Influence of aging effects on the conversion efficiency of automotive exhaust gas catalysts

The influence of chemical and thermal aging effects on catalytic activity was analyzed for a vehicle (bifuel) aged pre- and underfloor three-way catalyst (p-/u-TWC) as well as an engine aged diesel oxidation catalyst (DOC). The conversion results were compared with the respective new catalysts. Although the vehicle aged p-TWC showed massive thermal aging, its CO conversion rate was comparable to that of the vehicle aged u-TWC. On the other hand, the conversion rate for methane abatement was significantly affected above 325 °C. Methane conversion appeared as the parameter mostly affected by (thermal) aging. The DOC showed massive chemical aging with typical engine oil based contaminants like P and Zn but also with Si. The contamination is likely responsible for the shift of propene and NO light-off curves to higher temperatures by about 70 °C.