Exhaust purification device of internal combustion engine

Abstract

In an exhaust purification device of an internal combustion engine, a pair of upstream side NO x storage catalysts storing NO x contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean and releasing the stored NO x when the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or rich are arranged inside an engine exhaust passage. At the downstream side of the upstream side NO x storage catalysts, a downstream side NO x storage catalyst is arranged. The upstream side NO x storage catalysts and downstream side NO x storage catalyst are formed so that the spatial velocity in the downstream side NO x storage catalyst becomes larger than the spatial velocities in the upstream side storage catalysts.

1 . An exhaust purification device of an internal combustion engine arranging, inside an engine exhaust passage, an NO x  storage catalyst storing NO x  contained in exhaust gas when an air-fuel ratio of an inflowing exhaust gas is lean and releasing stored NO x  when the air-fuel ratio of the exhaust gas becomes the stoichiometric air-fuel ratio or rich, wherein said NO x  storage catalyst is comprised of an upstream side NO x  storage catalyst and a downstream side NO x  storage catalyst arranged at a downstream side from a downstream end of said upstream side NO x  storage catalyst across an exhaust passage space and wherein the upstream side NO x  storage catalyst and the downstream side NO x  storage catalyst are formed so that a spatial velocity in the downstream side NO x  storage catalyst becomes larger than a spatial velocity in the upstream side storage catalyst. 
     
     
         2 . An exhaust purification device of an internal combustion engine as claimed in  claim 1 , wherein said upstream side NO x  storage catalyst is comprised of a plurality of NO x  storage catalysts arranged in parallel, and said downstream side NO x  storage catalyst is comprised of at least one NO x  storage catalyst. 
     
     
         3 . An exhaust purification device of an internal combustion engine as claimed in  claim 2 , wherein said upstream side NO x  storage catalyst is compared of a pair of NO x  storage catalysts arranged in parallel, and said downstream side NO x  storage catalyst is comprised of one NO x  storage catalyst. 
     
     
         4 . An exhaust purification device of an internal combustion engine as claimed in  claim 1 , wherein said upstream side NO x  storage catalyst has a total cross-sectional area larger than a total cross-sectional area of said downstream side NO x  storage catalyst. 
     
     
         5 . An exhaust purification device of an internal combustion engine as claimed in  claim 1 , wherein said upstream side NO x  storage catalyst has a catalyst surface area per unit volume larger than a catalyst surface area per unit volume of said downstream side NO x  storage catalyst. 
     
     
         6 . An exhaust purification device of an internal combustion engine as claimed in  claim 5 , wherein said upstream side NO x  storage catalyst and said downstream side NO x  storage catalyst respectively have plurality of cells extending in a flow direction of the exhaust gas and wherein the upstream side NO x  storage catalyst has a number of cells per unit cross-sectional area larger than a number of cells per unit cross-sectional area of the downstream side NO x  storage catalyst. 
     
     
         7 . An exhaust purification device of an internal combustion engine as claimed in  claim 1 , wherein said upstream side NO x  storage catalyst and said downstream side NO x  storage catalyst carry a precious metal catalyst and an NO x  absorbent and wherein said downstream side NO x  storage catalyst has a basicity weaker than said upstream side NO x  storage catalyst. 
     
     
         8 . An exhaust purification device of an internal combustion engine as claimed in  claim 7 , wherein said downstream side NO x  storage catalyst has an amount of NO x  absorbent smaller than the amount of NO x  absorbent of said upstream side NO x  storage catalyst. 
     
     
         9 . An exhaust purification device of an internal combustion engine as claimed in  claim 7 , wherein as the NO x  absorbent of said downstream side NO x  storage catalyst, an ingredient weaker in basicity than the NO x  absorbent of said upstream side NO x  storage catalyst is used. 
     
     
         10 . An exhaust purification device of an internal combustion engine as claimed in  claim 7 , wherein as said precious metal catalyst, platinum Pt is used, while as the ingredient forming the NO x  absorbent, at least one element selected from potassium K, sodium Na, cesium Cs, or other alkali metal, barium Ba, calcium Ca, or other alkali earth, and lanthanum La, yttrium Y, or other rare earth is used.