Patent ID: 8230674

Claim:
A method for monitoring the nitrogen oxide storage capacity of a nitrogen oxide storage catalyst used as a starting catalyst in an exhaust-gas purification system of a motor vehicle with a lean-burn engine, the system including the starting catalyst and a main catalyst, which is likewise designed as a nitrogen oxide storage catalyst, the catalyst system in each case being regenerated by the engine being briefly switched from lean-burn mode to rich-burn mode when the evaluation of the nitrogen oxide slippage downstream of the catalyst system exceeds a regeneration criterion, wherein nitrogen oxide storage capacity of the starting catalyst is checked when regeneration of the catalyst system is due, by the rich-burn mode being terminated and the engine being switched back to lean-burn mode when a breakthrough of rich exhaust gas is recorded between the starting catalyst and the main catalyst, and by the time between the engine being switched back to lean-burn mode and the regeneration criterion being exceeded once again downstream of the catalyst system being measured as a measure of the nitrogen oxide storage capacity.