POISONING OF THE ADSORPTION OF CO, O-2 AND D-2 ON PT(111) BY PREADSORBED H2O

We have measured the influence of adsorbed H2O on the sticking coeffic ients and saturation coverages of CO, O-2 and D-2 on Pt(111). at simil ar to 100 K. Strong poisoning is observed for all three gases. For O-2 and D-2, the surface is essentially totally poisoned at 1 monolayer ( ML) water coverage. For CO, the effect is weaker, with some CO adsorpt ion still occurring at 2-3 ML H2O. The influence of these results on t he kinetics of the CO and H-2 oxidation reactions are discussed briefl y It is concluded that the influence of water must be included in kine tics simulations, at least at low temperatures, when significant humid ity levels are present in inlet gas mixtures, or produced by the react ions themselves.