Visualizing Structural and Chemical Transformations of an Industrial Cu/ZnO/Al₂O₃ Pre-catalyst during Activation and CO₂ Reduction

The typical industrial catalyst used for methanol synthesis is a multi-component catalyst based on Cu/ZnO/Al₂O₃. The synergies between various phases of this catalyst play a vital role in defining the overall catalytic function and performance. To gain insights into the role and interaction between the relevant components and phases, ex situ and in situ transmission electron microscopy (TEM) was deployed to investigate the structures and phases of an industrial Cu/ZnO/Al₂O₃ in its precursor, activated and reaction states. High structural inhomogeneity in this material is revealed, i. e. the presence of various phases with different morphologies and compositions. It is shown how structural and compositional changes occur during hydrogen treatment and how compositional inhomogeneity in the starting material translates into differences in the local composition of the activated and working catalyst. The formation of defective metallic copper particles (stacking faults and twins) that are in an intimate contact with zinc oxide (poorly crystalline, partially reduced ZnO_x and crystalline ZnO), alumina, Zn−Al oxide and carbon-zinc-oxygen containing phases (such as zinc formate) is observed. It is also uncovered that alumina plays a potentially important role in stabilizing cationic zinc species. This work provides atomic-level insight into the relevant state of an industrial methanol synthesis catalyst and the associated synergistic interplay between the involved phases in reactive atmosphere.