Transient oxidation of CO over a catalyst in the presence of subsurface oxygen

We consider a lattice model to study the transient oxidation of CO molecules over a catalytic surface. A precovered surface containing a variable number of monolayers of oxygen is taken at the initial time. When a flux of CO molecules impinges the surface, we observe the formation of CO2, due to the Langmuir–Hinshelwood mechanism. The flux of CO2 molecules depends on the number of monolayers of oxygen and on temperature. The temperature enters through the desorption of CO molecules, diffusion of active sites over surface and diffusion of subsurface O atoms towards the topmost layer. We employ Monte Carlo simulations in our calculations, and the (001) surface and subsurface planes of a simple cubic lattice are considered. Our results explain the main features of the reactive scattering of CO molecules at the oxygen-rich Ruthenium surface observed in the experiments performed by Böttcher and coworkers.