The Feasibility of an Alumina-Based Lean NOx Trap (LNT) for Diesel and HCCI Applications

An alumina-based LNT is being developed through laboratory studies, for diesel vehicle applications. This LNT provides high NOx conversion efficiency at low temperature (150 to 350°C, especially below 200°C), which is very important for the exhaust-gas after-treatment of diesel passenger vehicles. Addition of 2 to 4 wt% of alkaline-earth metal oxide or other metal oxides to the alumina LNT formulation improves NOx reduction activity at the high end of its active temperature window. More significantly, the alumina-based LNT can undergo the de-SOx process (the process of removing sulfur from the catalytic surfaces) very efficiently: within 1 minute at the relatively low temperature of 500 to 650°C under slightly rich conditions (λ = 0.98 to 0.987). Such a mild de-SOx process imposes minimal thermal exposure, causing almost no thermal damage to the LNT, and helps minimize the associated fuel penalty. The alumina-based LNT could thus provide a solution to the current LNT durability issue caused by sulfur poisoning and the need to aggressively de-SOx at high temperature. Possible applications of the alumina-based LNT for diesel and HCCI were studied in the laboratory. A multiple (staged) alumina-based LNT system was tested in the lab that provides high NOx reduction activity over a wide temperature range (150 to 550°C) and still maintains the unique efficient de-SOx process of the alumina-based LNT resulting in minimal thermal damage to the LNT. Lab results also suggest that the alumina-based LNT would work well with the catalyzed DPF (for diesel) and the TWC (for an HCCI exhaust system). Further studies, extending the laboratory experiments to engine and vehicle evaluations, are needed to fully assess the potential of the alumina-based LNTs.