JPH0573461B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a catalyst carrier for use in detoxifying hydrocarbons (HC), carbon monoxide (CO), and nitrided oxides ( _NOx ), and particularly for use in automobile exhaust gas and stationary The present invention relates to a catalyst carrier used for purifying engine exhaust gas. [Prior art] An integrated structure carrier (monolith carrier) has various materials,
Although there are various shapes and manufacturing methods, generally cordierite and square cell monolith carriers manufactured by Corning and Nippon Insulators are often used. This cordierite monolithic support is
Since the specific surface area is very small, about 1 m ² /g, even if a catalytic metal such as a noble metal is supported, it cannot be dispersed on the surface of the support. As a result, catalysts with poor initial performance and poor durability are obtained, and are not practical for use as a carrier as they are. Conventionally, in order to solve the above-mentioned drawbacks, an active alumina coating has been formed on a monolithic carrier to increase the specific surface area, improve the dispersibility of the catalyst metal, and improve the performance. Conventionally, the activated alumina used for this alumina coating is as shown in Japanese Patent Publication No. 56-27295.
Alumina having a specific surface area of about 50 m ² /g or more is used, and α has a specific surface area of less than 50 m ² /g,
There are few examples of active use of θ-alumina. In JP-A-54-148187, as seen in the description that δ-alumina is the main component and x, γ, κ, θ, and ρ-alumina are a part, θ-alumina is mixed in a part of the activated alumina. There is a view that it is also good. [Problems to be solved by the invention] The required performance for conventional catalysts for purifying automobile exhaust gas is that the upper limit of the catalyst inlet gas temperature is around 800℃, so it is necessary to have thermal durability up to 800℃. It was hot. However, in recent years, the catalyst installation position has been moved to the upstream part of the exhaust pipe and emphasis is placed on use at high speeds, so the upper limit of the catalyst inlet gas temperature has increased to around 900℃, and the catalyst temperature has increased to around 1000℃.
It is thought that the temperature is around ℃. As a result, high-temperature durability, which had not been given much importance in the past, has recently come to be viewed as a particular problem. Therefore, catalysts according to the prior art have insufficient high temperature durability.
The reason for this is that in the activated alumina species shown in Japanese Patent Publication No. 56-27295 and Japanese Patent Application Laid-open No. 54-148187, the crystals undergo transformation at a high temperature of 1000°C, and when new, the catalytic metal is Although the catalyst metal was supported in a highly dispersed manner, it is thought that sintering of the catalyst metal was promoted as a result, resulting in a decrease in catalyst performance. Furthermore, when durability tests were conducted to investigate the durability of the catalyst, it was found that the performance of the catalyst in the upstream half of the catalyst in the exhaust gas flow direction deteriorated to a greater extent than the performance of the remaining half of the catalyst. Furthermore, when the specific surface area of each catalyst was measured, the specific surface area of the upstream half of the catalyst was significantly reduced, and the reason for the performance deterioration is thought to be the high temperature that occurred in the upstream half. Therefore, the problem with conventional catalysts is that they lack high-temperature durability, particularly in the upstream half. [Means for Solving the Problems] The present inventors have conducted intensive research to solve the problems of the above-mentioned conventional techniques, and as a result, compared to conventional catalysts,
We have succeeded in providing a catalyst carrier that can be used as an exhaust gas purification catalyst with excellent high-temperature durability. That is, in the exhaust gas purifying catalyst carrier of the present invention, the activated alumina coating layer on the honeycomb monolith base material for supporting catalyst metal has an activated alumina coating layer containing α-alumina and θ-alumina on the upstream side in the exhaust gas flow direction. Consisting of
The downstream side is characterized by comprising at least one type selected from δ-alumina and γ-alumina. In this invention, the monolith carrier used as the base material is cordierite, mullite, etc.
The base material preferably has a triangular, square, or wavy cell structure. In addition, as the catalyst metal supported on the catalyst carrier of the present invention, it is preferable to use at least one of platinum, palladium, and rhodium. [Function] The catalyst carrier of the present invention has activated alumina containing α-alumina and θ-alumina, which is less susceptible to crystal transformation due to heat, applied as a coating layer on the upstream side, which is in a higher temperature state than the downstream side during use. Therefore, sintering of the catalyst metal supported thereon by heat under high-temperature conditions is less likely to occur, and as a result, a catalyst with excellent high-temperature durability can be provided. In addition, the downstream side is less prone to high temperatures compared to the upstream side, and is coated with δ-alumina and γ-alumina with a specific surface area of 50 m ² /g or more, so the supported catalyst metal has good dispersibility. It can provide a highly durable catalyst. [Example] Example 1 Alumina sol manufactured by Nissan Chemical Co., Ltd. (trade name AS-200)
700g (alumina content 70g), 60g of aluminum nitrate nonahydrate, 200g of ion-exchanged water, and alumina with a specific surface area of 100m ² /g and showing δ and γ in X-ray diffraction were calcined at 1100℃ for 3 hours. A slurry was prepared by mixing and stirring 1000 g of powder (having a specific surface area of 20 m ² /g and detecting θ- and α-alumina by X-ray diffraction) for 3 hours. This slurry was designated as A slurry. Next, as alumina powder, the specific surface area is 100m ² /g
Using alumina that shows δ and γ in X-ray diffraction,
The above A except that 350g of ion-exchanged water was used.
A slurry having the same composition as the slurry was mixed and stirred for 3 hours to prepare a slurry, and this slurry was designated as Slurry B. A cylindrical monolith carrier made of cordierite (manufactured by Nippon Insulators Co., Ltd., diameter 93 mm, length 100 mm, volume 0.679) having 300 cells per square inch is immersed in water, and after absorbing sufficient water, it is taken out and placed inside the cells. The remaining water was blown away with a stream of air (pressure of 5 kg/mm ² ). Half of this water-absorbed carrier (upstream part) is immersed in the previously prepared slurry A and taken out, and the excess slurry in the cells that has adhered to the half of the carrier is removed from the opposite side to which the slurry is not attached using an air flow. I blew it away. After drying the carrier to which A slurry was attached in this way at 110°C for 1 hour, it was fired in air at 700°C for 1 hour using an electric furnace to form a 43g A alumina coating on half of the monolithic carrier (upstream part). I let it happen. In addition, only half of the monolith carrier (the downstream part) on which the alumina coating is not formed is immersed in the B slurry, and taken out, and the excess slurry in the cell is removed from the opposite side to which the B slurry is not attached using an air flow. After blowing off and drying this carrier at 110℃ for 1 hour,
Baked in air at 700℃ for 1 hour using an electric furnace to yield 43g.
A B alumina coating was formed on half of the monolithic carrier (downstream portion) to obtain a catalyst carrier containing an alumina coating layer consisting of the A coating and the B coating, weighing a total of 86 g. When the alumina coating layer of this catalyst carrier was scraped off and the compounds were identified and analyzed by X-ray diffraction, θ-alumina and α-alumina were detected from the upstream portion. Furthermore, from the downstream part, δ−
Alumina and γ-alumina were detected. Next, half of this catalyst carrier is immersed in a platinum ammine aqueous solution to adsorb platinum, the catalytic metal, on the catalyst carrier.The other half is also adsorbed with platinum and further washed with water. The catalyst carrier was immersed in a rhodium chloride aqueous solution to support the catalyst metal rhodium, and then dried at 100°C.
An exhaust gas purifying catalyst was obtained by firing at 500°C for 30 minutes.
Chemical analysis of the amount of noble metal supported on this catalyst revealed that the amount of platinum supported was 1.0 g/-catalyst and the amount of rhodium supported was 0.1 g/-catalyst. Example 2 Similarly to Example 1, a coating film was formed on the upstream portion of the monolithic carrier using slurry A, and a coating film was formed on the downstream portion using slurry C prepared as follows. C slurry has a specific surface area as alumina powder.
It was prepared by mixing and stirring a slurry having the same composition as the slurry A above, except that activated alumina having a size of 130 m ² /g and showing γ-alumina in X-ray diffraction was used, and 350 g of ion-exchanged water was used. . When the alumina coating layer of this catalyst carrier was scraped off and the compounds were identified and analyzed by X-ray diffraction, θ- and α-alumina were detected from the upstream portion, and γ-alumina was detected from the downstream portion. Next, as in Example 1, 1.0 g/- of platinum and 0.1 g/- of rhodium were added to the coated carrier.
- A catalyst-supported catalyst for exhaust gas purification was obtained. Example 3 Similarly to Example 1, a coating film was formed on the upstream part of the monolithic carrier using slurry A, and a coating film was formed on the downstream part using slurry D prepared as follows. . Slurry D uses activated alumina that has a specific surface area of 50 m ² /g as alumina powder and shows δ- and θ-alumina in X-ray diffraction, and contains 300 m2 of ion-exchanged water.
This slurry was prepared by mixing and stirring a slurry having the same composition as the above slurry A except that g was used. When the alumina coating layer of this catalyst carrier was scraped off and identified by X-ray diffraction, θ- and α-alumina were detected from the upstream portion, and δ- and θ-alumina were detected from the downstream portion. Next, in the same manner as in Example 1, 1 g/- of platinum and 0.1 g/- of rhodium were supported on this catalyst carrier to obtain an exhaust gas purifying catalyst. Comparative Example 1 Slurry A used in Examples 1, 2 and 3 was coated on the entire monolithic carrier, dried and fired to form a film of 86 g. When this coating layer was scraped off and identified by X-ray diffraction, α and θ alumina were detected. As in Example 1, 1.0 g/- of platinum and 0.1 g/- of rhodium were supported on this coated carrier to obtain an exhaust gas purifying catalyst. Comparative Example 2 The entire monolithic carrier was coated with the B slurry used in Example 1, dried and fired to form a coating of 86 g. When this coating layer was scraped off and identified by X-ray diffraction, δ and γ alumina were detected. Example 1
In the same manner as above, 1.0 g/- of platinum and 0.1 g/- of rhodium were supported on the catalyst to obtain an exhaust gas purifying catalyst. Comparative Example 3 The entire monolithic carrier was coated with the C slurry used in Example 2, dried and fired to form a coating of 86 g. When this coating layer was scraped off and identified by X-ray diffraction, γ-alumina was detected. As in Example 1, 1.0 g of platinum/catalyst and 0.1 g of rhodium were added to this coated carrier.
g/- catalyst carrier to obtain an exhaust gas purifying catalyst.
Table 1 shows the forms of alumina in Examples 1 to 3 and Comparative Examples 1 to 3.

[Table] Example 4 and Comparative Example 4 Platinum ammine aqueous solution, palladium chloride aqueous solution and rhodium chloride aqueous solution were used on the catalyst supports obtained in Example 1 and Comparative Example 1, respectively.
In the same manner as in Example 1, platinum 0.5g/-catalyst,
Palladium 0.5g/-catalyst and rhodium 0.1
A catalyst for exhaust gas purification was obtained by supporting the catalyst. Example 5 and Comparative Example 5 Palladium 1.0 g/-catalyst and Rhodium 0.1g/
- A catalyst for exhaust gas purification was obtained by supporting the catalyst. Catalyst durability performance evaluation test results The durability test conditions were an engine with a displacement of 3800 c.c., a rotation speed of 3300 rpm, a boost of -100 mmHg, a catalyst inlet gas temperature of 890°C, and an air-fuel ratio (A/F) of 14.5 for 50 hours. The condition is that it is exposed to exhaust gas. In this way, the performance of the durable catalyst was evaluated using an engine with a displacement of 1600 c.c. at a rotation speed of 2600 rpm, a boost of -360 mmHg, a catalyst inlet gas temperature of 460°C, and an A/F of 14.5.
Exhaust gas was passed through the catalyst after durability under the following conditions, and the purification rate for hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO _x ) was calculated. These results are shown in Table 2.

[Table] [Effects of the Invention] As is clear from the above results, the catalyst carrier of the present invention is a catalyst with extremely superior high-temperature durability compared to conventional catalyst carriers that support the same catalyst metal. performance can be demonstrated.

Claims (1)

[Claims] 1 In a catalyst carrier for exhaust gas purification formed by applying a coating layer of activated alumina to a honeycomb monolith base material, the coating layer of activated alumina on the upstream side in the direction of the exhaust gas flow path contains α-alumina and θ-alumina.
- a coating layer made of activated alumina containing alumina, characterized in that the coating layer of activated alumina on the downstream side is a coating layer made of activated alumina containing at least one selected from δ-alumina and γ-alumina; Catalyst carrier for exhaust gas purification.