Exhaust After Treatment System

Abstract

In an exemplary embodiment of the present invention, an exhaust treatment system for reducing constituents in the exhaust gas of an internal combustion engine is provided. A ceramic monolith is disposed within the exhaust treatment system and has exhaust flow passages extending therethrough that are defined by longitudinally extending walls therebetween. A first catalyst composition for catalytic reduction of oxides of nitrogen in the exhaust gas is applied to a first portion of the exhaust flow passages. A second catalyst composition for catalytic oxidation of hydrocarbons and oxides of nitrogen in the exhaust gas is applied serially downstream to a second, portion of the exhaust flow passages. The second catalytic composition is configured to reduce ammonia and hydrocarbon slip past the first catalytic composition.

1 . An exhaust gas treatment system for reducing constituents in the exhaust gas of an internal combustion engine comprising:
 a ceramic monolith disposed within the exhaust gas treatment system having exhaust flow passages extending therethrough defined by longitudinally extending walls therebetween;   a first catalyst composition, for catalytic reduction of oxides of nitrogen in the exhaust gas, applied to a first portion of the exhaust flow passages; and   a second catalyst composition, for catalytic oxidation of hydrocarbon, carbon monoxide and ammonia in the exhaust gas, separately applied, serially downstream to a second, portion of the exhaust flow passages.   
     
     
         2 . The exhaust gas treatment system of  claim 1 , wherein the ceramic monolith is a wall flow monolith filter comprising:
 longitudinally extending passages including a first subset of inlet passages having an open inlet end and a closed outlet end and a second subset of outlet passages having a closed inlet end and an open outlet end, wherein the exhaust gas enters the wall flow monolith filter through the inlet end of the passages and migrates through the longitudinally extending walls to the outlet passages to remove particulates from the exhaust gas.   
     
     
         3 . The exhaust gas treatment system of  claim 1 , wherein the first catalyst composition comprises a reduction catalyst containing zeolite and one or more base metal components and the second catalyst composition comprises an oxidation catalyst containing one or more precious group metals. 
     
     
         4 . The exhaust gas treatment system of  claim 3 , wherein the reduction catalyst base metals comprise iron, cobalt, copper, vanadium or combinations thereof. 
     
     
         5 . The exhaust gas treatment system of  claim 3 , wherein the oxidation catalyst precious group metals comprise platinum, palladium, rhodium or combinations thereof. 
     
     
         6 . An exhaust gas treatment system for reducing constituents in the exhaust gas of an internal combustion engine comprising:
 a ceramic wall flow monolith filter disposed within the exhaust gas treatment system;   exhaust flow passages extending through the ceramic wall flow monolith filter defined by longitudinally extending walls therebetween;   a first subset of exhaust flow passages having an open inlet end and a closed outlet end defining inlet passages;   a second subset of exhaust flow passages having a closed inlet end and an open outlet end defining outlet passages, wherein exhaust gas enters the ceramic wall flow monolith filter through the inlet passages and migrates through, and is filtered by, the longitudinally extending walls to exit the ceramic wall flow monolith filter through the outlet passages;   a first catalyst composition, operable with an ammonia reductant to catalytically reduce oxides of nitrogen in the exhaust gas, applied to a first portion of the ceramic wall flow monolith filter; and   a second catalyst composition, for catalytic oxidation of hydrocarbon, carbon monoxide and ammonia in the exhaust gas, separately applied, serially downstream to a second portion of the ceramic wall flow monolith filter.   
     
     
         7 . The exhaust treatment system of  claim 6 , wherein the first catalyst composition comprises a reduction catalyst containing zeolite and one or more base metal components and the second catalyst composition comprises an oxidation catalyst containing one or more precious group metals. 
     
     
         8 . The exhaust treatment system of  claim 7 , wherein the reduction catalyst base metal comprises iron, cobalt, copper or vanadium or combinations thereof. 
     
     
         9 . The exhaust treatment system of  claim 7 , wherein the oxidation catalyst precious group metal comprises platinum, palladium, rhodium or combinations thereof. 
     
     
         10 . An exhaust gas treatment system for reducing constituents in the exhaust gas of an internal combustion engine comprising:
 an oxidation catalyst disposed within the exhaust gas treatment system;   a particulate filter downstream of the oxidation catalyst to remove particulates from the exhaust gas;   a first catalyst composition, operable to catalytically reduce oxides of nitrogen in the exhaust gas, applied to a first portion of the particulate filter; and   a second catalyst composition, for catalytic oxidation hydrocarbon, carbon monoxide and ammonia in the exhaust gas, applied serially downstream to a second portion of the particulate filter.   
     
     
         11 . The exhaust gas treatment system of  claim 10 , wherein the first catalyst composition comprises a reduction catalyst containing zeolite and one or more base metal components and the second catalyst composition comprises an oxidation catalyst containing one or more precious group metals. 
     
     
         12 . The exhaust treatment system of  claim 11 , wherein the reduction catalyst base metals comprise iron, cobalt, copper or vanadium or combinations thereof. 
     
     
         13 . The exhaust treatment system of  claim 11 , wherein the oxidation catalyst precious group metals comprise platinum, palladium, rhodium or combinations thereof.