Subsurface oxygen in monomer-dimer catalytic reaction: Influence of secondand third nearest neighbourhood

The presence of subsurface species adds two extra steps to the usual four o f simple Langmuir Hinshelwood mechanism of the monomer-dimer (NO-CO) surfac e reaction. In this model the influence of second and third nearest neighbo uring (nn) sites on the phase diagram of the system is studied in detail by the use of Monte-Carlo simulation. It is seen that reaction between surfac e second nn sites has more dominant effect on the width of the reactive win dow as compared to that of subsurface second and third nn sites. In another model, NO is adsorbed in such a way that N takes surface site whereas O ta kes its subsurface first nn site. In this model the reaction of CO with sub surface second and third nn sites gives an interesting situation: The usual second-order phase transition is destroyed and consequently a very wide st eady reactive window is observed. (C) 2001 Elsevier Science B.V. All rights reserved.