Abatement of NOx from Diesel Engines:Status and Technical Challenges

The technical issues related to NO_x abatement for diesel applications are summarized. Data on improved catalysts and a novel approach which involves temporarily trapping of NO_x before reduction are presented. New high temperature lean NO_x materials have been identified which have better hydrothermal stability than the state of the art Cu/ZSM-5. One of these materials, Catalyst A, was shown to reduce the NO_x emitted from a 2.5 L diesel engine at temperatures ≥ 350°C using injected diesel fuel as a reductant. Catalyst A also showed reasonably good durability after aging for 500 h at ca. 500°C on a 14 L diesel truck engine. Pt/Al₂O₃, a low temperature lean NO_x reduction catalyst (200-300°C), demonstrated fairly good performance after 125 h of aging on a 4 L diesel truck engine, however sulfate make and N₂O formation are high on this material. New low temperature NO_x traps show promise for transient removal of NO_x below 200-400°C.