SILVER ON ALUMINA - ADSORPTION AND DESORPTION STUDY OF MODEL CATALYSTS

The initial sticking probabilities of silver on an alumina thin film a nd an alpha-Al2O3 Single crystal were measured in the temperature rang e 100-1100 K and compared with measurements on Ru metal surfaces. On t he oxides the initial sticking probability is lower than on the metal or oxygen-treated metal surfaces. Thermal desorption spectra of Ag ads orbed on these surfaces were measured for coverages ranging from submo nolayer to multilayer. In contrast to the desorption behavior of silve r from Ru(001) and Ru(001)-O(2x2) surfaces, the Ag desorption spectra from both alumina surfaces are strikingly different. The complete anal ysis of Ag desorption data from alumina yields the activation energy f or desorption that is smaller than the Ag sublimation heat, and a frac tional order process for apparent Ag coverages to 60 ML. Isothermal me asurements of Ag/alumina film confirmed these results. Identical adsor ption/desorption behavior of Ag on both alumina surfaces shows that th e thin film alumina surface is a viable model of an alpha-alumina supp ort.