JPH05168949A - Manufacture of exhaust gas purification catalyst - Google Patents

Abstract

PURPOSE:To improve the low temperature activity of a catalyst by providing the first process for the preparation of the first alcohol solution or ethylene glycol solution, the second process for the preparation of the second solution, the third process for the formation of a hydrolytic product, the fourth process for the processing of said product into carrier powder and the fifth process for the formation of a catalyst. CONSTITUTION:The first process adjusts the first alcohol solution or an ethylene glycol solution which contains carrier powder carrying a catalytic metal and 10 to 50wt.% of aluminum alkoxide for the former. The second process adds a catalytic metal salt dissolved in the ethylene glycol solution to the first alcohol solution or ethylene glycol solution and thereby prepares these materials as the second solution containing the carrier powder, aluminum alkoxide and catalytic metal salt. The third process forms a hydrolytic product on the surface of the carrier powder by adding water to the second solution and allowing the mixture to undergo a hydrolytic process. The fourth process separates and bakes the carrier powder from the second solution to obtain carrier powder to be carried 2A. Finally the fifth process forms a catalyst 1A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, even when the exhaust gas temperature is low, such as when the engine is started in a cold state,
The present invention relates to a method for producing an exhaust gas-purifying catalyst capable of sufficiently exhibiting a catalytic function, efficiently oxidizing HC in exhaust gas to convert it into H ₂ O and CO ₂ , and purifying exhaust gas.

[0002]

2. Description of the Related Art Conventionally, a pellet type catalyst or a monolith type catalyst carrying a noble metal has been used as an exhaust gas purifying catalyst for purifying automobile exhaust gas. When purifying exhaust gas with an exhaust gas purifying catalyst (hereinafter referred to as a catalyst), harmful components HC, CO, N in the exhaust gas are used.
Among Ox, the performance of purifying HC is particularly strongly affected by the exhaust gas temperature.

For example, a conventional catalyst has an exhaust gas temperature of 30.
The catalyst function is sufficiently exhibited at a high temperature of 0 ° C or higher. Therefore, the HC (hereinafter, referred to as cold HC) component in the low-temperature exhaust gas when the engine is started may be exhausted into the atmosphere without being sufficiently purified by the catalyst. Further, generally, the engine at the time of starting in the cold state is supplied with a mixture having a higher concentration than that during normal operation, and the cold HC amount is accordingly higher than the amount of HC contained in the exhaust gas during warm-up operation. Many.

Therefore, conventionally, as a countermeasure against the cold HC, H is provided upstream of the catalyst arranged in the exhaust gas system of the engine.
It is known to dispose a C trapper and use it together (see Japanese Patent Laid-Open No. 2-75327). This HC trapper has a function of temporarily adsorbing cold HC by the HC adsorbing member when the exhaust gas temperature is low, and releasing the adsorbed HC as the exhaust gas temperature shifts to a high temperature.

However, in general, the HC trapper's HC adsorption performance is highest at an exhaust gas temperature of 200 ° C., and gradually decreases as the temperature rises above this temperature. Therefore, as a catalyst, it is desired to enhance the catalytic function in the range of the exhaust gas temperature of 250 ° C. or higher and lower than 300 ° C. to efficiently purify the cold HC. As a method for producing a catalyst for enhancing the catalytic function, for example, Japanese Patent Application Laid-Open No. 61-61645 proposes a sol-gel supporting method instead of the conventional dipping method. In this sol-gel loading method, a metal alkoxide and a catalytic metal salt are dissolved and mixed in an ethylene glycol solution, and then the solution is hydrolyzed to obtain a precipitate (fine powder), which is shaped into an arbitrary shape to form a catalyst Is.

[0006]

However, according to the sol-gel loading method, the precipitate produced by the hydrolysis, for example, the loading carrier powder A carrying the catalyst shown in an enlarged scale in FIG. Part of the catalytic metal B1 is taken in. Therefore, the amount of the catalyst metal B2 supported on the surface a of the carrier powder A becomes small. Therefore, for example, as shown in FIG. 6, when the pellet carrier C is used by granulating the carrier powder A into a predetermined size, the pellet catalyst C is incorporated into the carrier powder A. It is not possible to efficiently purify the cold HC because a part of the catalyst metal B1 is not effectively used and is wasted, and the amount of the catalyst metal B2 that contacts exhaust gas is small.

An object of the present invention is to provide a method for producing a catalyst, which is an improvement over the conventional sol-gel supporting method.

[0008]

A method for producing a catalyst for purifying exhaust gas according to the present invention comprises a carrier powder carrying a catalyst metal and a first alcohol solution containing 10 to 50 wt% of an aluminum alkoxide with respect to the carrier powder. Or a first step of preparing an ethylene glycol solution, and a catalyst metal salt dissolved in an ethylene glycol solution is added to the first alcohol solution or the ethylene glycol solution to obtain the carrier powder, the aluminum alkoxide, and the catalyst. A second step of preparing a second solution containing a metal salt; a third step of adding water to the second solution to form a hydrolysis product on the surface of the carrier powder by hydrolysis; , The second
It is characterized by comprising a fourth step of separating the solution from the solution and calcining it to obtain a carrier powder, and a fifth step of forming a catalyst from the carrier powder.

The carrier powder carrying the catalytic metal used in the first step has, for example, an average particle size of 5 to 50 μm.
m of activated alumina can be used. The reason for limiting the amount of aluminum alkoxide contained in the first alcohol solution to the range of 10 to 50 wt% with respect to the carrier powder carrying the catalyst metal in the first step is as follows.
If it is less than 10 wt%, the fixation of the precious metal becomes insufficient,
This is because the precious metal is buried when it exceeds 50 wt%.

As the first alcohol solution, one containing 1 to 20 wt% of alkoxide barium or lanthanum alkoxide with respect to the amount of the aluminum alkoxide can be used. Moreover, as the aluminum alkoxide used in the first step, for example, aluminum triisopropoxide, aluminum tributoxide, or the like can be used.

As the alcohol solution used in the first step, for example, a lower alcohol solution such as methanol, etal and isopropar can be used. This is because the alcohol-based solution easily disperses the aluminum alkoxide and the catalyst metal salt uniformly. As the catalyst metal salt used in the second step, for example, a salt of metal, noble metal or the like can be used.

The water used in the third step is preferably pure water or water that is as close to pure water as possible. As the water, for example, ion exchanged water subjected to ion exchange treatment, distilled water subjected to distillation treatment, or the like can be used. Fourth
In order to separate the carrier powder from the second solution in the step, a filtration device, a centrifugal separation device or the like can be used. The supported carrier powder formed in the fourth step is the carrier powder used in the first step, on which the catalytic metal is highly dispersed and supported.

As the catalyst formed in the fifth step, a pellet catalyst prepared by granulating a carrier powder having the above-mentioned catalytic metal carried in a highly dispersed manner into a predetermined size, or a slurry of the carrier powder on the surface of a monolith substrate. It can be coated as a catalyst supporting layer to form a monolith catalyst or the like.

[0014]

In the method for producing an exhaust gas purifying catalyst of the present invention, the first step, the second step, the third step, the fourth step, and the fifth step are sequentially carried out. First, in the first step, a predetermined amount of carrier powder and 10 to 50 wt% of aluminum alkoxide with respect to the carrier powder are added to a predetermined amount of alcohol solution or ethylene glycol solution, and heated and stirred.
Thereby, the first alcohol solution containing the carrier powder and the aluminum alkoxide or the ethylene glycol solution can be prepared.

In the second step, a predetermined amount of the catalytic metal salt dissolved in the ethylene glycol solution is added to the first alcohol solution or the ethylene glycol solution, and the mixture is heated and stirred. Thereby, the second solution containing the carrier powder, the catalytic metal salt, and the aluminum alkoxide can be prepared. In the third step, a predetermined amount of water is added to the second solution to cause hydrolysis to form a hydrolysis product on the surface of the carrier powder.
The hydrolysis product contains aluminum hydroxide and a catalytic metal.

In the fourth step, the hydrolysis product is separated from the second alcohol solution by using a filter device, a centrifugal separator or the like. Then, the separated hydrolysis product is washed, dried and calcined. Then, the aluminum hydroxide contained in the hydrolyzate is baked and becomes adhered activated alumina that adheres to and covers the surface of the carrier powder, and is fixed to the surface. On the other hand, the catalytic metal is retained in a highly dispersed state in the form of particles on the entire surface of the carrier powder by the function of the adhered activated alumina as a binder. That is, in the fourth step, a carrier powder having the catalytic metal particles fixed and held in a highly dispersed state by the adhered activated alumina formed on the surface is formed.

In the fifth step, the carrier powder obtained by the fourth step and having highly dispersed catalytic metal particles on the surface thereof is granulated into a predetermined size to form a pellet catalyst. Alternatively, the monolith catalyst is formed by making the carrier powder into a slurry and then coating the surface of the monolith substrate as a catalyst carrier layer.

[0018]

【Example】

[0019]

Example 1 A method for producing an exhaust gas purifying catalyst of Example 1 (hereinafter referred to as the production method of Example 1) comprises a first step, a second step, a third step, a fourth step and a fifth step. Consists of. A case where the monolith catalyst 1A shown in FIG. 1 is manufactured by the above respective steps will be described.

First, in the first step, the first alcohol solution is prepared. That is, the average particle size prepared in advance is 5
100 g of activated alumina powder (carrier powder) of ˜50 μm
And 50 g of aluminum triisopropoxide powder and 2 g of barium powder with respect to the activated alumina powder,
It is added to a predetermined amount of isopropanol solution. This solution is stirred for 2 hours while being heated and kept at 80 ° C. Thereby, the first alcohol solution can be prepared.

In the second step, the second alcohol solution is prepared. That is, separately from the first alcohol solution, a solution prepared by dissolving platinum chloride and rhodium chloride as a predetermined amount of noble metal salt in a predetermined amount of ethylene glycol is prepared. Next, a predetermined amount of this solution is added to the first alcohol solution prepared in the first step. This solution was heated and kept at 80 ° C for 2
Stir for hours. Thereby, the second alcohol solution can be prepared.

In the third step, pure water is added to the second alcohol solution to cause hydrolysis to precipitate a hydrolysis product in the second alcohol solution. The hydrolysis products are mainly aluminum hydroxide attached to the surface of the activated alumina powder, and platinum (Pt) and rhodium (Rh) attached to the aluminum hydroxide. In the fourth step, the hydrolysis product is separated from the second alcohol solution by a filtration device (not shown), washed, and then dried. Next, the dried hydrolysis product is fired at 600 ° C. for 5 hours in a firing furnace (not shown). Then, the aluminum hydroxide contained in the hydrolysis product is calcined to become adhered activated alumina 3 covering the surface 2a of the activated alumina powder 2 as shown in FIG. Fixed to. On the other hand, platinum (Pt) and rhodium (Rh) contained in the hydrolysis product are
The catalytic noble metal particles 4 are retained in a highly dispersed state on the entire surface 2a of the activated alumina powder 2 by the function of the above-mentioned adhered activated alumina 3 as a binder. That is, the supporting carrier powder 2A in which the catalytic metal particles 4 are fixed and held in a highly dispersed state by the adhered activated alumina 3 formed on the surface 2a is formed.

In the fifth step, about 100 g of the carrier powder 2A obtained in the fourth step was slurried, and then the cordierite monolith substrate 10 having a diameter of 100 mm and a length of 160 mm (see FIG. 1). The catalyst carrier layer 12 was formed by coating the carrier carrier powder 2A on the wall surfaces 11 of a large number of pores through which the exhaust gas of (1) passes. The catalyst-supporting layer 12 contains about 12.5 g of the adhered active alumina 3 shown in FIG. 2, 1.5 g of platinum (Pt) and 0.3 g of rhodium (Rh) as the catalytic noble metal particles 4, and the illustration thereof is omitted. 2 of barium (Ba)
g included.

After the production is completed by the production method of Example 1, the obtained monolith catalyst 1A has the catalyst supporting layer 12 in which the catalytic noble metal particles 4 are highly dispersed on the surface 2a of the activated alumina powder 2. Fixed and held carrier powder 2A
Is formed by. Therefore, monolith catalyst 1A
In comparison with the catalyst produced by the conventional sol-gel supporting method, the catalyst active point can be increased, the catalytic noble metal particles 4 can be effectively utilized, and the low temperature activity of the catalyst can be improved. Further, since the adhered activated alumina 3 supporting the catalytic metal particles 4 in a highly dispersed state on the surface 2a of the activated alumina particles 2 contains barium (Ba) (not shown), the heat resistance of the adhered activated alumina 3 itself. The durability and the like can be improved. (Example of use) As shown in FIG. 3, this monolith catalyst 1A is incorporated in a catalytic converter 7 arranged in an exhaust gas system E1 of an engine E, and is used together with an HC trapper 5 arranged upstream thereof. .. The HC trapper 5 has pelletized zeolite as the HC adsorbent 6. This HC adsorbent 6 temporarily adsorbs cold HC contained in the exhaust gas until the temperature at which the monolith catalyst 1A is heated by the exhaust gas and reaches its sufficient catalytic function at the time of starting the engine E, After reaching the above temperature, it has the function of releasing cold HC.

The monolith catalyst 1A of the embodiment has a catalytic function at a low temperature due to the catalytic action of the catalytic noble metal particles 4 highly dispersed and supported on the surface 2a of the activated alumina particles 2 existing in the catalyst supporting layer 12. Can be demonstrated. For this reason, the HC trapper 5 is more
Cold H that desorbs from the temperature range of 50 ℃ to 300 ℃
C is efficiently oxidized and converted into H ₂ O or CO ₂ to purify exhaust gas.

Therefore, according to the monolith catalyst 1A of the embodiment, since the low temperature activity is excellent, conventionally, the activation temperature of the catalyst is 30.
Since the temperature was 0 ° C. or higher, it could not sufficiently cope with the start of desorption of cold HC from the HC adsorbent in the temperature range before the catalyst was activated, and the problem that exhaust gas was discharged without being purified could be solved. ..

[0027]

Comparative Example In order to confirm the effect of the monolith catalyst 1A obtained by the production method of Example 1, the monolith catalyst of Comparative Example was produced. The monolith catalyst of Comparative Example has a diameter of 10 after slurrying the carrier powder prepared by the following steps (1) to (10) and carrying platinum and rhodium.
The surface of a cordierite monolith substrate having a length of 0 mm and a length of 160 mm was coated as a coat layer (catalyst supporting layer). The same amount of platinum and rhodium as the monolith catalyst of Example 1 was carried on the coat layer. The steps of producing the carrier powder will be described below. (1) Aluminum triisopropoxide powder 450 g
Is a mixed solution of 2 liters of isopropanol solution. (2) Add 2 g of barium powder to the mixed solution. (3) Platinum chloride and rhodium chloride are added to the mixed solution. The amounts of platinum chloride and rhodium chloride added are platinum (Pt) when loaded as a catalytic noble metal, respectively.
It is a value converted into 1.5 g and rhodium (Rh) 0.3 g. (4) The mixed solution of aluminum triisopropoxide, isopropanol solution, barium, platinum chloride and rhodium chloride is heated to 80 ° C. and stirred for 2 hours. (5) About 100 cc of distilled water is added dropwise to the mixed solution after stirring to allow the hydrolysis reaction to proceed. (6) The mixed solution of (5) is heated to 80 ° C. and stirred for 2 hours. (7) Isopropanol is removed from the mixed solution after being stirred in the above (6) by a rotary evaporator. (8) Isopropanol is removed in (7) above, and the remaining residue is vacuum dried. (9) The vacuum dried residue is calcined at 600 ° C. for 5 hours. (10) The fired body obtained by firing is crushed to a predetermined size to obtain a carrier powder carrying platinum and rhodium. (Catalyst activity and durability performance test conditions) Catalytic activity evaluation Using a commercially available engine with a displacement of 2000 cc, the relationship between the temperature of the gas containing the catalyst and the purification rate of the exhaust gas was evaluated. Here, as the data, the temperature of the gas containing the catalyst at which the exhaust gas purification rate becomes 50% is shown. The lower the temperature, the better the catalytic performance.

As the catalyst activity evaluation method, the relationship between the temperature of the gas containing the catalyst and the purification rate of the exhaust gas was evaluated. Durability test The monolith catalysts of Example 1 and Comparative Example were mounted on the left and right banks of a commercially available V-type engine with a displacement of 3000 cc, respectively, and the catalyst-containing gas temperature was 800 ° C, exhaust gas atmosphere stoichiometry, and durability time of 100 hr It was Evaluation results The numerical values shown in Table 1 as the evaluation results indicate the 50% purification temperature of HC, CO, and NOx after the initial and endurance tests, and the lower the catalyst activation temperature, the better the catalyst performance. ..

[0029] Performance Comparison Test Results of Example 1 and Comparative Example According to Table 1, the monolith catalyst obtained by the production method of Example 1 was
Since the catalytic noble metal particles are supported in a highly dispersed state, the catalytic activity points increase and the low temperature activity is improved, and the performance is superior even at the initial stage of use and after durability as compared with the monolith catalyst obtained by the production method of Comparative Example. Became clear.

[0030]

Example 2 A method of manufacturing an exhaust gas purifying catalyst of Example 2 will be described with reference to FIG. In the case of the second embodiment, the respective steps other than the fifth step are the same as the respective steps of the first embodiment. That is, in Example 2, the monolith catalyst 1 of Example 1 was used.
Instead of producing A, the pellet catalyst 1B shown in FIG. 4 is produced, and the carrier powder 2A (see Example 1) obtained in the first to fourth steps of Example 1 is treated in the fifth step. It is granulated to a predetermined size.

When the exhaust gas is purified using the pellet catalyst 1B obtained by the method for producing an exhaust gas purifying catalyst of Example 2, when the exhaust gas temperature is low and when the exhaust gas is at a high temperature, as in the monolith catalyst 1A of Example 1 described above. The exhaust gas containing cold HC can be purified more efficiently at the time of transition.

[0032]

[Effect] In the method for producing an exhaust gas purifying catalyst of the present invention, the exhaust gas purifying catalyst obtained by sequentially performing the first step, the second step, the third step, the fourth step, and the fifth step is By depositing hydroxide as a hydrolysis product on the surface of the carrier powder (activated alumina particles) and adhering activated alumina that covers the surface and acts as a binder, the catalytic metal is highly dispersed on the surface. A supported carrier powder that has been supported can be obtained. By forming a catalyst from this supported carrier powder, it is possible to increase the number of active sites of the catalyst and to effectively utilize the catalytic metal when using it, and to effectively utilize the catalyst at low temperature. Can be improved.

[Brief description of drawings]

FIG. 1 is a vertical view of a monolith catalyst obtained by the production method of Example 1, where a portion where a catalyst supporting layer is formed is formed on the wall surface (surface) of pores through which exhaust gas of the monolith substrate passes. The partial expanded longitudinal cross-sectional view which expands and shows.

FIG. 2 is an enlarged view of a supported carrier powder which is composed of activated alumina particles (support powder) and adhered active alumina which is formed on the surface of the support and supports the catalytic precious metal particles in a highly dispersed state. FIG.

FIG. 3 is a vertical cross-sectional view showing an example of use of the monolith catalyst obtained by the production method of Example 1.

FIG. 4 is an enlarged vertical cross-sectional view showing a pellet catalyst manufactured by the method for manufacturing a catalyst of Example 2 in a vertical section and enlarged.

FIG. 5 is an enlarged vertical cross-sectional view showing, in an enlarged manner, a state in which a part of the catalytic metal is taken into the inside of a carrier powder of a fine powder produced by a conventional sol-gel supporting method.

FIG. 6 is an enlarged vertical cross-sectional view showing a pellet catalyst produced by using the supported carrier powder shown in FIG.

[Explanation of symbols]

1A ... Monolith catalyst 12 ... Catalyst support layer
1B ... Pellet catalyst 2 ... Activated alumina particles (carrier powder) 2A ... Supported carrier powder 2a ... Surface of activated alumina particles 3 ... Adhering activated alumina 4 ... Catalyst noble metal particles

Claims (1)

[Claims] 1. A carrier powder carrying a catalytic metal, a first step of preparing a first alcohol solution or an ethylene glycol solution containing 10 to 50 wt% of an aluminum alkoxide with respect to the carrier powder, and an ethylene glycol solution. A second step of adding a dissolved catalyst metal salt to the first alcohol solution or the ethylene glycol solution to prepare a second solution containing the carrier powder, the aluminum alkoxide, and the catalyst metal salt; A third step of forming a hydrolysis product on the surface of the carrier powder by adding water to the second solution and hydrolyzing the carrier powder, and separating the carrier powder from the second solution and firing the carrier powder. A method for producing an exhaust gas purifying catalyst, comprising a fourth step and a fifth step of forming a catalyst from the supported carrier powder.