JPH05168863A - Removing method of nitrogen oxide - Google Patents

Abstract

PURPOSE:To provide a method to efficiently remove nitrogen oxides from exhaust gas discharged from automobiles, especially from a lean-burn engine by using a catalyst having excellent durability which hardly causes thermal deterioration compared to conventional exhaust gas purifying catalyst. CONSTITUTION:The catalyst is obtd. by depositing at least one of nickel, manganese and cerium on a zeolite containing copper or cobalt and having >=15 SiO2/ Al2O3 molar ratio in an org. solvent. An oxygen-excess exhaust gas containing nitrogen oxides and hydrocarbons is brought into contact with this catalyst, thereby, nitrogen oxides can efficiently be removed from the exhaust gas of oxygen-excess atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst for removing nitrogen oxides, carbon monoxide and hydrocarbons in exhaust gas discharged from internal combustion engines such as automobiles, and moreover, nitrogen from exhaust gas under excess oxygen. The present invention relates to a method for reducing oxides.

[0002]

2. Description of the Related Art At present, nitrogen oxides, carbon monoxide and hydrocarbons which are harmful to the human body in exhaust gas emitted from a gasoline engine are ternary in which platinum, rhodium and palladium are supported on a carrier. It has been removed by the catalyst. However, with regard to diesel engine exhaust gas, it is difficult to perform reductive denitration with a three-way catalyst because the oxygen concentration in the exhaust gas is higher than that of a gasoline engine.

In recent years, a lean-burn gasoline engine has been developed in order to reduce carbon dioxide emissions or reduce fuel consumption. However, since the exhaust gas of this lean-burn gasoline engine is in an oxygen excess atmosphere, it is difficult to denitrate with the conventional three-way catalyst as described above, and the method for removing nitrogen oxides has not been put to practical use.

Up to now, as a method for removing nitrogen oxides from exhaust gas having excess oxygen, there have been used a selective catalytic reduction method on V ₂ O ₅ / TiO ₂ using ammonia as a reducing agent and an absorption method to an alkaline solution. It is known, but in any case, the range of use is limited, and it is difficult to apply to automobiles and the like that are mobile sources.

Recently, it has been reported that nitrogen oxides in exhaust gas can be reduced and removed in the presence of excess oxygen by using a zeolite catalyst in which transition metals are ion-exchanged without adding a selective reducing agent such as ammonia. JP-A-63-28372
No. 7, Japanese Patent Laid-Open No. 1-1300375).

However, these conventional catalysts have a problem that their activity remarkably deteriorates when they are used at a high temperature for a long time, and it is necessary to improve the catalyst performance and durability.

As a catalyst for improving this, SiO ₂ / A
A zeolite catalyst having a molar ratio of l ₂ O ₃ of at least 15 and containing cobalt and an alkaline earth metal has been proposed (JP-A-3-196842).
Publication). Furthermore, manganese, nickel,
It has been reported that by supporting a transition metal such as copper, zinc or silver or a noble metal such as platinum or rhodium in an aqueous solution, the effects of expanding the active temperature range and improving durability are exhibited (Japanese Patent Application No. 2). -411254, Japanese Patent Application No. 2-411255
Japanese Patent Application No. 2-411256, Japanese Patent Application No. 2-41125
No. 7).

[0008]

However, although the exhaust gas purifying catalyst proposed above has some improvement in catalytic performance and durability, in order to use it as an automobile exhaust gas purifying catalyst, etc. Higher nitrogen oxide removing ability and durability are required.

An object of the present invention is to provide a method for more efficiently removing nitrogen oxides from exhaust gas discharged from an automobile or the like, especially a lean-burn engine, by using a catalyst which is resistant to thermal deterioration and has excellent durability. It is in the place of providing.

[0010]

Means for Solving the Problems As a result of extensive studies on the supported catalysts, the present inventors have previously proposed SiO ₂ /
By allowing the exhaust gas purifying catalyst, which is a zeolite having an Al ₂ O ₃ molar ratio of at least 15 or more, and containing copper or cobalt, to further carry at least one selected from nickel, manganese, and cerium in an organic solvent, The inventors have found that the catalyst has excellent nitrogen oxide removing ability and durability, and have completed the present invention. That is, the present invention contains a copper or cobalt, SiO ₂
A catalyst in which at least one selected from nickel, manganese and cerium is supported in an organic solvent on a zeolite having a / Al ₂ O ₃ molar ratio of at least 15 or more;
It is intended to provide a method for removing nitrogen oxide, which is characterized in that an exhaust gas containing excess oxygen containing nitrogen oxide and hydrocarbon is brought into contact with the exhaust gas.

The present invention will be described in detail below.

The exhaust gas purifying catalyst according to the present invention contains copper or cobalt, and a zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of at least 15 or more and further nickel, manganese or cerium in an organic solvent. It is a catalyst.

[0013] Zeolites typically _{xM 2 / n O · Al 2} O 3 · ySiO 2 · zH 2 O ( where n is the valence of the cation, x is a number in the range of 0.8 to 2, y is The zeolite used in the present invention has a SiO ₂ / Al ₂ O ₃ molar ratio of 15 or more. The upper limit of the SiO ₂ / Al ₂ O ₃ molar ratio is not particularly limited, but SiO ₂ / Al ₂ O ₃
When the molar ratio is less than 15, the heat resistance and durability of the zeolite itself are low, so that the catalyst cannot have sufficient heat resistance and durability. Generally, the SiO ₂ / Al ₂ O ₃ molar ratio is 15 to
About 1000 is used.

The zeolite constituting the catalyst of the present invention may be either a natural product or a synthetic product, and the manufacturing method of these zeolites is not particularly limited, but typically, it is ferrierite, Y, ZSM. -5, ZSM-11, Z
Zeolites such as SM-12 and ZSM-20 can be used. Further, these zeolites can be used as the catalyst of the present invention as they are or after being treated with an ammonium salt, a mineral acid or the like and subjected to ion exchange into NH ₄ type or H type.

The zeolite used in the present invention is the above zeolite containing copper or cobalt, and further nickel,
It is prepared by supporting manganese and cerium in an organic solvent.

Copper or cobalt can be generally contained by an ion exchange method, an impregnation-supporting method, an evaporation-drying method, etc. Among them, the ion exchange method is preferable.

As the ion exchange method, a commonly used method, for example, an ion exchange method using an aqueous solution containing copper or cobalt ions can be adopted. Copper or cobalt ion can be used in the form of a soluble salt, and as the soluble salt, nitrate, acetate, oxalate, chloride and the like can be preferably used.

The amount of copper or cobalt ions added during ion exchange is based on the number of moles of alumina in the zeolite.
It is preferably 0.1 to 10. If the added amount of copper or cobalt is less than 0.1, the content of copper and cobalt in the catalyst of the present invention may be low, and sufficient catalytic performance may not be obtained. There is a possibility that the effect will not be obtained. Regarding the treatment condition, a temperature which is usually performed from room temperature to 100 ° C. and a time of 1 hour to 10 days may be used. Further, the ion exchange operation can be repeated if necessary.

The zeolite containing copper or cobalt may further contain an alkaline earth metal. The method for containing the alkaline earth metal is not particularly limited, but an ion exchange method is desirable, and when it is contained, the alkaline earth metal and copper or cobalt may be sequentially contained,
It may be contained at once. Preferably, the alkaline earth metal is first added and then copper or cobalt is added.

Regarding the method of containing nickel, manganese and cerium, it is essential to carry out in an organic solvent,
It can be contained by an ion exchange method, an impregnation-supporting method, an evaporation-drying method or the like. Organic solvents include nickel, manganese,
There is no particular limitation as long as the compound such as cerium is dissolved, and for example, alcohol, ether, ketone and the like can be used. As alcohol, methanol, ethanol,
Lower alcohols such as propanol and ethylene glycol can be used, and ethers and ketones such as ethyl ether, acetone and ethyl methyl ketone can be used.
Ethanol is preferred.

When contained by the ion exchange method, the addition amount of nickel, manganese and cerium is preferably 0.1 to 10 with respect to the number of moles of alumina in the zeolite. If the addition amount is 0.1 or less, sufficient activity and durability may not be obtained, and if the addition amount is 10 or more, the effect commensurate with it may not be obtained. The treatment conditions may be a temperature of room temperature to 80 ° C. and a time of 1 hour to 10 days. In addition, the amount of addition when it is contained by the impregnation-supporting method can be arbitrarily set depending on the amount of the target catalyst to be supported. Of nickel, manganese and cerium, only one of them may be supported, or two or more thereof may be mixed and supported. When supporting multiple elements,
Prepared according to the method described above.

The content of copper or cobalt in the catalyst prepared by the above method is preferably 0.1 to 1.5 times the number of moles of alumina in the zeolite, and an alkaline earth metal is allowed to coexist. In this case, the content is preferably 1.0 times or less with respect to the number of moles of alumina. Further, the content of nickel, manganese and cerium, relative to the number of moles of alumina in the zeolite,
It is preferably 0.02 to 2.0 times, and the total amount of contained metals is preferably 1.0 to 2.5 times. If the content of copper or cobalt is less than 0.1, the content of nickel, manganese, and cerium is less than 0.02, and their total is less than 1.0, sufficient catalyst performance and durability may not be obtained. Even if cobalt is 1.5, nickel, manganese, and cerium are 2.0, and the total of these exceeds 2.5, there is a possibility that the effect corresponding to it may not be obtained. Further, when two or more kinds of nickel, manganese and cerium are contained, it may be prepared so that the total amount thereof is within the above range.

The catalyst prepared as described above can be used after calcining if necessary.

The exhaust gas purifying catalyst of the present invention can be used by mixing with a binder such as clay mineral and molding. In addition, zeolite is molded in advance and cobalt is added to the molded product.
It may also contain barium, nickel and / or manganese and / or cerium. The binder used when molding the zeolite is not particularly limited, but clay minerals such as carion, attapulgite, montmorillonite, bentonite, allophane and sepiolite, silica, alumina and the like can be used. Alternatively, it may be a binderless zeolite molded product obtained by directly synthesizing a molded product without using a binder. Further, it is also possible to use zeolite as a washcoat on a honeycomb-shaped substrate made of cordierite or metal.

The removal of nitrogen oxides from the oxygen-excess exhaust gas can be carried out by bringing the exhaust gas purification catalyst described above into contact with the exhaust gas. It is essential that the exhaust gas contains nitrogen oxides and hydrocarbons. Exhaust gas with excess oxygen targeted by the present invention refers to exhaust gas containing oxygen in excess of the amount of oxygen necessary to completely oxidize carbon monoxide, hydrogen and hydrocarbons contained in the exhaust gas, As such exhaust gas, for example, exhaust gas discharged from an internal combustion engine of an automobile or the like, particularly exhaust gas burned in a state where the air-fuel ratio is large is specifically exemplified.

The concentration of each component gas in the exhaust gas treated in the present invention is not particularly limited, but normally, nitrogen oxide is 50
To 2000 ppm, hydrocarbons from 10 to 5000 pp
m, oxygen is 0.1 to 20%.

The space velocity and temperature of the exhaust gas to be treated are not particularly limited, but preferably space velocity (volume basis) 5
00 to 500,000 hr ^-1 , temperature 100 to 800
° C, more preferably space velocity 2000 to 20000
The temperature is ⁰ hr ⁻¹ and the temperature is 200 to 600 ° C.

The exhaust gas purifying catalyst is carbon monoxide,
Even when applied to exhaust gas containing hydrocarbons and hydrogen and not in excess of oxygen, its performance does not change at all.

[0029]

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

Example 1 <Preparation of catalyst 1> ZS according to Example 5 of JP-A-59-54620.
M-5 similar zeolite was synthesized. It had the following composition, expressed as the molar ratio of the oxide in the anhydrous base.

1.0Na ₂ O · Al ₂ O ₃ · 40SiO ₂ An ammonium type ZSM-5 prepared by ion-exchanged this in an ammonium chloride aqueous solution was prepared, and 200 g of the ammonium type ZSM-5 was prepared therein. The mixture was added to an aqueous barium acetate solution having a concentration of 0.1 mol / liter, which was precisely weighed to be 5 times the number of moles of alumina contained, and stirred at 80 ° C. for 16 hours. After solid-liquid separation, it was thoroughly washed. Subsequently, the zeolite cake was put into a cobalt acetate aqueous solution which was twice as many as the number of moles of alumina, and the temperature was kept at 80 ° C.
It was stirred for 16 hours. After solid-liquid separation, thoroughly wash, 110
It dried at 10 degreeC for 10 hours, and obtained the cobalt and barium containing zeolite. This is designated as Co-Ba-ZSM-5.

Co-Ba-ZSM-5; 10 g of nickel nitrate ethanol with a concentration of 0.0387 mol / liter
Solution to 50 mL, and desolvated under reduced pressure with stirring,
Supported nickel. Then, the obtained powder is heated to 110 ° C.
After drying for 10 hours, catalyst 1 was obtained. This catalyst cobalt,
As a result of examining the contents of barium and nickel by chemical analysis, they had the following composition in terms of oxide molar ratio in anhydrous base.

0.57CoO ・ 0.57BaO ・ 0.4
NiO.Al ₂ O ₃ .40SiO ₂ Example 2 <Preparation of catalyst 2> 10 g of Co-Ba-ZSM-5 prepared in Example 1 was added to 50 ml of nickel acetate ethanol solution having a concentration of 0.0968 mol / liter. And stirred at 25 ° C. for 20 hours. After solid-liquid separation, it was thoroughly washed with ethanol and dried at 110 ° C. for 10 hours to obtain catalyst 2. This catalyst cobalt,
As a result of examining the contents of barium and nickel by chemical analysis, they had the following composition in terms of oxide molar ratio in anhydrous base.

0.59CoO ・ 0.53BaO ・ 0.0
8NiO.Al ₂ O ₃ .40SiO ₂ Example 3 <Preparation of catalyst 3> Catalyst 3 was prepared in the same manner as in Example 2 except that the stirring temperature in nickel acetate ethanol was changed to 60 ° C. .. As a result of investigating the contents of cobalt, barium and nickel of this catalyst by chemical analysis, the catalyst had the following composition in terms of oxide molar ratio in anhydrous base.

0.56CoO ・ 0.55BaO ・ 0.1
5NiO.Al ₂ O ₃ .40SiO ₂ Example 4 <Preparation of catalyst 4> Catalyst 4 was prepared in the same manner as in Example 1 except that nickel nitrate was changed to manganese nitrate. As a result of investigating the contents of cobalt, barium and manganese of this catalyst by chemical analysis, the catalyst had the following composition in terms of oxide molar ratio in anhydrous base.

0.57CoO ・ 0.57BaO ・ 0.4
MnO.Al ₂ O ₃ .40SiO ₂ Example 5 <Preparation of catalyst 5> Catalyst 5 was prepared by the same operation as in example 2 except that nickel acetate was replaced with manganese acetate. As a result of investigating the contents of cobalt, barium and manganese of this catalyst by chemical analysis, the catalyst had the following composition in terms of oxide molar ratio in anhydrous base.

0.60CoO ・ 0.54BaO ・ 0.5
_{5MnO · Al 2 O 3 · 40SiO} 2 Example 6 <Preparation of Catalyst 6> prepared in Example 1 Co-Ba-ZSM-5 ; of 10g concentration 0.0258Mol / l nitric Seriumuetano - added Le solution 50ml Then, the solvent was removed under reduced pressure with stirring. Then, the obtained powder was dried at 110 ° C. for 10 hours to obtain a catalyst 7. The content of cobalt, barium and cerium in this catalyst was examined by chemical analysis.
It had the following composition in terms of oxide molar ratio in the oxide.

0.57CoO ・ 0.57BaO ・ 0.1
_{3Ce 2 O 3 · Al 2 O} 3 · 40SiO 2 Example 7 ammonium type ZSM-5 prepared in Example 1 <Preparation of Catalyst 7>; 200
g to 2 with respect to the number of moles of alumina contained therein
The solution was added to an aqueous solution of copper (II) acetate having a concentration of 0.1 mol / liter precisely doubled, and 2.5% ammonia water was immediately added to adjust the pH of the slurry to 10.5, and the pH was adjusted to 15 at room temperature. Stir for hours. After solid-liquid separation, thoroughly wash, 11
It dried at 0 degreeC for 10 hours, and obtained ZSM-5 containing copper. This is designated as Cu-ZSM-5.

Cu-ZSM-5; 10 g at a concentration of 0.03
87 mol / liter nickel nitrate ethanol solution 5
It was added to 0 ml, and the solvent was removed under reduced pressure with stirring to support nickel. Then, the obtained powder was dried at 110 ° C. for 10 hours to obtain a catalyst 7. As a result of investigating the contents of copper and nickel of this catalyst by chemical analysis, the catalyst had the following composition in terms of oxide molar ratio in anhydrous base.

1.05Cu0 ・ 0.4NiO ・ Al ₂ O
₃ · 40SiO <Preparation of Catalyst 8> ₂ Example 8 except that nickel nitrate was changed to manganese nitrate was prepared catalyst 8 in the same manner as in Example 7. As a result of investigating the contents of copper and manganese in this catalyst by chemical analysis, the catalyst had the following composition in terms of oxide molar ratio in anhydrous base.

1.05 CuO.0.4 MnO.Al ₂ O
₃ · 40SiO ₂ Example 9 <Preparation of catalyst 9> 10 g of Cu-ZSM-5 prepared in Example 7 was added to 10 g of cerium nitrate ethano-nitrate with a concentration of 0.0258 mol / liter.
Solution (50 ml), and the solvent was removed under reduced pressure with stirring. Then, the obtained powder was dried at 110 ° C. for 10 hours to obtain a catalyst 9. As a result of investigating the contents of copper and cerium in this catalyst by chemical analysis, the catalyst had the following composition in terms of oxide molar ratio in anhydrous base.

1.05CuO · 0.13Ce ₂ O ₃ · A
1 ₂ O ₃ · 40SiO ₂ Example 10 <Catalyst activity evaluation test> Catalysts 1 to 9 were each press-molded and then pulverized to be sized to 12 to 20 mesh. For each sized catalyst, 800 while flowing a gas (hereinafter, reaction gas) having the composition shown below
After endurance treatment at 5 ° C. for 5 hours, 1 g of each was charged into a fixed pressure bed circulation reaction tube. As a reaction pretreatment, the reaction gas was flowed at 4000 ml / min, the temperature was raised to 500 ° C., and the temperature was maintained for 30 minutes. After that, the steady-state activity of the catalyst was examined at any temperature between 300 and 550 ° C. The space velocity (volume basis) at this time was 120,000 hr ⁻¹ .
Table 1 shows the NOx removal rate at each temperature.
The NOx removal rate is expressed by the following equation.

XNOx = {([NOx] in− [NOx] out) / [NOx] in} × 100 XNOx: NOx removal rate [NOx] in: NOx concentration of inlet gas [NOx] out: NOx concentration of outlet gas (Reaction gas composition) NO 1200 ppm O ₂ 4.3% C ₃ H ₆ 800 ppm CO 1200 ppm CO ₂ 12% H ₂ O 10% N ₂ balance Comparative Example 1 <Preparation of comparative catalysts 1 and 2 and catalytic activity evaluation> The same operation as in Example 1 was carried out except that it was not supported, and the same operation as in Example 7 was carried out except that nickel and cobalt-containing zeolite (comparative catalyst 1) were not supported. A zeolite containing copper (Comparative Catalyst 2) was prepared. This comparative catalyst 1,2
As a result of a chemical analysis, had the following composition in terms of oxide molar ratio. Comparative Catalyst 1: 0.57CoO · 0.57BaO · Al ₂
O ₃・ 40SiO ₂ Comparative catalyst 2: 1.05 CuO ・ Al ₂ O ₃・ 40SiO
₂ The NOx removal rates of these comparative catalysts 1 and 2 were measured under the same conditions as in Example 10.

Table 1 shows the NOx removal rate at each temperature.

Comparative Example 2 <Preparation of Comparative Catalysts 3 and 4 and Evaluation of Catalytic Activity> 10 g of Co-Ba-ZSM-5 prepared in Example 1 was added to 50 ml of a nickel nitrate aqueous solution having a concentration of 0.387 mol / liter, The mixture was dehydrated under reduced pressure with stirring. Then, the obtained powder was dried at 110 ° C. for 10 hours to obtain a comparative catalyst 3. As a result of investigating the contents of cobalt, barium and nickel of this catalyst by chemical analysis, the catalyst had the following composition in terms of oxide molar ratio in anhydrous base.

0.57CoO ・ 0.57BaO ・ 0.4
NiO.Al ₂ O ₃ .40SiO ₂ Also, 10 g of Cu-ZSM-5 prepared in Example 7 was added to 50 ml of a nickel nitrate aqueous solution having a concentration of 0.387 mol / liter, and dehydrated under reduced pressure with stirring. Then, the obtained powder was dried at 110 ° C. for 10 hours to obtain comparative catalyst 4. As a result of investigating the contents of copper and nickel of this catalyst by chemical analysis, the catalyst had the following composition in terms of oxide molar ratio in anhydrous base.

1.05CuO.0.4NiO.Al ₂ O
The ₃ · 40SiO ₂ NOx removal rate of the comparative catalyst 3 and 4 were measured in the same conditions as in Example 10.

Table 1 shows the NOx removal rate at each temperature.

[0049]

[Table 1]

[0050]

According to Table 1, it is clear that the catalyst of the present invention has a higher oxygen-exhaust gas purification ability, particularly a nitrogen oxide removing ability and a higher durability than the comparative catalyst. Therefore, by contacting the catalyst of the present invention with exhaust gas, nitrogen oxides can be more efficiently removed from the oxygen-excess exhaust gas.

Claims (1)

[Claims] 1. A film containing SiO ₂ / containing copper or cobalt.
A catalyst in which at least one selected from nickel, manganese, and cerium in an organic solvent is supported on a zeolite having an Al ₂ O ₃ molar ratio of at least 15 or more,
A method for removing nitrogen oxides, which comprises contacting an exhaust gas containing excess oxygen containing nitrogen oxides and hydrocarbons.