Dual Metal Active Sites in an Ir1/FeOx Single‐Atom Catalyst: A Redox Mechanism for the Water‐Gas Shift Reaction

• Published in: Angewandte Chemie International Edition Vol. 59; no. 31; pp. 12868 - 12875
• Main Authors: Liang, Jin‐Xia, Lin, Jian, Liu, Jingyue, Wang, Xiaodong, Zhang, Tao, Li, Jun
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 27.07.2020
• Edition: International ed. in English
• Subjects: active sites; Carbon dioxide; Catalysts; density functional theory; Electron transfer; Intermediates; Iron; Reaction mechanisms; redox mechanism; Shift reaction; Single atom catalysts; water-gas shift reaction
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.201914867

Herein, we report a theoretical and experimental study of the water‐gas shift (WGS) reaction on Ir1/FeOx single‐atom catalysts. Water dissociates to OH* on the Ir1 single atom and H* on the first‐neighbour O atom bonded with a Fe site. The adsorbed CO on Ir1 reacts with another adjacent O atom to produce CO2, yielding an oxygen vacancy (Ovac). Then, the formation of H2 becomes feasible due to migration of H from adsorbed OH* toward Ir1 and its subsequent reaction with another H*. The interaction of Ir1 and the second‐neighbouring Fe species demonstrates a new WGS pathway featured by electron transfer at the active site from Fe3+−O⋅⋅⋅Ir2+−Ovac to Fe2+−Ovac⋅⋅⋅Ir3+−O with the involvement of Ovac. The redox mechanism for WGS reaction through a dual metal active site (DMAS) is different from the conventional associative mechanism with the formation of formate or carboxyl intermediates. The proposed new reaction mechanism is corroborated by the experimental results with Ir1/FeOx for sequential production of CO2 and H2. Two sites are better than one: A redox mechanism with dual metal active site was found for the water‐gas shift (WGS) reaction on the Ir1/FeOx single‐atom catalyst by theoretical and experimental studies. The Ir1 and Fe atoms jointly facilitate the creation of an oxygen vacancy at the Fe species neighbouring the Ir1 atom, leading to sequential production of CO2 and H2.