Density functional study of water and ammonia activation by platinum

Fully optimized geometries and adsorption energies obtained from nonlocal density functional calculations are presented for the adsorption of H2O and NH3 on a Pt-6 cluster used as a model for the Pt(111) surface. Both molecular and dissociative adsorption are investigated. Molecular water and ammonia are adsorbed on the 1-fold site with adsorption energies of -8 and -26 kcal/mol respectively. There is no dissociation of water or ammonia on a clean Platinum surface. The dissociation is favourable only when atomic oxygen is present on the surface. The abstracted hydrogen atom goes to preadsorbed atomic oxygen, the most basic site on the surface, and forms a hydroxyl group.