JPH0929068A - Removal of nitrogen oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To more efficiently remove nitrogen oxide from oxygen excessive exhaust gas discharged from a car, especially, a diesel engine by using a catalyst excellent in denitration capacity from low temp. even in the coexistence of SOx without using a special reducing agent such as ammonia. SOLUTION: A catalyst consisting of zeolite containing one or more kinds of a transition metal (Cu or the like) and a composite hydroxide of the group VIII elements such as Co or Ni and the group IIa elements such as Mg or Ba or a composite oxide obtained from the composite hydroxide is brought into contact with oxygen excessive exhaust gas containing 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 exhaust gas in excess of oxygen containing nitrogen oxides discharged from a boiler, an automobile engine, etc., by using a catalyst. , SOx) and a method of removing nitrogen oxides using a catalyst having excellent activity even in the coexistence.

[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.

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

Further, there has been proposed an exhaust gas purifying catalyst in which a zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of at least 15 contains cobalt and alkaline earth and copper / or rhodium. (For example, JP-A-4-21914
No. 4 publication).

[0005]

However, the activity of these proposed catalysts, especially the low temperature activity in the presence of SOx, is insufficient, and they have not been put into practical use.

[0006] The object of the present invention is to use a catalyst having an excellent denitration performance from a low temperature even in the coexistence of SOx without using a special reducing agent such as ammonia or the like, and excess oxygen discharged from an automobile or the like, particularly a diesel engine. Another object of the present invention is to provide a method for more efficiently removing nitrogen oxides from the exhaust gas.

[0007]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have found that a zeolite containing a transition metal and a composite hydroxide of a Group VIII element and a Group IIa element or a composite hydroxide thereof. The inventors have found that exhaust gas can be efficiently purified from a low temperature by using a catalyst containing a composite oxide obtained from a product, and have completed the present invention.

That is, the present invention provides a method of removing nitrogen oxides from an oxygen-excess exhaust gas containing nitrogen oxides and hydrocarbons, wherein a zeolite containing a transition metal and a Group VIII element or a Group IIa element are used. It is intended to provide a method for removing nitrogen oxides, which comprises contacting exhaust gas with a catalyst containing a composite hydroxide or a composite oxide obtained from the composite hydroxide.

Hereinafter, the present invention will be described in more detail.

The catalyst used in the process of the present invention is
It is a catalyst containing a zeolite containing a transition metal and a composite hydroxide of a Group VIII element and a Group IIa element or a composite oxide obtained from this composite hydroxide.
The composite hydroxide mentioned here is a compound in which a hydroxide of a Group VIII element and a hydroxide of a Group IIa element coexist. Further, the complex oxide referred to here is an oxide obtained from this complex hydroxide. In addition, the complex oxide is 2
It may be one obtained from more than one kind of the composite hydroxide.

S of the zeolite used in the present invention
The iO ₂ / Al ₂ O ₃ molar ratio is not particularly limited, but in order to obtain more sufficient activity and durability, the SiO ₂ / Al ₂ O ₃ molar ratio is preferably 15 to ₂₀₀ .

The type of zeolite is not particularly limited. For example, zeolite Y, zeolite L, mordenite, ferrierite, zeolite β, ZSM-5, Z.
SM-8, ZSM-11, ZSM-12, ZSM-2
Zeolites such as 0, ZSM-22, ZSM-35, and ZSM-57 can be used. To obtain more sufficient activity, Z
SM-5 is preferred. Further, the method for producing these zeolites is not limited. Further, zeolites such as zeolite Y and zeolite L may be dealuminated.

The zeolite used in the present invention may be a synthetic product or a calcined product thereof.
Ions such as a can be treated with an ammonium salt or a mineral acid to be used as a proton ion exchange or ammonium ion exchange zeolite. Furthermore, K, Cs,
It can also be used by ion-exchange with Ba or the like.

It is important that the zeolite contains at least one transition metal. The transition metal species may be any transition metal that is usually purified by exhaust gas, for example,
Ib group such as Cu, Ag, Au, Fe, Co, Ni, R
Group VIII such as u, Rh, Pd, Pt and the group VIa such as Cr and Mo are used. Cu is preferable in order to obtain more sufficient activity.

The method of incorporating the transition metal is not particularly limited, but an impregnation-supporting method, an evaporation-drying method, an ion-exchange method and the like can be used. It is preferable to introduce the transition metal by the ion exchange method because the transition metal becomes more active when it exists in the ion site of zeolite. The ion exchange is performed by mixing zeolite with an aqueous solution containing a salt of a transition metal, stirring and washing.

As the transition metal salt, transition metal salts such as chloride, nitrate, sulfate and acetate are preferably used. Further, an ammine complex salt of a transition metal or the like is also preferably used.

The addition amount, concentration, exchange temperature, time, etc. of the transition metal at the time of ion exchange are not particularly limited, and a generally used method may be used. The addition amount of the transition metal is more preferably 0.2 to 20 in atomic ratio with respect to Al of the zeolite in order to obtain more sufficient activity. Further, the ion exchange slurry concentration is preferably 5 to 50% by weight, which is usually performed.
Further, the ion exchange temperature and time are more preferably room temperature to 100 ° C. and time of 5 minutes to 3 days in order to have more sufficient activity. Further, the ion exchange operation can be repeated if necessary.

The method for producing the composite hydroxide used in the present invention is not particularly limited, but for example, a method of precipitating a composite hydroxide from a solution in which a Group VIII element and a Group IIa element coexist, a method of depositing a complex hydroxide of both groups Method of mixing hydroxides, method of stacking each hydroxide, method of precipitating hydroxide containing group VIII element on hydroxide containing group IIa element, or group VIII element And a method of precipitating a hydroxide containing a Group IIa element on the hydroxide containing a.

The method of precipitating the composite hydroxide from the solution in which the Group VIII element and the Group IIa element coexist is not particularly limited, but for example, an aqueous solution containing elements of both groups may be added to aqueous ammonia or sodium hydroxide. Examples thereof include a method of obtaining a composite hydroxide by adding an alkaline aqueous solution such as an aqueous solution, a method of heating an aqueous solution containing an element of both groups to obtain a composite hydroxide, and the like.

The method for precipitating the hydroxide from the solution of the Group VIII element or the Group IIa element is not particularly limited, but for example, an aqueous solution containing one element may be aqueous ammonia or sodium hydroxide. And a method for obtaining a hydroxide by heating an aqueous solution containing one element, and the like.

As the source of the Group IIa element or the Group VIII element, a hydroxide or a soluble salt is used, and examples of the soluble salt include chloride, nitrate, acetate, sulfate and the like.

The type of the Group VIII element is not particularly limited, and Co, Ni, Fe, Ru, Rh, Pd, Os,
Ir or Pt is used, but Co, Ni or Fe is preferable, and more preferably, in order to obtain more sufficient activity.
Co and Ni are used. The type of the Group IIa element is not particularly limited, and Be, Mg, Ca, Sr, Ba, R
a is used, in order to obtain a sufficient activity, Mg,
Ca, Sr, and Ba are preferable, and M is more preferable.
g, Ba are used.

It is important that the composite oxide of the Group VIII element and the Group IIa element used in the present invention is a composite oxide obtained from the composite hydroxide. The method of obtaining the composite oxide from the composite hydroxide is not particularly limited, and for example, a method of firing the composite hydroxide can be used. Baking is 100 to 1500 ° C., more preferably 3
The temperature can be 0 to 1000 ° C., and the time can be 5 minutes to 100 hours, and the reaction can be performed in air or oxygen.

The composition of the composite hydroxide of the Group VIII element and the Group IIa element or the composite oxide obtained from this composite hydroxide is not particularly limited, but the atomic ratio of Group VIII element / Group IIa element is not limited. It may be 0.05 to 20. In order to obtain a more sufficient activity, 0.1-10 is preferable.

The catalyst used in the present invention is a zeolite containing one or more kinds of transition metals, a composite hydroxide of a Group VIII element and a Group IIa element, or a composite oxide obtained from this composite hydroxide. Must coexist. The transition metal-containing zeolite, and the coexistence method of the composite hydroxide or the composite oxide is not particularly limited, for example, a method of mixing the zeolite and the composite hydroxide or the composite oxide, the composite hydroxide on the zeolite or Examples thereof include a method of supporting a composite oxide, a method of laminating zeolite and a composite hydroxide or a composite oxide, and the like.

The mixing method is not particularly limited, but the zeolite and the composite hydroxide or the composite oxide are mixed in powder form or uniformly mixed in a slurry state, and then solid-liquid separation and drying are carried out. be able to. Also,
The method of supporting is not particularly limited, evaporation dryness method in the presence of zeolite containing one or more transition metals,
The coprecipitation method and the like can be mentioned. In order to obtain a more sufficient activity, the method of mixing is preferable.

The coexistence weight ratio of the composite hydroxide of the Group VIII element and the Group II element or the composite oxide obtained from this composite hydroxide and the zeolite containing one or more kinds of transition metals is not particularly limited. However, in order to obtain a more sufficient activity, 0.01 to 100 is preferable, and 0.5 to 5 is more preferable.

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

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. The binder used for molding is a clay mineral such as kaolin, attapulgite, montmorillonite, bentonite, allophane, and sepiolite. 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 important that the exhaust gas used in the present invention contains nitrogen oxides and hydrocarbons and is in excess of oxygen, and may contain SOx without any problem. It is also effective when the exhaust gas contains carbon monoxide, hydrogen 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).

If desired, the target exhaust gas may be fuel oil such as gasoline or light oil, or hydrocarbons such as cetane and octane added.

Although the concentration of each component in the exhaust gas is not particularly limited, NO = 0.005 to 1 mol%, hydrocarbon: THC = 0.01 to 3 mol%, O ₂ = _{2 to} 15 m
%, H ₂ O = 0 to 15 mol%, SOx = 0 to 0.
1 mol% is preferable. Here, THC is the concentration when converted to methane.

The space velocity, temperature, etc. when removing nitrogen oxides are not particularly limited, but the space velocity is 100 to 50,000.
It may be 0 hr ⁻¹ and a temperature of 100 to 800 ° C. In order to obtain sufficient activity, the temperature is preferably 100 to 600 ° C, more preferably 200 to 400 ° C.

[0034]

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

Production Example 1 Ammonium ion-exchanged ZSM-5 zeolite (SiO 2
₂ / Al ₂ O ₃ molar ratio is 41) 100 g 0.07 mol
The mixture was added to 1000 cc of a copper acetate aqueous solution of 1 / l, 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 ion-exchanged zeolite. As a result of chemical analysis, the composition had the following composition represented by the molar ratio of oxide on an anhydrous basis.

1.05 Cu0, Al ₂ O ₃ , 41 SiO ₂ Production Example 2 10 g of nickel chloride hexahydrate was dissolved in 50 g of water, and 2.5% ammonia water was added dropwise with stirring to obtain Ni hydroxide. It was The obtained Ni hydroxide and 8 g of barium hydroxide octahydrate were mixed in a mortar. 55 in air
It was baked at 0 ° C. for 3 hours to obtain a Ni / Ba oxide. As a result of the chemical analysis, the composition is represented by an atomic ratio of Ni / Ba of 1.
It was 50.

Production Example 3 7 g of cobalt nitrate hexahydrate was dissolved in 50 g of water, and 2.5% aqueous ammonia was added dropwise with stirring to obtain a Co hydroxide. The obtained Co hydroxide and 6 g of barium hydroxide octahydrate were mixed in a mortar. 550 the resulting mixture in air
The mixture was baked at ℃ for 3 hours to obtain a Co / Ba oxide. As a result of chemical analysis, its composition was expressed as an atomic ratio of Co / Ba of 0.9.
It was 5.

Production Example 4 11 g of cobalt nitrate hexahydrate was dissolved in 50 g of water, and 2.5% aqueous ammonia was added dropwise with stirring to obtain a Co hydroxide. Obtained Co hydroxide and magnesium hydroxide 2
g were mixed in a mortar. The mixture obtained is 550 ° C. in air.
And baked for 3 hours to obtain a Co.Mg oxide. As a result of chemical analysis, its composition is expressed by Co / Mg atomic ratio of 0.92.
Met.

Production Example 5 Cobalt nitrate hexahydrate (10 g) and magnesium chloride hexahydrate (7 g) were dissolved in water (50 g), and 2.5% aqueous ammonia was added dropwise with stirring to obtain a Co.Mg hydroxide. . The hydroxide obtained is calcined in air at 550 ° C. for 3 hours to give Co · M
g oxide was obtained. As a result of chemical analysis, its composition is Co / M
The atomic ratio of g was 1.21.

Production Example 6 10 g of cobalt nitrate hexahydrate and 7 g of barium chloride were added to 5 parts of water.
It was dissolved in 0 g, reduced in pressure with stirring at 70 ° C., and evaporated to dryness to obtain a mixed salt of Co and Ba. The obtained mixed salt was calcined in air at 550 ° C. for 3 hours to obtain a Co / Ba oxide. As a result of chemical analysis, the composition was 1.02 in terms of Co / Ba atomic ratio.

Production Example 7 Cu ion-exchanged zeolite (SiO 2) obtained in Production Example 1
₂ / Al ₂ O ₃ molar ratio is 41); 100 g of 0.07mo
l / l Cobalt acetate and 0.07 mol / l barium acetate in 1000 cc were added to the solution at 60 ° C. for 20
After stirring for a time, it was washed and Co and Ba ion exchange operations were performed. After repeating this operation twice, it is dried to obtain Co, B.
a Ion-exchanged zeolite was obtained. As a result of chemical analysis, the composition had the following composition represented by the molar ratio of oxide on an anhydrous basis.

0.40CuO, 0.32CoO, 0.5
2Ba0, Al ₂ O ₃ , 41SiO ₂ Production Example 8 7 g of cobalt nitrate hexahydrate was dissolved in 50 g of water, and 2.5% aqueous ammonia was added dropwise with stirring to obtain a Co hydroxide. The obtained Co hydroxide and 6 g of barium hydroxide octahydrate were mixed in a mortar to obtain Co.Ba hydroxide. As a result of chemical analysis, the composition was 0.95 in terms of Co / Ba atomic ratio.

Production Example 9 10 g of cobalt nitrate hexahydrate, 7 g of magnesium chloride hexahydrate and 7 g of copper acetate monohydrate were dissolved in 50 g of water, and 2.5% aqueous ammonia was added dropwise with stirring to Co.・ Mg
Cu hydroxide was obtained. The hydroxide obtained is 550 in air.
The mixture was baked at ℃ for 3 hours to obtain a Co.Mg.Cu oxide. As a result of chemical analysis, the composition was 1.21: 1: 1.20 in terms of the atomic ratio of Co: Mg: Cu.

Production Example 10 Ammonium ion-exchanged zeolite (SiO ₂ / Al ₂ O
₃ molar ratio 41); 100 g was added to 1000 cc of 0.07 mol / l cobalt acetate and 0.07 mol / l barium acetate aqueous solution, stirred at 60 ° C. for 20 hours, washed, and Co, Ba ion exchanged. The operation was performed. This operation was repeated twice and then dried to obtain Co, Ba ion-exchanged zeolite. As a result of chemical analysis, the composition had the following composition represented by the molar ratio of oxide on an anhydrous basis.

0.57CoO, 0.53Ba0, Al ₂
O ₃ , 41SiO ₂ Example 1 Catalyst 1 was prepared by mixing 2 g of the Cu ion-exchanged zeolite obtained in Production Example 1 and 4 g of the Ni.Ba oxide obtained in Production Example 2 in a mortar.

Example 2 Catalyst 2 was prepared by mixing 2 g of the Cu ion-exchanged zeolite obtained in Production Example 1 and 4 g of the Co.Ba oxide obtained in Production Example 3 in a mortar.

Example 3 Catalyst 3 was prepared by mixing 4 g of the Cu ion-exchanged zeolite obtained in Production Example 1 and 4 g of the Co.Mg oxide obtained in Production Example 4 in a mortar.

Example 4 Catalyst 4 was prepared by mixing 2 g of Cu ion-exchanged zeolite obtained in Production Example 1 and 4 g of Co.Mg oxide obtained in Production Example 5 in a mortar.

Example 5 11 g of cobalt nitrate hexahydrate and 7 g of magnesium chloride hexahydrate were dissolved in 50 g of water, and 4 g of Cu ion-exchange ZSM-5 obtained in Preparation Example 1 was dispersed therein. While stirring this solution, 2.5% aqueous ammonia was added dropwise to Co.
And Mg hydroxide were co-precipitated on ZSM-5. The obtained hydroxide-supporting ZSM-5 was calcined in air at 550 ° C. for 3 hours to obtain a Co / Mg oxide-supporting Cu ion exchange ZSM-5, which was used as a catalyst 5. As a result of chemical analysis, the composition is Co /
0.95 in terms of Mg atomic ratio, C for ZSM-5
The weight ratio of o.Mg oxide was 2.

Example 6 Catalyst 6 was prepared by mixing 2 g of Cu ion-exchanged zeolite obtained in Production Example 1 and 4 g of Co.Ba hydroxide obtained in Production Example 8 in a mortar.

(Activity evaluation) The activity evaluation was performed using the catalysts 1 to 6 obtained in Examples 1 to 6.

Each catalyst is press-molded and then crushed to 12 to
The size was adjusted to 20 mesh. After filling 2 cc of the reaction mixture in a fixed pressure fixed bed flow type reaction tube and performing a gas treatment simulating exhaust gas of a diesel engine (Table 1) at a space velocity of 60,000 / hr for 30 minutes at 550 ° C. The steady purifying activity at each temperature was measured. The steady-state purification activity was defined as the conversion rate after holding at each temperature for 30 minutes. Table 2 shows the obtained results.

[0053]

[Table 1]

[0054]

[Table 2]

Comparative Example 1 The Cu ion-exchanged zeolite prepared in Production Example 1 was used as Comparative Catalyst 1.

Comparative Example 2 The Co.Mg.Cu oxide prepared in Production Example 9 was crushed in a mortar and used as Comparative Catalyst 2.

Comparative Example 3 4 g of the Co.Ba mixed salt prepared in Preparation Example 6 and 2 g of the Cu ion-exchanged zeolite obtained in Preparation Example 1 were mixed in a mortar to obtain a comparative catalyst 3.

Comparative Example 4 The Cu / Co / Ba ion-exchanged zeolite prepared in Production Example 7 was used as Comparative Catalyst 4.

Comparative Example 5 The Co.Ba ion-exchanged zeolite prepared in Production Example 10 was used as Comparative Catalyst 5.

(Activity Evaluation) Using the comparative catalysts 1 to 5 obtained in Comparative Examples 1 to 5, the catalyst activity was evaluated in the same manner as described above. Table 3 shows the obtained results.

[0061]

[Table 3]

[0062]

As is apparent from Tables 2 and 3, according to the method of the present invention, the catalyst is used in the oxygen-excess exhaust gas containing hydrocarbons and nitrogen oxides, more specifically, SO.
Even in the presence of x, nitrogen oxides can be efficiently removed.

[0063]

Claims (1)

[Claims] 1. A method for removing nitrogen oxides from an oxygen-excess exhaust gas containing nitrogen oxides and hydrocarbons, wherein the zeolite contains at least one transition metal, and a Group VIII element and a Group IIa element. A method for removing nitrogen oxides, which comprises contacting exhaust gas with a catalyst containing the composite hydroxide according to claim 1 or a composite oxide obtained from the composite hydroxide.