JPH08281125A - Plate-like alumina carrier with high heat resistance, its manufacture, and catalyst body produced by carrying catalyst thereon - Google Patents

Abstract

PURPOSE: To produce a plate-like alumina carrier with high strength and heat resistance and having an anodized coating on at least one side, and a catalyst body with high strength and heat resistance produced by carrying a catalyst on the carrier and to provide its manufacturing method. CONSTITUTION: A plate-like alumina carrier is the one having an alumina layer on at least one side of a stainless plate and the carrier has a diffused layer in which aluminum component and iron component exist in an interface between the stainless plate and the alumina layer. The contents of the aluminum component and iron component in the diffused layer are made to change gradually and, at the same time, if necessary, numberless cracks are formed in the surface of the alumina layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plate-shaped alumina carrier, and more particularly to a plate-shaped alumina carrier which is made of stainless steel and has excellent heat resistance, a method for producing the same, and a catalyst body having a catalyst supported thereon.

[0002]

2. Description of the Related Art A catalyst is known in which an aluminum plate is anodized, the resulting porous anodized film is subjected to hot water treatment to increase its BET surface area, and a catalyst is supported on the surface (special feature: Kaihei 2-144154). Since such a planar catalyst body is excellent in a heat conductor, it is suitable for use as a wall material of a reaction chamber having a heat exchange ability, but since its base material is aluminum, it has low strength and Since it has a low melting point, it is poor in heat resistance, and the upper limit of its use is usually 200 ° C. Further, when aluminum is exposed on the outer surface, there is a problem that corrosion progresses from that portion.

Therefore, in order to improve strength and heat resistance, it was attempted to use aluminum obtained by rolling aluminum into stainless steel by a cladding method and directly bonding the aluminum and anodizing the obtained substrate. However, in this case, during the anodization, stainless steel and aluminum are often peeled off, the success rate of anodization is low, and even if the anodization succeeds, the strength of the substrate increases, but the heat of alumina and stainless steel increases. Due to the difference in expansion coefficient, the alumina coating peels off from the stainless steel plate when exposed to high temperatures, which is a drawback that the heat resistance is not sufficient.

Therefore, in order to improve the above-mentioned drawbacks, it has been attempted to use a substrate obtained by spraying aluminum on a stainless steel plate, but in this case, a large-sized apparatus is required for the production and the substrate is uniform. Since it was not possible to form a porous alumina cortex having uniform surface pores with a uniform thickness, not only the amount of supported catalyst decreased but also the heat resistance was not sufficient.

[0005]

DISCLOSURE OF THE INVENTION The inventors of the present invention have made extensive studies as a result of strengthening the bonding between aluminum and a stainless steel plate. As a result, aluminum was rolled into a stainless steel plate, and a pre-baking was performed by applying a load. In that case, the success rate of anodic oxidation is remarkably improved, and a carrier made of stainless steel and an alumina layer further post-baked after anodic oxidation has a diffusion layer in which aluminum atoms and iron atoms are diffused at the interface of the alumina-stainless steel plate. That the carrier at which the content of aluminum atoms and iron atoms in the diffusion layer changed gently, the strength of the alumina-stainless steel interface was remarkably increased, and the hydration between the anodic oxidation and the post calcination. It was found that the heat resistance can be further improved by carrying out the treatment, and the present invention has been reached.

Therefore, a first object of the present invention is to provide a plate-shaped alumina carrier having an anodized film on at least one surface and having excellent strength and heat resistance.
A second object of the present invention is to provide a method for producing a plate-shaped alumina carrier having an anodized film on at least one surface and having excellent strength and heat resistance. A third object of the present invention is to support a catalyst on the anodized film,
It is to provide a catalyst body having excellent strength and heat resistance.

[0007]

The above objects of the present invention are a plate-like alumina carrier having an alumina layer on at least one surface of a stainless steel plate, wherein an aluminum component and an iron are provided at the interface between the stainless steel plate and alumina. With a diffusion layer in which the components are present, the plate-shaped alumina carrier excellent in heat resistance, characterized in that the contents of aluminum and iron in the diffusion layer are gently changed, a method for producing the same, and This is achieved by a catalyst body in which a catalyst is supported on a carrier.

The stainless steel plate used in the present invention is not particularly limited and may be appropriately selected from known stainless steels. 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 and shape of the plate are not particularly limited and may be appropriately determined depending on the required strength, the catalyst used and the application.

In the present invention, first, an aluminum plate or foil is laminated on a stainless plate. Such lamination can be performed by spraying molten aluminum onto a stainless steel plate, but from the viewpoint of thickness uniformity and the ease of manufacturing, a stainless steel sheet is produced by using a rolling method (cladding method). It is preferable to adhere an aluminum plate or foil to the surface of the plate.

Such joining is so-called direct joining, in which the stainless layer and the aluminum layer are merely physically bonded, and the atoms of each layer diffuse into each other to form a chemical bond. Not that. The aluminum plate or foil used in the present invention is not limited to aluminum metal in particular, and a known aluminum alloy that can be anodized as described later can be appropriately selected.

In the present invention, the thickness of the aluminum plate or aluminum foil (hereinafter referred to as the aluminum layer) to be laminated on the stainless plate is preferably 10 μm to 300 μm from the viewpoint of favorably performing anodization described later, In particular, the range of 30 μm to 200 μm is preferable, and the range of 40 μm to 150 μm is most preferable. In the alumina carrier of the present invention, from the viewpoint of preventing the peeling of the stainless steel plate and the porous alumina layer and increasing the heat resistance, the layer of only aluminum is eliminated, and an iron atom and an iron atom are formed at the interface between the stainless steel layer and the alumina layer. A diffusion layer in which aluminum atoms diffuse into each other is formed.

In this case, the diffusion concentration of iron atoms and aluminum atoms needs to change gently between the stainless layer and the alumina layer, and if the diffusion concentration changes stepwise, sufficient heat resistance is obtained. I can't get it. Hereinafter, the method for producing a plate-shaped alumina carrier having excellent heat resistance according to the present invention will be described in detail.

In the present invention, in order to form a diffusion layer in which iron atoms and aluminum atoms are gently diffused into each other, pre-baking is performed before anodization to form a diffusion layer at the interface between the stainless layer and the aluminum of the clad plate. . In this pre-baking, it is preferable to apply a load of 0.5 g / cm ² or more to the interface between the stainless layer and the aluminum layer.
In the present invention, the aluminum layer is entirely converted to an alumina layer by anodic oxidation described later, and oxygen atoms are further diffused in this diffusion layer to more reliably strengthen the bond between the stainless plate and the alumina layer.

Pre-baking is preferably carried out at 400 ° C. to 600 ° C., particularly 450 ° C. to 550 ° C. If it is less than 400 ° C, a good diffusion layer cannot be provided. The pre-baking time varies depending on the pre-baking temperature, but may be 1 hour to 10 hours, and particularly preferably 5 to 9 hours. If it is less than 1 hour, it is difficult to provide a diffusion layer that can contribute to prevention of peeling, and firing for 10 hours or more is not only economically disadvantageous but also not preferable from the viewpoint of production efficiency. The pre-baking may be performed in air or in an inert gas.

The anodic oxidation of the aluminum surface can be easily performed using a known anodic oxidation technique. At the time of anodic oxidation in the present invention, it is preferable to use a strongly oxidizing acid such as chromic acid or sulfuric acid as the treatment liquid. As a result, all the aluminum layers are changed to alumina layers and anodic oxidation is advanced to the inside of the diffusion layer.
It becomes easy to diffuse oxygen atoms into the diffusion layer. The acid concentration of the treatment liquid may be appropriately determined. For example, when chromic acid is used, it is preferably 2 to 4% by weight.

The anodizing conditions 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 varies depending 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, after anodization,
1 hour or more at 350 ° C, preferably 450 ° C to 55
By further post-baking at 0 ° C, the anodic oxide film is γ
-Alumina layer, which is preferable as the surface of the catalyst carrier, and the change in the concentration of aluminum atoms and iron atoms in the diffusion layer is made gentler.

In the present invention, B on the surface of the anodic oxide film is
In order to increase the ET surface area, before post-baking, 5 ° C-1
It is preferable to carry out a hydration treatment with distilled water, ion-exchanged water, or steam at 00 ° C, preferably 40 ° C or higher. In particular, when it is intended to be used as a carrier for a catalyst body, it is preferably carried out at a temperature of 50 ° C. or higher in order to shorten the treatment time, and the pH does not have to be 7. The above hydration treatment can be easily carried out by immersing the plate-shaped carrier after anodization in hot water or by steaming. By these hydration treatment and post-baking,
The BET area on the surface of the anodized film is 3,000 times or more the apparent surface area of the metal substrate.

The treatment time of the hydration treatment in this case varies depending on the temperature of the treated water, but may be appropriately adjusted within the range of several minutes to several hours depending on the desired pore size distribution of the anodized surface coating. It is preferable that the time is longer than that. As a result, the peak of the pore size becomes approximately 20Å and the BET surface area becomes maximum. When post-baking is performed after the above hydration treatment, a crack structure appears on the surface of the alumina layer (see FIG. 3). It is presumed that this crack structure alleviates the stress strain of the alumina coating, and this further improves the heat resistance of the plate-shaped carrier of the present invention.

As described above, a highly active plate-shaped catalyst body can be obtained by supporting an ultrafine particle catalyst on the surface of the prepared substrate by a known impregnation method or electrodeposition method. Particularly, in the hydration 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 hydration treatment. In addition to simplifying the process for producing a 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 bake it at 450 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.

The plate-shaped catalyst body obtained as described above is
After being processed into a tubular shape, a honeycomb shape, or the like, the reaction tower can be appropriately filled, or a reaction chamber can be formed by using these catalyst bodies. Further, it can be naturally used for other conventional applications such as decoration. The reason why the plate-shaped carrier of the present invention has heat resistance is presumed to be that 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]

EFFECT OF THE INVENTION The plate-shaped alumina carrier of the present invention has high strength because it has a stainless steel layer as a base material, and has excellent heat resistance because the stainless steel layer and the alumina layer are chemically bonded. According to the production method of the present invention, a plate-like carrier for a catalyst body having excellent heat resistance, which has a porous alumina film having a uniform thickness and uniform pores on the surface, does not require a large-sized device, and can be easily prepared. Can be manufactured. Further, since the catalyst body of the present invention can sufficiently withstand use at high temperatures, its range of use can be expanded more than ever, and the life is extended, which is economical.

[0025]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.
In addition, "%" in the following represents "wt%" unless otherwise specified.

Example 1. Preparation of aluminum / stainless steel clad substrate Al was added to SUS430 (18% Cr, 4% A
l) Stainless steel having a thickness of 290 μm was used as a base material, and aluminum having a thickness of 40 to 50 μm was laminated on both surfaces thereof, and a rolling mill was used to obtain an aluminum-stainless clad base material. Precladding under load The clad substrate obtained is cut into 3.5 cm × 12.5 cm, and the temperature is increased from room temperature to 6 by using a gold furnace.
At 500 ° C / min to 500 ° C, and at 500 ° C for 3 hours,
Firing was performed in air under a load of 0.83 g / cm ² or without a load.

[0027] was masked to prevent current leakage from the cut surface of the clad base material when performing the anodic oxidation anodization. Further, in order to improve the adhesion of the masking, the substrate whose cross section is covered with vinyl tape is treated with a 20% sodium hydroxide solution for 3 minutes.
Surface treatment was performed by immersing in a 30% nitric acid aqueous solution for 1 minute. Then, after anodizing for 2 minutes to roughen the surface, the surface was washed with ion-exchanged water and dried, and a portion other than the anodizing was again coated with a masking agent and dried at room temperature for about half a day.

The substrate pretreated as described above was treated with a 2.5% chromic acid aqueous solution at a liquid temperature of 30 ° C. and a current density of 15.
Anodization was performed at 0 A / m ² for 12 hours. The success rate of anodization in the case of pre-firing without applying a load was about 33%, and the success rate of applying a load was about 91%.
In addition, in the case where the pre-baking was not performed, in all the samples after the anodization, partial peeling was observed at the interface between the stainless layer and the alumina layer.

Hydration Treatment The anodized substrate was immersed in ion-exchanged water at 80 ° C. for 1 hour. The total liquid volume was set so that the liquid surface ratio (liquid volume per apparent surface) was constant at 7.2. Post-baking The obtained substrate after hot-water treatment was washed with water, dried, and then heated from room temperature at 6 ° C / min to 500 ° C and baked at 500 ° C for 3 hours to obtain a plate-shaped carrier of the present invention.

Heat resistance evaluation test The obtained plate-shaped carrier was placed on a pumice sample stand provided in a quartz tube as shown in FIG. 1, both ends were sealed with glass wool, and inserted into an electric furnace. Then, a heat resistance evaluation test was performed with the following four patterns, and no peeling was observed in any case.

(1) The temperature is raised from room temperature to 6 ° C./min to 50
The temperature was set to 0 ° C., the temperature was kept at the same temperature for 3 hours, and then the temperature was lowered at −6 ° C./min to 25 ° C., and 5 cycles were repeated. (2) The temperature is raised from room temperature at 6 ° C / min to 600 ° C, kept at the same temperature for 3 hours, and then lowered at -6 ° C / min to 25 ° C.
5 cycles were repeated. (3) The temperature is raised from room temperature at 9 ° C / min to 650 ° C, the temperature is kept for 1 hour, and then the temperature is lowered at -9 ° C / min to 25 ° C.
5 cycles were repeated. (4) The temperature was raised from room temperature at 9 ° C / min to 700 ° C, kept at the same temperature for 1 hour, and then lowered at -9 ° C / min to 25 ° C.
5 cycles were repeated.

The results of analyzing the cross section of the carrier sample using an X-ray microanalyzer (EPMA) are shown in FIG.
As shown in. From FIG. 2, it was confirmed that a diffusion layer composed of aluminum atoms, iron atoms and oxygen atoms was formed, and that the concentrations of aluminum atoms and iron atoms were changed gently. Further, when the surface of the sample was observed by a scanning electron microscope (SEM), numerous cracks were observed on the surface of the alumina layer (FIG. 3).

Example 2. A catalyst substrate was prepared in exactly the same manner as in Example 1 except that no hydration treatment was carried out, and four heat resistance tests were conducted in exactly the same manner, but the test (4) could not be withstood. However, in the tests (1) and (2), 60% shows durability, and in the test (3), it is about 30%.
% Showed durability. It was confirmed that the alumina surface in this case did not have the cracks observed in Example 1. From this, it is considered that the cracks that occur when hydration treatment contributes to the stress relaxation of the alumina surface.

Comparative Example 1. An attempt was made to make a plate-shaped carrier in exactly the same manner as in Example 1 except that the pre-baking was not carried out and the post-baking temperature was 500 ° C., but the clad plate after anodization was partially exfoliated in all cases. Is recognized, 50
The post-baking at 0 ° C. resulted in severe peeling and could not be used as a catalyst carrier. Therefore, the post-baking temperature is set to 350.
The carrier sample was prepared at 0 ° C., and the result of the cross-sectional EPMA analysis of the obtained sample is as shown in FIG.
When this sample was further subjected to the heat resistance test of (1) above, it completely peeled off at the first time. from this result,
It was proved that sufficient heat resistance could not be obtained when the concentration distribution of aluminum atoms and iron atoms in the diffusion layer was not gentle and was stepwise.

[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 plate-shaped alumina carrier for a catalyst body of the present invention.

FIG. 3 is made by a process including a hydration treatment process,
It is a SEM photograph of the surface of the alumina layer of the plate-shaped alumina carrier for catalyst bodies of the present invention.

FIG. 4 is an EPMA analysis diagram of a cross section of a plate-shaped alumina carrier for a catalyst body of Comparative Example 1.

[Explanation of symbols]

 1 Quartz tube 2 Pumice sample holder 3 Sample (catalyst substrate) 4 Blocking glass wool 5 Thermocouple for internal temperature measurement

Claims (6)

[Claims] 1. A plate-shaped alumina carrier having an alumina layer on at least one surface of a stainless steel plate, the aluminum carrier having a diffusion layer containing an aluminum component and an iron component at the interface between the stainless steel plate and the alumina layer, and the diffusion. A plate-like alumina carrier having excellent heat resistance, characterized in that the contents of aluminum and iron in the layer are gently changed. 2. The plate-shaped alumina carrier excellent in heat resistance according to claim 1, wherein numerous cracks are present on the surface of the alumina. 3. A clad material obtained by rolling aluminum on at least one surface of a stainless steel plate and laminating the aluminum at 400 ° C. to 6 ° C.
After pre-baking at 00 ° C. for 1 to 10 hours, the surface of the aluminum is anodized, then washed and dried, and then 450 ° C.
The post-baking is further performed at 550 ° C. 3.
A method for producing a plate-shaped alumina carrier having excellent heat resistance as described in 1. 4. The pre-baking 0.5 g /
The method for producing a plate-shaped alumina carrier excellent in heat resistance according to claim 3, wherein a load of cm ² or more is applied. 5. The heat resistance according to claim 3, wherein hydration treatment is performed in water vapor or distilled water and / or ion exchange water at 40 ° C. or higher after anodization and before post-firing. An excellent method for producing a plate-shaped alumina carrier. 6. A catalyst body in which a catalyst is supported on the surface of alumina of the plate-shaped alumina carrier having excellent heat resistance according to claim 1 or 2.