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

Herein, we report a theoretical and experimental study of the water-gas shift (WGS) reaction on Ir-1/FeOx single-atom catalysts. Water dissociates to OH* on the Ir-1 single atom and H* on the first-neighbour O atom bonded with a Fe site. The adsorbed CO on Ir-1 reacts with another adjacent O atom to produce CO2, yielding an oxygen vacancy (O-vac). Then, the formation of H-2 becomes feasible due to migration of H from adsorbed OH* toward Ir-1 and its subsequent reaction with another H*. The interaction of Ir-1 and the second-neighbouring Fe species demonstrates a new WGS pathway featured by electron transfer at the active site from Fe3+-O...Ir2+-O-vac to Fe2+-O-vac...Ir3+-O with the involvement of O-vac. 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 Ir-1/FeOx for sequential production of CO2 and H-2.