In a simplified picture a heterogeneous catalyst can be described as a high energy material, which is composed of two important parts: bulk and surface. The bulk is defined by a certain crystal and electronic structure as well as defect concentration, and reflects the real structure of the catalyst. It is responsible for the formation and stabilization of the active surface. Although physical and chemical information on the real and surface structure can be obtained by integral methods, important local fluctuations from the ideal structure, which are essential for the catalytic performance, in the catalyst composition may be overlooked.¹ This highlights the significance of transmission electron microscopy (TEM) as the tool for the local description of the nano- and/or mesoscale of heterogeneous catalysts.

Here, we focus on a transmission electron microscopic (TEM) description of the local nano- and mesoscale of industrial relevant Cu/ZnO/Al₂O₃ catalyst for methanol synthesis. Methanol, one of the most important industrial chemicals, is produced from syngas (CO, CO₂, H₂) at high pressure (50-80 bar) and elevated temperature (240-280 °C) and is considered as a prospective key-compound for chemical energy and hydrogen storage. The working mechanisms of this industrial methanol catalyst have been investigated extensively.² However, its actual active phase is still debated controversially. On the one hand, the catalytic odyssey may be caused by material, pressure and time gaps, which often do not mirror industrial relevant conditions. On the other hand, the diversity of results indicates the difficulty of investigating and understanding this complex catalyst system, in particular due to the lack of visual local information.

Our local observations tackle a detailed description of the mesostructure of the catalyst, the real structure of Cu nanoparticles and the formation of a special polymorph of layered ZnO on top of the Cu nanoparticles after reductive activation on industrial relevant ternary Cu/ZnO/Al₂O₃ catalyst.^1b In addition, we will highlight the temperature, gas and time dependent evolution of this metastable layered ZnO polymorph from minutes to months (Figure 1).³

In conclusion, the results demonstrate the power of local TEM investigation in heterogeneous catalysis research. In combination with complementary integral data, they allow a detailed understanding of the system, which would be otherwise hard to obtain. The findings illustrate that methanol synthesis can be considered as an interface mediated process between Cu and ZnO.

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EMC Abstracts - https://emc-proceedings.com/abstract/local-information-powers-heterogeneous-catalysis-research-tem-investigation-of-industrial-relevant-cuznoal2o3-catalysts-for-methanol-synthesis/