Abstract
AbstractThe 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.
Highlights
Still today, partly due to the complexity of the applied catalysts,[4] the identification of such “active sites” is rather challenging.[5]
We report on the impact of the activation temperature on the performance of a Cu/ZnO : Al
The catalytic results are correlated with structural data provided by various in-situ characterization tools such as X-ray diffraction (XRD), ambient pressure X-ray absorption spectroscopy (XAS) combining near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) at the K-edges of Cu and Zn
Summary
Elias Frei,*[a] Abhijeet Gaur,[b] Henning Lichtenberg,[b] Leon Zwiener,[a] Michael Scherzer,[a]. The catalytic results are correlated with structural data provided by various in-situ characterization tools such as X-ray diffraction (XRD), ambient pressure X-ray absorption spectroscopy (XAS) combining near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) at the K-edges of Cu and Zn. Coupled with electron microscopy, surface titration techniques (reactive frontal chromatography, N2O-RFC and temperature programmed desorption, H2-TPD) and a kinetic evaluation (apparent activation energy, EA), the consequences of the activation temperature for the number and nature of active sites are discussed. The in-situ XRD data (measured at RT to distinguish alloying from thermal expansion effects) show an incremental increase in the lattice parameter as a function of the activation temperature starting at 300 °C. 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.
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