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

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• 作者：Alexey Voronov^a ; Nikolaos E. Tsakoumis^a ; Nina Hammer^a ; Wouter van Beek^b ; Hermann Emerich^b ; Magnus Rø ; nning^a ; ^{magnus.ronning@ntnu.no" class="auth_mail}
• 关键词：High-energy XAFS ; In situ characterisation ; Fischer&ndash ; Tropsch synthesis ; Rhenium
• 刊名：Catalysis Today
• 出版年：15 June, 2014
• 年：2014
• 卷：229
• 期：Complete
• 页码：23-33
• 全文大小：2097 K

文摘

A rhenium-promoted Co/Al₂O₃ catalyst and a sample containing Re/Al₂O₃ have been studied using XAS measured at both rhenium L_III (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 L_III 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.