PATTERN SELECTION IN A GENERAL-MODEL OF CONVECTION, DIFFUSION AND CATALYTIC REACTION

We study the process of pattern selection in a large class of heteroge neous models of catalytic reactors by analyzing the behavior of a simp le condensed model, which obeys reflection and inversion symmetries an d which captures the main features of a detailed model. The three-vari able model incorporates a very fast and long-ranged variable, which ma y describe the fluid phase in a mixed, plug-flow or an axial-dispersio n reactor or the pore phase in a catalytic particle, and two variables - a medium-ranged activator and a localized inhibitor - that describe the solid phase. Patterns are classified according to their symmetry properties. Patterns may emerge already with simple bistable kinetics in a plug-flow reactor (i.e., a single integrodifferential equation). Pattern selection is determined by the phase planes spanned by the rea ctor, by the ratio of front residence time to the period of oscillatio ns and by the ratio of convection to fluid-phase diffusions terms. Pat terns include stationary or oscillatory fronts or pulses, antiphase os cillations which appear at the transition from homogeneous solution, u nidirectional pulses that are the dominant patterns when mixing is wea k and stationary or oscillatory waves that emerge with strong fluid-mi xing. The simple form of the model allows us to suggest a general clas sification of emerging patterns and to identify the corresponding cond itions in term of realistic models of reactors.