Operando study of CO2 Hydrogenation Reaction Catalyzed By in2O3-Based Catalysts

Direct hydrogenation of CO₂ into transportable liquid fuels represents a promising way to mitigate the emission of a major greenhouse gas and to generate valuable energy carriers. Recently, In₂O₃-based catalysts have been recognized as highly active and selective with practical prospect for methanol synthesis via direct CO₂ hydrogenation. While almost exclusive formation of methanol have been reported by Martin and Pérez-Ramírez et al. [1], various of selectivity (20 % – 90 %) have been reported by several other groups using In₂O₃-based catalysts, even with catalysts of identical preparation method and composition [2]. Ambient pressure X-ray photoelectron spectroscopy (APXPS) has proven to be an excellent tool to investigate the surface chemical and electronic properties of heterogeneous catalysis before, during, and after reaction conditions and is here combined with information from TEM, XRD, and TPR.

We found that, under catalytically relevant conditions, bare In₂O₃ can be largely reduced and form an (In metal + InO_x)/In₂O₃ (0 < x < 1.5) core-shell structure. When loaded onto a semiconducting/insulating support, the In₂O₃ domains were progressively reduced and formed InO_x at the topmost region under elevated temperatures, but with less tendency to form metallic In, a primary surface species that leads to catalyst deactivation. Detailed ex situ TEM study of spent catalyst suggests reconstructed In₂O₃ at the subsurface. The observation of key reaction intermediates, i.e., carbonate, formate (HCOO-), and methoxyl (CH₃O-), as well as their inter-conversions under reaction conditions, offers an extra handle to mechanistically probe the CO₂ hydrogenation process. The APXPS data analysis was found in remarkable correlation with the practical catalysis.

Reference

1. Martin, O. et al. Chem. Int. Ed. 2016, 55, 6261
2. Chen, T. Y. et al. ACS Catal. 2019, 9, 8785