Hot spot formation on a catalyst

Stationary hot spots with an amplitude of 50-100K were observed by an IR imager during hydrogen oxidation on supported nickel-on-alumina catalytic rings placed in a mixed vessel. These states were found under reactor conditions for which the uniform system is bistable, i.e. when both uniformly ignited and extinguished states exist. The nonuniform states were generated either by short, local heating of an extinguished state or by slow cooling of a sufficiently large ignited ring. The hot spot could be created at any location on the ring. The width of the temperature fronts connecting the high- and low-temperature zones was rather insensitive to variations in the thickness and diameter of the ring. Stationary hot spots of slightly different shapes, with up to 8% different levels of conversion in the reactor effluent, were observed under the same operating conditions following different initial conditions. The region of reactor temperature vs feed concentration in which hot spots exist increases with ring diameter, and its boundaries are sensitive to the intensity of mixing in the vessel. The hot spots are stabilized bya global interaction between the catalytic surface and the oxygen concentration in the mixed vessel. Copyright (C) 1996 Elsevier Science Ltd