DRIFT STUDY OF THE OXIDATION AND THE AMMOXIDATION OF TOLUENE OVER A TIO2(B)-SUPPORTED VANADIA CATALYST

A DRIFT study of the adsorption and the (amm) oxidation of toluene was carried out at 150-300-degrees-C on a TiO2(B)-supported vanadia catalyst with a loading corresponding to 1.9 mg V2O5 per m2 of the support surface area. In the absence of NH3 and gaseous oxygen, the adsorption of toluene at 150-degrees-C produces benzyl and benzoate intermediates. After one hour at the same temperature, further conversion of benzyl species, probably benzyloxy, into benzoate species is observed. Upon introduction of NH3 into the reaction cell, some benzonitrile is formed together with intermediates which possibly are (C6H5)CH(NH2)O- and (C6H5)C(NH2) (O-)2 species. Subsequent heat treatment at 300-degrees-C causes an increase in the amounts of benzonitrile and CO2 formed and the simultaneous disappearance of the precursor intermediates. On the basis of identified intermediates and observed transformations, a mechanism for the partial (amm)oxidation of toluene is proposed. The formation of CO2 is believed to pass over intermediates, which are identified as benzoquinone and butenolide species.