JP7304147B2 - honeycomb structure - Google Patents

Description

The present invention relates to a honeycomb structure.

Exhaust gases emitted from internal combustion engines such as automobiles contain harmful gases such as carbon monoxide (CO), nitrogen oxides (NOx), and hydrocarbons (HC). Such an exhaust gas purifying catalyst that decomposes harmful gases is also called a three-way catalyst. things are common.

Patent Document 1 discloses an exhaust gas purifying catalyst in which a monolithic base material contains ceria-zirconia composite oxide particles and θ-phase alumina particles, and precious metal particles are supported on the monolithic base material.

JP 2015-85241 A

Regarding the exhaust gas purifying catalyst described in Patent Document 1, the temperature rise rate of the monolith base material at the start of driving the engine, etc., is increased so that the temperature of the monolith base material maintains a temperature equal to or higher than the activation temperature of the catalyst for a long time. It was required that the temperature was fast (easily warmed up). Furthermore, it is required that the engine does not easily cool down during idling, etc., so that the period during which the temperature above the activation temperature of the catalyst is maintained becomes longer.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a honeycomb structure in which the temperature of the catalyst easily rises and does not easily cool down when the catalyst is loaded.

A honeycomb structure of the present invention is a honeycomb structure comprising a honeycomb fired body in which a plurality of through holes are arranged in parallel in a longitudinal direction with partition walls interposed therebetween,
The honeycomb fired body comprises ceria-zirconia composite oxide particles and alumina particles,
It is characterized in that the amount of residual carbon in the partition walls is 500 to 1500 ppm.

In the manufacturing process of the monolith base material as described in Patent Document 1, a degreasing process is performed. In a normal degreasing process, sufficient degreasing is performed so as not to leave carbon, so the amount of residual carbon in the partition walls is 0 ppm. is assumed to be close to
On the other hand, in the honeycomb structure of the present invention, the residual carbon content in the partition walls is intentionally controlled to 500 to 1500 ppm.
When the amount of residual carbon in the partition walls is 500 to 1500 ppm, when the honeycomb structure cools down during idling or the like, the far-infrared effect of carbon suppresses the temperature drop of the honeycomb structure, and the honeycomb structure does not cool easily. Become. If the amount of residual carbon exceeds 1500 ppm, the carbon will burn when the temperature of the exhaust gas rises, the temperature of the honeycomb structure will rise abnormally, and the supported catalyst may be deactivated.
Further, a honeycomb structure composed of a honeycomb fired body composed of ceria-zirconia composite oxide particles and alumina particles is easy to warm due to its small heat capacity.
As described above, the honeycomb structure of the present invention is a honeycomb structure that is easily heated and hard to cool down. Therefore, when the catalyst is supported, the period during which the catalyst is effective for gas purification can be lengthened.

In the honeycomb structure of the present invention, the partition walls preferably have a porosity of 50 to 65%.
Further, it is preferable that the ratio of the through holes in the cross section perpendicular to the longitudinal direction of the honeycomb fired body is 60 to 80%.
Moreover, it is preferable that the volume of the honeycomb structure is 0.5 to 1.5L.
Satisfying these requirements makes the honeycomb structure lighter, which is preferable for making the honeycomb structure easy to heat up.
When the porosity exceeds 65%, or when the ratio of through holes exceeds 80%, or when the volume is less than 0.5 L, the substrate portion (partition wall portion) in the honeycomb structure is reduced, and accordingly, Since the amount of catalyst that can be supported is reduced, exhaust gas purification performance may be lowered.

In the honeycomb structure of the present invention, the proportion of the ceria-zirconia composite oxide particles in the honeycomb fired body is preferably 40 to 60% by weight.
By setting the ratio of the ceria-zirconia composite oxide particles to 40 to 60% by weight, it is possible to obtain a honeycomb structure that is easily heated. If it exceeds 60% by weight, the ratio of the ceria-zirconia composite oxide particles having a large specific gravity increases, and the weight of the honeycomb structure becomes heavy, which may make it difficult to raise the temperature. -Since the co-catalyst function of the zirconia composite oxide particles is lowered, the exhaust gas purification performance may be lowered.

FIG. 1 is a perspective view schematically showing an example of the honeycomb structure of the present invention.

(Detailed description of the invention)
[Honeycomb structure]
A honeycomb structure of the present invention will be described.
FIG. 1 is a perspective view schematically showing an example of the honeycomb structure of the present invention.
As shown in FIG. 1, a honeycomb structure 10 has a plurality of through holes 12 arranged side by side in the longitudinal direction (the direction indicated by the double arrow L in FIG. 1) with partition walls 13 interposed therebetween, and an outer peripheral wall 14 on the outermost periphery. It consists of a honeycomb fired body 11 provided.
The honeycomb fired body 11 contains ceria-zirconia composite oxide particles (hereinafter also referred to as CZ particles) and alumina particles.
As shown in FIG. 1, when the honeycomb structure 10 is composed of a single honeycomb fired body 11, the honeycomb fired body 11 is also the honeycomb structure itself.

In the honeycomb structure of the present invention, the amount of residual carbon in the partition walls is 500-1500 ppm.
The amount of residual carbon in the partition walls can be measured by the combustion volume method after cutting out the partition walls of the honeycomb structure and pulverizing them. Measurement by the combustion volume method is performed as follows.
A sample to be measured and a combustion improver are heated (for example, 1350° C.) in a tubular electric resistance furnace and burned in an oxygen stream to convert carbon into carbon dioxide.
The volume of total gas is measured by entraining it in a stream of excess oxygen and collecting it on a graduated burette.
Thereafter, a potassium hydroxide solution is passed through to absorb and remove carbon dioxide, and then the volume of residual gas is measured with a graduated burette, and the amount of residual carbon is calculated from the volume reduction.

In the honeycomb structure of the present invention, when the amount of residual carbon in the partition walls is 500 to 1500 ppm, the temperature drop of the honeycomb structure is suppressed by the far-infrared effect of carbon when the honeycomb structure cools down during idling. This results in a honeycomb structure that is hard to cool. If the amount of residual carbon exceeds 1500 ppm, the carbon will burn when the temperature of the exhaust gas rises, the temperature of the honeycomb structure will rise abnormally, and the supported catalyst may be deactivated.
Further, a honeycomb structure composed of a honeycomb fired body composed of ceria-zirconia composite oxide particles and alumina particles is easy to warm due to its small heat capacity.
As described above, the honeycomb structure of the present invention is a honeycomb structure that is easily heated and hard to cool down. Therefore, when the catalyst is supported, the period during which the catalyst is effective for gas purification can be lengthened.

In the honeycomb structure of the present invention, the partition walls preferably have a porosity of 50 to 65%.
Further, it is preferable that the ratio of the through holes in the cross section perpendicular to the longitudinal direction of the honeycomb fired body is 60 to 80%.
Moreover, it is preferable that the volume of the honeycomb structure is 0.5 to 1.5L.
Satisfying these requirements makes the honeycomb structure lighter, which is preferable for making the honeycomb structure easy to heat up.
When the porosity exceeds 65%, or when the ratio of through holes exceeds 80%, or when the volume is less than 0.5 L, the substrate portion (partition wall portion) in the honeycomb structure is reduced, and accordingly, Since the amount of catalyst that can be supported is reduced, exhaust gas purification performance may be lowered.

The porosity of the honeycomb fired body (the porosity of the partition walls) can be measured by the gravimetric method described below.
(1) Cut the honeycomb fired body into a size of 10 cells×10 cells×10 mm to obtain a measurement sample. After the measurement sample is ultrasonically cleaned using deionized water and acetone, it is dried at 100° C. using an oven. In addition, the measurement sample of 10 cells × 10 cells × 10 mm is a state in which 10 through-holes are arranged in the vertical direction and 10 in the horizontal direction, and the outermost through-hole and the partition wall constituting the through-hole are included, It refers to a sample cut out so that the length in the longitudinal direction is 10 mm.
(2) Using a measuring microscope (Measuring Microscope MM-40 manufactured by Nikon, magnification: 100 times), measure the dimensions of the cross-sectional shape of the measurement sample, and determine the volume from geometric calculations (geometric calculations If the volume cannot be obtained from the above, measure the weight in saturated water and the weight in water to measure the volume).
(3) From the calculated volume and the true density of the measurement sample measured with a pycnometer, calculate the weight of the measurement sample assuming that it is a completely dense body. The measurement procedure with the pycnometer is as shown in (4).
(4) Pulverize the honeycomb fired body to prepare 23.6 cc of powder. The powder obtained is dried at 200° C. for 8 hours. After that, the true density is measured according to JIS R 1620 (1995) using an Auto Pycnometer 1320 manufactured by Micromeritics. The evacuation time is 40 minutes.
(5) Measure the actual weight of the measurement sample with an electronic balance (HR202i manufactured by A&D).
(6) Obtain the porosity of the honeycomb fired body from the following equation.
(Porosity of honeycomb fired body) = 100 - (actual weight of measurement sample/weight when measurement sample is assumed to be a complete dense body) x 100 [%]
Even in the case where the honeycomb structure of the present invention directly supports a noble metal, the change in the porosity of the honeycomb fired body due to the supporting of the noble metal is so small that it can be ignored.

The ratio of through-holes in the cross section perpendicular to the longitudinal direction of the honeycomb fired body can be obtained from the ratio of the area of the end face of the honeycomb fired body and the area of the through-hole portion by image analysis after taking a photograph of the end face of the honeycomb fired body. can be done.
The volume of the honeycomb structure is the apparent volume of the honeycomb structure.

In the honeycomb structure of the present invention, the partition walls preferably have a uniform thickness. Specifically, the thickness of the partition walls of the honeycomb fired body is preferably 0.05 to 0.50 mm, more preferably 0.05 to 0.30 mm.

In the honeycomb structure of the present invention, the honeycomb fired body is an extruded body containing CZ particles and alumina particles. That is, the honeycomb structure of the present invention is composed of a fired honeycomb body produced by firing a formed honeycomb body obtained by extruding a raw material paste containing CZ particles and alumina particles.
It can be confirmed by X-ray diffraction (XRD) that the honeycomb structure has the above components.

The honeycomb structure of the present invention may have a single honeycomb fired body, or may have a plurality of honeycomb fired bodies. When the honeycomb structure of the present invention includes a plurality of honeycomb fired bodies, it is preferable that the plurality of honeycomb fired bodies are bonded with an adhesive layer.

In the honeycomb structure of the present invention, the content of CZ particles constituting the honeycomb fired body is preferably 40 to 60% by weight.
By setting the ratio of the ceria-zirconia composite oxide particles to 40 to 60% by weight, it is possible to obtain a honeycomb structure that is easily heated. If it exceeds 60% by weight, the ratio of the ceria-zirconia composite oxide particles having a large specific gravity increases, and the weight of the honeycomb structure becomes heavy, which may make it difficult to raise the temperature. -Since the co-catalyst function of the zirconia composite oxide particles is lowered, the exhaust gas purification performance may be lowered.

In the honeycomb structure of the present invention, the alumina particles forming the honeycomb fired body are preferably θ-phase alumina particles.
If the alumina particles are θ-phase alumina particles, they have high heat resistance, so that noble metals can be supported and high exhaust gas purifying performance can be exhibited even after long-term use.

In the honeycomb structure of the present invention, the content of alumina particles constituting the honeycomb fired body is preferably 15 to 35% by weight.

Examples of the shape of the honeycomb structure of the present invention include cylindrical, prismatic, cylindric, long cylindrical, and chamfered prismatic shapes (for example, chamfered triangular prism shapes).

In the honeycomb structure of the present invention, the shape of the through-holes of the honeycomb fired body is not limited to a square pillar shape, and may be a triangular pillar shape, a hexagonal pillar shape, or the like.
Although the through-holes may have different shapes, it is preferable that all the through-holes have the same shape. That is, it is preferable that the sizes of the through holes surrounded by the partition walls are the same in the cross section perpendicular to the longitudinal direction of the honeycomb fired body.

In the honeycomb structure of the present invention, it is preferable that the density of the through-holes in the cross section perpendicular to the longitudinal direction of the honeycomb fired body is 31 to 155/cm ² .

In the honeycomb structure of the present invention, the fired honeycomb body may further contain inorganic fibers and an inorganic binder.

Alumina fibers are preferred as the inorganic fibers.
Using alumina fibers as the inorganic fibers can improve the mechanical properties of the honeycomb structure.

Boehmite is preferred as the inorganic binder.
This is because most of the boehmite becomes γ-alumina through the firing process.

In the honeycomb structure of the present invention, the honeycomb fired body preferably supports a noble metal.
Examples of noble metals include platinum group metals such as platinum, palladium and rhodium.
The amount of noble metal supported on the entire honeycomb fired body is preferably 0.1 to 15 g/L, more preferably 0.5 to 10 g/L.
In the present specification, the supported amount of noble metal refers to the weight of noble metal per apparent volume of the honeycomb structure. The apparent volume of the honeycomb structure is the volume including the volume of the voids, and when the adhesive layer is included, the volume of the adhesive layer is included.

In the honeycomb structure of the present invention, an outer peripheral coat layer may be formed on the outer peripheral surface of the honeycomb fired body.
The thickness of the peripheral coat layer is preferably 0.1 to 2.0 mm.

[Manufacturing method of honeycomb structure]
Next, a method for manufacturing the honeycomb structure of the present invention will be described.
The honeycomb structure of the present invention is a honeycomb formed body in which a plurality of through-holes are arranged in parallel in the longitudinal direction with partition walls interposed therebetween by molding a raw material paste containing, for example, CZ particles, alumina particles, inorganic fibers, and an inorganic binder. a drying step of drying the honeycomb formed body formed in the forming step; a degreasing step of degreasing the honeycomb dried body dried in the drying step; and a honeycomb degreased in the degreasing step. By firing the body, it can be manufactured by a firing step of manufacturing a honeycomb fired body.

(Molding process)
In the molding step, first, CZ particles and alumina particles are mixed to prepare a raw material paste.
The raw material paste may further contain inorganic fibers, inorganic binders, molding aids, organic binders, organic solvents, pore-forming agents, dispersion media, and the like.
Organic components contained in the raw material paste (forming aid, organic binder, organic solvent, organic pore-forming agent and other components) serve as sources of residual carbon.

CZ particles are a material used as a co-catalyst (oxygen storage material) for an exhaust gas purification catalyst. As the CZ particles, those in which ceria and zirconia form a solid solution are preferable.

The CZ particles may further contain rare earth elements other than cerium. Rare earth elements include scandium (Sc), yttrium (Y), lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), gadolinium (Gd), terbium (Tb), dysprosium (Dy), Ytterbium (Yb), ruthenium (Lu) and the like can be mentioned.

The CZ particles preferably contain 30% by weight or more of ceria, more preferably 40% by weight or more, and preferably contain 90% by weight or less of ceria, more preferably 80% by weight or less. Also, the CZ particles preferably contain zirconia in an amount of 60% by weight or less, more preferably 50% by weight or less. Since such CZ particles have a small heat capacity, the temperature of the honeycomb structure can be easily increased, and the warm-up performance can be improved.

From the viewpoint of improving thermal shock resistance, the average particle size of the CZ particles is preferably 1 to 50 μm. Further, it is more preferable that the CZ particles have an average particle size of 1 to 30 μm. When the average particle diameter of the CZ particles is 1 to 50 μm, the honeycomb structure has a large surface area, so that the oxygen storage capacity can be increased.

Although the type of alumina particles is not particularly limited, θ-phase alumina particles (hereinafter also referred to as θ-alumina particles) are preferable.
By using the θ-phase alumina particles as a partition material for the CZ particles, it is possible to suppress the alumina particles from sintering each other due to heat during use, so that the catalytic function can be maintained. Furthermore, the heat resistance can be enhanced by making the alumina particles the θ phase.

Although the average particle size of the alumina particles is not particularly limited, it is preferably 1 to 10 μm, more preferably 1 to 5 μm, from the viewpoint of improving gas purification performance and warming up performance.

The average particle size of CZ particles and alumina particles can be determined by a laser diffraction particle size distribution analyzer (MASTERSIZER 2000 manufactured by MALVERN).

Materials constituting the inorganic fibers are not particularly limited, but examples thereof include alumina, silica, silicon carbide, silica-alumina, glass, potassium titanate, and aluminum borate, and two or more of them may be used in combination. Among these, alumina fibers are preferred.

The aspect ratio of the inorganic fibers is preferably 5-300, more preferably 10-200, even more preferably 10-100.
Inorganic fibers refer to those having an aspect ratio of 5 or more.

Boehmite is preferred as the inorganic binder.
Boehmite is an alumina monohydrate having a composition of AlOOH, and is well dispersed in a medium such as water. Therefore, it is preferable to use boehmite as the alumina binder.
Moreover, by using boehmite, the moisture content in the raw material paste can be lowered, and the moldability can be improved.

Examples of organic binders include, but are not limited to, methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, polyethylene glycol, phenolic resins, epoxy resins, and the like, and two or more of them may be used in combination.

Examples of the pore-forming agent include, but are not particularly limited to, acrylic resin, coke, starch, and the like.
A pore-forming agent is used to introduce pores into the honeycomb fired body when manufacturing the honeycomb fired body.

Examples of molding aids include, but are not limited to, ethylene glycol, dextrin, fatty acids, fatty acid soaps, polyalcohols, and the like, and two or more of them may be used in combination.

Examples of the dispersion medium include, but are not limited to, water, organic solvents such as benzene, and alcohols such as methanol, and two or more of them may be used in combination.

When CZ particles, alumina particles, alumina fibers and alumina binder are used as the raw materials described above, the blending ratio of these is CZ particles: 40 to 60 wt%, alumina with respect to the total solid content remaining after the firing process in the raw materials Particles: 15 to 35% by weight, alumina fibers: 5 to 15% by weight, alumina binder: 5 to 20% by weight are preferred.

When preparing the raw material paste, it is preferable to mix and knead, and the mixture may be mixed using a mixer, an attritor, or the like, or may be kneaded using a kneader or the like.

In the forming step, the raw material paste containing the CZ particles and the alumina particles is extruded to obtain a formed honeycomb body in which a plurality of through holes are arranged in parallel in the longitudinal direction with partition walls interposed therebetween.

The shape of the formed honeycomb body is not particularly limited, but a columnar shape is preferable. Moreover, it is preferable that the diameter in the case of a cylindrical shape is 150 mm or less.
Moreover, the honeycomb molded body may have a prismatic shape, and in the case of a prismatic shape, it is preferably a square prismatic shape.

(Drying process)
Subsequently, a drying step of drying the formed honeycomb body to obtain a dried honeycomb body is performed.
In the drying step, the formed honeycomb body is dried using a dryer such as a microwave dryer, a hot air dryer, a dielectric dryer, a reduced pressure dryer, a vacuum dryer, or a freeze dryer to produce a dried honeycomb body.

(degreasing process)
Subsequently, a degreasing step is performed to obtain a degreased honeycomb body by degreasing the dried honeycomb body.
In the degreasing step, the organic matter contained in the dried honeycomb body is removed using a degreasing furnace. The degreasing furnace may be integrated with the firing furnace used in the firing process described later, or may be performed continuously with the firing process.
It is preferable to adjust the conditions of the degreasing process by the following methods (a plurality of methods may be combined) so that the amount of residual carbon in the partition walls of the honeycomb structure is 500 to 1500 ppm.
(1) Adjust the heating rate and degreasing temperature.
(2) Change whether to ventilate the through holes of the dried honeycomb body. The amount of residual carbon increases when ventilation is not performed.
(3) Adjust the oxygen concentration in the degreasing furnace. The lower the oxygen concentration, the greater the amount of residual carbon.

(Baking process)
In the firing step, the honeycomb degreased body degreased in the degreasing step is fired to produce a honeycomb fired body.

The temperature of the firing step is preferably 800 to 1300°C, more preferably 900 to 1200°C. In addition, the time of the firing step is preferably 1 to 24 hours,
More preferably 3 to 18 hours. The atmosphere of the firing step is not particularly limited, but the oxygen concentration is preferably 1 to 20%.

Through the steps described above, the honeycomb structure of the present invention can be manufactured.

(Other processes)
The method for manufacturing the honeycomb structure of the present invention may further include a supporting step of supporting a noble metal on the honeycomb fired body, if necessary.
As a method for supporting a noble metal on a honeycomb fired body, for example, a method of immersing a honeycomb fired body or a honeycomb structure in a solution containing noble metal particles or a complex, then pulling out and heating the body, or the like can be mentioned.
When the honeycomb structure has a peripheral coat layer, the noble metal may be carried on the honeycomb fired body before forming the peripheral coat layer, or the noble metal may be loaded on the honeycomb fired body or the honeycomb structure after forming the peripheral coat layer. You can carry it.

In the method for manufacturing a honeycomb structure of the present invention, the amount of the noble metal supported in the supporting step is preferably 0.1 to 15 g/L, more preferably 0.5 to 10 g/L.

In the method of manufacturing the honeycomb structure of the present invention, when forming the outer peripheral coat layer on the outer peripheral surface of the honeycomb fired body, the outer peripheral coat layer is applied to the outer peripheral surface excluding both end surfaces of the honeycomb fired body with a paste for outer peripheral coat layer. After that, it can be formed by drying and solidifying. As the outer peripheral coat layer paste, one having the same composition as the raw material paste can be used.

(Example)
Examples that more specifically disclose the present invention are shown below. In addition, the present invention is not limited only to the following examples.

[Fabrication of honeycomb structure]
(Example 1)
26.5% by weight of CZ particles (average particle diameter: 2 μm), 13.2% by weight of θ-alumina particles (average particle diameter: 2 μm), alumina fibers (average fiber diameter: 3 μm, average fiber length: 60 μm) 5.3% by weight of boehmite as an alumina binder, 7.8% by weight of methyl cellulose as an organic binder, 1.9% by weight of acrylic resin as a pore-forming agent, and 2.0% by weight of graphite as a pore-forming agent. 3% by weight, 4.3% by weight of polyoxyethylene oleyl ether, which is a surface active agent as a forming aid, and 27.4% by weight of deionized water were mixed and kneaded to prepare a raw material paste.

Using an extruder, the raw material paste was extruded to produce a cylindrical honeycomb molded body.
Using a microwave dryer, the honeycomb molded body was dried at an output of 1.8 A and a microwave irradiation time of 110 seconds.

[Degreasing process]
A honeycomb degreased body was produced by degreasing the obtained dried body of the formed honeycomb body.
The degreasing conditions were a degreasing temperature of 600° C., a heating rate of 18° C./hour up to the degreasing temperature, ventilation through the through holes, and an oxygen concentration of 18% in the degreasing furnace.

[Baking process]
The obtained honeycomb degreased body was fired at 1100° C. for 10 hours to prepare a honeycomb fired body according to Example 1. The honeycomb fired body had a cylindrical shape with a diameter of 117.0 mm and a length of ⁸⁰ mm. .

(Examples 2 to 4 and Comparative Example 1)
A honeycomb structure was produced in the same manner as in Example 1, except that the rate of temperature increase to the degreasing temperature in the degreasing step, the presence or absence of ventilation in the through-holes, and the oxygen concentration in the degreasing furnace were changed as shown in Table 1.

[Measurement of residual carbon content]
The partition walls of the honeycomb structure according to each example and each comparative example were cut out and pulverized, and the amount of residual carbon in the partition walls was measured by the combustion volume method.
Table 1 shows the results.

[Measurement of heating time and cooling time]
Gas (air) at room temperature (20° C.) was allowed to flow into the through-holes of the honeycomb structure according to each example and each comparative example at a space velocity of 150000/hr at a space velocity of 150000/hr.
When the temperature of the honeycomb structure reached 450°C, the heater for heating the inflow gas was turned off to switch the inflow gas to room temperature (20°C) gas.
In this step, the time from when the gas started to flow until the temperature of the honeycomb structure reached 200° C. was defined as the temperature rising time.
In addition, the time from when the heater was turned off to when the temperature of the honeycomb structure dropped below 200° C. was defined as the cooling time.
Table 1 shows the results.

As shown in Table 1, in the honeycomb structure of the present invention, the amount of residual carbon in the partition walls is controlled to 500 to 1500 ppm. had become a body. Therefore, when the catalyst is supported, the period during which the catalyst is effective for gas purification can be lengthened.

10 Honeycomb structure 11 Honeycomb fired body 12 Through hole 13 Partition wall 14 Peripheral wall

Claims (5)

A honeycomb structure comprising a honeycomb fired body in which a plurality of through holes are arranged in parallel in the longitudinal direction with partition walls interposed therebetween,
The honeycomb fired body comprises ceria-zirconia composite oxide particles and alumina particles,
A honeycomb structure, wherein the amount of residual carbon in the partition walls measured by a combustion volume method is 500 to 1500 ppm. The honeycomb structure according to claim 1, wherein the partition walls have a porosity of 50 to 65%. 3. The honeycomb structure according to claim 1, wherein the ratio of the through holes in the cross section perpendicular to the longitudinal direction of the honeycomb fired body is 60 to 80%. The honeycomb structure according to any one of claims 1 to 3, which has a volume of 0.5 to 1.5L. The honeycomb structure according to any one of claims 1 to 4, wherein the proportion of the ceria-zirconia composite oxide particles in the honeycomb fired body is 40 to 60% by weight.

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