Ceria and Ce0.75Zr0.25O2 were characterized before and after SO2 exposure to determine the effect of sulfation on the structural, morphological and catalytic properties of the solids. The X-ray diffraction (XRD), scanning electron microscopy (SEM) data, and BET measurements show that both CeO2 and Ce0.75Zr0.25O2 are susceptible to crystallite grain size growth and surface area loss under exposure to gaseous mixtures containing 20-40 ppm SO2 at 600degreesC. The Ce0.75Zr0.25O2 is more resistant to morphological changes than CeO2. However, no bulk sulfites/sulfates were detected with either oxide. Both presulfation of the oxides and addition of 20 ppm SO2 to a 1% CO + 2% O-2 + N-2 reaction mixture results in a significant suppression of the CO oxidation reaction. The effect of SO2 on CO oxidation was much less pronounced for the Ce0.75Zr0.25O2 than for the CeO2. Surprisingly, 20 ppm SO2 in the 1100 ppm C3H6 + 2% O-2 + N-2 reaction mixture has a promoting effect on the oxidation of C3H6 catalyzed by CeO2. The influence of SO2 in the feed gas on the CO and C3H6 oxidation is discussed in terms of different mechanisms for these reactions. (C) 2003 Elsevier Science B.V. All rights reserved.