The thermal desorption of carbon monoxide from palladium and palladium-silver films

The extent of adsorption at 295 and 78 K and the thermal desorption of CO from Pd, Ag, and PdAg alloy films have been measured in an ultrahigh vacuum system. The adsorption data indicated that the surface of the alloys studied in this paper was enriched by Ag. Desorption spectra revealed several adsorption/desorption states, designed as γ 1 , γ 2 , α 1 , α 2 , and β . The nonspecific, most weakly bound γ 1 -state was observed with all adsorbents. The γ 2 -state, also weakly bound, was observed only on Pd. The α 1 - and α 2 -states were observed on Pd and PdAg alloys; they were completely missing on Ag. The population of α-states decreased with increasing Ag content. This is explained by assuming that upon alloying of Pd with Ag the number of large ensembles necessary for strong adsorption decreases.