Exhaust emission control apparatus for internal combustion engine

Abstract

An exhaust emission control apparatus that is used with an internal combustion engine to use both a NOx retention member and a catalyst while avoiding a decrease in the exhaust gas purification capacity. A NOx occlusion reduction type catalyst is placed in an exhaust path of an internal combustion engine. The NOx occlusion reduction type catalyst includes a base material. The base material includes an exhaust inflow cell, which is closed at its downstream side; and an exhaust outflow cell, which is closed at its upstream side and is adjacent to the first cell with the partition wall positioned in between. The exhaust inflow cell is configured so that a NOx retention layer is formed on the inner surface thereof, and the exhaust outflow cell is configured so that a catalyst layer is formed on the inner surface thereof, respectively.

1 . An exhaust emission control apparatus for an internal combustion engine, comprising:
 a NOx occlusion reduction type catalyst, which is positioned in an exhaust path of the internal combustion engine; and   ozone supply means, which supplies ozone so that the ozone mixes with an exhaust gas flowing into the NOx occlusion reduction type catalyst; wherein   the NOx occlusion reduction type catalyst includes two or more cells, which are partitioned by a partition wall that permits the passage of the exhaust gas,   the two or more cells including a first cell configured so that a downstream side of the first cell is covered and a NOx retention layer containing a NOx retention member is formed on an inner surface of the first cell; and a second cell configured so that the second cell is adjacent to the first cell with the partition wall positioned in between, an upstream side of the second cell is covered, a catalyst layer including a noble metal is formed on an inner surface of the second cell, and an amount of the NOx retention member contained in the catalyst layer is smaller than that in the NOx retention layer.   
     
     
         2 . The exhaust emission control apparatus according to  claim 1 , wherein the partition wall, which permits the passage of the exhaust gas, is a particulate filter for capturing particulates contained in the exhaust gas. 
     
     
         3 . The exhaust emission control apparatus according to  claim 1 , wherein the catalyst layer formed on the inner surface of the second cell is configured so that the amount of the NOx retention member contained in the catalyst layer is substantially zero. 
     
     
         4 . The exhaust emission control apparatus according to  claim 1 , further comprising:
 ozone supply amount adjustment means for adjusting the amount of ozone supply so that the mole ratio of ozone to nitrogen monoxide (NO) in a gas mixture flowing into the NOx occlusion reduction type catalyst is greater than 1.   
     
     
         5 . The exhaust emission control apparatus according to  claim 4 , wherein the ozone supply amount adjustment means adjusts the amount of ozone supply so that the mole ratio of ozone (O 3 ) to nitrogen monoxide (NO) in the gas mixture flowing into the NOx occlusion reduction type catalyst is not smaller than 2. 
     
     
         6 . An exhaust emission control apparatus for an internal combustion engine, comprising:
 a NOx occlusion reduction type catalyst, which is positioned in an exhaust path of the internal combustion engine; and   an ozone supply unit, which supplies ozone so that the ozone mixes with an exhaust gas flowing into the NOx occlusion reduction type catalyst; wherein   the NOx occlusion reduction type catalyst includes two or more cells, which are partitioned by a partition wall that permits the passage of the exhaust gas,   the two or more cells including a first cell configured so that a downstream side of the first cell is covered and a NOx retention layer containing a NOx retention member is formed on an inner surface of the first cell; and a second cell configured so that the second cell is adjacent to the first cell with the partition wall positioned in between, an upstream side of the second cell is covered, a catalyst layer including a noble metal is formed on an inner surface of the second cell, and an amount of the NOx retention member contained in the catalyst layer is smaller than that in the NOx retention layer.