Catalytic CO2 Hydrogenation on Nickel: Novel Insight by Chemical Transient Kinetics

Carbon dioxide hydrogenation on support-free nickel model catalysts was investigated by means of a time-resolved quantitative analysis of chemical transients triggered by abrupt changes in the reactant partial pressures. It was found that carbon dioxide adsorption is strongly affected by the presence of hydrogen and by coadsorption effects and thus influences the reaction rate in the buildup and back transients. The observed transients suggest that two reaction mechanisms operate in parallel, which is consistent with previous results obtained using a Ni single-crystal termination. The initial reaction rate involves fast direct hydrogenation of CO2, whereas the rate under steady-state conditions is lower due to a change in the mechanism involving an oxygen-containing intermediate.