Exhaust emission control apparatus for internal combustion engine

Abstract

An exhaust emission control apparatus that is used with an internal combustion engine to occlude and reduce NOx without blocking the exhaust gas purification function of a catalyst. An NOx occlusion reduction type catalyst and ozone supply device are provided in an exhaust path of the internal combustion engine. The NOx occlusion reduction type catalyst includes a cell into which an exhaust gas flows. An inner surface of the cell is coated with a NOx retention layer and a catalyst layer so that the NOx retention layer and the catalyst layer are provided in the order named from the inner surface of the cell.

1 : An exhaust emission control apparatus for an internal combustion engine, comprising:
 an 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 a cell in which the exhaust gas flows, an inner surface of the cell being coated with a first layer and a second layer, the first layer and the second layer being provided in the order named from the inner surface of the cell, the first layer containing an NOx retention substance, the second layer including a noble metal and permitting the passage of NOx, the amount of the NOx retention substance in the second layer is smaller than that in the first layer.   
   
   
       2 : The exhaust emission control apparatus according to  claim 1 , wherein the amount of the NOx retention substance contained in the second layer is substantially zero. 
   
   
       3 : The exhaust emission control apparatus according to  claim 1 , further comprising:
 ozone supply amount adjustment means for adjusting an ozone supply amount 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.   
   
   
       4 : The exhaust emission control apparatus according to  claim 3 , wherein the ozone supply amount adjustment means adjusts the ozone supply amount 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. 
   
   
       5 : An exhaust emission control apparatus for an internal combustion engine, comprising:
 an 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 a cell in which the exhaust gas flows, an inner surface of the cell being coated with a first layer and a second layer, the first layer containing an NOx retention substance, the second layer including a noble metal and permitting the passage of NOx, the amount of the NOx retention substance in the second layer is smaller than that in the first layer, and the first layer and the second layer being provided in the order named from the inner surface of the cell.