The state and location of Re in Co–Re/Al2O3 catalysts during Fischer–Tropsch synthesis: Exploring high-energy XAFS for in situ catalysts characterisation

•High energy XAFS is demonstrated as an attractive option for in situ studies of catalysis at demanding conditions.•Both sets of experiments (Re K and LIII edges) indicate that Re is atomically distributed inside the bulk Co particles.•The local distortion of the Co environment in intimate contact with the Re atoms may give rise to the enhanced activity of Re-promoted catalysts.

A rhenium-promoted Co/Al2O3 catalyst and a sample containing Re/Al2O3 have been studied using XAS measured at both rhenium LIII (10,535 eV) and K (71,676 eV) edges. Results obtained from both sets of experiments are consistent and demonstrate that the higher penetration power of the X-rays at the Re K edge is a viable option that gives less stringent requirements in the choice of reactor material and X-ray window material. The in situ cell used at the high-energy Re K edge is conveniently of the same dimensions and material as a typical lab-scale fixed-bed reactor. Catalyst performance from such measurements can be directly compared to the results from conventional fixed-bed catalytic experiments. High energy X-rays are thus an attractive option for in situ studies of catalysis at demanding conditions. Both sets of experiments (Re K and LIII edges) indicate that Re is atomically distributed inside the bulk Co particles. The results indicate a local distortion of the Co environment in intimate contact with the Re atoms, which may contribute to the observed increase in catalytic activity for the Re promoted catalysts. A minor fraction of Re (approx. 15%) remains in an oxidic state after a typical reduction procedure for Co-based Fischer–Tropsch synthesis catalysts.

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