Infrared study of the reaction of H2+ CO on a Ru/SiO2 catalyst

Abstract

The amount and dynamic behaviour of adsorbed hydrocarbon species formed during the reaction of H2+ CO on Ru/SiO2 were measured by the in situ infrared spectroscopic technique using Fourier-transform methods; the average chain length (the CH2/CH3 ratio), and the dependences of the rate of accumulation of such hydrocarbons on temperature and partial pressures of H2 and CO gases were investigated, together with their reactivities under various reaction conditions, such as hydrogenation. These adsorbed hydrocarbons grow in a linear form on a limited part of the Ru surface, whereas most of the rest of the surface is covered by adsorbed CO. The adsorbed hydrocarbons are readily dehydrogenated to form carbon and hydrogen on evacuation, are also hydrogenated to form mainly CH4 with some higher hydrocarbons, and exchange their hydrogen with molecular hydrogen. Their reactivities, however, were markedly retarded by adsorbed CO when CO was present in the gas phase.Infrared observations demonstrated that small amounts of carbon deposited by the CO disproportionation reaction or of accumulated hydrocarbon cuts down the amount of weakly held adsorbed CO markedly, which suggests that the sites for the weakly held CO play an important role in carbon deposition, which is followed by its hydrogenation to form reaction products.