Apparatus for purifying exhaust gas

An apparatus for purifying an exhaust gas, comprising:

• a catalytic converter disposed on an exhaust pipe and including a lean NOx trap (LNT) device in which a first LNT catalyst is coated and a catalyzed particulate filter (CPF) in which a second LNT catalyst is coated, the LNT device and the CPF being sequentially disposed in the catalytic converter;
• and
• a controller determining or detecting an inlet lambda of the LNT device, an outlet lambda of the LNT device, and an outlet lambda of the CPF, determining or detecting a temperature of the LNT device and a temperature of the CPF, determining nitrogen oxide (NOx) amounts absorbed in the LNT device and the CPF, and controlling regeneration of the LNT device and the CPF,
• wherein the controller performs the regeneration of the LNT device and the CPF according to the temperature of the LNT device and the temperature of the CPF when the NOx amount absorbed in the LNT device is greater than a threshold NOx amount, and
• the controller performs regeneration of both of the LNT device and the CPF when the temperature of the LNT device is higher than a first predetermined temperature and the temperature of the CPF is higher than a second predetermined temperature.