New Insights into the Role of Al2O3 in the Promotion of CuZnAl Catalysts: A Model Study

5 years ago

New Insights into the Role of Al2O3 in the Promotion of CuZnAl Catalysts: A Model Study

Jun Hu, Huilin Wan, Yangyang Li, Yanying Song, Mingshu Chen, Junjie Huang

The Cu/Al2O3/ZnO(0001)-Zn ternary model catalysts and their binary analogues were prepared and characterized. It was found that Al2O3 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 Al2O3 on the ZnO(0001)-Zn, Cu/Al2O3 can be considered without the effect of ZnO. Ternary model catalyst Cu/Al2O3/ZnO(0001)-Zn, which has all three parts on the surface, was prepared by deposition of Cu on the surface of Al2O3/ZnO(0001)-Zn. Low-energy ion scattering spectra showed that Cu preferred to locate at the Al2O3/ZnO interfaces. Compared with Cu/ZnO, the addition of Al2O3 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 ZnOx overlayers after reduction of Cu/Al2O3/ZnO(0001)-Zn by using H2. Therefore, the high activity of industrial Cu/ZnO/Al2O3 catalysts may origin from Cu+-rich clusters at the Al2O3/ZnO interface that are covered by thin ZnOx overlayers. The ternary model catalyst Cu/Al2O3/ZnO(0001)-Zn has been prepared and characterized. Cu clusters prefer to locate on the Al2O3/ZnO interfaces and an appropriate amount of Al2O3 could stabilize the Cu+ species. Cu clusters were covered by thin ZnOx overlayers after reduction with H2 (see figure). The high activity of industrial Cu/ZnO/Al2O3 catalysts may originate from Cu+-rich clusters at the Al2O3/ZnO interface, covered by thin ZnOx overlayers.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201701697