Dual Conflicting Roles of Preattached CO in the Water–Gas Shift Reaction Mediated by Iridium–Vanadium Oxide Clusters IrV₂O_3,4CO^–

A fundamental understanding regarding the interplay of coadsorbed reactants under realistic conditions is pivotal to develop advanced catalytic processes, while it is challenging owing to the complexity of heterogeneous catalysis. Herein, we demonstrated unambiguously that the preadsorbed CO plays dual conflicting roles in the water–gas shift (WGS) reaction mediated by iridium–vanadium oxide clusters IrV₂O_3,4CO^–. The reactions were characterized by advanced mass spectrometry and quantum-chemical calculations. The calculated results rationalize that the preattached CO on IrV₂O_3,4CO^–drives the generation of thermodynamically more favorable products IrV₂O_4,5CO^–following H₂O reduction by substantially suppressing the barriers of H atom transfer and H–H coupling, while CO oxidation by products IrV₂O_4,5CO^–become thermodynamically challenging compared to oxidation driven by IrV₂O_4,5^–and higher temperatures are required to close the catalytic cycle. This finding redefines the distinctive roles of preferentially anchored CO that can govern the overall efficiency of WGS through an unbalanced enthalpy redistribution in the H₂O reduction and CO oxidation elementary steps.