Dynamics of N2 and N2O peaks during and after the regeneration of lean NOx trap

Abstract The dynamics and selectivity of N 2 and N 2 O formation during and after the regeneration of a commercial NO x storage catalyst containing Pt, Pd, Rh, Ba on Ce/Zr, Mg/Al and Al oxides was studied with high-speed FTIR and SpaciMS analyzers. The lean/rich cycling experiments (60 s/5 s and 60 s/3 s) were performed in the temperature range 200–400 °C, using H 2 , CO, and C 3 H 6 individually for the reduction of adsorbed NO x . Isotopically labeled 15 NO was employed in combination with Ar carrier gas in order to quantify the N 2 product by mass spectrometry. N 2 and N 2 O products were formed concurrently. The primary peaks appeared immediately after the rich-phase inception, and tailed off with breakthrough of the reductant front (accompanied by NH 3 product). Secondary N 2 and N 2 O peaks appeared at the rich-to-lean transition as a result of reactions between surface-deposited reductants/intermediates (CO, HC, NH 3 , -NCO) and residual stored NO x . At 200–300 °C, up to 30% of N 2 and 50% of N 2 O products originated from the secondary peaks. The N 2 O/N 2 selectivity ratio as well as the magnitude of secondary peaks decreased with temperature and duration of the rich phase. Among the three reductants, propene generated secondary N 2 peak up to the highest temperature. The primary N 2 peak exhibited a broadened shoulder aligned with movement of reduction front from the zone where both NO x and oxygen were stored to the NO x -free zone where only oxygen storage capacity was saturated. N 2 formed in the NO x -free zone originated from reaction of NH 3 with stored oxygen, while N 2 O formation in this zone was very low.