Patent attributes
An exhaust system (10) for a lean-burn internal combustion engine comprises a nitrogen oxide (NOx) absorbent (28), a catalyst (30) for catalyzing the selective catalytic reduction (SCR) of a NOx with a NOx specific reactant, first means (18, 22) for introducing a NOx specific reactant or a precursor thereof into an exhaust gas upstream of the SCR catalyst (30) and means (24) for controlling the introduction of the NOx-specific reactant or precursor thereof into the exhaust gas via the first introducing means (18, 22), wherein the SCR catalyst (30) is disposed upstream of the NOx absorbent (28) and optionally with the NOx absorbent, wherein the control means (24) is arranged to introduce the NOx-specific reactant or the precursor thereof to exhaust gas via the first introducing means (18, 22) only when the SCR catalyst (30) is active, whereby exhaustion of NOx-specific reactant to atmosphere is substantially prevented.
