JPH0760059A - Removing process for nitrogen oxide - Google Patents

Abstract

PURPOSE:To provide a process for cleaning exhaust gas by using an exhaust gas cleaning catalyst of superior durability at the high temperature in the presence of initial activity and water vapor, particularly exhaust gas containing oxygen excessively exhausted out of an internal combustion engine of an automobile or the like without using a reducer such as ammonia. CONSTITUTION:A catalyst composed of SiO2/Al2O3 molar ratio of at least 15 or more on which copper phosphate and active metallic seeds of one kind or more are supported, is brought into contact with exhaust gas of excessive oxygen containing a nitrogen oxide and hydrocarbon.

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 oxygen-rich exhaust gas containing nitrogen oxides discharged from a boiler, an automobile engine, etc. by using a catalyst, and more specifically, to a method for treating activity and durability. 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 diesel engines and lean-burn engines 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]

DISCLOSURE OF THE INVENTION The object of the present invention is to obtain exhaust gas discharged from an internal combustion engine such as an automobile, especially in excess of oxygen, without using a reducing agent such as ammonia, and to obtain initial activity and presence of water vapor. The present invention provides a method for purifying exhaust gas using an exhaust gas-purifying catalyst having excellent durability at high temperatures.

[0007]

Means for Solving the Problems As a result of diligent studies on the above problems, the present inventors have found that by using a catalyst into which copper phosphate and one or more kinds of active metals are introduced, the efficiency is improved even after being used at high temperature. Finding that exhaust gas can be purified well,
The present invention has been completed.

That is, the present invention uses a catalyst in which copper phosphate and one or more kinds of active metal species are contained in a zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of at least 15 or more, to obtain nitrogen oxides and carbonization. It is intended to provide a method for removing nitrogen oxides from an oxygen-excess exhaust gas containing hydrogen.

The present invention will be described in more detail below.

The catalyst used in the present invention is SiO ₂ / A
A catalyst in which copper phosphate and one or more kinds of active metal species are contained in a zeolite having an l ₂ O ₃ molar ratio of at least 15 or more.

It is essential that the raw material 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 limited. If the SiO ₂ / Al ₂ O ₃ molar ratio is less than 15, sufficient durability cannot be obtained. It is preferably 15 to 200.

The type of zeolite is not particularly limited, and examples thereof include mordenite, ferrierite, zeolite β, ZSM-5, ZSM-8, ZSM-11 and ZS.
Zeolites such as M-12, ZSM-20 and ZSM-35 can be used. 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 method of introducing copper phosphate into the catalyst is not particularly limited, but for example, an impregnation-supporting method using an ordinary aqueous solution or an organic solvent, an evaporative dryness method, or a method in which solid phase or liquid phase and copper phosphate and physical properties are used. Physical mixing method, or a copper salt aqueous solution (for example, soluble copper salts such as copper acetate, copper nitrate, copper sulfate, and copper chloride) and a phosphate aqueous solution (for example, orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid, A soluble phosphate such as ammonium dihydrogen phosphate, diammonium hydrogen phosphate, dipotassium hydrogen phosphate) may be mixed in the presence of zeolite, and copper phosphate may be precipitated by a precipitation method or the like. In this case, the introduction by the precipitation method is preferable. The amount of copper phosphate introduced is not particularly limited, but the amount of P atoms in copper phosphate is preferably 0.01 to 10 times, more preferably 0.10 to 1.00 times, the number of moles of Al atoms in the zeolite. Is more preferable.
100 ° C. to stabilize the catalyst containing copper phosphate
The heat treatment may be performed at up to 900 ° C, preferably 300 to 800 ° C. The atmosphere for heat treatment is not particularly limited,
Examples of the atmosphere include vacuum, air, and steam.

One or more kinds of active metal species are introduced into the zeolite into which copper phosphate is introduced. The active metal species may be any metal that is usually used for exhaust gas purification, such as C
Ib group such as u, Ag, Au, Fe, Co, Ni, Ru,
Group VIII such as Rh, Pd and Pt, VI such as Cr and Mo
Group a or Group VIIa such as Mn is used. Particularly preferred is Cu or Co.

The method of introducing the active metal is not particularly limited, and a method such as an impregnating and supporting method, an evaporation-drying method and an ion exchange method can be used. When the active metal exists in the ion exchange site of zeolite, it becomes more durable at high temperature,
It is preferable to introduce the active metal by the ion exchange method.

Ion exchange is carried out by mixing copper phosphate-introduced zeolite with an aqueous solution containing a salt of an active metal, stirring,
It is done by 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 addition amount, concentration, exchange temperature, time, etc. of the active metal at the time of ion exchange are not particularly limited, and a commonly used method may be used. The amount of the active metal added is preferably 0.5 to 20 times equivalent to Al in the zeolite in order to provide sufficient activity and durability. Further, the ion exchange slurry concentration is preferably 5 to 50% which is usually performed. Further, the ion exchange temperature and time are preferably room temperature to 100 ° C. and 5 minutes to 3 days in order to have sufficient activity and durability. Further, the ion exchange operation can be repeated if necessary.

The exhaust gas purifying catalyst used in the present invention can be prepared as described above.

It is also possible to introduce one or more active metals into the raw material zeolite and then introduce copper phosphate by the above method to use it as an exhaust gas purifying catalyst.

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 into which copper phosphate has been introduced in advance and introduce copper phosphate or an active metal into the formed body. Binders used when 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 an exhaust gas in excess of oxygen 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 discharged from an internal combustion engine of an automobile or the like, the air-fuel ratio is large (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.

[0025]

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.

1.03Na 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; the mixture was stirred at 60 ° C. for 20 hours, washed, dried and NH. _Four ion exchanges were performed to obtain an ammonium type zeolite.

10 g of this ammonium type zeolite; 142 cc of 0.034 mol / liter copper acetate aqueous solution
And stir. 71 cc of 0.092 mol / liter ammonium dihydrogen phosphate aqueous solution was added dropwise thereto to precipitate copper phosphate, and after stirring at 60 ° C. for 2 hours,
Washed and dried. Then, under air circulation, 500 ° C, 5
It was calcined for a time to obtain a copper phosphate-containing zeolite.

0.1 μm of this copper phosphate-containing zeolite
Add to 41 cc of ol / liter copper acetate aqueous solution at 50 ° C
After stirring at 20 ° C. for 20 hours, it was washed and subjected to Cu ion exchange operation. After repeating this operation 4 times, it dried and the catalyst 1 was prepared. As a result of chemical analysis, the composition had the following composition expressed as a molar ratio of oxides on an anhydrous basis.

2.39 CuO, 0.28 P ₂ O ₅ , Al ₂
O ₃ , 41SiO ₂ Example 2 Ammonium-type zeolite obtained in Example 1; 10 g
100 cc of 0.06 mol / liter copper sulfate aqueous solution
And stir. Then, 100 cc of 0.035 mol / liter dipotassium hydrogen phosphate aqueous solution was dropped,
After the copper phosphate was precipitated, it was washed and dried. Then
The mixture was calcined under air flow at 500 ° C. for 5 hours to obtain a copper phosphate-containing zeolite.

This copper phosphate-containing zeolite is
ol / liter copper acetate aqueous solution 41cc, 40 ℃
After stirring at 20 ° C. for 20 hours, it was washed and subjected to Cu ion exchange operation. After repeating this operation 3 times, it dried and the catalyst 2 was prepared. As a result of chemical analysis, the composition had the following composition expressed as a molar ratio of oxides on an anhydrous basis.

1.35 CuO, 0.12 P ₂ O ₅ , Al ₂
O ₃ , 41SiO ₂ Example 3 10 g of as-synthesized sodium-type zeolite prepared in the same manner as in Example 1; 10 g, was added to 100 cc of an aqueous solution containing 2.8 g of KCl, and the mixture was stirred at 60 ° C. for 20 hours. After washing, and repeating this operation twice, it was dried to obtain a potassium-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.

K ₂ O, Al ₂ O ₃ , 41SiO ₂ This potassium type zeolite; 10 g of 0.06 mol /
Add to 100 liters of copper sulphate aqueous solution and stir. Then, 100 cc of 0.035 mol / liter dipotassium hydrogen phosphate aqueous solution was added dropwise to precipitate copper phosphate, which was then washed and dried. Then 50 under air circulation
It was calcined at 0 ° C. for 5 hours to obtain a copper phosphate-containing zeolite.

0.1 μm of this copper phosphate-containing zeolite
ol / liter copper acetate aqueous solution 41cc, 40 ℃
After stirring at 20 ° C. for 20 hours, it was washed and subjected to Cu ion exchange operation. After repeating this operation 3 times, it dried and the catalyst 3 was prepared. As a result of chemical analysis, the composition had the following composition expressed as a molar ratio of oxides on an anhydrous basis.

1.71 CuO, 0.15 P ₂ O ₅ , 0.2
4K ₂ O, Al ₂ O ₃ , 41SiO ₂ Example 4 Ammonium-type zeolite prepared by the same method as in Example 1; 10 g of 0.1 mol / liter copper acetate aqueous solution 4
1 cc was added, pH was adjusted to 10.5 with aqueous ammonia, and the mixture was stirred at room temperature for 20 hours, washed, and subjected to Cu ion exchange operation. After repeating this operation twice, it was dried to obtain a Cu-exchanged zeolite.

10 g of this Cu-exchanged zeolite; 0.23 g of commercially available copper phosphate (manufactured by Katayama Chemical Industry Co., Ltd.) were mixed in a mortar and then calcined at 500 ° C. for 5 hours under air flow to prepare catalyst 4. did. As a result of chemical analysis, the composition had the following composition expressed as a molar ratio of oxides on an anhydrous basis.

1.49 CuO, 0.15 P ₂ O ₅ , Al ₂
O ₃ , 41 SiO ₂ Example 5 Ammonium-type zeolite prepared by the same method as in Example 1; 10 g of 0.1 mol / liter copper acetate aqueous solution 4
1 cc was added, pH was adjusted to 10.5 with aqueous ammonia, and the mixture was stirred at room temperature for 20 hours, washed, and subjected to Cu ion exchange operation. After repeating this operation twice, it was dried to obtain a Cu-exchanged zeolite.

10 g of this Cu exchange type zeolite;
Add to 100 cc of 06 mol / liter copper sulfate aqueous solution and stir. Then, 100 cc of 0.035 mol / liter dipotassium hydrogen phosphate aqueous solution was added dropwise to precipitate copper phosphate, which was then washed and dried. Next, the catalyst 5 was prepared by firing at 500 ° C. for 5 hours under air circulation.
As a result of chemical analysis, the composition had the following composition expressed as a molar ratio of oxides on an anhydrous basis.

2.85 CuO, 0.35 P ₂ O ₅ , Al ₂
O ₃ , 41SiO ₂ Example 6 A catalyst 6 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.

Zeolite carrying copper phosphate was added to 0.2
90 cc of 2 mol / liter aqueous Co (II) acetate solution
And stirred at 60 ° C. for 20 hours, then washed with Co
Ion exchange was performed. This operation was repeated twice and then dried to prepare catalyst 6. As a result of chemical analysis, the composition had the following composition expressed as a molar ratio of oxides on an anhydrous basis.

1.30 CoO, 0.78 CuO, 0.2
_{5P 2 O 5, Al 2 O} 3, were durability evaluation using the catalyst 6 obtained in 41SiO ₂ Example 7 Examples 1-6.

Each catalyst is press-molded and then pulverized to 12 to
The size was adjusted to 20 mesh. 2 cc of the mixture was charged into a fixed pressure fixed bed flow type reaction tube and subjected to a durability treatment at 800 ° C. for 5 hours while flowing a gas (Table 1) simulating the exhaust gas of a lean burn engine at a space velocity of 120,000 / hr. Then 5
After pretreatment at 50 ° C. for 30 minutes, the steady-state purification activity at each temperature was measured. The steady-state purification activity was defined as the conversion rate after holding at each temperature for 1 hour. The obtained results are shown in Table 2.

[0044]

[Table 1]

[0045]

[Table 2]

Comparative Example 1 Cu type ZSM-5 (Comparative Catalyst 1) was obtained in the same manner as in Example 5 except that copper phosphate was not carried. As a result of chemical analysis, the composition had the following composition represented by the molar ratio of oxides in the anhydrous base.

1.03 CuO, Al ₂ O ₃ , 41 SiO ₂ Comparative Example 2 Co-type ZSM-5 (comparative catalyst) was prepared in the same manner as in Example 6 except that copper phosphate was not supported. 2) was obtained. As a result of chemical analysis, the composition had the following composition represented by the molar ratio of oxides in the anhydrous base.

1.40 CoO, Al ₂ O ₃ , 41 SiO ₂ Comparative Example 3 Comparative catalysts 1 and 2 obtained in Comparative Examples 1 and 2 were used to evaluate the catalyst durability in the same manner as in Example 7. The results obtained are shown in Table 3.

[0049]

[Table 3]

[0050]

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

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B01D 53/36 102 H

Claims (1)

[Claims] 1. A SiO ₂ / Al ₂ O ₃ molar ratio of at least 1.
A method for removing nitrogen oxides, which comprises contacting a catalyst in which 5 or more zeolites contain copper phosphate and one or more active metal species with exhaust gas in excess of oxygen containing nitrogen oxides and hydrocarbons. .