Steady-State Multiplicity and Superadiabatic Extinction Waves in the Oxidation of CO/H2 Mixtures over a Pt/Al2O3-Coated Monolith

Steady-state multiplicity was observed in the catalytic oxidation of mixtures of H 2 and CO over a cordierite monolith wash-coated with Pt/Al 2 O 3. Increasing the CO concentration or decreasing the H 2 concentration across the hysteresis limit results in extinction, whereas decreasing the CO concentration or increasing the H 2 concentration across the other hysteresis limit causes ignition. CO inhibits the ignition of H 2, whereas H 2 assists the ignition of CO. Extinction of the reaction due to a step increase of CO or a step decrease of H 2 occurred in the form of a downstream-moving wave accompanied by a sharply localized superadiabatic temperature excursion. Axial temperatures were recorded by five equally spaced thermocouples. The superadiabatic rise in temperature and the speed of the extinction wave are related in a complex way to the size of the CO jump into the hysteresis zone. The greater the H 2 jump downward in concentration, the lower the maximum temperature and the greater the speed of the reaction front.