CATALYTIC REACTION-KINETICS NEAR A 1ST-ORDER POISONING TRANSITION

Various simple models of CO oxidation on surfaces, incorporating irreversible adsorption and reaction steps, exhibit first-order CO-poisoning and second-order O-poisoning kinetic phase transitions. Mean-field theories (MFT) can often accurately determine such quantities as the steady-state reaction rate near the first-order transition. However, we reveal the limitations of MFT predictions for the location of the spinodal point above this transition via a scaling analysis of the CO-poisoning kinetics. Furthermore, we note that MFT sometimes erroneously predicts evolution to a metastable or poisoned state rather than to the stable steady state. For example, just below the first-order transition, MFT predicts that a near CO-poisoned state will evolve to a completely CO-poisoned state, in contrast to the actual evolution towards the reactive steady-state. The latter behavior is elucidated here through an "oxidation epidemic" analysis wherein we consider the spreading of reaction from an initially empty patch embedded in a CO-poisoned sea. Spreading characteristics are quite distinct from analogous epidemic processes describing behavior near second-order (e.g., O-poisoning) transitions.