JPH08323151A - Method for purifying NOx-containing exhaust gas - Google Patents

Abstract

(57) [Summary] [Structure] NOx-containing exhaust gas in the presence of a catalyst for purifying NOx-containing exhaust gas, which comprises synthetic mordenite containing iron in the mordenite structure by using a raw material containing iron during the synthesis of mordenite, Purification is performed using a reducing agent composed of aqueous ammonia, an aqueous solution of an ammonium salt, or an aqueous solution of an amine compound. Aqueous solutions of ammonium salts include ammonium formate and ammonium carbonate.
Aqueous urea or the like is used as the aqueous solution of the amine compound. [Effect] According to the present invention, an effective and excellent NOx removal effect can be obtained by using a specific catalyst and a specific reducing agent. The NOx concentration in the exhaust gas is, for example, 73 pp
NOx removal rate 70-87 even when m is extremely low
%, An extremely excellent purification effect can be obtained, and therefore, an extremely small amount of NOx in the lean combustion exhaust gas from a gas engine or the like can also be effectively reduced and purified.

Description

Detailed Description of the Invention

[0001]

The present invention relates to the exhaust gas containing NOx,
By using a NOx-containing exhaust gas purification catalyst composed of synthetic mordenite containing iron (Fe) in the structure of mordenite by using a raw material containing iron during the synthesis of mordenite, a specific compound is present as a reducing agent. The present invention relates to a method for purifying by treating.

[0002]

2. Description of the Related Art When incinerating industrial waste or municipal waste, it depends on the origin, type, composition, etc. of the waste.
NOx, CO, or SOx, hydrogen chloride, odor, etc. are generated. For this reason, various measures have been taken against exhaust gas containing these substances, and further research and development are under way. In this respect, it is a goal to use automobiles, thermal power generation, gas engines, etc.
The same applies to the exhaust gas discharged from the generation system and the like.

Among the harmful components in exhaust gases, various methods are known as so-called flue gas denitration technology for treating NOx (nitrogen oxide), and a catalyst is used for the treatment. The catalytic reduction method for purification usually attracts special attention because it usually changes NOx into N ₂ and makes it harmless. There are various catalysts used in this catalytic reduction method, and a zeolite-based catalyst is known as one of them. This zeolite is
The catalyst can be effectively used not only as the catalyst itself but also as a carrier for the catalyst.

Zeolite is composed of aluminosilicate in its composition, is crystalline and has a three-dimensional network structure, is bound to water weakly retained therein, ie, zeolitic water, and is a cation having a large ion exchange property. However, there are many types depending on the composition ratio of the alumina (Al ₂ O ₃ ) component and the silica (SiO ₂ ) component, the crystal structure, etc., which make up the component. Examples include analcime, chabazite, mordenite, faujasite, clinoptilolite and the like.

Not only natural zeolite but also synthetic zeolite produced by hydrothermal synthesis and the like are produced and commercially available. Depending on its use, reaction, etc., its modification,
Modifications and other improvements have been made successively. Of these, N
As one system related to a catalyst for purifying Ox-containing exhaust gas, a proposal has been made to improve the purification efficiency and the like by supporting a metal such as copper or iron on zeolite.

[0006] For example, in Japanese Unexamined Patent Publication (Kokai) No. 2-194819, an exhaust gas containing nitrogen oxides is introduced into an exhaust gas containing oxygen by introducing the exhaust gas containing nitrogen oxides onto an acid-resistant zeolite catalyst containing Cu and / or Fe, and also Ce and Mo. A method of reducing existing nitrogen oxides using ammonia has been introduced. The method for incorporating these metals is to use existing zeolite by ion exchange, impregnation, or precipitation. However, it is not included in the synthesis process of the zeolite itself.

Further, JP-A-2-4453 proposes a method for producing a denitration catalyst which uses a zeolite carrying a transition metal and catalytically reduces nitrogen oxides in flue gas in the presence of ammonia. Here, the zeolite catalyst is
l, Si, a compound of an alkali metal or an alkaline earth metal and a salt of a transition metal are used as raw materials, the molar ratio of the raw material components is set to a predetermined ratio, and the gel solution having an adjusted effective alkali concentration is hydrothermally treated. It is said to be manufactured.

As the above-mentioned raw material transition metal, specifically, C
u, Fe, Ni, Co, and V are shown, and the zeolites obtained here are mordenite and pentasil-type zeolite. However, most of the specific examples described therein carry Cu, and only one example (Example 23) carrying Fe is shown. Moreover, in this case, ammonia as a reducing agent is used as ammonia itself, not as an aqueous solution, and
The quantitative ratio to x is 1.2 times (NOx = 200pp
m, NH ₃ = 240 ppm) is also used. The denitration rate is 96%, but no description of temperature conditions is found.

By the way, NO in the NOx-containing exhaust gas
In the catalytic reduction denitration method for purifying x using a catalyst, a reducing agent is required in addition to the catalyst. Generally, ammonia, hydrogen, hydrocarbons such as propane, carbon monoxide, etc. can be used as the reducing agent, but the effective reducing agent types include the composition of exhaust gas to be treated, the type of catalyst, and the reaction temperature. It is different for each condition such as. Among them, ammonia is particularly adopted as a practical denitration method because it has excellent selective reactivity with NO. For example, JP-A-2-194819 and JP-A-2-445 are mentioned above.
In all of the publications, the use of this ammonia is indispensable as its premise.

In this respect, according to Japanese Patent Application Laid-Open No. 2-203923, ammonia itself is harmful and dangerous, and at low temperatures, salts such as ammonium sulfate are formed on the catalyst surface, leading to a reduction in the denitration rate. However, it has been proposed to use ammonium salts or amine compounds as an alternative. As the ammonium salt, ammonium carbonate, ammonium hydrogencarbonate, ammonium formate and ammonium acetate are shown, and as the amino compound, urea is exemplified. On the other hand, as the catalyst, known catalysts such as carrier-supporting type, non-supporting type and Raney-type can be used, and in particular, anatase-type titania supported with a metal oxide such as V ₂ O ₅ is used. Although it is said that it exhibits excellent denitration performance, there is no description about the zeolite-based catalyst therein, and specifically, only this V ₂ O ₅ catalyst is described.

On the premise of these known techniques, the inventors of the present invention, regarding the catalytic reduction denitration method of NOx-containing exhaust gas, the catalyst itself used here, the combination of the catalyst and the reducing agent, the interaction between the two, etc. Experiments and researches from various aspects were made, and among the zeolites as the catalyst or its support, particular attention was paid to mordenite to improve or improve it, and to obtain a series of results in the case of using ammonium acetate as a reducing agent. After that, they applied for a patent (Japanese Patent Application No. 6-42000, Japanese Patent Application No. 6-194799, Japanese Patent Application No. 6-27609, etc.).

[0012] In these inventions, it is indispensable to use ammonium acetate as the reducing agent. Among them, in Japanese Patent Application No. 6-42000, a zeolite-based catalyst is used as the catalyst. As a result, both NOx and CO in the exhaust gas can be effectively removed, and due to the unique characteristics of ammonium acetate, it is possible to obtain an effect of removing more than the original equivalent amount to the NOx amount. Also, in Japanese Patent Application No. 6-194799, NOx in exhaust gas is extremely effectively removed by using a "mordenite catalyst in which iron is ion-exchanged and supported" or a "mordenite catalyst modified by iron" as a catalyst. It is a thing.

Further, in Japanese Patent Application No. 6-276009, "a synthetic mordenite catalyst containing iron in its structure by using a raw material containing iron during the synthesis of mordenite" is used as the NOx-containing exhaust gas catalyst. As a result, for example, the NOx removal rate equivalent to or higher than the NOx removal rate under instantaneous and severe purification treatment conditions reaching a space velocity (SV) of 220,000 h ⁻¹ and at a relatively low treatment temperature of 300 to 325 ° C. can get.

The inventor of the present invention pays attention to the peculiar NOx purification characteristics when using "a synthetic mordenite catalyst containing iron in its structure by using a raw material containing iron during the synthesis of mordenite". , When this catalyst was not an ammonium acetate reducing agent but was used in combination with a reducing agent other than this, an experiment and a study were conducted to find out whether the catalyst is ammonia water, an aqueous solution of an ammonium salt other than ammonium acetate, or an amine compound. It has been found that when combined with the aqueous solution of 1., an excellent NOx purification effect equivalent to or higher than the case where the ammonium acetate reducing agent is used can be obtained.

[0015]

That is, the present invention is
NOx containing NOx-containing exhaust gas composed of "synthetic mordenite in which iron is contained in the structure of mordenite by using a raw material containing iron in mordenite synthesis"
An object of the present invention is to provide a method for purifying NOx-containing exhaust gas, which comprises using, as a reducing agent, aqueous ammonia, an aqueous solution of an ammonium salt other than ammonium acetate, or an aqueous solution of an amine compound in the purification treatment with the exhaust gas-purifying catalyst. And

[0016]

The present invention is directed to a catalyst for purifying NOx-containing exhaust gas, which is made of synthetic mordenite in which iron is contained in the mordenite structure by using a raw material containing iron during the synthesis of mordenite. The present invention provides a method for purifying NOx-containing exhaust gas, which comprises treating with a reducing agent consisting of aqueous ammonia, an aqueous solution of ammonium salt (excluding ammonium acetate) or an aqueous solution of an amine compound in the presence of the above.

In this case, examples of the reducing agent include aqueous ammonia (aqueous solution of ammonium hydroxide), aqueous solution of amine compound such as urea and formamide, and aqueous solution of ammonium salt such as ammonium formate, ammonium oxalate, ammonium carbonate and ammonium bicarbonate. be able to. In addition, an aqueous solution of cyanuric acid or the like can be used. As described above, the case of using ammonium acetate has been previously developed and filed, and the term “ammonium salt” as used herein means that ammonium acetate is not included.

The above "catalyst for purifying exhaust gas of NOx containing synthetic mordenite in which iron is contained in the structure of mordenite by using a raw material containing iron during the synthesis of mordenite" produces mordenite by hydrothermal synthesis. In addition to the alumina raw material such as sodium aluminate as the synthetic raw material component, silica raw material such as amorphous silica and alkali metal compound or alkaline earth metal compound such as caustic soda, as the raw material component itself. It is produced by allowing a raw material containing iron such as iron nitrate to exist and subjecting the aqueous solution of the raw material to a hydrothermal reaction in an autoclave.

Here, as the alumina raw material, in addition to sodium aluminate, alumina sol, alumina gel, aluminum sulfate, aluminum nitrate, aluminum hydroxide or the like can be used, and as the silica raw material, amorphous silica or water glass is used. , Silica sol, silica gel, diatomaceous earth, clay mineral and the like can be used. In the present invention, in addition to these raw materials, a raw material containing iron as the raw material component itself is present. As the raw material containing iron, in addition to the above iron nitrate, iron chloride, iron bromide, iron oxide, iron sulfate , Organic iron compounds and the like can be used. Further, the quantitative ratio of each of these raw materials is such that an amount corresponding to the composition capable of obtaining a product having a mordenite structure is used.

FIG. 1 shows the results of an experiment conducted on the relationship between the amount of Fe contained in the corresponding mordenite product obtained by varying the amount of the Fe raw material in the manufacturing raw material during the synthesis of mordenite. Yes, in the raw material "Fe /
The "Fe / (Al + Fe)" molar ratio in the produced mordenite with respect to the (Al + Fe) "molar ratio is shown.

As shown in FIG. 1, the amount of Fe added to the raw material is contained in the produced mordenite structure almost as it is until the "Fe / (Al + Fe)" molar ratio is slightly less than 0.4, and thereafter the amount of Fe is gradually increased. It can be seen that the rate of incorporation into the formed mordenite structure is reduced. Further, in Na-type mordenite, Na / Al (atomic ratio) = 1,
Even if Fe is present in the mordenite structure,
Na was contained in an amount corresponding to Na / (Al + Fe) = 1, and no change was observed in this content.

Mordenite is a kind of aluminosilicate, and is orthorhombic and has a tunnel structure therein. The catalyst of the present invention has this structure, and its composition has a Si / Al molar ratio. NOx in the range of 5 to 50 (= 10 to 100 in SiO ₂ / Al ₂ O ₃ molar ratio)
It can be effectively applied as a contained exhaust gas catalyst. Therefore, the quantitative ratio of the silica raw material and the alumina raw material is
It can be selected depending on these final compositions, and it is necessary. The quantitative ratio of the Fe raw material is shown in FIG.
Based on the tendency or fact as shown in the above, the Fe content in the product is added to be about 0.5 to 15.0% by weight,
use.

As the heating conditions in the hydrothermal reaction, the temperature is about 100 to 200 ° C., preferably 150 to 19
It is carried out at about 0 ° C, and the pressure during the reaction is autoclave.
It can be carried out under autogenous pressure or higher pressure in the bath. Although this reaction can be carried out in a stationary state, iron is surely and strongly present in the structure of the produced mordenite, and in terms of its yield, reaction rate, etc., under stirring conditions, especially under mild stirring. It is desirable to carry out.
Further, regarding the operation of mixing the respective raw materials, to the aqueous solution containing the alumina raw material, the silica raw material and the alkali metal compound or the alkaline earth metal compound, the aqueous solution of the raw material containing iron is gradually added dropwise under stirring conditions. By devising a uniform mixed solution or the like, iron can be surely present in the structure itself of the produced mordenite.

The "synthetic mordenite in which iron is contained in the structure of mordenite by using a raw material containing iron in the synthesis of mordenite" obtained through the above-mentioned production process is a compound containing a specific reducing agent according to the present invention. N when used
It has excellent characteristics as an Ox-containing exhaust gas purification catalyst,
This catalyst has an excellent NOx purification ability even when the NOx concentration in the exhaust gas is extremely low, and exhibits an excellent catalytic effect.

The above-mentioned catalyst of the present invention is in the form of particles in a fluidized bed form or a fixed bed form, in the form of pellets in a fixed bed form, or in the form of a monolith supported on a monolith carrier (in this case, in this case). It is used by arranging it so that its monolith opening faces the flow direction of the exhaust gas in the reaction tube), and it is particularly preferable to use it in the monolith form. In this and the form, the experimental results showed that the NOx removal rate tended to decrease (albeit slightly) in the presence of CO ₂ and / or CO, whereas in the monolith form, the reason was Unknown,
This is because the presence or absence of CO ₂ and / or CO does not affect the NOx removal rate.

Among the above items, the monolith body in the case of carrying out in a monolith form supported on a monolith carrier is
(1) Using "a synthetic mordenite containing iron in the structure of mordenite by using a raw material containing iron during the synthesis of mordenite" using a binder such as silicate (water glass) or phosphate Mold it into a monolith,
Or (2) "Synthetic mordenite containing iron in the structure of mordenite by using a raw material containing iron during the synthesis of mordenite" in a preformed monolithic carrier.
It can be produced by supporting.

As the form of this monolith body, any one can be used as long as it has a honeycomb shape in cross section or a shape conventionally known as a monolith carrier. Figure 2 (a)
2A to 2B are one or two examples that can be used in the present invention, and FIGS. 2A to 2B are enlarged cross-sectional views, that is, the cross sections are enlarged and schematically shown. In addition, in the case (2) in which the above-mentioned synthetic mordenite is supported on the preformed monolith carrier of the above-mentioned two modes, the material of the monolith carrier is not particularly limited, but ceramics or metal is preferably used. As the ceramic, cordierite or the like is preferably used, and as the metal, iron-aluminum-chromium alloy or stainless steel can be preferably used.

In this case, as one mode of the supporting method,
During the synthesis, the iron-containing synthetic mordenite powder was mixed with water and a binder such as alumina sol and stirred, and the monolith carrier was impregnated into this aqueous suspension (that is, after wash coating), and then an air gun. The monolith-supported catalyst can be obtained by removing excess deposit slurry by other appropriate means, drying and then calcining. After the firing, excess deposits are further removed by an air gun or the like, if necessary.

Further, the purification method of the present invention is usually carried out by passing exhaust gas through a catalyst layer arranged in a reaction tube or the like. In this case, NOx in the NOx-containing exhaust gas
The amount of the reducing agent added with respect to the amount does not need to be used in excess with respect to NOx, and an equivalent amount or a slight excess is sufficient.
This makes it possible to eliminate slip ammonia in the exhaust gas after the purification treatment, and the present invention is also advantageous in this respect.

Further, as a method of adding the reducing agent, ammonia water, an aqueous solution of an ammonium salt or an aqueous solution of an amine compound is injected into the exhaust gas stream at (a) the catalyst layer or upstream thereof by spraying or other method. b) The catalyst itself is previously impregnated and supported, (c) these (a) and (b)
Although various modes such as the combined use of the above can be adopted, it is preferable to adopt the mode (a) among these for stable operation over a long period of time.

[0031]

EXAMPLES Examples of the present invention will be described below, but it goes without saying that the present invention is not limited to these examples. In this example, sequentially, along with Comparative Example, a production example of a synthetic mordenite containing iron in its structure in the production process, a preparation example of a monolith-supported catalyst in which the synthetic mordenite catalyst is supported on a monolith carrier, and these are used. An example of a purification test of NOx-containing exhaust gas carried out as described below.

<< Production Example of Synthetic Mordenite Catalyst Containing Iron in Structure During Synthesis >> First, commercially available sodium aluminate, sodium hydroxide and amorphous silica (Nipsil VN3, manufactured by Nippon Silica Industry Co., Ltd., Product name)
And iron nitrate nonahydrate [Fe
_{(NO 3) 3 · 9H 2} O ] was prepared. Of these, sodium aluminate and sodium hydroxide were used as a beaker (capacity:
(2000 ml) was added to distilled water, stirred and dissolved, and amorphous silica was added to this to prepare a liquid A. On the other hand, iron nitrate 9
The hydrate was dissolved in distilled water in a beaker (volume: 1000 ml) to prepare a solution B. The quantitative ratios of the respective raw materials and the distilled water in the respective liquids A and B are as shown in Table 1.

Next, with respect to the total amount of each liquid A, each liquid B was gradually added dropwise with stirring to add the total amount thereof to form a uniform mixed solution, which was provided with a rotary stirrer inside Teflon. After transferred to a stainless steel autoclave equipped with a container (internal volume: 2000 ml) and sealed, hydrothermal synthesis was carried out. As for this condition, while maintaining the temperature at 180 ° C,
The treatment was carried out under stirring (300 rpm), this treatment state was continued for 3 days and nights (72 hours), the heating was stopped and the mixture was allowed to stand and cooled to room temperature by natural cooling. Subsequently, the product was filtered, washed with water until the pH of the slurry became 10 or less, and then dried overnight at a temperature of 80 ° C. to obtain a powdery product.

X-ray diffraction analysis (XRD) of these products
Upon application, each sample exhibited a clear mordenite structure (Na type). In addition, as a result of X-ray fluorescence analysis, it was found that in all the samples obtained by adding iron nitrate nonahydrate to the synthetic raw material, a predetermined amount of F was obtained.
It was found that e minutes were contained in the product.
The above conditions and results for each sample (manufacturing example) are as described in Table 1. In Table 1,
The case of manufacturing without adding the liquid B is shown as a comparative example.

Then, 1 mol of each of the Na-type Fe-containing mordenites (Products of Production Examples Nos. 1 to 5 in Table 1) was added.
/ L (162 g / 2000 ml) ammonium nitrate aqueous solution was added (about 5 times equivalent of Na = 1000 ml / Na-type Fe mordenite 40 g), and the mixture was stirred at a temperature of 60 ° C. for 1 hour, filtered, washed with water, and then treated. Was repeated again, and then dried at a temperature of 110 ° C. for about 5 hours. Further, it was fired at 500 ° C. for 2 hours to obtain H-type Fe-containing mordenite for each of the above-mentioned samples. In addition, the H-type was similarly used for the comparative example. When each sample obtained by converting the Na-type Fe-containing mordenite into the H-type was subjected to the fluorescent X-ray analysis in the same manner as described above, no change was observed in the Fe content.

<< Preparation Example of Monolith-Supported Catalyst >> The respective synthetic mordenite powders obtained in the above << Preparation example of the synthetic mordenite catalyst containing iron in the structure during synthesis >> and the comparative mordenite powders were respectively applied to the monolith carrier. It was carried as follows. This carrier is a cordierite honeycomb carrier obtained by cutting out a carrier having the cross-sectional shape shown in FIG. 2 (a) into a cylindrical shape and having a diameter of 20 mmφ (radius r = 10 m.
m = 1 cm), length L = 23 mm, and number of cells 200 cells / inch square.

On the other hand, 20 g of each catalyst powder was added to distilled water 30
g and 20 g of alumina sol (Alumina sol-200, manufactured by Nissan Chemical Industries, Ltd.) were mixed and stirred to obtain an aqueous suspension. The above-mentioned cordierite honeycomb type carrier was impregnated in this aqueous suspension for 30 seconds to perform wash coating, and then an excess attached slurry was removed by an air gun, and the temperature was kept at 115 ° C for 1 hour. And dried. This process 3
Repeated times. Next, this dried product was held at a temperature of 110 ° C. for 6 hours, and subsequently calcined at a temperature of 500 ° C. for 2 hours, and excess deposit was removed by an air gun to obtain a monolith-supported catalyst. The amount of catalyst supported on these honeycomb-supported catalysts was as shown in Table 1.

<< Purification test >> Each of the test catalysts obtained above (Table 1
In Comparative Example and Production Example No. Using the monolith-supported H-type catalysts 1 to 5), a purification test of exhaust gas containing NOx was performed. The test catalysts used in Examples 1 to 9 are as described in "Catalyst type" in Table 2. Exhaust gas to be treated is NO = 73 ppm, CO = 909 ppm, C
O ₂ = 6.8%, O ₂ = 9.1%, steam (steam)
= 9.1%, using a gas containing N ₂ = balance amount, also shown in Table 2, the space velocity (SV) in the Examples 1~8 66000h ^-1, Example 9, 99000H ^-1, processing The temperature was 350 ° C., 375 ° C. and 400 ° C., respectively.

In this purification test, urea water, an aqueous solution of ammonium formate and ammonium carbonate, and ammonia water were used as a reducing agent, and these were sprayed into the reaction tube immediately before the catalyst bed, and the reducing agent amount was 73 ppm in the exhaust gas to be treated. (N conversion: That is, for example, in the case of urea, "H ₂ N-CO-N
It was carried out while injecting so as to become 1/2) of "H ₂ ".
The results are shown in Table 2. Here, the NOx removal rate is calculated by the following equation (1), where the NOx concentration before the treatment is X and the NOx concentration after the treatment is Y.

As shown in Table 2, Production Example No. With the catalysts 1 to 5, N in the exhaust gas in the presence of the above reducing agents such as urea water
It is clear that Ox is removed and purified very effectively. The NOx removal rate is zero% at any temperature in the comparative example, whereas in Examples 1 to 8, both show a high rate of 70% or more at the reaction temperature of 350 ° C. and 375 ° C. and 400. 80 ° C (except for Example 7)
The NOx removal rate is not less than%. In Example 9, the space velocity was 99000 h ^-1, that is, 1.5 in Examples 1 to 8.
Although it was carried out twice, the removal rate was still 67% at the reaction temperature of 375 ° C. (NO concentration in exhaust gas: decreased from 73 ppm to slightly less than 25 ppm), showing an effective removal effect.

Further, FIG. 3 shows that in Example 3 (reducing agent:
(Urea water), Example 8 (reducing agent: ammonia water), and the case of using an aqueous solution of ammonium acetate as a reducing agent are graphs comparing experimental data at reaction temperatures of 300 ° C to 425 ° C. . As is clear from FIG. 3, all of these three examples show high NOx conversion rates (NOx removal rates), but especially when urea water is used as a reducing agent, NOx exceeding 80% at a temperature of 350 ° C. or higher.
The removal rate is shown.

[0042]

According to the purification method of the present invention, "NOx-containing exhaust gas purification catalyst consisting of synthetic mordenite containing iron in the structure during the synthesis of mordenite" is used as a catalyst, and ammonia water is used as a reducing agent. By using an aqueous solution of an ammonium salt (excluding ammonium acetate) or an aqueous solution of an amine compound, an effective and excellent NOx removal effect can be obtained.

The NOx concentration in the exhaust gas is 73 p, for example.
NOx removal rate 70 to 8 even at extremely low pm
You can get a very good purification effect of 7%,
Therefore, it is possible to effectively reduce and purify even a trace amount of NOx in the lean combustion exhaust gas from a gas engine or the like. Further, in the purification method of the present invention, the amount of the reducing agent added to the NOx amount in the NOx-containing exhaust gas does not need to be excessively used with respect to NOx, and an equivalent amount or a slight excess is sufficient. The slip ammonia in the exhaust gas can be eliminated.

[0044]

[Table 1]

[0045]

[Table 2]

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the amount of Fe in a manufacturing raw material and the amount of Fe contained in generated mordenite.

FIG. 2 is a view (schematic cross-sectional view) showing an example of a monolith catalyst applied in the present invention.

FIG. 3 is a graph showing NOx conversion rates (NOx removal rates) when Examples 3, 8 and an ammonia acetate reducing agent were used.

Claims (5)

[Claims] 1. A NO composed of synthetic mordenite in which iron is contained in the mordenite structure by using a raw material containing iron in the NOx-containing exhaust gas when mordenite is synthesized.
A method for purifying NOx-containing exhaust gas, which comprises treating with a reducing agent consisting of aqueous ammonia, an aqueous solution of an ammonium salt (excluding ammonium acetate) or an aqueous solution of an amine compound in the presence of an x-containing exhaust gas purification catalyst. 2. The method for purifying NOx-containing exhaust gas according to claim 1, wherein the aqueous solution of ammonium salt is an aqueous solution of ammonium formate, ammonium oxalate, ammonium carbonate or ammonium bicarbonate. 3. The method for purifying NOx-containing exhaust gas according to claim 1, wherein the aqueous solution of the amine compound is urea water. 4. The method for purifying NOx-containing exhaust gas according to claim 1, 2 or 3, wherein the catalyst for purifying NOx-containing exhaust gas is a catalyst formed as a monolith body. 5. The method for purifying NOx-containing exhaust gas according to claim 4, wherein the monolith body is made of ceramics or metal.