Nitrogen release from a NOx storage and reduction catalyst

In a NOx storage and reduction (NSR) catalyst, the release and reduction of NOx occurs over a very short period. The speed of the NOx release and reduction creates difficulties in analyzing the chemistry using normal analytical techniques, which are typically better suited to slower, steady-state studies. We have investigated the time dependence of NO, NO2, NH3, N2O and N2 released by an NSR catalyst using a combination of FT-IR and gas chromatographic techniques. Nitrogen was detected with the GC by using He rather than N2 as the background gas. The FT-IR was used not only to monitor NO, NO2, NH3 and N2O, but also to establish cycle-to-cycle reproducibility. Under these conditions we used the GC to sample the effluent at multiple times over many lean–rich cycles. To the extent that the chemistry was truly periodic and reproducible, we obtained the time dependence of the release of nitrogen after the lean-to-rich transition. Similar information was obtained for O2, H2 and N2O. Combining the FT-IR and GC data, we obtained good cycle averaged nitrogen balances, indicating that all the major products were accounted for.