Regeneration of a model NOX storage/reduction catalyst using hydrocarbons as the reductant

Regeneration of a model NOX storage and reduction (NSR) catalyst using hydrocarbons, H2, or CO as reducing agents was investigated. As previously shown, at low temperature, 200 °C, H2 proved best, while both CO and hydrocarbons were found to poison Pt sites. At 250 °C, again H2 was better but the decreased performance with CO and hydrocarbons was also due to slow kinetics and not solely as a result of Pt site poisoning. At T ≥ 300 °C, hydrocarbons were found to regenerate the catalyst as efficiently as CO and H2. Hydrocarbon steam reforming experiments were performed to investigate the improved performance at T ≥ 300 °C. Steam reforming did not occur with either dodecane or m-xylene below 450 °C. Additionally, although propylene steam reforming occurred at 375 °C, the small amount of H2 formed was insufficient for steam reforming to be the sole reason for improved regeneration. TPR experiments show that propylene was activated on the catalyst at T ≥ 217 °C and, under the conditions examined, the complete reduction of NO by propylene was achieved at 287 °C. Furthermore, propylene was observed to reduce surface chemisorbed NOX species at T > 200 °C, with high rates by 264 °C, with this activity ultimately resulting in the comparable performance with either CO or H2 at similar temperatures during NOX cycling experiments.