Filter for filtering particulate matter from exhaust gas emitted from a compression ignition engine
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 removing particulate matter from exhaust gas comprising:
a. a filter comprising a porous substrate having inlet surfaces and outlet surfaces, wherein the inlet surfaces are separated from the outlet surfaces by the porous substrate;
b. a first catalyst washcoat on the inlet surfaces, wherein the first catalyst washcoat has a mean particle size greater than the mean pore size of the filter;
c. a second catalyst washcoat within the porous substrate, wherein the second catalyst washcoat has a mean particle size less than the mean pore size of the porous filter.
2. The filter of claim 1 , wherein the first catalyst washcoat has a mean particle size of 10 to 40 μm.
3. The filter of claim 1 , wherein the second catalyst washcoat has a mean particle size of 0.1 to 20 μm.
4. The filter of claim 1 , wherein the first catalyst washcoat has a D 90 particle size of 10 to 40 μm second catalyst washcoat has a D 90 particle size of 3 to 12 μm.
5. The filter of claim 1 , wherein a least one of the first catalyst washcoat and the second catalyst washcoat comprise platinum and/or palladium on a high surface area support.
6. The filter of claim 1 , wherein filter further comprises a third catalyst washcoat on the outlet surface.