JPH0212622B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for supporting a catalyst for purifying exhaust gas from an automobile, which can firmly adhere and hold the catalyst for purifying automobile exhaust gas on a heat-resistant metal-supported matrix together with oxide-based support. Exhaust gas purification catalysts for oxidizing, reducing, and decomposing harmful gases such as CO, hydrocarbons (hereinafter referred to as HC), and NOx contained in automobile exhaust gas are made of platinum (Pt), palladium (Pd), rhodium ( Rh) and other precious metals such as Pt, Pt+Pd, Pt
Precious metal catalysts such as +Pd+Rh are mainstream, and these catalysts are deposited on a carrier supported on a support matrix such as honeycomb-shaped, pellet-shaped, or spherical ceramics, or honeycomb-shaped metal. It is used. In other words, for honeycomb type ceramics, the surface of the skeleton of cordierite ceramics is coated with γ-Al ₂ O ₃ is mainly used, while for pellet type and spherical types, porous Al ₂ O ₃ is used. ing. In order to support the catalyst on the support supported by these support bodies, Pt,
A method is known in which the material is impregnated with a solution of a soluble salt of a noble metal such as Pd or Sh, such as a chloride, and then heat treated. Furthermore, in the case of a metallic carrier, a method is known in which a noble metal catalyst substance is deposited and supported on the metal surface using an adhesive such as silicone resin or water glass. Since the reactor for exhaust gas purification is exposed to high temperatures, the heat resistance, thermal shock resistance, and robustness of the catalyst, carrier, and support matrix, as well as an increase in the supporting area of the catalyst, i.e., high activation and durability, are required. The level of demand for sexuality is increasing. For this purpose, a catalyst,
It is desired to improve not only the carrier and the supporting matrix, but also the supporting method.
Compared to ceramic support bases, metallic support bases can significantly increase the supporting area of the support by making the base material thinner, allowing for smaller reactors, ease of matrix processing, and superior thermal shock resistance. It is desirable because it has many advantages such as: However, in the case of a metallic supporting matrix, there is a problem in supporting the carrier and catalyst firmly and imparting heat resistance in order to support the carrier and catalyst by the method described above. As a result of extensive research into catalyst supporting materials, supports, and supporting methods, with a focus on improving heat resistance, thermal shock resistance, and high activation, the present inventors determined that a heat-resistant metal was used as a supporting material, and this and an oxide carrier were used as a supporting material. The present invention was made based on the discovery that Cr ₂ O ₃ and a noble metal catalyst substance can be firmly adhered to each other by chemical bonding of Cr 2 O 3 . That is, the first aspect of the present invention is to heat-resistant a slurry of at least one kind of soluble salts of platinum, palladium, and rhodium and a concentrated aqueous solution of a chromium compound containing alumina or/and chromium oxide and hexavalent chromium. This is a method for supporting a catalyst for exhaust gas purification, in which the steps of depositing on a metal-supported matrix, drying and heat treatment, impregnating a concentrated aqueous chromic acid solution, drying, and heat treatment are repeated at least once. In the invention, a slurry of alumina or/and chromium oxide and a concentrated aqueous solution of a chromium compound containing hexavalent chromium is deposited on a heat-resistant metal support, dried and heat-treated to form a thin film, and then platinum and
After impregnating a thin film with an aqueous solution of at least one kind of soluble salts of palladium and rhodium and chromic acid, drying and heat-treating the thin film, further impregnating a concentrated aqueous solution of chromic acid, drying, and heat-treating at least once. This is a method of supporting a catalyst for exhaust gas purification that is carried out repeatedly. The heat-resistant metal-supporting matrix in the present invention includes:
For example, SUS302B, SUS304, SUS410L,
Heat-resistant steel such as SUH409, stainless steel, etc. are used. Therefore, in order to fit the reactor with thin plates of these metal materials, for example, a flat plate and a corrugated plate are rolled up and processed into a honeycomb shape. Degreasing and then chemical corrosion treatment, e.g.
It is preferable to carry out surface roughening treatment in advance by etching the matrix using a mixed solution of HNO ₃ , HCl, and FeCl ₃ +FeCl ₂ . The carrier to be deposited on the surface of the carrier matrix is as follows:
For example, porous oxides such as alumina and chromium oxide, with a particle size of 15 μm or less, and an average particle size of 5 μm.
Hereinafter, it is preferable that the fine powder has a specific surface area of 75 m ² /g or more and the range of particle size distribution is as narrow as possible, and these porous oxides are used alone or in appropriate combinations (for example, γ-Al ₂ O ₃ 30 ~100 parts by weight, _{Cr2O30 ~}
It is preferable to mix it in a range of 70 parts by weight. ) is used. The catalyst is a noble metal such as platinum, palladium, or rhodium, and their soluble salts such as chloroplatinic acid (H ₂ PtCl ₆ 6H ₂ O), palladium chloride (PdCl ₂ 2H ₂ O), rhodium chloride (RhCl ₃・_3H2O )
It is preferable to use it as such. However,
At least one of these is used, and each may be used alone or in an appropriate combination. Catalysts are usually Pt, Pt+Pd, Pt
Since it is used in the form of +Pd+Rh, etc., it is preferable to use it in the form of a solution dissolved in chromic acid.
When each of these is used alone, the soluble salt is preferably in the range of 0.6 to 2.2 parts by weight per 100 parts by weight of the carrier material, and when two types are combined, for example, in the case of Pt + Pd, the Pt salt In the case of 0.6 to 1.2 parts by weight, 2 to 0.4 parts by weight of Pd salt, and Pt+Rh,
1.0 to 1.5 parts by weight of Pt salt, 0.2 to 0.4 parts by weight of Rh salt, or 1.0 to 2.0 parts by weight of Pd salt, Rh salt in the case of Pd+Rh
A blending ratio of 0.3 to 0.6 parts by weight is preferred. Furthermore, in the case of three types such as Pt + Pd + Rh, Pt salt
Preferably, the proportions are 1.0 to 1.5 parts by weight, Pd 0.5 to 1 part by weight, and Rh 0.2 to 0.4 parts by weight. Also, when dissolved in chromic acid, the concentration of chromic acid is
It is preferably in the range of 1.6 to 1.75. Concentrated aqueous solutions of chromium compounds containing hexavalent chromium used to firmly adhere the support and catalyst to the heat-resistant metal-supported matrix include CaCrO ₄ , CoCrO ₄ ,
The solution is preferably one in which at least one of ZnCrO ₄ , CaCO ₃ , CoCO ₃ , ZnO, Cr ₂ O ₃ , etc. is dissolved in a concentrated aqueous solution of H ₂ CrO ₄ , and the content ratio of the compound is determined in the total amount. amount per mole of H ₂ CrO ₄
A suitable proportion is 0.1 to 0.4 mole.
Concentrated aqueous solutions of H ₂ CrO ₄ alone can also be used, and the concentrations of these solutions all have a specific gravity of 1.5 to 1.5.
It is preferable to adjust it to 1.7. Such a carrier and catalyst are applied to a carrier matrix together with a concentrated aqueous solution of a chromium compound containing hexavalent chromium or chromic acid by a coating method or a dipping method, and then:
The supporting method will be explained. In the first method of the invention, in which the support and the catalyst are deposited as a slurry with a concentrated aqueous solution of a chromium compound containing hexavalent chromium and impregnated with a chromic acid solution, the catalyst (for example, H ₂ PtCl ₆・6H ₂ O2 parts by weight,
0.7 parts by weight of PdCl _2.2H 2 _O and 0.3 parts by weight of RhCl _{3.3H 2} O), γ-Al ₂ O ₃ fine powder (for example, particle size 10 μm)
Below, average particle size 3μm, specific surface area 158m ² /g, 170
(parts by weight), a concentrated aqueous solution of a chromium compound containing hexavalent chromium (for example, a concentrated aqueous solution of H ₂ CrO ₄ ).
A slurry is prepared by adding 40 parts by weight of CaCO ₃ dissolved at a ratio of 0.2 mol to 1 mol of H ₂ CrO ₄ to have a specific gravity of 1.6) and water (35 parts by weight).
Heat-resistant metal support (e.g. chrome steel SUH409
The thin plate) is processed into, for example, a honeycomb pole (for example, by the method disclosed in JP-A-54-25321 and JP-A-56-4373) and subjected to surface roughening treatment. After such preparation, a heat-resistant metal carrier base is immersed in the slurry to be coated, dried, and then heat-treated. The drying time after the slurry is applied varies depending on the size of the material, but it is usually at room temperature to 70℃.
It is preferable to carry out the heat treatment for a period of 30 to 60 minutes, and the heat treatment is performed by raising the temperature at a heating rate of 5 to 6 °C/min.
It is preferable to carry out the reaction at 550 to 600°C for 1 to 3 hours. The thickness of the film deposited in this way is
It can be controlled by the concentration of the slurry, dipping conditions, etc. In the numerical example in the above-mentioned box, a film in which the catalyst is uniformly dispersed and supported on the carrier can be obtained with a film thickness of about 60 to 200 μm. Next, the coating is impregnated with an aqueous chromic acid solution, dried, and heated. The chromic acid aqueous solution used here is preferably a concentrated aqueous solution with a specific gravity in the range of 1.6 to 1.75, and is impregnated into the film obtained by the above treatment by a coating method or a dipping method. After that, dry at room temperature to 70℃ for 30 to 60 minutes.
550-600℃ at a heating rate of ~6℃/min 40-60℃
Preferably, the heat treatment is performed for a minute. Therefore, these treatments are repeated at least once, preferably 2 to 5 times. In this way, the catalyst, carrier, and support matrix can be strongly bonded to each other. Next, the support is slurried with a concentrated aqueous solution of a chromium compound containing hexavalent chromium and deposited on a heat-resistant metal matrix, and the catalyst is impregnated with an aqueous solution of chromic acid, followed by a second process in which a chromic acid aqueous solution treatment is performed. In the method of the invention, for example, the same γ-
A mixture of Al ₂ O ₃ powder and Cr ₂ O ₃ powder (for example, particle size of 10 μm or less, average particle size of 2 μm, specific surface area of 146 m ² /g) (for example, 50 parts by weight of γ-Al ₂ O ₃ , Cr ₂ O ₃ 50 parts by weight) and a concentrated aqueous solution of a chromium compound containing hexavalent chromium (e.g. 0.1 to 1 mole of H ₂ CrO ₄
mol of CoCO ₃ , and 0.1 mol of CaCO ₃ and H ₂ CrO ₄
A solution whose specific gravity was adjusted to 1.6 by dissolving it in a concentrated aqueous solution of
A slurry was prepared with 35 parts by weight) and water (35 parts by weight), and a carrier made of 304 stainless steel processed into a honeycomb shape and roughened as described above was immersed in the slurry to cover the carrier. wear. The specific surface area of the carrier film obtained in this way was measured by peeling the carrier from the supporting matrix using an acid dissolution method125
~155m ² /g (152m ² /g in the example of the above figure)
g) is obtained. Then, an appropriately selected catalyst (e.g.
H ₂ PtCl ₆・6H ₂ O1 parts by weight, and PdCl ₂・2H ₂ O0.4
parts by weight) in a chromic acid aqueous solution (for example, specific gravity 1.7,
140 parts by weight), and the supporting matrix having the carrier coated thereon is immersed in this solution to impregnate it, and after drying, heat treatment is performed to support the catalyst. Drying in this step is preferably carried out at 50 to 60°C for 30 to 60 minutes, and heat treatment is preferably carried out at 550 to 600°C for 1 to 2 hours at a rate of 4 to 6°C/min. . Note that the chromic acid used here is preferably a concentrated aqueous solution with a specific gravity of 1.6 to 1.75. Next, the coating is impregnated with an aqueous chromic acid solution, dried, and heated. The chromic acid used here is preferably a concentrated aqueous solution with a specific gravity in the range of 1.6 to 1.75, and is impregnated into the film obtained by the above treatment by a coating method or a dipping method. After that, dry at room temperature to 70℃ for 30 to 60 minutes, and dry for 5 to 7 minutes.
Increase the temperature at a rate of ℃/min to 40~ at 550~600℃
It is preferable to perform the treatment under conditions such as heating for 60 minutes. However, these processes require at least one
This is carried out repeatedly, preferably 2 to 5 times. In this way, the catalyst, carrier, and support matrix can be strongly bonded to each other. In the present invention, a heat-resistant metal is used as a support base, and an oxide-based support and a noble metal-based catalyst substance are adhered to the support through chemical bonding of Cr ₂ O ₃ . It was possible to arrive. Therefore, when the support matrix is made of a heat-resistant metal, for example, in a honeycomb shape, the wall thickness of the cells of the honeycomb core can be made as thin as about 40 to 50 μm, and a support matrix with a large specific surface area can be obtained and exhaust gas can pass through. The cross-sectional area of the free space can be increased to reduce pressure loss.
Furthermore, the specific surface area, that is, the catalyst supporting area of the carrier adhered to this carrier matrix can be significantly increased, and these factors can collectively lead to smaller size, higher activity, and longer life of the catalytic reactor. In addition,
γ-Al ₂ O ₃ and Cr ₂ O ₃ , as well as CaO and CoO, which can be contained in small amounts in these, are known to have many excellent effects, including the ability to act as a co-catalyst for oxidation and reduction. It is a thing,
Since this method is relatively simple to operate and requires a low heat treatment temperature, it is suitable as an industrial catalyst supporting method. Next, examples of the method of the present invention will be described. Example 1 (1) Preparation of carrier/catalyst slurry 50 parts by weight of CrO ₃ was dissolved in 30 parts by weight of water.
Dissolve 12 parts by weight of CaCO ₃ in a concentrated aqueous solution of H ₂ CrO ₄ and add water to make an aqueous solution with a specific gravity of 1.65.
Particle size 10μm in 36 parts by weight of aqueous solution containing valent chromium.
Below, γ with an average particle size of 1 μm and a specific surface area of 178 m ² /g
−150 parts by weight of fine powder of Al ₂ O ₃ as catalyst
1.5 parts by weight of H ₂ PtCl _{6.6H 2} O was added to dissolve the catalyst, and the mixture was thoroughly mixed using an alumina ball mill to prepare a slurry. (2) Preparation of supporting matrix A stainless steel SUS 304 thin plate with a thickness of 0.05 mm was processed into a honeycomb shape, and the surface was roughened to prepare a material with a surface area of about 3700 cm ² and external dimensions of 39φ×100 mm. (3) Supporting carrier/catalyst The supporting matrix prepared in (2) was immersed in the slurry prepared in (1), the slurry was coated on the surface of the supporting matrix, and after drying at 52°C for 60 minutes, electric Raise the temperature at 6℃/min using a furnace to 600℃.
Heat treatment was performed at ℃ for about 100 minutes. Then, it was immersed in an aqueous solution of simple chromic acid prepared to have a specific gravity of 1.6 to contain chromic acid, and then heated to 60℃ for 30 minutes.
After drying for 1 minute, heat treatment was performed at 600℃ for 40 minutes in the electric furnace, and this impregnation-drying-heat treatment process was repeated three times to strengthen the adhesion of the carrier and catalyst to the carrier matrix. I did it. (4) Test results The thickness of the film deposited on the support base in this way was approximately
91 μm, specific surface area 174 m ² /g, and the amount of catalyst was about 0.62% by weight based on the amount of carrier. Next, the catalyst was placed in a 40φ×100mm cylindrical reaction vessel made of SUS 304, and a catalyst activity test was conducted at SV 5000h ^-1 . The gas composition used in the experiment was 10% CO, HC, assuming idling.
(C ₃ H ₈ ) 0.15%, NO 0.03%, O ₂ 7%, N ₂ balance
The conversion rate was determined as 82.82% (volume ratio). As shown in Table 1, the experimental results showed that a good conversion rate was maintained for a long time.

[Table] The adhesion strength between the carrier and the catalyst coating was measured by a peel test using an epoxy resin adhesive attached to the surface of the carrier and the catalyst coating. The weight was over 435Kg/ ^cm2 . Example 2 (1) Preparation of supporting matrix It was prepared in the same manner as in Example 1. (2) Preparation of carrier slurry Particle size 10 μm, average particle size 1 μm, specific surface area 178
70 parts by weight of γ-Al ₂ O ₃ fine powder of m ² /g and particle size
10μm, average particle size 3μm, specific surface area 146m ² /g.
Add 24 parts by weight of CrO 3 to 70 parts by weight of Cr _{2 O 3} fine powder and 16 parts by weight of water.
A concentrated aqueous solution of H ₂ CrO ₄ having a specific gravity of 1.65 dissolved in parts by weight and 30 parts by weight of water were added and thoroughly mixed using an alumina ball mill to prepare a carrier slurry. (3) Preparation of catalyst H ₂ PtO ₆・6H ₂ O1.6 parts by weight, PdCl ₂・2H ₂ O0.7
It was prepared by dissolving 0.3 parts by weight of RhCl _{3.3H 2} O in 120 parts by weight of a concentrated aqueous solution of H ₂ CrO ₆ adjusted to a specific gravity of 1.6. (4) Supporting the carrier/catalyst The carrier matrix prepared in (1) was immersed in the carrier slurry prepared as in (2), the carrier slurry was coated on the surface of the carrier matrix, and the mixture was dried in the same manner as in Example 1. Thereafter, the temperature was increased at a rate of 5.5°C/min and heat treatment was performed at 600°C for 40 minutes to form a carrier film. Next, the support matrix carrying the carrier was immersed in the catalyst solution prepared as in (3) to impregnate the carrier with the catalyst, and after drying at 55°C for 60 minutes,
The temperature was increased at a rate of 55.5°C/min, and heat treatment was performed at 600°C for 100 minutes. Furthermore, the impregnation-drying-heat treatment process was repeated four times in the same manner as in Example 1 using a concentrated aqueous solution of H ₂ CrO ₄ prepared to have a specific gravity of 1.6, thereby strengthening the adhesion of the carrier and catalyst to the carrier matrix. I did this. (4) Test results The film deposited on the support base in this way was
The film thickness was 74 μm, the specific surface area was 162 m ² /g, and the amount of catalyst was about 0.48% by weight based on the amount of carrier. Next, the activity test of the catalyst was conducted in the same manner as in Example 1. As shown in Table 2, which shows the experimental results in terms of conversion rates, it was observed that good conversion rates were maintained for a long period of time.

[Table] The adhesion strength of the carrier-catalyst film was measured in the same manner as in Example 1, and the tensile strength was 450 Kg/cm ² or more.

Claims (1)

[Claims] 1. A slurry of at least one of soluble salts of platinum, palladium, and rhodium and a concentrated aqueous solution of a chromium compound containing alumina or/and chromium oxide and hexavalent chromium as a heat-resistant metal supporting matrix. 1. A method for supporting an exhaust gas catalyst, which comprises repeating at least once an operation of depositing, drying and heat treatment, impregnating with a concentrated aqueous chromic acid solution, drying and heat treatment. 2 A slurry of alumina or/and chromium oxide and a concentrated aqueous solution of a chromium compound containing hexavalent chromium is deposited on a heat-resistant metal-supporting matrix, dried and heat-treated to form a thin film. The thin film is impregnated with an aqueous solution of at least one type of soluble salt and chromic acid, dried and heat treated, and then impregnated with a concentrated aqueous solution of chromic acid, dried, and then heat treated, which is repeated at least once. A method for supporting a catalyst for exhaust gas purification, characterized in that: