NH3NH3 SCR of NOxNOx for diesel exhausts aftertreatment: role of NO2NO2 in catalytic mechanism, unsteady kinetics and monolith converter modelling

A chemically consistent dynamic kinetic model of the NH3–NO/NO2NH3–NO/NO2 reacting system was developed on the basis of an extensive fundamental research carried out over a commercial V2O5–WO3/TiO2V2O5–WO3/TiO2 selective catalytic reduction (SCR) catalyst for automotive applications. Intrinsic kinetics of all the selective and non-selective reactions were estimated by fitting a systematic set of transient runs over the powdered catalyst. The resulting model accounts for the complex SCR chemistry over a wide range of experimental conditions (T=160–450∘C; NO/NO2=0→∞NO/NO2=0→∞): in particular, it takes into account formation, storage, decomposition and reaction of NH4NO3NH4NO3, which resulted in a good description of the selectivity to all the major N-containing products (N2N2, NH4NO3NH4NO3, HNO3HNO3, N2ON2O). The model was validated by independent dynamic runs both over powdered catalyst at the microreactor scale and over monolith catalysts in engine test bench runs at the full scale.