Re‐dispersion of Cobalt on a Model Fischer–Tropsch Catalyst During Reduction–Oxidation–Reduction Cycles

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Reduction–oxidation–reduction treatment is employed to regenerate cobalt Fischer–Tropsch synthesis catalysts. Reduction–oxidation–reduction cycles on a model supported‐cobalt Fischer–Tropsch catalyst showed that hollow‐sphere formation occurs during the oxidation step, followed by the formation of a catalyst with an improved metal dispersion. It is deduced that the metal particles consist of both hexagonal close packed Co and face‐centered cubic Co. High‐pressure oxidation led to smaller cobalt oxide crystallites, resulting in a more facile reduction and an increase in metal surface area. Hence, oxidative regeneration is an attractive method to improve the dispersion of cobalt metal on a sintered deactivated catalyst. However, metallic cobalt crystallites may become too small after regeneration, and the intrinsic activity per unit surface area in the Fischer–Tropsch synthesis may drop.