DEHYDROGENATION MECHANISM FOR AMMOXIDATION OF ALKYLAROMATIC HYDROCARBONS

Ammoxidation of toluene and other alkylaromatics over supported V-Sb-Bi oxide catalysts is studied by means of pulse, flow, temperature-programmed reactions, and IR spectroscopy. It has been found that reaction occurs by alternate reduction and oxidation of the catalyst surface. Aromatic nitrile is formed at the reduction stage via amine- and amine-like intermediates. Ammonia exhibits an activation effect on the overall hydrocarbon conversion. According to this study and data on the reactivity of different substituted toluenes and on the activity of alkali-doped catalysts, the hydrocarbon activation is assumed to take place by the attack of a basic site of the catalyst via heterolytic dissociation of a CH bond in a benzylic position. On the basis of these results a "dehydrogenation" mechanism for ammoxidation of alkylaromatics is proposed and used for the analysis of reaction kinetics. © 1991.