Abstract. This paper considers a first-order, irreversible exothermic reaction in a bounded porous catalyst, with smooth boundary, in one, two, and three space dimensions. It is assumed that the characteristic reaction time is sufficiently small for the chemical reaction to be confined to a thin layer near the boundary of the catalyst, and that the thermal diffusivity is large enough for the temperature to be uniform in the reaction layer, but that it is not so large as to avoid significant thermal gradients inside the catalyst. For appropriate realistic limiting valúes of the several nondimensional parameters of the problem, severa! time-dependent asymptotic models are derived that account for the chemícal reaction at the boundary (that becomes essentially impervious to the reactant), heat conduction inside the catalyst, and exchange of heat and reactant with the surrounding unreacted fluid, These models possess asymmetrical steady states for symmetric shapes of the catalyst, and some of them exhibit a rich dynamic behavior that includes quasiperiodic phenomena. In one case, the linear stability of the steady states, and also the local bifurcatíon to quasi-periodic solutions via center manifold theory and normal form reduction, are analyzed.Key words, porous catalysts, weakly nonlinear stability, normal forms
AMS(MOS) subject classifications. 35B32, 35KS7, 80A30, 80A32I. Introductiort and formulation. This paper deals with a well-known model for the evolution of the reactant concentration u and of the temperature v in a porous catalyst, in which a first-order, irreversible, exothermic reaction occurs. After suitable nondimensionalization (length is referred to a characteristic dimensión of the catalyst, time is referred to the thermal diffusion time within the catalyst, and the reactant concentration and temperature are referred to their respective valúes at the external unreacted fluid), the principie of conservaron applied to the reactant and to enthalpy leads to the following model [1, Vol. I]:for t >0, with appropriate initiai conditions at í -0. Here A is the Laplacian operator, n is the outward unit normal to the smooth boundary of the domain (1<=W (p -1, 2, or 3), and all the parameters are positive. 2 (Damkohler number) is the ratio of the reaction rate to the difíusion rate, y is the acüvathn energy (or temperature) of the chemical reaction, L (Lewis number) is the ratio of thermal to material diífusivity, 0 (Prater number) is a measure of the chemicai heat reiease (/3L is a measure of the heat of reaction relative to the thermal energy of the catalyst), and a-and v (diffusional and thermal Biot numbers) are measures of the rates of mass and heat transfer between the surface of catalyst and the external fluid, relative to the rates of mass and heat transfer within the cataiyst.Usually, the thermal diffusivity of the soiid (metallicorwithmetalliccomponents) catalyst is very high, and, consequently, ¡3 is quite small, v is fairly small or of order