Structural changes of model Cu/ZnO catalysts during exposure to methanol reforming conditions

Cu/ZnO/Si model catalysts were prepared by resistive evaporation of Cu on ZnO thin films deposited on Si(1 0 0) by DC magnetron sputtering. Exposure of the Cu/ZnO/Si model catalysts to methanol reforming conditions at 550 K causes agglomeration of the supported Cu islands as shown by XPS, AFM and spectroscopic ellipsometry. The Cu remains in the metallic state for O2/CH3OH molar ratios ⩽0.25 but is oxidised to Cu(I) for higher oxygen content. When Cu is in the metallic state the degree of agglomeration is larger in the presence of O2 in the gas phase. On the other hand oxidation of the Cu islands is associated with a less pronounced agglomeration upon methanol reforming treatment. The origin of this phenomenon is discussed.