SILVER ON ALUMINA - ADSORPTION AND DESORPTION STUDY OF MODEL CATALYSTS

The initial sticking probabilities of silver on an alumina thin film and an alpha-Al2O3 Single crystal were measured in the temperature range 100-1100 K and compared with measurements on Ru metal surfaces. On the oxides the initial sticking probability is lower than on the metal or oxygen-treated metal surfaces. Thermal desorption spectra of Ag adsorbed on these surfaces were measured for coverages ranging from submonolayer to multilayer. In contrast to the desorption behavior of silver from Ru(001) and Ru(001)-O(2x2) surfaces, the Ag desorption spectra from both alumina surfaces are strikingly different. The complete analysis of Ag desorption data from alumina yields the activation energy for desorption that is smaller than the Ag sublimation heat, and a fractional order process for apparent Ag coverages to 60 ML. Isothermal measurements of Ag/alumina film confirmed these results. Identical adsorption/desorption behavior of Ag on both alumina surfaces shows that the thin film alumina surface is a viable model of an alpha-alumina support.