An experimental and computational investigation on structural evolution of the In₂O₃ catalyst during the induction period of CO₂ hydrogenation

As one of the most important industrially viable methods for carbon dioxide (CO₂) utilization, methanol synthesis serves as a platform for production of green fuels and commodity chemicals. For sustainable methanol synthesis, In₂O₃ is an ideal catalyst and has garnered significant attention. Herein, cubic In₂O₃ nanoparticles were prepared via the precipitation method and evaluated for CO₂ hydrogenation to produce methanol. During the initial 10 h of reaction, CO₂ conversion gradually increased, accompanied by a slow decrease of methanol selectivity, and the reaction reached equilibrium after 10-20 h on stream. This activation and induction stage may be attributed to the sintering of In₂O₃ nanoparticles and the creation of more oxygen vacancies on In₂O₃ surfaces. Further experimental studies demonstrate that hydrogen induction created additional oxygen vacancies during the catalyst activation stage, enhancing the performance of In₂O₃ catalyst for CO₂ hydrogenation. Density functional theory calculations and microkinetic simulations further demonstrated that surfaces with higher oxygen vacancy coverages or hydroxylated surfaces formed during this induction period can enhance the reaction rate and increase the CO₂ conversion. However, they predominantly promote the formation of CO instead of methanol, leading to reduced methanol selectivity. These predictions align well with the above-mentioned experimental observations. Our work thus provides an in-depth analysis of the induction stage of the CO₂ hydrogenation process on In₂O₃ nano-catalyst, and offers valuable insights for significantly improving the CO₂ reactivity of In₂O₃-based catalysts while maintaining long-term stability.