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

Highlights

• CO₂ activation on In/Cu model catalysts was characterized in situ by using NAP-XPS.

• In forms surface alloy with Cu substrate which can be oxidized by CO₂.

• Oxygen vacancies from In₂O_3-x are stable under CO₂ hydrogenation conditions.

• The activation of CO₂ is enhanced due to the synergistic effect of Cu-In and In₂O_3-x.

Abstract

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 In₂O_3-x and Cu remains metallic. Due to the presence of In₂O_3-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.