Co/SiO2 catalysts prepared from CO2(CO)(8) for CO hydrogenation into alcohols and hydrocarbons: characterization by magnetic methods and temperature-programmed hydrogenation

The hydrogenation of carbon monoxide over Co/SiO2 catalysts obtained by red uction of precursors prepared by the reaction of dicobaltoctacarbonyl with silica gives rise to a mixture of alcohols and hydrocarbons. The chain grow th probability a! for hydrocarbon synthesis is similar to that observed ove r conventional catalysts prepared by the ammonia method (alpha = 0.74) with a comparable metal dispersion (metal particle size 4 nm). Alcohol formatio n yields a smaller chain growth probability (alpha = 0.42). Magnetic measur ements have shown that in the latter catalyst, small cobalt clusters (simil ar to1 nm) are likely to be present together with the cobalt particles (4 n m), this observation reconciles apparently conflicting results from the lit erature. It has been speculated that alcohol formation might be related to the presence of these clusters according to a concerted mechanism. Furtherm ore, the observation of large amounts of acetates by temperature-programmed hydrogenation, not detected in hydrocarbon selective catalysts, suggests t hat they may play a role in ethanol synthesis. (C) 2001 Elsevier Science B. V. All rights reserved.