Abstract
The catalytic activities of Pd ribbons for the hydrogenation of C2H4 and for the oxidation of H2 were markedly increased by chemical pretreatments of the surface of the ribbons such as their thermal oxidation by O2 and further reduction by H2. Such a chemical treatment of the catalyst did not noticeably change the surface area and the surface structure of the catalyst. These findings were found to be very similar to those previously observed for Pt. It is suggested that some surface defects serving as active sites for the reactions are generated by these chemical treatments. In the case of the oxidation of CO over fresh annealed-catalysts, an acceleration in reaction was always observed during the reaction. We propose an interpreta- tion that this acceleration period corresponds to the stage of the production of new active sites by the oxidation reaction itself, which is similar to the one proposed by Baddour et al. for the oxidation of CO over supported Pd catalysts.
