Adsorption and oxidation of carbon monoxide on rhodium and copper-rhodium catalysts

The influence of copper admixtures on adsorption and oxidation of CO on deposited and film rhodium catalysts was studied. The activity and the degree of dispersity of a Rh(5 wt %)/SiO2 catalyst were found to increase in the presence of Cu (30-75 at. % based on Rh); under similar conditions, the activity of a film Rh catalyst with a degree of coverage by Cu of∼0.30 remained almost unchanged. The amount of carbon monoxide reversibly adsorbed at 253-333 K and strongly adsorbed (desorption temperature 473-723 K) on Rh increased in the presence of Cu. At high temperatures, desorplion of CO from Rh and RhCu films was accompanied by the formation of CO2. The promoting action of copper is explained by the formation of Cu clusters, which increase the amount of adsorbed CO and oxygen on the surface of rhodium. The inhibiting action of copper is due to the formation of small clusters, which block active sites on the surface of rhodium.