The Desulfation Characteristics of Lean NOx Traps 2002-01-0733
This paper summarizes results from a large study on the desulfation characteristics of lean NOx traps. Degreened and thermally aged NOx trap formulations were poisoned with SO2 multiple times in a flow reactor. The effect of desulfation time and temperature on the recovery of NOx trapping efficiency was evaluated after the poisonings. The relative effectiveness of the reducing agents (CO and H2) used during the desulfation was evaluated for one of the formulations.
The results indicate that the high temperatures required for desulfation (e.g., 700°C and above) result in thermal degradation of NOx traps that had been degreened at a lower temperature (e.g., 600°C), and therefore desulfation studies should be performed with traps that have already been exposed to the desulfation temperatures or higher prior to the poisoning. NOx trap formulations can differ in their desulfation characteristics, as two of the formulations studied could be desulfated effectively at 725°C, whereas the third formulation was more difficult to desulfate and required a desulfation temperature near 750°C. The results indicate that hydrogen is the more effective desulfation agent, as higher levels of H2 in the feedgas or additional H2 produced by the water-gas-shift reaction resulted in improved NOx trapping efficiency following the desulfation.