Method and apparatus to for regeneration of an NOx storage catalyst

Regenerating a nitrogen oxides (NOx) storage catalyst (16) in the exhaust gas pipe (12) of an IC engine comprises regenerating in a first phase with the addition of a reductant stream determined by a modeled catalyst condition before introducing the regeneration. Regenerating a nitrogen oxides (NOx) storage catalyst (16) in the exhaust gas pipe (12) of an IC engine comprises regenerating in a first phase with the addition of a reductant stream determined by a modeled catalyst condition before introducing the regeneration, in which the duration of the first phase is established so that it leads to a complete regeneration; and introducing a lower reductant stream than in the first phase until the end of the regeneration is displayed by a gas-sensitive measuring device (18) downstream of the NOx storage catalyst. An Independent claim is also included for a device for regenerating a NOx storage catalyst in the exhaust gas pipe of an IC engine. Preferred Features: Control or regulation of the reductant streams is carried out during regeneration based on a lambda value measured upstream of the NOx storage catalyst. The exhaust gas has a lambda value of 0.7-0.95, especially 0.75-0.9 during the first phase, and a lambda value of 0.8-1.0, especially 0.9-0.97 during the second phase.