The synergistic Cu–metal oxide (Cu–MO_x) 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.

Insight into mechanisms of heterogeneously catalyzed reactions holds importance in the development and optimization of new catalytic materials. Yet, the approaches often used in such investigations heavily rely on assumptions concerning the reactor and kinetics. Herein we report a new kind of kinetic investigation taking CO₂ hydrogenation reaction, specifically the reverse water–gas shift (RWGS) reaction over 3 wt% Pt/CeO₂, as an exemplifying case. The reported approach is based on spatially resolved steady-state isotopic transient kinetic analysis (SSITKA) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) identifying gaseous/surface species and their spatial variations along the reactor. This approach allows accurate evaluation of reaction mechanism by identifying correlations among the concentrations of gaseous/surface species and by quantitative description of their spatial variations by a kinetic model. Spatially resolved SSITKA-DRIFTS experiments show carbonate decomposition via a Pt-bound carbonyl to be the main route towards the production of carbon monoxide. Further kinetic modeling of the spatially resolved data confirms this mechanism proposal, and points to the production of water as the rate-limiting step.