Catalytic oxidation of 1,2-dichlorobenzene over supported transition metaloxides

The catalytic oxidation of 1,2-dichlorobenzene has been systematically inve stigated over a series of transition metal oxides (i.e., Cr2O3, V2O5, MoO3, Fe2O3, and Co3O4) supported on TiO2 and Al2O3. The activity of the differe nt catalysts for this reaction depends on the nature of the transition meta l oxide used, with Cr2O3-and V2O5-based catalysts being the most active one s. With the exception of the cobalt oxide catalysts, the TiO2-supported sys tems were more active than the corresponding Al2O3-supported ones, indicati ng that the metal oxide-support interactions are significant in this reacti on. Experiments conducted in the presence of water indicate an inhibiting e ffect for the V2O5- and Cr2O5-based catalysts and a promoting effect for Co 3O4/TiO2. The Fe2O3- and MoO3-based catalysts were unaffected by the presen ce of water. Competitive adsorption between the surface species and water i s suspected to be the reason for the inhibition, while the promoting effect can be attributed to the reaction of water with surface Cl-. In situ FTIR studies indicate the presence of carboxylates (i.e., acetates and formates) , maleates, and phenolates on the surfaces of all catalysts studied under r eaction conditions. These surface species were reactive in the presence of gas-phase oxygen and are potential intermediates for the oxidation of 1,2-d ichlorobenzene. (C) 2000 Academic Press.