The activity of carbonyl cluster derived Co-Ru/SiO2 and Co-Rh/SiO2 catalysts in CO hydrogenation

We studied systematically the use of tetranuclear cobalt, cobalt-ruthenium, cobalt-rhodium and rhodium carbonyl clusters as catalyst precursors, The catalytic activities and the product distributions of the hydrogenation of carbon monoxide over Co4-nRun/SiO2 and Co4-nRhn/SiO2 catalysts (where n = 0-4) and (Co-4 + Ru-4)/SiO2 and (Co-4 + Rh-4)/SiO2 catalysts derived from the transition-metal carbonyl clusters were compared, Activities were highest for the catalysts derived from homometallic clusters, and lowest for catalysts with 1:1 ratio of Co/Ru or Co/Rh. Interestingly enough, the highly active homometallic cobalt catalyst was the most resistant to deactivation. On Co4-nRhn/SiO2 catalysts the deactivation was stronger on bimetallic sites and on the Co4-nRun/SiO2 catalysts the deactivation was closely related to the presence of ruthenium. The selectivities for oxygenated compounds were clearly promoted by the bimetallic sites of Co-Rh catalysts. This result is very plausible since the probability to find dual active sites responsible for the formation of oxygenates is greater in bimetallic than in homometallic catalysts.