The effects of regeneration-phase CO and/or H-2, and their amounts as a function of temperature on the trapping and reduction of NOx over a model and a commercial NOx storage/reduction catalyst have been evaluated. Overall, for both catalysts, their NOx removal performance improved with each incremental increase in H-2 concentration. For the commercial sample, using CO at 200 degrees C, beyond a small amount added, was found to decrease performance. The addition of H-2 to the CO-containing mixtures resulted in improved performance at 200 degrees C, but the presence of the CO still resulted in decreased performance in comparison to activity when just H-2 was used. With the model sample, the presence of CO resulted in very poor performance at 200 degrees C, even with H-2. The data suggest that CO poisons Pt sites, including Pt-catalyzed nitrate decomposition. At 300 degrees C, H-2, CO, and mixtures of the two were comparable for trapping and reduction of NOx, although with the model sample H-2 did prove consistently better. With the commercial sample, H-2 and CO were again comparable at 500 degrees C, but mixtures of the two led to slightly improved performance, while yet again H-2 and H-2-containing mixtures proved better than CO when testing the model sample. NH3 formation was observed under most test conditions used. At 200 degrees C, NH3 formation increased with each increase in H-2, while at 500 degrees C, the amount of NH3 formed when using the mixtures was higher than that when using either H-2 or CO. This coincides with the improved performance observed with the mixtures when testing the commercial. (C) 2008 Elsevier B.V. All rights reserved.