Effects of Lean/Rich Timing and Nature of Reductant on the Performance of a NOx Trap Catalyst

A NOx trap catalyst was studied in a laboratory reactor under simulated diesel passenger car conditions. The effects of lean/rich duration and the nature of reductant are investigated. At 300°C, the average NOx conversion decreases with increasing lean duration; conversely the NOx conversion increases with increasing rich duration. The NOx conversion at this temperature was found to be a direct function of reaction stoichiometry. That is, the quantity of trapped NOx under lean conditions must be balanced by the quantity of reductant during the rich trap regeneration step. At extreme temperatures, other factors, reaction kinetics (at lower temperatures) and NOx storage capacity (at higher temperatures), dominate the NOx conversion process. Overall, carbon monoxide was found to be the most effective reductant. Hydrocarbon, e.g., C3H6, is effective at higher temperatures (T>350°C), while H2 is more efficient than other reductants at low temperatures (T<200°C). The individual steps of the NOx conversion process are discussed.