CO₂ Adsorption and Hydrogenation on Inverse InO_x/Cu(111) Catalysts: Active Role of the Oxide-Metal Interface

The direct conversion of carbon dioxide (CO₂) into methanol via hydrogenation is essential for industrial applications. Recent studies on catalysts that contain an inverse oxide/metal configuration have shown very good catalytic performance for the CO₂ hydrogenation to methanol process. In this study, we investigated the behavior of indium oxide-Cu(111) interfaces under pure CO₂ and CO₂/H₂ mixtures by using synchrotron-based ambient-pressure X-ray photoelectron spectroscopy (AP-XPS). Initially, a single layer of copper oxide (Cu_xO) was grown on the Cu(111) surface by controlled oxidation. On this surface, indium was deposited at room temperature. Oxygen atoms are transferred from Cu_xO/Cu(111) to the indium metal upon deposition, forming In-O-Cu bonds and active interfaces. Although Cu(111) is not very active for the binding and activation of CO₂, the formed InO_x-Cu(111) interfaces had no problem adsorbing and dissociating the molecules at room temperature. The reaction of CO₂ with H₂ on InO_x-Cu(111) yielded surface-bound H₃CO, CO₂^δ-, CO₃, and CH_x species, which are typical intermediates in the production of methanol and other oxygenates. The InO_x-Cu(111) interface underwent dynamic chemical changes under reaction conditions, forming In-Cu alloys at low indium coverages (<0.05 monolayer), while at higher indium coverages, a mixture of In-Cu and InO_x was detected in XPS. These findings indicate that InO_x/In-Cu interfaces can play a key role in processes aimed at the trapping and valorization of CO₂.