A system for the treatment of exhaust gases from an internal combustion engine with a combustion chamber includes an upstream DEF injector disposed to introduce DEF to the combustion chamber and a close-coupled SCR catalyst downstream of and in close-coupled relation to the internal combustion engine. Downstream of the close-coupled SCR catalyst may be a primary SCR catalyst and a primary DEF injector. The system may operate to reduce NO2 in the close-coupled SCR catalyst during low-load conditions of the internal combustion engine and reduce NO2 in the primary SCR catalyst during loaded conditions.