PtZn Versus PtGa in CO₂ Hydrogenation: When Alloy Stability and Redox Dynamics Drive Selectivity

Abstract

Controlling the selectivity of CO₂ hydrogenation remains a challenge in catalysis. In this study, we demonstrated that the well-defined silica(SiO₂)-supported PtGa and PtZn alloy nanoparticles, synthesized via a surface organometallic chemistry (SOMC) approach, displayed greatly different product selectivity in CO₂ hydrogenation: While the PtZn@SiO₂ catalyst showed almost exclusive CO selectivity (∼99%), PtGa@SiO₂ primarily produced CH₃OH with 54% selectivity, despite both catalysts showing similar activities. While both PtM (M = Zn or Ga) formed bulk alloys, in situ spectroscopic studies complemented with density functional theory (DFT) calculations revealed that their surface properties differed under reaction conditions, determining the product selectivity. The surface of the PtZn alloy remained stable without undergoing surface oxidation during CO₂ hydrogenation, resulting in the decomposition of formate (HCOO*) species to produce CO. In contrast, the surface of the PtGa alloy underwent a dynamic redox process, forming PtGa-GaOx interfaces under defined reaction conditions, which was key to promoting methanol synthesis via a HCOO*→CH₃O* reaction pathway.