Kinetics and Mechanisms in the Ammoxidation of Toluene over a Titania TiO2(B)-Supported Vanadium Oxide Monolayer Catalyst. 2.Combustion Reactions

To obtain knowledge about combustion mechanisms operating in the ammoxidation of toluene, the formation of carbon oxides was studied over a Ti02(B)-supported vanadium oxide catalyst with monolayer loading. The partial pressures of reactants were varied and kinetic rate expressions, completely describing experimental data, were derived. A comparison of the expressions obtained with those for the formation of nitrile and aldehyde shows that carbon oxides are formed at sites that are not involved in the mechanism of partial oxidation. Furthermore, C02 and CO are formed in routes having a common type of active ensemble. All of the adsorption steps are fast and in equilibrium. For the formation of C02 and CO, the rate-limiting step in both cases comprises a chemical transformation of which the details are unknown. The introduction of ammonia leads to a strong decrease of the rates for formation of carbon oxides