JPH09201533A - Catalyst for nitrogen oxide catalytic reduction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce nitrogen oxides in exhaust gas efficiently without using a large amount of a reducing agent by making a solid acid carrier support silver aluminate as a catalyst for the catalytic reduction of nitrogen oxides using a hydrocarbon, etc., as the reducing agent. SOLUTION: In a catalyst for the catalytic reduction of nitrogen oxides using a hydrocarbon and/or an organic compound containing oxygen as a reducing agent, 0.01-10wt.% of silver aluminate is supported on a solid carrier such as alumina. In the use of the catalyst, since nitrogen oxides react selectively with the reducing agent even in the presence of oxygen especially in the presence of oxygen, sulfur oxides, and water, nitrogen oxides in exhaust gas are reduced efficiently without using a large amount of a reducing agent. Furthermore, the catalyst has good durability even when used in the presence of water of at high temperatures.

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 which uses a hydrocarbon or an oxygen-containing organic compound as a reducing agent. 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 are obtained by oxidizing the nitrogen oxides and then absorbing them into an alkali, or by using a reducing agent such as ammonia, hydrogen, carbon monoxide, or a hydrocarbon. It has been removed by a method of converting to nitrogen. However, according to the former method, it is necessary to take measures for treating the generated alkaline waste liquid to prevent the occurrence of 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 reduction activity of the catalyst is reduced. In addition, even when hydrogen, carbon monoxide, hydrocarbons, and the like are used as a reducing agent, since they react with oxygen present at a higher concentration than nitrogen oxide present at a lower concentration, it is necessary to reduce nitrogen oxides. Has the problem that a large amount of reducing agent is required.

[0003] For this reason, recently, a method of directly decomposing nitrogen oxides with a catalyst in the absence of a reducing agent has been proposed.
There is a problem that it is difficult to be put to practical use due to low nitrogen oxide decomposition activity.

As a new catalyst for catalytic reduction of nitrogen oxides using a hydrocarbon or an oxygen-containing compound as a reducing agent, various zeolites have been proposed.
M-5 and H-type _{ZSM-5 (SiO 2 / Al} 2 O 3 molar ratio = 30 to 40) are to be optimal. However, it is difficult to say that even such Cu-ZSM-5 or H-type ZSM-5 still has sufficient reducing activity. Particularly, when the gas contains water, aluminum in the zeolite structure is removed. Since the performance of aluminum is drastically reduced, there is a demand for a catalyst for catalytic reduction of nitrogen oxides, which has higher reduction activity and further has excellent durability even when the gas contains water. .

Therefore, a catalyst in which silver or silver oxide is supported on an inorganic oxide has been proposed, but such a catalyst has a high oxidation activity and a low selective reactivity to nitrogen oxides. The removal rate of nitrogen oxides is low. Further, there is a problem that the catalytic activity is significantly deteriorated in the presence of sulfur oxides (Japanese Patent Laid-Open No. 5-317647). Furthermore, the conventional catalyst for catalytic reduction of nitrogen oxides does not have sufficient heat resistance,
Depending on the application, even higher heat resistance is strongly desired.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has as its object to use hydrocarbons and oxygen-containing organic compounds as reducing agents. Even in the coexistence of oxygen, and in particular, in the coexistence of oxygen, sulfur oxides and moisture, the nitrogen oxides selectively react with the reducing agent. An object of the present invention is to provide a catalyst for catalytic reduction of nitrogen oxides which can efficiently reduce nitrogen oxides and has excellent durability even in the presence of moisture and at high temperatures.

[0007]

A catalyst for catalytic reduction of nitrogen oxides using a hydrocarbon and / or an oxygen-containing organic compound as a reducing agent according to the present invention is characterized in that a solid acid carrier carries silver aluminate. And

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The solid acid carrier according to the present invention is
It refers to a carrier that exhibits solid acidity in the temperature range in which the catalyst is used. Solid acidity can be confirmed by thermal desorption method using ammonia, or in situ F using ammonia or pyridine.
It is performed by the TIR (Fourier transform infrared absorption spectrum) method. Examples of such a solid acid carrier that can be preferably used in the present invention include the following oxide solid acid carriers and zeolite solid acid carriers.

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.

[0010] The zeolite-based solid acid carrier includes Na-mordenite, Na-ZSM-5, Na-USY (USY: ultrastable or ultra-stable Y-type zeolite), and a part or all of aluminum in zeolite as another metal element. ,
In particular, metallosilicates substituted with iron, gallium, zinc, lanthanum, copper, molybdenum, chromium, germanium, titanium, boron and the like, zeolite having excellent heat resistance are treated with an aqueous solution of ammonium salt such as ammonium sulfate or an acid such as sulfuric acid. After treatment, a part or all of the alkali metal in the zeolite can be obtained by ion exchange with ammonium ions or hydrogen ions. 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:

[0012]

Embedded image

An acid-type mordenite obtained by acid-treating a mordenite-type zeolite represented by:
_{A 2} / Al ₂ O ₃ molar ratio of 13 to 20, 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.

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

[0015]

Embedded image

Of the ions M'in the zeolite represented by
Part or all of the lanthanum ion (La ³⁺), Gallium y
On (Ga³⁺), Cerium ion (Ce⁴⁺), Titanium
ON (Ti⁴⁺), Zirconium ion (Zr⁴⁺), Tin
Ion (Sn⁴⁺) Etc. to obtain the zeolite
Can be mentioned. However, in the above formula, M'is alkali gold
Group ions, alkaline earth metal ions or hydrogen ions
, NA = p (n is the valence of the ion M), q / p.
≧ 5.

Other examples of the solid acid carrier include a kind of crystalline aluminum phosphate (ALPO) having a porous structure or a layered structure similar to zeolite, 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 or 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 in an acidic region at a higher temperature (approximately 150 ° C. or higher).

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
Is represented by Further, in the case of SAPO or MAPO, the maximum amount of silica and metal to be substituted 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 the ALPO-type phosphate obtained by the hydrothermal synthesis method is used as a carrier, generally, the one obtained by washing with water, drying, and then calcination in air to remove the remaining template by incineration is used.

In the present invention, among the various solid acid carriers described above, the obtained catalyst has high durability even in the coexistence of water and in a high temperature environment, and at the same time, the silver aluminate Alumina, which has an excellent supporting effect, is particularly preferably used. In particular, among alumina, as described in JP-A-7-171347, the content of alkali metal and alkaline earth metal is 0.
5% by weight or less, the volume of pores formed from pores having a diameter of 60 Å or less is 0.06 cm ³ / g or more, and a diameter of 8
Alumina having a pore volume of 0.1 cm ³ / g or more formed from pores of 0 Å or less is particularly preferably used. Porous alumina having such a pore volume promotes appropriate oxidation of the reducing agent and cooperates with silver aluminate carried thereon to effectively catalytically reduce nitrogen oxides. it can.

The catalyst according to the present invention can be prepared, for example, according to any of the following methods (1) to (4). (1) A water-soluble silver salt such as silver nitrate is charged into a chiller in which a solid acid is dispersed, and the pH of the slurry is maintained at around 8.0 where no silver hydroxide is generated, so that the ion exchange site of the solid acid is Fix silver ions. Here, when alumina is used as the solid acid, the solid acid in which silver ions are fixed in this way is converted into an aqueous solution containing sufficient chloride ions to fix the silver ions, for example, an aqueous hydrochloric acid solution. After immersion to generate silver chloride, excess chloride ions are removed by washing with water or the like to prepare a solid acid catalyst supporting silver chloride. Then, this is placed in an oxidizing atmosphere such as air, preferably in the presence of water vapor, at about 600 to 800 ° C., preferably 700 to 80 ° C.
If silver aluminate is produced by heating and baking at a temperature of about 0 ° C., a powdery solid acid catalyst supporting silver aluminate can be obtained.

(2) For example, a water-soluble salt which is a precursor of a solid acid such as aluminum nitrate and a water-soluble silver salt such as silver nitrate are homogeneously mixed to prepare an aqueous solution. A precipitate is formed by a method such as neutralization in the presence, and then the precipitate is repeatedly filtered, washed with water, and repulped, dried, and calcined to produce a solid acid, and at the same time, chlorided. Silver is supported on the solid acid. Then, in the same manner as described above, in an oxidizing atmosphere, preferably in the presence of steam, 600 to 800
If silver aluminate is generated by heating and baking at a temperature of about 700C, preferably about 700 to 800C, a powdery solid acid catalyst carrying silver aluminate can be obtained.

(3) Hydrated alumina was immersed in an aqueous solution of a water-soluble aluminum salt such as aluminum nitrate and a water-soluble silver salt such as silver nitrate to impregnate the pores of the alumina with the above-mentioned aluminum salt and silver salt. After that, it is dried by a suitable means such as a spray dryer, and thereafter, as described above,
In an oxidizing atmosphere, preferably in the presence of steam, 600
When silver aluminate is generated by heating and baking at a temperature of about 800 ° C., preferably about 700 ° C. to 800 ° C., a powdery solid acid catalyst supporting silver aluminate can be obtained. it can.

(4) Furthermore, as another method, an alkali metal aluminate such as sodium aluminate and its 1
By mixing and drying an aqueous solution of silver nitrate equivalent to ４4 times equivalent by spray drying and drying, and eutecticizing the obtained granules at a temperature of 300 to 800 ° C. in the absence of moisture, silver aluminate is obtained. The resulting product is washed with water to remove excess silver nitrate and sodium nitrate, whereby a highly purified product can be obtained. This silver aluminate and a solid acid such as alumina are uniformly mixed and pulverized by a wet method using a ball mill or the like, and then dried, whereby alumina supporting silver aluminate can be obtained as a powdery catalyst.

In the catalyst according to the present invention, the supported amount of silver aluminate is preferably in the range of 0.01 to 10% by weight in terms of silver weight based on the total weight of the solid acid carrier and silver aluminate. When the supported amount of silver aluminate exceeds 10% by weight in terms of silver weight, the oxidizing power of the obtained catalyst is too high and the selectivity is poor, and the supported amount is 0 in terms of silver weight.
If it is less than 01% by weight, the catalytic activity is insufficient. Particularly, in the present invention, the supported amount of silver aluminate is preferably in the range of 0.1 to 5% by weight in terms of silver weight. When the amount of silver aluminate supported on the solid acid carrier is within this range, S of the catalytic reduction reaction of nitrogen oxides
It is possible to obtain an excellent characteristic that V (space velocity) dependence is extremely small.

According to the present invention, a catalyst in which silver aluminate is supported on a solid acid carrier in the above-mentioned supported amount is
Compared to solid oxide catalysts on which silver oxide or silver is supported, it has an appropriate oxidizing power, and the reason is not completely clear,
Since partial oxidation or cracking of hydrocarbon is promoted, it is considered to have extremely high activity and selectivity in the catalytic reduction reaction of nitrogen oxide using hydrocarbon as a reducing agent. Similarly, when an oxygen-containing organic compound is used as a reducing agent, it has extremely high activity and selectivity.
Moreover, the catalyst according to the present invention has excellent heat resistance, and
Since it has excellent resistance to sulfur oxides, it can be suitably used as, for example, a denitration catalyst for exhaust gas from a diesel engine or a catalyst for lean-burn gasoline vehicles.

Since the catalyst according to the present invention can be generally obtained as a powder or granules, it can be molded into various shapes such as honeycomb and sphere by itself by a conventionally known molding method. You can During this molding,
A molding aid, a molded body reinforcing material, an inorganic fiber, an organic binder and the like may be appropriately mixed. Of course, if necessary, any other known method for preparing a catalyst may be used.

In particular, the catalyst according to the present invention is wash-coated with a powdery catalyst obtained by forming an inert base material into a desired shape in advance and supporting silver aluminate on the solid acid carrier as described above. The catalyst structure can be advantageously used as a catalyst structure which is coated and supported by an appropriate method such as a method. As the inert substrate, for example, a mineral substance such as cordierite is used, and this is used as a structure such as a honeycomb, a sphere, a ring, or the like, and a catalyst is supported on these. It is advantageous to do so.

According to the present invention, as described above, a catalyst layer is formed on the surface of a structure such as a honeycomb or a spherical material or an annular material made of an inert base material by a wash coat method or the like, When the catalyst is supported, it is preferable to support the catalyst on the surface of the structure so that the catalyst layer has a thickness of 30 μm or more from the surface (hereinafter, referred to as catalyst layer thickness for simplicity). By making the thickness of the catalyst layer supported on the structure 30 μm or more from the surface in this way, the reactivity with respect to nitrogen oxides,
That is, it is possible to obtain a catalyst structure having high selectivity for reducing nitrogen oxides. However, according to the present invention, the thickness of the catalyst layer may usually be 300 μm or less. This is because even if the thickness of the catalyst layer exceeds 300 μm, it is not possible to obtain a corresponding improvement in the selective reduction property, which is not preferable from the viewpoint of the cost of catalyst production.

A catalyst structure such as a honeycomb or a sphere formed of the catalyst itself by supporting silver aluminate on a solid acid carrier can be obtained as follows, for example. That is, after γ-alumina, an aqueous solution of a water-soluble silver salt, and an appropriate organic binder are kneaded, a honeycomb structure is formed, dried, and then baked to support silver (and / or silver oxide) γ -Preparing a honeycomb structure made of alumina, treating it with hydrochloric acid to form a honeycomb made of γ-alumina supporting silver chloride, and then heating and firing this in an air atmosphere, silver aluminate is obtained. A honeycomb catalyst structure composed of γ-alumina itself supported can be obtained.

As described above, a powdery catalyst prepared by previously supporting silver aluminate on γ-alumina is prepared,
This may be formed into a honeycomb structure using an appropriate organic binder.

According to such a honeycomb catalyst structure,
The thickness of the catalyst layer formed by supporting silver aluminate on γ-alumina is substantially uniform in the thickness direction of the cell walls of the honeycomb structure. Therefore, the cell wall of the honeycomb structure is 60μ
If it is m or more, the catalyst is supported over the thickness of 30 μm or more from the surface of the cell wall. This is because the cell wall is brought into contact with exhaust gas on both surfaces thereof.

In the catalytic reduction of nitrogen oxides using the catalyst according to the present invention, examples of the reducing agent composed of hydrocarbon include gaseous compounds such as methane, ethane, propane, propylene, butylene, etc., and liquids. 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. In particular, according to the present invention, among the above, lower alkenes such as ethylene, propylene, isobutylene, 1-butene and 2-butene, lower alkanes such as propane and butane, and light oil are preferably used as the reducing agent. These hydrocarbons may be used alone or in combination of two or more as needed.

Examples of the reducing agent comprising 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 and ethyl acetate. Examples thereof include esters such as fats and oils, and ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone. These oxygen-containing organic compounds may also be used alone,
Or you may use together 2 or more types as needed. Furthermore, in the present invention, a mixture of the hydrocarbon and the oxygen-containing organic compound may be used as a reducing agent.

In the present invention, the reducing agent varies depending on the specific hydrocarbon or oxygen-containing organic compound used, but is usually in the range of about 0.1 to 2 in molar ratio to nitrogen oxide. Used. When the amount of the reducing agent used is less than 0.1 in terms of molar ratio with respect to nitrogen oxides, sufficient reducing activity cannot be obtained for nitrogen oxides.
When the molar ratio exceeds 2, the amount of unreacted reducing agent discharged increases, so that after the catalytic reduction treatment of nitrogen oxides, a post-treatment for recovering the nitrogen oxides is required.

Unburned or incomplete combustion products such as fuel present in the exhaust gas, that is, hydrocarbons and particulates are also effective as reducing agents, and these are also included in the hydrocarbons of the present invention. It is. 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 and particulates in exhaust gas.

Of the above reducing agents, the temperatures at which hydrocarbons selectively reduce nitrogen oxides increase in the order of alkyne <alkene <aromatic hydrocarbon <alkane. Further, in the same type of hydrocarbon, 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 with respect to nitrogen oxides varies depending on the reducing agent and catalyst species used, but is usually 100 to 800 ° C. In this temperature range, space velocity (SV) 500 to 1000
It is preferable that the exhaust gas is circulated at about 00. In the present invention, a particularly suitable temperature range is 200 to 500 ° C.

[0039]

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 4.75 g of silver nitrate (AgNO ₃ ) was added to 100 m of ion-exchanged water.
l. Γ-alumina (KC-50 manufactured by Sumitomo Chemical Co., Ltd.) previously dried at 120 ° C. for 24 hours
1) Charge 60 g of powder, and set the pH to 8 under stirring.
While adjusting the pH with an H controller, 1/10 normal ammonia water was added dropwise. After completion of dropping, the mixture was aged for 1 hour, and silver ions were supported on the γ-alumina by ion exchange.

The slurry thus obtained was filtered to collect γ-alumina powder carrying silver ions, which was thoroughly washed with ion-exchanged water, and then the hydrochloric acid aqueous solution 1
After stirring for 10 minutes, the slurry was filtered, sufficiently washed with ion-exchanged water, and γ-alumina powder loaded with 5% by weight of silver chloride in terms of silver weight. I got

Next, the silver chloride-supported γ-alumina powder was heated and calcined at 800 ° C. for 3 hours in an air atmosphere containing 10% by weight of water to carry 5% by weight of silver aluminate in terms of silver weight. % To obtain a γ-alumina powder catalyst. In this way, γ supporting silver aluminate
FIG. 1 shows an X-ray diffraction pattern of -alumina, and FIG. 2 shows an X-ray diffraction pattern of only γ-alumina. In FIG. 1, ◯ indicates a peak due to silver aluminate, x indicates a peak due to γ-alumina, and Δ indicates a peak due to silver.

60 g of this γ-alumina powder catalyst and 6 g of silica sol (Snowtex N, manufactured by Nissan Kagaku Co., Ltd.) were mixed with an appropriate amount of water, and this was wet-ground for 5 minutes with a planetary mill using 100 g of zirconia balls as a grinding medium, Wash ·
A slurry for coating was prepared. This slurry was used for 2 cells.
The catalyst was applied to a honeycomb substrate made of cordierite No. 00 and supported at a rate of about 150 g / l (catalyst layer thickness 78 μm). This catalyst is called A-1.

Example 2 In the same manner as in Example 1 except that 2.85 g of silver nitrate was used, silver aluminate was supported at a supported amount of 3% by weight in terms of silver weight. -Alumina powder catalyst is obtained. In the same manner as in Example 1, the γ-alumina powder catalyst was applied to a honeycomb substrate made of cordierite at about 150.
It was supported at a rate of g / l (catalyst layer thickness 85 μm). This catalyst is referred to as A-2.

Example 3 In the same manner as in Example 1 except that 0.95 g of silver nitrate was used, the amount of silver aluminate supported was 1% by weight in terms of silver weight. -Alumina powder catalyst is obtained. In the same manner as in Example 1, the γ-alumina powder catalyst was applied to a honeycomb substrate made of cordierite at about 150.
It was supported at a rate of g / l (catalyst layer thickness 88 μm). This catalyst is referred to as A-3.

[0046] Example 4 aluminum nitrate _{(Al (NO 3) 3 ·} 9H 2 O) 8.6
9 g, 3.94 g of silver nitrate and 100 g of hydrated alumina (manufactured by Mizusawa Chemical Industry Co., Ltd.) were mixed with an appropriate amount of water to prepare a paste. This was kneaded and dried using a heating kneader, and then dried under an air atmosphere containing 10% by weight of water.
Heated and baked at 00 ° C for 3 hours.
An alumina powder catalyst carrying 5% by weight of silver aluminate was obtained. In the same manner as in Example 1, about 15 parts of this alumina powder catalyst was applied to a honeycomb substrate made of cordierite.
It was supported at a rate of 0 g / l (catalyst layer thickness 83 μm).
This catalyst is referred to as A-4.

Example 5 1 kg of the same γ-alumina as in Example 1, 79.2 g of silver nitrate,
Polyethylene oxide (Sumitomo Seika's PEO-1
0) 1 kg and a proper amount of water were sufficiently kneaded, and then extruded into a honeycomb structure having 200 cells by an auger screw type extruder. This honeycomb structure was dried by ventilation at room temperature, then heated and dried at 100 ° C. overnight, and further dried at 500 ° C.
Firing was performed for 3 hours at 0 ° C. to obtain a honeycomb structure (honeycomb wall thickness 205 μm) made of alumina supporting silver (and / or silver oxide).

Next, this honeycomb structure made of alumina supporting silver (and / or silver oxide) is put into an aqueous hydrochloric acid solution to chlorinate silver (and / or silver oxide), and in terms of silver weight. A honeycomb structure made of γ-alumina on which silver chloride was supported at a supported amount of 5% by weight was obtained. Next, this honeycomb structure was heated and fired at a temperature of 800 ° C. for 3 hours in an air atmosphere containing 10% by weight of water, and silver aluminate was supported at a supported amount of 5% by weight in terms of silver weight. A honeycomb catalyst structure (catalyst layer thickness 102 μm) made of alumina was obtained. This catalyst is designated as A-5.

[0049] Example 6 aluminum nitrate _{(Al (NO 3) 3 ·} 9H 2 O) 8.6
9 g, 3.94 g of silver nitrate and 100 g of hydrated alumina (manufactured by Mizusawa Chemical Industry Co., Ltd.) were mixed with an appropriate amount of water to prepare a paste. This was kneaded and dried using a heating kneader, and then dried under an air atmosphere containing 10% by weight of water.
Heated and baked at 00 ° C for 18 hours, and carried amount in terms of silver weight
An alumina powder catalyst supporting silver aluminate at 2.5% by weight was obtained.

In the same manner as in Example 1, this alumina powder catalyst was applied to a honeycomb substrate made of cordierite at about 150.
It was supported at a rate of g / l (catalyst layer thickness 71 μm). This catalyst is called A-6. The X-ray diffraction pattern of γ-alumina / cordierite supporting silver aluminate in this manner is shown in FIG. In FIG. 3, ○ indicates a peak due to silver aluminate, and X indicates a peak due to γ-alumina.

Example 7 1 kg of the same γ-alumina as in Example 1, 79.2 g of silver nitrate,
Polyethylene oxide (Sumitomo Seika's PEO-1
0) 1 kg and a proper amount of water were sufficiently kneaded, and then extruded into a honeycomb structure having 200 cells by an auger screw type extruder. This honeycomb structure was dried by ventilation at room temperature, then heated and dried at 100 ° C. overnight, and further dried at 500 ° C.
The honeycomb structure was fired at 3 ° C. for 3 hours to obtain a honeycomb structure (honeycomb wall thickness 200 μm) made of alumina supporting silver (and / or silver oxide).

Next, this honeycomb structure was heated and fired at a temperature of 600 ° C. for 18 hours in an air atmosphere containing 10% by weight of water to carry a supported amount of silver aluminate of 5% by weight in terms of silver weight. A honeycomb catalyst structure (catalyst layer thickness 100 μm) made of alumina was obtained. This catalyst is
7

Example 8 The supported amount of silver aluminate obtained in Example 1 was 5 in terms of silver weight.
Using a γ-alumina powder catalyst supported by weight%, a catalyst was applied to a honeycomb substrate made of cordierite by a wash-coat method in the same manner as in Example 1 to give a catalyst of about 100 g / l ( The catalyst layer was supported at a ratio of 52 μm). This catalyst is designated as A-8.

Example 9 The supported amount of silver aluminate obtained in Example 1 was 5 in terms of silver weight.
Using a γ-alumina powder catalyst supported by weight%, a catalyst was applied to a honeycomb substrate made of cordierite by a wash-coat method in the same manner as in Example 1 to give about 70 g / l of catalyst ( The catalyst layer was supported at a ratio of 36 μm). This catalyst is called A-9.

Comparative Example 1 In the same manner as in Example 1, a γ-alumina powder catalyst was obtained in which silver ions were loaded at a loading amount of 5% by weight. Example 1
This alumina powder catalyst was added to a honeycomb substrate made of cordierite in an amount of about 150 g / l (catalyst layer thickness 7
8 μm). This catalyst is called B-1.

Comparative Example 2 A honeycomb catalyst structure made of γ-alumina having a supported amount of silver (and / or silver oxide) of 5% by weight prepared in Example 5 (honeycomb wall thickness 205 μm, catalyst layer thickness 102 μm)
Let m-2 be B-2.

Comparative Example 3 The amount of silver aluminate obtained in Example 1 was 5 in terms of silver weight.
Using a γ-alumina powder catalyst supported by weight%, a catalyst was applied to a honeycomb substrate made of cordierite by a wash coating method in the same manner as in Example 1 to give a catalyst of about 50 g / l ( The catalyst layer was supported at a thickness of 26 μm). This catalyst is called B-3.

(2) Evaluation test Using the catalysts (A-1 to 9) according to the present invention and the catalysts (B-1 to 3) of the comparative examples, the nitrogen oxide-containing gas was tested under the following test conditions. Nitrogen oxide catalytic reduction was performed, and the nitrogen oxide removal rate was determined by the chemical luminescence method.

(Test Conditions) (1) Gas Composition NO 500 ppm O ₂ 10% by volume Reducing agent 500 ppm Water 6% by volume Nitrogen balance (However, when light oil was used as the reducing agent, the light oil was C12 in terms of C) (2) Space velocity 25000 (Hr ^-1 ) (3) Reaction temperature 250 ° C, 300 ° C, 350 ° C, 400 ° C, 450 ° C or 500 ° C The results are shown in Table 1.

[0060]

[Table 1]

Next, by using the catalysts prepared in Example 5 and Comparative Example 2, NO 500 ppm O _2, 10 vol% propylene 500 ppm SO ₂ 200 ppm water, 6 vol% nitrogen oxidation of a nitrogen oxide-containing gas consisting of the balance of nitrogen. After the catalytic catalytic reduction at a temperature of 700 ° C. and a space velocity of 25000 (Hr ⁻¹ ) for 500 hours, the catalytic catalytic reduction of the nitrogen oxide-containing gas is performed under the conditions (2) and (3) above. The heat resistance and sulfur oxide resistance of the catalyst were evaluated. Table 2 shows the results.

[0062]

[Table 2]

As is clear from the results shown in Tables 1 and 2, all the catalysts according to the present invention have a high nitrogen oxide removal rate, whereas the catalysts according to the comparative examples generally have a low removal rate. Moreover, the catalyst according to the present invention has excellent heat resistance and sulfur oxide resistance.

[0064]

INDUSTRIAL APPLICABILITY As described above, the catalyst for catalytic reduction of nitrogen oxides according to the present invention uses a hydrocarbon and / or an oxygen-containing organic compound as a reducing agent to reduce the amount of exhaust gas in exhaust gas even in the presence of oxygen and water. Nitrogen oxides can be efficiently catalytically reduced, and further, they have excellent durability and sulfur oxide resistance even in the presence of water and at high temperatures.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction pattern of γ-alumina supporting silver aluminate prepared in Example 1.

FIG. 2 is an X-ray diffraction diagram of γ-alumina.

FIG. 3 is an X-ray diffraction diagram of γ-alumina / cordierite supporting silver aluminate prepared in Example 6.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Keiichi Tabata 5-1-1 Ebisushimacho, Sakai City, Osaka Sakai Chemical Industry Co., Ltd.

Claims (5)

[Claims] 1. A catalyst for catalytic reduction of nitrogen oxides using a hydrocarbon and / or an oxygen-containing organic compound as a reducing agent, which is obtained by supporting silver aluminate on a solid acid carrier. 2. The catalyst for catalytic reduction of nitrogen oxides according to claim 1, wherein the supported amount of silver aluminate is in the range of 0.01 to 10% by weight. 3. The catalyst for catalytic reduction of nitrogen oxides according to claim 1, wherein the solid acid carrier is alumina. 4. A catalyst structure for catalytic reduction of nitrogen oxides, comprising the structure according to claim 1, wherein the catalyst is 30 μm from the surface of the structure.
A catalyst structure for catalytic reduction of nitrogen oxides supported over the above thickness. 5. The catalyst structure for catalytic reduction of nitrogen oxides according to claim 4, wherein the structure is a honeycomb or a spherical material.