Theoretical Study of Selective Hydrogenation of CO2 to Methanol over Pt4/In2O3 Model Catalyst

The In2O3 supported Pt catalyst has been experimentally confirmed to be a highly selective one for CO2 hydrogenation to methanol. However, the mechanism for this selective hydrogenation is still unclear. Herein, density functional theoretical calculations were conducted to investigate the reaction mechanism of methanol synthesis from CO2 hydrogenation on a Pt4/In2O3 model catalyst. The strong metal–support interaction (SMSI) induced by the presence of surface oxygen vacancy is confirmed by the adsorption energy of −3.76 eV between the Pt4 cluster and the defective In2O3 (111). The results of Bader charge analysis indicate the electron transfer from In2O3 to the Pt4 cluster, leading to the negatively charged Pt4 cluster. The interfacial site between the supported Pt4 cluster and the surface oxygen vacancy promotes the dissociation of CO2 due to the weaker strength of C–O bond, confirmed by the calculations based on the crystal orbital Hamilton population (COHP) method. The CO hydrogenation route, the reverse water gas shift (RWGS) route, and the formate route of the methanol synthesis from CO2 hydrogenation on the interfacial site were examined. It was confirmed that the methanol synthesis takes the CO hydrogenation route, initiated from CO2 dissociation on the interfacial site of Pt4/In2O3. The formate route and the RWGS route, started from the direct hydrogenation of CO2, are both not feasible because of the high activation barrier of the formation of HCOO intermediate (1.60 eV) and the hydrogenation of CO intermediate of the RWGS route (1.33 eV).