Abstract
The influence of Pt metal dispersion and metal-support interactions on the rate of the catalytic oxidation of CO has been studied. The effect of Pt dispersion appears to be greater on Pt-Al 2O 3 catalysts than on Pt-SiO 2. The higher oxidation rates observed on large Pt particles on Pt-A1 2O 3 and (2) a decrease in the number of Pt sites having low surface coordinations. By contrast, the effect of support was much more significant. Turnover numbers for CO 2 formation are nearly an order of magnitude larger on Pt-SiO 2 than on Pt-A1 2O 3. This is explained by considering the strength of the CO bond as measured using in situ infrared spectroscopy. Catalyst deactivation was observed for an of the catalysts studied but was found to be somewhat larger on the poorly dispersed catalysts. This is explained in terms of the greater number of edges, corners and centers of low surface coordination present on small metal particles. Arrhenius plots obtained for the oxidation of CO on small Pt particles revealed a discontinuity at about 150°C. This discontinuity was not observed on large Pt particles. The reason for this discontinuity is explained by invoking differences in site selectivity as a function of temperature. Hysteresis rate curves are used to reinforce this argument.
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