The feasibility study of the indium oxide supported silver catalyst for selective hydrogenation of CO₂ to methanol

Silver catalyst has been extensively investigated for photocatalytic and electrochemical CO₂ reduction. However, its high activity for selective hydrogenation of CO₂ to methanol has not been confirmed. Here, the feasibility of the indium oxide supported silver catalyst was investigated for CO₂ hydrogenation to methanol by the density functional theoretical (DFT) study and then by the experimental investigation. The DFT study shows there exists an intense Ag-In₂O₃ interaction, which causes silver to be positively charged. The positively charged Ag species changes the electronic structure of the metal, facilitates the formation of the Ag-In₂O₃ interfacial site for activation and dissociation of carbon dioxide. The promoted CO₂ dissociation leads to the enhanced methanol synthesis via the CO hydrogenation route as CO₂*→CO*→HCO*→H₂CO*→H₃CO*→H₃COH*. The Ag/In₂O₃ catalyst was then prepared using the deposition-precipitation method. The experimental study confirms the theoretical prediction. The methanol selectivity of CO₂ hydrogenation on Ag/In₂O₃ reaches 100.0% at reaction temperature of 200 ℃. It remains more than 70.0% between 200 and 275 ℃. At 300 ℃ and 5 MPa, the methanol selectivity still keeps 58.2% with a CO₂ conversion of 13.6% and a space-time yield (STY) of methanol of 0.453 g_methanol g_cat^-1 h^-1, which is the highest methanol STY ever reported for silver catalyst. The catalyst characterization confirms the intense Ag-In₂O₃ interaction as well, which causes high Ag dispersion, increases and stabilizes the oxygen vacancies and creates the active Ag-In₂O₃ interfacial site for the enhanced CO₂ hydrogenation to methanol.