Studies on self-sustained reaction-rate oscillations: III. The carbon model.

A simple model based upon the combination of the Langmuir- Hinshelwood surface reaction, slow catalyst deactivation by carbon, and reactive regeneration of these deactivated sites by oxygen is presented and analyzed by a singular perturbation approach. It is shown that this model is capable of describing the major features of the slow, relaxation oscillations observed experimentally during CO oxidation over Pt. These features can also be described equally well by a model based on slow catalyst oxidation/reduction cycles proposed by Sales, Turner, and Maple. However, the carbon model and the oxide model predict vastly different behavior in the steady, high reaction-rate regime observed at low P(CO)/P(0(2) ratios, suggesting an experimental study in this nonoscillatory regime which permits discrimination between these two models.