Exhaust after treatment system

Abstract

A selective catalytic reduction system for reducing oxides of nitrogen in the exhaust gas flow of an internal combustion engine is disclosed. The system has a ceramic monolith disposed within said exhaust gas flow and includes exhaust flow passages extending therethrough. A high temperature selective catalytic reduction catalyst composition is applied to an inlet portion of the exhaust flow passages and a low temperature selective catalytic reduction catalyst composition applied to an outlet portion of the exhaust flow passages. The high and the low temperature catalytic reduction catalysts are operable to reduce oxides of nitrogen at high load and low load operation of the internal combustion engine.

1 . A selective catalytic reduction system for reducing oxides of nitrogen (“NO X ”) in the exhaust gas of an internal combustion engine comprising:
 a ceramic monolith disposed within the exhaust gas and having exhaust flow passages extending therethrough defined by longitudinally extending walls therebetween;   a high temperature catalyst composition for high temperature catalytic reduction applied to an inlet portion of the exhaust flow passages;   a low temperature catalyst composition for low temperature catalytic reduction applied to an outlet portion of the exhaust flow passages; and   the high temperature and the low temperature catalytic reduction catalysts operable to reduce oxides of nitrogen at high load and low load operation of the internal combustion engine.   
     
     
         2 . The selective catalytic reduction system of  claim 1 , wherein the internal combustion engine is a diesel engine. 
     
     
         3 . The selective catalytic reduction system of  claim 1 , wherein the internal combustion engine is a gasoline engine. 
     
     
         4 . The selective catalytic reduction system of  claim 2 , wherein the ceramic monolith is a wall flow ceramic monolith, the longitudinally extending passages including inlet passages having an open inlet end and a closed outlet end and outlet passages having a closed inlet end and an open outlet end wherein the exhaust gas enters the wall flow monolith through the inlet end of the passages, and migrates through the longitudinally extending walls to the outlet passages. 
     
     
         5 . The selective catalyst reduction system of  claim 4  wherein the high temperature catalyst composition for high temperature catalytic reduction is applied to the longitudinally extending walls of the inlet passages and the low temperature catalyst composition for low temperature catalytic reduction is applied to the longitudinally extending walls of the outlet passages. 
     
     
         6 . The selective catalyst reduction system of  claim 1 , the high temperature catalyst composition for high temperature catalytic reduction comprising a zeolite and a first base metal component and the low temperature catalyst composition for low temperature catalytic reduction comprising a zeolite and a second base metal component. 
     
     
         7 . The selective catalyst reduction system of  claim 6 , the first base metal component comprising iron. 
     
     
         8 . The selective catalyst reduction system of  claim 6 , the second base metal component comprising copper. 
     
     
         9 . The selective catalyst reduction system of  claim 1  wherein the loading of the first and the second catalyst compositions may be varied along the axial length of the ceramic monolith resulting in a relatively uniform catalyst loading along the length of the monolith. 
     
     
         10 . A selective catalytic reduction system for reducing oxides of nitrogen (“NO X ”) in the exhaust gas flow of an internal combustion engine comprising:
 a ceramic wall flow monolith disposed within the exhaust gas flow;   exhaust flow passages extending through the ceramic wall flow monolith and defined by longitudinally extending walls therebetween;   the exhaust flow passages including inlet passages having an open inlet end and a closed outlet end and outlet passages having a closed inlet end and an open outlet end; wherein the exhaust gas enters the ceramic wall flow monolith through the inlet end of the passages inlet passages and migrates through the longitudinally extending walls to the outlet passages;   a high temperature catalyst composition for high temperature catalytic reduction, applied to an inlet portion of the exhaust flow passages;   a low temperature catalyst composition for low temperature catalytic reduction applied to an outlet portion of the exhaust flow passages; and   the high temperature and the low temperature catalytic reduction catalysts operable to reduce oxides of nitrogen at high load and low load operation of the internal combustion engine.   
     
     
         11 . The selective catalytic reduction system of  claim 10 , wherein the internal combustion engine is a diesel engine. 
     
     
         12 . The selective catalytic reduction system of  claim 10 , wherein the internal combustion engine is a gasoline engine. 
     
     
         13 . The selective catalyst reduction system of  claim 10 , wherein the catalyst composition for high temperature catalytic reduction is applied to the longitudinally extending walls of the inlet passages and the catalyst composition for low temperature catalytic reduction is applied to the longitudinally extending walls of the outlet passages. 
     
     
         14 . The selective catalyst reduction system of  claim 10 , wherein the high temperature catalyst composition for high temperature catalytic reduction comprises a zeolite and a first base metal component and the low temperature catalyst composition for low temperature catalytic reduction comprises a zeolite and a second base metal component. 
     
     
         15 . The selective catalyst reduction system of  claim 14 , wherein the first base metal component comprises iron. 
     
     
         16 . The selective catalyst reduction system of  claim 14 , wherein the second base metal component comprises copper. 
     
     
         15 . The selective catalyst reduction system of  claim 10  wherein the loading of the high temperature and the low temperature selective catalytic reduction catalyst compositions is varied along the axial length of the ceramic monolith resulting in a relatively uniform catalyst loading along the length of the monolith.