JPH06170169A - Removal of nitrogen oxide - Google Patents

Abstract

PURPOSE:To efficiently remove nitrogen oxide from oxygen excessive exhaust gas containing nitrogen oxide and hydrocarbon even after a catalyst is used at high temp. by using a catalyst consisting of zeolite treated with an alkoxysilane in an org. solvent and at least one or more kind of an active metal. CONSTITUTION:Nitrogen oxide is removed from oxygen excessive exhaust gas containing nitrogen oxide and hydrocarbon by using a catalyst consisting of zeolite with an SiO2/Al2O3 mol ratio of at least 15 or more treated with an alkoxysilane in an org. solvent (e.g.; toluene) and one or more kind of an active metal. As a result, oxygen excessive exhaust gas is efficiently purified using this exhaust gas purifying catalyst excellent in durability at high temp. in the presence of steam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating an exhaust gas containing nitrogen oxides, which is discharged from a boiler, an automobile engine, etc., in excess of oxygen using a catalyst. The present invention relates to a method for removing nitrogen oxides using a very excellent catalyst.

[0002]

2. Description of the Related Art As a method for removing nitrogen oxides in exhaust gas discharged from a boiler, an automobile engine, etc., a selective catalytic reduction method using ammonia in the presence of a catalyst, and an unburned gas by passing the exhaust gas through the catalyst The non-selective catalytic reduction method of reducing carbon monoxide and hydrocarbons has been put to practical use.

JP-A-60-125250 proposes a copper ion-exchanged zeolite as a catalyst capable of directly catalytically decomposing nitrogen oxides in the absence of a reducing agent.

Further, for purification of exhaust gas of a diesel engine and a lean-burn engine for the purpose of reducing fuel consumption, nitrogen oxides are selectively removed by reducing components such as unburned carbon monoxide and hydrocarbons even in the presence of excess oxygen. As a catalyst that can be reduced, a catalyst in which a base metal is contained in zeolite or the like has been proposed (JP-A-63-100919).

However, these proposed catalysts have problems in durability, especially at high temperatures, and have not been put into practical use.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to efficiently purify exhaust gas discharged from an internal combustion engine such as an automobile, particularly in excess of oxygen, without using a reducing agent such as ammonia, and It is intended to provide a method for purifying exhaust gas by using an exhaust gas purifying catalyst having excellent durability at high temperature in the presence of water vapor.

[0007]

Means for Solving the Problems The inventors of the present invention have made extensive studies on the above problems, and as a result, by using a catalyst obtained by treating an zeolite with an alkoxysilane in an organic solvent, the exhaust gas can be efficiently purified even after being used at a high temperature. The present invention has been completed and the present invention has been completed.

That is, the present invention uses an alkoxysilane-treated zeolite in an organic solvent, which has a SiO ₂ / Al ₂ O ₃ molar ratio of at least 15 or more, and a catalyst composed of one or more active metals to produce nitrogen. A method for removing nitrogen oxides from an oxygen-excess exhaust gas containing oxides and hydrocarbons.

Although the reason why the durability of the catalyst is improved by the alkoxysilane treatment in an organic solvent is not clear, this treatment uniformly coats the surface of the zeolite with Si.
Al, which is the cause of zeolite destruction in the presence of high temperature steam, is protected and Al near the zeolite surface is protected.
It is presumed that the invasion of water vapor, which causes the catalyst deterioration into the pores due to the hydrophobization of the zeolite surface, was prevented, and the durability of the catalyst was improved.

The present invention will be described in more detail below.

The catalyst used in the present invention comprises a zeolite having an SiO ₂ / Al ₂ O ₃ molar ratio of at least 15, which has been alkoxysilane-treated in an organic solvent, and one or more active metals.

The raw material zeolite used in the present invention may have a SiO ₂ / Al ₂ O ₃ molar ratio of 15 or more after the alkoxysilane treatment in an organic solvent, and 15 or more is used. The upper limit of the SiO ₂ / Al ₂ O ₃ molar ratio is not limited. SiO ₂ / Al ₂
If the O ₃ molar ratio is less than 15, sufficient durability cannot be obtained.

The type of zeolite is not particularly limited, and examples thereof include mordenite, ferrierite, ZSM.
-5, ZSM-8, ZSM-11, ZSM-12, ZS
Zeolites such as M-20 and ZSM-35 can be used, and among them, ZSM-5 is preferably used. Further, the method for producing these zeolites is not limited. Alternatively, the zeolite such as zeolite Y or zeolite L may be dealuminated.

As the raw material zeolite, a synthetic product or a calcined product thereof is used, but it is also possible to treat the ions such as Na in the raw material zeolite with an ammonium salt or a mineral acid and use it as an H type or an ammonium type. Further, K, Cs, Ba or the like can be used after ion exchange.

The raw material zeolite is treated with an alkoxysilane in an organic solvent, and one or more active metals are introduced.

The order of the alkoxysilane treatment and the introduction of the active metal in the organic solvent is not particularly limited, and the active metal may be introduced after the raw material zeolite is treated with the alkoxysilane in the organic solvent. After that, it is also possible to carry out an alkoxysilane treatment in an organic solvent.

The alkoxysilane that can be used in the present invention is tetraalkoxysilane. As the alkoxyl group, methoxyl group, ethoxyl group, propoxyl group, butoxyl group and the like can be used.

The conditions of the alkoxysilane treatment in the organic solvent are not particularly limited, and the raw material zeolite or the zeolite containing at least one active metal is added to the organic solvent containing the alkoxysilane and the treatment is performed in the liquid phase. I'm fine.

The concentration of alkoxysilane in the organic solvent is not particularly limited, but is preferably 0.1 to 20%. As the organic solvent, any solvent in which alkoxysilane is stably present may be used, and cyclohexane, hexane, toluene, benzene or the like is used. When H ₂ O is contained in the organic solvent, the alkoxysilane changes into an oxide or the like and uniformly co-forms.
It is desirable that the amount of H ₂ O in the organic solvent be as small as possible because it may not be generated. Further, when water is used as a solvent, alkoxysilane is deposited as an oxide or the like and a uniform coat cannot be obtained.

The temperature for the alkoxysilane treatment in the organic solvent is not particularly limited, but it may be any temperature as long as the alkoxysilane is stably present and the reaction with the OH groups on the outer surface of the zeolite proceeds. It is carried out at a temperature up to the boiling point of the organic solvent used.

The method of treating with alkoxysilane in an organic solvent is not particularly limited, but it can be carried out by mixing zeolite in an organic solvent containing alkoxysilane and stirring or dispersing by ultrasonic irradiation. The treated zeolite is preferably subjected to solid-liquid separation in order to prevent excess alkoxysilane from adhering. Moreover, you may wash using an organic solvent.

When the alkoxysilane treatment is carried out in an organic solvent, H ₂ O adsorbed in the zeolite is removed,
And OH on the surface of the zeolite that reacts with the alkoxy group
In order to allow the group to exist in an active state, it is preferable to perform pretreatment at 300 to 800 ° C. under vacuum or in an inert gas atmosphere.

The alkoxysilane-treated zeolite in an organic solvent is used in order to further stabilize the Si-coat layer on the surface of the zeolite, at a temperature of 100 ° C. to 800 ° C., under vacuum, in an inert gas atmosphere, or in air. You may heat-process.

It is essential that the SiO ₂ / Al ₂ O ₃ molar ratio of the alkoxysilane-treated zeolite in an organic solvent is 15 or more. If the SiO ₂ / Al ₂ O ₃ molar ratio is less than 15, sufficient durability at high temperature cannot be obtained. Also,
The upper limit is not particularly limited, but is preferably 200 or less in order to have sufficient catalytic activity.

When the alkoxysilane treatment is carried out in an organic solvent, Si is coated on the surface of the zeolite, so some S
An increase in the iO ₂ / Al ₂ O ₃ molar ratio occurs.

The catalyst used in the present invention has one or more active metals introduced therein. The active metal may be any metal that is normally used for exhaust gas purification, such as Cu, Ag,
Ib group such as Au, Fe, Co, Ni, Ru, Rh, P
Group VIII such as d and Pt, group VIa such as Cr and Mo, or group VIIa such as Mn are used. Particularly preferred is Cu or Co.

The method of introducing the active metal is not particularly limited, and an impregnation-supporting method, an evaporation-drying method, an ion exchange method or the like can be used. The active metal shows high activity even when it is supported on the surface of zeolite, but when it is present at the ion exchange site of the zeolite, it has high activity and high durability.
It is preferable to introduce the active metal by the ion exchange method. The ion exchange is performed by mixing the starting zeolite or the zeolite treated with alkoxysilane in an organic solvent into an aqueous solution containing a salt of an active metal, stirring and washing.

As the active metal salt, salts of active metal chlorides, nitrates, sulfates, acetates and the like are preferably used. Further, an ammine complex salt of an active metal or the like can also be preferably used.

The amount of active metal added, the concentration, the exchange temperature, the time, and the like at the time of ion exchange are not particularly limited, and a commonly used method may be used. In order to provide sufficient activity and durability, the amount of the active metal added is preferably 0.5 to 20 times equivalent to Al in the raw material zeolite or zeolite treated with alkoxysilane in an organic solvent. Also,
The ion exchange slurry concentration is usually 5 to 50%.
Is preferred. In addition, the ion exchange temperature and time are from room temperature to 100 ° C., 5 in order to have sufficient activity and durability.
Minutes to 3 days is preferred. Further, the ion exchange operation can be repeated if necessary.

As described above, the exhaust gas purifying catalyst used in the present invention can be prepared.

The SiO ₂ / Al ₂ O ₃ molar ratio of the exhaust gas-purifying catalyst containing the active metal used in the present invention does not substantially change before and after the introduction of the active metal. Also, the crystal structure of the exhaust gas purifying catalyst is not essentially different before and after the alkoxysilane treatment in the organic solvent and before and after the ion exchange.

The exhaust gas-purifying catalyst used in the present invention is
It can also be used by mixing with a binder such as clay mineral and molding. It is also possible to preform the raw material zeolite or zeolite that has been treated with an alkoxysilane in an organic solvent in advance, and subject the molded body to the alkoxysilane treatment or to introduce an active metal in the organic solvent. Binders used for forming zeolite are clay minerals such as kaolin, attapulgite, montmorillonite, bentonite, allophane, and sepiolite. Alternatively,
It may be a binderless zeolite molded product obtained by directly synthesizing a molded product without using a binder. Further, the exhaust gas-purifying catalyst used in the present invention can be wash-coated on a honeycomb-shaped substrate made of cordierite or metal.

The exhaust gas purifying catalyst thus prepared is contacted with oxygen-excess exhaust gas containing nitrogen oxides and hydrocarbons to remove nitrogen oxides. It is essential that the exhaust gas used in the present invention contains nitrogen oxides and hydrocarbons and is in excess of oxygen, but it is also effective when it contains carbon monoxide, hydrogen, ammonia and the like. Exhaust gas in excess of oxygen means that excess oxygen is contained in excess of the amount of oxygen required to completely oxidize carbon monoxide, hydrocarbons and hydrogen contained in the exhaust gas. For example, in the case of exhaust gas emitted from an internal combustion engine of an automobile or the like, the air fuel consumption is high (lean region).

The space velocity, temperature, etc. for removing nitrogen oxides are not particularly limited, but the space velocity is 100 to 50,000.
It is preferable that the temperature is 0 hr ⁻¹ and the temperature is 200 to 800 ° C.

[0035]

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples.

Example 1 A sodium silicate aqueous solution (SiO ₂ ; 250 g) was placed in an overflow type reaction tank having an actual volume of 2 liters in a stirring state.
/ L, Na ₂ O; 82 g / L, Al ₂ O ₃ ;
2.8 g / liter) and an aluminum sulfate aqueous solution (A
L ₂ O ₃ ; 8.8 g / liter, H ₂ SO ₄ ; 370 g / liter) and 3 liter / hr, 1 liter / hr, respectively.
It was continuously fed at a rate of hr. Reaction temperature is 30-32
C., the pH of the discharged slurry was 6.7 to 7.0.

After solid-liquid separation of the discharged slurry and sufficient washing with water, Na ₂ O; 0.75 wt%, Al ₂ O ₃ ; 0.77 w
t%, SiO ₂ ; 36.1 wt%, H ₂ O; 62.5 wt
% Of granular amorphous aluminosilicate homogeneous compound was obtained. The homogenous compound (2,860 g) and 3.2 wt% NaOH aqueous solution (6,150 g) were charged into an autoclave, and crystallized at 160 ° C. for 72 hours with stirring. The product was subjected to solid-liquid separation, washed with water and dried to obtain ZSM-5 type zeolite. As a result of chemical analysis, the composition had the following composition expressed as a molar ratio of oxides on an anhydrous basis.

1.3Na ₂ O, Al ₂ O ₃ , 41SiO ₂ 10 g of this zeolite was added to 100 cc of an aqueous solution containing 2 g of NH ₄ Cl, stirred at 60 ° C. for 20 hours, washed, dried and ammonium. Ion exchange
An ammonium type zeolite was obtained.

This ammonium type zeolite: 10 g
Was charged in a reaction vessel and pretreated at 400 ° C. for 1 hour under exhaust to remove H ₂ O and the like adsorbed on zeolite. Then, 40 cc of toluene containing 0.7% of tetramethoxysilane in a nitrogen atmosphere was dropped into the reaction vessel. Then, the mixture was stirred and refluxed at 117 ° C. for 1 hour. The treated zeolite is filtered and then air-circulated at 600 ° C,
It was baked for 1 hour. SiO ₂ / Al ₂ of treated zeolite
The O ₃ molar ratio was 42.

Tetramethoxysilane-treated zeolite was added to 41 cc of 0.1 mol / liter copper acetate aqueous solution, pH was adjusted to 10.5 with aqueous ammonia, and the mixture was stirred at room temperature for 20 hours, washed, and then Cu ion-exchanged. The operation was performed. After repeating this operation twice, it is dried to prepare the catalyst 1.
Got As a result of chemical analysis, the composition had the following composition expressed as a molar ratio of oxides on an anhydrous basis.

0.94CuO, Al ₂ O ₃ , 42SiO ₂ Example 2 Catalyst 2 was prepared in the same manner as in Example 1 except that K ion exchange was carried out instead of ammonium ion exchange.
K ion exchange was carried out using ZSM-5 type zeolite;
KCl; added to 100 cc of an aqueous solution containing 2.8 g, 6
The mixture was stirred at 0 ° C. for 20 hours, washed, and this operation was repeated twice, and then dried.

The SiO ₂ / Al ₂ O ₃ molar ratio of the tetramethoxysilane-treated zeolite was 42.

Further, the catalyst 2 after Cu ion exchange had the following composition represented by the molar ratio of oxides on an anhydrous basis.

0.97CuO, 0.14K ₂ O, Al ₂ O
_3, instead of the toluene solution containing 42SiO ₂ Example 3 tetramethoxysilane,
A catalyst 3 was prepared in the same manner as in Example 1 except that the treatment was performed with toluene containing 0.9% of tetraethoxysilane.

The SiO ₂ / Al ₂ O ₃ molar ratio of the tetraethoxysilane-treated zeolite was 42.

Further, the catalyst 3 after Cu ion exchange had the following composition expressed by the molar ratio of oxides on a dry basis.

0.89CuO, Al ₂ O ₃ , 42SiO ₂ Example 4 A catalyst 4 was prepared in the same manner as in Example 1 except that Co ion exchange was performed instead of Cu ion exchange. C
o Ion exchange was performed as follows.

The tetramethoxysilane-treated zeolite was added to 90 cc of a 0.22 mol / liter aqueous solution of Co (II) acetate, and the mixture was stirred at 60 ° C. for 20 hours, washed, and Co ion-exchanged. This operation was repeated twice and then dried to obtain catalyst 4.

Catalyst 4 had the following composition, expressed as the molar ratio of oxides on a dry basis.

1.43 CoO, Al ₂ O ₃ , 42SiO ₂ Example 5 The catalysts 1 to 4 obtained in Examples 1 to 4 were used to evaluate catalytic activity and durability.

Each catalyst is press-molded and then pulverized to 12 to
The size was adjusted to 20 mesh. 2 cc of the mixture was filled in a normal pressure fixed bed flow type reaction tube, and a gas simulating the exhaust gas of a lean burn engine (Table 1) was flowed at a space velocity of 120,000 / hr. After pretreatment at 550 ° C. for 30 minutes, the steady-state purification activity at each temperature was measured. The steady-state purification activity was the NO purification rate after holding at each temperature for 1 hour.

For each catalyst, a gas having the composition shown in Table 1 was flowed at a space velocity of 120,000 / hr at 800 ° C.
Durable for 5 hours. Then, the steady-state purification activity was measured by the same method as described above, and the durability test was conducted.

The results obtained are shown in Table 2.

[0054]

[Table 1]

[0055]

[Table 2]

Comparative Example 1 A Cu-type ZSM was prepared in the same manner as in Example 1 except that the tetramethoxysilane treatment was not carried out.
-5 (Comparative Catalyst 1) was obtained. As a result of chemical analysis, the composition had the following composition expressed as a molar ratio of oxides on an anhydrous basis.

1.03 CuO, Al ₂ O ₃ , 41 SiO ₂ Comparative Example 2 In the treatment of tetramethoxysilane in Example 1, H ₂ O was used instead of toluene as the solvent, and the mixture was stirred at 100 ° C. for 1 hour. Comparative catalyst 2 was prepared in the same manner as in Example 1 except for the above. As a result of chemical analysis, the composition had the following composition expressed as a molar ratio of oxides on an anhydrous basis.

1.05 CuO, Al ₂ O ₃ , 42 SiO ₂ Comparative Example 3 Co-type ZSM was carried out in the same manner as in Example 4 except that the tetramethoxysilane treatment was not carried out.
-5 (Comparative Catalyst 3) was obtained. As a result of chemical analysis, the composition had the following composition expressed as a molar ratio of oxides on an anhydrous basis.

1.40 CoO, Al ₂ O ₃ , 42SiO ₂ Comparative Example 4 Comparative catalysts 1, 2 and 3 obtained in Comparative Examples 1, 2 and 3 were used in the same manner as in Example 5 for catalytic activity and durability. The sex was evaluated. The results obtained are shown in Table 3.

[0060]

[Table 3]

[0061]

As is clear from Tables 2 and 3, according to the method of the present invention, nitrogen oxides can be efficiently removed, and the nitrogen oxides can be efficiently oxidized even after the catalyst is used at a high temperature. Things can be removed.

[0062]

Claims (1)

[Claims] 1. Nitrogen oxides and catalysts are prepared by using a catalyst which is alkoxysilane-treated in an organic solvent and has a SiO ₂ / Al ₂ O ₃ molar ratio of at least 15 and at least one active metal. A method for removing nitrogen oxides from an oxygen-rich exhaust gas containing a hydrocarbon.