Transient in situ DRIFTS and flow-reactor experiments were performed to study the storage and reduction of NO X over Pt/BaCO 3/Al 2O 3, Pd/BaCO 3/Al 2O 3, and Rh/BaCO 3/Al 2O 3 samples using CO, H 2, C 3H 6, or C 3H 8 as the reducing agent. The DRIFTS results show that exposure of the examined samples to NO 2 results in the formation of nitrite/nitrate peaks over alumina and barium and that the reduction of stored NO X is influenced by the type of precious metal and reducing agent. Using CO as the reductant results in a lower NO X reduction capacity for Pt/BaCO 3/Al 2O 3 compared with Pd- and Rh-based samples, whereas H 2 shows a significant ability to reduce the stored NO X on all samples examined. In addition, the reduction with CO and C 3H 6 proceeds via the formation of isocyanate species over both barium and alumina sites. The intensity of barium-isocyanate species for Pt/BaCO 3/Al 2O 3 is significantly lower than the corresponding intensity for the Pd- and Rh-based samples, suggesting that the interaction between barium and Pt is lower than the corresponding interaction in the Pd/BaCO 3/Al 2O 3 and Rh/BaCO 3/Al 2O 3 samples.