Patent ID: 8763373

Claim:
A system for purifying an exhaust gas, comprising: a lean NOx trap (LNT) catalyst adapted to absorb nitrogen oxides contained in the exhaust gas at a lean atmosphere, release the absorbed nitrogen oxides at a rich atmosphere, and reduce or slip the released nitrogen oxides according to a temperature thereof; a particulate filter adapted to trap particulate matters contained in the exhaust gas and regenerate the trapped particulate matters by slipped from the LNT catalyst; and a controller adapted to selectively create the rich atmosphere when the temperature of the LNT catalyst is higher than or equal to a first predetermined temperature or a temperature of the particulate filter is higher than or equal to a second predetermined temperature; wherein the LNT catalyst is adapted to absorb the nitrogen oxides contained in the exhaust gas as nitrates and to release the absorbed nitrogen oxides as nitrogen dioxides (NO 2 ); and wherein the nitrogen dioxides (NO 2 ) released from the LNT catalyst are slipped in a case that the temperature of the LNT catalyst is lower than the first predetermined temperature.