Spillover hydrogen-driven CO₂ hydrogenation on a Pd/Cu(111) single atom alloy model catalyst at room temperature studied by ambient pressure X-ray photoelectron spectroscopy

We report that a single-atom alloy (SAA) model catalyst, Pd/Cu(111), promotes CO₂ hydrogenation to formate and methoxy species via hydrogen dissociation and spillover at room temperature, as revealed by ambient-pressure X-ray photoelectron spectroscopy (AP-XPS). Under a CO₂ atmosphere at 298 K, carbonate and atomic oxygen species were observed on the surface. This indicates that CO₂ dissociation and disproportionation proceeded, similar to the cases on Cu(111) and Zn/Cu(111). Additional H₂ introduction leads to the formation of formate and methoxy species even at 298 K; their amounts increase by heating to 380 K. A hydrogen-induced chemical shift in the Pd 3d_5/2 core level confirms H₂ dissociation at Pd sites, and hydrogen spillover onto Cu sites where hydrogen drives CO₂ hydrogenation. These results demonstrate that isolated Pd atoms embedded in a Cu(111) surface effectively overcome the inherent limitation of Cu catalysts in H₂ activation, promoting the hydrogenation step of CO₂ at significantly mild temperatures. Furthermore, semi-quantitative AP-XPS analysis indicates that carbonate species act as reactive intermediates, supporting a carbonate-mediated hydrogenation pathway. These findings provide new valuable mechanistic insights into room-temperature methanol synthesis and provide design principles for the development of next-generation catalysts.