JPH07289899A - Heat resistant substrate for catalyst body and its production - Google Patents

Abstract

PURPOSE:To produce a substrate for a catalyst body having a porous alumina layer and excellent in heat resistance. CONSTITUTION:When an alumina layer is laminated on a stainless steel sheet to obtain a substrate for a catalyst body, a porous alumina layer is formed as the alumina layer by anodic oxidation and a diffusion layer in which Al, Fe and O atoms coexist is interposed between the stainless steel sheet and the alumina layer. Thus, the objective heat resistant substrate for a catalyst is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate for a catalyst body and a method for producing the same, and more particularly to a substrate for a catalyst body having excellent heat resistance and a method for producing the same.

[0002]

2. Description of the Related Art A plate-shaped substrate for a catalyst body obtained by anodizing an aluminum plate is inferior in heat resistance because the aluminum has low strength and a low melting point. The usage limit is up to. Therefore, conventionally, a substrate obtained by rolling aluminum into stainless steel to increase heat resistance and directly bonding the substrate (called a clad method) and anodizing it has been used. However, although this increases the strength of the substrate, the alumina coating is peeled off from the stainless steel plate at high temperatures, so that there is a drawback that the heat resistance is not sufficient.

Therefore, as a solution to the above-mentioned drawbacks, a substrate obtained by irradiating a stainless steel plate with aluminum is used. In this case, a large-sized apparatus is required for manufacturing, and the substrate has a uniform thickness. Since it is not possible to form a porous alumina film having uniform pores on the surface, there is a drawback that the amount of supported catalyst is small and the heat resistance is not sufficient.

[0004]

Therefore, as a result of intensive investigations by the present inventors to solve the above-mentioned drawbacks, the inventors have found that an aluminum layer is rolled on a stainless steel layer, and the aluminum layer is sufficiently baked and then oxidized. When anodizing with a strong acid, it forms a diffusion layer between the stainless steel layer and the alumina layer. The present invention has been achieved by finding out that the above is done.

Therefore, a first object of the present invention is to provide a substrate for a catalyst body which has a porous alumina film on the surface and is excellent in heat resistance. A second object of the present invention is to provide a method for producing a substrate for a catalyst body having a porous alumina film on the surface and having excellent heat resistance.

[0006]

The above-mentioned various objects of the present invention are a substrate for a catalyst body which is obtained by laminating an alumina layer on a stainless plate, wherein an aluminum atom is provided between the stainless layer and the alumina layer. And a substrate for a heat-resistant catalyst body having a diffusion layer in which iron atoms and oxygen atoms coexist, and the alumina layer is a porous alumina layer formed by anodic oxidation, and a method for producing the same. .

The stainless steel plate used in the present invention is not particularly limited and may be appropriately selected from known stainless steels. However, from the viewpoint of easy formation of a diffusion layer described below, ferrite stainless steel or It is preferable to use austenitic stainless steel. The thickness, shape and the like of the stainless steel plate used in the present invention are not particularly limited and may be appropriately determined depending on the required strength, the catalyst used and the application.

In the present invention, in order to laminate the alumina layer, first, the aluminum plate or the foil is laminated on the stainless plate. Such lamination can be performed by spraying molten aluminum on a stainless steel plate, but from the viewpoint of thickness uniformity and the ease of manufacturing, a rolling method (cladding method) is used. It is preferable to carry out.

[0009] Such joining is so-called direct joining, and the stainless steel layer and the aluminum layer are merely physically bonded, and the atoms of each layer diffuse to each other to form a chemical bond. It does not mean that there is (see Figure 7). Aluminum plate or foil used in the present invention,
In particular, it is not limited to aluminum metal,
It is also possible to appropriately select a known aluminum alloy that can be anodized as described later.

In the present invention, the thickness of the aluminum plate or aluminum foil to be laminated on the stainless plate is 10 μm to 30 from the viewpoint of favorably performing anodization described later.
It is preferably 0 μm, particularly 30 μm to 200 μm
m is preferable, and the range of 60 μm to 150 μm is most preferable.

In the catalyst substrate of the present invention, from the viewpoint of preventing the stainless steel plate from separating from the porous alumina layer and increasing the heat resistance of the substrate, at least aluminum atoms are contained in the stainless steel layer in contact with the aluminum plate or foil. To form a diffusion layer. Further, in the present invention, it is preferable that iron atoms in stainless steel diffuse into the aluminum layer, and it is preferable to form a diffusion layer in which these atoms mutually diffuse.

Such a diffusion layer can be easily formed by firing described later. By this diffusion layer,
The bond between the stainless plate and the aluminum plate or foil becomes strong. In the present invention, the aluminum layer is converted into an alumina layer by anodic oxidation which will be described later, and oxygen atoms are further diffused in this diffusion layer, whereby peeling between the stainless steel plate and the alumina layer is prevented as described later.

The catalyst substrate of the present invention has a porous alumina layer from the viewpoint of increasing the amount of catalyst supported and heat resistance. Such a porous alumina layer can be easily formed by anodizing the aluminum plate or foil provided on the stainless plate as described later. Next, the method for producing the substrate for heat resistant catalyst of the present invention will be described in detail.

The substrate for heat-resistant catalyst of the present invention is produced by rolling an aluminum plate on a stainless steel plate to prepare a clad plate, followed by firing so that at least aluminum atoms are diffused in the stainless steel, and then anodizing. It can be easily manufactured. Rolling an aluminum plate into a stainless plate can be easily performed using a known rolling machine.

The firing is preferably carried out at 300 ° C to 600 ° C, particularly 450 ° C to 550 ° C. If it is less than 300 ° C, a good diffusion layer cannot be provided. The firing time depends on the firing temperature, etc., but is 1
It should be done for 15 to 15 hours. If it is less than 1 hour, it is difficult to provide a diffusion layer that can contribute to prevention of peeling.
Firing for 5 hours or more is not only economically disadvantageous but also not preferable from the viewpoint of production efficiency. The firing atmosphere may be air or an inert gas.

The anodic oxidation of the aluminum surface can be easily performed by using a known anodic oxidation technique. At the time of anodic oxidation in the present invention, it is necessary to use a strongly oxidizing acid such as chromic acid or sulfuric acid as the treatment liquid. As a result, anodic oxidation can be advanced to the inside of the diffusion layer, and oxygen atoms can be diffused to the inside of the diffusion layer. The acid concentration of the treatment liquid may be appropriately determined, but when chromic acid is used, it is preferably 2 to 4% by weight.

The conditions for the anodic oxidation may be appropriately set so that the BET surface area of the alumina layer is large. In the present invention, the temperature of the anodizing treatment solution is 0 to 50 ° C., particularly room temperature to 40 ° C. Preferably. B below 0 ° C
The ET surface area does not become so large, and if it exceeds 50 ° C., the dissolution is severe and it becomes difficult to economically form an oxide film.

Although the treatment time of this anodic oxidation depends on the treatment conditions, for example, a 2.5 wt% chromic acid aqueous solution is used as the treatment liquid, the treatment bath temperature is 38 ° C., and the current density is 1
When it is 9.0 A / m ² , it is preferably 2 hours or longer, particularly 4 hours or longer. In the present invention, it is preferable to further increase the surface area of the catalyst body by treating the surface of the substrate provided with the alumina layer by anodic oxidation as described above with hot water or steam at 50 to 350 ° C.

The pH of the hot water in this case is 7 or more, especially 1
It is preferable to set it to 0 to 12 in order to shorten the processing time. Although the treatment time of the hot water treatment varies depending on the pH of the hot water, it is preferably 1 hour or longer, and the BET surface area can be significantly increased by treating the hot water for about 2 hours regardless of the pH value. Also, after hot water treatment,
It is preferable to bake at 400 to 550 ° C. for 10 minutes to 3 hours.

A highly active plate-shaped catalyst body can be obtained by supporting an ultrafine particle catalyst on the surface of the substrate prepared as described above by a known impregnation method or electrodeposition method. In particular, in the hot water treatment, when hot water containing a fine particle catalyst at 70 to 90 ° C., preferably 80 to 85 ° C. is used, the catalyst can be supported on the surface of the substrate simultaneously with the hot water treatment. In addition to simplifying the process of manufacturing the plate-shaped catalyst body, it is possible to obtain a plate-shaped catalyst body that is particularly excellent in terms of catalytic activity.

Therefore, it is particularly preferable to treat with hot water containing a fine particle catalyst, dry it, and then calcine at 400 to 550 ° C. In this case, the amount of the ultrafine particle catalyst contained in the hot water is not particularly limited, but 0.2
It is preferably in the range of 5 g / liter to 1.0 g / liter. If the concentration is too high, it becomes uneconomical, and if it is too low, the required treatment time becomes long.

Examples of the ultrafine particle catalyst used include platinum group metals, platinum group metal alloys, gold, gold alloys, chromium, manganese, iron, zinc, copper, nickel, nickel alloys, cobalt and cobalt alloys, ruthenium, etc. Alternatively, a combination of these catalyst substances can be mentioned.
The particle size of the ultrafine particle catalyst is about 1 nm to 100 nm, preferably about 1 nm to 50 nm. or,
The BET surface area as a plate-shaped catalyst body is preferably 3000 times or more the apparent surface area of the metal substrate from the viewpoint of catalytic activity.

The plate-shaped catalyst body obtained as described above is processed into a tubular shape, a honeycomb shape or the like and then charged into a high-temperature reaction tower as appropriate, or a high-temperature reaction chamber is formed using these catalyst bodies. You can It is presumed that the catalyst substrate of the present invention has heat resistance because the stainless steel layer and the alumina layer are chemically bonded in the diffusion layer between the stainless steel layer and the alumina layer.

[0024]

The substrate for a catalyst body of the present invention has a large amount of supported catalyst and has a diffusion layer which is strong against thermal stress between the stainless layer and the alumina layer, and therefore has good heat resistance. is there. Further, according to the production method of the present invention, it is possible to easily produce a substrate for a heat-resistant catalyst body having a porous alumina film having a uniform thickness and uniform pores on the surface without requiring a large-scale device. it can.

[0025]

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

Example 1. Preparation of Aluminum / Stainless Clad Substrate An aluminum / stainless clad substrate was obtained by providing a 40 μm thick aluminum layer on both sides of a ferritic stainless steel plate having a length of 12.5 cm, a width of 30 cm and a thickness of 2 mm, using a rolling mill. Firing The obtained clad substrate was fired in air at 500 ° C. for 13 hours using an electric furnace.

The anodized and baked substrate was washed with 5% by weight of sodium hydroxide for 5 minutes, then washed with water, then with 30% by weight of nitric acid, and further washed with water. The substrate pretreated as described above was treated with a 2.5 wt% chromic acid aqueous solution at a liquid temperature of 30 ° C. and a current density of 1
Anodization was performed at 5.0 A / m ² .

Heat resistance evaluation test The obtained catalyst substrate was placed on a pumice sample holder provided in a quartz tube as shown in FIG. 1, both ends were sealed with glass wool, and inserted into an electric furnace. Then, the temperature was raised from room temperature at 9 ° C / min to 650 ° C, and the temperature was kept at the same temperature for 1 hour.
Repeat the cycle of lowering the temperature at 9 ° C / min to normal temperature,
The number of cycles until the alumina layer was peeled off was measured. The results are as shown in Table 1.

The cross section of the anodized substrate was analyzed using an X-ray microanalyzer (EPMA), and the results are shown in FIG. From FIG. 2, it was confirmed that a diffusion layer composed of aluminum atoms, iron atoms and oxygen atoms was formed. A schematic sectional view based on the above results is shown in FIG.

Example 2. A catalyst body substrate was prepared in exactly the same manner as in Example 1 except that the firing time was changed to 1 hour.
A heat resistance test was conducted in exactly the same manner. The results are shown in Table 1. From the result of the EPMA analysis of the cross section of the substrate, it was confirmed that the diffusion layer had few oxygen atoms. A schematic sectional view of the substrate is shown in FIG.

Comparative Example 1. Table 1 shows the results of a heat resistance test conducted in the same manner as in Example 1 except that the catalyst substrate was prepared except that no calcination was performed. It was confirmed that a diffusion layer composed of aluminum atoms, iron atoms and oxygen atoms was not formed as in Comparative Example 1.

Comparative Example 2. A heat resistance test was conducted in the same manner as in Example 1 except that the anodizing conditions were changed as follows, and a catalyst body substrate was prepared.
As shown in. The anodized and baked substrate was washed with 5% by weight of sodium hydroxide for 5 minutes, then washed with water, then with 30% by weight of nitric acid, and further washed with water using a 4% by weight oxalic acid aqueous solution. Anodization was performed at 20 ° C. and a current density of 50.0 A / m ² .

The results of analyzing the cross section of the substrate after anodization using EPMA are as shown in FIG. In the case of this example, it was confirmed that the penetration of oxygen atoms by diffusion was hindered and a diffusion layer composed of aluminum atoms, iron atoms and oxygen atoms was not formed.

Comparative Example 3. Table 1 shows the results of the heat resistance test in which anodic oxidation was performed in exactly the same manner as in Comparative Example 2 except that a clad substrate that was not fired was used, and the heat resistance test was performed in exactly the same manner. The EPMA analysis diagram in this case is as shown in FIG.

[0035]

[Table 1] The above results demonstrate that the catalyst substrate of the present invention has excellent heat resistance.

[Brief description of drawings]

FIG. 1 is a cross-sectional perspective view of a container used for a heat resistance test.

FIG. 2 is an EPMA analysis diagram of a cross section of a substrate for a catalyst body of the present invention.

FIG. 3 is a schematic sectional view of a substrate for a catalyst body of the present invention.

FIG. 4 is a schematic cross-sectional view of a catalyst body substrate of Example 2.

5 is an EPMA analysis view of a cross section of a substrate for a catalyst body of Comparative Example 2. FIG.

FIG. 6 is an EPMA analysis diagram of a bonded portion of a substrate obtained in Comparative Example 3.

[Explanation of symbols]

 1 Quartz tube 2 Pumice sample holder 3 Sample (catalyst substrate) 4 Glass wool for sealing 5 Thermocouple for measuring internal temperature 6 Aluminum layer 7 Diffusion layer of oxygen atom and aluminum atom 8 Iron atom, aluminum and oxygen Diffusion layer with atoms 9 Stainless layer

Claims (6)

[Claims] 1. A substrate for a catalyst body, comprising a stainless steel plate and an alumina layer laminated on the stainless steel plate, wherein a diffusion layer in which aluminum atoms, iron atoms and oxygen atoms coexist is provided between the stainless steel layer and the alumina layer. At the same time, the substrate for heat resistant catalyst is characterized in that the alumina layer is a porous alumina layer formed by anodic oxidation. 2. The substrate for heat resistant catalyst according to claim 1, wherein the stainless steel is ferritic stainless steel or austenitic stainless steel. 3. After rolling an aluminum plate or foil on a stainless plate, it is baked so that at least aluminum atoms are diffused in the stainless plate, and then anodized with an acid having strong oxidizing power until the aluminum layer disappears. The method for manufacturing a substrate for a heat-resistant catalyst body according to claim 1, wherein 4. The firing is performed at 450 ° C. to 550 ° C.,
A method for producing a substrate for a heat resistant catalyst according to claim 3. 5. The method for producing a substrate for a heat resistant catalyst according to claim 4, wherein the baking is performed for 1 to 3 hours. 6. The method for producing a substrate for a heat-resistant catalyst body according to claim 3, wherein hot water treatment is performed after anodizing.