Bifurcation, Periodicity and Chaos by Thermal Effects in Heterogeneous Catalysis
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In the case of reactions far from equilibrium under isothermal conditions in homogeneous liquid media the interaction of a non-linear reaction mechanism with diffusion of reaction components determines the dynamical behaviour of the reacting system and the formation of dissipative structures. Contrary to this, in the case of the heterogeneous gas-solid media of catalysis that will be dealt with in the following, the reaction is restricted to the surface of (usually porous) pellets, and their superheating by an exothermic reaction gives rise to non-isothermal conditions. The dynamical behaviour of such heterogeneous reacting systems far from equilibrium is determined by the interaction of the non-linearities of the reaction mechanism at the catalyst surface with the processes of heat transfer, predominantly conduction and convection. The strongest non-linearity is the exponential-like increase of the reaction rate with increasing catalyst temperature due to the Arrhenius law. Besides this, other types of non-linearities, too, may occur in the reaction mechanism at the surface, controlling the dynamical behaviour under isothermal conditions, and leading in some cases to isothermal oscillations of the reaction rate as they have been observed at single catalyst pellets [1,2], at samples of catalyst powder [2–4], and at specimens of single crystal planes of the catalytically active metal [5–8].
KeywordsTubular Reactor Ethane Oxidation Deterministic Chaos Feed Temperature Catalyst Temperature
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