INDEX heterogeneous-homogeneous catalytic

We have dealt above with a pure case of doublet reaction and other reactions. It is only natural that there can be some quite reasonable deviations. The bonds requiring activation must come into contact with the catalyst. If, for instance, one part of the index of the doublet reaction does not require activation, it can react without coming into contact with the catalyst. Such a half-doublet scheme for esterification in solution was given by the author 37). Hence, the transition from heterogeneous to homogeneous catalytic reactions occurs, and in the extreme case in which both the bonds of the doublet group do not require activation for the reaction, to noncatalytic reactions. 

This classification is important not only for kinetics and for the equilibrium of the heterogeneous catalytic reactions with a doublet mechanism, but for the equilibrium of homogeneous catalytic and non-catalytic reactions as well, because the equilibrium does not depend on the mechanism of the reaction. It is interesting to note that the cyclic activated 4- and 6-complexes, postulated by Syrkin 355), are nothing but doublet and triplet index groups, and consequently the multiplet classification must be proper for them as well hence it can also be applied to the kinetics of catalytic reactions that are not heterogeneous. 

The principles of homogeneous reaction kinetics and the equations derived there remain valid for the kinetics of heterogeneous catalytic reactions, provided that the concentrations and temperatures substituted in the equations are really those prevailing at the point of reaction. The formation of a surface complex is an essential feature of reactions catalyzed by solids and the kinetic equation must account for this. In addition, transport processes may influence the overall rate heat and mass transfer between the fluid and the solid or inside the porous solid, > that the conditions over the local reation site do not correspond to those in the bulk fluid around the catalyst particle. Figure 2.1-1 shows the seven steps involved when a molecule moves into the catalyst, reacts, and the product moves back to the bulk fluid stream. To simplify the notation the index s, referring to concentrations inside the solid, will be dropped in this chapter. 

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