An exhaust system for an internal combustion engine comprises an exhaust gas recirculation (EGR) circuit 12, 14 that connects an exhaust stream to an intake of the engine. A surface 18 of a heat exchanger 10 in the EGR circuit comprises a urea hydrolysis catalyst. A urea injector 16 provides urea to the surface of the urea hydrolysis catalyst. The resulting ammonia 20 is introduced to the exhaust stream. The EGR circuit may be low pressure or high pressure. The ammonia may be introduced upstream of a selective catalytic reduction (SCR) catalyst, which may be loaded on the same substrate as a downstream ammonia oxidation catalyst. There may be a particulate filter. A surface of the heat exchanger that is contacted by the exhaust stream may be catalytically coated to discourage soot accumulation. A lean burn internal combustion engine, i.e. a compression ignition engine, comprises the exhaust system. The heat from the EGR circuit assists the conversion of urea to ammonia.
