Catalytic properties-reaction mechanism relationship

V-Sb-oxide based catalysts show interesting catal)dic properties in the direct synthesis of acrylonitrile from propane [1,2], a new alternative option to the commercial process starting from propylene. However, further improvement of the selectivity to acrylonitrile would strengthen interest in the process. Optimization of the behavior of Sb-V-oxide catalysts requires a thorough analysis of the relationship between structural/surface characteristics and catalytic properties. Various studies have been reported on the analysis of this relationship [3-8] and on the reaction kinetics [9,10], but little attention has been given to the study of the surface reactivity of V-Sb-oxide in the transformation of possible intermediates and on the identification of the sxirface mechanism of reaction. 

This study was undertaken with the objective of closely following the relationships of silica/alumina ratio with catalytic properties of ZSM-5 zeolite in toluene transformation under hydrodealkylation process conditions. It was hoped that the data would reveal the reaction pathway of the dealkylation and subsequently shed light on the mechanism of H-ZSM-5 catalyzed transformation of toluene. 

Studies of the selective oxidation of propylene, which is an important application of the tin-antimony oxide catalyst, have resulted in the description of several mechanisms and the subject was recently reviewed by Keulks et al. (7). It is not the purpose of this article to give a similar in depth consideration of this aspect of the catalytic properties of tin-antimony oxides. However, it is important that the improved knowledge of the bulk and surface properties of the catalyst and their relationship with the catalytic character should be considered in terms of the formulation of reaction mechanisms. 

The accessibility of new techniques such as EXAFS brings researchers a powerful tool for unambiguous determination of the true core metallic framework of such systems. Thus, the relationship between the parent carbonyl precursor, the support and the final metal-supported particles has been studied at the structural atomic level in some cases. This can allow differentiation of the catalytic behavior of supported metal particles with bulk-like properties from that of supported metal clusters, opening the way to understanding the mechanism of metal-catalyzed reactions and extending the concept of sensitive or insensitive structure reactions from metal aggregates to clusters. 

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