JPH06320006A - Catalyst for catalytic reduction of nox - Google Patents

Abstract

PURPOSE:To obtain a catalyst for catalytic reduction of NOx capable of efficient reduction of NOx in exhaust gas without using a large amt. of a reducing agent and excellent in durability even in the presence of moisture by carrying cerium oxide on a solid acid carrier. CONSTITUTION:Cerium oxide is carried on a solid acid carrier to obtain the objective catalyst for catalytic reduction of NOx with hydrocarbon or an oxygen-contg. org. compd. as a reducing agent. The solid acid carrier is a carrier exhibiting solid acidity in a temp. region in which the catalyst is used. A zeolite type or oxide type solid acid carrier may be used as the solid acid carrier and the pref. amt. of the cerium oxide carried on the solid acid carrier is 5-80wt.% of the total amt. of them. The catalyst itself can be formed into one of various shapes such as a honeycomb or sphere shape by a known forming method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for catalytic reduction of nitrogen oxides using a hydrocarbon or an oxygen-containing organic compound as a reducing agent, and more specifically, it is contained in exhaust gas discharged from factories, automobiles and the like. The present invention relates to a catalyst for catalytic reduction of nitrogen oxides, which is suitable for reducing and removing harmful nitrogen oxides.

[0002]

2. Description of the Related Art Conventionally, nitrogen oxides contained in exhaust gas have been produced by oxidizing nitrogen oxides and then absorbing it in an alkali, or by using a reducing agent such as ammonia, hydrogen, carbon monoxide, or hydrocarbon. It is removed by a method such as conversion to nitrogen. However, according to the former method, it is necessary to treat the generated alkaline waste liquid to prevent pollution. On the other hand, according to the latter method, when ammonia is used as the reducing agent, it reacts with the sulfur oxide in the exhaust gas to form salts, and as a result, the reducing activity of the catalyst is lowered. Even when hydrogen, carbon monoxide, hydrocarbon, etc. are used as a reducing agent, they react with oxygen present in a higher concentration than nitrogen oxide present in a low concentration, and therefore, in order to reduce nitrogen oxides. Has a problem that it requires a large amount of reducing agent.

For this reason, recently, a method of directly decomposing a nitrogen oxide with a catalyst in the absence of a reducing agent has been proposed. However, such a conventionally known catalyst has been proposed as a nitrogen oxide. There is a problem that it is difficult to put it into practical use because of its low decomposition activity. Further, as a new nitrogen oxide catalytic reduction catalyst using a hydrocarbon or an oxygen-containing organic compound as a reducing agent,
H-type zeolite and Cu ion exchange ZSM-5 have been proposed. In particular, H-type ZSM-5 (SiO ₂ / Al ₂ O
₃ molar ratio = 30-40) is said to be optimal. However, even with such H-type ZSM-5, it is hard to say that it still has sufficient reducing activity, and in particular, when water is contained in the gas, aluminum in the zeolite structure is dealuminated, resulting in poor performance. Because it drops sharply
There is a demand for a catalyst for catalytic reduction of nitrogen oxides, which has a higher reduction activity and has excellent durability even when the gas contains water.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and its object is to use a hydrocarbon or an oxygen-containing organic compound as a reducing agent. Even in the presence of oxygen, and
In particular, since nitrogen oxides selectively react with hydrocarbons or oxygen-containing organic compounds even in the presence of oxygen and water, nitrogen oxides in exhaust gas can be efficiently reduced without using a large amount of reducing agent. Another object of the present invention is to provide a catalyst for catalytic reduction of nitrogen oxides, which can be obtained and has excellent durability even in the presence of water.

[0005]

A catalyst for catalytic reduction of nitrogen oxides using a hydrocarbon or an oxygen-containing organic compound as a reducing agent according to the present invention is characterized in that cerium oxide is supported on a solid acid carrier. The solid acid carrier in the present invention means a carrier which exhibits solid acidity in the temperature range in which the catalyst is used. Solid acidity can be confirmed by the thermal desorption method using ammonia, or in situ using ammonia or pyridine.
It is performed by the FTIR (Fourier transform infrared absorption spectrum) method. Examples of the solid acid carrier include the following zeolite-based solid acid carriers and oxide-based solid acid carriers.

Zeolite-based solid acid carriers include Na-mordenite, Na-ZSM-5, Na-USY (USY: ultrastable or ultra-stable Y-zeolite), and some or all of the aluminum in the zeolite to other metal elements. ,
Particularly, iron, gallium, zinc, lanthanum, copper, molybdenum, chromium, germanium, titanium, metallosilicate substituted with boron, etc., such as zeolite having excellent heat resistance, an aqueous solution of ammonium salt such as ammonium sulfate or an acid such as sulfuric acid. Can be obtained by ion-exchange of a part or all of the alkali metal in the zeolite with ammonium ion or hydrogen ion. In the case of the method of performing ion exchange with ammonium ions, a calcination treatment is finally required.

As an example of the zeolite-based solid acid carrier, for example, the following formula

[0008]

[Chemical 1]

An acid-type mordenite obtained by acid-treating a mordenite-type zeolite represented by
₂ / Al ₂ O ₃ molar ratio is 13-40, and Si
An acid type mordenite having an O ₂ / H ₂ O molar ratio of 25 to 200 can be mentioned. However, in the above formula, M represents an alkali metal ion, and r is a value that varies depending on the synthesis conditions of zeolite.

Another example of the zeolite-based solid acid carrier is, for example, the following formula

[0011]

[Chemical 2]

Part or all of the ions M in the zeolite represented by lanthanum ion (La ³⁺ ), gallium ion (Ga ³⁺ ), cerium ion (Ce ⁴⁺ ), titanium ion (Ti ⁴⁺ ), zirconium A zeolite obtained by exchanging ions (Zr ⁴⁺ ) and tin ions (Sn ⁴⁺ ) can be mentioned. However, in the above formula, M ′ represents an alkali metal ion, an alkaline earth metal ion, or a hydrogen ion, nA = p (n is the valence of the ion M), q / p.
≧ 5.

As the oxide type solid acid carrier, Al is used.
₂ O ₃ , TiO ₂ , TiO ₂ / SO ₄ ^2- , ZrO ₂ , Z
Single metal oxides such as rO ₂ / SO ₄ ^2- , SiO ₂ / A
l ₂ O ₃ , TiO ₂ / Al ₂ O ₃ , TiO ₂ / ZrO ₂
And other complex oxides. Among these, from the viewpoint of heat resistance, Al ₂ O ₃ , ZrO ₂ , SiO ₂
/ Al ₂ O ₃ is preferred.

As another example of the solid acid carrier, a kind of crystalline aluminum phosphate (ALPO) having a zeolite-like porous structure or a layered structure, and its related substance, crystalline aluminum silicate phosphate (SAPO). ), ALPO
The crystalline aluminum metal phosphate (MAPO) in which a part of phosphorus or phosphorus-aluminum of (1) is substituted with a metal such as titanium, iron, magnesium, zinc, manganese, or cobalt.

The ALPO type phosphate is a so-called template such as amine and quaternary ammonium in a desired combination selected from the above-mentioned phosphoric acid source and metal source and silica, silica sol, sodium silicate and the like. It can be prepared by a hydrothermal synthesis method from a mixed raw material under conditions similar to those for synthesizing zeolite. The main difference from the case of synthesizing zeolite is that it is generally synthesized at a higher temperature (approximately 150 ° C. or higher) in a pH acidic region.

The composition of the ALPO type phosphate is generally Al ₂ O _3. (0.8 to 1.2) .P ₂ O ₅ .nH ₂ O
It is represented by. Further, in the case of SAPO or MAPO, the maximum amount of silica and metal to be replaced is about 1/10 of the total amount of aluminum and phosphorus, but in the present invention, it does not necessarily fall within this composition range. That is, a material containing an amorphous material may be used.

When an ALPO type phosphate obtained by the hydrothermal synthesis method is used as a carrier, it is generally one that is washed with water, dried and then calcined in air to remove the remaining template by incineration. Used. The cerium oxide in the present invention includes cerium hydroxide (Ce (OH) ₃ , cerium nitrate (Ce (NO ₃ ) ₃ ), cerium acetate (Ce).
It can be obtained by firing (CH ₃ COO) ₃ ) or the like in air or in an oxygen atmosphere.

The catalyst according to the present invention can be prepared, for example, by the method (1), (2) or (3) shown below. (1) A water-soluble salt such as a cerium nitrate salt or an alcohol solution of these alkoxides is put into a thriller in which a solid acid carrier is dispersed to neutralize or hydrolyze them, or a spray drying method or a frozen method. A precursor of cerium oxide such as cerium hydroxide is supported on a solid acid carrier by a dry method or the like, and then filtration, washing with water and repulping are repeated, followed by drying and firing. (2) The solid acid carrier and separately prepared cerium oxide are thoroughly wet-milled and mixed by a planetary mill or the like. (3) A method of neutralizing or hydrolyzing a solution in which a precursor such as a water-soluble salt or hydroxide of a solid acid carrier and a water-soluble salt such as cerium nitrate or an alcohol solution of alkoxide are homogeneously mixed. Then, a precipitate is formed, and the precipitate is filtered, washed with water and repulped repeatedly, dried, and calcined.

The preferred loading of cerium oxide is in the range of 5-80% by weight of the total weight of cerium oxide and solid acid support. Even if the supported amount of cerium oxide exceeds 80% by weight,
Not only the effect of addition corresponding to such increase in amount cannot be obtained, but also in the reaction system in which oxygen coexists, the consumption of hydrocarbons and oxygen-containing organic compounds by oxygen increases. On the other hand, when the supported amount is less than 5% by weight, the reducing activity of the catalyst cannot be sufficiently improved. Particularly, in the present invention, it is preferable that the supported amount is 20 to 50% by weight. When the supported amount is within this range, it is possible to obtain the excellent property that the SV dependence of the catalytic reduction reaction of nitrogen oxide is extremely small.

The catalyst according to the present invention can be formed into various shapes such as a honeycomb shape and a spherical shape by itself by a conventionally known forming method. At the time of this molding, a molding aid, a molded body reinforcing material, an inorganic fiber, an organic binder and the like may be appropriately mixed. Further, the catalyst according to the present invention can be coated and supported on a preformed inert substrate by a wash coat method or the like. As the base material, for example, a honeycomb structure made of clay such as cordierite can be supported. Further, if necessary, any conventionally known method for preparing other catalysts can be used.

In the catalytic reduction of nitrogen oxides using the catalyst according to the present invention, examples of the reducing agent composed of a hydrocarbon include a gaseous hydrocarbon gas such as methane, ethane, propane, propylene, butylene, and a liquid. As the material, a single-component hydrocarbon such as pentane, hexane, octane, heptane, benzene, toluene, xylene, and a mineral oil hydrocarbon such as gasoline, kerosene, light oil, and heavy oil can be used. Particularly, according to the present invention, among the above, acetylene, methylacetylene, 1-
Lower alkyne such as butyne, lower alkene such as ethylene, propylene, isobutylene, 1-butene and 2-butene,
Lower dienes such as butadiene and isoprene, and lower alkanes such as propane and butane are preferably used as the reducing agent. These hydrocarbons may be used alone or in combination of two or more as required.

Examples of the reducing agent composed of an oxygen-containing organic compound include alcohols such as methanol, ethanol, propanol and octanol, ethers such as dimethyl ether, diethyl ether and dipropyl ether, methyl acetate, ethyl acetate and oils and fats. Carboxylic acid esters such as, acetone, ketones such as acetone, methyl ethyl ketone and the like can be mentioned as preferred examples, but
It is not limited to these. Such oxygen-containing organic compounds may be used alone or in combination of two or more as required. Further, the above-mentioned hydrocarbon and oxygen-containing organic compound may be used in combination.

The hydrocarbon or oxygen-containing organic compound used as the reducing agent varies depending on the specific hydrocarbon or oxygen-containing organic compound used, but it is usually 0.1 to 2 in molar ratio to nitrogen oxide. Used in a range of degrees. In the present invention, when the amount of the reducing agent used is less than 0.1 in terms of molar ratio with respect to nitrogen oxides, the catalyst cannot obtain sufficient reducing activity with respect to nitrogen oxides. Ratio is 2
When it exceeds, the amount of unreacted hydrocarbon or oxygen-containing organic compound is increased, so that after the catalytic reduction treatment of nitrogen oxides, a post-treatment for recovering this is required.

Unburned or incompletely burned products such as fuel existing in the exhaust gas, that is, hydrocarbons and patty chelates are also effective as reducing agents, and these are also included in the hydrocarbons of the present invention. . From this point of view, it can be said that the catalyst according to the present invention is also useful as a catalyst for reducing or removing hydrocarbons, patty chelates and the like in exhaust gas.

The temperature at which the reducing agent shows a selective reduction reaction with respect to nitrogen oxides increases in the order of oxygen-containing organic compound <alkyne <alkene <aromatic hydrocarbon <alkane.
Further, in the hydrocarbons of the same system, the temperature becomes lower as the carbon number becomes larger. The optimum temperature at which the catalyst according to the present invention exhibits reducing activity for nitrogen oxides varies depending on the reducing agent and the catalyst species used, but is usually 100-80.
It is 0 ° C. In this temperature range, the space velocity (S
V) It is preferable to circulate the exhaust gas at about 500 to 100,000. In the present invention, the particularly suitable temperature range is 2
It is 00-500 degreeC.

[0026]

The present invention will be described below with reference to examples.
The present invention is not limited to these examples. (1) Preparation of catalyst

Example 1 8.0 g of cerium nitrate (Ce (NO ₃ ) ₃ .6H ₂ O) was dissolved in 100 ml of deionized water. 120 ℃ in advance
60 g of H-type mordenite powder (HM-23 manufactured by Nippon Kagaku Co., Ltd.) that had been dried for 24 hours was charged, and 1/10 normal ammonia water was added dropwise while stirring and adjusting the pH with a pH controller set to pH 8. did. After completion of dropping, the mixture was aged for 1 hour to deposit and support cerium hydroxide on the H-type mordenite.

The slurry thus obtained was filtered to collect H-type mordenite powder carrying cerium hydroxide, which was thoroughly washed with ion-exchanged water and then
Baking for 3 hours at 00 ° C, loading 5% by weight of cerium oxide
The H-type mordenite powder supported by was obtained. This catalyst is called A-1.

Example 2 In the same manner as in Example 1 except that 37.8 g of cerium nitrate was used, the loading ratio of cerium oxide was 20.
An H-type mordenite powder supported by weight% was obtained. This catalyst is called A-2.

Example 3 In the same manner as in Example 1 except that 64.9 g of cerium nitrate was used, a cerium oxide loading rate of 30 was obtained.
An H-type mordenite powder supported by weight% was obtained. This catalyst is called A-3.

Example 4 In the same manner as in Example 1 except that 100.9 g of cerium nitrate was used, a cerium oxide loading rate of 4 was obtained.
An H-type mordenite powder supported at 0% by weight was obtained.
This catalyst is called A-4.

Example 5 In the same manner as in Example 1 except that 151.4 g of cerium nitrate was used, a cerium oxide loading rate of 5 was obtained.
An H-type mordenite powder supported at 0% by weight was obtained.
This catalyst is called A-5.

Example 6 In the same manner as in Example 1 except that 353.2 g of cerium nitrate was used, a cerium oxide loading rate of 7 was obtained.
An H-type mordenite powder supported at 0% by weight was obtained.
This catalyst is called A-5.

Example 7 Instead of the H-type mordenite in Example 3, HZ
H-ZSM-5 powder carrying cerium oxide at a loading rate of 30% by weight was prepared in the same manner as in Example 3 except that SM-5 (SiO ₂ / Al ₂ O ₃ molar ratio 40) powder was used. Obtained. This catalyst is called A-7.

Example 8 In the same manner as in Example 3 except that γ-alumina powder (A-11 manufactured by Sumitomo Chemical Co., Ltd.) was used in place of the H-type mordenite, the loading rate of cerium oxide was 30. weight%
To obtain γ-alumina powder. This catalyst is A
-8.

Example 9 (Preparation of H-Fe silicate) While stirring, a mixture of 162 g of 50% silica sol and 500 g of water was prepared by first adding 9.23 g of ferric nitrate (Si / Fe atomic ratio 60) to water 200.
An aqueous solution dissolved in g, then potassium hydroxide 22.
An aqueous solution prepared by dissolving 26 g in 200 g of water was dropwise added and mixed for about 30 minutes.

Tetrapropylammonium bromide 3
5.19 g was dissolved and mixed. This mixture was placed in an autoclave and mixed by stirring at 160 ° C. for 16 hours. The reaction product is separated by filtration, washed with water and dried, and further at 500 ° C. for 3 minutes.
By firing in air for a period of time, a ZSM-5 type Fe silicate (K exchanger) was obtained. 30 g of this Fe silicate was added to an aqueous solution of ammonium nitrate having a concentration of 0.5 mol / liter.
The mixture was added to 0 ml, stirred on an oil bath at 60 ° C. for 3 hours, and then separated by filtration. After repeating this operation 3 times, the filtered and separated product was washed with water, dried, and further calcined in air at 500 ° C. for 3 hours to obtain a proton-type Fe silicate (H—Fe silicate) powder.

(Preparation of catalyst) In the same manner as in Example 3 except that the H-Fe silicate powder was used in place of the H-type mordenite in Example 3, cerium oxide was carried at a loading rate of 30% by weight. A supported H-Fe silicate powder was obtained. This catalyst is called A-9.

Example 10 (Preparation of MAPO-5) Aluminum isopropoxide 56. finely crushed with stirring in a liquid prepared by dissolving 4.9 g of manganese acetate and 4.1 g of cupric acetate in 129 g of water. Three
g was added little by little and mixed with stirring until uniform.

To this solution, a mixture of 85% phosphoric acid (55.4 g), diethylethanolamine (56.3 g) and water (55.5 g) was added little by little with stirring, and the mixture was stirred and mixed until uniform. This solution was charged into an autoclave and heated to 200 ° C.
After reacting for 25 hours, the product is separated by filtration, washed with water,
Dried. After this, calcination with air for 3 hours at 500 ° C
APO-5 powder was obtained. This MAPO-5 powder is A
l, P, Mn and Cu are 19.0 wt% and 19.0 respectively.
The composition had a composition containing 1% by weight, 2.8% by weight and 4.4% by weight.

(Preparation of catalyst) In the same manner as in Example 3, except that the above-mentioned MAPO-5 powder was used instead of the H-type mordenite, the cerium oxide loading rate was set to 3.
MAPO-5 powder supported at 0% by weight was obtained. This catalyst is called A-10.

Example 11 (Preparation of Zr-mordenite) 100 g of Na mordenite (NM-100P manufactured by Nippon Kagaku Co., Ltd.) was immersed in an aqueous zirconyl nitrate solution (100 g / 1 concentration aqueous solution as ZrO ₂ ) and stirred at 70 ° C. Hold for 1 hour and add Na to Zr
I was exchanged with. The zeolite cake obtained by filtration and washing with water was dried and then calcined at 650 ° C. for 4 hours. The Zr content of this zeolite (Zr-mordenite) is 3.3.
The specific surface area was 391 m ² / g.

(Preparation of catalyst) In the same manner as in Example 3 except that the above Zr-mordenite powder was used instead of the H-type mordenite, cerium oxide was loaded at a loading rate of 30% by weight. The Zr-mordenite powder thus obtained was obtained. This catalyst is called A-11.

Example 12 (Preparation of Silica-Zirconia) 100.0 g of silica sol O type (manufactured by Nissan Kagaku Co., 20 wt% concentration as SiO ₂ ) and 97.20 g of zirconium chloride (ZrCl ₄ ) were sufficiently stirred. Mixed and made up to 500 ml with water. A 121 g / 1 concentration aqueous sodium hydroxide solution was added dropwise to this solution to adjust the pH to 10. After completion of the precipitation reaction, stirring was continued for 18 hours, and then filtration, washing with water and repulping were repeated,
A filter cake was obtained. The filter cake was dried at 120 ° C. for 18 hours and calcined for 3 hours. The specific surface area of the obtained silica-zirconia was 297 m ² / g.

(Preparation of catalyst) In the same manner as in Example 3 except that the silica-zirconia powder was used instead of the H-type mordenite in Example 3, cerium oxide was loaded at a loading rate of 30% by weight. The allowed silica-zirconia powder was obtained. This catalyst is called A-12.

Example 13 (Preparation of La-mordenite) 100 g of H-type mordenite (HM-23 manufactured by Nippon Kagaku Co., Ltd.) was put into 250 ml of ion-exchanged water, and (1 + 5) hydrochloric acid was added thereto to adjust the pH to 6.0. And Under sufficient stirring, to a slurry of the H-type mordenite, lanthanum nitrate _{(La (NO 3) 3 ·} 6H 2 O) 3.
A lanthanum ion (La ³⁺ ) aqueous solution prepared by dissolving 12 g of the ion-exchanged water in 50 ml was added for lanthanum ion exchange. During this period, as the pH decreased, 2% by weight of aqueous ammonia was added to maintain the pH at 6.0. In this way, a predetermined amount of the lanthanum ion aqueous solution was added to the H-type mordenite slurry, and stirring was continued for 2 hours.

Thereafter, the solid content was filtered from the obtained slurry to obtain a lanthanum ion-exchanged mordenite powder having a lanthanum ion carrying rate of 1% by weight.

(Preparation of catalyst) In the same manner as in Example 3 except that the lanthanum ion-exchanged mordenite powder was used in place of the H-type mordenite, the cerium oxide was carried at a loading of 30% by weight. A supported lanthanum ion-exchanged mordenite powder was obtained. This catalyst is A-13
Say.

Example 14 (Preparation of SAPO-34) 90.7 g of finely crushed aluminum isopropoxide was added little by little to 129.6 g of water with stirring, and the mixture was stirred and mixed until uniform. To this mixed solution, 51.3 g of an 85% phosphoric acid aqueous solution was added dropwise, and the mixture was stirred and mixed until it became uniform. Then, 16.0 g of 50% silica sol was further added, and the mixture was sufficiently stirred and mixed until it became uniform.

Next, 81.6 g of tetraethylammonium hydroxide was added, and the mixture was sufficiently stirred and mixed. This mixture was charged into an autoclave and reacted at 200 ° C. for 24 hours, then the product was separated by filtration, further washed with water and dried, and then 50
It was baked in air at 0 ° C. for 3 hours to obtain SAPO-34. The SAPO-34 contained 9.5% by weight, 18.0% by weight and 19.0% by weight of Si, Al and P, respectively.

(Preparation of catalyst) In the same manner as in Example 3, except that the above SAPO-34 powder was used in place of the H-type mordenite, cerium oxide was loaded at a loading rate of 30% by weight. The resulting SAPO-34 powder was obtained.
This catalyst is called A-14.

Example 15 The procedure of Example 1 was repeated except that 3.0 g of cerium nitrate was used.
In the same manner as in Example 1, an H-type mordenite powder supporting cerium oxide at a supporting rate of 20% by weight was obtained. This catalyst is called A-15.

Example 16 In the same manner as in Example 1 except that 605.5 g of cerium nitrate was dissolved in 300 ml of ion-exchanged water, H prepared by loading cerium oxide at a loading rate of 80% by weight was used.
A type mordenite powder was obtained. This catalyst is called A-16.

Example 17 (Preparation of Ce-mordenite) 100 g of H-type mordenite (HM-23 manufactured by Nippon Kagaku Co., Ltd.) was put into 250 ml of ion-exchanged water, and (1 + 5) hydrochloric acid was added thereto to adjust the pH to 6.0. And Under sufficient stirring, to a slurry of the H-type mordenite, cerium nitrate _{(Ce (NO 3) 3 ·} 6H 2 O) 3.
A cerium ion (Ce ³⁺ ) aqueous solution prepared by dissolving 1 g of the ion-exchanged water in 50 ml was added to carry out cerium ion exchange. During this period, as the pH decreased, 2% by weight of aqueous ammonia was added to maintain the pH at 6.0. In this way, a predetermined amount of the cerium ion aqueous solution was added to the H-type mordenite slurry, and stirring was continued for 2 hours.

After that, the solid content was filtered from the obtained slurry to obtain a cerium ion-exchanged mordenite powder having a cerium ion supporting rate of 1% by weight.

(Preparation of catalyst) In the same manner as in Example 3 except that the above cerium ion-exchanged mordenite powder was used in place of the H-type mordenite, the cerium oxide was carried at a loading rate of 30% by weight. A supported cerium ion exchange mordenite powder was obtained. This catalyst is A-17
Say.

[0057] Comparative Example 1 cerium nitrate _{(Ce (NO 3) 3 ·} 6H 2 O) 151.4g
Was dissolved in 200 ml of deionized water. In this aqueous solution,
While stirring and adjusting the pH with a pH controller set to pH 8, 1/10 normal ammonia water was added dropwise, and after completion of the addition, aging was carried out for 1 hour to produce cerium hydroxide.

The slurry thus obtained was filtered to collect cerium hydroxide, which was thoroughly washed with ion-exchanged water and then calcined at 500 ° C. for 3 hours to give a specific surface area of 47 m ² A cerium oxide powder having a / g was obtained. This catalyst is called B-1.

Comparative Example 2 H-type mordenite (HM-23 manufactured by Nippon Kagaku) itself was used as a catalyst B-2.

(2) Preparation of catalyst structure 60 ml of silica sol was added to 60 g of each of the catalyst powders of Examples 1 to 17 and the catalyst powders of Comparative Examples B-1 and B-2, and the mixture was pulverized and mixed in a planetary mill for 30 minutes. The viscosity was adjusted with ion-exchanged water to give a slurry for washcoat.
This slurry was applied to a cordierite honeycomb having a pitch of 1.25 mm at a rate of 0.9 to 1.0 g per 1 ml of the honeycomb and dried to manufacture a honeycomb catalyst structure.

(3) Evaluation Test Using the above-mentioned catalysts (A-1 to 17) according to the present invention and the catalysts (B-1 and 2) of the comparative examples, a honeycomb catalyst structure was carried out under the following test conditions. Then, the nitrogen oxide-containing gas was subjected to nitrogen oxide catalytic reduction, and the nitrogen oxide removal rate was determined by the chemiluminescence method. (Test conditions) (1) Gas composition NO 500 ppm O ₂ 10% by volume Reducing agent 500 ppm Water 6% by volume Nitrogen balance (2) Space velocity 10,000, 20000 or 30
000 (Hr ^-1 ) (3) Reaction temperature 250 ° C, 300 ° C, 350 ° C,
The results at 400 ° C. or 450 ° C. are shown in Tables 1 and 2.

[0062]

[Table 1]

[0063]

[Table 2]

As is clear from the results shown in Table 1, all the catalysts according to the present invention have a high removal rate of nitrogen in the nitrogen oxides, whereas the catalysts according to the comparative examples generally have a low removal rate.

[0065]

INDUSTRIAL APPLICABILITY As described above, the catalyst for catalytic reduction of nitrogen oxides according to the present invention uses a hydrocarbon or an oxygen-containing organic compound as a reducing agent, and even in the presence of oxygen and water,
The nitrogen oxides in the exhaust gas can be efficiently catalytically reduced, and the durability is also excellent.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiromitsu Shimizu 5-1, Ebisu-cho, Sakai City, Osaka Prefecture Central Research Institute, Sakai Chemical Industry Co., Ltd. (72) Ritsu Yasukawa 5-1-1, Ebisu-cho, Sakai City, Osaka Prefecture Central Research Laboratory, Sakai Chemical Industry Co., Ltd. (72) Inventor Katsumi Miyamoto 1-11-7 Washimiya, Washimiya Town, Kitakatsushika-gun, Saitama Prefecture

Claims (2)

[Claims] 1. A catalyst for catalytic reduction of nitrogen oxides using a hydrocarbon or an oxygen-containing organic compound as a reducing agent, which is obtained by supporting cerium oxide on a solid acid carrier. 2. The catalyst for catalytic reduction of nitrogen oxides according to claim 1, which contains cerium oxide in the range of 5 to 80% by weight.