JPH02251247A - Catalyst for decomposing nitrogen oxide - Google Patents

Abstract

PURPOSE:To obtain a catalyst for efficiently removing nitrogen monoxide even from gas low in the concn. of nitrogen monoxide by containing Cu and a metal such as Co or Ni in zeolite. CONSTITUTION:Copper and one or more kind of a metal selected from Co, Ni, La and Ce are introduced into zeolite of xM2/nO.Al2O3.ySiO2.zH2O (wherein n is a valency of a cation M, x=0.8-2.0, y>=2.0 and z>=0) by an ion exchange method or an impregnation method. Since the catalyst thus obtained is enhanced in the decomposition activity of NO, said catalyst removes nitrogen monoxide efficiently even from gas low in the concn. of nitrogen monoxide.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a catalyst that removes nitrogen oxides from a gas containing nitrogen oxides by decomposition. This invention relates to a zeolite-based decomposition catalyst that decomposes nitrogen oxide.

[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 compounds contained in gases emitted from factories, which are stationary sources, and automobiles, which are mobile sources, are said to be the cause of photochemical smog and are harmful to the human body. In particular, -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 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 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 mobile sources such as cars.

On the other hand, various catalysts have been developed and are commonly used to purify the exhaust gas of gasoline engines in a reducing atmosphere where the exhaust gas contains almost no oxygen. However, these catalysts are not suitable for practical use in the coexistence of oxygen.

By the way, catalytic decomposition of NO, that is, directly converting NO into N2 and 0
The method of decomposition into 2 requires only passing the exhaust gas through the catalyst layer, and is extremely simple and can be used in a wide range of applications. Catalysts have been found for this as well. That is, Pt
, Cu0SCo-based catalysts are effective in NO decomposition activity, but both have the problem of being poisoned by the generated oxygen. 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-80-12-250 discloses that a special zeolite containing copper is effective in decomposing NO in a system containing oxygen. It is also known that perovskites containing copper are effective for this purpose.
Y LETTBR Magazine J, 1988, No. 1797~
However, although these are effective when the No concentration is quite high, their activity is low at low concentrations, and it is necessary to develop catalysts with even higher activity.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to provide a nitrogen oxide decomposition catalyst with further improved NO decomposition activity.

[Means for Solving the Problems] As a result of conducting studies to achieve the above object, the present inventor found a highly active catalyst by supporting a plurality of metals on zeolite, and completed the present invention. It happened.

That is, the present invention includes zeolite, steel, CoqNi,
The present invention provides a nitrogen oxide decomposition catalyst characterized by containing at least one metal selected from La and Ce.

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

XM2ym O・Aj 20s Fst 02
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 of 2.0 or more, 2 is a number of 0 or more) The basic structure of zeolite is a regular three-dimensional combination of Sl, AJ, and O, and due to the difference in structural units , adopts various crystal structures. 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, chabasite, etc., and synthetic products include A type, X type, Y type, ZSM-5, etc.

The zeolite used in the present invention is 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.

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.

810□/A j 20 of the zeolite used in the present invention
3 (molar ratio) is preferably 2 or more, particularly in the range of 2 to t, ooo.

In the present invention, the method of introducing metal into zeolite is not particularly limited. Examples include an ion exchange method in which cations in the zeolite are exchanged with the desired metal cations, and an impregnation method in which the zeolite is immersed in a solution containing the desired metal.

The metal raw material compound used in the present invention may be in any form. For example, sulfates, hydrochlorides, nitrates, organic acid salts,
Examples include metal complex salts. Also, when introducing metals,
The order in which copper and at least one metal selected from C0% Ni and 5LaSCe are introduced does not matter first.

In the present invention, copper and Co, N i SL a s C
The molar ratio of Cu/M to at least one metal selected from e (hereinafter referred to as M) is 0.1 to 100.
゜Preferably 1.0 to 1O. The total supported amount varies depending on the Si 02 /AJ20s ratio of the zeolite, but if expressed as the exchange rate between cations in the zeolite and metal, the exchange rate is 5 to 500%, preferably 10 to 3.
It is 00%.

The operating temperature of the catalyst of the present invention is in the range of 300 to 800 °C,
Preferably it is 400-700°C. Further, the contact time between the catalyst of the present invention and the processing gas is not limited.

An industrial method of using the catalyst of the present invention includes charging the catalyst into a reactor in an appropriate form. For example, it is possible to use inorganic oxides such as silica or alumina or clay as a binder to form a spherical, columnar, or honeycomb shape.

Another method is to mold the zeolite before introducing the metal, and then introduce the metal. In any case, it is not particularly limited.

[Effects of the Invention] By using the catalyst of the present invention, nitrogen monoxide can be efficiently removed even from a gas with a low concentration of -nitrogen oxide.

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

Examples 1 to 4 Using a commercially available NaY type zeolite (SiO2/AJ20, ratio of about 5), copper was added to the zeolite using a normal ion exchange method so that the ion exchange rate was about 30%. Introduced. Furthermore, Co s N 1 , L was added to this copper-introduced zeolite so that the ion exchange rate was about 30%.
Catalysts were obtained by introducing as Ce by an ion exchange method.

Examples 5 to 8 Contrary to Example 1, Co s N i , L a SCe
were first introduced into the zeolites used in Examples 1 to 4 by an ion exchange method, and then copper was introduced to obtain a catalyst. Note that the ion exchange rate is the same as in Example 1.

Comparative Examples 1 to 5 Catalysts were obtained by introducing only Cu, Co, Nl, La, and Ce into the zeolite used in Examples 1 to 8 so that the ion exchange rate was about 30%.

Experimental Examples The catalysts obtained in Examples 1 to 8 and Comparative Examples 1 to 5 were molded into tablets, and the catalysts were molded into tablets and the particle sizes were made uniform, and the activity was evaluated. 1.0 g of the catalyst was placed in a flow reactor, and the temperature was gradually raised to 500° C. while flowing He gas. Therefore, He gas containing 5.0 voJ% of -nitrogen oxide was caused to flow, and the product was analyzed by gas chromatography to determine the conversion rate (%). Note that the conversion rate values are obtained 2.0 hours after the reaction.

These results are shown in Table 1.

As shown in Table 1, it can be seen that the catalysts of Examples 1 to 8 exhibit higher catalytic activity than the catalysts of Comparative Examples 1 to 5, regardless of the order of metal introduction.

Table 1 Patent applicant: Masakazu Iwamoto

Claims (1)

[Claims] 1. A catalyst for decomposing nitrogen oxides, characterized in that zeolite contains copper and at least one metal selected from Co, Ni, La, and Ce.