Filter
The present invention provides a filter comprising a base material and a catalytic substance provided within the base material, wherein the base material comprises a plurality of cells forming gas flow paths and having a gas inflow-side end portion and outflow-side end portion, and a plurality of porous partition walls defining said cells, the end portions of at least some of the cells being closed off, and the void occupancy of the catalytic substance within the pores of the partition walls is 10% or less.
1. A filter comprising a base material and a catalytic substance provided within the base material,
wherein the base material comprises a plurality of cells forming gas flow paths and having a gas inflow-side end portion and outflow-side end portion, the base material has a length wherein the length is the distance from the gas inflow-side end portion and outflow-side end portion, and a plurality of porous partition walls defining said cells, the end portions of some of the cells being closed off, wherein only one of the gas inflow-side end portion and outflow-side end portion is partially closed off, the catalytic substance is present on the gas inflow portion of the base material, and the void occupancy of the catalytic substance within the pores of the partition walls is 10% or less.
2. The filter as claimed in claim 1 , wherein the catalytic substance has a mean particle size D50 of 1/10 or less of the mean pore size D50 of the pores in the partition walls.
3. The filter as claimed in claim 1 , wherein the catalytic substance comprises noble metals and the concentration ratio of noble metals contained in the catalytic substance at the gas inflow-side end portion and outflow-side end portion is between 10/90 and 90/10.
4. The filter as claimed in claim 1 , wherein the catalytic substance is included in a range of between 10% and 50% of the total length of the partition walls in the lengthwise direction, from the gas inflow-side end portion.
5. The filter as claimed in claim 1 , comprising Pt and Pd in a ratio of between 1:1 and 10:1 as the catalytic substance.
6. The filter as claimed in claim 1 , further comprising at least one material selected from the group consisting of oxygen storage materials, alkali metals and perovskite materials.
7. The filter as claimed in claim 1 , wherein the porosity of the base material is between 40% and 70%.
8. The filter as claimed in claim 1 , wherein the void occupancy of the catalytic substance is less than 5%.
9. The filter as claimed in claim 1 , wherein the amount of catalytic substance is present as a gradient in the lengthwise direction of the filter.