Heterogeneous catalysis solid supports

Chapter 7 introduces the concept of absolute electrode potential in solid state electrochemistry. This concept has some important implications not only in solid state electrochemistry but also, potentially, in heterogeneous catalysis of supported catalysts. 

In heterogeneous catalysis, solids catalyze reactions of molecules in gas or solution. As solids - unless they are porous - are commonly impenetrable, catalytic reactions occur at the surface. To use the often expensive materials (e.g. platinum) in an economical way, catalysts are usually nanometer-sized particles, supported on an inert, porous structure (see Fig. 1.4). Heterogeneous catalysts are the workhorses of the chemical and petrochemical industry and we will discuss many applications of heterogeneous catalysis throughout this book. 

This series covers recent advances in electrocatalysis and electrochemistry and depicts prospects for their contribution into the present and future of the industrial world. It illustrates the transition of electrochemical sciences from a solid chapter of physical electrochemistry (covering mainly electron transfer reactions, concepts of electrode potentials and stmcture of the electrical double layer) to the field in which electrochemical reactivity is shown as a unique chapter of heterogeneous catalysis, is supported by high-level theory, connects to other areas of science, and includes focus on electrode surface structure, reaction environment, and interfacial spectroscopy. 

We might view clusters as the borderline between molecular catalysis and solid-state heterogeneous catalysis. Heterogeneous catalysis on supported metals is often not well understood because of the complexity of structures, which may contain corners, faces, edges, etc. Each of these sites may prove to be active sites for the variety of catalytic intermediates and, therefore, may influence selectivity and activity 21). 

An important research area of catalysis is the heterogenization of metal complexes showing excellent activity and selectivity in the homogeneous phase (hybrid catalysts) [1]. The main advantage of supported metal complexes over unsupported ones is the ease of separation from the reaction media, which makes them economically convenient [2]. On the other hand, the main problems related with the heterogenization on solid supports are metal complex leaching and decrease in catalytic activity. 

Soluble polymer-bound catalysts can be expected to receive continued attention as they offer specific advantages. By comparison to aqueous two-phase catalysis, a range of substrates much broader with respect to their solubility can be employed. By comparison to heterogenization on solid supports, the selectivity and activity of homogeneous complexes can be retained better. However, it must also be noted that to date no system has been unambiguously proven to meet the stability and recovery efficiency required for industrial applications. 

Ernst H, Freude D, Mildner T, Wolf 1. Laser-supported high-temperature MAS NMR for time-resolved in situ studies of reaction steps in heterogeneous catalysis. Solid State Nucl Magn Reson 1996 6 147-56. 

Consequently the absolute potential is a material property which can be used to characterize solid electrolyte materials, several of which, as discussed in Chapter 11, are used increasingly in recent years as high surface area catalyst supports. This in turn implies that the Fermi level of dispersed metal catalysts supported on such carriers will be pinned to the Fermi level (or absolute potential) of the carrier (support). As discussed in Chapter 11 this is intimately related to the effect of metal-support interactions, which is of central importance in heterogeneous catalysis. 

For most applications, enzymes are purified after isolation from various types of organisms and microorganisms. Unfortunately, for process application, they are then usually quite unstable and highly sensitive to reaction conditions, which results in their short operational hfetimes. Moreover, while used in chemical transformations performed in water, most enzymes operate under homogeneous catalysis conditions and, as a rule, cannot be recovered in the active form from reaction mixtures for reuse. A common approach to overcome these limitations is based on immobilization of enzymes on solid supports. As a result of such an operation, heterogeneous biocatalysts, both for the aqueous and nonaqueous procedures, are obtained. 

In this chapter, we demonstrate the potential of such agents as catalysts/promoters in key steps for the derivatization of sugars. The most significant catalytic approaches in carbohydrate chemistry that use aluminosilicate porous materials, namely zeolites and montmorillonite clays, are reviewed and discussed. Silica gel is a porous solid silicate that has also been used for heterogeneous catalysis of organic reactions in general. We include here its usefulness as promoter and reagent support for the reactions under consideration. 

Although the history of rigid monolithic polymers is relatively short, a number of applications have already been explored. These applications cover a rather broad range of fields from heterogeneous catalysis and solid-phase extraction, to polymer-supported chemistry and a variety of separation processes. 

Keywords Catalysis, polymer-supported oxidovanadium (IV) complex, Solid supported catalysts, heterogenized homogeneous catalysts... 

Application of transmission electron microscopy (TEM) techniques on heterogeneous catalysis covers a wide range of solid catalysts, including supported metal particles, transition metal oxides, zeolites and carbon nanotubes and nanofibers etc. 

With rapid development of zeotypic materials and mesoporous solids and their application in heterogeneous catalysis, HRTEM shows its advantages in distinguishing the ultrastructural features [40, 41], Carbon materials are used as support in catalytic reactions due to some of their specific characteristics and many publications report the TEM investigations on various forms of carbon related materials [42-48],... 

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