Kinetic modelling of the hydrogen-oxygen reaction on Pt(111) at low temperature (< 170 K)

Abstract

Recently a kinetic model was proposed for describing the hydrogen-oxygen reaction on Pt(111). This model is based on the reactive-site mechanism, i.e. only a very limited number of Pt sites are considered to be catalytically active for the actual water formation reaction. Here we consider the implications of the model for the H 2O 2 reaction at low temperatures (< 300 K) in more detail. Additional autocatalytic reaction steps between oxygen, H 2O and reaction intermediates are taken into account which enable the complete conversion of oxygen to H 2O. The model is consistent with the observed transition from a reaction mechanism through which H 2O can be formed at temperatures as low as 130 K to the much slower diffusion-controlled mechanism which was found to dominate at low oxygen coverages at higher temperatures (> 250–300 K). Using the same reaction parameters, data sets of Ogle et al. and Germer et al. can be simulated quite well with the model. The actual water-formation reaction (at the reactive site), the reaction between H 2O and O atoms (at the “reaction front”) and the adsorption of hydrogen appear to be the rate-limiting steps. The simulations indicate that the adsorption of hydrogen proceeds via a rather complex process, which is difficult to incorporate correctly in the model.