JPH03258345A - Catalyst for cracking of nitrogen oxide and method of catalytic cracking - Google Patents

Abstract

PURPOSE:To efficiently remove nitrogen oxides in a combustion exhaust gas by incorporating copper ions and at least one kind of ion selected from Ca, Sr, and Ba into a zeolite having SiO2/Al2O3 molar ratio of >=20 to prepare the catalyst. CONSTITUTION:A zeolite having SiO2/Al2O3 molar ratio of >=20 is dipped in an aq. solution in which soluble salt of copper and at least one kind of soluble salt of Ca, Sr, or Ba are dissolved to exchange ions and to make the zeolite to carry. Thus, a cracking catalyst of nitrogen oxide is prepared. The exchange amt. of copper ions is preferably 0.01-1.5 in terms of Cu/Al atomic ratio, and exchange amt. of Ca, Sr or Ba ions is >=0.01 by atomic ratio. The cracking catalyst for nitrogen oxide is brought into contact with gas containing nitrogen oxide to efficiently decompose and remove nitrogen oxides from the gas at high temp.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a catalyst for removing nitrogen oxides from a gas containing nitrogen oxides and a method for using the same. The present invention provides a catalyst for the catalytic cracking of , and a method of using the same. Furthermore, the present invention provides a catalyst that exhibits little deterioration even when oxygen or sulfur oxides coexist.

(Prior art) Nitrogen oxides in combustion exhaust gases emitted from industrial plants, automobiles, etc. are substances that can cause photochemical smog, and from the standpoint of environmental conservation, the development of methods for removing them is necessary.
This is a serious and urgent social issue. Among nitrogen oxides, nitric oxide (NO) is particularly difficult to remove, and various methods have been studied so far. For example, the catalytic reduction method has been proposed and is being developed as an effective method, but it requires a reducing agent such as ammonia, hydrogen, or carbon monoxide, and it also requires a special method to recover or decompose the unreacted reducing agent. Requires equipment. On the other hand, the catalytic cracking method does not require special additives such as reducing agents, and decomposes into nitrogen and oxygen simply by passing it through a catalyst layer, and is the most desirable method because it is a simple process. . According to conventional research, No decomposition activity was found in Pt, Cub, CO304, etc., but they could not be used as practical catalysts because they were all subject to the poisonous effect of oxygen, which is a decomposition product.

In contrast, the present inventors have conducted extensive research on catalysts for catalytic cracking, and have found that several types of zeolite with exchanged copper ions exhibit steady activity. Furthermore, we found that zeolite containing copper ions and having a specific crystal structure not only shows extremely high steady-state activity as a catalyst for catalytic cracking of No, but also maintains its activity even in the coexistence of sulfur oxides. (Japanese Unexamined Patent Publication No. 125250/1983).

However, the above catalyst does not have sufficient activity and heat resistance, especially at high temperatures, and has not yet been put into practical use.

(Problems to be Solved by the Invention) The purpose of the present invention is to efficiently remove nitrogen oxides from combustion exhaust gases emitted from industrial plants, automobiles, etc., even at high temperatures, without using ammonia as a reducing agent. ,
Moreover, the present invention provides a catalytic cracking catalyst that maintains high activity even in the coexistence of sulfur oxides and oxygen.

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

That is, in the present invention, copper ions and Ca, Br, B
A nitrogen oxide catalytic cracking catalyst containing one or more alkaline earth ions selected from a and a method for removing nitrogen oxides from a nitrogen oxide-containing gas,
A catalyst comprising a zeolite having a p, 12o3 molar ratio of at least 20 containing copper ions and one or more alkaline earth ions selected from Ca, Br, and Ba is brought into contact with a nitrogen oxide-containing gas. The present invention provides a method for catalytic decomposition of nitrogen oxides.

The present invention will be explained in more detail below.

The zeolite used in the present invention is S L 02
/Al20s molar ratio is essential to be 20 or more. The upper limit of the S i 02 /At 20s molar ratio is not particularly limited.

When the S i 02 / AJ 203 molar ratio is less than 20, sufficient heat resistance cannot be obtained. Generally 5i02
/Al2O5 molar ratio of about 20 to 200 is used.

Examples of the zeolite constituting the catalyst of the present invention include:
ZSM-5, ZSM-8, ZSM-11, ZSM-12
, ZSM-20, ZSM-35, etc. can be used, and among them, ZSM-5 is preferably used. Furthermore, the method for producing these zeolites is not limited. Further, dealuminated zeolites such as mordenite, ferrierite, Y-type zeolite, and L-type zeolite may also be used. In addition, these zeolites can be used as they are or treated with ammonium salts, mineral acids, etc.
It can also be used after performing Ha ion exchange or H ion exchange.

In the catalytic cracking catalyst of the present invention, it is essential that the zeolite having a SiO2/Al2O* molar ratio of at least 20 contains copper ions and one or more alkaline earth ions selected from Ca, Br, and Ba.

The above zeolite contains copper ions and Ca, Sr or Ba.
The method for incorporating ions is not particularly limited, but an ion exchange method is preferred. As the ion exchange method, a commonly used method can be employed. For example, ion exchange may be performed using an aqueous solution containing copper ions and Ca, Sr, or Ba ions, or after copper ion exchange, C
a.

Ion exchange with Sr or Ba ions, or Ca
, Sr or Ba ions may be used for ion exchange, followed by copper ion exchange. The concentrations of copper ions and Ca, Sr, or Ba ions in the aqueous solution during ion exchange can be arbitrarily set depending on the ion exchange rate.

Further, copper ions and Ca, Sr, or Ba ions can be used in the form of soluble salts, and nitrates, acetates, oxalates, hydrochlorides, etc. can be preferably used as the soluble salts.

When performing copper ion exchange in the above, ammonia may be added to adjust the pH in order to increase the copper ion content.

Since the copper ions present at the ion exchange sites are active sites, it is desirable that the copper be exchanged at the ion exchange sites. It is also desirable to ion-exchange Ca, Sr, or Ba ions at ion-exchange sites, but the effect is also exhibited not only when ions are supported on zeolite using oxides or the like.

The ion-exchanged sample is used after solid-liquid separation, washing, and drying. Moreover, it can be used after being fired if necessary.

The amount of copper ion exchange is 0.01 to 1.5 expressed as Cu/A, e atomic ratio, and the amount of Ca, Sr or Ba ion exchange is A! It is desirable that the atomic ratio to atoms is 0.01 or more. Cu/AI atomic ratio is 0.
If it is less than 01, there are few copper ions, which are active sites, and sufficient catalytic activity cannot be obtained, and if it exceeds 1 or 5, copper exists on the zeolite surface as an oxide, increasing the copper ion content. There is a risk that the desired effect will not be obtained.

If the atomic ratio of Ca, Sr or Ba ions exchanged with respect to AI atoms is less than 0.01, the effect of the coexistence of Ca, Sr or Ba ions will be small and there is a risk that sufficient heat resistance will not be obtained.

S i 02 / AI 20 of the catalytic cracking catalyst of the present invention
3 molar ratio is SiO□/Ai of the zeolite base material used
' 203 molar ratio is not substantially different. Furthermore, the crystal structure of the catalytic cracking catalyst is not essentially different before and after ion exchange.

The catalytic cracking catalyst of the present invention can also be used by being mixed with a binder such as a clay mineral and molded. Alternatively, zeolite may be formed in advance and the formed body may contain copper and one or more alkaline earth ions selected from Ca, Br, and Ba by ion exchange or the like. Binders used in forming zeolite include clay minerals such as kaolin, attapulgide, montmorillonite, bentonite, allophane, and seviolite. Alternatively, it may be an indales zeolite molded product that is directly synthesized without using an inder. Furthermore, it is also possible to use a nodicum-shaped base material made of cordierite or metal coated with zeolite.

Catalytic cracking of nitrogen oxides in exhaust gas can be carried out by bringing the catalytic cracking catalyst of the present invention into contact with exhaust gas containing nitrogen oxides.

The above catalytic cracking catalyst has the same catalytic performance as the conventional copper-supported zeolite catalyst even when applied to exhaust gas containing ammonia, carbon oxides, hydrocarbons, moisture, oxygen, sulfur oxides, etc. able to demonstrate.

(Function) As shown in JP-A-60-125250, crystalline aluminosilicate containing copper ions and having a specific crystal structure can remove nitrogen oxides even in exhaust gas without a reducing agent. It can be removed efficiently. This is due to the unique crystal structure of the crystalline aluminosilicate.
This is because the redox cycle of ion-exchanged copper ions becomes easier, and nitrogen oxides are decomposed into nitrogen and oxygen through this redox cycle. In addition, copper ions are less susceptible to the poisonous effects of oxygen, which is a decomposition product of nitrogen oxides, and maintain high activity over a long period of time.

However, the copper ion-exchanged crystalline aluminosilicate described above undergoes too much reduction of copper ions at high temperatures, hindering the redox cycle of copper ions and failing to obtain sufficient activity.

The catalyst of the present invention contains zeolite with copper ions and Ca, Br.
, Ba, and one or more alkaline earth ions selected from Ba.

It is believed that the coexistence of Sr or Ba ions improves the heat resistance of the zeolite itself and has the effect of preventing excessive reduction of copper ions, resulting in a catalytic cracking catalyst that is highly active and stable even at high temperatures. It will be done.

(Effects of the Invention) The nitrogen oxide catalytic cracking catalyst of the present invention has the effect of efficiently removing nitrogen oxides from combustion exhaust gas even at high temperatures without using a reducing agent such as ammonia.
Moreover, it has the effect of exhibiting extremely excellent heat resistance. Therefore, by bringing the catalyst of the present invention into contact with exhaust gas, nitrogen oxides can be purified even at high temperatures.

(Example) 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 (Si02; 1P→1・□ 153 g/1, N a 20 ; 50 g
/ 1.

Al10s; 0.8 g/j) and aluminum sulfate aqueous solution CA12O5; 38.4 g/j.

H2SO4; 275g/j) and 3,2j/h, respectively.
r, was continuously fed at a rate of 0.81/hr. The reaction temperature is 30-32℃, and the pH of the discharged slurry is 6.4.
It was ~6.6.

After separating the discharged slurry into solid and liquid and thoroughly washing it with water,
; 1.72wt%, AJ! 203; 2.58wt%,
SiO2; 39.3 wt%.

N20: A granular amorphous aluminosilicate homogeneous compound containing 56.4 wt% was obtained. 2,840 g of the homogeneous compound and 1.
39 wt% NaOH aqueous solution5. 160g of 100g of 100g were placed in an autoclave, and crystallized under stirring at 160°C for 72 hours. The product was subjected to solid-liquid separation, washed with water, and dried to obtain ZSM-5 type zeolite. As a result of chemical analysis, its composition, expressed as molar ratio of oxides on an anhydrous basis, was as follows:

1, lNa2O, AJ! 203.2B, BS io2 10 g of this zeolite was added to 0.012N calcium nitrate aqueous solution 11. The mixture was stirred at 60° C. for a day and night and washed to obtain calcium ion exchange zeolite. Then 0
．． 024N copper acetate aqueous solution 1j. Catalyst 1 was prepared by stirring at 60°C all day and night, washing and drying. As a result of chemical analysis, its composition, expressed as molar ratio of oxides on an anhydrous basis, was as follows:

0, 45 Ca O* 0, 65 Cu Or
A j 203r23.3SiO□ Example 2 Catalyst 2 was prepared in the same manner as in Example 1 except that 10 g of ZSM-5 type zeolite obtained in Example 1 was used and strontium acetate was used instead of calcium nitrate. .

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

0.25Sr0, 0.88CuO, Al103°23.
3SiO2 Example 3 Catalyst 3 was prepared in the same manner as in Example 1 except that 10 g of ZSM-5 type zeolite obtained in Example 1 was used and barium nitrate was used instead of calcium nitrate.

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

0.40BaO, 0.76CuO, AJ! 20s
.

23.3SiO2 Example 4 Catalytic cracking performance was investigated using the catalysts obtained in Examples 1, 2, and 3.

The catalyst was press-molded and pulverized to form a 42-8o mesh. 2 cc of it was filled into an atmospheric fixed bed flow reaction tube. After pretreatment in He gas at 500''C for 1 hour, He gas containing 48% No was passed through the sample so that the contact time was 4.0 g-5 ec/ml.

Table 1 shows the No conversion rate at each temperature.

Using the catalyst obtained in Comparative Example 1 in Table 1, the catalytic cracking performance of the comparative catalyst was investigated in the same manner as in Example 2.

The results are shown in Table 2.

Table 2 Comparative Example] 10 g of ZSM-5 type zeolite obtained in Example]
After adding it to 1k of 0.012N copper acetate aqueous solution, it was stirred at 60°C all day and night, washed and dried to prepare a comparative catalyst.

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

0, 64 N a 20. 0゜69CuO, Aj
20. .

23.3Si02 As is clear from Tables 1 and 2, the nitrogen oxide catalytic cracking catalyst of the present invention can efficiently remove nitrogen oxides from gas even at high temperatures by contacting it with gas, and has excellent heat resistance. shows very good performance.

Comparative example 2

Claims (2)

[Claims] (1) Zeolite with a SiO_2/Al_2O_3 molar ratio of at least 20 containing copper ions and Ca, Br, Ba
A nitrogen oxide catalytic cracking catalyst containing one or more alkaline earth ions selected from. (2) In a method for removing nitrogen oxides from a nitrogen oxide-containing gas, copper ions and Ca, Br are added to a zeolite having a SiO_2/Al_2O_3 molar ratio of at least 20.
A method for catalytic decomposition of nitrogen oxides, which comprises bringing a nitrogen oxide-containing gas into contact with a catalyst containing one or more alkaline earth ions selected from , Ba, and Ba.