Modeling and analysis of spatiotemporal oscillatory patterns during CO oxidation in the catalytic converter

In spite of numerous reports of kinetic instabilities during CO oxidation o n supported noble-metal catalysts, previous models of the catalytic convert er typically employed explicit rate-expressions. Such oscillatory motions o r bistable behavior occur at low temperatures and should affect the convert er cold-start performance. In this work we incorporate an oscillatory eleme ntary-step kinetic model of CO oxidation into the converter model and analy ze its behavior. The kinetic model was suggested by Sales et al. (1982 Surf ace Science, 114, 381-394) and we modify the suggested parameters to assure that the steady-state rate is monotonically increasing with temperature. W e draw typical bifurcation maps, in the temperature vs. P-CO plane, for the isothermal kinetic model, for the catalyst surface (the lumped problem) an d for the whole reactor and analyze the various boundaries by means of phas e plane analysis. The domain of oscillations in the catalyst problem is qui te similar to that in the converter and is bound by Hopf and global-saddle- node bifurcations. The converter may exhibit either a stable steady behavio r or an oscillatory motion. In typical oscillations, which may be periodic or chaotic, a hot domain enters the reactor exit and moves quickly upstream ; the following extinction occurs almost simultaneously due to strong coupl ing by convection. New avenues of cold-starting the converter, which is an excitable system, b y means of periodic local perturbations upstream that send fronts propagati ng downstream are also suggested. The analysis shows, however, that this ap proach is not advantageous due to the slow relaxation of the surface activi ty during CO oxidation. (C) 1999 Elsevier Science Ltd. All rights reserved.