JPH05154381A - Exhaust gas purifying catalyst forming process - Google Patents

Abstract

PURPOSE:To manufacture a catalyst converter of stabilized purifying performance and without generating rust by forming a mixed layer of precious metal catalyst of specified range of thickness on the surface of a metal belt base by the vacuum film forming process. CONSTITUTION:A mixed layer of precious metal catalyst of platinum, rhodium, palladium and the like having a thickness of 0.2mum or over to 2mum or less is formed on the surface of a metal belt base of stainless steel or the like of Fe-Cr-Al alloy, SUS304 or the like by the vacuum film forming process. Also a simple layer or a mixed layer of a cocatalyst layer of the thickness of 0.1mum or over to 2mum or less in which oxide or composite oxide of cerium, lanthanium or the like is a composite formed with the precious metal catalyst or used as a cocatalyst is formed on the surface of the metal belt base by the vacuum film forming process over which a mixed layer of precious metal catalyst is formed. The catalyst thus manufactured is free from residual chlorine and no red rust is generated thereon, and the catalyst is used as a catalyst converter of purifying performance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an exhaust gas purifying catalyst for automobiles, etc. on a metal strip substrate, and can also be applied to purifying combustion gas for industrial equipment. ..

[0002]

2. Description of the Related Art There are ceramic bases and metal bases for automobile exhaust gas purifying catalytic converters. Currently, the catalyst forming method for both bases is JP-A-52 / 52.
No. 126692, it is a method of immersing in an aqueous solution containing a chloride of a catalytic metal and drying.

As a catalyst, carbon dioxide (CO ₂ ) and water (H ₂ O) are obtained by oxidizing hydrocarbons (C ₇ H ₁₄ etc.) and carbon monoxide (CO) in automobile exhaust gas, and nitrogen oxides. (NO
Noble metal catalysts that accelerate the reaction of reducing _x ) to nitrogen (N ₂ ) are used. These are generally called three-way catalysts because they contribute to the oxidation and reduction reactions of three types of substances, hydrocarbons, carbon monoxide, and nitrogen oxides. The noble metal catalyst is a catalyst composed of one or more of platinum (Pt), rhodium (Rh), and palladium (Pd). The mainstream is a mixture ratio Pt / Rh = 7/1 to 5/1, and Pd / Rh or Pt / Pd / Rh is partially used. In addition, an oxide of cerium (Ce) or lanthanum (La) or a composite oxide of cerium and lanthanum is used as a co-catalyst for further promoting the redox reaction when used in combination with a noble metal catalyst. An oxide of aluminum (Al) may be used alone or as a mixture with the above oxide.

As shown in FIG. 4, the manufacturing process of the conventional metal band-based catalytic converter is mainly made of F.
It is an e-Cr-Al alloy, and is subjected to corrugation processing, and after being cylindrically formed, a catalyst is formed. The catalyst formation method is as follows. First, a metallic substrate is subjected to an oxidative heat treatment in the atmosphere to generate acicular alumina (Al ₂ O ₃ whiskers) on the frame surface,
Next, a solution containing chloride of a noble metal catalyst such as platinum (sol A
・ The product is soaked in B), taken out and dried. The acicular alumina is generated to improve the adhesion of the noble metal catalyst when immersed in the solution.

[0005]

A catalytic converter in which a catalyst is formed on a metal substrate is provided with exhaust gas pressure loss and platinum,
It is effective from the viewpoint of recycling precious metal catalysts such as rhodium and palladium, compared to the currently mainstream catalytic converter made of cordierite, but it has the following problems.

Firstly, the cost is high because the catalyst forming process including the surface oxidation heat treatment is complicated, and it is not yet widely used. The price after the catalyst is formed is said to reach 2 to 3 times that of the single metal frame before the formation. Secondly, the attachment of the catalyst to the flame is due to the catalyst chloride (H ₂ PtC
l ₆ ) Rusting is likely to occur on the surface of the material of the metal frame, since it is carried out by repeating the immersion in the aqueous solution and the firing at a temperature of 400 to 900 ° C. A large number of rusts can be seen in the substrate after catalyst formation. Thirdly, in the aqueous solution immersion method, it is difficult to control the film thickness, so that the exhaust gas purification characteristics of the product vary.

The present invention is intended to solve the above-mentioned problems, and by applying a vacuum film-forming method to a substrate, rust is not generated, a uniform desired thickness is obtained, and stable purification is performed. It is intended to provide a catalytic converter having high performance.

[0008]

The inventors of the present invention can omit steps such as whisker formation on the surface of a substrate by depositing a catalyst substance on the surface of a metal strip substrate with high energy by a vacuum film forming method, and at the same time, a film can be formed. We have found that the thickness or the deposition density on the surface can be controlled freely. Further, in vacuum film formation, there is no concern about rusting as in the solution dipping method.

The present invention has been made based on the above findings, and its gist is (1) mixing a noble metal catalyst of 0.2 μm or more and 2 μm or less on the surface of a metal strip substrate by a vacuum film forming method. A method for forming an exhaust gas purifying catalyst, characterized in that a layer is provided.
A single layer or a mixed layer of a promoter layer having a thickness of 0.1 μm or more and 2 μm or less is provided by a vacuum film forming method, and a mixed layer of a noble metal catalyst having a thickness of 0.2 μm or more and 2 μm or less is further provided by a vacuum film forming method. A method for forming an exhaust gas purifying catalyst, characterized in that

Heat-resistant steel is preferably used as the metal strip, and the thickness of the metal strip substrate is 25 μm or more and 100 μm.
The following is preferable. Further, the catalyst can be formed by continuously passing the metal strip substrate through a chamber in which a plurality of vacuum film forming apparatuses are incorporated. Such a method is also one of the features of the present invention. Is one.

The manufacturing process of the catalyst-molded metal frame according to the present invention is shown in FIG. The vacuum film formation method is a physical vapor deposition method in which a substance evaporated from an evaporation source in a vacuum is condensed and adhered to a substrate, or a gas atom is used instead of an evaporated atom to cause a chemical reaction to condense the product into a gas. It is a chemical vapor deposition method of attaching. Typical vacuum film forming methods include ion plating, sputtering, and plasma CVD. All of these vacuum film forming methods use plasma,
It can be attached to a substrate with high energy. Also,
Since the catalytic converter is used in the combustion gas exhaust system,
As the metal substrate, Fe-Cr-Al alloy or SUS30
4, a metal band having relatively high heat resistance, which can withstand a high temperature of about 800 ° C., such as stainless steel such as 4, SUS430, SUS309S, and SUS310S is desirable. If the thickness is less than 25 μm, sufficient strength after canning (cylindrical) processing cannot be secured, and if it exceeds 100 μm, the evening area of the honeycomb increases and exhaust resistance increases, and the processing strength increases and corrugation becomes difficult to perform. Therefore, the thickness of the alloy used as the substrate is 25 μm or more 1
It is preferably 00 μm or less. If the thickness of the noble metal catalyst formed by the vacuum film formation method is less than 0.2 μm, the redox reaction of the exhaust gas is not sufficiently performed, and if it exceeds 2 μm, it takes too much time to form a thin film, which is uneconomical (output, If the gas pressure is the same, the film thickness is controlled by the time the substrate is exposed to plasma in the film formation tank). Therefore, the noble metal catalyst layer has a thickness of 0.
It was set to 2 μm or more and 2 μm or less. On the other hand, CeO in the promoter layer
₂ , LaO ₂ , Ce and La complex oxides have a role of oxygen storage material that absorbs the fluctuation of the air-fuel ratio and a role of promoting the reaction of the noble metal catalyst (for example, Automotive Technology, Vol. 43, N.
o. 4, 1989). Al ₂ O ₃ is said to improve NO _x conversion efficiency when used in combination with a noble metal catalyst, and thus may be used in combination with CeO ₂ , LaO ₂ or a Ce-La composite oxide. These co-catalysts have a film thickness of 0.1 μm or more and improve the exhaust gas purification performance.
If it exceeds μm, the effect becomes negative. Therefore, the thickness of the co-catalyst layer is set to 0.1 μm or more and 2 μm or less.
The continuous formation method of the catalyst or co-catalyst on the metal strip substrate in the present invention is carried out by continuously passing these steel strips through a pumped chamber of a vacuum film forming apparatus such as ion plating or sputtering. Is desirable. A schematic diagram of an example of the device is shown in FIG. Ion plating 1, sputtering devices 2, 3 and plasma-C
Since the VD device 4 and the steel strip feeding / winding devices 5 and 6 are connected while being shielded from the outside air, a co-catalyst tank, a noble metal catalyst layer, etc. are continuously laminated on a coiled alloy substrate in vacuum. Can be wound into a coil.

[0012]

As shown in FIG. 3, the process of forming a thin film substance on a substrate is roughly divided into three processes: (a) three-dimensional nucleation, (b) coalescence of nuclei, and (c) continuous film formation. Be done. The nuclei generated in (a) gather to form clusters,
The clusters coalesce into island-shaped particles, and secondary nuclei are formed between the islands, and the islands coalesce into a continuous film. Generally, the core, clusters, island-shaped particles, and continuous films are called thin films (see Thin Film Materials Engineering, Kitada, Iritono, Osaka, Kaibundou). Next, regarding the action of the catalyst, since the action of the catalyst is a reaction between the surface atoms of the catalyst and the reaction molecules, it is necessary for the formed substance to have a large specific surface area in order to function as a catalyst. In the thin film forming step (b) described above, the hemispherical catalyst is attached to the substrate, the size of the cluster is several tens to several hundreds of angstroms, and in the case of platinum, the specific surface area is 50 to 100 m. ² / g
Therefore, it is suitable as a method for forming a catalyst. Such a cluster-shaped thin film can be formed easily by passing the steel sheet through the film forming chamber at a high speed as compared with the continuous film formation.

The catalyst film-forming alloy foil thus formed is usually processed into a corrugated shape in the same manner as in the conventional case, and is made into a product.

[0014]

EXAMPLE Exhaust gas purification performance was examined under the following conditions for test materials prepared with the substrates, film types and film thicknesses shown in Tables 1 to 6. A test piece of a test material on which a catalyst having a size of 2 cm × 2 cm was vacuum-deposited was put into a silica tube and heated to 450 ° C., and carbon monoxide and oxygen or propane and oxygen or dinitrogen pentoxide were added at a flow rate of 50 ml / min. Carbon monoxide was allowed to flow by 0.05 ml, and the oxidation ratios of carbon monoxide and propane and the reduction ratio of dinitrogen pentoxide were measured by gas chromatography. The results are also shown in Tables 1 to 6. Table 7 shows the purification performance of the comparative example by the conventional solution immersion method. The converter produced by the present invention has a purification performance equivalent to or higher than that produced by the conventional method.

Further, the catalyst forming method of the present invention has the following advantages. a. Since the catalyst is formed in vacuum, there is no concern that chlorine will remain as in the case of the conventional wet forming method, and therefore red rust will not occur. b. In the catalyst formation by the vacuum film formation method, the surface oxidation heat treatment is not necessary, so the process can be simplified and the cost can be reduced. c. The oxide co-catalyst can also be formed by the vacuum film forming method, and a catalytic converter with high purification performance can be obtained. d. Since it is not necessary to use high Al-containing steel that is difficult to melt and process as the metal strip substrate, the cost such as the processing cost can be reduced. e. By adjusting the output and the plate passing speed, the deposition amount and morphology of the catalyst film can be controlled, and thus the minimum required precious metal catalyst can be effectively used. f. By passing the film-forming chamber through the coiled steel plate, the catalyst, the co-catalyst, etc. can be continuously formed at once, so that the process is simple and the cost can be reduced as compared with the conventional solution dipping / drying method.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

[Table 3]

[0019]

[Table 4]

[0020]

[Table 5]

[0021]

[Table 6]

[0022]

[Table 7]

[0023]

EFFECTS OF THE INVENTION According to the present invention, the purification performance is equal to or more than that of the conventional method in a simpler step than the conventional solution dipping method, and the uniform purification performance of the catalyst membrane is stable without rusting. A catalytic converter can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process of an exhaust gas purifying converter according to the present invention.

FIG. 2 is a schematic view of an example of a continuous vacuum film forming apparatus of the present invention.

FIG. 3 is a diagram showing a process of vacuum film formation, in which (a) shows three-dimensional nucleation and (c) shows continuous film formation.

FIG. 4 is a diagram showing a catalyst forming step by a conventional solution dipping method.

[Explanation of symbols]

 1 Ion plating device 2, 3 Sputtering device 4 Plasma CVD device 5 Steel strip feeding or winding device 6 Steel strip winding or feeding device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yusuke Oikawa 3434 Shimada, Hitsu-shi, Yamaguchi Prefecture, Nippon Steel Works, Ltd., Hikari Works, Ltd. Hikari Steel Works, Ltd.

Claims (5)

[Claims] 1. An exhaust gas purifying and forming method, wherein a mixed layer of a noble metal catalyst having a thickness of 0.2 μm or more and 2 μm or less is provided on the surface of a metal strip substrate by a vacuum film forming method. 2. A single layer or a mixed layer of a promoter layer having a thickness of 0.1 μm or more and 2 μm or less is provided on the surface of a metal strip substrate by a vacuum film forming method, and further, a thickness of 0.2 μm is formed by a vacuum film forming method.
A method for forming an exhaust gas purifying catalyst, comprising providing a mixed layer of a noble metal catalyst having a size of m or more and 2 μm or less. 3. The method for forming an exhaust gas purifying catalyst according to claim 1, wherein heat resistant steel is used as the metal strip substrate. 4. A metal strip substrate having a thickness of 25 μm or more, 10
The exhaust gas purifying catalyst forming method according to claim 1, wherein the exhaust gas purifying catalyst has a diameter of 0 μm or less. 5. The exhaust gas purifying catalyst according to claim 1, wherein the metal strip substrate is continuously passed through a chamber in which a plurality of vacuum film forming apparatuses are incorporated. Forming method.