Patent ID: 7178331

Claim:
An exhaust system for a lean-burn internal combustion engine, comprising: a nitrogen oxide (NO x ) absorbent; a first catalyst for catalysing the selective catalytic reduction (SCR) of NO x with a NO x -specific reactant disposed upstream of the NO x absorbent; first means for introducing a NO x -specific reactant, or a precursor thereof, into an exhaust gas upstream of the first catalyst; and means for controlling the introduction of the NO x -specific reactant, or the precursor thereof, into the exhaust gas via the first introducing means, wherein the means for controlling: (a) causes the introduction of a first amount of NO x -specific reactant, or the precursor thereof, to contact the NO x absorbent insufficient to completely reduce the total NO x stored on the NO x absorbent when the first catalyst is inactive for reducing NO x to N 2 ; and (b) causes the introduction of a second amount of NO x -specific reactant, or the precursor thereof, to contact the first catalyst when the first catalyst is active for reducing NO x to N 2 , wherein the second amount of NO x -specific reactant is of a sufficient amount such that NO x -specific reactant slips the first catalyst and contacts the NO x absorbent to reduce the NO x stored on the NO x absorbent and regenerate the NO x absorbent.