Cu−Zn Alloy Formation as Unfavored State for Efficient Methanol Catalysts

The active sites of Cu/ZnO‐based catalysts, commercially applied for the hydrogenation of CO2 or CO2‐rich synthesis gas, are still subject of current debates. Generally, the discussion is focused on the nature of the interfacial contact between Cu and ZnO, particularly whether it is rather of oxidic (Cu−ZnO) or alloying (Cu−Zn) character. We report on kinetic investigations on a Cu/ZnO : Al high performance catalyst activated at different temperatures. Incrementally increasing temperature under reductive conditions leads also to increased CuZn‐alloy formation, analyzed by in‐situ X‐ray diffraction, in‐situ X‐ray absorption spectroscopy and high resolution transmission electron microscopy. The combination of the catalytic data and the complementary characterization techniques provide valuable insights on the relevant reaction sites for CH3OH formation. Our results highlight the complexity of the interfacial contact with evidence for Cu−ZnO reaction sites and clarify the negative impact of CuZn alloy formation on the nature of the active site. Methanol synthesis: The activation temperature induced CuZn‐alloy formation is investigated by in‐situ XRD and an analysis of the Cu lattice parameter, respectively. The nature of the interfacial Cu−O−Zn active site is negatively affected by the CuZn‐alloy formation. As a consequence, an incremental increase of the alloy formation leads to also to an increased app. EA and decreased catalytic CH3OH activity. In‐situ XAFS analysis reveals an “in parts” reversable CuZn‐alloy formation, if solely the surface is modified.