The influence of the preparation procedure on the performance of NOx storage and reduction catalysts was investigated by means of flow reactor experiments. Three catalysts were examined; one Pt/Al and two Pt/Ba/Al samples. One of the Pt/Ba/Al samples was prepared with Pt impregnated on Al/Ba and one with Ba impregnated on Al/Pt. The results clearly show that the preparation procedure influences the behavior of NOx storage and reduction catalysts both during lean and rich conditions. The order of the impregnation steps is crucial especially at higher temperatures; a higher storage capacity is obtained when impregnating Al/Pt with Ba than when impregnating Al/Ba with Pt. The storage increased with as much as 54% when adding Ba in the last step. The N2O and NH3 formation is also affected by the preparation procedure; there is a clear dependency on the order of impregnation steps. Moreover, N2O is not only formed during rich conditions but also in the beginning of the lean period over the Pt/Al and Al/Pt/Ba samples. (C) 2008 Elsevier B.V. All rights reserved.