EXCLUDED-VOLUME EFFECTS IN HETEROGENEOUS CATALYSIS - REACTIONS BETWEEN DOLLARS AND DIMES

We introduce a lattice model of catalysis which involves a small particle (a dime) and a large particle (a dollar). The larger diameter of the dollar prevents its adsorption next to a site which is already occupied by a dollar. The catalytic process is the reaction and immediate desorption of nearest-neighbour dime-dollar adsorbates. As a function of the reaction rate and the relative deposition rates of the two species, this system exhibits a second-order kinetic phase transition which separates a dime-saturated phase from a reactive steady state. The features of the phase transition are examined by numerical simulations and analytic techniques, including a systematic mean-field cluster expansion.