Preferential CO Oxidation in a H2-Rich Stream on Pt-ReOx/SiO2: Catalyst Structure and Reaction Mechanism

Modification of Pi/SiO2 with ReOx 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-ReOx/SiO2 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-ReOx/SiO2 catalyst by means of EXAFS, XANES, temperature-programmed reduction, and CO adsorption measurements suggested the formation of the ReOx clusters on the surface of Pt metal particles with the average valence of Re of +2.7. The CO adsorption on Pt-ReOx/SiO2 gave a higher wavenumber then that on Pt/SiO2 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-ReOx/SiO2 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 -ReOx/SiO2 can activate O-2 even when the catalyst surface is saturated with CO These tendencies can be explained by the mechanism where the reduced ReOx species activates O-2 and the oxidizing species is spilled over from the ReOx species to the Pt surface