JP2507146B2 - Method for forming catalyst coating layer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a catalyst for catalytic combustion used for catalytic combustion after mixing liquid fuel such as kerosene or gaseous fuel such as city gas with air, or household appliances. The present invention relates to a method for producing a purification catalyst used for detoxifying exhaust gas generated from equipment, automobiles and the like.

2. Description of the Related Art Conventional conventional catalysts have a specific surface area of usually 10 by forming a coating layer made of activated alumina called washcoat on honeycomb ceramics made of cordierite.
The carrier coating layer was prepared by supporting a catalyst metal of a platinum group metal, such as platinum, palladium, rhodium, ruthenium, etc., on the carrier coating layer. Here, rare earth metal oxides (cerium oxide, lanthanum oxide, etc.) are often added to the coating layer activated alumina as a promoter. Also,
The particle size of the activated alumina used is often properly selected depending on the application (relationship of the contact speed with the gas to be reacted). That is, when the contact speed is remarkably increased, the reaction gas becomes diffusion-controlled in the small activated alumina, and the catalyst cannot act effectively.

Problems to be Solved by the Invention As a catalyst, it is desired that a small amount of highly efficient activity can be raised, and for that purpose, it is essential that the catalyst metal is supported on the carrier coating layer with high dispersion and high density. is there. This method of supporting with high dispersion and high density not only improves the active alumina or the active alumina to which the rare earth metal oxide is added as a carrier, but it is also effective to refine the carrier powder particles with it. is there.

However, if the carrier powder particles are made finer, the cohesive force between the powder particles becomes too strong, and the slurry is coated on the honeycomb-shaped substrate, and cracks in the coating are likely to occur during drying. If cracks occur, the coating layer will peel off from the honeycomb substrate when the catalyst is used, and it will not be possible to function as a catalyst.

The present invention has been made in view of the above points, and provides a method for forming a catalyst coating layer that enables highly dispersed loading of a platinum group metal on a finely divided carrier without causing cracks in the catalyst coating layer. The purpose is to

Means for Solving the Problems The method for forming a catalyst coating layer of the present invention is at least alumina, alumina and barium oxide, alumina and barium oxide and cerium oxide, alumina and barium oxide and lanthanum oxide, alumina and cerium oxide, and alumina and oxide. Powder particles consisting of lanthanum, alumina, cerium oxide, or lanthanum oxide as a component system, a platinum group metal salt, glycerin, or a slurry prepared by containing one of polyethylene glycol as an additive to form a honeycomb substrate. It is to coat.

Action In the present invention, in order to support the catalyst metal on the powder particles serving as a carrier in a highly dispersed manner, raw material powder particles such as alumina, barium oxide and cerium oxide (average particle size of about 5 to 30 μm), a platinum group metal salt, Aluminum nitrate or nitric acid as a pH adjuster is ball-milled before forming the coating layer, and the powder particles are further pulverized to an average particle size of about 1 to 3 μm to obtain a slurry. At this time, the platinum group metal ions are adsorbed and carried on the surface of the powder particles. Next, either glycerin or polyethylene glycol is added to this slurry as an additive, and alumina sol is added as a binder for the coating layer. Then, the honeycomb substrate is dipped in the obtained slurry, taken out, excess slurry is removed by an air gun or the like, and then dried. At this time, cracks are likely to occur in the slurry containing the finely divided powder particles. However, in the present invention, by adding a small amount of glycerin or polyethylene glycol, the agglomeration action of the powder particles occurring during drying is buffered, and the generation of cracks in the coating layer is prevented.

Examples Examples of the present invention will be described below.

Examples of the honeycomb substrate used in the present invention include honeycomb ceramics such as cordierite produced by ordinary extrusion and a metal honeycomb produced by forming a Fe—Cr—Al foil into a corrugated shape. However, this is not a limitation as long as it is an integral structure having heat resistance equivalent to these.

Alumina used in the present invention, alumina and barium oxide, alumina and barium oxide and cerium oxide, alumina and barium oxide and lanthanum oxide, alumina and cerium oxide, alumina and lanthanum oxide, alumina and cerium oxide and lanthanum oxide are platinum group metal. A specific surface area of 50 to 300 m 2 / g is preferred for high dispersion support.

(Example 1) Al2O3 / CeO2 (Al2O3: Ce) having a specific surface area of 130 m2 / g
O2 = 10: 5.16 weight ratio) 1000g, aluminum nitrate 9 hydrate 15
g, 1000 g of water and dinitrodiamminepalladium (4.5w
t%) 444 g of aqueous solution was ball-milled for 48 h, 24 h, 12 h, 4 h and 1 h to have average particle sizes of 0.6, 1.0, 2.0, 3.0 and 4.0 μm, respectively. After that, 100g of alumina sol with 20wt% alumina content
Add a predetermined amount of water and ball-mill for 20 minutes to reduce the viscosity to about 80c.
Adjusted to ps. Finally, the additive polyethylene glycol (molecular weight 20,000) was added to the slurry in 0.5 and 1.
A total of 25 kinds of slurries were prepared by adding 0, 2.0, 3.0 and 4.0 wt% and further ball-milling for 10 min.

Next, using each of the obtained slurries, honeycomb ceramics consisting of cordierite (diameter 100 mm, thickness 10 mm
The catalyst layer was coated on a disk having a wall thickness of 0.25 mm and a cell pitch of 1.47 mm. After the above honeycomb ceramics were dipped in the slurry, they were pulled up, and the excess slurry remaining in the lattice of the honeycomb ceramics was removed using an air gun of 0.5 kg / cm 2. Then, dry at 120 ℃ for 1h, 500
Heat treatment was carried out at ℃ for 1 hour, and the honeycomb-shaped ceramic was coated with about 5 g of the catalyst layer at one time.

The evaluation of the obtained catalyst coating layer is carried out by microscopically observing the surface of the coating layer to confirm that no cracks are generated, and the coating strength is such that the catalyst layer is lightly traced by a human hand and the catalyst layer does not adhere to the hand. It was confirmed. As a result, when n = 10 pieces, the coating layer had no cracks and had sufficient coating strength, it was evaluated as ○, and the coating layer had some cracks or the coating strength was slightly affected by the additive. Inferior ones were evaluated as Δ, and all cracks in the coating layer or inferior coating strength due to the effect of additives were evaluated as x.

(Example 2) Similar to Example 1, Al2O3 having a specific surface area of 130 m2 / g
-CeO2 (Al2O3: CeO2 = 10: 5.16 weight ratio) 1000g, aluminum nitrate 9-hydrate 15g, water 1000g and dinitrodiammine palladium (4.5wt%) aqueous solution 444g 48h, 24h, 12h, 4
Ball mill for h and 1h to obtain average particle sizes of 0.6, 1.0 and 2.
It was set to 0, 3.0 and 4.0 μm. After that, alumina content 20wt
% Of alumina sol and a predetermined amount of water were added, and the mixture was ball-milled for 20 minutes to adjust the viscosity to about 80 cps. Finally, the additive glycerin was added to the slurry at 0.5, 1.0 and 2.
Add 0, 3.0, 4.0wt%, ball-mill for 10min, total 25
Different types of slurries were prepared.

Next, using each slurry obtained in the same manner as in Example 1, about 5 g of a catalyst layer was coated once on a honeycomb ceramic made of cordierite. The subsequent catalyst coating layer was evaluated in the same manner.

(Comparative Example 1) Al2O3 having a specific surface area of 130 m2 / g as in Example 1
-CeO2 (Al2O3: CeO2 = 10: 5.16 weight ratio) 1000g, aluminum nitrate 9-hydrate 15g, water 1000g and dinitrodiammine palladium (4.5wt%) aqueous solution 444g 48h, 24h, 12h, 4
Ball mill for h and 1h to obtain average particle sizes of 0.6, 1.0 and 2.
It was set to 0, 3.0 and 4.0 μm. After that, alumina content 20wt
% Alumina sol and a predetermined amount of water were added, and the mixture was ball-milled for 20 minutes to adjust the viscosity to about 80 cps to prepare a total of five types of slurries.

Next, using each slurry obtained in the same manner as in Example 1, about 5 g of a catalyst layer was coated once on a honeycomb ceramic made of cordierite. Then, the catalyst coating layer was evaluated in the same manner.

In Comparative Example 1, a slurry having an average particle size of 3 μm or less was used, and it was not possible to form a film without cracks. However, in Examples 1 and 2 of the present invention, by using an appropriate amount of the additive polyethylene glycol or glycerin, a slurry having an average particle size of 1 to 3 μm could be formed into a film without cracks. Also, the additive polyethylene glycol was effective in forming a film in a smaller amount than glycerin.

(Example 3) Al2O3 having a specific surface area of 130 m2 / g as in Example 1
-CeO2 (Al2O3: CeO2 = 10: 5.16 weight ratio) 1000 g, aluminum nitrate nonahydrate 15 g, water 1000 g, and dinitrodiammine palladium (4.5 wt%) aqueous solution 444 g were ball-milled for 24 hours to obtain an average particle size of 1.0 µm. After that, alumina content 20wt
% Alumina sol 100g and a predetermined amount of water are added and ball milled for 20 minutes to obtain viscosities of about 130, 100, 80, 65 and 50 cps respectively
It was adjusted. Finally, an additive of polyethylene glycol (molecular weight 20,000) was added to each of the slurry in an amount of 2.0 wt% and further ball-milled for 10 minutes to prepare a total of five types of slurries.

Next, using each slurry obtained in the same manner as in Example 1, about 7.5, about 6.2, about 5.0, about 3.8, and about 2.5 g of a catalyst layer was coated once on a honeycomb ceramic made of cordierite. Then, the catalyst coating layer was evaluated in the same manner.

From the results shown in Table 4, no matter how effective the additive polyethylene glycol was for forming a film, it was found that
When the amount of coating increases in times It has cracked. When this result was analyzed by the thickness of the coating layer, it was confirmed that cracks were likely to occur when the thickness of the coating layer exceeded 20 μm with respect to the honeycomb substrate. Therefore, the thickness of coating the slurry on the honeycomb substrate at one time is preferably 20 μm or less.

Next, a catalyst having an average particle size of 1 μm obtained by using 2 wt% of the additive in Example 1 and an average particle size of 4 obtained in Comparative Example 1 were used.
The following tests were conducted using a catalyst of μm.

A kerosene catalytic combustion device was assembled, and a continuous combustion life test was conducted at 1000 kcal / h and an air-fuel ratio (air / kerosene) of 1.5 to measure the temperature change on the upstream side of the catalyst. FIG. 1 shows changes with time in the upstream surface temperature of the catalysts of Examples and Comparative Examples.

As a result, the catalyst of the present invention showed excellent life performance as compared with the catalyst of Comparative Example.

EFFECTS OF THE INVENTION According to the present invention, by using polyethylene glycol or glycerin as an additive in a slurry, it is possible to carry out highly dispersed loading of a platinum group metal on a finely divided carrier without causing cracks in the catalyst coating layer. It has been possible to provide an excellent combustion and purification catalyst.

[Brief description of drawings]

The figure is the result of a kerosene catalyst combustion life test conducted to evaluate one example of the present invention and the catalyst of the comparative example.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Nora Ono, Nora Ono 1006, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Hidenobu Wakita, 1006, Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Within the corporation

Claims (4)

(57) [Claims] 1. At least one of alumina, alumina and barium oxide, alumina and barium oxide and cerium oxide, alumina and barium oxide and lanthanum oxide, alumina and cerium oxide, alumina and lanthanum oxide, alumina and cerium oxide and lanthanum oxide. Forming a catalyst coating layer characterized in that a honeycomb substrate is coated with a slurry prepared by containing powder particles consisting of the component system of, a platinum group metal salt, glycerin, or polyethylene glycol as an additive. Method. 2. The average particle size of the powder particles in the slurry is 1.0-.
The method of forming a catalyst coating layer according to claim 1, wherein the thickness is 3.0 μm. 3. The method for forming a catalyst coating layer according to claim 1, wherein the additive is 0.5 to 4 wt% with respect to the slurry. 4. The thickness of coating the honeycomb substrate with the slurry at one time is 20 μm or less.
2. The method for forming a catalyst coating layer according to 2 or 3.