JPH0760063A - Removing process for nitrogen oxid - Google Patents

Abstract

PURPOSE:To provide a process of cleaning efficiently exhaust gas by using an exhaust gas cleaner which can clean particularly excessive oxygen to be exhausted out of an internal combustion engine of an automobile or the like without utilizing a reducer such as ammonia and is of superior durability at the high temperature containing water vapor. CONSTITUTION:Nitrogen oxides are removed out of exhaust gas of excessive oxygen containing nitrogen oxides and hydrocarbon by using a catalyst composed of zeolite having the SiO2/Al2O3 molar ratio of at least 15 or more treated using a germanium compound and active metal of one kind or more.

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, or a method of passing an exhaust gas through a catalyst and unburned A non-selective catalytic reduction method of reducing with carbon monoxide and hydrocarbon 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.

Therefore, Al near the surface of the zeolite is replaced by S.
Attempts have been made to improve the durability of zeolite in the presence of high temperature steam by substituting it with i to make the outer surface of the zeolite hydrophobic (JP-A-4-271843). However, in this proposed method, since Si substitution is carried out in an aqueous solution using ammonium silicofluoride, zeolite pores are generated by hydrofluoric acid produced by hydrolysis of part of the ammonium silicofluoride in the aqueous solution. However, sufficient Al durability was not obtained due to the removal of Al inside.

[0007] Further, as an attempt to introduce germanium into zeolite, for example, The Journal of Physical Chemistry (The Journal of Physi
calChemistry), vol.97, No.21, 1993. 5678-5684. However, in this report, germanium chloride was added to the hydrofluoric acid solution at the time of zeolite synthesis, and not only the effect of improving the durability of the zeolite crystal was not obtained by such a method, but the zeolite crystal was treated in this way. If it is applied, the zeolite will be eroded by the coexisting hydrofluoric acid, and the durability will be reduced.

[0008]

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.

[0009]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have found that treating a zeolite with a germanium compound enables efficient exhaust gas purification even after being used under high temperature steam. They have found the present invention and completed the present invention.

That is, the present invention provides a germanium compound-treated SiO ₂ / Al ₂ O ₃ molar ratio of at least 15
It is intended to provide a method for removing nitrogen oxides from an oxygen-excess exhaust gas containing nitrogen oxides and hydrocarbons by using the above zeolite and a catalyst composed of one or more active metals.

The treatment of the germanium compound is carried out by bringing the germanium compound vapor into contact with the zeolite and / or bringing the germanium compound into contact with the zeolite in an organic solvent. This treatment allows Ge into the zeolite lattice without destroying the zeolite pore structure.
It is considered that since the zeolite can be introduced, the zeolite becomes hydrophobic, the entry of water vapor into the pores, which causes the catalyst deterioration, is suppressed, and the durability of the catalyst is improved.

The present invention will be described in more detail below.

The catalyst used in the present invention comprises a germanium compound-treated zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of at least 15 and one or more active metals. Raw material zeolite Si used in the present invention
The O ₂ / Al ₂ O ₃ molar ratio may be 15 or more after the treatment with the germanium compound. In addition, SiO ₂ / Al ₂ O
The upper limit of the ₃ molar ratio is not limited. SiO ₂
If the / Al ₂ 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 and ZSM-.
5, ZSM-8, ZSM-11, ZSM-12, ZSM
Zeolites such as -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 raw material zeolite is treated with a germanium compound and one or more active metals are introduced.

The order of treating the germanium compound and introducing the active metal is not particularly limited, and the active metal may be introduced after treating the starting zeolite with the germanium compound.
A germanium compound treatment can also be performed after the introduction of the active metal.

The treatment of the germanium compound is carried out by contacting the germanium compound vapor with the starting zeolite or the zeolite containing at least one active metal and / or treating the germanium compound with the starting zeolite or zeolite containing at least one active metal in an organic solvent. It is performed by bringing them into contact.

During the treatment with the germanium compound, in order to remove the water adsorbed on the raw material zeolite and to keep the hydroxyl groups on the surface of the zeolite in an active state, they are vacuumed or inert gas or dried. Pretreatment is preferably performed at 300 to 800 ° C. in an air atmosphere.

Examples of the germanium compound that can be used in the present invention include halogenated germanium compounds such as germanium fluoride, germanium chloride, germanium bromide and germanium iodide, and organic germanium compounds such as alkyl germanium and alkoxy germanium.
Of these, a germanium halide compound is preferable.

In the germanium compound vapor treatment, the concentration of the germanium compound is not particularly limited, but from the viewpoint of operability, the concentration of the germanium compound is adjusted to 0.1 to 0.1 with a diluent gas.
It is preferable to use it after diluting it to 20%. The diluting gas may be any gas in which the germanium compound is stably present, and N ₂ , He, Ar, dry air or the like can be used. If the diluent gas contains water, the germanium compound on the outer surface of the zeolite will be aggregated after hydrolysis, and the effect of improving the durability of the zeolite may be unclear, so the water content in the treated gas is It is desirable to reduce it as much as possible.

The temperature of the germanium compound vapor treatment varies depending on the compound used and the treatment method, but a temperature of room temperature to 800 ° C. is preferable in order to stably exist some compounds and to prevent the decomposition of the starting zeolite.

The method of vaporizing the germanium compound is not particularly limited, but a method such as treating the zeolite in a closed container filled with the germanium compound-containing gas, or circulating the germanium compound-containing gas in the zeolite-filled layer is used. To be The space velocity when circulating the germanium compound-containing gas is 10 to 10000 / h.
r is enough. The contact time may be about 10 minutes to 30 hours.

On the other hand, in the treatment of the germanium compound in the organic solvent, the concentration of the germanium compound is not particularly limited, but it is preferably 0.1 to 20%. The organic solvent may be any solvent in which the germanium compound is stably present, such as hexane, cyclohexane, benzene,
Toluene or the like is used. If the organic solvent contains water, the germanium compound may change into an oxide or the like and aggregate on the outer surface of the zeolite. Therefore, it is desirable to remove water in the solvent as much as possible. Further, when water is used as the solvent, germanium is deposited as an oxide or the like, and a catalyst having excellent durability cannot be obtained.

The temperature for treating the germanium compound in an organic solvent varies depending on the compound used and the treatment method, but may be any temperature at which the reaction with hydroxyl groups on the outer surface of the zeolite proceeds, for example from room temperature to the boiling point of the organic solvent. The treatment can be carried out at temperature.

Zeolite treated with a germanium compound in an organic solvent is preferably subjected to solid-liquid separation in order to prevent excess germanium compound from adhering. Or acid,
The germanium compound may be removed by washing with an organic solvent or the like or by reducing the pressure. In the present invention, the treatment with the germanium compound vapor and the treatment with the germanium compound in an organic solvent may be performed together, if necessary.

The zeolite treated with the germanium compound by the above-mentioned method is heat-treated at a temperature of 100 to 800 ° C. under vacuum or in an inert gas or air atmosphere in order to remove the excess germanium compound. good.

The zeolite thus obtained is composed of Si
The O ₂ / GeO ₂ molar ratio may be in the range of 20 to 20,000. At this time, the introduction state of Ge into the zeolite lattice differs depending on the method of treating the germanium compound,
When Ge is introduced only near the outer surface of the zeolite, the durability of the obtained catalyst is remarkably improved even if the amount of Ge present in the zeolite is very small.

One or more active metals are introduced into the catalyst used in the present invention. The active metal may be any metal that is usually used for exhaust gas purification, such as Cu or A.
Ib group such as g, Au, Fe, Co, Ni, Ru, Rh,
VIII group such as Pd and Pt, VIa group such as Cr and Mo,
Alternatively, a 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, an ion exchange method 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 zeolite, it has higher activity and durability, so it is necessary to introduce the active metal by the ion exchange method. Is preferred.

The ion exchange is carried out by bringing the starting zeolite or the zeolite treated with a germanium compound into contact with an aqueous solution containing a salt of an active metal and washing it. Examples of the active metal salt include active metal chloride, nitrate, sulfate,
A salt such as acetate is 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 starting zeolite or the zeolite treated with the germanium compound in order to provide sufficient activity and durability. 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 provide sufficient activity and durability. Further, the ion exchange operation can be repeated if necessary.

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

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 treatment with the germanium compound 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. Alternatively, the raw material zeolite or the zeolite treated with a germanium compound may be molded in advance, and the molded body may be treated with the germanium compound or introduced with an active metal. 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 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 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. when 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 and the temperature is 200 to 800 ° C.

[0038]

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. 2860 g of the homogeneous compound and a 3.2 wt% NaOH aqueous solution 6
150g and charged into an autoclave, 72 at 160 ℃
Crystallized under stirring for hours.

The product is solid-liquid separated, washed with water and dried to obtain ZSM.
-5 type zeolite 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.

1.03Na ₂ O, Al ₂ O ₃ , 41SiO ₂ 10 g of this zeolite was added to 100 cc of an aqueous solution containing 6.4 g of CsCl, stirred at 60 ° C. for 20 hours, washed and dried to obtain Cs. Ion exchange was performed to obtain Cs-type zeolite.

The Cs-type zeolite was filled in a reaction tube and pretreated at 500 ° C. for 1 hour under He flow to remove H ₂ O and the like adsorbed on the zeolite. Next, He gas containing 3.2% germanium tetrachloride; 100
cc / min was passed through the zeolite layer at 100 ° C for 2 hours. The treated zeolite is washed with a 0.1N hydrochloric acid aqueous solution, and then with pure water, and then 600 times under air flow.
Firing was performed at ℃ for 1 hour.

The zeolite treated with germanium tetrachloride was added to 100 cc of an aqueous solution containing 0.7 g of copper acetate, the pH was adjusted to 10.5 with aqueous ammonia, the mixture was stirred at room temperature for 20 hours, and then washed to obtain Cu ions. Exchange operation was performed. This operation was repeated twice and then dried to obtain a catalyst 1. As a result of chemical analysis, the composition had a SiO ₂ / GeO ₂ molar ratio of 13700, and had the following composition represented by the molar ratio of oxides on an anhydrous basis.

1.35CuO, 0.003GeO ₂ , A
l ₂ O ₃ , 41SiO ₂ Example 2 10 g of the Cs-type zeolite obtained in Example 1; 10 g was charged into a reaction vessel, pretreated at 400 ° C. for 1 hour under exhaust, and adsorbed on the zeolite H ₂ O and the like were removed. Then, under a nitrogen atmosphere, hexane containing 5% germanium tetrachloride; 40 cc was dropped into the reaction vessel, and the temperature was 30 ° C.
After stirring for 20 hours, the mixture is filtered, and hexane is added; 200 cc
Washed with.

The treated zeolite was treated with C as in Example 1.
The catalyst 2 obtained by u ion exchange is SiO ₂ / GeO ₂
The molar ratio was 4100 and had the following composition, expressed as the molar ratio of oxides on an anhydrous basis.

1.05 CuO, 0.01 GeO ₂ , Al ₂
O ₃ , 41 SiO ₂ Example 3 The durability evaluation was performed using the catalysts 1 and 2 obtained in Examples 1 and 2.

Each catalyst was press-molded and then pulverized to 12 to
The size was adjusted to 20 mesh. 2 cc of the gas was filled in a fixed pressure fixed bed flow type reaction tube, and a gas simulating the exhaust gas of the 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.

Each catalyst was subjected to a durability treatment at 800 ° C. for 5 hours while flowing a gas having the composition shown in Table 1 at a space velocity of 120,000 / hr. 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.

[0051]

[Table 1]

[0052]

[Table 2]

Comparative Example 1 A Cu type ZSM-was prepared in the same manner as in Example 1 except that the germanium tetrachloride 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. Resulting 1.03CuO, in Al ₂ O _3, 41SiO ₂ Comparative Example 2 Example 2, except that H ₂ O was used as a solvent in the same manner as in Example 1, Cu-type ZSM-5 (Comparative Catalyst 2) It was As a result of chemical analysis, the composition is SiO ₂ / G
The eO ₂ ratio was 18, and had the following composition, expressed as the molar ratio of oxides on an anhydrous basis.

1.05 CuO, 2.23 GeO ₂ , Al ₂
O ₃ , 41SiO ₂ Comparative Example 3 Using Comparative Catalysts 1 and 2 obtained in Comparative Examples 1 and 2,
The catalyst durability was evaluated in the same manner as in Example 3. The results obtained are shown in Table 3.

[0055]

[Table 3]

[0056]

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.

[Procedure amendment]

[Submission date] September 2, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

[0007] Further, as an attempt to introduce germanium into zeolite, for example, The Journal of Physical Chemistry (The Journal of Physi
calChemistry), vol.97, No.21, 1993 , 5678-5684. However, in this report, germanium chloride was added to the hydrofluoric acid solution at the time of zeolite synthesis, and not only the effect of improving the durability of the zeolite crystal was not obtained by such a method, but the zeolite crystal was treated in this way. If it is applied, the zeolite will be eroded by the coexisting hydrofluoric acid, and the durability will be reduced.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0022

[Correction method] Change

[Correction content]

The temperature of the germanium compound vapor treatment varies depending on the compound used and the treatment method, but is preferably room temperature to 800 ° C. in order to stably exist the compound to be used and to prevent the starting zeolite from collapsing.

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

Claims (3)

[Claims] 1. Treated with a germanium compound,
Nitrogen oxides are removed from oxygen-rich exhaust gas containing nitrogen oxides and hydrocarbons by using a catalyst composed of zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of at least 15 and one or more active metals. how to. 2. The method for removing nitrogen oxides according to claim 1, wherein the treatment with the germanium compound is a treatment with a vapor of the germanium compound and / or a treatment with the germanium compound in an organic solvent. 3. The method for removing nitrogen oxides according to claim 1 or 2, wherein the germanium compound used is a germanium halide compound.