Particulate Filter Regeneration and NOx Catalyst Re-Activation

A system having an engine with an emission control system, comprising:

• a lean NOx trap;
• a particulate filter coupled downstream of the lean NOx trap,
• a control system for:
• during a first operating mode, after lean exhaust gas air-fuel ratio regeneration of the particulate filter at an elevated regeneration temperature, providing a rich or intermittently rich exhaust air-fuel ratio for a duration lasting until LNT temperature falls to a minimum threshold, where said rich or intermittently rich operation reactivates catalytic materials in the LNT and reverses deactivation caused by the elevated temperature lean operation associated with previous particulate filter regeneration;
• during a second operating mode, after lean exhaust gas air-fuel ratio regeneration of the particulate filter at said elevated regeneration temperature, continuing lean operation based on operating conditions;
• and
• selecting between the first and second operating mode based on temperature reached during the particulate filter regeneration and a duration of the particulate filter regeneration