A molecular orbital study of surface-adsorbate interactions during the oxidation of CO on the Pt(111) surface

A Langmuir-Hinshelwood type pathway for the oxidation of CO on the Pt(1 1 1 ) surface is analysed within a tight binding scheme based on the extended H uckel method. A partitioning of the total electronic energy serves to highl ight both CO and O derived contributions to the reaction barrier, the exten t to which the surface mediates interactions between the adsorbates and the roles of the individual CO and O orbitals in OC-O bond formation. The reaction barrier is interpreted to be the result of a surface-mediated coactivation of CO and O on the surface. In the initial stages of OC-O bond formation a "side-on" donation of electron density from the p-orbitals on O to the empty CO(2 pi) orbitals on CO occurs. The transition from reactant s to products is characterized by the formation of a carboxylate (CO;) moie ty on the surface. The role of the O s and p orbitals in OC-O bonding is di scussed. (C) 2001 Elsevier Science B.V. All rights reserved.