JPS60187339A - Process for supporting catalyst for purifying exhaust gas deposited on carrier by carrier base - Google Patents

Abstract

PURPOSE:To stick the titled catalyst together with oxide carrier to a carrier base comprising heat resistant metal firmly by sticking the oxide carrier and noble metal catalyst firmly to a carrier base comprising a heat resistant metal by the chemical bonding force of Cr2O3 to each other. CONSTITUTION:A slurry comprising concn. aq. soln. contg. at least one soluble salt among salts of Pt, Pd, Rh, alumina and/or Cr2O3, and Cr compd. contg. hexavalent Cr, is coated on a heat resistant metal (e.g heat resistant steel), and the coated product is dried and heat-treated. Acidic concd. aq. soln. of Cr compd. is impregnated thereto and dried. The procedure is repeated at least once more. As the result, a carrier base having high specific surface area is obtd. and a larger sectional area of the free space for passing exhaust gas is obtd.; thus, reduction of pressure drop is realized. Further, the specific surface area of the carrier sticking to the carrier base, namely the area of the catalyst carried on the carrier, is increased remarkably. The catalytic reactor is miniaturized, the activity and the life of the catalyst are improved.

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 is capable of firmly adhering and holding the catalyst for purifying automobile exhaust gas on a heat-resistant metal support together with an oxide carrier.

CO1 hydrocarbons (hereinafter referred to as EC) contained in automobile exhaust gas
Exhaust gas purification catalysts for oxidizing, reducing, and decomposing harmful gases such as Pt, Pt, Pd, Pt, and other noble metals, such as platinum (PT), palladium (PA), and rhodium (Rh), are used to oxidize, reduce, and decompose harmful gases such as Precious metal catalysts such as Pd+Rh are the 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 as That is, in honeycomb type ceramics, γ-A120. In the case of takuret type or spherical type, porous AJaO is used.
In order to support the catalyst on these carriers (page 3) on which r5 is used, it is impregnated with a solution of a soluble salt of a noble metal such as pt, pa, sh, etc., such as a chloride solution, and heat treated. A method is known. In the case of a metallic support matrix, 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 supporting matrix, as well as the increase in the supporting area of the catalyst, i.e., high activation and durability, are required. The level of demand for sexuality is increasing.

To this end, it is desired to improve not only the catalyst, the carrier, and the supporting matrix, but also the method of supporting the catalyst, but as for the supporting matrix, metallic carriers require thinner base materials than ceramic carriers. It is preferable because it has many advantages such as significantly increasing the supporting area of the carrier, making the reactor smaller, making it easier to process the matrix, and having excellent thermal shock resistance. However, in the case of a metallic supported matrix,
In order to support a carrier and a catalyst using the above-mentioned method, there is a problem in firmly supporting the carrier and catalyst to impart heat resistance.

The inventor of the present invention has conducted intensive research on catalyst support materials, carriers, and supporting methods with a focus on improving heat resistance, thermal shock resistance, and high activation.
This and the oxide-based carrier and noble metal-based catalyst material are combined into Cr20
The present invention was made by discovering that metals can be firmly adhered to each other through the chemical bonds of 3. That is, the first invention of the present invention is based on the discovery that soluble salts of platinum, radium, and rhodium can be firmly attached to each other through chemical bonds. A slurry of at least one of these and a concentrated aqueous solution of a chromium compound containing alumina or/and chromium oxide and hexavalent chromium is deposited on a heat-resistant metal supporting base, dried and heat treated, and then impregnated with a concentrated aqueous solution of chromic acid. The second invention is a method for supporting a catalyst for exhaust gas purification, which comprises repeating the steps of drying, drying, and heat treatment at least once. A slurry of the compound with a concentrated aqueous solution is deposited on a heat-resistant metal-supported matrix, dried and heat-treated to form a thin film.
(Page 5) / A thin film is impregnated with an aqueous solution of at least one of soluble salts of radium and rhodium and chromic acid, dried and heat treated, and then further impregnated with a concentrated aqueous solution of chromic acid, dried and heated. This is a method for supporting a catalyst for exhaust gas purification, in which a treatment operation is repeated at least once.

Examples of the heat-resistant metal support base in the present invention include SUS 302E, SUS 304, and BUS 410.
Heat-resistant steel such as L, 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. is degreased and then subjected to chemical attack treatments such as HNO3, HCI and FeCl3.
It is preferable to perform surface roughening treatment in advance by etching the matrix using a mixed liquid of +FeCJ2.

The carrier deposited on the surface of the supporting matrix is, for example, a porous oxide such as alumina or chromium oxide,
Particle size: 15 μm or less, average particle size: 5 μm or more (Page 6) It is a fine powder with a specific surface area of 75 m2/ or more, and the particle size distribution range is preferably circumferentially narrow. Or in an appropriate combination (for example, γ-A
IIIa0330-100 parts by weight, Cr2030-70
It is preferable to mix within a range of parts by weight. ) is used.

The catalyst is a noble metal such as platinum, palladium, rhodium, etc., and their soluble salts such as chloroplatinic acid (H2Pt
C1e・6H20), palladium chloride (PdCJ2・2
H2O), rhodium chloride (RhC15.3H20), etc. are preferably used. Therefore, at least one of these is used, and each can be used alone or in an appropriate combination.

Catalysts are typically Pt, Pt+Pd, Pt+Pc
Since it is used in the form of 1+Rh, etc., it is preferably used 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 based on 100 parts by weight of the carrier material, and when two types are blended, for example, Pt+P
In the case of d, 0.6 to 1.2 parts by weight of pt salt, (7th part
R) 2 to 0.4 parts by weight of Pd salt, in the case of 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 parts by weight of Pd salt in the case of Pd and Rb.
．． 0 parts by weight, 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, P
t salt 1.0-1.5 parts by weight, pao, 5-1 parts by weight, R
It is preferable to blend h0.2 to 0.4 parts by weight.

Moreover, when dissolving in chromic acid, the concentration of chromic acid is preferably in the range of specific gravity 1.6 to 1.75.

The concentrated aqueous solution of a chromium compound containing hexavalent chromium used for firmly adhering the support and catalyst to the heat-resistant metal-supported matrix includes CaCrO4, CoCrO4, ZnCr0. ,
It is preferable that the solution is formed by dissolving at least one of CaCO3, CoCO3, ZnO, Cr2O3, etc. in a concentrated aqueous solution of H2CrO4, and the content ratio of the above compound is 0.1 to 0 in total per 1 mole of H2CrO4. ．．
A ratio of 4 moles is suitable. Also, H2CrO
Concentrated aqueous solutions of 4 monomers can also be used, and the concentrations of these solutions are preferably adjusted to a specific gravity of 1.5 to 1.7.

Such carriers and catalysts are deposited on 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. Explain. 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, HaPtCA! a・6H202 parts by weight, PdCJ2・2H200,7 parts by weight and RhC
A3 ・3 H2O0.3 parts by weight), γ-A/203 fine powder (for example, particle size ioμm or less, average particle size 3μm
, specific surface M! , 158 rn2/f , 170 parts by weight), CaCO3 was dissolved in a concentrated aqueous solution of a chromium compound containing hexavalent chromium (for example, a concentrated aqueous HgCr0t solution at a ratio of 0.2 mol to 1 mol of HzCrOt, and the specific gravity was adjusted to 1.
6) and water (35 parts by weight) to prepare a slurry. Heat-resistant metal matrix (
For example, a thin plate of chromium steel 5UH409) is processed into a honeycomb shape (for example, according to the method disclosed in Japanese Patent Application Laid-open No. 54-25321 and No. 56-4373) and subjected to surface roughening treatment.

After such preparation, the heat-resistant metal carrier base is immersed in the slurry to be coated, dried, and then heat-treated. Drying after the slurry has been applied varies depending on the size of the material, but it is usually preferably carried out at room temperature to 70°C for 30 seconds and 60 minutes, and the heat treatment is performed at 5 to 6° (:, /
It is preferable to raise the temperature at a heating rate of min. to 550 to 600° C. for 1 to 3 hours. The thickness of the coating thus deposited can be controlled by the concentration of the slurry, dipping conditions, and the like. In the above numerical example in parentheses, a film in which the catalyst is uniformly dispersed and supported on the carrier can be obtained with a thickness of about 200 μm.

Next, the coating is impregnated with an aqueous chromic acid solution, dried, and heated. The chromic acid aqueous solution used here is
It is preferably a concentrated aqueous solution with a specific gravity in the range of 1.6 to 1.75, and is impregnated into the coating obtained by the above treatment by a coating method or a dipping method. Thereafter, it is dried at room temperature to 70°C for (9) to (a) minutes, and heat-treated at a heating rate of 4 to 6°C/min to 550 to 600°C for 40 to (a) minutes (page 1O). preferable. 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. For example, in the invention method of
The same γ-A/a03 powder as above and Cr, O, powder (for example, particle size 10 μm or less, average particle size 2 μm, specific surface area 146 m2/l) are blended (for example, r-xg,, o3
50 parts by weight, Cr, 0,350 parts by weight) and a concentrated aqueous solution of a chromium compound containing hexavalent chromium (for example, H2Cr).
0.1 mole to 0.1 mole of CoCO3, and 0.1 mole to 0.1 mole of CoCO3;
A solution prepared by dissolving 1 mol of CaCO3 in a concentrated aqueous solution of H2CrO and adjusting the specific gravity to 1.6, 1 part by weight) and water (3 parts by weight).
5 parts by weight), and a carrier made of stainless steel 304, processed into a honeycomb shape and roughened as described above, is immersed in the slurry (page 11) to coat the carrier. . The specific surface area of the carrier film obtained in this way was determined to be 125 to 155 m2/, as measured by peeling the carrier from the supporting matrix using an acid dissolution method. i'(
In the above example of the numerical value in parentheses, 152 m2/E/) is obtained.

Then, an appropriately selected catalyst (for example, H2ptc'l
, 6H201 parts by weight, and PdC15-2H,00,
4 parts by weight) in a chromic acid aqueous solution (for example, specific gravity 1.7.
140 parts by weight), and the supporting matrix coated with the carrier 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 for I-ω minutes at temperatures between
Raise the temperature at a rate of 4-6°C/min to 550-600°C
It is preferable to carry out the treatment for 1 to 2 hours. 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 has a specific gravity of 1.
Preferably, it is a concentrated aqueous solution in the range of 6 to 1.75,
The film obtained by the above treatment is impregnated by a coating method or a dipping method. After that, at room temperature ~ 70℃ (g) ~
(b) Dry for 5 minutes and raise the temperature at a rate of 550 to 60
It is preferable to perform the treatment under conditions such as heating at 0° C. for 40 to 60 minutes.

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.

In the present invention, a heat-resistant metal is used as a supporting matrix, and the oxide carrier and noble metal catalyst material are adhered to each other by chemical bonding of Cr2O, so that these are strongly bonded to each other. It could have been covered. However, when the supporting matrix is made of a heat-resistant metal and the trap is of a honeycomb type, the wall thickness of the cells of the honeycomb core can be made as thin as about 40 to 50 μm, and a supporting matrix with a large specific surface area can be obtained. The cross-sectional area of the free space through which exhaust gas passes can be increased, and pressure loss can be reduced. Furthermore, the specific surface area, that is, the catalyst supporting area, of the carrier adhered to the supporting matrix can be significantly increased, and these together lead to smaller size, higher activity, and longer life of the catalytic reactor. can be done. In addition, γ-8he203 and Cr2O3
Or CaO or C that can be contained in small amounts in this
Both nO and other catalysts are expected to act as co-catalysts for oxidation and reduction, and many excellent effects have been recognized, and they are used as industrial catalysts because they require relatively simple operations and low heat treatment temperatures. This is suitable as a supporting method.

Next, examples of the method of the present invention will be described.

Example 1 (1) Preparation of carrier/catalyst slurry 12 parts by weight of CaCO3 was dissolved in a concentrated aqueous solution of H2Cr04 in which parts of Cr0s50 ii were dissolved in 9 parts by weight of water, and water was added to form an aqueous solution with a specific gravity of 1.65. To 36 parts by weight of this aqueous solution containing hexavalent chromium, r
150 parts by weight of fine powder of klao3, H2P as a catalyst
1.5 parts by weight of tC1e.6HaO was added to dissolve the catalyst, and the mixture was thoroughly mixed using an alumina (page 14) ball mill to prepare a slurry.

(2) Preparation of the supporting matrix A stainless steel 5US304 thin plate with a thickness of 0.05 m is coated into a honeycomb shape, and the surface is roughened to increase the surface area to 3.
It was prepared to have a length of 700 cm and an external dimension of 39φxroom.

(3) Compatibility of carrier and catalyst The support matrix prepared in (2) was immersed in the slurry prepared in (1), the slurry was coated on the surface of the carrier matrix, and after drying at 52°C for ω minutes, the The temperature was raised at 6° C./min using a furnace, and heat treatment was performed at 600° C. for about 100 minutes. Then, it was immersed in an aqueous solution of chromic acid prepared to have a specific gravity of 1.6 to impregnate it with chromic acid.
ω'G K After drying for 30 minutes, 600
C. for 40 minutes, and the impregnation-drying-heat treatment process was repeated three times to reinforce the adhesion of the carrier and catalyst to the carrier matrix.

(4) Test results (15th test) The thickness of the film deposited on the supporting matrix in this way was approximately 91 μm.
The specific surface area was 174 m2/I, and the amount of catalyst was about 0.62% by weight based on the amount of support.

Next, the catalyst was placed in a cylindrical reaction vessel made of SUB 304 measuring 40φ×100 mm, and an activity test of the catalyst was conducted at sv 5000 h−1. The gas composition used in the experiment was assumed to be idling, and included 1.0% Co, HC (~C3
H8) 0.15%, No 0.03%, 0□7 excellent, N,
The remaining amount was 82.82 cm (volume ratio), and the conversion rate was calculated.

The experimental results showed that the conversion rates shown in Table 1 were good and maintained for a long time.

Table 1 The adhesion strength of the carrier-catalyst coating was measured by a peel test using an epoxy resin adhesive attached to the surface of the carrier and the catalyst coating. Saha 4
It was over 35 kg/male.

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
m”/E γ-person l, o, 70 parts by weight of fine powder and particle size 1
0μm1 average particle diameter 3μm, specific surface area 146m7. l
CrO3 to 70 parts by weight of Cr203ffIl powder of i'
? H with a specific gravity of 1.65 by dissolving parts by weight of A in 16 parts by weight of water
3crots of concentrated aqueous solution and parts by weight of water were added and thoroughly mixed using an alumina ball mill to prepare a carrier slurry.

(3) Preparation of catalyst a2ptoa・61 (1.6 parts by weight of IaO, PdCJ
2.2 H, OO, 7 parts by weight and RhCmu・3H200
, 3 parts by weight were dissolved in 120 parts by weight of a concentrated H2CrOa aqueous solution prepared to have a specific gravity of 1.6K.

(4) Supporting the carrier/catalyst (page 17) The carrier matrix prepared in (1) was immersed in the carrier slurry prepared as in (2), and the carrier slurry was coated on the surface of the carrier matrix. After drying in the same manner as 5.5℃/mi
A heat treatment was performed at 600° C. for 40 minutes by increasing the temperature at a rate of n to form a carrier film.

Next, the carrier matrix carrying the carrier is immersed in the catalyst solution prepared as in (3) to impregnate the carrier with the catalyst.
After drying at 5° C. for ω minutes, heat treatment was performed at 600° C. for 100 minutes at a rate of 5.5° C./min.

Further, the impregnation-drying-heating treatment was repeated four times in the same manner as in Example 1 using a concentrated aqueous solution of Hm Cr O 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 thickness of 9
The specific surface area was 162 m2/I, and the amount of catalyst was about 0.48% by weight based on the amount of support.

Next, the activity test of the catalyst was conducted in the same manner as in Example 1. As shown in Table 2 (page 18), which shows the experimental results in terms of conversion rate, it was found that the conversion rate remained good for a long time.

Table 2 Also, the adhesion strength of the carrier-catalyst coating was measured in the same manner as in Example 1, and the tensile strength was 450 kg/(ML+1 or more).

Patent applicant: Usui Kokusai Sangyo Co., Ltd.

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. After drying and heat treatment,
A method for supporting an exhaust gas catalyst, which comprises repeating at least one operation of impregnating a concentrated aqueous solution of chromic acid, drying, and then heat-treating. 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, and then platinum, palladium, rhodium The thin film is impregnated with an aqueous solution of at least one of the soluble salts and chromic acid, dried and heat treated, and then impregnated with a concentrated aqueous chromic acid solution, dried, and heat treated at least once. Compatible method for catalysts for exhaust gas purification (page 2).