Effects of oxygen vacancy formation energy and Pt doping on the CO2 hydrogenation activity of In2O3 catalysts†

Abstract

Hydrogenation of CO₂ into value-added chemicals and fuels, such as methanol, is a promising solution to mitigate the greenhouse effect, and In₂O₃-based catalysts have shown high activity and stability in the CO₂ hydrogenation reactions. In this study, the effects of oxygen vacancy formation energy and bulk Pt doping on CO₂ reactivity and methanol selectivity in CO₂ hydrogenation catalyzed by In₂O₃ and Pt-doped In₂O₃ were studied using density functional theory (DFT) calculations and microkinetic simulations. Upon oxygen vacancy formation, the number of electrons lost by the In atoms surrounding the oxygen vacancies decreased substantially, which correlated with the oxygen vacancy formation energy, and Pt doping further increased the oxygen vacancy formation energy. DFT-based microkinetic simulations revealed that Pt doping also enhanced the overall reaction rate and methanol selectivity. Among the different surface oxygen vacancy sites, no methanol was predicted to be formed for V_O3 and V_O6 between 473 K and 673 K; however, the methanol selectivities for Pt-V_O3 and Pt-V_O6 were calculated to be 50% at 473 K. Nevertheless, the reactivities of these oxygen vacancy sites were found to be lower than those of the previously studied V_O7 and Pt-V_O7, further confirming our previous conclusions. Degree of rate control (DRC) calculations showed that the fast direct dissociation of CO₂ to CO at Pt-V_O3, Pt-V_O6 and Pt-V_O7 inhibited methanol formation, especially at relatively high reaction temperatures. This study sheds new physical insights into the quantitative structure–activity relationship between the oxygen vacancy formation energy and the catalytic performance of the In₂O₃-based catalysts and reveals the effect of bulk Pt doping on the catalytic activity of the In₂O₃ catalyst for CO₂ hydrogenation reaction.