Dynamics of SO2 adsorption–oxidation in SOx traps for the protection of NOx adsorbers in diesel engine emissions

The SO2 uptake behaviour at different temperature and SO2 concentration of a reference SOx trap is studied in a thermobalance apparatus and in a flow reactor under reaction conditions close to those in the emissions from a diesel engine. The data of the latter apparatus are also kinetically modelled to derive which controlling regime dominates the performances. The results evidence that at 200 °C the behaviour is largely controlled by the slow solid-state diffusion of the sulphate species, while above 300 °C there is an initial region controlled by the surface reaction, although for levels of SO2 uptake above a weight increase of 4–5% (due to sulphation) the solid-state diffusion dominates the performances also at high temperature.