Charge transfer across the metal/oxide interface determines the rate of CO2 hydrogenation to methanol over Cu/ZnO catalysts

Composite nanomaterials are crucial in a wide range of applications with the industrial Cu/ZnO catalyst used to convert CO ₂ into methanol being an important example. The reaction rate scales with the Cu surface area ^1,2 implying that the rate-limiting part of the reaction occurs on the metal surface. However, the turnover frequency (TOF, rate per Cu surface atom) is one order of magnitude higher for Cu supported on ZnO compared to pure Cu samples ^3–6 . This materials synergy, which is responsible for 90% of the catalytic activity, is still poorly understood ^7–9 , and the copper in Cu/ZnO is sometimes described ^10,11 as an element with properties radically different from the pristine metal. An understanding of this synergy thus has a direct impact on Power-to-X processes to produce methanol for storage of renewable energy and on heterogeneous catalysis in general. Here we establish the mechanism for the hugely important conversion of CO2 into methanol and how it is accelerated on the composite nanomaterial. We show that charge from donor states created by ad-/absorbed H in the ZnO transfers to the metal and distributes across the metal surface. The surface charging influences the bonding of the adsorbates on the metal and lowers the energy barrier for HCOOH dissociation, which we identify as the rate-limiting step in methanol formation. The lower barrier accounts for the order of magnitude increase in the methanol synthesis rate. The charge transfer phenomenon is general in nature and found to be essential for understanding catalytic phenomena and thus for the rational development of improved future catalysts.