Poisoning of the adsorption of CO, O2 and D2 on Pt(111) by preadsorbed H2O

We have measured the influence of adsorbed H2O on the sticking coefficients and saturation coverages of CO, O2 and D2 on Pt(111) at ∼100 K. Strong poisoning is observed for all three gases. For O2 and D2, the surface is essentially totally poisoned at 1 monolayer (ML) water coverage. For CO, the effect is weaker, with some CO adsorption still occurring at 2–3 ML H2O. The influence of these results on the kinetics of the CO and H2 oxidation reactions are discussed briefly. It is concluded that the influence of water must be included in kinetics simulations, at least at low temperatures, when significant humidity levels are present in inlet gas mixtures, or produced by the reactions themselves.