JPH0824645A - Denitration catalyst and denitration method using the same - Google Patents

Abstract

PURPOSE:To provide a denitration catalyst and to denitrate NOx in exhaust gas of an internal combustion engine of a lean air/fuel ratio with a high efficiency and high reliability by using the catalyst. CONSTITUTION:Activated alumina is used as a carrier and strontium or barium and silver and/or silver oxide are supported on the carrier to obtain the denitration catalyst. In this catalyst, the pore distribution in the activated alumina is characterized by that B is 30% or more of A and C is 15% or less of A when the sum total value of pore vol. occupied by pores with a pore radius of 300Angstrom or less is set to A and the sum total value of pore vol. occupied by pores with a pore radius of 50Angstrom or less is set to B and the sum total value of pore vol. occupied by pores with a pore radius of 100-300A is set to C in the relation between a pore radius and pore vol. measured by a nitrogen gas adsorbing method. When exhaust gas of an internal combustion engine operated in a lean air/fuel ratio passes through the denitration catalyst bed, the inlet temp. of the catalyst bed is set to 400-600V.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying NOx removal catalyst used for purifying nitrogen oxides in exhaust gas, particularly exhaust gas of an internal combustion engine such as an automobile.
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 Various combustion exhaust gases emitted from an internal combustion engine such as an automobile engine are mixed with water, which is a combustion product, and carbon dioxide (CO ₂ ) and nitric oxide (NO).
And nitrogen oxides (NOx) such as nitrogen dioxide (NO ₂ ).
Is included in considerable quantity. NOx not only affects the human body and increases the morbidity rate of respiratory diseases, but it is 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, the method using the three-way catalyst system has not been sufficiently effective in purifying the exhaust gas in the lean-burn gasoline engine of the lean air-fuel system. 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 applicant has previously found that when using a catalyst containing silver as a reducing agent with a hydrocarbon as an reducing agent in an oxygen-excess atmosphere, NOx is used.
It was found that the reduction reaction selectively and preferentially proceeded, and a patent application was filed for this (JP-A-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 proposed a denitrification catalyst and a denitrification method using the same, which are capable of advancing the NOx reduction reaction by a hydrocarbon with high efficiency even in an oxygen excess atmosphere. As a result of intensive research, it is intended to achieve the above-mentioned demands in a catalyst in which activated alumina having specific pore characteristics is used as a carrier and strontium or barium and silver and / or silver oxide are supported on the catalyst. The present inventors have completed the present invention by finding that it is possible to provide such performance.

That is, the present invention is a catalyst comprising activated alumina as a carrier, on which strontium or barium and at least one of silver and silver oxide are supported, wherein the activated alumina is adsorbed with nitrogen gas. The relationship between the pore radius and the pore volume measured by the
Let A be the total value of the pore volumes occupied by the pores of 0 angstrom or less, and let B be the total value of the pore volumes occupied by the pores of 50 angstrom or less.
When the total value of the pore volume occupied by the pores in the range of 300 Å is C, B is 30% or more of A,
A denitration catalyst in which C has a pore distribution of 15% or less of A, and a denitration method of the exhaust gas in which an exhaust gas in an internal combustion engine operated at a lean air-fuel ratio is passed through a denitration catalyst layer. In the above, the denitration catalyst constituting the denitration catalyst layer is the denitration catalyst having the above-mentioned configuration, and the exhaust gas passing through the denitration catalyst layer is 4
The denitration method is characterized in that the temperature range is from 00 to 600 ° C.

According to the method of the present invention, the space velocity of the exhaust gas passing through the denitration catalyst layer is 10,000 hr.
^Even if the denitration reaction is performed at ^-1 or more, the denitration of exhaust gas can be sufficiently purified, and NOx in the exhaust gas can be effectively removed even in an oxygen atmosphere.

[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 volumes occupied by the pores of 0 angstrom or less is 30% or less of the total value A of the pore volumes occupied by the pores of 300 angstrom or less, and the pore radius is 100 to 300 angstrom. When the total value C of the pore volume occupied by the pores is 15% or more 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 activated alumina that is effective as a carrier in the alumina catalyst supporting strontium or barium and silver and / or silver oxide of the present invention has B of 30% or more and A of 15 or more. It is limited to γ-type or η-type activated alumina having a pore distribution of not more than%.

In the catalyst of the present invention, the method of supporting strontium or barium and silver and / or silver oxide on activated alumina is different from the method of first supporting silver on activated alumina in terms of denitration performance. The supporting method is not particularly limited, and a general supporting method such as an adsorption method,
An impregnation method such as a pore filling method, an incipient wetness method, an evaporation-drying method, a spray method, a kneading method, or a combination thereof may be appropriately employed. Also strontium or barium, silver and /
Alternatively, the supporting rate of silver oxide is 5% by weight of strontium or barium in terms of metal with respect to the activated alumina of the present invention.
Less, silver is preferably in the range of 1 to 10% by weight. Further, when the strontium or barium loading rate is 5% by weight or more, the denitration performance decreases, while when the silver loading rate is less than 1% by weight, satisfactory denitration activity cannot be obtained and 10% by weight is not obtained. If it exceeds, the combustion reaction of hydrocarbon as a reducing agent proceeds excessively, and the catalytic activity and reaction selectivity are rather lowered, which is not preferable.

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 less than 300 ° C, sufficient firing is not performed, and if it exceeds 800 ° C, a phase transformation 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 with a powdery catalyst is suitable for use.

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

By contacting such exhaust gas with the denitration catalyst of the present invention, NOx is reduced to N ₂ , CO ₂ and H ₂ O by a reducing agent component which is present in a small amount in the exhaust gas such as HC. At the same time, the reducing agent such as HC is 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.

In order to efficiently purify NOx in exhaust gas by HC in an oxygen-rich atmosphere using the catalyst of the present invention, the inlet temperature of the installed catalyst layer is set to 400 ° C to 600 ° C.
Need to be This is because the strontium or barium and silver and / or silver oxide-supported alumina catalyst of the present invention requires a temperature of 400 ° C. or higher in order to exert the denitration performance, and when the temperature is lower than this, HC is not activated. It is estimated that this is because of the reason. Further, in this case, when the inlet temperature of the catalyst layer becomes a high temperature of 600 ° C. or higher,
Since the combustion of HC, which is a side reaction, 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 The pore distribution of γ-alumina obtained from aluminum hydroxide by a general method using a Sorptomatic made by Carlo Erba Co., which utilizes a pore distribution measurement method by a nitrogen gas adsorption method, The measurement was performed, and the total value of the pore volumes of the pores having a pore radius of 300 angstroms or less was set to A, the total value of the pore volumes of the pores having a pore radius of 50 angstroms or less was set to B, and a pore radius of 100 Assuming that the total value of the pore volumes of the pores of ˜300 Å was C, γ-alumina having a pore distribution in which A, B and C had the following six different relationships was obtained.

Alumina a: B is 40.4% of A, C is A
Γ-alumina having a pore distribution such that it is 4.4%.

Alumina b: B is 74.7% of A, C is A
? -Alumina having a pore distribution such that it is 2.4%.

Alumina c: B is 57.8% of A, C is A
Γ-alumina having a pore distribution such that it is 3.9%.

Alumina d: B is 32.1% of A, C is A
Γ-alumina having a pore size distribution such that it is 10.8%.

Alumina e: B is 14.0% of A, C is A
Γ-alumina having a pore distribution such that it is 45.9%.

Alumina f: B is 31.0% of A, C is A
? -Alumina having a pore distribution such that it is 22.7%.

A. Preparation of catalyst sample (strontium and
And silver supported) Examples 1 to 4, Comparative Examples 1 to 2 a. Preparation of 0.1% Sr / 3Ag / Al ₂ O ₃ Catalyst Samples Alumina a, Alumina b, Alumina c and Alumina d were used in Example 1, Example 2, Example 3 and Example 4, respectively, and comparisons were made. Alumina e and alumina f were used in Example 1 and Comparative Example 2, respectively. In each Example and Comparative Example, 100 g of alumina was immersed in 1,000 ml of an aqueous solution containing 4.9 g of silver nitrate, and stirred at 100 First, an Ag / Al ₂ O ₃ catalyst was obtained by heating to ˜110 ° C. to evaporate the water content and calcining in air at 500 ° C. for 3 hours. Next, this catalyst was immersed in an aqueous strontium nitrate solution, and the same procedure was applied to obtain a Sr / Ag / Al ₂ O ₃ catalyst. The loadings of Sr and Ag in these catalysts are 0.1% and 3%, respectively, in terms of metal, based on alumina. Example 5 b. Preparation of 1.0% Sr / 3% Ag / Al ₂ O ₃ catalyst sample In Example 1, the loading ratio of strontium was 1.0%.
Sr / Ag / Al in the same procedure as in Example 1 except that
_{A 2} O ₃ catalyst was obtained. Comparative Example 3 c. Ag / Al supporting only Ag without supporting Sr
Preparation of ₂ O ₃ Catalyst Sample An Ag / Al ₂ O ₃ catalyst was obtained by the same procedure as in Example 1 except that only silver was supported on alumina a and strontium was not supported.

B. Evaluation test of catalyst performance a . Evaluation Test 1 Using the catalyst samples of Examples 1 to 5 and Comparative Examples 1 to 4, the catalyst samples were pressure-molded into a predetermined shape and then pulverized to have a particle size of 250 to 500 μm. The granules were sized as described above, and then the sized granules were filled in a stainless steel reaction tube having an inner diameter of 12 mm and mounted in an atmospheric fixed bed reactor. NO1,0 is added to this catalyst layer as model exhaust gas.
_{00ppm, C 3 H 6 1,000ppm,} O 2 5%, H
₂ O 10%, mixed gas consisting of the balance N ₂ with space velocity 3
It was passed at 10,000 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 chromatograph / thermal conductivity detector equipped with a Porapack Q column. The catalyst layer inlet temperature was set to a predetermined temperature in the range of 400 to 600 ° C., and the value at the time when the reaction tube outlet gas composition 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 to NO ₂ , N ₂ O and / or N ₂ , but when passing through the catalyst of the present invention, N is converted. _Since it has been found that ₂ O is hardly generated, the denitration rate (NO conversion rate) in the present invention is expressed by the following formula.

[0039] Table 1 below shows the NOx removal rates (%) at the catalyst layer inlet temperatures of 450 ° C. and 500 ° C. in the above performance evaluation test 1.

From the results shown in Table 1, the catalysts of Examples 1 to 5 of the present invention show remarkably high denitration performance even at a high space velocity in a lower temperature region than the catalysts of Comparative Examples 1 to 3. I understand.

[0041]

[Table 1] ─────────────────────────────────── Catalyst denitration rate Execution number Catalyst Activated alumina 450 ℃ 500 ℃ ─────────────────────────────────── Example 1 0.1% Sr / 3% Ag / Al ₂ O ₃ a 69.1 72.5 Example 2 〃 b 72.3 78.3 Example 3 〃 c 71.5 74.6 Example 4 〃 d 71.1 72.9 Example 5 1.0% Sr / 3% Ag / Al ₂ O ₃ a 65.6 68.8 Comparative Example 1 0.1% Sr / 3% Ag / Al ₂ O ₃ e 33.9 39.9 Comparative Example 2 〃 f 46.4 41.7 Comparative Example 3 3% Ag / Al ₂ O ₃ a 47.0 − ────────────────── ────────────────── 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 denitration rate (%) at the catalyst layer inlet temperature of 450 ° C. at the above space velocity. The results in Table 2 show that the catalyst of Example 1 of the present invention exhibits excellent denitration rate even at a shorter contact time, that is, at a higher space velocity.

[0043]

[Table 2] ───────────────────────── Catalyst denitration rate (%) Space velocity (hr ⁻¹ ) 450 ° C ────── ─────────────────── 60,000 78.1 ───────────────────────── A. Preparation of catalyst sample (in the case of supporting barium and silver) Examples 6 to 9, Comparative Example 5 and Comparative Example 6 a. Preparation of 0.1% Ba / 3% Ag / Al ₂ O ₃ Catalyst Samples Alumina a, Alumina b, Alumina c and Alumina d were used in Example 6, Example 7, Example 8 and Example 9, respectively. Alumina e and alumina f were used in Comparative Examples 5 and 6, respectively, and 100 g of alumina and 4.9 g of alumina were used in each of the Examples and Comparative Examples.
Dipped in 1,000 ml of an aqueous solution containing silver nitrate, heated to 100 to 110 ° C. with stirring to evaporate the water content, and then calcined in air at 500 ° C. for 3 hours to obtain Ag / A.
An I ₂ O ₃ catalyst was obtained. This catalyst was immersed in an aqueous solution of barium nitrate, and the same method as above was performed to form Ba / Ag / Al ₂ O.
₃ catalysts were obtained. Note that Ba and Ag in each catalyst sample
The loadings of 0.1% by weight and 3%, respectively, in terms of metal.
% By weight. Example 10 b. Preparation of 1.0% Ba / 3% Ag / Al ₂ O ₃ Catalyst Sample Ba / Ag / Al was prepared in the same procedure as in Example 1 except that the loading ratio of barium was 1.0% by weight. _Two
An O ₃ catalyst was obtained.

B. Evaluation test of catalyst performance a . Evaluation Test 1 For each catalyst sample obtained in Examples 6 to 10 and Comparative Examples 6 and 7, the above Ni / Ag / Al _{2 was used.}
An evaluation test using the same model gas was performed by the same method as the performance evaluation test of the O ₃ catalyst sample. Table 3 shows the catalyst layer inlet temperatures of 450 ° C and 600 ° C for each catalyst sample.
Shows the denitration rate (%). From the results of Table 3, it can be seen that the catalysts of Examples 6 to 10 according to the present invention have a higher denitration performance especially at low temperatures than the catalysts of Comparative Examples 6 and 7.

[0045]

[Table 3] ─────────────────────────────────── Catalyst denitration rate (%) Implementation number Catalytic activity Alumina 450 ℃ 500 ℃ ─────────────────────────────────── Example 6 0.1% Ba / 3% Ag / Al ₂ O ₃ a 69.8 72.5 Example 7 〃 b 73.1 77.3 Example 8 〃 c 72.2 75.6 Example 9 〃 d 71.8 73.8 Example 10 1.0% Ba / 3% Ag / Al ₂ O ₃ a 66.3 69.8 Comparative Example 4 0.1% Ba / 3% Ag / Al ₂ O ₃ e 34.6 40.3 Comparative Example 5 〃 f 42.1 47.2 ───────────────────────────── ─────── b. Evaluation Test 2 The denitration performance of the catalyst sample according to Example 6 was evaluated by the same procedure as in Evaluation Test 1 except that the space velocity was 60,000 hr ⁻¹ . Table 4 shows the denitration rate (%) at the catalyst bed inlet temperature of 450 ° C. and 600 ° C. at the above space velocity of the catalyst.

From this result, Ba / Ag / according to the present invention
The Al ₂ O ₃ catalyst is the Sr / Ag / Al ₂ O ₃ shown above.
It can be seen that as in the case of the catalyst, excellent denitration performance is maintained even at a higher space velocity.

[0047]

[Table 4] ───────────────────────── Catalyst denitration rate (%) Space velocity (hr ⁻¹ ) 450 ° C ────── ─────────────────── 60,000 78.9 ─────────────────────────

[0048]

As described above, when the exhaust gas denitration is performed by the denitration method of the present invention using the catalyst of the present invention, even in a high oxygen atmosphere in the presence of water vapor, even at low temperature and high space velocity. Since it is possible to reduce and purify nitrogen compounds in exhaust gas with a high conversion rate, it can be said that the invention is highly practical.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B01D 53/36 102 D 104 A

Claims (3)

[Claims] 1. A catalyst comprising activated alumina as a carrier, on which strontium or barium and at least one of silver and silver oxide are carried, the pore distribution of said activated alumina being determined by nitrogen gas adsorption. As for the relationship between the pore radius and the pore volume measured by the method, let A be the total value of the pore volumes occupied by the pores having a pore radius of 300 angstroms or less, and the fineness occupied by the pores having a pore radius of 50 angstroms or less. The total value of the pore volume is B, and the pore radius is 100 to 30.
A denitration catalyst characterized in that B is 30% or more of A and C is 15% or less of A, where C is a total value of pore volumes occupied by pores in the range of 0 angstrom. . 2. A denitration catalyst for forming the denitration catalyst layer in a denitration method for the exhaust gas, wherein exhaust gas in an internal combustion engine operated at a lean air-fuel ratio is passed through the denitration catalyst layer. A denitration method using a denitration catalyst, wherein the gas inlet temperature in the catalyst layer is 400 ° C 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.