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Lean NOx Traps (LNTs) are one type of lean NOx reduction technology typically used in smaller diesel passenger cars where urea-based Selective Catalytic Reduction (SCR) systems may be difficult to package . However, the performance of lean NOx traps (LNT) at temperatures above 400 C needs to be improved. The use of Rapidly Pulsed Reductants (RPR) is a process in which hydrocarbons are injected in rapid pulses ahead of a LNT in order to expand its operating window to higher temperatures and space velocities. This approach has also been called Di-Air (diesel NOx aftertreatment by adsorbed intermediate reductants) by Toyota. There is a vast parameter space which could be explored to maximize RPR performance and reduce the fuel penalty associated with injecting hydrocarbons. In this study, the mixing uniformity of the injected pulses, the type of reductant, and the concentration of pulsed reductant in the main flow were investigated.

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.

Promising lean NOx trap (LNT) results on lean-burn gasoline engines have encouraged the development of LNTs for diesel applications. Although the fundamentals of LNT are common for both gasoline and diesel applications, there are major differences due to the character of engine operation and control strategies. The sulfur tolerance and thermal durability of current state-of-the-art diesel LNTs under the conditions that represent the thermal and chemical conditions in diesel exhaust were investigated in a laboratory flow reactor. Sulfur poisoning and thermal aging are unavoidable factors contributing to diesel LNT deactivation. The results show that sensitivity to sulfur poisoning varies with the catalyst formulations, and in some formulations the sulfur poisoning appears reversible. However, the thermal deactivation is permanent regardless of its cause, i.e., LNT de-sulfation (deSOx) or diesel particular filter (DPF) regeneration.