Reaction channels for the catalytic oxidation of CO on Pt(111)

The catalytic, oxidation of CO on O-precovered Pt(111) surfaces has been mo deled via ab initio local-density-functional calculations. It is shown that at coverages of Theta(O)similar to 0.5 the coadsorption of CO stabilizes t he chemisorbed molecular precursor of O-2 over the dissociated atomic oxyge n. The barrier for the reaction between the coadsorbed molecules is lowest if first the molecular OZ bond is broken. However, at this high coverage th e barrier-for the O-2 + CO reaction is higher than for O-2 desorption. Ther efore oxidation will be, proceded by a partial desorption of O-2. At reduce d coverage, the barrier for the oxidation reaction is strongly reduced. At the,transition state the nascent O atoms are only bridge or top bonded and therefore quite reactive. After desorption of CO2, the adsorbed atomic O ca n react with a second CO molecule via a transition state similar to that fo r the molecular reaction. [S0163-1829(99)07807-8].