JPH06238131A - Removing method for nitrogen oxide - Google Patents

Abstract

(57) [Summary] [Purpose] Efficiently purifies exhaust gas discharged from internal combustion engines such as automobiles, especially in excess of oxygen, without using reducing agents such as ammonia, and at high temperatures where steam is present. A method for removing nitrogen oxides using an exhaust gas-purifying catalyst having excellent durability is provided. [Composition] A catalyst in which phosphorus and one or more active metal species are contained in zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of at least 15 or more is contacted with an oxygen-excess exhaust gas containing nitrogen oxides and hydrocarbons. To remove nitrogen oxides.

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, or a method of passing an exhaust gas through a catalyst and unburning it 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]

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 As a result of extensive studies on the above problems, the present inventors have found that by using a catalyst into which phosphorus and one or more kinds of active metals are introduced, exhaust gas can be efficiently discharged even after being used at high temperatures. They have found that they can be purified, and have completed the present invention.

That is, the present invention uses a catalyst containing phosphorus and one or more active metal species in zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of at least 15 or more to remove nitrogen oxides and hydrocarbons. It is intended to provide a method for removing nitrogen oxides from an exhaust gas containing excess oxygen.

The present invention will be described in more detail below.

The catalyst used in the present invention is SiO ₂ / A
It is a catalyst in which phosphorus and at least one 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, but 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 phosphorus into the catalyst is not particularly limited, but a usual aqueous solution, an impregnation-supporting method using an organic solvent,
It can be introduced by evaporation to dryness. It can also be introduced by a physical mixing method in which the phosphorus compound is physically mixed in the solid phase or the liquid phase. It is also possible to treat and introduce the zeolite by using a gas containing a phosphorus compound. The type of phosphorus compound that can be used to introduce phosphorus is not particularly limited, but soluble phosphorus compounds such as orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, dipotassium hydrogen phosphate, etc. , Or calcium pyrophosphate, calcium phosphate,
Insoluble phosphorus compounds such as calcium hydrogen phosphate and barium phosphate, phosphorus alkyl compounds such as trimethylphosphine and triphenylphosphine, phosphorous esters such as trimethyl phosphite, and halogenated phosphorus such as phosphorus pentachloride. Etc. can be used. The content of phosphorus is not particularly limited, but is preferably 0.01 to 10 times, and more preferably 0.10 to 10 times the number of moles of Al atoms in the zeolite.
1.00 times is more preferable. The phosphorus-containing catalyst has a temperature of 100 to 900 ° C., preferably 3 to stabilize phosphorus.
You may heat-process at 00-800 degreeC. The atmosphere for the heat treatment is not particularly limited, and examples thereof include an atmosphere such as vacuum, air and water vapor.

The phosphorus-introduced zeolite has one or more active metal species introduced therein. The active metal species may be any metal that is usually used for exhaust gas purification, such as Cu,
Ib group such as Ag, Au, Fe, Co, Ni, Ru, R
VIII group such as h, Pd, Pt, etc., VIa such as Cr, Mo etc.
Group 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 is present at the ion exchange site of zeolite, it becomes more durable at high temperatures, so it is preferable to introduce the active metal by the ion exchange method.

Ion exchange is carried out by mixing phosphorus-introduced zeolite with 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 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. The ion exchange temperature and time are from room temperature to 100 ° C for 5 minutes to 3 in order to have sufficient activity and durability.
It is preferably day time. Also, if necessary,
The ion exchange operation can be repeated.

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

It is also possible to introduce phosphorus by the above-mentioned method after introducing one or more active metals into the raw material zeolite and 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. Further, it is also possible to shape the starting material zeolite or zeolite into which phosphorus has been introduced in advance, and introduce phosphorus or an active metal into the formed body. As the binder used when molding the zeolite, kaolin,
Examples include clay minerals such as 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 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.

[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 homogeneous 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.

1.3 Na ₂ O, Al ₂ O ₃ , 41 SiO 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 and dried. NH ₄ ion exchange was performed to obtain an ammonium-type zeolite.

10 g of this ammonium type zeolite; 1.2 wt% diammonium hydrogen phosphate aqueous solution; 70
After soaking in cc, it was dried. Then 5 under air circulation
It was baked at 50 ° C. for 5 hours to obtain a phosphorus-containing zeolite.

0.1 mol of this phosphorus-containing zeolite
/ Liter copper acetate aqueous solution; added to 41 cc, adjusted to pH = 10.5 with aqueous ammonia, stirred at room temperature for 20 hours, washed, and subjected to Cu ion exchange operation. This operation was repeated twice and then dried to prepare a blue-violet catalyst 1. As a result of chemical analysis, the composition had the following composition expressed as a molar ratio of oxides on an anhydrous basis.

1.05CuO, 0.41P ₂ O ₅ , Al ₂
O ₃ , 41SiO ₂ Example 2 The same procedure as in Example 1 was repeated except that 1.9 wt% orthophosphoric acid aqueous solution; 33 cc was used instead of 1.2 wt% diammonium hydrogen phosphate aqueous solution, and a blue-violet color was obtained. Catalyst 2 of 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.

0.88CuO, 0.39P ₂ O ₅ , Al ₂
O ₃ , 41SiO ₂ Example 3 Ammonium-type zeolite prepared in the same manner as in Example 1;
10 g of 0.1 mol / liter copper acetate aqueous solution; 41c
The pH was adjusted to 10.5 with ammonia water, 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;
2 wt% diammonium hydrogen phosphate aqueous solution; 70 cc
And then dried. Then 550 under air circulation
The catalyst was calcined at 5 ° C. for 5 hours to prepare a blue-violet catalyst 3. As a result of chemical analysis, the composition had the following composition expressed as a molar ratio of oxides on an anhydrous basis.

1.01CuO, 0.46P ₂ O ₅ , Al ₂
O ₃ , 41SiO 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.

Zeolite loaded with phosphorus is 0.22 m
It was added to 90 cc of an aqueous solution of Co (II) acetate (ol / liter); This operation was repeated twice and then dried to prepare a pink catalyst 4.

As a result of chemical analysis, the catalyst 4 had the following composition represented by the molar ratio of oxides on an anhydrous basis.

1.43CoO, 0.23P ₂ O ₅ , Al ₂
O ₃ , 41SiO ₂ Example 5 A blue-violet catalyst 5 was prepared in the same manner as in Example 1 except that calcination at 550 ° C. was not performed after phosphorus was supported. As a result of chemical analysis, the composition had the following composition expressed as a molar ratio of oxides on an anhydrous basis.

1.28 CuO, 0.02 P ₂ O ₅ , Al ₂
O ₃ , 41SiO ₂ Example 6 The same procedure as in Example 1 was repeated except that a 2.4 wt% diammonium hydrogen phosphate aqueous solution was used in place of the 1.2 wt% diammonium hydrogen phosphate aqueous solution, and was blue. Purple catalyst 6 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.

0.74 CuO, 1.20 P ₂ O ₅ , Al ₂
O ₃ , 41 SiO ₂ Example 7 A blue-green catalyst 7 was prepared in the same manner as in Example 1 except that K ion exchange was performed instead of ammonium ion exchange. K ion exchange is ZSM-5 type zeolite;
10 g of KCl; an aqueous solution containing 2.8 g; 100 cc
Was added, and the mixture was stirred at 60 ° C. for 20 hours, washed, and this operation was repeated twice, followed by drying. As a result of chemical analysis, the composition had the following composition expressed as a molar ratio of oxides on an anhydrous basis.

1.20 CuO, 0.79 P ₂ O ₅ , 0.1
0K ₂ O, Al ₂ O ₃ , 41SiO ₂ Example 8 1.2 wt% aqueous solution of calcium acetate; 143 cc of 1.5 wt% ammonium dihydrogen phosphate aqueous solution; 71
cc is added dropwise to precipitate the phosphate compound. 10 g of the ammonium-type zeolite obtained in Example 1 was put therein, stirred at 60 ° C. for 2 hours, washed, and dried. Then, the mixture was calcined under air flow at 500 ° C. for 5 hours to obtain a phosphorus-containing zeolite. As a result of X-ray diffraction measurement of this phosphorus-containing zeolite, calcium pyrophosphate was observed.

0.1 mol of this phosphorus-containing zeolite
/ Liter copper acetate aqueous solution; added to 41 cc, adjusted to pH = 10.5 with aqueous ammonia, stirred at room temperature for 20 hours, washed, and subjected to Cu ion exchange operation. After repeating this operation twice, it was dried to prepare a blue-violet catalyst 8. As a result of chemical analysis, the composition had the following composition expressed as a molar ratio of oxides on an anhydrous basis.

1.02CuO, 1.46CaO, 0.7
2P ₂ O ₅ , Al ₂ O ₃ , 41SiO ₂ Example 9 3.4 wt% aqueous solution of calcium acetate; 143 cc 3.1 wt% aqueous solution of ammonium dihydrogen phosphate; 71
An aqueous solution of cc adjusted to pH = 10.5 with aqueous ammonia is added dropwise to precipitate the phosphate compound. 10 g of the ammonium-type zeolite obtained in Example 1 was put therein, stirred at 60 ° C. for 2 hours, washed, and dried. Then, the mixture was calcined under air flow at 800 ° C. for 5 hours to obtain a phosphorus-containing zeolite. As a result of X-ray diffraction measurement of this phosphorus-containing zeolite, β-calcium phosphate was observed.

0.1 mol of this phosphorus-containing zeolite
/ Liter copper acetate aqueous solution; added to 41 cc, adjusted to pH = 10.5 with aqueous ammonia, stirred at room temperature for 20 hours, washed, and subjected to Cu ion exchange operation. After repeating this operation twice, it was dried to prepare a blue-violet catalyst 9. As a result of chemical analysis, the composition had the following composition expressed as a molar ratio of oxides on an anhydrous basis.

0.67CuO, 6.84CaO, 2.4
2P ₂ O ₅ , Al ₂ O ₃ , 41SiO ₂ Example 10 Phosphorus-containing zeolite prepared in the same manner as in Example 1;
Instead of exchanging 10g of Cu ion, 0.035mo
1 / liter copper acetate aqueous solution; after soaking in 100 cc,
It was dried and loaded with Cu. Then 600 under air circulation
It was calcined at 1 ° C. for 1 hour to prepare a gray-brown catalyst 10. 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, 0.90 P ₂ O ₅ , Al ₂
O ₃ , 41SiO ₂ Example 11 Durability evaluation was performed using the catalysts 1 to 10 obtained in Examples 1 to 10.

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 results obtained are shown in Table 2.

[0048]

[Table 1]

[0049]

[Table 2]

Comparative Example 1 A blue-violet Cu type ZSM-5 was prepared in the same manner as in Example 1 except that phosphorus was not supported.
(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 A pink Co type ZSM-5 was prepared in the same manner as in Example 4 except that phosphorus was not supported.
(Comparative catalyst 2) 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 , 41 SiO ₂ Comparative Example 3 Gray Cu-supporting ZSM-5 was prepared in the same manner as in Example 8 except that phosphorus was not supported.
(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.

1.01 CuO, Al ₂ O ₃ , 41SiO ₂ Comparative Example 4 Comparative catalysts 1 to 3 obtained in Comparative Examples 1 to 3 were used to evaluate the catalyst durability in the same manner as in Example 11. The results obtained are shown in Table 3.

[0054]

[Table 3]

[0055]

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

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location F01N 3/08 ZAB B F23J 15/00 ZAB A 7367-3K

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 containing 5 or more zeolites containing phosphorus and one or more active metal species with an oxygen-excess exhaust gas containing nitrogen oxides and hydrocarbons.