Fischer-Tropsch synthesis: Metal-support interfacial contact governs oxygenates selectivity over CeO₂ supported Pt-Co catalysts

The catalytic performance during Fischer-Tropsch synthesis (FTS) of Pt promoted Co/CeO₂ catalysts at two different cobalt metal loadings was investigated using a slurry-phase reactor. CeO₂ supported Pt-Co catalysts exhibit higher selectivities to oxygenates and especially linear alcohols (14.8%) at lower cobalt loadings. A plausible pathway for the formation of alcohols was proposed based on Co-CeO₂ interfacial catalysis, in which termination of chain growth occurs at the metal-oxide junction and involves bridging OH groups on partially reduced ceria. As cobalt content increases, the selectivity to oxygenates decreases. The resulting increase in cobalt metal particle size accelerates the mechanism involving normal FT termination, since the on-top surface area of cobalt increase at the expense of the interfacial area at the junction with ceria. Compared to γ-Al ₂O₃, CeO₂ supported Pt-Co catalysts exhibit significantly higher oxygenates at similar CO conversions. Selectivity control is thus achieved by controlling the surface fugacity of bridging OH groups (i.e., located on ceria) in contact with cobalt sites on a per Co surface atom basis.