MECHANISMS OF METHANATION OF CO AND CO2 OVER NI

The mechanisms of the title reactions over Ni were studied by the transient response and the temperature-programmed-reaction method. These reactions were markedly different in their kinetics under the transient states. At the steady state of the CO methanation, adsorbed carbon, C(a), and strongly adsorbed carbon monoxide, CO(a), were appreciably present together with a small amount of reversibly adsorbed CO. In the CO2 methanation, the amount of C(a) was much smaller than that of CO(a). The amount of reversibly adsorbed CO was negligible. On analysis of the response curves obtained, it was shown that the dissociation of CO(a) was unaffected by H2. The hydrogenation of C(a) proceeded in proportion to 0.39th order in the partial pressure of H2. This process was suggested to be greatly retarded in the presence of reversibly adsorbed CO.