Comparison of carbon dioxide and carbon monoxide with respect to hydrogenation on Raney ruthenium catalysts

On Raney ruthenium catalysts pretreated with a mixed gas of water vapor and helium, the rate of hydrogenation of CO2 was higher by three orders of magnitude than that of the hydrogenation of CO. However, the former reaction gives methane almost exclusively, while the latter reaction can give methanol. Since supported ruthenium catalysts usually catalyze both hydrogenations of CO and CO, with almost the same rate, Raney ruthenium catalysts were shown to be uniquely active for hydrogenation of CO2 under the conditions studied here. The weight-based activity of methane production from CO2 and hydrogen is much higher than that of the supported catalysts at 353-413 K and under 80 kPa. Methanol was also produced from CO2 on Raney ruthenium catalysts, though the selectivity was negligibly lower than that from CO. With the mixtures of CO, CO2, and H-2 at 353 K and under 80 kPa, CO was preferentially hydrogenated, unless composition of CO was very small. Reaction mechanisms of CO-CO2 hydrogenation are proposed.