaped in ZSM-5 and ZSM-8. ZSM-5 consists of an orthorhombic prism penetrated by two pyramidal fragments. The ZSM-8 crystals studied here consist of species with two-dimensional hour-glass like shapes embedded in orthorhombic prisms. The orientations of the optical indicatrices of ZSM-5 and ZSM-8 are identical after calcination. This confirms recent work which showed that the framework structures of ZSM-5 and ZSM-8 are essentially identical. INTRODUCTION
ZSM-5 (and its aluminum free form silicalite) and ZSM-8 belong to the family of pentasil type zeolites. ZSM-5 and silicalite are commonly synthesized using TPA as template, ZSM-8 is synthesized with TEA. While there is no paucity of ZSM-5 studies, there is only little knowledge of the crystal structure and the intergrowth effects of ZSM-8. It has been assumed that the crystal structures are closely related but only recently [1] it could be shown that the crystal structures are essentially identical. Intergrowth effects observed in the crystallization process of ZSM-5 have been described by several authors [2,3,4]. The
intergrowth of prismaticly shaped silicalite
crystals is described as an interpenetration of t w o twin components related by a 90 ~ rotation round the common c-axis [2]. We present here a detailed description of the optical behavior of ZSM-5 and ZSM-8. Experimental details are given in [1]. RESULTS A N D DISCUSSION
Optical analyses of template-containing ZSM-5 and silicalite samples reveal a threedimenional hour-glass structure along the c-axis. Two pyramidal species (11) interpenetrate an orthorhombic prism (I) laterally (Fig.la). A, B, and C in Figs. l a and l b describe the main directions of the crystal, roman numerals I and II refer to the t w o different species. Simultaneous and parallel extinction of all crystal sectors indicate that the axes of the optical indicatrix and the crystallographic axes are parallel. All sectors have a negative sign of elongation in directions A and B. Therefore, the refractive index nx of both individuals must coincide with the crystallographic c-axis. The different interference colors which appear in the sectors of the t w o individuals indicate different refractive indices and the optical effects down the c-axis (direction C) reveal that ny of the prismatic individual coincides with n z of the pyramid species and vice versa. The
253 optical
orientations
are interchanged
in agreement
with the
interchanged
crystal-
lographic a and b axes. Calcined ZSM-5 and silicalite samples show the hour-glass structure and a laminar decomposition. The orientation of the optical indicatrices for the calcined crystals is the same as for the template-containing forms. The ZSM-8 crystals are also composed of t w o individuals. An hour-glass like central part (I) is embedded in an orthorhombic prism (11) (Fig.lb). The optic signs of elongation are different for the t w o individuals. The optical effects in orientation A and B reveal that the intermediate refractive index ny of both individuals coincides w i t h the common c-axis, n x and n z of both individuals are interchanged. The calcined ZSM-8 crystals show the hour-glass structure but no laminar decomposition. All sectors show a negative sign of elongation in orientation A and B. Therefore, n x of both individuals coincides with the crystallographic c-axis. The refractive index ny of the hour-glass species coincides with n z of the orthorhombic prism and vice versa. The different templates, TPA for ZSM-5 and TEA for ZSM-8, determine mainly the differences in the optical behavior of the t w o
zeolites. After
calcination,
the
template-free ZSM-8 crystals show the same orientation of the optical indicatrices as observed for calcined ZSM-5.
[ ~ II a)
/
II.._ C, n x
I
~
fizz ~ 1 ....t ........2;::::. i ..........
.~f
~
.
........................
..............
F/.
["
C,nx
b,n z [ ~ II Fig.l" a) Model of the ZSM-5 and silicalite intergrowth, b) Model of the intergrowth of ZSM-8. The orientation of the optical indicartix for the orientations A, B, and C is given together with the assignments of the crystal axes for both individuals.
REFERENCES
[1] Weidenthaler,C.; Fischer, R.X. & Shannon, R.D. (1994). Proceedings of the 10th International Zeolite Conference. [2] Price, G.D.; Pluth, J.J.; Smith, J.V.; Bennett, J.M. & Patton, R.L. (1982). J. Am. Chem. Soc, 104, 5971. [3] Hay, D.G.; Jaeger, H. & Wilshier, K.G. (1990). Zeolites, 10, 571. [4] Geus, E.R., Jansen, J.C. & van Bekkum, H. (1994). Zeolites, 14, 82
This work is supported by the Deutsche Forschungsgemeinschaft under grant Fi442/2. We thank F. Scheth for providing the ZSM-5 samples studied here.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
254
Is the V F I T o p o l o g y C o m p a t i b l e with T e t r a h e d r a l AI? Javier de Ornate, Christian Baerlocher and Lynne B. McCusker Crystallography, ETH, Zurich, Switzerland
Summary X-ray powder diffraction data shows that the unit cell for dehydrated VPI-5 is doubled in the c direction. Restrained Rietveld refinements in the space groups P31m, P3 and Cm reveal a distortion of the crankshaft chains associated with the fused 4-rings. The best fit was obtained in Cm, and this symmetry is compatible with the 31p MAS NMR spectrum.
Introduction One third of the framework A1 atoms in the as synthesized form of VPI-5 are octahedrally coordinated. 1 In addition to the four framework oxygens, two water molecules are included in the coordination sphere of the A1 located between the fused 4-rings, and this reduces the geometric strain inherent to the fused 4-ring conformation. However, it has been shown by 27A1 MAS NMR measurements, that all AI atoms in VPI-5 become tetrahedral upon dehydration. 2 The same investigation showed that the 31p MAS NMR spectrum also changes significantly upon dehydration: instead of three peaks with equal intensities, three peaks with the intensity ratios 1:5:3 are observed. Furthermore, one signal has an extreme chemical shift o f - 17 ppm. Similar results were obtained in an independent study by Perez et al. 3 In an attempt to understand how tetrahedral A1 can be accommodated in the V F I topology, a structural investigation of dehydrated VPI-5 using powder diffraction data was undertaken.
Experimental Section A flat plate sample was mounted in a furnace on a Scintag 0-0 powder diffractometer, heated very quickly (ca. 2 min) to 5000C under vacuum, evacuated for two hours at that temperature, and then cooled to 100*C (still under vacuum) for data collection. This procedure was found to produce dehydrated VPI-5 with a minimum amount of A1PO4-8 impurity. Data were then collected from 4 to 80~
with CuK~ radiation.
Results and Discussion The pattern could only be indexed with a unit cell doubled in the c direction. Small but significant reflections requiring the larger cell are clearly apparent in the pattern (see Figure 1) and have been observed for samples from several different sources. In order to retain the VFI topology with a doubled unit cell, the space group has to be reduced from P63cm to P31m or lower. Distance least squares (DLS) refinement of the framework structure in the small unit cell showed a clear improvement in the geometry when the symmetry was changed from
P63cm or P63 to P31m. However, doubling the unit cell brought no further improvement in P 3 1 m , P3 or Cm (highest symmetry compatible with the 31p MAS NMR results). Consequently, geometrically restrained Rietveld refinements of the structure in all three space
255
I
'
10
I
'
'
20
'"r
30
,
i
40
,
"20
Figure 1. Observed (top), calculated (middle) and difference (bottom) profiles for a representative section of the data reflecting the current status of the Rietveld refinement of dehydrated VPI-5 in the space group Cm. Two regions containing reflections which require the doubling of the unit cell (marked with asterisks) have been expanded in the insets.
groups were performed. All refinements involve high pseudosymmetry, so caution must be exercised in the interpretation of the results. In Cm, for example, there are 3104 reflections in the powder pattern, 452 geometric restrictions, and 330 (!) positional parameters. The best fit of the X-ray data obtained thus far is in the space group Cm (RF = 0.061 and Rwp = 0.171), but refinement in all space groups is still in progress. The reason for the doubling of the unit cell, however, is apparent. The crankshaft chains associated with the fused 4-rings are distorted in the manner shown in Figure 2 in all three space groups. The distortion of those associated with 6-rings only is less dramatic. A similar distortion might be responsible for the disorder observed by Poojary et al. in their refinement of the structure in the smaller unit cell. 4 Of the 76 symmetrically independent P-O-A1 angles in Cm, 24 are less than 135" and 14 of these less than 130" (i.e.
unacceptably small).
With only one exception, all of the
oxygens involved are in both the 18-ring and the fused 4-rings.
l
c = 16.7A
A subgroup of these may provide an explanation for the extreme chemical shift observed in the 31p MAS N M R spectrum.
It is worth noting that there is an obvious
relationship between the space group Cm, which is compatible with the 3 l p MAS N M R results and so far gives the best fit to the X-ray data, and C m c 2 1 , which is the space group for Figure 2. Distortion ofthe cranksA1PO4-8. 1 2 3 4
haft chain responsible for the doubling of the c-axis.
L.B. McCusker, Ch. Baerlocher, E. Jahn & M. Biilow, Zeolites 1991, 11, 308-313. J.A. Martens, E. Feijen, J.L. Lievens, P.J. Grobet & P.A. Jacobs, J. Phys. Chem. 1991, 95, 10025-10031. J.O. Perez, P.J. Chu & A. Clearfield, J. Phys. Chem. 1991, 95, 9994-9999. D.M. Poojary, J.O. Perez & A. Clearfield, J. Phys. Chem. 1992, 96, 7709-7714.
256
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
Rietveld refinement of the tetragonal variant of AIPO4-16 prepared in fluoride medium J. Patarin, C. Schott-Darle, P.Y. Le Goff, H. Kessler Laboratoire de Mat6riaux Min(~raux - URA 428 -Ecole Nationale Sup6rieure de Chimie de Mulhouse 68093 Mulhouse Cedex, FRANCE E. Benazzi Institut Fran(;ais du P6trole, Rueil Malmaison, FRANCE SUMMARY The tetragonai variant of AIPO4-16 isostructural of the clathrasil octadecasil was obtained by using quinuclidine as a template in the presence of fluoride anions. The structure was refined in the space group 14 (a= 9.3423(1) A, c - 13.4760(2)A) from powder X-ray data. Part of the fluoride present In the material was found in the D4R units of the structure. The final Rietveld residuals are RF=0.034 and Rwp-0.114.The powder structure analysis was confirmed by 13C, 19F,and 31pNMR spectroscopy. INTRODUCTION The structure of AIPO4-16 was recently determined from synchrotron powder diffraction data [1]. AIPO4-16 (AST structure-type) is cubic with a = 13.3832(6) A; the most probable space group being F23. On the other hand, octadecasil, a purely siliceous AST-type material, was obtained in our laboratory from a mixture containing fluoride anions [2]. The structure was determined on a single crystal, the symmetry is tetragonal, space group 14/m, with a = 9.194(2) ,~ and c = 13.396(4) A.In this work are described the synthesis in a fluoride medium and the characterization of the tetragonal variant of AIPO416 (named AIPO4-16 (Tet.). A Rietveld refinement of the powder X-ray diffraction data is also reported. EXPERIMENTAL The AIPO4-16 (Tet.) samples were obtained by hydrothermal synthesis at 150-170 ~ according to an extension of the procedure developped in our laboratory [3] in which fluoride ions are used as mineralizing agents. Quinuclidine was used as templating agent.The materials were characterized by conventional techniques. The powder X-ray data were refined using the Rietveld full pattern refinement program XRS-8214]. RESULTS AND DISCUSSION A typical starting composition leading to a pure AIPO4-16(Tet.) sample is 1P205:1AI203:1Q:1HF:(40-60)H20
pH=6.5-7.0. Without fluoride in the starting
mixture,the pure cubic form crystallizes [1]. Such a result shows that in addition to their mineralizing effect, the fluoride anions have a structure directing effect.The crystals are of a tetrahedral shape, their size is in the range 0.5 to 3 I~m. The unit-cell formula of the assynthesized sample used for the Rietveld refinement is (AI10P10040)Q2.2F1.6~
257
Rietve/d refinement The atomic coordinates of the isostructural octadecasil (space group 14/m) were used as starting coordinates for the refinement of the aluminophosphate framework. In order to take into account the strict alternation of AI and P atoms, the symmetry was reduced and the space group 14 was chosen. The atomic coordinates were refined by using the DALS option in XRS-82 with 21 variables and 30 soft restrictions. After refinement of the unit cell and the profile parameters, the positional parameters associated with the framework atoms were refined using appropriate constraints. A difference Fourier map revealed a high residual electron density maximum within the D4R units of the structure. This was interpreted as a F- position as already observed in octadecasil [2]. From the refined site occupancy factor (0.48) and taking into account the multiplicity of this site, it appears that half of the D4R units are occupied. This result can be understood by considering the analytical results (i.e., number of F atoms per 20 T atoms < 2) and the 19 F solid state NMR results (see below).Four highest maxima were found inside the large cage of the aluminophosphate framework. The positional parameters of these maxima as well as the site occupancy factors and the isotropic displacement parameters were refined. However these maxima are not a physical model for the guest species but represent the best possible fit for the guest molecule within the octadecahedral cages. After the removal of the geometric restrictions, the Rietveld refinement converged with final RF=0.034 and Rwp=0.114, which compare with the statistically expected Rexp=0.056.
Solid State NMR spectroscopy By 13C NMR spectroscopy, quinuclidine was found protonated. The 31p MAS NMR spectrum of AIPO4-16(Tet.) shows two lines at-19 and -29 ppm. These two components with an intensity ratio close to 1:4 can be attributed to the two types of crystallographic sites present in the structure. From19F MAS NMR spectroscopy two chemical shifts can be distinguished, one at -89.1 ppm and the other at -143.2 ppm. The first signal is attributed to F in the D4R units, the second to a species of the type AI-F. This species would thus correspond to the excess of fluorine found by chemical analysis with respect to that found in the D4R units by the structure refinement (0.96 F per 20T compared to 1.56 F by chemical analysis). REFERENCES
1 Bennett, J.M. and Kirchner, R.M. Zeolites 1991, 11,502 2.Caullet, P., Guth, J.L., Hazm, J., Lamblin, J.M. and Gies, H. Eur. J. Solid State Inorg. Chem. 1991, 28, 345 3.Guth, J.L., Kessler, H. and Wey, R. in New Developments in Zeolite Science and Technology (Eds. Y. Murakami, A. lijima and J.W. Ward) Elsevier, Amsterdam, 1986, p.121 4.Baerlocher, Ch.,XRS-82, the X-Ray Rietveld System, Institute for Crystallography and Petrography, ETH, Zurich, 1982
H.G. Karge and J. Weitkamp (F_As.) 258
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
Structure of the Microporous Titanosilicate ETS-IO M.W. Anderson (1)_, O. Terasaki(2), T. Ohsuna(3), A. Philippou(1), S.P. MacKay(l), A. Ferreira(4), J. Rocha(4), S. Lidin(5) 1)Department of Chemistry, UMIST, P.O. Box 88, Manchester M60 1QD, U.K. 2)Department of Physics, Tohoku University, Aramaki Aoba, Sendai 980, Japan. 3)College of Science and Engineering,Iwaki Meisei University,5-5-1 Iino Chuoudai, Iwaki, Fukushima 970, Japan. 4)Department of Chemistry, Universityof Aveiro,3800 Aveiro, Portugal. 5)Inorganic Chemistry 2, Chemical Centre, Ltmd University,l.amd, Sweden. Until the early 1980's the majority of known framework structures were either aluminosilicates or silicates(I) consisting of tetrahedrally coordinated alumimum and silicon. The aluminosilicate family are collectively termed zeolites. In 1982 Union Carbide discovered the synthesis of a variety of a l u m i n o p h o s p h a t e s ( 2 ) (AIPO4's) and two years later reported the silico aluminophosphates(3) (SAPO's). It was also found possible to substitute other metals into tetrahedral positions in these materials to form the so-called MeAPO's(4). In all these materials the framework metal is normally in tetrahedral coordination although under certain hydration conditions framework atoms become 5- or 6-coordinate. In 1983 an important metal substituted silicate TS-1(5)was discovered which is a titanium-doped form of the purely siliceous silicalite. The titanium (IV) again adopts tetrahedral coordination and these materials are highly active as oxidation catalysts. An important new class of materials contains both octahedral and tetrahedral framework atoms(6-8). Two titanosilicate members of this family are ETS-4 and ETS-10 (_Engelhard Corporation Titanosilicate) which showed adsorption characteristics of microporous materials and in the case of ETS-10 displayed characteristics indicating a wide-pore material. However, the structure of neither of these materials has been solved to date a factor which severely limits their usefulness for application. There are some indications that ETS-4 is similar to the natural mineral zorite(9), however, no structural analysis has been performed. We have solved the structure of ETS-10 by using a combination of high-resolution electron microscopy, electron diffraction, powder x-ray diffraction, solid-state NMR, energy minimisation and chemical analysis. The difficulty solving the structure of either ETS-4 or ETS-10 resides in the fact that (i) they can only be synthesized as powders - particle size ca. 5/am and (ii) they exhibit a high degree of disorder - exemplified by broad powder x-ray diffraction reflections. A similar situation existed for zeolite 13, a wide-pore zeolite which was first synthesized in 1967(10) but the structure of which was only determined in 1 ~ I 1 ) .
259 The strategy adopted for structural elucidation was (i) target the framework ring connectivity and local disorder with high-resolution electron microscopy (HREM) (ii) determine the atomic makeup of the material by chemical analysis (iii) determine the local silicon environment using 29Si solid-state NMR (iv) determine a trial structure and optimize this by energy minimization (v) use the minimized structure to simulate the high-resolution electron microscope images (vi) combining the minimised structure and the known disorder simulate both the powder x-ray diffraction and electron diffraction data. The stoichiometry of the framework is Si5TiO13 2- which fits with the chemical analysis and the connectivity is exactly that suggested by 29Si MASNMR. The basic building block can best be considered as a Si40Ti8010416- unit. The framework charge will be balanced by either sodium or potassium cations. The titanium atoms are octahedrally coordinated and are linked to one another in a straight chain. These chains are aligned either along the a or the b zone axis, alternating as they are stacked along c. The titanium octahedra are buried beneath 4Si atoms (each Si(3Si, 1Ti)) connected in such a way as to produce two three rings. These Si atoms are themselves connected together in purely siliceous 5-rings where the apical Si of each five ring is the remaining Si(4Si, 0Ti). Rods consisting of a chain of titanium octahedra surrounded on both sides by a coating of silicon 5-rings are joined together in a perpendicular arrangement to generate 7-rings and the complete stacking of these rods encompasses the large 12-rings (8.62/~ x 9.24/~). ETS-10 is a disordered structure made up of sheets of the basic unit stacked together in a random arrangement. Two ordered polymorphs can be considered: polymorph A with space group C2/c; polymorph B with space group P41. Polymorph B is chiml and has a spiral 12-ring channel running down the c-axis. 1. 2. 3. 4.
5 6. 7. 8. 9. 10. 11.
Breck, D. W. "Zeolite Molecular sieves", John Wiley and Sons 1974. Wilson, S. T., Oak, S.,Lok, B. M., Flanigen, E. M.& W. Plains, U.S. Pat. 4,310,440 (1982). Lok, B. M., Messina, C. A., Gajek, R. T., Carman, T. R., & Flanigen, E. M. U.S. Pat 4,440,871 (1984). Wilson, S. T., Oak, S. & Flanigen, E. M. U. S. Pat. 4,567,029 (1986).
Taramasso, M. et al, U.S. Pat. 4,410,501 (1983). Kuznicki, S. M. U.S. Pat. 4,853,202 (1989). Kuznicki, S. M. & Thrush, A. K. Eur. Pat. 0405978A1 (1990). Chapman, D. M. & Roe, A. L. Zeolites 10, 730 (1990). Sandomirskii, P. A. & Bilov, N. V.Sov. Phys. CrystaUogr 24(6), 686 (1979). Newsam, J. M., Treacy, M. M. J., Koetsier, W. T. &. de Gruyter, C. B. Proc. R. Lond. A 420, 375 (1988). Wadlinger, R. L., Kerr, G. T. & Rosinski, E. J. U.S. Pat. 3,$08,069 (1967).
260
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
Avoidance of 2 AI atoms in a 5-Ring A New Rule Complementing the Loewenstein's Rule Masanao KATO and Hidenori ARAKI
Toyohashi University of Technology, Toyohashi, 441 JAPAN Keiji ITABASHI
Chemical Research Laboratory, TOSOH CORPORATION, Yamaguchi, 746 JAPAN A new rule is proposed which restricts the distribution of A1 atoms in zeolitic frameworks complementing the Loewenstein's rule. The new rule shows that any 5-ring in a siliceous zeolitic framework can not contain two A1 atoms, and is applied to determine the lowest limit of Si/A1 ratio in these zeolites. The ordered distribution of A1 atoms in the framework of mordenite (Na8A18Si40096) was determined so as to explain consistently all physical and chemical properties, i.e., adsorption capacities for benzene, ~) XRD, 2) 29Si MAS NMR3) and extraframework cation-sites. The results show that there is no 5-ring containing 2 A1 atoms, although there are many T-sites which can be occupied by A1 atom without violating the Loewenstein's rule. If one more A1 atom is substituted for Si atoms in Si(0A1) in mordenite, a 5ring containing 2 A1 atoms is generated. We named it the 2 A1/5-ring avoidance rule. The applicability of the new rule to ferrierite and others was examined.
Determination of distribution of AI atom in the zeolitic framework Connectivity matrix: The connectivity matrix of nline by n-row ( n represents the number of T-sites per unit cell) is constructed at first. It represents the connectivity correlation between T-sites in a given zeolitic framework. Any symmetry of the framework is ignored. Configuration matrix: Possible configuration of Al atoms in the
261 framework are searched using the conectivity matrix under the restriction of both Loewenstein's and the new 2 A1/5-ring avoidance rules. Many possible configuration matrices of A1 atoms are generally obtained in this stage. The lowest limit of Si/A1 ratio: The maximum number of A1 atoms in the unit cell can be estimated by the configuration matrices, which is much less than that estimated by the Loewenstein's rule alone. Table 1 shows the lowest limits of Si/AI ratio ontained for mordenite, ferrierite and clinoptilolite/heulandite. These values are in good agreement with those of natural and synthetic isostructural ones. Table 1 The upper limit of the A1 atom content and minimum Si/A1 ratio in the zeolitic framework calculated from the new rule. [Al]max/UC [Si]/[A1]min zeolites typical formula mordenite
Nas[AlsSi40096]
8
5
ferrierite
Na2Mg2[A16Si30072]
6
5
clinoptilolite heulandite
(Na,K)6[A16Si30072] Ca4[A18Si28072]
8
5
Determination of A1 atom sites: Topologically independent configurations are selected from the configuration matrices, and candidates with P1 symmetry are omitted because it is considered that they are unstable by distortion of the framework. The most probable configuration of A1 atom sites is determined by the aid of results obtained by XRD, 29Si MAS NMR and by considering defects among the candidates with higher symmetric configuration. Details of results of mordenite, ferrierite and heulandite/clinoptilolite will be demonstrated in the conference. References 1 K . Itabashi, T. Fukushima, K.Igawa, Zeolites, 6, 30 (1986) 2 K. Shiokawa, M. Ito, K.Itabashi, Zeolites 9, 170 (1989) 3 K.Itabashi, T.Okada, K.Igawa, Proceeding of 7th International Zeolite Conference 369 (1986)
H.G. Karge and J. Weitkamp (Eds.)
262
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
THE CRYSTAL STRUCTURE OF THE NEW BORON CONTAINING ZEOLITE RUB-13 S. Vortmann, B. Marler, P. Daniels, I. Dierdorf and H. Gies Institut far Mineralogie, Ruhr-Universit~t Boehum, D-44780 Bochum
INTRODUCTION RUB-13 was first synthesized in 1987 [1] and characterized as a zeolite containing trace amounts of boron. We report here on an improved synthesis and the crystal structure of RUB13 which represents a new porous structure type.
EXPERIMENTAL RUB- 13 was synthesized in the system SiO2:H3BO3:1,2,2,6,6-pentamethylpiperidine: Ethylenediamine: H20 under hydrothennal conditions at 160~ in silica tubes. The twinned crystals were investigated using Weissenberg- and precession methods in order to determine the twinning law. The structure determination was performed with single crystal intensity data collected from one twin individuum on a SYNTEX R3 diffractometer (2Omax=55 ~ ~L--0.7107]~). 29Si CP/MAS NMR experiments were run on a BRUKER MSL 400 spectrometer. The boron content after calcination was determined with an ICP spectrometer (Phillips PU 7000). The density of the as-synthesized material was measured using the swim and sink method.
RESULTS AND DISCUSSION RUB-13 crystallizes as lath shaped, transparent crystals which often form spherulitic bundles. The density of the as-synthesized material is 1.92 gcm -3. Optical microscopy and single crystal diffraction experiments showed all crystals to be twinned with twin plane (001). The host structure was solved with direct methods as provided in the SIEMENS structure solution package leading to 4 T(Si, B)- and 10 O atoms in the asymmetric unit. The boron analysis by ICP spectroscopy of RUB-13 after calcination showed a content of 1.53 B/32 T-atoms. The 29Si CP/MAS NMR spectrum contains only 2 signals which are interpreted as resulting from Si(4Si 0B) and Si(3Si 1B) environments. Using the formalism as described by Engelhardt et al. [2] the analysis of the intensity ratio of the two peaks leads to a boron content of 1.6 B/32 T-atoms which is in good agreement with the ICP analysis of the calcined sample. Due to the twinned structure the refinement was performed with a reduced set of intensity data by omitting those intensities which contain parts of both twin individuals. From the electron density map and the distribution of T-O-distances, no ordering of boron was detected and it was therefore assumed that boron is statistically distributed on the T-sites. Anisotropic refinement of the host framework in space group C2/m with a=9.659(2)~, b=20.461(4)A, c=9.831(2)~ and 1=96.58(1) ~ led to R--0.059. [TO4]-tetrahedra are corner-linked to form the 3-dimensional framework of RUB-13, which has a framework density of 16.6T/1000A 3. The host lattice can be completely constructed from [4454J-cages, which are the fundamental cages of the structure. Neighboring [4454]-cages share
263 two of the four 4MR to form zig-zag columns parallel [100]. Two columns are connected via additional O-bridges parallel [001] to layers (Fig. 1) which again are linked via additional oxygen bridges parallel [010] to build a 3-dimensional framework (Fig. 2). This leads to the formation of straight channels in [100] and [001] which intersect and therefore represent a 2-dimensional channel system. The void space at the intersection is a cage confined by 22 faces, the[465s6'8']-cage (V--550/~3), (Fig. 3).
Fig. 1: Two columns of [445'I-cages.
Fig. 2: Schematic representation of the RUB-13 framework, viewed down [001].
Although 1,2,2,6,6-pentamethylpiperidine was expected to act as the template for the formation of the material, it was not detected inside the large 22-hedra. However, Fourier synthesis revealed 4 residual electron density maxima which agree well with the geometry of the ethylenediamine molecule. Taking the guest molecule into consideration the structure refinement improved to R=0.056. The f i a l composition of RUB13 per unit cell including the template molecule is 5i3o.7,B1.5306, 9X (C2N2Hs). Fig. 3: The [46586484]-cage. REFERENCES
[ 1] Gies, H. (1987):"Synthesis, crystallographic, and thermal properties of a new porous silica"; Journal of Inclusion Phenomena, 5, 283-287 [2] Engelhardt, G., Michel, D. (1987):"High-Resolution Solid-State NMR of Silicates and Zeolites"; John Wiley & Sons, Chichester
264
H.G. Karge and J. Weitkamp (F_As.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
SYNTHESIS AND STRUCTURE OF A NOVEL M I C R O P O R O U S GALLOPHOSPHATE" Na2Gas(PO4)40(OH)3-4H20. Martin P. Attfield "a, Russell E. Morris a, Enrique Gutierrez-Puebla a, c, Angeles MongeBravoa. c and Anthony K. Cheetham a. a Materials Department, University of Califomia, Santa Barbara CA 93106, USA. c Instituto de Ciencia de Materiales, C. S. I. C., Serrano 113, 28006 Madrid, Spain.
SUMMARY
The synthesis and structural characterization of the title compound are described; its structure consists of corner sharing GaO6 octahedra, GaOs trigonal bipyramids and PO4 tetrahedra that link to form an open structure containing channels (ca 4A diameter) running along [001].
INTRODUCTION The discovery of a series of microporous aluminophosphates by Wilson et al I led the way to the synthesis of many novel zeolitic materials with interesting sorbtion and catalytic properties. The replacement of aluminum by gallium in such syntheses has led to the formation of some novel phases 2-3 as well as compounds that are analogous to known aluminophosphates and aluminosilicates4-5. The stereochemical environment of the gallium cations in these compounds may vary between different structures or within the same structure 7. Here we present the synthesis and crystal structure of Na2Ga5(PO4)iO(OH)3-4H20, in which, as in the aluminosilicate zeolites, the stoichiometry of the framework requires the presence of charge compensating cations.
EXPERIMENTAL SECTION The title compound was synthesized using hydrothermal techniques from a reaction mixture containing GaCI3, H3PO3 and 1,4-diazobicyclo[2.2.2.]octane in deionized water. Solid NaOH was added to the reaction mixture until a pH ca. 10 was reached. The reaction mixture was heated to 190oc and held at this temperature for 100hr. The product was obtained as single crystals, one of which was isolated and its structure determined by four circle X-ray diffractometry.The material has also been synthesised as a microcrystalline powder in the pH range 7- 10.
RESULTS AND DISCUSSION The structure consists of two types of chains of polyhedra running along the [001] direction. One type of chain consists of alternately arranged, corner sharing GaO6 octahedra and PO4 tetrahedra, while the other contains corner sharing distorted GaO5 trigonal bipyramids. Two of the former chains and one of the latter combine to form a tube containing a small channel running along the [001] direction. Four of these such tubes are linked together by short chains of polyhedra to form an open structure
265 containing channels ( ca. 4 A diameter) running parallel to the c axis (see Fig. 1). The short chains of polyhedra occur every 3.19 A (c/2) along the c axis, and consist of a GaO6 octahedra in between two PO4 tetrahedra. The sodium cations reside in the space between the PO4 tetrahedra in adjacent short chains, and help to make up the walls of the channels. The interatomic distances and bond valence calculations show that two water molecules are present in the main channels. The thermal stability and sorbtion properties of the title compound will be discussed. REFERENCES
1 S. T. Wilson, B. M. Lok, C. A. Messing, T. R. Cannan and E. M. Flanigen, J. Am. Chem. Soc., 1982, 104, 1146. 2 M. Estermann, L. B. McCusker, C. Baerlocher, A. Merrouche and H. Kessler, Nature, 1991, 352, 320. 3 T. Loiseau and G. Ferey,. J. Chem. Soc., Chem. Commun., 1992, 1197. 4 J. B. Parise, J. Chem. Soc., Chem. Commun., 1985, 606. 5 J. B. Parise, Inorg. Chem., 1985, 24, 4312. 6 J. B. Parise, Acta Crystallogr., Sect. C, 1986, 42, 144. 7 G. Yang, S. Feng and R. Xu, J. Chem. Soc., Chem. Commun., 1987, 1254.
Figure 1. View of the structure along the [001] direction.
H.G. Karge and J. Weitkamp (Eds.) 266
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
STRUCTURE DETERMINATION FROM POWDER D I F F R A C T I O N DATA OF A NEW CLATHRASIL, TMA SILICATE R. W. Broach, UOP Research Center, 50 E. Algonquin Rd., Des Plaines, IL 60017; N. K. McGuire and C. C. Chao, UOP Tarrytown Technical Center, Tarrytown, NY 10591; R. M. Kirchner, Manhattan College, Chemistry Department, Bronx, NY 10471 Summary The structure of as-synthesized TMA Silicate was solved using powder diffraction data. Intensities extracted from high-resolution synchrotron powder diffraction data were used for direct methods solution of the structure. The postulated topology was confirmed by DLS ref'mement, and the structure was confirmed by successful Rietveld refinement. The space group is C2/m: and lattice parameters are a = 13.35171(15) A, b = 13.05496(13) A, c = 12.52970(13) A, and/3 = 113.2863(6) ~
Experimental For the X-ray diffraction experiments, the sample was sealed in a 1.0 mm glass capillary. High resolution powder data were collected at NSLS beam line X7A. Peak intensities extracted from the raw powder data using the program BNLFIT x were used to solve the structure using direct methods (SHELXTL PLUS2). To check the reasonableness of the framework topology found, a distance least-squares (DES 3) refinement was done, assuming an ideal Si-O distance of 1.628 A and an ideal Si-O-Si angle of 145 ~ The refinement converged with a final R-value of 0.0036, which indicates that the framework topology is reasonable. A Rietveld refinement was done using the GSAS 4 set of programs. The refinement converged, giving final residuals of ~ = 0.103 and RF = 0.065.
Results and Discussion The structure of as-synthesized TMA Silicate contains only 4-connected T-atoms in 4-, 5-, 6-, and 8-rings. Two types of cages are interconnected by no larger than 6-rings. The larger cage is a peanutshaped 30-hedron [4s51261~ This cage is the fundamental polyhedral building unit; the threedimensional structure being formed by linking these cages through the 4-, 5-, and 6-ring faces. The three-dimensional structure obtained contains a smaller 10-hedron cage [445462]. Both cages have crystallographic 2/m site symmetry. A stereo projection of the framework structure is shown below. Elemental analysis shows a Si:Al ratio of about 22:1. If A1 is in the framework, it can not be determined from this data whether it is preferentially located on one site. The one
Peanut-shaped 30-hedron cage
lO-hedron cage
267 crystaUographically independent tetramethyl ammonium cation was found to sit on a mirror plane in the center of each lobe (by symmetry) of the peanut-shaped large cage. Large isotropic thermal parameters are a good indication that the cation is disordered.
Stereoprojection of framework (Si only) for as-synthesized TMA Silicate
Acknowledgments Thanks are expressed to D. E. Cox for his assistance at the National Synchrotron Light Source, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Division of Materials Sciences and Division of Chemical Sciences.
References
.
3.
.
"BNLFIT", a locally modified version of the Rietveld-Hewat program, Brookhaven National Laboratory. "Shelxtl Plus," Siemens Analytical X-Ray Instruments, Inc., Madison, WI (1990). Ch. Baerlocher, A. Hepp, and W.M. Meier, "DLS-76, a Program for the Simulation of Crystal STructures by Geometric Refinement," Institute of Crystallography and Petrography, ETH, Zurich, 1977. A.C. Larson and R.B. Von Dreele, "GSAS- General Structure Analysis System," Los Alamos National Laboratory Report LA-UR 86-748 (1986).
H.G. Karge and J. Weitkamp (Eds.) 268
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
THE P O R E STRUCTURE OF ALUMINA PILLARED CLAYS DEPENDING ON THE KIND OF INTERCALATED AL-CATION V. Seefeld, R. Trettin*, W. GeBner ACA Berlin, *INW TU Berlin, Germany SUMMARY Pillaring of smectites with the different oxo-hydroxo-aluminium cations All3 and Alpoly gives products with similar surface areas and x-ray data (basal spacings) after a thermal treatment at 573K. Investigation of the micropore structure shows a relatively broad but more uniform distribution of pore size between 5 and 10A for the product got due to intercalation of the well defined tridecameric species (All3) while the polymeric cations (Alpoly) cause the formation of a micropore system with bimodal pore size distribution. INTRODUCTION Thermal stable expanded layer structures possess molecular sieve properties and can be used for adsorption and catalysis. In the case of smectites the intercalation of polymeric metal cations - e.g. oxo-hydroxo-aluminium cations - leads to the formation of pillared clays. The oxo-hydroxo-aluminium cations present a complex system including a wide scale of species. Among these the tridecameric (All3 with e - Keggin - structure) and the polymeric (Alpoly with unknown structure) cations are relevant for the pillaring-process. In both cases the products give the typical pillared clay characteristics after a thermal treatment at 573K. Here are shown first attempts to investigate the pore structure of alumina pillared clays depending on the kind of the used Al-species. E X P E R I M E N T A L SECTION Natural smectites were purified by ion exchange (Na+-Form) and sedimentation (separation of the 2~tm-fraction). The solution of Al-cations (either A113 or Alpoly) was given to a stirred aqueous suspension of the parent clay adjusted to pH=5,5. After washing, freeze drying and heating up to 573K (samples called All3-PILC and AlpolyPILC, respectively) the specific surface area and pore size distribution were determined volumetrically at 77K by nitrogen sorption using an ASAP 2000 with micropore system. For calculation of the micropore volume distribution discussed here the technique after Horvath and Kawazoe - a model valid for zeolites - was chosen. RESULTS AND DISCUSSION Compared with the parent clay - an essential a mesoporous material - the pillared clays possess a considerable amount (about 70%) of micropores. The results of the micropore analysis after a thermal treatment at 573K show that the cumulative pore volume up to 15.A.pore diameter is significant higher for AI13-PILC and Alpoly-PILC (samples contain a comparable amount of
269 pillar-Al per cation exchange capaticity) than for the starting material but similar for both pillared clay samples.
parent clay
sample BET surface area [m2/g]
AII3-PILC
63,1
Aipoly-PILC
322,5
363,2
0,1353
0,1415
cumulative pore volume up to 15A [cm3/g]
9
9
i
.
.
0,0217
.
.
.
i
.
.
.
.
.
!
'"
9
9
The calculation of the pore size distribution suggests that in an A113-PILC pores excist
0,03
with a relative broad but uniform distribu-
~"
~
Alpoly - PILC
tion while for an Alpoly-PILC two separate domains dominate about 5,8 and 8,5A in diameter. This observation can be inter-
=~" 0,02
preted as a result of the structure of the A1cation used as pillaring agent: The tridecamerir cation is known as a well defined 0,01
species while the polymeric cations - their
~5
structure is still unknown - may vary in size so .... .po
0,00
9'
' 5
and charge per A1. So possibly a mixture of
..,,..,.. "" ........
. . . . .
,= . . . . . . . .
' . . . . . . . . . 10 15
Pore Diameter (A)
different species may serve as origin for the resulting pillars in the latter case and cause the bimodal distribution of the pore size.
The development of the micropore structure upon thermal treatment in high vacuum was studied for a sample of AI13-PILC. It can be stated that the essential formation of the pore system is already finished in the pillared clay precursor after drying and outgassing at room temperature. An increase of temperature up to 334K doesn't change the BET surface area and the total pore volume. A significant higher value for the surface area is achieved after heating at 573K while the pore volume was only slightly higher. The median pore diameter increases simultaneously. This effect is attributed to the dehydroxylation of the interlayer cation. CONCLUSION The submitted results imply that the pore structure of alumina pillared clays may be influenced by the nature of the intercalated Al-cation. Further investigation should be devoted to the behaviour of polymeric Al-cations in the interlayer space of smectites and consider the possible influence of hydrolysis.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
270
SYNTHESIS AND STRUCTURE DETERMINATION OF A NEW ALUMINOPHOSPHATE FROM FLUORIDE MEDIUM Nata~a Zabukovec 1, Ljubo Goli~2 and Ven~.eslav Kau~i~ 1,2 1National Institute of Chemistry, Ljubljana, Slovenia 2Department of Chemistry and Chemical Technology, University of Ljubljana, Slovenia. SUMMARY Hydrothermal crystallisation of cobalt-substituted aluminophosphates from media containing F" anions and organic template has been studied. Under such conditions single crystals with a novel structure were obtained and for structure determination a crystal of Co0.22[AI2P2Os{OH)0.44(OH2}I.56] 9H20 was used. Intensity data were collected on an Enraf-Nonlus CAD4 diffractometer with MoKcz radiation. The orthorhombic unit cell has the following parameters: a - 9.444(1 )./~, b - 9.588(1 )./~, c = 9.928(1)]~. The space group is P212121. The structure consists of PO 4 tetrahedra and octahedral and trigonal-bipyramidal AI co-ordination polyhedra, building threedimensional network of 3-, 4-, 5- and 6-member rings. There is no evidence for fluorine atoms and organic molecules to be incorporated in the formed material. Nonframework cobalt atoms and water molecules are located in the openings. INTRODUCTION Synthesis of zeolites and AlPO4-based materials from fluoride medium brought about the formation of many new materials assuming F~ structure directing and templating roles. On the other hand there are also known fluoride beneficial effects on nucleation and crystal growth rate (Guth et al.). l The presence of fluoride anions in reaction mixture may result in their incorporation into the formed material or may only influence the gel chemistry with no further occlusion in the crystalline solids. The fluoride influence on crystallisation was of our great interest, since the aim of our work was to synthesise Co-substituted A1PO4-molecular sieves, known to be useful for catalytic and absorption applications, with an additional request obtaining large enough crystals for single-crystal structure determination. EXPERIMENTAL SECTION
The synthesis of the new compound has been performed using the reaction gel of molar composition 0.4 Co(ac)2 : 0.8 A1203 : 1.0 P205 : 2.0 en : 1.5 NH4F : 70 H20 (en - ethylenediamine, ac - acetate) using moderate-condition hydrothermal techniques described by Wilson&Flanigen. 2 In a Teflon-lined autoclave under static conditions at 468 K over 4 days, purple prismatic crystals were obtained. A crystal of 0.53 x 0.34 x 0.27 mm3 in size was used for data collection. The crystal structure was solved by direct methods. No absorption correction was made (l~ - 1.103 ram1).
271 Structure refinement was straightforward for the P, A1 and O atomic sites assigned to a framework, but was not quite conclusive for the contents of the channels. It was also not possible to locate all H atoms with certainty. Water H atoms were identified in an electron density map, while the others were calculated from refined O-positions assuming ideal O-H distances and angles and were not refined. Non-hydrogen atoms were refined anisotropically. The final R (on F) was 0.042, Rw = 0.032 for 1506 contributing reflections and 164 parameters. RESULTS AND DISCUSSION The structure represents one of the more condensed structures of aluminophosphates. The framework is built of cross-linked aluminium and phosphorous units enclosing cavities, where Co-cations and water molecules are trapped. The access to the cavities is through six-member rings only. The ordered AI-P distribution is modified with O atoms connecting two AI sites and forming 3- and 5- member rings in addition to 4and &member rings. Octahedral A1 - O distances have values from 1.817(1)/~ to 1.903(1)/~. and the bond angles from 87.3(1 )o to 176.4(1)~ The A1- O distances in the five-co-ordinated A1 are in the range of 1.772(1)/~ to 1.912(1)/~ and the bond angles from 88.15(1) ~ to 175.0(1) ~ Phosphorous tetrahedral bond distances and angles are comparable with those of related materials. Occluded Co atoms are disordered between two positions, one 8% and the other 15% occupied. The water molecule located in the cage is stabilised, forming a hydrogen bond with a framework O(9) atom (the distance O(11)- 0(9) is 2.72(2)/~) and 0(6) atom (the distance O(11)- O(6) is 2.98(2)/~). There is also an evidence of some additional O-H-0 hydrogen bonding, which helps us to identify the presence of H atoms, especially in the vicinity of AI-AI bridging O atoms, causing additional stabilisation of the framework.
CONCLUSIONS The synthesised material confirmed the previous anticipation of F" influence on gel chemistry and crystallisation. Structure determination yields a novel structure, which appears as a complex framework with small pores and occluded Co cations. For the remained uncertainties about the framework H atoms positions, IR spectroscopy should provide an accurate answer. REFERENCES (1) J. L. Guth, H. Kessler, P. CauUet, J. Hazm, A. Merrouche & J. Patarin, (1993), in 'Proceedings from the Ninth International Zeolite Conference, Montreal 1992' (Eds.: R. von Ballmos et al.), Butterworth-Heinemann, Boston, 215-222. (2) S. T. Wilson & E. M. Flanigen, (1986), US Patent 4. 567. 029.
H.G. l~arge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
272
O4 M O L E C U L E
IN THE
PORE
OF
Cas-A
ZEOLITE
by Tetsuo Takaishi* Toyohashi University of Technology, J A P A N The existence of 04, dimer of 02 molecules, has been subjected to long discussion, without a decisive conclusion. Recently we caught diamagnetic 04 molecule in the pore of Cao-A zeolite at near liq.N2 temperature. The dimerization heat, from two adsorbed 02 to adsorbed 04, was 2.1 4- 0.1 kJ/mol, and 04 has a linear shape. Exp e r i x n e n t a l An improved Chan electro-balance 1) was used in a Lewis type magneticsusceptibility meter, 2) and the amount of 02 adsorbed and magnetic susceptibility of the sample were simultaneously measured. Cao-A was prepared by ion-exchanging Na12-A synthesized by Charnell's method. An adsorbent was baked out at 400~
for a long
time under a slow flow of 0~. Results Fig. 1 shows curves of Xobo/X(02) vs. n~,,~,, where sad, denotes the total number of adsorbed O2/u.c., Xobo the observed susceptibility of the sample, (adsorbent + adsorbate)/u.c., 2:(O2) the susceptibility of gaseous oxygen molecule, and Xob,/X(02) the number of monomer 02 in the adsorbed phase. The difference between the broken line and observed curve gives the amount of diamagnetic species, i.e., 04 produced from O2 molecules. Fig. 2 shows relations between [ O4(ads) ] thus evaluated and [ monomer O~(ads) ]2, and lines give equilibrium constants, g = [ O4(ads) ]/[ monomer O2(ads) ]2. Fig. 3 shows the dependence of InK on 1/T, from which we have A H = -2.1 4. 0.1 kJ/mol, and
A S = - 5 2 5= 2 J/mol-K .
The isotopic scrambling reaction, XSo~
+
1602
--~
2 180180 ,
did not take place in the pore of Cas-A at the concerned temperature, and hence it is concluded that 04 has a linear shape.
* Retired ; permanent address is Hayama-cho, Nagae 1461-251, Kanagawa Prefecture, 240-01 JAPAN.
273
'
,'I
'
~5 6
,,//123~
0••10-
. . . .
77V
'9
2
0
I
//
m
5
0
==_..=
9
i,
5
10
!
~.~,/molec./u.c.
I
15
20
I
40
I
I
60
I
80
[monomer 02(ads)]2 / molec.2 u.c.-2
Fig. 1 Magnetic susceptibility of
Fig. 2 Amount of O4(ads) vs.
0 2 (ads) -I- Cas-A ,
t
[ amount of adsorbed monomer 02 ]2 ~
,
u. - 3 7
J O
Fig. 3 Equilibrium constant for dirnerization vs. 1/T
-4
I
-5 8
~
I
10
~
I
12
14
1 / T / 10 -8 K -1
The author thanks his old students, T.Matsuoka, A.Endo, A.Shimono and K.Hayashi, for their assistances. References 1) T.Takaishi, k.Yusa, Y.Ogino and S.Ozawa, ].C.S. Faraday Trans. I, (1974), 70, 671. 2) R.T.Lewis, Rer. Sci. In,ft., (1971), 42, 31; J. Vac. Sci. Tech., (1974), 11,404.
H.G. Karge and J. Weitkamp (Eds.)
274
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved. STRUCTURE AND PROPERTIES OF Cd,,See+ NANO CLUSTERS ENCAPSULATED IN AN ALUMINATE FRAMEWORK.
MATTHEW E. BRENCHLEY AND MARK T. WELLER
DEPARTMENT OF CHEMISTRY, UNIVERSITY OF SOUTHAMPTON, SOUTHAMPTON, ENGLAND.
SUMMARY - The framework expanded aluminate sodalite, Cds[A102]12.Seq was prepared by reducing the parent selenite containing sodalite in a flow of pure hydrogen. The resulting material was characterised by powder X-ray diffraction data and shows the presence of distinct tetrahedral Cd4Se6+ clusters. The clusters of II-VI type semiconductor have similar Cd-Se distances to the bulk, but they are dispersed by the framework. The diffuse reflectance UV-Visible spectrum shows a blue shift from the bulk CdSe, with a sharper onset of absorption. INTRODUCTION- Alurninate sodalites of general formula (M2+)8[AIO2112.(X2)2 have been shown to form for a variety of metals (M =Mg, Ca, St, Ba, Cd) and anions (X =WO4, CrO4, MOO4, SO4, SeO3, S, Se) ~. They are of interest due to the fact that they disobey Loewenstein's rule of aluminium avoidance 2 and their ability to entrap II-VI type semiconducting nano units 3. The structure of the aluminate framework is comprised of comer sharing AIO4 tetrahedra in four and six rings, generating the basic 13 cage unit adopted by zeolites. The 13 cages are linked by both the four and six rings producing the classic sodalite structure. The anion is located on the origin with tetrahedral coordination to the divalent metals, the 2 + metals are in tern tetrahedrally coordinated to the framework oxygens. The metals also interact with anions in neighbouring 13 cages through the six rings, but with larger clustercluster separations than in the bulk M-X materials, hence modifying the electronic structure.
E X P E R I M E N T A L - The parent selenite baring sodalite, Cds[A102]i2.(SeO3)2 was prepared by sintering a finely ground stoichiometric mixture of CdO, AI203 and CdSeO3 in a sealed evacuated silica glass ampoule at 1000~
for 24 hours. The resulting material was m
characterised by XRD and FT-IR and shown to be a sodalite in the space group I43m, with a=9.0093(1)A and the IR active SeO32- modes observed. The selenite sodalite was then reduced in a flow of pure hydrogen at 600~
for 8 hours to yield a brown crystalline
product. This was also shown to be a single cubic sodalite phase with systematic absences
275 m
consistent with the space group I43m, and with a=8.8679(1),~. FT-IR confirmed the loss of the IR active SeO32-modes. Diffuse reflectance UV-Visible spectra for both the CdSe sodalite and bulk were obtained. Structure determination was performed using the DBWS-9006PC package of Wiles and Young 4 on powder X-ray diffraction data. Refinement proceeded with the addition of background, peak shape, atomic position and temperature factor parameters until convergence was achieved. Towards the end AlzOs was added as a second phase to compensate for a small amount of impurity found in the sample. Final atomic positions and temperature factors are, A1 (1A, IA, 0) B=0.88: O (0.1412, 0.1412, 0.4139) B=0.89: Cd (0.1709, 0.1709, 0.1709) B= 1.07: Se (0, 0, 0) B= 1.09. See Figure 1
RESULTS AND DISCUSSION- Bond lengths and angles from the refined coordinates fit well the trends observed in other aluminate sodalites. AI-O 1.755/L AI-O-A1 126.6 ~ AI tilt 31.4 ~ Cd-O 2.187A and Cd-Se 2.626A. The tetrahedral Cd-Se bond distance matches almost exactly that of the bulk material. The inter-unit distance of 5.054A as determined as Cd-Se (next nearest neighbour) is somewhat larger than that of the bulk wurtzite type material which has an equivilent distance of 4.379,~,. This increased separation remits in the blue shift m the UV-Visible spectra from the bulk, and can be seen in Figure 2 as a shift of 50nm. 0.9 0.8 ~ .7 "~ 0.6 '~ 0.5 0.4 ~
0.5 0.2 0,1
500
0
6(30
7()0 8()0 WAVl/LENO'I~I/ (am)
Figure 1, Cd4Se clusters entrapped
Figure 2, UV-Vis of bulk CdSe (left)
in the aluminate framework.
and CdSe sodalite (right).
REFERENCES 1) R. Kondo, Yogyo Kyokia Shi, 1965, 17, 1. 2) Loewenstein, Am. Miner. 1954, 39, 92 3) M. E. Brenchley and M. T. Weller, Angew. Chemic, 1993, 32, 1663. 4) D. B. Wiles and R. A. Young, J. Appl. Crystallogr., 1981, 14, 149.
~._
960 '
.
1000
VIII. New Materials
This Page Intentionally Left Blank
H.G. Karge and J. Weitkamp (Eds.) 276
Zeolite Science 1994: Recent Progress and Discussions
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
A NEW ONE-DIMENSIONAL-MEMBI~kNE: ALIGNED M O L E C U L A R S I E V E C R Y S T A L S IN A N I C K E L F O I L
ALPO4-5
Manfred Noack, Peter KOlsch, Dieter Venzke, Petra Toussaint and Jfirgen Caro Institut for Angewandte Chemie, Rudower Chaussee 5, 12489 Berlin, Germany
Summary Oriented A1PO4-5 crystals have been embedded by galvanic nickel deposition in a metallic matrix. The membrane so made is thermally stable up to 650K. The AlPO4-5-in-nickelmembrane has been tested in the separation of binary mixtures of n-heptane and an aromatic compound of different bulkiness.
Introduction During the last few years, increasing attempts have been made to develop zeolite membranes for separation and catalysis applications. We have shown the zeolite-in-metal-membrane as a new type of a high-temperature molecular sieve membrane with ZSM-5 crystals [ 1]. In this paper, however, we present a novel type of molecular sieve membrane obtained by the electrochemical embedding of oriented AIPO4-5 crystals in a nickel matrix. Experimental Large AIPO4-5 single crystals of prismatic shape (mean crystal size 47~tm long, 10~tm thick) have been synthesized by microwave heating [2]. The membranes were sealed in the permeation cell with Kalrez-O-rings. After activating the membrane in vacuo, the absence of pin holes was proven by 1,3,5 tri-isopropylbenzene. For testing the membrane, the pervaporation of binary mixtures which consist of n-heptane and a differently substituted 1,3,5 aromatic compound has been studied. On the feed side of the membrane was always the liquid binary n-heptane:aromate = 1:1 (mole ratio) mixture at 1 bar and 364 K, the permeate side was evacuated. Results A perforated 100m thick nickel foil with 20~tm wide holes has been used as hosting matrix for the AIPO4-5 crystals. By means of an electric field perpendicular to the plane of the perforated Ni-foil, the AIPO4-5 crystals were oriented vertically in the holes of the nickel foil [3]. Then the nickel foil containing in its holes the oriented AIPO4-5 crystals was used as the cathode in a galvanic nickel bath to seal by metal deposition the voids between the crystals [1]. When the growing Ni film reached the top level of the crystals, the electrolysis was stopped. Fig. 1: Oriented AIPO4-5 crystals in the Ni-membrane with a total diameter of 17 mm. The separation factor of n-heptane with an aromatic compound (Fig.3) is near 1 if the aromatic component is smaller than the diameter of the AIPO4-5-pores. However, when the aromatic compound is bulkier than the pore diameter, i.e. > 0.73nm, a increases immediately to a value greater than 1000 for tri-isopropylbenzene (TiPB) and greater than 100 for triethylbenzene (TEB), later with increasing pervaporation time a decreases. It should be noted that the migrating molecules can not pass each other in the pore (pearl-string-like behaviour).
277
:"
"'-~03.
"~'..-~:
~.~,
.
....,.
9F =.... , :
..~
9 '~slg: "
)~"i. I
~.~
I . .~
"" g~c:l i ,
"~'.i '. 9
.... -
N. N
'
Fig.2 SEM images of vertical and horizontal cross sections of the AIPO4-5-in-nickelmembrane. The connection between the crystal habitus and the channel system is shown schematically. Fig.3 Flux density and separation factor Otn_C7/aromate as a function of the diameter of the aromatic compound.
,3,9 mole
10 -6 s e c "l c m 2
Conclusions .~,., We have demonstrated that it is possible to bring oriented AIPO4-5 ~" ' 0.S.I crystals, by galvanic metal deposition, gas-tight in a Ni-matrix. The /r /mass transport proceeds through the / / / , / , unidimensional straight pores. In the study of several binary mixtures consisting of n-heptane and a substituted benzene of different bulkiness we find that the membrane acts like a sieve: if the diameter of a component is larger 0.73 nm this component is excluded and only n-heptane can pass the molecular sieve pores, but later with increasing time-on-stream the separation factor decreases. The new unidimensional high-temperature AIPO4-5 and SAPO-5 membranes can be used for stereo-selective mass separation and/or catalytic reaction in a membrane reactor. Acknowledgement We thank the DFG for financial support ( Ca 147/2-1). We are grateful to Mrs. I. Girnus for the AIPO4-5 synthesis, Mrs. E. Lieske for GC analysis, Mr. J. Richter-Mendau for SEM. References 1. a) P. Kolsch, J. Caro, M. Noack, D. Venzke, P. Toussaint and H. Nickel. Preparation of High-Temperature Molecular Sieve Membranes for Molecular Sieving and Catalysis, DD Patent No. 4 330 949.6, Appl. from 8.9.1993, b)P. Krlsch, D. Venzke, M. Noack, E. Lieske, P. Toussaint and J. Caro, Proc. 10th Intern. Zeolite Conf., in press, c) P. Krlsch, D.Venzke, M. Noack, P. Toussaint and J.Caro, J.Chem.Soc., Chem.Commun., (1994) 2491. 2. a) I.Girnus, K.Hoffmann, F. Marlow, J. Caro and G. Drring, Microp. Mat.,2 (1994) 537, b) l.Girnus, K. Jancke, R. Vetter, J. Richter-Mendau and J. Caro, Zeolites, 15 (1995) 1. 3. a) M. Noack, P. K61sch, D. Venzke, P. Toussaint, J. Caro, Microp. Mat., 3 (1994) 201, b) J. Caro, M. Noack, J. Richter-Mendau, F. Marlow, D. Petersohn, M. Griepentrog and Kornatowski, J. Phys. Chem., 97 (1993) 13685, c) J. Cam, G. Finger, J. Kornatowski, J. Richter-Mendau, L. Werner and B. Zibrowius, Adv. Mater., 4 (1992) 273.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions
278
Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
SYNTHESIS OF A ZEOLITE MEMBRANE O N A MERCURY SURFACE Y. Kiyozumi, tC Maeda and F. Mizukami National Institute of Materials and Chemical Research, Higashi 1-1, Tsukuba, Ibaraki 305, Japan
SUMMARY The crystallization of ZSM-5 was carried out in the presence of a m e r c u r y surface. Uniform thickness and translucent zeolite membranes with s m o o t h surfaces are obtained. The crystallization rate and crystaUinity of the m e m b r a n e s were m u c h higher o n the mercury surface compared with Teflon, suggesting a certain strong relationship b e t w e e n the zeolite crystallization and the high surface tension of mercury. INTRODUCTION Great interest has been focused on zeolite membranes or films a n d their fabrication m e t h o d s because of their great importance in fields such as catalysis, separation a n d sensing. However, u n d e r conventional synthesis conditions of zeolit~es, synthetic zeolites have been crystallized directly into a p o w d e r y form. There is much literature related to zeolite membranes [1-6]. In this work, w e will describe the synthesis of a pure zeolite membrane on a mercury surface a n d characterization of the membrane. EXPERIMENTAL The h y d r o t h e r m a l synthesis of the ZSM-5 membrane was p e r f o r m e d as follows. A l u m i n u m nitrate and coloidal silica (Cataloid SI-30 from Shokubai Kasei Co.; 30.4 wt% SiO2, 0.38 wt% Na20, 69.22 wt% water) were a d d e d to a stirred mixture of t e t r a p r o p y l a m m o n i u m bromide (TPABr) and sodium h y d r o x i d e in solution, to give a hydrogel with a composition of 0.1TPABr-0.05Na20-(0~0.02)A1203-SiO240~400H20. Then, the hydrogel was transferred to a 50 ml Teflon-lined stainless steel autoclave. Clean mercury was placed on the bottom of the Teflon liner. The autoclave was placed in an air-heated oven at 120~ ~180~ for 3 ~ 48 h. After the completion of crystallization u n d e r autogeneous pressure w i t h o u t stirring, the autoclave was cooled down. The ZSM-5 membrane was w a s h e d with deionized water a n d dried at 120~ for 24 h. Afterwards the ZSM-5 m e m b r a n e was calcined at 300 - 500~
for 20 h in order to decompose the organic base occluded in the
zeolite framework.
279 RESULTS AND DISCUSSION Typical results are summarized in Table 1 together with the synthesis conditions. M e m b r a n e s were attached only to the surface of the mercury, a n d not to the Teflon-liner. All of the starting h y d r o g e l was completely c o n v e r t e d into the m e m b r a n e , the thickness of the m e m b r a n e was uniform, a n d the thickness appeared to increase with increasing crystallization time. The silicalite m e m b r a n e was obtained w h e n the molar ratio of H 2 0 / S i O 2 was more than 70 and the m e m b r a n e was p r o d u c e d at shorter crystallization times compared to the synthesis with only a Teflon sleeve. The m e m b r a n e crystallized on the surface of the mercury could be easily detached from the surface. After 10 and 20 h of reaction, the membrane was transparent. This result suggests that the m e m b r a n e has orientated a n d / o r size-controlled zeolite crystals. From the above results, it was concluded that such m e m b r a n e s were p r o d u c e d due to the high surface tension (484 m N / m at 20~
of mercury. It is possible to
apply the membrane to many fields such as gas separation, electrical devices, a n d hydrocarbon processing. Table I
Run No.
Preparation of ZSM-5 and silicalite m e m b r a n e s on a m e r c u r y surface u n d e r various synthesis conditions
Type* Si/A12
1 2 3 4 5 6 7 8 9 10 11
S S S S S S S S S Z Z
~ ~ ~ ~ ~ ~ ~ ~ ~ 200 100
Synthesis conditions Temp. (~ Time (h) 120 120 150 170 170 170 180 180 180 170 170
48 72 48 10 20 36 5 10 20 20 20
Thickness (Bm)
Yield (%)
20 30 25 40 65 100 50 75 120 50 50
95 98 100 100 100 100 100 100 100 100 100
*S = Silicalite, Z = ZSM-5 REFERENCES [1] T. Sano, Y. Kiyozumi et al., Zeolites 11 (1991) 842; Bull. Chem. Soc. Jpn. 65 (1992) 146.
280 [2] [3] [4] [5] [6]
J.G. Tsikoyiannis et al., Zeolites 12 (1992) 126. M.W. Anderson et al., J. Mater. Chem. 2 (1992) 255. J. Dong et al., J. Chem. Soc., Chem. Commun. (1992) 1056. G.J. Myatt et al., J. Mater. Chem. 2 (1992) 1103. E.R. Geus et al., J. Chem. Soc. Faraday Trans. 88 (1992) 3101; Microporous Materials 1 (1993) 131.
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
281
MOLECULAR RECOGNITION IN ZEOLITE THIN FILM SENSORS. GROWTH OF ORIENTED ZEOLITE FILMS
Sue Feng, Yongan Yan and Thomas Bein* Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA FAX 317-494-0239 SUMMARY We describe chemical sensors based on selective sorption in zeolite thin films on piezoelectric devices. Zeolite crystals with different pore sizes were coupled onto the gold electrodes of quartz crystal microbalances (QCM), via molecular attachment on the surface. A self-assembled monolayer of thiolalkoxysilane coupling agent on the gold surface was used to attach the zeolite crystals to the QCM, and the resulting films were coated with thin glass layers. The sorption behavior and selectivity of the devices was determined via dynamic vapor sorption isotherms, and nitrogen sorption isotherms at liquid nitrogen temperature. Uptake of molecules small enough to enter the zeolite pores can be one hundred times greater than that of molecules with kinetic diameters greater than the pores. The selective adsorption can be tailored by variation of the zeolite composition, pore sizes, and other parameters. The selectivity of these stable films was further controlled by ion exchange into the film. We will compare the above films with recently discovered, oriented zeolite films grown on organic multilayers on gold. 1 INTRODUCTION A chemical sensor is a device that can monitor concentrations of gases or liquids on site by converting a chemical interaction into an electronic or optical response. There is a growing need for selective coatings for microsensors. Our recent development of molecular sieve-based composite films has introduced a novel means for controlling vapor/surface interactions.2,3,4,s,6,7,8 A sensor coated
with molecular sieve crystals discriminates different molecules according to their sizes and shapes, with the ability to modify pore opening sizes in the range of 0.31.2 nm and beyond. In this contribution we describe the selective adsorption behavior of single layer zeolite crystal coatings on quartz crystal microbalances (QCM), and further control of this behavior by adding 'gate' functions into the layers. EXPERIMENTAL
SECTION Zeolite crystals were anchored to the gold electrodes of quartz crystal microbalances (QCM) from toluene suspension after formation of an interracial monolayer of 3-mercaptopropyltrimethoxysilane. A thin glass layer (ca. 10-20
282
i~g/cm 2) was formed by dip-coating in an acid catalyzed sol derived from Si(OEt)4. The oriented growth of zeolite crystals is described in ref. 1. Some of the layers were ion exchanged with alkali ions. Vapor sorption isotherms were measured in an automated flow system that produces different vapor concentrations from a diffusion cell with mass flow controllers. Nitrogen adsorption isotherms were obtained at 77K in a second automated gas dosing system.
RESULTS AND DISCUSSION Representative sorption results for the molecularly attached crystals are presented in this abstract. We have developed strategies to enhance and tailor selective adsorption, for example by varying the surface polarity by means of different zeolite composition, by changing the zeolite Bronsted acidity, and the zeolite pore sizes. For example, the sorption of ethanol in a silicalite-based film is many times favored over water in the ppm partial pressure range at room temperature. This behavior can form the basis for a useful ethanol sensor in the ambient atmosphere. We have also utilized the ion-exchange capabilities of the attached zeolite crystals to further modify the pores such that they respond to other types of molecules. For instance, films of zeolite CaA absorb nitrogen and vapors of water, ethanol and n-hexane, while the Na form (prepared by immersing the sensor in aqueous Na(I)) already shuts down for hexane, and sorbs ethanol only weakly. We thank the National Science Foundation and the Department of Energy WERC Program for financial support of this work.
REFERENCES Feng, S.; Bein, T. Nature 1994, 368, 834. Bein, T.; Brown, K.; Frye, G. C.; Brinker, C. J., U. S. Patent 5,151,110, Sep. 29, 1992 Bein, T.; Brown, K.; Enzel, P.; Brinker, C. J. Mat. Res. Soc. Symp. Proc.; Materials Research Soc.: Pittsburgh, 1988; Vol. 121,761 Bein, T.; Brown, K.; Brinker, C.J. Stud. Surf. Sci. Catal. 49 (Zeolites: Facts, Figures, Future), P. A. Jacobs, R. A. van Santen, Eds., Elsevier,Amsterdam, 1989, p. 887 Bein, T.; Brown, K.; Frye, G. C.; Brinker, C.J.J. Am. Chem. Soc. 1989, 111, 7640 Yan, Y.; Bein, T., MRS Symp. Proc. 233 ('Synthesis/Characterizationand Novel Applications of MolecularSieve Materials') (1991) 175 Yan, Y.; Bein, T. Chem. Mater. 1992, 4, 975 Yan, Y.; Bein, T. J. Phys. Chem. 1992, 96, 9387
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
283
PHASE FORMATIONS IN THE SINTER PROCESS OF CORDIERITE/MULLITE CERAMICS FROM MG-EXCHANGED ZEOLITES A, P, AND X B. RLidinger and R.X. Fischer Institut fur Geowissenschaften der Universit~it, D-55099 Mainz, Germany ABSTRACT The phase formations in the calcination process of zeolites Mg-P, Mg-X and Mg-A are investigated by differential thermal analyses and X-ray diffraction methods. The weight fractions were calculated from the scale factors of multi phase Rietveld refinements. The phase reactions, formations, and transformations are more complex than described before for similar systems. INTRODUCTION
Sintering ceramics from zeolite precursors has been described frequently as an alternative route to the production of ceramics by melting oxide precursors or by sol-gel syntheses [1,2,3]. The homogeneous distribution of atoms at the atomic scale, the uniform particle size, low calcination temperatures, the possibility of a single firing step and the low costs of commercially produced zeolites are some of the advantages of using zeolites as ceramic precursors. VVe studied the phase formations in the sinter process of Mg-exchanged zeolites X, A and P. The crystalline phases could be simulated with high accuracy using Rietveld refinement procedures. EXPERIMENTAL
The Na-forms of the zeolites were first NH4-exchanged in 10% NH4NO 3 and subsequently Mg-exchanged in a Mg(NO3) 2 solution. The chemical compositions of two differently prepared zeolites from X-ray fluorescence analyses are P: (1) Mg3.0[NH4]1.2AI7.2Si8.8032
(2) Mg2.4[NH412.4AI7.2Si8.8032
X: (1) Mg27[NH4125Na1Ca1AI82Si1100384 (2) Mg17[NH4145Na1Ca1AI82Si1100384 A: (1) Mg3.2[NH4]5.7Nao.1All 2.2Sil 1.8048 (2) Mg1.7[NH418.6Na0.2AI12.2Sil 1.8048 Four series of analyses were performed for the zeolite precursors to describe qualitatively and quantitatively the phase formations and reactions during the calcination.
(1) Differential thermal analyses (DTA) followed by qualitative
powder diffraction phase analyses of the samples quenched after endothermic and exothermic
reactions.
(2)
In situ
high
temperature
X-ray diffraction
experiments and qualitative analyses of the crystalline phases. (3) Quantitative powder diffraction analyses of the amorphous components of calcined samples quenched to room temperature with admixed fluorite as internal standard.
284
(4) Standardless quantitative powder diffraction
analyses of the crystalline
components. This gives a total of about 40 powder diffraction patterns analyzed using the PC-Rietveld plus program package [4] for each of the Mg-exchanged zeolites A, P, and X. Weight fractions of the phases were determined using the scale factors derived from the Rietveld refinements.
RESULTS AND DISCUSSION The phase formations in the calcination process of the zeolites studied here are more complex than described before for similar systems. The weight fractions of the Mg-P and Mg-X zeolites are shown in Figures 1 and 2 as a function of the calcination temperature. Two samples were held at 1 4 0 0 ~
for
an additional period of time. Mullite is the first crystallization product in all samples accompanied by Mg-I~-quartz (Mg-P, Mg-A) and by spinel (Mg-A, MgX). Based on the results of the quantitative
analyses, we can derive the
complete crystallization path and possible phase reactions starting from the amorphitized
zeolite
and yielding the final
cordierite/mullite.
The
chemical
composition of the solid solution compounds mullite and Mg-I~-quartz is derived from lattice constant refinements correlated with the composition. Phase formation: AM =amorphous phase, CO =cordierite, CR =cristobalite, SA = sapphirine, EN = enstatite, SP = spinel, MQ = Mg-I~-quartz, MU = mullite
REFERENCES 1Chowdhry, U., Corbin D.R., Subramanian, M.A. (1989), U.S. Pat. No. 4814303 2Subramanian, M.A., Corbin, D.R., Chowdhry, U. (1990), Adv. Ceramics 26,239 3Bedard, R.L., Flanigen, E.M. (1990), U.S. Pat. No. 4980323 4Fischer, R.X., Lengauer, C., Tillmanns, E., Ensink, R., Reiss, C.A., Fantner, E.J. (1 993) Mater. Science Forum 133-136, 287 Acknowledgement We thank the Deutsche Forschungsgemeinschaft for financial support under grant Fi442/1.
H.G. Karge and J. Weitkamp (EAs.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
285
.
SlLICALITE WITH P O L Y C Y A N O G E N E Y. Schumacher, R. Nesper; Laboratorium fuer Anorganische Chemie, ETH Zentrum, CH-8092 Zuerich Switzerland SUMMARY Silicalte-1 was loaded with gaseous dicyanogene. Temperature induced polymerization yielded a composite of a polymer (CN)x confined in the zeolite framework. INTRODUCTION As recently reported, dicyanogene promotes the formation of linear dicyanopolyines while present during the Kraetschmer synthesis of fullerens [1].These polyines polimerize easily and form extended pi-electron-systems. Dicyanogene itself polimerizes at elevated temperatures ( 573 K). To study the properties and structure of the confined polymer, a sample of silicalite-1 was loaded with gaseous dicyanogene. EXPERIMENTAL 0.2 g of Silicalite-1 (hydrothermal fluoride-synthesis, Si/AI ratio >1000, particle size 10-15 micron, [3]) was calcined and activated at 573 K. It was then placed directly into the teflon container and evacuated. The gaseous precursor dicyanogene evolved upon pyrolysis of diacetylglyoxime [2]. It was collected as a colorless liquid into a small teflon lined autoclave at 77 K. Loading of the zeolite with the purified dicyanogene (about 30 mmol) was allowed to proceed at room temperature for 12 hours under the autogeneous pressure of the dicyanogene. This was followed by a heat treatement at 493 K for 48 hours. RESULTS All of the gaseous dicyanogene had reacted with the zeolite and to a minor extent with the teflon lining. The resulting zeolite material was of a homogeneous texture as inspected by light microscope and had an dark yellow color. Reaction with strong acid resulted in partial distruction of the polymer, as indicated by the loss of color and gas evolution with the characteristic HCN smell. Extraction of the polymer with diethylether, chloroforme or acetonitrile was not possible. The IR-spectrum of a KBr pellet revealed no extraframework absorption band. Thus the absence of any CN stretch vibration suggests, that there are most likely no large amounts of unconfined polymer present in the sample. The differential thermoanalysis under static argon atmosphere from 300 -1300 K
286
yielded pure silicalite-1 and a black film on the crucible walls. It proceeded in two stages: the maximum of the first exothermic peak was reached at 800 K, during which process, the polymer turned black. At the second maximum at 1100 K the 'fume off' of the polymer was complete. The solid state 13C NMR showed one broad peak at about 110 ppm. The integration of the 29Si MAS spectrum revealed 24 T-atom positions. This corresponds to the monoclinic topology P21/n according to [4]. Conductivity measurements of a pressed sample from 4 - 300 K indicated semiconducting properties. The X-ray diffraction pattern before and after loading with the polymer showed practically the same lattice constants, but with drastically changed intensities at lower 2 theta angles, as given by the difference plot (silicalite-1 minus silicalite-1/(CN)x) : INe
o
o.o
~0
"
,o'.o
'
o,~,
q:
High-temperature recording 0f the x-ray d'iffraction pattern from 300-1000 K of the composite, proved that the structure was not damaged while the polymer fumed off. The loss of intensity was about 14 %. Rietveld refinement of an X-ray powder diffraction measurement of the composite is indicating considerable extraframework electron density. However, it is disordered and to distinguish between C and N is rather difficult. CONCLUSION This method of confining polymers into zeolite hosts is an elegant way to synthesize new materials. The final structure of the polymer is yet to be enlighted. REFERENCES [1] T. Groesser, A. Hirsch; Angew. Chem. 105, 1390 (1993) [2] D.J.Park, A.G.Stern, R.L.Willer; Synth. Commun. 20, 2901 (1990) [3] J.L.Guth, H.Kessler, M.Bourgogne; French Patent No. 2 546 451 (18.5.1984) [4] B.F.Mentzen, M.Sacerdote-Peronnet, J.-F.Berar, F.Lefebvre; Zeolites 13, 485 (1993)
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All fights reserved.
287
A l k y l a t i o n of a n i l i n e w i t h m e t h a n o l o n B e t a a n d E M T zeolites exchanged with alkaline cations P. R. Hari Prasad Rao, Pascale Massiani and Denise Barthomeuf Laboratoire de l~activit~ de Surface, URA 1106 CNRS Universit~ Pierre et Marie Curie, 75252 Paris Cedex 05 Fax 33-1-44 27 60 33 The exchange of alkaline cations in Beta and EMT is compared for solid state and solution procedures. Experimental conditions are chosen so that a simplified method can be used for solid state exchange with no loss of crystalline structure. Both methods gave comparable extent of exchange. The catalytic properties in the alkylation of aniline with methanol do not depend significantly on the procedure used to prepare the samples. The Nalkylation is favoured with any cation and both Beta and EMT. A very important aging occurs which is parallel to the expected zeolite basicity. It is explained by an anionic polymerization of aviline and methanol. 1. I N T R O D U C T I O N The methylation of aniline may be carried out in the gas phase using zeolite catalysts (1-10). Most of the work describes methanol as alkylating agent (1-7,9,10) and a large part of the research has been devoted to faujasite type zeolites (1,2,8-10) or ZSM-5 (3-6). A study on Na forms of FAU, EMT, LTL and MOR shows that the catalytic properties are strongly affected by the structure of the zeolite in addition to their acido-basic character (6). For a given structure ZSM-5 (3,5,6) or FAU (9) the selectivity towards C- or N- alkylation depends on the acidic or basic properties respectively. The present paper describes the results obtained with two other structures, Beta and EMT. The zeolites are exchanged with alkaline cations in order to generate basic properties. Few results are known on the way the exchange of the ions occurs in these zeolites (11,12). The objective of the work is first to study the conditions of introduction of the alkaline ions into the two zeolites and then to evaluate the catalytic properties of the materials in the alkylation of aniline with methanol. 2. E X P E R I M E N T A L H-Beta zeolite provided by PQ Corporation and Na-EMT from Elf company are used as starting materials. Their formulae are H4.5 Na0.4 (A102)4.9 (Si02)59.1 for H-Beta and Na18(A102)20 (SIO2)76 for Na-EMT. Prior to any modification, Na-EMT free of template was again calcined at 773K in an oven for 12 hrs in order to remove the traces of template. The various cationic forms of Beta and EMT were obtained in two ways, exchange with liquid solution (LS) or solid state exchange (SS). For liquid exchange
288 (LS) 2 g of zeolites were mixed with 150 ml of the 0.5 M cationic chloride solution at 333 K for 3 hrs ( F o r Cs exchange, 0.25 M CsC1 solution was used). After centrifugation the solid is recovered and the process is r e p e a t e d for 3 times. The m a t e r i a l s are t h e n w a s h e d with distilled w a t e r at p H 5.5, centrifuged, dried a n d calcined at 723 K for 12 hrs. H-EMT was p r e p a r e d using ~mmonium nitrate solution. For solid s t a t e exchange 2 g of zeolite is thoroughly mixed in a m o r t a r with cationic chloride (2.44.10 -3 moles for B e t a a n d 6.5.10 -3 moles for NaEMT). After calcination a t 793 K for 12 hrs, the m a t e r i a l s are w a s h e d with distilled water, centrifuged and dried in a n oven at 373 tC The chemical analysis results are given in table 1. The crystallinity was checked with a S I E M E N S D500 diffractometer. T h e a l k y l a t i o n of a n i l i n e w i t h m e t h a n o l w a s c a r r i e d out in a microreactor with about 30 mg of zeolite. The catalysts were p r e t r e a t e d in situ u n d e r a flow of oxygen (120 ml/min) for 12 hrs at 723 K a n d u n d e r nitrogen flow for about I h r before starting the reaction. The catalytic tests were carried out at 573 K (except otherwise specified) with N2 as c a r e e r gas (flow rate 54.5 ml/min). Aniline and methanol are introduced through nitrogen a t a p a r t i a l p r e s s u r e s of 4 a n d 12 torr respectively. T h e selectivity is expressed % as the ratio of moles of a given product to the s u m of moles produced. 3. R E S U L T S A N D D I S C U S S I O N
3.1 Cation exchange The solid s t a t e exchange of protonic zeolites with chlorides is usually carried out u n d e r v a c u u m or flow of gas in order to remove quickly the HC1 evolved (13). The SS exchange of H -Beta and H-EMT as described here does not involve any particular care for the elimination of acid vapour. Considering first H-Beta the SS exchange was performed with a ratio of A1 cation of 1"1 of the solid mixture in order to avoid excess of chloride. The X-ray crystallinity of the H Beta samples exchanged in both ways (LS a n d SS) is v e r y high and comparable to t h a t of H B e t a (Fig. 1) It is noticeable t h a t w i t h o u t special care for the HC1 evolved d u r i n g the solid s t a t e exchange no loss of s t r u c t u r e is observed. The r e s u l t s are quite in a g r e e m e n t with w h a t was already reported for the case of La ions introduced in this way in H-Beta (14). By c o n t r a s t introduction of t h e K cations in HEMT using SS procedure destroyed the structure w h e n the ratio of A1 : K is 1:1 ( s p e c t r u m not shown). This is in line with the case of o t h e r protonic zeolites w h e r e HC1 formed h a s to be e l i m i n a t e d in order to p r e v e n t the s t r u c t u r e collapse. The crystallinity of EMT was m a i n t a i n e d w h e n A1 : K ratio is 4 : 1 (Fig 1) since less HC1 is formed. Starting from Na-EMT no HC1 should be evolved, t h e n it is possible to exchange the m a t e r i a l at A1 " K ratio of 1:1 with no loss of crystallinity (Fig. 1),as it was seen for N a F A U (15). The results show t h a t the solid state exchange gives with Beta and EMT, highly crystalline solids w h e n the a m o u n t of HC1 evolved is zero (NaEMT) or small (low A1 content i. e. low exchange capacity in Beta or small K e x c h a n g e w h e n A1 : K is 4:1 for H-EMT). Both zeolites h a v e very open structure which in addition favours the fast diffusion of gases. The extent of exchange could be very likely improved by repeated exchanges. The chemical analysis shows for Beta (table 1) t h a t it is not possible to exchange easily all the protons by alkaline cations. Such a limitation in cation exchange was already observed and explained by the location of some
289 alkaline ions in inaccessible cavities (11,16). The results also indicate a slightly lower cation exchange for SS procedure which might arise from restricted diffusion of ions to inner sites. In the case of N a - E M T table 1 shows that with any cation or exchange procedure only a part of N a ions can be exchanged. It was previously shown that N a ions prefer less the SI site in the hexagonal prism in E M T than they do in faujasite (17-19). In the present experimental conditions (liquidand solid state exchange) some N a ions remain in the more energetic sites which could be different from SI sites. A systematic difference is seen between the LS and SS exchanges for the Si/Al values in Beta. The H-Beta, as provided or after washing gives Si/AI values around 12 like the solid state exchange materials. After the LS exchange this ratio goes up to 13-14 indicating very likely a slight dealumination. Such a difference between the two procedures was also observed in the preparation of La-Beta (14). This could arise from the p H of chloride solutions between 5 and 5.5. Neverthless such a dependence of Si/Al ratio on exchange method is not observed in the table 1 for E M T . This suggests a specificbehaviour for Beta which might be related to its high level of defects and to the distorsion of AIO4 tetrahedra in the protonic form (20). Some of them weakly bonded to the framework (21) could be easily detached during the liquid exchange process by water hydrolysis at p H 5 - 5.5. 3.2 Catalysis
a. Effect 0f time on stream and percent conversion The figure 2 reports the changes in percent conversion and selectivity as a function of time on stream at 573 K. The products obtained correspond to N-alkylation (N-methyl aniline (NMA), N,N-dimethyl aniline (NNDMA)), C-alkylation (ortho and para toluidines ( o and pT)) and to alkylation of both and N and C (N,N
290 the difference in catalytic properties since the similar pore aperture of the 12-R windows cannot involve different access to active sites. c. Effect of cation exch~m~r procedure The percent conversion and selectivity are given in figures 2C and 2 D for Na- Beta and in the table 3 after 6 hours on stream for the other Beta cationic forms obtained either by (LS) or (SS) procedure. In both cases the Nalkylation is favoured giving NMA + NNDMA. No major trend in selectivity characteristics of the one or the other procedure can be pointed out. The slight differences in the percent conversion between the (LS) and (SS) catalysts in table 3 may arise from different chemical analysis i.e. extent of exchange (table 1). d. Effect of the cation identity Figure 4A reports the changes in percent conversion at 573 K with time on stream for the various Beta (LS) cationic forms. A general comment is the increasing aging in the alkaline cation series from Li to Cs. As a consequence the catalytic activity after more than 6 hours decreases in the same order. Similar results are obtained for (SS) catalysts (figure 2D). For EMT (Fig. 4B) the protonic form is very active but with the change of protons to alkaline cations the activity ceases drastically. Table 3 shows a trend after 6 hours on stream for an increased selectivity to N-alkylation (NMA + NNDMA) as the cations move from Li to Cs in Beta. This may result from the decreased percent conversion, since this not observed in table 2 at isoconversion. The main characteristic feature is the loss of activity as the cations are less electronegative from Li to Cs. Table I shows that in the Beta (LS) series the extent of exchange is similar for all the cations. A comparable a m o u n t of protons is available for all the samples. This suggests t h a t the aging is related to the identity of the alkaline ions and their content. The exchange of protons in zeolites for alkaline cations generates basic properties (16,23). It was already proposed that Na-Beta and Cs-Beta similar to the present (LS) samples have basic properties despite the presence of some protons, in order to explain specific benzene adsorption behaviour (16). The results suggested that the Cs form is more basic than the Na one. The conversion changes in Figure 4A may be explained using this basis. Usually one would not expect any aging in basic catalysis, since no coke, issued from carbenium ions, should be formed. In the present case it ma y be suggested that the aging is due to secondary polymerization reaction between aniline and methanol favoured in the presence of basic sites. Since the electronegativity of cations decreases from H to Li and then from Li to Cs (24), the charge on framework oxygen i.e. th eir basic strength, i n c r e a s e s in the order H << Li < Na
291 particularly i m p o ~ t in EMT. The high A1 content of this zeolite (compared to Beta) should generate higher number of strongly basic sites. As a conclusion, the results presented in this paper indicate with regard to ion-exchange, t h a t a simplified solid state exchange procedure can be applied to Beta and EMT. No specific elimination of HC1 is required as long as the amount formed is low ( low Al content or high Al : cation chloride ratio). The exchange extent of alkaline cations are comparable for solid state or liquid solution methods. The catalytic properties in the alkylation of aniline with methanol are similar for the two types of exchange with regard to percent conversion and selectivity indicating very close chemical properties of the zeolites i.e. very likely similar cation location. For both exchange procedures and for Beta and EMT structures an i m p o ~ t aging is observed as the zeolite presents a more basic character. This is explained by the possible occurrence of an anionic polymerization reaction involving aniline and methanol which poisons alkylation sites. Due to this important aging the best catalysts are the two protonic zeolites H-Beta and H-EMT. Table 1. Chemical analysis of zeolites. Zeolite
Si/A1
H-Beta H-Beta (Washed) Li- Beta(LS) Na-Beta(LS) K-Beta(LS) C s-Beta(LS) Na-Beta(SS) Rb-Beta(SS)
12.3 12.0 13.8 14.5 13.7 13.7 11.8 11.7
H-EMT(LS) Li-EMT(LS) Na-EMT(LS) K-EMT(LS) Cs-EMT(LS) HKNa-EMT(SS) c KNa-EMT(SS) d
4.2 3.9 3.8 3.9 4.0 4.0 4.0
Alkaline Cation a (except Na)
Na a
Alkaline Cation/A1b
0 0 2.9 0 3.4 3.3 0 3.2
0.4 0.3 450 e 3.0 290 e 100 e 2.9 320 e
0.08 0.06 0.67 0.73 0.77 0.75 0.59 0.63
0 12.8 0 18.7 14.8 3.5 11.9
3.8 6.2 18.0 0.7 6.0 3.7 11.2
0.19 0.95 0.90 0.96 1.04 0.72 1.10
(a) atom/U.C. (b) Difference with 1 arises from unexchanged protons (c) Prepared from H-EMT (A1 : K = 4:1). (d) Prepared from Na-EMT (A1 : K = 1:1) (e) ppm
292 Table 2. Product distribution on various alkaline forms of Beta and EMT zeolites at 30 % conversion. Zeolite
NNDMA
NNDMPT
NMA
o-Tol
4.0 9.3 12.3 10.0 8.5 11.4
53.0 45.2 41.4 48.3 44.3 66.6
11.5 16.2 14.7 9.0 16.7 4.0
4.9 7.8 7.2
54.5 58.9 48.8 47.8
16.8 14.6 16.9
p-Tol.
NMA + NNDMA
o-Tol + p-Tol
5.5 8.8 5.2 1.6 10.0 4.0
79.0 65.7 67.8 79.4 64.8 80.6
17.0 25.0 19.9 10.6 26.7 8.0
3.9 4.1 9.1 7.3
74.4 95.9 68.5 68.6
17.0 4.1 23.7 24.2
Liquid exchange Li-Beta Na-Beta K-Beta Rb-Beta Cs-Beta Na-EMT
26.0 20.5 26.4 31.1 20.5 14.0
Solid state exchange Li-Beta Na-Beta K-Beta Rb-Beta
19.9 37.0 19.7 20.8
Table 3. Catalytic activity and selectivity after 6 hours on s t r e a m on Beta and EMT zeolites Zeolite
H-Beta Li-Beta (LS) Na-Beta(LS) K-Beta (LS) Rb-Beta (LS) Cs-Beta (LS) Li-Beta (SS) N a - B e t a (SS) K-Beta (SS) Rb-Beta (SS) Cs-Beta (SS) H-EMT Na-EMT
% conversion
NMA + NNDMA
o-Tol + p-Tol
87.4 55.0 50.1 49.4 39.4 6.4 44.8 64.1 34.3 17.3 3.8 98.4 1.4
61.4 64.8 57.1 64.7 76.4 100 67.0 65.2 76.5 69.5 100 44.0 100
10.1 21.1 25.5 14.3 9.3 0 20.7 13.8 12.8 24.1 0 5.5 0
NNDMPT
28.5 14.1 17.4 21.0 14.3 0 12.3 21.0 10.7 6.4 0 50.5 0
NNDMA : N,N-Dimethyl aniline; NNDMPT: N,N-Dimethyl p-Toluidine; N M ~ N-Methyl aniline; o-Tol & l>Tol : o- & p- Toluidines.
293
Figure 1. XRD pattern of H-Beta: a; Na-Beta (LS) : b; Na-Beta (SS) : c; Na-EMT: d; H-EMT:e; KEMT (SS) - ex HEMT, Al: K = 4:1: f and K-EMT (SS)- ex NaEMT: g. o
~6 ~ ~ o
io ~o:~o2o
,oo
!
7$
C
75 l
SO
:.~
25
Figure 2. Percent conversion (a) and selectivity (%) at 573 K for H-Beta : A; H-EMT : B; Na-Beta (LS): C and N a - B e t a (SS) : D. N N D M A ( 9 ), NNDMPT ( A ), NMA ( . ) , o-Toluidine
25
0
7$
75
50
50
( I ) and p-Toluidine ( O ).
2S 00
10
20
-0
10 20
Time, (hrs) 50
Figure 3. Change in selectivity % for N a - B e t a (LS) versus conversion %. NNDMA ( 9 ), NNDMPT (A), NMA ( . ) , o- Toluidine ( 1 ) and p-Toluidine
2s
(O). 25
35
45
55
Conversion, (%)
~ ~._~-,~ :--BI
.o~ lO0~TS~o_.l~ob SO
i -io T~e, ~s)
F i g u r e 4. C h a n g e in p e r c e n t conversion at 573 K for Beta zeolites 9 A and E M T ' B . Cationic forms H (a, a'), Li (b), Na (c, c'), K (d), Rb (e) and Cs (f).
294 REFERENCES
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24 25.
tL Kunikata, Japan Kokai, 78 28,128 G.O. Chivadze and L.Z. Chkheidze, Izv. Akad. Nauk. Gruz. SSR., Ser Khim., 10 (1984) 232. P.Y. Chen, M.C. Chen, H.Y. Chu, N.S. Chang and T.IL Chuang, Proceed. 7th Int. Zeol. Conf., Kodansha, Elsevier, Tokyo, (1986) 739. P.Y. Chen, S.J. Chu, N.S. Chang and T.K. Chuang in "Zeolites: Facts,Figure, Future", (P.A. Jacobs and R.,~ Van Santen,eds), Stud. Surf. Sci. Catal., 49B (1989) 1105. ICG. Ione and O.V. Kikhtyanin, in "Zeolites: Facts, Figure, Future", (P.A. Jacobs and R.A. Van Santen,eds), Stud. Surf. Sci. Catal., 49B (1989) 1073. S.I. Woo, J.IC Lee, S.B. Hong, Y.tL Park, Y.S. Uh in "Zeolites: Facts, Figure, Future", (P.A. Jacobs and R.A. Van Santen,eds), Stud. Surf. Sci. Catal., 49B (1989) 1095. S. Prasad and B.S. Rao, J. Mol. Catal., 62 (1990) L17. Zi-Hua and Y. Ono, Catal. Lett., 22 (1993) 277. Bao Lian Su and D. Barthomeuf, Appl. Catal. (submitted). Bao Lian Su and D. Barthomeuf, Appl. Catal. (submitted). M.M. Treacy and J.M. Newsam, Nature (London), 332 (1988) 249. J.M. Newsam, M.M. Treacy, W.T. Koetsier and C.B. De Gruyter, Proc. Roy. Soc. London, Ser. A, 420 (1988) 375. J.L. Lievens, J.P. Verduijn, A.J. Bons and W.J. Mortier, Zeolites, 12 (1992) 698. H.G. Karge, V. Mavrodinova, Z. Zheng and H.tL Beyer, Appl. Catal., 75 ( 1991) 343. Chun Juan Jia, P. Massiani and D. Barthomeuf, Appl. Catal. A genereal, 106 (1993) L185. G. Borb61y, H.IC Beyer, L.Radics, P.Sandor and H.G. Karge, Zeolites, 9 (1989) 428. S. Dzwigaj, A. de Mallmann and D. Barthomeuf, J. Chem. Soc. Farad. Trans., 86 (1990) 431. F. Doughier, J. Patarin ,J. L. Guth and D. Anglerot, Zeolites, 12 (1992) 160. Bao Lian Su, J. Manoli, C. Potvin and D. Barthomeuf, J. Chem. Soc. Farad. Trans., 89(1993) 857. C. Baerlocher, L.B. McCusker and R. Chiapetta, Microporous Materials, (1994)in press. E. Bourgeat-Lamy, P. Massiani, F. di Renzo, P. Espiau, F. Fajula and T. des Courieres, Appl. Catal., 72 (1991) 139. Chun Juan Jia, P. Massiani and D. Barthomeuf, J. Chem. Soc. Farad. Trans., 89 (1993) 3659. Bao Lian Su and D. Barthomeuf, Zeolites, 13 (1993) 626. D. Barthomeuf, J. Phys. Chem., 88 (1984) 42. R.T. Sanderson in "Chemical bonds and bond energy, Academic Press, New York 1976. D. Barthomeuf in" Catalysis and adsorption by zeolites" (G.Ohlmann, H. Pfeifer and R. Fricke eds), Stud. Surf. Sci. Catal., 65 (1991) 157.
295
Recent Research Reports u Author Index ABRAMS, L ....................................... 248 ADAMS, C. J. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 0 6 AHN,
W. S ............................................
AKPORIAYE, ALTHOFF,
D .................................
54 180
R ........................................
36
CARDOSO, D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CARDOSO, M. J. B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CARLI,
174 174
R ............................................
178
CARO, J. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
276
CARR,
206
S. W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ANDERSON, M. W . . . . . . . . . . . . . . . . . . . . . . . . . . . .
258
CATANA,
G ........................................
ARAKI,
H ...........................................
260
CATLOW,
R ....................................... 234
ARAYA,
A ..........................................
206
CAULLET,
ARMOR,
J. N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
140
CENTI,
G ............................................
150
ATTFIELD,
M ....................................
264
CHAO, C. C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
266
AZIMOVA,
Y. I ..................................
196
CHAO,
133
P ...........................................
K.-J ...........................................
5
67
BACK, G . - H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . BAERLOCHER, CH . . . . . . . . . . . . . . . . . . . . . . . . . . .
254
CHEETHAM,
BAKKER,
W . J. W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
215
CHELISHCHEV,
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CHIEN, S H U - H U A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 CHIPPINDALE, A. M . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 6
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77
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CttMELKA,
B. F ................................... 91
CIAMELLI,
P ........................................
110
CONSTANTIN
15 204 232
69
SCU, F ...................... 133
CORBIN, D. R . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 9 , 2 4 8 CORBO, P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 9 CORKER, J. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 2
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234 256 81 211
DALL'OLIO, DANIELS,
E ................................
186
L ....................................
150
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262
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BIANCHI, C. L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
178
BLUM,
A. K .............................. 264
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BHATIA,
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CHAPPLE, A. P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C ....................................
9
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A ...........................................
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M ...............................
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129
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A .............................................
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266
EIC, M . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
213
BORDIGA, S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . BORNHOLDT,
104, 112
K ...............................
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221
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BUHL,
C ...............................
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129 40
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R. S .................................
EL DUSOUQUI,
186
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104
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248
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BUTTERSACK,
CAMACHO,
M .....................................
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296 ESTERMA.NN,
G. H ............................. 73
FAJULA,
F .......................................... 136
FARRIS,
T. S ...................................... 140
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M ................................... 238
FREEMAN,
C. M ............................... 2 4 8
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153
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HAYHURST,
DAVID
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HEERIBOUT, L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7 HER, J. C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 HIRAIWA,
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W ................................... 46
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Q ................................................. 26
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P ....................................... 206
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KAPTEIJN, KARGE,
F ...................................... 215
n . G ........................................ 71
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J ......................................... 204
KARLSSON, KATADA, KATO,
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50, 256
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MILESTONE, N. B ............................... 4 2
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A .......................................
lS0
LIETZ, G 116 L I N , L . - H .............................................. 67 L I N , M . C ............................................... 7 L I N D V O R S , L. E ............................... 184 L I U , S ................................................. 2 8 7 L O F F L E R , E ......................................... 11 L O H S E , U ............................................ 11 L O C K E , B .......................................... 116 L U G S T E I N , A .................................... 163 L U G T , P. A ......................................... 146 L U N I N A , E. V .................................... 188 L U T Z , W .............................................. 13 M a c K A Y , S. P .................................... 258 M A E D A , K .................................... 44, 278 M A R L E R , B ........................ 5, 17, 38, 2 6 2 M A S S I A N I , P ..................................... 129 M A T I - I E , Z ............................................ 34 M c C O R M I C K , A. V ........................... 227 M c C U S K E R , L. B ............................... 2 5 4 M c D E R M O T T , A ............................... 287 M c G U I R E , N. K .......................... 3, 9, 266 M E D E N B A C H , O ............................... 2 5 2 M E L N I K O V , V. B .............................. 196 M E N O R V A L , L. DE ........................... 136 MERGLER, Y. L ................................ 146 M E T H I V I E R , A .................................. 198 M E Y E R , H ......................................... 120 MIESSNER, H .................................... 124 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
298
PIRYUTKO,
L. V ............................... 188
P L A T O , M ............................................ 71 P L O G , C ............................................... 58 P O L G A R I , M ........................................ 34 POLISSET-THFOIN,
S C H U L Z - E K L O F F , G . . . . . . . . . . . . . . . . . . . . . . . . . 108 S C H U M A C H E R , Y ............................. 285
scn
q
r ........................................... 36
S C H U T H , F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
M ....................... 65
S E A L Y , S ............................................ 238
P O R T A , P ............................................. 69 P S A R O , R ........................................... 126 P T A S Z Y N S K I , J ............................ 93, 118 P T A S Z Y N S K I , J ................................... 93 P Y U N , C . - H .......................................... 54
S E A R S , M ............................................... 3 S E E F E L D , V ....................................... 268 SEILER, H .......................................... 246 S E M M E R , V ......................................... 97
Q I , M .................................................... 87
S E R R A N O , D ........................................ 2 4
RACtg)I,
SEO, J. S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
V ......................................... 136
S H A N N O N , R. D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 5 2
R A D E S , T ............................................. 65 R A G A I N I , V ....................................... 178
SHAW, K. M . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
R A M A R A O , A. V .............................. 161
S H I M A Z U , S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
RAMACHANDRA
S H / R A K I , T . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
R A O , R ................ 161
R E C C H I A , S ....................................... 126 R E D D Y , J. S ....................................... 157 R E D D Y , K. M ...................................... 19 R E E S , L. V. C ..................................... 223 R E I C H , A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 REITMAIER,
S ..................................... 36
RESCHETILOWSKI,
W ..................... 180
R H E E , H Y U N - K U .............................. 169 RICCHIARDI,
G ................................. 104
SI-IEN, D. M . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 3
SI-IPIRO, E. S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
SINGER, A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 S I R K E C I O G L U , A .............................. 219
SKEELS, G. W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 S M O R R O D I N S K A , Y. A . . . . . . . . . . . . . . . . . . . . 196 S N U R R , R ........................................... 240
SOBOLEV, V. I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 SPANO, G . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 S P O J A K I N A , A L L A .............................. 75
R O C H A , J ........................................... 2 5 8
SPOTO, G . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
RODUNER,
P E R O L A ........................ 176
S T A K H E E F , S. A . . . . . . . . . . . . . . . . . . . . . . . . 108, 148 S T O C K M E Y E R , R .............................. 200 S T O N E S T R E E T , P. J. . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 STOCKER, M . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 S U B R A H M A _ N Y A M , M ...................... 161
ROOS, K ............................................. 180 R O T H , W. J.......................................... 15 ROZWADOWSKI, M ........................... 13 R U B I N , M. K ...................................... 2 5 0
S U N , H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 S Y C H E V , M . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 T A K A I S H I , T ...................................... 272
E ....................................... 73 ROESSNER, F .................................... 182 ROLISON, D. R .................................. 114 R O M A N O V S K Y , B. V ....................... 196
RONNING,
99, 104, 112
SULIKOWSKI, B . . . . . . . . . . . . . . . . . . . . . . . . . . 93,
118
B ................................... 283
T A N A K A , V ........................................ 2 2 9
RUSSU, E. R ...................................... 133 RYOO, RYONG ................................... 65 SAGNOWSKI, S ................................... 93
T E A R L E , K . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
RUDINGER,
S A U E R , J ..................................... 242, 2 4 4 S A U V A G E , . ...................................... 129 S A W A , M ........................................... 101
T E R A S A K I , O ......................... 50, 52, 2 5 8 T E Z E L , r. H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1 9 T H E O D O R O U , D . N ............................ 240 T H O M A S , J. M . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 T I L L M A N N S , E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
S A Y A R I , A ......................................... 157 S A Y A R I , A ........................................... 19 S C A R A N O , D .............................. 104, 112
T O P A L O V I C , I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
S C H M I D T , R ...................................... 180
T O Z Z O L A , G . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
T O T I ~ M . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 T O U S S A I N T , P ................................... 276
A. M ............................ 2 3 2
TRESCOS, E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
S C H N E L L , R ........................................ 56
T R E T T I N , R ........................................ 268
S C H O T T - D A R I E , C ...................... 50, 2 5 6 S C H R A M M , S. E .................................. 15 S C H R E I E R , E ....................................... 11
T R I E B E , R. W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1 9 TSENG, Y. K . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 T U R R O , N. J. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 8 7
SCHRODER,
UEMATSU,
SCHNEIDER,
K . - P .............................. 2 4 4
T . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
299
UGLIENGO, P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
99
UGUINA,
24
M. A ....................................
UH, Y. S ...............................................
54
LINGER, K. K . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . UNNEBERG, E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
36 144
UVAROVA,
148
E. B ................................
VAN BEKKUM, H . 3 0 , 1 4 6 , 1 6 5 , 1 8 6 , 2 1 5 VAN DE VEN, L. J. M . . . . . . . . . . . . . . . . . . . . . . . . . 9 5 VAN DEN BLEEK, C. . . . . . . . . . . . . . . . . . . . . . . . . 1 4 6 VAN DEN GOOR, G . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 0 VAN DER WAAL, J. C . . . . . . . . . . . . . . . . . . . . . . 1 6 5 VAN GKIEKEN, R . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 4 VAN HOOFF, J. H. C . . . . . . . . . . . . . . . . . . . . . . . . . 1 5 5 VAN KONINGSVELD, H . . . . . . . . . . . . . . . 6 1 , 6 3 VAN S A N T E N , R . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 5 VAN TASSEL, P. R . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 7 VARTULI, J. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 VENZKE, D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 7 6 VERHULST, VINEK,
H .....................................
H ...........................................
95 163
VITAL, J . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 6 5 VORBECK, G . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 5 VORTMANN, S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 6 2 VOLTER, J . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 6 WALTON, R . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 6 WATANABE, n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 0 , 5 2 WEIDENTHALER, C . . . . . . . . . . . . . . . . . . . . . . . . . 2 5 2 WELLER, M. T . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 7 4 WELTERS, W.J.J. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 5 WILSON, S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 WITZEL, F. O. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 WU,
C. G ............................................
138
XU, R . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
26
XUE,
87
Z .................................................
YAMAZAKI, YAN,
A ............................. 32, 192
Y ...............................................
YU, J.-S ................................................
281 77
ZABUKOVEC, N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
270
ZAKHARIEVA,
236
ZECCHINA, ZHANG,
O ..............................
A ....................... 99, 104, 112
Y ............................................
ZtIENG, G . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ZIBROWlUS,
87 215
B ............................... 28, 36
300 Recent Research Reports u Subject Index ot-PINENE
ISOMERIZATION
AB-INITIO ACIDITY
........... 1 6 5
.................................. 242, 244 ............................... 97, 101, 184
ADSORPTION
...................................
AIR PURIFICATION
.........................
CO HYDROGENATION
Co-ZSM-5
219
CoAPO
..................................................
.............................
260
CoAPO~
! 74
CoAPSO-44
91
COMPLEX
AI DOR
NMR
.......................................
AIMAS
NMR
.......................................
A1 P I L L A R E D
CLAY
.........................
89
AI-FREE
ZEOLITE
244
METAL
CLUSTER
............... 81
FORMATION
.......................
AIMePO
................................................
136
11 13 8
180
...................................... 67
CsX ..................................................... Cu ION EXCHANGE
129
.................... 69, 150
................................................
83
AIPO ...................................................
122
Cu-Y ......................................................
83
AIPO-5 ................................................
276
Cu~
AIPO4--16 .............................................
256
CVD ....................................................
AMINE
.........................
157
CYCLOHEXANE
.........................................
101
DAWSON
ANION
........ 161
DECASIL
..............................................
........................ 9 9
DENSITY
FUNCTIONAL
OXIDATION
AMMONIA
AMMOXIDATION
CATALYST
AMORPHOUS
SILICA
ANHYDROUS
GLYCOL
B-BETA
44
..................... 4 2
..............................................
118
BASICITY
..........................................
194
BENZENE
................................... 204, 240
ALKYLATION BIMETALLIC
............................... SPECIES
BOROSILICATE
....................
MCM-22
SITE ................................ CALCINATION CANCRINITE CATALYST
O F P d ( N H s ) 4 ............ 1 2 9 ......................................
ACTIVITY
42
.............. 1 4 8 , 1 8 8
CATALYTIC CRACKING
....................................
PROPERTIES CATION Cd MAS
.................................
EXCHANGE
196 194
....................... 2 1 1
38
TtEORY..227
223
........................................
SYNTHESIS
246 167
........................ 196
................................
190
DISPROPORTIONATION . . . . . . . . . . . . . . . . . . 1 7 4 DOUCIL A 2 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 0 6 DRY POWDER ......... i . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 6 ELECTROCHEMISTRY ELECTRON
..................... 114
DIFFRACTION
................ 48
EMT ....................................................
167
ENCAPSULATION
............................. 274
ENCLATttRATION
.............................. 46
EPR ..................................................... 112 ESEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 7 ESR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1 , 7 5 , 7 7 , 7 9 , 81 ETHANE
ACTIVATION
.................... 182
87
ETHYLBENZENE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ETS- 10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 ,
258
NMR
......................................
87
CdS CLUSTER
.....................................
Ce EXCHANGE
174
.................................
146
ETS-4 ....................................................
22
........................................
283
EXAFS
65
1 ...............................................
192
EXTRA-LARGE
CERAMICS CFC~
................................ 28
DIFFUSION
DISACCHARIDE
198
................................ 200
206
DIRECT
104, 1 8 2 , 2 4 2
58 126
DETERGENT BUILDER . . . . . . . . . . . . . . . . . . . . DIALKYLBENZENE . . . . . . . . . . . . . . . . . . . . . . . . . . DIELS-ALDER R E A C T I O N . . . . . . . . . . . . . . .
171
................ 2 5 0
................................
.............................................
138
BREAKTHROUGH C U R V E .............. 2 1 3 BRONSTEDT A C I D I T Y ...................... 9 7 Cs AROMATICS
Cu-RHO
131
...................... 198
........................................
CATALYST
11
..................................... 283
CRACKING
118
ALLOY
..........................................
COUNTERDIFFUSION
............................................. ............................
...........................................
CORDIERITE
140
11, 7 9
...........................................
268
AI-BETA ALKALI
.........................................
...................................
DISTRIBUTION
........................... 270
...........................................
CoAPO-5 EXTERNAL
....................... 163
Co SUBSTITUTION
192
AI
.................... 178
Co INCORPORATION
CHLOROFLUOROCARBONS CLATHRASIL
........... 2 4 8
................................ 40,266
CLINOPTILOLITE ...................... CLOVERITE
FMAS
50
NMR
PORE ....................... 180
.........................................
FAU ............................................... Fe
89
81, 120
Ga2Os-. ..............................................
208, 219
........................................
..................................................
93
301
EXTRAFRAMEWORK
.................. 112
LZ-277 ..................................................... 3
- S I L I C A L I T E .................................. 112
M 4 1 S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
- Z S M - 11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 - Z S M - 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159, 2 3 4 - Z S M - 5 ........................................... 234
MAP .................................................... 206 M A S N M R . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 MCM-22 .............................................. 250 M C M - 4 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17, 19, 1 3 8
FISCHER-TROPSCH FLUORIDE
SYNTHESIS...
SYNTHESIS
178
............ 2 5 6 , 2 7 0
F L Y A S H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 FRAMEWORK TOPOLOGY
................................... 2 5 0
VIBRATION
................................... 110
FREQUENCY
RESPONSE
................ 2 2 3
MECHANISTIC MEMBRANE
S T U D I E S ................. 176 .............................. 276, 278
M E R C U R Y S U R F A C E ....................... 2 7 8 METAL-ORGANIC C O M P L E X ........... 4 0 METHANE ......................................... 202 OXIDATION
................................... 159
F T I R . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 G a - Z S M - 11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 G a 2 O a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 GALLOPHOSPHATE ......................... 2 6 4
CONVERSION ............................... 176 DEHYDRATION ............................ 144 MFI MEMBRANE .............................. 215
G R O U P [I'IA M O D I F I C A T I O N .......... 133 H - B - Z S M - 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
MFI ..................................................... 150 MIOCENE TUFF .................................. 34
H-BETA .................................................. 7 H-NMR ................................................. 97
Mn2(CO)lo ........................................... 126 MODELLING ............... 6 1 , 2 2 7 , 2 3 6 , 2 3 8
H--Y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
MODIFIED
H - Z S M - 1 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
MOLECULAR
H-ZSM-5
................. 61, 63, 104, 116, 148
METHANOL
ELECTRODES
DYNAMICS
................ 114
............................ 2 3 2 , 2 4 0
HETEROPOLYOXOMETALLATE ..... 28 HEXADECANE ................................. 180 HIGH MODULUS Y .......................... 196 H R E M . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48, 50, 52
MODELING .................................... R E C O G N I T I O N ...................... 1 4 2 , SIMULATION ................................ M O L L E R - P L E S S E T - T H E O R Y ..........
HYDROCARBON
MONTE CARLO ................................. 229 M O R .............................................. 97, 146
OXIDATION
........ 153
HYDRODESULPHURIZATION HYDROFLUOROCARBON HYDROGEN
........ 163 ................. 8 9
ADSORPTION
HYDROLYSIS
............. 2 1 7
................................... 190
HYDROTREATING
CATALYST
...... 163
HYDROXYL G R O U P ........................ 106 INTERGROWTH ............................... 2 5 2 INTRAZEOLITIC CHEMISTRY 126, 136 ION EXCHANGE RESIN
............................... 140
............................................ 208
I R . . . . . . . . . . . . . . . . . . . . . . . . . . . 81, 104, 106, 110, 2 1 7 ISOTOPIC
LABELLING
K EXCHANGE
.................... 176
..................................... 32
K - L T L ................................................... 52 LATTICE
ENERGY
........................... 2 3 4
LAUMONTITE .................................... 3 2 L A Y E R C O M P O U N D ........................ 142 LAYERED ALUMINOPHOSPHATE... 26 L E O N H A R D I T E ................................... 3 2 LEWIS ACIDS
..................................... 71
LIQUID PHASE
OXIDATION
LOEWENSTEIN
R U L E ..................... 2 6 0
LLIMINISCENCE
........... 155
SPECTROSCOPY...
54
LZ-276 .................................................... 3
DEALUMINATED MULLITE
232 281 248 242
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
........................................... 283
MULTI-NMR N-HEXANE
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 ISOMERIZATION
......... 1 6 9
N2 A D S O R P T I O N . . . . . . . . . . . . . . . . . . . . . . . . . . . 11, 6 9 N20 D E C O M P O S I T I O N ............. 1 4 8 , 1 5 9 Na DOR NMR
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
EXCHANGE
..................................... 32
S I T E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Na-X ...................................................... 56 N a A Z E O L I T E .............................. 85, 2 2 7 NANOCLUSTER ................................ 274 N a X ...................... 129, 192, 2 0 0 , 2 2 1 , 2 2 3 N a Y ........................ 65, 126, 136, 1 7 8 , 2 0 2 NEOPENTANE ................................... 236 N E U T R O N S C A T T E R I N G ................. 2 0 0 N i E X C H A N G E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Ni-SALEN ........................................... 120 NO ADSORPTION CONVERSION NON-AQUEOUS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 ............................... 150 MEDIUM
................. 26
302
N O N - F R A _ M ~ W O R K C o .................... 2 7 0 N O x R E D U C T I O N ............................. 146 N U - 1 ....................................................... 5 N U C L E A T I O N ..................................... 3 0
PHOTOOXIDATION ...................... 153 S E M ...................................................... 50 S E P A R A T I O N .................... 2 1 5 , 2 4 8 , 2 7 6
N U M E R I C A L M O D E L ...................... 2 4 6 1 s O - L A B E L L I N G ................................ 110
S H E L L M O D E L .................................. 2 4 4 Si C P - M A S - N M R
04 INCORPORATION
S I L I C A L I T E ........................................ 2 8 5
OH-VIBRATION
....................... 2 7 2
................................ 110
ONE-POINT-TECHNIQUE ORGANIC
G R O U P .............................. 4 4
ORGANOPALLADIUM OUTER
................ 101 COMPLEX..
122
S U R F A C E ............................. 188
.............. 1 7 1 , 2 4 6
................................ 2 6 2
S I L I C A L I T E - 1 .................................... 2 2 3 S I M S ..................................................... 67 SIMULATED
N M R S P E C T R A ............. 9 5
SIMULATION
.................................... 2 2 9
S I N G L E C R Y S T A L S U P P O R T ............ 3 0 S I N T E R I N G ........................................ 2 8 3
OXIDATION
CATALYST
OXIDATION
S I T E ............................... 73
SKELETAL
G R O U P ........................... 2 3 8
OXIDATIVE
DEHYDROGENATION.
SMECTITE
......................................... 2 6 8
p-DICHLOROBENZENE PARAFFIN
Pd LOCATION
93
................ 61, 63
ADSORPTION
Pb-CONTAINING
................. 161
SHAPE SELECTIVITY
SO2 ...................................................... 2 1 3
................ 2 1 7
ZEOLITES
........... 194
-CONTAMINATION SODALITE
..................................... 77
........................ 5 8
................................... 4 2 , 2 7 4
S I L I C A - . .................................... 4 0 , 2 3 2
P d H - S A P O - 3 4 ....................................... 7 7
SOL-GEL TECHNIQUE
PERMEATION
SOLVENT
E F F E C T S .......................... 1 5 7
P F G - N M R ........................................... 2 0 4
SORPTION
......................................... 2 2 7
POLYCYANOGENE
S S Z - 2 6 .................................................. 48 S S Z - 3 3 .................................................. 48
................................... 2 1 5 .......................... 2 8 5
P O R O S I L .............................................. 38 PROPENE PROTEIN
ISOMER/ZATION PURIFICATION
........... 2 3 8
................ 2 2 5
Pt
SUCROSE HYDROLYSIS SUPRAMOLECULAR SURFACTANT
CARBONYL
................................... 108
C L U S T E R .................................. 52, 108 Z E O L I T E ........................................ 169 Pt-BETA-ZEOLITE Pt-Pd CATALYST
............................ 186 ................................ 65
P t / K L Z E O L I T E ................................. 108 P T 2§ L O C A L I Z A T I O N ......................... 56
....................... 2 4
SYNTHESIS
.................. 1 9 0
TEMPLATING.
CHEMISTRY
15
.............. 15
..... 5, 7, 9, 15, 17, 2 2 , 2 4 , 2 6 ,
..................... 30, 32, 36, 38, 4 0 , 4 2 , 4 4 , 4 6 Tb I N C O R P O R A T I O N TEA-ZSM-8
.......................... 5 4
........................................ 2 5 2
T E M .............................................. 6 5 , 1 8 6 TERPENE
........................................... 165
T G A ...................................................... 58
Q E N S ........................................... 2 0 2 , 2 0 4
T h U P T A K E ........................................ 131
RADICAL
C A T I O N S ........................... 73
THERMAL
F R .................................... 2 2 1
R A D I O A C T I V E W A S T E ................... 2 0 8 R A M A N .............................................. 118
THERMAL
S T A B I L I T Y ....................... 4 6
REGIOSELECTIVITY RELATIVE
Rh COMPLEX RIETVELD
....................... 186
A C I D I T Y .......................... 9 9 .................................... 124
REFINEMENT
T H E T A - 1 ............................................ 2 2 3 T H I N F I L M S E N S O R ......................... 2 8 1 Ti I N C O R P O R A T I O N
........................... 19
Ti
254, 256, 266
- S I L I C A L I T E .................................. 1 5 7
R u - E T S - 10 .......................................... 178
- B E T A ................................................. 7
R U B - 3 ................................................... 38 R U B - - 4 ................................................... 38
T M A S I L I C A T E .................................. 2 6 6 T O L U E N E A L K Y L A T I O N ................. 1 4 4
R U B - 1 3 ............................................... 2 6 2
T P A - Z S M - 5 ......................................... 2 5 2
SALT ENCAPSULATION
T P D ............................................... 7 9 , 101
................... 4 6
S A P O - 5 ............................................ 75, 91
T P R ....................................................... 65
S A P O - - 4 0 ............................................. 106
TRANSISTION
S A P O - 5 6 ................................................. 9
TRANSITION
M E T A L ........................... 7
COMPLEX
...................................... 1 1 4
SELECTIVE OXIDATION
...................................... 7
S T A T E ...................... 2 4 0
TS-1 ...................................................... 24
303
U U P T A K E ......................................... 131 U V - V I S ............................................... 112 V SILICALITE
................................... 157
V S I T E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 V - B E T A .................................................. 7 V a - Z E O L I T E I N T E R A C T I O N ............. 6 7 INCORPORATION
.......................... 19
V A P O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 V A P O - 5 .............................................. 155 VPI-5, DEHYDRATED ...................... 2 5 4 V S A P O ............................................... 161 W A T E R A D S O R P T I O N .............. 2 2 1 , 2 2 9 129XE N M R ........................................... 83 Xe CLUSTER
....................................... 85
X P S ....................................................... 69 X R D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56, 63, 2 5 4 , 2 6 2 ZEOLITE
3 A ...................................... 2 1 3
ZEOLITE
A ........................................ 2 7 2
MONOLAYER
................................. 3 0
Z E O L I T E B E T A .................. 165, 167, 2 2 3 Z E O L I T E S T A B I L I Z A T I O N .............. 124 Z E O L I T E Y ..... 69, 87, 167, 198, 2 2 5 , 2 3 6 Z E O L I T I Z A T I O N ................................. 34
Zn PROMOTION ................................ 116 Z n - Z S M - 5 ........................................... 182 Z r A P O - 5 ............................................... 13 Z S M - 5 ............................ 6 9 , 133, 174, 2 7 8
Discussion Transcripts
This Page Intentionally Left Blank
304
I. Synthesis
PLO1
Zeolites and their M e c h a n i s m of Synthesis by E.J.P. Feijen, J.A. Martens and P.A. Jacobs, Catholic University of Leuven, Heverlee, Belgium
Question by R. von Ballmoos, Engelhard Corp., lselin, New Jersey, USA: Could you expand on how you achieved the synthesis of a material with the aaa stacking of MAZ sheets by replacing the secondary cation (Na + for MAZ)? Can you identify the secondary cation you used? Answer by P.A. Jacobs: Computer modelling shows that aaa stacking of mazzite layers is possible. It also indicates what the nature of a secondary cation in terms of shape, size and charge density should be to effect stacking of mazzite layers according to this sequence. Question by S.A.I. Barri, University of Manchester, Institute of Science and Technology, Manchester, UK: Could you please comment on whether there is a unifying mechanism for zeolite synthesis or, in fact, there are many mechanisms involved and that the over-tiding mechanism is determined by the system and conditions applied and the structure-type being formed? Answer by P.A. Jaeobs: There is complex chemistry involved in zeolite synthesis. Depending on the experimental conditions, certain transformations will become more important than others. In this presentation, I have avoided therefore to make any formal distinction between crystallization from clear solutions or from a gel, as I am convinced that the same basic transformations are involved. The nature of the final products from a complex chemical reaction network will therefore be determined by several parameters.
Question by D. Barthomeuf, Universit~ Pierre et Marie Curie, CNRS, Paris, France: You described the role of the template, for instance of alkaline cations or organic templates. In the case of zeolite ZSM-5, the first synthesis was made with an organic template. Later, it became possible to prepare this material using alkaline cations. What are the general rules for moving from one type of template to another one? Can one foresee that for the A1PO4/SAPO/MeAPO family, inorganic cations can be used instead of organic templates? Answer by P.A. Jacobs: The possible roles of template molecules (inorganic or organic) have been dealt with in detail during the lecture. In principle, it should be possible to find
305 mixtures of primary and secondary cations (organic or not) which template the synthesis for A1PO4-type materials. It seems to me that, in such syntheses, the addition of template (usually a basic organic molecule) to the acid sol (gel) aluminophosphate mixture starts the (pre-)nucleation. In how far an inorganic base can take over this role, will depend on the particular case.
Question by E.N. Coker, Fritz Haber Institute of the Max Planck Society, Berlin, Germany: You mentioned that the addition of seed crystals to a synthesis batch will result in growth of the seeds. The extent to which this occurs will depend to a large extent upon the quality of the seeds employed. For instance, the presence of micro-crystalline fragments or dust on the surface of the seeds will promote the formation of a large population of small particles and very little growth of the seed crystals themselves. Can you please comment on this? Answer by P.A. 3aeobs: In every handbook of industrial crystallization one finds the exact conditions for growth of crystals via seeding, as well as the exact conditions to avoid secondary nucleation at the surface of the seed crystals. It is therefore possible to avoid the phenomena mentioned by carefully determining the nature and amount of seed crystals.
Question by J.M. Garc~s, The Dow Chemical Co., Midland, Michigan, USA: What is your thinking on the role of pressure, in particular very high pressure (2000 to 3000 bar), on the formation of zeolites? Answer by P.A. Jaeobs: Pressure is the only parameter which was not treated specifically in the paper. As far as pressure influences the specific parameters dealt with, it will be important for zeolite synthesis. It may, e.g., influence the viscosity of the liquid phase and consequently crystallization kinetics. It can also shift the equilibrium of certain reactions and thus affect the crystallization. Questions by IL Kumar, National Chemical Laboratory, Pune, India: I very much appreciate your excellent effort to critically review zeolite synthesis. I have, however, two questions: 1) Is the concept of change in pH, which accompanies crystallization, applicable to all zeolite systems in general or to high silica zeolites only? 2) Could you please comment on the major factor which is responsible for the connectivities between small silicate/aluminosilicate species as well as between larger oligomeric layers occurring in a particular way only? Answers by P.A. Jaeobs: 1) Given the hydrolysis-condensation mechanism of silicate species, the change in pH during nucleation and growth should be clearly seen for siliceous zeolites. For Si species, there is a pH dependent ratio of protonated-to-deprotonated species. For A1 present almost exclusively in an Al-tetra-hydroxide form, the change in pH during
306 crystallization will be different. 2) When zeolite synthesis is explained by Vaughan's "extended structure approach", the shape and size of the secondary cations will be crucial.
Question by M.G. White, Georgia Institute of Technology, Atlanta, Georgia, USA: Could you please comment on the use of chiral cations as agents to form chiral solids? Answer by P.A. Jacobs: Just as for chiral catalysis through strict templation, it seems to me that arrangement of inorganic polymers around a chiral template in specific cases could give rise to "chiral" zeolites. More specifically, this could be a way to make the zeolites with BEA topology enantiomerically pure.
A001
of Diquaternary Zeolite Synthesis The
Role
Cations
as Directing
Agents
in
by A. Moini, K.D. Schmitt, E.W. Valyocsik and R.F. Polomski, Mobil Research and Development Corp., Princeton, New Jersey, USA Question by G. Bellussi, Eniricerche S.p.A., San Donato Milanese, Italy: Did you observe a tendency of diquaternary cations to direct the synthesis towards the formation of layered silicates and, if so, did you observe some influence of the length of the alkyl chain? Answer by A. Moini: Some of the syntheses involving diquats with longer chains did lead to layered phases. In most cases, longer reaction times led to the formation of zeolitic phases at the expense of the layered phases. Questions by R. Kumar, National Chemical Laboratory, Pune, lndia: Let me first express my compliments for the presentation of a nice correlation between the chain length of the template and the zeolite structure. I have two questions: 1) Did you also try to vary systematically the length of the side chain, i.e., did you use hexamethonium diquat-6, hexaethonium diquat-6, hexaproponium diquat-6, etc. keeping the carbon number of the central spacer constant? What is the effect of such a variation of the template? You are certainly aware of our paper on NCL-1, presented at the past International Zeolite Conference held in Montreal. There we describe the synthesis ofNCL-1 with hexaethonium diquat-6. NCL-1 is a large pore zeolite. Using hexamethonium diquat-6 gives ZSM-48 or EU-1 which are both 10-membered ring zeolites. 2) What is the effect of the aluminum content of the gel on the structure directing effect of these templates? Answers by A. Moini: 1) Variations in the alkyl groups attached to the nitrogen lead to completely different phases compared to those discussed in the present work. A good example is ZSM-57 which cannot be classified in the same category as the structures discussed here. We believe that our specific mechanism does not apply to alkyl groups other
307 than methyl. 2) In regards to the aluminum content, the formation of some of these phases, e.g., NU-87, is found to be very sensitive to the Si/AI ratio of the original gel. The proposed mechanism applies only to the fixed compositional parameters that we had defined.
Question by R.F. Lobo, California Institute of Technology, Pasadena, California, USA: How does the model which you propose for NU-87 and ZSM-50 apply to the structure of NU-86 which is also formed with similar organic molecules? Answer by A. Moini: NU-86, which seems to be rather difficult to synthesize, falls into a different composition range with higher amounts of aluminum. It is, therefore, not included in the present model. Question by C.-L. O'Young, Texaco lnc., Beacon, New York, USA: What kind of zeolite phases will be formed if a mixture of diquat-6 and diquat-10 is used as template? Answer by A. Moini: We have not conducted extensive studies in this area. Limited investigations have led to mixtures of phases. Questions by R. Szostak, Clark Atlanta University, Atlanta, Georgia, USA: 1) Do the monoquat equivalents of your diquats, which would be equivalent to diquat-6, produce the same or similar structures? 2) Is there a 1:1 correlation between the number of diquats and the number of cavities like that which is observed with TPA in ZSM-5? Answers by A. Moini- 1) Our studies indicate that the monoquats do not result in an equivalent situation. The unique feature of the diquats is the fixed distance between the two charged units. Individual monoquat molecules are not expected to maintain such a fixed distance relative to each other, and pairs of these cations are not found to lead to the same structures that are obtained with the diquats. 2) Significant amounts of the organic diquats are found in the zeolite framework. These amounts do not always add up to a stoichiometric correlation, but they are close.
Question by J. Wu, W.R. Grace & Co., Columbia, Maryland, USA: Have you looked at diquats with alkyl groups other than methyl, such as ethyl or propyl? Answer by A. Moini: We have studied these systems, but they form completely different phases that do not seem to be related to the present model.
A002
of Guest/Host Energetics for the Synthesis of C a g e Structures N O N and C H A
A
Study
by T.V. Harris and S.l. Zones, Chevron Research and Technology Co.,
Richmond, California, USA
308
Question by H. van Bekkum, Delft Universityof Technology, Delft, The Netherlands: On
the basis of the structures of the templates used, large differences in the ease of Hofmann degradation are to be expected. For instance, the endo-norbomene system will undergo relatively rapid Hofrnann elimination, whereas the exo-derivative is expected to be rather inert. Were such differences indeed observed? The rate of the Hofmann reaction might also have a beating on the required temperature of calcination. Answer by T.V. Harris: Generally, we are able to observe and have observed Hofmann degradation in zeolite crystallization with tetraalkylammonium hydroxide templates. We see this decomposition at higher temperatures than we have used in this work (150 or 160 ~ for NON, 135 ~ for CHA). We have no evidence in this work that Hofrnann degradation occurs during synthesis. I agree that different temperatures for template decomposition could be observed during calcination and could be affected either by the relative ease of Hofmann degradation or by the energetics of template/zeolite fit. We have not investigated this, but the suggestion is excellent and we will do so.
Questions by F. Fajula, Ecole Nationale Supdrieure de Chimie de Montpellier, CNRS, Montpellier, France: 1) Can we expect, in your opinion, that the progress in zeolite modelling will allow, in the near future, calculations on the templating effect of inorganic ions? 2) You showed nicely the correlation between crystallization time and stabilization energy. Could such an approach be used as well for predicting crystal sizes? Answers by T.V. Harris: 1) Yes. The difficulty is that for hydrated metal cations good potential parameters are just being developed. The inclusion of hydration spheres is, of course, a difficult computational problem, but I believe that this will soon be possible. 2) No, at least not by using our methodology. We looked at the energetics of one template molecule in a host lattice. In actuality, crystal size is the result of the interaction of a number of factors, including relative rates of nucleation and crystal growth, rates of nucleation, surface energies, etc. However, there are computational techniques becoming available which can simulate surface energies and morphologies as a function of crystal size and "dopants". These are being developed by Richard Catlow's group, among others. I believe such computational methods may help in predicting crystal size, if used in conjunction with appropriate experimental data.
Question by J.C. Jansen, Delft University of Technology, Delft, The Netherlands: Are there water molecules stabilized between the template and the zeolite wall? Answer by T.V. Harris" We have not investigated experimentally whether water molecules are also occluded in the NON and CHA cages. For the larger templates, I believe that this is not possible because there is so little void space left. As an example, if the methyl groups of
309 template IX are replaced by ethyl groups, NON is no longer formed, and ZSM-12 is made instead. For the smallest templates, it may be possible for water molecules to be occluded.
Question by F. Trouw, Argonne National Laboratory, Argonne, Illinois, USA: How does the thermodynamic stability of the product affect the kinetics of the reaction? Could the different water solvation energies be a possible reason, i.e., could a hydrophilic/hydrophobic interaction change the energy of the "transition state"? Answer by T.V. Harris: We view the process as beginning with a water solvated organic template. Water molecules in the solvation sphere are replaced by silicate species, which eventually become ordered and polymerize to give, ultimately, a crystalline product. We are not able to directly model the arrangement of silicate fragments around the template in a bulk aqueous medium, although we are exploring the possibility. Instead, we chose to model template interactions with the final zeolite structure. In this case, the reference states are the zeolite and non-hydrated template molecules in the vacuum at infinite separation. These stabilizations gave us the correlation with crystallization rates that we reported. Using arguments from physical organic chemistry, we postulate that the intermediate in the rate determining step must have a structure more related to the final product (which we modelled) than to the reactants. This argues, of course, for organization of silicate species around the template. The nature of the modelling, which was done for a series of templates of similar size and structure inside the same molecular sieve cage, suggests that differences of water solvation around the limited series of templates are less than the energy differences seen for modelling. We agree, of course, that the better modelling approach is to attempt to model the hydration sphere and replacement of water molecules by silicate species in aqueous medium.
A003
Zeolite MCM-22: Characterization
Synthesis,
Dealumination
and
Structural
by S. Unverricht, M. Hunger, S. Ernst, H.G. Karge and J. Weitkamp, University of Stuttgart, Stuttgart, Germany; Fritz Haber Institute of the Max Planck Society, Berlin, Germany Questions by P.A. Jacobs, Catholic University of Leuven, Heverlee, Belgium: 1) Dealumination by SIC14 normally generates secondary pores. Is this also the case here? 2) By applying catalytic tests, e.g., the n-decane test, one can correctly predict the pore architecture ofMCM-22 (cf. J. Chem. Soc., Chem. Commun. 1994, 1671-1672). I would like to hear your views on this, from your experience with other test reactions.
310
Answers by S. Ernst: 1) We have not yet looked at the formation of mesopores (e.g., by adsorption studies) during SiCI4 dealumination of MCM-22. 2) Isomerization and hydrocracking of long chain n-alkanes (e.g., n-decane) is no doubt a valuable tool for probing the pore architecture of zeolites with unknown structures. By using this method, we obtained results similar to those described in your above-mentioned paper. From the results of ethylberLzene disproportionation and hydrocracking of butylcyclohexane (determination of the Spaciousness Index) we concluded that MCM-22 possesses 10-membered ring pore openings and larger intracrystalline cavities. However, no conclusions concerning the dimensionality of the pore system could be drawn. A comprehensive evaluation including an assessment of proposed test reactions for probing the pore width and architecture of microporous materials was published recently (J. Weitkamp and S. Ernst, Catal. Today 19, 1994, 107-150).
Question by M. Stiieker, SINTEF, Oslo, Norway: The structure of MCM-22 proposed by Lawton et al. could be confirmed by recording 2 D connectivity solid state NMR spectra (like 2 D COSY, INADEQUATE) on highly siliceous samples of MCM-22. Have you tried other dealumination methods than treatment with SiCI4 vapors (such as steaming) in order to receive such samples? Answer by S. Ernst: Thank you for this suggestion. Presently, we are indeed testing other dealumination procedures as well, such as steaming and others.
A004
Molecular Sieves from Pillaring of Layered Silicates by S.-T. Wong, S.-H. Wong, S.-B. Liu and S. Cheng, National Taiwan University, Taipei, Taiwan, R. O. C.; Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan, R. O. C.
Question by F. Di Renzo, Ecole Nationale Sup~rieure de Chimie de Montpellier, CNRS, Montpellier, France: Can you comment on the inverse correlation between the aluminum content and the interlayer spacing of the hexylamine expanded materials? Answer by S. Cheng: In this series of Al-free silicates, the acidity of Si-OH groups, which point towards the interlayer space, is very low. As a result, the hexylammonium ions incorporated between the layers have a rather low stability. In the process of AI-Keggin ion exchange, the hexylamine tends to diffuse out of the interlayer space before ion exchange occurs. This is why we have not been able to introduce a large amount of aluminum which could have served as pillars.
311
Question by F. Fajula, Ecole Nationale Supdrieure de Chimie de Montpellier, CNRS, Montpellier, France: Pore size determinations based on sorption studies revealed apertures smaller than 0.7 nm, whereas the d spacings obtained by XRD are above 2.0 nm. What is the reason for this discrepancy? Answer by S. Cheng: I think there is some misunderstanding: The XRD patterns showed that the free interlayer spacing was larger than 2.0 nm for hexylamine expanded derivatives. However, the free spacings shrank upon introducing pillaring agents and calcining.
Question and Comment by K. Kuroda, Waseda University, Tokyo, Japan: 1) The 29Si NMR spectrum of ilerite is rather different from those published in the literature. What is your explanation for this difference? 2) The 29Si NMR spectrum of H-kanemite has shown the presence of Q4 units. Therefore, I think you should check the 29Si NMR spectrum of the H-kanemite/hexylamine complex. Answers by S. Cheng: 1) Since the XRD pattern of ilerite synthesized by us was identical to those reported in the literature, we did not check and compare the 29Si NMR spectrum of our sample with spectra from the literature. Your suggestion is appreciated, and we will make this comparison. 2) The presence of Q4 resonances in the 29Si NMR spectrum of Hkanemite was consistent with what has been reported in the literature, viz. that H-kanemite is easily dehydrated in an acidic environment. We thought it was important to look at hexylammonium kanemite, because the XRD pattern showed a widely expanded interlayer spacing.
A010
Development o f a Formation Mechanism for M41S Materials by J.C. Vartuli, K.D. Schmitt, C.T. Kresge, W.J. Roth, M.E. Leonowicz, S.B. McCullen, S.D. Hellring, J.S. Beck, J.L. Schlenker, D.H. Olson and E.W. Sheppard, Mobil Research and Development Corp., Princeton, New Jersey, USA, and Paulsboro, New Jersey, USA
Questions by J. van Hooff, Eindhoven University of Technology, Eindhoven, The Netherlands: 1) In the lecture, the reinforcement of crystallization products by the addition of TEOS is mentioned. Is it possible to give a more detailed description of this treatment? 2) Concerning the dimensions of the pores, their diameter is mentioned only. Is it possible to give some information on the length of the pores? Answers by J.C. Vartuli: 1) To stabilize the lamellar structure we combined at room temperature 1 g of tetraethylorthosilicate per 1 g of as-synthesized lamellar material. We allowed this moist combination to stand for 4 to 16 h before washing with ethanol and air drying. Then we calcined the stabilized product in air to 540 ~ to obtain the MCM-50
312 product shown. 2) We do not have any precise measurement of the length of the MCM-41 tubes.
Question by H. Robson, Louisiana State University, Baton Rouge, Louisiana, USA: Is there a sharp distinction between a surface active agent used in the synthesis of M41S types and conventional structure directing additives in a templated synthesis? If these surfactants had shorter chains, would they continue to be active? Answer by J.C. Vartuli: We have a Recent Research Report (# RP7) in which we demonstrate the effect of chain length of the surfactant and temperature on the ability to synthesize these mesoporous materials. As you would expect, longer chain lengths and lower temperatures favor aggregation of surfactant molecules and ultimately mesoporous products. Conversely, smaller chain lengths of the surfactant and higher synthesis temperatures favor unimolecular templating and the formation of zeolites or crystalline microporous materials.
Question by F. Schiith, University ofMainz, Mainz, Germany: What is the mechanism of MCM-50 stabilization by TEOS? If the rod stack model for the lamellar phase is correct, why isn't it stable upon calcination without TEOS treatment? Answer by J.C. Vartuli: If MCM-50 is a variation in the stacking of surfactant rods as shown in my slide, I believe that TEOS functions to "patch" the areas of the silicate wall that has incomplete condensation. I believe that the TEOS is adsorbed into the surfactant within the oxide structure preferentially and then diffuses to the silicate wall structures to react with the silanol nests. On the other hand, if MCM-50 is a more classical layered structure, then TEOS is used for pillaring of the silicate sheets. The rod stacking model could be stable to calcination without TEOS stabilization if the wall formation was complete. I believe that the hexagonal stacking would be more stable than that proposed for MCM-50. Comment by G.D. Stueky, University of California, Santa Barbara, California, USA: This comment is in reference to your discussion of our model. As shown in Figure 5 and the accompanying discussion in our Science article (ref. 16 in A010), and as stated explicitly in our article in J. Mol. Liq. Cryst., the lamellar array is not a necessary precursor to the MCM41 phase. We believe that the solution inorganic species determines the surfactant array assembly. No preorganized organic array (including micella) is required and if present will be restructured by the anion. This is true even at low temperatures (< 70 ~ where surfactant organization is more important. Answer by J.C. Vartuli: My discussion of your model was based on your Figure 4 (I believe) of the same Science article. I described your model to contrast it with that proposed by M. Davis' group. I have no argument with your interpretation on the importance
313 of the inorganic species in determining the M41S structure. This is the basis for our mechanism pathway #2 which we proposed in our papers (J. Am. Chem. Soc., 1992, ref. 2 in AOIO).
Question by K. Unger, University of Mainz, Maim, Germany: You showed the narrow pore size distribution of MCM-41 (hexagonal) derived from adsorption measurements of argon applying the traditional procedures. What is the proof of the regularity of the pore structure? Did you use adsorptives with larger molecular diameter than argon to check the diffusivity/adsorption through the tubes? Answer by J.C. Vartuli: As you know, larger molecules (than argon or benzene) are more difficult to use for sorption measurements. The limited work we did using C12 molecules indicated no change in the sorption/desorption rate. Also the pore volume calculations using either small or large molecules are equivalent which suggests no major irregularity of the pore structure.
A011
Synthesis of AI-Containing Interaction and Removal
MCM-41
Materials:
Template
by R. Schmidt, D. Akporiaye, M. Stiicker and O.H. Ellestad, SINTEF, Oslo, Norway; University of Oslo, Oslo, Norway
Question by G. Engelhardt, University of Stuttgart, Stuttgart, Germany: You observed a considerable portion of tetrahedral framework aluminum. What are the charge compensating cations in the as-synthesized and detemplated forms? Answer by R. Schmidt: As we conclude from TGA experiments, the charge is compensated by the template in the as-synthesized form. We assume that a proton is left behind upon thermal degradation of the template. We are not certain, however, that all the aluminum is present in the framework after heat treatment. Question by IL GRiser, University of Stuttgart, Stuttgart, Germany: Do you have any idea as to why the regularity of aluminum-rich MCM-41 is better than the one of purely siliceous materials? One could expect that incorporating a second element into the framework disturbs the formation of the ordered nanophase. Answer by R. Sehmidt: We have no real explanation for this observation. Question by J.C. Jansen, Delft University of Technology, Delft, The Netherlands: The calcination temperature applied here (as well as in the preceding paper) is rather high. In
314 particular, the aluminum containing material needs very high calcination temperatures. Might this be due to stacking faults? Answer by R. Schmidt: There seems to be more regularity with aluminum in the lattice, hence I do not believe that stacking faults are the cause.
Questions by E.C. Keller, Haldor Topsoe A/S, Lyngby, Denmark: 1) One of the major problems in TGA experiments with as-synthesized zeolites is the continuous dehydration of the material upon increasing the temperature. How did you distinguish between the removal of water and the removal of the template? 2) NMR spectroscopy reveals that, upon calcination, the AI coordination decreases. Could this have its origin in a collapse of the structure due to the evolution of a large amount of heat, caused by the combustion of the template, and a concommitant local increase of the temperature? Answers by R. Schmidt: 1) Firstly, the TGA instrument was coupled with a mass spectrometric detector. Secondly, the TGA results were compared with those obtained on template-free samples. However, even on such samples there is a steady (but small) dehydration on account of structural collapse. 2) Yes, this is probably what happens. Applying a more careful calcination might mitigate the problem and lead to much smaller changes in the 27A1 MAS NMR spectrum. Question by M. Remy, Catholic University of Leuven, Louvain-la-Neuve, Belgium: You showed by 27A1 MAS NMR that, upon thermal treatment, tetrahedral AI in the sample with Si/A1 = 4 is transformed into extra-framework AI. Did you observe the same transformation on the other A1 containing samples? Answer by R. Schmidt: Yes, the same effect was observed on all AI containing samples. With increasing A1 content, the effect became even more pronounced. Question by H. Robson, Louisiana State University, Baton Rouge, Louisiana, USA: There are parallels between your research and the problems in amorphous silica-alumina cracking catalysts of the early 1950's. Then the problem was to put the maximum alumina content in the catalyst while maintaining the other physical properties. The tool of preference then was temperature-programmed desorption of ammonia. Have you applied this technique to your materials? Answer by R. Sehmidt: Yes, we have applied NH 3 TPD to the calcined materials and found the acidity comparable to that of amorphous silica-alumina. Question by J.C. Vedrine, Institut de Recherches sur la Catalyse, CNRS, Villeurbanne, France: How is the acidity of the materials upon (i) removal of part of the template by
315
solvent dissolution and (ii) complete removal of the template by calcination in comparison to silica-alumina and zeolites? Answer by R. Schmidt: Preliminary NH 3 TPD and IR studies indicate that the acidity is not too different from that of amorphous silica-alumina.
A012
Preparation and Properties of Ti-Containing M C M - 4 1 by A. Corma, M.T. Navarro, J. P~rez-Pariente and F. Sfinchez, Instituto de Tecnologla Quimica, CSIC-UP V, Valencia, Spain
Question by G. Bellussi, Eniricerche S.p.A., San Donato Milanese, Italy: The activity of TS-1 was surprising since it shows very good activity with H202, but it performs very badly with TBHP. Exactly the reverse behavior was observed with TiO2/SiO 2 gel catalysts. It is now possible to prepare TiO2/SiO 2 gel catalysts - actually, they are commercial products with a small amount of Ti very well distributed through the silica gel, with a high surface area and a porosity falling into the region of mesoporous materials. It appears, therefore, worthwhile to compare the catalytic behavior of these materials with that of Ti-MCM-41. Could you comment on this and have you already tried to make such kind of comparisons? Answer by J. P~rez-Pariente: Probably, the activity of Ti-MCM-41 is the same as that of SiO2frio 2 gels, but we have not yet compared both types of catalysts.
Question and Comment by L. Bonneviot, Laval University, Ste.-Foy, Quebec, Canada: 1) In 1993, we proposed a controversial point of view on how the Ti might be linked to the framework in TS-1 materials. This was based on EXAFS data. TS-1 and TS-2 are very active in the oxyfunctionalization reaction, by contrast to Ti-beta and Ti-MCM-41 materials. Have you compared your EXAFS data for both materials to those of TS-1 and TS-2 and do you think that we are dealing with the same type of sites in all these materials? 2) We are now using the multiple scattering analysis to fit the Ti site. The average Ti-O-Si bond angle is found to be 158 ~ and the Ti-Si distance 0.34 nm. These data are consistent with a lattice expansion contrary to the classical Single scattering analysis which gives a TiSi distance of 0.32 nm.
Answer by J. P~rez-Pariente: 1) The results obtained from EXAFS data corresponding to the first coordination shell of titanium in Ti-MCM-41 are quite similar to the ones reported in the literature for TS-1 and TS-2 in the dehydrated calcined state. Therefore, I think that, under our experimental conditions, we are basically dealing with the same type of Ti environment. However, one must be careful in deriving catalytic properties from these data only, since the coordination of Ti under reaction conditions (liquid phase) is probably higher
316 than four. Besides, other parameters, such as hydrophobicity, can affect the catalytic behavior as well.
Question by A. Zecehina, University of Turin, Turin, ltaly: XANES, EXAFS and UV-VIS spectra of your best sample are very similar to those of titanium silicalite. Also, the behavior upon contact with water (XANES) is very similar. On the contrary, the IR spectrum looks different as the band at ca. 960 cm -1 is definitely broader. Is this due to the presence of silanol groups only? As the presence of adsorbed water broadens the finger-print peaks, did you try to obtain the IR spectra under controlled atmosphere? Answer by J. P~rez-Pariente: Yes, there is a large amount of silanol groups in these samples. The strong intensity of the Si-O stretching band at 960 cm -1 prevents a clear identification of this band due to the presence of Ti in the framework. The samples investigated by IR spectroscopy did contain some water, but its influence on the band is probably much lower than the influence of the silanol groups.
A013
New Mesoporous Titanosilicate Molecular Sieve by O. Franke, J. Rathousl~, G. Schulz-Ekloff, J. St~irek and A. Zukal, University of Bremen, Bremen, Germany; J. Heyrovslc~ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Prague, Czech Republic
Question by F. Fajula, Ecole Nationale Sup~rieure de Chimie de Montpellier, CNRS, Montpellier, France: Could you please comment on the yields in your synthesis? Answer by J. Rathousk~: Our yields were about 80 wt.-%. Comment by J. van Hooff, Eindhoven University of Technology, Eindhoven, The Netherlands: In the introduction you mentioned the possible application of the mesoporous titanosilicates developed by you, as photocatalysts. But as you report that the obtained materials contain highly disperse titanium, photocatalytic activity is not very likeley because semiconducting properties are a prerequisite for that. Answer by J. Rathousl~: Our synthesis procedure enables us to prepare MCM-41 sieves containing titanium in different forms: from built-in pore walls, over highly disperse oxidic phases to titania nanoparticles. They are expected to have semiconductor properties suitable for photocatalysis.
Questions by C. Lortie, Universitd Laval, Ste. Foy, Quebec, Canada: It has been proven that for TS-1 materials, the maximum amount of framework incorporated titanium is about 2 %. Have you estimated the limit of titanium that can be included in the framework of your
317 materials? And have you characterized that extra-framework species? Could it be a titanium silicate rather than anatase? Answers by J. Rathousk~: Titanium-containing MCM-41 behaves analogously to TS-1, i.e., when the TiO 2 content exceeds about 2 mol-%, extra-wall titanium species form. They were characterized by means of diffuse reflectance spectroscopy only. Therefore, only a preliminary assignment is possible. The spectra ofTi-MCM-41 samples with about 4 mol-% of TiO2 are characterized by two bands at about 230 and 280 nm. The former band may be ascribed to isolated molecular TiOx-species. It cannot be excluded that the latter one corresponds to an amorphous titanium silicate phase. Samples with even larger amounts of titanium prepared by a modified procedure contain TiO2 nanoparticles.
A014
Amorphous Mesoporous Silica-Alumina with Controlled Pore Size as Acid Catalysts by G. Bellussi, C. Perego, A. Carati, S. Peratello, E. Previde Massara and G. Perego, Eniricerche S.p.A., San Donato Milanese, Italy
Question by E.G. Derouane, Facult~s Universitaires Notre-Dame de la Paix, Namur, Belgium: How do you explain the high cumene selectivity of your material or, in other words, the low yield in diisopropylbenzenes? Could the catalysis occur on nanodomains of ZSM-5 in the mesoporous gel? Answer by C. Perego: The selectivity we reported was in comparison with other mesoporous materials with controlled or broad distribution of porosity. Under the same reaction conditions, ZSM-5 was not active. The differences in cumene selectivity with respect to benzene are not very large, hence it appears dangerous to draw any conclusions from these differences.
Question by F. Di Renzo, Ecole Nationale Supdrieure de Chimie de Montpellier, CNRS, Montpellier, France: Does water play any role in the stabilization of TPA clusters? And which is the water content of the final solid? Answer by C. Perego: Surely, the relative content of TPAOH, EtOH and H20 influences the structure of the final gel. At present, there is not enough information to define exactly the roles of the different compounds. As the gel is formed it looses water continuously, and the final water content depends on the thermal treatment.
Question by P.A. Jacobs, Catholic University of Leuven, Heverlee, Belgium: Prior to this work, similar systems have been described using slightly different procedures. In some work (e.g., P.A. Jacobs, E.G. Derouane and J. Weitkamp, J. Chem. Soc., Chem. Commun. 1981,
318 591; ref. 17 in A014), it was claimed that ZSM-5 nuclei might be active species, based mainly on the shape selectivity in the products from alkane isomerization. With the present materials, can this possibility be excluded? Answer by C. Perego: The paper you are mentioning encouraged us to proceed into this direction. However, our system turned out to be different from the one described in your paper. We prepare a clear sol from TPAOH, TEOS, H20 and aluminum isopropoxide in the absence of alkali cations. Upon partial evaporation of the solvents, the clear sol gave a clear dense gel which was dried and characterized. A solid precipitate was never formed. In the clear gel, we have probably TPA clusters which are responsible for mesopore formation, and TPA + ions which act as counterions of acidity generated by tetrahedral aluminum sites. Certainly, there is a local order as evidenced by IR and 27A1 MAS NMR spectroscopy, but this does not necessarily imply the existence of real ZSM-5 nuclei. In any case, based on tests we performed with different catalytic reactions, shape selectivity effects, as they are typical for the ZSM-5 structure, seem to be absent.
Question by E.G. Derouane, Facult~s Universitaires Notre-Dame de la Pair,, Namur, Belgium: How does your material compare to those described in the literature in the late 1970's, namely X-ray amorphous ZSM-5 zeolites (P.A. Jacobs, E.G. Derouane and J. Weitkamp, ref. 17 in A014) or controlled pore size silicas (M.R. Manton and J.C. Davidtz, ref. 18 in A014)? Answer by C. Perego: Concerning the paper on X-ray amorphous ZSM-5 zeolites, cf. my reply to Professor P.A. Jacobs. With respect to the work of Manton and Davidtz, the major difference lies in the fact that these authors prepared a sol with tetraalkylammonium hydroxide, TEOS and H20 at high pH, then they added HCI until a pH around 9 was reached, where a precipitation occurred. Upon the addition of HC1, probably a large portion of aluminum tends to switch from tetrahedral coordination with a modification of the local symmetry (this was clearly shown by Professor Livage at the Summer School of the 10th IZC and by Professor Fripiat in the early 1970's). As a consequence, the method proposed in the above-mentioned paper led to a material which was less active than MSA (mesoporous silica-alumina) and poorly reproducible. As far as the formation of mesoporosity is concerned, we cannot exclude that it is produced by similar mechanisms in both cases.
Question by C. Naccache, Institut de Recherches sur la Catalyse, CNRS, Villeurbanne, France: The advantages of medium pore zeolites in catalysis are that deactivation by coke deposition occurs less rapidly than with mesoporous amorphous materials and that the reactions can be conducted in a shape selective manner. This is particularly true for the alkylation of benzene. What are the real advantages of using MSA instead of zeolites for
319 catalytic purposes? I presume that MSA deactivates faster and leads to larger amounts of polyalkylated benzene. Answer by C. Perego: The MSA material allows one to performbenzene alkylation with propene at very low temperature because of reduced diffusion problems. In fact, the reaction takes place below 160 ~ at 40 bar, so that the system is in the liquid phase. These conditions prevent coke formation with respect to gas phase experiments. More dialkylbenzene products are formed than on a zeolite catalyst. However, dialkylbenzenes can be transformed into monoalkylbenzene in a subsequent transalkylation step.
Questions by C.T. O'Connor, Universi~, of Cape Town, Rondebosch, South Africa: Could you comment on 1) the catalyst utilization value (g product/g catalyst) and 2) the octane or cetane numbers of the products obtained in the propene oligomerization over MSA and HZSM-5? Answers by C. Perego: 1) I am very sorry, but your first question is dealing with confidential information. 2) As MSA doesn't show any shape selective behavior, the reaction products are different from those obtained on H-ZSM-5. The gasoline produced has very high RON and MON, higher than with H-ZSM-5. The middle distillate has a cetane number which is lower than that of the middle distillate formed on H-ZSM-5.
Question by M. Stiieker, SINTEF, Oslo, Norway: You demonstrated clearly the difference in the long-range ordering of your amorphous material compared with the well ordered mesoporous material by XRD. What about the differences in the short-range ordering for your amorphous material in comparison with the well ordered mesoporous material: do you have any information about the local environment, such as the degree of condensation of the Si-units? Answer by C. Perego: The lack of long-range ordering is also demonstrated by the absence of any coherent scattering in electron diffraction patterns of MSA, in addition to XRD analysis. The short-range structure features are still under investigation. However, 27A1 MAS NMR data clearly indicate that A1 is mostly in tetrahedral coordination with relatively high symmetry, as indicated by the narrowness of the NMR lines. This suggests a tendency of the structure to organize locally to some extent.
A024
Nonaqueous
Synthesis of Large Zeolite and Molecular Sieve
Crystals
by S. Nadimi, S. Oliver, A. Kuperman, A. Lough, G.A. Ozin, J.M. Garc~s, M.M. Oiken and P. Rudolf, University of Toronto, Toronto, Ontario, Canada; The Dow Chemical Co., Midland, Michigan, USA
320
Question by J.-L. Guth, Ecole Nationale Sup~rieure de Chimie de Mulhouse, CNRS, Mulhouse, France: We reproduced your synthesis of silica-ferrierite, and according to the unit cell formula we expected an intense and well defined 19F MAS NMR signal. But this was not the case. Have you performed 19F NMR? Answer by A. Kuperman: We observed a very broad 19F signal on our materials. This could be due to the fact that there are two F in every unit cell of ferrierite in the 20 T-atom channel disordered between two different positions each. Question by J.C. Jansen, Delft University of Technology, Delft, The Netherlands: What is the orientation of the large pores in the ferrierite crystals? Answer by A. Kuperlnan" The large pores are running perpendicularly to the largest crystal plane. Question by R. Jones, University ofKeele, Keele, UK: In the sheet aluminum phosphate A13P4016 3-, where is the template located, and does it block the channels? Answer by A. Kuperman: There are tetraethylene glycol molecules between the sheets and triethylamine molecules in the 12-membered tings. Questions by R. Szostak, Clark Atlanta University, Atlanta, Georgia, USA: 1) In 1991 we reported the same type of synthesis from gels containing high levels of alcohol which produce "jello" or jelly-like phases resulting in crystals of 1 mm size. This phase was transparent. Are your preparations also transparent? 2) In our synthesis we have observed a secondary crystallization to smaller crystals of the same phase with extended time. Did you observe a similar recrystallization? Answers by A. Kuperman: 1) I believe that our synthesis procedure is unique in both reaction mixture composition and the size and uniformity of the final products. This method works because of the combination of an organic solvent with anhydrous source of HF and reagent amounts of water that provide ideal growth conditions for large single crystals. With respect to the transparency of the gels, they are indeed transparent in some cases, in other cases they are not. It depends on the final composition of a reaction mixture in each individual case. 2) There is no secondary nucleation possible in our synthesis method. All crystals are of uniform size. Comment by K. Unger, University of Mainz, Mainz, Germany: The term "nonaqueous synthesis" in the title of your paper seems to be somewhat misleading, simply because the synthesis is not performed under totally nonaqueous conditions. Firstly, your reagents (silica and alumina precursors, pyridine) are not free from water and, secondly, you even add water in stoichiometric amounts.
321
Answer by A. Kuperman: We call our synthesis procedure "nonaqueous" because the solvents we use are of organic nature in contrast to hydrothermal syntheses procedures where water is the solvent. In our work we use water in reagent amounts to promote SiO 2 dissolution.
Comment by D.E.W. Vaughan, Exxon Research and Engineering Co., Annandale, New Jersey, USA: Probably the first crystallization of large zeolites was by E.A.D. White and coworkers at the General Electric Co. (UK) in the late 1950's and early 1960's. They grew sodalite and cancrinite single crystals up to 5 mm in diameter using techniques similar to those developed for the crystallization of large quartz crystals (reported much later in J. Crystal Growth). Their interest was in developing computer coding materials. Answer by A. Kuperman: I am sorry, but I am not aware of this work. Any way, what we report today is not just the fact that we have grown large crystals of few materials, but a general method for growth of large zeolite and molecular sieve s'~gle crystals.
Question by J. Wu, W.R. Grace & Co., Columbia, Maryland, USA: You have shown the synthesis of ferrierite and silicalite. My question is: what is the limitation of your method to prepare large single crystals? Can it be applied to other zeolites? Answer by A. Kuperman: Given sufficient time, there is no limit to the size of crystals that can be prepared by our procedure. It can be used for any other zeolite synthesis, provided that we can find a good complexing agent for aluminum.
A025
Diversity of the System Ga203-P2Os-H20-HF in the Presence of Organic Species by C. Schott-Darie, H. Kessler, M. Soulard, V. Gramlich and E. Benazzi, Ecole Nationale de Chimie Sup~rieure de Mulhouse, CNRS, Mulhouse, France; Swiss Federal Institute of Technology Zurich, Zurich, Switzerland; lnstitut Frangais du Pdtrole, Rueil Malmaison, France
Question by D. Akporiaye, SINTEF, Oslo, Norway: Some researchers obtained an orthorhombic AIPO4-5. Did you come across a similar phase? Answer by H. Kessler: No, we have not observed this phase in the synthesis of A1PO4-5 using fluoride.
Question by L.B. McCusker, Swiss Federal Institute of Technology Zurich, Zurich, Switzerland: Are there any zeolite structure types with double 4-rings that you have not synthesized in the gallophosphate-fluorine system?
322
Answer by H. Kessler: Yes, for example the AFY type. The corresponding structure comprises D4R's. Di-n-propylamine is an organic template for its synthesis. In the Ga203P2Os-HF-H20 system, di-n-propylamine directs the synthesis towards the formation of the LTA type gallophosphate. We have tried to prepare the AFY type CoAPO (CoAPO-50) in the presence of fluoride, but so far, these attempts were not successful.
Question by W.M. Meier, Swiss Federal Institute of Technology Zurich, Zurich, Switzerland: What is known about the charge of the fluorine in the double 4-ring units you described? If nothing much should be established, would you be prepared to speculate?
Answer by H. Kessler: Presumably, fluorine is not very negatively charged because the repulsion with the oxygens would be too strong. One should be able to get an idea on the charge from the 19F NMR chemical shift, but we have not done such experiments so far.
A027
Convenient Synthesis of Crystalline Microporous Metal Silicates Using Complexing Agents
Transition
by R. Kumar, A. Raj, S.B. Kumar and P. Ratnasamy, National Chemical Laboratory, Pune, India Questions by G. Kuehl, formerly Mobil Research and Development Corp., Paulsboro, New Jersey, USA: 1) [Fe]ZSM-5 can be obtained in a pure state without using a complexing agent. Does the addition of oxalic acid bring about the formation of a complex which is stable under crystallization conditions? 2) Or does the oxalic acid only adjust the pH? 3) Can a similar result be obtained at the same pH in the absence of oxalic acid? Answers by R. Kumar: [Fe]ZSM-5 (and many other [Fe]-zeolites) can be obtained using very specific synthesis conditions, provided that the formation of brown iron hydroxide is carefully avoided. The hydrothermal chemistry of iron and iron silicates has been discussed in detail, e.g., in our review article (Catal. Today 9, 1991, 329-416). The answers to your questions are: 1) The iron oxalate complex undergoes slow and stepwise hydrolysis (see Martell's book, ref. 5 in A027). 2) Oxalic acid or sodium oxalate is used in small quantities, and the pH is adjusted as usually by sulfuric acid, if required. The details are given in our paper. 3) It has been clearly shown that in the absence of oxalate ions, iron incorporation is very poor (in the case of ZSM-5) or does not occur at all (in the case of beta).
Question by M.S. Rigutto, Delft University of Technology, Delft, The Netherlands: I wonder about the "standard" method you used for the preparation of TS-1 since it is relevant to the interpretation of your results. In a recent paper by Millini et al. in the
323
J. CataL your Ti(OBu)4/i-PrOH method is strongly criticized. Would you mind to comment on this?
Answer by R. Kumar: As far as I know, Millini et al. reported in their paper in the J.. Catal. that they were unable to reproduce the synthesis of TS-1 samples with very high titanium content (sifri < 24), i.e., with an sifri ratio below the limit covered by their patents. Our method has, however, been found to be very useful and far more simple than earlier methods for synthesizing TS-1 samples with moderate titanium content by a large number of groups. The approach in our earlier papers, e.g., in the J. Catal., as well as in the present paper is to provide an easy and convenient synthesis method which is based on scientific grounds rather than on mere skill and art. My comment to your question is that Millini et al. did not criticize our method or our approach, but only TS-1 with a high titanium content. Let me criticize, in turn, here that, even for TS-1 with a high titanium content, MiUini et al. used just one characterization technique, viz. XRD, whereas we employed a variety of techniques, viz. XRD, UV-VIS, thermal stability, adsorption etc., and this enabled us to show the presence or absence of extra-framework TiO 2.
Question by S.I. Zones, Chevron Research and Technology Co., Richmond, California, USA: What do you know about the stability of the titanium acac complex as you go to high pH and elevated temperature in the synthesis of the zeolite? Answer by R. Kumar: The stability of Ti(acac)x(OR)4_ x complexes is very well documented in the literature on sol-gel chemistry (e.g., A.E. Martell, ref. 5 in A027, or D.L. Kelpert, ref. 7 in A027). These complexes undergo slow hydrolysis as opposed to the instantaneous hydrolysis of Ti(OR)4 complexes. It is our approach to use the Ti(acac)2 (OR)2 complex as an agent which slowly releases Ti 4+ ions which can combine with "Si4+(OH)nn-'' species formed by the slow hydrolysis of Si(OR)4. However, acac was not present in the solid TS-1, and Ti 4+ ions were absent in the mother liquor aider synthesis, which suggests that the Ti(acac) complex was completely hydrolyzed during hydrothermal crystallization.
A028
Simultaneous Occurrence of Differently Coordinated Framew o r k Heteroatoms in one Zeolite" MFI Type Vanadium Silicalite, KVS-5 by J. Kornatowski, B. Wichterlovfi, M. Rozwadowski and W.H. Baur, J.W. Goethe University, Frankfurt am Main, Germany; N. Copernicus University, Torun, Poland; J. Heyrovsk~ Institute of Physical Chemistry, Czech Academy of Sciences, Prague, Czech Republic
324
Question by F. Di Renzo, Ecole Nationale Sup&ieure de Chimie de Montpellier, CNRS, Montpellier, France: How do you explain the large differences in the degree of vanadium incorporation depending on the source of vanadium? Could this be due to different solubilities of vanadium species or different yields of the zeolite? Answer by J. Kornatowski: It is generally known that various metallic compounds behave and react in different ways during synthesis because of their different chemical nature and reactivities. We cannot correlate these experimental observations, but the yield of the zeolite on SiO 2 was always 100 %, and the syntheses were reproducible. Questions by C. Naccache, lnstitut de Recherches sur la Catalyse, CNRS, Villeurbanne, France: 1) Could you comment on the charge compensation when V 5+ is incorporated into the zeolite framework? 2) The characteristics of grafted vanadium on silica surfaces are identical to those described by you in your lecture. Would your results or their interpretation have been different if you consider that the material you studied is vanadium grafted on silica? Answers by J. Kornatowski: 1) The charges are perfectly compensated in the cases B' and C' of our scheme (Figure 4 in A028) which provide incorporation of vanadium as VO 3+. In the cases B" (primarily square pyramidal) and C" (octahedral), electroneutrality is given as well due to the presence of non-acidic OH groups. A lack of acidity of the KVS-5 samples has been found by several methods. 2) The spectroscopic characteristics of the vanadium species in our vanadosilicates are to some extent similar to those of vanadium grafted on silica. However, we see no reasons why large differences would be expected. The spectroscopic methods applied here furnish primarily information about the very local effects nearest to vanadium. Moreover, even in the case of vanadium grafted onto silica, vanadium coordinations similar to those in vanadosilicate molecular sieves can be present. The main differences observed are: a) A high stability of vanadium ions residing in our vanadosilicates and b) the reversibility of the redox reaction between V 4+ and VS+.
Comment by M.S. Rigutto, Delft University of Technology, Delft, The Netherlands: To me, structure B" in Figure 4 of your paper seems very unlikely. It consists of a symmetrical V 5+ tetrahedron with a net positive charge and a free hydroxide group. Do you really propose such species or is this a drawing error? Your 51V NMR spectrum for V 5+ does not indicate C3v symmetry and is therefore not consistent with B'. I think the species is partially hydrolyzed. We found that one should measure thoroughly dehydrated samples. Answer by J. Kornatowski: The drawing of the B" structure might indeed be somewhat misleading, please note the pertinent text of the paper. What we wanted to express somehow is a difference between this "either/or" possibility and the structures B' and/or A. The structure should be primarily looked upon as the square pyramidal one though, probably,
325 with one bond weakened. Quite similar 51V NMR spectra have been reported recently by Tuel and Ben Taarit (Zeolites 14, 1994, 18) for vanadium silicate with the ZSM-48 structure. They interpreted their spectra in terms of a tetrahedral coordination of vanadium. We do not think that the vanadium species are partially hydrolyzed. This would be inconsistent with the high stability of vanadium in our samples and with the reversibility of the redox reaction between V 4+ and V 5+. Similarly, the reversibility of the hydration/dehydration cycle seems to support our model.
Comment by J.C. Vedrine, Institut de Recherches sur la Catalyse, CNRS, Villeurbanne, France: Can you tell me whether an ESR spectrum exists as well for the coloured sample. If not, the reversibility of the redox reaction you propose leads me to think that the vanadium ion is grafted onto the silicate matrix in a defect type structure rather than truly incorporated into the framework on T positions where it should be stable. Moreover, the axial symmetry in ESR indicates the presence of VO 2+ species rather than of V 4+ (orthorhombic symmetry). Such a defect species will not affect the adsorption capacity either. Answer by J. Kornatowski: ESR spectra do exist for all coloured samples, and they differ only in the relative intensity of signals I and II. We agree with what you pointed out in your comment, and it is stated in the paper that the V4+ ESR spectra reflect the presence of vanadyl species with axial symmetry (I, II or traces of III) which, however, differ in their parameters from those of vanadyl species introduced into the ZSM-5 structure by cation exchange. Moreover, the spectra do not reflect the presence of tetrahedrally coordinated vanadium. This is in contrast to the conclusions of Fejes et al. (Stud. Surf. Sci. Catal. 69, 1991, 173) concerning V-ZSM-5 and of Tuel and Ben Taarit (Zeolites 14, 1994, 18) who ascribed the V 4+ species in vanadosilicates to tetrahedrally coordinated V 4+ on framework positions and to exchanged V 4+ species. The incorporation of vanadyl species into the silicate framework continues to be a matter of debate. Based on the redox behavior of the vanadium species it is assumed that they are attached to the framework by strong bonds, as proposed for the first time by Rigutto and van Bekkum (Appl. Catal. 68, 1991, L 1). We do not believe that our vanadosilicates contain vanadium species embedded in random defect sites of the silicate and compare them with vanadium species present in surface layers of silicates modified by vanadium impregnation. The strong bonding of the vanadyl species to the framework must occur in defined structural sites because we observe identical spectral parameters of signals I and II in VAPO, however, with the opposite intensity ratio of the vanadyl signals I and II. The presence of vanadyl species does not exclude the occurrence of V 4+ and VS+ in other coordinations, which follows from the UV-VIS spectra. Moreover, it should be mentioned that the ESR spectra in most cases do not reflect all coordinations of vanadium. You are right in that vanadium species in defect sites would not affect the
326 adsorption capacity. We observed a clear dependence of the adsorption capacity for water on the vanadium content.
Questions by B.M. Weckhuysen, Catholic University ofLeuven, Heverlee, Belgium: 1) Did you try to quantify your ESR signals after simulation? Such an approach is, in my opinion, more valid than your rough estimate of intensities. 2) Do you really believe that there is a third ESR signal? It must be very weak, if it is present at all. 3) How do the two intense ESR signals differ from those in VAPO-5 and vanadium silicalite? 4) How can you relate the tetrahedral V 4+ in the diffuse reflectance UV-VIS spectrum (band at ca. 600 nm) with an ESR signal of V 4+ with axial symmetry? Are DRS and ESR not sensitive for the same V 4+ species? Answers by J. Kornatowski: 1) We did not attempt to simulate the ESR spectra, mostly because of the dependence of the A value on the magnetic field. You are right in that such an approach is more valid than an estimate of intensities. For this reason and because spinspin interactions can occur, we did not draw quantitative conclusions. 2) We are satisfied of the presence of the third vanadium signal even though it is weak. The signal was found in the spectra of all vanadosilicates. 3) As already mentioned in my reply to J.C. Vedrine, we observed the signals I and II in VAPO materials as well, but their intensities were reversed. This also points to a defined rather than a random siting of vanadium. 4) The tetrahedral coordination of V 4+ as indicated by DRS and the axial symmetry of the vanadyl species suggested by the ESR signals are discussed in more detail in our paper. Due to the low intensity of the DSR spectra for samples with a low vanadium content and the occurrence of strong overlap and spin-spin interactions in the ESR spectra, it was difficult to arrive at a complete agreement between both techniques.
A029
Synthesis and Characterization of Highly Ordered Mesoporous Material; FSM-16 from a Layered Polysilicate by S. Inagaki, Y. Fukushima and K. Kuroda, Toyota Central Research &
Development Laboratories, Inc., Aichi, Japan; Waseda University, Tokyo, Japan
Questions by B.F. Chmelka, University of California, Santa Barbara, California, USA: 1) What was the size of the kanemite particles you used as starting material for the transformation of the layered into the hexagonal material? 2) Do the time scales you measure for the transformation produce reasonable values for the diffusivity of the charged surfactant species into the pore spaces? Answers by S. Inagaki: 1) We used kanemite particles with 1 to 3 ~m in diameter as starting material, and this was measured by scanning electron microscopy. 2) Yes. The
327 transformation was accomplished in 3 to 6 hours at a pH above 11.5 and 70 ~ The high pH of the dispersed kanemite solution will loosen the interlayer interaction and accelerate the cation exchange of surfactants.
Questions by R. Schmidt, SINTEF, Oslo, Norway: 1) What is the reason for the occurrence of the high pressure hysteresis observed in the adsorption/desorption isotherm of sample D? 2) How can you rule out that kanemite is just another silicon source for the formation of an MCM-41 material? Answers by S. Inagaki: 1) The high pressure hysteresis is attributable to macropores of uniform size between the particles. 2) Our preparation conditions distinctly differ from those for an MCM-41 material: the reaction time is shorter (ca. 6 h), the concentration of the surfactants is lower (ca. 3.2 wt.-%), and the reaction temperature is 70 ~ Moreover, the fact that the morphology of the original kanemite particles is preserved for the mesoporous material, supports our conclusion that the solid formed is different from MCM-41. Question by J. Wu, W.R. Grace & Co., Columbia, Maryland, USA: Could you please comment on the hydrothermal stability of your material? Answer by S. Inagaki: The mesoporous silica withstood temperatures up to 800 ~ in an atmosphere containing 10 % steam, but upon incorporation of aluminum the hydrothermal stability was lower.
POOl
Zeolite Synthesis Using Catalytic Amounts of Template: Structure Blocking Effects and Stoichiometric Syntheses by J.L. Casei, ICI Katalco, Billingham, UK
Question by E.N. Coker, Fritz Haber Institute of the Max Planck Society, Berlin, Germany: You speculate that hexamethoniumdibromide (HexBr2) may be binding to the surface of growing MFI crystals and inhibit further growth. Have you tried adding HexBr 2 to a mixture which initially contained no HexBr 2 (i.e., would form MFI) at points during the synthesis where MFI crystals of known size are known (from independent experiments) to be present, and then continuing the synthesis to reach a final product. The results should give insight into whether HexBr2 inhibits the growth of MFI, or has some other effect to block MFI formation (e.g., to prevent nucleation of MFI). Answer by J.L. Casei: Your suggestion is an interesting one, and one which, although I have considered, has not been carried out. I can further speculate that if HexBr 2 was added soon after gel make up or reaction initiation, it would block MFI. If it was added at later
328 stages (in a series of systematic experiments) it may not only shed light on the mechanism but reveal when nucleation of MFI occurs.
P020
Synthesis and MAS NMR Analysis of Highly Stable Pillared Clays by J. Espinosa, S. G6mez and G.A. Fuentes, University A. MetropolitanaIztapalapa, Mexico, D.F., Mexico
Questions by I. Kiricsi, J6zsefAttila University, Szeged, Hungary: 1) I presume that in the All2Ga type Keggin ion the gallium is located on tetrahedral positions. How did you evidence this? 2) Has the presence of gallium any influence on the acidity of Gal3, AI12Ga PILC's? Answers by G.A. Fuentes: 1) We performed liquid phase Ga NMR of the AI12Ga Keggin ion in solution and found Ga on tetrahedral positions, in agreement with the work of Prof. Kydd and his group in Alberta. 2) We are presently analyzing the results concerning acidity variations caused by Ga in Gal3 and AI12Ga based PILC's.
C020
Oriented Coatings of Silicalite-1 for Gas Sensor Applications by J.H. Koegler, H.W. Zandbergen, J.L.N. Harteveld, M.S. Nieuwenhuizen, J.C. Jansen and H. van Bekkum, Delft University of Technology, Delft, The
Netherlands; Prins Maurits Laboratory, TNO, Rijswijk, The Netherlands Question by J. Caro, Institute of Applied Chemistry, Berlin, Germany: How did you overcome the problem of the mismatch in the thermal expansion coefficient between the silicon wafer and the silicalite film? Did you use an equilibrating interfacial layer in between? Answer by J.H. Koegler: Actually, yes. There is a natural oxide layer on the silicon wafer. Thus the zeolite lattice is connected in a fragmentary way to the oxide layer which, in turn, is firmly connected to the silicon wafer.
Question by P.K. Dutta, Ohio State University, Columbus, Ohio, USA: What is the mechanism of growth of the layer? How is this intermediate gel phase retained on the silicon surface; through chemical bonding or physisorption? Answer by J.H. Koegler: The mechanism of growth of the layer is based on the formation of a thin gel film on the support containing only SiO2. At the interface of the liquid, which
329 contains TPA +, and the gel surface, nucleation and crystallization of MFI start. The crystals then grow into the gel film to the support.
Question by H. Lechert, University of Hamburg, Hamburg, Germany: Is it in principle possible to measure the partial pressure of small molecules other than CO 2 with your method as well? Answer by J.H. Koegler: Yes.
Question by D.H. Olson, Mobil Research and Development Corp., Princeton, New Jersey, USA: Is the sensitivity to water due to small amounts of aluminum or is the effect inherent in the water/carbon dioxide co-adsorption?
Answer by J.H. Koegler: I don't believe that aluminum is present in the crystals, however, we didn't perform any measurements to check this. The silicon source was very pure (TEOS from Aldrich), and absolutely no aluminum from the transducers was dissolved. Water coadsorption is probably due to the presence of lattice defects. By calibration to the amount of humidity, the CO 2 signal can still be evaluated quantitatively.
Question by F. Schiith, University of Mainz, Mainz, Germany: The films were grown on quartz and silicon which have Si-OH surface groups to which the zeolite can attach. These substrates, however, are dissolved by the same solvents as zeolites. Is it possible to grow zeolites on other substrates which can be dissolved to obtain a free membrane?
Answer by J.H. Koegler: In principle, it is indeed possible to use a substrate that can be dissolved afterwards. However, the mechanical strength of such a sub-micron film may not be very high. Question by E.T.C. Vogt, Akzo Nobel Chemicals B. V., Amsterdam, The Netherlands: In the side view of the layer grown on the silicon substrate, there appears to be a different material, or a gap between the substrate and the zeolite layer. Can you comment on the nature of this layer?
Answer by J.H. Koegler: Indeed, a gap can be observed between the silicalite film and the silicon support. This was due to the relatively harsh preparation of the TEM sample. Before this treatment, the film was attached to the support. Furthermore, this was an uncalcined film. After calcination the film was attached more firmly to the support and did not come off even after preparation of the TEM sample.
330 C021
Synthesis and Characterization of a Novel Microporous BoronAluminum C h l o r i d e w i t h a Cationic Framework by J. Yu, K. Tu and R. Xu, Jilin University, Changchun, People's Republic of
China
Question by F. Di Renzo, Ecole Nationale Sup~rieure de Chimie de Montpellier, CNRS, Montpellier, France: Which kind of reversibility did you observe in the sorption isotherms? Answer by R. Xu: Reversibility of type I is observed in the sorption isotherms.
Question by R. Roque Malherbe, Instituto de Tecnologia Quimica, CSIC-UPV, Valencia, Spain: Do you know something about the charge compensation mechanism? Answer by R. Xu: Chemical analysis gives the empirical formula BAI2(OH)6.4OI.ICI0. 4 for this microporous boron-aluminum chloride in which part of the CI" can be exchanged by Br'. So, there are anions in this compound. The charge and structure of the cationic framework remain to be elucidated in further structural studies, e.g., by powder XRD structure analysis. Questions by Y.S. Uh, Korea Institute for Science and Technology, Seoul, Korea: 1) Do you think that your crystals are built from a 3-dimensional framework or by a 2-dimensional layered structure? 2) In ease you believe you are dealing with a 3-dimensional framework, what is the evidence? 3) Did you cheek the d-spacing after ion exchange with anions of different size? Answers by R. Xu: We have studied the ion exchange with anions of different size, and as expected, no change in the d-spacing occurred. The adsorption isotherms for H20 and N 2 are of type I, as with NaX, A1PO 4-17 or siliealite, from which we conclude that the material possesses a 3-dimensional framework. Question by J.C. Vedrine, Institut de Recherches sur la Catalyse, CNRS, Villeurbanne, France: Aluminoborates may be interesting catalysts. Did you study catalytic activities of your molecular sieve after calcination? Has your sample acidic properties and if so, where does the Bronsted acidity come from (maybe from hydrated Lewis sites)? Answer by R. Xu: We have investigated the catalytic properties of this boron-aluminum chloride. The results of a catalytic study with boron chlorides were published by J. Yu and R. Xu in J. Materials Chemistry 3, 1993, 77-82.
331
C022
Use of Diels-Alder Derived Templates with Multidimensional Pore Systems
to Prepare
Zeolites
by Y. Nakagawa, Chevron Research and Technology Co., Richmond, California,
USA Question by J.L. Casei, ICI Katalco, Billingham, United Kingdom: My question i s - if you had two samples, one of NU-87 and one of SSZ-37 both of which had been calcined to remove the template- how would you distinguish the materials? Answer by Y. Nakagawa: The X-ray diffraction patterns of the two materials do differ slightly. We have obtained good quality synchrotron data on our SSZ-37 material and have tried to index it to the NU-87 space group (monoclinic: P21/c ). However, we were not getting good agreement. Indexing to the orthorhombic space group (Fmmm) results in better agreement, but there are still inconsistencies. R.C. Medrud at CRTC is continuing to work on indexing our SSZ-37 material. Questions by C.G. Coe, Air Products and Chemicals, lnc., Allentown, Pennsylvania, USA: Did you observe any distortion in the chabazite produced when you used template D in the aluminum-rich synthesis? Do the unit cell parameters change compared to chabazites made using inorganic cations? Answer by Y. Nakagawa: We did not do any further analysis of our chabazite products made from the Diels-Alder derived templates.
Questions by E.N. Coker, Fritz Haber Institute of the Max Plan& Society, Berlin, Germany: 1) Does the template in SSZ-37 fill the total pore volume? 2) Considering the Si/Al-ratios of NU-87 and SSZ-37 which you quoted, some of the template in SSZ-37 must be present as cation/anion pairs, to preserve electroneutrality. Have you studied the effects of altering the counter-anion? Considering the relatively close packing of the template which you showed, the size of the anion may be important. Answers by Y. Nakagawa: 1) Yes, the template in SSZ-37 appears to fill the total pore volume. 2) We worked primarily with the hydroxide salts of our organic templates in order to keep the total alkali (K +) concentration low. We believe that, in the as-synthesized SSZ-37, the positively charged template is paired with a defect Si-O- site in the framework and not with its original counter-ion. Questions by R. Kumar, National Chemical Laboratory, Pune, India: 1) What makes you so sure about the possibility of synthesizing zeolites with multidimensional channel systems in the SSZ series (expect, perhaps, SSZ-33)? 2) Changing the side chain, e.g., from methonium to ethonium, results in the large-pore material NCL-1 which seems to be quite
332 similar to SSZ-31. What is your view on the influence of the gel composition, especially the Si/Al-ratio, vis-a-vis the shape and size of the template? Answer by Y. Nakagawa: We attempted to show that the gel composition is a very important factor to consider in zeolite synthesis reactions. Unfortunately, we are not yet at the stage where we can predict in what manner the gel composition will affect the crystallization pathway.
Questions by T.D. Uematsu, Chiba University, Chiba, Japan: I am very much interested in the complexation of silica blocks and the templates from the viewpoint of host/guest chemistry: 1) If you vary the ratio of the template (guest) and SiO 2 (host), to what extent can you expect to change the pore size (more than 10-membered tings)? 2) Were the stabilization energies you gave corresponding to the model of 10 91 host/guest complexes? Answers by Y. Nakagawa: 1) We believe that the pore size of molecular sieves prepared using organic cations as templates is very dependent on the size of the template. We showed that once the organic cation is too large to fit in the cavity of nonasil, then large-pore zeolites are made. We have not observed any products with unidimensional 10-membered ring pores. 2) We presented stabilization energies encompassing a filling of the 12membered ring channels by either one or two template molecules. We obtained greater stabilization when two template molecules filled the 12-membered ring channel.
333
II.
PL02
Structure and Characterization
Advances in Powder Structure Analysis
Diffraction
Methods
for
Zeolite
by L.B. McCusker, Swiss Federal Institute of Technology Zurich, Zurich,
Switzerland
Questions by D.B. Akolekar, The University of New South Wales, Sydney, Australia: 1) What are the factors that affect the distribution of the cations (single, two or three types) in faujasite type materials? 2) Can you suggest good sample preparation methods for the collection of XRD data? Answers by L.B. McCusker: As I understand your question (from a private discussion after this session), you are asking how the powder diffraction pattern is affected by the cation distribution. Since the intensities of the reflections depend upon the positions and types of cations in the structure, the primary effect of different cation distributions is on the peak intensities - especially those at low angles. The degree of intensity change will depend upon the atomic number(s) of the cation(s) involved, since the scattering power of an atom depends upon the number of electrons it has. This also means that cations with similar numbers of electrons are difficult to distinguish from one another. In the specific case of faujasite, with its very high symmetry, not all symmetry equivalent positions are occupied and cation site occupancy factors can be very low. This can severely hinder the location of the cation. In general, however, difference Fourier methods are very good for locating cations, since their positions are usually well-defined because of their strong interaction with framework oxygens. 2) It is difficult to give a universal recipe for sample preparation. This will always depend on the material and the purpose of the experiment. If preferred orientation is likely (i.e., the crystallites have needle or platelet morphology), a capillary is probably better than a flat plate sample holder. If the sample is sensitive to the atmosphere, it is easily protected in a sealed capillary. If the sample is to be treated in-situ, it is more accessible in a fiat plate. Ideally, the crystallites should be between 1 and 10 ~tm. If they are smaller, line broadening due to particle size is likely. If they are larger, a random orientation of crystallites becomes difficult to achieve.
334
Question by D. Barthomeuf, Universit6 Pierre et Marie Curie, CNRS, Paris, France: For an understanding of the correlations between acidity, basicity, catalysis and the structure of zeolites it is important to know precisely the local TOT angles for specific Si-O-A1 sites. Theoretical calculations in the late 70's showed that the charge on the oxygen depends on the TOT angle. Crystallography gives average values of these angles. Do you foresee any approach which would give an estimate of the angle at a specific oxygen location in the structure and in dependence of the nature of the T atom (Si or AI)? Answer by L.B. McCusker: Powder diffraction is a bulk technique and only yields information about the average periodic structure. This means, of course, that local structure such as an Si-O-AI angle in a specific unit cell at a specific oxygen (i.e., one that does not have long range order) cannot be seen. I am afraid that the nature of the experiment will continue to obscure this information. Question by J.M. Bennett, Mobil Research and Development Corp., Princeton, New Jersey, USA: Is there likely to be any help in the future, that will allow us to solve the space group problem? Or will we still have to determine the topology and then determine the space group? Answer by L.B. McCusker: It will probably remain easier to take advantage of pseudosymmetry to solve framework structures. That is, the structure determination will continue to be done in the highest possible space group simply to reduce the size of the problem. Refinement of the structure must then be done in a lower, more correct, space group. Unfortunately, I do not anticipate any developments in powder diffraction techniques that will make the true space group determination easier. However, MAS NMR methods can yield very useful symmetry information that might help in the solution of this problem.
Question and Comment by A.K. Cheetham, University of California, Santa Barbara, California, USA: 1) There is a further technique for pattern decomposition to which you did not refer: maximum entropy/likelihood. Do you think that this might be effective for systems with severe overlap for which FIPS is inadequate (e.g., cloverite)? 2) I would like to point out that neutron diffraction gives much better sensitivity to Si, AI or P, A1 ordering due to better contrast and better accuracy on T-O distances. Answer by L.B. McCusker: ! should have mentioned maximum entropy as an alternative approach to structure determination. In that case, the decomposition of overlapping reflections is integrated into the structure determination process itself, and this would certainly be a possible approach to FIPS-intractable systems such as cloverite. However, as far as I know, sigrna-2, for which the powder data is of almost single-crystal quality, is the only zeolite-like structure that has been solved using this method, and that was only as a test example. Cloverite is a complex structure involving 10 T-atoms, and I imagine the computer
335 time needed to solve such a problem would be considerable. As our computers become more and more powerful though, such algorithms become more and more feasible.
Question by J.P. Coulomb, C.R.M.C., CNRS, Marseille, France: During the adsorption of simple molecules in zeolites, the diffraction spectrum of the base zeolite presents strong modifications of the diffraction peak intensities in the regimes of low and medium loadings, where the sorbed phase is disordered. Do you think that the Rietveld method can explain these strong modifications of the intensities? Answer by L.B. McCusker: If a diffraction pattern changes significantly after a sorption experiment, Rietveld refinement combined with difference Fourier analysis should yield information about the location of the sorbed molecules, since intensity changes are a reflection of structural changes. The structural detail that can be extracted in this way will vary from case to case.
Question by V. Kaucic, National Institute of Chemistry, University of Ljubljana, Ljubljana, Slovenia: What is the potential of the anomalous dispersion method in single crystal diffraction, especially in pinpointing small amounts of metals that exchange aluminum atoms in A1PO4 frameworks? Answer by L.B. McCusker: The single crystal case is directly analogous to the powder diffraction one, except that even more information is available, because the full 3D data can be measured. The use of anomalous scattering is, of course, limited to samples containing sufficient quantities of the anomalous scatterer. In the case of metals which may substitute for a few percent of the A1 atoms in an A1PO4 framework, this technique is not sufficiently sensitive.
Question by F. Trouw, Argonne National Laboratory, Argonne, Illinois, USA: For the case of the crown ether electron density map example, does the loss of a mirror plane yield extra reflections? Does the peak overlap problem obscure these or is the crown ether equally distributed about the mirror plane, maintaining that symmetry element? Answer by L.B. MeCusker: If the crown ether molecules were ordered in the medium and large cages (i.e., located consistently on one side or the other), the space group would change from P63/mmc to P63mc. Since both these space groups belong to the same Laue class (6/mmm), no additional reflections would be observed. However, refinement in the lower symmetry should lead to better agreement between the observed and calculated intensities if the ordering is truly present. We did try to refine such an ordered model, but found no significant improvement in the agreement factors. This probably means that although there may be local ordering, disorder is present over the longer range.
336
B001
Low-Temperature IH MAS NMR Investigations on the Nature of Acid Sites Causing Enhanced Catalytic Activity in H-Zeolites by E. Brunner, I~ Beck, M. Koch, H. Pfeifer, B. Staudte and D. Zscherpel, University of Leipzig, Leipzig, Germany
Question by D.B. Akolekar, The University of New South Wales, Sydney, Australia: How is the proton mobility affected by the presence of different cations? Answer by E. Brunner: This has not been studied systematically yet. Studying proton mobilities by 1H MAS NMR spectroscopy requires higher temperatures since the mean residence time of the protons at room temperature is long in the NMR time scale. Question by G. Engeihardt, University of Stuttgart, Stuttgart, Germany: Are there correlations between the "strongly acidic sites" and the broad signals observed in the 27AI NMR spectra of hydrothermally treated zeolite samples? Answer by E. Brunner: It is generally accepted that the relatively broad signal at ca. 30 ppm in the 27A1 NMR spectra of hydrated zeolites is caused by aluminum species of lower symmetry than the framework aluminum. However, no definite statements concerning the structure of these species can be given yet. It appears likely that the structure of the corresponding aluminum species is not uniform and depends on the pretreatment procedure. We have shown in a previous paper (E. Brunner, H. Ernst, D. Freude, T. Fr6hlich, M. Hunger and H. Pfeifer, J. Catal. 127, 1991, 34-41) that there is in fact a correlation between these aluminum species of lower symmetry and the enhancement of the catalytic activity after "mild" steaming as described in the literature (R.M. Lago, W.O. Haag, R.J. Mikovsky, D.H. Olson, S.D. Hellring, K.D. Schmitt and G.T. Kerr, Stud. Surf. Sci. Catal. 28, 1986, 677-684). The aluminum species formed after such a "mild" steaming, which gives rise to the enhanced catalytic activity, are not affected by weak acids (e.g., HCOOH). By contrast, after "severe" hydrothermal treatment, which does not bring about an enhanced catalytic activity, the aluminum species of lower symmetry can easily be transferred into species of octahedral symmetry by weak acids such as HCOOH. These octahedrally coordinated aluminum complexes then give rise to a narrow signal at 0 ppm, whereas the intensity of the broad signal at 30 ppm decreases.
Question by S. Kaliaguine, Laval University, Ste.-Foy, Quebec, Canada: My question deals with the nature of the species responsible for your 7.0 ppm band in the 1H MAS NMR spectrum of H-ZSM-5. In work we performed on XPS Nls signals of chemisorbed pyridine, we found that a significant portion of the Bronsted acid sites were of low acidity compared to the one responsible for the 3610 cm -1 IR signal. Do you have any indication that your
337 7.0 ppm species could also be a weak Bronsted acid located close to the external surface of the H-ZSM-5 crystals? Answer by E. Brunner: Our investigations indicate that the species causing the signal at 7 ppm are of the same (or nearly the same) acid strength as the species giving rise to the signal at 4.2 ppm, since they form identical complexes with CO.
Question by J.A. Lereher, University of Twente, Enschede, The Netherlands: Your interpretation implies that you are removing framework aluminum (and, hence, Bronsted acid sites). These aluminum species interact as Lewis acids with the oxygen of other bridging OH groups. Is there evidence that other cations may act in the same manner as well and enhance the Br~nsted acid strength? Answer by E. Brunner: Indeed, there is evidence for the possibility that other cations may be used to enhance the catalytic activity. For example, it has been shown (R. Carvajal, P.-J. Chu and J.H. Lunsford, J. Catal. 125, 1990, 123-131) that lanthanum may cause enhanced catalytic activity in HLaY zeolites. It should, however, be mentioned that these sites are weaker than the corresponding sites in dealuminated HY, i.e., aluminum seems to be more efficient in the generation of highly active sites.
Question by J. Sauer, Working Group Quantum Chemistry at the Humboldt University, Max Planck Society, Berlin, Germany: You have mentioned that there is a broad band in the OH region of the IR spectrum which corresponds to the NMR line at 7 ppm. Does this band also vanish upon adsorption of CO? Answer by E. Brunner: It has indeed been shown (V.L. Zholobenko, L.M. Kustov, V. Yu. Borovkov and V.B. Kazansky, Zeolites 8, 1988, 175-178) that the broad IR band at ca. 3250 cm-1 vanishes upon adsorption of probe molecules.
B002
Bronsted Acidity in US-Y Zeolites by M.A. Makarova, A. Garforth, V.L. Zholobenko, J. Dwyer, G.J. Earl
and D. Rawlence, University of Manchester, Institute of Science and Technology, Manchester, UK; Crosfield, Warrington, UK Questions by J. Datka, Jagiellonian University, Cracow, Poland." 1) How did you obtain the relationship between PAoH, the proton affinity of a hydroxyl, and A~OH, the shift in the position of hydroxyls upon CO adsorption? 2) Did you look at the fine structure of the bands of the OH groups in the original zeolite during interaction with CO? Answers by M.A. Makarova: 1) The correlation we used for the dependence of PAoli on A~OH (after CO adsorption) is taken from the literature (E.A. Paukshtis and E.N.
338 Yurchenko, Usp. Khim. 53, 1983, 426, cf. ref. [6] in paper B002). 2) The initial HY zeolite represents the first and third components in the hydroxyl region (corresponding to OH's in supercages and sodalite cages, respectively). CO interacts only with the first component (hydroxyls in the sodalite cages are not accessible).
Comment by C. Naccache, Institut de Recherches sur la Catalyse, CNRS, Villeurbanne, France: Most of the physical methods used to characterize acidity changes in zeolites deal with energetic factors. However, the experimental results on enhancement of catalytic activity seldom indicate any change in the activation energy. Instead of invoking changes in the acid strength, one could suggest that the rate limiting step of the reaction has changed. For example, an alkane could be polarized or ionized on the extra-framework aluminum, the polarized/ionized alkane being then attacked by H +. Answer by M.A. Makarova: In fact, changes in activation energy are observed as a function of conversion. At T > 400 ~ the initial cracking of hexane is protolytic at low conversion and is dominated by bimolecular hydrogen transfer at higher conversion. Protolytic cracking and bimolecular hydrogen transfer have different activation energies. Other changes in the mechanism (e.g., via radicals or radical ions) could also be reflected in the activation energies. Moreover, activation energies do change somewhat with acid strength, and since rates are exponential in E a, small changes in E a result in large changes in rates. Other factors, e.g., sorption properties, are not likely to acccount for the changes in rate, which we therefore assume to be correlated to energetic parameters.
Questions by S.I. Woo, Korea Advanced Institute of Science and Technology, Taejon, Korea: 1) The deconvolution of the OH bands must be affected by the number of bands and their half-widths. What is the justification for the very broad band width of the OH bands between 3500 and 3600 cm-l? Couldn't one assume that narrower bands are more adequate? 2) Why does the extinction coefficient of the OH band increase upon adsorbing weak bases? Answers by M.A. Makarova: 1) The widening of the OH band as a result of the perturbation is a salient feature of hydrogen bonding. It is believed that, due to the presence of the additional molecule in the complex (O-H ..... B as compared to the single O-H), the O-H vibration becomes "less homogeneous". 2) The extinction coefficient increases because the dipole moment of the bond increases after the perturbation, and the infrared absorbance depends on the dipole moment. Questions by J. Wu, W.R. Grace & Co.. Columbia, Maryland, USA: 1) Have you compared the Bronsted acidity of US-Y zeolites made by different dealumination methods, such as hydrothermal and chemical dealumination? 2) A follow-up question: Do you imply that the non-framework A1203 has a stronger Bronsted acidity?
339
Answers by M.A. Makarova: 1) No. All the samples were dealuminated hydrothermally. We leached the non-framework AI203 with acid. In this case, the intensities of the second and fourth peaks decreased (these peaks appear at 3599 cm -1 and 3525 cm -1, respectively, and the corresponding OH groups desorb ammonia at higher temperatures than the groups corresponding to the first and third peaks). 2) No.
Question by A. Zecehina, University of Turin, Turin, Italy: The method you used to obtain the difference spectra, i.e., subtracting the spectrum obtained before the interaction from the spectrum after the interaction, is only justified if the acid-base complexes are not absorbing in the OH stretching region. While this is true for CO (CO stretching at ca. 2150 to 2200 cm -1) it does not hold for NH 3 which is, in fact, absorbing in the relevant region. Did you consider this problem? Answer by M.A. Makarova: N'H4 + species start absorbing at 3450 cm -1 and proceed to lower wavenumbers. The main region for the analysis of the Bronsted hydroxyls is 3800 to 3400 cm -1. Therefore, the absorption from NH4 + can slightly affect the shape of the right edge of the fourth component, but it does not cause major problems.
B003
Acidic Properties of Metal Substituted Aluminophosphates Studied by Adsorption Calorimetry and IR Spectroscopy by J. J~inchen, M.J. Haanepen, M.P.J. Peeters, J.H.M.C. van Wolput, J.P. Wolthuizen and J.H.C. van Hooff, Eindhoven University of Technology, Eindhoven, The Netherlands
Question by G. Calzaferri, University of Bern, Bern, Switzerland: You have interpreted a band in one of your spectra as Fermi resonance. It looks to me as an Evans hole (caused by Fermi resonance) which is the resonance interaction between a broad and a narrow band. Looking at completely deuterated samples can help to support or reject the Evans hole hypothesis. Did you do these experiments? Answer by J. J~inehen: Yes, we did these experiments, and they support Fermi resonance causing an Evans hole. We have another paper on this subject at this Conference (paper P095), and more evidence in support of our interpretation is given there. Questions by C. Naecache, Institut de Recherches sur la Catalyse, CNRS, Villeurbanne, France: 1) Proton acidity of MeAPOs is generated by replacement of aluminum or/and phosphorus by the metal. Could you comment on the nature of the Bransted acid sites H I
generated? 2) Are there always AI/O/,~M~ species (Me = Si, Zn, Co)? In the ease of CoAPO,
340 the template is generally removed by 0 2 treatment at high temperature, thus oxidizing Co 2+ to Co 3+. What difference exists in the acidity of Co2+APO and Co3+APO? Answers by J. Jiinehen: 1) The Bronsted acid sites generated by isomorphous substitution (AP + by Me 2+) are weaker than those in HY zeolites. These sites resemble the medium H
acidic P-OH, because the equilibrium Me,-~-,p
H
Me ~o\p i is shit~ed to the right-hand side.
2) We did not investigate the acidic properties of the oxidized CoAPOs because they change the oxidation state very easily upon contacting them with proton donors. Secondly, we are not so sure whether the non-framework cobalt isn't oxidized exclusively.
Questions by M.M. Ramirez de Agudelo, 1NTEVEP S.A., Caracas, Venezuela: 1) Quantum chemical calculations indicate very low polarity of acetonitrile which is confirmed by the fact that its hydrolysis takes place only in the presence of very strong acids. Did you observe hydrolysis products upon adsorption on your molecular sieves? 2) How strong do you think the Bronsted sites might be? Answers by J. J~inehen: 1) No, we have not. 2) The strength of the Bronsted sites is between the ones of silanol groups and zeolite HY. Question by J.C. Vedrine, Institut de Recherches sur la Catalyse, CNRS, Villeurbanne, France: In a MeAPO substituted A1PO4 matrix you create acidity by P substitution, while no acidity is created if AlP pairs are substituted, e.g., for silicon. You have used microcalorimetry of acetonitrile adsorption and shown that acidity is indeed created. The data (strength and amount) are given in mmol/g. Wouldn't it be better to express it in molecules per unit cell so that it can be directly compared to the value of metal substituted per unit cell? Can you tell me in such units whether all metal atoms substituted phosphorus atoms or only part of them? Could you, moreover, tell me which stoichiometry of adsorption was chosen? Answer by J. Jiinchen: Our results on the CoAPOs (see also ref. 2 in the paper) lead us to conclude that the strongly adsorbed acetonitrile is coordinatively bonded to the framework metal ions. Thus, all Co 2+ ions on framework positions give a strong Lewis site (first step in the heat curve). The Bronsted acidity is weak and arises from P-OH groups (second step in the heat curve). The ratio acetonitrile/cobalt for the most strongly bonded molecules amounts to 0.9 for CoAPO-11 (0.4 Co/UC) and CoAPO-5/1 (0.25 Co/UC) and to 0.75 for CoAPO-5/2 (0.5 Co/UC). Taking into account that one acetonitrile/framework Co is strongly adsorbed and not all Co is on framework positions (the given values are AAS results), it looks more like a 1:1 ratio.
341
B004
Multinuclear N M R Studies of Acid Sites in Zeolites by H. Ernst, D. Freude, H. Pfeifer and I. Wolf, University of Leipzig,
Leipzig, Germany Question by A.K. Cheetham, University of California, Santa Barbara, California, USA: In the 1H spectra of HY samples, are you able to drfferentiate between protons attached to crystallographically inequivalent oxygen atoms (of which there are four)? Answer by D. Freude: Line (b) in our spectrum is due to hydroxyl protons on O 1 positions pointing towards the large cavity. Line (c) is explained by hydroxyl protons on 03 positions pointing to other oxygen atoms in the 6-membered ring, which causes an additional electrostatic interaction. NMR cannot give information on whether or not other positions are occupied.
Question by E.G. Derouane, Facultds Universitaires Notre-Dame de la Paix, Namur, Belgium: Your proposal that extra-framework aluminum is more symmetrical than what we believe today is highly relevant to our understanding of the interaction of such species with Bronsted sites. Do you have a model for them which would reconcile high symmetry and the need to have coordination unsaturation as they behave as Lewis acids? Answer by D. Freude: No. Without considering models for non-framework aluminum, we arrived at the conclusion that the majority (70 - 100 %) of the non-framework aluminum nuclei in mildly steamed zeolites H-ZSM-5 is in a higher symmetry compared to aluminum atoms in framework positions (- SiOHAI --).
Questions by G. Engelhardt, University of Stuttgart, Stuttgart, Germany: 1) Were the effects of selective/non-selective excitation considered in the quantification of the 27A1 NMR spectra of the samples showing A1 with strong and weak quadrupole interactions? 2) Are there indications of proton exchange between bridging hydroxyl protons and water molecules in the partly rehydrated samples? Answers by D. Freude: 1) Yes. The relative amount of the satellite transitions excited by a pulse of the duration 9 and the bandwidth of about 1/z is increasing with decreasing width of the 27A1 signal, if the spectrum cannot be excited non-selectively as in our experiments. However, for non-spinning samples, the central transition signal can be easily distinguished from a possible satellite transition signal which was not observed in our spectra. 2) If the number of adsorbed water molecules per unit cell does not exceed the number of Lewis sites (two per unit cell) where the molecules can be locked, then the water loading will not influence the mobility of hydroxyl protons. For higher loading, a line broadening of the signal of some or all bridging hydroxyls (for n < 16 or n > 16, respectively) can be observed
342 which is indicative of proton exchange between the water molecules and the bridging hydroxyl groups.
Question by J. Fraissard, Universit~ Pierre et Marie Curie, CNRS, Paris, France: You have measured the lifetime of H on oxygen (acidic OH groups). But the frequency of jumps from one oxygen O- to the nearest one should depend on the distance between the two oxygens, so it should depend on the aluminum concentration. Is this correct, and did you verify it? Answer by D. Freude: The jump frequency should indeed depend on the aluminum concentration. Unfortunately, we could not measure the jump frequency, just an upper limit was obtained. This upper limit seems to depend on the longitudinal relaxation time T 1 of aluminum atoms near the hydroxyl species under study. Question by P.J. Grobet, Catholic University ofLeuven, Heverlee, Belgium: By your echo 27A1 NMR you are able to detect A1 sites with high coupling constants (+ 10 MHz). What is the upper limit of coupling constants you can observe? Answer by I. Wolff With the technique employed here (B 0 = 11.7 T), the upper limit for the detectable quadrupole broadening is Cqcc ~ 25 MHz. Questions by J.B. Nagy, Facult~s Universitaires Notre-Dame de la Paix, Namur, Belgium: 1) In the hydrated form, one is distinguishing between framework tetrahedral, framework distorted tetrahedral, pentacoordinated, and extraframework octahedral aluminum species. Could you observe all these species in the dehydrated form as well? 2) Can you perform NMR measurements at temperatures of catalytic reactions in order to detect the nature of possible Lewis acid sites? Answers by D. Freude: 1) No. Our measurements were done on the dehydrated (activated) zeolite which is different from the hydrated form. Unfortunately, the resolution of the signal of the dehydrated zeolite, which was hitherto considered "NMR invisible", is very low compared to the signal obtained on hydrated samples. 2) Yes. We have another contribution at this Conference (paper No. P139), and it is shown there that we are able to measure reaction rates at high temperatures and their dependence on both Bronsted and Lewis acid sites.
343
B010
Tracing the Production of Spinel Based Ceramics from the Heat Induced Transformations of Zinc and Cobalt Exchanged Zeolite A Using Combined XRD/XAFS Techniques by L.M. Colyer, G.N. Greaves, A.J. Dent, S.W. Carr, K.K. Fox and University of Keele, Keele, UK; The SERC Daresbury Laboratory, Daresbury, UK; Unilever Research, Port Sunlight Laboratory, Bebbington, UK R.H. Jones,
Question by U. ttatje, University of Hamburg, Hamburg, Germany: Did you take phase corrections into account? Concerning the zinc data at the Zn K-edge: as the data are not phase corrected, the second shell looks like Zn-Zn interaction, rather than Zn-Si/Zn-AI interactions because of the distance.
Answer by L.M. Colyer: The experiment traced the change from zeolite ZnNaA to gahnite (ZnAI204). A change in Zn 2+ coordination from octahedral to tetrahedral was expected and observed from the analysis of the first Zn-O interaction, shown in the Fourier transforms of XAFS collected from the Zn K-edge. Because of this and the greater difficulty in obtaining accurate information from second and subsequent shells, the EXAFS has not yet been analyzed beyond the first shell. Given the high loading of zinc in the sample, the formation of some kind of zinc cluster, giving rise to the interaction suggested, is a possibility which will now be investigated. I thank Dr. Hatje for bringing this to my attention.
Questions by S.-E. Park, Korea Research Institute of Chemical Technology, Taejon, Korea: 1) Was the ion exchange done via a solid-state reaction and is it affected by the nature of the anion? 2) Did you try to combine heat treatment for ceramic formation with solid-state ion exchange?
Answers by L.M. Colyer: 1) The salt for ion exchange was chosen to be the least acidic in order to minimize damage to the zeolite framework. I am not aware of any effects of anion species remaining in the zeolite. 2) We have not attempted a combined solid-state ion exchange and heat treatment. However, G. Sankar et al. have studied the Zn 2+ promoted transformation of zeolite beta to cordierite, on station 9.3 SRS of Daresbury Laboratory starting with a solid-state mix of zeolite Mg-beta and ZnO. This work follows the diffusion of Zn 2+ into the zeolite and its subsequent collapse. Their work was published in d. Phys.
Chem. in 1993.
Questions by E.S. Shpiro, N.D. Zelinsky Institute of Organic Chemistry, Moscow, Russia: 1) In your Fourier transforms of the Zn K-edge XAFS of the parent zeolite ZnA, more than one ZnO peak is observable. It looks as if zinc species were present in an aggregated state
344 rather than as isolated cations. For example, the second peak could be ascribed to a Zn(O)Zn distance similar to the one in ZnO. Could you comment on this? 2) Can you give any example for your systems where the combination of QEXAFS/XRD was really efficient for following the reaction dynamics, for detecting transient species having short order without long order or the like?
Answers by L.M. Colyer: 1) See answer to question by U. Hatje. 2) Solid-state reactions often require more than one probing technique to reveal the mechanisms involved. The advantages of the combined XRD/XAFS technique are obvious in that the same sample is used under exactly the same conditions for both types of measurement. These two techniques are particularly useful where a reaction passes through both crystalline and amorphous phases. In the case of the heat treatment of zeolite ZnNaA, the Zn 2§ coordination falls from 6 to 4 upon zeolite collapse and remains at this value as re-crystallization occurs. In this case, no short-lived intermediate is detected by XAFS. The data from the heat treatment of zeolite CoNaA has not yet been fully analyzed, but the indications are that, in the amorphous phase, the coordination of cobalt falls to a value of less than four indicating the presence of cobalt in a glass-like environment, before it increases again upon spinel crystallization.
BOll
Synthesis and Characterization by X-Ray Diffraction and Solid-State N M R of ULM-5, a N e w Fluorinated Gallophosphate Ga16(PO4)14(HPO4)2(OH)2F7 9 4 H3N(CH2)6NH3 9 6 H 2 0 with 16-Membered Rings by T. Loiseau, D. Riou, F. Taulelle and G. F6rey, Universitd du Maine, CNRS, Le Mans, France; Institut de Chimie Le Bel, Strasbourg, France
Questions by
P.-S.E. Dai, Texaco Chemical Co., Port Arthur, Texas, USA: 1) Could you please define the pore size of ULM-5? 2) Do you have information about the
location of (HPO4) in ULM-5?
Answers by T. Loiseau: 1) The pore size is 1.22 x 0.83 nm. 2) The location of the (HPO4) group has been identified by valence bond calculations. In this PO 4 tetrahedron, one of the oxygen atoms is terminal and linked to another group.
Question by H. Kessler, Ecole National Supdrieure de Chemie de Mulhouse, CNRS, Mulhouse, France: Have you been able to determine adsorption properties for ULM-5? Answer by T. Loiseau: We are determining the adsorption properties of ULM-5 at this time.
345
B012
Framework Fe Sites in Sodalite: A Model for F e T Sites in Zeolites by D. Goldfarb, M. Bernardo, K.G. Strohmaier, D.E.W. Vaughan and H. Thomann, Exxon Research and Engineering Co., Annandale, New Jersey, USA
Question by G. Engelhardt, University of Stuttgart, Stuttgart, Germany: Is it possible to derive quantitative information from the ENDOR spectra? Answer by D. Goldfarb: In principle yes, on a relative basis and making sure that all experimental conditions are the same. One also has to consider relaxation time differences and hyperfine enhancement factors. Question by L. Guczi, Institute of Isotopes of the Hungarian Academy of Sciences, Budapest, Hungary: What is the advantage of your ENDOR method compared to M6ssbauer spectroscopy? It seems that M6ssbauer can give you all information you received from ENDOR, but perhaps with a higher sensitivity. Answer by D. Goldfarb: The advantages of ENDOR are: (i) Iron sites with different EPR signals can be measured separately. (ii) Orientation selective experiments can be performed. (iii) One can use different pulse sequences and experimental conditions to help assign and resolve peaks. (iv) M6ssbauer spectrometers are rather "rare species" and not readily available as they are highly specific. (v) Pulse ESR/ENDOR has a larger scope as it can be applied to any paramagnetic system. The disadvantages of ENDOR are: (i) When the zero field splitting is very large, ENDOR lines are broadened beyond detection. (ii) It cannot detect Fe 2+.
Question by V. Kaucic, National lnstiute of Chemistry, University of Ljubljana, Ljubljana, Slovenia: Why is the ESR spectrum of 57FeZSM-5 broadened and the 57FeSOD spectrum very sharp? Is it because of more than one 57Fe framework position or are there 57Fe positions in the cavities? Answer by D. Goldfarb: I think that the major source of broadening is the larger zero field splitting due to somewhat more distorted tetrahedra along with the different T sites.
Question by L. Kevan, University of Houston, Houston, Texas, USA: If you use both ESR and pulsed ENDOR to study Fe 3+ in other zeolites, do you think you can then use ESR only to "fingerprint" different iron sites? Answer by D. Goldfarb: I do not think so, because you may have different Fe 3+ contributing at g = 2, and you would need another method to make sure it is indeed one species.
346
Question by B. Wichterlovfi, J. Heyrovslc~ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Prague, Czech Republic: The presence of iron on framework forming sites is also evidenced by the trivalent iron stability with respect to reduction even in hydrogen and no changes in coordination in a hydration/dehydration procedure. Did you perform such types of investigations as well, and if so, what was the stability of the coordination of iron on the framework sites? Answer by D.E.W. Vaughan: The responses of framework Fe3+ to cycles of hydration and dehydration are highly structure dependent. For SOD and LTL, the framework Fe 3+ is not changed. In contrast, for FAU, Fe 3+ is readily hydroxylated and can easily be removed from the framework by such treatments.
B013
Microporous Study
Titanosilicate
ETS-10:
Electron
Microscopy
by T. Ohsuna, O. Terasaki, D. Watanabe, M.W. Anderson and S. Lidin, lwaki Meisei University, lwaki, Japan; Tohoku University, Sendai, Japan; University of Manchester, Institute of Science and Technology, Manchester, UK; University of Lund, Lund, Sweden Question by A.K. Cheetham, University of California, Santa Barbara, California, USA: ETS-10 contains a large number of sodium and potassium cations. Do you have any information about the location of these cations and have you worried about their influence on the lattice image simulations? Answer by O. Terasaki: ETS-10 does contain two monovalent cations for every titanium atom. Owing to the disorder in ETS-10, finding the location of the cation sites is very difficult. This is comparable to zeolite beta where cation sites cannot be located. Consequently, we do not know, to-date, the cation location, and all diffraction and image calculations were done without cations. We are confident that we can determine the cation location by a combination of energy minimization/EXAFS/diffraction/HREM image (from thin specimen) coupled with cation exchange. Such work is in progress.
Question by M. Hunger, University of Stuttgart, Stuttgart, Germany: Is it possible to study the kind of material located at the outer surface by HREM? Answer by O. Terasaki: Yes, it is possible to observe surface precipitates from HREM images using the "profile method". Furthermore, it is possible to determine the nature of terminating groups at the crystal surface (V. Alfredsson, T. Ohsuna, O. Terasaki and J.-O. Bovin, Angew. Chem. lntern. Ed. Engl. 32, 1993, 1210-1213).
347
Question by D.H. Olson, Mobil Research and Development Corp., Princeton, New Jersey, USA: Did you observe any crystals which were either pure polymorph A or pure polymorph B? Answer by O. Terasaki: From X-ray powder diffraction data, there is no evidence for either pure polymorph A or pure polymorph B. It is possible only by HREM to determine the stacking sequence in the system. For the identification of pure polymorphs, it is necessary to observe images along two orthogonal axes (x and y) which is not readily possible. Therefore, we are unable to evaluate this point exactly (cf. our paper: M.W. Anderson et al., Philos. Mag., in press).
B014
Exploring Cation Siting in Zeolites by Solid-State N M R of Quadrupolar Nuclei by G. Engelhardt, M. Hunger, H. Koller and J. Weitkamp, University of Stuttgart, Stuttgart, Germany
Question by S.W. Carr, Unilever Research, Port Sunlight Laboratory, Bebbington, UK: Have the 23Na spectra for EMT been taken with the 18-crown-6-ether present? Have you thought of doing these experiments? Answer by G. Engelhardt: In addition to the calcined and dehydrated EMT, we have also measured the 23Na MAS NMR spectra of the as-synthesized NaEMT sample before dehydration, but no particular experiments were carried out to study the effect of the crown ether on the sodium distribution.
Question by E.N. Coker, Fritz Haber Institute of the Max Planck Society, Berlin, Germany: Since this technique is dependent upon the presence of sufficient sodium for NMR detection, can you comment on the maximum Si/A1 ratio of materials which can be studied? Answer by G. Engelhardt: The detection limit depends heavily on the strength of the quadrupole interaction of the sodium cations. For narrow lines with no or only small interaction, less than one Na § per unit cell should be clearly detectable in the spectra.
Question by H. F~irster, University of Hamburg, Hamburg, Germany: Congratulations for having developed this method! It should be a valuable tool for the study of solid-state ion exchange in competition with far-infrared spectroscopy. Has there already been an application for this? Answer by G. Engelhardt: Yes, we studied La 3§ solid-state ion exchange in some detail, and the results are presented at this Conference in another paper (cf. paper No. P066).
348
Question by D. Goldfarb, Weizmann Institute of Science, Rehovot, lsrael: The sites II and I' you have shown are axially symmetrical, so how do you explain the significant asymmetry parameter you get? Answer by G. Engelhardt: The asymmetry parameters for sites II and r are in the range of ca. 0.1 to 0.2, i.e., not very large, and may possibly arise from small dislocations of the cations from the ideal position above the centers of the 6-membered ring windows. I should also mention that the asymmetry parameters cannot be determined with high accuracy from the simulation of the MAS NMR spectra, but have been found consistently to deviate from zero for the SII and SI' sodium positions in dehydrated zeolite NaY. Comment by W.J. Mortier, Exxon Chemical International, Machelen, Belgium: Regarding the predicted/measured sodium distribution in FAU-type zeolites with different cation loadings (Na/H) and Si/A1 ratios, a comprehensive statistical thermodynamical method has been developed by Van Dun and Lievens, and this can be perfectly used to calibrate your technique (see J.J. Van Dun, K. Dhaeze and W.J. Mortier, J.. Phys. Chem. 92, 1988, 67476754; J.L. Lievens, W.J. Mortier and K.-J. Chao; or. Phys. Chem. Solids 53, 1992, 11631169; J.L. Lievens and W.J. Mortier, Proc. 9th lntern. Zeolite Conf., Vol. 1, 1993,373-380). Answer by G. Engelhardt: Thank you for this comment. In fact, we have already used some of the results of these papers for comparing site occupations from NMR with the values predicted by thermodynamics. Question by J.B. Nagy, Facultds Universitaires Notre-Dame de la Paix, Namur, Belgium: When you adsorb organic molecules into the supercage of zeolite Y, you are favoring the exchange of Na + ions between different sites. So the decrease in the quadrupole coupling constant could be due, at least partly, to exchange narrowing of the NMR lines. Did you study the temperature effect on the NMR spectra in order to determine the exchange rate? Answer by G. Engelhardt: Yes, we just started temperature dependent 23Na NMR measurements, but detailed results cannot be presented yet. Comment by G. Vorbeck, Eindhoven University of Technology, Eindhoven, The Netherlands." I would like to make a comment on our work you were referring to in your presentation. In order to be able to assign the four signals needed for a satisfactory simulation of the experimental DOR NMR spectra of dehydrated NaY, we made an additional experiment: we adsorbed Mo(CO)6 on NaY, dried before at 670 K, under conditions which allowed a full saturation of the zeolite with two molecules of Mo(CO)6 per supercage [Mo(CO)6 cannot enter the smaller cages of this zeolite]. For such a sample we found that two out of four signals were shifted, and this was accompanied by a decrease and equalization of the corresponding quadrupole coupling constants. On the other hand, the
349 remaining two signals were not influenced. This provided additional support for assigning the first two signals to SII and SIII positions located in the supercages. The other two signals were then assigned to sodium in the inaccessible positions inside the sodalite cages and hexagonal prisms. Answer by G. Engelhardt: As I mentioned already in my lecture, the main arguments for the different line assignment given by us are the agreement of the calculated quadrupole coupling constants with the experimental ones and the fact that position III is not occupied in dehydrated NaY zeolites as shown by a number of detailed XRD studies in the literature. However, it should be considered that cation migration may occur upon your Mo(CO)6 adsorption experiment, and the spectra cannot directly be compared with those of the nonloaded samples. Reply by G. Vorbeek: Yes, of course, we know that cation migration can take place. We even found a migration of some sodium cations from the supercages into the sodalite cages upon adsorption of Mo(CO)6. This is probably due to the lack of space for the sodium cations in the supercages when two of the large Mo(CO)6 complexes have been accommodated. However, we agree that some experimental collaboration and fi'uitful discussions are needed to solve this assignment problem convincingly. Reply by G. Engelhardt: Thank you for this comment.
B018
An In-situ X-ray and N M R Layered Mesophase Materials
Study
of the Formation
of
by L.M. Bull, D. Kumar, S.P. Millar, T. Besier, M. Janicke, G.D. Stucky and B.F. Chmelka, University of California, Santa Barbara, California, USA Question by D. Klint, University ofLund, Lund, Sweden: Did all of the precursor silicate solutions contain methanol in order to favor the octameric SisO20-form? If so, then you have to account for that and use a ternary, instead of a binary, phase diagram when considering the different surfactant phases. Answer by B.F. Chmelka: We formed silicate-surfactant mesophases with and without CH3OH in the precursor silicate solution. At high pH and room temperature, the methanol stabilizes cubic octamer silicate species, which appear to be favorable for forming stable silicate-surfactant liquid crystal mesophases. As you suggest, the formation of such mesophases from dilute silicate and surfactant (CTAB) precursor solutions cannot be predicted from the binary phase diagram of pure CTAB in water alone. Instead, many factors may effect the phase diagram, and in our system, the combination of surfactant species, water, multiply charged silicate anions, base (TMAOH), and organic additives, such as methanol and trimethylbenzene, produces entirely different phase behavior from aqueous
350 CTAB. A more complicated multicomponent phase diagram is needed to describe this system.
B019
Rub-10, a Boron Containing Analogue of Zeolite Nu-1 by U. Oberhagemann, B. Marler, I. Topalovic and H. Gies, Ruhr University, Bochum, Germany
Comments by G. Engelhardt, University of Stuttgart, Stuttgart, Germany: 1) The 29Si NMR spectrum with the two broad lines may also be explained by two groups of silicon atoms characterized by different mean bond angles instead of boron in the second coordination sphere. This explanation is used, for example, in the interpretation of the 29Si MAS NMR spectra of uncalcined ZSM-5.2) There is no doubt that the broad pattern in the liB NMR spectrum arises from a quadrupolar broadened line shape of trigonal boron. Answers by H. Gies: 1) We concluded from the close match of the boron analysis by ICPAES with the boron content calculated from the NMR spectrum, assuming that the Q4(1B) and the Q4(0B) environments in borosilicates lead to distinct 29Si NMR signals, that this is the correct assignment of the spectrum. In addition, from crystal chemical considerations, the boron content corresponds roughly to the maximum value (one boron T site per large cage as carrier of the position charge), and a geometrical analysis of Si-O distances or Si-O-Si bond angles does not indicate a bimodal distribution of values which might have been an alternative explanation for the two 29Si signals in the spectrum. 2) We agree that boron in the calcined form of Rub-10 is in trigonal coordination. Questions by H. Kessler, Ecole Nationale Supdrieure de Chimie de Mulhouse, CNRS, Mulhouse, France: 1) Does the liB MAS NMR spectrum of the calcined material correspond to a fully hydrated sample? 2) Has the influence of the hydration state on the ratio of tetracoordinated boron and tricoordinated boron been determined? Answers by H. Gies: 1) Rub-10 is a clathrasil with 4-, 5- and 6-membered ring windows only, and this prevents water from penetrating into the clathrasil pores. 2) After calcination, boron is tricoordinated and does not become hydrated within the time span of the experiment (several days).
Question by W. Schnick, University of Bayreuth, Bayreuth, Germany: How was the structure solved?
Answer by H. Gies: The structure of Rub-10 was solved "ab-initio" using the Patterson search method. A fragment Si(Si4) yielded a good fit of hk0 reflections which were
351 consequently used to calculate an electron density projection. From this, the threedimensional structure was derived.
Questions by K. Serf, University of Hawaii, Honolulu, Hawaii, USA: 1) Was any hydrogen present (as H § in your calcined sample? 2) Were your boron atoms then 3-coordinated? Answers by H. Gies: 1) The 1H NMR spectrum could not be interpreted unambiguously. 2) We know from the NMR experiments that boron is 3-coordinated in the calcined form of Rub- 10.
B020
S t r u c t u r a l A n a l y s i s b y Neutron Diffraction of Simple Gases (H2, A r , C H 4 and C F 4 ) S o r b e d Phases in AIPO4-5
by J.P. Coulomb, C. Martin, Y. Grillet and C.R.M.C. - CNRS, Campus de Luminy, Marseille, France
N. Tosi-Peilenq,
Questions by Ch. Baerlocher, Swiss Federal Institute of Technology Zurich, Zurich, Switzerland: 1) You are questioning the published pore size of A1PO4-5. Did you observe any lattice parameter changes during the adsorption of methane? 2) You have reported large changes in the intensities of the neutron diffraction pattern after sorption of methane. What was your reason for not using the Rietveld refinement technique to determine the structure of sorbed molecules? Answers by J.P. Coulomb: 1) We found that the methane sorption capacity for our "best" AIPO4-5 sample is 6 molecules per unit cell. From this we conclude that the widely accepted pore diameter of A1PO4-5, i.e., 0.73 nm, has to be questioned. During the sorption of methane, we observed only a very small modification of the AIPO4-5 lattice parameter (around 0.03 %) by neutron diffraction. 2) In the regimes of low and medium methane loadings the sorbed phase is a fluid phase (the translational diffusion coefficient Dtr. amounts to about 10-5 cm2/s). Nevertheless, we observe a strong modification of the neutron diffraction peak intensity. We believe that in these regimes of loading, the Rietveld method is not appropriate for explaining this modification. In the regime of high loadings where we observe crystallization of the sorbed methane phase, the Rietveld method can be useful but the difficulties stem from the different configurations of the methane "chains". For the "dimers chain" and for the "trimers chain", four and six possibilities exist, respectively.
Question by M. Bonn, FOM Institute for Atomic and Molecular Physics, Amsterdam, The Netherlands: What is the order of the observed phase transition? Answer by J.P. Coulomb: From the observation of a hysteresis loop, we conclude that the phase transition of sorbed methane is first order.
352
Question by J. Caro, Institute of Applied Chemistry, Berlin, Germany: You found that, at low loadings, the guest molecules behave like a fluid. This is a surprising result, and it differs from those obtained by Jobic by means of quasi-elastic neutron scattering. He found - for zeolites with other structures - that the molecules perform activated jumps, and that the jump lengths and residence times depend on the loading. What is your experimental evidence for (i) the fluid model and (ii) the one-dimensional diffusion patterns? Answer by J.P. Coulomb: In the regimes of low and medium methane loadings, the sorbed phase is characterized by a rather high translational mobility (Dtr" ~ 10-5 cm2/s). Our incoherent quasi-elastic neutron scattering spectra are well represented by a simple scattering law of the Brownian type. The quasi-elastic broadening is Q2 dependent in the whole range of Q (0.06 nm < Q < 0.15 nm). We think that this is a consequence of the low corrugation value of the inner A1PO4-5 surface. The one-dimensional diffusion behavior will be studied in more detail with a bulkier molecule such as neopentane.
B022
Temperature Programmed Desorption Studies of Octahedral Molecular Sieves
and
Reduction
by Y.-G. Yin, W.-Q. Xu, R. DeGuzman, Y.-F. Shen, S.L. Suib and C.-L. O'Young, University of Connecticut, Storrs, Connecticut, USA; Texaco, Inc., Beacon, New York, USA Questions by J.N. Armor, Air Products & Chemicals, Inc., Allentown, Pennsylvania, USA: 1) Do those octahedral molecular sieves (OMS) exhibit any exchange with labelled 02? 2) How did you perform the ion exchange with Cu2+? Are you sure that the cations you describe are "exchanged" into sites on OMS-1 or OMS-2? Answers by S.L. Suib: 1) We have not yet tried to exchange OMS materials with labelled 02, however, this is an excellent suggestion, and we have had some on order for a while. 2) For incorporation in tunnel sites, we have used solutions of Cu 2+ ions in contact with OMS-1 for several hours at room temperature. EPR data suggest that Cu 2§ ions have been exchanged into tunnel sites and have an octahedral geometry. Electrochemical experiments suggest that these Cu 2+ ions can be replaced with supporting electrolyte (Li +, K +, etc.). We have also intentionally tried to incorporate Cu 2§ into the framework of OMS-1 by doping the starting gel. In this case the materials are EPR silent and electrochemically inactive, very likely due to quenching via framework Mn 4+ ions. TEM data for the exchanged and framework substituted materials have different lattice parameters. The two sets of materials also have different binding energies of Cu 2+ in the Cu 2p region, different catalytic properties, and different thermal properties, i.e., O desorption properties are quite different. So we believe that at least some of the Cu 2§ ions are exchanged in OMS-1 and OMS-2. In
353 the case of Cu a+ in OMS-2, however, it appears that some of the Cu 2+ is not exchangeable and perhaps in the framework.
Questions by J.N. Armor, Air Products & Chemicals, lnc., Allentown, Pennsylvania, USA: 1) What is the thermal stability of OMS-1 and cation exchanged OMS-1 materials? 2) Have you ever tried to measure 0 2 isotopicaUy exchanged into OMS-1 ? Answers by C.-L. O'Young: 1) The thermal stability of Mg-OMS-1 is around 500 to 550 ~ the thermal stabilities of Cu-OMS-1, Ni-OMS-1, and Zn-OMS-1 decrease slightly to about 450 ~ 2) No, but this is another good technique for studying the reactivity of oxygen species.
Question by M. HSlscher, R WTH Aachen, University of Technology, Aachen, Germany: Were adsorption experiments with N 2 or H20 performed to study the micropore volume or the surface area? Answer by S.L. Suib: Such probes have been used by several other groups. Perhaps a better probe for such systems is Ar.
A026
Effect of the Stacking Probability on the Properties of the Molecular Sieves CIT-1, SSZ-26 and SSZ-33 by R.F. Lobo, S.I. Zones and M.E. Davis, California Institute of Technology, Pasadena, California, USA; Chevron Research and Technology Co., Richmond, California, USA
Question by D.E. Akporiaye, SINTEF, Oslo, Norway: Have you considered the similarities of this system to boggsite in which the view along the 12-membered ring pore is rotated by 90 ~ and the other view is similar to ZSM-11 ? Might this give some insight into the synthesis ofboggsite? Answer by R.F. Lobo: Yes, both structures are related because both materials have the same projection along the 12-membered ring pores (the AFI projection). Also, both materials contain the 4 = 4 -1 secondary building unit (SBU) in their frameworks. However, the way these SBU's are put together is quite different. This led me to think that the synthesis conditions of boggsite are going to be different from the synthesis conditions of SSZ-26.
Questions by H. Kessler, Ecole Nationale Sup&ieure de Chimie de Mulhouse, CNRS, Mulhouse, France: 1) In the synthesis of CIT-1, is the use of silica tubes necessary? 2) How
354 strongly is boron incorporated into the framework, and does it become trigonally coordinated upon calcination? Answers by R.F. Lobo: 1) No, the use of silica tubes is not necessary, but usually leads to better products. 2) Boron is a little unstable but can be maintained in the framework by calcining the material first in N 2 and then in dry 02. If this is not done, a fraction of boron becomes trigonally coordinated upon calcination.
Question by L.B. McCusker, Swiss Federal Institute of Technology Zurich, Zurich, Switzerland." Have you refined the CIT-1 structure? Answer by R.F. Lobo: We are currently refining the structure of CIT-1 by Rietveld refmement.
B030
Muon Spin Relaxation Studies of Cyclohexadienyl Radicals in N a U S Y by M. Shelley, D.J. Arseneau, M. Senba, J.J. Pan, R. Snooks, S.R. Kreitzman, D.G. Fleming and E. Roduner, University of British Columbia, Vancouver, British Columbia, Canada; University of Zurich, Zurich, Switzerland
Question by H. F~irster, University of Hamburg, Hamburg, Germany: Would you please outline your experimental set-up. Do you need special facilities? This would be important for a breakthrough and further application of this sensitive method. Answer by M. Shelley: Muon spin relaxation (MSR) experiments are conducted using spin polarized muon beams that are produced at cyclotron facilities such as TRIUMF, Canada, PSI, Switzerland, RAL, United Kingdom, KEK, Japan, or LAMPF, USA. The situation is, therefore, similar to other experiments that need a central facility such as neutron or synchrotron radiation studies. Apart from the need for a muon beam, the experimental set-up in typical MSR experiments is simple: a magnet, a temperature control system, detectors (scintillation counters), and electronics. I think that MSR should be considered as a special tool which can provide information which is otherwise difficult to obtain. With its extraordinarily high sensitivity, MSR has much to offer to the zeolite research field. Question by R. Roque-Malherbe, Instituto de Tecnologia Quimica, CSIC-UPV, Valencia, Spain." I would like to know the exact microphysical situation in your experiments. Answer by M. Shelley: Positive muons have a high kinetic energy when they are injected into a sample. They either thermalize into a diamagnetic state (e.g., by occupying interstitial sites in metals or forming molecular ions) or capture an electron to become muonium (Mu =
355 M+e-). Muonium may further react with an organic molecule to form a radical. Regardless of such different chemical states, a positive muon decays to produce a positron, preferentially in the same direction as the instantaneous muon spin polarization. The direction of decay positrons contains information that can be used for studying motions of organic radicals, the magnetic penetration depth of superconductors, charge state dynamics of hydrogen impurities in semiconductors, chemical reaction dynamics involving H or H § spin exchange processes, quantum diffusion of light atoms in crystalline solids, etc.
B031
Factors Affecting the UV-Transparency of Molecular Sieves by S. Engel, U. Kynast, K.K. Unger and F. Schiith, University of Mainz, Maine, Germany; Philips Research Laboratories, Aachen, Germany
Comment by J. Caro, Institute of Applied Chemistry, Berlin, Germany: Your studies have filled a gap in the optical application of zeolites.
Answer by S. Engeh Thank you for your kind compliment. Question by F. Di Renzo, Ecole Nationale Supdrieure de Chimie de Montpellier, CNRS, Montpellier, France: Did you observe the same strong absorption between 200 and 250 nm in zeolite A that you observed in TPA-silicalite?
Answer by S. Engel: Yes, for zeolite A as well as all the other zeolites we observed a reduced reflectivity in that range. For zeolite A it is apparent that the onset of absorption, so to speak, is shined to lower wavelengths. The value for the reflection at 220 nm is comparable with that of ZSM-5, silicalite and many samples.
Questions by H. FSrster, University of Hamburg, Hamburg, Germany: 1) According to some Raman spectroscopists, defects should be responsible for the fluorescence disturbing the zeolite spectra. Do you assume some relations between these centers and those you want to eliminate in order to get highly transparent materials? 2) Can you tell something about the commercial background of your investigations? Answers by S. Engeh 1) Yes, however, the color centers which are responsible for the fluorescence have to be known exactly in order to avoid them. Since we do not know which color centers are responsible for certain absorptions, it remains to be determined how to get rid of those centers which cause the fluorescence. 2) The main purpose of the project was finding new phosphors to replace currently used expensive ones. They may be used in fluorescent lamps.
356
Question by M. Hunger, University of Stuttgart, Stuttgart, Germany: What is the influence of SiOH groups on the reflectivity? Did you control the number of these defect centers?
Answer by S. Engeh We have tried to investigate the influence of SiOH groups. We were, however, unable to evaluate their influence quantitatively.
Question by P. Knops-Gerrits, Catholic University ofLeuven, Heverlee, Belgium: Do you think that for the development of new fluors, a broader emission range can be achieved by combined exchange (rare earths or transition metal ions) and are your studies going into this direction? Answer by S. Engeh Yes, possibly. To achieve, e.g., white light such as in a fluorescent lamp, one needs to have a combination of different emissions. At this time we are only investigating a Tb doped material which does emit green light. Question by P.L. Llewellyn, Centre de Thermodynamique et de Microcalorimetrie, CNRS, Marseille, France: Did you try the direct inclusion of Tb 3+ into the zeolite structure during the synthesis? If so, were the properties of these samples enhanced? Answer by S. Engeh Since the luminescence investigations reflect very recent work, we have not done this as yet. We are, however, planning to do it.
Question by F. Marlow, Institute of Applied Chemistry, Berlin, Germany: Could it be possible to create your structural defects in a controlled manner and to use them in a luminescent material, maybe in an A1PO4? Answer by S. Engel: Yes, I think so. However, since we do not know which defect sites do exist in the crystals, it is difficult to control them. Calcination under oxygen may be a possible way of increasing the number of defect sites.
Question by E. Roduner, Un&ersity of Zurich, Zurich, Switzerland: Part of the reason why light is reflected by the cx3'stallites is due to the fact that the index of refraction does not match that of the environment. Have you considered imbedding the erystallites in an environment that has the same index of refraction? Answer by S. Engel: Yes, we have been thinking about such experiments with index matching which would have enabled us to measure transmission instead of reflection. At this stage of the investigation, these experiments have not yet been done.
Question by M. Wark, Ecole Nationale Sup6rieure de Chimie de Mulhouse, Mulhouse, France: Do you observe a dependence of the wavelength with a maximum reduction of reflectivity on the Si/Al-ratio of the host after exchange with terbium?
357
Answer by S. Engei: No, however, we have not been looking very deeply into the absorption properties of incorporated Tb so far. The reflectivity changes drastically for the doped material compared with the "empty zeolite".
Questions by B.M. Weckhuysen, Catholic University of Leuven, Heverlee, Belgium: 1) How does the UV-transparency vary with the composition of the lattice: a) Si/Al-ratio, b) presence of Fe 3+, and c) substitution by Ga3+? 2) Did you try other rare earth ions for doping zeolites? Answers by S. Engel: 1) The transparency is independent of the Si/Al-ratio. We have not done any experiments with isomorphously substituted ZSM-5 since we regarded such additional centers within the structure as possible "defect sites". 2) We are thinking about this.
B032
The Study of the Surface Topography Materials Using Atomic Force Microscopy
of Microporous
by M.L. Occelli, S.A.C. Gould and G.D. Stucky, Georgia Tech. Research
Institute, Atlanta, Georgia, USA; Claremont Colleges, Claremont, California, USA; University of California, Santa Barbara, California, USA
Question by E. Creyghton, Delft University of Technology, Delft, The Netherlands: Would it be possible to study noble metal, e.g., platinum clusters occluded in a zeolite atter cutting the crystal into two parts, and how rough can a surface be for obtaining reasonable pictures? Answer by M. Oeeelli: Atomic force microscopy (AFM) images of the surface of zeolites have generally been more challenging to obtain than those of layered materials such as mica; however, it has been accomplished. When imaging zeolite surfaces, we believe that the presence of metal clusters would disrupt the well ordered pattern of the surface and disrupt the presence of repeat distances. At present, we can image surfaces up to a corrugation of 3 to 4 ~tm. However, scanners are available which would allow imaging of surfaces with a corrugation up to approximately 10 lam. Question by P.K. Durra, Ohio State University, Columbus, Ohio, USA: How does one address the artifacts that are common with this technique?
Answer by M.L. Oeeelli: There are numerous common techniques in AFM imaging which tell us of artifacts on the surface or within the microscope. For example, changing the image acquisition time should not affect the image, changing the imaging direction should rotate the image, increasing the scan width should decrease the size of the features on the surface.
358
Question by J. Fraissard, Universitd Pierre et Marie Curie, CNRS, Paris, France: Do you think that we can use AFM for studying adsorption and, more specifically, the restructuring of the surface of metals in the presence of a gas? The same question holds for a bimetallic catalyst. Answer by M.L. Occelli: AFM has been used in the past to study adsorption phenomena and the surface modifications that they can bring about (see references in paper B032). We believe that it is also possible to observe surface variations due to the presence of bimetallic phases.
Questions by U. Hatje, University of Hamburg, Hamburg, Germany: 1) How are your samples prepared, is ultra-high vacuum (UHV) needed? 2) How long does the collection of an image take? Answers by M.L. Occelli: 1) The samples do not need to be imaged under UHV. The fluid cracking catalysts tend to possess little water on the surface. 2) AFM images are usually obtained within 2 to 10 seconds. The image time depends upon the stability of the tipsurface. For example, imaging of steam-aged pillared clays requires more time (30 to 50 seconds) due to the presence of debris from pillar decomposition on the surface. Question by K. Kuroda, Waseda University, Tokyo, Japan: Pillaring agents could not be observed on the clay surfaces. Where are the pillaring agents located after the AFM measurement? Answer by M.L. Occelli: The pillaring agent is located between the clay silicate layers. In all the images we obtained, we could not see an indication of the pillaring agent being located on top of the silicate layers. Question by O. Terasaki, Tohoku University, Sendal, Japan: You showed us many interesting AFM images, some of which show fine structures in the 10 to 100 nm scale. Is it possible to observe similar fine structures (not on an atomic scale) by SEM with a field emission gun (FEG)? Answer by M.L. Occelli: Using SEM we could not see the surface details that we have reported. However, we did not try to compare large scale images obtained by SEM and AFM. Question by J. Wu, W.R. Grace & Co., Columbia, Maryland, USA: You have shown macropores of several ~tm in the GSZ-1 catalyst. Have you seen mesopores and micropores in the AFM?
359
Answer by M.L. Occeili: With the AFM we have seen pores in the meso and micro range. However, our attention was given mainly to the observation of the catalyst surface architecture.
B033
Time Dependence of Vibrational Relaxation Hydroxyls in Acidic Zeolites
of Deuterated
by M. Bonn, M.J.P. Brugmans, A.W. Kleyn, R.A. van Santen and A. Lagendijk, FOM Institute for Atomic and Molecular Physics, Amsterdam, The Netherlands; Eindhoven University of Technology, Eindhoven, The Netherlands Question by E. Brunner, University of Leipzig, Leipzig, Germany: Is it possible to determine the strength of the hydrogen bond, i.e., the hydrogen bond length of hydrogen bonded species by this method? Answer by M. Bonn: No, a quantification is not possible with this method. Question by E.N. Coker, Fritz Haber Institute of the Max Planck Society, Berlin, Germany: How long does it take for thermal equilibrium to be re-attained following the generation of heat through the dissipation of the vibrational energy?
Answer by M. Bonn: As yet, this is not clear. This is not measurable, at least not with the present set-up.
Question by D. Freude, University of Leipzig, Leipzig, Germany: How do the observed results depend on the radiation power and/or the pulse duration of the pump pulse?
Answer by M. Bonn: Only the observed transmission levels after vibrational relaxation change. T1 times are independent of both.
Questions by W.M.H. Sachtler, Northwestern University, Evanston, Illinois, USA: 1) You conclude that H atoms form simultaneously a strong chemical bond to one zeolite 02- ion and a weak bond to a different 02- ion. This model requires close proximity. In the side pockets of mordenite, an O-H .... O complex is conceivable, but in wider channels or cages, H the o / \ o bond angle will be smaller than 180 ~ Could you elaborate on this? 2) What is the size of the O-H dipole? Answers by M. Bonn: 1) The hydrogen atoms must not necessarily be H-bonded to neutral lattice oxygen on the opposite side of the cage. Indeed, the bond angle might be different
360 from 180 ~ 2) The transition dipole moments are known, but I do not have this information at hand.
Question by R. Salzer, Dresden University of Technology, Dresden, Germany: What is the reason for the bleaching observed before the pump pulse arrived at the sample? Answer by M. Bonn: Pulses have Gaussian temporal shape. Before the maximum in bleaching, there is already some temporal overlap. Question by A. Zeeehina, University of Turin, Turin, Italy: The mordenite structure is characterized by two types of channels (one is linear and the other occluded forming lateral pockets). Do the OD groups located in the two different channels release at different rates? Answer by M. Bonn: If there were two bands with intrinsically different Tl's, this would be indicated by a non-single-exponential decay, which was not observed.
B034
Characterization Voltammetry
of
Titanium
Silicalites
Using
Cyclic
by S. de Castro-Martins, A. Tuel and Y. Ben Tafirit, Universidade Federal de Uberlandia, Brazil; Institut de Recherches sur la Catalyse, CNRS, Villeurbanne, France
Question by M. Baker, University of Guelph, Guelph, Ontario, Canada: The charge passed in your voltammograms is very small indicating that only 10-10 moles of Ti 4+ are electroactive. This indicates that electroactive Ti 4+ exists at the external surface of zeolite particles only. In view of the fact that you propose electron transport to framework titanium within the bulk of the zeolite can you explain the manner in which electrons are transported through the zeolite which is an insulator? Answer by A. Tuel: The carbon paste electrode contains about 20 wt.-% zeolite. A rough calculation shows that, for a 6 mm diameter electrode, more than 75 % of the Ti atoms in the zeolite crystals in contact with the electrolyte solution are involved in the process. Concerning the second remark, electron transport occurs, of course, via the electrolyte that is present in the channels of the zeolite. Comment by D.R. Rolison, Naval Research Laboratory, Washington, D.C., USA: The evolution of current in time for your (TS-1) modified carbon pastes to a steady-state response need not arise from the slow sorption of solvent and cations into the TS-1 crystallites but more likely can be explained by slow ingress of H20 and cations into the carbon paste, thereby exposing more extracrystalline Ti centers. This would be completely
361 analogous to findings by Derouane et al. (Electrochim. Acta, 1993) with (MV2+-modified Y)-modified carbon paste. Their electrochemical and analytical data did not support intracrystalline redox. I agree with Prof. Baker that the very small amount of coulombic charge you measure indicates that such a small fraction of Ti centers are electrochemically communicating that they need only be present in extracrystalline or near external sites. Your data with 0.2 ~tm and 2 ~tm TS-1 crystals need not invoke intracrystalline redox either as you use the same amount of C to prepare either as a carbon paste. The contact of zeolite with useful conductor (i.e., the carbon) will differ. A further worry is how the oil binder associates with the powders when the size of the modified silicalite crystal increases - the oil may not preferentially associate with the carbon only: this would affect the rate of ingress of 1-120 and cations into the modified carbon paste. I agree that your control studies with TiO 2 and TiO2-modified zeolites show the electroinactivity of Ti in an octahedral oxygen environment. You may be observing the voltammetry of tetrahedral Ti 4§ in the framework, but it is extracrystalline (or very near-exterior) framework Ti 4§ You have presented no data that demonstrate electron transfer to intracrystalline tetrahedral Ti 4+ in the framework. The very low coulombic charge passed, which represents a miniscule fraction of the available Ti centers, has already told you so. Answer by A. Tuel: If the electrochemical process was limited to extracrystalline Ti centers, it would not be possible to explain why currents are only observed with small electrolytes (bulky tetraalkylammonium cations do not enter the zeolite channels, whereas tetramethylammonium cations do). I agree that changing the crystal size may influence the way the oil binder associates with the zeolite. However, if it was the sole reason to explain the experimental observations, it would also drastically modify the resistivity of the carbon paste and, thus, the observed current. We did not observe such modifications, and I think that the differences can be attributed to diffusion limitations of the cations in large crystals. We are now working with large pore and mesoporous materials which will offer the possibility of using bulky electrolytes.
B035
Copper Exchanged Zeolites Studied with 13C and N M R of Adsorbed Carbon Monoxide and Xenon by M. Hartmann and B. Boddenberg,
129Xe
University of Dortmund
Dortmund, Germany Questions by C.J. Jameson, University of Illinois, Chicago, Illinois, USA: 1) Your model provides 5 values for ions at specific sites. How did you arrive at these numbers? 2) What about the contributions to the Xe chemical shifts from interactions of Xe with the oxy.gen atoms? The Xe interacts with many more oxygen atoms than cations. In our work, we are
362 able to reproduce the Xe chemical shifts in clusters Xe, Xe2, Xe3,. ..... , Xe 8 trapped in NaA at room temperature and also as a function of temperature by using ab-initio derived Xe shielding functions for Xe-O and Xe-Na § interactions. The Xe-O interactions are an important part of the Xe shift for each cluster. Under fast exchange, as in your spectra, the Xe is not interacting only with the cation.
Answers by M. H a r t m a n n : 1) The procedure of the site characteristic determination was not presented in this paper, but can be found in our recently published paper (Microporous Materials 2, 1994, 127-136). Basically, you need systems which predominantly exhibit one special site, e.g., NaX, NaY, Cu(95)Y or Cu(70)YSE. Such samples allow the determination of the k i and 5 i values. 2) Basically, I agree that there is an interaction of xenon with the cage wall forming oxygens. One of the basic assumptions of our model is the predominant adsorption of xenon at strongly adsorbing cationic sites. In a weighted average in the fast exchange regime, the sites with a stronger adsorption capacity have a greater contribution to the observed 5 value. Calculations from our group indicate that the minima of the potential energy for xenon in a faujasite supercage are near the SII or SIII positions, so that the contribution of those sites to the measurable adsorption or shift is enhanced. At our proposed site 2, xenon interacts predominantly with the oxygens at that site, because of the minor contribution of the cation which is probably located in the 6-membered ring between the supercage and the sodalite cage. So this may be considered the oxygen-xenon interaction in our model, but we will consider your remark in the future. Question by L. Kevan, University of Houston, Houston, Texas, USA: The luminescence of Cu § is also used to follow Cu § concentrations in zeolites. Does this method also distinguish between supercage sites versus other sites in the presence of CO? Answer by M. H a r t m a n n : I think you are referring to the work of Strome and Klier (J. Phys. Chem. 84, 1980, 981) who investigated the migration of copper cations in the presence of CO. Although they were able to distinguish between supercage and nonsupercage sites, no figures for the site populations were given.
B036
Two-Dimensional 129Xe Exchange Xenon Dynamics in NaA Zeolite
NMR
Measurements
of
by M. Janicke, B.F. Chmelka, R.G. Larsen, J. Shore, K. Schmidt-Rohr, L. Emsley, H. Long and A. Pines, University of California, Santa Barbara, California, USA; University of California, Berkely, California, USA Question by C.J. Jameson, University of Illinois, Chicago, Illinois, USA: As you know, we have also measured the same cage-to-cage rate constants for the Xe n clusters (J. Chem.
363
Phys. 101, 1994, 1775). Have you tried to calculate the equilibrium distributions of the Xe n clusters from your rate constants, since there is a relationship between these rate constants and the fractional populations of the Xe atoms in the cage? Answer by B.F. Chmelka: We determine the rate coefficients for xenon transport among cavities with different Xe occupancies by exploiting the relationship you suggest through its influence on the off-diagonal peak intensities in the 129Xe 2D exchange spectra. The measurements explicitly incorporate initial (tmix = 0) equilibrium Xe population distributions, statistical or otherwise, which are obtained from 129Xe 1D NMR spectra. The rate coefficients are extracted directly from the off-diagonal peak intensities, by approximating xenon transport as a first-order process with single xenon exchanges between adjacent cavities containing populations in global equilibrium. The diagonalization procedure used to obtain the rate coefficient matrix from the input intensities assures that the long time distribution is identical to the input 1D distribution.
Question by J. Klirger, University of Leipzig, Leipzig, Germany: The off-diagonal peaks in the 129Xe NMR exchange spectra appear to be more intense in the vicinity of the diagonal. Does this mean that there is a higher probability that adjacent cavities contain a similar number of xenon atoms (i.e., that there exists some spatial correlation in the occupancy numbers) rather than that the cavity occupancy numbers are distributed completely randomly over the crystallites? Answer by B.F. Chmelka: In 12aXe 2D exchange NMR spectra for xenon adsorbed in NaA zeolite, off-diagonal peaks once removed from the diagonal arise mainly from passive exchange processes in which xenon atoms undergoing no transport themselves experience changes in frequency because an actively exchanging xenon atom is transported into or out of their cavity. For short mixing times, 129Xe peaks that are far off the diagonal correspond predominantly to xenon atoms undergoing active exchange and thus will reflect adjacencies of xenon populations according to their distribution, whether random or otherwise. This is an interesting issue and relies on increasing the signal associated with the far-off-diagonal peaks to allow meaningful quantitative comparison among various distribution possibilities. Question by L. Kevan, University of Houston, Houston, Texas, USA: If you use less than complete Ca 2+ exchange, do you see other than a 109 ~ tetrahedral jump for benzene exchange among different calcium cation sites in Ca-LSX zeolite? This would seem to be a good test for your model. Answer by B.F. Chmelka: We have not yet made the 13C 2D exchange NMR measurements you suggest on benzene adsorbed on LSX zeolite containing a mixture of charge-balancing cations, e.g., Na + in addition to Ca2+. For the Ca-LSX system and the experimental conditions employed in our study, namely a low adsorbate loading and
364 exchange measurements at room temperature, benzene adsorbs preferentially at Ca2+ sites. Under these conditions, it is unlikely that partial sodium cation exchange will alter the benzene reorientation angle measured, providing no accompanying changes occur in the positions of the remaining calcium cations. In support of this, the Ca-LSX zeolite sample we used contains a bulk average of approximately 3.4 Ca2+ cations in SII sites per supercage, which is less than the full complement of four SII cations per cavity. Our current results, nevertheless, reveal a well-defined elliptical pattern in the 13C 2 D exchange NMR spectrum of benzene adsorbed on Ca-LSX indicating benzene exchange among different Ca 2+ adsorption sites with 109 ~ orientations relative to one another. Despite the incomplete SII cation loading, therefore, our results show that Ca2+ cations still occupy tetrahedrally arranged SII sites, consistent with separate neutron diffraction experiments. We are pursuing several avenues to probe our exchange model further, including variable temperature experiments, use of variable Si/Al-ratio faujasite materials, and computational modelling of the transport process.
B037
Electron Transfer Reactions in H-Mordenite by R. Crockett and E. Roduner, University of Zurich, Zurich, Switzerland
Comment by W.O. Haag, Mobil Research & Development Corp., Princeton, New Jersey, USA: I would like to congratulate you on this free work and particularly to support your last conclusion that radical cations are not intermediates but rather indicators. We have reached the same conclusion from kinetic studies of a series of LaY zeolites with different water contents where the rates of various carbenium ion reactions were compared with the concentration of radical cations of suitable probe molecules. Also, the conversion of cyclopentene is a well known acid-catalyzed reaction to yield octalin. Answer by E. Roduner: Thank you for your comment.
Question by B.V. Romanovsky, Moscow State University, Moscow, Russia: In your earlier work, you suggested a carbenium ion mechanism for the formation of octalin from cyclopentene, did you change your view now? Answer by E. Roduner: You are referring to our work in J. Chem. Soc., Perkin Trans. 2, 1993, 1503. We have not identified any intermediates of cyclopentene dimerization, so the mechanism discussed is nothing else than a proposal. In particular, we have no evidence for a radical cation reaction.
365
P080
Optical, Electric and Photoelectric Properties of Pure and C d S o r C u C I C l u s t e r Doped Zeolite Single C r y s t a l s by Y.A. Barnakov, M.S. Ivanova, V.P. Petranovskii, V.V. Poborchii and V.G. Soloviev, A.F. Ioffe Physical Technical Institute, St. Petersburg, Russia; S.M. Kirov State Pedagogical Institute, Pskov, Russia
Question by G. Tel'biz, Institute of Physical Chemistry, Academy of Sciences of Ukraine, Kiev, Ukraine: What is known about the location and distribution of the clusters in the zeolite structure?
Answer by V.P. Petranovskii: The most probable location of the CdS clusters generated in aqueous media is inside the large cavities. It is more difficult to answer your question concerning the distribution of the clusters over the zeolite X crystals. This question is related to the size of the clusters. If one assumes that they can be represented by Cd4S 4, there will be approximately one such cluster per 4 to 5 cavities. We believe that these clusters are distributed statistically over the crystallites.
366
III. Modification
A005
Genesis of Rh0 n Clusters Zeolite "Protons"
in
Zeolite
Y;
Interaction
with
by D.C. Tomczak, V.L. Zholobenko, H. Trevifio, G.-D. Lei and W.M.H. Sachtler, Northwestern University, Evanston, Illinois, USA Question by M. de Agudelo, INTEVEP S.A., Caracas, Venezuela: Do the metal-proton adducts give rise to specific 1H-NMR signals? If so, could you please give me some details on their M R parameters? Answer by W.M.H. Saehtler: We have done preliminary experiments with IH-NMR at liquid helium temperature, but the results are not yet conclusive.
Comment by P. Gallezot, Institut de Recherches sur la Catalyse, CNRS, Villeurbanne, France: We have shown before (G. Bergeret et al., d. Catal. 104, 1987, 279-287) that, upon adsorption of CO on Rh metal clusters in Y zeolites, the clusters are first disrupted into Rh I (CO)2 species which, subsequently, can reorganize into Rh6(CO)I 6 molecular clusters. So these molecular clusters are not formed directly from Rh clusters but via a two-step mechanism involving two redox reactions with the transient formation ofRh I (CO)2. Answer by W.M.H. Sachtler: The formation of [Rh(CO)2] + from Rh und CO as well as Rh4(CO)12 and Rh6(CO)16 has been reported by numerous authors. A problem was, however, to understand the nature of the electron acceptors. We have shown by mass spectrometry that in zeolites, protons are able to act as oxidants" RhO + H + + 2 C O > ~ (CO)2] + + 89H 2.
Question by H.G. Karge, Fritz Haber Institute o f the Max Planck Society, Berlin, Germany: Professor Sachtler, can you provide us with an estimate of the cluster size of the Rh0n clusters inside the Y structure? Answer by W.M.H. Sachtler: The size of the Rh clusters depends on the reduction temperature and the concentration of protons in the zeolite. Rh/HY, when reduced at fairly low temperature, contains very small Rh clusters which are hardly detectable in the electron microscope which shows all zeolite fringes. However, as with other metals, hydrogen chemisorption is low when the metal dispersion is high as a consequence of metal adduct formation.
367
Comment by C. Naccache, Institut de Recherches sur la Catalyse, CNRS, Villeurbanne, France: The chemistry of rhodium in zeolites is identical to that in solution, as we had shown several years ago. Rh 3+ in the sodium form of zeolite Y is converted to Rh+(CO)2 by CO and H20. It seems that there is no need to start with HY and Rh 0 to form the dicarbonyl rhodium (I) complex. Could you please comment on this. Answer by W.M.H. Sachtler: As we have now demonstrated, Rh 3+ ions undergo hydrolysis: Rh 3+ + H20 < > (RhO) + + 2 H +, and the rhodyl ion, (RhO) +, is easily reduced with CO" (RhO) + + 3 CO ~
['Rh(CO)2]+ + CO 2.
An alternative pathway to the [Rh(CO)2] + ion is to oxidize Rh 0 with protons in the presence of CO: Rh0 + H + + 2 CO <
A006
> [Rh(CO)2] + + 89H2.
Novel Generation of Ionic Clusters within Zeolites by Y.S. Park, Y.S. Lee and K.B. Yoon, Sogang University, Seoul, Korea
Question by H.G. Karge, Fritz Haber Institute of the Max Planck Society, Berlin, Germany: Dr. Yoon, are you able to derive from your experiments the loading and dispersion (distribution) of the ionic clusters? Answer by K.B. Yoon: Upon longer stirring, up to eight alkali atoms per unit cell could be observed. The remaining unreacted metal particles are so small that it is not easy to judge on the exact amount of loading. The distribution of the ionic clusters within the zeolite crystals cannot be derived from our experiments.
Questions by M. Schriider, University of Hamburg, Hamburg, Germany: 1) Mr. Yoon, you have presented a large amount of both EPR and UV-VIS spectroscopic measurements. Since optical spectroscopy may detect clusters which are invisible for EPR, could you please comment on how you would assign the UV-VIS absorptions? Would you attribute the huge absorption covering the whole wavenumber range to larger sodium particles? 2) Comparing the different preparation methods, which one would you consider most appropriate for the generation of uniform Na43+/Na54+ clusters without metallic particles? 3) Could you please specify the experimental conditions for (i) the solid-solid reaction and (ii) the Na/THF procedure? How long and at which temperature did you stir? Answers by K.B. Yoon: 1) Na43+ is red and has its absorption maximum at 490 nm (in NAY), while K43+ is blue and has its absorption maximum at 560 nm. Therefore, absorption maxima occurring at these wavenumbers can be readily assigned. The broad absorptions
368 over the entire NIR region have not been assigned. I personally believe that the broad absorption arises from the electrons trapped in the zeolite framework. 2) Na43+ can be best prepared in NaX with K in the presence of 18-crown-6. K43+ can be similarly prepared in KY with K. 3) A small amount of zeolite, e.g., NaY, which had been dried under vacuum, was stirred with Na or K (8 atoms per unit cell) in a glove box charged with argon for 1 to 2 hours. Small amounts of the corresponding organic solvents were added to the mixture. Question by G. Schulz-Eldoff, University of Bremen, Bremen, Germany: Do the electronic structures of the clusters depend on the acidity or basicity of the zeolites? Answer by K.B. Yoon: The difference reflectance spectra of Na43+ in zeolite X and in zeolite Y are different, i.e., Emax. of Na43+ in zeolite Y is at 460 nm, whereas in zeolite X it is at 490 nm. If one accepts that the basicity of the zeolite increases with the aluminum content, then the answer to your question is yes.
Question by G. Tel'biz, Institute of Physical Chemistry, Academy of Sciences of Ukraine, Kiev, Ukraine: Is there a difference in the mechanism of generation of ionic clusters in sodalite and faujasite structures? Answer by K.B. Yoon: The evidence which has been collected so far strongly suggests that the formation of ionic clusters occurs by electron transfer from any powerful reducing agent to a couple (3 to 6) of alkali metal cations which preexist within sodalite units, maybe through the 6-membered oxygen rings. The reducing agent may stay at the external surface, outside the pore system of sodalite, in which case electron transfer from one sodalite unit to another is assumed to occur. In the case of faujasite, the reducing agent may reside either in the supercages or at the external surface of the zeolite crystals.
A007
Electronic Modifications in Supported Palladium Catalysts by B.L. Mojet, M.J. Kappers, J.C. Muijsers, J.W. Niemantsverdriet, J.T. Miller, F.S. Modica and D.C. Koningsberger, University of Utrecht, Utrecht, The Netherlands; Eindhoven University of Technology, Eindhoven, The Netherlands; Amoco Oil Co., Naperville, Illinois, USA
Questions by S.C. 0 Domhnaiil, University of Mainz, Mainz, Germany: 1) You prepared your catalyst by the method of incipient wemess - would you consider using metal carbonyls such as Fex(CO)y, Ni(CO)4 or Co2(CO)8? 2) If you consider an alkylation reaction over your acidic catalyst, would you expect a variation in coke content as a function of metal loading, and if so, why?
369
Answers by B.L. Mojet: 1) We don't have experience with organometallic precursors. 2) The coke content does not only depend on the metal loading but also on the particle size distribution of the catalysts.
Comment by P. Gallezot, Institut de Recherches sur la Catalyse, CNRS, Villeurbanne, France: Your data give further evidence that the electronic state of metal clusters strongly depends upon their environment in the zeolite cages making them "electron rich" or "electron deficient". The experimental data are well established, but theoreticians are now urgently needed to rationalize the data. Answer by B.L. Mojet: I agree with you. Comment by W.M.H. Sachtler, Northwestern University, Evanston, Illinois, USA: As zeolites are no semiconductors, electron donation to or acceptance from zeolites by metal clusters requires discrete electron acceptor/donor centers. In the case of electron-deficient Pd, Pt or Rh, zeolite protons have been identified as electron acceptors, i.e., metal-proton adducts are formed. Since you assume that in Pd/KL zeolite, electrons are donated to Pd, the donor center has to be identified. If 02- ions play this role, I am unable to understand why this is so specific for this particular zeolite. Answer by B.L. Mojet: By altering the acidity of the support (from acidic to alkaline) the charge distribution on the oxygen ions is changed. The electronic properties of the metal particles which are most probably in contact with the support oxygens are changed too. The details of the metal-support interaction model remain to be studied. However, at this moment it is clear that there seems to be a close correlation between the electronic properties of the metal particles and their catalytic activity. Question by D. Barthomeuf, Universit~ Pierre et Marie Curie, CNRS, Paris, France: A very interesting problem is to find out how the palladium particles and the support are interacting. Could you comment on this point for the two cases: Zeolite KL with K/AI close to 1 and KKL zeolite with an excess of potassium. In the latter case, there should be K20 clusters in the zeolite channels. How do palladium particles become electron rich? Answer by B.L. Mojet: See my answer to W.M.H. Sachtler's comment. Comment by R.A. van Santen, Eindhoven University of Technology, Eindhoven, The Netherlands: The electron deficiency or electron excess measured on the Pd particles can only be apparent, because no electron transfer between metal and zeolite is possible. However, a protonic environment of the Pd particles or embedding the Pd particles in a K20 environment will change the effective work function of the particles, a parameter that appears to be of importance to the catalytic reaction you study.
370
Answer by B.L. Mojet: The XPS measurements were carried out on dry samples, whereas the IR experiments were done to exclude ion-dipole interactions. These ion-dipole interactions are prevented by adsorption of water onto the cations; similarly, the polarizing effect of the cations on the Pd particles should be diminished. If there were a polarizing effect (resulting in a change in the work function), this would have been measured with XPS only, but not with IR spectroscopy. However, both the XPS and IR results show a similar trend: a clearly increasing electron density at the Pd particles with decreasing support acidity.
Question by F. Schmidt, SfM-Chemie A G, Bruckmiihl-Heufeld, Germany: You were using hydrogen as the reducing agent in all three cases. Upon reduction, this causes additional acidity. How do you take this into account in your considerations? Answer by B.L. Mojet: Our catalysts have been prepared by the incipient wetness impregnation method. So, reduction does not bring about additional acidity in the catalysts. Questions by E.S. Shpiro, N.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, Russia: 1) Since both XPS and IR shiPts are very sensitive to the size of the particles, I am wondering whether you have the same particle size distribution for all three catalysts. 2) Do you think that all particles with a size of 1.0 to 1.5 nm are located inside the channels of zeolite L? Answers by B.L. Mojet: 1) Yes, we do have the same particle size distribution for all three catalysts. EXAFS results show that the mean particle size is 1.4 nm, 1.0 nm and 1.2 nm for Pd/HL, Pd/KL and Pd/KKL, respectively. Besides, for Pd on carbon supports, a maximum XPS shift of 0.5 eV to higher binding energy is reported, as the particle size is decreased from 5.0 nm to 1.0 nm (see ref. 24 in our paper). Also, the observed shiit of ca. 80 cm -1 in the IR is too large to be due to the particle size distribution. 2) From previous IR experiments on the catalysts, we have shown that CO species adsorbed on metal particles interact with the charge compensating cations of the zeolite. This indicates that the metal particles are inside the zeolite pores. We cannot exclude, however, that there may be a small fraction of the particles outside the zeolite channels.
Question by G. Tel'biz, Institute of Physical Chemistry, Academy of Sciences of Ukraine, Kiev, Ukraine: Is there a possibility for a strong metal-zeolite interaction in your systems? Answer by B.L. Mojet: A salient feature of strong metal-support interactions is a decrease in hydrogen adsorption capacity after reduction at high temperatures. However, we have not observed such phenomena in our systems.
371
A008
Zeolite Encapsulated Metal-Schiff Base Synthesis and Electrochemical Characterization
Complexes.
by F. Bedioui, L. Roue, J. Devynck and K.J. Balkus, Jr., Ecole Nationale Sup~rieure de Chimie de Paris, CNRS, Paris, France; University of Texas at Dallas, Richardson, Texas, USA Question by M. Baker, University of Guelph, Guelph, Ontario, Canada: I consider that the interpretation of your electrochemical data is incorrect. In the case of your modified electrodes containing silver, you claim the formation of molecular wires. The overwhelming conclusion with Ag+-zme's is that electron transfer occurs subsequent to ion exchange of Ag + with the electrolyte cation. That is, electron transfer occurs outside the zeolite pore system. My question is: in view of overwhelming evidence to the contrary you claim that the silver deposits extend into the zeolite pores. What proof do you have for this? Answer by F. Bedioui: The electrochemical reduction of zeolite Y exchanged with Ag + ions leads to the formation of silver particles on the external zeolite surface, since the electron transfer occurs subsequent to the ion exchange of Ag + with the electrolyte cations. Anyhow, some authors are claiming a migration of metallic silver clusters back to the zeolite pores, and there is no direct or clear evidence for the fact that the silver deposits extend into the pore system. Our interpretation of the large increase in the electroactivity of the Fe(III)salen encapsulated in Y supercages is based on the fact that, upon Ag + reduction, many new contact points are created between the zeolite and the electrode (electronic collector). Thus, the silver deposit will play the role of dispersed microelectrodes on the zeolite, and we will see the reduction of a larger amount of near surface Fe(III)salen complexes. In fact, we observed an enhancemem by 400 % of the electroactivity of the encapsulated complexes. Even if we do not have clear proof or evidence for the intrazeolite formation of silver particles, and since this idea is not completely ruled out in the literature, one should bear it in mind (without claiming the exclusive formation of intrazeolite molecular wires).
Question and comment by D.R. Rolison, Naval Research Laboratory, Washington, D.C., USA: 1) In the cobalt(II)(bpy)3-mediated system with Fe(III)salen-modified Y, the cyclic voltammogram at a potential of ca. -1 V could also be explained by additional cathodic current due to the reduction of molecular oxygen, rather than a Co(I)(bpy)3-mediated reduction of near-surface Fe(III)salen to Fe(II)salen. How did the voltammogram appear when it was reversed after re-oxidizing Co(I) to Co(II)? If the near-surface Fe-salen complexes are not re-oxidized and the extra cathodic current was due to the reduction of, e.g., oxygen, larger currents than ascribable to Co(II) reduction will flow. This should also be studied as a function of scan rate of the applied voltage. 2 ) You refer to the voltammetric
372 work on TS-1 (by de Castro-Martins et al.) as supporting the possibility of direct intracrystalline redox reactions. This seems premature, as an alternate explanation for their data exists. Answers by F. Bedioui: 1) The reduction of molecular oxygen in DMSO takes place at - 0.8 V and never appeared under our experimental conditions (argon atmosphere). The cyclic voltammogram of the adsorbed cobalt(II)(bpy)aY shows clearly the reversible redox process Co(II)/Co(I) at - 1.1 V, and it shows also that there is no reduction of molecular oxygen. Hence, the large cathodic current observed in the Co(II)(bpy)3-mediated system with Fe(III)salen-Y has to be attributed to the mediated reduction of Fe(III) to Fe(II) by the external Co(I)(bpy)3 complex: Co(II)(bpy)3 (external) + e- <
> Co(I)(bpy)3 (external)
Co(I)(bpy)3 (external) + Fe(III)salen (internal) >~ > Co(II)(bpy)3 (external) + Fe(II)salen (internal) whereupon the external Co(II)(bpy)3 is again reduced, and so on ............ Thus, we have a mediated (or catalytic) reduction of Fe(III) by Co(I) since E~ ~ - 1.1 V ~ E~ ~, - 0.3 V. Furthermore, it is obvious that no reoxidation of the Fe(II)salen by the external redox mediator can take place, on account of the differences in the potentials of the redox steps (v. s.). When the potential scan was reversed after reoxidizing Co(I) to Co(II), the cyclic voltammogram appeared very similar to the reversible one shown by Co(II)(bpy)3 adsorbed on zeolite Y, i.e., without any large cathodic current, since the Fe(III)salen near the surface was previously reduced to Fe(II) which was not reoxidized. 2) Our reference to the voltammetric work on TS-1 was meant to support the possibility of direct intracrystalline redox reactions and is based on results published by de Castro-Martins et al. To our knowledge, no alternate explanation for their data has been proposed in the literature. Therefore, the possibility of direct redox processes cannot be ruled out.
A009
Preparation, Characterization and Catalytic Properties of Cobalt Phthalocyanine Encapsulated in Zeolite EMT by S. Ernst, Y. Traa and U. Deeg, University of Stuttgart, Stuttgart, Germany
Question by P.A. Jacobs, Catholic University of Leuven, Heverlee, Belgium: The high ketone/alcohol ratios in the oxidation products of ethylbenzene with oxygen seems to point to a radical chain-type mechanism. Alternatively, it might be possible that, in the hypercages of EMT, dinuclear complexes of CoPc activate 02. Do the authors prefer or have evidence for one of these two possible mechanisms for 02 activation?
373
Answer by Y. Traa: At present, we do not have enough experimental data which would allow us to draw conclusions with respect to the type of reaction mechanism. Although clear differences in the catalytic behavior are observed for different cobalt phthalocyanine loadings of zeolite EMT, we cannot rule out a radical chain-type mechanism. So far, we have no evidence for the formation of dinuclear complexes in the hypercages of zeolite EMT.
Question by R. Patton, Catholic University of Leuven, Heverlee, Belgium: I also believe that a free-radical reaction takes place, hence my question is: what about the stability of your catalyst in a medium containing radicals? Answer by Y. Traa- The colour of the catalysts remains essentially unchanged during the reaction. Moreover, no degradation products of the complex were observed in the liquid reaction mixture. Therefore, we have no indication that the encapsulated cobalt phthalocyanine is destroyed during the catalytic experiment.
A023
Solid-State Dealumination of Zeolites by H.K. Beyer, G. Borb61y-P~ln6 and J. Wu, Central Research Institute of Chemistry, Hungarian Academy of Sciences, Budapest, Hungary; W.R. Grace & Co., Columbia, Maryland, USA
Question by G. Engelhardt, University of Stuttgart, Stuttgart, Germany: Zeolites with Si/AI = 1 are notoriously difficult to dealuminate by conventional methods. Do you think that solid-state dealumination is also applicable to such types of zeolites? Answer by H.K. Beyer: Yes, I think that solid-state dealumination is also applicable to zeolites with low Si/Al-ratios. Zeolite X with Si/AI = 1.25 could easily by dealuminated. Of course, the method cannot be applied to zeolite A, but the reason is that the pore diameter is not large enough to allow the penetration of the [SiF6]2- anion.
Question by D.H. Olson, Mobil Research and Development Corp., Princeton, New Jersey, USA: Is there any evidence for non-uniform aluminum removal using (NH4) 2 (SiF6)? Answer by H.K. Beyer: We do not have direct experimental proof for a uniform dealumination. However, the stoichiometric product inhibition observed, i.e., the occupancy of a structure-dependent number of sites per unit cell by [A1F4]', implies a uniform removal of aluminum.
374
Question by R. Roque Malherbe, Instituto de Tecnologia Quimica, CSIC-UPV, Valencia, Spain: Is it possible to induce dealumination by a tribochemical reaction under your conditions?
Answer by H.K. Beyer: The dealumination method described here is probably not induced by a tribochemical reaction. It proceeds only if the mixture is heated up to at least 120 ~ independent of the intensity of grinding.
C009
The Application of Ru-Exchanged Zeolite NaY in Ammonia Synthesis by J. Wellenbfischer, F. Rosowski, U. Klengler, M. Muhler, G. Ertl, U. Guntow and R. SchlSgl, Fritz Haber Institute of the Max Planck Society, Berlin, Germany; University of Frankfurt, Frankfurt am Main, Germany
Question by H. Miessner, Eniricerche S.p.A., San Donato Milanese, Italy: Did you compare the results you obtained with zeolite Y as support with those obtained on other supports, and why did you use a zeolitic support? Answer by M. Muhler: Ruthenium supported on activated carbon and promoted with cesium and barium is the most active catalyst for ammonia synthesis ever described in the literature. By using zeolite NaY we were able tO prepare a catalytic system with a narrow particle size distribution which is stable for long times and at high temperature. Thus it becam~ possible to study the structure sensitivity of ammonia synthesis on ruthenium and the effect of alkali promotion. Question by W.M.H. Sachtler, Northwestern University, Evanston, Illinois, USA: As dissociative adsorption of N 2 is supposed to be rate limiting on iron and ruthenium, Topsf~e et al. showed for iron that the turnover frequency is independent of crystal size if N 2 chemisorption is used to count the sites. Can you use N 2 chemisorption for your catalysts to express catalytic rates as remover frequencies? Answer by M. Muhler: Unfortunately, the dissociative adsorption of N 2 on ruthenium is highly activated. Therefore, it is not possible to use N2 chemisorption to determine the number of active sites.
Questions by E.S. Shpiro, N.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, Russia: 1) To prove your Conclusion on the structure sensitivity, you should extend your activity measurements to larger particles. Did you do this? 2) As many other authors, you showed drastic sintering of the particles after oxidation and re-reduction.
375
In other words, one great disadvantage of ruthenium catalysts remained, viz. the formation of very mobile and volatile ruthenium oxides. Could you comment on this? Answers by M. Muhler: 1) We are presently repeating these measurements. Upon re-reduction, the surface area is lower by a factor of about 5. However, the rate of ammonia synthesis decreases much less, yielding an increase of the turnover frequency. 2) I agree completely. It is not possible to use ruthenium catalysts under oxidizing conditions. Under the reducing conditions of ammonia synthesis, however, the Ru zeolite catalysts were found to be stable for long times and at high temperatures. Question of S.I. Woo, Korea Advanced Institute of Science and Technology, Taejon, Korea: When the particle size of transition metals is less than 1.3 nm, the suppression of chemisorption was observed previously. The decrease in turnover frequency in the case of the RuNaY catalyst might be due to the suppression of H 2 chemisorption. Did you measure the H 2 chemisorption on your samples of different Ru metal cluster sizes? Answer by M. Muhler: The Ru particle sizes which we determined by extrapolating the H 2 adsorption isotherms to zero pressure were in good agreement with the particle sizes observed by TEM. Please note that the Ru/NaY zeolite with the smallest Ru metal particles had the lowest catalytic activity.
C010
PtCo Bimetallic Particles in NaY between Morphology and Reactivity
Zeolite:
Correlation
by L. Guczi, G. Lu, Z. Zsoldos and Z. Kopp~iny, Institute of Isotopes of the Hungarian Academy of Sciences, Budapest, Hungary Question by M.M. Ramirez de Agudelo, 1NTEVEP S.A., Caracas, Venezuela: Co itself is a CO hydrogenation catalyst, have you compared the bimetallic catalysts with a monometallic cobalt catalyst? Answer by L. Guczi: When large bimetallic particles are present, such as in the case of bimetallic samples, the particles are more "metal-like", and metallic cobalt is the major active site modified by platinum. So, there is an enhanced C2+-formation, and practically no oxygenates are among the products. Upon decreasing the particle size, the interface between charged sites (e.g., protons) and metallic particles increases, which makes the cobalt convert to Co2+ and other oxidation states, and this influences the metal to form oxygenates. Question by J. van Hooff, Eindhoven University of Technology, Eindhoven, The Netherlands: The TPR experiments on your ion-exchanged samples show for the first reduction cycle one large peak at about 530 K which you ascribe to the formation of PtCo
376 alloy particles. However, upon re-oxidation, you observe two separate peaks, one for platinum at low temperature and one for cobalt at high temperature (not shown). The platinum peak, however, has only a very small size compared to the size of the PtCo peak suggesting that not all Pt has been oxidized under the re-oxidation conditions. Can you comment on this behavior? Answer by. L. Guczi: The smaller peak being responsible for Pt reduction after oxidation was surprising to us too. Using the results of model experiments on an unsupported PdCo system (A. Sarkany et al., J. Catal., submitted), the explanation is as follows (L. Guczi, Appl. Catal., submitted): in the reduced sample, Pt o occupies the outermost layer backed by Co ~ and Co 2+. As the sample is now oxidized using a 0.5 K/min ramp rate, cobalt oxide is segregated to the surface leaving a Pt o nucleus inside the particle. Since Co 2+ is then removed and migrates into the small cages, a Pt-fich and, ultimately, a platinum sample is left in the supercage, which cannot be fully oxidized, and only a surface layer is converted to Pt 2+. After repeated reduction, the hydrogen uptake is smaller than the one during the initial reduction.
Question by W.M.H. Saehtler, Northwestern University, Evanston, Illinois, USA: Reduction of ion-exchanged (and calcined) Co and Pt ions with H 2 leads to the formation of a stoichiometric quantity of protons (Co 2+ + pt2+ + 2 H 2 ---> Co ~ + Pt o + 4 H+). No protons are formed when impregnated nitrates (or oxides) are reduced. What is the effect of the protons on the catalytic performance of your catalyst? Do you find the same leaching which we found, e.g., for PdFe (PdFe + 2 H § --->Pd + Fe 2§ + H2)? Answer by L. Guezi: The effect of the protons is twofold. Firstly, after reduction, when bimetallic particles are formed, these are enriched in Pt, and the [PtH+]n adduct will stabilize the particles. The presence of protons can be noticed by the selectivity of the CO/H 2 reaction, when initially, the major product of the oxygenates is dimethylether. On the other hand, when the sample is oxidized for the second time, Co n+ is segregated to the surface leaving Pt as a nucleus, and due to this erosion, Co 2+ ions are eroded ~om the surface and leave the supercage. The effect mentioned by you for iron leaching cannot be excluded either, although it can take place to a smaller extent only, because of the electronegativity difference between iron and cobalt. Impregnated samples form significantly larger particles which possess a more "metallic" character, thus all these effects are not operative.
Questions by E.S. Shpiro, N.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, Russia: 1) What do you think about the correlation between activity and particle morphology? Do you expect different morphologies for particles located inside and outside of the zeolite? 2) After re-oxidation and, possibly, reaction, PtCo bimetallic
377 particles no longer exist. Which effect is responsible for different selectivities, a size effect or some others? Answers by L. Guezi: Primarily, morphology is dictated by the particle size and surface composition. The fact that in one case, bimetallic particles are inside the supercage and outside on the external surface further modifies the morphology. From the table, one can draw conclusions concerning not only the rate of reaction catalyzed by different samples, but also the selectivity. 2) As far as the re-oxidized samples are concerned, the change in composition is primarily operative here (e.g., the lack of a cobalt/oxide interface), whereas the particle size has only a marginal effect.
Question by J. Viilter, Institute of Applied Chemistry, Berlin, Germany: As discussed earlier, the TPR peak of Pt is considerably decreased upon re-oxidation. The reason could be that the re-oxidation within the supercages is restricted to Pt 2+. Do you agree? Answer by L. Guczi: Your explanation may be correct for the Pt nucleus covered by Pt 2+. At present, we do not have experimental facts for distinguishing between the two explanations. Question by S.I. Woo, Korea Advanced Institute of Science and Technology, Taejon, Korea: You concluded that, after re-oxidation of PtCo(IE) bimetallic clusters, the TPR spectrum does not show the reduction peaks assigned to Co 2+ or cobalt oxide and Pt 2+ or PtO x species. However, we have published that the TPR spectrum of Pt clusters prepared via ion exchange and reduction by H x after re-oxidation clearly shows the reduction peak. How do you explain this discrepancy? Answer by L. Guczi: The reduction peak characteristic of Pt reduction for the (IE) sample aider re-oxidation is indeed visible in our case too, the peak maximum being at 373 K. A second peak at about 870 K can be assigned to the reduction of the Co 2+ ions located in the hexagonal or sodalite cage. Thus, I cannot see any discrepancy between our results.
C011
Silver Agglomeration in SAPO-42 and Isostructural Zeolite A: EPR and ESEM Studies by J. Michalik, M. Zamadics, J. Sadlo and L. Kevan, Institute of Nuclear
Chemistry and Technology, Warsaw, Poland; University of Houston, Houston, Texas, USA Questions by G. Calzaferri, University of Bern, Bern, Switzerland: 1) Did you monitor the color change of your samples aider 7-irradiation? If yes, what did you observe? 2) We have found that C1- occluded in zeolite A strongly influences the photochemical oxygen evolution
378 and the electrochemical behavior of AgA zeolites. Did you investigate the influence of occluded CI" on the EPR signals (We have a paper on the photochemistry and electrochemistry coming out in J. Photochem. and Photobiol. A: Chemistry and a poster at IPS-10, July 24-29, 1994, Interlaken, Switzerland)? 3) Has the autoreduction hypothesis been testified by direct measurements of 02 evolution? Answers by J. Michalik: 1) Dehydrated silver A zeolites are very colorful. AglNaA is yellowish, while Ag6NaA is brick-red. The colors remain unchanged after )'-irradiation, however, diffuse reflectance spectra show for Ag6NaA the growth of absorption at 580 nm after irradiation. 2) For cation exchange we always used AgNO 3. But we will try to investigate the influence of CI" as suggested by you. 3) The silver autoreduction hypothesis is based only on the EPR results, namely on the fact that the Ag6n+ signal in dehydrated Ag6NaA zeolite is recorded directly atter ),-irradiation at 77 K.
C012
Chemistry and Spectroscopy of Chromium in Zeolites by B.M. Weckhuysen and R.A. Schoonheydt, Catholic University of Leuven,
Heverlee, Belgium Question by L. Guezi, Institute of Isotopes of the Hungarian Academy of Sciences, Budapest, Hungary: My question concerns the reducibility over Ga-AI. Ga is considered a porthole for hydrogen desorption in the dehydrogenation of n-paraffins. Could this be the explanation for the diminished reducibility, as on GaY there is a depleted hydrogen concentration available for reduction? Answer by B.M. Weckhuysen: In my opinion, this cannot explain our order of redox behavior, because we have done CO-reduction instead of H2-reduction. We interpreted the order of redox behavior in terms of hardness and softness: Ga is a harder atom than AI, thus structures containing Ga, like our Cr-GaY, are harder supports. The harder the support, the less susceptible it is for electron fluctuations which are necessary for reduction. In other words, the harder the support, the less reducible will be the chromium. This is the case for the Cr-GaY samples.
Question by B. Wichterlovfi, ~ Heyrovslcy, Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Prague, Czech Republic: You have shown that chromium exhibits an octahedral ligand field synmletry in your CrAPO and that it can be oxidized to Cr 5+ and Cr 6+. We observed a similar behavior for zeolite Y exchanged with chromium. With Cr 5+- and Cr6+-Y, chromium possessed firmly bonded extra-framework oxygen, which could be released by evacuation at distinct temperatures, thus following the process Cr 6+ -->
379 Cr 5+ ~ Cr 3+. Therefore, can one assume that your chromium is well dispersed on the aluminum phosphate material and not directly embedded in the framework sites?
Answer by B.M. Weckhuysen: Yes, our results indicate that Cr 3+, as an octahedral ion, is well dispersed in CrAPO-5 materials. Their redox behavior is similar to that of ionexchanged zeolites, i.e., formation of Cr6+ and Cr 5+. Both species can be envisaged as anchored species with two lattice oxygens and extra-lattice oxygens. Reduction with carbon monoxide results in the formation of Cr 3+ and some Cr 2§ Thus, in essence, the redox behavior of chromium is similar in inorganic oxides, whatever their composition, preparation method and structure. In each case, a reversible redox couple is observed which is useful for redox catalysis.
C013
CrAPO-Catalyzed Oxidations of Alkylaromatics and Alcohols with TBHP in the Liquid Phase (Redox Molecular Sieves, Part 8) by J.D. Chen, M.J. Haanepen, J.H.C van Hooff and R.A. Sheldon, Delft University of Technology, De~, The Netherlands; Eindhoven University of Technology, Eindhoven, The Netherlands
Question by M.H.W. Burgers, Delft University of Technology, Delft, The Netherlands: The AIPO4-framework has a high polarity, so added water may selectively adsorb on the surface. Therefore, it will have an influence on the adsorption of reactants and products. Did you measure the adsorption of the reactants in the presence of water, as you did in the absence of water?
Answer by J.D. Chen: No, the adsorption of the reactants in the presence of water was not measured, but this is a good suggestion.
Comment by E. Creyghton, Delft University of Technology, Delft, The Netherlands: In your conclusions you stated that there is Cr 3+ in a tetrahedral coordination in the lattice. In the introduction, you showed that you were starting with tetrahedral Cr 6+ which, after calcination, becomes octahedral Cr3+. In other words, there is no isomorphous substitution[ Answer by J.D. Chen: Yes, we provided evidence for chromium substitution for aluminum, but it might be non-isomorphous. In as-synthesized CrAPO-5 samples, Cr 3+ is sharing four oxygen atoms with phosphorus and coordinates with two H20 ligands, which corresponds to an octahedral coordination. After thermal outgassing up to 350 ~ to remove H20 only, we found that most of the chromium changed its coordination from octahedral to tetrahedral, which gave strong evidence for chromium substitution because extra-framework chromium
380 with tetrahedral coordination is very unlikely. Upon calcination, Cr 3+ becomes Cr 6+ with tetrahedral coordination.
Questions by R. Gliiser, University of Stuttgart, Stuttgart, Germany: 1) Could it be helpful to use oxidizing agents of different reactivities, e.g., H202 or 02, in order to learn more about the oxidation properties versus the enhanced acidic properties of the catalyst? 2) You just used TBPOOH with a fairly high reactivity. Did you look, for example, at the selectivities for by-products like styrene to evaluate the acidic properties of your materials? Answers by J.D. Chen" This is an interesting point. We were placing emphasis on the liquid phase oxidation. However, the use of CrAPOs as acidic catalysts might be possible as well. Some work along this line has been done by other groups showing that SAPOs and A1PO4s substituted by divalent elements are highly active catalysts for, e.g., a dehydration reaction. In spite of their weak acidity, CrAPOs will possibly be used as bifunctional catalysts in some particular cases. At this moment, we found that the oxidation properties of these materials are more interesting than their acidic properties.
Comment by B.M. Weckhuysen, Catholic University of Leuven, Heverlee, Belgium: Because DRS only takes into account the first coordination sphere around chromium, you have no evidence in support of your coordination model. In my opinion, oxidation of CrAPO-5 molecular sieves results in the formation of local defect sites with Cr 6+ surrounded by two framework and two extra-framework oxygen atoms. Answer by J.D. Chen: I agree with you that, after calcination, Cr6+ creates local defect sites. Therefore, Cr6+ is surrounded by two framework and two other extra-framework oxygen atoms. The locally isolated dioxochromium species are believed to be the stable catalytic sites, and this was supported by DRS and framework acidity measurements. We can also prove experimentally that one out of two phosphorus atoms not connected with chromium is terminal P-OH. Indeed, we assumed that the other neighboring phosphorus is present as ~ P=O; in view of the charge balance, this is not proven yet. As I pointed out, our model still has the features of an assumption, for which some evidence was provided but which needs further confirmation.
P030
Chemical H-Beta
Vapor
Deposition
of
Si(OEt)4
on
Zeolite
by Y. Chun, X. Chen, A.-Z. Yan and Q.-H. Xu, Nanjing University, Nanjing, People's Republic of China
381
Question by E. Unneberg, UniversityofOslo, Oslo, Norway: In Table 2 of your paper, you report a conversion of TMB's above 90 % in some experiments on H-beta. Approximately how much of the products were TMB isomers? If isomerization was the only reaction one would expect that the conversion cannot exceed the thermodynamic equilibrium value. Answer by Q.-H. Xu: The products of this reaction are not limited to isomers of" TMB, but some cracking products and other products are formed as well, especially at higher reaction temperatures.
IV. Diffusion and Adsorption
PL03
Exciting New Advances in Diffusion o f S o r b a t e s in Z e o l i t e s and Microporous M a t e r i a l s by L.V.C. Rees, University of Edinburgh, Edinburgh, UK
Question by J. Caro, Institute of Applied Chemistry, Berlin, Germany: We just witnessed fireworks of sophisticated methods and remarkable results. However, you gave me the feeling that we are still far away from reaching the ultimate goal, i.e., the direct observation of molecular mobilities in a multi-component mixture at catalytic temperatures during a catalytic conversion. Will this remain a task for molecular modelling or are there experimental methods in sight? Answer by L.V.C. Rees: I think that the measurement of individual mobilities of a multicomponent mixture at catalytic temperatures during a catalyzed reaction is not in sight. However, the frequency-response method can study mobilities and reaction rate constants at high temperatures. We are planning to attempt to extend the frequency-range to the kilohertz region, so with some luck we may be starting to get nearer your goal. Even modelling will find this a difficult problem to solve.
Question by W.M.H. Sachtler, Northwestern University, Evanston, Illinois, USA: Classical pore diffusion control is known to lower the apparent activation energy. In the case of single file diffusion we expect, and our data confirm this, that the apparent activation energy is
higher than the true ( i.e., chemical) activation energy, because product molecules that are formed deep inside the pores are trapped at low temperature but can escape at high temperatures (see B.T. Carvill, B.A. Lemer, B.J. Adelman, D.C. Tomczak and W.M.H. Sachtler, J. Catal. 144, 1993, 1; Z. Karpinski, S.N. Gandhi and W.M.H. Sachtler, J. Catal. 141, 1993, 337; G.-D. Lei and W.M.H. Sachtler, d. Catal. 140, 1993, 601; B.A. Lemer, B.T. Carvill and W.M.H. Sachtler, Catal. Letters 18, 1993, 227). Can you provide a general mathematical model for the apparent activation energy when catalysis is controlled by single file diffusion? Answer by L.V.C. Rees: My answer is no. As the temperature rises, the concentration of molecules decreases. For the single file diffusion case, this means that the product molecules have a greater chance to escape. The net result is an activation energy which may be larger
383 than that of the chemical reaction. Modelling of this situation is extremely difficult, and this problem has not been solved as far as I am aware.
C001
Simulation
of
Single
Pellet
Adsorption Kinetics E x p e r i m e n t a l l y D e t e r m i n e d D u s t y - G a s Coefficients
with
by R. Hartmann and A. Mersmann, Munich University of Technology,
Munich, Germany Question by J. Caro, Institute of Applied Chemistry, Berlin, Germany: In the dusty-gas model, the mass transport resistance originating from molecular diffusion is described by the product C2 9DI2, C 2 being a parameter and DIE the binary gas diffusivity. In my opinion, zeolitic diffusion cannot be described adequately in this simple way by a reduced gas phase diffusivity. Is this a general limitation of the dusty-gas model, and how do you handle zeolitic diffusion? Answer by R. Hartmann: In the paper presented here, only gas phase diffusion has been considered. The good agreement with the experimental results shows that zeolitic diffusion does not limit the overall kinetics in our specific case. However, zeolitic diffusion could be included in the simulation model as an additional mass transfer mechanism. The dusty-gas model is not restricted to gas phase transport in general.
C002
Separation of Permanent Clathrasil D D 3 R
Gases
on
the
All-Silica
8-Ring
by M.J. den Exter, J.C. Jansen and H. van Bekkum, Delft University of
Technology, Delft, The Netherlands Question by K. de Boer, Eindhoven University of Technology, Eindhoven, The
Netherlands: Do atomic parameters exist for the DD3R structure without the template? Answer by M.J. den Exter: At variance to my reply given orally aider my lecture, there are no data on the atomic positions after removal of the template. No single crystal structure analysis was done on the calcined sample. XRD analysis shows that the structure does not change (high temperature XRD up to 800 ~ does not give evidence for changes). There is a subtle difference between the spectrum of the as-synthesized and the calcined crystals: the 19-hedron cage (with the 8-membered ring) becomes ca. 0.5 % longer and 0.5 % thinner (the c- and a-direction, respectively).
384
Questions by K. Unger, University of Mainz, Maim, Germany: 1) Did you use seed crystals to synthesize DD3R (the application of adamantane is not an economical process)? 2) What is the degree of pore filling in your adsorption experiments (equilibrium conditions)? The degree of pore filling is defined as the actual pore volume filled divided by the theoretically calculated pore volume. Answers by M.J. den Exter: 1) No seed crystals were used to synthesize DD3R. The reason is that we need a synthesis procedure for "in-situ growth" of the material (for preparation of a molecular sieve membrane) on macroporous supports. Seeding under such conditions would bring about non-reproducibility in the preparation of membranes. One has to start from a clear solution. 2) The 19-hedron cage has a volume of 0.350 nm 3. This accounts for approximately 8 CO2 molecules at 25 ~ and 1 bar. An average filling of 2 CO2 molecules per cage is reached, so ca. one fourth of the theoretically calculated pore volume is occupied.
C003
Zeolite Filled Pervaporation
Membranes
for
Gas
Separation
and
by J.P. Boom, D. Bargeman and H. Strathmann, University of Twente, Enschede, The Netherlands Question by J. Caro, Institute of Applied Chemistry, Berlin, Germany: You discussed your results in terms of a resistance model. However, with zeolite concentrations above 30 vol.-% in the polymer, direct mass transport between the zeolite crystals could more and more contribute to the flux density. My question is, therefore, whether it would be justified to describe the permeation process by a superposition of a resistance and a percolation model? Answer by J.P. Boom: No, if direct mass transport between crystals played a role, the molecules would hop from particle to particle without passing the rubber phase. This could only take place if the pores at the surface of the particles were perfectly connected. Taking into account the random distribution of the particles in the membrane, this appears unlikely.
Question by A. Erdem-Senatalar, Istanbul University of Technology, Istanbul, Turkey: In the solution-diffusion mechanism, the zeolite crystals in the polymeric membrane matrix are acting as a reservoir, increasing the concentration profile for one of the components across the membrane, as a result of their selective sorption properties. Hence, permeability increases with adsorption as well as diffusion. Could you please comment on the possibility of adsorption by the zeolite being too strong so that desorption may not take place readily? Answer by J.P. Boom: In the case of permeation of n-hexane through polymers filled with silicalite-1, we have observed a decrease in flux only. This was explained by the strong
385 adsorption of n-hexane on the zeolite. In this case, the zeolite acts as an inpermeable particle.
Question by J.M. van de Graaf, Delft University of Technology, Delft, The Netherlands: In the paper, only single component permeation measurements of ethane and ethylene through a zeolite filled EPDM membrane are described. You derive an ideal selectivity from these data. Why didn't you do a binary permeation experiment in order to measure the real selectivity? Do you think the real and ideal selectivities compare well? Answer by J.P. Boom: The reason we didn't do permeation experiments with gas mixtures is that it was not possible to analyze the mixtures on-line with the available equipment. However, Duval showed that, for CO2/CH 4 mixtures, the selectivity is equal to the one obtained with the pure gases. Since the concentrations in the present study are comparable to those in Duval's investigations, I expect that the real selectivity is more or less equal to the ideal selectivity.
Question by. J. Klirger, University of Leipzig, Leipzig, Germany: Incorporating zeolite crystallites into a polymeric membrane will probably lead to the formation of additional transport resistances on the outer surface of the crystallites ("surface barriers"). Could you please comment on this possibility and on the consequences for the separation efficiency. Are you considering to trace such surface resistances? Answer by J.P. Boom: The additional resistance is probably present. Evidence for such resistances can be obtained by incorporating one and the same zeolite into various rubbers and comparing the permeabilities. It appears that the calculated zeolite permeability increases with increasing overall permeability.
Question by M. Matsukata, University of Osaka, Osaka, Japan: Have you investigated the effect of the crystal size of the zeolite on the flux and/or the selectivity? Answer by. J.P. Boom: In the case of pervaporation of ethanol/water mixtures by means of zeolite filled membranes based on silicone rubber, no difference could be observed in selectivity and flux for 0.3 ~tm and 3.0 ~tm zeolite particles.
C004
Potentials of Silicalite Membranes Alcohol/Water Mixtures
for
the
Separation
of
by T. Sano, M. Hasegawa, Y. Kawakami, Y. Kiyozumi, H. Yanagishita, D. Kitamoto and F. Mizukami, Japan Advanced Institute of Science and
Technology, Ishikawa, Japan; National Institute of Materials and Chemical Research, Ibaraki, Japan
386
Comment by J.P. Boom, University of Twente, Enschede, The Netherlands: The separation factor you obtain is around 50 for a mixture of 5 vol.-% ethanol in water. If you extrapolate the results of te Hennepe et al., who incorporated silicalite in rubber membranes, to a volume fraction of 1, then you fred a value of 60 which is similar to your result. Answer by T. Sano: I am aware of the results of te Hennepe et al. who found that the performance of a silicon rubber membrane is considerably improved by the addition of silicalite crystals. Based on their results, we investigated the liquid separation potential of pure zeolite membranes. As mentioned in our paper, there are small pores with a size of about 1 nm originating from the silicalite crystals, these pores being larger than the intrinsic zeolitic pores. More work is necessary to elucidate the detailed mechanism of pervaporation through our membrane. Question by J. Caro, Institute of Applied Chemistry, Berlin, Germany: Your method consists of crystallizing a thin silicalite layer onto mesoporous ceramics or a stainless steel support. The same method has been applied by H. van Bekkum and J.C. Jansen at Delft University of Technology, The Netherlands. Are there differences between both methods? Who was first?
Answer by T. Sano: Pure zeolite membranes consisting of polycrystalline films were prepared simultaneously and for the first time by W.O. Haag, Mobil Research and Development Corp., and myself. There is no difference between our method and the method of the Delft group.
C005
Preparation of a Thin Zeolitic M e m b r a n e by M. Matsukata, N. Nishiyama and K. Ueyama, University of Osaka,
Osaka, Japan Question by H. van Bekkum, Delft University of Technology, Delft, The Netherlands: Regarding your interesting results it may be noted that the alumina surface will be reactive under the conditions applied and might partly dissolve. Do you expect this to have a bearing on the porosity of the interface? Answer by M. Matsukata: In agreement with what you pointed out, we qualitatively observed dissolution of the alumina surface. The dissolved alumina was largely incorporated into the zeolite layer. The porosity of the parent surface was ca. 50 %, and it might change with alumina dissolution and zeolitization. The porosity of the interface was difficult to determine, but we presume on the basis of SEM observations, that the change of the porosity was not so serious.
387
Comment by J. Caro, Institute of Applied Chemistry, Berlin, Germany: The preparation technique, i.e., conversion of the dry gel into a zeolite layer is an original and good idea. However, I am not fully convinced that, upon calcination, your membrane is free from cracks. The permeabilities as a function of the square root of the reciprocal molecular weight follow a straight line indicating that mass transport is controlled by a Knudsen mechanism rather than by intrazeolitic diffusion. Could you please comment on this? Answer by M. Matsukata: Only hydrogen and helium permeated through the membrane following a Knudsen mechanism. Both molecules are considered to have almost no interaction with the zeolite surface. By contrast, other gases did not follow a Knudsen mechanism, and their permeation was facilitated to some extent. These results indicate that gases which interact with the zeolite surface permeate via a surface diffusion mechanism. Thus we believe that the membrane was fairly compact. However, the possibility that there exist micro-cracks with dimensions in the order of 1 to 5 nm cannot be ruled out. We are now planning further work with the aim to identify such micro-cracks, if they are present. Question by T. Cheetham, University of California, Santa Barbara, California, USA: How did you determine the Si/AI ratios from the 29Si NMR spectra of the ZSM-5 and ferrierite samples, both of which have multiple T-sites? Answer by M. Matsukata: We did not observe distinct multiple T-sites for the samples used in the present study. However, we checked the SIO2/A1203 ratios determined from the 29Si NMR spectra by chemical analysis in some cases. Question by C.G. Coe, Air Products & Chemicals, lnc., Allentown, Pennsylvania, USA: Does the vapor phase synthesis for conversion of dry aluminosilicate gels allow one to expand the range of Si/Al-ratios possible for known topologies? Answer by M. Matsukata: It seems to be difficult to synthesize MFI with an SiO2/AI203ratio smaller than ca. 20. I believe that there is a similar limit for the range of the SiO2/Al203-ratio as in the conventional hydrothermal synthesis.
B015
Sorption and Sorption Kinetics of Pyridine in H - Z S M - 5 and H-Mordenite by W. Niessen and H.G. Karge, Fritz Haber Institute of the Max Planck Society, Berlin, Germany
Question by M. Kocirik, J. Heyrovsk: Institute of Physical Chemistry, Prague, Czech Republic: I noted that most of the uptake curves are S-shaped. Therefore, I do not expect that a pure intracrystalline diffusion would explain the kinetics. In our opinion, the equation
388 of diffusion should be solved with a radial boundary condition to get proper values of the diffusion coefficients. Can you comment on this? Answer by W. Niessen: The particular shape of the uptake curves is due to the fact that there is a time-lag between the injection of the adsorbate into the carrier gas stream and the build-up of a steady state concentration on the external surface. Moreover, the initial part of the curve is affected by a superimposition of increasing concentration of the adsorbate in the intercrystalline space and the onset of the intracrystalline sorption. This is indeed accounted for by a time-dependent function of the surface concentration (cf. Ref. [6]). The validity of this approach was checked and confirmed by measurements of, e.g., diffusion of benzene in H-ZSM-5 by our FTIR method. The results were in excellent agreement with those of independent techniques such as NMR tracing, barometric sorption, frequency response and the zero length column technique (cf. Ref. [8]).
Question by E. Unneberg, University of Oslo, Oslo, Norway: In your lecture, you showed that the diffusivities of pyridine followed the order D (silicalite) >D (H-ZSM-5) >D (HMOR) in the experimental temperature region. Do you think that the reason for the slow diffusion of pyridine in H-MOR (compared to H-ZSM-5) is only the fact that H-MOR has one-dimensional pores (as you pointed out), or will it also be partly because the Si/Al-ratio in your H-ZSM-5 was 5 times larger than the Si/Al-ratio in your H-MOR? Answer by W. Niessen: I completely agree with your suggestion. We did not ascribe the lower diffusivity of pyridine in hydrogen mordenite solely to the fact that this zeolite has a one-dimensional pore system compared to the two-dimensional pore structure of the MFItype samples. Indeed, as is suggested by the comparison of silicalite and H-ZSM-5, the density of the Bronsted acid sites plays an important role too. The higher density of these sites in H-mordenite compared to H-ZSM-5 will increase the number of strong contacts of the migrating pyridine molecule with the walls of the channel and, thus, the average residence time per unit length.
B016
The Measurement of Diffusion Jetloop Recycle Reactor
and
Adsorption
Using
a
by I~P. Miiller and C.T. O'Connor, University of Cape Town, Rondebosch,
South Africa Question by J. Kiirger, University of Leipzig, Leipzig, Germany: It is probably a disadvantage of your method that the correlation between the intracrystalline diffusion and the experimentally accessible data must be based on a model involving a series of parameters. Did you consider enhancing the reliability of your results by varying the
389 experimental conditions (adsorption/desorption, particle size, two-component diffusion) in order to obtain experimental dependencies which may be compared with the theoretically expected trends? Answer by K. M~iller: This method is limited to pellets only, and thus it will always be controlled by a number of resistances in series. A pulse experiment includes both adsorption and desorption phenomena, i.e., it yields an average diffusivity. It is, in principle, possible to do adsorption and desorption steps separately to confirm the pulse results. It would also be interesting to change the carrier gas to argon or helium and to confirm the results obtained. Using the jetloop in conjunction with a mass spectrometer, it would, in principle, be possible to measure multi-component diffusion in catalyst pellets at low concentrations.
Question by D. Kallr, Central Research Institute of Chemistry, Hungarian Academy of Sciences, Budapest, Hungary: Did you vary the pellet size in order to estimate the rate of macropore diffusion? In this way, the accuracy of the corresponding calculations could have been controlled. Answer by K. Miiller: The pellet size was not varied. A particle size of 0.5 mm was already near the lower limit. To use larger pellets, it would have been necessary to get larger pellets and then crush them down, thus maintaining the same crystal size. It is only in this way that the effect of pellet size can be tested. Larger pellets with the same crystal size were not available. For the current results, the effect of pellet size would only be important at the low temperatures (high Kc).
B017
Separation of Cyclohexane from 2,2Pentanes by Adsorption in Silicalite
and
2,4-Dimethyl
by C.L. Cavalcante, Jr. and D.M. Ruthven, University of New Brunswick, Fredericton, New Brunswick, Canada Question by D. Kallr, Central Research Institute of Chemistry, Hungarian Academy of Sciences, Budapest, Hungary: Are the kinetic separation factors reliable since they are defined using values determined for pure components. It has been shown in paper B015 by Niessen and Karge as well as in the present paper that the adsorption coverage and other factors may influence diffusivities. Answer by D.M. Ruthven: Single component experiments can only provide an indication of what might be possible. Further experiments with binary and ternary feed mixtures would obviously be needed before an informed decision can be made on the feasibility of this type of process.
390
Question by C.T. O'Connor, University of Cape Town, Rondebosch, South Africa: Could you comment on the role which membrane technology using zeolites (e.g., work at Delft University of Technology) may play in the future in the separation of various streams in the petrochemical industry? Answer by D.M. Ruthven: I am sure you know this has been a hot topic for research during the last few years - not only for separations per se but also in relation to membrane reactor systems, in which the products of reaction are continuously separated in order to drive the reaction. Operation at reactor temperatures requires a thermally stable (inorganic) membrane, and the membranes produced by the DelR group are obvious candidates for this kind of application. The major problem at present is that, although selectivities are high, the permeabilities, even at elevated temperatures, are relatively low. For an economic process, a very thin membrane is therefore required, and this poses serious problems of mechanical strength etc. Nevertheless, this seems to be a very promising direction for research, and I would not be surprised to see the commercial development of zeolite membrane separations within the next decade.
B023
D E X A F S Studies on the Diffusion of A m m o n i a into Zeolite CuNaY by M. Hagelstein, U. Hatje, H. FSrster, T. Ressler and W. Metz, European Synchrotron Radiation Facility, Grenoble, France; University of Hamburg, Hamburg, Germany
Question by A. Zikainovfi, J. Heyrovslc: Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Prague, Czech Republic: You have measured the uptake curves for the plate pressed from individual zeolite crystals of a dimension of about 1 ~tm. The thickness of the plate was about 200 ~tm. Under these experimental conditions, the overall transport process may be influenced by at least two additional processes, in addition to intracrystalline diffusion. These are intercrystalline mass transport and the release of heat. Did you analyse the influence of these two processes from the shape of the uptake curves? Answer by M. Hagelstein: We are aware of the additional processes of intercrystalline diffusion and heat release. The results obtained with our new technique DEXAFS are not yet reliable enough to take these processes into account. We could calculate an effective diffusion coefficient into the zeolite pellet only. Further experiments should allow separation of the different processes.
391
B024
FTIR Microscopy with Polarized Radiation for the Analysis of Adsorption Processes in Molecular Sieves by F. Schiith, D. Demuth and S. Kallus, University of Mainz, Mainz,
Germany Question by J. Caro, Institute of Applied Chemistry, BeNin, Germany: I highly appreciate the new method you introduced into zeolite science. Can you please comment on three future fields of application which would require very high resolution in space and time: 1) orientation of protonated reactants and products at active sites, 2) pathways of molecules during their sorption uptake in anisotropic pore systems, and 3) identification of sorption sites and guest orientation at sorption equilibrium? Answer by F. Schiith: I think all three kinds of experiments are possible: 1) we are just building a reaction cell which, as we hope, allows the identification of the orientation of intermediates. 2) Provided we have large single crystals with anisotropic pore systems, it should be possible to analyze the uptake with polarized radiation and even to get elements of the diffusion tensor. 3) Such experiments have already been performed as demonstrated for p-xylene attached to the OH-groups of SAPO-5.
Comment by J.P. Coulomb, C.R.M.C., CNRS, Marseille, France: May I suggest that you measure a methane sorption isotherm at T = 77.3 K to characterize your sample. As a matter of fact, methane sorbed in AIPO4-5 undergoes a phase transition which is, in our opinion, a fine probe of the quality of the AIPO4-5 internal surface. Answer by F. Schfith: This is a good suggestion. However, even a less sophisticated probe like nitrogen sorption gives you already a fairly good assessment of the crystal quality. Questions by E. Roduner, University of Zurich, Zurich, Switzerland: 1) You suggest that melting of the adsorbate occurs in the channels. From a look at your spectra it seems to me that this is not a sharp phase transition but rather a more continuous process which extends over a certain temperature range. Can you comment on this? 2) Did you also observe "melting" in other systems? Answers by F. Schiith: 1) We think that there is a distribution of dipole chains with different lengths in the channels, leading to different strengths of H-bonds. The "melting" is thus observed over a relatively broad temperature range between ca. 100 ~ and 250 ~ 2) We did not study other systems in that respect.
392
B038
Investigation
of Hydrogen
and
Deuterium
Spillover
on
Y Zeolites b y F T - I R M i c r o s c o p y - Rate Determining Steps by U. Roland, R. Salzer and S. Stolle, Dresden University of Technology,
Dresden, Germany
Question by N.E. Bogdanchikova, Boreskov Institute of Catalysis, Novosibirsk, Russia: Do you have experimental data or, if not, can you speculate on the influence of the platinum particle size on the hydrogen and deuterium spillover? Answer by U. Roland: To study the spillover phenomenon under different experimental conditions (presence or absence of platinum, loading pressure, CO preadsorption, magnetic field) we tried to carry out our experiments using a model catalyst with well def'med properties. Our samples were either platinum-free, or they contained 0.5 wt.-% platinum with a cluster size of 1 to 2 nm. Thus, a standard spillover source was employed in all our experiments. It is well known from the literature, however, that very small clusters consisting of a few atoms only are not active for the formation of spilt-over species. This may be due to the necessity of hydrogen and deuterium dissociation for the formation of activated species. On the other hand, the activity of metallic platinum (e.g., platinum wire or platinum black) was shown for many reactions in which spillover is known to be involved, such as bronze formation, reduction of oxides or hydrogenation reactions. We did not try to optimize the platinum activity by changing the cluster size, but we plan to investigate the role of charge transfer for spillover activation which is expected to depend strongly on the cluster size. Questions by A.C.M. van den Broelc, Eindhoven Un&ersity of Technology, Eindhoven,
The Netherlands: H o w did you calculatethe amount of hydrogen or deuterium which can be adsorbed on the platinum (H:Pt)? So my questions are: I) how did you determine the size of your platinum particles?2) What was your assumption concerning the (maximum) number of hydrogen atoms per platinum atom? Answers by U. Roland: Let me first state that all platinum containing samples were prepared by ion exchange with an aqueous solution of [Pt(NH3)4]C12 leading to a platinum content of 0.5 wt.-%. The answers to your questions are as follows: 1) the samples were activated by treatments in oxygen and hydrogen at 450 ~ as described in the literature. The resulting clusters were estimated to be 1 to 2 nm in size (cf., e.g., N.I. Jaeger et al., Stud. Surf Sci. Catal. 49, 1989, 1005). We did not vary the cluster size because we tried to use a model catalyst prepared under identical conditions for all spillover experiments. As discussed below, the interpretation of our results (e.g., the nature of the species forming the deuterium reservoir) is independent of the platinum cluster size. 2) For the characterization of the deuterium reservoir formed after exposure of the platinum containing zeolite to
393 deuterium at room temperature, the deuterium adsorbed on platinum has to be taken into account. We could exclude the possibility that the reservoir consisted of such species only, because the amount of deuterium which could be adsorbed on platinum was too low to account for the observed H-D exchange atter pumping off and sealing the samples. For this estimation, we used the upper limit of deuterium (or hydrogen) adsorption on platinum, viz. one deuterium (or hydrogen) atom per platinum atom. Additionally, we assumed that all platinum atoms were surface atoms. As stated here and in another paper published recently (U. Roland et al., J. Chem. Soc., Faraday Trans. 87, 1991, 3921), the reservoir consists of spilt-over species adsorbed on the zeolite support (cf. U. Roland, H.G. Karge and H. Winkler, paper No. P074 at this Conference).
Question by W.O. Haag, Mobil Research and Development Corp., Princeton, New Jersey, USA: Do you have any information on the possible role of residual water on the rate of deuterium exchange and the nature of the spilt-over hydrogen? Answer by U. Roland: We very carefully tried to exclude residual water by activating the sample at 450 ~ and purifying the deuterium and hydrogen applied for gas loading. Nevertheless, some water is expected to remain adsorbed on the walls of the vacuum system. We would have been able to detect traces of water in the zeolite by IR spectroscopy, but in none of the samples discussed here was water found. The influence of different H20 and D20 concentrations on the H-D exchange was not investigated because we could not exclude another pathway for the deuteration of the OH groups: it is well known that, in the presence of heavy water (possibly formed by a D2/H20 reaction on Pt), the hydroxyl groups are rapidly deuterated. The nature of the spilt-over hydrogen and deuterium species has been a matter of debate for more than 30 years, and H atoms, H ions (H + and H-), ion pairs and H a species have been envisaged. We have shown that the diffusion of the activated hydrogen and deuterium species is hindered by a magnetic field perpendicular to the direction of diffusion from P t ~ a Y to HNaY (see U. Roland et al., J. Chem. Soc., Faraday Trans. 87, 1991, 3921). Hence, the spilt-over species are likely to be electrically charged. We believe that these species are surface electron donors, i.e., their nature is best described as coexisting H atoms and H + ions. Their relative concentrations depend on the electronic parameters of the adsorbate-zeolite system according to Fermi-Dirac statistics.
Questions by M. Hunger, University of Stuttgart, Stuttgart, Germany: 1) How was the deuterium exchange rate determined? 2) What was the difference in the exchange rates of the so-called high-frequency and low-frequency bands? Answers by U. Roland: 1) The DRIFT spectra of the samples placed in quartz tubes were transformed according to the Kubelka-Munk function. Non-adsorbing KBr in an identical quartz tube was used as a reference. The degree of H-D exchange (A) was estimated by
394 A = area of the OD bands/(area of the OH bands + area of the OD bands). The method was found to be correct in an exchange experiment with a one-component PtAtNaY sample. Upon admission of D 2, the H-D exchange was monitored, and the sum of the areas of the OH and OD bands (after the Kubelka-Munk transformation) was found to be constant within the experimental accuracy (ca. 5 %). Thus, the extinction coefficients for an OH band and the corresponding OD band seem to be equal. They were found to be independent of the degree of H-D exchange. We furthermore observed that the extinction coefficients for the hf and If bands are nearly equal, because the ratio of the areas (ca. 1 : 1) observed for the nondeuterated HNaY zeolite coincided with the density ratio determined for the same zeolite by, e.g., NMR. Therefore, we concluded that the ratio A represents the degree of H-D exchange. 2) The degrees of exchange for the hf and If bands were estimated after exposure of the onecomponent Pt/HNaY sample and the HNaY component of the Pt/NaY-HNaY sample to deuterium. Especially in the latter case, a measurable exchange could be observed only for the hf band during the first hours. Therefore, a quantitative evaluation of the exchange rates was not possible during this period, especially for the If band. For both samples, the initial exchange rates for the hf bands were considerably higher. After some weeks, the isotopic equilibrium had been established, and the ratio of the degrees of exchange (hf:lf) was then around 2 (ca. 5 % accuracy) for both samples. The higher exchange rates for the hf bands may be due to preferred diffusion paths. According to the adsorption model for the spiltover species based on the Wolkenstein isotherm (cs Th. Braunschweig et al., Stud. Surf. Sci. Catal. 77, 1993, 183), the concentration of the adsorbed activated species depends on the electronic properties of the adsorption sites. Thus, the adsorption energy of the spilt-over species is expected to differ for the different zeolitic framework sites. Independent evidence for different diffusion paths was obtained from the influence of a homogeneous magnetic field on the rate of diffusion of the spilt-over species (R. Salzer et al., Vibr. Spectroscopy 1, 1991, 363): The formation of the hf OD bands was more strongly hindered by the magnetic field. This could be due to different jump frequencies for the diffusion paths (see U. Roland et al., J. Chem. Soc., Faraday Trans. 87, 1991, 3921).
Question by L. Kevan, University of Houston, Houston, Texas, USA: Can you measure a rate difference between diffusion of the H species versus the D species and so determine the mass of the diffusing species? Answer by U. Roland: There are several difficulties associated with the determination of the mass of the diffusing species, namely the complexity of the exchange process including spillover, the difficulties in observing the spilt-over species directly and in determining their concentrations, and the necessity to know all other kinetic parameters or to calibrate the diffusion process, in order to calculate the absolute mass. Using IR microscopy, we are only able to observe the formation of OD/OH groups as a result of the presence of spilt-over
395 deuterium/hydrogen species. Their concentration cannot be determined directly. Thus, the difference in the exchange rates stems from a mass dependent factor (diffusion coefficient) and mass independent factors (e.g., activation energies of diffusion). To obtain the mass ratio of deuterium and hydrogen spilt-over species from the exchange rates requires the assumption that the exchange rate is a known function of the mass. In the simplest case, the formation of OD groups can be assumed to be proportional to the concentration of spilt-over species (at least immediately after deuterium admission) which would have to be determined by solving the diffusion equation for the two-component sample. However, a lot of experimental data on the exchange process taking place over several weeks would be required to fit the obtained model equation. Of course, no conclusions on the nature of the spilt-over species could be drawn from their mass ratio: it is expected to be 2, regardless of whether they consist of H/D atoms, H+/D+ ions, ion pairs or H3/D 3 species.
P074
Hydrogen and Deuterium Adsorption on Zeolite Supported Platinum. Evidence for Hydrogen and Deuterium Spillover by U. Roland, H.G. Karge and H. Winkler, Dresden University of Technology, Dresden, Germany; Fritz Haber Institute of the Max Planck Society, Berlin, Germany; Universityof Leipzig, Leipzig, Germany
Question by L. Kubelkovfi, Jr. Heyrovsl~ Institute of Physical Chemistry, Prague, Czech Republic: Can you make a suggestion as to the zeolite which is able to trap spilt-over (or activated) hydrogen?
Answer by U. Roland: The question of which adsorption sites are necessary for the diffusion of spilt-over species has not been fully clarified. With the exception of carbon supports, hydrogen and deuterium spillover has only been observed for oxygen-containing supports (metal oxides, silica, zeolites). Thus, oxygen may play an important role as an adsorption site for the spilt-over species. In the case of our adsorption studies on platinumcontaining zeolites we obtained H/O and D/O ratios of about 0.023. Some authors (e.g., Cavallos-Candau et al.; J. Catal. 106, 1987, 378) observed, by carrying out H-D exchange experiments, that the associated OH groups were deuterated with a significantly higher rate. They concluded that the diffusion of the spilt-over deuterium species occurs via the hydroxyl groups. However, the origin of this experimental result may also be a lower activation energy for the H-D exchange for the associated hydroxyls in comparison with the isolated OH groups. Therefore, the role of the zeolitic hydroxyls as trapping sites for the spilt-over species is still unclear. We can only assume that the oxygen bridges in the zeolitic framework are adsorption sites for the spilt-over species. The electronic interaction between the spilt-over species, which act as electron donors, and the zeolite is delocalized, i.e., the
396 adsorbed spilt-over deuterium and hydrogen species cannot be considered as additional OD and OH groups, respectively.
397
V.
PL07
Catalysis
Zeolites in Environmental Catalysis by M. Iwamoto, Hokkaido University, Sapporo, Japan
Questions by J.N. Armor, Air Products and Chemicals, lnc., Allentown, Pennsylvania, USA: 1) When you first reported your work with CuZSM-5 for 2 NO --->N 2 + 02, there was a stress on "over-exchanged" copper ions. For NO decomposition, what do you believe the active state of copper is: Cu 2+, CuOH +, CuO, Cu20? 2) If there is "excess" copper present, does precipitated copper oxide have a role in the catalysis, or is only ion-exchanged copper the active form?
Answers by M. lwamoto: 1) We believe that Cu + ions are the active sites for the decomposition of NO. The Cu + ions could be produced through the dehydroxylation of Cu(OH) § ions exchanged into the channels, 2 Cu(OH) § --->2 Cu § + H20 + 890 2. The nearby two Cu § ions would be active for the decomposition. 2) For the selective reduction of NO by hydrocarbons, copper oxide and copper ions would both be active. In this case, too high an activity for the oxidation of hydrocarbons results in the useless consumption of reductants; therefore, too much loading of copper is not good for the selective reduction.
Question by G. Moretti, Universith "La Sapienza", Rome, Italy: In the case of NO decomposition, it is now established that for CuZSM-5 catalysts with a degree of copper exchange above 90 % the activity increases with the aluminum content of the parent ZSM-5 zeolite (G. Moretti, Catal. Lett., in press). What is the effect of the Si/Al-ratio in the case of NO x lean bum reduction over CuZSM-5 catalysts? Answer by M. Iwamoto: We have used several kinds of zeolites with various Si/Al-ratios as catalysts. On the basis of our preliminary data, we wish to suggest that in the selective reduction of NO the activity would be dependent not on the Si/Al-ratio but on the amount of copper loaded if the structures of the zeolites used are the same.
Question by W.M.H. Sachtler, Northwestern University, Evanston, Illinois, USA: The lifetime of CuZSM-5 and CoZSM-5 catalysts in actual exhaust emission gases with a large excess of HzO over NO is very short. What is, in your opinion, the prevailing cause of deactivation? Answer by M. Iwamoto: We think that there are two reasons for the deactivation of metal ion exchanged zeolites such as CuZSM-5 and CoZSM-5 in the presence of excess water.
398 The first cause is the dealumination of the zeolite lattice and the resultant migration of exchanged metal ions to form metal or metal oxide particles. The second cause is the change of position of a metal ion from the catalytically active site to an inert but more stable site during the reaction at high temperature. These problems are common in catalysis over zeolites. Very recently, Osaka Gas Co. and Air Products and Chemicals, Inc. have independently reported that CoZSM-5 zeolites are very stable even in the presence of excess water and they could have success in using them in actual exhausts from gas engines. In addition, Mazda Motor Co. has claimed that Pt-loaded metallosilicates are active for the reduction of NO in the emission of lean-bum gasoline engines. I believe there could exist a possible way to use zeolites as practical catalysts.
Questions by E.S. Shpiro, N.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, Russia: 1) Can you comment on the resistance of CuZSM-5 and PtZSM-5 to SO2? 2) Do you believe that Bronsted acid sites play a significant role in the reaction mechanism for SCR of NOx? Answers by M. lwamoto: 1) CuZSM-5 has low resistance to SO2. The catalytic activity decreases in the presence of SO2 at all temperatures. In contrast, the activity of PtZSM-5 changes little upon the introduction of SO 2. PtZSM-5 would be one of the candidates for practical catalysts. 2) I believe indeed that acid sites play a significant role in the reduction of NO by hydrocarbons. In fact, there are several suggestions that the acid sites are active for the activation of hydrocarbons or NO, though their detailed role remains unclear.
A015
Adipic Acid Synthesis via Oxidation of Cyclohexene Zeolite Occluded Manganese Diimine Complexes
over
by P.P. Knops-Gerrits, F. Thibault-Starzyk and P.A. Jacobs, Catholic University of Leuven, Heverlee, Belgium Question by P. Gallezot, lnstitut de Recherches sur la Catalyse, CNRS, Villeurbanne, France: In your experiments, compounds with asymmetric carbon atoms are formed, such as 1,2-cyclohexanediol. Have you measured any optical activity in the oxidation products formed on the cis-bipyridyl manganese complex? Answer by P.P. Knops-Gerrits: No, not yet.
Question by W.F. Hiilderich, R WTH Aachen, University of Technology, Aachen, Germany: Congratulations, this is a nice piece of work. However, can you tell us whether the homogeneous part of your catalyst is attacked by the adipic acid? Do you find leaching of that part? What is the lifetime of this catalyst system?
399
Answer by P.P. Knops-Gerrits: If sufficient solvent is used to meet the solubility requirements of adipic acid, no significant leaching of the cis-manganese-bis-bipyridyl is observed. After reaction and drying of the catalyst at 320 K, a catalyst with the same initial activity can be re-obtained. After five catalytic cycles of 100 hours, no changes in catalytic activity and spectroscopic properties (FT-IR, FT-Raman, DRS) could be detected. These spectra of the catalyst, before and after catalytic operation, have been published previously. Question by J.C. Vedrine, lnstitut de Recherches sur la Catalyse, CNRS, Villeurbanne, France: I was surprised that the ESR spectrum of the Mn 2+ complex in NaY zeolite was hardly resolved. Could it be that it is so well restricted in motion? In such a case, catalytic activity should be low (the more immobilized the complex, the less room for reactants). Could it be that the complex forms oxygenates outside the zeolite? What happens if you deposit the complex on the zeolite rather than synthesizing it inside, and what are the repercussions for catalysis and the ESR spectrum? Answer by P.P. Kaops-Gerrits: Our signals of the manganese bipyridyl complexes with bis-bpy coordination show asymmetric coordination. The dipolar broadening of the hyperfine structure is a result of the high concentration of the complex (1 per supercage). In part, Dowsing et al. (R.D. Dowsing, J.F. Gibson, D.M.L. Goodgame, M. Goodgame and P.J. Hayward, Nature 219, 1968, 1037-1038) have shown that, for such manganese bisdiimine complexes, it is difficult to predict cis- or trans-arrangement from the EPR parameters.
A016
Oxidation of Cyclohexanone and Cyclohexane Acid by Iron-Phthalocyanine on Zeolite Y
to
Adipic
by F. Thibault-Starzyk, R.F. Parton and P.A. Jacobs, Catholic University of Leuven, Heverlee, Belgium Question by H. van Bekkum, Delft University of Technology, Delft, The Netherlands: A recent Leuven thesis (I. Vankelecom) mentions the use of ship-in-the-bottle systems, such as FePc in zeolite Y embedded in a polymeric membrane. Could you comment on any advantages of such a composite catalyst in oxidation reactions? Answer by F. Thibault-Starzyk: The issue mentioned has now been accepted as a letter to Nature. Such a catalytic membrane is a true high-order mimic of Cytochrome P 450. It allows the performance of oxidations in the absence of a solvent by mixing the apolar substrate and the polar oxidant. The apolar dense membrane further regulates the concentration of the reactants near the active complexes, thus enhancing the catalytic activity very much.
400
Question by W.F. H~ilderich, R WTH Aachen, University of Technology, Aachen, Germany: You obtained 80 % conversion of cyclohexanone and 30 % selectivity for adipic acid after roughly 30 000 min (ca. 20 days). Do you think this can be improved? Can you comment on the TON? I look at this from a more technical point of view. Answer by F. Thibault-Starzyk: Our system opens a new way for the production of adipic acid, and we paid particular attention to reach high turnovers, thus allowing us to use a very small amount of catalyst. Further studies will surely lead to an improved reaction time. This involves examining the influence of the support, the polarity of which plays a key role in the reaction chain. TONs are in the same range as those observed with the same catalyst in the oxidation of cyclohexane to cyclohexanone. The Used catalyst was employed, after washing, in a second reaction, with no sign of deactivation.
Question by G.E. Parris, Air Products and Chemicals, Inc., Allentown, Pennsylvania, USA: In host/guest facilitated catalytic reactions, the loading of the catalyst, e.g., with iron phthalocyanine, affects the connectivity of the cavities. Could this be a reason for the slow desorption of adipic acid, and what are the results for lower catalyst loadings? Answer by F. Thibault-Starzyk: The loading of the material with phthalocyanine is so low (less than 1 per 5 supercages) that the slow desorption of polar products cannot be caused by the phthalocyanine complexes themselves.
Question by G. Schulz-Eldoff, University of Bremen, Bremen, Germany: It has been stated that the polarity of the zeolite host affects the mobility of reactant and product molecules and, hence, the performance of the catalyst. Is it possible to apply dealuminated (hydrothermal, isomorphously substituted) faujasite hosts? Answer by F. Thibault-Starzyk: Dealuminated faujasite hosts (provided they have still enough anchoring points) will be more hydrophobic and thus influence the retention of polar molecules in the zeolite. However, with respect to molecules such as adipic acid, the dealuminated FAU framework is still highly "hydrophilic".
A017
The Effect of Zeolitic Textural Properties on the Catalytic Activity in Hydrocarbons Oxidation by F. Cavani, G. Giordano, M. Pedatella and F. Trifir6, University of Bologna, Bologna, ltaly; University of Calabria, Arcavacata di Rende, Italy
Comment and question by H. van Bekkum, Delft University of Technology, Delft, The Netherlands: 1) Other oxidative dehydrogenations over MFI include methanol-toformaldehyde, ethanol-to-acetaldehyde and ethanol/ammonia to pyridines. 2) Regarding the
401 observed deactivation, I would like to ask whether water could be added in order to retard coke formation? Answers by F. Trifir6: 1) We have also observed the formation of formaldehyde in the oxidation of methanol on MFI zeolites. 2) The oxydehydrogenation reactions and the formation of tars can both be explained by a radical mechanism. We introduced 10 % H20 and we observed a small decrease in activity but not a reduction of tar formation.
Question by C. Naccache, Institut de Recherches sur la Catalyse, CNRS, Villeurbanne, France: The aromatization of alkanes and alkenes over acid catalysts is known to be enhanced with increasing temperature. Could you exclude in your examples for the enhancement of aromatic yield in the presence of oxygen a thermal effect brought about by combustion reactions which would result in an increase of the effective reaction temperature? Answer by F. Trifir6: The phenomena observed cannot be explained by local overheating for the following reasons: (i) upon introducing oxygen, we observed the same effects at very high (1:10) dilution of the zeolite with inerts; (ii) the introduction of oxygen does not only bring about increased yields of aromatics, but also of tars; (iii) the increase in yield to aromatics was observed at low temperature, viz. 280 ~ At this temperature, no formation of CO2 was observed (one would expect that the occurrence of over-temperatures is mainly associated with the formation of CO2); (iv) the increased yields of aromatics were also observed at higher temperatures (350 ~ with very low oxygen concentrations. However, at high temperatures where the yield of aromatics strongly decreases and large amounts of CO x begin to form, overheating effects surely can be present.
Question by J.B. Nagy, Facultrs Universitaires Notre-Dame de la Paix, Namur, Belgium: Did you analyze the distribution of products formed in the butane reaction with and without oxygen? Are these distributions similar or different under the two conditions? Answer by F. Trifir6: We have found the same distribution of products in the first minutes after addition of oxygen which we had found in its absence. These findings may suggest that also in the absence of oxygen the aromatization mechanism is radical-like. Question by G. Tel'biz, Institute of Physical Chemistry, Academy of Sciences of Ukraine, Kiev, Ukraine: Your data were collected in the presence of molecular oxygen only. Would you expect differences with other oxidants, for example with N20? Answer by F. Trifir6" We have not done experiments with N20, but this is a good suggestion to discriminate between a radical chain mechanism and redox reactions on metal impurities.
402
A018
Selective Hydrogenation of Cinnamaldehyde Controlled by Host/Guest Interactions in Beta Zeolite by P. Gallezot, B. Blanc, D. Barthomeuf and M.I. Pa'is da Silva, lnstitut de Recherches sur la Catalyse, CNRS, Villeurbanne, France; Universit6 Pierre et Marie Curie, CNRS, Paris, France
Questions by E. Creyghton, Delft University of Technology, Delft, The Netherlands: 1) My first question concerns the highly dispersed Pt~a-beta catalyst. You proposed the existence of both channel filling clusters and very small clusters in the same catalyst. If this were true, I would expect to see a particle size distribution in TEM, even if the smallest particles are invisible. Did you observe such a distribution? 2) Referring to Figure 3a in your paper, I would like to come back to the mechanism you propose for selective hydrogenation. Couldn't the lower selectivity observed on the catalyst with the high platinum dispersion be explained by entrance of the cinnamaldehyde molecule from a direction perpendicular to the direction you envisaged, thus leaving enough space for adsorption of both double bonds? Note that the channel intersections are quite spacious (> 1 nm). Answers by P. Gallezot: 1) It is already a great technical achievement to detect particles smaller than 1 nm inside zeolite pores, you should not expect us to measure a size distribution! 2) There is a high probability for the cluster to fill the intersection between two perpendicular pores so that a molecule will experience a tip-on adsorption, whatever the pore in which it diffuses. Questions by W.F. Hiilderich, R WTH Aachen, Un&ersity of Technology, Aachen, Germany: 1) Pierre, you showed us nicely how the selective hydrogenation of the aldehyde group in the neighborhood of a double bond can be managed by steric constraints caused by the cluster-loaded zeolites. Is that a general recipe or is that only possible in the case of cinnamaldehyde having a bulky phenyl group? 2) Concerning conversion, selectivity and lifetime, what about your results in comparison to the work done by Donna Blackmond in the presence of alkali-containing (e.g., potassium) Ru-, Pt- or Rh-catalysts? Answers by P. Gallezot: Molecular constraints and, thus, selectivity depend upon the relative size and structure of the zeolite pores and of the organic molecule. Cinnamaldehyde on zeolites Y or beta are well adapted to each other in that respect. Smaller molecules in the same zeolites do not experience the same constraints and are not hydrogenated selectively. 2) In our joint paper with Donna Blackmond (Jr. Catal. 131, 1991, 401-411)we stressed that steric effects are first order effects with respect to selectivity. When there are no steric constraints, electronic or bimetallic effects (polarization of the C=O bond by an electropositive second metal) may come into play.
403
Questions by P.A. Jacobs, Catholic University ofLeuven, Heverlee, Belgium: 1) Given the requirements of the catalyst in this reaction which you arrive at in your conclusions, would Pd/beta not be a good case to prove further and confirm these conclusions? 2) You explain the effects by geometric factors, although it is known (cf. your own earlier work, now theoretically confirmed by van Santen et al.) that such clusters on a very acidic support are electron-deficient. Could you exclude completely the electronic factor in rationalizing your results? Answers by P. Gallezot: 1) Similar effects with Pd/beta would indeed bring further evidence because palladium hydrogenates C=C bonds with a great selectivity. Any change would indicate that C=C bond hydrogenation is hindered when palladium clusters fill the pores. 2) Electronic effects could indeed play a role in this reaction. We have shown that selectivity increases on "electron-rich" metal particles (Ru, Pt). This is why we have also tried in this investigation to render the zeolite more basic by ion exchange with Cs +. However, steric effects are always predominant in this case. Question by H.G. Karge, Fritz Haber Institute of the Max Planck Society, Berlin, Germany: Dr. Gallezot, your preparation Pt/Na-beta (II), in particular, exhibited very small metal aggregates in the electron micrograph (Figure 1a of your paper). Most likeley, another fraction has sizes below the detection limit of TEM. Do you think that, during the reaction, particle growth may occur at the expense of those very small species leading to an increasing yield with increasing conversion (time on reaction)? Answer by P. Gallezot: This is correct. The sintering of the smaller clusters is proved by the higher selectivity to unsaturated alcohol with time and by the recycling experiment showing that the initial selectivity in the second run is similar to the final selectivity at the end of the first run.
Question by J.B. Nagy, Facultrs Universitaires Notre-Dame de la Paix, Namur, Belgium: Did you study the nature of the adsorbed complexes on the small platinum particles and on the bigger ones formed by sintering during the reaction? IR or 13C NMR could be used, for example. Answer by P. Gallezot: In-situ characterization, i.e., under reaction conditions in the presence of a solvent and under hydrogen pressure is not possible. Ex-situ characterization under static conditions far from the reaction conditions usually leads to false interpretation (cracked species, spectator species ...... ). Question by F. Schmidt, Siid-Chemie A G, Bruckmiihl, Germany: What is the reason for the different particle size of platinum in zeolites beta and Y?
404
Answer by P. Gallezot: This is a good question. To give a clear answer would require a systematic study of all factors which could be considered.
Question by T. Uematsu, Chiba University, Chiba, Japan: You have explained the regioselective hydrogenation in terms of (i) host/guest interaction with the wall favoring end-on adsorption of the substrate and (ii) small clusters in the cage controlling the conformation. In our studies of regioselective hydrogenation of geraniol on multiply modified hectorite (Pd complex + alkylamine RN+), the "tuning guest" RN + controls the orientation with the cooperation of Pd-OH-interaction. What do you think about such an idea of applying a "tuning guest", for example a basic organic amine, the role of which is to activate the aldehyde and to control its orientation? Answer by P. Gallezot: This is an interesting idea. Indeed, any factor (e.g., a surface ligand) favoring the orientation and approach of the molecule should modify the selectivity.
Question by J. Weitkamp, University of Stuttgart, Stuttgart, Germany: Upon reduction of the noble metal, Bronsted acid sites are inevitably formed. Do these acid sites interfere in the catalysis, e.g., do they bring about undesired double bond shift reactions if a substrate with one more carbon atom in the side chain is used? Answer by P. Gallezot: The reaction temperature being low (60 ~ there is a small chance for isomerization reactions catalyzed by acid sites. Furthermore, we have checked that reexchanging the zeolite after reduction with alkali cations (Na +, Cs +) does not change the results.
A019
Benzoylation of Xylenes Using Zeolitic Catalysts by R. Fang, H.W. Kouwenhoven and R. Prins, Swiss Federal Institute of
Technology Zurich, Zurich, Switzerland Comment by H. van Bekkum, Delft University of Technology, Delft, The Netherlands: The formation of 2,6-dimethylbenzophenone seems sterically rather hindered. Another option for the side product might be 3,5-dimethylbenzophenone. Answer by H.W. Kouwenhoven: We assumed that 2,6-dimethylbenzophenone was the by-product, but we did not verify this.
Question by M.H.W. Burgers, Delft University of Technology, Delft, The Netherlands: The dealumination of the zeolite may be related to the presence of benzoic acid in the solution, formed via hydrolysis of the acid chloride. Did you observe the presence of the acid in the solution?
405
Answer by H.W. Kouwenhoven: It was indeed checked whether benzoic acid was present in the solution, and it was found that its concentration was lower than 0.2 %. We therefore assume that HC1 was the dealuminating agent.
Question by P.-S. E. Dai, Texaco Research and Development, Port Arthur, Texas, USA: You showed the effect of mesoporosity on the activity of acylation. Could you please comment on the effect of porosity on the selectivities to 2,4- and 2,6-dimethylbenzophenone? Answer by H.W. Kouwenhoven: No effect of mesoporosity on the selectivities to 2,4- and 2,6-dimethylbenzophenone was found. Question by R. Hoppe, University of Bremen, Bremen, Germany: I would appreciate it if you could provide some information concerning extra-framework aluminum based on NMR data. Likewise, I am interested in whether you have observed your Si/Al-ratio by 29Si NMR. Answer by H.W. Kouwenhoven: 27A1 MAS NMR data for the samples 2YH and 3YH indicated that both tetra- and hexa-coordinated aluminum was present, and in addition a peak at 35 ppm was observed. Acid extraction (sample 3YI-I --> sample 3YHA) removed the latter peak and almost all hexa-coordinated AI. The 29Si MAS NMR data were not accurate enough to calculate the Si/Al-ratio. A measure of the Si/Al-ratio may, however, be derived from the XRD data. Questions by D. Kall6, Central Research Institute of Chemistry of the Hungarian Academy of Sciences, Budapest, Hungary: 1) What is the mechanism of this typically acid catalyzed reaction? 2) Axe zeolitic pores or the surface of mesopores involved in the catalytic conversion? The catalytic activity seems to increase upon increasing the mesopore surface. Answers by H.W. Kouwenhoven: 1) The acylating agent is presumably an acylium ion adsorbed on the catalyst. 2) The large effect of surface area outside zeolitic pores on catalyst activity and the finding that the number of acid zeolitic sites had no positive effect on the catalytic activity indeed suggest that the acidic sites in the zeolitic pores are less effective in this reaction.
A020
A l k y l a t i o n o f Aniline with M e t h a n o l on Z e o l i t e s E x c h a n g e d w i t h A l k a l i n e Cations
Beta
and
EMT
by P.R.H. Prasad Rao, P. Massiani and D. Barthomeuf, Universit~ Pierre et Marie Curie, CNRS, Paris, France
406
Questions by D.B. Akolekar, The University of New South Wales, Sydney, Australia: 1) Can you comment on the positions of the cations (Li +) in the materials prepared by liquid and solid-state ion exchange? 2) Are the materials prepared by solid-state ion exchange from the hydrated and dehydrated form of the zeolite the same or do they differ? Answer by D. Barthomeuf: We don't have any information on cation positions other than Na + in beta or EMT after ion exchange in liquid medium and the solid state.
Question by J. Fraissard, Universitd Pierre et Marie Curie, CNRS, Paris, France: The exchange of cations between two solids is possible in the presence or absence of water. In the case of non-complete exchange, it seems that the cation distribution in the crystallites depends on the initial water concentration in the zeolite. Do you have some details about the initial sample? Answer by D. Barthomeuf: We used hydrated samples taken from the bench. As stated in the paper, not much information is available on the ion location in beta and EMT whether hydrated or not. Our main purpose was to compare the two exchange procedures. We were not expecting information on the ion distribution in each of the two materials.
Question by M. Remy, Catholic University of Leuven, Louvain-la-Neuve, Belgium: You have observed that the aging of your catalysts depends on the cations they contain. You have explained this observation by the fact that the cations you have studied differ in basicity. However, these cations also differ in size. Do you think that the size of the cation incorporated in your zeolites can influence their deactivation? Answer by D. Barthomeuf: At first, alkaline cations are Lewis acids. They are not basic. We say that the aging is due to the increased basicity of the framework oxygen when the cations are exchanged from Li + to Na +, then K +, then Rb +, then Cs +. We don't think that the cation size influences aging. Results recently obtained in this laboratory with alkylating agents other than methanol show that the nature of this alkylating agent determines the aging, and not the size of the cations. Question by G. Tel'biz, Institute of Physical Chemistry, Academy of Sciences of Ukraine, Kiev, Ukraine: Are there differences in the cation positions in EMT and beta zeolites prepared by ion exchange in the solid state or in liquid solution? Answer by D. Barthomeuf: For beta and EMT, not much information is available on the location of the various cations. From the conversion and selectivity data in catalysis we can suggest that there should not be much difference in the cation locations resulting from one method of exchange or the other.
407
Comments by B. Wiehterlovfi, J. Heyrovsl~ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Prague, Czech Republic: 1) It surprises me that, during ion exchange in solution, leaching of aluminum from zeolite beta took place. On the other hand, this could explain the higher activity of the zeolite treated in this way compared to the zeolite which was exchanged in the solid state. 2) The solid-state ion exchange strongly depends on the atmosphere in which it occurs. The presence of water vapor enhances the process. Answers by D. Barthomeuf: 1) As stated in the paper, the removal of aluminum may be related to the presence of aluminum at defect sites in zeolite beta. These sites would be unstable under liquid exchange conditions. This might explain the higher activity of the LS samples compared to the SS ones, as you suggest. 2) We did not study the solid-state ion exchange in dehydrated beta and EMT. Therefore, we don't know if the enhancing effect of water vapor exists in these two structures too.
Question by S.I. Woo, Korea Advanced Institute of Science and Technology, Taejon, Korea: What is the catalyst lifetime in view of a potential commercial application? I think that, in the alkylation of aniline with methanol, methanol must be activated by acid sites, the aromatic ring must be activated by acid sites to get ring alkylation, and basic sites are needed to activate the N-H bond in aniline. Can you propose a mode of aniline activation by basic sites? If so, what is the structure of the basic sites; alkali ions or oxygen anions? Answer by D. Barthomeuf: Alkali ions are Lewis acids. The basic sites are framework oxygens. Aniline may be adsorbed in the 12-membered ring window, the CH interacting with framework oxygen. This was shown to occur by neutron diffraction studies (see H. Fuess et al., Zeolites). The NH 2 group which is rather basic should not be activated much by basic sites.
A021
Solvent Effects in Liquid Phase Friedel-Crafts Alkylation over Zeolites: Control of Reaction Rate and Selectivity by Adsorption by P.H.J. Espeel, K.A. Vercruysse, M. Debaerdemaker and P.A. Jacobs, Catholic University of Leuven, Heverlee, Belgium
Question by H. van Bekkum, Delft University of Technology, Delft, The Netherlands: The dicyclohexylphenols seem rather bulky. Did you check that they can adsorb on and desorb from zeolites Y and beta? They might be formed at the external crystal surface. Answer by P.A. Jaeobs: The message of the paper is related to the cyclohexylation reaction of substituted arenes. Formation of dicyclohexylphenols is a secondary reaction, the yield of
408 which will, to a certain extent, be dependent on the void space of the zeolite used. For the present discussion it is not relevant whether such bulky Secondary products are formed at the external surface of the zeolite or in the intracrystalline space. It was meant to show that, by solvent effects, the reaction rate and selectivity of the primary alkylation reaction in the absence of any steric constraint can still influence intracrystalline Friedel-Crafts catalysis.
Comments by D. Kallr, Central Research Institute of Chemistry of the Hungarian Academy of Sciences, Budapest, Hungary: 1) In terms of Langrnuir-Hinshelwood kinetics, the reaction between surface species adsorbed on similar sites should be considered. 2) Diffusion hindrance can be disregarded when an increase of the revolution number does not result in an increase of the reaction rate any more. Answers by P.A. Jaeobs: 1) As stated in the experimental section, the reactions are carried out in a well stirred batch-type reactor. The stirring rate in this reactor (800-1000 rpm) is always far beyond the minimum stirring rate required for operation free of film diffusion. 2) The results show that the rate and selectivity changes can be easily rationalized by competitive sorption. Site heterogeneity in terms of Hougen-Watson-LangrnuirHinshelwood kinetics is not invoked in any stage of the rationalization process.
Question by M.S. Rigutto, Delft University of Technology, Delft, The Netherlands: It seems that your model allows for the extraction of true intrinsic rate constants for this second order reaction. This would allow one to quantify solvent effects inside the pore, if present. Did you try this? Answer by P.A. Jacobs: The rate constants determined in the present work are first order rate constants and only indicate how fast the reacting solution moves towards equilibrium conversion under the influence of the heterogeneous catalyst, irrespective of the exact molecular mechanism in the zeolite pores. It was attempted to show that competitive sorption between reactants and solvents is a major parameter to rationalize so-called solvent effects.
A022
13C M A S N M R H-ZSM-5
and Related Studies of C o k e F o r m a t i o n
on
by H.G. Karge, H. Darmstadt, A. Gutsze, H.-M. Vieth and G. Buntkowsky, Fritz Haber Institute of the Max Planck Society, Berlin,
Germany," Free University of Berlin, Berlin, Germany Question by F. Bauer, University of Leipzig, Leipzig, Germany: You have clearly shown the influence of reaction temperature and zeolite acidity on the nature of coke species and
409 the deactivation rate. But the crystallite sizes of your samples are quite different. I assume that larger crystallites will produce higher amounts of alkylaromatic coke and exhibit higher deactivation rates (as H-ZSM-5(1) really shows). Would you agree with that? Answer by H. Darmstadt: I completely agree, even though with the materials used it is difficult to discriminate between the effect of acidity (density and strength) on the one hand and crystallite sizes on the other. As pointed out, the higher density of active Bronsted sites in H-ZSM-5(1) should favor the reaction between smaller adsorbed molecules and result in the formation of bulkier species (alkylaromatics, polycyclic aromatics) whereas the higher acidity strength of sites in H-ZSM-5(2) would tend to stabilize the polyenylic carbocations. However, the difference in the particle sizes between H-ZSM-5(1), viz. 8.8 x 5.2 x 3.2 gm, and H-ZSM-5(2), viz. about 0.4 gm, would act in the same direction: the longer diffusion pathways of species out of the larger particles of H-ZSM-5(1) will most probably facilitate polymerisation, cyclization and condensation of coke precursors which would lead to deposition of bulkier species. In fact, in the methanol-to-gasoline reaction a significantly higher rate of coke deposition and deactivation was observed with H-ZSM-5(1), in full agreement with your assumption.
Question by G. Engelhardt, University of Stuttgart, Stuttgart, Germany: If you have radicals in your samples, considerable line broadening may appear in the spectra. Did you find some indications of it? Answer by H. Darmstadt: Radicals were indeed formed and detected upon reaction of either methanol or ethene over the H-ZSM-5 samples used (el. response to J.B. Nagy). However, no particular attention was paid to the effect of line broadening of the 13C MAS NMR spectra which may indeed be caused by the presence of radicals. Question by J. Fraissard, Universitd Pierre et Marie Curie, CNRS, Paris, France: It has been proven that during cracking reactions the first species of coke are in strong interaction with non-framework aluminum (A1)~. As your samples contain a large concentration of (AI)~, I would like to know if you tried to detect such interactions, for example by 27A1 NMR. Answer by H. Darmstadt: We did not look for an interaction between coke species and extra-framework A1 by 27A1 MAS NMR. However, IR spectroscopy revealed an intense interaction of olefinic species and Bronsted sites (acidic OH groups related to the framework A1). Combined IR and GC investigations using an IR-flow-reactor cell showed that (in the case of ethene reaction over mordenite) no coke formation occurred if all of the acidic OH groups were removed even though large fractions of non-framework A1 were present (to be published).
410
Question by A.O.I. Krause, Helsinki University of Technology, Helsinki, Finland: You showed 13C MAS NMR results of coked catalysts as a function of temperature. Did you observe any changes in the spectra as a function of time at a constant temperature? Answer by H. Darmstadt: The effect of time was not investigated by 13C MAS NMR. Thermogravimetric experiments combined with GC measurements showed, however, that at a constant temperature the coke lost hydrogen, i.e., the H/C-ratio decreased. Thus, extended heating causes "ageing" of the coke (el. Ref. [1]). Ageing of the coke at a constant temperature with increasing time of reaction was also observed by UV/VIS spectroscopy (cf. Ref. [81).
Question by J.B. Nagy, Facult~s Universitaires Notre-Dame de la Paix, Namur, Belgium: Did you observe, in addition to earbenium ions, cation radicals which also could be true intermediates in the coke formation? Answer by H. Darmstadt: Indeed, radicals of earboeations have been identified by ESR (publication in preparation) similar to results in earlier work on coke formation upon reaction of ethene over hydrogen mordenites (J. Catal. 114, 1988, 136-143). Indeed, it may well be that they also act as intermediates in coke formation. Question by H. Schulz, University ofKarlsruhe, Karlsruhe, Germany: I enjoy the reported measurements and the obtained data about chemisorbed, deposited or entrapped species, however, I feel there is a lack in relating these to the kinetic regimes and mechanisms of their formation. In particular, I want to ask, how you distinguish between species or deposits within the pore system and those on the surface of the erystallites which is a dominant question in reactions on H-ZSM-5 zeolite. Answer by H. Darmstadt: Since the 13C MAS NMR and UV-VIS spectroscopic results reported in this presentation were obtained from static measurements, it is not possible to derive from these data any information about the kinetics. Also, they do not provide information about the location of the coke. However, from adsorption experiments with uncoked and coked samples (not yet published) it appears that the low-temperature coke species were preferentially located inside the pores whereas the bulkier high-temperature coke species were frequently deposited on the external surface. Question by A. Zecchina, University of Turin, Turin, Italy: When CH-CH interacts with H-ZSM-5 Bronsted sites at room temperature, ~CH=CH2, aCH=CH-CH=CH2 etc. species are formed which are characterized by well defined peaks in the UV-VIS spectrum. Did the frequencies attributed to monoenyl and dienyl carbocations compare with those previously mentioned? The species formed upon CH-CH dosage, although written in the ionic form, have largely covalent structure, e.g.,
411
Si Si AI >OH + CH=CH ---> AI >O-CH=CH2 ....... Are the monoenyl and dienyl species fully ionic? Answer by H. Darmstadt: The wavelengths of the bands around 300 and 360-370 nm, which we ascribe to enylic carbocations, agree well with those reported in the literature for such species (cf. T.S. Sorenson, in "Carbonium lons", Vol. II, G.A. Olah and P. von R. Schleyer, Eds., Wiley-Interscience, New York, 1970, p. 870; G.A. Olah, C.U. Pittman and M.C.R. Symons, "Carbonium lons", Vol. I, loc. tit., p. 153). We indeed assume that these species are largely ionic in character.
B021
Correlation of Adsorption Zeolite Catalyzed Amination
Structure
and
Reactivity
in
by A. Kogelbauer, Ch. Griindling and J.A. Lercher, University of Twente,
Enschede, The Netherlands
Questions by J.N. Armor, Air Products and Chemicals, lnc., Allentown, Pennsylvania, USA: Can you be specific about the source of your mordenite: 1) Was the H-mordenite made from Na-mordenite? 2) Did you look for extra-lattice aluminum before and after reaction for each of your catalysts? (You seem to assume that the A1 form is the same in all catalysts, is it?) Answers by J.A. Lercher: 1) The mordenite samples were obtained from the Japanese Catalysis Society. The Si/A1 ratio was determined by 29Si MAS NMR to be 5 and 10, respectively. HMOR and NaMOR were from one batch. 2) The concentration of extra-lattice material was below the detection limit for both samples, before and after use (checked by NH 3 adsorption and one set of 29Si MAS NMR experiments).
Question by K. Segawa, Sophia University, Tokyo, Japan: How can the selectivity differences between NaMOR and HMOR be accounted for in terms of your model? Answer by J.A. Lereher: In our opinion, the difference in selectivities between HMOR and NaMOR is due to different transition states. With HMOR, the ammonium ion or protonated methylamines react with weakly physisorbed methanol. Over NaMOR, ammonia is inserted into the carbon-oxygen bond of surface bound methanol. This is sterically rather difficult for methylamines. Thus, monomethylamine will be preferentially formed. On HMOR, the insertion of the methyl group into the protonated and surface bound amines is more facile, leading to a mixture of methylamines in the zeolite pores.
412 A035
Structure, Cu-ZSM-5
Chemistry and Activity of Well-Defined Catalysts in the Selective Reduction o f N O x
by E.S. Shpiro, R.W. Joyner, W. Griinert, N.W. Hayes, M.R.H. Siddiqui and G.N. Baeva, University of Liverpool, Liverpool, UK Question by J.N. Armor, Air Products and Chemicals, Inc., Allentown, Pennsylvania, USA" It is important to understand why CuZSM-5 is active for NO x. Recent work from Southwest Research Institute indicates that CuZSM-5 is not stable for long term periods with real engine exhausts. The presence of large levels of water is thought to be the reason for the irreversible catalyst decay. In characterizing CuZSM-5, you must also look at the effect of water on the catalyst. It would be useful to understand why water vapor irreversibly kills the catalyst. Have you studied the impact of catalysts aged in the presence of water? Answer by E.S. Shpiro: I think I have tried to answer the first part of your question in my talk. The specific property of CuZSM-5 is that two types of dispersed copper species are stabilized inside the channels: Cu-O-Cu clusters and isolated copper cations, both functioning as active sites for selective catalytic reduction (SCR) of NOx. CuY or Cumordenite conventionally exchanged contain mostly isolated ions, and they are less active. In addition, Cu 1+ and Cu 2+ species in ZSM-5 have a specific low symmetry, and they can be readily and reversibly reduced and oxidized which is in line with our reaction mechanism. I also think that the rate of deactivation by water will depend on the ratio between type I, type II and type III sites. The more sites of type III there are, the more severe poisoning by water will be. As far as I know, CuZSM-5 is more tolerant to water than most other copper catalysts. Possibly, in the case you were referring to, the CuZSM-5 sample contained a significant portion of sites II and III (clusters and aggregates) and was therefore poisoned by water so severely. Up to now, we have only briefly looked at this problem. When we studied the interaction of CuZSM-5 with water at 400 ~ we were quite surprised to observe large crystals of metallic copper which possibly originate from splitting of water or the reaction with residual CO, hydrocarbons etc. This might happen even under lean NO x conditions where there are many reductants. It is known that long term deactivation occurs by steaming, and copper agglomeration rather than zeolite destruction is responsible for this. We are now going to study poisoning by water in detail, and I am confident that we do have tools for its elucidation.
Question by G. Moretti, Universit~ La Sapienza, Rome, Italy: In your chemical state plot for copper it appears that small copper clusters have an Auger parameter (AP) value which is by ca. 3 eV lower than the one of bulk Cu ~ We know that small Cu ~ clusters entrapped in zeolite A have an AP value which is by ca. 3 eV higher than bulk Cu ~ (see G. Moretti, Zeolites, in press). Do you have an explanation for these two very different results?
413 Answer by E.S. Shpiro: Yes, the copper Auger parameter for small Cu ~ clusters in zeolite ZSM-5 is 3 to 4 eV lower than the one for bulk copper metal. This is in full agreement with literature data (see, e.g., M. Gautier, J.P. Durand and L. Pham Van, Surf Sci. 249, 1991, L327-L332) which show the same trend, viz. a decrease of the kinetic energy CuL3VV and ct'-Cu for thin films (small clusters) approaching the bulk values for larger particles. This is a general trend for all metals (see M.O. Mason, Phys. Rev. B 27, 1983, 748-762). In our case, the metallic clusters were also characterized by EXAFS, and an average coordination number of 6.3 was obtained which corresponds to a particle size of 1.0 to 1.5 nm. The only data which deviate from this are those published by Sexton et al. (J. Electron Spectroscopy 35, 1985, 27-43) which were re-interpreted in your paper (Surf Interface AnaL 20, 1993, 675). We have recently discussed possible reasons for the anomalous increase of the Auger parameter for 1.0 nm copper particles in zeolite NaA (W. Griinert et al., J. Phys. Chem., submitted). I have some doubts that the data reported by Sexton et al. are correct. The authors themselves believed that their value was too high due to problems in the analysis of the Auger line. In any case, we are not aware of any other example for so high ct' values for small metallic clusters, and we believe that we have very convincing evidence for the values for the Cu ~ clusters shown on the chemical plot. Comment and Question by M. Remy, Catholic University of Leuven, Louvain-la-Neuve, Belgium: 1) Looking at your Cu Auger lines, one realizes that there is an asymmetric broadening of the peaks. I think that this broadening is due to the presence of different types of Cu in your samples. May I suggest that you decompose your Cu Auger lines in order to quantify the different Cu species. 2) Do you observe a modification of this line and/or of the Cu/Si XPS ratio in your used samples? Answer by E.S. Shpiro" In some obvious cases, for example with physical mixtures, we did observe strong broadening or even splitting of the CuL3VV Auger band into two peaks. We used this to identify two different copper species. I agree that it would be worth while to analyze the asymmetry of the Auger bands. I am, however, worried about whether a simple deconvolution procedure would be appropriate for these complicated Auger bands consisting of several Auger transitions and satellites. We are interested in your deconvolution procedure for Auger lines. 2) We measured the XPS spectra after the catalytic reaction. No marked difference in the Cu/Si-ratio was found. Major changes of the Cu/Siratio were observed during catalyst activation due to copper redistribution over the zeolite crystals.
Question by H. Schulz, University of Karlsruhe, Karlsruhe, Germany: My question concerns the specificity of zeolite ZSM-5 as compared with other zeolites for this conversion. You have suggested an allyl species as an important intermediate. I wonder
414 whether, under these conditions, aromatic species might be formed as well and efficiently stored in the zeolite as reducing agent.
Answer by E.S. Shpiro: Indeed, we observed a storage effect when CuZSM-5 was treated with either NO + propene or with the full reaction mixture at 275 to 300 ~ but this effect was not observed with propene alone. The stored intermediates can then be selectively combusted at reaction temperature to N 2, CO 2 and H20. FTIR shows that these species consist of RNO2, RNO and RCH compounds, where R is an aliphatic rather than an aromatic group. These observations as well as the low Bronsted acidity of the overexchanged CuZSM-5 zeolites found by pyridine adsorption allow the conclusion that aromatics, even if they are formed, are not the major reactive intermediates for SCR of NO x.
A036
Copper Ion Exchanged Silicoaluminophosphate (SAPO) as a Thermostable Catalyst for Selective Reduction of NOx with Hydrocarbons by T. lshihara, M. Kagawa, F. Hadama and Y. Takita, Oita University,
Oita, Japan
Question by J.N. Armor, Air Products and Chemicals, lnc., Allentown, Pennsylvania, USA: I was pleased to see that you looked at the stability to SO2, water vapor and temperature. But you must look at lower levels of NO and hydrocarbons, with 15 % water for months, not hours. Did you do any testing under more extreme but typical limits of engine exhausts? Answer by T. Ishihara: We have only tested the activity of CuSAPO-34 under the typical conditions. Therefore, we have no results on the catalytic properties and durability of CuSAPO-34 under more extreme conditions. However, the activity of CuSAPO-34 is almost independent of the molar ratio NO/C3H 6, and complete reduction of NO can be attained on CuSAPO-34 when the concentration of C3H 6 is four times higher than that of NO. Therefore, the high NO conversion can be expected on CuSAPO-34 even at low levels of NO and C3H6, if the molar ratio NO/C3H 6 is higher than 1.0. In addition, the activity loss of CuSAPO-34 was extremely small after calcination at 973 K in a wet atmosphere. Therefore, we expect that the activity loss of CuSAPO-34 is not large over longer periods than those examined, if the temperature is below 973 K.
Question by W. Griinert, Ruhr University, Bochum, Germany: I was very much impressed by the good stability of your CuSAPO catalysts. On the other hand, I wonder why the activity of your reference catalyst CuZSM-5 i s s o low. For the typical NO and propene concentrations, you found conversions between 40 and 65 % at space velocities below
415 10 000 h -1. At this Conference, much higher activities have been reported. Could you provide us with some more information concerning the preparation of your CuZSM-5 catalyst (wt.-% copper, degree of exchange, pretreatments)? Answer by T. Ishihara: The feed gas composition which was applied in this study was rather severe for selective reduction of NO, viz. the partial pressure of NO was 5 times larger than that of C3H 6 as a reductant. Therefore, taking into account the dependence of the NO reduction rate on the partial pressures of NO, C3H 6 and Ox over CuZSM-5, the activity of our CuZSM-5 reference catalyst was almost at the same level as the typical activities reported by Professor Iwamoto or other researchers. The Cu loading and the degree of Cu x+ ion exchange of CuZSM-5 prepared in this study amounted to 3 wt.-% and 180 %, respectively.
Question by S.B. Hong, Korea Advanced Institute of Science and Technology, Taejon, Korea: SAPO-34 is the analogue of chabazite. My question is whether you have tested CuH-chabazite as catalyst in the same reaction.
Answer by T. Ishihara: The active site in this reaction seems to be ion-exchanged copper, and the crystal structure of the ion exchanger has little influence on the activity in NO reduction. Therefore, a high activity is predicted for Cu-chabazite, but it is doubtful whether the material is thermally stable. It has indeed been reported in the literature that various types of zeolites exchanged with copper exhibit a high activity in the selective reduction of NO with hydrocarbons.
Question by G. Schulz-Ekloff, University of Bremen, Bremen, Germany: You compared CuZSM-5 with CuSAPO-34. What is the basis for this comparison? Are they similar in framework structure, copper content, pore volume and acidity? Answer by T. Ishihara: The crystal structure of SAPO-34 is closely analogous to chabazite, but different from that of ZSM-5. In this study, the activity of CuSAPO-34 was compared with that of CuZSM-5 in spite of the different crystal structures. This was done because CuZSM-5 was predominantly used in previous studies as a catalyst for the selective reduction of NO with hydrocarbons and, consequently, there is a large amount of data on the catalytic properties and the thermal stability of CuZSM-5 in this reaction.
Question by E. S. Shpiro, N.D. Zelinsky Institute of Organ& Chemistry, Russian Academy of Sciences, Moscow, Russia: What do you consider as the major difference between copper in SAPO-34 and ZSM-5 which makes CuSAPO-34 more resistant against water? Answer by T. Ishihara: Since the crystal structure of SAPO-34 was retained even in the humidified atmosphere, we believe that Cu 2+ existed on cation sites in the pores of SAPO34. On the contrary, ZSM-5 is easily dealuminated resulting in an aggregation of ion-
416 exchanged copper. As a result, the activity loss of CuSAPO-34 in the selective reduction of NO was negligibly small below 973 K, even in the humidified atmosphere.
Question by B. Wichterlovd, 3'. Heyrovsl~ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Prague, Czech Republic: The catalytic activity of CuZSM-5 per one Cu differs dramatically depending on the copper content, because of the two copper species differently populated and exhibiting different activity. Therefore, the activities of CuSAPO-34 and CuZSM-5 can be hardly compared, as the state of copper in the SAPO has not been specified until now. Could you comment on this? Answer by T. Ishihara- It is suggested that, in CuZSM-5, the cluster consisting of two copper species exhibits the high activity for NO decomposition. However, the two Cu species do not exhibit different activities in the selective reduction of NO with hydrocarbons. This is why the activity for NO reduction with hydrocarbons over CuZSM-5 and CuSAPO-34 increased with increasing amount of ion-exchanged Cu. However, the excess amount of ion-exchanged copper markedly decreased the NO conversion in the case of the selective reduction of NO in the presence of 02 . From the dependence of the activity on the amount of ion-exchanged copper, we conclude that the amount of Cu loading is important for determining the activity in the selective reduction of NO. From this point on, the activity of CuSAPO-34 was compared in this study with that of CuZSM-5 at the same amount of Cu loading.
A037
Active State of Copper in Copper-Containing ZSM-5 Zeolites for Photocatalytic Decomposition of Dinitrogen Monoxide by K. Ebitani, M. Morokuma and A. Morikawa, Tokyo Institute of
Technology, Tokyo, Japan
Questions by P.J. Chong, Korea Research Institute of Chemical Technology, Seoul, Korea: 1) Could you please comment on whether the main effect of irradiation is on the CuZSM-5 zeolite or fragmentation of gas molecules. 2 ) Y o u are reporting two types of photoluminescence peaks. What kind of light source was used to detect these peaks? Answers by K. Ebitani: 1) N20 is transparent for the light of the wavelength (> 240 nm) applied in this experiment. 2) The result shown in Figure 5 of the paper was obtained using a xenon lamp. The quenching experiment shown in Figure 6 of the paper was carried out using laser beam excitation.
417
Question by J. Dedecek, J. Heyrovsk~ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Prague, Czech Republic: Why was decomposition of N20 observed only below 300 nm? 300 nm is the maximum of absorption of Cu + in ZSM-5, but 50 % of the maximal absorption is observed at 340 nm, so at this wavelength decomposition should also be observed if it is a photochemical effect and not a thermal effect. Answer by K. Ebitani: The rate of N20 photodecomposition was dependent on the wavelength. To discuss this dependence in more detail, we should have measured the quantum yields at various wavelengths.
Comment by B. Wichterlovfi, J. Heyrovsk~ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Prague, Czech Republic: I am surprised that you found a qualitative agreement in the catalytic activities of CuZSM-5 exchanged to 145 % and 445 %. At the very high loading of the latter zeolite, the copper species are likely to be of the oxidic type, i.e., (Cu-O)n, and not those dimeric species reflected by the emission at 540 nm. The maximum content of the copper sites reflected by the emission at 540 nm can be that corresponding to the number of framework aluminum atoms, which is equivalent to an exchange level of 200 %. Answer by K. Ebitani: It is possible that the emission at 540 nm is not due to the dimeric species of monovalent copper. To clarify the correlation between the emission of CuZSM-5 and the plausible structure of copper species such as (Cu-O)n, the relationship between the degree of copper exchange and the quantum yield of the emission at 540 nm must be investigated, along with other items.
P065
Decomposition of S o d i u m A z i d e on F a u j a s i t e s of Different Si/AI-Ratios by M. Brock, C. Edwards, H. Fiirster and M. Schriider, University of
Hamburg, Hamburg, Germany Question by I. Hannus, J6zsefAttila University, Szeged, Hungary: The lower amount of evolved N 2 for proton containing zeolites may indeed reflect the formation of ammonia. Such an exchange leads to the elimination of Bronsted acidity. We used elementary sodium produced by thermal decomposition of NaN 3 in-situ in zeolites for this pupose years ago. Do you have additional evidence which supports that this exchange reaction takes place? Answer by H. F~rster: We agree that the generation of basic catalysts is another interesting feature of zeolites containing sodium clusters. IR spectra of NaN3/HY mixtures no longer show the vibrations typical of Bronsted acid sites in HY.
418 Pl17
R e a c t i o n M e c h a n i s m of Selective R e d u c t i o n o f N i t r i c O x i d e b y M e t h a n e on G a - u n d I n - Z S M - 5 C a t a l y s t s by K. Yogo and E. Kikuchi, Waseda University, Tokyo, Japan
Question by R. Carli, University of Milan, Milan, Italy: Did you try to re-activate your catalyst (H 2, 500 ~ in order to re-disperse the Ga203 phase? Answer by K. Yogo: This is a good idea, since one can expect that such a treatment would lead to a re-dispersion of the Ga203 phase. However, we have not yet tried this.
P145
Aromatization of n - P e n t a n e o v e r N i - Z S M - 5 C a t a l y s t s by S.-K. Ibm, K.-H. Yi and Y.-K. Park, Korea Advanced Institute of Science
and Technology, Taejon, Korea Question by R. Carli, University of Milan, Milan, Italy: Did you try to prepare a catalyst with multiple metal functions, e.g., Ga203/Ni-HZSM-5 or ZnO/Ni-HZSM-5? Answer by S.K. Ibm: No, we have not tried so far. However, this is no doubt a good idea, and one could take advantage of well known catalysts, such as Ga- or Zn-ZSM-5, and make use of their catalytic properties for aromatization reactions.
419
VI. Theory and Modelling
PL05
Structure and Reactivity of Zeolite Modelling Using Ab-Initio Techniques
Catalysts:
Atomistie
by J. Sauer, Working Group Quantum Chemistry at the Humboldt University,
Max Planck Society, Berlin, Germany
Question by J. Datka, Jagiellonian University, Cracow, Poland: What do you think about the application of semiempirical methods for calculating the properties of zeolites? Answer by J. Sauer: Semiempirical methods have big computational advantages over abinitio methods and, hence, can be applied to much larger zeolite models. One of their disadvantages is that they are only applicable in the area for which they have been parametrized and that there is no systematic way to improve them if it turns out that they do not perform satisfactorily. I looked into the performance of different semiempirical methods for zeolite problems many years ago and did not find that they are of general use in the field of zeolites, e.g., they do not yield satisfactory framework structures. Even more recent parametrizations such as AM1 produce errors of 0.01 nm in the Si-O bond length. Moreover, they have problems with describing H-bonds and molecule-cation interactions. Most of the semiempirical methods simulate chemical bonds even for interactions which are of different nature. This is understandable as their home territory is organic chemistry. Still, I believe, they can be useful for limited purposes, provided that their performance is carefully checked. Question by J. Fraissard, Universit~ Pierre et Marie Curie, CNRS, Paris, France: The formation of H30 + after adsorption of H20 has been proved by NMR spectroscopy at 4 K " and neutron diffraction, even when the concentration of H20 is lower than the concentration of OH, and after homogenization of adsorbed H20 in order to be sure that there is no formation of H20-H20 hydrogen bonds. How do you explain the disagreement between these experimental results and the calculations? Answer by J. Sauer: First of all, I would like to stress that there is disagreement between the interpretation of different experiments and even between different interpretations of the same spectra observed by different authors. For instance, the characteristic bands of the infrared spectra of water adsorbed on zeolitic Bronsted sites (coverage up to 1:1) are interpreted as due to either an ion-pair complex (hydronium ion formation) or a neutral
420 H-bonded complex. Our calculated potential energy surface does not support the assumption of a hydronium surface ion because we predict that this species is a transition structure. Of course, these calculations refer to an abstract acidic site, and the methods used involve approximations. Therefore, the comparison between infrared spectra and 1H NMR chemical shifts predicted for the two structures and the data observed for a particular zeolite become crucial. Only our 1H NMR chemical shif~ calculated for the neutral H-bonded adsorption structure (Krossner, Haase, Sauer, paper in preparation) agree with shifts between 4.3 and 7.1 ppm reported for water adsorbed on a variety of zeolites. Moreover, it seems that the vibrational data show more agreement with the predictions for a neutral H-bonded complex than for an ion-pair complex.
Question by J.A. Lercher, University of Twente, Enschede, The Netherlands: Your calculations on the proton transfer energy indicate that there is no change in the equilibrium between protonated and non-protonated species (e.g., NH3). This suggests that protonation is mainly governed by entropy. What are the interpretations of the physical causes for the entropy difference between the two adsorbed forms? Answer by J. Sauer: The two species differ by vibrational degrees of freedom only. Their entropy difference originates from a delicate balance between the contributions from changes of intra- and intermolecular vibrational modes, in particular of the intra- and intermolecular OH-bonds. A more specific discussion cannot be provided without referring to the values which have been explicity computed from the vibrational data.
Questions by H. Robson, Louisiana State University, Baton Rouge, Louisiana, USA: Do your calculations apply to T-atom substitution? For example, structures with 5-membered rings are always Si-rich while structures with 4- and 6-membered tings tend to have more AI (limit: nsi/nA1 = 1). Is there more involved than Loewenstein's rule? Why is boron accepted in zeolite structures only to a very limited extent? Answers by J. Sauer: We did not investigate boron substitution. As far as the AIdistribution is concerned the calculations performed are always in accord with Loewenstein's rule. However, we found an interesting preference for A1 to occupy next nearest neighbor pairs of T-sites in the 4-membered silicate rings of the D6R secondary building unit. In contrast, Dempsey's rule assumes that the A1 is as far apart as possible for a given Si/Al-ratio. This preference for next nearest neighbor pairs was found for protonated zeolites. (See also ref. 21 of my paper in the Proceedings). Question by R. Roque-Malherbe, Instituto de Tecnolog& Quimica, CSIC-UPV, Valencia, Spain: Is it possible to take into account from the beginning the crystalline character of the zeolite and to impose conditions upon the wave function to fulfill the Bloch theorem?
421
Answer by J. Sauer: A periodic treatment of zeolites is possible and has been done by several people. At the ab-initio level, however, due to the enormous size of their unit cells, only relatively simple zeolite structures have been considered and small basis sets have been used. At the moment, no gradient techniques are available for getting relaxed structures, which also hampers the use of periodic calculations. Nevertheless, they will play an increasing role in the future and have already provided results which are very important as benchmarks for cluster calculations. Almost all periodic ab-initio calculations on zeolites were performed with the CRYSTAL code.
C006
Computer Zeolites
Simulations
of
Benzene
in
Faujasite-Type
by N.J. Henson, A.K. Cheetham, A. Redondo, S.M. Levine and J.M. Newsam, University of California, Santa Barbara, California, USA; Los Alamos National Laboratory, Los Alamos, New Mexico, USA; Biosym Technologies, Inc., San Diego, California, USA Question by D. Barthomeuf, Universitd Pierre et Marie Curie, Paris, France: We observed by infrared spectroscopy that benzene is adsorbed on cations on SII and SIII sites and in the 12-membered ring window. The 12-membered ring window location is more favored in NaX than in NaY at benzene loadings between 0.3 and 4 molecules per supercage (which corresponds to 2.4 to 32 benzene molecules per unit cell). What do you think about the effect of increasing loading on your calculation? Answer by N.J. Henson: The result that the 12-membered ring window site is favorable for NaX is very interesting. We certainly hope to investigate this further with computational methods when we extend our technique to look at higher loadings.
Questions by K. de Boer, Eindhoven University of Technology, Eindhoven, The Netherlands: 1) Why were only constant volume calculations performed? 2) How do you check for saddle points if you only have first derivatives in the minimization routine?
Answers by N.J. l-lenson: 1) The main thrust of the work was to refine the zeolite/guest interactions to bring the energies more in line with experimental data, rather than spending time developing a new zeolite-only forcefield. Whereas the representation of the faujasites is adequate with the unit cell volume fixed, it is less exact under constant pressure minimization. 2) This is indeed a problem with any first derivative method. The system is too large for standard Hessian methods to be used. For the minima presented in this work, we have further probed the region close to the minimum/saddle point using simulated annealing.
422
Question by S.W. Carr, Unilever Research, Bebbington, UK: Have you looked at the effect of benzene loading on the modelled location, and how important are adsorbate-adsorbate interactions? This may explain the discrepancy with the experimental data published by Fitch et al. (ref. 3 in C006). Answer by N.J. Henson: No, all the results presented here were for the low loading system of one benzene molecule per unit cell, however, this will be the next stage of the calculations. The discrepancy of the calculated binding site with the diffraction data to which you refer (the window site in NaY) is a fairly subtle effect, and it may be that the forcefield is insufficiently precise to pick it up. Question by H. Jobic, Institut de Recherches sur la Catalyse, CNRS, Villeurbanne, France: We have measured by inelastic neutron scattering the vibrational density of states of benzene in NaY, especially the low frequency range where one can observe the external modes of benzene with respect to the sodium cations on SII sites. Have you computed from your forcefield the low frequency domain of the VDOS so that a comparison could be made with the experimental data?
Answer by N.J. Henson: Your measurements of the vibrational spectra of benzene at the SII site in NaY provide additional data with which we can further validate and refine our forcefield. We hope to take this into our work in the next stage of this project.
Question by J. Sauer, Working Group Quantum Chemistry at the Humboldt University, Max Planck Society, Berlin, Germany: Did you check whether the position of benzene in the 12-membered ring window is a local minimum? Did you calculate the second derivatives of the energy with respect to nuclear replacements? It could be that this structure is a saddle point. Answer by N.J. Henson: Unfortunately, for the size of the systems we are considering ( > 600 atoms) it is impractical to store the Hessian, so this question cannot be adequately answered currently. We plan to re-run the calculations for the minima of interest on the primitive unit cell of faujasite to verify that the minima are not saddle points.
Suggestion by F. Trouw, Argonne National Laboratory, Argonne, Illinois, USA: Quasielastic neutron scattering (QENS) would provide the rate of benzene ring rotation and the geometry of the motion. The temperature dependence of the rotational diffusion constant would also provide the rotational barrier for comparison with the calculations. Answer by N.J. Henson" The basis of the data to which we compared our rotational activation barriers of benzene at the SII site comes from 2H NMR spin lattice relaxation measurements. I would expect that QENS could give us a much richer data set for this subtle
423 form of motion, and we would certainly like to make comparisons with suitable experimental data in the future.
C007
Aromatic Molecules Catalytic Processes?
in
Zeolite Y. A Model System for
by H. Klein and H. Fuess, Darmstadt University of Technology, Darmstadt, Germany Question by D. Barthomeuf, Universitd Pierre et Marie Curie, CNRS, Paris, France: It is very stimulating and interesting to have model systems for catalytic processes. You published that aniline is adsorbed on Na + cations on SII positions or in the 12-membered ring window slightly tilted from the oxygen ring. Do you think that, at typical reaction temperatures for, e.g., alkylation (300 to 450 ~ the aniline would still occupy these two sites? Answer by H. Klein: Aniline is an exceptional case, because it occupies both the cations on the SII and the window site. The conclusions drawn from our experimental studies primarily hold for benzene, xylenes and mesitylene. The only thing we can do for aniline is to speculate that it is located at both sites under reaction temperatures.
Comment by A.K. Cheetham, University of California, Santa Barbara, California, USA: In relation to the 23Na NMR spectrum of LaNaY, it should be recalled that J.V. Smith showed almost 20 years ago that the proportions of lanthanum cations in the s r and SI sites are strongly dependent upon the calcination temperature. This effect will clearly influence the 23Na spectrum. Answer by H. Klein: Recent publications clearly show that La 3+ is never on the SI position. This can presumably be explained by the formation of lanthanum-oxygen clusters in the sodalite cages.
Questions by N.J. Henson, University of California, Santa Barbara, California, USA: 1) My first question concerns the xylene position at the SII site: is the binding site out of the plane of the 6-membered ring in diffraction and modelling? 2) What is the shape of the trajectory from the SII to the SIII site? How close is it to the wall? Answers by H. Klein: The answers to both questions are given in another paper (H. Klein, C. Kirschhock and H. Fuess, J. Phys. Chem., in press), where the results of the computer simulation are presented in much more detail. Here, I can give very brief answers: 1) benzene is out of plane in modelling by about 5 ~ With increasing size of the guest molecule, this angle increases. 2) The shape of a minimum energy pathway is along the
424 [ 111 ] axis, where the position of minimum energy in the plane perpendicular to this axis was determined and these minimum points of different sections were combined. This pathway is along the zeolite wall (the distance to the center of the cage is about 0.35 to 0.50 nm, depending on the position), the center of the cage is avoided.
Question by J.M. Newsam, Biosym Technologies, lnc., San Diego, California, USA: The dinitrobenzene result is interesting, suggesting occupancy by sodium of a site at the center of the supercage. How well defined is this site in the diffraction analyses? Answer by H. Klein: We have found electron density on this site, and we attributed it to a sodium cation based on distance criteria. However, the complementary method, i.e., 23Na MAS NMR spectroscopy using spectrum simulation, which will be carried out in the near future, will hopefully give more evidence for this.
Questions by M.M. Ramirez de Agudelo, 1NTEVEP S.A., Caracas, Venezuela: 1) Have you fixed the charges on the atoms for your modelling work? 2) Is the electrostatic effect a conclusion derived from a conformational study or only from the study of the effect of hydrocarbon-zeolite distances? Answers by H. Klein: 1) We have used a point-charge model, and therefore the charges are fixed. However, the charges for the different guest molecules differ. They were determined by Mulliken's population analysis of ab-initio calculations. 2) The electrostatic effect is the conclusion of the whole project. The result was derived by analysis of many guest molecule/zeolite interactions in the whole configurational space.
C008
Computer Modelling Microporous Materials
of
Sorbates
and
Templates
in
by R.G. Bell, D.W. Lewis, P. Voigt, C.M. Freeman, J.M. Thomas and C.R.A. Catlow, The Royal Institution of Great Britain, London, UK; Biosym Technologies, lnc., San Diego, California, USA Comment by A.K. Cheetham, University of California, Santa Barbara, California, USA: I would like to question the wisdom of ignoring the electrostatic contribution to the interactions between template cations (e.g., TPA) and the zeolite host. These make a very substantial contribution to the binding energy. Answer by D.W. Lewis: Although the neglect of coulombic interactions will indeed have a significant effect on the absolute value of the binding energy, our experience suggests that it will not alter our general conclusions. The inclusion of these interactions does not change the results on template selection such as those shown. Furthermore, the work of Cox et al.
425 presented at this Conference (C018) has suggested that the electrostatic characteristics of templates are not as crucial as the size effects. However, we are aware of the possible problems connected with the approximation, and future work on template interactions with zeolitic fragments will have to re-address this question.
Comment by T.V. Harris, Chevron Research and Technology Co., Richmond, California, USA: Please comment on the possibility of including Coulomb calculations using the modelling methods reported. Experimentally, framework substitution can alter the phase made by a given template, and the location of substituted sites can be important. Thus Coulomb effects will be important. Answer by R.G. Bell: Difficulties will arise with the current methods due to the use of a finite cluster of framework. However, it is possible to perform periodic boundary condition calculations. Framework substitution may be important, however, it raises many questions - s u c h as location of this substituent--which will greatly increase the computational expense. This reduces the ability to perform rapid scanning of templates but may be advantageous in a more detailed study. Furthermore, we refer to the work presented by Cox et al. (CO 18) who concluded that there is little correlation between the electrostatic character and a molecule's ability to form zeolites. Question by E.J. Maginn, Un&ersity of California, Berkeley, California, USA: When the diffusion pathway is calculated for butene using energy minimization, you are neglecting entropic effects. That is, you are calculating the diffusion pathway at 0 K. To calculate the actual diffusion pathway, shouldn't you consider the free energy? Answer by R.G. Bell: Yes, the entropic contribution will affect the diffusion pathway, and will moreover drive the diffusion by favoring migration away from the pore sites, at finite temperature. Our conclusions regarding pore accessibility are unlikely to be affected. Question by J.M. Newsam, Biosym Technologies, lnc., San Diego, California, USA: The trend relating the degree of interaction of the template molecule with the zeolite and the templating efficacy implies that template screening is viable in these types of cases. Does it also provide insight into the mechanism by which templating occurs during synthesis? Answer by D.W. Lewis: The calculations as presented do not explicitly provide information on the mechanism of templating. However, futu, work will consider the interaction of template molecules with fragments of zeolite frameworks, and this work may provide further insight into the mechanistic aspects.
426
C014
Interatomic Potentials for Zeolites. Ab-Initio Shell M o d e l Potential
Derivation
of
an
by K. de Boer, A.P.J. Jansen and R.A. van Santen, Eindhoven University of
Technology, Eindhoven, The Netherlands Question by N.J. Henson, University of California, Santa Barbara, California, USA: The reproduction of structural data is less exact than for other potential models, and also less exact than the reproduction of elastic constant data. Have you considered a fitting of the parameters to (periodic) structural data to improve your representation of siliceous crystal structures? Answer by K. de Boer: The adjustment of the potential to periodic structural data was not the aim of our research as we wanted to develop a method for deriving the potential from ab-initio data of clusters. A semi-empirical approach, in which the covalent parameters are fitted to the ab-initio cluster data and the charges are adjusted to structural data on a-quartz, is now subject of a current study.
Questions by F. Trouw, Argonne National Laboratory, Argonne, Illinois, USA: 1) Why does the accuracy of the ab-initio calculations decrease with the cluster size? 2) What is the origin of the phonon dispersion curve measurements? A comparison of experiment and theory for the phonon density of states would be helpful as molecular sieves are not available in large enough crystals for phonon dispersion measurements. Answers by K. de Boer: 1) We did the cluster calculations using MP2. The basis sets used are: 6-31G(d) on Si, 6-311G(d) on O and 6-31G(p) on H. Due to a limited computer capacity at our university at that time (about two years ago) the use of larger clusters would have forced us to choose a smaller basis set and/or a less sophisticated method, which would have been less accurate. We notice that potential derivations based on ab-initio data which are presented in the literature so far, are all based on SCF calculations. We used the MP2 data on the small clusters as a first test of our parametrization method which is a fully automatic procedure now and can thus easily be used for ab-initio data derived from larger clusters which can be calculated nowadays with larger basis sets and more accurate methods. 2) Many papers have been published on the measured phonon spectra of ~-quartz. I will just mention two recent ones. Measurements in the [ ~ 0 ] and [~00] direction: B. Domer, G. Grimm, G. Rzany, J. Phys. C: Solid St. Phys. 13, 6607 (1980). Measurements in the [00~] direction: D. Straueh, B. Domer, J. Phys. Condens. Matter 5, 6149 (1993). Furthermore, for the study of structures for which no experimental phonon spectra are obtained yet, we will consider your suggestion to compare the calculated phonon density of states with the experimental ones.
427 C015
Vibrational Structure of Zeolite A by M. B~irtsch, P. Bornhauser, G. Calzaferri and R. Imhof, University of
Bern, Bern, Switzerland
Question by S.W. Carr, Unilever Research, Bebbington, UK: Have you considered using the building units to assemble zeolite structures with organic building units and to substitute heteroatoms in the building units? Answer by G. Calzaferri: Yes, some preliminary results are available. I consider this a very attractive route which may lead to new porous materials with interesting properties. Question by C. Dossi, University of Milan, Milan, Italy: In your model with Co carbonyl, you had a direct Si-Co bond. I wonder whether it would be possible to synthesize a compound with Si-O-Co bonds, since it would be a better model of metal-support interactions in zeolites and on silica surfaces. Answer by G. Calzaferri: Yes, this should be possible. We have not tried it. One would have to work out an appropriate synthesis procedure. Another interesting approach to study Si-O-metal interactions has been taken by F.J. Feher, T.A. Budzichowski, K. Rahimian and J.W. Ziller (see, e.g., J. Am. Chem. Soc. 114, 1992, 3859).
Question by P.K. Durra, The Ohio State University, Columbus, Ohio, USA: Have you simulated the spectrum of zeolite A starting with the calculated spectrum of the sodalite cage rather than the double 4-membered ring? If so, are there any differences in these two predictions? Answer by G. Calzaferri: We have not yet carded out these calculations, but we plan to do this. At least two sodalite cages must be connected to simulate the 8-membered ring pore opening, and this requires some computational effort, but it can be done. The sodalite cage is a good starting structure for a number of other zeolites, and it is worthwhile to extend this work.
Comment by F. Trouw, Argonne National Laboratory, Argonne, Illinois, USA: You commented on the importance of the ring breathing modes for diffusion of adsorbates. Perhaps a collaboration with molecular dynamicssimulation to explore this issue via normal coordinate analysis would be productive. Answer by G. Calzaferri: MD simulations of the pore opening modes (based on our normal coordinate analysis) would certainly be interesting, and it would be worthwhile to collaborate. We should discuss more details privately.
428 C016
Low-Occupancy Sorption Thermodynamics of Long Alkanes in Silicalite via Molecular Simulation by E.J. Maginn, A.T. Bell and D.N. Theodorou, University of California, Berkeley, California, USA
Question by K. de Boer, Eindhoven University of Technology, Eindhoven, The Netherlands: Is the phase transition orthorhombic --> monoclinic which takes place in the temperature range from 300 K to 800 K accounted for in your calculations? Answer by E.J. Maginn: The monoclinic to orthorhombic phase transition occurs for the empty silicalite lattice at about 340 K. However, the adsorption of small molecules induces this phase transition at even lower temperatures. We conducted our simulations using the orthorhombic form, which we expect to be stable upon adsorption of n-alkanes in the temperature range of 300 K to 800 K.
Comment by J. J~inehen, Eindhoven University of Technology, Eindhoven, The Netherlands: We measured the adsorption of n-decane on silicalite using the isosteric method. The results of your calculations agree with our findings in that the heat of adsorption is constant over a wide range of temperatures (300 to 500 K). However, from the shape of the heat curve and the adsorption capacity of the zig-zag channels we concluded that n-decane is adsorbed first in these narrowed channels with a higher heat of adsorption. This is followed by filling up the rest of the structure. Can you comment on this? Answer by E.J. Maginn: This is a very interesting result. Richards and Rees also proposed that the zig-zag channels fill first for long chains. However, Thamm has concluded that all regions of the zeolite are filled at equal times. Our calculations suggest that at high temperature, n-decane fills both the straight and the zig-zag channel regions equally. Chains longer than C 6 tend to span one intersection region, and so we believe it is incorrect to say that the chains are in a particular channel. In fact, long chains appear to probe all of the pore volume in the zeolite. At low temperature (300 K), n-decane favors alignment along the straight channels, spanning one intersection region. The disagreement between our results may stem from the fact that you have matched the n-decane chain length and the zig-zag channel length, when in fact the chains seem to prefer spanning channel segments.
Question by W.J. Mortier, Exxon Chemical International, Inc., Machelen, Belgium: Would your method easily pick up the influence of the pore size on the adsorption energy? Answer by E.J. Maginn: Yes, the bias Monte Carlo method is completely general and can be applied to any system involving chain molecules and regular, microporous materials. Free energies are readily calculated, and so the enthalpy of sorption is a result of the
429 calculation. One needs only perform the calculation for different zeolites to obtain a dependence of the sorption entropy on pore size.
C017
Molecular Dynamics Symmetry Zeolite
Simulations
of Diffusion
in a Cubic
by P. Demontis and G.B. Suffritti, University ofSassari, Sassari, Italy
Question by W.J. Mortier, Exxon Chemical International Inc., Machelen, Belgium: Regarding the breathing of your 8-ring windows (dl/d2), it seems hard to believe that this could be as much as 0.09 nm. How much do you need to explain your intercavity diffusion results? Answer by G.B. Suffritti: I think it is not so easy to give a clear-cut answer to that question, as a dynamic phenomenon is involved. On the basis of the results shown in the paper by Fritzsche et al. (P090), differences as large as about 10 kJ/mol in the barrier height to cross the windows can be expected for shifts of the window diameter of about 0.07 nm. Therefore, the observed deformations are sufficient to account for large variations of the diffusion coefficient, assuming that it shows an Arrhenius behavior. Questions by N.J. Henson, University of California, Santa Barbara, California, USA: 1) If the dominant mechanism of diffusion is jumping through the 8-ring window, why do we not see steps in your mean square displacements (MSD) plots? 2) Have you looked at the effect of explicit aluminum substitution on the motion of CH 4 through the window? Answers by G.B. Suffritti: 1) The mean square displacements are, as usual, averaged over time and guest molecules, and therefore they are smooth. The differences between the different diffusive regimes are evidenced by 10g-log plots of MSD versus time (see a forthcoming paper in Chem. Phys. Lett. by P. Demontis and G.B. Suffritti). 2) In the simplified model that we are using, the methane molecules interact with the framework via the oxygen atoms of the framework, hence explicit aluminum substitution is not taken into account. Work is in progress, however, to study the same systems by using a new model potential (Demontis, Suffritti, Bordiga and Buzzoni, submitted) including explicitly all atoms and coulombic interactions. In other words, the influence of explicit aluminum substitution will become detectable in the near future.
430 C018
Molecular Modelling Studies of Zeolite Synthesis by P.A. Cox, A.P. Stevens, L. Banting and A.M. Gorman, University of Portsmouth, Portsmouth, UK; Biosym Technologies, Inc., San Diego, California, USA
Question by W.J. Mortier, Exxon Chemical International Inc., Machelen, Belgium: In cases where you have many templates which make the same structure type, would the energetics tell you something about the ease with which the crystallization occurs? Answer by P.A. Cox: We have not investigated these effects, but the paper presented by Harris and Zones (A002) showed a clear correlation between the binding energy for a template and the crystallization time for the zeolite product.
C019
Ti Substitution Mechanical Study
in
MFI
Type
Zeolites: A Quantum
by R. Millini, G. Perego and K. Seiti, Eniricerche S.p.A., San Donato Milanese, Italy; Biosym Technologies, Orsay, France Questions by W.J. Mortier, Exxon Chemical International, Inc., Machelen, Belgium: 1) For the design of an active oxidation catalyst, would you prefer a Ti located at a stable site or at a less stable site? 2) We consistently found that the most reactive oxygens are at the inner surface of the channels- do you agree with that? Answers by R. Millini: 1) It is difficult to answer this question. However, I can remark that the stability of Ti sites in TS-1 is probably optimal as the sites are sufficiently reactive to undergo a reversible coordination change without any appreciable removal of Ti as observed in the investigated oxidation reactions. 2) Up to now, we have no clear indications about this point.
Comment by J. Sauer, Working Group Quantum Chemistry at the Humboldt University, Max Planck Society, Berlin, Germany: My question refers to the calculation of relative titanium substitution energies. From previous studies on aluminum substitution it is well known that the result depends (i) on the reference structure assumed and (ii) on the degree of geometry relaxation. From a theoretical point of view, only energies of fully relaxed structures can be compared. Answer by R. Millini: In the beginning of this work, we took into consideration cluster relaxation and, as expected, on the basis of the open structure of the cluster, this led to an unrealistic geometry. For this reason, and because of the requirement to limit the cluster
431 size, the assumption of invariant T-O-T (and O-T-O) angles to preserve the main structural features of the MFI framework seemed to be a reasonable compromise. Comment by L. Bonneviot, Laval University, Ste. Foy, Quebec, Canada: My comment is related to the previous one by Professor Sauer and to reactivity. Your model implies that the Si-O-Ti angle is smaller than the Si-O-Si angle. According to model compounds, the Si-OTi angle is close to 180 ~ so not only the Ti-O distance, but also the angle will cause a drastic local expansion and a related lattice relaxation. Since the stability of these Si-O-Ti bridges is very important for the reactivity, the calculation should take into account the lattice relaxation. One might then be able to explain the fact that TS-1 and TS-2 are active for oxyfunctionalization while MCM-41 and zeolite beta containing titanium are not. Answer by R. Millini: The assumption of invariant T-O-T angles (which were kept fixed to the crystallographic values during the calculations) was already addressed in my answer to Professor Sauer's comment. In any case, the good agreement between the experimental lattice expansion (from XRD) and that expected for a Ti-O distance of 0.180 nm confirms that the assumption of invariant T-O-T angles is essentially valid. To me, it seems difficult to enter into considerations about the reactivity of the titanium containing materials you mentioned, taking into account the non-crystalline structure of Ti-MCM-41. A much deeper investigation is needed for tackling this problem.
Question by A. de Man, Working Group Quantum Chemistry at the Humboldt University, Max Planck Society, Berlin, Germany: To what extent can a pentameric unit be used to describe 12 different sites, regarding the expected change of the Ti-O-Si angles upon full relaxation of the molecule while the Ti-O-Si angles are the only parameters which really differ in the models of the sites? Answer by R. Millini: See my reply to Professor Sauer's comment.
Comment by G. Ricchiardi, University of Turin, Turin, Italy: My experience with the substitution is that the structure exhibits severe relaxation up to the first complete shell of tetrahedra. Moreover, the T-O-T angles are important: ab initio calculations on (HO)3Ti-OSi(OH)3 indicate that the energy minimum occurs for a linear T-O-T angle. Answer by R. Millini: See my reply to Professor Sauer's comment. Question by E.T.C. Vogt, Akzo Nobel Chemicals, Amsterdam, The Netherlands: I realize that the absence of derivatives in your present results makes it difficult, but would it be possible in your future work to calculate the IR spectrum? This could yield support for the assignment of the 960 cm -1 band. Answer by R. Millini: We believe it should be possible to calculate the features of the IR spectrum, though a larger reference cluster has to be considered.
432
Comment by A. Zeeehina, University of Turin, Turin, Italy: Just a short comment concerning the coordination of Ti in titanium silicalite: I want to stress that four-fold (tetrahedral) coordination is observed only in vacuo (by XANES, EXAFS, UV-VIS etc.) and that ligands such as H20, NH 3, H202 etc. are able to enter the coordination sphere of Ti, with the consequence of an increase of the coordination number. Answer by R. Millini: I agree partly with your comment. In fact, it is our experience that, in a well crystallized and carefully calcined TS-1 sample, the tetrahedral coordination of Ti should be mostly retained at room temperature in air, as evidenced by IR analysis. Experiments made in our laboratories confirm that an exchange reaction occurs between TS-1 and 170 and 180 labelled water, but the kinetics is very slow (see G. Bellussi, A. Carati, M.G. Clerici, G. Maddinelli and R. Millini, J. Catal. 133, 1992, 220).
P096
Heterogeneity of Hydroxyl Groups in Faujasites of Various Si/Ah IR and NMR Studies, Quantum Chemical MNDO Calculations by J. Datka, E. Broclawik, J. Klinowski and B. Gil, Jagiellonian University, Cracow, Polan& Institute of Catalysis, Polish Academy of Sciences, Cracow, Polan& Cambridge University, Cambridge, United Kingdom
Question by L. Kubelkovfi, J. Heyrovsl~ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Prague, Czech Republic: Your experimental IR data on proton affinities (PA) of bridging hydroxyls in faujasites seem to be too high (PA = 1300 to 1419 IO/mol) in view of the generally accepted value of 1390 kJ/mol for the PA of silanol groups in silica gel. Could you please comment on this discrepancy? Answer by J. Datka: Our PA values of OH(l) to OH(4) in NaH-faujasites calculated from the Bellamy-Hallam-Williams (BHW) relation are indeed too high in comparison with SiO 2. Our PA values were calculated using acetic, chloroacetic, trifluoroacetic and benzoic acids and phenol as standards. If SiO 2 were taken as standard, the following PA values would result: 1382, 1356, 1296 and 1281 10/mol. These values are lower than the one of SiO 2, in agreement with all experimental facts. We did not use, however, PA values calculated on the basis of SiO2 as a standard, because they differ distinctly from the PA obtained with all other standards. It should be noted that the PA values calculated from MNDO are lower than those from the BHW relation and in better agreement with the experimental facts. It is important to discuss not only the absolute values of the PA, but also the difference between the PA values for OH(l) - OH(4) and to compare the experimental data with the theoretical ones.
VII. Industrial Applications and Novel Materials
PL06
Industrial Applications of Zeolite Catalysis by J.E. Naber, K.P. de Jong, W.H.J. Stork, H.P.C.E. Kuipers and M.F.M. Post, Koninklijke/Shell-Laboratorium, Amsterdam, The Netherlands;
Shell Internationale Petroleum Maatschappij, The Hague, The Netherlands
Question by D. Barthomeuf, Universit6 Pierre et Marie Curie, CNRS, Paris, France: Could you please comment on the possible use of SAPO's as additives in FCC, for instance of SAPO-37 which has the structure of faujasite? SAPO's are thermally very stable and give less hydrogen transfer than faujasite type catalysts. Answer by J.E. Naber: We have indeed considered SAPO's as additives, but so far we have the impression that they do not comply with the hydrothermal stability requirements. Questions by C.T. O'Connor, University of Cape Town, Rondebosch, South Africa: Would you please comment on: 1) To what extent is ZSM-5 being used today as an additive in fluid catalytic cracking units (FCCU's)? 2) What is your prediction of the supply/demand situation for isobutene in the medium term? Answers by J.E. Naber: 1) I can't give exact figures, but I do know that within Shell there is significant use of ZSM-5 at the 1 to 2 wt.-% addition rates, for octane enhancement purposes. I would expect a similar situation elsewhere. We expect to see significantly higher addition rates for olefin production reasons, probably starting in the USA. 2) Again, ! can't give you exact numbers. Judging from several reports from consultants, as published in several journals, the supply/demand situation may be somewhat constrained in the USA, but not elsewhere in the period up to 2005.
Question by M.M. Ramirez de Agudelo, INTEVEP S.A., Caracas, Venezuela: There is some research going on concerning the application of zeolites for MTBE production. Do you foresee a future competition of zeolite catalysts with the ion exchange resins presently in use? Answer by J.E. Naber: While I cannot give a real answer because I don't know enough about the specifics, I would not expect much competition due to the relatively low cost and simplicity of the present MTBE process.
434
Question by H. Robson, Louisiana State Un~,ersity, Baton Rouge, Lou&iana, USA: In the 1980's, hydrocracking was regarded as an obsolete process. The cost of hydrogen mined the incentive to build new units. But now you predict increasing use of hydrocracking. What has happened to change the economics of the process? Answer by J.E. Naber: The increase in distillate/residue differentials has played a significant role, as well as the improvement in economics due to much higher selectivities and stabilities (run times). Furthermore, in many cases outside the USA, the capability of hydrocracking to furnish middle distillates is more favorable than that of fluid catalytic cracking.
B005
Nitrido Zeolites - a Novel and P r o m i s i n g Class o f C o m p o u n d s by W. Schnick, University of Bayreuth, Bayreuth, Germany
Question by R.W. Broach, UOP Research Center, Des Plaines, Illinois, USA: Can you describe some of the synthesis conditions? Do the reactions occur in the solid state, in the gas phase, or ....... ? Answer by W. Schnick: The synthesis of the nitrido sodalites most probably proceeds via a heterogeneous solid-gas reaction involving solid P3N5 or HPN 2 and volatile NH3, NHnCI or metal halide. The formation of Zn6P 12N24 starting from the binary nitrides is supposed to be a solid state reaction.
Question by F. Cubero, University of Stuttgart, Stuttgart, Germany: You mentioned that P-N zeolites with the sodalite structure are able to store hydrogen. Could you please explain how the hydrogen storage capability was measured? Answer by W. Schniek: When the synthesis of Zn6[P12N24] with "empty" 13-cages is performed in a hydrogen atmosphere at low temperatures, the material evolves H 2 when heated up to temperatures above 500 to 600 ~ It seems that this material might be used as a material for hydrogen storage in a similar manner to the isotypic Na6[Si6A16024 ]. Question by J.M. Garc4s, The Dow Chemical Co., Midland, Michigan, USA: Have you tried to use polyphosphazenes as starting materials for P-N zeolites? Answer by W. Sehniek: Using (PNC12)3 as a reactant yields oligo- or polyphosphazenes as intermediates during the syntheses of our P-N zeolites. Furthermore, phosphorus nitride imide HPN2, which we used as a starting material as well, might be looked upon as a threedimensionally crosslinked polyphosphazene. Accordingly, polyphosphazenes may indeed be used as starting materials too.
435
Question by R. Hoppe, University of Bremen, Bremen, Germany: You were showing some UV/VIS spectra of your cobalt containing nitrido zeolites, and the maxima were assigned to CT bands. Did you investigate a change in the coordination sphere caused by interaction with solvents, such as water, toluene etc.? This might bring about a shift of the maxima in the UV/VIS spectra. Answer by W. Schnick: Up till now we have investigated our samples in a very pure and well def'med state only, i.e. water, oxygen etc. were thoroughly and completely excluded. Question by S.l. Zones, Chevron Research and Technology Co., Richmond, California, USA: Could this synthesis work be carded out in molten salt systems with high amounts of charge at 250 to 300 ~
Answer by W. Schnick: In principle, this should be possible, and we did undertake some preliminary experiments in this direction. However, up to now we have found no significant advantage of using molten salt systems.
B006
The Synthesis and Structure of a N e w Zinc Phosphate Z n 2 P 2 0 8 C 2 N 2 H 1 0
Open Framework
by R.H. Jones, J. Chen, G. Sankar and J.M. Thomas, University of Keele, Keele, UK; The Royal Institution of Great Britain, London, UK
Questions by L.B. McCusker, Swiss Federal Institute of Technology Zur&h, Zurich, Switzerland: 1) 437 reflections were used in the structure determination step. Do you know to what degree they overlap? 2) You suggest that the assumption of too high a symmetry may be responsible for the poor profile fit. Is there any further possible explanation? Answers by R.H. Jones: 1) I don't have an exact idea. The data was decomposed up to 20 = 90 ~ If I were to put up a plot of the observed and difference profiles, we would see at the higher angles that there is very severe overlap of reflections. 2) I am basing this on analogy to the cobalt phosphate structure. This was single crystal data and was collected using an area detector. When we merged equivalent data, we could quite clearly see a reduction in the Laur symmetry, so this may be the case. Another possibility is that interaction with the template or trapped water may be responsible for the lowering of symmetry, as was reported for natrolite at the 9th IZC. We might also see some increase in the size of the unit cell by ordering of guest species (I have mentioned some examples in the published paper).
436
B007
Novel Molecular Sieves of the Aluminophosphate Family: A I P O 4 and Substituted Derivatives with the L T A , F A U and A F R Structure-Types by L. Sierra, J. Patarin, C. Deroche, H. Gies and J.L. Guth, Ecole Nationale Sup~rieure de Chimie de Mulhouse, CNRS, Mulhouse, France; Ruhr University, Bochum, Germany
Question by Z. Gabelica, Facult& Universitaires Notre-Dame de la Paix, Namur, Belgium: You succeeded in preparing A1PO4-40, but not AIPO4-37 , obviously by selecting the appropriate templates in the former case. Do you believe that the preparation of A1PO437 does also require the use of optimized templates? Or should some other factors be considered which are possibly related to the particular FAU structure? Answer by L. Sierra: In addition to the problem of selecting more appropriate templates, crystallization conditions probably have to be adjusted as well, for instance towards lower temperatures than in the syntheses of MeAPO's with the FAU structure.
Questions by R. Szostak, Clark Atlanta University, Atlanta, Georgia, USA: 1) Did you try other sources of aluminum? 2) Your AIPO4-AFR crystallizes over a very narrow range of conditions. Is it difficult to consistently obtain this phase, i.e., if you repeat the synthesis exactly, on six different occasions, do you obtain AFR each time? Answers by L. Sierra: 1) We tried aluminum isopropoxide only for the syntheses of the FAU- and AFR-type, but without success. 2) For AIPO4-AFR and SAPO-AFR, the syntheses are reproducible in a large range of conditions (from 120 to 170 ~ total TPA/P205 between 2 and 2.5, part of TPAOH being replaced by TPABr in order to have a pH close to 7.5). For MeAPO-AFR and MeAPSO-AFR, the syntheses are more difficult (best conditions: Me = Co, 150 to 200 ~ total TPA/P205 = 2.0, pH = 7.5).
B008
Titanium-Containing Large Pore Molecular Sieves from Boron-Beta: Preparation, Characterization and Catalysis by M.S. Rigutto, R. de Ruiter, J.P.M. Niederer and H. van Bekkum, Delft University of Technology, Delft, The Netherlands
Comment by A. Corma, Instituto de Tecnologia Quimica, CSIC-UPF, Valencia, Spain: Since you have a large amount of oligomeric titanium, I doubt that the selectivity on H202 could be larger than when using a direct synthesis of [Ti, Al]-beta. I believe that the selectivities with respect to Ha02 which you presented for [Ti, Al]-beta are not correct.
437 I agree, however, that the selectivity for the epoxide appears to be larger on the deboronated zeolite as a consequence of the acidity of [Ti, Al]-beta. Answer by M.S. Rigutto" What I have been comparing are selectivities towards the epoxide. The figures on [Ti, Al]-beta are taken directly from your paper. I agree that [Ti, A1]-beta gives a more efficient incorporation of oxygen from H202, but one cannot control which hydrolysis/solvolysis products are formed because of the acidity of that material. The oligomeric titanium is estimated to account for about 25 % of the total titanium in the best of our materials. It decomposes H202 indeed, but the most important factor determining overall H202 efficiency is the influence of oligomeric titanium on the activity of framework titanium because of the hydrophobicity of the former species.
Question by S. Kaliaguine, Laval University, Ste.-Foy, Quebec, Canada: Did you try any other reaction involving H202, say for example, n-hexane oxyfunctionalization with your [Ti]-beta catalysts? Answer by M.S. Rigutto: No, not yet.
Question by R. Kumar, National Chemical Laboratory, Pune, lndia: As you mentioned at the beginning of your lecture, the main objective to synthesize [Ti]-beta was to oxyfunctionalize bulky organic molecules. However, the only reaction you reported was epoxidation of C 8 alkenes. Did you carry out reactions involving large molecules? Answer by M.S. Rigutto: We are currently working on the epoxidation of terpenes. Camphene gives a moderate selectivity to epoxide + aldehyde (without rearrangement of the bicyclic skeleton) of about 60 % at 15 % camphene conversion, but its reactivity is lower than that of octene. Perhaps, the rigidity of the molecule makes a proper approach to the active complex difficult.
Questions by E.T.C. Vogt, Akzo Nobel Chemicals, Amsterdam, The Netherlands: 1) Could you speculate on the reasons why it is possible to directly synthesize TS-1, whereas it is not possible to directly prepare [Ti]-beta? 2) Does this observation have any implications for the possible coordination of the titanium in the material? Answers by M.S. Rigutto: 1) The tetraethylammonium ion is not a very good or specific template for the beta structure. We have recently shown that it is possible to prepare the allsilica form of beta using dibenzyldimethylammoniumhydroxide, and we believe that further progress along this line is possible. 2) It may be that the structure of beta is more flexible than that of ZSM-5 or that the steric constraints on titanium for expanding its coordination shell are weaker, which might lead to lower activity. Hydrophilicity is in my view just as important, however, one needs a true [Ti]-beta free of internal hydroxyls or trivalent ions with a low titanium content to make a fair comparison.
438
Question by S.l. Zones, Chevron Research and Technology Co., Richmond, California, USA" How does the micropore volume change with the various beta zeolites at Si/B = 12 to 28 after the titanium insertion by method 2?
Answer by M.S. Rigutto: At this time, we have only data for Ti 1 (12) (0.17 cm3/g), Ti 2W(12) (0.18 cm3/g), Ti 2 (12) (0.20 cm3/g) and Ti 2 (21) (0.22 cm3/g). We expect that the pore volume of Ti 2 (28) is somewhat higher. The maximum in pore size distribution (measured with argon after the Horvath/Kawazoe method) also shifts to higher values in the same series.
B025
Comparative Spectroscopic Study of TS-1 and ZeoliteHosted Extra-framework Titanium Oxide Dispersions by J. Klaas, K. Kulawik, G. Schulz-Ekloff and N.I. Jaeger, University of Bremen, Bremen, Germany
Question by L. Bonneviot, Laval University, Ste.-Foy, Quebec, Canada: In the presence of sodium, silicon and oxygen of the framework, you may expect during the reaction of TiCI 4 with the silanol group that a sodium form of titanium silicate might be generated. The UV absorption spectra of such silicates could explainan intermediate red shift of the absorption identical to the shift associated to the single linked TiO x species (Si-O-TiOx) which you proposed here. Is that possible under your preparation and thermal conditions? Answer by J. Klaas: Samples showing the UV band assigned to single linked TiO x species were dry faujasites treated with TiCl 4 at 100 ~ No destruction of the zeolite framework was observed by XRD, nor was a new phase formed. The same is observed for samples treated at 400 ~ but anatas is formed and no silicate species form. Thus at 100 ~ titanium is linked to the framework, although it cannot be excluded that sodium is coordinated to the Siframework-O-TiOx units.
Questions by H.G. Karge, Fritz Haber Institute of the Max Planck Society, Berlin, Germany: 1) Dr. Klaas, the species Si--O
C1 Ti
Si--O ~
and
-- Si-- O - - TiC13
~C1
which you have proposed should be distinguishable by the different IR modes of, e.g.,
( ( ~ SiO)2Ti.z )
and
SiO --Ti
439 in the mid IR. Did you observe differences in the IR spectra? 2) Since you assume insertion of Ti upon reaction of TiC14 with internal silanol groups, the question arises, whether you could also incorporate Ti via this insertion into tetrahedral framework coordination. Could this be evidenced by, e.g., observation of the band around 960 cm -1 in the IR or Raman spectra?
Answers by J. Klaas: 1) The species mentioned are only intermediate species. Since no insitu treatments with TIC14 were performed, it was not possible to record spectra of samples containing these species. With our equipment it was not possible to take spectra of the hydrolyzed samples in that range, since our vacuum cell is not transparent in the region below 900 cm -1. 2) The existence of tetrahedral titanium in freshly prepared TiONaY treated with TiC14 at 400 ~ was proven by UV/VIS spectroscopy. However, the band around 960 cm -1 was not found in the IR or Raman spectra. The precise origin of this band is not clear, it is probably due to an Si-O vibration which is influenced by adjacent framework titanium. Hence it can be expected that this band is not found in the faujasite structure, even if tetrahedral titanium is present. Our spectra seem to indicate this, although they do not prove it. IR or Raman spectra were not recorded soon after the synthesis, and we have no indication of the amount of tetrahedral titanium present in these samples, thus it may be a question of sensitivity as well.
Question by W.M.H. Sachtler, Northwestern University, Evanston, Illinois, USA: In similar work we used chemical vapor deposition (CVD) of GaCI 3 and PdCI 2 on zeolites. With the H+-form, high dispersion was achieved via reactions such as (i) GaCI 3 + H+zeol. -+ Ga(C12)+zeol. + HClvapor, followed by (ii) Ga(Cl2)+zeol. + H20 --+ (GaO)+zeol. + 2 HCI. Could you please explain why you prefer to use the Na§ of the zeolite in your work rather than the H+-form? Answer by J. Klaas: In the literature, the H+-form has been described to be less stable under the conditions of our TiCI 4 treatment, so we started with the Na+-form to avoid destruction of the zeolite framework to the largest possible extent. The desired high dispersion was achieved. The H+-form will probably prefer one reaction pathway with TiC14. The identification of different TiO species required that different faujasite samples preferred different reaction pathways leading to different TiO species.
Questions by F. Schfith, University ofMainz, Mainz, Germany: 1) How do the I.W spectra compare with the one of rutile? 2) What are the loadings you can achieve, and can you react all OH-groups?
Answers by J. Klaas: 1) The absorption edge of rutile is at an even longer wavelength than that of anatas and was omitted for clarity. 2) It was not the aim of our work to achieve high loadings. For NaX, the maximum loading was reached after a TiCI4 treatment of less than
440 20 min at 100 ~ corresponding to less than 1 wt.-% of titanium. Probably all accessible OH-groups reacted in that case. With NaY, by contrast, accessible OH-groups were still present even after a TiCl 4 treatment of 60 min at 100 ~ corresponding to about 4 wt.-% of titanium. The different behavior may be due to the pretreatment of NaX: it was calcined in oxygen at 400 ~ to remove the template, whereas NaY was synthesized template-free and not calcined. Probably, some reorganization of the framework happened during the calcination of NaX, reducing the number of defects and of the accompanying OH-groups.
Question by K. Unger, University of Mainz, Maim, Germany: During the reaction with TiCI4, hydrogen chloride is evolved which will affect the properties of the product. How did you achieve a complete removal of HCl and how did you monitor analytically its removal? Answer by J. Klaas: HCI was removed by heating the sample in a stream of dry nitrogen (5 l/h) up to 250 ~ for at least one hour. The complete removal was checked by washing the sample with water and analyzing the water for Cl- with AgNO 3. Furthermore, no chlorine could be detected by XPS.
B026
Conducting Polymer Wires in Mesopore Hosts by C.-G. Wu and T. Bein, Purdue University, West Lafayette, Indiana, USA
Comment and Question by J.S. Beck, Mobil Research and Development Corp., Princeton, New Jersey, USA: 1) In the example of polymerization of acrylonitrile within MCM-41, it would seem that the graphitic ribbon-like materials formed could be characterized in several ways. For example, the TEM should show these domains when the silicate portion is dissolved. 2) Do the polymers formed in the channels of MCM-41 have any effect on polymer linearity and branching dispersity compared to the bulk? Answer by T. Bein: 1) TEM would indeed be an interesting characterization method for the isolated materials. 2) We have not observed any striking differences in the GPC results for encapsulated versus bulk polyacrylonitrile, except the shorter chain length in the former. The large MCM-41 channels could be the reason.
Questions by H. van Bekkum, Delft University of Technology, Delft, The Netherlands: 1) What is the percentage of the loaded aniline participating in the polymerization? 2) Is a difference in reactivity expected between wall-associated and "inner bulk" aniline? Answers by T. Bein: 1) Not all of the absorbed aniline polymerizes inside the host. Details are in our recent Science paper on this subject. 2) There may be a subtle reactivity difference between the two types of aniline (if they are sufficiently different), but we have not observed such an effect directly. The end result of the polymerization suggests that the channel walls
441 are coated with PANI and could point to either different reactivities or easier removal of "inner bulk" aniline into solution.
Questions by J. Caro, Institute of Applied Chemistry, Berlin, Germany: 1) By changing the frequency in the microwave conductivity measurements, you should get information on the chain length of the PANI. Did this chain length coincide with the pore length of MCM-41 ? 2) In your schematic drawing, you always show PANI as isolated parallel chains. Why do you exclude a random orientation of PANI as in the bulk PANI? Answers by T. Bein: 1) Frequency-dependent measurements are on the way. So far, we have determined the PANI chain length with GPC and found the chains to be shorter than in the bulk (and shorter than the average crystal size of our MCM-41). 2) The drawings are simplified to enhance clarity. We believe that there are different orientations, but we do not have clear evidence concerning order at this time.
Question by B.F. Chmelka, University of California, Santa Barbara, California, USA: Given the presumably intimate contact between the polyacrylonitrile (PAN) and the MCM41 host lattice, how do you account for the similarity of the PAN-MCM-41 material's 13C MAS NMR spectrum compared with that from bulk PAN? No confinement effects or surface influences on molecular order or mobility are apparently observed. Answer by T. Bein: We have not studied the PAN-MCM-41 interactions with MAS NMR in great detail. There may be some differences detectable on closer scrutiny.
Question by R. Hoppe, University of Bremen, Bremen, Germany: I would expect that, upon pyrolyzing your polymer (e.g., PPANZ or PPAN), the pressure inside the MCM-41 channels increases. Did you observe destruction of the crystallites by explosions or the like brought about by such an increase of the internal pressure? Answer by T. Bein: No, XRD shows that the zeolites remain intact. Question by J.B. Nagy, Facultds Universitaires Notre-Dame de la Paix, Namur, Belgium: On your schemes, you have shown the nice polymers and carbon sheets inside the crystallites. Do these chains or sheets grow beyond the length of the MCM-41 channels and, if yes, did you observe a secondary porosity which could be created by these chains? We have recently synthesized fullerene nanotubes in HY zeolite, and we have observed by high resolution TEM the tubes coming out of crystallites. Answer by T. Bein: No, the polymers and sheets are not observed to protrude from the channels, but this may be due to limited TEM resolution. Not much external material is expected on the crystal faces because the d. c. conductivity of pressed pellets is as low as that of unloaded zeolites.
442
Questions by D.R. Rolison, Naval Research Laboratory, Washington, D.C., USA: 1) Professor Chuck Martin has been demonstrating for years with nanoporous membranes the concept you describe: use narrow pores to control the orientation and morphology of conducting polymer fibers and thereby enhance the longitudinal conductivity of such constrained polymers relative to their bulk isotropic values. You see this with polyacrylonitrile pyrolyzed in the presence of the mesoporous h o s t - why don't you see a similar enhancement for the polyaniline-MCM-41 system? 2) Why can't your diminution of sorption capacity for the polyaniline-MCM-41 system be explained by partially clogged pores in the face of the mesoporous host rather than by partially filled channels behind the pore? Such an arrangement would yield islands or plugs of porous polyaniline at the surface and would lower adsorption capacity and still yield minimal d. c. electronic conductivity as the conduction path through a pressed pellet of PANI-MCM-41 would be erratic and incomplete. Answers by T. Bein: 1) The reason for lower conductivity in the encapsulated PAN] is not clear at this time. We might speculate that most of the charged PANI has close interactions with the host, leading to trapping of charge carriers. 2) Partial pore clogging could contribute to apparently reduced pore volume, but we also observe a shift of the inflection point of the isotherm to lower P/Po, i.e., to smaller pore diameters. Question by R. Roque-Malherbe, Instituto de Tecnologia Quimica, CSIC-UPV, Valencia, Spain: Are the benzene tings opened during polymerization? Answer by T. Bein: No, vibrational spectroscopy shows the typical aromatic/quinoid ring vibrations similar to bulk materials.
Questions by K.K. Unger, University of Mainz, Mainz, Germany: 1) What are the differences in the structural properties of the polymer formed in the pores of MCM-41 as compared to the polymer formed in the bulk? 2) You showed the molecular weight distributions of both types of PAN assessed by means of GPC. GPC, however, requires a calibration. What kind of standards did you use for the calibration? Answers by T. Bein: 1) So far, we have not observed any significant differences between encapsulated and bulk PAN, except a smaller molecular weight in the former. This may be due to the wide channels of the host. 2) The GPC standard was commercial PAN with known molecular weight distribution.
443
B027
Optical Properties in Zeolites
of
Self-Assembled
Dipole
Chains
by F. Marlow, K. Hoffmann, W. Hill, J. Kornatowski and J. Caro, Institute of Applied Chemistry, Berlin, Germany; Institute of Spectrochemistry and Applied Spectroscopy, Dortmund, Germany; Johann Wolfgang yon Goethe University, Frankfurt am Main, Germany Question by H. van Bekkum, Delft University of Technology, Delft, The Netherlands: I would expect a temperature effect on the quality of the alignment of the molecules. Did you adsorb at some different temperatures? Answer by J. Caro: If the composite consisting of a self-assembled dipole chain in the pore is warmed up, pyroelectricity is observed due to the rising fluctuation of the dipolar molecules (see J. Caro et al., Adv. Mater. 6, 1994, 413). The decrease of molecular alignment with increasing temperature was also observed by polarized IR microscopy (see F. Schtith et al., paper No. B024 of this Conference). Quite another temperature dependent effect can be observed during the loading procedure. When bringing guest molecules like para-nitroaniline into the zeolite pores via the gas phase at elevated temperatures (100 to 150 ~ both ends of the AIPO4 crystals become sorbate free after cooling to room temperature, since the para-nitroaniline dipole chains contract in the middle of the AIPO4-5 crystal. Temperatures between 100 and 150 ~ must be applied to enable both a sufficiently high gas phase pressure of the dye and intracrystalline diffusivity. We solved this problem by applying liquid phase loading with the dye dissolved in a solvent the molecules of which are too large to enter the zeolite pores, e.g., triisopropylbenzene for loading A1PO4-5. Question by D. Kall6, Central Research Institute of Chemistry of the Hungarian Academy of Sciences, Budapest, Hungary: Was the same arrangement and rearrangement of paranitroaniline observed in the MFI structure? A stepwise adsorption isotherm may result due to optical recognition. Answer by J. Caro: For the MFI structure we know from single crystal X-ray analysis that the adsorbed para-nitroaniline molecules are located at the channel intersections with their length axes nearly parallel to the straight channels. No adsorbed molecules were in the sinusoidal channels. We therefore think that there is only one kind of adsorbed paranitroaniline. Consequently, we do not expect steps to occur in the isotherms for the system para-nitroaniline/MFI.
Question by J.H. Koegler, Delft University of Technology, Delft, The Netherlands: Did you try to load the AIPO4-5 crystals with para-nitroaniline from one side of the crystal, e.g., with the help of the membrane you developed?
444
Answer by J. Caro: Yes, we did. However, no significant effect on the frequency doubling was observed. This is understandable since the second harmonic generation of the two crystal halves is generated in macroscopically separated systems (each being ca. 50 ~tm in length and, hence, much larger than the wave length of light) and can, therefore, not cancel each other.
A030
Examination of the "Decomposition Behavior" of Zeolite A in Freshwater, Particularly Taking into Consideration Environmentally Relevant Conditions by P. K u h m and W. Lortz, Henkel KGaA, Diisseldorf, Germany; Degussa AG, Hanau, Germany
Questions by P.J. Chong, Korean Research Institute of Chemical Technology, Seoul, Korea: The particle size is important in the degradation or solubility of zeolite A. 1) Which particle size distribution did you use in your work? 2) Could you please comment on the effects of the crystallite size on the decomposition rate? Answers by W. Lortz: 1) We used Wessalith P, the trade name of Degussa's zeolite NaA. The particle size of this particular product is controlled during the synthesis such as to achieve optimum performance as a water-softening builder in detergents. Typically, the particle size distribution is d 5 = 7 ~tm, d50 = 3.5 pm and d90 = 2 ~tm. 2) I think that the larger particles must be more stable than the smaller ones, but this effect is probably not very pronounced because after one week we do not see any difference between the electron diffraction images of crystallites of different size.
Question by E.N. Coker, Fritz Haber Institute of the Max Planck Society, Berlin, Germany: You described very clearly what happens to the aluminum released from decomposing zeolite A. However, what happens to the silica species which are released?
Answer by W. Lortz: We do not know at the moment what happens to the silica species which are released from the zeolite, but we believe that, with the increasing amount of soluble sodium silicates in detergents, this will become much more a matter of concern. Perhaps, ortho-silicates are responsible for increasing contents of silica algae in sea waters.
Question by K.G. Ione, Boreskov Institute of Catalysis, Novosibirsk, Russia: The drinking water of industrial cities is rich in heavy metal cations. Did you look at the stability of zeolite NaA and the immobilization of heavy metal cations? Answer by W. Lortz: The ion exchange of zeolite NaA is very selective for heavy metal ions, hence zeolite A is able to eliminate these metal ions from contaminated waste water.
445 However, zeolite A is not able to re-mobilize heavy metals from sediments, because these metals are normally immobilized in sediments as sulphides. So we did not investigate the stability of zeolite A loaded with heavy metals, because their expected content of heavy metals will be much lower than their sodium or calcium content.
Question by W.M. Meier, Swiss Federal Institute of Technology Zurich, Zurich, Switzerlanc~ At one time not so long ago, aluminum was considered to be responsible for Alzheimer's disease. This is no longer maintained, however, soluble aluminum is still anything but harmless in this context. Would you please comment on this? Answer by W. Lortz: Yes, soluble aluminum is not harmless, especially to fish, but this pertains to concentrations (approximately > 0.150 mg/l) which will be reached only in some specific lakes at pH < 6. For example, the contents of soluble AI 3+ in the rivers Main and Rhine amount to 5 ppb and 10 to 20 ppb, respectively. The small portions of zeolite NaA which pass the sewage treatment will be transformed quantitatively into stable and insoluble calcium-aluminum-silicate-phosphates.
A031
Zeolite Catalysis for Upgrading Gasoline by C.Y. Yeh, H.E. Barner and G.D. Suciu, ABB Lummus Crest, Inc., Bloomfield, New Jersey, USA
Question by S.M. Csicsery, Lafayette, California, USA: Although benzene alkylation improves the overall octane number of the whole gasoline, the octane number of the light gasoline fraction (the so-called "front-end octane") will decrease. A large decrease in the front-end octane could require the addition of octane improvers, such as MTBE. How much does the octane number of the light gasoline fraction decrease al~er the removal of benzene? Answer by C.Y. Yeh: If you refer to the simplified scheme in the slide or the paper, you will see that we are dealing with the complete reformate stream. At the fractionation column, the benzene-rich light reformate fraction was separated from the heavy fraction for alkylation. Benzene in the light fraction was alkylated, eventually combined with the heavy fraction and sent to the gasoline pool. Theretbre, no components or fractions were removed from the original "total reformate stream" to cause a decrease in octane. Benzene was not removed in the process; it was converted to the alkylbenzenes. Therefore, there is a net increase in the octane value and octane barrel of the reformate stream by this alkylation process.
Questions by E.G. Derouane, Facultds Universitaires Notre-Dame de la Paix, Namur, Belgium: 1) When you add propylene, cumene formation appears to explain almost
446 completely the decrease in benzene. Self-alkylation is then reduced. Am I correct? 2) At low temperatures and on large-pore zeolites, reactions such as alkylation of aromatics usually result in severe catalyst deactivation. Can you comment on this? What is your catalyst lifetime? Answers by C.Y. Yeh: 1) Since the catalyst has the characteristics of cracking long-chain paraffins to light olefins and other product(s), we believe that the olefin(s) formed as the result of cracking will always be available for (self-)alkylation. Depending on the amount of propylene added (or aromatics to olefins ratio), the proportion of alkylated products derived from (self-)alkylation and (enhanced) alkylation will be different. 2) Generally speaking, the catalyst life in the reformate alkylation will be shorter than in the alkylation of pure benzene with ethylene or propylene. This is the reason why we chose to use a slurry reactor which enables continuous regeneration of the catalyst. The actual catalyst life or regeneration rate will be different from one refinery to another, depending on the composition of deleterious impurities in the feed streams (reformate and FCC off-gas). We do not have actual catalyst life on commercial streams. However, preliminary calculations based on the actual size of commercial streams and estimated catalyst purge rates (to FCC unit), indicate that a portion of the existing fresh catalyst make-up to the FCC unit can be fed into the alkylator. This scheme can eliminate the requirement or cost of a new separate catalyst regenerator.
Question by K.G. lone, Boreskov Institute of Catalysis, Novosibirsk, Russia: Do you know that in Siberia, Russia, an industrial plant for upgrading of low octane gasoline has been in operation since three years ago? In the final products, the concentration of benzene is less than 5 % and that of paraff'ms less than 12 %. The patents are held by the Siberian Academy of Sciences of Russia. Answer by C.Y. Yeh: We are not aware of what happened in Siberia, Russia. A process for improving the octane number of gasoline is always highly desirable. However, our first objective was to reduce the benzene content in gasoline to meet the specifications (i.e., < 1.0 vol.-%) set by the U.S. government. An increase in the octane number and in the octane barrel are the accompanying benefits. Based on what you said, the Russian process which achieved a product with less than 5 % benzene most likely cannot meet the specifications for the U.S. standard in the complex model for the reformulated gasoline.
A032
Studies on W a x Isomerization for L u b e s and Fuels by
S.J.
Miller,
California, USA
Chevron Research and Technology Co., Richmond,
447
Question by E.G. Derouane, Facult~s Universitaires Notre-Dame de la Paix, Namur, Belgium: The unique behavior of SAPO-11 in isomerization dewaxing definitely results from its elliptical pore shape. In the late 80's, when we were developing our ideas about conf'mement effects, we observed unexpectedly large differences between the sorption heats of n- and iso-paraffins, at equivalent carbon content, in SAPO-11. These differences were explained by confinement effects. Could this be, in part, an explanation for the high selectivity of SAPO- 11 ? Answer by S.J. Miller: The effects you mention could very well be relevant. Certainly, pore geometry is very important to catalyst selectivity. As mentioned in the paper, other intermediate-pore sieves with unidimensional pores similar in size to SAPO-11 also show attractive isomerization selectivities.
Question by P.A. Jacobs, Catholic University of Leuven, Heverlee, Belgium: For the isomerization of n-hexadecane on Pt/SAPO-11, you report equilibrium distributions of the methylpentadecanes. If the catalysis were purely intracrystalline conversion, one would expect selectivities for the 2-methyl isomer above equilibrium, even at these high conversions. Does this mean that most of the catalysis is "at or near" the external surface? Why is this topology then so specific? Answer by S.J. Miller: At lower hexadecane conversion (ca. 70 ~ or less), there is a definitely enhanced formation of the 2-methyl isomer (see S.J. Miller, Microporous Materials 2, 1994, 439-449). At very high conversion (ca. 95 %), that enhancement is lost. This does not necessarily mean that "most" of the conversion now takes place at or near the external surface. We do believe, however, that a considerable fraction of the chemistry does occur there, as evidenced by the 2,2,4-trimethylpentane/n-octane data.
Question by D.C. Koningsberger, Utrecht University, Utrecht, The Netherlands: You mentioned an increase in hydrogenation activity by adding nitrogen. Platinum is doing the hydrogenation. Do you understand why nitrogen enhances the hydrogenation activity of Pt? Answer by S.J. Miller: The catalyst is bifunctional, with both hydrogenation and acid activity. By reducing the acidity through nitrogen addition, the ratio of hydrogenation to acid activity should increase. This is evidenced by an increase in the feed isomerization selectivity with a decrease in cracking.
Question by C. Perego, Eniricerche S.p.A., San Donato Milanese, Italy: I would expect some influence of the sulfur content on the catalyst life. Do you have any evidence of this? If yes, did you succeed in catalyst regeneration? Answer by S.J. Miller: High sulfur feeds necessitate higher operating temperature, which reduces run life. In cases where the sulfur content was increased to high levels (100 ppm or
448 more), nearly all the activity could be recovered by returning to feedstocks with a low sulfur content. This allowed the catalyst to be run for several thousand hours without the need for regeneration.
A033
S k e l e t a l Isomerization of Olefins with the Zeolite Ferrierite as C a t a l y s t
by H.H. Mooiweer, K.P. de Jong, B. Kraushaar-Czarnetzki, W.H.J. Stork Koninklil'ke/Shell-Laboratorium, Amsterdam, and B.C.H. Krutzen, The Netherlands Question by E.G. Derouane, Facult~s Universitaires Notre-Dame de la Paix, Namur, Belgium: What is the relative importance of the bimolecular and the cyclopropyl intermediate routes for the formation of isobutene? 13C NMR using labelled molecules could elucidate this problem. Do you have data available which could clarify this point? Answer by B. Kraushaar-Czarnetzki: I have shown 13C NMR spectra of labelled 2butene-2-13C loaded on ferrierite. These spectra, which were taken with closed ampoules, clearly indicate that dimerization readily takes place in the FER pores at low temperatures. We are presently carrying out the isomerization reaction under "real" conditions in a plug flow reactor implemented in an NMR spectrometer. These in-situ NMR studies will probably contribute to a clarification of the reaction mechanism. Question by F. Fajula, Ecole Nationale Sup6rieure de Chimie de Montpellier, CNRS, Montpellier, France: One would expect that the two important parameters which determine the activity and selectivity are the Si/Al-ratio and the size of the crystals. Could you please comment on this? Answer by B. Kraushaar-Czarnetzki: Questions referring to the synthesis and to the finetuning of the catalyst are touching confidential matters. Please understand that I cannot comment on the two items. Question by J. Fraissard, Universit6 Pierre et Marie Curie, CNRS, Paris, France: There are two different types of channels in ferrierite: unlimited b channels and sphere-like c ones. What is their relative importance in the isomerization reaction? Answer by B. Kraushaar-Czarnetzki: Normal butenes have access to both types of pores, while isobutene as well as isooctenes can only migrate through the 10-membered ring pores. Accordingly, the 8-membered ring channels play only a minor role as diffusion pathways.
449
Question by J. van Hooff, Eindhoven University of Technology, Eindhoven, The Netherlands: You prefer the dimerization-cracking mechanism to explain the high selectivity of the ferrierite catalysts to isobutene. Propene can be formed as well by cracking, so what is your explanation for the absence of an extended propene formation in your experiments? Answer by B. Kraushaar-Czarnetzki: Both site density and site location in FER apparently promote the selective formation of 2,2,4-trimethylpentane or 2,4dimethylhexane, which are the precursors of isobutene. If these species are selectively formed, the cracking must be very selective too. In "non-optimized" FELL, other dimeric species and, correspondingly, other cracking products are also formed. However, as shown in the experiment with the propene/1-butene feed mixture, propene itself can be involved in consecutive dimerization reactions.
Question by J. K~irger, University of Leipzig, Leipzig, Germany: Olefins adsorbed in ferrierite may be assumed to represent an ideal single file system. The correlation of molecular motion in such systems has been shown to lead to a dramatic accumulation of the reaction products in the interior of the channels, which results in rather low effectiveness factors. The efficiency of the use of such catalysts should be substantially enhanced, therefore, by using small crystallites and/or crystallites with structure defects allowing molecular exchange between different channels. Could you please comment on this? Answer by B. Kraushaar-Czarnetzki: It is true that the pore filling of FER with dimers or even with oligomeric products is extremely high. Maybe we are even dealing with chains which move forward in a stepwise manner, while n-butenes enter the pore mouth and isobutene leaves at the other end. However, we observed that the isobutene yield is not decreased, but rather increased, by internal coke deposition. Accordingly, the degree of porosity or channel interconnectivity is not a limiting parameter. Question by J.A. Lercher, University ofTwente, Enschede, The Netherlands: One might be able to differentiate between the monomolecular and the bimolecular route on the basis of reaction orders. Do you have information on the reaction orders that would help to differentiate between the possible mechanisms? Answer by B. Kraushaar-Czarnetzki: In case of the bimolecular mechanism, the rate determining step is the cracking of the 2,2,4-trimethylpentene or the 2,4-dimethylhexene. Therefore, the reaction order, which is 1, does not really give evidence for a monomolecular pathway. With this reaction order of 1, both mechanisms are still possible.
450 A034
Effect of Temperature on Propane Aromatisation by Ga/HMFI(Si, AI) Catalysts by S.B. Abdui Hamid, E.G. Derouane, P. M6riaudeau, C. Naccache and M. Ambar Yarmo, Petronas Research and Scientific Services, Hulu Klang, Selangor, Malaysia; Facult6s Universitaires Notre-Dame de la Paix, Namur, Belgium; Institut de Recherches sur la Catalyse, CNRS, Villeurbanne, France; Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia
Question by J. van Hooff, Eindhoven University of Technology, Eindhoven, The Netherlands: On the one hand you are claiming that little hydrogen transfer occurs between the small molecules; but on the other hand, you observe large amounts of aromatics formed from oligomerization products. Do you exclude hydrogen transfer reactions in this case as well?
Answer by E.G. Derouane: Our results clearly indicate, indeed, that hydrogen transfer does not occur much at low conversion. As shown by Iglesia et al., the role of Ga is to provide a porthole for the recombination desorption of dihydrogen. The most active species for such H a desorption were identified in Dr. Abdul Hamid's thesis as being extra-framework, intracrystalline, well dispersed gallium species.
Questions and Comment by Y. Ono, Tokyo Institute of Technology, Tokyo, Japan: 1-) You assume that aromatic hydrocarbons are formed from propene through hexenes. How do you explain the formation of toluene and xylenes? 2) The presence of methyl groups is not taken into consideration in your arguments for aliphatic hydrocarbons. Does this cause any problems in your conclusion on the reaction mechanism? 3) Hexanes easily decompose into propane and propene. This should be included in your mechanism. Answers by E.G. Derouane: 1) The formation of toluene and xylenes is accounted for by the same mechanism, by combining propene and butene or two butenes, respectively. 2) We do only observe the methyl group resonances of ethane, propane and butanes. Other species are only present in very small concentrations at low conversion. Thus, our answer is no. 3) You are perfectly correct. In fact, this route is opposite to the propane-propene reaction. The corresponding arrow in our scheme does not mean that the propane-propene reaction is irreversible. It only indicates the "flow" of reactants.
Question by M.M. Ramirez de Agudelo, INTEVEP S.A., Caracas, Venezuela: Your data showed a difference in activation energy for cracking and dehydrogenation of only 4 kJ/mol which is less than 5 % of the actual value. So, how would you explain your conclusion on the optimization of the cracking/dehydrogenation at higher temperature?
451 Answer by E.G. Derouane: Our conclusion is substantiated by literature data (see, e.g., Harris). Also, we show results at very low conversion, where cracking is not dominant yet. Many secondary reactions, as you well know, take place at higher conversion and affect aromatization selectivity.
452
List of Participants (sorted by countries)
MANUEL, A. K. C.P. 1756 Luanda ANGOLA
AKOLEKAR, D. B. Univ. of New South Wales Dept. of Physical Chemistry P.O. Box 1 Kensington, NSW AUSTRALIA HE, S. J. X. Univ. of New South Wales School of Chemistry Sydney NSW 2052 AUSTRALIA LONG, M. A. Univ. of New South Wales School of Chemistry Sydney NSW 2052 AUSTRALIA SMITH, T. D. Monash University Chemistry Dept. Clayton, Victoria 3168 AUSTRALIA
BARTH-WIRSCHING, U. Technische Universit~t Graz Inst. fiir Techn. Geologie und Angewandte Mineralogie Rechbauerstrasse 12 8010 GRAZ AUSTRIA HOCHTL, M. TU Wien Institut fttr physik. Chemie Getreidemarkt 9 1060 Wien AUSTRIA
JENTYS, A. Technische Universitat Wien Institut far Physik. Chemie Getreidemarkt 9/156 1060 Wien AUSTRIA
KLAMMER, D. Teclmische Universit~t Graz Inst. far Technische Geologie Reckbauerstrasse 12 8010 Graz AUSTRIA KLEMENT, A. Minnova Mineralien Handelsgesellschaft UImgasse 12 8501 Lieboch AUSTRIA KORANYI, T. Technische Universitat Wien Inst. ftir Physik. Chemie Getreidemarkt 9/156 1060 Wien AUSTRIA LENGAUER, C. Universitat Wien Institut flit Mineralogie Dr.-Karl-Lueger-Ring 1 1010 Wien AUSTRIA LUGSTEIN, A. Inst. far Physik.Chemie TU Wien Getreidemarkt 9/156 1060 Wien AUSTRIA STOCKENHUBER, M. Technische Universit~t Wien Institut fiir Phys. Chemie Getreidemarkt 9 1060 Wien AUSTRIA VINEK, H. Technische Universit/it. Wien Institut fiir Physik. Chemie Getreidemarkt 9/156 1060 Wien AUSTRIA
ANTHONIS, M. Exxon Chem. Int.Inc. Hermeslaan 2 1831 Machelen BELGIUM BODART, P. FINA Research S.A. Centre du Recherche du Groupe Petrofina Zone Industrielle C 7181 FELUY BELGIUM
DAKKA, J. Exxon Chemicals Hermeslaan 2 1831 Machelen BELGIUM DELMON, B. Univ. Catholique de Lovain Place Croix du Sud 2117 1348 Lovain-la-Neuve BELGIUM DEROUANE, E. Facult~s Univ. de Namur Laboratory of Catalysis Rue de Bruxelles 61 5000 Namur BELGIUM ESPEEL, P. H. J. K U Leuven C e n t m m voor Oppervlaktechemie en Katalyse 92, Kardinaal Merciedaan 3001 Heverlee (Leuven) BELGIUM
FEIJEN, E. J. P. KU Leuven Centntm voor Oppervlaktechemie en Katalyse 92, Kardinaal Mercielaan 3001 Heverlee (Leuven) BELGIUM GABELICA, Z. Facult6s Univ. de Namur Laboratoire de Catalyse 61 Rue de Bruxelles 5000 Namur BELGIUM
453
GROBET, P. J. KU Leuven Centntm Oppervlaktechemie Kardinaal Mercierlaan 92 3001 Leuven (l-Ieverlee) BELGIUM
ONIDA, B. Facult6s Universitaires de Namur Laboratoire de Catalyse 6 I, Rue de Bruxelles 5000 Namur BELGIUM
VANSANT, E. University of Antwerp Department of Chemistry Universiteitsplein 1 2610 Wilrijk BELGIUM
HIROSE, K. Toyota Motor Europe Avenue Du Bourget 60 1140 Brussels BELGIUM
PARTON, R. K.U. Leuven Center voor Oppervlaktenchemie en Katalyse Kardinaal Mercierlaan 92 3001 Leuven (Heverlee) BELGIUM
WECKHUYSEN, B. M. KU Leuven Centnma voor Oppervlaktechemie en Katalyse Kardinaal Mercierlaaan 92 3001 Heverlee BELGIUM
PONCELET, G. Universit~ de Lovain Unite Cam Place Croix du Sud 2-17 1348 Lovain La Netrve BELGIUM
XIONG, Y.-L. KU Leuven Centmm voor Oppervlaktenchemie en Katalyse 32, Kardinaal Mercierlaan 3001 Heverlee (Leuven) BELGIUM
IVANOVA, I. Facult~s Universitaires de Namur Laboratoire de Catalyse Rue De Bruxelles 61 5000 Namur BELGIUM JACOBS, P. A. KU Leuven Centnma Oppervlaktechemie & Katalyse Kardinaal Mercierlaan 92 3001 Leuven (Heverlee) BELGIUM JANSSEN, M. J. G. Exxon Chemical International Inc. Hermeslaan 2 1831 Machelen BELGIUM KNOPS-GERRITS, P. P. KU Leuven Centrum voor Oppervlaktechemie en Katalyse Kardinaal Mercierlaan 92 3001 Herverlee BELGIUM MARTENS, J. A. KU Leuven Centrum voor Oppervlaktechemie en Katalyse Kardinaal Mercierlaan 92 3001 Leuven Heverlee BELGIUM MORTIER, W. J. Exxon Chemical International Inc. Hermeslaan 2 1831 Machelen BELGIUM NAGY, B. J. Facult6s Universitaires de Namur Laboratoire de Catalyse 61 Rue De Bruxelles B-5000 Namur BELGIUM
PREVOO, H. University of Namur Departement de Chimie 61, Rue de Bruxelles 5000 Namur BELGIUM REMY, M. KU Leuven Unite CATA Place Croix du Sud 2 1348 Lotwain la Neuve BELGIUM SCHOONHEYDT, R.A. KU Leuven Centnma Oppervlaktechemie en Catalyse Kardinaal Mercierlaan 92 3001 Leuven (Heverlee) BELGIUM SU, B. Facult6s Universitaires de Namur Laboratoire de Catalyse 61, rue de Bruxelles 5000 Namur BELGIUM THIBAULT-STARZYK, F. KU Leuven Centrum voor Oppervlaktechemie en Katalyse Kardinal Mercierlaan 92 3001 Heverlee BELGIUM VAN OORSCHOT, C. Exxon Chemical International Inc. Hermeslaan 2 1831 Mechelen BELGIUM
CARDOSO, D. Federal University San Carlos Chemical Engineering Department P.O. Box 676 13565-905 San Carlos BRAZIL MONTEIRO, J. L. F. NUCAT-PEQ/COPPE Universidade Federal do Rio de Janeiro BRAZIL SCHUCHARDT, U. Universidade Estadual de Campinas Instituto de Quimica C.P. 6154 13083-970 Campinas-SP BRAZIL VELOSO, C. O. Univ. Federal do Rio de Janeiro COPPE Ilha do Fundao CP 68502 Rio de Janeiro 21945-870 BRAZIL
454
BEZOUKANOVA, C. University of Sofia Faculty of Chemistry 1, J.D. Bourchier Avenue 1126 Sofia BULGARIA DAVIDOVA, N. Bulgarian Academy of Sciences Institute of Kinetics and Catalysis 1040 Sofia BULGARIA MINCHEV, CH. Bulgarian Academy of Sciences Faculty of Organic Chemistry 1113 Sofia BULGARIA MINTOVA, 5. Bulgarian Academy of Sciences Institute of Applied Mineralogy Rakovsky Str. 92 1000 Sofia BULGARIA PENCHEV, V. Bulgarian Academy of Sciences Institute of Organic Chemistry Nezabratka BI 1 Sofia 1113 BULGARIA POPOVA, Z. University of Sofia Faculty of Chemistry 1126 Sofia BULGARIA VALTCHEV, V. Bulgarian Academy of Sciences Institute of Applied Mineralogy 92, Rakovsky Str. 1000 Sofia BULGARIA ZAKHARIEVA, O. University of Sofia Physical Faculty 1000 Sofia BULGARIA
BAKER, M. University of Guelph Chemistry and Biochemistry Guelph, Ontario N1G 2W 1 CANADA
BONNEVIOT, L. Laval University Departmem of Chemistry St-Foy Quebec GIK-7P4 CANADA DARMSTADT, H. Universit6 Laval Facult6 des Sciences et de g6nie D6pt. de g6nie chimique Sainte-Foy (Qu6bec) G1K7P4 CANADA EIC, M. University of New Bnmswick Dept of Chemical Engineering P.O. Box 4400 Fredericton, N.B. E3B 5A3 CANADA KALIAGUINE, S. Universit6 Laval Dept of Chemical Engineering Pavillion Pouliot Ste Foy, Quebec, G1K 7P4 CANADA KOKOTAILO, GEORGE T. University of British Columbia Vancouver BC V6T IY6 CANADA KUPERMAN, A. University of Toronto Lash Miller Laboratories Adv. Zeolite Mat. Science Group Toronto, Ontario M5S 1A1 CANADA LEWIS, A. R. University of British Columbia 2036 Main Hall, UBC Vancouver, BC V6T 1ZI CANADA
SHELLEY, M. University of British Columbia and Dept. of Chemistry 4004 Wesbrook Mall Vancouver BC V6T 2A3 CANADA
ANTONIC, T. Ruder Boskovic Institute P. O. Box 54 41001 Zagreb CROATIA BRONIC, J. Ruder Boskovic Institute Bijnicka 54 41001 Zagreb CROATIA CIZMEK, A. Ruder Boskovic Institute Bijnicka 54 41001 Zagreb CROATIA SUBOTIC, B. Ruder Boskovic Institute P.O. Box 1016 4 I001 Zagreb CROATIA
BRABEC, L. J. Heyrovsky Institute of Physical Chemistry Dolejskova 3 182 23 Prague 8 CZECH REPUBLIC
LORTIE, C. Laval University Chemistry Department Quebec G1K 7P4 CANADA
CEJKA, J. J. Heyrovsky Institute of Physical Chemistry Dolejskova 3 182 230 Prague 8 CZECH REPUBLIC
RUTHVEN, D.M. University of New Bnmswick Dept. of Chemical Engineering P.O. Box 44 00 Fredericton, NB E3B 5FA3 CANADA
DEDECEK, J. J. Heyrovsky Institute of Physical Chemistry Dolejskova 3 18223 Prague 3 CZECH REPUBLIC
SAYARI, A. University Laval Dept of Chemical Engineering and CERPIC Saint-Foy, QC G1K 7P4 CANADA
455
KOCIRIK, M. J. Heyrovsky Institute of Phys. Chem. Dolejskova 3 18223 Prague 8 CZECH REPUBLIC
BLOM, N. Haldor Topsoe MS P.O. Box 213 Nymollevej 55 2800 Lyngby D E I ~
KUBELKOVA, L. J. Heyrovsky Institute of Physical Chemistry and Electrochemistry Dolejskova 3 18223 Prague 2 CZECH REPUBLIC
DONNIS, B. Haldor Topsoc MS Nym611evej 55 2800 Lyngby DENMARK
RATHOUSKY, J. J. Heyrovsky Institute of Physical Chemistry and Electrochemistry Dolejskova 3 182 23 Prague 8 CZECH REPUBLIC SOBALIK, Z. J. Heyrovsky Institute of Physical Chemistry Dolejskova 3 182 23 Prague 8 CZECH REPUBLIC WlCHTERLOVA, B. J. Heyrovsky Institute of Physical Chemistry and Electrochemistry Dolejskova 3 18223 Prague 8 CZECH REPUBLIC ZIKANOVA, A. J. Heyrovsky Institute of Physical Chemistry Dolejskova 3 182 23 Prague CZECH REPUBLIC
ANDERSEN, I. G. K. Odense University Chemistry Dept. 5230 Odense DENMARK ANDERSEN, E. K. Odense University Chemistry Dept. 5230 Odense DENMARK
KELLER, E. Haldor Topsoc MS Nymollevej 55 2800 LYNGBY DENMARK SLABIAK, T. Haldor Topsoe MS NymOllevej 55 2800 Lyngby DENMARK
HABIB, RAMZI M. Egyptian Petroleum Research Institute P.O. Box 169 Ataba Cairo 11511 EGYPT
KRAUSE, A. O. I. Helsinki University of Technology Department of Chemical Engineering Kemistintie 1 02150 Espoo FINLAND
TIITrA, M. Neste O Y Technology Centre P.O. Box 310 06101 Porvoo FINLAND
TYmAL& P. University of Joensuu Department of Chemistry P. O. Box 111 80101 Joensuu FINLAND
ANDERSEN, A. M. K. Universitd Mont~llier 2 LAMMI - URA 79 Place Eugene Bataillon 34095 Montpellier FRANCE A U R O U X , A. CNRS Institutde Rechcrchcs sur la Catalysc 2 Av Albert Einstein 69626 Villeurbanne FRANCE
BARTHOMEUF, D. Universite Paris 6 Lab Reactive Surf & Struc 4, Place Jussieu 75252 Paris Ccdcx 05 FRANCE BEDIOU, F. ENS de Chimie Paris Laboratoire d'Olectrochimie 11 rue Pierre et Marie Curie 75231 Paris CEDEX 05 FRANCE
PAKKANEN, T. T. University of Joensuu Dept of Chemistry P.O. Box 111 80101 Joensuu FINLAND
BENAZZI, E. Institut Francais du Pdtrole BP 311 1 et 4, Av. de Bois-Prdau 92500 Rucil-Malmaison FRANCE
RAULO, P. Ncste OY Technology Centre Oil Refining Zeolite Catalysts P.O.B. 310, SF-06101 Porvoo FINLAND
BOUGEARD, D. Universitd des Sciences de Lille Laboratoire de Spectrochmimie Infrarouge ct Raman UPR 2631 L CNRS 59655 Villeneuve d'ascq Cedex FRANCE
456
BOURDIN, V. Universit6 du Paris-Sud LIMSI-CNRS 91404 Orsay Cedex FRANCE BRUMARD, C. Universit~ de Lille Laboratoire de Spectrochimie Infrarouge et Raman UPR 2631 L CNRS B~itiment C5 59655 Villeneuve d'Ascq Cedex FRANCE CAULLET, PH. ENS de Chimie de Mulhouse Laboratoire des Mat6riaux Min~raux 3 Rue A. Werner 68093 Mulhouse Cedex FRANCE CHAPUS, TH. Institut Francais du P~trole 1-4 Avenue Bois Bereau Rueil Malmaison FRANCE CHATELAIN, T. ENS de Chimie de Mulhouse 3, rue Alfred Wemer 68093 Mulhouse Cedex FRANCE CHEVREAU, TH. ISMRA Universitd Catalyse ET Spectrochimie 14050 Caen Cedex FRANCE COULOMB, J. P. C.tLM.C. - CNRS Campus de Luminy, Case 901 13288 Marseille Cedex FRANCE DES COURIERES, T. ELF Solaize Centre de Recherche B.P. 22 69360 Solaize FRANCE DI RENZO, F. ENS de Chimie de Montpellier Laboratoire de Chimie Organique et Physique Appliqu6es 8, rue de gEcole Normale 34053 Montpellier Cedex 1 FRANCE
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464
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1ONE, K. K. Russian Academy of Sciences Boreskov Institute of Catalysis Prospekt Akademika Lavrentieva 5 Novosibirisk 630090 RUSSIA
MISHIN, I. N.D. Zelinsky Institute of Organic Chemistry Leninsky Prospekt 47 Moscow 117 913 RUSSIA
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S T U D I E S IN S U R F A C E SCIENCE A N D CATALYSIS Advisory Editors: B. Delmon, Universite Catholique de Louvain, Louvain-la-Neuve, Belgium J.T. Yates, University of Pittsburgh, Pittsburgh, PA, U.S.A.
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Volume 12 Volume 13 Volume 14
Preparation of Catalysts I.Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the First International Symposium, Brussels, October 14-17,1975 edited by B. Delmon, P.A. Jacobs and G. Poncelet The Control of the Reactivity of Solids. A Critical Survey of the Factors that Influence the Reactivity of Solids, with Special Emphasis on the Control of the Chemical Processes in Relation to Practical Applications by V.V. Boldyrev, M. Bulens and B. Delmon Preparation of Catalysts I1. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Second International Symposium, Louvain-la-Neuve, September 4-7, 1978 edited by B. Delmon, P. Grange, P. Jacobs and G. Poncelet Growth and Properties of Metal Clusters. Applications to Catalysis and the Photographic Process. Proceedings of the 32nd International Meeting of the Societe de Chirnie Physique, Villeurbanne, September 24-28, 1979 edited by J. Bourdon Catalysis by Zeolites. Proceedings of an International Symposium, Ecully (Lyon), September 9-11, 1980 edited by B. Imelik, C. Naccache, Y. Ben Taarit, J.C. Vedrine, G. Coudurier and H. Praliaud Catalyst Deactivation. Proceedings of an International Symposium, Antwerp, October 13-15,1980 edited by B. Delmon and G.F. Froment New Horizons in Catalysis. Proceedings of the 7th International Congress on Catalysis, Tokyo, June 30-J uly4, 1980. Parts A and B edited by T. Seiyama and K. Tanabe Catalysis by Supported Complexes by Yu.l. Yermakov, B.N. Kuznetsov and V.A. Zakharov Physics of Solid Surfaces. Proceedings of a Symposium, Bechyhe, September 29-October 3,1980 edited by M. Lazni~,ka Adsorption at the Gas-Solid and Liquid-Solid Interface. Proceedings of an International Symposium, Aix-en-Provence, September 21-23, 1981 edited by J. Rouquerol and K.S.W. Sing Metal-Support and Metal-Additive Effects in Catalysis. Proceedings of an International Symposium, Ecully (Lyon), September 14-16, 1982 edited by B. Imelik, C. Naccache, G. Coudurier, H. Praliaud, P. Meriaudeau, P. Gallezot, G.A. Martin and J.C. Vedrine Metal Microstructures in Zeolites. Preparation - Properties- Applications. Proceedings of a Workshop, Bremen, September 22-24, 1982 edited by P.A. Jacobs, N.I. Jaeger, P. Jir~ and G. Schulz-Ekloff Adsorption on Metal Surfaces. An Integrated Approach edited by J. Benard Vibrations at Surfaces. Proceedings of the Third International Conference, Asilomar, CA, September 1-4, 1982
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edited by C.R. Brundle and H. Morawitz Heterogeneous Catalytic Reactions Involving Molecular Oxygen by G.I. Golodets Preparation of Catalysts III. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Third International Symposium, Louvain-la-Neuve, September 6-9, 1982 edited by G. Poncelet, R Grange and P.A. Jacobs Spillover of Adsorbed Species. Proceedings of an International Symposium, Lyon-Villeurbanne, September 12-16, 1983 edited by G.M. Pajonk, S.J. Teichner and J.E. Germain Structure and Reactivity of Modified Zeolites. Proceedings of an International Conference, Prague, July 9-13, 1984 edited by P.A. Jacobs, N.I. Jaeger, P. Jia3, V.B. Kazansky and G. Schulz-Ekloff Catalysis on the Energy Scene. Proceedings of the 9th Canadian Symposium on Catalysis, Quebec, P.Q., September 30-October 3, 1984 edited by S. Kaliaguine and A. Mahay Catalysis by Acids and Bases. Proceedings of an International Symposium, Villeurbanne (Lyon), September 25-27, 1984 edited by B. Imelik, C. Naccache, G. Coudurier, Y. Ben Taarit and J.C. Vedrine Adsorption and Catalysis on Oxide Surfaces. Proceedings of a Symposium, Uxbridge, June 28-29, 1984 edited by M. Che and G.C. Bond Unsteady Processes in Catalytic Reactors by Yu.Sh. Matros Physics of Solid Surfaces 1984 edited by J. Koukal Zeolites: Synthesis, Structure, Technology and Application. Proceedings of an International Symposium, Portoro~-Portorose, September 3-8, 1984 edited by B. Drs S. Ho~evar and S. Pejovnik Catalytic Polymerization of Olefins. Proceedings of the International Symposium on Future Aspects of Olefin Polymerization, Tokyo, July 4-6, 1985 edited by T. Keii and K. Soga Vibrations at Surfaces 1985. Proceedings of the Fourth International Conference, Bowness-on-Windermere, September 15-19, 1985 edited by D.A. King, N.V. Richardson and S. Holloway Catalytic Hydrogenation edited by L. Cerveny New Developments in Zeolite Science and Technology. Proceedings of the 7th International Zeolite Conference, Tokyo, August 17-22, 1986 edited by Y. Murakami, A. lijima and J.W. Ward Metal Clusters in Catalysis edited by B.C. Gates, L. Guczi and H. Kn6zinger Catalysis and Automotive Pollution Control. Proceedings of the First International Symposium, Brussels, September 8-11, 1986 edited by A. Crucq and A. Frennet Preparation of Catalysts IV. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Fourth International Symposium, Louvain-la-Neuve, September 1-4, 1986 edited by B. Delmon, P. Grange, P.A. Jacobs and G. Poncelet Thin Metal Films and Gas Chemisorption edited by P. Wissmann Synthesis of High-silica Aluminosilicate Zeolites edited by P.A. Jacobs and J.A. Martens Catalyst Deactivation 1987. Proceedings of the 4th International Symposium, Antwerp, September 29-October 1, 1987 edited by B. Delmon and G.F. Froment
489 Volume 35 Volume 36 Volume 37 Volume 38 Volume 39 Volume 40 Volume 41
Volume 42 Volume 43 Volume 44
Volume 45 Volume 46
Volume 47 Volume 48 Volume 49 Volume 50
Volume 51 Volume 52 Volume 53
Keynotes in Energy-Related Catalysis edited by S. Kaliaguine Methane Conversion. Proceedings of a Symposium on the Production of Fuels and Chemicals from Natural Gas, Auckland, April 27-30, 1987 edited by D.M. Bibby, C.D. Chang, R.F. Howe and S. u Innovation in Zeolite Materials Science. Proceedings of an International Symposium, Nieuwpoort, September 13-17, 1987 edited by P.J. Grobet, W.J. Mortier, E.F. Vansant and G. Schulz-Ekloff Catalysis 1987. Proceedings ofthe 10th North American Meeting ofthe Catalysis Society, San Diego, CA, May 17-22, 1987 edited by J.W. Ward Characterization of Porous Solids. Proceedings of the IUPAC Symposium (COPS I), Bad Soden a. Ts., April 26-29,1987 edited by K.K. Unger, J. Rouquerol, K.S.W. Sing and H. Kral Physics of Solid Surfaces 1987. Proceedings of the Fourth Symposium on Surface Physics, Bechyne Castle, September 7-11, 1987 edited by J. Koukal Heterogeneous Catalysis and Fine Chemicals. Proceedings of an International Symposium, Poitiers, March 15-17, 1988 edited by M. Guisnet, J. Barrault, C. Bouchoule, D. Duprez, C. Montassier and G. Perot Laboratory Studies of Heterogeneous Catalytic Processes by E.G. Christoffel, revised and edited by Z. Paal Catalytic Processes under Unsteady-State Conditions by Yu. Sh. Matros Successful Design of Catalysts. Future Requirements and Development. Proceedings ofthe Worldwide Catalysis Seminars, July, 1988, on the Occasion of the 30th Anniversary of the Catalysis Society of Japan edited by T. Inui Transition Metal Oxides. Surface Chemistry and Catalysis byH.H. Kung Zeolites as Catalysts, Sorbents and Detergent Builders. Applications and Innovations. Proceedings of an International Symposium, W6rzburg, September 4-8,1988 edited by H.G. Karge and J. Weitkamp Photochemistry on Solid Surfaces edited by M. Anpo and T. Matsuura Structure and Reactivity of Surfaces. Proceedings of a European Conference, Trieste, September 13-16, 1988 edited by C. Morterra, A. Zecchina and G. Costa Zeolites: Facts, Figures, Future. Proceedings of the 8th International Zeolite Conference, Amsterdam, July 10-14, 1989. Parts A and B edited by P.A. Jacobs and R.A. van Santen Hydrotreating Catalysts. Preparation, Characterization and Performance. Proceedings of the Annual International AIChE Meeting, Washington, DC, November 27-December 2, 1988 edited by M.L. Occelli and R.G. Anthony New Solid Acids and Bases. Their Catalytic Properties by K. Tanabe, M. Misono, u Ono and H. Hattori Recent Advances in Zeolite Science. Proceedings of the 1989 Meeting of the British Zeolite Association, Cambridge, April 17-19, 1989 edited by J. Klinowsky and P.J. Barrie Catalyst in Petroleum Refining 1989. Proceedings of the First International Conference on Catalysts in Petroleum Refining, Kuwait, March 5-8, 1989 edited by D.L. Trimm, S. Akashah, M. Absi-Halabi and A. Bishara
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Future Opportunities in Catalytic and Separation Technology edited by M. Misono, Y. Moro-oka and S. Kimura Volume 55 New Developments in Selective Oxidation. Proceedings of an International Symposium, Rimini, Italy, September 18-22, 1989 edited by G. Centi and F. Trifiro Volume 56 Olefin Polymerization Catalysts. Proceedings of the International Symposium on Recent Developments in Olefin Polymerization Catalysts, Tokyo, October 23-25, 1989 edited by T. Keii and K. Soga Volume 57A Spectroscopic Analysis of Heterogeneous Catalysts. Part A: Methods of Surface Analysis edited by J.L.G. Fierro Volume 57B Spectroscopic Analysis of Heterogeneous Catalysts. Part B: Chemisorption of Probe Molecules edited by J.L.G. Fierro Volume 58 Introduction to Zeolite Science and Practice edited by H. van Bekkum, E.M. Flanigen and J.C. Jansen Volume 59 Heterogeneous Catalysis and Fine Chemicals II. Proceedingsof the 2nd International Symposium, Poitiers, October 2-6, 1990 edited by M. Guisnet, J. Barrault, C. Bouchoule, D. Duprez, G. Perot, R. Maurel and C. Montassier Volume 60 Chemistry of Microporous Crystals. Proceedings of the International Symposium on Chemistry of Microporous Crystals, Tokyo, June 26-29, 1990 edited by T. Inui, S. Namba and T. Tatsumi Volume 61 Natural Gas Conversion. Proceedingsof the Symposium on Natural Gas Conversion, Oslo, August 12-17, 1990 edited by A. Hoimen, K.-J. Jens and S. Kolboe Volume 62 Characterization of Porous Solids II. Proceedingsof the IUPAC Symposium (COPS II), Alicante, May 6-9, 1990 edited by F. Rodriguez-Reinoso, J. Rouquerol, K.S.W. Sing and K.K. Unger Volume 63 Preparation of Catalysts V. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedingsof the Fifth International Symposium, Louvain-la-Neuve, September 3-6, 1990 edited by G. Poncelet, P.A. Jacobs, P. Grange and B. Delmon Volume 64 New Trends in CO Activation edited by L. Guczi Volume 65 Catalysis and Adsorption by Zeolites. Proceedings of ZEOCAT 90, Leipzig, August 20-23, 1990 edited by G. Ohlmann, H. Pfeifer and R. Fricke Volume 66 Dioxygen Activation and Homogeneous Catalytic Oxidation. Proceedings of the Fourth International Symposium on Dioxygen Activation and Homogeneous Catalytic Oxidation, BalatonfL~red, September 10-14, 1990 edited by L.I. Simandi Volume 67 Structure-Activity and Selectivity Relationships in Heterogeneous Catalysis. Proceedings of the ACS Symposium on Structure-Activity Relationships in Heterogeneous Catalysis, Boston, MA, April 22-27, 1990 edited by R.K. Grasselli and A.W. Sleight Volume 68 Catalyst Deactivation 1991. Proceedings of the Fifth International Symposium, Evanston, IL, June 24-26, 1991 edited by C.H. Bartholomew and J.B. Butt Volume 69 Zeolite Chemistry and Catalysis. Proceedings of an International Symposium, Prague, Czechoslovakia, September 8-13, 1991 edited by P.A. Jacobs, N.I. Jaeger, L. Kubelkova and B. Wichterlova Volume 54
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Poisoning and Promotion in Catalysis based on Surface Science Concepts and Experiments by M. Kiskinova Catalysis and Automotive Pollution Control II. Proceedings of the 2nd International Symposium (CAPoC 2), Brussels, Belgium, September 10-13, 1990 edited by A. Crucq New Developments in Selective Oxidation by Heterogeneous Catalysis. Proceedings ofthe 3rd European Workshop Meeting on New Developments in Selective Oxidation by Heterogeneous Catalysis, Louvain-la-Neuve, Belgium, April 8-10, 1991 edited by P. Ruiz and B. Delmon Progress in Catalysis. Proceedings of the 12th Canadian Symposium on Catalysis, Banff, Alberta, Canada, May 25-28, 1992 edited by K.J. Smith and E.C. Sanford Angle-Resolved Photoemission. Theory and Current Applications edited by S.D. Kevan New Frontiers in Catalysis, Parts A-C. Proceedings of the 10th International Congress on Catalysis, Budapest, Hungary, 19-24 July, 1992 edited by L. Guczi, F. Solymosi and R T(~tenyi Fluid Catalytic Cracking: Science and Technology edited by J.S. Magee and M.M. Mitchell, Jr. New Aspects of Spillover Effect in Catalysis. For Development of Highly Active Catalysts. Proceedings of the Third International Conference on Spillover, Kyoto, Japan, August 17-20, 1993 edited by T. Inui, K. Fujimoto, T. Uchijima and M. Masai Heterogeneous Catalysis and Fine Chemicals III. Proceedings ofthe 3rd International Symposium, Poitiers, April 5- 8, 1993 edited by M. Guisnet, J. Barbier, J. Barrault, C. Bouchoule, D. Duprez, G. Perot and C. Montassier Catalysis: An Integrated Approach to Homogeneous, Heterogeneous and Industrial Catalysis edited by J.A. Moulijn, RW.N.M. van Leeuwen and R.A. van Santen Fundamentals of Adsorption. Proceedings of the Fourth International Conference on Fundamentals of Adsorption, Kyoto, Japan, May 17-22, 1992 edited by M. Suzuki Natural Gas Conversion II. Proceedings ofthe Third Natural Gas Conversion Symposium, Sydney, July 4-9, 1993 edited by H.E. Curry-Hyde and R.R Howe New Developments in Selective Oxidation II. Proceedings of the Second World Congress and Fourth European Workshop Meeting, Benalmadena, Spain, September 20-24, 1993 edited by V. Cortes Corberan and S. Vic Bellon Zeolites and Microporous Crystals. Proceedings of the International Symposium on 7eolites and Microporous Crystals, Nagoya, Japan, August 22-25, 1993 edited by T. Hattori and T. Yashima Zeolites and Related Microporous Materials: State of the Art 1994. Proceedings of the 10th International Zeolite Conference, Garmisch-Partenkirchen, Germany, July 17-22, 1994 edited by J. Weitkamp, H.G. Karge, H. Pfeifer and W. H61derich Advanced Zeolite Science and Applications edited by J.C. Jansen, M. St6cker, H.G. Karge and J.Weitkamp
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Oscillating Heterogeneous Catalytic Systems by M.M. Slin'ko and N.I. Jaeger Characterization of Porous Solids III. Proceedings of the IUPAC Symposium (COPS III), Marseille, France, May 9-12, 1993 edited by J.Rouquerol, F. Rodriguez-Reinoso, K.S.W. Sing and K.K. Unger Catalyst Deactivation 1994. Proceedings of the 6th International Symposium, Ostend, Belgium, October 3-5, 1994 edited by B. Delmon and G.F. Froment Catalyst Design for Tailor-made Polyolefins. Proceedings of the International Symposium on Catalyst Design for Tailor-made Polyolefins, Kanazawa, Japan, March 10-12, 1994 edited by K. Soga and M. Terano Acid-Base Catalysis I1. Proceedings of the International Symposium on Acid-Base Catalysis II, Sapporo, Japan, December 2-4, 1993 edited by H. Hattori, M. Misono and Y. Ono Preparation of Catalysts VI. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Sixth International Symposium, Louvain-La-Neuve, September 5-8, 1994 edited by G. Poncelet, J. Martens, B. Delmon, P.A. Jacobs and P. Grange Science and Technology in Catalysis 1994. Proceedings of the Second Tokyo Conference on Advanced Catalytic Science and Technology, Tokyo, August 21-26, 1994 edited by Y. Izumi, H. Arai and M. Iwamoto Characterization and Chemical Modification of the Silica Surface by E.F. Vansant, P.Van Der Voort and K.C. Vrancken Catalysis by Microporous Materials. Proceedings of ZEOCAT'95, Szombathely, Hungary, July 9-13, 1995 edited by H.K. Beyer, H.G.Karge, I. Kiricsi and J.B. Nagy Catalysis by Metals and Alloys by V. Ponec and G.C. Bond Catalysis and Automotive Pollution Control III. Proceedings of the Third International Symposium (CAPoC3), Brussels, Belgium, April 20-22, 1994 edited by A. Frennet and J.-M. Bastin Zeolites: A Refined Tool for Designing Catalytic Sites. Proceedings of the International Symposium, Quebec, Canada, October 15-20, 1995 edited by L. Bonneviot and S. Kaliaguine Zeolite Science 1994: Recent Progress and Discussions. Supplementary Materials to the 10th International Zeolite Conference, Garmisch-Partenkirchen, Germany, July 17-22, 1994 edited by H.G. Karge and J. Weitkamp
