Ceramic honeycomb structure and its production method
A ceramic honeycomb structure comprising large numbers of cells partitioned by porous cell walls, the cell walls having (a) porosity of 50-80%, and when measured by mercury porosimetry, (b) a median pore diameter being 25-50 μm, (c) (i) a cumulative pore volume in a pore diameter range of 20 μm or less being 25% or less of the total pore volume, (ii) a cumulative pore volume in a pore diameter range of more than 20 μm and 50 μm or less being 50% or more of the total pore volume, and (iii) a cumulative pore volume in a pore diameter range of more than 50 μm being 12% or more of the total pore volume.
1. A method for producing a catalyst-carrying ceramic honeycomb structure exhibiting high capability of removing NOx, comprising blending material powder comprising a cordierite-forming material and a pore-forming material to obtain a moldable material, extruding said moldable material to obtain a honeycomb-shaped green body, drying and sintering said green body to obtain a ceramic honeycomb structure, and applying catalyst slurry to cell wall surfaces and pores in the cell walls of the ceramic honeycomb structure,
(a) said cordierite-forming material comprising 10-25% by mass of silica having a median particle diameter of 1.0-60 m;
(b) said pore-forming material having
(i) a median particle diameter of more than 75 μm and 180 μm or less,
(ii) in a curve of a cumulative volume (cumulative volume of particles up to a particular particle diameter) to a particle diameter, a particle diameter D90 at a cumulative volume corresponding to 90% of the total volume being 129.0-250 μm, and a particle diameter D10 at a cumulative volume corresponding to 10% of the total volume being 15-160 μm; and
(iii) a particle diameter distribution deviation SD being 0.3 or less; and (c) said pore-forming material added being 1-20% by mass per said cordierite-forming material.
2. The method for producing a ceramic honeycomb structure according to claim 1 , wherein said particle diameter of D90 at a cumulative volume corresponding to 90% of the total volume is 135.8-250 μm.
3. The method for producing a ceramic honeycomb structure according to claim 1 , wherein said pore-forming material is hollow resin particles.
4. The method for producing a ceramic honeycomb structure according to claim 3 , wherein said hollow resin particles are hollow particles of methylmethacrylate/acrylonitrile copolymers.
5. The method for producing a ceramic honeycomb structure according to claim 3 , wherein said hollow resin particles have shells with a thickness of 0.1-2 μm and contain hydrocarbon gas.
6. The method for producing a ceramic honeycomb structure according to claim 5 , wherein said hollow resin particles contain 70-95% of moisture.