Oxygen Species Regulating Carbon Monoxide Oxidation with Multi-Reaction Pathways over a Silver Catalyst*

The reaction route of CO oxidation by nitrous oxide and oxygen over a silver catalyst has been studied from the analysis of their transient behavior at 20℃. Half of the total surface sites are active for the adsorption of oxygen and one third of them are active for the decomposition, of N_2O, indicating the heterogeneity of the silver surface. At a reaction steady state of CO oxidation in the N_2O-CO relation and the O_2-CO systems, the surface in the N_2O-CO reaction is in a more reduced state than that in the O_2-CO reaction. The activation energy is evaluated to be 14kcal/mol for the O_2-CO reaction and 10kcal/mol for the N_2O-CO reaction, suggesting a different rate controlling step between both reactions. The adsorbed oxygen (presuming diatomic oxygen) from gaseous oxygen, not from N_2O, is responsible for the oxidation of CO. In a Eley-Rideal type mechanism, the rate of CO oxidation with diatomic oxygen is estimated to be about fourteen times faster than that of N_2O decomposition. The graphical analysis of transient response curves obtained in the two reactions leads us to a conclusion that the formation rate of the diatomic oxygen species is a sort of rate-controlling step in the N_2O-CO reaction