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The diesel oxidation catalyst (DOC) plays a key role in diesel exhaust treatment systems. Typical noble metals used as active components are platinum (Pt) and palladium (Pd). During lightoff/lightout experiments, the catalyst reactivity during heating is in some cases different from the reactivity during cooling in the same reaction mixture. These so called hysteresis phenomena have repeatedly been reported for CO, NO, and HC conversion and are mostly attributed to noble metal oxidation and/or surface coverage effects. Hauff et al. have developed a kinetic model that is able to account for the hysteresis effects observed in NO conversion on Pt-only catalysts due to noble metal oxidation. The model was only validated for a limited range of NO concentrations and temperatures. In this follow-up, further experiments on Pt-only as well as on Pd-only catalysts will be presented for additional feed compositions. General transferability of the Pt-only model to Pd-only catalysts for NO-only is demonstrated. By addition of CO and propene to the feed, additional hysteresis phenomena are observed and will be discussed. On Pd-only, results indicate that under lean exhaust conditions, the noble metal can only be slightly reduced by CO. Interestingly, with a mix of CO and NO no reactivation is observed whereas the combination of CO, NO, and propene again shows reducing tendency. Based on these informations, a possible modeling approach will be proposed.

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Recent findings in the conversion behavior of diesel oxidation catalysts (DOCs) show a strong dependence between performance and oxidation state of the catalyst. Furthermore, a slow and reversible change of catalyst oxidation state has been observed under cyclic temperature changes with realistic exhaust gas conditions, which can result in a significant inverse hysteresis during light‐off and subsequent light‐out. In this contribution, an existing 1D global kinetic model for Pt‐only DOCs is developed further, considering CO and hydrocarbon interaction. It is also applied to a Pd‐only and PtPd‐alloyed catalyst.

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