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

Abstract

Oxygen vacancies (O v ) in reducible metal oxides are the vital active sites for methanol synthesis via a CO 2 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 In 2 O 3 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 CO 2 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 In 2 O 3 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 In 2 O 3 crystal regulated the particle size and O v concentration of In 2 O 3 by varying the oxidation temperature. The In 2 O 3 -5 catalyst carbonized and oxidized at 500 °C exhibits good methanol selectivity (72.3%) at a CO 2 conversion of 9.9% under 330 °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 CO 2 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.

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