JP2000296340A - Ceramic honeycomb carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic honeycomb carrier deposited with a high-specific surface area material which is lessened in the deterioration of a low thermal impact characteristic by deposition of active alumina which improves the adhesiveness of the high-specific surface area material, such as active alumina, and has the coefficient of thermal expansion larger than the coefficient of thermal expansion of a honeycomb structure. SOLUTION: The area ratio of the holes of >=1 to <3 times the average grain size of the high-specific surface area material in the minimum diameter when the holes of the cell wall surface of the honeycomb structure of the ceramic honeycomb carrier consisting of the ceramic honeycomb structure deposited with the high-specific surface area, material are viewed in a direction perpendicular to the surface is specified 1 to 12% and the area rate of the pores of >=10 times the average grain size of the high-specific surface area material in the minimum diameter of when the holes existing in the cell wall surface are vied from the direction perpendicular to the surface is specified to <=10%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst carrier having a cordierite honeycomb structure, and particularly to a catalyst carrier having excellent durability used for a catalyst for purifying automobile exhaust gas.

[0002]

2. Description of the Related Art In general, ceramic honeycomb catalysts used for purifying automobile exhaust gas carry a high specific surface area material such as γ-alumina to increase the specific surface area on the surface of a honeycomb structure made of cordierite ceramic having low thermal expansion. Further, it is produced by supporting a catalytic metal such as platinum. Cordierite ceramic is used as a ceramic honeycomb carrier because cordierite has the smallest coefficient of thermal expansion among ceramics, so it generates sudden heat due to the catalytic reaction of unburned hydrocarbons and carbon monoxide in exhaust gas and engine This is because the honeycomb structure has high thermal shock resistance to withstand thermal stress caused by a temperature difference generated in the honeycomb structure due to rapid heat and rapid cooling during start and stop.

However, the thermal expansion coefficient of γ-alumina is more than twice that of cordierite ceramic honeycomb, and it is necessary to burn and support the γ-alumina so as not to be peeled off even during vibration during use in an automobile. Therefore, the thermal expansion coefficient of the carrier supporting the high specific surface area material is about 1.5 to 3 times the thermal expansion coefficient of the carrier not supporting the high specific surface area material, and the thermal shock resistance of the honeycomb carrier is reduced. There was a problem that it was lower than plain. Furthermore, there has been a problem that the high specific surface area material is peeled off due to vibration during use due to a difference in thermal expansion coefficient between the high specific surface area material and the honeycomb structure due to an increase in exhaust gas temperature accompanying the recent tightening of exhaust gas regulations.

[0004]

The following contents have been proposed for improving the thermal shock resistance of a ceramic honeycomb carrier by supporting a material having a high specific surface area. JP-A-62-2
Japanese Patent No. 4441 discloses a catalyst which does not support a material having a high specific surface area and which has a specific surface area of a substrate increased by an acid treatment and a heat treatment to reduce a thermal expansion coefficient. However, a problem with the technique of acid-treating the honeycomb is a decrease in mechanical strength. In particular, in recent catalytic converters, the thickness of the cell wall of the honeycomb structure is designed to be reduced from 150 μm in the related art to about 100 μm, which is ２ of the conventional value. There was a problem that the present technology in which the mechanical strength was reduced by half could not be adopted.
Further, since this technique does not support a high specific surface area material such as γ-alumina, there is a problem that the purification performance is low even if the specific surface area is large.

In Japanese Patent Publication No. 62-8210,
First, by coating with methylcellulose or the like, and then supporting and baking a material having a high specific surface area to eliminate the methylcellulose or the like, the width of 0.5 μm existing in the honeycomb substrate
A technique has been disclosed in which a carrier is prevented from entering microcracks of a degree or less to prevent an increase in thermal expansion coefficient. However, according to the present invention, it is possible to achieve the object that the coefficient of thermal expansion does not increase because a material having a high specific surface area such as γ-alumina does not enter the microcracks. As a result of the weakening of the effect, the honeycomb structure and the high specific surface area material have a reduced adhesive strength, and may not be able to withstand the severe vibration of the automobile, and may be peeled off,
There has been a problem that the number of man-hours for coating increases and the cost increases significantly.

To solve these problems, Japanese Patent Publication No. 5-5
8773, JP-A-6-165939,
The porosity is more than 30% and not more than 42%, and the diameter is 0.5 to 5 μm.
The total pore volume of the pores is 40% or more of the total pore volume, the total volume of the pores having a diameter of 10 μm or more is 30% or less of the total pore volume, and the thermal expansion of the honeycomb structure in the flow direction. A catalyst having a coefficient of 0.3 × 10 ⁻⁶ / ° C. or less and a thermal expansion coefficient in a direction perpendicular to the flow channel of 0.5 × 10 ⁻⁶ / ° C. or less improve a catalyst supporting property and a high specific surface area material. And that the deterioration of thermal shock resistance due to the loading of the catalyst component is reduced. However, even in the present invention, there is no description about the releasability of the material having a high specific surface area, and although the deterioration of the thermal shock resistance is reduced, it is still insufficient. Further, although there is a description of the particle size of activated alumina as a material having a high specific surface area of 5 to 10 μm, there is no description of the correlation between the particle size of the material having a high specific surface area and the pore size of the honeycomb structure.

Further, Japanese Patent Publication No. 6-69534 discloses the above-mentioned Japanese Patent Publication No. 5-58773 and Japanese Patent Laid-Open Publication No. 6-1659.
No. 39, the ratio of the total pore volume of the pores having a diameter of 0.5 to 5 μm to the total pore volume is 40% or more to 70%.
% Or more, more preferably 80% or more, and the coefficient of thermal expansion between 40 and 800 ° C. after supporting the activated alumina is set to 1.0 × 10 ⁻⁶ / ° C. or less to improve catalyst supportability. It discloses that deterioration of thermal shock resistance due to the loading of a high specific surface area material and a catalyst component is reduced. However, as described above, even in the present invention, there is no description about the releasability of the material having a high specific surface area, and even though the thermal shock resistance deterioration is reduced, it is still insufficient. Further, although there is a description of the particle size of activated alumina as a material having a high specific surface area of 5 to 10 μm, there is no description of the correlation between the particle size of the material having a high specific surface area and the pore size of the honeycomb structure.

In Japanese Patent Application Laid-Open No. 9-262484, 4
The average coefficient of thermal expansion from 0 to 800 ° C. is 0.4 × 10 ⁻⁶ / ° C.
A ceramic honeycomb substrate having a carrier such as γ-alumina supported on a ceramic honeycomb substrate having an average thermal expansion coefficient of 0.7 × 10 ⁻⁶ / ° C. at 40 to 800 ° C. reduces mechanical strength as follows. There is disclosed a ceramic honeycomb catalyst having high thermal shock resistance in which the carrier does not peel off. However, even in the present invention, there is no description about the releasability of the high specific surface area material, and there is no description about the correlation between the particle diameter of the high specific surface area material and the pore size of the honeycomb structure.

An object of the present invention is to solve the above-mentioned problems, improve the adhesion of a material having a high specific surface area such as activated alumina, and carry activated alumina having a larger thermal expansion coefficient than a cordierite honeycomb structure. An object of the present invention is to provide a ceramic honeycomb carrier on which a material having a high specific surface area with little thermal shock resistance deterioration is carried.

[0010]

The ceramic honeycomb carrier of the present invention is a ceramic honeycomb carrier comprising a ceramic honeycomb structure supporting a material having a high specific surface area.
The area ratio of pores having a minimum diameter of 1 to more than 3 times the average particle diameter of the high specific surface area material when the pores on the cell wall surface of the honeycomb structure are viewed from a direction perpendicular to the surface is 1 to 12
% And the area ratio of pores having a minimum diameter of 10 times or more of the high specific surface area material when the pores existing on the cell wall surface are viewed from a direction perpendicular to the surface is 10% or less. It is characterized by the following.

Further, the material having a high specific surface area in the ceramic honeycomb carrier of the present invention is characterized by having an average particle size of 1 to 10 μm.

[0012]

In the present invention, the adhesion of a material having a high specific surface area such as activated alumina is good because the material having a high specific surface area and the pore size on the surface of the honeycomb structure are within a certain range. This is due to finding a range where the strength is maximized. Originally, it is considered that the adhesive force between the honeycomb structure and the high specific surface area material occurs because of the so-called anchor effect caused by the high specific surface area material entering pores or microcracks on the surface of the honeycomb structure. Further, regarding the supportability of a material having a high specific surface area, it has been pointed out that correlation with water absorption and porosity and pores in a specific pore diameter region significantly contribute to the supportability. More than these factors,
It has been clarified that the combination of a high specific surface area material with a certain particle size and a certain size of pores on the honeycomb structure cell wall surface significantly contributes to the adhesive force acting between them. That is, the mercury intrusion method has been used for measuring the pore diameter and the pore volume, which is known in the prior art, but this method has been widely used as a general method for measuring pores since ancient times. However, according to the method, all the open pores included in the honeycomb structure are measured.

[0013] However, the present inventors have made
As a result of intensive experiments, the minimum diameter of the pores on the cell wall surface of the honeycomb structure when viewed from the direction perpendicular to the surface is smaller than the size of the open pores obtained by the mercury intrusion method. It was found that it greatly contributed to sex. This is also due to the fact that the form of the pores present in the ceramic honeycomb is different between the case where the pores exist inside the ceramic body and the case where it exists on the outermost surface of the ceramic body. Specifically, when the pores on the surface of the honeycomb structure cell wall are viewed from a direction perpendicular to the surface, the area ratio of pores whose minimum diameter is 1 to 3 times the average particle diameter of the high specific surface area material is 1 to 3 １２12%. As shown in FIG. 2, the minimum diameter is defined as the minimum diameter which passes through the center of gravity of each pore and
Define the smallest diameter connecting the points. If the minimum diameter of the pores when viewed from the direction perpendicular to the cell wall surface is less than one time that of the high specific surface area material, the so-called anchor effect for the high specific surface area material to enter the pores cannot be obtained, so that the adhesive force is not obtained. Cannot be obtained. On the other hand, when the minimum diameter of the pores when viewed from the direction perpendicular to the cell wall surface exceeds three times that of the high specific surface area material, the high specific surface area material having a large thermal expansion coefficient enters the inside of the honeycomb structure. As a result, the thermal expansion coefficient of the honeycomb carrier increases, and the thermal shock resistance deteriorates.

Further, when the pores on the surface of the cell wall of the honeycomb structure are viewed from a direction perpendicular to the surface, the area ratio of pores whose minimum diameter is at least 1 to less than 3 times the average particle diameter of the high specific surface area material is as follows. If it is less than 1%, the anchor effect can be obtained, but the size is small and sufficient adhesion cannot be obtained. On the other hand, when the pores on the surface of the honeycomb structure cell wall are viewed from the direction perpendicular to the surface, the area ratio of the pores whose minimum diameter is 1 to 3 times the average particle diameter of the high specific surface area material is 12% or less. If it exceeds, although the adhesive force increases, the number of places where the high specific surface area material having a large coefficient of thermal expansion enters the honeycomb structure increases, so that the coefficient of thermal expansion of the honeycomb carrier increases and the thermal shock resistance deteriorates. It will be.

Further, in the present invention, when the pores present on the cell wall surface are viewed from a direction perpendicular to the surface, the minimum diameter is 10% or less of the area ratio of pores having an average particle diameter of 10 times or more of the high specific surface area material. And That is, pores having a maximum diameter of 10 times or more the average particle diameter of the high specific surface area material when the pores existing on the cell wall surface are viewed from the direction perpendicular to the surface are considerably larger than the particle diameter of the high specific surface area material. Therefore, the contribution to the adhesion between the honeycomb wall and the high specific surface area material is small. In addition, the high specific surface area material having a large coefficient of thermal expansion penetrates into the inside of the honeycomb wall, so that the coefficient of thermal expansion of the honeycomb carrier becomes large, and when the area ratio exceeds 10%, the influence becomes large. On the other hand, it is naturally said that the thermal shock resistance of the ceramic material is proportional to the mechanical strength and inversely proportional to the Young's modulus and the coefficient of thermal expansion. In order to increase the mechanical strength, defects inherent in the ceramic material, for example, pores, crystal grains, crystal grain boundaries, brittle fracture progresses starting from the transition, etc., by reducing the size of these defects It is common to achieve. Therefore, when the pores present on the cell wall surface are viewed from a direction perpendicular to the surface, the maximum diameter is the average particle diameter of the high specific surface area material.
By setting the area ratio of the pores of 0 times or more to 10% or less, the pore size can be suppressed to a certain small range, and therefore, the mechanical strength of the honeycomb structure is improved, and as a result, the thermal shock is improved. It is.

In the present invention, the reason why the average particle size of the high specific surface area material is 1 to 10 μm is that the adhesive force between the honeycomb structure and the high specific surface area material is maximized particularly in this range.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an actual embodiment of the present invention will be described. (Example 1) As raw material powder, kaolin, calcined kaolin,
Talc, alumina, using aluminum hydroxide, these are blended cordierite composition _{(5SiO 2 · 2Al 2 O 3} · 2MgO) to become so, stearic acid was added thereto methylcellulose as a binder, as a lubricant, a further water In addition, it was kneaded to obtain an extrudable clay. Next, the kneaded material of each batch was subjected to a rib thickness 19 by a known extrusion molding method.
A honeycomb structure having a diameter of 93 mm and a height of 150 mm having a quadrangular cell shape of 0 μm and 62 cells per square centimeter was formed. After drying the honeycomb structure, 141
Baking is performed at a temperature of 5 ° C. Thus, a cordierite-based honeycomb structure No. 1 was obtained. FIG. 1 and Table 1 show the measurement results of the minimum diameter of the pores when the pores on the cell wall surface of the honeycomb structure at this time were viewed from a direction perpendicular to the surface. Table 1 shows the area of pores having a specific range of sizes from the graph of the relationship between the minimum diameter and the cumulative pore area shown in FIG. 1 by numbers. The area occupied by all pores is 156112 μm ² ,
The area ratio of the pores was 17.7%. When observing the pores of the cell wall surface in a direction perpendicular to the cell wall surface, a photograph was taken of the cell wall surface at a magnification of 80 times with a scanning electron microscope, and the obtained photographic data was imaged with a scanner. The data was read as data, and the obtained image data was analyzed using commercially available image analysis software (Image Pro Plus version 3.0, manufactured by Media Cybernetics). Here, the minimum diameter is defined as the smallest diameter passing through the center of gravity of each pore and connecting two points on the outer periphery, as shown in FIG. The obtained cordierite honeycomb structure was immersed in a slurry obtained by adding an aluminum nitrate solution to a commercially available activated alumina / ceria powder (average particle size: 2 μm, 5 μm, 10 μm), taken out, and then the excess slurry was blown off. After drying at 150 ° C. for 2 hours, it was fired at a temperature of 550 ° C.

[0018]

[Table 1]

Next, these honeycomb carriers were subjected to a thermal shock test. The thermal shock test was performed at 620 at room temperature of 20 ° C.
The sample is placed in an electric furnace kept at 0 ° C., and after 30 minutes, the sample is taken out of the electric furnace and naturally cooled in the air. After cooling was completed, the external appearance was visually observed, and the outer peripheral surface of the honeycomb carrier was lightly tapped with a thin metal rod over the entire circumference. At the same time, the presence or absence of peeling of the activated alumina was also confirmed. In this case, furnace temperature 620 ° C-room temperature 20 ° C
= 600 ° C is the thermal shock temperature difference. Subsequently, the temperature of the electric furnace was increased by 25 ° C., and the same process was repeated until cracks and peeling were observed or the hammering sound became dull. The highest temperature that passed was defined as the thermal shock temperature. Table 2 shows the test results for three types of activated alumina / ceria powder.
Shown in The rejection judgment content in Table 2 is the thermal shock temperature difference +2
The content at the time of a failure judgment at 5 ° C is shown. Contents,
There are two cases: when a crack occurs in the honeycomb structure, and when the high specific surface area material peels off.

[0020]

[Table 2]

(Comparative Example 1) A rib thickness of 190 μm and a number of cells per square centimeter of 62 were determined in the same manner as in Example 1.
93mm in diameter and 150mm in height with 4 cell shapes
Are formed, dried, and fired, and three types of honeycomb structures NO. 2, 3, 4 were obtained. Here, a honeycomb structure having different pore sizes on the cell wall surface was obtained by adjusting the particle size, grade, and firing conditions of the raw material powder to be used. Table 3 shows the measurement results of the minimum diameter of the pores when the pores on the cell wall surface of the fired body were viewed from a direction perpendicular to the surface. The area ratio of the total pores of the three kinds of honeycomb structures was between 17.6 to 18.2. As in Example 1, a commercially available activated alumina / ceria powder (average particle size of 5%) was applied to the obtained cordierite honeycomb structure.
μm), and immersed in a slurry containing an aluminum nitrate solution and taken out.
After drying at 0 ° C. for 2 hours, firing was performed at a temperature of 550 ° C.
Next, the results of a thermal shock test performed in the same manner as in Example 1 are also shown in Table 2. As is evident from the results in Table 2, among the pores on the cell wall surface, the area ratio of those having a minimum diameter of 1 to 3 times the average particle diameter of the high specific surface area material is 1 to 12%, Further, in Example 1 in which the minimum area among the pores on the cell wall surface is 10% or less in the area ratio of the pores having an average particle diameter of 10 times or more of the high specific surface area material, the thermal shock temperature difference is smaller than that in Comparative Example 1. It is confirmed that the present invention is extremely effective because the material is high and the high specific surface area material does not peel off. On the other hand, the honeycomb structure NO. In 2, the area ratio of pores having a minimum diameter of 10 times or more of the high specific surface area material among the pores on the cell wall surface exceeds 10%, so that the honeycomb structure is cracked at a thermal shock temperature difference of 600 ° C. There has occurred. The honeycomb structure NO. In 3, the area ratio of pores having a minimum diameter of 1 to 3 times the average diameter of the high specific surface area material among the pores on the cell wall surface exceeds 12%,
A crack occurred in the honeycomb structure at a thermal shock temperature difference of 650 ° C. The honeycomb structure NO. In 4, since the area ratio of pores having a minimum diameter of 1 to 3 times the average particle diameter of the high specific surface area material among the pores on the cell wall surface is less than 1%, the adhesion of the high specific surface area material is reduced, At a thermal shock temperature difference of 625 ° C., peeling of the high specific surface area material occurred.

[0022]

[Table 3]

The present invention is not limited to the above-described embodiment. For example, in the embodiment, the ceramic honeycomb structure having a circular cross section is used. It is natural that the effect is obtained.

[0024]

As is apparent from the above description, according to the present invention, the difference between the particle size of the high specific surface area material to be supported and the size of the pores existing on the cell wall surface of the honeycomb structure on the cell wall surface is obtained. Since the relationship is defined, it is possible to obtain a ceramic honeycomb carrier having high thermal shock resistance in which the high specific surface area material does not peel off.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the minimum diameter of pores existing on the cell wall surface of a honeycomb structure and the cumulative area of pores when viewed from a direction perpendicular to the cell wall surface in Example 1.

FIG. 2 is a diagram showing a definition of a minimum diameter of a pore.

[Explanation of symbols] 1 pore, 2 center of gravity, 3 minimum diameter,

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Claims (2)

[Claims] 1. A ceramic honeycomb carrier comprising a ceramic honeycomb structure carrying a material having a high specific surface area, wherein the minimum diameter of pores in the cell wall surface of the honeycomb structure when viewed from a direction perpendicular to the surface is the high ratio. The area ratio of pores that are 1 to 3 times the average particle size of the surface area material is 1 to 3
When the pores present on the cell wall surface are viewed from a direction perpendicular to the surface, the minimum diameter is 12% and the area ratio of pores having an average particle diameter of 10 times or more of the high specific surface area material is 10% or less. A ceramic honeycomb carrier, characterized in that: 2. The high specific surface area material has an average particle size of 1 to 10 μm.
The ceramic honeycomb carrier according to claim 1, wherein m is m.