JPH06238169A - Catalyst structure for catalytic reduction of nitrogen oxides - Google Patents

Abstract

PURPOSE:To provide a catalyst structure for catalytic reduction of nitrogen oxides using hydrocarbon as a reducing agent. CONSTITUTION:This catalyst structure for catalytic reduction of nitrogen oxides consists of a base body which constitutes the catalyst structure, and a multilayer structure having an inner layer having catalytic component and a surface layer. The inner layer has a catalyst component of ion exchanged material or oxide of metal selected from Cu, Cr, Mn, Fe, Co, Ni and V. The surface layer has the catalytic component prepared by depositing at least one kind of metal or ion or oxide of groups Ib, IIa, IIb, IIIa, IIIb, IVa, IVb and Va (excluding V) on at least one kind of a carrier selected from aluminum oxide, titanium oxide, zirconium oxide, and H-type zeolite.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst structure for catalytic reduction of nitrogen oxides using hydrocarbon as a reducing agent, and more specifically, harmful nitrogen contained in exhaust gas discharged from factories, automobiles and the like. The present invention relates to a catalyst structure for nitrogen oxide catalytic reduction having high selectivity and high activity, which is suitable for reducing and removing 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.

Therefore, 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 a nitrogen oxidation method. There is a problem that it is difficult to put it into practical use because of its low activity of decomposing substances. Further, H-type zeolite, copper ion exchange ZSM-5 and the like have been proposed as new catalysts for catalytic reduction of nitrogen oxides using hydrocarbons and oxygen-containing compounds as reducing agents. In particular, H type _{ZSM-5 (SiO 2 / Al} 2
It is said that the optimum O ₃ molar ratio is 30 to 40).
However, even with such H-type ZSM-5, it cannot be said that the H-type ZSM-5 still has sufficient reducing activity and selectivity. Particularly, when the gas contains water, aluminum in the zeolite structure is dealuminated. Therefore, there is a demand for a nitrogen oxide catalytic reduction catalyst which has a higher reduction activity and further has excellent durability even when the gas contains water because the performance thereof is drastically reduced.

[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 as a reducing agent in the presence of oxygen. Also, and particularly, in the presence of oxygen and water, the nitrogen oxides selectively react with the hydrocarbons, so that the nitrogen oxides in the exhaust gas can be made highly active and highly active without using a large amount of reducing agent. Another object of the present invention is to provide a catalytic structure for catalytic reduction of nitrogen oxides, which can be selectively reduced and has excellent durability even in the presence of water.

[0005]

A catalyst structure for catalytic reduction of nitrogen oxides using a hydrocarbon as a reducing agent according to the present invention comprises an inner layer having a catalyst component, and an inner layer having a catalyst component on a substrate constituting the catalyst structure. What is claimed is: 1. A catalyst structure for catalytic reduction of nitrogen oxides having a multilayer structure, comprising a surface layer having a catalyst component supported on an inner layer, wherein the inner layer is Cu, Cr, Mn, F.
e, Co, Ni, and at least one metal oxide selected from the group consisting of V as a catalyst component, the surface layer is at least 1 selected from aluminum oxide, titanium dioxide, zirconium oxide and H-type zeolite The carrier of the species may include Ib, IIa, IIb, IIIa, III of the Periodic Table.
It is characterized by having a catalyst component which carries at least one metal of group b, IVa, IVb and Va (excluding V) or an ion thereof or an oxide thereof.

In the present invention, the active component means a component which effectively acts as a catalyst for catalytic reduction of nitrogen oxides, and the carrier means a component carrying such an active component, and the catalyst component. When the active ingredient is carried on a carrier, is composed of such an active ingredient and the carrier. However, when the catalyst component does not include a carrier, the active component means the catalyst component.

A catalyst structure for catalytically reducing nitrogen oxides using a hydrocarbon as a reducing agent according to the present invention comprises a base material constituting the catalyst structure, an inner layer having a first catalyst component, and It has a multilayer structure including a surface layer having a second catalyst component supported on the inner layer. That is, the surface layer is an exhaust gas containing nitrogen oxides to be treated, that is, a layer in which the reaction gas first comes into direct contact with the catalyst in the catalytic reduction treatment of the reaction gas, and is the layer of the catalyst structure. The innermost layer means the catalyst layer located on the outermost surface side, and the inner layer means the catalyst layer which can reach the inner side of the surface layer only when the reaction gas diffuses and moves inside the surface layer.

In the catalyst structure according to the present invention, the above-mentioned base material means a three-dimensional structure such as a honeycomb, a spherical material, and a pellet, and as described above, the catalyst of the inner layer and the surface layer. It is a substrate that forms a multilayer structure of layers. Such a substrate may be an inert structure that does not participate in any catalytic reaction, but may also serve as a carrier or a catalyst for the inner layer. In the case of also serving as a carrier for the inner layer, for example, as will be described later, preferably, a conventionally known inorganic oxide such as γ-alumina or the like, or silica such as zeolite containing silica and aluminum as main components. A three-dimensional structure such as a honeycomb made of an acid salt, a spherical object, a pellet, or the like is formed. However, in the present invention, the base material may have any other shape as long as it has a three-dimensional shape capable of supporting a catalyst layer having a multilayer structure thereon.

Generally, the inner layer is formed by impregnating the carrier with the first active ingredient, depositing, or ion-exchange,
A combination of these methods or the like can be used to form the active ingredient by supporting it on a base material or a carrier. In the present invention, the first active ingredient may thus be supported on an inert base material as described above to form an inner layer, or the base material itself may be formed from a carrier, The carrier may be loaded with the first active ingredient to form the inner layer. Alternatively, the inner layer may be formed by forming the substrate with the active ingredient.

After forming the inner layer in this way, the surface layer is coated with a slurry containing the second catalyst component, for example, by a wash coat method or the like to form the second catalyst component. By supporting the above, it can be formed on the inner layer. The catalyst structure for catalytic reduction of nitrogen oxides according to the present invention basically has a multilayer structure as described above. First, the surface layer will be described.

In the catalyst structure according to the present invention, the carrier for the active ingredient constituting the surface layer is at least selected from aluminum oxide (alumina), titanium dioxide (titania), zirconium oxide (zirconia) and H-type zeolite. One kind is used. The surface layer is formed on such a carrier by using Ib, IIa, IIb, IIIa, III of the periodic table.
b, IVa, IVb and Va (but excluding V), at least one metal selected from the group, or an ion thereof or an oxide thereof.

As examples of the above-mentioned metals, for example, metals of Group Ib of the periodic table include Cu, Ag and Au,
Group IIa metals include Mg, Ca, Sr and Ba
Zn as a group IIb metal, Y as a group IIIa metal, G as a lanthanide group metal, and G as a group IIIb metal.
a, the group IVa metal is Ti and Zr, the group IVb metal is Ge and Sn, and the group Va metal is N.
b can be mentioned. In the present invention, these active ingredients may be supported on the carrier in the form of metal ions or metal oxides.

In order to support the above metal or metal ion or metal oxide on a carrier such as aluminum oxide, titanium dioxide, zirconium oxide or H-type zeolite, for example, the ion-exchange group of these carriers is replaced with these metal ions. A method that uses ion exchange, a precursor that produces metal oxides by firing (eg, nitrates, sulfates, carbonates, hydroxides, chlorides, etc.) is supported on a carrier by an impregnation method or a deposition method. After that, by firing, a method of converting the precursor into a metal oxide and supporting it, to prepare a metallosilicate in which the metal as the active ingredient is incorporated into the zeolite structure during the production of the zeolite, and then the metallo By exchanging, for example, an alkali metal ion in a silicate with a hydrogen ion or an ammonium ion, the above metal or its ion is obtained. Can be adopted a method in which a H-type zeolite containing as an active ingredient.

In the catalyst structure according to the present invention, the commercially available γ-alumina can be used as the aluminum oxide (alumina) used as a carrier for the active ingredient constituting the surface layer, but it may be alkali or alkali-containing. It is preferable to use high-purity γ-alumina having an extremely low rate. Titanium dioxide (titania) preferably contains sulfate ions obtained by firing metatitanic acid obtained from the production process of titanium dioxide by the sulfuric acid method. The zirconium oxide (zirconia) is preferably zirconium oxide containing sulfate ions obtained by adding sulfuric acid to commercially available zirconium hydroxide and firing this.

The H-type zeolite includes alkali metal or alkaline earth metal-ZSM-5, mordenite, US
Those obtained by ion-exchanging zeolite such as Y with ammonia and calcining, or those obtained by subjecting these zeolites to hydrogen ion exchange under acidic conditions are preferably used. In the surface layer, the loading of the active ingredient is usually 0.1 to 30% by weight. here,
The loading rate is (weight of active ingredient / weight of carrier) × 100
(% By weight). In the surface layer, when the loading rate of the active ingredient is less than 0.1% by weight, sufficient catalytic activity cannot be obtained. On the other hand, even when the loading rate exceeds 30% by weight, the catalytic activity corresponding to it cannot be obtained. No gain can be obtained. However, if necessary, the carrier may be loaded with the active ingredient in an amount of more than 30% by weight.

Next, the inner layer in the catalyst structure according to the present invention will be described. In the catalyst for reducing nitrogen oxides according to the present invention, the inner layer has Cu, Cr, Mn, Fe and C.
The catalyst component is an oxide or ion exchanger of at least one metal selected from the group consisting of o, Ni and V, and these catalyst components may be supported on alumina, titania, zirconia, H-type zeolite, silica or the like. it can.

In the present invention, the method for supporting the active component of the catalyst on the carrier is not limited at all, and for example, any suitable method known in the art, such as the above-mentioned impregnation method, deposition method, or ion method can be used. The exchange method or a combination thereof can be used. In particular, in the present invention, the ion exchanger of the metal, in addition to the above-mentioned alumina, silica, titania, zirconia, etc., such as niobium pentoxide and stannic oxide, a metal oxide having a hydroxyl group on its surface. Is used as a carrier, and a hydrogen ion having a hydroxyl group of such a carrier is ion-exchanged with the metal ion to support the carrier.

In the present invention, various commercially available products can be used as the metal oxide as the carrier, and if necessary, a neutralizing agent is added to the aqueous solution of the water-soluble salt of the metal to cause hydrolysis. Or hydrolyzed under heating conditions,
It can be obtained by forming a precipitate, separating the precipitate, thoroughly washing with water, and then calcining. The above-mentioned ion exchange method is not particularly limited, and it can be carried out by a conventionally known conventional method. For example, the metal oxide as the carrier is dispersed in water, the cation or complex cation of the metal to be ion-exchanged does not cause precipitation under sufficient stirring, and the cation is maintained at a pH as high as possible. Alternatively, a complex cation may be added. Thus, in ion exchange, the cation or complex cation of the metal to be ion-exchanged does not cause precipitation, and
By keeping the pH as high as possible, it is possible to increase the exchange capacity of ions that exchange ions with the hydrogen ions of the hydroxyl group.

As the ion exchange proceeds, the pH of the liquid is lowered by the exchanged hydrogen ions. Therefore, a neutralizing agent such as ammonia is added to maintain the pH at a high level as described above. Good to do. When the metal ion to be exchanged is not hydrolyzed by heating as in the case of copper, nickel, etc., the ion exchange may be performed under the condition of increasing the temperature in order to increase the ion exchange rate. Good. The ion species to be ion-exchanged may be a single species or a mixture of two or more species.

After the ion exchange, the metal oxide as a carrier is filtered, washed with water, dried and, if necessary, 200 to 8
By calcining at 00 ° C., a catalyst component can be obtained in which the metal oxide as a carrier is ion-exchanged with the metal to carry it. In the inner layer of the catalyst structure for catalytic reduction of nitrogen oxides according to the present invention, the loading rate of the active ingredient on the carrier is
Usually, it is 0.1 to 30% by weight. In the inner layer of the catalyst structure according to the present invention, when the loading rate of the active ingredient is less than 0.1% by weight, sufficient catalytic activity cannot be obtained, while the loading rate exceeds 30% by weight. However, a corresponding increase in catalytic activity cannot be obtained. However, if necessary, the carrier may be loaded with the active ingredient in an amount of more than 30% by weight.

In the catalyst structure for nitrogen oxide catalytic reduction having a multilayer structure according to the present invention, in order to obtain effective nitrogen oxide catalytic reduction activity, the surface layer preferably has a thickness of 5 μm or more. The activity increases with the increase.
In particular, according to the invention, the surface layer has a thickness of 20-100.
It is in the range of μm. On the other hand, the thickness of the inner layer is 5 μm or more, preferably 10 to 50 μm. Even if the thickness of the inner layer exceeds 50 μm, there is no particular problem,
The layer having a thickness of more than 50 μm is located too deep inside the carrier, is difficult to contact with the reaction gas, and does not function effectively as a catalyst.

The catalyst structure for catalytic reduction of nitrogen oxides according to the present invention has a multi-layer structure as described above, typically a two-layer structure as described above, and has high activity and selectivity. The reason for this is not yet clear in detail, but the surface layer in which the reaction gas first contacts the catalyst does not completely oxidize the hydrocarbons as the reducing agent and is mainly activated by adsorption, while the surface layer of this surface layer is activated. Since the inner layer located on the inner side mainly adsorbs and activates nitrogen oxides, the reactivity with nitrogen oxides is significantly increased at the interface between the surface layer and the inner layer, and as a result, the activated hydrocarbons or Since the oxygen-containing compound generated from such hydrocarbons reacts with the activated nitrogen oxide, it is considered that the nitrogen oxide is reduced with high activity and high selectivity.

As described above, the catalyst structure according to the present invention can have various shapes such as a honeycomb shape, a pellet shape, and a spherical shape. When molding or manufacturing such a structure, a molding aid, a molded body reinforcement, an inorganic fiber, an organic binder or the like may be appropriately used. In the catalytic reduction of nitrogen oxides using the catalyst structure according to the present invention, examples of the reducing agent composed of hydrocarbon include a gaseous reducing agent,
Hydrocarbon gas such as methane, ethane, propane, propylene, butylene, etc., as a liquid form, pentane, hexane, octane, heptane, benzene, toluene, xylene and other single component hydrocarbons, gasoline, kerosene, gas oil,
Mineral oil-based hydrocarbons such as heavy oil can be used. Particularly, according to the present invention, among the above, acetylene,
Lower alkynes such as methylacetylene and 1-butyne, lower alkenes such as ethylene, propylene, isobutylene, 1-butene and 2-butene, lower dienes such as butadiene and isoprene, lower alkanes such as propane and butane are preferable as the reducing agent. Used. These hydrocarbons may be used alone or in combination of two or more as required.

The hydrocarbon as the reducing agent varies depending on the specific hydrocarbon used, but is usually used in a molar ratio of about 0.1 to 2 with respect to nitrogen oxides. When the amount of hydrocarbon used is less than 0.1 in terms of molar ratio to nitrogen oxide, sufficient reducing activity cannot be obtained for nitrogen oxide, while when the molar ratio exceeds 2. Since the amount of unreacted hydrocarbons emitted is large, after-treatment for recovering nitrogen oxides is required after the catalytic reduction treatment of nitrogen oxides.

Incidentally, unburned substances or incompletely burned products such as fuel existing in the exhaust gas, that is, hydrocarbons and particulates are also effective as the reducing agent, and these are also included in the hydrocarbon in the present invention. Be done. From this point of view, it can be said that the catalyst structure according to the present invention is also useful as a catalyst for reducing or removing hydrocarbons and particulates 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 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 structure according to the present invention exhibits reduction activity with respect to nitrogen oxides varies depending on the reducing agent and the catalyst component used, but is usually 100 to 800 ° C. In this temperature range, the space velocity (SV) 500
It is preferable to circulate the exhaust gas at about 100,000. In the present invention, a particularly suitable temperature range is 200 to 50.
It is 0 ° C.

[0027]

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

(1) Preparation of Catalyst Structure Example 1 4.56 g of copper nitrate (Cu (NO ₃ ) ₂ .3H ₂ O) was dissolved in 50 ml of deionized water to prepare an aqueous solution of copper ion (Cu ²⁺ ). Was prepared. This was preliminarily dried at 120 ° C. for 24 hours, and a pellet of γ-alumina with a diameter of 3 mm (N manufactured by Sumitomo Chemical Co., Ltd.
K-324) was added to 200 ml of water containing 100 ml (60 g) with sufficient stirring to exchange copper ions with hydrogen ions in alumina. During this period, as the pH dropped,
2% by weight aqueous ammonia was added to maintain the pH at 5.5.
In this way, a predetermined amount of copper nitrate aqueous solution was added to the water containing the γ-alumina pellets, and the mixture was stirred at 70 ° C. for 2 hours.

Then, the pellets of γ-alumina ion-exchanged with copper ions are filtered in this manner,
After being dried at ℃ for 18 hours, it was baked at 600 ℃ for 4 hours to obtain γ-alumina carrying 2% by weight of copper ions. The thickness of the copper ion layer thus supported on γ-alumina was about 20 μm as a result of the line analysis of copper by an electron probe microanalyzer.

Separately, lanthanum nitrate (La (NO ₃ ) ₃
6.8 g of 6H ₂ O) was dissolved in 5 liters of ion-exchanged water to prepare an aqueous solution having pH 6.0. To this lanthanum nitrate aqueous solution at a temperature of 70 ° C., 500 g of sodium type ZSM-5 (manufactured by Nippon Mobil Co., SiO ₂ / Al ₂ O ₃ molar ratio 34) was added, and lanthanum was added to ZSM-5 at a loading rate of 0.5% by weight. Ions (La ³⁺ ) were supported by ion exchange. This lanthanum ion-supported ZSM-5 was crushed with a sample mill to obtain a powder whose particle size was adjusted to 100 mesh or 150 mesh.

The copper ion-supported γ-alumina pellets were charged in a rolling granulator, and further, the powder and 10 times diluted water of silica gel (Nissan Chemical's Snowtex N) used as a binder were charged. , ZSM-supporting the lanthanum ions on the surface of γ-alumina pellets
5 was coated. At this time, the thickness of the coating layer was examined by a line analysis of silica by an electron probe microanalyzer and adjusted to an average of 5 μm, and thus copper ions having lanthanum ion exchange H type ZSM-5 as a coating on the surface were obtained. Supported γ-alumina was obtained as a catalyst structure A-1.

Example 2 As in Example 1, the coating layer thickness was about 20 μm.
Copper ion-supported γ-alumina having m lanthanum ion-exchanged H-type ZSM-5 as a coating on the surface was obtained as a catalyst structure A-2.

Example 3 As in Example 1, the coating layer thickness was about 50 μm.
Copper ion-supporting γ-alumina having m lanthanum ion-exchanged H-type ZSM-5 as a coating on the surface was obtained as a catalyst structure A-3.

Example 4 As in Example 1, the coating layer thickness was about 100.
Copper ion-supported γ-alumina having a lanthanum ion-exchanged H-type ZSM-5 as a coating on its surface was obtained as a catalyst structure A-4.

Example 5 As in Example 1, the coating layer thickness was about 200.
Copper ion-supported γ-alumina having a lanthanum ion-exchanged H-type ZSM-5 as a coating on its surface was obtained as a catalyst structure A-5.

[0036] Example 6 chromium nitrate _{(Cr (NO 3) 3 ·} 9H 2 O) 4.62g was dissolved in ion-exchanged water 50 ml, chromium ions (Cr
An aqueous solution of ³⁺ ) was prepared. This is preheated at 120 ℃ 24
Water containing 100 ml (60 g) of γ-alumina pellets (Sumitomo Chemical NK-324) having a diameter of 3 mm and dried for 20 hours
In addition to 0 ml with sufficient stirring, the chromium ions and the hydrogen ions in the alumina were exchanged. During this period, as the pH decreased, 0.2% by weight of ammonia water was added to adjust the pH.
It was kept at 5.0. Thus, a predetermined amount of the chromium nitrate aqueous solution was added to the water containing the γ-alumina pellets, and the mixture was stirred at 70 ° C. for 2 hours.

Then, the pellets of γ-alumina ion-exchanged with chromium ions in this manner are filtered to obtain 1
After being dried at 20 ° C. for 18 hours, it was calcined at 600 ° C. for 4 hours to obtain γ-alumina carrying 1% by weight of chromium ions. The thickness of the chromium ion layer thus supported on γ-alumina was about 20 μm as a result of the line analysis of chromium by an electron probe microanalyzer.

Separately, cerium nitrate (Ce (NO ₃ ) ₃
6H ₂ O) (1425 g) was dissolved in ion-exchanged water (5 liters). In addition to this, γ-alumina (G manufactured by Mizusawa Chemical Industry Co., Ltd.)
B) After adding 500 g and stirring sufficiently, γ-alumina was filtered, dried, and calcined at 500 ° C. for 3 hours to obtain γ-alumina on which cerium oxide was loaded at a loading rate of 10% by weight. It was This γ-alumina was pulverized with a sample mill to obtain powder having a particle size adjusted to 100 mesh or 150 mesh. Thereafter, in the same manner as in Example 1, γ-supported cerium oxide having a coating layer thickness of about 50 μm on average was used.
-Catalyst structure A-6 consisting of γ-alumina supporting chromium ions coated on the surface of alumina was obtained.

Example 7 Manganese dioxide (MnO ₂ , obtained by calcining manganese carbonate (MnCO ₃ ) at 400 ° C. for 3 hours (MnO ₂ , specific surface area 73.0 m ² /
g) and an aqueous solution of silica sol (Snowtex N made by Nissan Chemical Co., Ltd.)
Was supplied to a tumbling granulator (Marumerai Q-23 manufactured by Fuji Paudal Co., Ltd.) to obtain a manganese dioxide pellet having a diameter of 3 mm.

Separately, 500 g of sodium mordenite (NM-100P manufactured by Nippon Kagaku Co., Ltd.) was dipped in an aqueous zirconyl nitrate solution (concentration of 100 g / l as ZrO ₂ ) and kept at 70 ° C. for 1 hour while stirring, so that sodium ions were zirconium. Ions were exchanged with ions (Zr ⁴⁺ ). After filtering and washing the obtained zeolite cake with water, 6
It was baked at 50 ° C. for 4 hours.

The zirconium content of this zeolite (zirconium mordenite) was 3.3% by weight, and the specific surface area was 39 m ² / g. This zirconium mordenite was pulverized with a sample mill to obtain a powder having a particle size adjusted to 100 mesh or 150 mesh. Less than,
In the same manner as in Example 1, a catalyst structure A-7 made of manganese dioxide coated with zirconium ion exchange mordenite having a coating layer thickness of about 50 μm on average was obtained.

Example 8 Goethite (FeOOH) was calcined at 400 ° C. for 3 hours.
Obtained ferric oxide (Fe ₂O₃, Specific surface area 118m²/ G)
And using the same silica sol aqueous solution as in Example 7,
As in Example 7, ferric oxide pellets having a diameter of 3 mm
Got Separately, gallium nitrate (Ga (NO₃)₃・ NH₂
18.9% by weight as O and Ga) 118 g of ion-exchanged water
Dissolved in 1 liter. H-type mordenite (Nippon Kagaku)
HM-23) made by HM-23), temperature adjusted to 70 ° C, pH 2.5
Sufficiently add the above aqueous solution of gallium nitrate to the slurry.
In addition to stirring, ion exchange was performed. During this time, the pH drops
Along with this, 2% by weight aqueous ammonia was added to bring the pH to 2.5.
Maintained. In this way, a certain amount of gallium nitrate
After adding the liquid, the mixture was stirred for 2 hours.

Then, the gallium ion-exchanged mordenite thus ion-exchanged is filtered, washed with ion-exchanged water, dried at 120 ° C. for 18 hours, and then 70
It was baked at 0 ° C. for 5 hours. In this way, mordenite supporting 5% by weight of gallium ions was obtained. Less than,
In the same manner as in Example 7, a catalyst structure A- consisting of ferric oxide coated with gallium ion-exchanged H-type mordenite having a coating layer thickness of about 50 μm on average.
Got 8.

Example 9 Cobalt tricarbonate (CoCO ₃ ) obtained by calcining cobalt carbonate (CoCO ₃ ) at 400 ° C. for 3 hours (Co ₃ O ₄ , specific surface area 130)
m ² / g) and the same silica sol aqueous solution as in Example 7 were used in the same manner as in Example 7 to obtain a pellet of cobalt trioxide having a diameter of 3 mm.

Separately, 500 g of commercially available zirconium hydroxide (manufactured by Daiichi Rare Elements Co., Ltd.) was added to niobium pentachloride (NbCl ₅ ).
After gradually adding 200 ml of the ethanol solution (15 g / l as Nb), the mixture was sufficiently kneaded. The resulting kneaded product is air-dried and dried at 100 ° C. for 18 hours, and then 50
It was calcined at 0 ° C. for 3 hours to obtain zirconium oxide carrying 10% by weight of niobium oxide (Nb ₂ O ₅ ) as Nb. Thereafter, in the same manner as in Example 7, a catalyst structure A-9 made of cobalt tetraoxide coated with zirconia supporting niobium oxide having a coating layer thickness of about 50 μm on average was obtained.

Example 10 Nickel oxide (NiO, specific surface area 194 m ² / g) obtained by firing nickel carbonate (NiCO ₃ ) at 400 ° C. for 3 hours
And using the same silica sol aqueous solution as in Example 7,
In the same manner as in Example 7, a nickel oxide pellet having a diameter of 3 mm was obtained. Separately, γ-alumina powder (A- manufactured by Sumitomo Chemical Co., Ltd.
11) 50 g was added to 100 ml of ion-exchanged water, and stannic chloride aqueous solution of hydrochloric acid (1 as SnCl ₄ was added thereto).
7.3 g) 50 ml was added, and the mixture was heated to boiling and hydrolyzed while supplying ammonia gas. After washing the solid content with ion-exchanged water, it is baked at 500 ° C. for 4 hours to obtain S
A metal oxide mixture powder having a nO ₂ / Al ₂ O ₃ weight ratio of 20/100 was obtained. Thereafter, in the same manner as in Example 7, a catalyst structure A-10 made of nickel oxide coated with stannic oxide-supported alumina having an average coating layer thickness of about 50 μm was obtained.

Example 11 Commercially available titanium oxide carrier (S-200 manufactured by Sakai Chemical Industry Co., Ltd.)
-24) was immersed in a vanadium oxalate aqueous solution (50 g / l as V ₂ O ₅ ) to sufficiently impregnate it, and then the excess liquid was removed. Then, after gradually drying at room temperature, 10
It was dried at 0 ° C. for 18 hours. Then, it was baked at 450 ° C. for 3 hours to obtain a titanium oxide pellet carrying 5% by weight of V ₂ O ₅ . Separately, commercially available calcium mordenite (Ca-M-100P manufactured by Nippon Kagaku Co., Ltd.) was pulverized with a sample mill to obtain a powder having a particle size adjusted to 100 mesh under and 150 mesh over. Hereinafter, in the same manner as in Example 1,
A catalyst structure A-11 made of V ₂ O ₅ -supported titanium oxide coated with Ca-mordenite on the surface of the γ-alumina pellets and coated with Ca-mordenite having an average coating layer thickness of about 50 μm.
Got

Comparative Example 1 Sodium type ZSM-5 (SiO ₂ manufactured by Japan Mobile Co., Ltd.
/ Al ₂ O ₃ molar ratio = 34) by hydrogen substitution to give H-type ZS
M-5 was formed into a spherical body having a diameter of 2.4 mm by using silica sol (Snowtex N made by Nissan Chemical Industry) as a binder. This was dried at 120 ° C. for 18 hours and then calcined at 500 ° C. for 4 hours to obtain a catalyst structure B-1.

Comparative Example 2 In the same manner as in Example 11, a catalyst structure B-2 made of titanium oxide pellets carrying 5% by weight of V ₂ O ₅ was obtained.

Comparative Example 3 In the same manner as in Example 1, a catalyst structure B-3 made of γ-alumina carrying 2% by weight of copper ions was obtained.

(2) Evaluation test Using the catalyst structures (A-1 to 11) according to the present invention and the catalyst structures (B-1 to 3) of Comparative Examples described above, nitrogen oxidation was conducted under the following test conditions. The nitrogen-oxide catalytic reduction of the substance-containing gas was performed, 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 10000 or 20000 Hr ^-1 (3) Reaction temperature 200 ° C, 250 ° C, 300 ° C ,
The results are shown in Tables 1 and 2.

[0052]

[Table 1]

[0053]

[Table 2]

As is clear from the results shown in Tables 1 and 2, the catalyst structures according to the present invention have a high nitrogen removal rate of nitrogen oxides, whereas the catalyst structures according to the comparative examples Generally, the removal rate is low. The catalyst structure according to Comparative Example 1 is a conventionally known typical catalyst structure for catalytic reduction of nitrogen oxides composed of H-type ZSM-5, and generally has a low nitrogen removal rate of nitrogen oxides. .

Comparative Example 2 is a catalyst structure having a single layer structure in which V ₂ O ₅ is supported on titanium oxide. On the other hand, Example 11 is a _two- layer structure in which V ₂ O ₅ is supported on titanium oxide as an inner layer, and a coating layer of mordenite supporting calcium ions is formed thereon as a surface layer. In a catalyst structure having a structure, the nitrogen removal rate of nitrogen oxides is improved.

Comparative Example 3 is a catalyst structure having a single layer structure in which copper ions are supported on γ-alumina. On the other hand, in Example 3, copper ions were supported on γ-alumina to form an inner layer, and lanthanum ion-substituted H was formed on the inner layer.
A catalyst structure having a two-layer structure having a coating layer of type ZSM-5 as a surface layer, the removal rate of nitrogen in nitrogen oxides is improved.

[0057]

INDUSTRIAL APPLICABILITY As described above, the catalyst structure for catalytic reduction of nitrogen oxides according to the present invention has a surface layer having a predetermined catalyst component and a predetermined catalyst component, and is located inside the surface layer. It has a multi-layer structure with the inner layer, and has higher activity and higher selectivity than the conventional catalyst structure in catalytic reduction of nitrogen oxides using hydrocarbon as a reducing agent, and further coexistence of oxygen and water. Even under the conditions, the nitrogen oxides in the exhaust gas can be efficiently catalytically reduced over a wide temperature range, and the durability is excellent.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location B01J 23/82 ZAB A 8017-4G 23/84 ZAB 8017-4G 301 A 8017-4G 29/24 ZAB A 9343-4G (71) Applicant 000174541 Sakai Chemical Industry Co., Ltd. 1-2-1, Nishi, Hinocho-machi, Sakai City, Osaka Prefecture (74) The above two agents, Attorney Makoto Makino (72) Inventor Tadao Nakatsuji Sakai, Osaka Prefecture 5-1, Ebishima-cho, Ichi, Central Research Institute, Sakai Chemical Industry Co., Ltd. (72) Inventor, Hiromasa Shimizu, Osaka, 5-1, Ebisu-machi, Sakai Chemical Industry Co., Ltd., Central Research Laboratory (72) Inventor, Ritsu Yasukawa Osaka Prefecture Sakai Chemical Industry Co., Ltd. Central Research Laboratory, 5-1, Ebishima-cho, Sakai City (72) Inventor Mitsunori Tabata 1134-2, Gongendo, Satte City, Saitama Prefecture (72) Takehiko Ito Tsukuba City, Ibaraki Prefecture East 1-1 Institute of Industrial Science and Technology, National Institute of Materials Science and Engineering (72) Inventor Hideaki Hamada 1-1, East Tsukuba, Ibaraki Prefecture

Claims (2)

[Claims] 1. A nitrogen oxide having a multi-layered structure comprising an inner layer having a catalyst component and a surface layer having the catalyst component supported on the inner layer on a substrate constituting the catalyst structure. A catalytic structure for catalytic reduction, wherein an inner layer contains an oxide or ion exchanger of at least one metal selected from the group consisting of Cu, Cr, Mn, Fe, Co, Ni and V as a catalyst component, and the surface The layer has at least one carrier selected from aluminum oxide, titanium dioxide, zirconium oxide and H-type zeolite on the periodic table Ib, IIa, IIb, IIIa, IIIb, IV.
Nitrogen oxidation using a hydrocarbon as a reducing agent, which has a catalyst component carrying at least one metal of group a, IVb and Va (excluding V), or an ion thereof or an oxide thereof. Catalyst structure for catalytic reduction of substances. 2. A metal of Group Ib of the periodic table is at least one selected from Cu, Ag and Au, and a metal of Group IIa is M.
at least one selected from g, Ca, Sr and Ba,
The Group IIb metal is Zn, the Group IIIa metal is at least one selected from Y and lanthanide group metals, the Group IIIb metal is at least Ga, and the Group IVa metal is at least one selected from Ti and Zr; The catalyst structure for catalytic reduction of nitrogen oxides according to claim 1, wherein the group IVb metal is at least one selected from Ge and Sn, and the group Va metal is Nb.