Near ambient-pressure X-ray photoelectron spectroscopy study of CO2 activation and hydrogenation on indium/copper surface

Indium-based catalysts exhibit excellent performance for CO2 hydrogenation to methanol, yet their nature and chemical evolution under reaction conditions are still elusive, thus hindering an understanding of their reaction mechanism. In this work, near ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) is employed to investigate the chemical properties and the catalytic role of indium/copper model catalysts under CO2 hydrogenation conditions. We found that the deposition of In on the surface of a Cu foil led to the formation of Cu-In alloy, whereas upon CO2 exposure, In was partially oxidized to In2O3-x and Cu remains metallic. Due to the presence of In2O3-x, CO2 was activated on the surface of In/Cu samples mainly in the form of carbonate. In addition, compared with the pure In foil reference, both the fraction of oxygen vacancies and the coverage density of carbonate were higher on the In/Cu samples, indicating the promotion effect of Cu-In alloy in the activation of CO2. These results reveal the evolution of the active sites of indium/copper catalysts and inspire the design of advanced In-based bimetallic catalysts for CO2 hydrogenation.