The effects of different regeneration times, but with a constant total amount of reductant delivered, were investigated over a model NO X storage and reduction (NSR) catalyst. The different regeneration times were 4, 8 and 16s with 4, 2, and 1% H 2 as the reductant amounts, respectively. The lean time was kept the same during these experiments, resulting in a constant inlet NO X -to-reductant amount in the cycles. Overall, the results show clear improvements with longer regeneration times in both NO X 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 NO X release coincident with a small increase in the trapping performance resulted in an overall decrease in NO X conversion with increasing regeneration time. The data demonstrate that the different concentrations of H 2 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.