Analysis and Simulation of the Dynamics of a Catalyzed Model Reaction: CO Oxidation on Zeolite Supported Palladium

The particle size effect on the oscillatory behavior during CO oxidation over zeolite-supported Pd catalysts is simulated with the help of a deterministic point model and a stochastic mesoscopic model. The point model is developed on the basis of the well-known Sales–Turner–Maple model, which is modified to consider the slow processes of oxidation and reduction of the Pd bulk as well as the effects of the bulk oxidation on the catalyst activity. It is demonstrated that the point model developed can simulate many experimental trends, e.g., the dependence of the catalytic activity and the waveform of the oscillations on the particle size and the pretreatment of the catalyst, as well as the counterclockwise hysteresis, depending on the reaction rate during the cyclic variation of the CO inlet concentration. The higher activity of the smaller particles can be explained by the attainment of a more reduced state of Pd in smaller particles in the course of the reaction. The stochastic model simulates the reaction by a Markovian chain of elementary stages of the reaction. The model variables are the numbers of reagent atoms. Transition probabilities of the stochastic model are chosen in accordance with the rates of the developed point model. It is shown that intrinsic fluctuations and correlations of stochastic variables can significantly change the reaction dynamics on nm-sized particles by extending the oscillatory region in the parameter space.