Modelling the CO-induced surface phase transition on Pt{100}: implications for kinetic oscillations

Abstract

A recent molecular beam study of the CO-induced hex →(1 × 1) surface phase transition on Pt{100} showed that the rate of phase transformation has a high reaction order (ca. 4.1) with respect to the local CO coverage on the rotated hexagonal (hex-R) phase. This result is used to formulate a new kinetic model for the CO + Pt{100} system. It is used to investigate features of CO temperature-programmed desorption spectra, and to predict the temperature and pressure dependence of the CO and NO coverages on the (1 × 1) phase during the hex →(1 × 1) surface phase transition (SPT) and under equilibrium conditions. At temperatures of around 450 K, where kinetic oscillations in the CO + NO reaction on Pt{100} are accompanied by oscillations in the relative area of the (1 × 1) phase, the adsorbate coverages on the (1 × 1) phase are too low to inhibit NO dissociation. An alternative mechanism for these oscillations is presented, involving the hex ↔(1 × 1) SPT and not the rate limitation of NO dissociation as the driving force. Our new model is used to develop a more detailed understanding of this new mechanism.