JPH0435747A - Catalyst for decomposition of nitrogen oxide - Google Patents

Abstract

PURPOSE:To obtain a catalyst having very high activity in the decomposition reaction of NO and maintaining its activity over a long time by using crystalline silicate having a specified compsn. and a specified crystal structure. CONSTITUTION:Cu and a rare earth element are incorporated into crystalline silicate having a chemical compsn. represented by a formula (1.0+ or -0.4)R2O. (aM2O3.bAl2O3).ySiO2 (where R is an alkali metal ion and/or an H ion, M is ions of one or more kinds of elements selected among group VIII elements, rare earth elements, Ti, V, Cr, Nb and Sb, a+b=1, a>0, b>0, y>12 and these figures show the molar ratio among the oxides) in a dehydrated state to form a catalyst for decomposition of NO. This catalyst has a wider service temp. range than the conventional catalyst and is used within the range of 300-1,000 deg.C, preferably 400-700 deg.C.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a catalyst that removes NOx from gas containing nitrogen oxides (hereinafter abbreviated as NOx). It provides a catalyst for decomposition.

[Conventional technology]

NOx in combustion exhaust gas emitted from industrial plants, automobiles, etc. is a substance that can cause photochemical smog, and the development of a method for removing it from the standpoint of environmental conservation is a serious and urgent social issue. Among NOx, NO is particularly difficult to remove, and various methods have been studied so far.

For example, the catalytic reduction method has been proposed as an effective method and is being developed;

It requires a reducing agent such as hydrogen or carbon monoxide, and also requires special equipment to recover or decompose the unreacted reducing agent. On the other hand, the catalytic cracking method does not require special additives such as reducing agents, and decomposes into nitrogen and oxygen simply by passing through a catalyst layer, and is the most desirable method because the process is simple. According to previous research, Pt
, CuO, CO3O4, etc. were found to have NO decomposition activity, but they could not be used as practical catalysts because they were poisoned by the decomposition product oxygen [Reference: Toshio Uchijima, Surface, Vol. 18 No. 3, (1980) p.
, 132).

[Problem to be solved by the invention]

A method of ion-exchanging Cu with silica gel or zeolite has been proposed as a catalyst to replace the above catalyst, but there are the following problems.

(1) A catalyst in which copper ions are supported on silica gel by an ion exchange method has a fairly high initial activity, but the activity rapidly decreases over time.

(2) Catalysts that are ion-exchanged with copper using Y-type zeolite or mordenite have low decomposition activity in the presence of oxygen.

(3) A catalyst in which ZSM-5 type zeolite is used for ion exchange with copper has been proposed, but although the NO decomposition activity is high, the selectivity of converting NO to N2 (2NO→N2+
02) is low. (Unexamined Japanese Patent Publication No. 60-12
5250).

[Means to solve the problem]

The present invention is aimed at solving the above-mentioned problems of the prior art, and a catalyst containing copper and rare earth elements using a crystalline silicate having a specific composition and crystal structure is capable of contacting NO. It was discovered that it not only exhibits extremely high activity as a decomposition catalyst, but also has high selectivity for NO to N2, and that its activity is stable even in the coexistence of oxygen and SOx, leading to the completion of the present invention.

That is, in the present invention, in a dehydrated state, the molar ratio of oxides is (1,0±0.4) R2O.CaM2O. *bA1
2O3E ・ySiL (in the above formula, R: alkali metal ion and/or hydrogen ion, M: ion of one or more elements from the group consisting of ■ group elements, rare earth elements, titanium, vanadium, chromium, niobium, and antimony, a- 1-b=1
．． a>0. b>0. The present invention is a nitrogen oxide decomposition catalyst characterized by containing copper and rare earth elements in a crystalline silicate having a chemical composition of y>12).

[Effect]

The catalyst of the present invention exhibits extremely high activity in the No decomposition reaction, and this activity lasts for a long time. Regarding the action of the catalyst of the present invention, the redox cycle of ion-exchanged copper ions (Cu'', ICu('') is easy, and the mechanism of releasing oxygen at a relatively low temperature, and the specific crystal structure of the catalyst of the present invention are explained. Its structural stability, heat resistance, etc. act in a complex manner, and by further containing rare earth elements, N
It is thought that the decomposition reaction of O is promoted and the copper ions ion-exchanged by the rare earth element are stabilized, thereby improving heat resistance.

Hereinafter, the catalyst used in the present invention will be explained in detail.

Zeolite is a crystalline aluminosilicate containing zeolite water, as shown by its origin from the Greek word "soaring stone", and its composition is generally expressed by the following formula.

×M2/Note・ALL・ys+oi・ZH2O (where n is the valence of the cation M, X is a number in the range of 0.8 to 2, y is a number of 2 or more, and 2 is a number of 0 or more. ) Its basic structure is D/(AI
+Si) are regularly bonded three-dimensionally by sharing oxygen with each other so that the atomic ratio is 2. As a result, a three-dimensional network structure having pores of different sizes and shapes is formed due to the different bonding methods between the tetrahedra.

Further, the negative charges of the AlO4 tetrahedron are electrically neutralized by bonding with cations such as alkali metals or alkaline earth metals. Generally, the pores formed in this way have a size of 2 to 3 to more than 10 pores, but AID
, the pore size can be changed by replacing the metal cation associated with the tetrahedron with another metal ion of different size or valence.

Zeolite can be used as a gas or liquid industrial desiccant that utilizes these pores, or as a molecular sieve that adsorbs and separates molecules in a mixture of two or more molecules. Zeolite can also be used as a solid acid in which metal cations are exchanged with hydrogen ions. Because of this property, it is widely used as an industrial catalyst.

There are many types of zeolites, each with a different zeolite salt attached to them depending on their crystal structure, which is characterized by X-ray diffraction patterns.

Naturally occurring zeolites include chabasite, erionite 9 mordenite, clinoptilolite, etc., and synthetic zeolites include A.

x, y, large port mordenite, ZSM
-5 etc. are well known.

Among these many zeolites, those that can be used in the present invention are limited to crystalline silicates having a specific compositional structure. The crystalline silicate of the present invention does not exist in nature, but can be synthesized by the following method.

The crystalline silicate used in the present invention is a source of silica, a source of group Ⅰ elements, rare earth elements, titanium, vanadium, chromium, niobium, and antimony oxides, a source of alumina, a source of alkali, and a source containing water and organic nitrogen. It is synthesized by forming a reaction mixture containing the compounds and heating the mixture for a time and at a temperature that results in the formation of a crystalline silicate.

The source of silica can be any silica compound commonly used in zeolide synthesis, such as solid silica powder, colloidal silica, or silicates such as water glass. is used.

■Group elements, rare earth elements, titanium, vanadium, chromium,
Compounds such as sulfates, nitrates, and chlorides of these are used as sources of niobium and antimony.

Examples of group (2) elements include iron, cobalt, ruthenium, rhodium, platinum, palladium, etc., and rare earth elements include lanthanum, cerium, neodymium, etc.

The source of alumina is most preferably sodium aluminate, but compounds such as chlorides, nitrates, sulfates, oxides or hydroxides can be used.

As the alkali source, a hydroxide of an alkali metal such as sodium, or a compound with aluminic acid or silicic acid is used.

As the organic nitrogen-containing compound which is one of the raw materials for hydrothermal synthesis of crystalline silicate, the following can be used.

(1) Organic amines;
secondary amines such as dipropylamine and jetanolamine, and tertiary amines such as tripropylamine and triethanolamine.
(2) Organic substances other than organic amines, such as ethylenediamine, diglycolamine, etc., or mixtures of the above compounds with halogenated hydrocarbons (propyl bromide, etc.), and other quaternary ammonium salts such as tetrapropylammonium salts. Nitrogen compounds: These various organic compounds such as pyridine, pyrazine, and pyrazole are illustrative, and the present invention is not limited to these.

The crystalline silicate used in the present invention is one in which part of A1 in the structure of conventional zeolite is replaced with group II elements, rare earth elements, titanium, vanadium, chromium, niobium, and antimony, and furthermore, S+02/( M2O3+A
l2O3) ratio is 12 or more,
It is prepared from a reaction mixture of the following molar composition.

5i02/ 1t2o3+ A12O3) 12~3
000 (preferably 2O-2O0) OH-/S+02O-1.0 (preferably 0.2-0
．． 8) 8.0/Si0. 2-1000 (preferably 10-2O0) organic nitrogen-containing compound/(M2O3+
Al2O3) (preferably 5 to 50) The crystalline silicate used in the present invention is synthesized by heating the raw material mixture at a temperature and time sufficient to produce crystalline silicate, but the hydrothermal synthesis temperature is 80 to 50. ~30
The temperature is preferably in the range of 0°C to 200°C, and the hydrothermal synthesis time is 0.5 to 14 days, preferably 1 to 10 days. The pressure is not particularly limited, but it is preferable to use autogenous pressure.

The hydrothermal synthesis reaction is continued by heating the raw material mixture to the desired temperature, with stirring if necessary, until crystalline silicate is formed. After crystals have thus formed, the reaction mixture is cooled to room temperature, filtered, washed with water, and the crystals are separated.

Furthermore, drying is usually performed at 100° C. or higher for about 5 to 24 hours.

The crystalline silicate produced by the above-mentioned method can be molded into an appropriate size as it is or mixed with a binder etc. conventionally used for catalyst molding, using well-known techniques, and used as a catalyst. used vine.

The crystalline silicate used in the present invention is a regularly porous crystalline material having a certain crystal structure and generally exhibits the X-ray diffraction pattern shown in Table 1.

Table VS: Very strong M: Intermediate S: Strong W: Weak The crystalline silicate obtained by the above hydrothermal synthesis is Na+
It contains alkali metal ions such as ions, and ions of organic nitrogen-containing compounds such as (C3H1)4N+. In order to replace some or all of these ions with hydrogen ions, organic compounds are removed by baking in air at a temperature in the range of 400 to 700°C for 2 to 48 hours, and then the organic compounds are removed by immersion in a strong acid such as hydrochloric acid. A method of dipping directly into H type, or dipping in an aqueous solution of an ammonium compound to form N11. There is a method of forming the material into a mold and then baking it into an H shape.

Ion exchange sites such as alkali metal ions and hydrogen ions in the crystalline silicate obtained by the above method are exchanged with copper ions and further rare earth element ions by the following method. The catalyst of the present invention is obtained by supporting an oxide.

Copper ion exchange is performed by a conventional method such as immersing the crystalline silicate in an aqueous solution containing a mineral acid salt such as copper sulfate or copper nitrate or an organic acid salt such as copper acetate. The concentration of copper ions in the aqueous solution can be arbitrarily selected depending on the desired copper ion exchange rate.
The cations in the crystalline silicate are exchanged with the cations in the crystalline silicate in the form of Cu"Cu0H+. After the ion exchange is completed, the catalyst is thoroughly washed with water and then dried. The copper ion exchange rate of the catalyst used in the present invention is It is essential that it accounts for at least 10% of the total exchangeable cations contained in the crystalline silicate that is the catalyst base, and the higher the exchange rate, the higher the NO decomposition activity, so it is preferably 40 to 180%. If the exchange rate is less than 10%, no effective No decomposition activity is exhibited.

The ion exchange rate of copper indicates the proportion of copper ions in ion exchange sites, and is calculated assuming that two Na'' atoms and one Cu'' atom undergo ion exchange.

Therefore, an exchange rate of 2O0% indicates a state in which all ion exchange sites are ion-exchanged with copper (one Cu is ion-exchanged). When ion-exchanging copper ions and rare earth element ions, a mixed aqueous solution of a copper compound and a rare earth element compound is used in the above step.

As a method for supporting rare earth metals or oxides on crystalline silicate after copper ion exchange, a method is used in which the crystalline silicate is immersed in an aqueous solution of a rare earth element compound, dried, and fired, and further reduced. .

When supporting CuO and rare earth elements on crystalline silicate, a method is used in which the crystalline silicate is immersed in an aqueous solution containing a compound of Cu and rare earth elements, dried, and fired.

The rare earth elements here refer to La, Ce, and Nd. The content of rare earth elements is preferably in the range of 0.1 to 20% by weight (based on the total weight of the catalyst).

The NO decomposition catalyst of the present invention has a wider operating temperature range than conventional catalysts, preferably in the range of 300 to 1000°C,
It is used in the range of 400 to 700°C.

When the catalyst of the present invention is used industrially, it is desirable to form it into an appropriate shape. For example, using an inorganic oxide such as silica or alumina or clay as a binder, and optionally using a forming aid such as an organic substance, the material is formed into a spherical, columnar, or honeycomb shape. The crystalline silicate before being exchanged with copper ions may be shaped in advance, and the size of the shaped body is not particularly limited.

[Example 1] Crystalline silicate was synthesized as follows.

Water glass, ferric sulfate, aluminum sulfate.

Water 36 Na2O-(0,l Pe2O3-0.9^
12O. )・80SlO□・1600H2O, add an appropriate amount of sulfuric acid, and adjust the pH of the mixture to around 9. Propylamine and propyl bromide are added as organic compounds. Fe5Os,
Add 2O times the total number of moles of A12O3, mix well,
It was placed in a 500cc stainless steel autoclave.

The above mixture was heated to 160 ml while stirring at about 50 Orpm.
The reaction was carried out at ℃ for 3 days. After cooling, the solid content was filtered, washed thoroughly with water until the p+ of the washing water became approximately 8, and heated at 110°C for 12 hours.
It was dried for an hour and fired at 550°C for 3 hours.

The crystal grain size of this product is around 1μ, and the composition expressed in molar ratio of oxides is expressed in dehydrated form (H,N
a) zD ・(0,I Pe2'30.9AI2O3
)・80 S+[]2. This is called crystalline silicate 1.

When synthesizing this crystalline silicate 1, it is possible to use hydrochloric acid instead of sulfuric acid among the raw materials, ferric chloride instead of ferric sulfate, or silica sol instead of water glass. A similar silicate was obtained using

Furthermore, similar silicates were obtained by reacting at 170°C or 180°C for 2 days instead of at 160°C for 3 days as the hydrothermal synthesis conditions.

PE the amount of ferric sulfate and aluminum sulfate added when preparing the raw materials for crystalline silicate 1! Crystalline silicates 2 to 4 were prepared by repeating the same operation as in the case of crystalline silicate 1, except that the molar ratio of 2O- and ^l, 0° was changed as shown below.

When preparing crystalline silicate 1, hydrochloric acid was used instead of sulfuric acid, and cobalt chloride, ruthenium chloride, rhodium chloride, lanthanum chloride, cerium chloride, titanium chloride, vanadium chloride, chromium chloride,
Antimony chloride is converted to Pe2O. Crystalline silicates 5 to 13 were prepared by repeating the same operation as for crystalline silicate 1, except that the same number of moles were added. The composition of these crystalline silicates excluding organic compounds is expressed as the molar ratio of oxides (dehydrated form): (H,N
a) zO・(0, lM2O3-0,9A12O3)・8
It was 0 Sin. Here M is Co, Ru, R
h, La, Ce, Ti, V, Cr, Sb
(in numerical order of crystalline silicates 5 to 13).

In addition, in crystalline silica) 1, SiL/(0
, IPezO++ o, 9AIJs) ratio to 2O. 2O
Crystalline silicates 14 and 15 were prepared by repeating the same procedure as for crystalline silicate 1 except that the concentration was changed to 0.

It was confirmed that the powder X-ray diffraction patterns of the above crystalline silicates 1 to 15 showed the patterns shown in Table 1.

10 g of each of the above crystalline silicates 1 to 15 was placed in an aqueous solution in which 1 g of copper acetate was dissolved in 500 cc of water, and an ion exchange operation was performed by stirring at room temperature for 12 hours. After repeating this ion exchange operation three times, wash with water,
After further immersion in a lanthanum nitrate aqueous solution of a predetermined concentration, 1
Dry at 10℃ for 12 hours, bake at 500℃ for 3 hours,
Catalyst 1 supporting 2% by weight of awn3 (based on the total amount of catalyst)
~15 (corresponding to the number of crystalline silicate) were prepared.

Catalysts 1 to 15 were sized into 16 to 32 meshes, and catalysts 0.
5 g was packed into an atmospheric fixed bed flow reactor and an activity evaluation test was conducted under the following reaction conditions. The results are shown in Table 2.

Gas composition: NO: 0.5%, [1,: 1%.

He: balance gas flow rate: INl'h, reaction temperature = 500°C table (2NO→N2+[12)L, and it was found that the selectivity was high.

[Example 2] Crystalline silicate 1 of Example 1 was subjected to Cu ion exchange (Cu ion exchange rate 120%) in the same manner as in Example 1, and an aqueous solution of cerium nitrate, neodymium nitrate, and praseodymium nitrate at a predetermined concentration was prepared. After immersion in water, it was dried at 110°C for 12 hours and calcined at 500°C for 3 hours to prepare catalysts 16 to 18.

Further, the crystalline silicate 1 of Example 1 was placed in an aqueous solution of each nitrate of lanthanum, cerium, and neodymium at a predetermined concentration, and stirred at 80°C for 5 hours to obtain an ion exchange rate of 30% for each of La, Ce, and Nd. After preparing the product, Cu ion exchange was performed in the same manner as in Example 1 (Cu ion exchange rate 100%).
Then, catalysts 19-2O were prepared.

The activity of these catalysts was evaluated in the same manner as in Example 1. The results are shown in Table 3.

All of the reacted NO was converted to 82°0. Table (Example 3) 0.5 g of catalyst 1 from Example 1 was charged into an atmospheric pressure fixed bed flow reactor, and the reaction conditions were changed to evaluate the activity. The test was conducted.

The results are shown in Table 4.

Note that all of the reacted NO was converted to N2,0□.

As described above, the catalyst of the present invention has 1. It was found that the activity was high even when using a gas containing S02, and that the activity did not change over time.

[Example 4] A mixture of ferric chloride and chromium chloride was used instead of ferric sulfate when preparing the raw material for crystalline silicate 1 in Example 1,
36 Na2D ・(0,09Fe2D3・0,01
Cr2L + o, 9^12O3) -8OSin,
Crystalline silicate 16 was obtained in the same manner as crystalline silicate 1, except that the molar ratio was adjusted to -160082O, and Cu ion exchange was performed in the same manner (however, the ion exchange operation was repeated twice). , (Cu ion exchange rate 110%) La, O in the same method.

A catalyst 22 was prepared in which two weights of the following were supported.

As a result of the same activity evaluation as in Example 1, the No. conversion rate was 8.
It was 0%.

[Comparative example]

36Na2[] ・Al1O0・80S10 without adding ferric sulfate when preparing raw materials for crystalline silicate 1 in Example 1
2.1600)1. [Blend to have a molar ratio of I,
After adding an appropriate amount of hydrochloric acid to the mixture so that the pH of the mixture was around 9, the same operation as in Example 1 was repeated except that tetrapropylammonium bromide was added 20 times as much as Al2O3 as an organic compound.

As in Example 1, the activity was evaluated under the same conditions as ion exchange with copper (Cu ion exchange rate 105%), and the No conversion rate was as high as 74%, but the conversion rate of reacted NO to N2 was , 72%, indicating that there are many by-products such as NO2.

〔Effect of the invention〕

As shown in the examples above, the catalyst containing copper in crystalline silicate of the present invention can reduce NOx in exhaust gas by N,
0. It can be used as a catalyst to decompose into

Claims (1)

[Claims] In a dehydrated state, the molar ratio of oxides is (1.0
±0.4) R_2O・[aM_2O_3・bAl_2O
_3]・ySiO_2 (in the above formula, R: alkali metal ion and/or hydrogen ion, M: group element, rare earth element,
Ions of one or more elements of the group consisting of titanium, vanadium, chromium, niobium, and antimony, a+b=1, a>0
, b>0, y>12) A catalyst for decomposing nitrogen oxides, comprising a crystalline silicate having a chemical composition of , b>0, y>12) containing copper and a rare earth element.