Multifunctional Mesoporous Inorganic Solids PDF
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Multifunctional Mesoporous Inorganic Solids NATO ASI Series Advanced Science Institutes Series A Series presenting the results of activities sponsored by the NA TO Science Committee, which aims at the dissemination of advanced scientific and technological knowledge, with a view to strengthening links between scientific communities. The Series is published by an international board of publishers in conjunction with the NATO Scientific Affairs Division A Life Sciences Plenum Publishing Corporation B Physics London and New York C Mathematical Kluwer Academic Publishers and Physical Sciences Dordrecht, Boston and London D Behavioural and Social Sciences E Applied Sciences F Computer and Systems Sciences Springer-Verlag G Ecological Sciences Berlin, Heidelberg, New York, London, H Cell Biology Paris and Tokyo I Global Environmental Change NATO-PCO-DATA BASE The electronic index to the NATO ASI Series provides full bibliographical references (with keywords and/or abstracts) to more than 30000 contributions from international scientists published in all sections of the NATO ASI Series. Access to the NATO-PCO-DATA BASE is possible in two ways: - via online FILE 128 (NATO-PCO-DATA BASE) hosted by ESRIN, Via Galileo Galilei, 1-00044 Frascati, Italy. - via CD-ROM "NATO-PCO-DATA BASE" with user-friendly retrieval software in English, French and German (© WTV GmbH and DATAWARE Technologies Inc. 1989). The CD-ROM can be ordered through any member of the Board of Publishers or through NATO-PCO, Overijse, Belgium. Series C: Mathematical and Physical Sciences -Vol. 400 Multifunctional Mesoporous Inorganic Solids edited by Cesar A.C. Sequeira Instituto Superior Tecnico, Universidade Tecnica de Lisboa, Lisboa, Portugal and Michael J. Hudson Department of Chemistry, University of Reading, Reading, U.K. Springer-Science+Business Media, B.Y. ProceedingsoftheNATOAdvancedStudyInstituteon MultifunctionalMesoporousInorganicSolids Sintra,Portugal April5-17, 1992 AC.I.P.Cata/oguerecordforthisbookisavailabletromtheUbraryofCongress. ISBN978-90-481-4275-0 ISBN978-94-015-8139-4(eBook) DOI 10.1007/978-94-015-8139-4 Printedonacid-freepaper AllRightsReserved ©1993SpringerScience+BusinessMedia Dordrecht and copyright holders as specified on appropriatepageswithin. OriginallypublishedbyKluwerAcademicPublishersin1993. Softcoverreprintofthehardcover Istedition 1993 No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical, including photo copying, recordingorby anyinformationstorageandretrievalsystem,withoutwritten permissionfromthecopyrightowner. PREFACE 1. Introduction. There is much interest in the general subject of porous inorganic materials with respect to their use as sorbents or catalysts. Such inorganic solids may be microporous, mesoporous or macroporous according to the sizes of the pores within the solid. Often there is a range of pore sizes within any given solid and so there is special interest in the synthesis, characterisation and application of porous inorganic solids with well defined pores. Pores of diameter larger than 50 nm are generally termed macropores. Those with diameters of less than 2 nm are micropores and pores of intermediate size are called mesopores. Solids, which contain only mesopores, are correctly called mesoporous but very often there is a combination of different types of porosities within one given solid. The synthesis, characterisation and application of microporous solids is much more advanced than is the case with mesoporous substances. Moreover, the synthesis of crystalline mesoporous materials is one clear goal for the future but which has not been attained so far. Consequently, it is of interest to examine the current state of our knowledge of microporous materials and to examine how this may apply to mesoporous materials. Both catalytic and sorption processes could benefit from studies of mesoporous solids because the mesopores could permit diffusion of larger reactants or products than is the case in microporous materials. 2. Pore Size Distribution One source of interest in the pore-size distribution for inorganic solids stems from the need to predict the effective diffusivity in a porous solid in relation to the ease of access of reactant molecules to the interior of a sorbent. Another source stems from the need to relate sorptive or catalytic properties to pore-sizes and surface areas. The first part of this book deals with the theory and practice of some aspects of the measurements of pore-size distributions. Many sorbents or catalysts such as inorganic oxides have bimodal pore-size distribution curves. The fine pores are v vi frequently in the range of 1 to 10 That is to say the oxides DID. have micropores and mesopores, which account for most of the surface area. The large pores are macropores typically in the range of 102 to 103 DID. The mixed porous nature of such solids is sometimes useful as the macropores allow mass transfer into the reaction sites within the micro- and mesopores. The fine pores are considered to be within the particles whereas the larger pores are the residual spaces between the particles. The fine pores may be developed within the particles by calcination and/or reduction procedures. However, there is always clear need to attempt to improve the synthesis and methods of characterisation of mesoporous materials. Clearly, mesopores may be formed when the particles are abutting one another but it is important to consider mesoporous materials in which the pores are within structural parts of the particles themselves. In the case of zeolites, which are microporous, there are well defined pores which may be prepared by methods such as the hydrothermal methods discussed later. It is of interest to examine as to whether these and other methods could be extended to mesoporous materials. In layered solids such as oxides or hydrogen phosphates, the layers may be separated by means of pillars of either an organic or inorganic nature. There is interest in establishing whether the distances between the layers and between the pillars themselves could be above 2 so that the materials DID could be mesoporousrather than microporous. Sol-gel methods, which are discussed later, have lead to the synthesis of porous materials with a range of pore sizes and there is now a great interest in such methods of synthesis. 3. Porous Crystalline Materials Zeolites are, by definition, microporous but it 1S important to understand the mechanisms whereby such crystalline porous materials are formed so that it will be possible to suggest methods by which mesoporous materials are made. There are two alternative views regarding the mechanisms of controlled synthesis. One is the conventional "secondary building unit" model and the other involves the extended structures model. Many related structures based on the same or similar sheets, columns and large cages, cocrystallise or intergrow with one another. These data, based on examining the products of synthesis rather than the precursor gel structures indicate that the process of building the structures comprises two steps. The first involves the formation of an intermediate extended structure and the second step is the clipping or joining of them together in specific ways. The gathering body of high resolution microscopy data indicates ordered and disordered intergrowths and overgrowths of related structures. Consequently, there is interest in seeing whether these and other ideas can be extended to the synthesis of mesoporous materials. 4. Pillared Layered Solids In pillared layered solids (PLS), there is a pillar between the layers host formed by an organic or inorganic guest molecule or ion. At the moment, these PLS are principally microporous materials but there are clear indications that they can have microporosity combined with mesoporosity and, as reported in this book, there may be pillared layered solids which are solely mesoporous. 5. Sol-gel Methods Recently, there have been important developments in the synthesis of oxides by the sol-gel route and these new materials promise to be of high purity with well defined pore sizes. Sol-gel chemistry is based on the polymerisation of molecular precursors such as metal oxides of the type M(OR)n' Hydrolysis and condensation of these alkoxides lead to the formation of oxo-polymers which are then transformed into an oxide network. Sol-gel chemistry offers the possibility of designing molecular precursors and to control the polymerisation process so that, in principle, materials of the required porosities and surface areas can be prepared. Thus molecular design and engineering of metal alkoxides could permit the synthesis of mesoporous solids. Monodispersed colloids or long chain polymers can be synthesised via the chemical modification of metal alkoxides by nucleophilic reagents. Organic and inorganic polymerisation reactions can be performed during the sol-gel synthesis leading to the formation of new materials made of an organic-inorganic polymeric network. Thus, it can be seen that it was timely to have a NATO Advanced Study Institute on the subject of Multifunctional Mesoporous Inorganic Materials (MMIS) in which specialists in the different areas were brought together. Michael Hudson ACKNOWLEDGEMENTS It is a pleasure to acknowledge with gratitude the financial support for the Course on Multifunctional Mesoporous Inorganic Solids by NATO, the Luso-American Foundation, the Portuguese Air Force, the Bank Pinto & Sotto Mayor, and the Tourism Office in Sintra. We also wish to thank our colleagues in the field for many helpful suggestions on the organization of the Course. In addition, we would like to thank all the lecturers, particularly to my co-director Dr. Michael J. Hudson, the discussion groups chairmen and the participants for making the program so stimulating and successful. Finally it is necessary to thank all of those people involved in the local organization of the Institute. In particular, a great deal of the administrative load was carried by my wife, Maria Elisa, who helped also with the production of this volume. Cesar Sequeira vili North Atlantic Treaty Organization ADVANCED STUDY INSTITUTE on MULTIFUNCTIONAL MESOPOROUS INORGANIC SOLIDS Hotel Tivoli Sintra, Sintra, Portugal, April 5-17, 1992 DIRECTORS Prof. Cesar A C Sequeira Dr. Michael J. Hudson Lab. de Electroquimica Dept. of Chemistry Instituto Superior Tecnico University of Reading Av. Rovisco Pais Whiteknights 1096 Lisboa Codex P.O. Box 224 PORTUGAL Reading RG6 2AD, U.K. SCIENTIFIC COMMITTEE Prof. Giulio Alberti Prof. Abraham Clearfield Dipartimento di Chimica Texas A&M University Universita di Perugia Dept. of Chemistry 06100 Perugia College Station ITALY Texas 77843-3255, U. S.A. Prof. N.H.J. Gangas Prof. J.D. Mackenzie Straton hi-tec Ltd Univ. of California, LA 108, Kifissias Ave Dept. of Mat. Sci. & Eng. GR-115 26 Athens 405 Hilgard Avenue GREECE LA California 90024-1595 s. U. A. Prof. Jacques Roziere Prof. Shoji Yamanaka URA CNRS 79 Dept. of Applied Chern. Place Eugene Bataillon Hiroshima University 34060 Montpellier Cedex Higashi-Hiroshima 724 FRANCE JAPAN ix
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