The Cu–ZnO synergy in methanol synthesis from CO2, Part 1: Origin of active site explained by experimental studies and a sphere contact quantification model on Cu + ZnO mechanical mixtures

• The Cu–ZnO synergy is markedly influenced by the catalyst composition.
• 100% selectivity to methanol is observed for all core–shell structures.
• ZnOx active sites originate from contacts between Cu and ZnO.
• A predictive geometrical model for contact quantification was developed.
• Structure–activity relationship was demonstrated for mechanical mixtures.

Cu/ZnO-based catalysts are of industrial importance for the methanol synthesis. However, the selectivity is generally moderate since methanol formation is accompanied with similar amounts of CO. The understanding of how the active site is created is a key for understanding the central role of the Cu–ZnO synergy and for the rational design of active and selective catalysts. Model Cu + ZnO mechanical mixtures with variable composition as well as core–shell structures were employed as a tool for correlating physical to catalytic properties and identify the active site. The catalyst activity was correlated to the number of contact points between Cu and ZnO particles (that generates reactive oxygen vacancies) using a mathematical model for Cu and ZnO contact quantification based on the geometry of spherical particle agglomerates, which is applicable to mechanical mixtures. The structure–activity relationships highlighted in this work opens a way to the rational design of ideal structures of catalysts.

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