Supported Au Catalysts for Low-Temperature CO Oxidation Prepared by Impregnation

Gold catalysts supported on γ-Al2O3 powder were prepared by impregnation with solutions of HAuCl4 which were aged in pH ranging from 5 to 11 for 15–720 min. During aging, hydrolysis of the AuCl4− complex gave rise to various species as observed by UV/vis spectroscopy. Au loading and particle size were determined by AAS and XRD. Activity of the catalysts was evaluated at room temperature under stoichiometric as well as excess oxygen concentrations. Au particle size and loading were influenced by the precursor speciation, demonstrating that intermediate values of aging pH and time are required for maximum CO conversion. The state of support, wet or dry before impregnation, did not seem to influence catalyst activity, while an excess of oxygen improved conversion. The preparation method was extended to washcoated monoliths and similar high activity was observed.