Statistical Fluctuations of Temperature and Conversion at the Catalytic CO Oxidation in an Adiabatic Packed Bed Reactor

Abstract

AbstractThe oxidation of CO with air at a Pt/γ‐Al2O3 supported catalyst employed in an adiabatic fixed‐bed reactor, is accompanied by nonperiodic variations of CO2 concentration and temperature at the reactor exit. The occurrence of these variations is confined to the region of bifurcation from monostable to bistable behaviour of the fixed‐bed reactor. The variations originate from small temporal and local fluctuations of the reaction rate—and hence the temperature—in the entrance cross‐section of the catalyst bed. In the bifurcation region the temperature humps of these fluctuations (ΔT ≈ 0.5 K) are strongly amplified and finally form reaction zones (ΔT ≈ 120 K) which move to the reactor exit with velocities of 3.5 to 11 mm/min. Measurements at a cluster of 10 catalyst pellets exposed to the CO/air gas stream showed that the fluctuations at the entrance of the fixed bed can be attributed to kinetic oscillations occurring in the regime of descending reaction rate with increasing CO feed. By periodic variations of the CO feed the reaction can be forced to show harmonic or subharmonic resonance. In the latter case, the quasiperiodic Fourier spectrum of the unperturbed reaction turns to a spectrum with a sextet at the subharmonic frequency.