The influence of subsurface oxygen in monomer–dimer catalytic reaction: a Monte Carlo study

The influence of the subsurface oxygen in monomer–dimer (CO–NO) surface reaction is studied by Monte Carlo simulation. Three different reaction mechanisms are considered. In mechanism A, the presence of subsurface adds two extra steps to the usual four steps of simple Langmuir–Hinshelwood mechanism of the system. In mechanism B, one single step is added to the usual four steps in order to incorporate diffusion of oxygen from surface to subsurface (which has experimental evidence). In mechanism C, the presence of subsurface modifies two steps of the usual four. Mechanism A reveals a phase diagram with two transition points and a steady reactive state. Mechanisms B and C do not generate any steady reactive state. The effect of the diffusion of adsorbed species on the surface is also considered. The diffusion of N atoms has significant effect on the phase diagrams of mechanisms A and B. In mechanism C, the diffusion of CO molecule presents an interesting situation in which usual “second-order” transition has been eliminated. The usual “first-order” transition has been changed into second order.