SELF-SUSTAINED OSCILLATIONS DURING CO OXIDATION ON A Pt/γ-Al2O3 CATALYST

A systematic study of the effect of reaction environment and catalyst surface on self-sustained oscillations during CO oxidation on a Pt/γ-Al2O, catalyst is presented in this paper. The catalyst, consisting of a fixed bed of small particles, was subjected to three different pretreatments: fresh, O2 - H2 treated and poisoned by SO2. Self-sustained oscillations, lasting for as long as desired, were manifest in a narrow range of temperatures and O2/CO ratios. The structure of the oscillatory pattern varied with catalyst pretreatment, however, in all cases the predominant feature consisted in transitions between low and high conversion levels (ignition-quenching). The amplitude and frequency of the oscillations varied with surface pretreatment, however, they decreased as temperature and O2:/CO ratio increases. Small temperature fluctuations of less than 6°C, which mirrowed concentration oscillations were also observed. A unique feature observed under certain conditions, was an overshoot of CO2 outlet concentration in excess to the 100% conversion, which indicated the participation of surface stored CO. The results are discussed in terms of competitive CO and O2 adsorption-reaction coupled with reactor and surface balances.