A method for lowering the nitrogen oxide content in the exhaust gas from an internal-combustion engine

A method for lowering the nitrogen oxide content in the exhaust gas from an internal-combustion engine 1 which can be operated alternately under lean and rich conditions, has a control unit 11 and has an exhaust pipe 2, in which a starting catalytic converter 3, a nitrogen oxide storage catalytic converter 4 and an SCR catalytic converter 5 are arranged one behind the other as seen in the direction of flow, and with recurring nitrate regeneration phases for regeneration of the nitrogen oxide storage catalytic converter 4. The NH3 loading of the SCR catalytic converter is determined by the control unit 11, and the formation of nitrogen oxides by the internal-combustion engine 1 is increased at least within the nitrate regeneration phases, the SCR catalytic converter 5 in the exhaust pipe 2 being arranged at least sufficiently far downstream of the nitrogen oxide storage catalytic converter 4 for a temperature which is approximately 50{C to approximately 150{C lower than at the entry to the nitrogen oxide storage catalytic converter 4 to be established at the entry to the SCR catalytic converter 5 in most of the intended operating range of the internal-combustion engine 1.