Heteropoly catalysts based on the mixed PMoV heteropoly compounds (HPC) with Keggin structure were prepared. The behaviors of the samples (in bulk and in titania-supported form) as a function of temperature treatment in the range of 343-923 K and the number of introduced V atoms into the heteropoly anions were studied. The catalytic activity of titania-supported catalysts was evaluated in the reaction of total oxidation of Cl-benzene at 473 K. The samples were characterized by S-BET method, thermogravimetric analysis (TGA), Fourier transform infrared,spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The XRD, IR and Raman results provided clear evidence that V indeed is incorporated into the Keggin unit. Introduction of one V atom into heteropolyanion leads to a significant increase of its thermal stability. On the other hand, the presence of the vanadium centers appears to be responsible for the increased activity of the titania-supported samples in the reaction of total oxidation of chlorobenzene. (c) 2006 Elsevier B.V. All rights reserved.