Unlocking the Potential of Oxide-Based Catalysts for CO₂ Photo-Hydrogenation: Oxygen Vacancies Promoted C─O Bond Cleavage in Key Intermediates.

Abstract

Oxygen vacancies are generally recognized to play significant roles in CO₂ adsorption and activation during CO₂ hydrogenation. However, by revisiting its structural/electronic affinity for a range of oxygen-containing intermediates in CO₂ hydrogenation processes, the additional roles of oxygen vacancies can be long overlooked and underestimated. Herein, using CO₂ (photo-)methanation as a model reaction, Co₃O₄ with abundant oxygen vacancies is employed to investigate the relationship between oxygen vacancies and the formation/conversion of oxygen-containing intermediates. Combined analyses of in situ diffuse reflectance infrared Fourier transform spectroscopy and theoretical calculations reveal that the key intermediate is formate, whose C─O bond cleavage is inferred to be the rate-limiting step during CO₂ methanation on Co₃O₄. Remarkably, leveraging the oxygen vacancy-mediated C─O bond scission to accelerate the conversion of formate, the CH₄ production activity (1108.1 mmol g^-1 h^-1) and selectivity (93%) are improved significantly. This comprehensive study provides valuable insights into the multifaceted roles of oxygen vacancies in CO₂ hydrogenation reactions, establishing a solid foundation toward the design and development of high-performance oxide-containing/-based catalysts for the conversion of CO₂ into various valuable chemicals.