Nickel-modified In₂O₃ with inherent oxygen vacancies for CO₂ hydrogenation to methanol

Abstract

Methanol synthesis is one of the most important industrially-viable approaches for carbon dioxide (CO₂) utilization, as the produced methanol can be used as a platform chemical for manufacturing green fuels and chemicals. The In₂O₃ catalysts are ideal for sustainable methanol synthesis and have received considerable attention. Herein, Co-, Ni- and Cu-modified In₂O₃ catalysts were fabricated with high dispersion and high stability to improve the hydrogenation performance. The Ni-promoted In₂O₃ catalyst in the form of high dispersion possessed the largest amount of oxygen vacancies and the strongest ability for H₂ activation, leading to the highest CO₂ conversion and space time yield of methanol of 0.390 g_MeOH g_cat⁻¹ h⁻¹ with CH₃OH selectivity of 68.7%. In addition, the catalyst exhibits very stable performance over 120 h on stream, which suggests the promising prospect for industrial applications. Further experimental and theoretical studies demonstrate that surface Ni doping promotes the formation of oxygen defects on the In₂O₃ catalyst, although it also results in lower methanol selectivity. Surprisingly, subsurface Ni dopants are found to be more beneficial for methanol formation than surface Ni dopants, so the Ni promoted In₂O₃ catalyst with a lower surface Ni content at the similar Ni loading can reach higher methanol selectivity and productivity. This work thus provides theoretical guidance for significantly improving the CO₂ reactivity of In₂O₃-based catalysts while maintaining high methanol selectivity.