EVOLUTION OF THE Cu/ZnO METHANOL SYNTHESIS CATALYST DURING ITS REDUCTION AND RE-OXIDATION

摘要

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 Cu~0 with the formation of nanoparticles with the characteristic size of ca.1.6 nm.The copper metal particles were re-oxidized to Cu~(2+) at 523 K in a helium 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.