ON THE SELF-POISONING OF SMALL PARTICLES UPON ISLAND FORMATION OF THE REACTANTS IN A MODEL FOR A HETEROGENEOUSLY CATALYZED REACTION

Assuming the Langmuir-Hinshelwood mechanism, the reaction A + (1/2) B2 double-line-arrow-pointing-right AB is studied on both small homogeneous and disordered surfaces by means of computer simulations. The occurrence of a new self-poisoning regime, where for a determined initial condition the substrata could be completely covered for each of the reactants with a certain probability, is observed and discussed. Large fluctuations in the size of adsorbed islands formed by A and B particles would cause the observed behavior. A crossover from the new self-poisoning regime to a steady state with AB production occurs at L congruent-to 30 +/- 5 and p(A) congruent-to 0.36 +/- 0.02 for incipient percolation clusters and at L congruent-to 12 +/- 2 and p(A) congruent-to 0.51 +/- 0.02 on the square lattice, where L and p(A) are the lattice size and the mole fraction of the specie A in the gas phase, respectively. It is shown that surface diffusion of A particle does not influence the location of the self-poisoning regime.