Hydrogen activation on silver: A computational study on surface and subsurface oxygen species

Clean silver is known to be inert toward H₂ dissociation. Nevertheless, silver catalysts recently have been found to exhibit a noteworthy selectivity in the hydrogenation of unsaturated aldehydes to unsaturated alcohols. Experimental studies indicate that pretreatment in oxygen atmosphere activates the catalyst. To examine the role of oxygen in activation of hydrogenation catalysts, we carried out a density functional study on periodic slab models of H₂ dissociation at various oxygen species on silver surfaces, including subsurface oxygen. According to our calculations all oxygen forms under scrutiny promote dissociation of molecular hydrogen. With hydrogenation reactions in mind, we discuss a mechanism according to which an oxygen species, before it desorbs as a water molecule, produces one or two active hydrogen atoms on a metal terrace.