Exhaust gas aftertreatment system with two SCR catalysts

An exhaust gas aftertreatment system for an internal combustion engine of a vehicle, the exhaust gas aftertreatment system comprising:

• an exhaust gas line;
• a main SCR catalyst;
• a diesel particulate filter arranged upstream of the main SCR catalyst;
• a first reducing agent injector associated with the main SCR catalyst;
• a close-coupled SCR catalyst;
• a second reducing agent injector associated with the close-coupled SCR catalyst;
• a sensor arrangement;
• and
• a control unit configured to detect sensor signals from the sensor arrangement to control components of the exhaust gas aftertreatment system and to determine an efficiency of the main SCR catalyst and an efficiency of the close-coupled SCR catalyst,
• wherein the control unit is configured to:
• determine the efficiency of the main SCR catalyst and the efficiency of the close-coupled SCR catalyst based on the sensor signals of the sensor arrangement,
• operate the main SCR catalyst at a highest possible efficiency to minimize emissions, and
• modulate the efficiency of the close-coupled SCR catalyst as a function of the efficiency of the main SCR catalyst to further reduce the emissions.