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

Oxygen vacancies (O-v) in reducible metal oxides are the vital active sites for methanol synthesis via a CO2 hydrogenation technology. However, the relationship between the density of O-v and the methanol synthesis performance is still ambiguous, and it still shows a lack of a versatile strategy to precisely tailor the number of O-v. In this study, with In2O3 as a representatively catalytic component, the density functional theory computation confirms that the O-v property, especially O-v 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 O-v. To verify the theoretical results, we report a protocol to optimize the concentration of O-v 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 O-v concentration of In2O3 by varying the oxidation temperature. The In2O3-5 catalyst carbonized and oxidized at 500 degrees C exhibits good methanol selectivity (72.3%) at a CO2 conversion of 9.9% under 330 degrees C, 3 MPa, and high space velocity of 12,000 L-1 kg(cat)(-1) h(-1). Multiple in situ characterizations clarify that the proposed O-v 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 O-v density.