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Dynamic kinetic data collected over commercial V2O5-WO3/TiO2 and Fe-zeolite catalysts analyzing the standard NH3-SCR of NO for the abatement of NOx from vehicle exhausts showed transient effects at low temperatures related to the inhibiting action of excess ammonia. In order to describe such transient effects, a specific rate expression accounting for NH3 inhibition of the standard SCR reaction is needed in mathematical models of real SCR converters. We present herein a dual-site Mars-Ven Krevelen-type rate equation suitable to describe dynamic features associated with ammonia injection and shut-off over both V-based and Fe-zeolite catalysts. Les données cinétiques dynamiques recueillies sur des catalyseurs V2O5-WO3/TiO2 et Fe-zéolite commerciaux en analysant le RCS-NH3 standard du NO pour la réduction des NOx des gaz d’échappement de véhicules ont montré des effets transitoires à basse température, liés à l’action inhibitrice d’ammoniac en excès. Afin de décrire de tels effets transitoires, une expression de la vitesse spécifique prenant en compte l’inhibition par NH3 de la réaction de RCS standard est nécessaire pour des modèles mathématiques de convertisseurs par RCS réels. Nous présentons ici une équation de vitesse de type Mars-Van Krevelen à double site pour décrire les caractéristiques dynamiques associées à l’injection et à l’arrêt de l’ammoniac sur des catalyseurs à la fois à base de V et Fe-zéolite.

This work aims to investigate the possibility to apply open-cell foams as catalytic substrates in SCR systems for Diesel engines, as a replacement of traditional honeycombs. In the literature, many studies compare the performance of foams and honeycombs as catalytic substrates, showing, in general, a better mass transfer behavior in foams, compensated on the other hand by a higher pressure drop. In this work, we consider the low-pressure injection of Ad-Blue and we evaluate the performance of the open-cell foam in enhancing the mixing and the evaporation of the spray. A Eulerian-Lagrangian CFD model has been adopted to simulate the spray evolution and its interaction with the microstructure of the open-cell foam. The model has been applied to evaluate the spray evaporation and the uniformity of the ammonia distribution in different sections of the substrate. Different operating conditions were tested comparing substrates with different geometrical properties. The results of this preliminary analysis can be regarded as promising, showing the capability of the foam to enhance the mixing of the spray and to achieve a uniform distribution of the ammonia over all the catalyst substrate.