Ceramic honeycomb structure

1. A ceramic honeycomb structure having pluralities of flow paths partitioned by porous cell walls,

(a) said cell walls having porosity of 50-63%; and

(b) in a pore diameter distribution in said cell walls measured by mercury porosimetry,

(i) a pore diameter d2 at a cumulative pore volume corresponding to 2% of the total pore volume being more than 180 μm and 250 μm or less,

a pore diameter d5 at 5% being 55-150 μm,

a pore diameter d10 at 10% being 17-40 μm,

a pore diameter (median pore diameter) d50 at 50% being 10-20 μm,

a pore diameter d85 at 85% being 5.5-10 μm,

a pore diameter d90 at 90% being 3.5-9 μm,

a pore diameter d98 at 98% being 2.5 μm or less,

(d10−d90)/d50 being 1.3-2,

(d50−d90)/d50 being 0.45-0.75, and

(d10−d50)/d50 being 0.75-1.4;

(ii) σ[=log d20−log d80] being 0.39 or less, wherein σ represents the difference between a logarithm of the pore diameter d20 at a cumulative pore volume corresponding to 20% of the total pore volume and a logarithm of the pore diameter d80 at 80%; and

(iii) the volume of pores of more than 100 μm being 0.03 cm 3 /g or less.

2. The ceramic honeycomb structure according to claim 1 , wherein the volume of pores of 20 μm or more is 0.12 cm 3 /g or less.

3. The ceramic honeycomb structure according to claim 1 , wherein said porosity is 52-60%.

4. The ceramic honeycomb structure according to claim 1 , wherein said median pore diameter d50 is 10-18 μm.

5. The ceramic honeycomb structure according to claim 1 , wherein said σ is 0.3 or less.