JP3120518B2 - Method for producing exhaust gas purifying catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is applicable to a case where 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 catalyzing, 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 carrying a noble metal or the like has been used as an exhaust gas purifying catalyst for purifying exhaust gas from automobiles. Here, when purifying exhaust gas with an exhaust gas purifying catalyst (hereinafter referred to as a catalyst), the performance of purifying HC among harmful components HC, CO, and NOx in the exhaust gas is particularly strongly affected by the level of the exhaust gas temperature. .

For example, a conventional catalyst has an exhaust gas temperature of 30.
At a high temperature of 0 ° C. or more, the catalytic function is sufficiently exhibited. For this reason, HC (hereinafter, referred to as cold HC) component in low-temperature exhaust gas at the time of engine start or the like may not be sufficiently purified by the catalyst and may be discharged to the atmosphere. In general, the engine at the start in the cold state is supplied with a mixture having a higher concentration than in the normal operation, and accordingly, the cold HC amount is smaller than the HC amount contained in the exhaust gas during the warm-up operation. Many.

Therefore, conventionally, as a countermeasure against the cold HC, H is provided upstream of a catalyst provided in an exhaust gas system of an engine.
It is known that a C trapper is provided and used in combination (see JP-A-2-75327). The 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 cold HC as the exhaust gas temperature shifts to a high temperature. However, the cold HC adsorption performance of the HC trapper is generally highest at an exhaust gas temperature of 200 ° C., and gradually decreases as the temperature rises.

[0005] Therefore, as a catalyst, the exhaust gas temperature is 2
It is desired to enhance the catalytic function in the range of 50 ° C. or more to less 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 a conventional immersion method. In this sol-gel loading method, after dissolving and mixing a metal alkoxide and a catalyst metal salt in an ethylene glycol solution,
Alumina powder or the like is added to a precipitate composed of a fine powder obtained by hydrolyzing this solution to form a slurry, which is coated on the cell surface of the monolithic carrier.

[0006]

However, according to the sol-gel supporting method, when the slurry is coated on the cell surface of the monolithic carrier, a part of the catalyst metal on the surface of the fine powder generated by hydrolysis is reduced. It cannot be used as a catalyst (the catalyst metal present at the contact point between the fine powder and the fine powder does not work effectively).

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]

According to the present invention, there is provided a method for producing an exhaust gas purifying catalyst, comprising the steps of:
A first step of preparing an alcohol solution or an ethylene glycol solution of the above, and adding a catalytic metal salt dissolved in the ethylene glycol solution to the first alcohol solution or the ethylene glycol solution; A second step of preparing a second solution containing a salt, a third step of attaching water to the surface of the catalyst carrier having a catalyst support layer to form a water-containing carrier, and contacting the water-containing carrier with the second solution. A fourth step of forming a hydrolysis product on the surface by hydrolysis, and a fifth step of calcining the catalyst carrier having the hydrolysis product.

In the first step, the amount of aluminum alkoxide contained in the first alcohol solution is, for example,
The amount of the activated alumina coated on the surface of the catalyst carrier used in the third step to form the catalyst supporting layer is 10 to 50 w.
It can be used in the range of t%. Further, the first alcohol solution may contain barium alkoxide or lanthanum alkoxide in an amount of 1 to 20 wt% based on the amount of the aluminum alkoxide. As the aluminum alkoxide, 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, ethanol and isopropanol 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, a salt of a catalyst metal, a catalyst noble metal or the like generally used for an exhaust gas purifying catalyst can be used alone or in combination as a compound.

As the catalyst carrier having a catalyst carrier layer used in the third step, for example, a cordierite monolith carrier whose surface is coated with activated alumina as a catalyst carrier layer, or a metal monolith carrier can be used. As the water to be attached to the surface of the catalyst support having the catalyst support layer in the third step,
It is preferable to use water as close to pure water as possible. As the water, for example, ion-exchanged ion-exchanged water, distilled water, or the like can be used. Third
In order to attach water to the surface of the catalyst support having the catalyst support layer in the process, for example, immersing the catalyst support in water or spraying water directly on the surface of the catalyst support layer on the catalyst support. it can.

[0012]

In the method for producing an exhaust gas purifying catalyst according to the present invention, a first step, a second step, a third step, a fourth step, and a fifth step are sequentially performed. First, in the first step, a predetermined amount of aluminum alkoxide is added to a predetermined amount of an alcohol solution or an ethylene glycol solution, and the mixture is heated and stirred. Thus, a first alcohol solution containing an aluminum alkoxide or an ethylene glycol solution can be prepared.

In the second step, a predetermined amount of a catalytic metal salt dissolved in a predetermined amount of an ethylene glycol solution is added to the first alcohol solution or the ethylene glycol solution,
Heat and stir. Thereby, the second solution containing the aluminum alkoxide and the catalyst metal salt can be prepared. In the third step, the catalyst carrier having the catalyst carrier layer is immersed in an aqueous solution or water is sprayed on the catalyst carrier to attach water to the surface of the catalyst carrier to form a water-containing carrier.

In the fourth step, the water-containing carrier obtained in the third step is brought into contact with the second solution prepared in the second step. Thereby, a hydrolysis product precipitates on the surface of the water-containing carrier by hydrolysis. As a result, a catalyst support having a hydrolysis product over the entire surface is obtained. The hydrolysis product contains aluminum hydroxide and a catalyst metal.

In the fifth step, the catalyst carrier having the hydrolysis product obtained in the fourth step is calcined. Then, the aluminum hydroxide contained in the hydrolysis product is fired to form a granular carrier (active alumina particles) that forms the surface of the catalyst support layer and the surface layer of the catalyst support layer.
Becomes an adhered activated alumina that adheres and covers the surface, and is fixed to the surface. On the other hand, the catalytic metal contained in the hydrolysis product acts on the surface of the catalyst supporting layer (the surface region excluding the surface where the adjacent granular carriers are in contact) by the function of the adhered activated alumina as a binder. ,
It is held in a state of being highly dispersed in a granular form.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing an exhaust gas purifying catalyst according to an embodiment (hereinafter referred to as a manufacturing method according to an embodiment) includes a first step, a second step, a third step, a fourth step, and a fifth step. The case where the monolith carrier 1 is used as a target to be subjected to each of the above steps to produce the monolith catalyst 1A will be described. For the sake of explanation, FIG. 1 and FIG. 2 show the monolith carrier 1 and the monolith catalyst 1A placed vertically and cut longitudinally, and the wall surfaces (cell surfaces) 11 of the pores through which the exhaust gas of the cordierite monolith substrate 10 passes.
2 shows an enlarged view of a portion where the activated alumina coat layer (catalyst supporting layer) 12 is formed.

The monolith carrier 1 includes a monolith substrate 10 and
An active alumina coat layer 12 (see FIG. 1). The monolith substrate 10 has a diameter of 100 mm × length of 16 mm.
It has a cylindrical shape of 0 mm, and the exhaust gas flows along its length direction P, and has a large number of honeycomb-shaped pores when viewed from the front side (inflow side of the exhaust gas). In addition, the wall surface 11 of a large number of pores of the monolith substrate 10 is subjected to a wash coat treatment in a pre-process prior to the execution of the manufacturing method of the embodiment,
A large number of activated alumina particles (particulate carriers) 2 are coated in layers on the wall surfaces 11 of the large number of pores to form an activated alumina coating layer 12. The coating amount of the activated alumina particles 2 on the monolith substrate 10 is 100 g.

In the first step, a first alcohol solution is prepared. That is, 50 g of aluminum triisopropoxide powder and 5 g of barium are added to a predetermined amount of an isopropanol solution. This solution is stirred for 2 hours while being heated and kept at 80 ° C. Thereby, the first alcohol solution can be adjusted. In the second step, a second alcohol solution is prepared. That is, a solution prepared by dissolving platinum chloride and rhodium chloride as a predetermined amount of a noble metal salt in a predetermined amount of ethylene glycol separately from the first alcohol solution is prepared. Next, a predetermined amount of this solution is added to the first alcohol solution adjusted in the first step. The solution is heated to 80
The mixture is stirred for 2 hours while being kept at ° C. Thereby, a second alcohol solution containing aluminum triisopropoxide, 5 g of barium, platinum chloride and rhodium chloride can be prepared.

In the third step, the monolith carrier 1 is taken out after being immersed in pure water, and is blown with air to wipe off excess pure water. As a result, the monolithic carrier 1 has a surface 12a of the activated alumina coating layer 12 and a surface 2a of the activated alumina particles 2 present in the surface layer portion 12b near the surface 12a in the thickness direction (adjacent activated alumina particles 2 contact each other). The water-containing monolithic carrier is obtained by adhering an appropriate amount of pure water to a surface region excluding the surface 20a (see FIGS. 1 and 3).

In a fourth step, the water-containing monolithic carrier is immersed in the second alcohol solution adjusted in the second step for a predetermined time and then pulled up. When the water-containing monolithic carrier is immersed in the second alcohol solution, by contacting the water adhering to the surface 2a of the activated alumina particles 2, aluminum triisopropoxide in the second alcohol solution becomes Is hydrolyzed to aluminum hydroxide. Along with this, on the surface 2a of the activated alumina particles 2, aluminum hydroxide generated by hydrolysis and platinum (Pt) supported on aluminum hydroxide,
Rhodium (Rh), barium oxide and the like are precipitated as hydrolysis products. Further, a hydrolysis product-containing monolith carrier having a predetermined amount of hydrolysis product is obtained on the surface 2a of the activated alumina particles 2 forming the surface layer portion 12b of the activated alumina coating layer 12. The third step and the fourth step can be repeated as necessary.

In the fifth step, the hydrolysis product-containing monolithic carrier is dried for a predetermined time, and then dried in a firing furnace.
C. for 2 hours. As a result of this firing, the aluminum hydroxide contained in the hydrolysis product present on the surface 2a of the activated alumina particles 2 changes to adhered activated alumina 3 adhered to the surface 2a as shown in FIG. . This attached activated alumina 3 is made of barium (B
a) and covers the surface 2a of the activated alumina particles 2 and acts as a binder for fixing and holding the catalytic noble metal particles 4 of platinum (Pt) and rhodium (Rh) in a highly dispersed state on the surface. And the monolith catalyst 1A shown in FIG. 2 is obtained. The amount of the catalyst noble metal particles 4 supported on the monolithic catalyst 1A is 1.75% for platinum (Pt).
5 g and rhodium (Rh) are 0.3 g.

After completion of each step by the manufacturing method of the embodiment, the obtained monolithic catalyst 1A is a surface layer portion 12b of the activated alumina coat layer 12 where exhaust gas is most likely to contact.
The catalyst noble metal particles 4 are supported in a highly dispersed state, and activated alumina particles 2 having an increased catalytic active point are present. The surface 20a (FIG. 3) where the activated alumina particles 2 forming the activated alumina coat layer 12 are in contact with each other.
Since the catalyst noble metal particles 4 are not supported in the reference noble metal particles 4, the catalyst noble metal particles 4 can be effectively used without waste.

Therefore, the monolithic catalyst 1A can improve the low-temperature activity of the catalyst as compared with a catalyst produced by a conventional sol-gel supporting method. In addition, barium (Ba) is contained in the adhered activated alumina 3 that supports the catalytic noble metal particles 4 in a highly dispersed state on the surface 2a of the activated alumina particles 2, so that the adhered activated alumina 3 itself has heat resistance and durability. Etc. can be improved. (Example of Use) As shown in FIG. 4, this monolithic catalyst 1A is incorporated in a catalytic converter 7 disposed in an exhaust gas system E1 of an engine E, and used together with an HC trapper 5 disposed upstream thereof. . The HC trapper 5 has pellet-shaped zeolite as the HC adsorbent 6. This HC adsorbent 6 temporarily adsorbs cold HC contained in the exhaust gas until the temperature of the monolith catalyst 1A is heated by the exhaust gas and the catalyst function can be sufficiently exhibited when the engine E is started, After reaching the temperature, it has a function of releasing cold HC.

The monolithic 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 which are highly dispersed and supported on the surface 2a of the activated alumina particles 2 present in the activated alumina coating layer 12. Can be demonstrated. Therefore, the cold HC desorbed from the temperature range of 250 ° C. to 300 ° C. from the HC adsorbent 6 of the HC trapper 5 is efficiently oxidized and converted into H ₂ O or CO ₂ to purify the exhaust gas.

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

[0026]

Comparative Example In order to confirm the effect of the monolith catalyst obtained by the production method of the above example, a monolith catalyst of a comparative example was produced by a conventional production method using an immersion method. The monolith catalyst of the comparative example has a diameter of 100 mm × length of 16 mm.
A monolith substrate made of cordierite having a thickness of 0 mm was coated with 100 g of activated alumina to form an activated alumina coating layer (catalyst supporting layer), and the same amount of platinum (Pt) and rhodium as in the examples was applied to the activated alumina coating layer. Except that (Rh) was carried by the immersion method, it was the same as that of the example.

(Conditions for Testing Catalytic Activity and Durability Performance) Evaluation of Catalytic Activity Using a commercially available engine with a displacement of 2000 cc, the relationship between the temperature of a gas containing a catalyst and the purification rate of exhaust gas was evaluated. Here, the catalyst-containing gas temperature at which the exhaust gas purification rate becomes 50% is shown as data. The lower the temperature, the better the catalytic performance.

As a 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. Endurance Test The monolithic catalysts of Example 1 and Comparative Example were mounted on the left and right banks of a commercially available V-type engine having a displacement of 3000 cc, respectively, and were subjected to endurance at a catalyst-containing gas temperature of 800 ° C., an exhaust gas atmosphere stoichiometry, and a durability time of 100 hours. Was. Evaluation Results The numerical values shown in Table 1 as the evaluation results indicate the initial and endurance 50% purification temperatures of HC, CO, and NOx. The lower the temperature at which the catalyst is activated, the better the catalytic performance. .

[0029] Performance Comparison Test Results of Example and Comparative Example As shown in Table 1, the monolith catalyst obtained by the production method of the example has a catalytic noble metal supported in a highly dispersed state. It was found that the performance was excellent at the beginning of use and after the endurance, as compared with the exhaust gas purifying catalyst obtained by the production method of (1).

[0030]

According to the method for producing an exhaust gas purifying catalyst of the present invention, the exhaust gas purifying catalyst obtained by performing the first, second, third, fourth, and fifth steps sequentially is The hydroxide is precipitated as a hydrolysis product on the catalyst carrier, and on the surface of the catalyst carrier layer of the catalyst carrier, the catalyst metal is deposited in a highly dispersed state by the adhered active alumina that adheres over the surface and acts as a binder. It can be securely held and carried. Therefore, the catalyst active point in the region of the catalyst carrier that is most likely to come into contact with exhaust gas during use can be increased as compared with the conventional sol-gel loading method, and the low-temperature activity of the catalyst can be improved.

[Brief description of the drawings]

FIG. 1 shows a monolith carrier used in a method for producing a monolith catalyst according to an embodiment, which is placed vertically and cut longitudinally, and an activated alumina coat layer (catalyst supporting layer) is formed on a wall surface (surface) of a pore through which exhaust gas of a monolith substrate passes. FIG. 5 is a partially enlarged longitudinal sectional view showing a part shown in an enlarged manner.

FIG. 2 shows the monolith catalyst obtained by the production method of the example placed vertically and cut longitudinally, and an activated alumina coat layer (catalyst support layer) on the wall surface (surface) of the pores through which the exhaust gas of the monolith substrate passes.
FIG. 5 is a partially enlarged longitudinal sectional view showing a portion where is formed in an enlarged manner.

FIG. 3 shows that the catalytic noble metal particles are fixed and held in a highly dispersed state on the adhered activated alumina formed on the surface of the activated alumina particles (particulate carrier) constituting the activated alumina coat layer (catalyst supporting layer) in FIG. FIG. 3 is an enlarged vertical sectional view showing the state in an enlarged manner.

FIG. 4 is a longitudinal sectional view showing an example of use of the monolith catalyst obtained by the production method of the example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Monolith support 1A ... Monolith catalyst 12 ... Active alumina coat layer (catalyst support layer) 12
a: Surface 12b: Surface layer 2: Activated alumina particles (particulate carrier) 2a: Surface of activated alumina particles 3: Adhered activated alumina 4: Catalyst noble metal particles

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B01J 21/00-37/36

Claims (1)

(57) [Claims] 1. A first step of preparing a first alcohol solution or an ethylene glycol solution containing an aluminum alkoxide, and a catalyst metal salt dissolved in the ethylene glycol solution is added to the first alcohol solution or the ethylene glycol solution. A second step of adding and preparing a second solution containing the aluminum alkoxide and the catalyst metal salt, a third step of attaching water to the surface of the catalyst carrier having a catalyst supporting layer to form a water-containing carrier, A fourth step of contacting the water-containing carrier with the second solution to form a hydrolysis product on the surface by hydrolysis, and a fifth step of calcining the catalyst carrier having the hydrolysis product. A method for producing a catalyst for purifying exhaust gas.