JPS63264150A - Production of catalyst - Google Patents

Abstract

PURPOSE:To enhance high-temp. durability of a catalyst by forming a coated porous layer on a base material having many through-holes with slurry contg. specified fine powder and also allowing a catalytic active component to be incorporated into the coated layer. CONSTITUTION:Slurry of mixed liquid of both fine powder which contains at least one or more kinds selected from among lanthanum-beta-alumina, neodymium-beta-alumina and praseodymium-beta-alumina and is not larger than 500mum and precursor sol of beta-alumina is prepared. After immersing a honeycomb base material into this slurry to coat it thereon, the honeycomb base material is dried at prescribed temp. and then preliminarily calcined. Furthermore a catalyst is produced by depositing a catalytic active component most suitable for the aimed reaction e.g. noble metal, metallic oxide, sulfide and carbide, etc., thereon. This catalyst especially exhibits effect in the reaction for purifying exhaust gas of an internal combustion engine and the reaction of catalytic combustion of methane and ethane or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a heat-resistant honeycomb catalyst having a high specific surface area at high temperatures.

[Conventional technology]

Conventionally, pellets such as spherical, cylindrical, and ring-shaped pellets were generally used as catalyst carriers, but since honeycomb-shaped carriers have been used for catalysts for purifying exhaust gas from internal combustion engines, other shapes have been used. Honeycomb-shaped carriers have come to be widely used in the field. A honeycomb-shaped carrier having a large number of through-holes is characterized by a smaller pressure loss than a granular carrier.

Up until now, ceramics such as cordierite, mullite, aluminum titanate, α-alumina, and zirconia have been used mainly as materials for honeycomb carriers used at high temperatures due to their heat resistance and thermal shock resistance. A honeycomb carrier made of a material of 1 usually has a specific surface area of 1 m/
g or less, and as it is, it is not possible to effectively support catalyst active components such as platinum and palladium5.

These ceramic honeycombs have α-
It is coated with alumina and used by supporting a catalytically active component such as platinum or palladium on this α-alumina layer. When coating a honeycomb base material with a porous material such as α-alumina, improve adhesion to the honeycomb base material.
Alumina sol has been commonly used as a binder to prevent flaking. However, in this case, when the alumina sol (aqueous slurry of alumina hydroxide) is fired at a high temperature, it transforms into α-alumina, resulting in a decrease in specific surface area, or reacts with the coating agent, causing the coating agent itself to have a high specific surface area. However, since alumina sol was used, the specific surface area decreased, causing problems with heat resistance. Furthermore, if the materials of the binder and the coating agent are different, the coefficients of thermal expansion will also usually be different, so that the adhesion to the honeycomb substrate deteriorates at high temperature values, resulting in a peeling phenomenon.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology does not take into consideration the maintenance of the porosity of the catalyst and the peeling-off thereof, and there are problems with catalyst performance, particularly durability.

An object of the present invention is to provide a honeycomb catalyst with excellent high-temperature durability by improving the method of coating a honeycomb substrate with a heat-resistant material.

The above object is achieved by using a precursor sol made of the same material as the coating agent, which has excellent high temperature resistance, as a binder.

[Means for solving the problem 3 The inventors investigated hundreds of materials in combination with various oxides such as alumina, silica, and magnesia, and found that L
Lanthanum beta alumina (hereinafter referred to as La・β・Aa2o3) with a composition of azOa・11~14AQ20a is replaced by neodymium beta alumina (hereinafter referred to as Nd・β・
(denoted as AQzOa).

Alternatively, Bramoodium beta alumina (hereinafter Pr
- It has been found that using a composite oxide containing at least one type of β·A (referred to as lzos) has good thermal stability and a high specific surface area.

[Effect]

When coating a conventional honeycomb substrate with this heat-resistant carrier, a slurry liquid containing a precursor sol of La, Nd, Pr/β/Al1xOs and fine powder of La, Nd, Pr/β/AQzOa is coated. Due to heat resistance,
It was also found that it has excellent peelability.

β・AI of L a m N d * P r! The coating agent containing zoa as a main component can be produced by the usual precipitation method,
Deposition methods, kneading methods, impregnation methods, evaporation methods, sol-gel methods, etc. can be applied. A particularly preferred method is La.

La, Nd, a method of adding an alkali to a mixed aqueous solution of one or more salts of Nd and Pr and an aluminum salt to form a tight coprecipitate, and heating and calcining this.

Examples include a method of adding water to a mixed solution of at least one alkoxide of Pr and an alkoxide of aluminum to generate a hydrolyzed coprecipitate, and heating and calcining the coprecipitate. Raw materials for aluminum include soluble salts such as nitrates, sulfates, and chlorides, organic salts such as alkoxides,
Hydroxides, oxides, etc. can be used. On the other hand, La, Nd,
As the raw material for Pr, soluble salts such as nitrates, chlorides, and oxalates, hydroxides, and oxides can be used.

La, Nd used as a binder in the present invention.

Pr・β・AQzOs sol is produced by adding a precipitant to a mixed solution of one or more of La, Nd, and Pr and containing AQ, filtering the resulting coprecipitate, and diluting the resulting cake-like substance with water. It is a slurry liquid made into a paste. In addition, when the slurry liquid is fired at 1000°C or higher after water is evaporated, La, Nd, Pr
・Since it becomes β・Af1203, La, Nd, Pr
・β・A (defined as lzos precursor sol. The above-mentioned La・β・AOzO3, Nd-β・AQzOa, Pr・
A fine powder containing at least one of β·AQzOa and a precursor sol are mixed, and a honeycomb substrate is dipped into the mixed solution to coat it. After coating, it is dried at a predetermined temperature and then pre-baked. Next, a catalytically active component most suitable for the desired reaction, such as a noble metal, metal oxide, sulfide, carbide, etc., can be used, and is not particularly limited.

In addition, the following methods are also effective. That is, La, N
d, a catalytically active component is supported on a fine powder containing at least one of Pr, β, and AJlzOa by a conventional method such as impregnation, kneading, and deposition, and then a precursor sol is mixed to form a slurry liquid, and then a honeycomb group is formed. A catalyst can also be obtained by coating a material, drying and firing it. This method is an effective means for reducing uneven impregnation of the active ingredient.

La・β・A Q zos, N d・β・A of the present invention
The precursor sol of Q zos, P r ・β ・AQ203 is a sol obtained by adding water to a cake-like substance obtained by filtering the precipitate obtained by coprecipitation, but the concentration is 1 to 1. 50% by weight (weight after heating at 1000°C/sol weight xlOO), preferably 2 to 10% by weight. It has no effect as a binder at less than 1 wt%, and 50
This is because if the amount of ffi is more than %, the viscosity is too high and coating cannot be performed.

La・β・Aρ203. added to this precursor. Nd・β・
AQ203 or a fine powder containing one or more of Pr, β, AQzO8, or a fine powder supporting a catalytic active component is 5.
After pulverizing the powder to 00 μm or less, preferably 100 μm or less, it is desirable to mix it with a precursor sol and plasticize it with water to form a slurry. The mixing ratio of the precursor sol, fine powder, and water is not particularly limited, and can be mixed at a desired ratio depending on ease of coating, amount of coating, etc.

The catalyst using the carrier according to the present invention is particularly effective in reactions carried out at high temperatures, particularly reactions carried out at 800°C or higher. The types of reactions are not particularly limited, but include exhaust gas purification reactions of internal combustion engines, catalytic combustion reactions of fuels such as methane, ethane, acidic carbon, and hydrogen, and high-temperature steam reactions.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

The method of the present invention is not limited to these examples.

<Example 1> 376 g of aluminum nitrate and 22.8 g of lanthanum nitrate
was dissolved in 2Q of distilled water. CAQ/La=9515
3N ammonia water was added dropwise to this solution while stirring it to neutralize it to pH 7.

The obtained coprecipitate of AQ and La is washed by decantation, and then filtered to obtain a cake-like substance. Divide this into two,
To one side, water was added to make the sol concentration 8%. The other one is 180℃
After drying for 10 hours, it was fired at 800°C for 2 hours. The fired product is pulverized to 20 μm or less. 20g of the aforementioned precursor sol
Add 60 g of water to 20 g of fine powder fired at 800'C to prepare a coating slurry. Next, 201! I
II×20+! Cordierite honeycomb with III square and length 3 CI11 (cell diameter 1.4 mm square, rib thickness 0.2 m)
m) Immerse the substrate in the slurry with sufficient stirring. After removing the slurry liquid within the cell diameter with an air blower after immersion,
Dry at 80°C for 1 hour, then bake at 800°C for 2 hours. Since a sufficient coating amount could not be obtained by dipping - times, the above-mentioned dipping operation was repeated three times in this example to obtain a coating amount of 15 wt %. Next, PD was supported on the carrier as a catalytically active component. The honeycomb carrier of the coating agent was immersed in a palladium nitrate solution adjusted to have a pd of 0.5 wt% relative to the carrier, dried at 180°C for two hours, and pre-fired at 500°C.

A catalyst was obtained by main firing at 1200"C for 2 hours.The coating agent for this catalyst was found to contain La, β, Ant from the X-ray diffraction results.
's, and the specific surface area was 38 rd/g.

<Example 2> While stirring an alkoxide mixed solution in which 140 g of aluminum-5ec-butoxide and 9.5 g of lanthanum isopropoxide were dissolved in 600 ml of benzene, an aqueous solution containing 15% ethanol was gradually added dropwise to obtain a coprecipitate. . After thoroughly washing this coprecipitate with water, it is filtered to form a cake. This cake was divided into two parts, one was added with water to make a 10% precursor sol, and the other cake was dried at 120°C for 12 hours and then baked at 800°C for a working time. 20μm after firing
It was crushed below. The fine powder, precursor sol, and water were mixed in a weight ratio of 1:1:4 to prepare a coating slurry. Using this slurry liquid, coating and PD was carried out in the same manner as in Example 1 to obtain a completed catalyst. As in Example 1, the coating agent for this catalyst was determined by X-ray diffraction from La.
It was confirmed that it was β・AQzOa. Further, the specific surface area was 42 resistance/g.

<Example 3> In the same manner as in Example 2, a coprecipitate cake of AQ and La is obtained. This cake is divided into two parts and one part is made with water to form a 3% precursor sol. After drying the other cake at 120℃,
Bake at 00℃ for a working time.

After firing, it is ground to 20 μm, and the pd is 5 for the ground product.
The pulverized product is impregnated with a palladium nitrate solution adjusted to % by weight, and dried at 120°C for a working time. Then 800
It is fired at ℃ for a certain period of time to obtain a PD-supported fine powder. This pd
The weight ratio of supported fine powder, precursor sol and water is 1:1:3.
The slurry liquid mixed with the above was coated in the same manner as in Example 1.

The coating amount was 10% by weight based on the honeycomb base material. This example is compositionally similar to Example 2, but the manufacturing method is different. That is, in Example 2, the active ingredient was supported after coating the honeycomb substrate with the coating agent. On the other hand, in Example 3, the active ingredient is already supported on the coating agent and then coated.

<Example 4> The preparation method of this example was the same as that of Example 1, but Nd was used instead of La. 250 g of aluminum nitrate and 15.4 g of neodymium nitrate were dissolved in 2p of water, and in the same manner as in Example 1, a cordierite honeycomb substrate was coated with Nd, β, AQzOa, and 0.5% of PD was supported. did.

The coating agent when baked at 1200'C is X.
From line diffraction, it is Nd・β・AQxOs, and the specific surface area is 2.
It was 8 po/g.

<Example 5> The preparation method of this example was the same as that of Example 1, but Pr was used instead of La. 250 g of aluminum nitrate and 15.3 g of praseodymium nitrate were dissolved in 2Q of water, and a cordierite honeycomb substrate was coated with Pr.β.AQxOs in the same manner as in Example 1, and the pd was 0.5. % loading. The coating agent when baked at 1200℃ was determined by X-ray diffraction as Pr, β, AQ2.
0a, and the specific surface area was 26 rd/g.

<Comparative Example 1> Same preparation method as Example 1, but without adding La and using AQ
I went there alone. 300g of aluminum nitrate in 2Q of distilled water
3N ammonium water is added dropwise to the solution with stirring until the pH reaches 7. The resulting Aff precipitate is washed with water and then filtered to obtain a cake-like substance. To one side, water was added to make the sol concentration 10%. The other layer is dried at 180° C. for 10 hours, then fired at 800° C. for a working time and pulverized to 20 μm or less. 20 g of alumina sol, 20 g of finely pulverized product, and 60 g of water are mixed and stirred thoroughly to prepare a coating slurry. Hereinafter, after coating in the same manner as in Example 1,
A comparative catalyst was obtained by supporting 0.5% pd and firing at 1200°C for a working time. The coating agent for the catalyst is α-AQzOa according to the X-ray diffraction results, and the specific surface area is 4.8 n?
/g.

<Comparative Example 2> In this comparative example, La, β, AQ2 was used as a coating agent.
Alumina sol was used as a binder for the fine powder of No. 03. First, in the same manner as in Comparative Example 1, 10% alumina sol was obtained as a binder. Next, in the same manner as in Example 1, AQ and L
After obtaining the coprecipitate of a, it is calcined at 800°C to obtain a fine powder of 20 μm or less.

A slurry liquid for coating is prepared by mixing 20 g of alumina sol, 20 g of fine powder, and 60 g of water.

After coating in the same manner as in Example 1, pd
is supported at 0.5%. A comparison catalyst was obtained by firing at 1200°C for a working time. The coating agent for the catalyst was determined by X-ray diffraction.
-AQzOa, LaAQO3, La ・β・AQzOs
It was a mixture of. In addition, the specific surface area is 12rrr/g
Met.

The performance of the catalysts prepared in Examples 1 to 5 and Comparative Examples 1 to 2 was investigated. The measurement method is to fill a quartz reaction tube with an inner diameter of 30+ nm with a catalyst, and heat the catalyst with an external electric furnace.

Air containing 11,000 pp of methane was introduced into the catalyst layer, and the reaction rate was determined from the difference in methane concentration before and after the catalyst layer at a constant temperature.

Table 1 shows the results of measuring the above-mentioned methane reaction rate at a reaction temperature of 450°C.

Table 1 As shown in Table 1, it can be seen that the catalytic activities of Examples fs1 to fs5 of the present invention are significantly higher than those of the conventional Comparative Examples 1 to 2. This is because by using the precursor sol of La, Nd, Pr/β/AQzO3, the specific surface area of the coating agent can be maintained large, and therefore, it is possible to maintain excellent catalytic performance at high temperatures. can.

〔Effect of the invention〕

Claims (1)

[Claims] 1. A catalyst in which a porous coating layer is formed on a support having a large number of through holes, and a catalytically active component is supported on the porous coating layer, wherein lanthanum, β・alumina, neodymium・β・alumina, praseodymium・β
- A method for producing a catalyst, which comprises coating with a mixed slurry of a fine powder of 500 μm or less containing at least one type of alumina and the β-alumina precursor sol, and then supporting a catalytically active component. 2. Claim 1, characterized in that a catalytically active component is supported on the β-alumina fine powder and coated with a mixed slurry of the β-alumina precursor sol and the fine powder. A method for producing a catalyst. 3. In claim 1, the concentration of the β-alumina precursor sol is 1 to 50% by weight.
A catalyst manufacturing method characterized by: