CRITICAL-BEHAVIOR OF AN IRREVERSIBLE MULTIPLE-REACTION PROCESS

A multiple-reaction irreversible surface reaction model (M-R) involving one monomer (A) and two different dimers (B2 and C2) is proposed and studied by means of Monte Carlo simulations. In the absence of the monomer species the M-R model reduces to the DD model (Maltz et al. Surf. Sci. 277 (1992) 414), while in the absence of one of the dimer species the M-R gives the ZGB model (Ziff et al. Phys. Rev. Lett. 56 (1986) 2553). The M-R model is suitable to investigate: on the one hand, the influence caused by the presence of H-2-traces (H-2 is C2) on the catalytic oxidation of carbon monoxide, e.g. A + (1/2)B2 --> AB where A is CO2 B2 is O2 and AB is CO2, and on the other hand, the effect of CO-traces on the catalytic oxidation of hydrogen, e.g. (1/2)B2 + C2 --> C2B. Furthermore, the M-R model exhibits irreversible phase transitions (IPTs) between poisoned states with the surface saturated by adsorbed species and reactive regimes with production of both AB and C2B. The critical points at which the first and second-order IPTs characteristic of the M-R take place are determined. Interesting theoretical possibilities which become opened when studying the observed critical behavior of the M-R model are discussed.