Density functional theoretical study of Au4/In2O3 catalyst for CO2 hydrogenation to methanol: The strong metal-support interaction and its effect

Density functional theoretical (DFT) study was conducted to investigate the feasibility of CO2 hydrogenation to methanol on an Au4/In2O3 model catalyst. A strong metal-support interaction is confirmed by the binding energy between Au-4 cluster and In2O3 support, which is 5.31 eV. This causes the electron redistribution at the interfacial sites and leads to a positively charged Au delta+ cluster instead of metallic Au-0. The positive oxidation state of Au delta+ cluster is originating from neighboring O atoms, i.e., the electron of Au cluster is transferred to adjacent O atom through Au-O bond. This electron redistribution can activate Au delta+ cluster by generating electron depleted regions, which are active for H-2 dissociation. The feasibility and reaction route of methanol synthesis from CO2 hydrogenation at Au-In2O3 interface is further examined to understand the effect of Au-In2O3 interaction on the catalytic performance. CO2 is activated at the interface, and formate is the key intermediate during the reaction. The rate-limiting step is hydroxyl spills over from Au cluster to In2O3 surface to release active Au site, with a reaction barrier of 0.95 eV. This can prevent hydroxyl from binding strongly with Au cluster and deactivate the catalyst. Compared with CH2OH intermediate, CH3O intermediate is more favorable in the final hydrogenation step. The DFT study suggests that the Au/In2O3 catalyst is a promising one for methanol synthesis from selective hydrogenation of CO2.