Patent ID: 7972400

Claim:
A honeycomb filter system comprising a first honeycomb filter disposed upstream and a second honeycomb filter disposed downstream to be lined up in series; wherein the first honeycomb filter is provided with a porous partition wall matrix partitioning and forming a plurality of cells functioning as fluid passages, predetermined cells each having an open end portion on one side and a plugged end portion on the other side and the remaining cells each having a plugged end portion on one side and an open end portion on the other side are alternately disposed, and the first honeycomb filter satisfies the conditions of (F1) and (F2), and the second honeycomb filter is provided with partition walls having a porous partition wall matrix partitioning and forming a plurality of cells functioning as fluid passages and a surface layer disposed on one side of the partition wall matrix, predetermined cells each having an open end portion on one side and a plugged end portion on the other side and the remaining cells each having a plugged end portion on one side and an open end portion on the other side are alternately disposed, and the second honeycomb filter satisfies the conditions of (R1) to (R5): (F1) in the first honeycomb filter, the partition wall matrix has a mean pore diameter of 25 μm or more and below 70 μm and a porosity of 40% or more and below 70%, (F2) in the first honeycomb filter, an oxidation catalyst containing at least one material selected from the group consisting of platinum (Pt), palladium, ceria, and alumina is supported on a part or whole of the inner surfaces of the pores of the partition wall matrix, (R1) in the second honeycomb filter, the surface layer has a peak pore diameter equivalent to or smaller than that of the partition wall matrix and a porosity higher than that of the partition wall matrix, (R2) in the second honeycomb filter, the surface layer has a peak pore diameter of 0.3 μm or more and below 20 μm and a porosity of 60% or more and below 95% (measured by mercury intrusion technique), (R3) in the second honeycomb filter, thickness L 1 of the surface layer is 0.5% or more and below 30% of thickness L 2 of the partition wall, (R4) in the second honeycomb filter, a mass per filtration area of the surface layer is 0.01 mg/cm 2 or more and below 6 mg/cm 2 , and (R5) in the second honeycomb filter, the partition wall matrix has a mean pore diameter of 10 μm or more and below 60 μm and a porosity of 40% or more and below 65%.