Kinetic Monte Carlo simulations of the oscillatory CO oxidation at high pressures: The surface oxide model

Abstract

The oxidation of CO on metal surfaces is known to exhibit interesting oscillatory behaviour and spatiotemporal patterns. Oscillations arising at high pressures (mbar to atmospheric) are attributed to the “oxide model”, in which the slow oxidation and subsequent reduction of the surface is coupled to the steps of the CO oxidation mechanism. In the present work a mesoscopic skeleton model of this system is formulated in the form of a kinetic Monte Carlo (KMC) scheme which implements the Langmuir–Hinshelwood (LH) mechanism of CO oxidation with additional mechanistic steps taking into account the surface oxide formation. Oscillations in this KMC oxide model are obtained when a different reactivity is attributed to the two phases – metal surface and oxidised surface. The parameter space is explored and the ranges where oscillations are prominent are reported. As a general conclusion of this work, oscillations and clustering of the species are observed within the system’s “reactive” regions when either of the two phases has a considerably higher reactivity than the other. Larger amplitude oscillations are attained when the metal surface is assumed to be more reactive than the oxidised surface.