JPH04122441A - Preparation of catalyst for cleaning exhaust gas - Google Patents

Abstract

PURPOSE:To prevent the generating of the sintering of the catalytic noble metal, supported on alumina in a catalyst support layer, and the lowering of exhaust gas cleaning function due to the catalytic noble metal by supporting the catalytic noble metal on an aqueous mixture containing a heat-treated alumina powder and a ceria powder having a high specific surface area. CONSTITUTION:An aqueous mixture containing at least a heat-treated alumina powder having a specific surface area of 50-200m<2>/g and a ceria powder having a high specific surface area is bonded to the surface of a base material to be dried and baked to form a catalyst supporting layer. Next, a catalytic noble metal is supported on the catalyst supporting layer to obtain a catalyst for cleaning exhaust gas. Since this catalyst contains the heat-treated alumina powder in its catalyst supporting layer, the thermal deterioration of alumina is not almost advanced at the time of cleaning the exhaust gas. Therefore, the sintering of the catalystic noble metal due to the thermal deterioration of alumina is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a catalyst for purifying exhaust gas.

[Prior Art] In recent years, various studies have been conducted on automobile exhaust gas purification devices.
The factors that influence the exhaust gas purification rate are largely related to the catalyst composition and the performance of the catalyst carrier (base material). Since such catalyst carriers are required to have impact resistance and abrasion resistance at high temperatures during use, the materials forming them are required to have a low coefficient of thermal expansion and high mechanical strength. ing.

Here, crystalline ceramic slants have been proposed as a promising catalyst support. In addition to having a relatively small surface area, the catalyst carrier made of ceramic 471 has a cylindrical skeleton structure with low pressure loss, such as a honeycomb or lattice cross section, for the purpose of reducing the influence of back pressure. If it is formed into a body shape, its surface area becomes even smaller, resulting in poor catalytic efficiency and reduced performance as an exhaust gas purification catalyst.

Here, as a manufacturing method for obtaining a ceramic catalyst carrier having a high surface area, for example, 1> Japanese Patent Publication No. 55-26
As disclosed in Publication No. 912, the particle size is 0.1~
An aqueous mixture containing alumina and amorphous silica selected from alpha, comma, delta, eta, theta, kappa, [1 or chi type, having a surface area of 5 to 600 m2/g, and a ceramic substrate of 100 m2/g. It is known to form a catalyst support layer by coating a catalyst (a base material), drying and firing the base body.

2) Also, as disclosed in Japanese Patent Publication No. 55-1818, alumina having a particle size of 0.1 to 100 microns and a surface area of 5 to 600 m2/Ω, or its precursor which provides the alumina by firing. It is known that a ceramic substrate is coated with an aqueous mixture containing amorphous alumina hydrate and amorphous alumina hydrate, and the substrate is dried and fired to form a catalyst support layer.

[Problems to be Solved by the Invention] However, when the exhaust gas purifying catalyst formed by the above-mentioned conventional manufacturing method and having a catalytic noble metal supported on the catalyst supporting layer is used by being incorporated into the exhaust gas system of an automobile engine, Thermal deterioration of activated alumina in the catalyst support layer progresses due to exhaust dregs, and the accompanying sintering phenomenon of the catalyst noble metal may cause performance deterioration of the exhaust gas purification catalyst action. For example, as shown in FIG. 3a in the catalyst support layer, a plurality of adjacent granular activated aluminas 20a, 20a, each supporting a catalyst precious metal 3a, may undergo thermal deterioration due to progress of thermal deterioration.
As shown in FIG. 3, the plurality of catalytic noble metals 3a, 3a move during sintering, and further, sintering occurs as shown in FIG. 3C.

In this way, as the activated aluminas 20a and 20a are thermally degraded, the catalyst precious metal 3a is sintered (see Figure 3C).
Then, the surface area for catalytic action decreases by this amount, and the exhaust gas purification rate decreases.

An object of the present invention is to provide a method for manufacturing an exhaust gas purifying catalyst that solves the above-mentioned conventional problems.

[Means for Solving the Problems] The method for producing an exhaust gas purifying catalyst of the present invention provides a method for producing a catalyst for purifying exhaust gas according to the present invention, in which the surface of a base material has a heat-treated specific surface area of 50 to 200 m2.
A first step of depositing an aqueous mixture containing alumina powder of /CI and ceria powder with a high specific surface area (4), drying and firing to form a catalyst support layer;
It is characterized by the second step of supporting the catalyst precious metal.

This method for producing an exhaust gas purifying catalyst includes a first step and a second step.

The base material used in the first step has a so-called catalyst support layer formed on its surface, and is usually referred to as a monolith carrier. The base material may be made of ceramic or metal, for example.

Further, as for the material of the base material, the same materials as conventional ones can be used, such as ceramics such as cordierite, mullite, alumina, and spinel, and heat-resistant metals such as ferritic steel.

The greatest feature of the present invention lies in the catalyst support layer formed in the first step. The material forming the catalyst support layer is an aqueous mixture containing at least heat-treated alumina powder having a specific surface area of 50.about.200 m<2>/Ω and ceria powder having a high specific surface area.

The heat-treated alumina powder is artificially thermally degraded before supporting the catalytic precious metal, and the specific surface area is reduced to a certain range. When used in the exhaust gas system of an engine, thermal deterioration hardly progresses in the catalyst support layer, and sintering of the precious metal catalyst supported on the alumina does not occur. Therefore, the exhaust gas purification function of the catalytic noble metal does not deteriorate.

The heat-treated alumina powder preferably has a specific surface area of 50 to 200 m2/Ω after being heat-treated and thermally degraded. The reason for this is that the specific surface area of the thermally degraded alumina powder contained in the catalyst supporting layer is 5.
0m2/Q or more 200m? /F or less, the reduction in the specific surface area of the entire catalyst support layer can be sufficiently compensated for by using a certain amount of ceria powder with a high specific surface area as described later), This is because it is possible to prevent a decrease in the exhaust gas purification rate. In addition, if the specific surface area of the alumina powder after thermal deterioration is less than 50 m2/g, even if a certain amount of high specific surface area ceria powder is used in combination, the decrease in the specific surface area of the entire catalyst support layer cannot be compensated for. .

The heat treatment of the alumina powder is performed at a heat treatment humidity of 1000~
Preferably, the heat treatment time is 5 hours or less at 1200°C. If the heat treatment temperature is as low as 1000'C, the rate of thermal deterioration that occurs during heat treatment of alumina will be low and appropriate thermal deterioration will not be obtained, so an exhaust gas purification catalyst is installed in the exhaust gas system. When used, thermal deterioration progresses and sintering of the metal occurs due to thermal deterioration.

If the heat treatment temperature is higher than 1200'C, the activity of alumina will be lost at a higher rate than the progress of thermal deterioration. Further, if the heat treatment time is 5 hours or more, the rate at which thermal deterioration progresses becomes too high, and the effect of obtaining appropriate thermal deterioration over time is small.

The high specific surface area ceria powder is used in combination with the heat-treated alumina powder and is included in the catalyst support layer, thereby increasing the specific surface area of the catalyst support layer and improving the exhaust gas purification rate. In other words, this is to compensate for the fact that the specific surface area of the catalyst support layer decreases and the exhaust gas purification rate decreases due to heat treatment of the aluminum powder in advance to advance thermal deterioration.

For example, high specific surface area ceria powder has a specific surface area of 10○m2/
It is preferable to use 10 to 50 wt% of those having a weight of 10 to 50 g or more.

Further, when forming the catalyst supporting layer, lanthana powder can be used in addition to the heat-treated alumina powder and the high specific surface area ceria powder.

The amount of lantana mixed into heat-treated alumina powder is 1
-5W% is preferable, more preferably 2-4. wt%
It is. If the amount of lanthana is less than 1w1-%, the activation effect of alumina will not be stabilized, and if it exceeds 5wt%, the activation effect of alumina will decrease.

As other components, an amorphous alumina hydrate having a structure in which amorphous alumina and water are combined or bonded can be used as in the conventional case.

The amount of amorphous alumina is preferably 1 to 10 wt%.

Typical noble metals for the catalyst are platinum, rhodium, and palladium, and it is preferable to use at least one of these. In addition, catalytic noble metals such as iridium, luteum, and osmium, or base metals such as chromium, nickel, vanadium, copper, cobal, and manganese may be added.

The catalyst metal is supported on the catalyst support layer.

The supported amount can be selected from various types as in the past, depending on the desired performance, cost, and other conditions.

[Operations and Effects] In the method for producing an exhaust gas purifying catalyst of the present invention, in the first step, the surface of the substrate is at least heat-treated to have a specific surface area of 5.
An aqueous mixture containing alumina powder of 0 to 200 m2/Cl and ceria powder with a high specific surface area is deposited, dried and fired to form a catalyst support layer.

In the second step following the first step, a catalyst noble metal is supported on the catalyst support layer, thereby producing an exhaust gas purifying catalyst.

Since the exhaust gas purification catalyst obtained in the above manufacturing process contains heat-treated alumina powder in its catalyst support layer, thermal deterioration of alumina does not proceed at all during exhaust gas purification. Therefore, sintering of the catalyst precious metal due to thermal deterioration of alumina is less likely.

Therefore, the exhaust gas purification function of the catalytic noble metal can be fully demonstrated. Further, the specific surface area of the catalyst supporting layer is:
The reduction due to the heat-treated alumina powder can be increased by including ceria with a high specific surface area, and the surface area per unit volume of the catalyst can be maintained at an appropriate level. Therefore, the exhaust gas purification rate of the entire catalyst support layer is superior to that of a catalyst support layer that does not contain ceria with a high specific surface area.

Furthermore, in the present invention, when forming the catalyst support layer, since the high specific surface area ceria powder contained in the aqueous mixture is an oxide, it does not react with the alumina powder. Here, in the present invention, as a phenomenon that occurs when cerium is included in an alumina slurry (aqueous mixture) as in the case of forming a conventional catalyst support layer, alumina and cerium are mixed together due to water absorption and support of cerium. There is no reduction in the surface area of alumina due to the reaction, and there is no reduction in the surface area of the catalyst support layer.

[Example] The method for producing an exhaust gas purifying catalyst of the present invention is as follows: J in FIG.
The first step of forming the catalyst support layer 2 on the surface 11 of the catalyst and the second step of supporting the catalyst noble metal 3 on the catalyst support layer 2 are carried out in order to produce an exhaust gas purification catalyst.

(Example 1) In the first step, 64 honeycomb passages/cm2 were prepared in advance.
0 and a slurry are prepared. The slurry is made of lantana (La20) in advance.
3) containing 3.5wt:% Specific surface area before thermal deterioration is 180
Alumina of rn2/CI was heated at 1100'C13 in air.
Baked for an hour. Alumina 2 after thermal deterioration due to this heat treatment
The specific surface area of 0 decreased to 100 m2/g. High specific surface area ceria (CeO2) powder with a specific surface area of 130 m2/Q and an average particle size of 7 μm was added to this heat-degraded alumina 20 at 30 W.
1:%, and this mixed powder 57W1-%
, 3 wt % of amorphous alumina hydrate and 40 wt % of water were mixed and stirred. The group vJ' 1 is then immersed in this slurry for 10 seconds. As a result, the base material 1 with slurry attached to the surface 11 of the honeycomb passage 10
is taken out from the slurry and heated with pressurized air 10n/
It is sprayed for 5 seconds and blows away excess slurry.
-1 layer formed (after firing at 600'C) -1 - amount is +
It was coated to give a resistance of 170Ω per 1.0. ) Next, the catalyst supporting layer 2 was immersed in a platinum ammine aqueous solution to support platinum 1.2 Ω/Q-Cat, and after drying, it was immersed in a rhodium chloride aqueous solution to support rhodium 0.4 g/ρ-Cat. Dry for 2 hours at °C and 400 °C in a kiln.
It was baked at 'C for 1 hour. In this way, the catalyst supporting layer 2
The exhaust gas purifying catalyst of test sample A shown in the table was obtained by supporting catalyst precious metal 3 on the catalyst.

(Example 2) In Example 2, base material 1 was used in the same manner as in Example 1, and alumina containing 3.5 wt% of lantana (La203) and having a specific surface area of 100 m2/g before thermal deterioration was exposed to 11
It was fired for 13 hours at 00'C. As a result of this heat treatment, the specific surface area of alumina 20 after thermal deterioration was reduced to 50 m2/Q.

This heat-degraded alumina 20 was mixed with 3Qwt% of high specific surface area ceria (CeO2) with a specific surface area of 130 m2/q and an average particle size of 7 μm, the same as in Example 1. Powder 57wt%, amorphous alumina hydrate 3
A slurry prepared by mixing and stirring 40 wt% of water and 40 wt% of water was used. Thereafter, in the same manner as in Example 1, an exhaust gas purifying catalyst of test sample B shown in the table was obtained.

[Comparative Example] For comparison, test sample CiJ3 J of Comparative Example 1 and test sample D of Comparative Example 2 were used as exhaust gas purification catalysts.
was produced.

(Comparative Example 1) Test sample C of Comparative Example 1 was made of lantana (La203
) A slurry was prepared from 57 wt % of alumina with a specific surface area of 5 Qrn2/Ω containing 3.5 wt %, 3 wt % of amorphous hydrate, and 4 Qwi-% of water, and this slurry was added to the surface 11 of the honeycomb passage 10 with the same group +41 as in Example 1. temperature (600°C)
The coating was carried out so that the amount after firing was 120 g per 1 Q of the base material. 〉Cerium (Ce) 0.3 per gram per month using a cerium nitrate aqueous solution in the -1 layer
The catalyst was supported in moles and fired at 600°C to obtain a catalyst support layer. Thereafter, a catalytic precious metal was supported on the catalyst supporting layer in the same manner as in Example 1 to obtain a test sample C catalyst for exhaust gas purification.

(Comparative Example 2) In Comparative Example 2, base material 1 was used as in Example 1, and alumina containing 3.5 wt% of lanthana (La203> and having a specific surface area of 50 m2/g before thermal deterioration) was exposed to 110 m2/g in the air.
It was fired for 13 hours at 0'C. As a result of this heat treatment, the specific surface area of the alumina after thermal deterioration was reduced to 30 m210. The alumina after thermal deterioration has a specific surface area of 130 m, the same as in Example 1.
2/g, high specific surface area ceria (Ce0
2> to be 3Qwt%, this mixed powder 57W↑%, amorphous alumina hydrate 3W1:%, water 40%.
A slurry prepared by mixing and stirring W↑% was used. Thereafter, in the same manner as in Example 1, exhaust gas purifying catalysts of Tests 1 to Submuru D were obtained.

(Evaluation) Example 1.2 Rice Comparative Example 1 obtained in the above manner
．． 2 each death 1 ~ sample △, B and C1D 2.8
．． A durability test was conducted by installing the test tube in the exhaust system of a 0 engine (model 5M-GFU) with a catalyst in it and operating it for 50 hours at a humidity of 900°C.

After that, in order to evaluate each sample A, B, C, and D, the catalyst gas temperature was set at 300°C and the temperature was set at 400°C.
The purification rates of 1-IC, Co, and NOx were measured.

The results are shown in the table.

The evaluation method is to install it in the exhaust system of a 3000cc inline 6-cylinder engine.
1.6. Durability was carried out for 300 hours at a temperature of 950°C in a pattern simulating urban and high-speed driving. After the durability, the purification rate % was measured using the same engine under the conditions of 200 rpm and negative pressure of -360 mm1-F. Furthermore, the peeling rate of the activated alumina layer was determined by the following method. These results are shown in the table.

Peeling rate (%) - (Weight before durability - Weight after durability) / [Weight before durability] x 100 From this result, the specific surface area of alumina 20 after thermal deterioration is
Samples 1 to 1 of Sample B of Example 2, which were set at 50 m2/Q or more, had a higher scum discharge than Test Sample C of Comparative Example 1 and Test Sample D of Comparative Example 2. It was found that the purification rate was excellent. Further, the specific surface area of alumina that had undergone thermal deterioration during durability in test sample C was 40 m2/Ω.

Note that the exhaust gas purifying catalysts of Test Samples A and B of each Example 1.2 are the same as those of Test Samples A and B of each Comparative Example 1.2.
The reason why the exhaust gas purification rate is better than that of D is that the catalyst supporting layer 2 contains alumina 20 which has been thermally degraded in advance as shown in FIG. It carries 3.3 of precious metals. Therefore, even if the alumina 20 is heated to a high temperature during exhaust gas purification, thermal deterioration hardly progresses, and as shown in Fig. 2, sintering of the catalyst precious metal 3.3 does not occur, so It is considered that the exhaust gas purification function of 3.3 is being fully utilized without any deterioration.

[Brief explanation of the drawing]

FIG. 1 is a partially enlarged sectional view showing the main parts of the exhaust gas purifying catalyst manufactured in Example 1.2. Figure 2a
FIG. 2 is an enlarged view showing a state in which a catalytic noble metal is supported on heat-treated alumina of this example. Figure 2 is an enlarged view showing that the alumina and catalytic precious metal hardly change during exhaust gas purification. Figures 3 and 3C are enlarged views showing the state in which the alumina and catalyst precious metal shown in Figure 3 are thermally degraded during exhaust gas purification and the state in which they are sintered. +A 2...Catalyst supporting layer 20.
... Alumina 3 ... Catalyst metal 10 ... Honeycomb passage 11 ... Surface Patent applicant 1 - Yota Hakudosha Co., Ltd. Cataler Industries Co., Ltd.

Claims (1)

[Claims] (1) Attaching an aqueous mixture containing at least heat-treated alumina powder with a specific surface area of 50 to 200 m^2/g and high specific surface area ceria powder on the surface of the base material, and
A method for producing an exhaust gas purifying catalyst, comprising: a first step of drying and firing to form a catalyst support layer; and a second step of supporting a catalyst noble metal on the catalyst support layer.