In dieser Dissertation werden Methoden entwickelt, die die Beschreibung der Katalysatoralterung verbessern. Der Fokus liegt hierbei auf der Realalterung in Pkws und Lkws. Die ständig wechselnden Bedingungen im realen Einsatz stellen dabei eine besondere Herausforderung dar. Es wird ein physikalisches Modell entwickelt, das das Wachstum der Edelmetall-Kristallite im Washcoat beschreibt. Anhand der Kristallitgröße wird die katalytische Restaktivität des Katalysators bestimmt. Das Modell kann die Konvertierungsleistung der wesentlichen gasförmigen Schadstoffe CO, HC und sogar NOx berechnen. Es arbeitet vollumfänglich unter stationären thermischen Bedingungen einer Ofenalterung. Weitere Tests könnten es auch zur Anwendung für thermische Realalterung zulassen. Als weitere Methode wird eine empirische Korrelation entwickelt, die die Temperaturbelastung der Katalysatoren kategorisiert und diese damit hinsichtlich ihrer thermischen Realalterung zueinander einordnet. Die thermische Realalterung wird an Diesel-Oxidations-Katalysatoren (DOC) untersucht, die aus einer Edelmetall-Legierung aus Platin und Palladium bestehen. Hinsichtlich der chemischen Realalterung wird eine Diesel-AGN auf ihre Empfindlichkeit gegenüber Ablagerungen und Deaktivierung durch ungerafften Betrieb mit reinem Biodiesel untersucht. Der Biodiesel drängt sich hier in den Fokus, da in diesem, im Vergleich zu fossilem Diesel, deutlich mehr Vergiftungselemente enthalten sein können. / The combustion engine is a very important drive system. An exhaust-aftertreatment system (ATS) is widely mandatory for exhaust-gas purifcation, but the contained catalysts suffer from deactivation by aging effects. To handle the catalyst aging, its description is very significant. This PhD thesis develops two methods to improve the description of thermal real-world aging.
The diesel-oxidation-catalyst (DOC) executes crucial conversion-reactions with platinum and palladium as precious metals. They are spread as small particles across the washcoat. Thermal catalyst aging is driven by temperature stress, duration and exhaust-gas atmosphere. It is irreversible and usually the dominating aging-type. Main path of the thermal aging is the precious-metal sintering, at which small precious-metal particles agglomerate to bigger ones. As result the access of the exhaust-gas to the catalyst detoriates, what leads to a deactivation. Chemical catalyst aging originates from negative effect of catalyst poisons and exhibits a very individual behaviour.
The developed physical crystallite-size model calculates in its 'base version' the conversion of a catalyst after oven-aging. Input is an arbitrary oven-aging scenario to calculate the resulting crystallite-size and finally to conclude to the catalytic activity. This is possible for every species, thus CO, HC and even NO. Thereby, thermal oven-aging is described by a physical parameter. Furthermore, it is to mention, that the correlation between crystallite size and conversion is explicit for all species. The model is developed at an Pt/Pd-DOC and therefore it is expected, that general catalysts, with and without precious-metal alloys, can be described. The crystallite-size provides also the advantage, that it is independent from chemical aging. So a closed look on thermal aging is possible. The 'base version' of the model can be used in research and development as well for post-mortem analysis.
The enhancement of the physical crystallite-size model could allow the description of thermal real-world aging. Input is an inconstant temperature-run for the calculation of the resulting crystallite-size to conclude again to the remaining catalytic activity. A confirmation is not possible with the available data, also the potential of the enhancement cannot be proved. But if the confirmation could get achived, for completely arbitrary thermal real-world aging scenarios the calculation of the conversion for every species would be possible. The field of application would be research and development, on-board operation as well as post-mortem analysis.
The developed empirical correlation for real-world aging uses as input inconstant temperatureruns of several DOCs. They are treated by a combination and ranking system. Finally the method outputs a ranking, which represents the remaining catalytic activity. Thereby, the result for the DOCs is qualitative and relative to each other. The available seven real-world aged Pt/Pd-DOCs can get sorted completely correct by the method. The field of application is research and development, on-board operation as well as post-mortem analysis.
The chemical real-world aging gets investigated by three ATS, which are driven with DIN EN 14214 biodiesel. Phosphorus and calcium indicate a B100 influence for accumulation. B100 operation clearly causes catalytic deactivation. The activity of the samples at the DOC-outlet correlates with the P+Ca accumulation. But this is not valid for the samples at the DOC-inlet.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:82363 |
| Date | 22 November 2022 |
| Creators | Bahr, Mario |
| Contributors | Michaelis, Alexander, Zikoridse, Gennadi, Atzler, Frank, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | German |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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