Cracking heterogeneous catalysis

Nowadays, based on the amount of processed material, hydrotreating is the largest process in heterogeneous catalysis. On the basis of catalysts sold per year, hydro-treating ranks third after automotive exhaust and fluid catalytic cracking [R. Prins, V.H.J. de Beer and G.A. Somorjai, Catal. Rev.-Sci. Eng. 31 (1989) 1]. 

The phenomena of promotion is a common feature of heterogeneous catalysis. Generally, the presence of promoter increases the peaks and cracks on the surface of the catalyst and therefore is responsible for increasing the rate of reaction by increasing the activity of the catalyst. 

This section concerns catalytic processes that transform chemicals from renewables by C-C bond breaking. Among these are thermochemical processes, such as pyrolysis and also gasification, catalytic reactions, such as catalytic cracking and different reforming reactions, and decarbonylation and decarboxylation reactions. Many of these reactions occur simultaneously, particularly in the thermochemical processes. Another technically important class of C-C bond breaking reactions is the fermentation processes, however, they will not be considered in this section since they do not involve heterogeneous catalysis. 

Mochida, I. and Y. Yoneda, Linear Free Energy Realationships in Heterogeneous Catalysis L Dealkylation ofAlkylbenzenes on Cracking Catalysts., J. of Catal., 7, 386-396,1967. 

We use the activation of linear alkanes and their conversion to isomers and cracked products as the main motive of our discussion. This class of reactions catalyzed by acidic zeolites is an ideal choice to illustrate the state of the art of theoretical molecular heterogeneous catalysis, because the reaction mechanisms, zeolite micropore structure, and structure of the catalytically reactive sites are rather well understood. 

Heterogeneous catalysis is especially important in industry. Some of the major industrial processes that use solid catalysts include the synthesis of inorganic chemicals such as NH3, SO3 and NO, the various reactions used in the refining of crude petroleum such as cracking, isomerisation and reforming, and many of the major reactions of the petrochemical industry, such as the synthesis of methanol, the hydrogenation of aromatics and various controlled oxidations. Some of the major industrial processes to be catalysed by inorganic solids are shown in Table 1.3. 

The majority of catalysts are subject to deactivation, e.g. to changes (deterioration) of activity with operation time. The time scale of deactivation depends on the type of process and can vary from a few seconds, as in fluid catalytic cracking (FCC), to several years, as in, for instance, ammonia synthesis. Due to the industrial importance, the modelling of deactivation was mainly developed for heterogeneous catalysis. Although the reasons for deactivation (inactivation) of homogeneous and enzymes could differ from solid catalysts, the mathematical approach can sometimes be very similar. 

For a variety of reasons, silica and alumina structures are important frameworks for the subject of heterogeneous catalysis 11-3]. Aluminas, and perhaps to a lesser extent silicas, are employed directly as cracking catalysts or as substrates for assorted catalytic systems (see Chapter 4). The silylation of silica surfaces also provides a strategy for immobilizing a catalytic center that has been found useful in the context of homogeneous catalysis [4], Furthermore, many heterogeneous catalytic systems based on zeolites, clays, or silica-aluminas have aluminosilicate frameworks for which silica and alumina structures serve as structural prototypes. 

Continuing this policy, the third volume presents a variety of subjects, such as magnetic phenomena, poisoning effects, geometrical theory in heterogeneous catalysis as well as subjects of immediate industrial importance such as studies of catalytic cracking and liquid air production. The editors hope that future discussions, comments, and criticism will continue to arrive at an undiminishing rate. 

Heterogeneous catalysis, with lanthanides Zeolites, lanthanide exchanged, in catalysis Cracking catalysts, lanthanide Activity-stabilization, lanthanide Homogeneous catalysis, with lanthanides... 

Recent reviews (31-34,36,37,51) provide a comprehensive survey of the types of heterogeneous catalytic reactions investigated at supercritical conditions including alkylation, amination, cracking, disproportionation, esterification, Fischer-Tropsch synthesis, hydrogenation, isomerization, and oxidation. Table 2 summarizes reported investigations under these classes of reaction. Some of these examples are described here to show how to systematically exploit supercritical media in heterogeneous catalysis. 

The catalytically active surface opens another, and in many cases faster, reaction path for the gas phase reactants. Therefore, heterogeneous catalysis is used in numerous technical processes, e.g., in the production of basic industrial chemicals as well as the cracking and reforming of crude oil [1-3]. Catalysts are also useful in stabilizing flames and in fuel combustion at low temperatures, a precondition for reducing pollutants (e.g., NOx) [4-6]. 

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