Process for regenerating a nitrogen oxides storage catalyst

A process for regeneration of a nitrogen oxide storage catalyst having nitrogen oxides stored during a storage phase, wherein during said regeneration the stored nitrogen oxides are released and converted to nitrogen, said process comprising:

• (a) applying a first regeneration strategy when an exhaust gas temperature is above a threshold temperature, wherein said first regeneration strategy comprises changing a lean air/fuel-ratio to a rich air/fuel-ratio during a first regeneration period;
• and
• (b) applying a second regeneration strategy when the exhaust gas temperature is below said threshold temperature, wherein said second regeneration strategy comprises switching the air/fuel-ratio between a lean air/fuel-ratio and a rich air/fuel-ratio back and forth forming a sequence of rich pulses and lean pulses, and said sequence has between 2 and 10 rich pulses and between 2 and 10 lean pulses during a second regeneration period, wherein the threshold temperature is between 170° C. and 250° C.