JPH09206593A - Catalyst for purification of exhaust gas and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a catalyst having excellent durability and high activity even in a high temp. region by applying a catalyst component comprising alumina as a carrier and gold as an active component on a base body. SOLUTION: This catalyst for purification of exhaust gas has a catalyst component applied on a base body. The catalyst component consists of alumina as a carrier and gold as an active component. Preferably, the thickness of the carrier is 10 to 500μm. The obtd. catalyst for purification of exhaust gas is produced by mixing an alumina powder, alumina sol and water to obtain a slurry, dipping the base body in the obtd. slurry to coat the base body with the alumina, drying and calcining to obtain the carrier, and then dipping the base body in a soln. of a gold compd., drying and baking to form the active component. The obtd. catalyst for purification of exhaust gas has high catalytic activity against exhaust gas at high temp. as about >=450 deg.C and hardly causes deterioration of the catalytic activity due to high temp. exhaust gas.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an exhaust gas purifying catalyst capable of significantly reducing nitrogen oxides (NOx) and hydrocarbons (HC) in exhaust gas of a diesel engine, and a method for producing the same, more specifically, a high temperature The present invention relates to an exhaust gas purifying catalyst having high catalytic activity against exhaust gas, and a method for producing the same.

[0002]

2. Description of the Related Art In order to reduce nitrogen oxides (NOx) and hydrocarbons (HC) contained in exhaust gas from diesel engines, copper-zeolite (Cu-ZSM-) is currently used.
5) Catalysts and platinum-alumina (Pt / Al ₂ O ₃ ) catalysts are widely used.

However, copper-zeolite has a problem that it is easily deteriorated by coexisting steam or heat, and the platinum-alumina catalyst has a high catalytic activity in the relatively low temperature range of 150 to 350 ° C. In the region, there is a problem that the catalytic activity is significantly reduced. For this reason,
Under the present circumstances, there is a demand for the development of an exhaust gas purifying catalyst that has a high catalytic activity with little deterioration in catalytic activity even with high-temperature exhaust gas.

[0004]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an exhaust gas purifying catalyst which has a high catalytic activity even with a high temperature exhaust gas and has a small deterioration of the catalytic activity due to the high temperature exhaust gas. Another object of the present invention is to provide a simple method for producing the above-mentioned purification catalyst.

[0005]

As a result of intensive studies to solve the above problems, the present inventors have found that a specific catalyst can achieve the above object, and have completed the present invention.

That is, the exhaust gas purifying catalyst of the present invention is an exhaust gas purifying catalyst having a catalyst component on a substrate, and the catalyst component comprises alumina as a carrier and gold as an active component. It is characterized by being. Preferably, the carrier has a thickness of 10 to 500 μm.

The above exhaust gas purifying catalyst is prepared by mixing alumina powder, alumina sol and water to obtain a slurry, immersing a substrate in the resulting slurry to coat alumina, drying and firing to form a carrier. The substrate can then be successfully manufactured by a manufacturing process that involves dipping the substrate in an aqueous solution of a gold compound, drying and firing to form the active ingredient. Preferably, the gold compound is chloroauric acid (HAuCl ₄ · nH ₂ O), and the concentration of the chloroauric acid in the aqueous solution is 0.5.
〜１０10 g / l. Further, preferably, the mixing ratio of the alumina powder and the alumina sol (dry weight) is 25 to 0.1 parts by weight with respect to the alumina powder: 75 to 99.9 parts by weight. Also, preferably,
The alumina is dried by heating at 80 to 150 ° C. for 3 to 10 hours, and calcined at 500 to 700 ° C. for 2 to
It is performed by treating for 5 hours. Further, preferably, the substrate is dipped in an aqueous solution of a gold salt or a double salt and then dried at 80 to 150 ° C. for 3 to 10 hours, and baked at 500 to 700 ° C. for 2 to 5 hours. It is done by processing.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The exhaust gas purifying catalyst of the present invention will be described in more detail below.

The exhaust gas purifying catalyst of the present invention is an exhaust gas purifying catalyst having a catalyst component on a substrate, and the catalyst component comprises alumina as a carrier and gold as an active component. It is characterized by.

Here, the substrate is a three-dimensional structure such as a honeycomb, a sphere or a pellet on which a catalyst component composed of a carrier and an active component can be supported. A honeycomb structure is preferable. The substrate may be composed of an inactive substance not participating in the catalytic reaction, or may be composed of an active substance participating in the catalytic reaction. Typically, it is made of a ceramic having excellent mechanical strength and heat resistance, such as cordierite, alumina, or magnesia. When manufacturing the substrate, a molding aid, a reinforcing material, an inorganic fiber, an organic binder and the like may be appropriately mixed. The base may also serve as a carrier.

The carrier provided on the substrate is composed of alumina as a main component, and preferably has a BET of 5
It is 0 to 300 m ² / g. As a reinforcing component, up to 30 parts by weight of a heat-resistant component such as silica, zirconia, magnesia, and titania and having a particle size range similar to that of alumina can be added. Preferably, the carrier has a thickness of 1 to 500 μm. Although the catalytic activity is improved as the thickness is increased, if the thickness exceeds 500 μm, it becomes difficult for the deepest part to come into contact with the reaction gas and the catalytic function cannot be effectively exhibited.

The active ingredient supported on the carrier is gold, which may be supported in the form of oxide, atomic or ionic, but is preferably oxide. The supporting rate of gold is preferably 0.1 to 20% by weight. It should be noted that the upper limit is merely provided because the catalytic function cannot be expected to increase in proportion to the increase in the active component if the upper limit is exceeded, and therefore the upper limit can be exceeded as necessary.

When the above-mentioned exhaust gas purifying catalyst is manufactured, for example, in a form in which a catalyst component is provided on a ceramic honeycomb substrate, alumina powder, alumina sol, and water are mixed to obtain a slurry. The substrate constituting the catalyst structure is dipped in the slurry, coated with alumina, dried and calcined to form a carrier, and then the substrate is dipped in an aqueous solution of a gold salt or double salt, dried and calcined to form the active ingredient. Can be successfully manufactured by a manufacturing method including forming a.

Alumina powder having a commercially available particle size of 1 to 10
Γ-alumina having a BET of 50 to 300 m ² / g at 0 micron can be used as it is, but one having a lower alkali concentration is preferable. The alumina sol preferably has an alumina colloidal particle size of 10 to 1000 liters. Also,
Alumina powder and alumina sol (dry weight) are wt%
Then, it is preferable to mix them in a ratio of 75-99.9: 25-0.1. If the amount of alumina sol exceeds 0.1% by weight, it will be evenly distributed between the alumina powder and between the alumina powder and the substrate, and will contribute significantly to the increase in adhesiveness. Further improvement cannot be expected, but rather causes reduction in mechanical strength, so the above range was made the preferred range. Further, water may be added to the alumina sol,
Further, it may be added after mixing the alumina powder and the alumina sol. It is preferable to use ion-exchanged water in order to prevent contamination of impurities.

In addition, precious metal elements such as platinum, ruthenium, rhodium, palladium, osmium and iridium, rare earth elements such as lanthanum, yttrium, cerium, samarium and praseodymium, transition metal elements such as cobalt, nickel and iron, magnesium, barium, Alkaline earth elements such as sodium and strontium may also be included as cocatalyst up to 20 parts by weight per 100 parts by weight of the catalyst component.

To coat the substrate with alumina,
The substrate is dipped in the above-mentioned alumina slurry, pulled up, dried and fired. During the dipping, it is preferable to stir the slurry so that the alumina uniformly and completely covers the surface of the substrate. Further, in order to promote coating, a surfactant, preferably a polyoxyethylene-based nonionic surfactant can be added. It is preferable to coat the substrate with alumina by dipping and pulling up several times, such as immersing the substrate in the slurry, pulling it up to dry it, then dipping it again and pulling it up to dry it. Drying of coated alumina is 80
It is preferably carried out by heating at ~ 150 ° C for 3 to 10 hours. Further, the firing is 500 to 700 ° C.
Preferably for 2 to 5 hours.

Next, gold is supported on the carrier by an impregnation method. Usually, a gold compound capable of forming an aqueous solution (that is, an inorganic salt, an organic salt, a metal acid or a salt thereof, and the salt includes a double salt) is dissolved in water to form an aqueous solution, and the carrier is added to the aqueous solution. The fixed substrate is dipped and pulled up to impregnate the carrier with the aqueous solution. Then, it is dried to fix and carry the active ingredient. Further, it is fired as an activation treatment. The gold _{compounds, (2 O HAuCl 4 · nH} ) chloroauric acid, there are other gold compounds, preferably, chloroauric acid (HAuCl ₄ ·
nH ₂ O). Note that n is preferably 4.
The concentration of the chloroauric acid (HAuCl ₄ ) in the aqueous solution is 0.1 to 10 g / l. During the immersion, it is preferable to stir or add a surfactant in the same manner as in the above-mentioned step of fixing alumina to the substrate. Preferably, the catalyst structure is immersed in an aqueous solution of a gold compound and pulled up, and then dried by heating in air at 80 to 150 ° C. for 3 to 10 hours, and calcination as an activation treatment is performed at 500 to 7
It is carried out by treating at 00 ° C. for 2 to 5 hours. The firing may be performed in an oxidizing atmosphere such as air, or a hydrogen-containing inert gas (for example, nitrogen gas).
It may be carried out in a reducing atmosphere such as, but is preferably carried out in an oxidizing atmosphere.

The loading is not limited to the impregnation method, and various known methods such as a deposition method and an ion exchange method can be used. The above impregnation method can also be used in combination with the deposition method.

[0019]

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

[Example] 100 parts by weight of alumina powder made of γ-alumina having an average particle size of 12 μm (particle size distribution of 5 to 100 μm) and BET of 150 m ² / g, and sold as BK112 by Sumitomo Chemical Co., Ltd. 5 parts by weight of the aqueous solution of alumina sol (3 parts by weight of alumina sol (dry weight)) and 110 parts by weight of ion-exchanged water were combined and sufficiently stirred to obtain a slurry. A surfactant of methyl cellulose was added to the obtained slurry, and a honeycomb substrate made of cordierite was immersed in the slurry for 1 minute so that the surface of the substrate was sufficiently and uniformly covered with alumina. At this time, the slurry was stirred. Then, it was pulled up and left in the air for 20 minutes. After repeating this operation 5 times (that is, after soaking 5 times), it was dried in air and coated with alumina so that the film thickness of the alumina coating after firing was in the range of 50 to 1000 μm. Then, after heating and drying in air at 100 ° C. for 10 hours, it was further heated and baked in air at 500 ° C. for 3 hours.

Next, chloroauric acid (HAuC) was added to ion-exchanged water.
l ₄ · nH ₂ O) and the concentration of the chloroauric acid is 2 g / l
Was prepared, and the ceramic honeycomb body coated with alumina was immersed in the aqueous solution for 10 minutes.
During the dipping, stirring was performed in the same manner as in the coating of alumina, and the surfactant was added. After that, after supporting the pulled-up gold (Au), it was heated and dried in air at 100 ° C. for 10 hours to fix the gold, and further calcined in air at 500 ° C. for 3 hours to obtain the exhaust gas purifying catalyst of the present invention. Obtained.

Comparative Example As a comparative example, a copper-zeolite catalyst and a platinum-alumina catalyst were prepared. For comparison, the catalyst components were all fixed on the substrate made of cordierite, and the loading rate was substantially the same as in the examples.

[Catalyst Performance Test 1] In order to confirm the catalyst performance of the obtained exhaust gas purifying catalysts, the catalysts prepared in Examples and Comparative Examples were attached to fixed bed flow reactors, respectively, and then the diesel engine was used. A gas having the following composition, which is assumed to be the exhaust gas of No. 1, was passed through at the following space velocity (SV), and the reduction rate of nitrogen oxides (NOx) and hydrocarbons (HC) was measured.

NO: 1000 ppm C ₃ H ₆ : 1360 ppm O ₂ : 10 wt% SO ₂ : 20 ppm H ₂ O: 4 wt% N ₂ : balance SV: 20,000 h ^-1

The results are shown in FIG. In the figure, Au-Al
₂ O ₃ is the catalyst of the example, Cu-ZSM5 and Pt-Al ₂
O ₃ means the catalyst of the comparative example.

As is clear from the results shown in FIG. 1, the exhaust gas purifying catalyst of the present invention has a maximum of 40% (compared to the comparative example) with respect to NOx when the exhaust gas temperature is 550 ° C.
It showed a significantly higher reduction rate. Cu-ZSM5 showed a maximum NOx reduction rate of 32% when the catalyst inlet temperature was 425 ° C. Further, Pt-Al ₂ O ₃ showed a maximum NOx reduction rate of 30% when the catalyst inlet temperature was 225 ° C. Therefore, it can be seen that the catalysts of the examples have high activity in the high temperature range.

[Catalyst performance test 2] In order to confirm the durability, the Au-Al ₂ O ₃ catalyst of the example and Cu-ZS of the comparative example were used.
The M5 catalyst and Pt-Al ₂ O ₃ catalyst were placed under the same gas conditions as in Test 1 for 100 hours except that the catalyst inlet temperature was 500 ° C. and H ₂ O was 10%. The result is shown in FIG. As is clear from the results shown in FIG. 2, the catalysts of Examples had significantly superior durability. Therefore, it can be seen that the catalysts of Examples are catalysts having high durability.

[0028]

EFFECT OF THE INVENTION The exhaust gas purifying catalyst of the present invention has a high catalytic activity for high temperature exhaust gas at 450 ° C. or higher, and has little deterioration in catalytic activity due to high temperature exhaust gas.

[Brief description of drawings]

FIG. 1 is a chart showing nitrogen oxide reduction rates of exhaust gas purifying catalysts of Examples and Comparative Examples.

FIG. 2 is a chart showing durability of exhaust gas purifying catalysts of Examples and Comparative Examples.

Claims (7)

[Claims] 1. An exhaust gas purifying catalyst, comprising a catalyst component comprising alumina as a carrier and gold as an active component on a substrate. 2. The exhaust gas purifying catalyst, wherein the carrier has a thickness of 10 to 500 μm. 3. An alumina powder, an alumina sol, and water are mixed to obtain a slurry, and a substrate is dipped in the obtained slurry to coat alumina, and dried and baked to form a carrier. The method for producing an exhaust gas purifying catalyst according to claim 1, which comprises soaking in an aqueous solution of a gold compound, drying and firing to form an active component. 4. The gold compound is chloroauric acid (HAuCl).
₄ · nH ₂ O), and the concentration of the chloroauric acid in the aqueous solution is 0.5 to 10 g / l. 5. The blending ratio of the alumina powder and the alumina sol (on a dry basis) is alumina powder: 75 to 99.
The method for producing an exhaust gas purifying catalyst according to claim 3 or 4, wherein the amount of alumina sol is 25 to 0.1 part by weight based on 9 parts by weight. 6. The alumina is dried by heating at 80 to 150 ° C. for 3 to 10 hours and calcined at 500 to
The method for producing an exhaust gas purifying catalyst according to any one of claims 3 to 5, wherein the method is performed by treating at 700 ° C for 2 to 5 hours. 7. The substrate is dipped in an aqueous solution of gold salt or double salt and dried at 80 to 150 ° C. for 3 to 10 hours, and calcined at 500 to 700 ° C. for 2 to 5 hours.
The method for producing an exhaust gas purifying catalyst according to claim 6, wherein the method is performed for a time.