We investigated the suppression of SO2 oxidation activity by vanadium oxide in Pt-based diesel oxidation catalyst using reaction experiments, temperature programmed desorption (TPD), infrared (IR) and X-ray photoelectron spectroscopy (XPS). There was no interaction between Pt and S indicated by the XPS results. SO2 was not adsorbed on Pt at room temperature indicated by the absence of peak arising from SO2 in SO2 TPD spectra. SO2 molecules were adsorbed on the hydroxyl groups of TiO2 and migrated to Pt particles to react with oxygen adsorbed on it. V2O5 decreased the adsorption of SO2 on TiO2 by the blockage of V2O5 on TiO2. (C) 2003 Elsevier B.V. All rights reserved.