Selective Conversion of CO₂ to Methanol on a In₂O_3-x-TiO₂(110) Interface: Importance of Oxide-Oxide Interactions

Methanol is a strategic energy vector for the storage and delivery of energy and is a widely used precursor for the synthesis of many high-value chemicals. The hydrogenation of carbon dioxide (CO₂) into methanol is a key process in industrial operations. In this study, we show that an oxide-oxide interface generated by a low loading (0.15 ML) of In₂O_3-x on a TiO₂(110) substrate has a high activity and selectivity as a catalyst for the CO₂ + 3H₂ → CH₃OH + H₂O process. The properties of the In₂O_3-x-TiO₂ interface under reaction conditions were investigated using a combination of synchrotron-based ambient pressure X-ray photoelectron spectroscopy (AP-XPS), temperature-programmed desorption (TPD), and catalytic testing. The In₂O_3-x overlayer spread out on top of the titania and was rich in defects and O vacancies that activated CO₂ and H₂ as reactants, without destroying CH₃O and CH₃OH as reaction products. The In₂O_3-x/TiO₂(110) catalyst is at least 1 order of magnitude more active than bulk indium oxide while maintaining a very high selectivity (∼80%) toward methanol production. Under the rich hydrogen environment of methanol synthesis, the oxide-oxide interactions allowed only a partial reduction of the In cations, preventing the formation of metal alloys as seen in the case of catalysts with metal-indium oxide interfaces. Thus, the dispersion of low loadings of In₂O_3-x on a stable oxide substrate is a valid and low-cost approach for generating efficient catalysts for CO₂ valorization.