System and Method for Reducing NOx Emissions

Abstract

An exhaust system, comprising of a first emission control system in the exhaust system, said emission control system having a at least a first region and a second region, said second region physically segregated from the first region and at least partially downstream of the first region, said first region including a precious metal component dispersed on a metal oxide support that stores NOx and said second region including a precious metal component and a NOx sorbent component dispersed on a metal oxide support, where said second region includes more of said NOx sorbent component than said first region; and a second emission control system including an SCR catalyst coupled downstream of said first emission control system.

1 . An exhaust system, comprising:
 a first emission control system in the exhaust system, said emission control system having a at least a first region and a second region, said second region physically segregated from the first region and at least partially downstream of the first region, said first region including a precious metal component dispersed on a metal oxide support that stores NOx and said second region including a precious metal component and a NOx sorbent component dispersed on a metal oxide support, where said second region includes more of said NOx sorbent component than said first region; and   a second emission control system including an SCR catalyst coupled downstream of said first emission control system.   
   
   
       2 . The exhaust system of  claim 1 , wherein the precious metal component is selected from at least one of platinum, palladium, rhodium, iridium, ruthenium, osmium, rhenium, silver, gold and/or mixtures thereof. 
   
   
       3 . The exhaust system of  claim 1 , wherein the precious metal component includes platinum. 
   
   
       4 . The exhaust system of  claim 1 , wherein the NOx sorbent component is selected from at least one of alkali metal (lithium, sodium, potassium, rubidium, cesium) and alkaline earth metal (beryllium, magnesium, calcium, strontium, barium) oxides and carbonates of said groups and/or mixtures thereof. 
   
   
       5 . The exhaust system of  claim 1 , wherein the NOx sorbent component includes barium oxide, and wherein the metal oxide support that stores NOx is selected from at least one of alumina, zeolite, silica dispersed on alumina, titania dispersed on alumina, zirconia dispersed on alumina, and/or mixtures thereof. 
   
   
       6 . The exhaust system of  claim 1 , wherein the metal oxide support that stores NOx includes alumina. 
   
   
       7 . The exhaust system of  claim 1 , wherein the metal oxide support is selected from at least one of alumina, zeolite, silica, titania, zirconia, and/or mixtures thereof. 
   
   
       8 . The exhaust system of  claim 1 , wherein a washcoat in the first catalyst region consists essentially of a precious metal component dispersed on a metal oxide support that stores NOx. 
   
   
       9 . The exhaust system of  claim 1 , wherein the first catalyst region further comprises a NOx sorbent component. 
   
   
       10 . The exhaust system of  claim 1 , wherein at least the second region further comprises a ceria component. 
   
   
       11 . The exhaust system of  claim 1 , where the first region and the second region further comprise a ceria component where said second region includes more of said ceria component than said first region. 
   
   
       12 . The exhaust system of  claim 1 , where the first region and the second region further comprise a ceria component where said first region includes more of said ceria component than said second region. 
   
   
       13 . The exhaust system of  claim 1 , wherein the first and second regions are disposed on a monolithic flow-through substrate. 
   
   
       14 . The exhaust system of  claim 1 , wherein the first and second regions are disposed on a wall flow filter substrate. 
   
   
       15 . The exhaust system of  claim 1 , wherein the first region and the second region are disposed on a single substrate. 
   
   
       16 . The exhaust system of  claim 15 , wherein the first region and the second region are segregated by a segment of the substrate. 
   
   
       17 . The exhaust system of  claim 1  wherein the first region and the second region are separated by an area of separation. 
   
   
       18 . The exhaust system of  claim 1  further comprising a urea reductant injection system, wherein urea from the urea reductant injection system is introduced between the first emission control system and the second emission control system. 
   
   
       19 . The exhaust system of  claim 1  further comprising a particulate filter system, wherein said filter system is located upstream of the first emission control system. 
   
   
       20 . The exhaust system of  claim 1  further comprising a particulate filter system, wherein said filter system is located downstream of the second emission control system. 
   
   
       21 . The exhaust system of  claim 1  further comprising a sensor coupled in the exhaust system and a controller for adjusting engine operation to vary an exhaust air-fuel ratio in response to said sensor. 
   
   
       22 . An exhaust system, comprising:
 a first emission control device with a washcoat having a first amount of precious metal physically segregated from NOx storage material and a second amount of precious metal physically mixed with NOx storage material, where first amount is upstream of said second amount; and   a second emission control device downstream of said first device, said second device including an SCR catalyst configured to store NH3.   
   
   
       23 . An exhaust system, comprising:
 a first emission control system in the exhaust system, said emission control system having a at least a first region and a second region, said second region physically segregated from the first region and at least partially downstream of the first region, said first region including a precious metal component and said second region including a precious metal component and a NOx sorbent component, where said second region includes more of said NOx sorbent component than said first region, and said first and second regions are substantially free of ceria; and   a second emission control system including an SCR catalyst coupled downstream of said first emission control system.