JPH03143547A - Catalyst for decomposition of nitrogen oxide - Google Patents

Abstract

PURPOSE:To obtain a catalyst having very high activity to the decomposition reaction of NO and maintaining the activity by incorporating copper into crystalline silicate having a specified compsn. CONSTITUTION:Crystalline silicate represented by a chemical formula (1.0+ or -0.4)R2 O.(aM2O3 bAl2O3).ySiO2 (where the oxides show molar ratio, R is an alkali metal ion and/or H, M is an ion of an element such as a group VIII element or a rare earth element, a+b=1, a>0, b>0 and y>12) in a dehydrated state is used. Copper is incorporated into the crystalline silicate by immersion in an aq. soln. of copper sulfate, copper nitrate, etc., or other method. The resulting catalyst has very high activity to the decomposition reaction of NO and maintains the activity over a long time.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a catalyst that removes NOx from gas containing nitrogen oxides (hereinafter abbreviated as NOx), and more particularly relates to a catalyst that directly decomposes NOx. .

[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 under development, but it requires a reducing agent such as ammonia, hydrogen, or carbon monoxide, and it also requires a reduction agent to recover or decompose the unreacted reducing agent. Requires special equipment. 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 [Surface, author,
Toshio Uchijima, νol.

18. Nα3 (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 ion-exchanged with copper has been proposed, but although the NO decomposition activity is high, the selectivity for converting NO to N2 (2NO-, N,
+o2) is low. (Unexamined Japanese Patent Publication No. 60-12
5250).

[Means to solve the problem]

The purpose of the present invention is to solve the above-mentioned problems of the prior art, and the present invention is based on the fact that copper is ion-exchanged with crystalline silicate having a specific composition and crystal structure. The present inventors have found that not only does it exhibit activity, but it also has high selectivity for NO to N2, and 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)R2[]' [a-M2o3-b
-A12o3]・ysio2 (in the above formula, R is an alkali metal ion and/or hydrogen, M: one or more elements selected from the group consisting of group ■ elements, rare earth elements, titanium, vanadium, chromium, niobium, and antimony) ion, a+b
=1. a>0. The present invention is a nitrogen oxide decomposition catalyst characterized by containing copper in a crystalline silicate having the chemical formula: b>O, 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"≠Cu") 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. It is thought that the structural stability, heat resistance, etc. act in a complex manner.

The present invention will be explained in detail below.

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

XM2/II O"^1203 ・ys+zo HZ+
(20 (where n is the valence of the cation M, X is 0.8~
A number in the range of 2, y is a number greater than or equal to 2, and 2 is a number greater than or equal to 0. ) Its basic structure consists of a Si tetrahedron with silicon at its center and four oxygen atoms coordinated at its vertices, and an AIO tetrahedron with aluminum at its center instead of silicon.
+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 charge of the AIOi tetrahedron is electrically neutralized by bonding with a cation such as an alkali metal or an alkaline earth metal. Generally, the pores formed in this way have a size of 2 to 3 to more than 10 pores, but AlO
The pore size can be changed by replacing the metal cation associated with the tetratrahedron with another metal cation 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, mordenite, clinoptilolite, etc., and zeolite A is the bottom zeolite.

X, Y, large, boat mordenite, 23M5, 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. Although the crystalline silicate of the present invention does not exist in nature, it can be obtained 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. This is accomplished 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 platforms, such as solid silica powder, colloidal silica, or silicates such as water glass. etc. are 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: primary organic amines such as n-propylamine and monoethanolamine
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.), other quaternary ammonium salts such as tetrapropylammonium salts, etc. Nitrogen-containing compounds: These various organic compounds such as pyridine, pyrazine, and pyrazole are illustrative, and the present invention is not limited thereto.

The crystalline silicate of the present invention has a part of A1 in the structure of conventional zeolite replaced with a group II element, a rare earth element, titanium, vanadium, chromium, niobium, or antimony, and further contains S102/(M203 Eighteen + twenty
3) It is characterized by a ratio of 12 or more, and is produced from a reaction mixture having the following molar composition.

5iO7/(M203+Al203) 12~3
000 (preferably 20-200) OHVSiOz O-1.0 (preferably 0.2-0.8) lf, o/5iOz 2-1000 (preferably 10-200) Organic nitrogen-containing compound/ (M203+Al203 ) (preferably 5 to 50) The crystalline silicate of the present invention is stabilized by heating the raw material mixture at a temperature and for a time sufficient to form the crystalline silicate, but the hydrothermal synthesis temperature is 80 to 300. The temperature is preferably in the range of 130 to 200°C, and the hydrothermal synthesis time is 0.5 to 14 days, preferably 1 to 10 days.

Although the pressure is not particularly limited, 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. can be used.

The crystalline silicate of 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.

The crystalline silicate obtained by the hydrothermal synthesis shown in the table above is Na+
It contains alkali metal ions such as (C3L), ions of organic nitrogen-containing compounds such as N''. In order to replace some or all of these ions with hydrogen ions, it is necessary to After removing organic nitrogen-containing compounds by calcination at a temperature in the range of 2 to 48 hours, immersion in a strong acid such as hydrochloric acid to form H-form directly, or immersion in an aqueous solution of an ammonium compound to form NH4 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 by the following method, and the catalyst of the present invention (hereinafter referred to as
(abbreviated as “this catalyst”) is asked.

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 in the form of u''CuDH+. After ion exchange, the catalyst is obtained by thoroughly washing with water and drying. Copper ion exchange rate of the catalyst is essential to be at least 10% of the total exchangeable cations contained in the crystalline silicate that is the catalyst base, and the higher the exchange rate is, the higher the NO decomposition activity is, so it is preferably 40~ The range is 200%.

No effective No decomposition activity is shown at an exchange rate of 10% or less.

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 200% indicates a state in which all ion exchange sites are ion-exchanged with copper (one Cu is ion-exchanged).

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

When using this catalyst industrially, it is desirable to use it in an appropriate bottom 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 bottom shape is formed into a spherical, columnar, or honeycomb shape.

A crystalline silicate that has not yet been exchanged with copper ions is shaped into a bottom shape and the formed body is exchanged with copper ions can also be considered as the catalyst of the present invention. The size of the molded body is not particularly limited.

[Example 1] The crystalline silicate was prepared as follows.

Water glass, ferric sulfate, aluminum sulfate, water to 36Na20' (0,1Fe2 [13" 0.9A]
203) ' Mix to a molar ratio of 80SiL/1600H20, add an appropriate amount of sulfuric acid to make the pH of the mixture around 9, and add propylamine and propyl bromide as organic nitrogen-containing compounds. was added in an amount 20 times the total number of moles of Fe2O+ and 81203, mixed well, and placed in a 500CC stainless steel autoclave.

The above mixture was heated at 160 rpm while stirring at approximately 500 rpm.
The reaction was carried out at ℃ for 3 hours. After cooling, the solid content was filtered, thoroughly washed with water until the pH of the washing water became approximately 8, and then heated at 110°C for 1 hour.
It was dried for 2 hours and fired at 550°C for 3 hours.

The crystal grain size of this product is around lμ, and the composition expressed in terms of molar ratio of oxides is (H,Na)20'(0,IFf32L'0
．． 9A1.03)" 80SiL. This is referred to as crystalline silicate 1.

When making this crystalline silicate 1, it is possible to use nitric acid instead of hydrochloric acid, lanthanum nitrate instead of dentane chloride, or silica sol instead of water glass among the raw materials. A similar silicate was obtained.

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.

Same as for crystalline silicate 1, except that the amounts of ferric sulfate and aluminum sulfate added when preparing the raw materials for crystalline silicate 1 were converted into molar ratios of Fe, O, and Al2O3 and changed as shown below. Repeat the operation to obtain crystalline silicate 2
~4 was prepared.

When preparing crystalline silicate ■, hydrochloric acid is 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 into oxide as Fe2O
Crystalline silicate 1 except that the same number of moles as + was added.
Crystalline silicates 5 to 13 were prepared by repeating the same operation. The composition of these crystalline silicates, excluding organic nitrogen-containing compounds, is expressed as the molar ratio of oxides (in dehydrated form): (H,Na)20'(0,1M203'0.
9AI, 03)' 80Si[12. Here, M is Ca, Ru, Rh, La.

Ce, Ti, V, Cr, Sb (in numerical order of crystalline silicates 5 to 13).

In addition, in crystalline silicate 1, 5102/
(0,IFeJ,+0.9A1203) ratio to 20.2
Crystalline silicate 14 and 15 were prepared by repeating the same operation as for crystalline silicate 1, except that 00 was used.

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 were 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,
Catalysts 1 to 15 (corresponding to the crystalline silicate numbers) were prepared by drying at 100° C. for 12 hours.

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 group 11j2 + NO: 0.5%, 0.1%, 11
e Balance gas flow rate: INl/h, reaction temperature: 50
0℃ table Note that all of the reacted NO is converted to N2,0□ (2NO→
N2+02), indicating high selectivity.

[Example 2] 0.5 g of the catalyst 1 of Example 1 was charged into an atmospheric fixed bed flow reactor, and an activity evaluation test was conducted under different reaction conditions. The results are shown in Table 3.

Note that all of the reacted NO was converted to N2.02.

As described above, it was found that the catalyst of the present invention has high activity even when using a gas containing S02, and that the activity changes little over time.

[Example 3] 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, and 36Na20'(0,09Fe2L' 0.0IC
rzL' 0.9AI203)・80SiO□・16
Crystalline silicate 16 was obtained in the same manner as crystalline silicate 1, except that it was prepared in a molar ratio of 00H2[1], and Cu ion exchange was performed in the same manner (however, the ion exchange operation was repeated twice). 16 (Cu ion exchange rate 110%) was obtained.

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

[Comparative example]

When preparing raw materials for crystalline silicate (■) in Example 1, ferric sulfate was not added.
The mixture was mixed to have a molar ratio of 0H, 0, and an appropriate amount of hydrochloric acid was added thereto so that the pH of the mixture was around 9. After that, tetrapropylammonium bromide was added as an organic nitrogen-containing compound to AIzOz. The same operation as in Example 1 was repeated except that the amount was added 20 times.

As in Example 1, ion exchange with copper (Cu ion exchange rate 105%) and activity evaluation under the same conditions revealed that 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 reduces NOx in exhaust gas to N2.
It can be effectively used as a catalyst for decomposing into 02.

Claims (1)

[Claims] In a dehydrated state, the molar ratio of oxides is (1.0±
0.4) R_2O・[a・M_2O_3・b・Al_2
O_3]・ySiO_2 (in the above formula, R is an alkali metal ion and/or hydrogen, M: group VIII element, rare earth element,
Ions of one or more elements selected from the group consisting of titanium, vanadium, chromium, niobium, and antimony, a+b=
1, a>0, b>0, y>12) A nitrogen oxide decomposition catalyst characterized by containing copper in a crystalline silicate having the chemical formula: