OSCILLATORY REACTIONS IN HETEROGENEOUS CATALYSIS

This chapter focuses on the oscillatory reactions in heterogeneous catalysis. Oscillations are possible on all levels in a catalytic reactor, from the single-crystal plane to the crystallite to the catalyst pellet to the packed-bed reactor, and each level adds another degree of complexity. So, it is necessary to isolate the major influences at each level and to separate the characteristics of the oscillations on one level from the effects caused by coupling with other levels. Only when each level is well understood is it possible to fully understand the overall oscillatory behavior. Oscillations in heterogeneous catalysis, therefore, remain an intriguing and demanding problem. There are four primary reasons for studying oscillatory catalytic reactions. (1) Many surface reactions oscillate; probably all bimolecular oxidation reactions on transition metals will exhibit oscillations under some conditions. (2) They are intriguing and poorly understood phenomena, with no universally acknowledged mechanism. (3) Oscillatory states of reactors are potentially dangerous in chemical plants. In order to avoid these states, it is important to learn about the conditions favoring the occurrence of oscillations. (4) In spite of the potential hazards of oscillatory states, there are in some cases possible benefits to operating reactors in unstable regimes. © 1993, Academic Press Inc.