The catalytic oxidation of 2,4,6-trichlorophenol (TCP) was investigated over two commercial vanadia/titania-based catalysts both in the presence and the absence of water. The two catalysts exhibited significant activity for the oxidation of TCP producing carbon dioxide and HCl as the main reaction products. Furthermore, these catalysts-as well as the bare titania support-have a high capacity for the reversible adsorption of TCP at 200 degreesC. The presence of water affects the adsorption capacity, steady state activity and product distribution observed. This behavior can be attributed to the competitive adsorption of TCP and water, and the surface reactions of hydroxyl groups with Cl- species and adsorbed chlorinated hydrocarbon derivatives. In situ FTIR studies indicate the presence of phenolate, catecholate, ether, benzoquinone, aldehyde and carboxylate species on the catalyst surface following the adsorption of TCP as well as under reaction conditions. These partial oxidation products are formed during the reaction of TCP with surface oxygen and are intermediates of the oxidation process. (C) 2003 Elsevier B.V. All rights reserved.