JPH03213149A - Manufacture of nitrogen oxide decomposing catalyst - Google Patents

Abstract

PURPOSE:To obtain a highly active catalyst by dispersing zeolite in an aqueous copper compound solution and subsequently adding a solution of alkaline earth metal hydroxide thereto to adjust the pH of the resulting dispersion to introduce copper into zeolite within a short time. CONSTITUTION:Y-type or mordenite type zeolite is dispersed in an aqueous solution of a copper compound such as copper sulfate. Next, a solution of alkaline earth metal hydroxide such as magnesium hydroxide or calcium hydroxide is added to the resulting dispersion to adjust the pH of the dispersion to 6.0 or more. Thereafter, zeolite is recovered. By this method, a predetermined amount of a metal can be easily introduced into zeolite within a short time and no ammonia is generated even in pretreatment and nitrogen monoxide is efficiently removed with high activity.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for producing a catalyst that removes nitrogen oxides from a gas by decomposition, and more specifically relates to a method for producing a catalyst that removes nitrogen oxides from a gas by decomposition. The present invention relates to a method for producing a catalyst of this type.

[Prior Art] From the perspective of environmental conservation, the removal of air 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 oxides contained in gases emitted from factories, which are fixed sources, and automobiles, which are mobile sources, are said to be the cause of photochemical smog, and are gases that remain in the human body. Especially - Nitrogen oxide (No)
It is difficult to remove and is an issue to be considered.

Several methods have been considered so far. For example, a method called catalytic reduction method is a method of removing NO by converting it into N2 and N20 on a catalyst using a reducing agent such as ammonia or hydrogen. However, since a reducing agent is used,
It is advantageous for large-scale stationary sources that require measures to recover and prevent leakage, but 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, is extremely simple and can be used in a wide range of applications because it only requires passing exhaust gas through a catalyst layer. Catalysts have been found for this as well. Although p-, c-, and 1c-based catalysts are effective in reducing NO decomposition activity, they all have the problem of being poisoned by the produced oxygen. Diesel engine waste gas usually contains oxygen, which cannot be handled by conventional catalysts, and the development of new catalysts is desired.

[Problem to be solved by the invention] Several catalysts have been proposed to address the above problems.

For example, JP-A-60-125250 discloses that a special zeolite containing copper is effective in decomposing NO in a system containing oxygen. Chemistry Letters (CH
EMI 5T-RY LETTER), 1988, pages 1797-1800. In particular, zeolite has excellent properties when it comes to formulation, but ion exchange requires a long time when introducing copper. However, recently, Japanese Patent Application Laid-Open No. 1-9E3011 discloses a method of easily supporting the particles using ammonia.

However, ammonia has the disadvantage that it has a strong odor and is time-consuming to handle, and when ammonia is used, there is a problem 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 solving the above problems. That is, the present invention disperses zeolite in an aqueous solution of a copper compound, adds an alkaline earth metal hydroxide solution therein, and adjusts the pH to at least 6.0 to support copper on the zeolite. The present invention relates to a method for producing a catalyst for decomposing nitrogen oxides, characterized in that:

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

XM2/II O"A1203" YS io2"
ZH20 (n is the valence of the cation M, X is 0.8-2.
A number in the range of 0, 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 that 5i1A110 is regularly bonded in three dimensions, and it takes on various structures depending on the difference in the unit structure. 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, as a natural product, mordenite,
Examples of synthetic products such as erionite and chabasite include A type, X type, Y type, and ZSM-5.

Generally, a synthetic product of zeolite can be easily obtained by mixing a suitable silica source, alumina source, and alkali source and crystallizing the mixture under hydrothermal conditions at about 100 to 250°C. It can also be obtained by hydrothermal synthesis by adding a material called a template to the above mixture.

Zeolites used in the present invention are not particularly limited. Either natural products or synthetic products may be used, but synthetic products are preferably used because the former contain impurities and require time and effort to purify.

The zeolite used in the present invention is preferably Y type, mordenite type, or ZSM-5, and more preferably ZSM-5.

5iOz/A1□03 of zeolite used in the present invention
The molar ratio is 2.0 or more, preferably 2-t, ooo, more preferably 20-200.

The aqueous solution of a copper compound used in the present invention is a solution in which a copper compound is dissolved, and the compound may be in any form. For example, sulfates, hydrochlorides, nitrates, ionic salts,
There are also complex metal salts. As the metal species, those that generate cations are preferred. The concentration of copper compounds is 0.1-10
0 g/l is preferable, and 0.5 to 50 g/l is more preferable.

As the alkaline earth metal hydroxide used in the present invention, magnesium hydroxide, calcium hydroxide, strontium hydroxide, and barium hydroxide are preferable.

Note that the alkaline earth metal hydroxide solution may be prepared by dissolving the hydroxide in water, or by dissolving the oxide of the metal in water.

In the present invention, the alkaline earth metal hydroxide solution may be added in an amount such that a predetermined pH is achieved. In the present invention the pH range is at least 6.0, preferably 6.0.
~13.0, particularly preferably 1) H is 7.0~10.
It is to adjust it to 0. When the pH is 6.0, the amount of copper supported is small and the activity as a catalyst is low.

In the present invention, the zeolite is recovered after adjusting the pH, but the method may be any known method, and commonly used filtration or centrifugation is preferred.

In the present invention, the recovered zeolite may be dried. Drying may be performed at room temperature, or under normal pressure or reduced pressure. For example, drying is performed at 50° C. or higher for 5 to 24 hours. Furthermore, the zeolite is heated at a temperature of 100 to 600°C, preferably 300 to 50°C.
It may be baked at a temperature of 0° C. for 8 to 24 hours, preferably 8 to 16 hours.

In the present invention, the copper content of the zeolite is preferably at least 0.5 wt%, more preferably at least 1.0 wt%, particularly preferably 2.0 to 5.0 wt%.

In an industrial method of using the catalyst of the present invention, an inorganic oxide such as silica or alumina or clay is mixed as a binder, and the catalyst is formed into a suitable shape such as spherical, columnar, or honeycomb shape, and is filled into a reaction apparatus. Alternatively, a method may be adopted in which zeolite is molded before copper is introduced, and the copper is then introduced. In any case, it is not particularly limited.

The temperature at which the catalyst of the present invention is used is preferably in the range of 500 to 850°C, more preferably 550 to 800°C. Further, the contact time between the present catalyst and the treatment gas for nitrogen oxidation anastomosis is not limited.

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

Actually "L example"! 3.0 g of ZSM-5 zeolite with a molar ratio of 8iO3/Al2O of about 50 was added to 500 g of ZSM-5 zeolite containing 0.5 g of copper nitrate.
ml solution, and a saturated aqueous solution of barium hydroxide was added dropwise little by little to adjust the pH to a predetermined value. Thereafter, the zeolite was filtered and thoroughly washed with ion-exchanged water. The obtained zeolite was dried under reduced pressure to obtain catalysts A-E.

Ratio "Example L" - The same procedure as in Example was carried out except that the pH was adjusted to 4.0. Catalyst F was thus obtained.

Using the same zeolite as in the Example, it was dispersed in 500 ml of a solution containing 0.5 g of copper nitrate, and stirred for 20 hours. Thereafter, the zeolite was filtered and thoroughly washed with ion-exchanged water.

The obtained zeolite was dried under reduced pressure to obtain catalyst G.

Real JJL Turtle: 1- Preparation of a saturated aqueous solution of calcium hydroxide The pH was adjusted to 8.0 in the same manner as in Example 1, and Catalyst H was obtained.

Furthermore, a saturated solution of magnesium oxide was prepared, and this solution was used as a magnesium hydroxide solution, and the pH was adjusted to 8.0 in the same manner as in the example, to obtain catalyst I.

Evaluation Example 1 - The catalyst obtained above was calcined at 500°C, and the amount of copper supported was determined by atomic absorption spectrometry.

In addition, after the catalyst was compressed into tablets, it was crushed to have a uniform particle size, and the reaction was evaluated. That is, 1.0 g of catalyst was placed in a flow reactor, and the temperature was gradually raised while He was flowing.
The temperature was set to 0°C. So - He containing 500 ppm nitrogen oxide
was flowed at a rate of 50 ml/min, and the products were analyzed by gas chromatography. The analysis value is 2.0 after the reaction.
It is something that has passed over time.

The results are summarized in Tables 1 and 2.

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

As shown in Table 1 and Table 2, it can be seen that various alkaline earth metal hydroxide solutions can be used.

[Effects of the Invention] By the method of the present invention described above, metals can be easily introduced into zeolite in a predetermined amount in a short time, and there is no generation of ammonia in the pretreatment. Furthermore, the resulting catalyst has high activity and can efficiently remove nitrogen monoxide even from gases with low concentrations of nitrogen oxide.

Claims (1)

[Claims] (1) Copper is supported on the zeolite by dispersing the zeolite in an aqueous solution of a copper compound, adding an alkaline earth metal hydroxide solution therein, and adjusting the pH to at least 6.0. A method for producing a nitrogen oxide decomposition catalyst.