Simulation of oscillatory behaviour in the reduction of NO by hydrogen on Pt{100}: the role of non-linear restructuring

Abstract

A new model is presented which simulates temporal behaviour in the NO + H2 reaction on Pt{100}. The model is based on a strongly non-linear power law for the (1 × 1)–NO island growth rate from the hex phase with an apparent reaction order of about four in the local NO coverage on the hex phase. The power law describes the phase transition from the hex to the (1 × 1) phase. Rate parameters are used from recent adsorption and desorption experiments. Variations of all adsorbate coverages, reaction rates and the surface phase are monitored to provide extensive information about the reaction. The driving force for oscillations has been found to be a combination of: (a) the hex ↔(1 × 1) phase transition, particularly the non-linearity in the (1 × 1) island growth; (b) low reactivity on the hex phase and high reactivity on the (1 × 1) phase leading to hysteresis between the two rate branches and (c) an autocatalytic reaction enabling a fast switch from the lower to the higher rate branch. The critical role of the surface structural phase transition has been demonstrated for the NO + H2/Pt{100} system for the first time. The quality of the new model is strongly supported by good agreement with the temperature dependence of the periods of oscillations observed experimentally.