JPH04215847A - Nitrogen oxide catalytic cracking catalyst and catalytic cracking method - Google Patents

Abstract

PURPOSE:To provide nitrogen oxide catalytic cracking catalysts which are scarcely deteriorated even if oxygen or sulfur oxides are present in the case that nitrogen oxides are removed from gases containing nitrogen oxides and a catalytic cracking method using the catalysts. CONSTITUTION:Copper ions and ions of transition metals other than copper are included in zeolite having the mole ratio SiO2/Al2O3 of at least 20 to provide nitrogen oxide catalytic cracking catalysts and a nitrogen oxide catalytic cracking method using the catalysts is provided.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a catalyst for removing nitrogen oxides from a gas containing nitrogen oxides and a method for using the same, and more particularly to a catalyst for catalytically decomposing nitrogen oxides and its use. It provides a method for using . Furthermore, the present invention provides a catalyst that exhibits little deterioration even when oxygen or sulfur oxides coexist.

0002

[Prior Art] Nitrogen oxides in combustion exhaust gas 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 an important and urgent task. It is a 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 any special additives such as reducing agents, and decomposes the material into nitrogen and oxygen simply by passing it through a catalyst layer, and is the most desirable method because the process is simple. According to conventional research, N is present in Pt, CuO, Co3O4, etc.
Although O decomposition activity was observed, they could not be used as practical catalysts because they were poisoned by oxygen, a decomposition product.

On the other hand, the present inventors have extensively researched catalysts for catalytic cracking and have found that several types of zeolite with exchanged copper ions exhibit steady activity. Furthermore, we discovered that zeolite containing copper ions and having a specific crystal structure not only exhibits extremely high steady-state activity as a NO catalytic cracking catalyst, but also maintains its activity even in the coexistence of sulfur oxides. (Unexamined Japanese Patent Publication 1986-
125250).

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.

[0005]

[Problems to be Solved by the Invention] An object 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. , and to provide a catalytic cracking catalyst that maintains high activity even in the coexistence of sulfur oxides and oxygen.

[0006]

[Means for Solving the Problems] The present inventors have completed the present invention as a result of extensive studies regarding the above-mentioned problems.

That is, the present invention provides a nitrogen oxide catalytic cracking catalyst in which copper ions and transition metal ions other than copper are contained in zeolite having a SiO2/Al2O3 molar ratio of at least 20, and The present invention provides a method for catalytic decomposition of nitrogen oxides, which comprises bringing the catalyst into contact with a nitrogen oxide-containing gas.

The present invention will be explained in more detail below.

The zeolite used in the present invention is S
It is essential that the iO2/Al2O3 molar ratio is 20 or more. The upper limit of the SiO2/Al2O3 molar ratio is not particularly limited. When the SiO2/Al2O3 molar ratio is less than 20, sufficient heat resistance cannot be obtained. Generally, those having a SiO2/Al2O3 molar ratio of about 20 to 200 are used.

Zeolites constituting the catalyst of the present invention include, for example, ZSM-5, ZSM-8, ZSM-11,
Zeolites such as ZSM-12, ZSM-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. Further, dealuminated zeolites such as mordenite, ferrierite, Y-type zeolite, and L-type zeolite may also be used. Further, these zeolites can be used as they are or after being treated with ammonium salts, mineral acids, etc. to exchange NH4 ions or H ions.

The catalytic cracking catalyst of the present invention is a SiO2/Al
It is essential that the zeolite having a 2O3 molar ratio of at least 20 contains copper ions and transition metal ions other than copper.

[0012] The method of incorporating copper ions and transition metal ions other than copper into the zeolite is not particularly limited;
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 transition metal ions other than copper, ion exchange with transition metal ions other than copper after copper ion exchange, or ion exchange with transition metal ions other than copper. After the exchange, copper ion exchange may be performed. The concentrations of copper ions and transition metal ions other than copper in the aqueous solution during ion exchange can be arbitrarily set depending on the ion exchange rate.

[0013] Copper ions and transition metal ions other than copper can be used in the form of soluble salts.
Nitrate, acetate, oxalate, hydrochloride, etc. can be suitably used.

[0014] When performing copper ion exchange in the above process, ammonia is added to increase the copper ion content and the pH is adjusted.
You can also adjust it.

[0015] 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. Furthermore, it is desirable to ion-exchange transition metal ions other than copper at ion-exchange sites, but the effect is also exhibited not only when ions are supported on zeolite using oxides or the like.

The transition metal ions used in the present invention are not particularly limited, but include, for example, Co, Ni, Cr, Fe,
Ions such as Mn, Zn, and Pt are preferably used.

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

The amount of copper ion exchanged is 0.01 to 1.5 in terms of Cu/Al atomic ratio, and the amount of ion exchanged with transition metals other than copper is 0.01 or more in atomic ratio to Al atoms. It is desirable that there be. When the Cu/Al atomic ratio is less than 0.01, there are few copper ions, which are active sites, and sufficient catalytic activity cannot be obtained, and when it exceeds 1.5, copper exists on the zeolite surface as an oxide, etc. There is a possibility that the effect of simply increasing the copper ion content will not be obtained. Furthermore, if the amount of ion exchange of transition metals other than copper is less than 0.01 in atomic ratio with respect to Al atoms, the effect of the coexistence of transition metal ions other than copper may be small and sufficient heat resistance may not be obtained.

SiO2/Al2 of the catalytic cracking catalyst of the present invention
The O3 molar ratio is SiO2/A of the zeolite base material used.
It is not substantially different from the l2O3 molar ratio. 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 transition metal ions other than copper by ion exchange or the like. Binders used in forming zeolite include clay minerals such as kaolin, attapulgite, montmorillonite, bentonite, allophane, and sepiolite. Alternatively, it may be a binderless zeolite molded product that is directly synthesized without using a binder. Furthermore, a honeycomb-shaped substrate made of cordierite or metal may be coated with zeolite.

Catalytic decomposition 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.

[0022] The above-mentioned catalytic cracking catalyst has the same performance as the conventional copper-supported zeolite catalyst even when applied to exhaust gas containing ammonia, carbon monoxide, hydrocarbons, moisture, oxygen, sulfur oxides, etc. Can exhibit catalytic performance.

[0023]

[Operation] As shown in JP-A No. 60-125250, crystalline aluminosilicate containing copper ions and having a specific crystal structure can generate nitrogen oxides even in exhaust gas without a reducing agent. It can be removed efficiently. This is because the unique crystal structure of the crystalline aluminosilicate facilitates the redox cycle of ion-exchanged copper ions, and this redox cycle decomposes nitrogen oxides into nitrogen and oxygen. 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, in the copper ion-exchanged crystalline aluminosilicate described above, the reduction of copper ions proceeds too much at high temperatures, and the redox cycle of copper ions is hindered, making it impossible to obtain sufficient activity.

The catalyst of the present invention is a zeolite containing copper ions and transition metal ions other than copper.
The coexistence of transition metal ions other than copper has the effect of preventing excessive reduction of copper ions, and by promoting the redox cycle of copper ions, it becomes a highly active and stable contact even at high temperatures. It is thought to act as a decomposition catalyst.

[0026]

EXAMPLES The present invention will be explained in more detail in the following examples. However, the present invention is not limited to these examples.

Example 1 A sodium silicate aqueous solution (SiO2; 153 g
/liter, Na2O; 50g/liter, Al2O3
;0.8g/liter) and aluminum sulfate aqueous solution (
Al2O3; 38.4g/liter, H2SO4; 27
5g/liter) and 3.2liter/hr, respectively.
It was fed continuously at a rate of 0.8 liters/hr. The reaction temperature was 30-32°C, and the pH of the slurry discharged was 6.
It was 4-6.6.

After separating the discharged slurry into solid and liquid and thoroughly washing with water, Na2O; 1.72wt%, Al2O3; 2.58w
t%, SiO2; 39.3wt%, H2O; 56.4w
A granular amorphous aluminosilicate homogeneous compound of t% was obtained. 2,840 g of the homogeneous compound and 1.39 wt% NaOH
Pour 5160g of aqueous solution into an autoclave,
Crystallization was carried out under stirring at <RTIgt;C</RTI> for 72 hours. solid-liquid separation of the product,
It was 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:

1.1Na2O, Al2O3, 23.3SiO2 10g of this zeolite was mixed with 11g of 0.012N cobalt nitrate aqueous solution.
Added to liters. The mixture was stirred at 60° C. for a day and night and washed to obtain a cobalt ion exchange zeolite. Then 0.
024N copper acetate aqueous solution. 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:

0.43CoO, 0.75CuO, Al2O3,2
3.3SiO2 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 nickel acetate was used instead of cobalt nitrate.

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

0.60NiO, 0.75CuO, Al2O3,2
3.3 SiO2 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 chromium acetate was used instead of cobalt nitrate.

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

0.09Cr2O3, 1.05CuO, Al2O3
, 23.3SiO2 Example 4 Catalyst 4 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 iron nitrate was used instead of cobalt nitrate.

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

0.41FeO, 0.92CuO, Al2O3,2
3.3SiO2 Example 5 Catalytic cracking performance was investigated using the catalysts obtained in Examples 1, 2, 3, and 4.

[0037] After press-molding the catalyst, it is pulverized to give 42 to 8
The particles were sized to 0 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 0.48% NO was
It was distributed so that the contact time was 4.0 g·sec/ml.

Table 1 shows the NO conversion rate at each temperature.

[0039]

[Table 1] Comparative Example 1 10 g of ZSM-5 type zeolite obtained in Example 1 was
After adding to 1 liter of 0.012N copper acetate aqueous solution, 6
A comparison catalyst was prepared by stirring at 0°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:

0.64Na2O, 0.69CuO, Al2O3,
23.3SiO2 Comparative Example 2 Using the catalyst obtained in Comparative Example 1, the catalytic cracking performance of the comparative catalyst was investigated in the same manner as in Example 5.

The results are shown in Table 2.

[0042]

[Table 2] Example 6 Catalyst 5 was prepared in the same manner as in Example 1 except that 10 g of the ZSM-5 type zeolite obtained in Example 1 was used and manganese nitrate was used instead of cobalt nitrate.

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

0.68MnO, 0.71CuO, Al2O3,2
3.3SiO2 Example 7 Catalyst 6 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 zinc acetate was used instead of cobalt nitrate.

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

0.62ZnO, 0.76CuO, Al2O3,2
3.3SiO2 Example 8 Catalyst 7 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 chloroplatinic acid was used instead of cobalt nitrate.

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

0.15PtO, 1.07CuO, Al2O3,2
3.3SiO2 Example 9 Using the catalysts obtained in Examples 6, 7 and 8, Example 5
The catalytic cracking performance of the comparative catalyst was investigated in the same manner as described above.

The results are shown in Table 3.

[0050]

[Table 3]

[0051]

Effects of the Invention As is clear from Tables 1, 2, and 3, 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. , exhibits excellent heat resistance.

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, and has excellent heat resistance. It has the effect of exhibiting very excellent performance. Therefore, by bringing the catalyst of the present invention into contact with exhaust gas, nitrogen oxides can be purified even at high temperatures.

Claims (2)

[Claims] 1. A nitrogen oxide catalytic cracking catalyst comprising a zeolite having a SiO2/Al2O3 molar ratio of at least 20 containing copper ions and transition metal ions other than copper. 2. A method for catalytic decomposition of nitrogen oxides, which comprises bringing the catalyst according to claim 1 into contact with the nitrogen oxide-containing gas.