Surface Science Studies on Cobalt Fischer–Tropsch Catalysts

Fischer–Tropsch (FT) synthesis is a process in which synthesis gas (CO/H2) is catalytically converted into hydrocarbons and oxygenates via surface polymerizations. With this process, clean liquid fuels can be made from abundant natural gas reserves and renewable biomass sources, after first being converted to synthesis gas. In the last several decades, FT synthesis has attracted renewed attention, primarily because of the increasingly stringent environmental requirements and the elevated price of crude oil. Co and Fe are used in catalysts for commercial FT synthesis. More recently efforts have focused on Co instead of Fe because of its superior activity, its higher chain growth probability, and its lower water gas shift activity. However Co is much more expensive with its relative cost being approximately 1000 times greater than Fe. Accordingly the optimal design of Co FT catalysts is essential for efficient use of the metal. Toward this end, it is crucial to understand the fundamental processes taking place on cobalt surfaces during FT synthesis. Surface science technologies can provide such information at the atomic level ; however, the complexity of heterogeneous systems limits the utilization of modern surface techniques to their fullest extent. To circumvent these experiment difficulties, various model catalysts have been developed over the last two decades. In this Minireview, we summarize the state-of-the-art surface science studies on cobalt FT synthesis model catalysts. This article is arranged in three sections starting from the simplest model catalysts moving to the more complex cases. The first section addresses FT synthesis on different single crystal surfaces; the second covers the results on submonolayer and polycrystalline cobalt; in the last section, studies on supported model catalysts are highlighted. Fischer–Tropsch Synthesis on Single Crystal Surfaces