THEORETICAL-ANALYSIS OF DISSOCIATIVE ADSORPTION OF H2O ON NI(100)

The Hartree-Fock method has been used to evaluate the interaction of H2O with clean and oxygen-modified Ni(100) surfaces in the cluster approximation; and on this basis, the energy relationship between associative and dissociative forms of water adsorption has been analyzed. A model is proposed for the surface reaction of water dissociation. Stationary points on the reaction path have been found. On a clean Ni(100) surface, the heat of molecular adsorption of water DELTAQ = 9 kcal/mole, the activation energy E(dis) = 31 kcal/mole, and the heat of reaction DELTAH = 26 kcal/mole. On an oxygen-modified surface, the corresponding values are as follows: DELTAQ = 16 kcal/mole, E(dis) = 4 kcal/mole, and DELTAH = 44 kcal/mole. The promoting effect of oxygen on the water dissociation process is due to localization of positive charge on the metal surface in the vicinity of sites of adsorption of the reaction product.