Modellering av åldring av dieseloxidationskatalysatorer

Sammanfattning: A conventional exhaust gas after treatment system (EATS) for the Euro VI legislation contains four different catalyst. The first two (particulate filter system) remove particulates and the last two (SCR system) remove nitrogen oxides (NOx). The particulate filter system also optimizes the gas composition with respect to nitrogen monoxide (NO) and nitrogen dioxide (NO2). The performance of the SCR system has a strong dependency on the NO:NO2 ratio as the so called selective catalytic reduction (SCR) reaction is kinetically favored at a NO:NO2 ratio of 1:1. The diesel oxidation catalyst (DOC) is placed first in the EATS. Due to this placement, the DOC is subjected to a rough environment, e.g. high temperatures and oil/fuel impurities that with time will affect its performance, i.e. the catalyst ages. In this master thesis, the aging of the DOC has been empirically correlated to thermal load and sulfur exposure. The study shows that it is possible to predict how the NO oxidation performance decays as a function of thermal and sulfur exposure. The empirical relation was fitted against two aging cycles and validated against an additional four. The results show that the loss of catalytic activity can to a large extent be explained by the cycle it has been used on.