Hot zones formation in packed bed reactors

Stationary and complex moving hot zones were observed during atmospheric oxidation of carbon monoxide on the top surface of a shallow packed bed, consisting of several layers of spherical catalytic pellets (Pd/Al2O3). The test reaction was atmospheric oxidation of carbon monoxide. The reactor was run under conditions for which steady-state multiplicity and hot zone existed for some feed temperatures. The size of the hot zones was much larger than that of individual particles. IR imaging revealed that the hot and cold regions (temperature difference of the order of 100(degree)C) were separated by a sharp (about 3 mm wide) temperature front. A very intricate periodic motion in which the hot zone repeatedly split and coalesced was observed in the shallow packed bed reactor. The transition from the branch of uniformly ignited to the states with a hot region was usually supercritical. It is not yet clear which rate processes generate the transversal hot zones in uniform packed bed reactors.