Effects of different regeneration timing protocols on the performance of a model NOX storage/reduction catalyst

The effects of different regeneration times, but with a constant total amount of reductant delivered, were investigated over a model NOX storage and reduction (NSR) catalyst. The different regeneration times were 4, 8 and 16 s with 4, 2, and 1% H2 as the reductant amounts, respectively. The lean time was kept the same during these experiments, resulting in a constant inlet NOX-to-reductant amount in the cycles. Overall, the results show clear improvements with longer regeneration times in both NOX trapping and overall reduction performance at all temperatures except 500 °C. At 500 °C, there was still an increase in trapping performance with longer regeneration time, but a more significant increased NOX release coincident with a small increase in the trapping performance resulted in an overall decrease in NOX conversion with increasing regeneration time. The data demonstrate that the different concentrations of H2 did not lead to different regeneration extents, but that the main factor for the improved performance was the regeneration time itself. With longer regeneration times, more nitrate/nitrite decomposition occurred, thereby leading to more extensive surface cleaning.