NH sub(3) formation over a lean NOx trap (LNT) system: Effects of lean/rich cycle timing and temperature

A commercial lean NO[subx] trap (LNT) catalyst containing Pt, Pd, Rh, BaO, and CeO[sub 2] was evaluated in this investigation. The effects of lean/rich cycle timing on the NO[subx], CO and C[sub 3]H[sub 6] conversions and on the NH[sub 3] and N[sub 2]O selectivities were considered. Two distinct lean/rich cycling regimes were identified. At low temperatures, NO[subx] release and reduction were relatively slow processes. As a result, a longer, lower-concentration rich dose favored increased cycle averaged NO[subx] conversions. For example, extending the rich period from 5 to 15 s at 250 [degrees]C, while holding the overall reductant dose constant, resulted in an increase in cycle averaged NO[subx] conversion from 59 to 87%. At high temperatures, the opposite was found to be true.