Surface speciation of Co based Fischer-Tropsch catalyst under reaction conditions: Deactivation by coke or by oxidation?

Loss of catalyst activity and selectivity with time-on-stream are one of the greatest limitations for the industrial use of Cobalt based Fischer-Tropsch (FT) catalysis. Despite much work on this area, there is still a lack of consensus about the causes leading to catalyst deactivation. Some of the most common hypotheses are oxidation and carbonization of the active phase. In our work we present the free energy of C alpha H beta O gamma surface deposition on Co (111) for a wide range of surface coverages under FT reaction conditions. These results present a comprehensive study in which the trends for hydrocarbon-species deposition, cobalt oxidation, and hydrocarbon-induced surface reconstruction are thoroughly compared. The formation of unavoidable branched species leads to deactivation by coke; O may be present in surface intermediates but direct Co-O interaction is unlikely at these conditions.