Development of Multi-Functioning Lean NOx Trap Catalysts for the On-board NH ₃ Generation

Improved Lean NOx Trap (LNT) catalysts with enhanced NH₃ generation feature were developed for the small diesel engine. The next generation LNT system needs to perform good NOx conversions over the wide temperature range including below 200°C for urban driving and above 400°C for motorway of real road driving. However, the extended use of BaO, a component of LNT known to be very effective for high temperature NOx storage, results in the decrease of low temperature NOx conversion due to the degradation of NO oxidation associating with sulfur over time. The improvement of the low-temperature LNT performance is a key requirement for the real driving emission control as the best operation temperature for urea-SCR is above ~250°C. In this study, our next generation LNT with new washcoat architecture has demonstrated improved NOx removal efficiencies under the wider operation temperature window than the current production technology. The new LNT technology also offered an enhanced on-board NH₃ generation from the engine out and stored NOx during the fuel-rich operation while preserving its NOx reduction activity by the implement of zone and layered architecture in the LNT washcoat. In addition, platinum group metal (PGM), oxygen storage capacity (OSC) and BaO content have been optimized for each zone and layer. The multi-functioning LNT catalyst then evaluated using both simulated gas bench and engine dyno tests. The newly developed LNT with enhanced NOx reduction as well as NH₃ production performance will enable the future diesel aftertreatment systems to meet the real world driving tailpipe emission requirement.