Heterogeneous catalysis basic principles

The hydrogenation of p-unsaturated alcohols is a classical example of competing reaction processes in heterogeneous catalysis. In principle, either isomerization to an enol followed by tautomerization to the ketone can occur, or direct hydrogenation to the saturated alcohol is possible (1). It is fair to state that interest in this type of chemistry is derived from both basic scientific... 

In principle, sites a, IT, and c need not be association sites as depicted by Ogston but could be steric sites that form obstructions such that the adsorbed molecule is chirally directed. Only one active site is actually required providing the remaining two sites (protuberances or cavities) are different from each other and from the active site that catalyzes the reaction. They could be identical providing they are not symmetrically oriented with respect to the active site (not an isosceles triangle). These are the basic concepts for a chiral environment on a surface and they lead to the three basic methods for creating chiral surfaces in heterogeneous catalysis. 

In this chapter, the basic principles of heterogeneous catalysis and surface reactions, and chemical, sustainable energy, and pollution abatement applications of heterogeneous catalysts are described [3-5],... 

Schlogl R. In situ characterisation of practical heterogeneous catalysis. In Baerns M, editor. Basic principles in applied catalysis. Berlin Springer Verlag 2004. p. 321-60. 

This chapter reviews in detail the principles and applications of heterogeneous electron transfer reaction analysis at tip and sample electrodes. The first section summarizes the basic principles and concepts. It is followed by sections dedicated to one class of sample material glassy carbon, metals and semiconductors, thin layers, ion-conducting polymers, and electrically conducting polymers. A separate section is devoted to practical applications, in essence the study of heterogeneous catalysis and in situ characterization of sensors. The final section deals with the experiments defining the state of the art in this field and the outlook for some future activities. Aspects of heterogeneous electron transfer reactions in more complex systems, such as... 

Surfaces and interfaces chemistry is the study of the structure and reactivity of liquid and solid surfaces. The surfaces may be extended or may be limited to the nanometer scale. The surface, often a transition metal, may be a catalyst for a chemical reaction. Such studies provide the fundamental principles of the commercially important area of heterogeneous catalysis, which is essential to fuel and metal production, food processing, and commodity chemical manufacturing. The surface may also be consumed as a reactant, such as in semiconductor etching. These studies provide the basic chemistry of the manufacturing of electronic components and devices. 

The basic principles of biphase catalysis is accordingly that the homogeneous catalyst is in solution in one of the phases and the reaction products are located in a second phase which is immiscible with the catalyst phase - heterogeneous -and are therefore easy to separate off (see below). 

Bond (1987) covers the basic principles of catalysis, adsorption on solid surfaces, chemisorption at metal and oxide surfaces, the kinetics of catalyzed reactions, the quantitative aspects of catalysis by metals and the structure, preparation and use of heterogeneous catalysts. The book also discusses the application of catalysts in different fields including energy conservation, production of hydrocarbon feedstocks, bifunctional catalysts in petroleum industry, oxidation catalysts in the petrochemical industry, heavy inorganic industry, hydrogenation of multiple bonds and catalysts used in atmospheric pollution control. 

Chiral separation or sorption is another important technique in chirotechnology. In fact, due to the high cost of chiral catalysts, industries generally prefer chiral separation over asymmetric catalysis to obtain optically pure compounds. As in asymmetric heterogeneous catalysis, a chiral selector (a chiral molecule in optically pure form) can be immobilized on a solid support to make a chiral stationary phase (CSP) of use in direct chiral separation. The basic principle of chiral separation is that the chiral selector interacts differently with the enantiomers of a racemic or enantioenriched mixture to form transient diastereoisomeric species of different stability, and this fine distinction leads to the separation of enantiomers during elution. This topic has also produced a huge number of papers and the readers are referred to the previous reviews for more knowledge on this field [70-73]. 

Rodemerck, U. and Baerns, M. (2004). High-throughput experimentation in the development of heterogeneous catalysts — Tools for synthesis and testing of catalytic materials, in Baerns M. (ed.), Basic Principles in Applied Catalysis, Springer, Berlin Heidelberg New York, pp. 261-279. 

Abstract Basic principles of calorimetry coupled with other techniques are introduced. These methods are used in heterogeneous catalysis for characterization of acidic, basic and red-ox properties of solid eatalysts. Estimation of these features is achieved by monitoring the interaction of various probe molecules with the surface of such materials. Overview of gas phase, as well as liquid phase techniques is given. Special attention is devoted to coupled calorimetry-volumetry method. Furthermore, the influence of different experimental parameters on the results of these techniques is discussed, since it is known that they can significantly influence the evaluation of catalytic properties of investigated materials. 

In principle, more or less stable BRC structures can be obtained in heterogeneous biomimics, especially when adsorption and catalytic sites are combined, i.e. active sites perform both functions fixation and transformation of the substrate. To put it another way, the above enumerated restrictions typical of homogeneous catalysis are absent in heterogeneous mimic-substrate complexes, where acidic-basic sites are fixed in required points of the active site. 

The rise of homogeneous catalysis, as well as the understanding of the mechanistic principles of many heterogeneously catalyzed reactions, is inextricably linked to the development of organometallic chemistry.1 Catalytic reactions can be understood on the basis of a limited number of basic reaction types. This chapter will consider the fundamental reaction steps involved in transition metal catalyzed reactions the next chapter will deal with catalytic reaction types and processes. 

The problem discussed in this section is caused to a considerable degree by the difference in approaches dominating two parts of chemical kinetics, namely gas-phase kinetics and in heterogeneous kinetics, including catalysis. Even the basic terminology and main principles of kinetic analyses formed in these two areas are different. This in turn causes serious difficulties in the description of borderline phenomena. 

---