Emission Treatment Systems and Methods

Abstract

Exhaust treatment filters, systems, and methods are disclosed. According to one or more embodiments, a particulate filter is zone coated with an oxidation catalyst and is used in an emission treatment system or method including a NOx reducing catalyst and an optional NH 3 destruction catalyst.

1 . An emission treatment system for treatment of an exhaust stream comprising NO x  and particulate matter, the emission treatment system comprising:
 a particulate filter having an axial length and elements for trapping particulate matter contained in an exhaust stream flowing through the filter and a light-off oxidation catalyst composition extending from the inlet end towards the outlet end to a length that is less than the axial length of the walls to provide an inlet zone in an amount sufficient to light-off at a temperature less than about 300° C. and generate an exotherm to burn soot trapped in the filter; and   a NOx reducing catalyst located upstream of the wall flow monolith.   
   
   
       2 . The emission treatment system of  claim 1 , wherein the particulate filter comprises a wall flow monolith disposed within the exhaust stream and having a plurality of longitudinally extending passages bounded by longitudinally extending walls, the passages comprising 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, the walls having a porosity of at least 40% with an average pore size of at least 5 microns and the wall flow monolith comprising a light-off oxidation catalyst composition permeating the walls. 
   
   
       3 . The emission treatment system of  claim 1 , further comprising an NH 3  destruction catalyst located downstream from the NO x  reducing catalyst. 
   
   
       4 . The emission treatment system of  claim 1 , wherein the NO x  reducing catalyst comprises a lean NO x  catalyst. 
   
   
       5 . The emission treatment system of  claim 4 , further comprising a reductant introduction port in fluid communication with a hydrocarbon reductant, the reductant introduction port located upstream from the lean NOx catalyst. 
   
   
       6 . The emission treatment system of  claim 4 , wherein the NO x  reducing catalyst comprises a lean NOx trap. 
   
   
       7 . The emission treatment system of  claim 4 , wherein the NO x  reducing catalyst comprises an SCR catalyst. 
   
   
       8 . The emission treatment system of  claim 6 , further comprising an introduction port located upstream from the SCR catalyst, the introduction port in fluid communication with an ammonia or ammonia precursor. 
   
   
       9 . The emission treatment system of  claim 6 , further comprising an injector in fluid communication with the introduction port, the injector configured to periodically meter the ammonia or an ammonia precursor into the exhaust stream. 
   
   
       10 . The emission treatment system of  claim 7 , further comprising an NH 3  destruction catalyst located downstream from the SCR catalyst. 
   
   
       11 . The emission treatment system of  claim 1 , further comprising an exotherm-producing agent introduction port located upstream of the wall flow monolith, the exotherm-producing agent introduction port in fluid communication with an exotherm-producing agent capable of generating a temperature sufficient to periodically burn particulate accumulated in the wall-flow monolith. 
   
   
       12 . The emission treatment system of  claim 11 , wherein the exotherm-producing agent comprises diesel fuel. 
   
   
       13 . An emission treatment system for treatment of an exhaust stream comprising NO x  and particulate matter, the emission treatment system comprising:
 a wall flow monolith disposed within the exhaust stream and having a plurality of longitudinally extending passages bounded by longitudinally extending walls, the passages comprising 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, the walls having a porosity of at least 40% with an average pore size of at least 5 microns and the wall flow monolith comprising a light-off oxidation catalyst composition permeating the walls and extending from the inlet end towards the outlet end to a length that is less than the axial length of the walls to provide an inlet zone;   an SCR catalyst located upstream of the wall flow monolith; and   an injector for injecting ammonia or ammonia precursor into the exhaust gas stream upstream of the SCR catalyst.   
   
   
       14 . The emission treatment system of  claim 13 , wherein the SCR catalyst comprises zeolite. 
   
   
       15 . The emission treatment system of  claim 13 , wherein the SCR catalyst comprises vanadia. 
   
   
       16 . The emission treatment system of  claim 13 , further comprising an NH 3  destruction catalyst located downstream from the SCR catalyst. 
   
   
       17 . The emission treatment system of  claim 16 , comprising an exotherm-producing agent injector located upstream of the wall-flow monolith. 
   
   
       18 . A method of treating exhaust stream from a diesel engine comprising:
 disposing within the exhaust stream containing particulate matter a wall flow monolith and having a plurality of longitudinally extending passages bounded by longitudinally extending walls, the passages comprising 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, the walls having a porosity of at least 40% with an average pore size of at least 5 microns and the wall flow monolith comprising a light-off oxidation catalyst composition permeating the walls and extending from the inlet end towards the outlet end to a length that is less than the axial length of the walls to provide an inlet zone;   disposing a NOx reducing catalyst upstream the wall flow monolith; and   periodically introducing an exotherm-producing agent upstream of the wall flow monolith to generate an exotherm in the wall flow monolith sufficient to combust particulate matter trapped within the wall flow monolith.