The effects of chloride, phoshate, and cesium ions on Au/γ-Al2O3 for selective CO oxidation in H2 was examined. The difference in activity between this catalyst and the catalyst not treated with Mg-citrate suggested that small Au particle size could not be a necessary requirement for high activity and the Cl- has a direct inhibitive effect on the catalyst. The transient behavior of the catalysts to which Cl- was added supported the proposal that Cl- poisons the active site by replacing the Au+ - OH- with Au+ - Cl-. Phosphate anions also acted to blocked the active sites for CO oxidation, while Cs ions adversely affected H2 oxidation.
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