JPS61242644A - Production of catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To obtain a catalyst excellent in the durability of the purifying performance by mixing both a liquid dispersed with the fine granular catalytic components in a dispersion medium and the slurry suspended with ZrO2 powder and Al2O3 powder and molding the mixture. CONSTITUTION:In relation to a catalyst for purifying an exhaust gas of an internal combustion engine, a dispersion liquid is prepared by dispersing the fine granular catalytic components in a dispersion medium such as water and alcohol and the slurry suspended with the catalyst deposition components consisting of ZrO2 powder and Al2O3 powder is prepared. After mixing the slurry to the dispersion liquid, a molding body is molded from this mixture and calcined and the catalytic components are deposited on the catalyst deposition components. By such a way, the flocculation of the catalytic components is prevented and simultaneously the alloying of the catalytic components with each other is prevented and the thereby, the catalyst for purifying an exhaust gas excellent in the durability of the purifying performance is obtained.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a method for producing a catalyst for purifying gas in an internal combustion engine, and more specifically, to a method for producing a catalyst with excellent purification performance and durability as a catalyst. It is related to the law.

[Prior Art 1] Catalysts for gas purification (1) for internal combustion engines, particularly automobile engines, are required to have extremely high performance in terms of durability, purification performance, etc. Automobile exhaust gas contains -carbon oxide (Co), hydrocarbons (+-IC>
Nitrogen oxides (NOx) contain harmful components, and a variety of catalysts have been proposed as effective catalysts for removing these components. . Among them, for example, IC catalysts, in which platinum (Pl), palladium (Pd), or rhodium (Rh) 41, etc. are supported on an alumina carrier in combination with palladium or silk, have relatively poor purification performance. It is known as the right thing.

Conventionally, the 4+ type used in internal combustion engines for automobiles, etc.
In the production of gas purification catalysts, an alumina carrier layer is formed on a monolithic carrier base made of alumina, porcelain, etc. Thereafter, the support layer is brought into contact with an aqueous solution of a chloride or the like of the catalyst component to coat the surface of the particles of the alumina carrier with fine particles of the catalyst component, and then dried and calcined to obtain a catalyst for gas purification. It was normal. Also, 1! [As seen in Kaimei No. 57-153737, zirconia (7r
There has also been proposed a catalyst for purifying gases that can achieve the same purification performance as the conventional one even if the amount of catalyst components supported is reduced.

[Problem to be Solved by the Invention 1] In the conventional manufacturing method of the exhaust gas purifying catalyst described in Section 2, the catalyst components are used as a solution, and after contacting with an alumina carrier, they are dried and calcined to form the surface of the alumina particles. [To achieve this coating, the catalyst components aggregate and cause particle growth.
Durability of purification performance as a gas purification catalyst
There was a problem that it deteriorated. In addition, there were cases in which catalyst components were alloyed with each other, causing a decrease in performance.

The present invention has been made in view of the above-mentioned problems, and it prevents the agglomeration of catalyst components and at the same time prevents alloying of catalyst components, thereby providing exhaust gas with excellent purification performance and durability for other purposes. 1] The purpose is to provide a method for producing a catalyst.

[Means for solving and overcoming the problems] The method for producing the exhaust gas purifying catalyst of the present invention is based on
- A dispersion process in which fine particulate catalyst components are dispersed in a dispersion medium such as a liquid to prepare a dispersion liquid, and a slurry in which a catalyst supporting component made of Zirnia 7 powder and alumina powder is suspended. A mixing step of mixing the slurry with a corresponding amount of liquid I'lI to obtain a mixture, a molding step of molding and covering the mixture into a molded body, and a baking process of the molded body to form a mixture. Catalyst supporting component (carrying this catalyst component)
! The catalyst is characterized in that it consists of 10 culms.

Dispersion T-culm is a process in which fine particles of catalyst components are dispersed in a dispersion medium. Water, methyl alcohol, alcohol, isopropyl alcohol, etc. can be used as the dispersion medium. In addition, as catalyst components, conventionally known platinum (Pt), palladium (Pd), iridium <lr)
, noble metals such as ruthenium (Ru), rhodium (R'h), osmium (Os), or (31 chromium (Cr)
, nickel <N i ), vanadium <V), copper (C
1. Base metals such as cobal (CO) and manganese (Mn) can be used alone or in combination. The particle size of this catalyst component is also 10 to 5 On.
It is desirable that the particle size is in the range of 5 On.
If it is larger than m, the surface area of the particles becomes small and the purification performance becomes poor, which is not preferable. Also, the particle size is 1
When OnmJ: is small, it tends to aggregate, and the surface area of the aggregated secondary particles is small, resulting in similarly poor purification performance.

To disperse the catalyst component in a dispersion medium, various methods can be considered, such as a method of dispersing using a dispersant and a method of forming a colloid, but it is preferable to use ultrasonic vibration. When using ultrasonic vibration, the particle size of the catalyst component is 20
It is preferable to set it to 30 nm. This allows the catalyst components to be uniformly dispersed in the dispersion medium and provides the desired surface area.

The suspension step is a step of preparing a slurry from alumina powder, zirconia powder, and water. Zirconia powder has a particle size of 0.5 to 10 μm, particularly an average particle size of 2 μm.
It is desirable that the degree of If the particle sizes are so different, the zirconia powder will be appropriately interposed between the fine particles of the catalyst component or between the alumina particles, and the agglomeration and alloying of the fine particles of the catalyst component will be prevented. It's possible to yell.

Alumina) Finally (J, as before, α body, 1 body 41
Although any one of them can be used, it is preferable to use one.j' Between the distribution of zirconia powder to Lumi-J powder (well, since the purification rate increases as the amount of zirconia powder increases) It is preferable to use a large amount of zirconia powder.However, if too much zirconia powder is used, problems may arise in terms of strength, so the zirconia powder is preferably in the range of 30-80% by weight.

The mixing step is a step of mixing the dispersion obtained in the 1-allocation step and the slurry added to the suspension step. In this case, if necessary, zirconia powder or alumina powder can be added. This mixture-
In the L culm, the surface of the alumina powder is coated with fine particles of the catalyst component. In this case, since the zirconia powder is present, the fine particles of the catalyst component are coated in a fine particle state while maintaining a small distance from each other.

The molding step is a step in which a slurry containing the upwind catalyst component is carved into a molded body into a predetermined shape. The term "molding" (well, it goes without saying that it is integrally molding a sheet of a predetermined shape from a slurry, but also refers to applying a slurry to a preformed body having a predetermined shape). For example, it can be formed into granules or pellets.In this case, even if the slurry is formed into pellets, etc., the slurry may be formed into pellets or pellets. It can also be molded by adhering and agitating the slurry.Also, alumina,
The slurry can be deposited on the pore surface of a monolithic carrier base material such as a henicum shape consisting of ~, etc., and then shaped. Note that when molding into a predetermined shape, heating is performed at a relatively low temperature to evaporate moisture and the like.

The catalyst supporting step is a step in which the molded body is fired at a temperature of 700° C. or higher, as in the conventional method, and the catalyst component is supported on the surface of the alumina contained in the molded body. .

In the compact, the catalyst component remains in the form of fine particles and covers the aluminum surface at a certain distance. Therefore, by firing in this state, the catalyst component remains in the form of fine particles on the surface of the aluminum 7.

[Operations and effects of the invention] Production of the exhaust gas purifying catalyst of the present invention 7! In the i method, the catalyst components are uniformly dispersed by ultrasonic vibration, etc., and are supported on the alumina surface while maintaining their fine particle structure. Furthermore, since the zirconia powder is interposed between the fine particles of the catalyst component (J) or the alumina powder and acts as a steric hindrance, agglomeration or alloying of the catalyst component is further prevented. The surface area of each particle of the component is significantly larger than that of conventional catalyst component particles.Furthermore, the Zir-lnia powder also contributes to improved purification ability and heat resistance.Therefore, the production method of the present invention For example, even with the same amount of catalyst components as the conventional one, it is possible to reliably produce the 4111 gas purifying catalyst in a cylinder, which has significantly superior purification performance than the conventional one.

[Example] The following will be explained using examples.

First, 100 channels of a catalyst component consisting of fine particles of a 1:1 mixture of platinum <pt> with a particle size of 20 to 30 nm and palladium (Pd) with a particle size of 20 to 30 nm were mixed with 150 channels of distilled water.
Add 1 to 1 milliliter and disperse in ultrasonic vibration.

Next, 1,500 g of an aqueous aluminum nitrate solution (aluminum nitrate content: 40 wt.%) was added to Alumino-Silua 009 with an alumina content of 10% by weight, and further 4 g of distilled water was added.
50 ml was added and stirred to prepare a mixed suspension. Furthermore, 1,009 m of hezirconia powder (average particle size: 2 .mu.m) was added to this mixed suspension to form a slurry, and 1,000 m of a dispersion of the catalyst described above was added thereto. Furthermore, 800 g of alumina powder was added and stirred to prepare a slurry. A cylindrical monolith carrier base material made of Corjelai 1-2 and having a diameter of 10 cm and a length of 15 cm was immersed in this slurry in which fine particles of alumina, zirconia, and catalyst components were suspended for 1 minute. After pulling, the excess slurry inside the cells of the cylindrical monolithic carrier base material was blown off by blowing air, and then the moisture was dried at 200°C for 1 hour. I did it.

Firing treatment was performed at 700° C. for 2 hours in a roughly inviscid gas. This was immersed again in the above slurry, and the slurry was similarly blown off, dried, and fired to produce an exhaust gas purifying catalyst according to the production method of the present invention. In this example, the amount of catalyst supported was 0.5 for both platinum (PL) and palladium (Pd) relative to the monolithic carrier base material.
! It/liter.

The catalyst prepared above was subjected to a durability test using a two-handed method. And after that endurance test,
Noru 1-IC's Kaka↑( was evaluated for ability.

The durability test conditions were as follows: ■The engine had an air-fuel ratio <Δ/F) of 14.
6. The catalyst was operated at a space velocity (SV) of 60,000 h-1 and a catalyst bed temperature of 720°C, and after operating for 300 hours, the purification rate of the famous catalyst was measured. The measurement of this purification rate is based on the air-fuel ratio (
This method was used to evaluate the temperature characteristics of the exhaust gas on the inlet side of the purification rate of the catalyst by setting Δ/F) to 14.6.The measurement results are shown in the figure.

<Conventional example> Alumina Silua 00 (J) with an alumina content of 10%
, aluminum nitrate aqueous solution (aluminum nitrate-containing i
1/10% by weight) was added to 150 G, and further distilled water was added to
A mixed suspension was prepared by adding 50 milliliters and stirring.

Then, 1000q of alumina powder was added to the mixed suspension and stirred to prepare a slurry. A cylindrical monolith carrier base material having the same shape and made of the same material as in the example was immersed in this slurry for 1 minute, and the same operations as in the example were repeated to form an alumina support layer on the monolith carrier base. Base for monolith carrier on which this activated alumina support layer was formed $4
was immersed in distilled water to absorb sufficient water, then pulled out and blown off excess water. Subsequently, dinit[1 diamine platinum aqueous solution “Pt (Nl-13)2 (NO2)2
] (0.5o/liter as dinitrodiammine platinum) for 1 hour. After drying the water at 200°C for 1 hour, add a palladium chloride aqueous solution [PdCfz] (0.5 (J/liter) as palladium chloride), A conventional catalyst was manufactured.The catalyst supporting layer in this conventional example was as follows:
Both platinum and palladium were in the same amount of 0.5 o/L to the monolithic u-form as in the example.

As for the catalyst of the conventional example, similarly to the catalyst of the example,
The figure shows the results of measuring the 1-IC purification rate using the method of evaluating the temperature characteristics of the purification rate of the catalyst with the air-fuel ratio (A/F) set at 14.6.

As is clear from the figure, the exhaust gas purification catalyst of the example manufactured by the manufacturing method of the present invention has a 300-hour burning time compared to the exhaust gas purification catalyst manufactured by the conventional manufacturing method. Even after the durability test M, it has excellent high-temperature purification performance. It is clear that this is due to the addition of zirconia powder and the catalyst component being supported in the form of fine particles. It should be noted that GO and NOX showed similar trends as shown in the figure, and the catalyst of the example was clearly superior to that of the conventional example.

[Brief explanation of drawings]

FIG. 1 is a graph showing the results of evaluating the humidity characteristics of the purification rate of the catalysts of the example and the conventional example.

Claims (5)

[Claims] (1) A dispersion process in which fine particulate catalyst components are dispersed in a dispersion medium such as water or alcohol to prepare a dispersion liquid, and a slurry in which a catalyst supporting component consisting of zirconia powder and alumina powder is suspended is prepared. a suspension step, a mixing step of mixing the dispersion liquid with the slurry to obtain a mixture, a molding step of molding a molded body from the mixture, and a molding step of firing the molded body to transfer the catalyst component to the catalyst supporting component. A method for producing an exhaust gas purifying catalyst, comprising the steps of supporting a catalyst. (2) The method for producing an exhaust gas purifying catalyst according to claim 1, wherein the particulate catalyst component is dispersed in a dispersion medium by ultrasonic vibration. (3) The method for producing an exhaust gas purifying catalyst according to claim 1, wherein the catalyst component has a particle size of 10 to 50 nm. (4) The method for producing an exhaust gas purifying catalyst according to claim 1, wherein the zirconia powder has an average particle size of about 2 μm. (5) The method for producing an exhaust gas purifying catalyst according to claim 1, wherein the zirconia powder is distributed in an amount of 30 to 80% by weight relative to the alumina powder.