Comparison of different kinetic models for NOX storage on a lean NOX trap

• Published in: Canadian journal of chemical engineering 2014-09, Vol.92 (9), p.1506-1516
• Main Authors: Watling, Timothy C., Bolton, Paul D., Swallow, Daniel
• Format: Article
• Language: English
• Subjects: aftertreatment; computer simulation; lean NOX trap (LNT); NOX storage; vehicle exhaust
• ISSN: 0008-4034; 1939-019X
• DOI: 10.1002/cjce.22015

The kinetics of NOX storage on a lean NOX trap (LNT) were studied using NOX breakthrough curves measured with a laboratory reactor. A much wider range of temperatures (125–450°C) was used than in most studies to facilitate discrimination between potential models. The breakthrough curves were run until the LNT was saturated to (i) enable NO oxidation to NO2 to be studied in the absence of NOX storage, (ii) to enable the effective NOX capacity as a function of temperature to be determined, and (iii) to provide a more demanding test for potential models. Breakthrough curves for 125 and 450°C were very similar, while curves at intermediate temperatures initially followed that for 125°C before breaking away from this curve at a point that became earlier with increasing temperature. Thus, the breakthrough curves have a temperature independent initial portion, followed by a temperature dependant portion. This was explained by there being two types of site: fast sites and slow sites. Fast sites are responsible for the initial part of the curve; both the rate of storage on these sites and the available capacity are independent of temperature. The rate of storage on slow sites, on the other hand, is temperature dependant, as is the available storage capacity. Slow sites are more abundant than fast sites. The performance of three NOX storage models for these sites was compared. The amount of NOX stored as a function of temperature was bell‐shaped. The models naturally predicted that storage was limited by kinetics at lower temperatures and nitrate stability at higher temperatures.