JPH0478444A - Catalyst for purification of exhaust gas and its using method - Google Patents

Abstract

PURPOSE:To obtain a catalyst which can efficiently purify an exhaust gas containing excess oxygen and has excellent heat resistance and durability and to establish the method of using this catalyst by incorporating potassium and transition metal into a zeolite having a specified SiO2/Al2O3 molar ratio. CONSTITUTION:Potassium and transition metal such as Fe, Cu, Co, etc., are incorporated into a zeolite having >=10 SiO2/Al2O3 molar ratio by depositing or ion exchange method. As for the procedure of ion exchange or deposition, potassium is first subjected to ion exchange and then the transition metal is subjected to ion exchange. The zeolite to be used is not especially limited, and for example, mordenite, ferrierite etc., can be used after removing ions such as Na or the like by ammonia treatment. By using the catalyst thus obtd. to treat a combustion exhaust gas containing nitrogen oxide by bringing the catalyst into contact with the gas, the exhaust has can be efficiently purified. The catalyst is excellent in heat resistance and durability.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a catalyst for treating exhaust gas containing nitrogen oxides discharged from boilers, automobile engines, etc., and more specifically, to a method for using the same. The present invention relates to an extremely durable exhaust gas purifying catalyst and a method for using the same.

(Prior art) Boiler As a method for removing nitrogen oxides from exhaust gas emitted from automobile engines, etc., there is a selective catalytic reduction method that uses ammonia in the presence of a catalyst. Non-selective catalytic reduction methods using carbon monoxide and hydrocarbons have been put into practical use.

JP-A-60-125250 proposes copper ion-exchanged zeolite as a catalyst that can directly catalytically decompose nitrogen oxides in the absence of a reducing agent.

In addition, we have developed a catalyst that can selectively reduce nitrogen oxides using reducing components such as unburned carbon monoxide and hydrocarbons, even under excessive oxygen conditions, for exhaust gas purification of diesel engines and lean-burn engines aimed at improving fuel efficiency. As such, a catalyst in which a base metal is contained in zeolite or the like has been proposed (Japanese Unexamined Patent Publication No. 100119/1983).

However, these proposed catalysts have problems in durability, especially at high temperatures, and have not been put into practical use.

(Problems to be Solved by the Invention) An object of the present invention is to efficiently purify exhaust gas, especially oxygen-excess gas, emitted from internal combustion engines such as automobiles without using a reducing agent such as ammonia, and to The present invention provides an exhaust gas purifying catalyst that has excellent durability at high temperatures in the presence of water vapor.

(Means for Solving the Problems) The present inventors have completed the present invention as a result of intensive study on the above problems.

That is, the present invention provides an exhaust gas purifying catalyst characterized in that potassium and a transition metal are contained in zeolite having a S l 02 / AI 203 molar ratio of at least 10, and a method in which a combustion exhaust gas containing nitrogen oxides is brought into contact with the catalyst. The present invention provides a method for treating exhaust gas characterized by:

The present invention will be explained in more detail below.

The exhaust gas purifying catalyst according to the present invention is a zeolite containing potassium and a transition metal and having a Si 02 /A47203 molar ratio of at least 10.

As the zeolite used in the present invention, Si
It is essential that the molar ratio of 02/AF203 is 10 or more. The upper limit of the S I 02 / All 20a molar ratio is not limited. 5iO7/A
When the lI2O3 molar ratio is less than 10, sufficient durability cannot be obtained.

The type of zeolite used in the present invention is not particularly limited; for example, mordenite, ferrierite, ZSM
-5, ZSM-3, ZSM-11, ZSM-12) ZS
Zeolites such as M-20 and ZSM-35 can be used, and among them, ZSM-5 is preferably used. Furthermore, the method for producing these zeolites is not limited. Alternatively, dealuminated zeolites such as Y-type zeolite and L-type zeolite may be used.

Moreover, the crystal diameter of the zeolite used in the present invention is not particularly limited, but is preferably 1a or more. If the crystal diameter is less than 1 μm, the heat resistance of the crystal itself will be poor, and the durability of the catalyst may be reduced.

It is essential that the exhaust gas purifying catalyst of the present invention contains potassium and a transition metal. The contents of potassium and transition metals are not particularly limited, but potassium is added to 20/Al2
O3 molar ratio is 0.2 to 1.0, transition metal is M2
．． ., 0/Al2O5 molar ratio (n is the valence of the transition metal M) is preferably 1.5 or less. If the potassium content is less than 0.2, sufficient durability may not be obtained, and if the potassium content exceeds 1.0 or the transition metal content exceeds 1.5, potassium or transition metals may become oxides, etc. However, there is a risk that it will be more likely to exist on the zeolite surface, reducing its durability. Mata, (Kz O+M, 7a
When the molar ratio of O)/AfI20a exceeds 2.0, potassium or transition metals exist as oxides on the zeolite surface and become bulky, which may reduce durability.

In addition, the content of sodium, etc. in the raw material zeolite of the exhaust gas purification catalyst of the present invention is not particularly limited, but N
! The L20/An20a molar ratio is preferably 0.01 or less.

If it exceeds 0.01, durability may be adversely affected.

The transition metal is not particularly limited, but includes, for example, Fe,
Cu, Co, Ni, Cr, Mn, etc. can be used.

The exhaust gas purifying catalyst of the present invention is produced by incorporating potassium and a transition metal into zeolite having a SiO2/Al201 molar ratio of at least 10 or more.

Potassium and transition metals are contained by support or ion exchange, but ion exchange treatment using a neutral salt of potassium and ion exchange treatment using a neutral salt of a transition metal are preferably performed.

The raw material zeolite may be a synthetic product or its waste product, but it is desirable to use it after removing ions such as sodium in the raw material zeolite, which have an adverse effect on the heat resistance of the raw material zeolite, by ammonia treatment or the like.

Ammonia treatment is performed by mixing raw material zeolite with an aqueous solution containing ammonia, stirring, and washing. As ammonia, ammonium chloride, ammonium nitrate, ammonium sulfate, ammonia water, etc. are used. It is preferable to select conditions for the ammonia treatment such that the ions such as sodium present in the ion exchange sites of the raw zeolite are reduced to 0.01 or less expressed as a Na2O/AΩ203 molar ratio. If the content of ions such as Na exceeds 0.01, the durability may decrease.

The amount of ammonia added is preferably 2 to 10 times equivalent to aluminum in the zeolite.

At less than 2 times the equivalent, ions such as Na are Na2O/Aρ20
There is a possibility that the molar ratio will not be 0.01 or less, and even if it exceeds 0 times, the corresponding effect will not be obtained. The slurry concentration for ammonia treatment is 5
% to 5090 is preferred.

Further, the treatment conditions are preferably a temperature of room temperature to 100° C. and a time of 1 hour to 3 days, which are usually carried out. At a temperature below room temperature and for a period of less than 1 hour, ions such as sodium have a mol ratio of 0.20/AΩ201.
01 or less, and if the temperature exceeds 100°C and the time exceeds 3 days, the corresponding effect will not be obtained.

Furthermore, as a method for removing ions such as sodium, a method of treatment with a mineral acid can also be used.

The raw material zeolite is ion-exchanged with potassium and transition metals. The order of ion exchange is preferably potassium ion exchange followed by transition metal ion exchange. Further, ion exchange may be performed simultaneously in the coexistence of potassium ions and transition metal ions. If potassium ions are exchanged after transition metal ion exchange, the ion-exchanged transition metal ions will be desorbed from the exchange site during potassium exchange, and oxides etc. will be present in large quantities on the zeolite surface, which may reduce durability. be.

Potassium ion exchange is performed by mixing raw material zeolite with an aqueous solution containing a neutral salt of potassium, stirring and washing.

As the neutral salt of potassium, neutral salts such as potassium chloride, nitrate, sulfate, and acetate are preferably used.

The amount of potassium ion added is preferably 1 to 30 times equivalent to aluminum in the zeolite. If the amount is less than 1 equivalent, potassium ions will not be exchanged sufficiently, and K 20 /
There is a possibility that the AΩ201 molar ratio will be less than 0.2, and even if it exceeds 30 times, no commensurate effect will be obtained. The slurry concentration for ion exchange is preferably 5% to 50°6, which is usually carried out.

In addition, the processing conditions are a temperature between room temperature and 100°C, which is usually carried out;
It is desirable that the time is 1 hour to 3 days. If the temperature is below room temperature and the time is less than 1 hour, the potassium ions will not be sufficiently exchanged, and the 320/AN 20q molar ratio will be 0.
．． Temperatures exceeding 100℃, 3.
If you spend more than a day, you won't get the desired effect.

Moreover, the ion exchange operation can be repeated as necessary.

In transition metal ion exchange, potassium ion-exchanged zeolite is mixed with an aqueous solution containing a neutral salt of a transition metal, stirred,
It is done by washing.

As the neutral salt of the transition metal, neutral salts such as chlorides, nitrates, sulfates, and acetates of transition metals are preferably used.

The amount of transition metal ions added is preferably 20 times or less equivalent to aluminum in the zeolite.

If it exceeds 20 times, M2. - There is a possibility that the molar ratio of -0/AN203 exceeds 1.5. The concentration of the slurry for ion exchange is preferably 5% to 50%, which is usually carried out.

In addition, the processing conditions are a temperature between room temperature and 100°C, which is usually carried out;
It is desirable that the time be 3 days or less.

If the temperature exceeds 100°C and the time exceeds 3 days, M2.
The z40/AN203 molar ratio may exceed 1.5. Moreover, the ion exchange operation can be repeated as necessary.

The 5io2/Alx0* molar ratio of the exhaust gas purification catalyst of the present invention is S i 02 /AD of the zeolite base material used.
There is no substantial difference from the 20s molar ratio. Further, the crystal structure of the exhaust gas purifying catalyst is not essentially different before and after ion exchange.

The exhaust gas purifying catalyst of the present invention can also be used by being mixed with a binder such as clay minerals and molded.

Alternatively, zeolite may be formed in advance and the formed body may contain potassium and a transition metal.

Binders used in forming zeolite include clay minerals such as kaolin, attapulgide, montmorillonite, bentonite, allophane, and seviolite. Alternatively, it may be a binderless zeolite molded product that is directly synthesized without using a binder.

Further, the exhaust gas purifying catalyst of the present invention can be washed and used on a honeycomb-shaped base material made of Nigelite or metal.

The combustion exhaust gas containing nitrogen oxides is treated by bringing the exhaust gas into contact with the exhaust gas purifying catalyst of the present invention. Although it is essential that the exhaust gas used in the present invention contains nitrogen oxides, it is particularly effective when it contains oxygen, carbon oxide, hydrocarbons, hydrogen 8 ammonia, and the like. Preferably, it is an oxygen-excessive exhaust gas containing nitrogen oxides, carbon oxides, and hydrocarbons. Excessive oxygen exhaust gas indicates that the exhaust gas contains oxygen 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 such as an automobile, the air/fuel pipe is in a large state (lean region).

(Function) The exhaust gas purifying catalyst of the present invention has very high durability and hardly deteriorates even when treated with high temperature exhaust gas containing water vapor. The reason why the exhaust gas purification catalyst of the present invention exhibits high durability is not known in detail, but it is also possible that the coexistence of potassium makes dealumination less likely to occur and improves the durability of the zeolite itself. It is possible to prevent activity deterioration due to aggregation of certain transition metals.

(Effects of the Invention) The exhaust gas purifying catalyst of the present invention can efficiently remove combustion exhaust gas containing nitrogen oxides, and exhibits extremely excellent heat resistance and durability.

(Examples) Hereinafter, the present invention will be explained in more detail in Examples. However, the present invention is not limited to these examples.

Example 1 A sodium silicate aqueous solution (SiO2; 250 g/N
, Na2O; 82g/fl.

Aff 203: 2.8 g/l) and aluminum sulfate aqueous solution CAN 203: 8.8 g/l.

H2SO4; 370g/l') and 31/l' respectively.
h r, lj! It was fed continuously at a rate of /hr. The reaction temperature is 30-32℃, and the p of the slurry discharged is
H was 6.7-7.0.

After separating the discharged slurry into solid and liquid and thoroughly washing it with water, NJ! 20
: 0.75wt%, All 203; 0.77wt%
, 5i02; 36.1 wt%.

H,0; 62.5 wt% of a granular amorphous aluminosilicate homogeneous compound was obtained. 2,860 g of the homogeneous compound and 3.2
1 g of wt% NaOH aqueous solution was charged into an autoclave and crystallized under stirring at 160"C for 72 hours. The product was solid-liquid separated, washed with water, and dried to form ZSM-5.
A similar zeolite Ts21 was obtained. The crystal diameter of TSZI is 2
~3μ, and as a result of chemical analysis, its composition, expressed as the molar ratio of oxides on an anhydrous basis, was as follows:

1.4Na20. A! ! 203.41. lSiO2 100 g of this zeolite was mixed with NH, CIl.

Add to 1000cc of aqueous solution containing 20.0g and heat at 60°C.
After stirring for 20 hours, washing and drying, NH, type T
Obtained SZI. The Na content of the obtained NH4 type TSZ1 is Na20/Ai! It was 0.01 or less expressed as a 20g molar ratio.

: NH4 type TSZI; 50 g, KCfI.

It was added to 500 cc of an aqueous solution containing 14.5 g, stirred at 60° C. for 20 hours, washed, and subjected to K ion exchange operation. After repeating this operation twice, dry and mold TSZ.
I got I.

Obtained ni-type TSZI; 20g to 0.1mol, 77g
The mixture was added to 76cc of aqueous copper acetate solution, stirred at room temperature for 20 hours, washed, and subjected to Cu ion exchange operation. After repeating this operation twice, it is dried to form (Cυ→-K) type TSZ.
1 (Catalyst 1) was obtained. As a result of chemical analysis, its composition, expressed as molar ratio of oxides on an anhydrous basis, was as follows:

('I1.68 to 20, 0.63CuO, Ajj 20
3.

41.2SiO2 Example 2 A sodium silicate aqueous solution (Sin2; 153 g/N
, Na2O; 50 g/l).

8N 20*: 0.8 g/l) and aluminum sulfate aqueous solution (AN 20v; 38.4 g/l)
I.

H2S04; 275g/F) and 3, respectively.
It was continuously fed at a rate of 2 g/hr, 0.8 N/hr. The reaction temperature was 30-32°C, and the pH of the slurry discharged was 6.4-6.6.

After separating the discharged slurry into solid and liquid and thoroughly washing it with water, Na,
0; 1. 72wt%, AN 20i2
．． 53wt%, Sin2; 39. 3wt
%, H20; 56.4 wt 96 granular amorphous aluminosilicate homogeneous compound was obtained. The homogeneous compound 2,8
40g and 5,160g of 1.39wt% NaOH aqueous solution
and were placed in an autoclave and crystallized under stirring at 160°C for 72 hours. The product is separated into solid and liquid, washed with water, and dried.
SM-5 similar zeolite TS22 was obtained. The crystal size of TSZ2 was 0.1 to 0.5 μm, and chemical analysis revealed that the composition had the following composition expressed in molar ratio of oxides on an anhydrous basis.

1,INa,,o,Ajj 203.23.3S io
2 100g of this zeolite was mixed with NH4Cl1 ;34,
Added to 1000cc of aqueous solution containing Og and heated at 60℃ for 2 hours.
After stirring for 0 hours, the mixture was washed and dried to obtain NH type TSZ2. The Na content of the obtained NH4 type TSZ2 is Na2
0/AIJ20s molar ratio was 0.01 or less.

50 g of this NH4 type TSZ2, KCI; 24
．． Added to 500 cc of aqueous solution containing 8 g, and heated at 60°C for 2 hours.
After stirring for 0 hours, the mixture was washed and subjected to K ion exchange operation. After repeating this operation twice, it was dried to obtain a mold TSZ2.

Obtained TSZ2; 20g to 0.1mol/g
The mixture was added to 120 cc of an aqueous copper acetate solution, stirred at room temperature for 20 hours, washed, and subjected to Cu ion exchange operation. After repeating this operation twice, it is dried and the (Cu+K) type TSZ2
(Catalyst 2) was obtained. As a result of chemical analysis, its composition, expressed as molar ratio of oxides on an anhydrous basis, was as follows:

0.54 to 20, 0.58 Cuo, AN 20s.

23.3SiO□ Example 3 ZS according to Example 6 of JP-A-56-45,819
TSZ3, an M-5 type zeolite, was synthesized. TS2
The crystal diameter of No. 3 is 3 to 5 μ, and as a result of chemical analysis,
Its composition, expressed as molar ratios of oxides on an anhydrous basis, was as follows:

0.4Na20. Al120. ．． 73.2S i TSZ3 calcined at 0°530°C for 5 hours; 100g;
NH4CD; 12. 1000cc of aqueous solution containing Og
After stirring at 60° C. for 20 hours, the mixture was washed and dried to obtain NH4 type TSZ3.

The Na content of the obtained NH, type TSZ3 is Na 20
/AD20g molar ratio was 0.01 or less.

50 g of this NH4 type TSZ3 was mixed with 1°8.
Added to 500 cc of aqueous solution containing 3 g, and heated at 60°C for 20 minutes.
After stirring for an hour, the mixture was washed and subjected to K ion exchange operation.

After repeating this operation twice, it was dried to obtain mold TSZ3.

Obtained mold TSZ3; 20g to 0.05mol/
i! It was added to 90 cc of an aqueous copper acetate solution, stirred at room temperature for 20 hours, washed, and subjected to Cu ion exchange operation. After repeating this operation twice, drying (Cu+K) type TSZ
3 (Catalyst 3) was obtained.

As a result of chemical analysis, its composition, expressed as molar ratio of oxides on an anhydrous basis, was as follows:

0.57 to 20, 0.49CuO, A1!203.

72.9SiO.

Example 4 20g of the diamond-shaped TSZI obtained in Example 1 was added to 200ml of an aqueous solution containing 10.1g of cobalt acetate (■) tetrahydrate.
After stirring at 60°C for 20 hours, washing and adding to C
o Ion exchange operation was performed.

After repeating this operation twice, drying (Co+K) type T
SZI (catalyst 4) was obtained. As a result of chemical analysis, its composition, expressed as molar ratio of oxides on an anhydrous basis, was as follows:

0, 36 to 20,1.23Co0.41) 20s, 4
],,05i02 Example 5 20 g of the TSZ2 obtained in Example 2 was mixed into an aqueous solution 20 containing 1.5.7 g of cobalt acetate (■) 4 eigen.
After adding to 0CC and stirring at 60°C for 20 hours, the mixture was washed and subjected to Co ion exchange operation.

After repeating this operation twice, drying (Co+K) type T
SZ2 (catalyst 5) was obtained. As a result of chemical analysis, its composition, expressed as molar ratio of oxides on an anhydrous basis, was as follows:

0.40 to 2 O, 1, 14 COO, A, Q 203
.

23.2SiO.

Example 6 20 g of the diamond-shaped TSZ3 obtained in Example 3 was mixed with 200 c of an aqueous solution containing 5.9 g of cobalt acetate (■) 4-eternal product.
[C] and stirred at 60°C for 20 hours] After washing,
A Co ion exchange operation was performed. This operation was repeated twice and then dried to obtain (Co+K) type TSZ3 (catalyst 6). As a result of chemical analysis, its composition, expressed as molar ratio of oxides on an anhydrous basis, was as follows:

0.41 to 20.1.18 COO, Ag2O,.

73, 3 S i 02 Example 7 Ni-type TSZ1. obtained in Example 1. ; 20g of an aqueous solution containing 10.2g of nickel acetate (■) tetrahydrate
c, stirred at 60°C for 20 hours, washed,
Ni ion exchange operation was performed.

After repeating this operation twice, dry (N i 10K)
Type TSZI (catalyst 7) was obtained. As a result of chemical analysis, its composition, expressed in molar ratio of oxides on an anhydrous basis, was as follows:

0.38 to 20, 1.17NiO, A, C' 203
.

41.08iO.

4 1, OS 1 02 Example 9 The same procedure as in Example 1 was carried out except that the order of K ion exchange operation and Cu ion exchange operation was reversed.
K+Cu) type TSZI (catalyst 9) was obtained. As a result of chemical analysis, its composition, expressed as molar ratio of oxides on an anhydrous basis, was as follows:

0.72CuO, 0.92 to 20. AN　203　.

41, 2S l 02 Example 8 A (Cu++Na) type TS was prepared in the same manner as in Example 1 except that the ammonia treatment was not performed.
ZI (catalyst 8) was obtained. As a result of chemical analysis, its composition, expressed as molar ratio of oxides on an anhydrous basis, was as follows:

0, 44 K20. 0. 57 Cu O.

0.04Na20, Al2O2゜Example 10 Durability evaluation was performed using catalysts 1 to 9 obtained in Examples 1 to 9.

Each catalyst was press-molded and then pulverized to size 42 to 80 mesh. 2 cc of it was filled into a normal pressure fixed bed flow reaction tube, and a gas simulating the exhaust gas of a lean burn engine (
Table 1) was flowed at a space velocity of 30,000/hr. 50
After 30 minutes of pretreatment at 0°C, steady-state purification activity was measured at 400°C. The steady-state purification activity was defined as the NOx purification rate after being held at 400°C for 1 hour.

Further, each catalyst was subjected to durability treatment at 800° C. for 15 hours while flowing a gas having the composition shown in Table 1 at a space velocity of 30,000/hr. Thereafter, the steady-state purification activity was measured in the same manner as above, and a durability test was conducted.

The results obtained are shown in Table 2.

Tables 1 and 2 are expressed as the ratio of crystallinity after treatment. The results obtained are shown in Table 3.

Table 3 Also, the crystallinity before and after the durability treatment was evaluated by X-ray diffraction to determine the durability of the zeolite crystals.

Crystal durability was determined based on the crystallinity before durability treatment in Comparative Example 1. In Examples 1.4 and 7, Cu Type TSZI, Co type TSZI and Ni type TSZI
I got it. As a result of chemical analysis, its composition, expressed as molar ratio of oxides on an anhydrous basis, was as follows:

Cu type TSZ1. (Comparative catalyst 1) 0, 82 Cu O, An 203 40.9SiO.

Co type TSZI (comparison catalyst 2) 1.35COO, AN 203 41.08iOz Ni type TSZI (comparison catalyst 3) 1.41NiO, AN 203.

40.8Si02 It had the following composition expressed as the molar ratio of oxides on an anhydrous basis.

2.5CoO, 0.87 to 20, Ag2O,.

41.2Si02 Comparative Example 3 Using Comparative Catalysts 1 to 4 obtained in Comparative Examples 1 and 2, exhaust gas purification performance and durability were evaluated in the same manner as in Example 10.

The results obtained are shown in Tables 4 and 5.

Comparative Example 2 20 g of Ni-type TSZI obtained in Example 1 was mixed with 100 ee of an aqueous solution containing 5.0 g of cobalt acetate (■) tetrahydrate, and the mixture was evaporated to dryness at 90°C to obtain Comparative Catalyst 4. Ta. As a result of chemical analysis, the composition of the exhaust gas purifying catalyst of the present invention is clear from the Examples and Comparative Examples in Table 4. The crystallinity of the zeolite also showed little deterioration, and it exhibited very excellent durability.

Claims (2)

[Claims] (1) An exhaust gas purifying catalyst characterized by containing potassium and a transition metal in zeolite having a SiO_2/Al_2O_3 molar ratio of at least 10. (2) A method for treating exhaust gas, which comprises bringing combustion exhaust gas containing nitrogen oxides into contact with the catalyst according to claim 1.