JPH0889813A - Catalyst for denitrification and method for denitrification using it - Google Patents

Abstract

PURPOSE: To provide a denitrification catalyst by means of which NOx in the exhaust gas of an internal engine with a dilute air-fuel ratio can be removed with a sufficiently high gas space velocity and efficiently and a method for denitrification with high efficiency and high reliability for NOx in the exhaust gas of the internal engine using the catalyst. CONSTITUTION: A denitrification catalyst wherein an active alumina is used as a carrier and silver and/or silver oxide is carried thereon and the active alumina has a specific surface area measured by means of a nitrogen gas adsorption method of at least 120m<2> /g and when the total value of the vol. of pores with the pore radius of at most 300Å is A and the total value of the vol. of pores with the pore radius of at most 50Å is B and the total value of the vol. of pores with the pore radius in the range of 100-300Å is C and the relation between the pore radii and the pore vol. are in such a way that B is at least 30% of A and C is at most 15% of A and sulfate ions therein are less than 0.9%, is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a denitration catalyst for purifying exhaust gas from a mobile generation source or a stationary generation source, particularly nitrogen oxide in exhaust gas of an internal combustion engine, and more specifically to a denitration catalyst. The present invention relates to a denitration catalyst capable of purifying nitrogen oxides in exhaust gas of an internal combustion engine having a lean air-fuel ratio with high space velocity and high efficiency, and a denitration method using the same.

[0002]

2. Description of the Related Art In various kinds of combustion exhaust gas discharged from an internal combustion engine such as an automobile engine or a large combustion apparatus such as a factory, nitric oxide (CO ₂ ) and nitrogen monoxide (CO ₂ ) are produced. NO) and nitrogen oxides (NOx) such as nitrogen dioxide (NO ₂ ) are contained in a considerable amount. NOx
Not only does SO and SOx adversely affect the human body, but they are also one of the causes of acid rain, which is a problem from the viewpoint of global environmental protection. Therefore, it is desired to develop a denitration catalyst for efficiently removing nitrogen oxides from these various exhaust gases.

An ideal method of removing NO in NOx is a method of directly decomposing NO as shown by the following reaction formula (1). The equation (1) is a reaction in which the production system on the right side is overwhelmingly dominant in terms of reaction equilibrium.

2NO = N ₂ + O ₂ (1) Japanese Patent Laid-Open No. 60-125 discloses a denitration technique that depends on this reaction.
The method described in Japanese Patent Publication No. 250 is cited. This denitration technique uses a catalyst in which Cu is supported on a zeolite by an ion exchange method, and this catalyst promotes the direct decomposition reaction of NO. However, this denitration technique has a problem that the denitration efficiency is gradually lowered because oxygen generated by the reaction of the formula (1) is preferentially attached to the catalyst active site. Further, there is a drawback that the reaction of the formula (1) is completely hindered under the condition that excess oxygen exists in the reaction system (oxygen excess atmosphere).

On the other hand, from the viewpoint of preventing global warming, an internal combustion engine of the lean burn type has recently been drawing attention. A conventional automobile gasoline engine performs controlled stoichiometric combustion in the vicinity of an air-fuel ratio λ = 1, and carbon monoxide (CO) in exhaust gas is used for exhaust gas treatment. Mainly hydrocarbons (HC) and NOx, platinum (Pt), rhodium (Rh), palladium (Pd) and ceria (Ce)
A three-way catalyst system has been adopted in which these harmful components are simultaneously removed by contacting with an alumina catalyst containing O ₂ ). However, this three-way catalyst method has not been sufficiently effective in purifying exhaust gas in a lean burn gasoline engine of a lean burn method. Also, although the diesel engine is originally a lean burn engine,
Recently, regarding the exhaust gas, suspended particulate matter and NOx
Both of them have come under strict regulation.

Conventionally, as a method for reducing and removing NOx in an oxygen-excess atmosphere, a method has been already established in which NH ₃ which is selectively adsorbed by a catalyst even in a small amount as a reducing gas is used. It is industrialized as a NOx removal catalyst for exhaust gas from boilers and diesel engines, which are fixed sources. However, this method requires a special device for the recovery treatment of unreacted reducing agent, and ammonia with a strong odor may be used for this purpose, which is a denitration technology for exhaust gas from mobile sources such as automobiles. Cannot be applied to.

[0007] In recent years, since it has been reported that unburned hydrocarbons remaining in a lean combustion gas in an oxygen excess atmosphere can be used as a reducing agent to promote the reduction reaction of NOx, various catalysts for promoting the reaction have been developed. Has been made. For example, many reports have been made that alumina or a catalyst in which a transition metal is supported on alumina is effective for NOx reduction reaction using hydrocarbon as a reducing agent. Further, in Japanese Unexamined Patent Publication No. 4-282828, there is 0.1
An example is described in which alumina or silica-alumina containing 4 wt% of Cu, Fe, Cr, Zn, Ni, V, etc. is used as a catalyst for NOx reduction.

Furthermore, by using a catalyst in which Pt is supported on alumina, the NOx reduction reaction can proceed in a low temperature range of 200 to 300 ° C.
67946, JP-A-5-68855, and JP-A-5-103949. However, when these noble metal-supported catalysts are used, there is a drawback that the selectivity of the NOx reduction reaction becomes poor because the combustion reaction of hydrocarbon as a reducing agent is excessively promoted.

The present inventors have previously found that when a catalyst containing silver as a reducing agent with hydrocarbon as a reducing agent is used under an oxygen-excessive atmosphere, NO.
It was found that the x reduction reaction selectively and preferentially proceeded, and a patent application was filed for this (Japanese Patent Laid-Open No. 4-281844).
issue). Even after that, the technique for removing NOx by using a similar NOx reduction catalyst using silver in this manner is disclosed in Japanese Patent Laid-Open No. HEI 4
Although many patent applications such as JP-A-354536 and JP-A-5-92124 are found, the denitration performance of these conventional silver-supported silver-supported catalysts is still insufficient.

On the other hand, it has been known that a catalyst using alumina as a carrier has a large space velocity dependency.
For example, at a space velocity of SV: 1000 to 10000 hr ^-1 , the NOx reduction performance is sufficiently exhibited, but S
V: N at a space velocity of 10000 hr ⁻¹ or more
As can be seen from the fact that the purification performance of Ox is significantly reduced (see “Catalyst”: 33, 61 (1991)), such a phenomenon was a well-known fact in the art. For example, in the exhaust gas treatment method disclosed in JP-A-5-92124, the contact time between the exhaust gas and the catalyst is 0.03 g. sec / cm ³ or more, preferably 0.1 g. This is the reason why it is limited to sec / cm ³ or more.

[0011]

However, in the exhaust gas treatment of a lean burn engine for vehicles such as automobiles, which is a typical internal combustion engine operated at a lean air-fuel ratio, other important factors which are indispensable for practical use are , Both the required space and the weight of the catalyst layer or the structure consisting of the supporting substrate coated with the catalyst (hereinafter, these are referred to as catalyst-containing layer in the present specification). That is, it is not practical to mount a catalyst-containing layer having a capacity of several times or more of the engine displacement when considering the engine displacement and work, and the capacity of the catalyst-containing layer is set to be equal to or less than the engine displacement. It is desirable to do so.

This means that in order to form a practical catalyst-containing layer, the space velocity of the exhaust gas passing through the catalyst-containing layer is made high (which means that the contact time becomes short), that is, Gas space velocity of 7,000 hr ⁻¹ or more,
It is preferably 10,000 hr ⁻¹ or more, that is, the contact time is 0.03 g. sec / cm ^{3 or} less, preferably 0.02 g. It means that it is required to be less than sec / cm ³ . However, the conventional silver-supported alumina catalyst using alumina as a carrier is still insufficient in denitrification performance for exhaust gas coexisting with steam at such a high space velocity (short contact time).

An object of the present invention is to solve the above-mentioned problems caused by the conventional method. NOx in exhaust gas of an internal combustion engine having a lean air-fuel ratio can be maintained at a sufficiently high gas space velocity (short contact time). An object of the present invention is to provide a denitration catalyst that can be efficiently removed, and a denitration method with high efficiency and reliability of NOx in the exhaust gas of an internal combustion engine with a lean air-fuel ratio using the catalyst. It is what

[0014]

DISCLOSURE OF THE INVENTION The present inventors have used a denitration catalyst capable of advancing the NOx reduction reaction by hydrocarbon with high efficiency even in an oxygen-excess atmosphere in which water vapor coexists, and by using the same. As a result of earnest studies on the denitration method, the activated alumina having a specific surface area of 120 m ² / g or more, specific pore characteristics, and a low sulfate ion content was used as a carrier. However, they have found that the above problems can be solved by using a catalyst in which a specific amount of silver and / or silver oxide is supported, and have completed the present invention.

That is, the present invention is a catalyst in which activated alumina is used as a carrier and silver and / or silver oxide is supported on the activated alumina, and the activated alumina has a specific surface area measured by a nitrogen gas adsorption method. The relationship between the pore radius and the pore volume is 120 m ² / g or more, and the total volume of the pores occupied by the pores having a pore radius of 300 Å or less is A
And the total value of the pore volume occupied by pores having a pore radius of 50 Å or less is B, and the pore radius is 100 to 300.
When the total value of the pore volume occupied by pores in the Angstrom range is C, B is 30% or more of A and C is 1 of A.
A denitration catalyst having a content of 5% or less and a sulfate ion content of less than 0.9% in the alumina carrier. And a denitration method for exhaust gas in an internal combustion engine operated at a lean air-fuel ratio, wherein the exhaust gas is brought into contact with the denitration catalyst layer through contact, wherein the denitration catalyst constituting the denitration catalyst layer is the denitration catalyst according to claim 1. The denitration method is characterized in that the exhaust gas passing through the denitration catalyst layer has a temperature range of 200 to 600 ° C. at the denitration catalyst layer inlet.

When the denitration method of the present invention is used, the space velocity (SV) of the exhaust gas passing through the denitration catalyst layer
Even if the denitration reaction is carried out at 10,000 hr ^-1 or more, the denitration purification of the exhaust gas can be sufficiently performed, and the exhaust gas can be effectively treated even under an oxygen excess atmosphere in which water vapor coexists. It is possible to reduce and remove NOx.

[0017]

The operation of the present invention will be described in detail below.

The activated alumina used in the production of the denitration catalyst of the present invention has a relationship between the pore radius and the pore volume obtained when the pores present therein are measured by the nitrogen gas adsorption method. Let A be the total value of the pore volumes occupied by the pores of 300 angstroms or less, and B be the total value of the pore volumes occupied by the pores of 50 angstroms or less in radius.
When C is the total value of the pore volume occupied by pores having a pore radius of 100 to 300 angstroms, B is 3
It has pore characteristics such that it is 0% or more and C is 15% or less of A. Further, the activated alumina is crystallographically classified into γ-type, η-type, or a mixed type thereof, and these activated aluminas are generally mineralogy of boehmite, pseudo-boehmite, and via-type. Aluminum hydroxide powder or gel classified as wright and norstrandalite is heated in air or vacuum at a heating temperature of 300 to 800 ° C, preferably 400 to 600 ° C.
It is obtained by heating and dehydrating at.

In this case, when the activated alumina as the catalyst carrier has another crystal structure, for example, α-alumina, the α-type alumina has an extremely small specific surface area and poor solid acidity. Therefore, δ-alumina is unsuitable as the denitration catalyst carrier of the present invention, and δ-alumina has a relatively small specific surface area of 100 m ² / g. It does not reach. Further, β-alumina and χ-alumina are also unsuitable as the denitration catalyst carrier of the present invention for almost the same reason.

In the present invention, when the pore characteristics of activated alumina are out of the range of the present invention described above, that is, the pore radius is 5
The total value B of the pore volume of 0 angstroms or less is less than 30% of the total value A of the pore volume of the pores of 300 angstrom or less, and the pore radius of 100
When the total value C of the pore volume occupied by the pores of ˜300 Å exceeds 15% of the value of A,
The denitration performance of the obtained catalyst in the presence of water vapor becomes insufficient, which is not preferable. That is, the alumina effective as a carrier in the alumina catalyst supporting indium and silver and / or silver oxide of the present invention is such that B is 30% or more of A and C is 15% or less of A. It is limited to activated alumina having a pore distribution. In addition to this, the content of sulfate ions contained in the alumina carrier of the present invention is limited to less than 0.9%. When the content of sulfate ion is 0.9% or more, the catalyst thus obtained can exhibit high denitration performance under dry conditions,
This is because the activity decreases in the presence of water vapor, and particularly the low temperature activity decreases remarkably.

In the catalyst of the present invention, the method of supporting silver and / or silver oxide on activated alumina is not particularly limited, and a general supporting method such as an adsorption method, a pore filling method, an incipient wetness method, or evaporation is used. An impregnation method such as a dry solidification method or a spraying method, a kneading method, or a combination thereof may be employed as appropriate. Further, the supporting rate of silver and / or silver oxide is preferably in the range of 1 to 10% by weight in terms of metal, based on the activated alumina of the present invention. When the loading rate of silver is less than 1% by weight, satisfactory denitration activity cannot be obtained, and when it exceeds 10% by weight, the combustion reaction of hydrocarbon as a reducing agent proceeds excessively, resulting in catalytic activity and reaction selection. On the contrary, the sex declines.

Further, the drying temperature is not particularly limited, and the drying is carried out in the temperature range of 80 to 120 ° C. which is usually performed.
After that, 300 to 800 ° C., preferably 400 to 60
Bake at 0 ° C. If the firing temperature is lower than 300 ° C, sufficient firing is not performed, and if it exceeds 800 ° C, a phase change of alumina occurs, which is not preferable.

The shape of the catalyst of the present invention is not particularly limited, such as powder, sphere, cylinder, honeycomb, and spiral, and the size can be appropriately determined according to the use conditions. Good. In particular, when purifying exhaust gas from an automobile engine, etc., since the gas space velocity is high, a fire-resistant integrated body having a large number of through holes in the exhaust gas flow direction in order to minimize pressure loss. A structure in which the channel surface of the supporting substrate is coated is suitable for use.

The catalyst of the present invention is used for CO, HC in exhaust gas.
And exhaust gas containing oxygen in excess of the stoichiometric amount required to completely oxidize reducing components such as H _{2 with} oxidizing components such as NOx and O ₂ , and more specifically, an internal combustion engine having a lean air-fuel ratio It is applied to the purification of NOx in exhaust gas from.

[0025] By contacting the denitration catalyst of the present invention to such an exhaust gas, NOx by the reducing agent component present in trace amounts in the exhaust gas such as HC, is reduced to N2, CO ₂ and H _{2 O} At the same time, reducing agents such as HC are also CO
₂ and H ₂ O. When the HC / NOx ratio of the exhaust gas itself is low, such as the exhaust gas of a diesel engine, several hundred to several thousand ppm of fuel HC as a reducing agent component is additionally added to the exhaust gas as a reducing agent component. After that, if the method of contacting the catalyst of the present invention is adopted, NOx can be purified more effectively.

Although the temperature range in which the activity varies depends on the type of reducing agent, the catalyst of the present invention is used in an exhaust gas containing C ₂ or more paraffins, olefins, and aromatic HCs in an oxygen excess atmosphere at a high space velocity. In order to efficiently purify NOx, the inlet temperature of the installed catalyst layer should be 400
℃ ~ 600 ℃, in the case of C ₁₀ or more 200 ℃ ~
It needs to be 600 ° C. The reason why the inlet temperature must be adjusted in this way is that the silver and / or silver oxide-supported alumina catalyst according to the present invention requires a minimum temperature which varies depending on the type of the reducing agent described above in order to exert the denitration performance. This is because HC is not activated when the temperature is lower than this, and it is a side reaction when the inlet temperature of the catalyst layer becomes higher than 600 ° C., although it slightly varies depending on the kind of the reducing agent. Since the combustion of HC becomes predominant, the reducing activity of NOx by HC decreases, and the purification capacity deteriorates.

[0027]

The present invention will be described in more detail based on the following examples and comparative examples. However, the present invention is not limited to these examples. Preparation of carrier alumina Using a Sorptomatic made by Carlo Erba Co., which uses a pore distribution measurement method by a nitrogen gas adsorption method, the pore distribution of γ-alumina obtained by a general production method from aluminum hydroxide was measured. , The total value of the pore volumes of the pores having a pore radius of 300 Å or less is A, the total value of the pore volumes of the pores having a pore radius of 50 Å or less is B, and the pore radius is 100 to 300 Å. Where C is the total value of the pore volumes of the pores, the nine types of γ-alumina having different specific surface areas and sulfate ion contents and the pore distributions in which A, B and C have the following relationships Obtained.

Alumina a: B is 74.7% of A, C is A
Has a pore size distribution of 2.4%, a specific surface area of 241 m ² / g, and a sulfate ion content of 0.1%.
Is γ-alumina.

Alumina b: B is 40.4% of A, C is A
Has a pore distribution of 4.4%, a specific surface area of 174 m ² / g, and a sulfate ion content of 0.1%.
Is γ-alumina.

Alumina c: B is 57.8% of A, C is A
Has a pore distribution such that the specific surface area is 219 m ² / g, and the sulfate ion content is 0.1%.
Is γ-alumina.

Alumina d: B is 32.1% of A, C is A
Has a pore size distribution of 10.8%, a specific surface area of 193 m ² / g, and a sulfate ion content of 0.1.
% Γ-alumina.

Alumina e: B is 84.4% of A, C is A
Has a pore size distribution of 4.2%, a specific surface area of 265 m ² / g, and a sulfate ion content of 0.3%.
Is γ-alumina.

Alumina f: B is 14.0% of A, C is A
Has a pore size distribution of 45.9%, a specific surface area of 241 m ² / g, and a sulfate ion content of 1.3.
% Γ-alumina.

Alumina g: B is 31.0% of A, C is A
Has a pore size distribution of 22.7%, a specific surface area of 266 m ² / g, and a sulfate ion content of 1.1.
% Γ-alumina.

Alumina h: B is 47.7% of A, C is A
Has a pore size distribution of 36.9%, a specific surface area of 149 m ² / g, and a sulfate ion content of 0.4.
% Γ-alumina. A. Preparation of Catalyst Sample Using each of the above-mentioned alumina as a carrier, silver was supported thereon to prepare a catalyst sample for denitration performance evaluation. Example 1
5 and Comparative Examples 1 to 3 and Comparative Example 5, Ag / Al ₂ O ₃ catalyst was used, and in Comparative Example 4, Ag was not supported and only carrier alumina was used as a catalyst. Examples 1-5, Comparative Examples 1-3 a. Preparation of 4% Ag / Al ₂ O ₃ Catalyst Samples Example 1, Example 2, Example 3, Example 4 and Example 5 contained alumina a, alumina b, alumina c, alumina d and alumina e, respectively. Alumina f, alumina g and alumina h were used for Comparative Example 1, Comparative Example 2 and Comparative Example 3, respectively, and in each Example and Comparative Example, 100 ml of alumina and 1,000 ml each containing 6.6 g of silver nitrate were used. Immerse in an aqueous solution, heat to 100-110 ° C. with stirring to evaporate water,
First, Ag was first burned for 3 hours at 500 ° C in air.
/ Al ₂ O ₃ catalyst was prepared. A in these catalysts
The supporting rate of g is 4% with respect to alumina in terms of metal. Example 6 b. Preparation of 5.8% Ag / Al ₂ O ₃ Catalyst Sample The procedure of Example 1 was repeated except that the silver nitrate content in the silver nitrate-containing aqueous solution was changed to 9.6 g. 8% Ag / Al ₂ O ₃ catalyst was obtained. Comparative Example 4 c. Preparation of Al ₂ O ₃ Catalyst Sample A catalyst sample was prepared using only alumina a without supporting Ag. Comparative Example 5 d. Ag / A on alumina carrier containing a large amount of sulfate ion
Preparation of l ₂ O ₃ catalyst Example 1 except that alumina a was used as the catalyst support.
A 4% Ag / Al ₂ O ₃ catalyst was prepared by the same procedure. Incidentally, the alumina carrier has the same specific surface area and pore distribution as the alumina carrier used in Example 1, but the sulfate ion content exceeds the range of the present invention. B. Evaluation test of catalyst performance a. Evaluation Test 1 Using the catalyst samples of Examples 1 to 6 and Comparative Examples 1 to 5,
These catalyst samples were pressure-molded into a predetermined shape, pulverized and sized to a particle size of 250 to 500 μm, and then the sized product was filled in a stainless steel reaction tube having an inner diameter of 12 mm. It was mounted in an atmospheric fixed bed reactor. NO is 1,000 ppm as model exhaust gas in this catalyst layer,
C ₃ H ₆ is 1,000 ppm, O ₂ is 5%, H ₂ O is 1
The space velocity of the mixed gas consisting of 0% and the balance N _{2 was set} to 30,00.
Passed at ⁰ hr ^-1 .

Regarding the gas composition at the outlet of the reaction tube, NO and NO
The concentration of ₂ was measured using a chemiluminescence type NOx meter, and the concentration of N ₂ O was measured using a gas chromatography thermal conductivity detector equipped with Porapack Q column. Set the catalyst layer inlet temperature to a predetermined temperature in the range of 400 to 600 ° C.,
The value at the time when the gas composition at the outlet of the reaction tube became stable at each predetermined temperature was taken as the measured value.

When the model exhaust gas passes through the catalyst layer, NO in the reaction gas is converted into NO ₂ , N ₂ O and / or N ₂ , but when passing through the catalyst layer of the present invention, almost no N is converted. _Since it was found that ₂ O was not produced, the denitration rate (NO conversion rate) is represented by the following formula in the present invention.

[0038] Table 1 shows the catalyst layer inlet temperature 40 in the above performance evaluation test 1.
The maximum denitration rate Cmax (%) between 0 degreeC and 600 degreeC is shown.

From the results shown in Table 1, it can be seen that the catalysts of Examples 1 to 6 of the present invention show remarkably high denitration performance even at a high space velocity as compared with the catalysts of Comparative Examples 1 to 5.

[0040]

[Table 1] ────────────────────────────────── Activity evaluation results Implementation number Catalyst Alumina Cmax (% ) ────────────────────────────────── Example 1 4% Ag / Al ₂ O ₃ a 91.9 Example 2 〃 b 87.8 Example 3 〃 c 91.0 Example 4 〃 d 90.0 Example 5 〃 e 89.6 Example 6 5.8% Ag / Al ₂ O ₃ a 82.9 Comparison Example 1 4% Ag / Al ₂ O ₃ f 62.4 Comparative Example 2 〃 g 69.8 Comparative Example 3 〃 h 56.2 Comparative Example 4 Al ₂ O ₃ a 12.5 Comparative Example 5 4% Ag / Al ₂ O ₃ a 62.0 ────────────────────────────────── b. Evaluation test 2 Next, only the space velocity in evaluation test 1 is 60,000.
The performance of the catalyst sample of Example 1 was evaluated by the same procedure as in Evaluation Test 1 except that the ^value was changed to hr ⁻¹ .

Table 2 shows the maximum denitration rate Cmax (%) in the above space velocity between the catalyst layer inlets of 400 to 600 ° C. The results in Table 2 show that the catalyst of Example 1 of the present invention exhibits an excellent denitration rate even at a shorter contact time, that is, at a higher space velocity.

[0042]

[Table 2] ─────────────────────── Evaluation results Space velocity (h ⁻¹ ) Cmax (%) ─────────── ───────────── 60,000 96.6 ───────────────────────

[0043]

As described above, when the exhaust gas is denitrated by the denitration method of the present invention using the catalyst of the present invention, a high conversion rate is obtained in an oxygen excess atmosphere in which water vapor coexists and at a high space velocity. Since it is possible to reduce and purify nitrogen compounds in exhaust gas, it can be said that the invention is highly practical.

Claims (3)

[Claims] 1. A catalyst comprising activated alumina as a carrier, and at least one of silver and silver oxide supported on the activated alumina, the activated alumina having a specific surface area of 120 m ² measured by a nitrogen gas adsorption method. / G or more, and the relationship between the pore radius and the pore volume is A, and the total value of the pore volumes occupied by pores having a pore radius of 300 angstroms or less is A, and the pores having a pore radius of 50 angstroms or less occupy When the total value of the pore volume is B and the total value of the pore volume occupied by the pores in the range of the pore radius of 100 to 300 angstrom is C, B is 30% or more of A and C is 15 of A. %, And the content of sulfate ions contained in the alumina carrier is less than 0.9%. 2. A denitration catalyst for forming the denitration catalyst layer in the denitration method for exhaust gas, wherein exhaust gas in an internal combustion engine operated at a lean air-fuel ratio is brought into contact with the denitration catalyst layer through contact. Exhaust gas which is the denitration catalyst of No. 2 and passes through the denitration catalyst layer is
A denitration method characterized in that the temperature range is from 00 to 600 ° C. 3. The denitration method according to claim 2, wherein the space velocity of the exhaust gas passing through the denitration catalyst layer is 10,000 hr ⁻¹ or more.