Catalysts derived from mixed PMoV and PWV heteropoly compounds with Keggin structure supported on titania were prepared. The samples were characterized by the S-BET method, Fourier transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The effect of the temperature pretreatment of the samples, the number of vanadium atoms in the starting heteropolyan ions and the nature of the peripheral atom on the surface properties and catalytic behavior of the samples in total oxidation of Cl-benzene was studied. The results provided clear evidence for the Keggin unit preservation in the heteropolyanions for pretreatments at temperature not exceeding 723 K. It was shown that the high-temperature (723 K) pretreated catalysts and/or replacement of W or Mo in the heterepoly anions with V atoms lead to an increase in the catalytic activity due to the redox capability of vanadium centers. (c) 2007 Elsevier B.V. All rights reserved.