Catalytic properties of cold-worked noble metals for the oxidation of carbon monoxide

Abstract

The oxidation of carbon monoxide was studied on cold-worked metals (Pd, Ag, and Au) to compare the characteristics of the catalytic properties. On palladium, when the reaction was carried out on the freshly prepared catalysts at reaction temperatures below 300℃, the two periods (acceleration and steady state period) were always observed in the course of the reaction. From the observation of the dependence of annealing temperature upon the catalytic activity, it was considered that the acceleration period is the process of the production of new active sites by the reaction itself and that the presence of lattice defects (dislocations) in the crystal plays a role for the reaction to initiate and serves to create the active sites. These facts were almost the same as in the case of platinum catalyst. In the cases of silver and gold, no acceleration period was observed and the annealing had no influence on the catalytic acivity. It is suggested that under the conditions of the present experiments the difference in the catalytic properties among these metals is due to the difference in the strength of metal-oxygen bond and in the stability of the active sites.