New Insights into the Role of Al 2 O 3 in the Promotion of CuZnAl Catalysts: A Model Study

The Cu/Al 2 O 3 /ZnO(0001)‐Zn ternary model catalysts and their binary analogues were prepared and characterized. It was found that Al 2 O 3 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 2 O 3 on the ZnO(0001)‐Zn, Cu/Al 2 O 3 can be considered without the effect of ZnO. Ternary model catalyst Cu/Al 2 O 3 /ZnO(0001)‐Zn, which has all three parts on the surface, was prepared by deposition of Cu on the surface of Al 2 O 3 /ZnO(0001)‐Zn. Low‐energy ion scattering spectra showed that Cu preferred to locate at the Al 2 O 3 /ZnO interfaces. Compared with Cu/ZnO, the addition of Al 2 O 3 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 x overlayers after reduction of Cu/Al 2 O 3 /ZnO(0001)‐Zn by using H 2 . Therefore, the high activity of industrial Cu/ZnO/Al 2 O 3 catalysts may origin from Cu + ‐rich clusters at the Al 2 O 3 /ZnO interface that are covered by thin ZnO x overlayers.