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, the filter 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,   wherein the filter further comprises 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, and   wherein at least one of the first and second washcoats comprise a metal selected from Cu, Fe, Ce, Pt, Pd, or Rh.   
     
     
         2 . The filter of  claim 1 , wherein the second washcoat layer is coated on the outlet surface of the wall flow filter. 
     
     
         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 1 , wherein either one or both of the inlet and outlet surfaces of the wall flow filter comprise a plurality of washcoat layers comprising the first washcoat layer and the second washcoat layer. 
     
     
         5 . The filter of  claim 2 , wherein the first washcoat is coated on the inlet surface of the wall flow filter. 
     
     
         6 . The filter of  claim 1 , 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. 
     
     
         7 . The filter of  claim 6 , wherein at least one of the first and second washcoats comprise an aluminosilicate molecular sieve. 
     
     
         8 . The filter of  claim 6 , wherein the second washcoat comprises an aluminosilicate molecular sieve containing a metal selected from Cu and Fe. 
     
     
         9 . The filter of  claim 6 , wherein the first washcoat comprises an aluminosilicate molecular sieve containing a metal selected from Cu and Fe. 
     
     
         10 . The filter according to  claim 1 , wherein the first washcoat comprises solid particles having a mean particle size of about 1 to 20 μm. 
     
     
         11 . 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. 
     
     
         12 . 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. 
     
     
         13 . The filter according to  claim 1 , wherein the pore size of the first washcoat is 5 nm to 5 μm. 
     
     
         14 . The filter according to  claim 1 , wherein pores at a surface of the porous substrate comprise a pore opening and the washcoat causes a narrowing of substantially all the pore openings.