Engine control method having an exhaust system comprising two NOx-catalysts in series

An automotive piston engine has an exhaust gas system with first and second NOx storage catalytic converters which, prior to start up, are below an initial pre-defined threshold temperature. In the start-up process, the engine operates with a stoichiometric fuel-air ratio, accompanied by continual monitoring of the temperature in the first catalyst. When the temperature in the first NOx catalytic converter passes a second operating threshold in the first catalyst, the motor is then operated with a lean mixture. The NOx catalytic converters are regenerated when the temperature in the first converter is above the second activation temperature. Also claimed is a commensurate operating process for an automotive engine.