We report on an inverse model Cu/MgO methanol catalyst modified with 5 % zinc oxide at the Cu surface to element‐specifically probe the interplay of metallic copper and zinc oxide during reductive activation. The structure of copper and zinc was unraveled by in situ X‐ray diffraction (XRD) and in situ X‐ray absorption spectroscopy (XAS) supported by theoretical modelling of the extended X‐ray absorption fine structure and X‐ray absorption near‐edge structure spectra. Temperature‐programmed reduction in H2 during in situ XAS showed that copper was reduced starting at 145 °C. With increasing reduction temperature, zinc underwent first a geometrical change in its structure, followed by reduction. The reduced zinc species were identified as surface alloy sites, which coexisted from 200 °C to 340 °C with ZnO species at the copper surface. At 400 °C Zn−Cu bulk‐alloyed particles were formed. According to in situ XRD and in situ XAS, about half of the ZnO was not fully reduced, which can be explained by a lack of contact with copper. Our experimental results were further substantiated by density functional theory calculations, which verified that ZnO with neighboring Cu atoms reduced more easily. By combining these results, the distribution, phase and oxidation state of Zn species on Cu were estimated for the activated state of this model catalyst. This insight into the interplay of Cu and Zn forms the basis for deeper understanding the active sites during methanol synthesis.
Active Zn species in Cu-based methanol synthesis catalysts have not been clearly identified yet due to their complex nature and dynamic structural changes during reactions. Herein, atomically dispersed Zn on ZrO 2 support is established in Cu-based catalysts by separating Zn and Zr components from Cu (CuÀ ZnZr) via the double-nozzle flame spray pyrolysis (DFSP) method. It exhibits superiority in methanol selectivity and yield compared to those with CuÀ ZnO interface and isolated ZnO nanoparticles. Operando Xray absorption spectroscopy (XAS) reveals that the atomically dispersed Zn species are induced during the reaction due to the strengthened ZnÀ Zr interaction. They can suppress formate decomposition to CO and decrease the H 2 dissociation energy, shifting the reaction to methanol production. This work enlightens the rational design of unique Zn species by regulating coordination environments and offers a new perspective for exploring complex interactions in multi-component catalysts.
Active Zn species in Cu-based methanol synthesis catalysts have not been clearly identified yet due to their complex nature and dynamic structural changes during reactions. Herein, atomically dispersed Zn on ZrO 2 support is established in Cu-based catalysts by separating Zn and Zr components from Cu (CuÀ ZnZr) via the double-nozzle flame spray pyrolysis (DFSP) method. It exhibits superiority in methanol selectivity and yield compared to those with CuÀ ZnO interface and isolated ZnO nanoparticles. Operando Xray absorption spectroscopy (XAS) reveals that the atomically dispersed Zn species are induced during the reaction due to the strengthened ZnÀ Zr interaction. They can suppress formate decomposition to CO and decrease the H 2 dissociation energy, shifting the reaction to methanol production. This work enlightens the rational design of unique Zn species by regulating coordination environments and offers a new perspective for exploring complex interactions in multi-component catalysts.
X‐ray absorption spectroscopy (XAS) is one of the powerful operando tools to track structural variations in heterogeneous catalysts. The nature of active sites in catalyst research is of great relevance, especially given the growing importance of energy storage using CO2 as feedstock and the need for dynamic availability of electric power. Due to the pressure/temperature prerequisite of catalyst performance, the characterization of catalyst structure during catalysis under such high‐pressure reaction conditions is important to further improve catalyst design at a molecular level. Investigating catalysts in a controlled reaction atmosphere, while probing with X‐rays, offers an excellent opportunity for developing infrastructure at the synchrotron. Herein, a mobile setup with a robust spectroscopic cell for in situ and operando XAS applications, including a high‐pressure gas dosing equipment for such catalytic systems, is presented. The in situ/operando cell is operational for both the transmission and the fluorescence XAS mode at up to 50 bar and 450 °C. The setup comes with a protective box with Kapton windows, which holds the cell and serves as a miniature fume hood, and on‐line product analysis. Furthermore, the gas dosing equipment is compact, light‐weighted and can be easily transported to different synchrotrons and allows an optimum pre‐mix of gas flows and pressure build‐up. Methanol and Fischer‐Tropsch syntheses are used as examples for the highly flexible instrumentation.
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