Influence of catalyst deactivation on N2O emissions from automobiles

Abstract

Though estimates of the total N₂O emitted by automobiles differ widely, automobiles are believed to be a significant source of non-agricultural anthropogenic N₂O emissions. At the Third Conference of the Parties (COP-3) UN Framework Convention on Climate Change, held in Kyoto in 1997, N₂O was designated as a greenhouse gas whose release into the atmosphere must be reduced. This action increased the need for more accurate estimates of automotive N₂O emissions. The wide variation in estimates may be attributed to differences in emission test modes, types of catalysts, and levels of catalyst deactivation involved in the tests. In this study, we examined the influence of automotive catalyst deactivation on N₂O emissions from the perspective of catalyst temperature frequency distribution. Using a model gas and deactivated three-way catalysts (TWCs), we applied the exhaust emission test modes of various countries. The results indicate that the factor behind the increase of N₂O emissions following catalyst deactivation is not growth in N₂O generation, but a decline in the N₂O decomposition capability of the catalyst. It was also found that the effect of catalyst deactivation differs according to the catalyst composition and the emission test mode.