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The removal of nitrogen oxides emitted by diesel and lean burn engines is one of the most important targets in catalytic exhaust aftertreatment research. Besides the selective catalytic reduction (SCR) reaction with ammonia the most promising approach is the NOx Storage and Reduction Catalyst (NSR) which utilizes the nitrogen oxides storage on barium sites to form nitrates during the lean phase and their reduction to nitrogen in a rich atmosphere. In this paper, we present a modeling approach for the description of the transient behavior of a NSR. The model applies a two-dimensional description of the flow field in the single channels coupled with detailed models for the chemical processes. The mechanism used for modeling the oxidation and reduction of carbon monoxide, hydrocarbons, and nitrogen oxides, respectively, is based on an elementary step reaction mechanism for platinum catalysts and a shrinking core model for the storage and reduction processes on the barium particles.

This combined numerical simulation and experimental study focuses on the effect of nitrogen dioxide (NO2) in strong diluted oxygen-rich NOx/NH3/O2/H2O gas mixtures representative at exhaust gas aftertreatment in diesel engines. Conversion of nitrogen oxides (NOx) and ammonia (NH3) and the change of the NO/NO2 and NH3/NOx ratios were analyzed by means of comparison between experimental measurements and kinetic simulations. Homogeneous gas-phase experiments have been carried out in a special countercurrent continuous flow reactor at intermediate temperature (473-923 K) and elevated pressure up to 5 bar. In the simulation with an ideal plug-flow model, the occurring reactions in the gas mixture were calculated. To explain the observations, a reactions flow analysis was also performed. The experimental and modeling results revealed that despite a high NH3 conversion, the NOx concentration stays nearly constant in the presence of NO2.

The selective catalytic reduction (SCR) based on urea-water-solution is an effective technique to reduce nitrogen oxides (NOx) emitted from diesel engines. A 3D numerical computer model of the injection of urea-water-solution and their interaction with the exhaust gas flow and exhaust tubing is developed to evaluate different configurations during the development process of such a DeNOx-system. The model accounts for all relevant processes appearing from the injection point to the entrance of the SCR-catalyst: momentum interaction between gas phase and droplets evaporation and thermolysis of droplets hydrolysis of isocyanic acid in gas phase heat transfer between wall and droplets spray/wall-interaction two-component wall film including interaction with gas phase and exhaust tube The single modeling steps are verified with visualizations, patternator measurements, phase-doppler-anemometer results and temperature measurements.

Hydrogen (H2) is commonly considered as one of the most promising carbon-free energy carriers allowing for a decarbonization of combustion applications, for instance by retrofitting of conventional diesel internal combustion engines (ICEs). Although modern H2-ICEs emit only comparably low levels of nitrogen oxides (NOx), efficient catalytic converters are mandatory for exhaust gas after-treatment in order to establish near-zero emission applications. In this context, the present study evaluates the performance of a commercial state-of-the-art oxidation catalyst (OC) and of a catalyst for selective catalytic reduction (SCR) that are typically used for emission reduction from diesel exhausts under conditions representative for H2-fueled ICEs, namely oxygen-rich exhausts with high water vapor levels, comparably low temperatures, and potentially considerable levels of unburnt H2.