New Insights into the Role of Al O in the Promotion of CuZnAl Catalysts: A Model Study.

The Cu/Al O /ZnO(0001)-Zn ternary model catalysts and their binary analogues were prepared and characterized. It was found that Al O grew on the ZnO(0001)-Zn surface by a layer-by-layer model, whereas Cu grew on the ZnO(0001)-Zn surface as two-dimensional clusters up to 0.2 monolayers (ML), and thereafter formed three-dimensional clusters. Because of the layer-by-layer growth of Al O on the ZnO(0001)-Zn, Cu/Al O can be considered without the effect of ZnO. Ternary model catalyst Cu/Al O /ZnO(0001)-Zn, which has all three parts on the surface, was prepared by deposition of Cu on the surface of Al O /ZnO(0001)-Zn. Low-energy ion scattering spectra showed that Cu preferred to locate at the Al O /ZnO interfaces. Compared with Cu/ZnO, the addition of Al O obviously suppressed the reduction of copper oxides and led to a higher concentration of Cu . The Cu clusters were found to be covered by thin ZnO overlayers after reduction of Cu/Al O /ZnO(0001)-Zn by using H . Therefore, the high activity of industrial Cu/ZnO/Al O catalysts may origin from Cu -rich clusters at the Al O /ZnO interface that are covered by thin ZnO overlayers.