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

Abstract

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 O 2/CH 3OH 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 O 2 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.