Methanol, an important chemical, fuel additive, and precursor for clean fuels, is produced by hydrogenation of carbon oxides over Cu-based catalysts. Despite the technological maturity of this process, the understanding of this apparently simple reac- tion is still incomplete with regard to the reaction mechanism and the active sites. Regarding the latter, recent progress has shown that stepped and ZnOx-decorated Cu surfaces are cru- cial for the performance of industrial catalysts. Herein, we inte- grate this insight with additional experiments into a full micro-kinetic description of methanol synthesis. In particular, we show how the presence or absence of the Zn promoter dra- matically changes not only the activity, but unexpectedly the reaction mechanism itself. The Janus-faced character of Cu with two different sites for methanol synthesis, Zn-promoted and unpromoted, resolves the long-standing controversy re- garding the Cu/Zn synergy and adds methanol synthesis to the few major industrial catalytic processes that are described on an atomic level.
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