Modification of silver surface with palladium and chlorine. The effect on the state of adsorbed oxygen and its interaction with hydrogen

Thermodesorption and hydrogen titration were used to study the effect of additives (palladium and chlorine) to a silver surface on the state of sorbed oxygen. Palladium(O) is distributed throughout the 8-nm subsurface layer, while Cl- mainly accumulates on the silver surface (X-ray photoelectron data). The dissociation of the primary Pd clusters and the uniform distribution of the palladium over the Ag surface are followed by the formation of a new mobile form O(2)I, which is more firmly bound to the silver surface and is most reactive toward hydrogen. The modifiers substantially increase the amount of form OI, preventing the formation of OII from absorbed oxygen at surface centers. The effect of Pd0 and Cl- on the state of adsorbed oxygen was explained by an increase in the electron density of the silver surface in the vicinity of Pd0 atoms and Cl- ions and by complexation between oxygen and palladium adatoms.