Kinetics of N2O and N2 Peaks During and After the Regeneration of Lean NOx Trap
David Mracek, Institute of Chemical Technology, Prague
While the NH3 dynamics during the LNT regeneration is relatively well understood, much less attention has been paid to dynamics of N2 and N2O peaks. Ammonia appears at the reactor outlet in a single peak with certain delay that is determined by the breakthrough time of the reducing front . On the contrary, both N2 and N2O exhibit double peak dynamics with primary peak immediately after the start of regeneration and secondary peak after the switch back to lean conditions .
In this contribution we summarize our recent investigation of N2O and N2 peaks formation based on lean/rich cycling experiments with varying lenght of rich phase, reductant and temperature of the regeneration. The evolution of products at the reactor outlet was analyzed using fast FTIR analyzer, and spatiotemporal profiles inside the catalyst were obtained with the spatially resolved capillary inlet mass spectrometer (SpaciMS). The dynamics of key species on the catalyst surface was further studied by means of DRIFTS. Primary N2O peak results from initial reaction of any reductant (H2, CO, C3H6, or NH3) with the stored NOx over poorly reduced PGM sites at the head of the reducing front [1, 2]. Secondary N2O peak indicates reaction of residual stored NOx with adsorbed reductants after incomplete LNT regeneration, and diminishes with increasing temperature, increasing regeneration length, and with the use of more active reductant .
 KoÄÃ P., BÃ¡rtovÃ¡ Å ., MrÃ¡Äek D., Marek M., Choi J.-S., Kim M.-Y., Pihl J.A., Partridge W.P. Effective Model for Prediction of N2O and NH3 Formation During the Regeneration of NOx Storage Catalyst. Topics in Catalysis 56 (2013), 118-124.
 BÃ¡rtovÃ¡ Å ., KoÄÃ P., MrÃ¡Äek D., Marek M., Pihl J.A., Choi J.-S., Toops T.J., Partridge W.P. New Insights on N2O Formation Pathways during Lean/Rich Cycling of a Commercial Lean NOx Trap Catalyst. Catalysis Today (2014), accepted.