Modification of Pt/SiO 2 with ReO x species enhanced the catalytic activity of the CO oxidation with O 2 in the presence of H 2 . The amount of Re modifier on Pt-ReO x /SiO 2 was optimized to be Re/Pt ) 0.5 on the molar basis. The promoting effect of Re species appeared after the reduction above 673 K. Characterization of the reduced Pt-ReO x /SiO 2 catalyst by means of EXAFS, XANES, temperature-programmed reduction, and CO adsorption measurements suggested the formation of the ReO x clusters on the surface of Pt metal particles with the average valence of Re of +2.7. The CO adsorption on Pt-ReO x /SiO 2 gave a higher wavenumber then that on Pt/SiO 2 at the same CO coverage, showing the weakened interaction between CO and the Pt surface, which is also supported by the desorption profile of the adsorbed CO. The CO coverage on Pt-ReO x / SiO 2 during the preferential CO oxidation was much smaller than that in the absence of H 2 , suggesting that an oxygen-containing species was coadsorbed on the reduced catalyst. The pulse reaction showed that the reduced Pt-ReO x /SiO 2 can activate O 2 even when the catalyst surface is saturated with CO. These tendencies can be explained by the mechanism where the reduced ReO x species activates O 2 and the oxidizing species is spilled over from the ReO x species to the Pt surface.

Clusters of ReO(x) are formed and attached to Pt metal particles during H(2) reduction treatment on Pt-ReO(x)/SiO(2), and the synergy between Pt metal surface and neighboring ReO(x) clusters gives high catalytic performance in the preferential CO oxidation in the presence of H(2)O and CO(2) as more realistic reaction conditions at low reaction temperature.