Active Site Dependent Reaction Mechanism over Ru/CeO2 Catalyst toward CO2 Methanation

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• 作者：Fei Wang ; Shan He ; Hao Chen ; Bin Wang ; Lirong Zheng ; Min Wei ; David G. Evans ; Xue Duan
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：May 18, 2016
• 年：2016
• 卷：138
• 期：19
• 页码：6298-6305
• 全文大小：667K
• 年卷期：0
• ISSN：1520-5126

文摘

Oxygen vacancy on the surface of metal oxides is one of the most important defects which acts as the reactive site in a variety of catalytic reactions. In this work, operando spectroscopy methodology was employed to study the CO₂ methanation reaction catalyzed by Ru/CeO₂ (with oxygen vacancy in CeO₂) and Ru/α-Al₂O₃ (without oxygen vacancy), respectively, so as to give a thorough understanding on active site dependent reaction mechanism. In Ru/CeO₂ catalyst, operando XANES, IR, and Raman were used to reveal the generation process of Ce³⁺, surface hydroxyl, and oxygen vacancy as well as their structural evolvements under practical reaction conditions. The steady-state isotope transient kinetic analysis (SSITKA)-type in situ DRIFT infrared spectroscopy undoubtedly substantiates that CO₂ methanation undergoes formate route over Ru/CeO₂ catalyst, and the formate dissociation to methanol catalyzed by oxygen vacancy is the rate-determining step. In contrast, CO₂ methanation undergoes CO route over Ru surface in Ru/α-Al₂O₃ with the absence of oxygen vacancy, demonstrating active site dependent catalytic mechanism toward CO₂ methanation. In addition, the catalytic activity evaluation and the oscillating reaction over Ru/CeO₂ catalyst further prove that the oxygen vacancy catalyzes the rate-determining step with a much lower activation temperature compared with Ru surface in Ru/α-Al₂O₃ (125 vs 250 °C).