JPS61197032A - Production of catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To form a film having a high covering strength by covering a carrier with a specified solid quantity of an alumina slurry composed of activated alumina powder having <=15mum average particle diameter and ammonium salts of polyacrylic acid oligomer. CONSTITUTION:The alumina slurry which is composed of activated alumina powder having <=15mum average particle diameter and ammonium salts of polyacrylic acid and whose solid matter content is 50-90wt% is prepared. By using said slurry an activated alumina film is formed on a monobloc structure carrier made from cordierite and further a catalytic metal is supported on said carrier on which said film is formed, thus the catalyst for purifying the exhaust gas is formed. The temp. at which the alumina slurry stuck onto the carrier is calcined is preferably to be 250-1,000 deg.C. Noble metals such as platinum, palladium, rhodium, etc., are used as a catalytic metal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a catalyst for purifying exhaust gas by detoxifying hydrocarbons, carbon oxides, and nitrogen agglomerates, and in particular for automobile exhaust gas and fixed gas. The present invention relates to a method for manufacturing a catalyst used for purifying exhaust gas from a type engine.

[Conventional technology]

Conventionally, exhaust gas purification catalysts have been produced by attaching activated alumina powder to a cordierite monolithic support (monolith support) using various methods to form an active alumina film, and then supporting the catalyst metal. It is manufactured by The cordierite monolithic support has a specific surface area of approximately lrr? Since it has a very low specific surface area of /g, if it is used as it is, the dispersibility will be poor when supporting the catalyst metal, so it is necessary to form an activated alumina liquid film with a high specific surface area in advance before supporting the catalyst metal. There is.

A common method for forming activated alumina coatings is to combine activated alumina powder, water, a thickener (e.g. alumina sol), a binder component (e.g. a soluble aluminum salt such as alumina nitrate sol) to a solids content of 20-50% by weight and 11% by weight. In this method, a slurry is prepared by mixing, stirring or finely pulverizing a PH regulator, etc., and a monolithic carrier is coated with gold using this slurry.

In addition, conventional methods for obtaining a stable slurry include increasing the viscosity with a thickener to prevent sedimentation of alumina particles, and using a pH adjuster (for example, increasing the dispersibility of alumina particles with hydrochloric acid or nitric acid). Another method is to mix various additives and then pulverize the mixture using a sol mill or the like to obtain a highly viscous slurry with thixotropic properties.

[Problem that the invention seeks to solve]

In the above conventional method, when the slurry solid content is 50% by weight or more, the viscosity becomes 1 000 CPS or more, or
Otherwise, it becomes dull and a practical slurry cannot be obtained, so the solid content usually needs to be 20 to 50% by weight.

Mayu: The conventional methods of adding various additives such as thickeners and PH sub-modifiers mentioned above or adding a pulverization process using a gall mill or the like are extremely expensive.

Furthermore, the strength of alumina coatings obtained by conventional techniques is still insufficient in terms of durability.

As mentioned above, there are problems with the conventional technology, but according to the knowledge of the present inventors, if the solid content of the slurry can be increased to 50 parts by weight or more, the strength of the alumina film will be even stronger than the current one, and It has been found that it is possible to increase the amount of alumina deposited by multiple coating operations.

However, simply increasing the solid content may cause an increase in viscosity or dullness.

[Means for solving problems]

The present invention provides a method for producing an exhaust gas purifying catalyst using a slurry that allows an activated alumina coating having sufficient coating strength to be formed on a cordierite monolithic support in a simple process and at low cost. This is what we provide. Therefore, in the method of the present invention, an alumina slurry having a solid content of 50 to 90% by weight, which is composed of activated alumina powder with an average particle size of 15 μm or less and an ammonium salt of a polyacrylic acid oligomer, is prepared. The present invention is characterized in that an activated alumina coating is formed on an integral structural support of cordierite material using the above method, and a catalytic metal is further supported on the support on which the coating is formed.

The slurry used in the method of this invention is prepared by mixing activated alumina powder with an average particle size of 15 μm or less and ammonium salt of polyacrylic acid oligomer, and has a much higher solid content than conventional slurry. It has a solid content of 50% by weight or more and a viscosity of 500CP8 or less, which is an appropriate viscosity value as a slurry for forming a coating on a monolithic carrier.

In this invention, preacrylic acid oligomers are used mixed with activated alumina powder in water.

It is used in neutralized form as Monicum salt.

It is desirable that the ammonium salt of the I-lyacrylic acid oligomer be added in an amount of 0.1 to 5% by weight relative to the alumina slurry.

In forming an activated alumina coating on a monolithic carrier using an alumina slurry in the method of this invention, the temperature at which the alumina slurry deposited on the monolithic carrier is fired is 2.
The temperature is preferably 50'C to 1000C, and examples of the catalytic metal include platinum and tsucladium.

[Function] A polyacrylic acid oligomer using a noble metal such as rhodium has a structure that has both lyophobicity and lyophilicity, so it has the effect of stabilizing the powder surface. Since the solid content in the alumina slurry can be reduced to 50% by weight, it is possible to maintain the peptized state without causing agglomeration of the powder.
Even if it is made more than 1 cup, the viscosity does not increase or thicken as in the conventional case.

Furthermore, when the average particle size of the activated alumina powder is set to 15 μm or less, the filling rate of the particles increases, thereby increasing the strength of the activated alumina coating.

When the average particle size exceeds 15 μm, the coating strength decreases as the particle size increases.

〔Example〕

Example 1 Specific surface area of average particle size 13.5 pm x 37n? /1 activated alumina powder, 20 g of ammonicum salt of polyacrylic acid oligomer (acrylic polymer A-stx4 manufactured by Toagosei Co., Ltd.), and 280 g of pure water were mixed at a rotation speed of 700 γpm using a Yamato Ugo stirrer. 1
Mix and stir for hours to obtain a solid content of 70% and a viscosity of 150 CF2.
A stable slurry was obtained. In this slurry, Nippon Insulators Co., Ltd. (NGK) 9 which had been sufficiently absorbed with water in advance
Cordierite cylindrical shape (diameter 93U, length 1QQJ
ljl, volume 0.6791)-shaped monolithic carrier (30
0 cells/inch" (approximately 47 cells/cIi)) After soaking for 15 minutes and taking out, the remaining slurry in the cells is blown away with a stream of compressed air. Then, at a temperature of 110°C for 1 hour. After ventilation drying, 500℃
It was baked at a temperature of 2 hours. As a result, the weight increase of the carrier coating material was 7517.

Next, this carrier is immersed in a platinum ammine aqueous solution to adsorb 1r of platinum onto the carrier, washed with water, and subsequently immersed in a rhodium chloride aqueous solution to support rhodium on the carrier,
Then, after drying at a temperature of 100°C, it was dried at a temperature of 500°C.
After firing for 0 minutes, a catalyst for purifying automobile exhaust gas was obtained. Chemical analysis of the amount of noble metal supported on this catalyst revealed that the amount of platinum supported was 1. Op/l-catalyst, rhodium was 0.11//l-catalyst.

For one of the two samples of the new catalyst obtained in this way, 5ti! ! A compressed air flow with a pressure of /crA was blown with an air gun for 10 minutes to determine the peeling rate (
The weight percent) was measured and found to be 0.6% by weight.

Next, another new catalyst sample was subjected to the following durability test, and the catalyst sample after durability was subjected to the following activity evaluation test, and the results of the activity evaluation are shown in the table below.

The durability test was conducted using an engine with an exhaust of 13,400 cr.
Rotation speed: 360 Orpm, Boost: 300 H, ii
l, catalytic gas temperature 750℃, air fuel ratio (A/F) 1
The test was carried out for 50 hours under the conditions of 4.8.

The catalyst activity evaluation test was carried out using an engine with a displacement of 1,600 cm, a rotation speed of 260 Orpm, and a booth) -360 ax.
Hg, catalytic gas temperature 460℃, air fuel ratio (A/F)
The gas purification rate of the catalyst with respect to hydrocarbons (HC), -carbon (CO), and nitrogen (NOx) was measured under the conditions of 14.5.

Example 2 Catalytic metals palladium and rhodium were applied to a monolithic carrier coated with activated alumina in the same manner as in Example 1, using palladium chloride aqueous solution and rhodium chloride aqueous solution sequentially. A catalyst was obtained by supporting.

Note that the weight increase of the coating material on the carrier is 77g. Moreover, the supported It of the catalyst metal is P d/Rh = 170.1
fill-catalyst.

The peeling rate (wt%) of the coat layer was measured in the same manner as in Example 1 for the catalyst obtained as described above.
It was 0.3% by weight.

In addition, Example 1 regarding the catalyst obtained as described above
A durability test was conducted in the same manner as above, and an activity evaluation test was conducted on the catalyst after the durability test, and the results of the activity evaluation are shown in the table below.

Example 3 A monolithic carrier coated with activated alumina was coated with a catalyst in the same manner as in Example 1 by sequentially using a platinum ammine aqueous solution, a chloride/mother radium aqueous solution, and a rhodium chloride aqueous solution. A catalyst was obtained by supporting the metals platinum, nocrasocum and rhodium.

Incidentally, the increase in the amount of coating material on the carrier was 74 g. The amount of catalyst metal supported is Pt/Pd/Rh=o, 51
0.510.19/l-catalyst.

The peeling rate (weight qb) of the coat layer of the catalyst obtained as described above was measured in the same manner as in Example 1, and was found to be 0.9% by weight.

In addition, Example 1 regarding the catalyst obtained as described above
A durability test was conducted in the same manner as above, and an activity evaluation test was conducted on the catalyst after the durability test, and the results of the activity evaluation are shown in the table below.

Comparative Example 1 Activated alumina powder with an average particle size of 18μ and a specific surface area of z08m"/, ?, 000!l, alumina sol (alumina content 10wt%) 350.li', aluminum nitrate nonahydrate crystal 60I and pure water 400g were mixed and stirred using a Waring blender at a rotational speed of 110,000 rpm for 10 minutes, and further milled for 17 hours using a ball mill. As a result, a stable slurry with a solid content of 41% was obtained. Using this slurry, Examples were prepared. In the same manner as in Example 1, an activated alumina coating was formed on the monolithic support, and a rough coating of Example 1 was formed.
A catalyst was obtained by supporting the catalyst metals platinum and ronium in the same manner as above. In addition, the increase in the amount of charge of the carrier coating material is 25g.
Met.

The peeling rate (wt%) of the coat layer was measured in the same manner as in Example 1 for the catalyst obtained as described above.
It was 17 weight it%.

Example 1 Regarding the catalyst obtained as described above
All durability tests were conducted in the same manner as above, and an activity evaluation test was conducted on the catalyst after the durability test, and the results of the activity evaluation are shown in the table below.

Comparative Example 2 A catalyst was obtained in the same manner as in Example 2, except that the monolithic support prepared in Comparative Example 1 and coated with activated alumina was used.

When the peeling rate (wt%) of the coat layer was measured for the thus obtained catalyst in the same manner as in Example 1, it was found that 2
It was a one-layer cake.

In addition, Example 1 regarding the companion medium obtained as described above
A durability test was conducted in the same manner as above, and an activity evaluation test was performed on the catalyst after the durability test, and the results of the activity evaluation are shown in the table below.

Comparative Example 3 A catalyst was obtained in the same manner as in Example 3, except that the activated alumina-coated monolithic support prepared in Comparative Example 1 was used.

The peeling rate (%) of the coating layer of the thus obtained catalyst was measured in the same manner as in Example 1, and it was found that 1
It was 9% by weight.

In addition, Example 1 regarding the catalyst obtained as described above
A durability test was conducted in the same manner as above, and an activity evaluation test was performed on the catalyst after the durability test, and the results of the activity evaluation are shown in the table below.

Table (Note) HC is hydrocarbon, CO is carbon monoxide and N
Ox represents nitrogen oxide.

〔Effect of the invention〕

As described above in detail, according to the method of the present invention, an exhaust gas purifying catalyst having a high film strength and excellent catalytic performance can be manufactured at low cost through simple steps.

Claims (1)

[Claims] An alumina slurry with a solid content of 50 to 90% by weight is prepared from activated alumina powder with an average particle size of 15 μm or less and an ammonium salt of a polyacrylic acid oligomer, and the slurry is used to prepare a cordierite monolithic structural support. 1. A method for producing an exhaust gas purifying catalyst, which comprises forming an activated alumina film on a catalyst, and further supporting a catalytic metal on the carrier on which the film is formed.