JPH03101837A - Production of catalyst for decomposition of nitrogen oxide - Google Patents

Abstract

PURPOSE:To introduce a prescribed amt. of copper into zeolite in a short time and to obtain a catalyst having high activity by dispersing the zeolite in an aq. soln. of a copper compd. and further adding an aq. soln. of an alkaline compd. CONSTITUTION:Zeolite such as ZSM-5 or mordenite type zeolite is dispersed in an aq. soln. of a copper compd. such as copper sulfate or hydrochloride and an aq. soln. of an alkaline compd. such as the hydrochloride of an alkali metal or an alkali metallic salt of a weak acid is further added to adjust the pH to >=6.0, preferably 6.0-13.0, especially preferably 7.0-10.0. A prescribed amt. of copper can be introduced into the zeolite in a short time and a catalyst having high activity is obtd. When this catalyst is used, ammonia is not generated during pretreatment and NO is efficiently removed.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a catalyst that removes nitrogen oxides from a gas by decomposition, and more particularly relates to a zeolite-based catalyst that decomposes nitrogen monoxide. A method for preparing a catalyst is provided.

[Conventional technology] From the perspective of environmental conservation, the removal of atmospheric l5 pollutants is a major social issue. In particular, purification of combustion waste gas accompanying the expansion of industrial activities is a current urgent issue. Nitrogen compounds contained in gases emitted from fixed sources such as factories and mobile sources such as automobiles are said to be the cause of photochemical smog and are harmful to the human body. Especially nitric oxide (No.
) is difficult to remove and is an issue to be considered.

Several methods have been considered so far.

For example, a method called a catalytic reduction method is a method of removing No by converting it into N2 and H20 on a catalyst using a reducing agent such as ammonia or hydrogen. However, since it uses a reducing agent, measures are needed to recover it and prevent leakage, and although it is effective for large-scale stationary sources, it is not suitable for sources such as automobiles. On the other hand, many catalysts have been developed and are commonly used to purify the exhaust gas of gasoline engines whose exhaust gas is a reducing gas. However, these catalysts cannot be used in the coexistence of oxygen.

By the way, the catalytic decomposition of No, that is, the method of directly decomposing No into N2 and O2, requires only passing the exhaust gas through the catalyst layer, and is extremely simple and has a wide range of applications. Catalysts have been discovered for this as well. PL, Cu
Although OSCo-based catalysts are effective in decomposing No, they all have the problem of being poisoned by the oxygen they produce. Diesel engine waste gas usually contains oxygen, which cannot be handled by conventional catalysts, and the development of new catalysts is desired.

[Problems to be Solved by the Invention] Several catalysts have been proposed to solve the above problems. For example, JP-A-80-125250 discloses that a special zeolite containing copper is effective in decomposing No in a system containing oxygen. Additionally, the effectiveness of copper-containing perovskites has also been shown in “rC}IEMISTR
Y LETTER Magazine J, 1988, No. {797-1
Copper-containing zeolite has particularly excellent properties, but ion exchange requires a long time to introduce copper.However, recently, JP-A-1-9
Japanese Patent No. 8011 discloses a method of easily supporting the particles using ammonia. However, when ammonia is used, there is a problem in that ammonia gas is generated during pretreatment of the catalyst.

Therefore, in order to solve the above problems, it is necessary to develop a method for preparing a highly active catalyst that can introduce a predetermined amount of copper into zeolite in a short time and does not generate ammonia during pretreatment.

[Means for Solving the Problems] The present invention relates to a method for producing a nitrogen oxide decomposition catalyst for solving the above problems. That is, the present invention disperses zeolite in an aqueous solution of a copper compound, and adds thereto an aqueous solution of one kind of alkaline compound selected from the group consisting of hydroxides of alkali metals and alkali metal salts of weak acids. , relates to a method for producing a nitrogen oxide decomposition catalyst, characterized in that copper is supported on the zeolite by adjusting the pH to at least 6.0.

The zeolite referred to in the present invention is a crystalline aluminosilicate, and the composition is represented by the following formula.

xM27n O-AJ 2 03 yst 02
ZH20 (n is the valence of the cation M, X is 0.8~
A number in the range of 20, y is a number greater than or equal to 2.0, and 2 is a number greater than or equal to 0. ) The basic structure of zeolite is a regular three-dimensional combination of SI Al and O, and it takes on various crystal structures depending on the structural units. Many types of zeolite are known, but they are characterized by X-ray diffraction and have different names depending on their crystal structure. For example, natural products include mordenite, erionite, and chabasite, and synthetic products include A type, X type, Y type, and Z SM-5.

Zeolites used in the present invention are not particularly limited. Either a natural product or a synthetic product may be used, but the former contains impurities and takes time to purify, so a synthetic product is preferably used.

Zeolite can be easily synthesized by mixing appropriate silica sources, alumina sources, and alkali sources and crystallizing the mixture under hydrothermal conditions at about 100 to 250°C.

There are also products obtained by hydrothermal synthesis by adding an organic substance called a template to the above-mentioned mixture. Zeolites are generally commercially available and may be used.

Zeolites preferably used in the present invention are Y-type, mordenite-type, ZSM-5, etc., and ZSM-5 is more preferable.

The aqueous solution of a copper compound referred to in the present invention refers to a solution in which a copper compound is dissolved, and the compound may be in any form. Examples include sulfates, hydrochlorides, nitrates, organic acid salts, and metal complex salts. As the metal species, those that generate cations are preferred.

The water-soluble alkaline compound referred to in the present invention refers to an aqueous solution of one type of compound selected from the group consisting of alkali metal hydroxides and alkali metal salts of weak acids. Among these, in the present invention, 1 selected from alkali metal hydroxides
An aqueous solution of the seed compound is preferably used. Examples of the alkali metals include sodium, potassium, and the like. Among these, sodium or potassium is preferably used. Examples of the weak acids include carbonic acid, acetic acid, and organic acids. In the present invention, the aqueous solution of the alkaline compound may be added in an amount such that a predetermined pH is achieved.

Zeolite is sufficiently dispersed in the prepared copper compound solution, and an aqueous solution of the alkaline compound used in the present invention is added thereto to adjust the pH. At this time, if the concentration of the aqueous solution of the alkaline compound is high, the pH will change abruptly, which is undesirable. In the present invention, the pH range is required to be at least 6.0, preferably from 6.0 to 13.0, and particularly preferably from 7.0 to 10.0. If the pH is less than 6.0, the amount of copper supported is low and the effects of the present invention cannot be obtained.

After adjusting the pH, the zeolite can be recovered by any method, but commonly used filtration and centrifugation are preferred.

In the present invention, the copper content of the zeolite is at least 0. 5vt%, preferably l. ．． Owt%.

The operating temperature of the catalyst obtained by the present invention is 500 to 85
The temperature is in the range of 0°C, preferably 550-800°C.

Further, the contact time between the present catalyst and the processing gas is not limited.

An example of an industrial method for using the catalyst obtained according to the present invention is to form the catalyst into an appropriate form and fill it into a reactor. For example, it is possible to use an inorganic oxide such as silica or alumina or clay as a binder to form a spherical, columnar, or honeycomb shape. Another method is to mold zeolite before introducing copper and then introduce copper. In any case, it is not particularly limited.

[Effects of the Invention] By the wide production method of the present invention shown above, it is possible to introduce a predetermined amount of metal into zeolite in a short time, and there is no generation of ammonia in the pretreatment, and the activity of the obtained catalyst is high. Nitric oxide can be efficiently removed even from gases with low concentrations of nitrogen monoxide.

[Example code] Next, the present invention will be described in more detail with reference to Examples.

Examples 1-5 3.0 g of ZSM-5 zeolite (Sf02/A-203 is about 5DCr) was added to 500r containing 0.44 g of copper nitrate.
d solution, and add 1.5 moJ/J of sodium hydroxide dropwise little by little to the predetermined pH shown in Table 1.
It was adjusted to Thereafter, the zeolite was filtered and thoroughly washed with ion-exchanged water. The obtained zeolite was dried under reduced pressure and further dried at 100°C for 3 hours. Catalysts A-E were thus obtained.

Comparative Example 1 The same operation as in Example was performed except that the pH was adjusted to 4.0. Catalyst F was thus obtained.

Comparative Example 2 Using the same zeolite as in Example, it was dispersed in 500 d of solution containing 0.44 g of copper nitrate, and stirred for 20 hours. Thereafter, the zeolite was filtered and thoroughly washed with ion-exchanged water. After drying the obtained zeolite under reduced pressure, it is further heated to 100°C.
It was dried for 3 hours. Catalyst G was thus obtained.

Evaluation Example Catalysts A-G obtained in the above Examples and Comparative Examples were
The amount of copper supported was determined by atomic absorption spectrometry.

In addition, after the catalyst was compressed into tablets, it was crushed to make the particle size uniform, and the reaction was evaluated. That is, the catalysts t and Og were placed in a flow reactor, and the temperature was gradually raised to 500° C. while flowing He gas. Therefore, He gas containing 5000 ppn of nitrogen monoxide was flowed at a rate of 501 nl/mjrl, and the product was analyzed by gas chromatography. The analytical values were obtained 2.0 hours after the reaction.

These results are summarized in Table 1.

Table 1 As shown in Table 1, by the manufacturing method of the present invention,
It can be seen that a catalyst with a large amount of supported copper and high activity can be obtained.

Claims (1)

[Claims] 1. By dispersing zeolite in an aqueous solution of a copper compound and adding thereto an aqueous solution of one kind of alkaline compound selected from the group consisting of alkali metal hydroxides and alkali metal salts of weak acids, the pH can be adjusted to at least 6.0, thereby supporting copper on the zeolite.