SIMPLE-MODELS FOR HETEROGENEOUS CATALYSIS WITH A POISONING TRANSITION

One- and two-dimensional simulations have been used to explore the effects of the Eley-Rideal process CO + OS → CO2 + S on a simple model for the catalytic oxidation of carbon monoxide by oxygen. In this model, CO and O2 are fed to the surface (lattice) to form the adsorbed species COS and 2OS. The addition of CO is assumed to require just one vacant surface site (S), while the adsorption of O2 requires two adjacent (nearest neighbor) sites. The only parameter in this model (YCO) is the relative rate at which the two reactants are fed to the surface. For small values of YCO (YCO < Y1), the surface becomes completely covered by OS, and for large values of YCO (YCO > Y2), the surface becomes completely covered by COS and the surface is poisoned. In an intermediate range of values of YCO (Y1 < Y CO < Y2), the surface is partially occupied by O S, COS, and S sites in the steady state regime and reaction can proceed indefinitely. In two dimensions, the main effect of adding the Eley-Rideal process is to remove the "continuous" transition at YCO = Y1 and shift the "discontinuous" transition at YCO = Y2. In the one-dimensional case, there is no reactive steady state regime. The Eley-Rideal process results in the formation of a new regime (YCO < YCOC) in which a continuous reaction can be sustained. Simulations have also been carried out using a model in which A and B species are added randomly to individual sites and ASBS pairs are eliminated randomly if they occupy adjacent sites. Addition of the asymmetric A + BS→S + P (product) Eley-Rideal process again leads to the formation of a new regime (YA < YAC) in which sustained reaction can occur under steady state conditions. For both models, the nature of the poisoning transition is investigated. © 1990 American Institute of Physics.