Patent attributes
An exhaust aftertreatment system including a lean NOx trap, an ammonia-SCR catalyst, and an additional catalyst configured in between. The lean NOx trap adsorbs NOx from lean exhaust and produces ammonia during regeneration. The SCR catalyst adsorbs most of that ammonia and subsequently uses that ammonia to reduce NOx. The additional catalyst is adapted to reduce the concentration of hydrocarbons in the exhaust during LNT regeneration and thereby mitigate hydrocarbon poisoning of the SCR. In one embodiment, the additional catalyst is a hydrocarbon-SCR catalyst. In another embodiment, the additional catalyst is an oxidation Catalyst. In a further embodiment, the additional catalyst is a hydrocarbon adsorbent. An oxidation catalyst can be made to store oxygen for hydrocarbon oxidation while avoiding excessive oxidation of ammonia by appropriately limiting that oxygen storage capacity.
