Filter for filtering particulate matter from exhaust gas emitted from a compression ignition engine

Abstract

A filter for filtering particulate matter (PM) from exhaust gas emitted from a compression ignition engine, which filter comprising a porous substrate having inlet surfaces and outlet surfaces, wherein the inlet surfaces are separated from the outlet surfaces by a porous structure containing pores of a first mean pore size, wherein the porous substrate is coated with a wash coat comprising a plurality of solid particles comprising a molecular sieve promoted with at least one metal wherein the porous structure of the wash coated porous substrate contains pores of a second mean pore size, and wherein the second mean pore size is less than the first mean pore size.

1 . A filter for filtering particulate matter (PM) from an exhaust gas comprising:
 a. a wall flow filter having inlet and outlet surfaces and a porous substrate between the inlet and outlet surfaces, wherein the porous substrate has pores of a first mean pore size,   b. a first washcoat coated on the inlet and/or outlet surface of the porous wall flow substrate and within the wall flow substrate, wherein the first washcoat has a second mean pore size that is less than the first mean pore size.   
     
     
         2 . The filter of  claim 1 , further comprising a layer of a second washcoat, wherein the first washcoat and second washcoat layer have different formulations and wherein substantially none of the second washcoat enters the wall flow substrate. 
     
     
         3 . The filter of  claim 1 , wherein the second washcoat layer is coated on the outlet surface of the wall flow filter. 
     
     
         4 . The filter of  claim 3 , wherein the first washcoat is coated on the outlet surface of the wall flow filter. 
     
     
         5 . The filter of  claim 3 , wherein the first washcoat is coated on the inlet surface of the wall flow filter. 
     
     
         6 . The filter of  claim 2 , wherein at least one of the first and second washcoats comprise a metal is selected from Cu, Fe, Ce, Pt, Pd, or Rh. 
     
     
         7 . The filter of  claim 6 , wherein one of the first or second washcoats comprise a metal is selected from Cu, Fe, and Ce, and the other of the first or second washcoats comprise a metal is selected from Pt, Pd, and Rh. 
     
     
         8 . The filter of  claim 7 , wherein at least one of the first and second washcoats comprise an aluminosilicate molecular sieve. 
     
     
         9 . The filter of  claim 7 , wherein the second washcoat comprises an aluminosilicate molecular sieve containing a metal selected from Cu and Fe. 
     
     
         10 . The filter of  claim 7 , wherein the first washcoat comprises an aluminosilicate molecular sieve containing a metal selected from Cu and Fe. 
     
     
         11 . The filter according to  claim 1 , wherein the first washcoat comprises solid particles having a mean particle size of about 1 to 20 μm. 
     
     
         12 . The filter according to  claim 1 , wherein the washcoat within the porous wall flow substrate comprises solid particles having a D90 particle size distribution of 0.1 to 20 μm. 
     
     
         13 . The filter according to  claim 1 , wherein the first washcoat comprises interparticle pores and/or pores made by formation of gas on decomposition or combustion. 
     
     
         14 . The filter according to  claim 1 , wherein the pore size of the first washcoat is 5 nm to 5 μm.