A computational study of H2 dissociation on silver surfaces:: The effect of oxygen in the added row structure of Ag(110)

We studied computationally the activation of H-2 on clean planar (111), (110) and stepped (221) as well as oxygen pre-covered silver surfaces using a density functional slab model approach. In line with previous data we determined clean silver to be inert towards H-2 dissociation, both thermodynamically and kinetically. The reaction is endothermic by similar to 40 kJ mol(-1) and exhibits high activation energies of similar to 125 kJ mol(-1). However, oxygen on the surface, modeled by the reconstructed surface p(2 x 1) O/Ag(110) that exhibits -O-Ag-O-added rows, renders H-2 dissociation clearly exothermic and kinetically feasible. The reaction was calculated to proceed in two steps: first the H-H bond is broken at an Ag-O pair with an activation barrier E-a similar to 70 kJ mol(-1), then the H atom bound at an Ag center migrates to a neighboring O center with E-a similar to 12 kJ mol(-1).