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

The presence of subsurface species adds two extra steps to the usual four of simple Langmuir Hinshelwood mechanism of the monomer-dimer (NO-CO) surface reaction. In this model the influence of second and third nearest neighbouring (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 surface second nn sites has more dominant effect on the width of the reactive window 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 takes its subsurface first nn site. In this model the reaction of CO with subsurface second and third nn sites gives an interesting situation: The usual second-order phase transition is destroyed and consequently a very wide steady reactive window is observed. (C) 2001 Elsevier Science B.V. All rights reserved.