Precursor mechanism for a dimer-dimer catalytic reaction on the surface ofsquare lattice: a Monte-Carlo simulation study

We have studied a model for a dimer-dimer surface catalytic reaction on the surface of square lattice through Monte-Carlo simulations. This reaction c orresponds to catalytic oxidation of hydrogen and assumes that the reaction can proceed via a "precursor mechanism". According to this mechanism, a mo lecule incident at a metal site breaks apart into two single atoms. Due to the exothermicity of the chemisorption reaction, these atoms gain excess en ergy. Therefore. they are mobile on the surface and can hop between neighbo uring sites. Since these atoms are not in thermal equilibrium with the surf ace, they are referred as "precursors". During this motion a precursor can either react with chemisorbed species or lose sufficient energy to become i mmobily attached to a particular site. The model predicts a steady reactive window, which is limited by continuous and discontinuous irreversible tran sitions, respectively. The width of this reactive window depends upon the m obility of the precursors. (C) 2001 Elsevier Science B.V. All rights reserv ed.