On the development of metallic particles and their initial catalytic properties in the CO + H2 reaction over Co/Al2O3 catalyst

Formation of Coo phases with different surface structure over 10 wt% Co/Al2O3 and their catalytic properties were induced by pretreatments in H2 at 570 K for 1 h or 20 h. Electronic behaviour of the Coo phase, which consists of small (after 1 h reduction) or large bulk-like particles (after 20 h reduction), did not change during the CO hydrogenation after 5 h on stream as was determined by XPS. On the basis of the measured C2+ hydrocarbon selectivities the CO molecules are suggested to dissociate on small Co particles to a larger extent than on large cobalt particles. The slight decrease in the catalytic activity with increasing time on stream obtained for the long-term reduced sample is explained by the change in the surface Coo content detected by XPS. The increase in the catalytic activity along with the change in olefin selectivity, measured for the sample reduced for 1 h, is interpreted by the change of a reaction path involving the Coo-support interface during the initial period of the reaction.