The activity of carbonyl cluster derived Co-Ru/SiO₂ and Co-Ru/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 Co_4-nRu_nSiO₂ and Co_4-nRu_nSiO₂  catalysts (where n = O-4) and Co_4-nRu_nSiO₂  and Co_4-nRu_nSiO₂  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 Co_4-nRu_nSiO₂  catalysts the deactivation was stronger on bimetallic sites and on the Co_4-nRu_nSiO₂  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.