Removing nitrogen oxides during a lean-burn engine cold start

22 2 An apparatus and a method for removing NOx from an exhaust stream of a lean-burn engine during an engine cold start are provided. The apparatus includes a close-coupled LNT coupled to a main LNT by a hollow conduit. NOx from the cold exhaust is initially stored on the close-coupled LNT. As the engine exhaust warms up, the close-coupled LNT reaches its operating temperature and reduces the stored NOx to N. When the temperature of the close-coupled LNT reaches approximately 350° C., NOx is released from the close-coupled LNT, is absorbed on the main LNT, and is converted to Nduring fuel-rich conditions, The close-coupled LNT can be regenerated after the engine is turned off by providing heat. The released NOx during the regeneration of the closed-coupled LNT is absorbed by the main LNT. The stored NOx on the main LNT can be reduced to Nduring the next vehicle operation.