Kinetic Modeling of NOx Storage and Reduction Using Spatially Resolved MS Measurements

Artikel i vetenskaplig tidskrift, 2014

A Global Kinetic NOX Storage and Reduction (NSR) Model based on flow reactor experiments was developed to investigate the NOX storage and reduction mechanisms with a focus on the breakthrough of NH3 and N2O during the rich phase. Intra-Catalyst Storage and Reduction Measurements (SpaciMS) were used to further validate the model, particularly with respect to the formation and utilization of ammonia along the catalyst axis. Two different catalysts were used in the model, denoted Cat. 1 and Cat. 2. The first catalyst was used in flow reactor experiments to create a global kinetic model and fitting the parameters using long NSR cycles validated against more realistic short NSR cycles, while the second catalyst was used in the SpaciMS experiments. However, due to some differences in the catalytic material, some parameters had to be re-tuned for the second catalyst. Two NOX storage sites were used for both catalysts, barium (Ba) and the support sites (S2). Furthermore, the Shrinking-Core Model was used to describe the mass transport of NOX inside the storage particles, S2. An oxygen storage component was necessarily included and denoted Ce for the first catalyst and representing ceria in the catalyst. The second catalyst did not contain any ceria, which is why the oxygen storage site was called S3 and can be interpreted as oxygen on the noble metal. During the rich period, NOX was reduced by H2 and CO, forming nitrogen and NH3. Produced NH3 reacted with stored NOX forming N2O and resulting in an N2O peak before NH3 breakthrough. The model agreed well with reactor experiments and SpaciMS measurements. The SpaciMS results showed that most NOX was stored in the first half of the catalyst, resulting in high ammonia production in the catalyst front and its subsequent consumption along the catalyst axis to reduce NOX stored downstream.