CO Coadsorption Effects on Water-Gas Shift Reaction over Cu Clusters on Cu(111): Insights from Machine Learning Force Field and Microkinetic Modeling

Abstract

CO-induced Cu clustering has been observed experimentally and theoretically, yet its catalytic implications remain insufficiently understood. Here, we combine machine learning force field (MLFF) with density functional theory and microkinetic modeling that explicitly incorporates CO coadsorption as lateral adsorbate–adsorbate interactions to elucidate the water-gas shift reaction (WGSR) on Cu clusters (Cu₃, Cu₄, Cu₃) supported on Cu(111). Stronger CO binding on clusters than on Cu(111) yields higher CO coverages, making coverage-dependent lateral interactions important for realistic predictions of Cu cluster activity. Across 450-550 K, Cu clusters are intrinsically more active than Cu(111) because the H₂O dissociation barrier is lower, with this step being rate determining on Cu(111). Including lateral interactions shows that coadsorbed CO suppresses activity at 350-500 K on Cu clusters by increasing the barriers for H₂O dissociation and H₂ recombinative desorption. At 450-500 K, the inclusion of lateral interactions on Cu clusters brings predicted turnover frequencies closer to experiment. Above 550 K, the influence of lateral interactions weakens as CO coverage declines. Altogether, while coadsorption effects on Cu(111) have been previously examined, their interplay with Cu cluster with different size under reaction conditions also significantly alters the predicted activity trends, and the combination of MLFF and microkinetic modeling enables rigorous evaluation of catalytic performance under realistic conditions.