The response of an exhaust-aged three-way catalyst to perturbations in the feedstream stoichiometry was examined in laboratory experiments. The air-fuel ratio was perturbed using both symmetric and asymmetric cycling and a range of net stoichiometries. The conversions of NO and CO were determined using the cycled feeds and steady feeds of equivalent net stoichiometry. At 550 O C cycling the feed benefited conversion at average air-fuel ratios away from the stoichiometric composition. This effect was more pronounced with asymmetric than symmetric cycles. Cycling the air-fuel ratio of the simulated exhaust gas during warm-up of the catalyst did not significantly benefit either NO or CO conversion.

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The exhaust composition in closed-loop emission control systems typically oscillates about the stoichiometric set point. We describe herein the laboratory system we developed to investigate catalyst behavior in such an environment. The design is such that the frequency, amplitude, and average composition of the oscillations can be varied independently of one another. In laboratory testing of a platinum-rhodium catalyst it was demonstrated that the "window" for three-way conversion could be Improved via oscillations of low frequency or large amplitude, but peak conversion efficiencies were sacrificed in the process. On samples aged in engine exhaust or at high temperature, cycling effects were most evident under near-stoichiometric conditions.

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Bei der NO‐Reduktion mit Ru‐Katalysatoren traten Schwierigkeiten bei der Reproduktion der Ergebnisse auf.

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