Oxidation and ammoxidation of toluene over vanadium-titanium oxide catalysts: A Fourier transform infrared and flow reactor study

Abstract

A Fourier transform infrared (FT-IR) study of the adsorption of toluene, and of some possible intermediates in its oxidation and ammoxidation, has been carried out on a monolayer vanadia-titania catalyst with and without preadsorbed ammonia in the presence and in the absence of gaseous oxygen at temperatures between 300 and 600 K. The results are discussed in relation to those obtained by ammoxidation of toluene and other methylaromatics in a tubular flow reactor. An intermediate, formed on the clean surface at room temperature, is identified as an adsorbed benzyl species probably having a radical character. Its oxidation produces benzaldehyde, adsorbed benzoates, and maleic anhydride. The coadsorption of toluene and ammonia produces adsorbed benzylamine, which is also observed as a by-product in the flow reactor at low oxygen and ammonia partial pressures, and benzonitrile. Based on these data a mechanism for both oxidation and ammoxidation is proposed and discussed.