Rational Control of Oxygen Vacancy Density in In2O3 to Boost Methanol Synthesis from CO2 Hydrogenation

Oxygen vacancies (Ov) in reducible metal oxides are the vital active sites for methanol synthesis via a CO2 hydrogenation technology. However, the relationship between the density of Ov and the methanol synthesis performance is still ambiguous, and it still shows a lack of a versatile strategy to precisely tailor the number of Ov. In this study, with In2O3 as a representatively catalytic component, the density functional theory computation confirms that the Ov property, especially Ov density, is pivotal to enhancing methanol selectivity of CO2 hydrogenation by suppressing the undesirable reverse water–gas shift reaction for CO formation, which is attributed to the unique electronic density of In atoms around Ov. To verify the theoretical results, we report a protocol to optimize the concentration of Ov on In2O3 by sequential carbonization and oxidation (SCO) treatments of In-based metal–organic frameworks, during which the consumption of carbon species and the structural reconstruction of the In2O3 crystal regulated the particle size and Ov concentration of In2O3 by varying the oxidation temperature. The In2O3-5 catalyst carbonized and oxidized at 500 °C exhibits good methanol selectivity (72.3%) at a CO2 conversion of 9.9% under 330 °C, 3 MPa, and high space velocity of 12,000 L–1 kgcat–1 h–1. Multiple in situ characterizations clarify that the proposed Ov property regulating the SCO strategy is convenient to boost methanol synthesis by altering the CO2 hydrogenation process to the HCOO* intermediate-dominated pathway. Our work provides the catalyst design strategy and will shed light on the rational design of reducible metal oxide-based catalysts with a controllable Ov density.