JPH10244155A - Catalyst for catalytic reduction of nox - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain efficient catalytic reduction of NOx in exhaust gas by using a catalyst for catalytic reduction of NOx using hydrocarbon and/or an oxygen-contg. org. compd. as a reducing agent obtd. by carrying Ag-Zr multiple oxide on a solid acid carrier. SOLUTION: An aq. soln. contg. a water-soluble compd. of Zr and a water-soluble compd. of Ag is prepd. and impregnated into a solid acid carrier which is a single metal oxide such as Al2 O3 , TiO2 , TiO2 /SO4 <-2> , ZrO2 or ZrO2 /SO4 <-2> or a multiple oxide such as SiO2 -Al2 O3 , TiO2 -Al2 O3 or TiO2 -ZrO2 , e.g. alumina. After drying, the carrier is fired by heating at 600-900 deg.C in an oxidizing atmosphere contg. steam to form Ag-Zr multiple oxide on the alumina and the objective catalyst for catalytic reduction of NOx using hydrocarbon and/or an oxygen-contg. org. compd. as a reducing agent is obtd.

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 particularly, to harmful substances 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 nitrogen oxides. Further, the present invention relates to a method for producing such a catalyst for catalytic reduction of 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. Also, hydrogen, carbon monoxide,
Even when hydrocarbons or the like are used as reducing agents, a large amount of reducing agents is required to reduce nitrogen oxides because these react with oxygen present at a higher concentration than nitrogen oxides present at a lower concentration. There is a problem of doing.

[0004] For this reason, recently, a method of directly decomposing nitrogen oxides with a catalyst in the absence of a reducing agent has been proposed. However, such a conventionally known catalyst 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 or H-type (acid type) ZSM-5 (SiO ₂ / Al ₂ O
₃ mol ratio = 30 to 40) is considered to be optimal. However, such Cu-ZSM-5 and H-type ZSM
Even in the case of -5, it is still difficult to say that it has a sufficient reducing activity. In particular, when moisture is contained in the gas, the aluminum in the zeolite structure is dealuminated and the performance is rapidly lowered, so that it is even higher. There is a need for a catalyst for catalytic reduction of nitrogen oxides that has reducing activity and has excellent durability even when the gas contains moisture.

Therefore, as described in Japanese Patent Application Laid-Open No. 5-317647, a catalyst comprising silver or silver oxide supported on an inorganic oxide has been proposed. And the selectivity to nitrogen oxides is low, so that the nitrogen oxide removal rate is low. Further, there is a problem that the catalyst activity is significantly deteriorated in the presence of sulfur oxide. Further, the conventional catalyst for catalytic reduction of nitrogen oxides does not have sufficient heat resistance, and depending on the application, further heat resistance is strongly demanded.

[0007]

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.

[0008]

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 comprises a solid acid carrier carrying a silver-zirconium composite oxide. It is characterized by.

[0009]

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

The oxide-based solid acid carrier includes Al
₂ O ₃ , TiO ₂ , TiO ₂ / SO ₄ ²⁻ , ZrO ₂ , Z
a single metal oxide such as rO ₂ / SO ₄ ^2- or SiO ₂ / A
l ₂ O ₃ , TiO ₂ / Al ₂ O ₃ , TiO ₂ / ZrO ₂
And the like. Among these, from the viewpoint of heat resistance, Al ₂ O ₃ , ZrO ₂ , SiO _2
2 / Al ₂ O ₃ is preferred, and in particular, Al ₂ O ₃ or Zr
O ₂ is preferred.

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, zeolites having excellent heat resistance, such as metallosilicates substituted with iron, gallium, zinc, lanthanum, copper, molybdenum, chromium, germanium, titanium, and boron, are treated with an aqueous solution of an ammonium salt such as ammonium sulfate or an acid such as sulfuric acid. It can be obtained by performing a treatment to ion-exchange part or all of the alkali metal in the zeolite with ammonium ions or hydrogen ions. In the case of the method of ion exchange with ammonium ions, a calcination treatment is required at last.

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 a crystalline aluminum phosphate (SAPO) which is a related substance thereof. ), ALPO
Crystalline aluminum phosphate (MAPO) in which a part of phosphorus or phosphorus-aluminum is replaced by a metal such as titanium, iron, magnesium, zinc, manganese, and cobalt.

In the present invention, among the various solid acid carriers described above, the resulting catalyst has high durability even in the coexistence of water and in a high-temperature environment, and has a silver-zirconium composite oxide. Alumina or zirconia, which has an excellent effect of supporting a substance, is particularly preferably used. Particularly, among aluminas, Japanese Patent Application Laid-Open No.
As described in JP-A No. 7, the content of alkali metal and alkaline earth metal is 0.5% by weight or less,
Alumina having a pore volume of 0.06 cm ³ / g or more formed from pores of 0 Å or less and a pore volume of 0.1 cm ³ / g or more formed of pores having a diameter of 80 Å or less is particularly preferable. Used. Porous alumina having such a pore volume promotes appropriate oxidation of the reducing agent and cooperates with the silver-zirconium composite oxide supported thereon to effectively catalytically reduce nitrogen oxides. be able to.

The catalyst according to the present invention can be prepared, for example, according to any of the following methods (1) to (4). (1) An aqueous solution containing a water-soluble compound of zirconium and a water-soluble compound of silver is prepared, and the aqueous solution is impregnated with a solid acid carrier, for example, alumina, preferably hydrated alumina, dried, and then dried. 60 under oxidizing atmosphere
Heating and sintering at a temperature in the range of 0 to 900C, preferably 700 to 800C, produces a silver-zirconium composite oxide on alumina.

In the above method, by using (hydrated) zirconia instead of (hydrated) alumina, a silver-zirconium composite oxide can be formed on alumina, on zirconia which is a solid acid carrier.

(2) An aqueous solution containing a water-soluble compound of zirconium and a water-soluble compound of silver is prepared, and this aqueous solution is neutralized in the presence of a solid acid carrier, preferably a powder thereof, and coprecipitated with a solid acid. After the product is produced and the obtained product is dried, the product is placed in an oxidizing atmosphere containing water vapor at 600 to 900
C., preferably at a temperature in the range of 700 to 800.degree. C. to form a silver-zirconium composite oxide on the solid acid. In this method, alumina or zirconia is preferably used as the solid acid carrier.

(3) An aqueous solution containing a water-soluble compound of zirconium, a water-soluble compound of silver, and a water-soluble aluminum compound is neutralized to form a coprecipitate, which is dried. Alumina is produced by heating and baking at a temperature in the range of 300 to 500 ° C., and a precursor of the silver-zirconium composite oxide is supported on the alumina, and then heated to 600 to 900 ° C. in an oxidizing atmosphere containing water vapor. ,
Preferably, it is heated and calcined at a temperature in the range of 700 to 800 ° C. to generate a silver-zirconium composite oxide.

According to the present invention, in such a method, as the water-soluble compound of zirconium, for example, zirconyl nitrate is preferably used, and as the water-soluble compound of silver, silver nitrate is preferably used. Aluminum nitrate is preferably used as the water-soluble aluminum compound. The oxidizing atmosphere may usually be air.

In the catalyst according to the present invention, the supported amount of the silver-zirconium composite oxide is 0.3% in terms of silver weight, based on the total weight of the solid acid carrier and the silver-zirconium composite oxide.
It is preferably in the range of 01 to 10% by weight. When the supported amount of the silver-zirconium composite oxide exceeds 10% by weight in terms of silver weight, the oxidizing power of the obtained catalyst is too high,
When the selectivity of the reaction is poor and the supported amount of the silver-zirconium composite oxide is less than 0.01% by weight in terms of silver weight,
Insufficient catalytic activity. In particular, in the present invention, the supported amount of the silver-zirconium composite oxide is 0.
It is preferably in the range of 1 to 5% by weight. When the loading amount of the silver-zirconium composite oxide is within this range, excellent characteristics that the SV (space velocity) dependence of the catalytic reduction reaction of nitrogen oxide is extremely small can be obtained.

Further, in the present invention, in the silver-zirconium composite oxide, the silver / zirconium atomic ratio is from 1 to 1.
3, and a catalyst in which such a silver-zirconium composite oxide is supported on a solid acid carrier,
Nitrogen oxide catalytic reduction activity is particularly high.

According to the present invention, the catalyst in which the silver-zirconium composite oxide is supported on the solid acid carrier in the above-described supported amount is more suitable in oxidation than the solid acid catalyst on which silver oxide or silver is supported. Although the reason is not completely clear, the partial oxidation or cracking of hydrocarbons is promoted, so that it has extremely high activity in the catalytic reduction reaction of nitrogen oxides using hydrocarbons as a reducing agent. It seems to have selectivity. Similarly, when an oxygen-containing organic compound is used as a reducing agent, it has extremely high activity and selectivity. In addition, the catalyst according to the present invention is excellent in heat resistance and also in sulfur oxide resistance, and thus, for example, as a denitration catalyst for exhaust gas from diesel engines and a catalyst for diesel vehicles and lean burn gasoline vehicles. Can be suitably used.

The catalyst according to the present invention can be usually obtained as a powder or a granular material. Therefore, by a conventionally known molding method, in addition to a structure such as a honeycomb, a spherical material or a cyclic material can be obtained. It can be formed into various shapes such as objects. During this molding, a molding aid, a reinforcing material such as an inorganic fiber, an organic binder and the like may be appropriately compounded. Further, the catalyst according to the present invention can also be obtained by forming a solid acid itself such as alumina into a structure such as a honeycomb in advance and supporting a silver-zirconium composite oxide on such a structure.

Further, according to the present invention, a powdery catalyst obtained by previously forming an inert substrate into a required shape and carrying a silver-zirconium composite oxide on a solid acid carrier as described above is washed.・ By an appropriate method such as a coating method,
By being coated and supported, it can be advantageously used as a catalyst structure. 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, a catalyst layer is formed on the surface of a structure such as a honeycomb, a sphere or a ring made of an inert substrate by a wash coat method or the like, as described above. When a catalyst is supported, it is preferable that the catalyst layer is supported on the surface of the structure such that the catalyst layer has a thickness of 30 μm or more from the surface thereof (hereinafter, referred to as a catalyst layer thickness for simplicity). By making the catalyst layer supported on the structure over a thickness of 30 μm or more from the surface in this way, the reactivity 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 be usually 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 selective reduction property corresponding to the thickness, which is not preferable from the viewpoint of the cost of producing the catalyst.

A catalyst structure such as a honeycomb or a sphere made of a catalyst by supporting a silver-zirconium composite oxide on a solid acid carrier can be obtained, for example, as follows.
That is, an aqueous solution containing a water-soluble zirconium compound and a water-soluble silver compound and alumina are kneaded with an appropriate organic binder, then formed into a honeycomb structure, dried, and then oxidized in the presence of steam. Atmosphere 600 ℃ ~
By heating and calcining at a temperature in the range of 900 ° C., preferably in the range of 700 to 800 ° C., it is possible to obtain a catalyst structure made of alumina loaded with a silver-zirconium composite oxide.

Further, as described above, a powdery catalyst in which a silver-zirconium composite oxide is supported on alumina in advance may be prepared, and 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 the silver-zirconium composite oxide on alumina is substantially uniform in the thickness direction of the cell walls of the honeycomb structure. Therefore, if the cell wall of the honeycomb structure is 60 μm or more, the catalyst is 30 minutes from the surface of the cell wall.
It is carried over a thickness of at least μm. The cell wall is
This is because the surfaces on both sides are brought into contact with the exhaust gas.

In the catalytic reduction of nitrogen oxides using the catalyst according to the present invention, examples of the reducing agent comprising a hydrocarbon include gaseous ones such as hydrocarbon gas such as methane, ethane, propane, propylene and butylene; Examples of the shape include single-component hydrocarbons such as pentane, hexane, octane, heptane, benzene, toluene, and xylene, and mineral oil-based hydrocarbons such as gasoline, kerosene, light oil, and heavy oil. 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 aldehydes such as acetaldehyde, formaldehyde and acrolein, and alcohols such as methanol, ethanol, propanol and octanol, for example, dimethyl ether, diethyl ether and dipropyl ether. And esters such as methyl acetate, ethyl acetate and fats and oils, and ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone. Among these oxygen-containing organic compounds, aldehydes are particularly preferred. Further, these oxygen-containing organic compounds may be used alone or in combination of two or more as necessary.

Further, 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 3 in molar ratio to nitrogen oxide. Used. When the amount of the reducing agent used is less than 0.1 in terms of the molar ratio to the nitrogen oxide, sufficient reducing activity for the nitrogen oxide cannot be obtained.
When the molar ratio exceeds 3, the discharge amount of the unreacted reducing agent increases, so that after the catalytic reduction treatment of the nitrogen oxide, a post-treatment for recovering the nitrogen oxide 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 useful as a catalyst for reducing or removing hydrocarbons and particulates in exhaust gas.

Among the above reducing agents, the temperature at which hydrocarbons undergo a selective reduction reaction with respect to nitrogen oxides increases in the order of alkyne <alkene <aromatic hydrocarbon <alkane. In the case of hydrocarbons of the same type, the temperature decreases as the number of carbon atoms increases.

The optimum temperature at which the catalyst according to the present invention exhibits a reducing activity on nitrogen oxides is usually from 100 to 800 ° C., though it depends on the reducing agent and the type of catalyst used. 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 preferable temperature range is 200 to 500 ° C.

[0035]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited by these examples.

(1) Preparation of catalyst

Example 1 1k of γ-alumina (KC503 manufactured by Sumitomo Chemical Co., Ltd.)
g and polyethylene oxide (PEO- manufactured by Sumitomo Seika Co., Ltd.)
10) After sufficiently kneading 1 kg with an appropriate amount of water, the mixture was extruded by an auger screw extruder into a honeycomb structure having 200 / square inch cells. The honeycomb structure was air-dried at room temperature, dried by heating at 100 ° C. overnight, and further fired at 500 ° C. for 3 hours to obtain a honeycomb structure made of alumina (having a honeycomb wall thickness of 205 μm).

Next, silver nitrate (AgNO_Three) 5.08g and
Zirconyl nitrate (ZrO (NO_Three) _Two・ 2H_TwoO) 4.0
0 g is dissolved in 100 mL of ion-exchanged water.
A mixed aqueous solution of zirconyl nitrate was prepared. To this,
After immersing the honeycomb structure made of Lumina for 10 minutes,
Pulling up, excess aqueous solution adhering to the honeycomb structure
Was removed and dried at 100 ° C. for 8 hours.

Next, the thus-treated honeycomb structure was placed at 800 ° C. in an air atmosphere containing 10% by weight of water.
At 3 ° C. for 3 hours, and a silver-zirconium composite oxide (Ag / Zr atomic ratio =
A honeycomb catalyst structure made of γ-alumina supporting 2) was obtained. This catalyst is called A-1.

FIG. 1 shows an X-ray diffraction pattern of a catalyst in which the silver-zirconium composite oxide thus obtained is supported on γ-alumina, and FIG. 2 shows an X-ray diffraction pattern of γ-alumina alone. In FIG. 1, ○ indicates a peak due to silver-zirconium composite oxide, and X indicates a peak due to γ-alumina. As can be seen in FIG. 1, the X-ray diffraction pattern of the catalyst according to the invention is clearly different from silver and silver oxide, indicating the formation of a silver-zirconium composite oxide.

Example 2 4.23 g of silver nitrate and 4.00 g of zirconyl nitrate were dissolved in 100 mL of ion-exchanged water to prepare a mixed aqueous solution of silver nitrate and zirconyl nitrate. A honeycomb structure made of the same alumina as in Example 1 (honeycomb wall thickness: 205 μm)
Was immersed for 10 minutes, then pulled up to remove the excess aqueous solution attached to the honeycomb structure, and dried at 100 ° C. for 8 hours.

Next, the honeycomb structure thus treated was placed in an air atmosphere containing 10% by weight of water at 600 ° C.
At 3 ° C. for 3 hours, and a silver-zirconium composite oxide (Ag / Zr atomic ratio =
A honeycomb catalyst structure made of γ-alumina supporting 2) was obtained. This catalyst is referred to as A-2.

Example 3 1 kg of γ-alumina and 1 kg of polyethylene oxide (PEO-10, manufactured by Sumitomo Seika Co., Ltd.) as in Example 1 were thoroughly kneaded with an appropriate amount of water, and the mixture was subjected to an auger screw extruder. And extruded into a honeycomb structure having 200 cells / square inch. After drying this honeycomb structure at a room temperature with ventilation, it was dried by heating at 100 ° C. overnight, and further dried at 500 ° C.
For 3 hours to obtain a honeycomb structure made of alumina (having a honeycomb wall thickness of 205 μm).

Next, silver nitrate (AgNO_Three) 5.08g and
Zirconyl nitrate (ZrO (NO_Three) _Two・ 2H_TwoO) 4.0
0 g is dissolved in 100 mL of ion-exchanged water.
A mixed aqueous solution of zirconyl nitrate was prepared. To this,
After immersing the honeycomb structure made of Lumina for 10 minutes,
Pulling up, excess aqueous solution adhering to the honeycomb structure
Was removed and dried at 100 ° C. for 8 hours.

Next, the honeycomb structure thus treated was placed in an air atmosphere containing 10% by weight of water at 600 ° C.
At 3 ° C. for 3 hours, and a silver-zirconium composite oxide (Ag / Zr atomic ratio =
A honeycomb catalyst structure made of γ-alumina supporting 2) was obtained. This catalyst is referred to as A-3.

Example 4 1 kg of γ-alumina and 1 kg of polyethylene oxide (PEO-10 manufactured by Sumitomo Seika Co., Ltd.) as in Example 1 were thoroughly kneaded with an appropriate amount of water, and then mixed with an auger screw extruder. And extruded into a honeycomb structure having 200 cells / square inch. After drying this honeycomb structure at a room temperature with ventilation, it was dried by heating at 100 ° C. overnight, and further dried at 500 ° C.
For 3 hours to obtain a honeycomb structure made of alumina (having a honeycomb wall thickness of 205 μm).

Next, silver nitrate (AgNO_Three) 5.08g and
Zirconyl nitrate (ZrO (NO_Three) _Two・ 2H_TwoO) 4.0
0 g is dissolved in 100 mL of ion-exchanged water.
A mixed aqueous solution of zirconyl nitrate was prepared. To this,
After immersing the honeycomb structure made of Lumina for 10 minutes,
Pulling up, excess aqueous solution adhering to the honeycomb structure
Was removed and dried at 100 ° C. for 8 hours.

Next, the thus-treated honeycomb structure was heated at 900 ° C. in an air atmosphere containing 10% by weight of water.
At 3 ° C. for 3 hours, and a silver-zirconium composite oxide (Ag / Zr atomic ratio =
A honeycomb catalyst structure made of γ-alumina supporting 2) was obtained. This catalyst is referred to as A-4.

Comparative Example 1 1 kg of γ-alumina and 1 kg of polyethylene oxide (PEO-10 manufactured by Sumitomo Seika Co., Ltd.) as in Example 1 were thoroughly kneaded with an appropriate amount of water, and then the mixture was subjected to an auger screw extruder. And extruded into a honeycomb structure having 200 cells / square inch. After drying this honeycomb structure at a room temperature with ventilation, it was dried by heating at 100 ° C. overnight, and further dried at 500 ° C.
For 3 hours to obtain a honeycomb structure made of alumina (having a honeycomb wall thickness of 205 μm).

Next, silver nitrate (AgNO_Three) 5.08g and
Zirconyl nitrate (ZrO (NO_Three) _Two・ 2H_TwoO) 4.0
0 g is dissolved in 100 mL of ion-exchanged water.
A mixed aqueous solution of zirconyl nitrate was prepared. To this,
After immersing the honeycomb structure made of Lumina for 10 minutes,
Pulling up, excess aqueous solution adhering to the honeycomb structure
Was removed and dried at 100 ° C. for 8 hours.

Next, the thus-treated honeycomb structure was placed in an air atmosphere containing no water at a temperature of 400 ° C. for 3 hours.
Baked for 2 hours, and carried silver and zirconium (Ag / Zr atomic ratio = 2) at a supported amount of 2% by weight in terms of silver.
Honeycomb catalyst structure composed of alumina (catalyst layer thickness 10
2 μm). This catalyst is called B-1. Comparative Example 2

1 kg of γ-alumina and polyethylene oxide (PEO-10, manufactured by Sumitomo Seika Co., Ltd.) as in Example 1
After adequately kneading with a suitable amount of water, the mixture was extruded into a honeycomb structure having 200 / square inch cells using an auger screw extruder. The honeycomb structure was air-dried at room temperature, dried by heating at 100 ° C. overnight, and further fired at 500 ° C. for 3 hours to obtain a honeycomb structure made of alumina (having a honeycomb wall thickness of 205 μm).

Next, silver nitrate (AgNO_Three7.62g
Zirconyl nitrate (ZrO (NO_Three) _Two・ 2H_TwoO) 4.0
0 g is dissolved in 100 mL of ion-exchanged water.
A mixed aqueous solution of zirconyl nitrate was prepared. To this,
After immersing the honeycomb structure made of Lumina for 10 minutes,
Pulling up, excess aqueous solution adhering to the honeycomb structure
Was removed and dried at 100 ° C. for 8 hours.

Next, the thus treated honeycomb structure was placed in an air atmosphere containing no water at a temperature of 800 ° C. for 3 hours.
Baked for 2 hours by weight in terms of silver to carry silver and zirconium (Ag / Zr atomic ratio = 3).
Honeycomb catalyst structure composed of alumina (catalyst layer thickness 10
2 μm). This catalyst is called B-2.

(2) Evaluation Test Using the catalysts (A-1 to 4) according to the present invention and the catalysts (B-1 to 2) of the comparative examples, the nitrogen oxide-containing gas was tested under the following test conditions. Nitrogen oxide catalytic reduction was performed, and the removal rate of nitrogen oxide was determined by a 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.

[0057]

[Table 1]

[0058] Is carried out at a temperature of 700 ° C. and a space velocity of 25,000 (hr ⁻¹ ) for 500 hours, and then under the conditions of the above (2) and (3), Was subjected to catalytic reduction with nitrogen oxides to evaluate the heat resistance and sulfur oxide resistance of the catalyst. Table 2 shows the results.

[0059]

[Table 2]

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

[0061]

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 contained in exhaust gas even in the presence of oxygen and moisture. Nitrogen oxides can be efficiently catalytically reduced, and have excellent durability and sulfur oxide resistance even in the presence of moisture and at high temperatures.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of a γ-alumina catalyst supporting a silver-zirconium composite oxide prepared in Example 1.

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

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Keiichi Tabata 5-1-1 Ebishima-cho, Sakai City, Osaka Sakai Chemical Industry Co., Ltd. (72) Inventor Kazuyuki Ueda 5-1-1 Ebishima-cho, Sakai City, Osaka Sakai Chemical Industry Central Research Laboratory

Claims (13)

[Claims] 1. A catalyst for catalytic reduction of nitrogen oxides using a hydrocarbon and / or an oxygen-containing organic compound as a reducing agent, characterized in that a silver-zirconium composite oxide is supported on a solid acid carrier. 2. The catalyst for catalytic reduction of nitrogen oxide according to claim 1, wherein the supported amount of the silver-zirconium composite oxide is 0.01 to 10% by weight in terms of silver. 3. The silver / zirconium composite oxide having an atomic ratio of silver / zirconium in the range of 1-3.
The catalyst for catalytic reduction of nitrogen oxides according to 1. 4. The catalyst for catalytic reduction of nitrogen oxides according to claim 1, wherein the solid acid carrier is alumina or zirconia. 5. The catalyst for catalytic reduction of nitrogen oxides according to claim 1, wherein the solid acid carrier is a structure comprising a honeycomb, a spherical substance or a cyclic substance. 6. An aqueous solution containing a water-soluble compound of zirconium and a water-soluble compound of silver is prepared, the aqueous solution is impregnated into a solid acid carrier, dried, and then placed in an oxidizing atmosphere containing water vapor at 600-900. Baking at a temperature in the range of ℃
A method for producing a catalyst for catalytic reduction of nitrogen oxides, comprising forming a silver-zirconium composite oxide on a solid acid carrier. 7. An aqueous solution containing a water-soluble compound of zirconium and a water-soluble compound of silver is prepared, and this aqueous solution is neutralized in the presence of a solid acid carrier to form a coprecipitate with a solid acid.
After drying the obtained product, it is heated and calcined at a temperature in the range of 600 to 900 ° C. in an oxidizing atmosphere containing water vapor to produce a silver-zirconium composite oxide on a solid acid carrier. For producing a catalyst for catalytic reduction of nitrogen oxides. 8. The water-soluble compound of zirconium is zirconyl nitrate and the water-soluble compound of silver is silver nitrate.
Or a method for producing a catalyst for catalytic reduction of nitrogen oxides according to 7. 9. The process for producing a catalyst for catalytic reduction of nitrogen oxides according to claim 6, wherein the solid acid carrier is alumina or zirconia. 10. An aqueous solution containing a water-soluble compound of zirconium, a water-soluble compound of silver, and a water-soluble aluminum compound is neutralized to form a coprecipitate, which is dried.
Baked at a temperature in the range of 500 to 500 ° C. to produce alumina, and to support a precursor of the silver-zirconium composite oxide on the alumina. A method for producing a catalyst for catalytic reduction of nitrogen oxides, comprising heating and calcining at a temperature in the range of 900 ° C. to produce a silver-zirconium composite oxide on alumina. 11. The catalyst for catalytic reduction of nitrogen oxides according to claim 10, wherein the water-soluble compound of zirconium is zirconyl nitrate, the water-soluble compound of silver is silver nitrate, and the water-soluble aluminum compound is aluminum nitrate. Production method. 12. The process for producing a catalyst for catalytic reduction of nitrogen oxides according to claim 6, wherein the supported amount of the silver-zirconium composite oxide is 0.01 to 10% by weight in terms of silver. 13. A method for preparing silver / zirconium composite oxide, comprising:
The method for producing a catalyst for catalytic reduction of nitrogen oxide according to any one of claims 6 to 12, wherein the zirconium atomic ratio is in the range of 1 to 3.