Highly Active Ir/In2O3 Catalysts for Selective Hydrogenation of CO2 to Methanol: Experimental and Theoretical Studies

Iridium (Ir) catalysts have been extensively applied in homogeneous and photocatalytic CO2 conversion. However, CO2 hydrogenation to methanol over the supported Ir catalyst in a heterogeneous flowing reactor has not been reported yet. Here, we report that indium oxide supported Ir catalyst (Ir/In2O3) of high dispersion is very active for CO2 hydrogenation to methanol. Compared to In2O3, Ir/In2O3 shows a significantly higher activity with even higher methanol selectivity. For example, CO2 conversion of 17.7% is achieved on Ir/In2O3 of 10 wt % Ir loading with methanol selectivity over 70% and high methanol space time yield of 0.765 gMeOH h–1 gcat–1 at 4/1 of the CO2/H2 feed ratio, 21 000 h–1, 300 °C, and 5 MPa. With the catalysts tested, the higher Ir loading causes the higher activity. The catalyst characterization confirms an intense interaction between iridium and In2O3, which causes the high dispersion of the Ir catalyst with the Ir–In2O3 interface as the active site for selective hydrogenation of CO2 into methanol. The Ir loading not only enhances the formation of oxygen vacancies but also stabilizes the vacancies for improved CO2 activation. Further density functional theory studies reveal that the reverse water–gas shift route is more favorable over the formate route for CO2 hydrogenation to methanol over Ir/In2O3 catalyst.