Kinetics of a dimer-dimer catalytic surface reaction type AB+C2to 1/2 A2+C2B

Abstract

Dimer-dimer catalytic surface reaction of the type AB+C2 to 1/2 A2+C2B is studied by Monte Carlo simulation both on square and hexagonal lattices. Various models are proposed and studied. For the case of a square lattice the three models in which we (i) ignore both the diffusion and desorption of various reactants (M1 model), (ii) consider diffusion of C species only (M2 model), and (iii) consider the diffusion of C atoms as well as their recombination and desorption (M3 Model) all give a final poisoned state for all feed concentrations. For model M1 there is a continuous crossover from one poisoned state to another, while for M2 and M3 an irreversible phase transition separates one poisoned state from the other. The diffusion of A atoms (M4 model) is found to be very crucial to the evolution of the system towards a final steady reactive state. The slightest movement of the A atoms releases the trapped vacancies and other reactants which are available for further reaction. An irreversible phase transition now separates a poisoned state from a steady reactive state. For the hexagonal lattice the M3 model already leads the system towards a steady reactive state. The role of increasing the number of nearest neighbouring sites is seen to be similar to that of the diffusion of A atoms.