Lean burn engines, such as diesel and lean burn gasoline engines, offer significant fuel economy benefits and reduced CO₂ emission. A major challenge with these types of engines is the difficulty of dealing with NO_x emissions. Under lean conditions, the currently used three-way emissions catalyst (TWC) is not effective in eliminating NO_x. Lean NO_x trap (LNT) catalysts provide one of the promising options to reduce lean NO_x for lean burn gasoline engines, with the engine working under so-called lean-rich repeatable operation cycles. Typical cycles consist of a longer lean period where NO is oxidized to NO₂ and then NO₂ is captured by BaO forming barium nitrate, followed by a shorter rich period where the trapped NO_x is released and then reduced by Pt.

Therefore, effective NO_x storage is critical to practical application of LNTs because the storage capacity determines the fraction of time an engine can be operated in the more fuel-efficient lean mode. Collaborating with Ford, we found that thermal gravimetric analysis (TGA) coupled with FT-IR can be effectively used to quantify highly dispersed and bulk-like BaO supported on Al₂O₃. The results are useful for optimizing BaO loading strategies for LNT catalysts.

Steam generated during fuel combustion is one of the major components in automotive emissions. While steam effects have been widely investigated for TWC catalysts, less is known about how steam effects NO_x reduction over LNT catalysts. Therefore, we are studying this steam effect under lean-rich cyclic operations in collaboration with General Motors. Of special interest is the generation of NH₃ over Pt-BaO/Al₂O₃ under steam during the rich cycle. A method has been established using a dual-bed reactor system containing a zeolite catalyst down-stream of the LNT bed. The zeolite traps NH₃ generated during the rich cycle. It also serves as selective catalytic reduction (SCR) catalyst to eliminate lean NO_x by using desorbed NH₃ as reductant when the rich cycle is switched to the lean cycle.