JPH10314593A - Exhaust gas purifying catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitrogen oxide occlusion type exhaust gas pyrifying catalyst in which the occlusion function of nitrogen oxide is not lowered in the case sulfur oxide is contained in exhaust gas and superior heat resistance is provided and, therefore, the nitrogen oxide in the exhaust gas can be reduced and purified efficiently for a long period of time. SOLUTION: A nitrogen oxide occlusion type exhaust gas purifying catalyst is composed of (a) a composite oxide of barium and aluminum and (b) at least one element selected out of a group formed of Pt, Rh, Pd and Ir. In addition to the above components, at least one kind selected out of zirconium oxide and aluminum oxide, or gallium oxide can be contained as one catalyst component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a process for treating an exhaust gas containing hydrocarbons and carbon monoxide together with nitrogen oxides in an oxygen-excess atmosphere to remove hydrocarbons and carbon monoxide along with these nitrogen oxides. More specifically, a catalyst for purifying and purifying exhaust gas is a catalyst for removing and purifying nitrogen oxides in exhaust gas discharged from factories, automobiles, and the like. Nitrogen is converted to nitrogen dioxide on the catalyst, and then, together with the nitrogen dioxide present in the exhaust gas from the beginning, these nitrogen dioxides are adsorbed on the catalyst, where a reducing agent such as fuel is intermittently introduced into the exhaust gas for a short time. That is, in addition to the pulsation, by periodically reducing the exhaust gas atmosphere to a reducing atmosphere, while performing catalytic reduction,
The present invention relates to a nitrogen oxide storage type exhaust gas purification catalyst for oxidizing and removing harmful components such as hydrocarbons and carbon monoxide in an oxidizing atmosphere.

[0002]

2. Description of the Related Art Conventionally, as a method of removing nitrogen oxides from exhaust gas discharged from factories, automobiles, etc., there is a method of oxidizing the nitrogen oxides and then absorbing the same with an alkali, ammonia, hydrogen, carbon monoxide. And a method of converting to nitrogen by using a reducing agent such as hydrocarbon. 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, there is a problem that the reducing 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, even with such Cu-ZSM-5 or H-type ZSM-5, it is still difficult to say that they have a sufficient reducing activity. In particular, when moisture is contained in exhaust gas, aluminum in the zeolite structure is removed. Since the performance of aluminum is rapidly lowered, a catalyst for nitrogen oxide catalytic reduction having higher reduction activity and having excellent durability even when the exhaust gas contains moisture is demanded. .

Therefore, various catalysts such as a catalyst comprising silver or silver oxide supported on an inorganic oxide have been proposed.
Among such catalysts, a catalyst having a high reaction rate has a high oxidizing activity and a low selectivity for nitrogen oxides, so that the removal rate of nitrogen oxides is low, and on the other hand, a reaction selectivity such as alumina is high. The catalyst has a serious problem in practical use, such as a low reaction rate and difficulty in use at a high SV (space velocity). Further, there is a problem that the catalyst activity is significantly deteriorated in the coexistence of sulfur oxide (JP-A-5-31764).
No. 7). 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.

Therefore, as one method for solving such a problem, nitric oxide (NO) is converted to nitrogen dioxide (NO ₂ ) on a catalyst under an excess of oxygen (lean condition), and thus the produced product is produced. Nitrogen dioxide is adsorbed on the catalyst, and a reducing agent, for example, a hydrocarbon such as fuel or an oxygen-containing organic compound is intermittently injected for a short period of time, that is, in a pulsating manner (hereinafter, referred to as pulsating)
Injecting "pulse". ), A nitrogen oxide storage catalyst that reduces nitrogen oxides to nitrogen under a reducing atmosphere (rich conditions) has been proposed. However, since exhaust gas usually contains sulfur oxides, according to this method, sulfur oxides are adsorbed at the adsorption points of nitrogen oxides, and hydrocarbons such as fuel are pulsed. Even when the fuel is injected into a reducing atmosphere, this sulfur oxide does not desorb from the catalyst, so that the amount of nitrogen oxide adsorbed on the catalyst gradually decreases, and the nitrogen oxide removal rate decreases. There is.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems in the conventional nitrogen oxide storage type exhaust gas purifying catalyst. Under the catalyst, nitric oxide is converted to nitrogen dioxide with high efficiency on the catalyst, and thus the generated nitrogen dioxide is adsorbed on the catalyst, and a reducing agent is injected in a pulsed manner to reduce the exhaust gas atmosphere to a reducing atmosphere. As a nitrogen oxide storage catalyst that reduces nitrogen oxides to nitrogen, even when the exhaust gas contains sulfur oxides,
Nitrogen oxide storage type exhaust gas that does not decrease the nitrogen oxide storage function of nitrogen oxides and is also poor in heat resistance, and therefore can efficiently reduce nitrogen oxides in exhaust gas over a long period of time. It is to provide a purification catalyst.

[0008]

The nitrogen oxide storage type exhaust gas purifying catalyst according to the present invention is selected from the group consisting of (a) a composite oxide of barium and aluminum and (b) Pt, Rh, Pd and Ir. It is characterized by comprising at least one element (hereinafter, may be simply referred to as a platinum group element).

The nitrogen oxide storage type exhaust gas purifying catalyst according to the present invention may further comprise (c) at least one selected from zirconium oxide and aluminum oxide,
(D) Gallium oxide or (e) at least one selected from zirconium oxide and aluminum oxide and gallium oxide can be contained.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An exhaust gas purifying catalyst according to the present invention comprises:
It is composed of 90 to 99.9% by weight of a composite oxide of barium and aluminum and 10 to 0.1% by weight of at least one element selected from the group consisting of Pt, Rh, Pd and Ir.

The composite oxide of barium and aluminum is
As already known, it is a composite oxide composed of barium, aluminum and oxygen, and is BaO.Al
₂ O ₃ or BaO.6Al ₂ O ₃ (Hirotsu Arai, Masato Machida, “Metal” June 1989, heat-resistant ceramic fine particles).

In the purification catalyst according to the present invention, the catalyst component composed of a platinum group element is expressed in terms of the total weight of the catalyst component.
When the amount is less than 0.1% by weight in terms of element, the resulting purification catalyst has extremely low nitrogen oxide catalytic reduction ability,
On the other hand, if the content exceeds 10% by weight, the catalytic reduction ability of the obtained purification catalyst for nitrogen oxides is not improved correspondingly, and the production cost of the catalyst is unnecessarily increased, which is disadvantageous.

As will be described later, in the purification of exhaust gas using the purification catalyst according to the present invention, an exhaust gas containing nitrogen oxide is brought into contact with the catalyst under an oxygen-excess atmosphere (lean condition) to remove nitrogen oxide, especially Nitrogen oxide is converted to nitrogen dioxide on a catalyst component composed of a platinum group element. Thus, the generated nitrogen dioxide is weakly adsorbed on a catalyst component composed of a composite oxide of barium and aluminum, and a reducing agent is injected into the catalyst. The exhaust gas is placed under a reducing atmosphere (rich conditions) by the method described above, and the nitrogen oxides adsorbed on the catalyst component are catalytically reduced to nitrogen by the reducing agent to be removed from the exhaust gas.

Therefore, the catalyst according to the present invention is preferably selected from zirconium oxide and aluminum oxide together with the above-mentioned composite oxide of barium and aluminum and the above-mentioned platinum group element in order to assist adsorption of nitrogen oxides to the catalyst. It has at least one kind as a catalyst component.

When the exhaust gas purifying catalyst according to the present invention has zirconium oxide as a catalyst component together with a composite oxide of barium and aluminum, the composite oxide of barium and aluminum / zirconium oxide is a composite of barium and aluminum. It is a mixture of an oxide and zirconium oxide. When the exhaust gas purifying catalyst according to the present invention has aluminum oxide as a catalyst component together with barium / aluminum composite oxide, the barium / aluminum composite oxide / aluminum oxide is a mixture of barium / aluminum composite oxide and aluminum oxide. Alternatively, a composite oxide in which a composite oxide of barium and aluminum coexists in the crystal of aluminum oxide may be used.

Further, the purification catalyst according to the present invention may have zirconium oxide and aluminum oxide as catalyst components. In this case, such a composite oxide of barium and aluminum / zirconium oxide and aluminum oxide are: A mixture of these may be used, and zirconium oxide and aluminum oxide may be a composite oxide containing zirconium ions in aluminum oxide crystals. According to the present invention, when zirconium oxide and aluminum oxide are thus contained as a composite oxide in the catalyst, the aluminum oxide adsorbs the sulfur oxide in the exhaust gas to oxidize hydrocarbons and nitric oxide of the catalyst. This is preferable because it prevents the performance from being reduced.

When the purification catalyst according to the present invention has at least one kind selected from zirconium oxide and aluminum oxide as a catalyst component, the amount of at least one kind selected from zirconium oxide and aluminum oxide is determined by the amount of the composite oxide of barium and aluminum. It is usually in the range of 50 to 200 parts by weight based on 100 parts by weight of the total weight of the platinum group element. When at least one selected from zirconium oxide and aluminum oxide is less than 50 parts by weight based on 100 parts by weight of the total weight of the composite oxide of barium and aluminum and the platinum group element, the catalyst has an ability to adsorb nitrogen dioxide on the catalyst. Little improvement effect. However, at least one selected from zirconium oxide and aluminum oxide
When the species is more than 200 parts by weight based on 100 parts by weight of the total weight of the composite oxide of barium and aluminum and the platinum group element, it impairs the ability to adsorb nitrogen dioxide on the catalyst and the ability to reduce nitrogen oxides. .

In particular, when the exhaust gas purifying catalyst according to the present invention has both zirconium oxide and aluminum oxide as catalyst components, the ratio of zirconium oxide to aluminum oxide is 75/25 to 75/25 by weight in terms of zirconium oxide / aluminum oxide. It is preferably in the range of 5/95, and particularly preferably in the range of 50/50 to 10/90.

Further, the exhaust gas purifying catalyst according to the present invention may have gallium oxide as a catalyst component. The gallium oxide plays a role in increasing the ability of a catalyst to oxidize nitrogen monoxide in exhaust gas to nitrogen dioxide. The amount of gallium oxide in the catalyst is usually 0.1 to 10 parts by weight, preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the total weight of the composite oxide of barium and aluminum and the platinum group element.
The range is 5 parts by weight.

In the present invention, the components of the exhaust gas purifying catalyst may be further added, if necessary, to a conventional heat-resistant carrier conventionally known as a catalyst carrier, such as alumina, silica, zirconia, silica-alumina, titania and the like. May be supported. The amount of these catalyst components carried is preferably in the range of 10 to 95% by weight, more preferably 50 to 95% by weight, based on the total weight of the carrier and the catalyst components. When the supported amount of the catalyst component is less than 10% by weight, the nitrogen oxide storage capacity of the obtained purification catalyst is significantly reduced, and the purification capacity of exhaust gas is further reduced.

Such a nitrogen oxide storage type exhaust gas purifying catalyst according to the present invention is exemplified by the following (1) or (2).
Can be prepared according to any one of the above methods. (1) For example, alumina and barium carbonate are dispersed in water, sufficiently mixed and pulverized using a ceramic pulverizing medium, and the obtained slurry is dried.
It is calcined in the air at a temperature of 00 to 1500 ° C. to obtain a composite oxide powder of barium and aluminum (powder A).

On the other hand, a water-soluble salt (eg, nitrate) which is a precursor of zirconium oxide or aluminum oxide is dissolved in ion-exchanged water, and an alkali such as ammonia is gradually added thereto to adjust the pH of the slurry. The precipitate is formed by raising the hydroxide from the neutral salt until a hydroxide is formed. Subsequently, the precipitate thus obtained was separated by filtration, washed with water,
After drying, this is oxidized atmosphere such as air,
About 400 to 800 ° C, preferably 600 to 800 ° C
By baking at about the temperature, powder of zirconium oxide or aluminum oxide can be obtained.

Next, the zirconium oxide or aluminum oxide powder is immersed in a separately prepared aqueous solution of a water-soluble salt of a platinum group element, dried, and fired in an oxidizing atmosphere. By calcining in an atmosphere, a powder (powder B) obtained by supporting a catalyst component composed of a platinum group element on the zirconium oxide or aluminum oxide is obtained. Then, by mixing the powder A and the powder B thus obtained, the exhaust gas purifying catalyst according to the present invention can be obtained as a powder.

(2) For example, an aqueous solution of a water-soluble salt which is a precursor of alumina such as aluminum nitrate or a water-soluble salt which is a precursor of zirconium oxide such as zirconium nitrate is prepared, or a homogeneous solution thereof is prepared. A mixed aqueous solution is prepared, an alkali such as ammonia is gradually added to the aqueous solution and neutralized to form a precipitate, and then the precipitate is repeatedly subjected to filtration, washing and re-pulp operations.
Get a wet cake. This wet cake is repulped in ion-exchanged water, barium hydroxide is added thereto, and hydrothermal treatment is performed in an autoclave at a temperature of 100 to 300 ° C. After this hydrothermal treatment, the solid content is filtered, washed with water, dried, and then calcined in air at a temperature of 800 to 1500 to obtain an alumina and / or zirconia powder supporting a composite oxide of barium and aluminum. .

Next, this powder is immersed in a separately prepared aqueous solution of a water-soluble salt of a platinum group element, dried, and fired in an oxidizing atmosphere, and in some cases, further fired in a reducing atmosphere. In addition, a purification catalyst according to the present invention in which a platinum-group element is supported on a composite oxide of barium and aluminum and zirconium oxide and / or aluminum oxide can be obtained as a powder.

The purification of exhaust gas using the purification catalyst according to the present invention is performed by the following mechanism. However, the present invention is not at all limited by such a mechanism or theory. That is, an exhaust gas containing nitrogen oxides is brought into contact with the purification catalyst of the present invention under an oxygen-excess atmosphere (lean condition), and first, the nitrogen oxides, particularly, nitrogen monoxide are converted to the platinum group element (and gallium oxide). Is converted to nitrogen dioxide on the catalyst component consisting of, and the generated nitrogen dioxide is adsorbed on the catalyst component consisting of a composite oxide of barium and aluminum (and zirconium oxide and / or aluminum oxide), and a reducing agent is added thereto. The exhaust gas is placed under a reducing atmosphere (rich conditions) by a method such as injection, and the nitrogen oxides adsorbed on the catalyst component are catalytically reduced to nitrogen by the reducing agent to be removed from the exhaust gas.

In the present invention, the oxygen-excess atmosphere (lean condition) refers to a hydrocarbon, carbon monoxide,
Atmosphere conditions that contain more oxygen than combustible components such as hydrogen are completely burned by oxygen contained in exhaust gas. That is, it refers to an atmosphere condition in which the exhaust gas contains more oxygen than the stoichiometric air-fuel ratio condition (stoichiometric condition). On the other hand, the reducing atmosphere (rich condition) is the opposite of the above-mentioned lean condition, which means that the hydrocarbon contained in the exhaust gas,
Atmosphere conditions in which combustible components such as carbon monoxide and hydrogen do not contain oxygen in an amount sufficient for complete combustion by oxygen contained in exhaust gas.

In the exhaust gas purifying catalyst according to the present invention, sulfur oxides are also adsorbed at the adsorption points of nitrogen oxides in the process of detoxifying nitrogen oxides in exhaust gas by contacting them with nitrogen. However, according to the exhaust gas purifying catalyst according to the present invention, sulfur oxides are easily desorbed into the exhaust gas under rich conditions. Purification ability does not decrease.
Therefore, the exhaust gas purifying catalyst according to the present invention can be used, for example, for lean burn gasoline, GD
I (Gasoline Direct Injecti
(on, gasoline direct injection) It can be suitably used as a catalyst exclusively for vehicles. Further, the exhaust gas purifying catalyst according to the present invention has excellent heat resistance.

As described above, the catalyst according to the present invention can be usually obtained as a powder or a granular material. Therefore, the catalyst itself can be formed into a honeycomb, spherical, or annular shape by a conventionally known ordinary molding method. , Etc., can be easily formed into various structures and shapes. When such a catalyst according to the present invention is formed into a required structure or shape, various conventionally known forming auxiliaries, a reinforcing material for a formed body, inorganic fibers, an organic binder and the like are appropriately compounded as necessary. May be.

A structure such as a honeycomb or a spherical body which itself comprises the exhaust gas purifying catalyst according to the present invention can be obtained, for example, as follows. That is, as described above, the catalyst according to the present invention may be prepared as a powder, kneaded with an organic binder using an appropriate solvent, formed into a honeycomb structure, dried, and fired.

According to the present invention, an inert substrate is formed into a required shape in advance, and the powdery catalyst according to the present invention is coated and supported by an appropriate method such as a wash coat method. It can also be a catalyst structure. Examples of the molded body made of the inert substrate include, for example, a corrugated honeycomb made of stainless steel foil, a honeycomb made of a mineral substance such as cordierite, a sphere, and a structure such as a ring. A three-dimensional catalyst structure can be obtained by carrying a catalyst on these.

According to the present invention, a catalyst layer is formed on the surface of a structure such as a honeycomb or a sphere or a ring made of an inert substrate by a wash coat method or the like. When the catalyst is supported, the catalyst layer has a thickness of 30 μm or more from the surface thereof (hereinafter, for simplicity,
It is called the catalyst layer thickness. ) Is preferably carried on the surface of the structure. By thus forming the catalyst layer supported on the structure over a thickness of 30 μm or more from the surface, a catalyst structure having high reactivity to nitrogen oxides, that is, high selective reduction of nitrogen oxides is obtained. be able to. However, according to the present invention, the thickness of the catalyst layer may be usually 300 μm or less. 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 the catalyst structure.

In the honeycomb catalyst structure itself composed of the catalyst component as described above, the thickness of the catalyst layer is substantially uniform in the thickness direction of the cell wall of the honeycomb catalyst structure. Therefore, if the cell wall of the honeycomb structure is 60 μm or more, the catalyst is supported over a 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 present invention, a hydrocarbon or an oxygen-containing organic compound is preferably used as the reducing agent for keeping the exhaust gas under rich conditions. Among them, hydrocarbons include, for example, methane, ethane, propane, ethylene, propylene, 1-butene,
-Hydrocarbon gas such as butene, as liquid, single component hydrocarbon such as pentane, hexane, octane, heptane, benzene, toluene, xylene, gasoline,
Mineral oil-based hydrocarbons such as kerosene, light oil and heavy oil can be mentioned. In particular, according to the present invention, among the above, ethylene, propylene, isobutylene, 1-butene, 2-
Lower alkenes such as butene, lower alkanes such as propane and butane, light oil and the like are preferably used. These hydrocarbons may be used alone or in combination of two or more as needed.

In particular, according to the present invention, when purifying automobile engine exhaust gas, the fuel can be suitably used as a reducing agent.

Examples of the oxygen-containing organic compound include alcohols such as methanol, ethanol, propanol, butanol and octanol; ethers such as dimethyl ether, diethyl ether and dipropyl ether; methyl acetate, ethyl acetate, oils and fats. , Such as acetone, methyl ethyl ketone, ketones such as methyl isobutyl ketone, acetaldehyde,
Aldehydes such as puspionaldehyde can be mentioned. 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 usually, the oxygen in the exhaust gas reacts with the reducing agent and the oxygen concentration becomes 0%. Is used in a molar ratio of about 0.9 to about 10 with respect to the minimum amount of the reducing agent required (i.e., stoichiometric amount). When the amount of the reducing agent used is less than 0.9 in a molar ratio with respect to the minimum amount (stoichiometric amount), the nitrogen oxides are not sufficiently reduced, while the molar ratio is 10%.
When the pressure exceeds 1, the amount of unreacted reducing agent discharged is increased, so that after the purification treatment of nitrogen oxides in the exhaust gas, a post-treatment for removing nitrogen oxides is required.

In the present invention, the respective conditions of the lean condition for oxidizing nitrogen oxides in the exhaust gas to be adsorbed on the catalyst and the rich condition for reducing and removing the adsorbed nitrogen oxides with a reducing agent are different in the exhaust gas treatment. Although it can be appropriately determined depending on the conditions, usually, the lean condition is 30 seconds to 1 second.
The minute and rich conditions are from 1 second to 1 minute.

The optimum temperature at which the catalyst according to the present invention exhibits a reducing activity on nitrogen oxides varies depending on the reducing agent and the type of catalyst used, but is usually from 100 to 800 ° C. In this temperature range, the space velocity (SV) 5000 to 1000
It is preferable that the exhaust gas is circulated at about 00 hr ^-1 . A particularly preferred reaction temperature range in the present invention is 200
~ 500 ° C.

[0041]

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 75.00 g of barium carbonate (BaCO ₃ ) and hydrated alumina (Al ₂ O ₃ .nH ₂ O, GB manufactured by Mizusawa Chemical Industry Co., Ltd.)
−45) 41.65 g (38.74 g as alumina) was dispersed in 200 mL of ion-exchanged water, 100 mL of zirconia balls were added as a grinding medium to this slurry, and the mixture was wet-pulverized with a planetary mill for 30 minutes. The slurry was separated by filtration, dried and then dried in air at 100
By firing at 0 ° C. for 3 hours, a composite oxide of barium and aluminum (BaO.Al ₂ O ₃ ) was obtained.

30 g of the barium / aluminum composite oxide powder and γ-alumina powder (Sumitomo Chemical Industries, Ltd.)
30 g of silica sol (Snowtex N, manufactured by Nissan Chemical Industries, Ltd.) and 6 g of silica sol were mixed with an appropriate amount of water. A slurry for coating was prepared. This slurry was applied to a honeycomb substrate made of cordierite having a cell number of 200 / in _2, and about 150 g of BaO · Al ₂ O ₃ / γ-alumina was applied.
/ L (layer thickness 79 μm).

Then, 6.25 g of an aqueous dinitrodiammine platinum solution (15.09% by weight as platinum) was made up to 30 mL with ion-exchanged water, and the above-mentioned BaO.Al
After dipping the honeycomb substrate supporting ₂ O ₃ / γ-alumina, the excess aqueous solution adhering to the substrate was removed, and 100 ° C.
For 12 hours, and further calcined in air at 600 ° C. for 3 hours to obtain BaO.Al ₂ O carrying 2% by weight of platinum.
_{A 3} / γ-alumina catalyst was obtained. This catalyst is called A-1. The component ratio (% by weight) of this catalyst is BaO.Al ₂
O ₃ /pt/γ-alumina=96.2/3.8/96.
It was 2.

Example 2 75.00 g of barium carbonate (BaCO ₃ ) and 49.98 g of hydrated alumina (GB-45 manufactured by Mizusawa Chemical Industry Co., Ltd.)
(46.48 g of alumina) in ion-exchanged water 200
Dispersed in mL. 100 mL of zirconia balls are added to this slurry as a grinding medium,
Wet pulverized. The slurry thus obtained was separated by filtration, dried, and calcined in air at 1200 ° C. for 3 hours to obtain a composite oxide of barium and aluminum (BaO · A).
mixed crystal of l ₂ O ₃ and BaO · 6Al ₂ O ₃ ).

Thereafter, in the same manner as in Example 1, the powder 3
A slurry for wash coating was prepared using 0 g, 30 g of γ-alumina powder, and 6 g of silica sol, applied to a honeycomb substrate made of cordierite, and the barium / aluminum composite oxide and γ-alumina were applied. It was loaded at a rate of about 150 g / L (layer thickness 81 μm).

Next, 6.25 g of dinitrodiammine platinum (15.09% by weight as platinum) was added to 30 parts of ion-exchanged water.
mL, and a honeycomb substrate supporting the barium / aluminum composite oxide and γ-alumina was immersed in the aqueous solution to remove an excessive amount of the attached aqueous solution.
Dry at 0 ° C for 12 hours, and further in air at 600 ° C for 3 hours.
After calcination for a period of time, a composite oxide of barium and aluminum / γ-alumina catalyst supporting 2% by weight of platinum was obtained. This catalyst is referred to as A-2. Component ratio of this catalyst (% by weight)
The mixed crystal of BaO · _Al 2 _{O 3} and _{BaO · 6Al 2 O 3 / pt} / γ- alumina = 96.2 / 3.8 / 96.2
Met.

Example 3 75.00 g of barium carbonate (BaCO ₃ ) and 38.74 g of hydrated alumina (GB-45 manufactured by Mizusawa Chemical Industry Co., Ltd.) were dispersed in 200 mL of ion-exchanged water. To this slurry was added 100 mL of zirconia balls as a grinding medium, and the mixture was wet-ground with a planetary mill for 30 minutes. The slurry thus obtained was separated by filtration and dried, and then dried in air.
By firing at 0 ° C. for 3 hours, a composite oxide of barium and aluminum (BaO.Al ₂ O ₃ ) was obtained.

On the other hand, aluminum nitrate (Al (NO ₃ )
₃ · _9H 2 O) _275.96g and zirconyl nitrate (Zr
O a _{(NO 3) 2 · 2H 2} O) 27.10g was dissolved in deionized water 2L. To this, 1/10 normal ammonia water was added dropwise with stirring while adjusting the pH with a pH controller set to pH 8. After completion of the dropwise addition, the mixture was aged for 1 hour to obtain a slurry of a mixture of aluminum hydroxide and zirconium hydroxide. This slurry was filtered, washed with water, and calcined at 700 ° C. for 3 hours in air to obtain a mixture of alumina and zirconia at a weight ratio of 75/25.

Next, 30 g of the above-mentioned barium / aluminum composite oxide powder, 30 g of γ-alumina / zirconia mixture powder and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) were mixed with an appropriate amount of water. This was wet-ground with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium to prepare a wash coat slurry. The slurry is applied to a honeycomb substrate made of cordierite having a cell number of 200 / square inch, and a composite oxide of barium and aluminum and γ-alumina / zirconia are supported at a ratio of about 150 g / L (layer thickness 79 μm). Was.

Then, 6.25 g of an aqueous dinitrodiammine platinum solution (15.09% by weight as platinum) was made up to 30 mL with ion-exchanged water, and the composite oxide of barium and aluminum and γ-alumina / zirconia were supported in the aqueous solution. After immersing the honeycomb substrate, the excess aqueous solution attached is removed, dried at 100 ° C. for 12 hours, and further baked in air at 600 ° C. for 3 hours to obtain 2% by weight of platinum.
-Supported composite oxide of barium and aluminum / γ
An alumina / zirconia catalyst was obtained. This catalyst is designated A-3
That. The component ratio (% by weight) of this catalyst is BaO · A
l ₂ O ₃ /pt/γ-alumina/zirconia=96.2
/3.8/72.1/24.0.

Example 4 75.00 g of barium carbonate (BaCO ₃ ) and 38.74 g of hydrated alumina (GB = 45 manufactured by Mizusawa Chemical Industry Co., Ltd.) were dispersed in 200 mL of ion-exchanged water. To this slurry was added 100 mL of zirconia balls as a grinding medium, and the mixture was wet-ground with a planetary mill for 30 minutes. The slurry thus obtained was separated by filtration and dried, and then dried in air.
By firing at 0 ° C. for 3 hours, a composite oxide of barium and aluminum (BaO.Al ₂ O ₃ ) was obtained.

On the other hand, aluminum nitrate (Al (NO ₃ )
₃ · _9H 2 O) _275.96g and zirconyl nitrate (Zr
27.10 g of O (NO ₃ ) ₂ .2H ₂ O) and 2.63 g of gallium nitrate (Ga (NO ₃ ) ₃ .nH ₂ O) were dissolved in ₂ L of ion-exchanged water. To this, 1/10 normal ammonia water was added dropwise with stirring while adjusting the pH with a pH controller set to pH 8. After dropping, the mixture was aged for 1 hour to obtain a slurry of a mixture of aluminum hydroxide, zirconium hydroxide and gallium hydroxide. This slurry was filtered, washed with water, and then calcined at 700 ° C. for 3 hours in air to obtain an oxide / alumina / zirconia / gallium oxide mixture having a weight ratio of 75/25/1.

Next, 30 g of the barium / aluminum composite oxide powder, 30 g of the above alumina / zirconia / gallium oxide powder, and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) were mixed with an appropriate amount of water. This was wet-milled with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium to prepare a slurry for wash coating. This slurry was applied to a honeycomb substrate made of cordierite having a cell number of 200 / square inch, and a composite oxide of barium and aluminum / alumina / zirconia / gallium oxide was applied at about 150 g / L (layer thickness 79 μm).
m).

Next, 6.25 g of an aqueous solution of dinitrodiammine platinum (15.09% by weight as platinum) was made up to 30 mL with ion-exchanged water, and the above-mentioned complex oxide of barium and aluminum / alumina / zirconia / gallium oxide was carried in this aqueous solution. After the immersed honeycomb, the excess aqueous solution attached was removed, dried at 100 ° C. for 12 hours, and further baked in air at 600 ° C. for 3 hours to obtain platinum 2
Thus, a composite oxide of barium and aluminum / alumina / zirconia / gallium oxide catalyst supporting the weight% was obtained.
This catalyst is referred to as A-4. The component ratio (% by weight) of this catalyst was BaO.Al ₂ O ₃ / pt / γ-alumina / zirconia / gallium oxide = 96.2 / 3.8 / 71.3.
/23.8/1.0.

Example 5 In Example 1, dinitrodiammineplatinum was used in place of dinitrodiammineplatinum.
Palladium nitrate aqueous solution (4.37% by weight as Pd) 2
1.7 g was made up to 30 mL with ion-exchanged water, and a honeycomb base material supporting the same composite oxide of barium and aluminum and γ-alumina as used in Example 1 was immersed in this aqueous solution, and the excess The aqueous solution of
The resultant was dried at 00 ° C. for 12 hours and further calcined in air at 600 ° C. for 3 hours to obtain a composite oxide of barium and aluminum / γ-alumina supporting 2% by weight of palladium. This catalyst is designated as A-5. The component ratio (% by weight) of this catalyst was BaO.Al ₂ O ₃ /Pd/γ-alumina=96.2/3.8/96.2.

Example 6 Rhodium nitrate aqueous solution (8.45% by weight as Rh) instead of palladium nitrate aqueous solution in Example 5
21 g was made up to 30 mL with ion-exchanged water. A honeycomb substrate supporting the barium / aluminum composite oxide and γ-alumina was immersed in this aqueous solution to remove the excess aqueous solution adhering thereto. Dry for 12 hours at
Further, it is baked at 600 ° C. for 3 hours in the air to obtain rhodium 2
Thus, a composite oxide of barium and aluminum / γ-alumina catalyst supporting the same by weight was obtained. This catalyst is called A-6. The component ratio (% by weight) of this catalyst is BaO.Al ₂
O ₃ /Rh/γ-alumina=96.2/3.8/96.
It was 2.

Example 7 In Example 5, an aqueous solution of chloroplatinic acid (15.09% by weight as platinum) 5.0 was used instead of the aqueous solution of palladium nitrate.
A mixture of 0 g and 2.24 g of an aqueous rhodium nitrate solution (8.45% by weight as Rh) was made up to 30 mL with ion-exchanged water, and a honeycomb group in which the above-mentioned barium / aluminum composite oxide and γ-alumina were supported in the aqueous solution The material was immersed to remove excess adhering aqueous solution, dried at 100 ° C. for 12 hours, and further calcined in air at 600 ° C. for 3 hours to obtain 1.6% by weight of platinum and 0.4% of rhodium. % By weight of a composite oxide of barium and aluminum / γ-
An alumina catalyst was obtained. This catalyst is called A-7. The component ratio (% by weight) of this catalyst is BaO.Al ₂ O ₃ / Pt.
/Rh/γ-alumina=96.1/3.1/0.8/9
6.2.

Example 8 Instead of the palladium nitrate aqueous solution in Example 5, 18.84 g of an iridium chloride aqueous solution (5.00% by weight as iridium) was made up to 30 mL with ion-exchanged water. A honeycomb substrate supporting the composite oxide and γ-alumina is immersed to remove the excess aqueous solution attached thereto, dried at 100 ° C. for 12 hours, and further baked in air at 600 ° C. for 3 hours. do it,
A composite oxide of barium and aluminum / γ-alumina catalyst supporting 2% by weight of iridium was obtained. This catalyst is designated as A-8. The component ratio (% by weight) of this catalyst is Ba
O.Al ₂ O ₃ /Ir/γ-alumina=96.2/3.
8 / 96.2.

Comparative Example 1 20 g of barium carbonate (BaCO ₃ ), 40 g of the same γ-alumina powder as above and 6 g of silica sol were mixed with an appropriate amount of water, and this was mixed for 5 minutes with a planetary mill using 100 g of zirconia balls as a grinding medium. A wet coat slurry was prepared by wet grinding. This slurry was used for 200 cells.
/ Square inch of cordierite and applied to a honeycomb substrate of barium carbonate and γ-alumina at about 150 g /
L (layer thickness 79 μm).

6.25 g of an aqueous solution of dinitrodiammine platinum (15.09% by weight as platinum) was added to 30 parts of ion-exchanged water.
mL, and a honeycomb substrate supporting the barium carbonate and γ-alumina was immersed in the aqueous solution to remove an excessive amount of the attached aqueous solution, and dried at 100 ° C. for 12 hours.
Further, it was calcined in air at 600 ° C. for 3 hours to obtain a barium oxide / γ-alumina catalyst supporting 2% by weight of platinum. This catalyst is called B-1. The component ratio (% by weight) of this catalyst was BaO / Pt / γ-alumina = 96.2 /
3.8 / 96.2.

(2) Evaluation Test Purification of exhaust gas containing nitrogen oxides under the following test conditions using the catalysts (A-1 to 8) of the above examples and the catalyst (B-1) of the comparative example. (Catalytic reduction of nitrogen oxides), and the removal rate of nitrogen oxides was determined by a chemical luminescence method. At this time, the nitrogen oxide removal rate was determined from an integrated value of the nitrogen oxide concentration time under a rich condition and a lean condition as a function.

(Test conditions) (1) Gas composition Rich condition NO 500 ppm O ₂ 0 vol% Propylene 5000 ppm SO ₂ 40 ppm water 6 vol% Nitrogen balance Lean condition NO 500 ppm O ₂ 10 vol% Propylene 500 ppm SO ₂ 40 ppm water 6 vol% Nitrogen balance The above rich condition and lean condition were alternately vibrated at one minute intervals. (2) Space velocity 5000 (hr ^-1 ) (3) Reaction temperature 200 ° C, 250 ° C, 300
Table 1 shows the results at ℃, 350 ℃ and 400 ℃.

[0064]

[Table 1]

Next, using the catalysts prepared in Example 4 and Comparative Example 1, the reaction was carried out for 3 hours under the above reaction conditions except that the reaction temperature was 600 ° C. Then, the exhaust gas was purified, and the heat resistance and sulfur oxide resistance of the catalyst were evaluated. Table 2 shows the results.

[0066]

[Table 2]

[0067]

As is evident from the results shown in Tables 1 and 2, the catalyst according to the present invention has a high removal rate of nitrogen oxides and is excellent not only in sulfur oxide resistance but also in heat resistance. Is also excellent.

 ──────────────────────────────────────────────────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 (5)

[Claims] 1. Nitrogen oxidation from exhaust gas characterized by comprising (a) a composite oxide of barium and aluminum and (b) at least one element selected from the group consisting of Pt, Rh, Pd and Ir. Exhaust gas purification catalyst for removing matter. (A) a composite oxide of barium and aluminum; (b) at least one element selected from the group consisting of Pt, Rh, Pd and Ir; and (c) selected from zirconium oxide and aluminum oxide. An exhaust gas purifying catalyst for removing nitrogen oxides from exhaust gas, comprising at least one of the following. 3. A method comprising: (a) a composite oxide of barium and aluminum; (b) at least one element selected from the group consisting of Pt, Rh, Pd and Ir; and (c) gallium oxide. Exhaust gas purifying catalyst for removing nitrogen oxides from exhaust gas. 4. A composite oxide of (a) barium and aluminum; (b) at least one element selected from the group consisting of Pt, Rh, Pd and Ir; and (c) selected from zirconium oxide and aluminum oxide. An exhaust gas purifying catalyst for removing nitrogen oxides from exhaust gas, comprising: at least one of the following: (d) gallium oxide. 5. A method for purifying an exhaust gas, wherein the exhaust gas containing nitrogen oxide is brought into contact with the catalyst according to any one of claims 1 to 4 for reduction treatment, wherein the treatment atmosphere for the exhaust gas is an oxygen-excess atmosphere and a reducing atmosphere. A method for purifying exhaust gas, wherein the exhaust gas is vibrated alternately.