Exhaust purification system of internal combustion engine

Abstract

An exhaust purification system of an internal combustion engine comprising an NO X holding material arranged in an engine exhaust passage, having a catalyst metal containing silver, holding NO X contained in the exhaust gas in the form of silver nitrate by the catalyst metal when an air-fuel ratio of inflowing exhaust gas is lean, and releasing the held NO X if the air-fuel ratio of the inflowing exhaust gas becomes a stoichiometric air-fuel ratio or rich. The NO X holding material has a scatter temperature at which catalyst metal scatters in the form of silver nitrate if the temperature rises. When it is time to perform control raising the temperature of the NO holding material to the scatter temperature or above, the NO X held in the NO X holding material is released by making the air-fuel ratio of the exhaust gas flowing into the NO holding material the stoichiometric air-fuel ratio or rich.

1 . An exhaust purification system of an internal combustion engine comprising an NO X  holding material arranged in an engine exhaust passage, having a catalyst metal containing silver, holding NO X  contained in the exhaust gas in the form of silver nitrate at the catalyst metal when an air-fuel ratio of inflowing exhaust gas is lean, and releasing the held NO X  if the air-fuel ratio of the inflowing exhaust gas becomes a stoichiometric air-fuel ratio or rich,
 wherein said NO X  holding material has a scatter temperature at which catalyst metal scatters in the form of silver nitrate if the temperature rises,   when it is time to perform control to raise the temperature of the NO X  holding material to the scatter temperature or above, the system makes the air-fuel ratio of the exhaust gas flowing into the NO X  holding material a stoichiometric air-fuel ratio or rich to thereby make the NO X  holding material release the held NO X .   
     
     
         2 . An exhaust purification system of an internal combustion engine as set forth in  claim 1 , further comprising an NO X  storage reduction catalyst arranged in the engine exhaust passage downstream of the NO X  holding material, including a catalyst metal and an NO X  absorbent holding NO X , holding the NO X  contained in the exhaust gas at the NO X  absorbent when the air-fuel ratio of the inflowing exhaust gas is lean, and releasing the held NO X  when the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or rich,
 wherein the NO X  storage reduction catalyst holds SO X  besides NO X , and, when it is time to perform sulfur poisoning recovery control raising the temperature of the NO X  storage reduction catalyst to an SO X  releasable temperature and making the air-fuel ratio of the exhaust gas flowing into the NO X  storage reduction catalyst the stoichiometric air-fuel ratio or rich so as to release the SO X , the NO X  holding material is made to release the held NO X .   
     
     
         3 . An exhaust purification system of an internal combustion engine as set forth in  claim 1 , further comprising a particulate filter arranged in the engine exhaust passage and trapping particulate matter contained in the exhaust gas,
 wherein when it is time to perform regeneration control raising the temperature of the particulate filter to the temperature where the trapped particulate matter burns, the NO X  holding material is made to release the held NO X .   
     
     
         4 . An exhaust purification system of an internal combustion engine as set forth in  claim 1 , performing control estimating the amount of catalyst metal remaining at the NO X  holding material when catalyst metal scatters from the NO X  holding material, and reducing the NO X  amount exhausted to the engine exhaust passage from the engine body in accordance with the drop in the amount of remaining catalyst metal. 
     
     
         5 . An exhaust purification system of an internal combustion engine as set forth in  claim 1 , performing control making the air-fuel ratio of exhaust gas flowing into the NO X  holding material the stoichiometric air-fuel ratio or rich so as to release NO X  when a held amount of NO X  of the NO X  holding material exceeds a predetermined held amount judgment value,
 estimating the amount of catalyst metal remaining at the NO X  holding material when the catalyst metal scatters from the NO X  holding material, and decreasing the held amount judgment value in accordance with the drop in the amount of remaining catalyst metal.   
     
     
         6 . An exhaust purification system of an internal combustion engine as set forth in  claim 1 , further comprising an NO X  selective reducing catalyst arranged in the engine exhaust passage downstream of the NO X  holding material and selectively reducing NO X  by feeding a reducing agent,
 estimating the amount of catalyst metal remaining at the NO X  holding material when catalyst metal scatters from the NO X  holding material, and increasing the feed amount of reducing agent to the NO X  selective reducing catalyst in accordance with the drop in the amount of remaining catalyst metal.   
     
     
         7 . An exhaust purification system of an internal combustion engine as set forth in  claim 1 , estimating the amount of catalyst metal remaining at the NO X  holding material when catalyst metal scatters from the NO X  holding material, and estimating the NO X  amount flowing out from the NO X  holding material based on the remaining amount of catalyst metal.