We construct and study a distributed mathematical model of oxidation of CO Introduction. The present paper is devoted to simulation of the oxidation of CO on a Pd zeolite catalyst. Experimental study of this reaction has revealed a complicated dynamic behavior of the chemical system, which includes both regular and chaotic oscillations of the reaction rate [ 1, 2]. Despite the fact that oxidation of CO is one of the most studied self-oscillatory systems of heterogeneous catalysis [3][4][5], the problem of modeling the complicated and chaotic oscillations continues to be of great interest. Slinko, Jaeger, and Svensson [6] conjectured that taking account of the diffusion of CO in the pores of the zeolite matrix could explain the complication of the shape of the oscillations and the appearance of chaos. As inhomogeneities arise in the concentration of CO inside the crystallites of zeolite, clusters of palladium located at different distances from the surface of the zeolite crystal wind up in unequal conditions. In this case the natural frequencies of oscillation of the reaction rate on the surfaces of individual Pd clusters may differ considerably, and the oscillations of the total reaction rate acquire a complicated character.The fn'st author and others [7] have constructed and studied a mathematical model of this reaction, taking account of the diffusion of CO gas in the pores of the zeolite catalyst in the case when all the crystallites that make up the zeolite catalyst are regarded as identical porous balls with palladium clusters uniformly distributed in them. The model is a chain of parametrically coupled nonlinear catalytic oscillators obtained by partitioning the crystallite into several spherical layers of equal volume. Depending on the values of the parameters, both regular and quasiperiodic and chaotic oscillations of the reaction rate were detected in the system. However, the spherical geometry of the system greatly increased the differences between the oscillators, and it remained unexplained to what extent this is essential for the formation of chaotic modes.In the present paper we construct and study an analogous model of the oxidation of CO in a zeolite catalyst; but, in contrast to [7], here all the crystallites are regarded as a single layer of porous material, which in order to take account of diffusion is divided into several identical planar layers. The mathematical model so constructed is also a chain of oscillators locally coupled through the gaseous phase. However, in this case the oscillators are perfectly identical and can differ only due to the appearance of nonuniform CO pressure inside a layer of the catalyst. Thus this model makes it possible to clarify the role of the internal diffusion of CO "in pure form" and better understand both the model of [7] and the causes of the complicated dynamic behavior of the system. In the present paper we study in detail the dynamic behavior of a pair of oscillators, and also make several generalizations to the case of a system of several coupled ...