Exhaust after-treatment system for a lean burn internal combustion engine

Abstract

An exhaust gas after-treatment system having a NO x storage material and a separate HC and CO oxidation section, such oxidation section having an oxidation catalyst substantially free of the NO x storage material.

1 . An exhaust gas after-treatment system for an internal combustion engine, comprising: 
 a lean NO x  trap, such lean NO x  trap comprising: 
 an oxidation section having an oxidation material for oxidizing hydrocarbons and carbon monoxide in the exhaust gas; and  
 a NO x  storage section, such NO x  storage section having a NO x  storing material for storing NO x  in the exhaust gas;  
   wherein the oxidation material in the oxidation section is physically separated from the NO x  storing material in the NO x  storage section.    
   
   
       2 . The exhaust gas after-treatment system recited in  claim 1  wherein the hydrocarbon and carbon monoxide oxidation material includes Pt.  
   
   
       3 . The exhaust gas after-treatment system recited in  claim 2  wherein the NO x  storing material includes Ba, Cs, Na, K, or Sr.  
   
   
       4 . The exhaust gas after-treatment system recited in  claim 2  wherein the physical separation between the two sections is provided by coating the two sections on separate pieces of catalyst material.  
   
   
       5 . The exhaust gas after-treatment system recited in  claim 2  wherein the physical separation between the two sections is provided by zone-coating both sections on the same catalyst body.  
   
   
       6 . The exhaust gas after-treatment system recited in  claim 1  wherein both the oxidation section and the NO x  storing section contain Pt, in various proportions, with the Pt providing a CO and HC oxidation catalyst in the oxidation section and primarily as a NO x  oxidation catalyst in the NO x  storing section second section.  
   
   
       7 . The exhaust gas after-treatment system recited in  claim 1  wherein the ratio of the volume of the oxidation section to the NO x  storing section, ranges from 1/10 to 1 and more preferably from 1/10 to ⅓.  
   
   
       8 . An exhaust gas after-treatment system, comprising: 
 a second section having therein: 
 a NO x  oxidation component;  
 a NO x  storage components; and  
 a NO x  reduction components; and  
   a first section for oxidizing hydrocarbons and carbon monoxide in the exhaust gas. such first section being physically separate from the second section, such first section being substantially free of the NO x  storage component and the NO x  reduction component.    
   
   
       9 . The system recited in  claim 9  wherein the first section is upstream of the second section.  
   
   
       10 . A method for treating exhaust gas produced by an internal combustion engine, comprising: 
 oxidizing hydrocarbons and carbon monoxide in the exhaust gas;    storing and reducing NO x  in the exhaust gas;    wherein the oxidizing and storing/reducing functions are performed as separate, sequential processes on the exhaust gas.    
   
   
       11 . An exhaust gas after-treatment system for an internal combustion engine, comprising: 
 a lean NO x  trap, such lean NO x  trap comprising: 
 an oxidation section having an oxidation material for oxidizing hydrocarbons and carbon monoxide in the exhaust gas; and  
 a NO x  storage section, such NO x  storage section having a NO x  storing material for storing NO x  in the exhaust gas and noble metal components for both oxidizing NO during NO x  storage and reducing released NO x  during trap regeneration; and  
   wherein the oxidation material in the oxidation section is physically separated from the NO x  storing material and noble metal components in the NO x  storage section.    
   
   
       12 . The exhaust gas after-treatment system recited in  claim 11  wherein the hydrocarbon and carbon monoxide oxidation material includes Pt and/or other oxidation catalyst material.  
   
   
       13 . The exhaust gas after-treatment system recited in  claim 12  wherein the NO x  storing material stores and releases NO x  in an operating temperature range of diesel exhaust gases.  
   
   
       14 . The exhaust gas after-treatment system recited in  claim 11  wherein both the oxidation section and the NO x  storing section contain Pt, in various proportions, such that the Pt is utilized primarily as a CO and HC oxidation catalyst in the oxidation section and primarily as a NO x  oxidation catalyst in the NO x  storing section.  
   
   
       15 . The exhaust gas after-treatment system recited in  claim 11  wherein the ratio of the volume of the oxidation section relative to the storing section ranges from 1/10 to 1 and more preferably from 1/10 to ⅓.  
   
   
       16 . An exhaust gas after-treatment system, comprising: 
 a second section having therein: 
 one or more NO x  oxidation components;  
 one or more NO x  storage components; and  
 one or more NO x  reduction components; and  
   a first section for oxidizing hydrocarbons and carbon monoxide in the exhaust gas. such first section being physically separate from the second section, such first section being substantially free of the NO x  storage component(s) and the NO x  reduction component(s).    
   
   
       17 . The system recited in  claim 16  wherein the first section is upstream of the second section.