NOX storage/reduction catalyst performance with oxygen in the regeneration phase

NOX storage/reduction (NSR) catalysts operate over a cycle where the catalyst is periodically regenerated with a reductant-rich gas mixture. In this study, the effects of including O2 during this regeneration phase on the performance, NOX reduction to N2, of a model NSR catalyst and a commercial NSR catalyst were investigated. The increased temperature associated with reductant oxidation when oxygen was available resulted in improved performance at temperatures below 375 °C for the model sample, but resulted in decreased performance at higher test temperatures. The improved performance primarily originated from increased trapping in the subsequent lean phase but was also improved by decreased byproduct formation during the rich phase under some conditions. The improved performance measure is based on an increase in the lean-phase time before a regeneration phase would need to be triggered, with the increase on the order of 10 s for 288 and 375 °C operating temperatures. The decreased trapping performance at higher temperatures is due to decreased nitrate stability, while the increased trapping performance at lower temperature is due to improved oxidation kinetics. Similar effects were observed with the commercial sample, although the presence of surface oxygen storage resulted in an already significant temperature increase with no O2 added in the regeneration gas composition. The results demonstrate that the time between regenerations can be increased significantly by tuning or optimizing the amount of reductant and oxygen added during the regeneration phase.