PtZn vs. PtGa in CO2 Hydrogenation: When Alloy Stability and Redox Dynamic Drives Selectivity

Controlling the selectivity of CO2 hydrogenation remains a challenge in catalysis. In this study, we demonstrate that the well-defined silica supported PtGa and PtZn alloy nanoparticles, synthesized via a surface organometallic chemistry (SOMC) approach, display greatly different product selectivity in CO2 hydrogenation. While the PtZn@SiO2 catalyst shows almost exclusive CO selectivity (~99%), PtGa@SiO2 primarily produces CH3OH with 54% selectivity, despite both catalysts showing similar activities. While both PtM (M = Zn or Ga) forms bulk alloys, in situ spectroscopic studies complemented with DFT calculations reveal that their surface properties differ under reaction conditions, determining the product selectivity. The surface of the PtZn alloy remains 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 undergoes dynamic redox process forming PtGa-GaOx interfaces during reaction conditions, key to promoting methanol synthesis via a HCOO*→CH3O* reaction pathway.