JPH03213148A - Nitrogen oxide decomposing catalyst - Google Patents

Abstract

PURPOSE:To obtain a catalyst efficiently decomposing nitrogen oxide in nitrogen oxide-containing gas to make said gas harmless by adding a copper ion and a rare earth element ion to zeolite. CONSTITUTION:A copper ion and a rare earth element ion such as lanthanum ion or a potassium ion are contained in mordenite or ZSM-5 type zeolite. At this time, zeolite is brought into contact with a copper salt such as copper acetate or copper nitrate and an rare earth element salt such as lanthanum nitrate or cerium nitrate to obtain copper ion and rare earth element ion exchange type zeolite. The catalyst thus obtained efficiently decomposes nitrogen oxide in nitrogen oxide-containing gas to make said gas harmless and is enhanced in the lasting properties of activity and can be used over a long period of time even in the coexistence of steam.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a nitrogen oxide decomposition catalyst, and more particularly,
It relates to a catalyst that decomposes nitrogen oxides in gas and converts them into harmless N2 and 0□.

[Conventional technology]

Some catalysts for decomposing nitrogen oxides are already known. For example, the Abstracts of the Chemical Society of Japan (198g, Spring, 1nE
33) reported copper ion-exchanged mordenite-type zeolite.0 Mordenite-type zeolite has a crystal structure belonging to the mordenite group, and generally has a SiO□ZA et al. It has a pore size of This is a catalyst in which copper ions are exchanged with mordenite-type zeolite.

Although it has excellent heat resistance, it has a problem of low decomposition activity.

Further, JP-A-60-125250 describes a nitrogen oxide decomposition catalyst in which ZSM-5 type zeolite contains copper ions. ZSM-5 type zeolite has a different crystal structure from conventionally known A type, Y type, mordenite type, etc. zeolites, and has the following structure: Sin, /i,
0° (mole ratio) is 20 to 200, and has a pore diameter of about 6 pores. Although such a nitrogen oxide decomposition catalyst made of ZSM-5 type zeolite containing copper ions has high initial activity, it has low heat resistance, and the activity decreases particularly in the coexistence of water vapor.

JP-A No. 60-25542 reports a catalyst in which platinum and cobalt are supported on a perovskite such as 5rFeO, but there is a problem in that it requires a high temperature of 800 to 1000°C.

[Problem to be solved by the invention]

The purpose of the present invention is to solve the above problems.

An object of the present invention is to provide a nitrogen oxide decomposition catalyst that has high activity for decomposing nitrogen oxides into N2 and 0□ and has excellent sustainability of activity.

[Means to solve the problem]

The present invention is a nitrogen oxide decomposition catalyst made of zeolite containing copper ions and rare earth ions.

As the zeolite used in the present invention, any type such as A type, Y type, mordenite type, ZSM-5 type can be used, and mordenite type and ZSM-5 type are particularly preferred.

Mordenite-type zeolite is a zeolite with a structure belonging to the normal mordenite group, and has a pore diameter of around 7λ, and is generally 5xoz/A0203 (molar ratio) 1
0-11 is used, but 5un2/AQ2
0. (molar ratio) may be outside the above range. Such mordenite-type zeolite may be produced by a synthetic method, or it may be naturally produced as a mineral containing it, or it may be dealuminated from these materials, but it may also be a synthetic product or a synthetic dealuminated product. is preferred.

Among the mordenite-type zeolites mentioned above, synthetic products can be prepared by known methods, for example, by adding silicic acid to the above molar ratio.
-5in2 raw materials such as aluminum, aluminum sulfate, etc. and A
It is produced by heating a mixture of Q, O, and raw materials to about 200° C. in the presence of a catalyst to cause a reaction, but commercially available products may also be used.

Also natural products or 5t02/AQzOi (molar ratio)2
A zeolite obtained by dealuminating a synthetic product with less than 0% aluminum can be prepared by acid-treating the mordenite-type zeolite to elute part or most of the aluminum, followed by washing with water, drying, and calcination.

ZSM-5 type zeolite is disclosed in the above-mentioned Japanese Patent Application Laid-open No. 12525-1983.
It has the structure described in No. 0 and has a molar ratio of 1
n.

/1203=20~200, Na2O/5i02=0
．． It is produced by mixing a silica source, an alumina source, an alkali source and water so that H20/5iO2=12-70 and heating it to 120-220°C to react. You may also use one made by Ichisaka from Mobil Corporation.

In the present invention, a catalyst containing copper ions and rare earth ions in zeolite as described above is used.

Copper ions may be monovalent or divalent. Rare earth ions are not particularly limited, but lanthanum ions and potassium ions are preferred. The content of copper ions in the catalyst is not particularly limited, but - usually used for boat fishing. 0.5-10% heavy starch,
Preferably it is 1 to 5% by weight. The content of rare earth ions is usually 0.01 to 1 in molar ratio to the copper ion content.
Preferably it is 0.03 to 0.5.

Zeolites containing copper ions and rare earth ions are
It can be manufactured by normal ion exchange treatment. Ion exchange treatment uses 1 to 10% by weight of copper salts such as copper acetate and copper nitrate, and rare earth salts such as lanthanum nitrate and cerium nitrate.
By contacting with an aqueous solution, a copper ion and rare earth ion exchange form of zeolite is obtained. It is preferable to introduce either the copper ion or the rare earth ion first, but they may be introduced at the same time.

The catalyst thus obtained may be used in the form of powder or pellets, or may be supported on a molded body such as a honeycomb body. Further, this catalyst can be used as it is for decomposing nitrogen oxides, but it may also be subjected to treatment such as steam treatment.

The nitrogen oxide decomposition catalyst of the present invention decomposes nitrogen oxides into N2 and 02 and renders them harmless when brought into contact with nitrogen oxide-containing gases such as NO2 and No discharged from automobiles, factories, combustors, etc. used for Since the above exhaust gas contains about 3 to 20% by volume of water vapor, water vapor resistance is required.5 The catalyst of the present invention has excellent water vapor resistance.
It can be used satisfactorily even in systems where water vapor coexists.

In order to decompose nitrogen oxides using the catalyst of the present invention, a nitrogen oxide-containing gas is passed through a packed bed of the catalyst and brought into contact with the nitrogen oxides. The reaction temperature at this time is usually 300 to 800°C, preferably 400 to 600°C, and gas hourly space velocity (GH5V).
is 500 to 200,0OOhr-1 preferably 1,00
0 to 100.000hr"".

〔Effect of the invention〕

According to the present invention, since zeolite contains copper ions and rare earth ions, nitrogen oxides can be efficiently decomposed and rendered harmless from nitrogen oxide-containing gas, and the activity is highly sustainable. It can be used for a long time even in the coexistence of water vapor.

〔Example〕

Examples of the present invention will be described below.

Example 1 Synthesis of mordenite-type zeolite TOG with a Sio2/AQzOx molar ratio of 30 and 2 g of copper nitrate in 500 cc of distilled water
In addition to.

Ion exchange was performed at room temperature all day and night. After filtration, washing with water, and drying, 3 g of lanthanum nitrate was added, and ion exchange was performed at room temperature. After washing with water and drying, it was calcined at 500°C for 2 hours to obtain a catalyst. The copper ion content of the obtained catalyst was 1.9%lt%, and the lanthanum ion content was 0.3vt%.

Fill a glass reaction tube with the above catalyst 5ilJ2 and
The temperature was raised to ℃. Table 1 shows the results after 3 hours of one reaction in which 2% No and 8206% He gas was supplied at GH5V 1,000 h'' to perform a No decomposition reaction.

Example 2 A catalyst was prepared under the same conditions as in Example 1 except that cerium nitrate was used instead of lanthanum nitrate, and a reaction was carried out. The results are shown in Table 1.

The copper ion content of this catalyst was 1.8 vt%, and the cerium ion content was 0.2 wt%.

Example 3 A catalyst was prepared under the same conditions as in Example 1 except that the mordenite type zeolite was changed to ZSM-5 type zeolite (SiO□/AQ20. molar ratio 60) shown in JP-A-60-125250. , the reaction was carried out. The results are shown in Table 1.

The copper ion content of this catalyst was 1.1 vt%, and the lanthanum ion content was 0.1 wt%.

Example 4 The catalyst of Example 1 was treated with steam at 600° C. for 6 hours and then used in one reaction. The results are shown in Table 1.

Example 5 The catalyst of Example 3 was treated with steam at 600° C. for 6 hours and then used in 5 reactions. The results are shown in Table 1.

Comparative Example 1 C prepared without adding La ions in Example 1
The reaction was carried out under the same conditions except that a u-mordenite type zeolite catalyst was used. The results are shown in Table 1.

Comparative Example 2 Cu prepared without adding La ions in Example 3
-The reaction was carried out under the same conditions except that a ZSM-5 type zeolite catalyst was used. The results are shown in Table 1.

Comparative Examples 3 and 4 The catalyst of Comparative Example 1 was treated with steam at 600°C for 6 hours (Comparative Example 3), and the catalyst of Comparative Example 2 was treated with steam at 600°C for 6 hours.
The reaction was carried out under the same conditions except that the catalyst was changed to a catalyst treated with steam for a period of time (Comparative Example 4). The results are shown in Table 1.

Claims (1)

[Claims] (1) A nitrogen oxide decomposition catalyst made of zeolite containing copper ions and rare earth ions.