N ₂O mitigation in a coupled LNT-SCR system

N ₂O formation and consumption were investigated over a coupled LNT-SCR system consisting of a low-precious metal loaded Pt/Rh LNT catalyst and a commercial Cu-zeolite SCR catalyst. Under lean-rich cycling conditions, N ₂O emissions from the LNT were found to be partially mitigated by the downstream SCR catalyst. N ₂O decomposition over the SCR catalyst was observed in the absence of reductant immediately after the switch to rich conditions, while N ₂O reduction occurred after subsequent breakthrough of the reductant from the LNT. Steady-state data indicate that the former process is weakly promoted by NO which breaks through the LNT at the same time as the N ₂O. Steady-state experiments revealed the order H ₂>NH ₃>CO>C ₃H ₆ for the efficacy of N ₂O reduction with different reductants. These findings suggest that coupled LNT-SCR systems can not only improve overall NO _x conversion levels but can also mitigate N ₂O emissions from the LNT catalyst under actual driving conditions.