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Über dieses Buch

A very wide range of catalytic conversions find industrial use in organic process chemistry. The scale of the ope­ rations varies enormously from very high volume pro­ cesses to specialty chemical preparations. Many of these processes are functional group conversions or class reac­ tions, and the more important of these will receive detailed treatment in specific chapters throughout this series. Nevertheless, the scope is very broad, and it is all too easy for the non-specialist to become lost in a large volume of detail. To try to avoid this, the first chapter in this volume, by Dr. Paul N. Rylander provides a working summary of the more important catalytic con­ versions of this type. In doing this, he also gives some valuable comments about catalyst selection, together with an indication of the reaction conditions used in practice, the more important of the problems usually encountered, and comments about the most important of the mechanistic features. It has long been recognized that an understanding of the chemical nature of solid surfaces is fundamental to an understanding of catalytic processes which may take place upon them. This question may be approached in two distinct ways. One is via surface crystallography which focuses attention upon long range order. The second concentrates upon the concept of the surface functional group where attention is mainly upon the chemistry characteristic of a particular localized atomic arrangement at the surface. In practice, of course, there exists a continuum between these idealized extremes.



Chapter 1. Catalytic Processes in Organic Conversions

Catalytic conversions of organic compounds are the heart of modern chemical industry. Few bulk or specialty organic chemicals are produced nowadays that have not been touched by catalysts either directly or indirectly in the synthetic sequence. This review of catalyzed organic reactions is limited to heterogeneous catalysts and mainly to chemicals of industrial importance having functionality beyond those of simple olefins and aromatics. Its aims are to illustrate the diversity of chemical transformations that can be achieved, to discuss the interplay of catalyst and chemical properties of the organic reactants, to show how various intrinsic problems can be minimized, and to suggest the type of catalyst suitable for various reactions.
Paul N. Rylander

Chapter 2. Nature and Estimation of Functional Groups on Solid Surfaces

The lattice of a crystal is abruptly terminated at its surface. In consequence, the constituents of the lattice are unsaturated in their coordination, giving rise to the surface energy. Adsorption of substances which are foreign to the lattice may lower the energy of the system and reduce the coordinative “unsaturation”. The interaction of the adsorptive with the adsorbent can very greatly in nature, i.e. from weak interaction by van der Waals forces, leading to physisorption, to strong chemical bonding or chemisorption. Chemisorption of molecules is frequently dissociative and often irreversible as well, that is the adsorptive cannot always be recovered in its original form. An example is the chemisorption of oxygen, O2, on carbon giving rise to surface oxides [1] which yield CO and CO2 on thermal decomposition.
Hanns-Peter Boehm, Helmut Knözinger

Chapter 3. Kinetics of Chemical Processes on Well-defined Surfaces

The rate of product formation in a catalytic reaction depends on ‘extrinsic’ parameters (which can be varied for a given catalyst) such as partial pressures, temperature, flow rate etc. as well as on ‘intrinsic’ parameters which are defined by the nature of the catalyst itself. The steady-state rate is in general a consequence of a rather complex series of elementary steps consisting of adsorption, desorption, surface reaction and migration processes whose rate constants in turn depend on various parameters. It is therefore practically impossible to draw any firm conclusions on the reaction mechanism or the individual rate constants on the basis of kinetic measurements for the overall reaction.
Gerhard Ertl


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