Surface spectroscopic characterization of the interaction between zinc ions and $gamma;-alumina

Interaction of zinc ions with γ-alumina has been investigated using the surface spectroscopic techniques of X-ray photoelectron spectroscopy (ESCA or XPS) and low energy ion scattering spectroscopy (ISS). In addition, the “bulk” techniques of laser Raman spectroscopy (LRS) and X-ray diffraction (XRD) were employed. Surface characteristics of ZnAl2O3 catalysts are affected by both metal loading and calcination temperature. The ZnAl intensity ratio was examined as a function of zinc content and calcination temperature. Plots of both ESCA and ISS intensity ratios (ZnAl) vs metal loading show changes in slope at high loadings, indicating a change in surface structure. ESCA, LRS, and XRD all show the ability to distinguish between ZnO and ZnAl2O4. Results indicate that at low zinc loadings (< 20%), a strong interaction occurs between zinc and γ-alumina resulting in the formation of an “aluminate type” phase (i.e., a “surface spinel”). This interaction involves diffusion of zinc ions into the tetrahedral lattice sites of the support. At higher loadings, bulk-like ZnO segregates on top of the interaction species and the support. ESCA has also been used to study the effects of reduction and sulfiding on the catalysts.