Evolution of the Cu/ZnO methanol synthesis catalyst during its reduction and re-oxidation

Abstract

Cu K EXAFS studies of the structure of Cu-Zn oxide catalyst were performed for the as prepared samples, those after its activation by hydrogen and after its subsequent re-oxidation. It was found that during the primary formation of the CuZnO solid solution, the copper ions are dissolved in the extended stacking faults of the ZnO lattice as ultra-small oxide clusters. Activation by hydrogen at 473 K leads to the reduction of most copper cations to Cu0with the formation of nanoparticles with the characteristic size of ca. 1.6 nm. The copper metal particles were re-oxidized to Cu2+at 523 K in ahelium flow containing 0.05 vol. % oxygen. The re-oxidized cations do not form a CuO phase. Instead, they return to the extended stacking faults of ZnO. However, this time they form stripe-like clusters of square-planar coordinated copper cations.