Effect of Different In₂O₃(111) Surface Terminations on CO₂ Adsorption

In₂O₃-based catalysts have shown high activity and selectivity for CO₂ hydrogenation to methanol; however, the origin of the high performance of In₂O₃ is still unclear. To elucidate the initial steps of CO₂ hydrogenation over In₂O₃, we have combined X-ray photoelectron spectroscopy and density functional theory calculations to study the adsorption of CO₂ on the In₂O₃(111) crystalline surface with different terminations, namely, the stoichiometric, reduced, and hydroxylated surface. The combined approach confirms that the reduction of the surface results in the formation of In adatoms and that water dissociates on the surface at room temperature. A comparison of the experimental spectra and the computed core-level shifts (using methanol and formic acid as benchmark molecules) suggests that CO₂ adsorbs as a carbonate on all three surface terminations. We find that the adsorption of CO₂ is hindered by hydroxyl groups on the hydroxylated surface.