JPH08215542A - Method for removing nitrogen oxide - Google Patents

Abstract

PURPOSE: To efficiently clean an exhaust gas, especailly an oxygen-excess exhaust gas, discharged from the internal combustion engine of an automobile, etc., at a high temp. in the presence of steam without using a reducing agent such as ammonia by using a highly durable exhaust gas cleaning catalyst. CONSTITUTION: A catalyst is brought into contact with an oxygen-excess exhaust gas contg. NOX and hydrocarbons to remove the NOX. A catalyst prepared by incorporating copper and >=1 kind of chloride selected from copper choride, magnesium chloride, nickel chloride, calcium chloride, yttrium chloride and chromium chloride into the zeolite treated with a soluble phosphorus compd., contg. copper and with the SiO2 -to-Al2 O3 molar ratio controlled to >=15 is used as the catalyst.

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-excess exhaust gas containing nitrogen oxides discharged from a boiler, an automobile engine, etc. by using a catalyst, and more specifically, to a method of treating extremely high durability. The present invention relates to a method for removing nitrogen oxides using an 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.

In recent years, as a catalyst for removing nitrogen oxides in exhaust gas under excess oxygen, for example, JP-A-60-125 is known.
JP-A-250 proposes a copper ion-exchanged zeolite capable of directly catalytically decomposing nitrogen oxides in the absence of a reducing agent.

Further, for purifying 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 (for example, Japanese Patent Laid-Open No. 63-100919).

Further, as a catalyst for reducing nitrogen oxides in the presence of excess oxygen, for example, JP-A-5-317725, JP
In Roppa Patent No. 585025, a zeolite containing Cu and P is disclosed in JP-A-6-226105 and JP-A-6-226105.
No. 226106 discloses Cu, P, Co and N.
Zeolites containing i, etc. have been proposed.

[0006]

However, the above-mentioned catalysts disclosed in the prior art have problems in durability, especially at high temperatures, and have not been put to practical use.

Therefore, an object of the present invention is to efficiently purify exhaust gas, especially in excess of oxygen, discharged from an internal combustion engine such as an automobile, without using a specific reducing agent such as ammonia, and to remove water vapor. The present invention provides a method for purifying exhaust gas using an existing exhaust gas-purifying catalyst having excellent durability at high temperatures.

[0008]

Means for Solving the Problems As a result of extensive studies on the above problems, the present inventors have found that a zeolite treated with a soluble phosphorus compound contains copper, copper chloride, magnesium chloride,
By using a catalyst containing one or more kinds of chlorides selected from nickel chloride, calcium chloride, yttrium chloride and chromium chloride, it was found that exhaust gas can be efficiently purified even after being used at high temperature, and the present invention is achieved. It came to completion.

That is, the present invention is a method for removing nitrogen oxides by contacting the catalyst with an oxygen-excess exhaust gas containing nitrogen oxides and hydrocarbons, wherein the catalyst is SiO ₂ / Al treated with a soluble phosphorus compound. Use of a catalyst in which a zeolite having a ₂ O ₃ molar ratio of at least 15 or more contains copper and one or more chlorides selected from copper chloride, magnesium chloride, nickel chloride, calcium chloride, yttrium chloride and chromium chloride. A method for removing nitrogen oxides is provided.

The soluble phosphorus compound-treated zeolite used in the process of the present invention is provided with one or more chlorides selected from copper and copper chloride, magnesium chloride, nickel chloride, calcium chloride, yttrium chloride and chromium chloride. It is not clear why the catalyst containing the substance exhibits a high specific effect on the durability, but the effect is to treat the zeolite with a soluble phosphorus compound, introduce copper and copper chloride, magnesium chloride, chloride. Cu, P, chloride (copper chloride, magnesium chloride, nickel chloride, calcium chloride, yttrium chloride) introduced into the zeolite by introducing one or more chlorides selected from nickel, calcium chloride, yttrium chloride and chromium chloride. And one or more chlorides selected from chromium chloride) individual effects of the component, Different from the effect of combination of each component, specific by the synergistic effect of three components of Cu + P + chloride (one or more chloride selected from copper chloride, magnesium chloride, nickel chloride, calcium chloride, yttrium chloride and chromium chloride) It is considered to be an effect.

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

The catalyst used in the present invention is a zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of at least 15 treated with a soluble phosphorus compound, copper, copper chloride, magnesium chloride, nickel chloride, calcium chloride, The catalyst contains at least one chloride selected from yttrium chloride and chromium chloride.

Zeolite S used in the present invention
The iO ₂ / Al ₂ O ₃ molar ratio is 15 or more. Also, S
The upper limit of the iO ₂ / Al ₂ O ₃ molar ratio is not limited, but it is preferably 15 to 200 from the viewpoint of obtaining sufficient durability.

The type of zeolite is not particularly limited, but for example, mordenite, ferrierite, zeolite β, ZSM-5, ZSM-8, ZSM-11, 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. It may also be a dealuminated zeolite such as zeolite Y or zeolite L.

As the zeolite, a synthetic product or a calcined product thereof is used, but the ion such as Na in the zeolite may be treated with an ammonium salt, a mineral acid or the like to be used as an H type or an ammonium type. Furthermore, K,
It can also be used by ion-exchange with Cs, Ba or the like.

The soluble phosphorus compound in the present invention refers to a phosphorus compound soluble in water or an organic solvent. Moreover, the treatment of the zeolite with the soluble phosphorus compound refers to introducing the soluble phosphorus compound into the zeolite by bringing the aqueous solution or the organic solvent in which the soluble phosphorus compound is dissolved into contact with the zeolite.

The method of treating the zeolite with the soluble phosphorus compound is not particularly limited as long as it is a method of bringing the aqueous solution or organic solvent in which the soluble phosphorus compound is dissolved into contact with the zeolite, but a usual method using an aqueous solution or an organic solvent is used. It can be introduced by the impregnation supporting method or the evaporation dryness method.

The type of soluble phosphorus compound that can be used to introduce the soluble phosphorus compound is not particularly limited, but soluble phosphates such as ammonium dihydrogen phosphate, diammonium hydrogen phosphate, dipotassium hydrogen phosphate, and orthophosphoric acid, Phosphoric acid such as pyrophosphoric acid and metaphosphoric acid is preferably used. Further, phosphite such as trimethyl phosphite may be used instead of the soluble phosphate or phosphoric acid. The amount of the soluble phosphorus compound introduced is not particularly limited, but it is preferably 0.001 to 10 times, and more preferably 0.
01 to 1.0 times is more preferable. The zeolite treated with the soluble phosphorus compound may be used as it is, but it is preferably 200 to 900 ° C., preferably 300 to stabilize the zeolite.
It is desirable to perform heat treatment at ~ 800 ° C. The atmosphere for the heat treatment is not particularly limited, and examples thereof include an atmosphere such as vacuum, air and water vapor.

Regarding the order of preparation of the catalyst used in the present invention, Cu to zeolite treated with soluble phosphorus compounds
The introduction order of the chlorides (one or more chlorides selected from copper chloride, magnesium chloride, nickel chloride, calcium chloride, yttrium chloride, and chromium chloride) may be arbitrary.

Cu is introduced as an active metal species into the zeolite treated with the soluble phosphorus compound. The method of introducing Cu 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. When Cu is present as Cu ions in the ion exchange site of zeolite, it becomes more durable at high temperatures, so it is preferable to introduce Cu by the ion exchange method.

The ion exchange is carried out by mixing the zeolite treated with the soluble phosphorus compound in an aqueous solution containing a Cu salt, stirring and washing. As the Cu salt, salts such as chlorides, nitrates, sulfates and acetates are preferably used. Also,
An ammine complex salt of Cu and the like can also be preferably used. The amount of Cu 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.

The amount of Cu added is, with respect to the number of moles of Al atoms in the zeolite, in order to provide sufficient activity and durability.
It is preferably 0.25 to 20 times. 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 catalyst used in the process of the present invention is one selected from copper chloride, magnesium chloride, nickel chloride, calcium chloride, yttrium chloride and chromium chloride.
Contains more than one chloride. The method of incorporating these chlorides is not particularly limited, but since these are water-soluble, methods such as an impregnating and supporting method, an evaporation-drying method, and a physical mixing method are preferably used. The amount of these chlorides added is not particularly limited, but is preferably 0.1 to 10% by weight, and more preferably 1.0 to 7.%, based on the amount of metal atoms with respect to the zeolite in the catalyst.
0% by weight is more preferred.

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. In addition, molding may be performed in the process of preparing the catalyst, and then the remaining steps may be performed. 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 containing excess 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 and the like. Exhaust gas with excess oxygen means
It indicates that 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.

[0027]

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 Ammonium-type ZSM-5 zeolite (containing Si
The composition of Al and Al is expressed by the molar ratio of oxides: SiO ₂ : Al ₂
10 g of O ₃ = 41: 1) was dipped in 70 cc of a 0.3 wt% diammonium hydrogen phosphate aqueous solution and then dried.
Then, it was calcined under air flow at 550 ° C. for 5 hours to obtain a phosphorus-treated zeolite.

This phosphorus compound-treated zeolite was added to 0.1
It was added to a mol / l copper acetate aqueous solution 41 cc, pH was adjusted to 10.5 with aqueous ammonia, and the mixture was stirred at room temperature for 20 hours, washed, and then subjected to Cu ion exchange operation. This operation was repeated twice and then dried to obtain a Cu-phosphorus treated zeolite. This composition had the following composition represented by the molar ratio of the oxide in the anhydrous base.

1.01CuO, 0.11P ₂ O ₅ , Al ₂
O _3, 41SiO ₂ CuCl this Cu- phosphorus treated zeolite and 0.70g
The ₂ · 2H ₂ O were mixed on a mortar to obtain a catalyst 1.

As a result of X-ray diffraction measurement of catalyst 1, peaks of copper chloride were confirmed in addition to zeolite.

Example 2 A catalyst 2 was obtained in the same manner as in Example 1 except that 0.84 g of MgCl ₂ .6H ₂ O was used instead of 0.70 g of CuCl ₂ .2H ₂ O.

Example 3 A Cu-phosphorus compound-treated zeolite obtained by the same method as in Example 1 was added to 50 cc of 0.042 mol / l nickel chloride aqueous solution, stirred, and then evaporated to dryness to obtain catalyst 3. It was

Example 4 A catalyst 4 was obtained in the same manner as in Example 1 except that 0.30 g of CaCl ₂ .2H ₂ O was used instead of 0.70 g of CuCl ₂ .2H ₂ O.

Example 5 A catalyst 5 was obtained in the same manner as in Example 1 except that 0.64 g of YCl ₃ .6H ₂ O was used in place of 0.70 g of CuCl ₂ .2H ₂ O.

Example 6 A catalyst 6 was obtained in the same manner as in Example 1 except that 0.56 g of CrCl ₃ .6H ₂ O was used instead of 0.70 g of CuCl ₂ .2H ₂ O.

Example 7 The durability evaluation was performed using the catalysts 1 to 6 obtained in Examples 1 to 6.

Each catalyst is press-molded and then pulverized to 12 to
The size was adjusted to 20 mesh. The 2 cc was filled in a fixed pressure fixed bed flow type reaction tube, and a gas simulating the exhaust gas of a lean burn engine (Table 1) was flowed to carry out durability treatment at 700 ° C. for 20 hours. Then, after pretreatment at 550 ° C. for 30 minutes, the steady-state purification activity at each temperature was adjusted to a space velocity of 120,000.
/ Hr. 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.

[0039]

[Table 1]

[0040]

[Table 2]

Comparative Example 1 A Cu-type zeolite (Comparative Catalyst 1) was obtained in the same manner as in Example 1, except that the phosphorus compound treatment and the addition of copper chloride were not carried out.

As a result of the X-ray diffraction measurement of the comparative catalyst 1, no peak other than zeolite was confirmed. Further, as a result of chemical analysis, the composition of the comparative catalyst 1 had the following composition represented by the molar ratio of the oxide in the anhydrous base.

1.05 CuO, Al ₂ O ₃ , 41 SiO ₂ Comparative Example 2 A Cu-phosphorus treated zeolite (Comparative Catalyst 2) was prepared in the same manner as in Example 1 except that copper chloride was not mixed. Got

As a result of the X-ray diffraction measurement of the comparative catalyst 2, no peak other than zeolite was confirmed. Further, as a result of chemical analysis, the composition of the comparative catalyst 2 had the following composition represented by the molar ratio of the oxide in the anhydrous base.

1.01CuO, 0.14P ₂ O ₅ , Al ₂
O ₃ , 41 SiO ₂ Comparative Example 3 Copper chloride-Cu-zeolite (Comparative Catalyst 3) was obtained in the same manner as in Example 1 except that phosphorus treatment was not performed.

As a result of X-ray diffraction measurement of comparative catalyst 3, peaks of copper chloride were confirmed in addition to zeolite. As a result of chemical analysis, the composition of the comparative catalyst 3 had the following composition expressed by the molar ratio of oxides in the anhydrous base.

2.10 CuO, Al ₂ O ₃ , 41SiO ₂ Comparative Example 4 The Cu-phosphorus compound treated zeolite obtained by the same method as in Example 1 was added to 50 cc of 0.042 mol / l nickel acetate aqueous solution and stirred. After that, it is evaporated to dryness and Ni (C
H ₃ COO) to give the ₂ -Cu- phosphorus compound-treated zeolite (Comparative Catalyst 4). As a result of chemical analysis, the composition of the comparative catalyst 4 had the following composition represented by the molar ratio of oxides in the anhydrous base.

1.07CuO, 0.60NiO, 0.1
_{1P 2 O 5, Al 2 O} 3, 41SiO 2 Comparative Example 5 Na-type -ZSM-5 zeolite (the composition of Si and Al containing expressed in terms of mole ratios of oxides _{SiO 2: Al 2 O 3 =} 4
After 10 g of 1: 1) was impregnated with 70 cc of 0.2 wt% diammonium hydrogen phosphate aqueous solution, it was dried at 150 ° C. for 20 hours. Then, it was added to 70 cc of 0.1 mol / l copper acetate aqueous solution, dried at room temperature for 12 hours to perform Cu ion exchange, and then washed to obtain a sample of 120
It dried at 20 degreeC and the Cu-phosphorus compound processing zeolite was obtained for 20 hours. This Cu-phosphorus compound treated zeolite has 0.0
After impregnating with 25 cc of 28 mol / l nickel acetate aqueous solution, it was dried at 150 ° C. for 20 hours. Then 50
The mixture was calcined at 0 ° C. for 2 hours to obtain Ni (CH ₃ COO) ₂ —Cu-phosphorus compound-treated zeolite (Comparative Catalyst 5).

As a result of X-ray diffraction measurement of comparative catalyst 5, no peak other than zeolite was observed. As a result of chemical analysis, the composition of the comparative catalyst 5 had the following composition in terms of the oxide molar ratio in the anhydrous base.

1.53 CuO, 0.20 NiO, 0.1
With _{5P 2 O 5, Al 2 O} 3, 41SiO comparative catalyst 5 obtained in ₂ Comparative Example 6 Comparative Example 1-5 was subjected to catalytic durability evaluated in the same manner as in Example 7. Table 3 shows the obtained results.

[0051]

[Table 3]

[0052]

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.

Claims (1)

[Claims] 1. A method for removing nitrogen oxides by contacting the catalyst with an oxygen-rich exhaust gas containing nitrogen oxides and hydrocarbons, wherein SiO ₂ / Al ₂ O ₃ treated with a soluble phosphorus compound is used as a catalyst. Use of a catalyst containing copper and at least one chloride selected from copper chloride, magnesium chloride, nickel chloride, calcium chloride, yttrium chloride and chromium chloride in zeolite having a molar ratio of at least 15 or more. And a method for removing nitrogen oxides.