The influence of the sub-surface oxygen in monomer-dimer (CO-NO) surface reaction was studied by Monte Carlo simulation. Three different reaction mechanisms were considered. In mechanism A, the presence of sub-surface adds two extra steps to the usual four steps of simple Langmuir-Hinshelwood mechanism of the system. In mechanism B, one single step was added to the usual four steps in order to incorporate diffusion of oxygen from surface to subsurface (which had 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 did not generate any steady reactive state. The effect of the diffusion of adsorbed species on the surface was also considered. The diffusion of N atoms had 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 was eliminated. The usual "first-order" transition was changed into second order.

The Influence of Subsurface Oxygen in Monomer-Dimer Catalytic Reaction: a Monte Carlo Study. K.M.Khan: Surface Science, 2000, 470[1-2], 155-63