Catalytic oxidation of 1,2-dichlorobenzene over supported transition metal oxides

The catalytic oxidation of 1,2-dichlorobenzene has been systematically investigated over a series of transition metal oxides (i.e., Cr(2)O(3), V(2)O(5), MoO(3), Fe(2)O(3), and Co(3)O(4)) supported on TiO(2) and Al(2)O(3). The activity of the different catalysts for this reaction depends on the nature of the transition metal oxide used, with Cr(2)O(3)-and V(2)O(5)-based catalysts being the most active ones. With the exception of the cobalt oxide catalysts, the TiO(2)-supported systems were more active than the corresponding Al(2)O(3)-supported ones, indicating that the metal oxide-support interactions are significant in this reaction. Experiments conducted in the presence of water indicate an inhibiting effect for the V(2)O(5)- and Cr(2)O(5)-based catalysts and a promoting effect for Co(3)O(4)/TiO(2). The Fe(2)O(3)- and MoO(3)-based catalysts were unaffected by the presence of water. Competitive adsorption between the surface species and water is 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 reaction conditions. These surface species were reactive in the presence of gas-phase oxygen and are potential intermediates for the oxidation of 1,2-dichlorobenzene. (C) 2000 Academic Press.