J. H. Yang

On the potential role of hydroxyl groups in CO oxidation over Au/Al2O3

The deuterium isotope effect in the steady state CO oxidation rate over Au/-Al2O3 in the presence of H2 or H2O and the effect of pretreatment on an uncalcined catalyst were studied. In a reaction feed containing 1% CO, 0.5% O2, and 40.5% H2 at room temperature, CO oxidation exhibited a deuterium isotope effect (kH/kD )o f 1.4 ± 0.2. The rate of D2 oxidation was also slower than the oxidation of H2, such that the selectivity for CO oxidation was 86% in the presence of D2 versus 77% in the presence of H2. In contrast, there was no deuterium isotope effect in a feed containing 1% CO, 0.5% O2, and 1.5% H2O. H2 was also more effective in regenerating a CO oxidation reaction deactivated catalyst than D 2, whereas H2O and D2O were equally effective. The difference was attributed to the different mechanisms with which H 2 or H2O prevented deactivation of the catalyst during CO oxidation. An uncalcined Au/-Al2O3 was rather inactive. It could be activated by treatment with a mixture of H2 and H2 Oa t 100 ◦ C, although treatment by either H2 or H2O alone was ineffective. The observations are consistent with the model of the active site consisting of an ensemble of metallic Au atoms and a cationic Au with a hydroxyl group.