Key Drivers of Activity and Selectivity in Cu-Based Catalysts for Methanol Synthesis From CO2: Insights From Atomically Dispersed Promoters.

The synergistic Cu-metal oxide (Cu-MOx) interface is critical for selective CO2 hydrogenation to methanol, yet its mechanistic function, the central, long-debated feature of industrial Cu/ZnO/Al2O3, remains ambiguous. Using operando transient DRIFTS-SSITKA, we elucidate the roles of M+ sites (Zn2+, Ga3+, and In3+) on model Cu─M/SiO2 catalysts prepared by surface organometallic chemistry (SOMC). X-ray absorption spectroscopy reveals that these promoters restructure from alloys after reduction to cationic species at the interface under reaction conditions. We find the promoter's electronic effect on formate bond strengths provides quantitative descriptors for both activity and selectivity. All catalysts follow a common formate spillover mechanism, with methoxy hydrogenation/desorption as the rate-limiting step. The intrinsic CH3OH formation rate follows a Sabatier-type volcano with C─O bond strength, while selectivity correlates linearly with C─H bond strength (a proxy for the formate decomposition barrier). Cu─Ga/SiO2 shows the fastest spillover, suppressing CO formation and yielding the highest selectivity; Cu─Zn/SiO2 has optimal binding for the highest activity; In3+ binds formate too strongly, creating a kinetic trap on the strong-binding side of the volcano. These findings bring mechanistic clarity to the debated Cu─Zn(O) synergy, showing selectivity is governed by a balance of electronic stabilization and spillover dynamics.