An exhaust system for treating an exhaust gas produced by a lean burn engine comprising: (i) a NOx absorber catalyst comprising a molecular sieve catalyst disposed on a substrate, wherein the molecular sieve catalyst comprises a noble metal and a molecular sieve, wherein the molecular sieve contains the noble metal; (ii) means for introducing hydrocarbons into the exhaust gas; and (iii) a lean NOx trap; wherein the NOx absorber catalyst is upstream of both the means for introducing hydrocarbons into the exhaust gas and the lean NOx trap.