KINETICS OF A DIMER-DIMER CATALYTIC SURFACE-REACTION OF THE TYPE AB-2-]1(C)2A(2)+C2B/

Dimer-dimer catalytic surface reaction of the type AB+C-2-->1/2A(2)+C2 B is studied by Monte Carlo simulation both on square and hexagonal la ttices. Various models are proposed and studied. For the case of a squ are lattice the three models in which we (i) ignore both the diffusion and desorption of various reactants (M1 model), (ii) consider diffusi on of C species only (M2 model), and (iii) consider the diffusion of C atoms as well as their recombination and desorption (M3 Model), all g ive a final poisoned state for all feed concentrations. For model M1 t here is a continuous crossover from one poisoned state to another, whi le for M2 and M3 an irreversible phase transition separates one poison ed 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 stea dy 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 st ate from a steady reactive state. For the hexagonal lattice the M3 mod el already leads the system towards a steady reactive state. The role of increasing the number of nearest neighbouring sites is seen to be s imilar to that of the diffusion of A atoms.