Dual metal active sites in an Ir1/FeOx single-atom catalyst: a redox mechanism for the water-gas-shift reaction.

Fundamental understanding of catalytic mechanism at the atomic level is essential for rational design of high-performance catalyst. Here we report a combinedtheoretical and experimental study of the water-gas-shift (WGS) reaction on Ir1/FeOx single-atom catalyst. It is found that water easily dissociates to OH* on the Ir1 single atom and H* on the nearby O atom bonded with a Fe site. The adsorbed CO on Ir1 reacts with the 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 synergistic interaction of Ir1 and the neighbouring Fe species demonstrates a new pathway vis-à-vis 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 via a synergetic 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.