Microporous Framework Solids (RSC Materials Monographs) - Hardcover

Wright, Paul A.

Hardcover

ISBN 10: 085404812X ISBN 13: 9780854048120

Verlag: Royal Society of Chemistry, 2007

Inhaltsangabe

The field of microporous solids in solid state chemistry has seen a huge expansion over the last decades with new developments in a diverse range of directions and applications. Drawing upon nature as an inspiration, scientists are continually extending known families and preparing porous solids with novel structures. In turn, the novel properties that these possess stimulate further research and applications. Microporous Framework Solids describes fundamental principles and experimental practices of the synthetic chemistry and physical characterisation of crystalline microporous solids. It also provides a clear and up to date discussion of different types of microporous materials, their applications and emerging areas of current interest, written from a personal research perspective. Topics include the different types of solids and their properties with key emphasis placed on the relationship between properties and structure. Structural methods are also discussed including the role of diffraction, NMR and computational studies. Finally, applications for catalysis are reviewed. This book is ideal for new researchers in the field of microporous solids both in academia and industry who require a detailed and informative overview of the subject. It provides a comprehensive review of microporous materials in an easily accessible style offering a valuable source of references over a wide range of topics.

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Über die Autorinnen und Autoren

Paul Wright is reader in the department of chemistry at the University of St Andrews. His research interests include microporous and mesoporous solids, organic-inorganic hybrids and zeolites, structural studies, adsorption and catalysis.

Paul Wright is reader in the department of chemistry at the University of St Andrews. His research interests include microporous and mesoporous solids, organic-inorganic hybrids and zeolites, structural studies, adsorption and catalysis.

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This book describes fundamental principles and experimental practices of the synthetic chemistry and physical characterisation of crystalline microporous solids. It also provides a clear and up to date discussion of different types of microporous materials, their applications and emerging areas of current interest, written from a personal research perspective. This book is ideal for new researchers in the field of microporous solids both in academia and industry who require a detailed and informative overview of the subject. It provides a comprehensive review of microporous materials in an easily accessible style offering a valuable source of references over a wide range of topics.

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Microporous Framework Solids

By Paul A. Wright

The Royal Society of Chemistry

Copyright © 2008 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-0-85404-812-0

Contents

Acknowledgements, xiv, 
Chapter 1 Introduction, 
Chapter 2 Families of Microporous Framework Solids, 
Chapter 3 Structure Determination: Experimental Techniques, 
Chapter 4 Computer Modelling, 
Chapter 5 Synthesis, 
Chapter 6 The Chemistry of Microporous Framework Solids, 
Chapter 7 Adsorption and Diffusion, 
Chapter 8 Microporous Solid Acid Catalysts and their Applications, 
Chapter 9 Further Catalytic Applications of Microporous Solids, 
Chapter 10 Advanced Applications and Current Trends, 
Subject Index, 417, 

CHAPTER 1

Introduction

1.1 Microporous Framework Solids: Definitions

First, a word on definitions. The materials I shall describe in this book will be those with ordered structures that are able to adsorb molecules reversibly and selectively based on differences in their size and shape. For a long time this definition would have applied almost exclusively to aluminosilicate zeolites, crystalline solids with pore sizes up to around 8 Å, and excluded those materials such as porous carbons or ceramics derived from sol-gel preparations that possess microporosity but no regularity of structure. Nowadays the term encompasses families of microporous solids with ever-increasing compositional variety, frameworks with metals in mixed coordination and hybrid metal-organic frameworks. The definition might also include some of the newly discovered class of mesostructured solids, discovered first by researchers at Mobil in the early 1990s. As molecular sieves, it is clear that the pore size of these solids, which extends from 10 Å upwards, enables the adsorption of much larger molecules than is possible for zeolites (Figure 1.1). I have excluded a consideration of layered solids such as pillared clays, which also show porosity, because their order is predominantly in two dimensions, rather than three.

A distinction should also be drawn between framework molecular sieves and the wealth of crystalline solids prepared in the presence of an organic species that becomes incorporated in voids within the structure but cannot be removed, thermally or otherwise, without structural collapse. These are better described as open framework solids. In practice the distinction is blurred and, although only materials that are thermally and hydrothermally robust are likely to be commercially exploited in traditional technologies, open framework solids containing organic species can possess properties that may make them suitable for more specialised use.

1.2 Historical Development of the Subject

There is great current interest in the use of combinatorial methods, or high throughput experimentation (in which a large number of experiments are performed to explore the different effects of many variables), to prepare new solids by optimised routes. I will give an example of this applied to zeolite synthesis in Chapter 5. In a sense, though, the range of geochemical situations that have existed naturally has acted in the same way, and solid state chemists have learnt much from observing and preparing laboratory analogues of natural minerals, including clays, zeolites and other porous silicates and phosphates. Natural zeolites have long been recognised as a class of solids with characteristic properties. The first recorded description of a zeolite mineral was of stilbite, by Cronsted in 1756. Crystals of natural stilbite are shown in Figure 1.2: routes have since been developed for the laboratory synthesis of zeolites with the same framework structure of stilbite, and with a wide variety of compositions. Figure 1.2 also shows a scanning electron micrograph of a synthetic, high silica version of stilbite that has recently been prepared, and a representation of its microporous structure. The property of zeolites to reversibly evolve adsorbed water when heated gives rise to their name (Zeo (Greek, boiling) Lithos (Greek, stone)). Zeolites are a class of 'tectosilicate' minerals that possess tetrahedrally linked, three-dimensional frameworks made up of corner-sharing aluminate and silicate tetrahedra that are sufficiently open to be able to reversibly adsorb molecules.

Under favourable geological conditions significant deposits of useful natural zeolites (such as clinoptililite and mordenite) have resulted and are mined and used in large quantities. More often, and certainly for many of the most important commercial zeolites, mineral forms of the zeolite types only occur in minute quantities. Very small amounts of natural analogues to the widely used zeolites Y, ZSM-5 and Beta have all been found, and are known as faujasite, mutinaite and czernickite, respectively. Such mineralogical occurrences (such as those found in Antarctica) are more than interesting curiosities to the zeolite chemist: they were essential to establishing a structural basis for zeolite science (many zeolite structures have been solved from natural samples) and they point the way to unexpected structural possibilities. Two zeolites reported only as natural minerals are shown in Figure 1.3. The recently discovered structure of tschörtnerite, for example, obtained from a few crystals from the Eifel region of Germany, includes the supercage shown, which has an internal free diameter of 17.3 Å. A synthetic tschörtnerite might be of considerable use in gas separation or in detergency. Boggsite, on the other hand (also shown), possesses an intersecting channel system that would be of more interest in catalysis. Structures such as these are attractive targets for synthesis.

Zeolite mineralogy is certainly interesting and informative, but the development of zeolite chemistry was made possible by their large scale synthesis under laboratory conditions. It was recognised that zeolites could be crystallised hydrothermally from reactive precursor gels under alkaline conditions on timescales of a few days. Early synthetic work, by Richard Barrer, in academia, and industrialists such as Robert Milton, Donald Breck, George Kerr and Edith Flanigen, explored the use of alkali and alkali earth metals to direct the crystallisation of aluminosilicate gels from the 1940s onwards. These pioneering studies gave rise to many of the zeolites that are currently widely used, in particular the zeolites A, X, Y and mordenite. The characteristic zeolitic properties of these materials, such as adsorption and ion exchange, were established, their study receiving impetus with their adoption in gas drying and separation technologies and by the need for replacements for environmentally threatening phosphate ion sequestering agents in detergents. They have since retained their large scale use in these industries, with innovations prompted by new developments and considerations of interest to individual manufacturers (such as the need to prepare new products that are outside existing patent restrictions).

The compositional similarity of zeolites to silica-aluminas in widespread use as solid acid catalysts in catalytic cracking processes suggested that they could also be used in these processes if they were suitably modified. Chemical routes to the incorporation of acid sites were found, and the resulting catalysts were found to be strong solid acids (Chapter 8). In particular, zeolites based on zeolite Y are now widely used on a massive scale in catalytic cracking. Furthermore, the unique pore structure of zeolites was found to give...

Details zur Ausgabe

• Verlag: Royal Society of Chemistry
• Erscheinungsdatum: 2007
• Sprache: Englisch
• ISBN 10: 085404812X
• ISBN 13: 9780854048120
• Einband: Gebundene Ausgabe
• Anzahl der Seiten: 444
• Kontakt zum Hersteller: Nicht verfügbar
• Verantwortliche Person: preigu; mail@preigu.de; ; Lengericher Landstr. 19; Osnabrück; 49078; Deutschland