Scr catalytic coating on particulate filters

Abstract

Coated particulate filters and methods for their manufacture disclosed. The particulate filters comprise a honeycomb body having a plurality of porous channel walls defining channels extending from an inlet end to an outlet end. The honeycomb body has an upstream zone having an upstream zone gas permeability and a downstream zone disposed closer to the outlet end than the upstream zone and having a downstream zone gas permeability. SCR catalyst is present in a loading in the downstream zone at localized loading in a range of from about 50 g/L to about 200 g/L such that the upstream zone gas permeability is in a range of about 5 to about 90 times the downstream zone gas permeability.

1 . A particulate filter comprising:
 a honeycomb body comprising an inlet end and an outlet end comprising a plurality of porous channel walls extending in an axial direction from the inlet end to the outlet end and defining a honeycomb body axial length L a , the plurality of porous channel walls defining channels extending from the inlet end to the outlet end, wherein at least a first set of the channels are plugged, the honeycomb body further comprising an upstream zone having an upstream zone gas permeability and a downstream zone disposed closer to the outlet end than the upstream zone and having a downstream zone gas permeability, and the upstream zone has an upstream zone axial length L u  that is less than the honeycomb body axial length L a , and the plurality of porous channel walls of the honeycomb body comprises a selective catalytic reduction (SCR) catalyst that promotes selective catalytic reduction of NO x , and the SCR catalyst is present in a loading in the downstream zone at localized loading in a range of from about 50 g/L to about 200 g/L such that the upstream zone gas permeability is in a range of about 5 to about 90 times the downstream zone gas permeability.   
     
     
         2 . The particulate filter of  claim 1 , wherein the upstream zone does not contain any SCR catalyst. 
     
     
         3 . The particulate filter of  claim 1 , wherein the honeycomb body comprises SCR catalyst disposed in or on the porous channel walls in the upstream zone. 
     
     
         4 . The particulate filter of  claim 1 , wherein the honeycomb body comprises SCR catalyst disposed in or on the porous channel walls in the downstream zone. 
     
     
         5 . The particulate filter of  claim 1 , wherein the first set of the channels are plugged proximate at least one of the inlet end or the outlet end. 
     
     
         6 . The particulate filter of  claim 1 , wherein the ratio (L u /L a ) of the upstream zone axial length L u  to the honeycomb body axial length L a  is greater than 0 and less than or equal to 0.75. 
     
     
         7 . The particulate filter of  claim 1 , wherein the ratio (L u /L a ) of the upstream zone axial length L u  to the honeycomb body axial length L a  is greater than 0.1 and less than or equal to 0.75. 
     
     
         8 . The particulate filter of  claim 1 , wherein the ratio (L u /L a ) of the upstream zone axial length L u  to the honeycomb body axial length L a  is greater than 0.15 and less than or equal to 0.75. 
     
     
         9 . The particulate filter of  claim 1 , wherein the ratio (L u /L a ) of the upstream zone axial length L u  to the honeycomb body axial length L a  is greater than 0.15 and less than 0.60. 
     
     
         10 . The particulate filter of  claim 1 , wherein the downstream zone has a localized catalyst loading in a range of from about 80 g/L to about 200 g/L. 
     
     
         11 . The particulate filter of  claim 1 , wherein the downstream zone has a localized catalyst loading in a range of from about 100 g/L to about 180 g/L. 
     
     
         12 . The particulate filter of  claim 1 , wherein the downstream zone has a localized catalyst loading in a range of from about 120 g/L to about 180 g/L. 
     
     
         13 . The particulate filter of  claim 1 , wherein the upstream zone axial length L u  is in a range of from about 50% L a  to 80% L a  and the downstream zone has a localized catalyst loading in a range of from about 100 g/L to about 180 g/L. 
     
     
         14 . The particulate filter of  claim 1 , wherein the porous channel walls have a porosity in a range of from about 45% to about 75% and a median pore size in a range from 5 micrometers to about 30 micrometers. 
     
     
         15 . A lean burn engine exhaust system comprising the particulate filter of  claim 1 , further comprising a nitrogenous reductant injector disposed upstream from the particulate filter. 
     
     
         16 .- 25 . (canceled) 
     
     
         26 . A method of manufacturing a catalytic particulate filter comprising:
 immersing an outlet end of a honeycomb body comprising porous channel walls in SCR catalyst slurry to a depth less than an axial length L a  of the honeycomb body to coat at least a first axial portion of a first plurality of the porous channel walls with SCR catalyst to provide a coated honeycomb body with a target SCR catalyst loading mass which is contained in less than or equal to 75% of the axial length L a  of the honeycomb body, wherein the porous channel walls extend in an axial direction from an inlet end to the outlet end.   
     
     
         27 . The method of  claim 26 , wherein the SCR catalyst is absent in a region greater than or equal to 25% extending from 5% to 30% of the axial length L a  of the honeycomb body. 
     
     
         28 . The method of  claim 26 , wherein the honeycomb body comprises a second axial portion wherein the porous channel walls are not exposed to the SCR catalyst slurry, wherein the second axial portion has a permeability which is in a range of about 7 to about 90 times a permeability of the first axial portion. 
     
     
         29 . The method of  claim 26 , wherein the SCR catalyst is present in a loading in the first axial portion in a range of from about 50 g/L to about 200 g/L. 
     
     
         30 . The method of  claim 26 , wherein, the target SCR catalyst loading mass is contained in the first axial portion in a range of from about 30% L a  to 60% L a . 
     
     
         31 .- 39 . (canceled)