H2 DISSOCIATION ON A Pt OVERLAYER ON Ni(111)

Abstract

The chemisorption of hydrogen atoms and the H 2 molecule was studied by the use of extended Hückel calculations in a cluster model to simulate a Pt (111) surface and a Pt overlayer in epitaxy on Ni (111). The result of epitaxy on the chemisorptive properties of Pt is to disfavor the H atom adsorption on the higher coordination sites, and to increase the activation energy of H 2 dissociation. This is due to two factors. First, the Pt – Pt distance shortening increases the repulsion produced by the Pt neighbors on the adatoms. Second, the study of the local electronic properties of the chemisorption site shows that the pure Pt surface tends to chemisorb the H 2 molecule in the dissociated state whereas the Pt/Ni system would favor the molecular adsorption only.