JPH1099698A - Manufacture of catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent exfoliation of an outside catalytic layer and maintain cleaning performance of the catalyst stably for a long period in an exhaust cleaning catalyst in which catalytic layers of two layers of an inside layer and an outside layer including a main base material of ceria are formed on a support surface of a honeycomb structure having, for instance, a cell of a wall thickness of 4 mil and about 600cpsi and a low coefficient of water absorption of 14.0% or less. SOLUTION: The outside catalytic layer 3 is formed by coating the surface of a support 1 with a base material of an inside catalytic layer 2 and by coating the base material of the inside catalytic layer 2 with slurry including a binder treated ultrasonically. Treating the binder ultrasonically highly disperses the binder and lowers its molecular weight to improve the adhesiveness of the base material by the binder. On the inside catalytic layer 2, palladium(Pd) as the catalytic component is supported on cerium (CeO2 ) and alumina (Al2 O3 ) as the base materials by aluminum hydrate as the binder, while on the outside catalytic layer 3, platinum(Pt) and rhodium(Rh) as the catalytic components are supported on cerium as the base material by the binder of aluminum hydrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst used for decomposing and purifying harmful substances and for decomposing oil, in particular, an exhaust gas for purifying HC, CO, NOx, etc. in an engine exhaust gas with a catalyst for decomposing gas. The present invention relates to a method for producing a gas purification catalyst, and particularly to a technical field of preventing separation of a catalyst layer from a carrier.

[0002]

2. Description of the Related Art Conventionally, as a method for producing this type of exhaust gas purifying catalyst, as disclosed in Japanese Patent Application Laid-Open No. 3-131343, cerium and zirconium oxide powders and alumina as a binder carrying noble metal are used. A method is known in which an aqueous slurry is formed by mixing with a powder, and the slurry is coated on a honeycomb carrier to form a catalyst layer on the surface of the carrier.

[0003]

In order to activate such an exhaust gas purifying catalyst, for example, a wall thickness of 4 mm (mil) and a thickness of 600 mm per square inch are required.
In some cases, a carrier having a honeycomb structure having about (cpsi) cells is used. In this case, the wall thickness of the carrier is small.
In order to secure the strength of the carrier, a carrier having a dense inside and high hardness is required.

[0004] However, with the demand for such a carrier, the number of pores inside the carrier is reduced and the water absorption of the carrier is reduced, and the catalyst component and the base material are adhered by sucking up moisture during wash coating of the slurry. As a result, there has been a problem that the catalyst layer is separated by receiving the exhaust gas flow, and the purification performance of the catalyst cannot be stably obtained over a long period of time.
In particular, if only ceria is used as a base material in order to enhance the purification performance of the catalyst, a large amount of a binder (for example, about 7.5% by weight based on the entire catalyst layer) is required, and the surface of the ceria is heated by exhaust gas heat. Since the catalyst layer shrinks and cracks easily occur, the catalyst layer is remarkably peeled off.

[0005] The present invention has been made in view of the above points, and an object of the present invention is to improve the treatment of a binder for bonding a base material to a carrier when a catalyst is produced, so that a catalyst layer can be formed. An object of the present invention is to prevent peeling and to stably maintain the purification performance of a catalyst for a long period of time.

[0006]

In order to achieve the above object, according to the present invention, the binder is subjected to ultrasonic treatment.

Specifically, according to the first aspect of the present invention, a slurry in which a base material and a binder are mixed is coated on the surface of the catalyst carrier, so that the base material is adhered to the surface of the catalyst.
A method for producing a catalyst comprising a catalyst component in the base material, characterized in that the binder before mixing with the base material is subjected to ultrasonic treatment. By performing the ultrasonic treatment on the binder in this manner, the binder is highly dispersed and the molecular weight is reduced. Therefore, in a state where the base material is subsequently supported on the carrier, the adhesiveness of the base material by the binder is increased, and the peeling of the catalyst layer can be stably prevented.

According to the second aspect of the present invention, the base material of the inner catalyst layer is previously coated on the catalyst carrier, and the slurry containing the binder subjected to the ultrasonic treatment is coated on the base material of the inner catalyst layer. Form an outer catalyst layer. Thus, in forming the inner and outer catalyst layers on the catalyst carrier, a good separation preventing effect can be obtained for the outer catalyst layer which is easily affected by the heat of the exhaust gas and the separation is apt to proceed.

According to a third aspect of the present invention, in the method for producing a catalyst of the first aspect, the base material contains ceria. Although the surface of the ceria shrinks due to the exhaust gas heat and cracks are easily formed, the catalyst layer can be prevented from peeling due to the cracks due to the high dispersibility and the improved adhesiveness by the ultrasonic treatment of the binder. The purification performance of the catalyst by the ceria base material can be enhanced while preventing the catalyst layer from peeling off.

[0010] In a fourth aspect of the present invention, in the method for producing a catalyst of the second aspect, the base material of the inner catalyst layer contains at least alumina.

According to a fifth aspect of the present invention, in the method for producing a catalyst of the first aspect, the carrier has a honeycomb structure, and its water absorption is 14.0% or less. That is, even if the water absorption of the honeycomb carrier is low, the base material can be effectively adhered and held on the carrier by the binder.

According to a sixth aspect of the present invention, in the method for producing a catalyst according to the first aspect, the substrate is made of a porous material. This effectively prevents the catalyst layer from peeling off even if the substrate is a porous substance.

According to a seventh aspect of the present invention, in the method for producing a catalyst according to the first or second aspect, the catalyst component is supported on the base material before being mixed with the binder. In this case, the dispersibility of the catalyst component can be improved.

[0014]

FIG. 2 shows a structure of an exhaust gas purifying catalyst C according to an embodiment of the present invention. This catalyst C is provided in an exhaust passage for exhausting an exhaust gas of a vehicle engine (in each case). (Not shown) in a state directly connected to the exhaust manifold of the engine or in the vicinity of the exhaust manifold,
The catalyst C purifies air pollutants such as HC, CO and NOx in the exhaust gas.

The catalyst C has a honeycomb-shaped carrier 1 made of cordierite, which is a carrier material having excellent heat resistance. This honeycomb carrier 1 has, for example, a cell of 400 cpsi with a wall thickness of 6 mil and a water absorption of 19%, a cell of 600 cpsi with a wall thickness of 4 mil and a water absorption of 14 cps.
% Or a cell having a wall thickness of 4 mils and 400 cpsi and a water absorption of 13% is used. The water absorption is a ratio obtained by dividing the water absorption when the carrier 1 is immersed in water by the weight of the dried carrier.

On the carrier 1, an inner catalyst layer 2 (lower catalyst layer) on the side close to the surface of the carrier 1 and an outer catalyst layer 3 (upper catalyst layer) on the side farther from the surface of the carrier 1 are provided. And two catalyst layers are coated.

The inner catalyst layer 2 contains palladium (Pd) as a catalyst component and cerium (Ce) as a base material.
Hydrated alumina is supported as a binder on O ₂ ) and alumina (Al ₂ O ₃ ). Nickel (Ni) may be contained as a catalyst component of the inner catalyst layer 2.

On the other hand, in the outer catalyst layer 3, platinum (Pt) and rhodium (Rh) as catalyst components are supported on cerium as a base material by a binder made of hydrated alumina. The amount of the binder in the outer catalyst layer 3 is desirably 10 to 15% by weight based on the entire outer catalyst layer 3. In addition, a small amount of alumina may be added as a base material of the outer catalyst layer 3, and zirconia can be supported in addition to the noble metal.

Next, a method for producing the catalyst C will be described with reference to FIG. First, palladium, ceria,
Water and a binder are added to and mixed with the mixed powder of alumina to prepare a slurry. The slurry is wash-coated on the carrier 1 and dried and fired. This forms the inner catalyst layer 2 on the support 1.

Next, a binder is mixed with water at a predetermined ratio, and the mixture is put into an inner tank of an ultrasonic treatment tank having a double inner / outer structure. Perform sonication. In this sonication,
For example, the oscillation frequency is 47 kHz, and the processing time is one hour. By performing the ultrasonic treatment on the binder in this manner, the binder is highly dispersed and the molecular weight is reduced.

[0021] A powder of ceria carrying platinum and rhodium is mixed with the binder and water thus ultrasonically treated to form a slurry. At this time, an ordinary mixer may be used as the mixer, but it is preferable to use an ultra disperser. Although not shown, the ultra disperser has a cylindrical rotating body that rotates at a high speed inside a housing having an inner / outer dual structure, and a number of slits are formed in each of the rotating body and an inner housing adjacent thereto. The slurry moved from the inner and outer housings into the inner housing through the slits of the inner housing and the rotating body is mixed so as to be chewed between the inner housing and the rotating body, whereby the slurry is mixed in the particle region. Is done.

After adjusting the pH to adjust the density and viscosity of the slurry, the slurry is wash-coated on the carrier 1 and dried and fired to form the outer catalyst layer 3 on the inner catalyst layer 2. Thus, the catalyst C is manufactured.

In the catalyst C thus obtained, since the binder of the outer catalyst layer 3 is highly dispersed and reduced in molecular weight by ultrasonic treatment, ceria as a base material is thereafter mixed with the binder. In the state of being coated on the carrier 1, the adhesiveness of ceria by the binder increases.
In addition, since the ultra-disperser is used when mixing the slurry obtained by adding the ceria powder carrying platinum and rhodium to the binder and water, the dispersibility of the powder component in the slurry is increased. For these reasons, ceria has the property that its surface shrinks due to the heat of the exhaust gas to easily crack, and even if the outer catalyst layer 3 is easily affected by the heat of the exhaust gas and the peeling is easy to proceed, The peeling of the outer catalyst layer 3 can be prevented. That is, the outer catalyst layer 3
The separation performance of the catalyst by ceria can be improved while preventing the separation of the catalyst.

The present invention can be applied to a catalyst in which the carrier 1 has a single catalyst layer. Further, the carrier 1 may have a structure other than the honeycomb structure. Further, the method for producing the present catalyst can be applied to a catalyst used for decomposing and purifying harmful substances and converting it to a decomposed oil, and particularly to a catalyst for decomposing gas. Purification of CO and NOx can be improved.

[0025]

Next, a specific embodiment will be described. (Example 1) Ceria and γ-alumina were mixed at a ratio of 1: 1 and mixed with palladium, and the mixed powder was mixed with water and a binder composed of hydrated alumina so that the amount of binder was 7.5 in the entire inner catalyst layer. The slurry was prepared by adding and mixing so as to obtain a weight%. After this catalyst slurry was wash-coated on a honeycomb structured carrier,
It was dried at a temperature of about 500C and baked at a temperature of about 500C for about 2 hours to form an inner catalyst layer.

Next, a binder made of hydrated alumina (inactive alumina) is added to ion-exchanged water so that the amount of the binder becomes 15.0% by weight of the entire outer catalyst layer, and ultrasonic treatment is performed. For 15 minutes. The conditions of the ultrasonic treatment were as follows: the oscillation frequency was 47 kHz, the treatment time was 1 hour, and the capacity of the treatment tank was 5.7 L.

Also, a pure ceria powder was impregnated with a nitrate solution of about 1% of platinum and rhodium so as to carry 0.34 g of a platinum component and 0.67 g of a rhodium component per 60 g of the ceria powder. And dried to produce a catalyst powder.

The binder and water subjected to the ultrasonic treatment were added to the catalyst powder and mixed, and the mixture was stirred with an ultra disperser for 1 hour to form a slurry. After adjusting the pH of the slurry to adjust the density and viscosity, the inner catalyst layer of the carrier is wash-coated, dried at a temperature of about 150 ° C., and calcined at a temperature of 500 ° C. for about 2 hours to obtain an inner catalyst. An outer catalyst layer was formed on the layer.

(Example 2) In the process of Example 1, after the ultrasonic treatment was performed on the binder of the outer catalyst layer, the mixture was stirred for 15 minutes using an ultra disperser instead of the mixer. In addition, nickel was mixed in the inner catalyst layer in an amount of 4 g / L (liter). Others are the same as the first embodiment.

Example 3 In the structure of Example 2, the amount of the binder in the outer catalyst layer was changed from 15.0% by weight to 10.0%.
% By weight. Others are the same as the second embodiment.

Example 4 In the structure of Example 2, the amount of the binder in the outer catalyst layer was changed from 15.0% by weight to 10.0%.
% By weight. In the process of Example 2, the catalyst-carrying ceria powder was slurried with 600 ml of ion-exchanged water and stirred for 15 minutes with an ultra-disperser.
This slurry was mixed with a binder that had been subjected to the same ultrasonic treatment and stirring treatment with an ultra disperser as in Example 2. Others are the same as the second embodiment.

(Example 5) In the process of Example 4, the catalyst-supported ceria powder was slurried with 600 ml of ion-exchanged water, subjected to ultrasonic treatment, and then stirred for 15 minutes by stirring using an ultra disperser. The mixture was mixed with a binder which had been subjected to the same ultrasonic treatment and stirring treatment by an ultra disperser as in Example 2. Others are the same as the fourth embodiment.

Comparative Example In the process of Example 1, the ultrasonic treatment for the binder of the outer catalyst layer was omitted. Others are the same as the first embodiment.

As the honeycomb carrier in each of the above examples, a cell having a wall thickness of 6 mil and 400 cpsi and having a water absorption of 19% or a wall thickness of 4 mil and 600 cps was used.
An i-cell having a water absorption of 14% was used.

With respect to the samples of Examples 1 to 5 and Comparative Example, the peeling rates of the catalyst layers were examined. In the test, each sample was treated by being held in an air atmosphere at 1000 ° C. for 24 hours, and then subjected to vibration for 3 hours by ultrasonic waves with water interposed. The value obtained by dividing the change in the dry weight before and after the vibration treatment by the original dry weight and multiplying the result by 100 was defined as the peeling rate. The peeling ratio is as shown in Table 1.

[0036]

[Table 1]

When Examples 1 to 5 and Comparative Example in Table 1 are compared, when the ceria base material of the outer catalyst layer is coated, at least the binder is subjected to an ultrasonic treatment to improve the releasability. You can see that. This is because the binder is highly dispersed by the ultrasonic treatment, and the catalyst component (catalyst carrying ceria)
Is also considered to be highly dispersed.

Also, the low peeling rates of Examples 4 and 5 indicate that it is desirable to perform the ultrasonic treatment only on the binder.

In addition, T50 and C4
A rig performance evaluation of 00 was performed. Table 2 shows the results.
The honeycomb carrier had a cell thickness of 6 mil and cells of 400 cpsi. Measure the sample at 1000 ° C
Performed after holding for 24 hours in an air atmosphere of
The conditions are SV = 60000, air-fuel ratio A / F = 14.7.
± 0.9. The composition of the exhaust gas at this time is as shown in Table 3.

[0040]

[Table 2]

[0041]

[Table 3]

Comparing Examples 2 and 3 in Table 2 and Table 1 above, from the viewpoint of improving the releasability, Example 2
It is preferable to set the amount of the binder to 15.0% by weight as described above, but in the T50 rig performance evaluation, it is preferable to set the amount of the binder to 10.0% by weight as in Example 3.

Further, N in Example 1 and Comparative Example
The Ox purification rate was examined. The result is shown in FIG. In the evaluation method, each sample was placed in the vicinity of an exhaust manifold of a 2-liter in-line four-cylinder engine and the exhaust gas was passed through to measure the NOx purification rate. Honeycomb carrier, wall thickness 4m
il with 600 cpsi cells.

In FIG. 3, Example 1 has a higher NOx purification rate than the comparative example, and in particular, A / F = 14.8-15.
It can be seen that the NOx purification rate is high in the lean region of 0. From this, it is considered that, with the ultrasonic treatment of the binder, platinum and rhodium in the outer catalyst layer are stably bonded and optimized by the binder, and the active points of these catalyst components can be maintained well.

Although this embodiment has been described as having two catalyst layers, the present invention has three or more catalyst layers, and the ultrasonic wave of the binder is applied to the catalyst layers other than the innermost one. Processing may be performed.

[0046]

As described above, according to the first aspect of the present invention, when a catalyst is produced by supporting a base material carrying a catalyst component on a carrier with a binder, the binder before mixing with the base material is super-absorbed. By performing sonication, the binder can be highly dispersed and reduced in molecular weight by ultrasonic treatment, and the adhesion of the base material with the binder can be increased to prevent the catalyst layer from peeling off, thereby stabilizing the performance of the catalyst. it can.

According to the second aspect of the present invention, in forming the inner and outer catalyst layers on the catalyst carrier, the inner catalyst layer substrate is coated on the carrier, and then the inner catalyst layer substrate is coated on the carrier. Since the outer catalyst layer is formed by coating the slurry containing the binder subjected to the ultrasonic treatment, the outer catalyst layer, which is easily affected by the heat of the exhaust gas, is prevented from peeling, and has two catalyst layers. The performance of the catalyst can be stabilized.

According to the third aspect of the present invention, since the substrate contains ceria, even if the ceria is easily shrunk by the heat of the exhaust gas and cracks easily formed, the catalyst layer can be prevented from peeling off. Therefore, it is possible to satisfactorily improve the purification performance of the catalyst using the ceria base material.

According to the fifth aspect of the present invention, since the carrier having a honeycomb structure has a water absorption of 14.0% or less, the effect of preventing separation of the catalyst layer can be particularly effectively obtained.

According to the sixth aspect of the present invention, since the base material is made of a porous material, peeling of the catalyst layer formed of the porous material base material can be effectively prevented.

According to the seventh aspect of the present invention, since the catalyst component is supported on the base material before being mixed with the binder, the dispersibility of the catalyst component can be improved.

[Brief description of the drawings]

FIG. 1 is a process diagram showing a process for producing an exhaust gas purifying catalyst according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a main part of an exhaust gas purifying catalyst.

FIG. 3 is a graph showing characteristics of a NOx purification rate for Example 1 and Comparative Example of the present invention.

[Explanation of symbols]

 C Exhaust gas purification catalyst 1 Carrier 2 Inner catalyst layer 3 Outer catalyst layer

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI B01J 35/04 301 B01D 53/36 102B 37/34 102H 104A B01J 23/56 301A (72) Inventor Hirozo Oda Takada-gun, Hiroshima Prefecture 360, Mukoharamachi, Tokyo Filter Container Co., Ltd.Hiroshima Plant (72) Inventor Tadashi Tokuyama 360, Mukoharacho, Takada-gun, Hiroshima Prefecture Tokyo Filter Container Co., Ltd., Hiroshima Plant (72) Inventor, Takashi Takemoto 3 No. 1 Mazda Co., Ltd. (72) Inventor Masahiko Shigetsu 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (72) Satoshi Ichikawa 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Stock Inside the company (72) Inventor Kazuo Misono 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Inside Mazda Co., Ltd. (72) Inventor Yuki Kokuda Hiroshima Prefecture Geigun Fuchu-cho Shinchi third No. 1 Mazda Motor Corporation in

Claims (7)

[Claims] 1. A method for producing a catalyst, comprising: coating a slurry containing a base material and a binder on a surface of a catalyst carrier, whereby the base material is attached to the catalyst surface, and the base material contains a catalyst component. The method for producing a catalyst according to any one of claims 1 to 3, wherein the binder is subjected to ultrasonic treatment before being mixed with the substrate. 2. The method for producing a catalyst according to claim 1, wherein the base material of the inner catalyst layer is previously coated on the catalyst carrier, and the slurry containing the binder subjected to ultrasonic treatment is coated with the base material of the inner catalyst layer. A method for producing a catalyst, comprising forming an outer catalyst layer by coating on the upper surface. 3. The method for producing a catalyst according to claim 1, wherein the substrate contains ceria. 4. The method for producing a catalyst according to claim 2, wherein the base material of the inner catalyst layer contains at least alumina. 5. The method for producing a catalyst according to claim 1, wherein the carrier has a honeycomb structure and the water absorption is 14.0% or less. 6. The method for producing a catalyst according to claim 1, wherein the base material is a porous substance. 7. The method for producing a catalyst according to claim 1 or 2, wherein the catalyst component is supported on a substrate before being mixed with the binder.