JPH10137584A - Exhaust gas purifying catalytic layer, exhaust gas purifying catalytic coated structure and exhaust gas purifying method by the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust waste gas purifying catalytic layer capable of efficiently removing NOx in a lean waste combustion gas, an gas purifying catalytic coated structure and an exhaust gas purifying method. SOLUTION: The exhaust gas purifying catalytic layer is constituted of a catalyst A composed of at least one kind selected from a group composed of silica, alumina, strontium and barium and a catalyst B composed of an alumina carrier, which has a fine pore structure having the following relation of fine pore diameter to fine pore volume measured by a gaseous nitrogen adsorption method, and silver. The relation is that Y is >=70% of X and Z is <=20% of X when total of fine pore volume occupied by a fine pore having <=300Å fine pore radium is expressed by X, total of fine pore volume occupied by a fine pore having >=25Å to <100Å fine pore radium is expressed by Y and total of fine pore volume occupied by a fine pore having >=100Å to <=300Å fine pore radius is expressed by Z.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to exhaust gas used for purifying nitrogen oxides contained in combustion exhaust gas of mobile and stationary internal combustion engines of automobiles, boilers, gas engines, gas turbines, ships and the like. The present invention relates to a purification catalyst layer and an exhaust gas purification catalyst-coated structure, and more specifically, it can purify nitrogen oxides in exhaust gas discharged from an internal combustion engine operated in a lean burn region at a high space velocity and with high efficiency. The present invention relates to an exhaust gas purifying catalyst layer and an exhaust gas purifying catalyst coated structure, and an exhaust gas purifying method using the same.

[0002]

2. Description of the Related Art Various combustion exhaust gases emitted from internal combustion engines such as automobiles contain nitrogen oxides (NOx) such as nitric oxide and nitrogen dioxide together with water and carbon dioxide as combustion products. NOx not only has an adverse effect on the human body, especially the respiratory system, but also is one of the causes of acid rain, which is regarded as a problem from the viewpoint of global environmental protection. Therefore, development of a denitration technology for efficiently removing nitrogen oxides from these various exhaust gases is desired.

On the other hand, in view of the prevention of global warming, lean-burn internal combustion engines have recently attracted attention. A conventional gasoline engine for an automobile has an air-fuel ratio (A / F) = 1.
Combustion at a controlled stoichiometric ratio near 4.7. For exhaust gas treatment, carbon monoxide, hydrocarbons and NOx in the exhaust gas are converted to alumina mainly containing platinum, rhodium, palladium and ceria. A three-way catalyst system has been employed in which three harmful components are simultaneously removed by contact with a catalyst.

[0004] However, since the absolute condition is that the engine is operated at a stoichiometric ratio, the three-way catalyst system can be applied to exhaust gas purification of a lean burn gasoline engine operated at a lean air-fuel ratio. Can not. In addition, diesel engines are originally lean burn engines, but strict regulations are being imposed on both the suspended particulate matter and NOx in the exhaust gas.

Conventionally, as a method of reducing and removing the ΝOx in an oxygen-rich atmosphere, a technique of using NH ₃ also adsorb selectively catalyst small amount as the reducing gas has already been established. This technology has been industrialized as a method for denitration of exhaust gas from boilers and diesel engines, which are so-called stationary sources. However, this method requires a special device for the recovery treatment of unreacted reducing agent and uses harmful ammonia, which has a strong odor, which is particularly dangerous for exhaust gas denitration technology from mobile sources such as automobiles. Not applicable.

In recent years, it has been reported that a NOx reduction reaction can be promoted by using unburned hydrocarbons remaining in a lean combustion exhaust gas in an oxygen-excess atmosphere as a reducing agent. Various catalysts have been developed and reported. For example, there are many reports that alumina or a catalyst in which a transition metal is supported on alumina is effective for a NOx reduction reaction using a hydrocarbon as a reducing agent. JP-A-4-284848 discloses that 0.1 to 4% by weight of Cu, Fe, Cr, Zn, Ni, V
Or silica-alumina containing ΝOx
An example of use as a reduction catalyst has been reported.

Further, when a catalyst in which Δt is supported on alumina is used, the NOx reduction reaction proceeds in a low temperature range of about 200 to 300 ° C., as disclosed in JP-A-4-267946 and JP-A-5-68855. Kaihei 5-1039
No. 49, for example. However, when these supported noble metal catalysts are used, the combustion reaction of hydrocarbons as a reducing agent is excessively promoted, and N ₂ O which is one of the substances causing global warming is by-produced, be advanced reduction reaction to harmless New ₂ selective had disadvantage is difficult.

One of the present applicants has previously found that the use of a catalyst containing silver with a hydrocarbon as a reducing agent in an oxygen-excess atmosphere causes the NOx reduction reaction to proceed selectively. -281844. Even after this disclosure was made, a similar ΝOx reduction and removal technique using a catalyst containing silver was disclosed in Japanese Patent Application Laid-Open No. 4-354536.
JP-A-5-92124, JP-A-5-92124
No. 125 and JP-A-6-277454.

[0009]

However, the alumina-supported silver catalysts described in these conventional publications still have practically insufficient denitration performance in the presence of steam and SOx.

The present invention has been made to solve the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide an exhaust gas purifying catalyst layer and a catalyst coating capable of efficiently removing NOx in lean combustion exhaust gas. An object of the present invention is to provide a structure and an exhaust gas purifying method for purifying NOx in lean burn exhaust gas with high efficiency and high reliability using the same.

[0011]

Means for Solving the Problems The present inventors have developed an exhaust gas purifying catalyst layer and an exhaust gas purifying catalyst coating structure having high denitration performance in a lean burn region where steam and SOx coexist, and using these. As a result of diligent studies on the exhaust gas purification method, the catalyst A comprising at least one selected from the group consisting of silica and magnesium, strontium and barium in the flow direction of the exhaust gas.
In the first stage, it was found that the above problems could be solved by disposing and arranging the catalyst B composed of alumina and silver having a specific pore structure in the second stage, and completed the present invention.

That is, a first embodiment of the present invention for solving the above-mentioned problems is to provide a catalyst A comprising silica, at least one selected from the group consisting of magnesium, strontium and barium, and a nitrogen gas adsorption method. The relationship between the pore radius and the pore volume measured by
Let X be the total value of the pore volume occupied by pores of 0 Å or less, and 10 if the pore radius is 25 Å or more.
The total value of the pore volume occupied by pores smaller than 0 Å is defined as Y, and 3 for a pore radius of 100 Å or more.
When the total value of the pore volume occupied by pores of not more than 00 Å is Z, an alumina carrier having a pore structure in which Y is 70% or more of X and Z is 20% or less of X, and silver An exhaust gas purifying catalyst layer comprising a catalyst B comprising: The catalyst layer is preferably disposed in a flow space of the exhaust gas in a powdered or molded state.

In a second embodiment of the present invention, there is provided a support substrate having an integral structure made of a refractory material having a large number of through holes, and the above-mentioned catalyst is divided at least on the inner surface of the through hole in the support substrate. It is characterized by a catalyst-coated structure coated by coating.

Still further, a third embodiment of the present invention removes NOx in exhaust gas containing hydrocarbons as a reducing agent, which comprises contacting the exhaust gas of an internal combustion engine operated at a lean air-fuel ratio with a catalyst-containing layer. Wherein the catalyst contained in the catalyst-containing layer is the catalyst layer according to the first embodiment or the catalyst-coated structure according to the second embodiment. Is characterized by an exhaust gas purifying method in which the catalyst B is divided and arranged in the former stage and the catalyst B is arranged in the latter stage.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention and its operation will be more specifically described below. (Structure of Catalyst and Production Method Thereof) Alumina, which is one of the main components of catalyst B in the catalyst layer for purifying exhaust gas of the present invention,
For example, an aluminum hydroxide powder or gel classified as boehmite, pseudo-boehmite, vialite, or norstrandite in mineralogy is placed in air or in a vacuum.
By heating and dehydrating at 0 to 800 ° C, preferably 400 to 900 ° C, crystallographically γ-type, η-type, δ-
It is preferable from the viewpoint of denitration performance that a phase transition is made to alumina classified into a type, a χ-type or a mixed type thereof. Alumina having another crystal structure, for example, α-type alumina, is unsuitable as the catalyst component of the present invention because of its extremely small specific surface area and poor solid acidity.

The alumina of the catalyst B has a total pore volume X of pores having a pore radius of 300 angstroms or less measured by a nitrogen gas adsorption method as X, and 100 angstroms when the pore radius is 25 angstroms or more. When the total value of the pore volume occupied by pores smaller than less than Y is Y, and the total value of the pore volume occupied by pores having a pore radius of 100 Å or more and 300 Å or less is Z, Y is 70% of Χ. As described above, it is necessary to use alumina having a pore structure in which Z is 20% or less of X. When alumina having a pore structure that does not satisfy the above conditions is used as a carrier in the catalyst B of the present invention, the exhaust gas purifying catalyst constituted thereby has insufficient denitration performance of exhaust gas in the presence of steam. there were. Therefore,
As the alumina effective as a main component of the catalyst B of the present invention, those having the above-mentioned crystal structure and pore characteristics are appropriate.

The exhaust gas purifying catalyst layer of the present invention is the following catalyst. The catalyst layer according to the present invention comprises silica, catalyst A comprising at least one selected from the group consisting of magnesium, strontium and barium, and catalyst B comprising alumina and silver having the above-mentioned crystal structure and pore characteristics. It is composed. At least one state selected from the group consisting of magnesium, strontium, and barium, which are one component of the catalyst A, is not particularly limited. The state of silver contained in the alumina of the catalyst B is not particularly limited, and examples thereof include a metal state, an oxide state, and a mixed state thereof. In particular, the composition of the combustion exhaust gas of an internal combustion engine such as an automobile changes each time depending on the operation state, and thus the catalyst is exposed to a reducing atmosphere and an oxidizing atmosphere. Therefore, it is assumed that the state of the active metal constituting the catalyst changes with the change of the atmosphere. The starting material of silver in the catalyst B and at least one selected from the group consisting of magnesium, strontium and barium, which are one component of the catalyst A, is not particularly limited.

The method for producing a catalyst comprising at least one selected from the group consisting of silica and magnesium, strontium and barium in the catalyst A according to the present invention, and the method for producing alumina and silver in the catalyst B are not particularly limited. Instead, conventional methods such as adsorption method, pore filling method, incipient wetness method, evaporation drying method, impregnation method such as spray method, kneading method, physical mixing method and a combination thereof are usually used. Any of the known methods that have been employed can be employed. In preparing the catalyst A, silica is mixed with at least one selected from the group consisting of a magnesium source, a strontium source, and a barium source, and then dried and calcined. Further, a method for producing a catalyst containing at least one selected from the group consisting of a magnesium source, a strontium source and a barium source when producing a silica carrier, for example,
After mixing an alcohol solution of silicon alkoxide with an alcohol solution containing at least one selected from the group consisting of a magnesium source, a strontium source and a barium source, heating and hydrolyzing the alkoxide method, a silica source, a magnesium source, and strontium A coprecipitation method in which an alkali is added to at least one mixed aqueous solution selected from the group consisting of a source and a barium source to cause precipitation is also applicable. In preparing catalyst B, a silver source is supported on alumina or an alumina precursor material, and then dried and calcined. Further, a method for producing a catalyst containing an active metal species at the time of producing alumina or an alumina carrier having a specific pore structure as described above, for example, an alcohol solution of aluminum alkoxide and an alcohol solution of a silver source are mixed and then heated. An alkoxide method of hydrolysis and a coprecipitation method of adding an alkali to an aqueous solution of a mixture of an aluminum source and a silver source to cause precipitation are also applicable.

Magnesium, which is one component of catalyst A,
The content of at least one selected from the group consisting of strontium and barium is not particularly limited, and can be arbitrarily selected according to required performance. Although the content of silver in terms of metal with respect to alumina in the catalyst B is not particularly limited,
The range of 0.1 to 10% by weight is preferable in terms of denitration performance.
A range of 8% by weight is particularly preferred.

The drying temperature of the catalyst A is not particularly limited, and is usually dried at about 80 to 120 ° C. The firing temperature is 200 to 800 ° C, preferably 400 to 600 ° C.
It is about ° C. If the sintering temperature exceeds 800 ° C., the specific surface area of silica decreases and at least one dispersibility selected from the group consisting of magnesium, strontium and barium decreases, which is not preferable. On the other hand, catalyst B
The drying temperature is not particularly limited and is usually 80 to 1
Dry at about 20 ° C. The firing temperature is 300 to 100
0 ° C., preferably about 400 to 900 ° C. If the firing temperature exceeds 1000 ° C., phase transformation to α-type alumina occurs, which is not preferable. The atmosphere at this time is not particularly limited, but each atmosphere such as in air, in an inert gas, or in oxygen may be appropriately selected according to the catalyst composition. In addition, each atmosphere may be alternately changed at regular intervals.

In the first embodiment of the present invention, when a catalyst layer for purifying exhaust gas is formed, the catalyst layer is formed into a predetermined shape or a predetermined shape through which a target exhaust gas flows in a powder state. Fill in the space. When the catalyst layer is formed into a molded body, its shape is not particularly limited, and various shapes such as a spherical shape, a cylindrical shape, a honeycomb shape, a spiral shape, a granular shape, a pellet shape, and a ring shape can be adopted. These shapes, sizes, and the like may be arbitrarily selected according to use conditions.

Next, an exhaust gas purifying catalyst-coated structure according to a second embodiment of the present invention will be described. Here, the catalyst-coated structure has a structure in which at least the inner surface of the through-hole is coated with the above-mentioned catalyst in a unitary support substrate made of a refractory material having a large number of through-holes. It is.

The support substrate is provided with a large number of through-holes along the flow direction of the exhaust gas. In a cross section perpendicular to the flow direction, the porosity is usually 60 to 90%, preferably 70 to 90%. And the number is one square inch (5.0
30 to 700, preferably 200 to 6, 6 cm ² )
00. The catalyst is coated on at least the inner surface of the through hole, but may be coated on the end surface or side surface of the supporting substrate.

As the material of the refractory support substrate, ceramics such as α-type alumina, mullite, cordierite, and silicon carbide, and metals such as austenitic and ferritic stainless steels are used. Conventional shapes such as honeycombs and foams can be used, but a honeycomb-shaped support substrate made of cordierite or stainless steel is preferred.

The method of coating the support substrate with a catalyst includes:
A so-called ordinary wash coat method or a sol-gel method, in which the catalyst of the present invention sized to a certain particle size is separately coated on the inner surface of the supporting substrate with or without a binder, can be applied. In the catalyst B, the support substrate was coated with alumina in advance,
This may be subjected to a treatment for supporting the catalytically active substance of the present invention to form a catalyst coating layer. The coating amount of the catalyst layer on the supporting substrate is not limited, but is 50 to 250 g per unit volume of the supporting substrate.
/ L, preferably about 100 to 200 g / l.

Next, an exhaust gas purifying method according to a third embodiment of the present invention will be described. A third embodiment of the present invention provides:
Using the catalyst layer of the first embodiment or the catalyst-coated structure of the second embodiment, CO, HC and H in the exhaust gas are used.
By contacting the exhaust gas containing excess oxygen from the stoichiometry near requiring ₂ such reducing component to be completely oxidized in the oxidizing components such ΝOx and O _2,
ΝOx simultaneously is reduced decomposed to the _{N 2 Η 2} O H
A reducing agent such as C is also oxidized to CO ₂ and H ₂ O.

In the present invention, the reason why the catalyst A is arranged in the former stage and the catalyst B is arranged in the latter stage is that the catalyst A in the former stage is
This is for improving the SOx durability in the total catalyst system by removing x by adsorption. The ratio between the catalyst A and the catalyst B may be arbitrarily selected according to the SOx durability performance and the NOx removal performance.

When the HC / NOx ratio of the exhaust gas itself is low, such as the exhaust gas of a diesel engine, the fuel ΗC having a concentration of several hundreds to several thousands ppm in terms of methane concentration in the exhaust gas.
If the system for contacting with the catalyst of the present invention is added after additionally adding, a sufficiently high NOx removal rate can be achieved. Note that HC referred to here includes paraffinic hydrocarbons, olefinic hydrocarbons and aromatic hydrocarbons, oxygen-containing organic compounds such as alcohols, aldehydes, ketones, and ethers, gasoline, kerosene, light oil, heavy oil A, and the like. Means something.

The gas space velocity (SV) at the time of purifying the combustion exhaust gas of the internal combustion engine operated in the lean air-fuel ratio range using the catalyst layer according to the present invention is not particularly limited. 200,000h ^-1 at ^-1 or more
It is preferable to set the following.

The denitration rate when the gas composition is constant depends on the type of catalyst and the type of HC. In the case of using the catalyst layer of the present invention, for example, C ₂ -C ₆ paraffin,
For aromatic HC olefins and _C 6 -C ₉ 4
50-600 ° C., 350-550 ° C. for C ₆ -C ₉ paraffins and olefins, 250-500 ° C. for C ₁₀ -C ₂₅ paraffins and olefins.
In order to show a high denitration rate, the catalyst layer inlet temperature is set to 100 ° C or higher and 700 ° C or lower, preferably 200 ° C or higher to 600 ° C.
It is necessary to:

[0031]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples. However, the present invention is not limited to the following examples. (1) Selection of Alumina for Catalyst B In order to select the alumina carrier to be used for Catalyst B, in various γ-type aluminas having specific surface areas and pore distributions as shown in Table 1, a to c of the present invention were used. Alumina falling within the range, and d to g are aluminas outside the scope of the present invention. In addition,
The pore distribution of the alumina particles a to g was measured by a soapmatic manufactured by Carlo Elba.

[0032]

[Table 1] ア ル ミ ナ Alumina specific surface area pore distribution (m ² / g) Y / Χ (%) Z / Χ (%) ─────────────────────────────────a 241 83.2 2.4 b 219 87.0 3.9 c 174 88.4 4.4 d 199 47.0 0.7 e 177 68.5 4.9 f 241 51.0 45.9 g 266 71.1 22. 7 ─────────────────────────────────

(2) Preparation of Catalyst Layer Hereinafter, preparation examples of preparation of each catalyst for constituting the catalyst layer of the present invention are shown as reference examples. (A) Preparation of Catalyst B: [Reference Example 1] 300 g of alumina hydrate, which is a precursor of γ-type alumina a in Table 1, was immersed in a 900 ml aqueous solution containing 16.1 g of silver nitrate, and then stirred. While heating, water was evaporated. This was air-dried at 110 ° C., and then calcined in air at 600 ° C. for 3 hours to obtain Catalyst 1. Incidentally, the content of Ag in terms of metal in the catalyst 1 was 4.5% by weight based on the whole catalyst.

Reference Examples 2 to 11 Similarly to Reference Example 1, except that alumina hydrate, which is a precursor substance from which γ-type aluminas b to g shown in Table 1 were obtained, was used. Catalyst 2 (Reference Example 2), Catalyst 3 (Reference Example 3), Catalyst 4 (Reference Example 4), Catalyst 5 (Reference Example 5), Catalyst 6 (Reference Example 6), and Catalyst 7 (Reference Example 7) Obtained. Catalyst 8 (Reference Example 1) was prepared in the same manner as in Reference Example 1 except that the silver content was 0%, 1%, 3%, and 8% by weight when preparing Catalyst 1 of Reference Example 1. 8), Catalyst 9 (Reference Example 9), Catalyst 10 (Reference Example 10), Catalyst 11 (Reference Example 1)
1) was obtained.

(B) Preparation of catalyst A: [Reference Example 12] 20 g of commercially available silica and 43 g of magnesium hydroxide were added to 300 ml of ion-exchanged water, and the mixture was added at room temperature.
After stirring for 0 minutes, the mixture was heated to evaporate water. This is 11
After ventilation drying at 0 ° C., the mixture was calcined in air at 550 ° C. for 3 hours to obtain Catalyst 12 (Reference Example 12). The content of Mg in the catalyst 12 in terms of metal was 36.2 with respect to the entire catalyst.
% By weight.

Reference Examples 13 to 16 Catalysts 13 (Reference Example 13) were prepared in the same manner as in Reference Example 12 except that strontium and barium were used in place of magnesium when preparing Catalyst 12 of Reference Example 12. Catalyst 15 (Reference Example 15) was prepared in the same manner as in Reference Example 12 except that the content of magnesium was set to 24.3% by weight, and that of Catalyst 14 (Reference Example 14) was changed to 22 g of magnesium hydroxide and 18 g of strontium hydroxide. Catalyst 16 (Reference Example 16) was obtained in the same manner as in Reference Example 12, except that Further, a catalyst composed of only commercially available silica was designated as catalyst 17 (Reference Example 17).

(C) Preparation of honeycomb catalyst: [Reference Examples 18 and 19]
g of alumina sol (Αl ₂ O ₃ solid content 10% by weight) 8
g and 120 ml of water were charged into a ball mill pot and wet-pulverized to obtain a slurry. Into this slurry, a 1 inch diameter bored from a commercially available 400 cpsi (cell / inch ² ) cordierite honeycomb substrate,
A 2.5-inch long cylindrical core was immersed and pulled up, and the excess slurry was removed by air blow and dried. Thereafter, the mixture was baked at 500 ° C. for 30 minutes to cover 150 g of solid content in terms of dry weight per liter of honeycomb.
Was obtained. Further, a honeycomb catalyst 19 of Reference Example 19 was obtained by the same preparation method as above except that the catalyst 12 was used instead of the catalyst 1 and the silica sol was used instead of the alumina sol.

The results of evaluating the denitration performance of the exhaust gas purifying catalyst layers formed using the catalysts of Reference Examples 1 to 19 under various conditions will be described below. Example 1 Catalyst 12 of Reference Example 12 and Catalyst 1 of Reference Example 1
Is press-molded, and then pulverized to a particle size of 350 to 5
The particle size is adjusted to 00 μm, and the catalyst 12
Was filled in a stainless steel reaction tube having an inner diameter of 21 mm so that the catalyst 1 was placed in the former stage to form a catalyst layer, and this was attached to a normal pressure fixed bed flow reactor. The weight ratio between the catalyst 12 and the catalyst 1 was 1: 1.

[Performance Evaluation Example 1] In this catalyst layer, NO: 750 ppm as model exhaust gas, and kerosene (C ₁ ): 450
0 ppm, O ₂ : 10%, H ₂ O: 10%, balance: N ₂
Was passed at a space velocity of 78,000 h ^-1 . In the analysis of the gas composition at the outlet of the reaction tube, NO and N
The concentration of O ₂ was measured with a chemiluminescent NOx meter,
_The 2O concentration was measured using a gas chromatograph / thermal conductivity detector equipped with a Ρorapack Q column. The catalyst layer inlet temperature was set to a predetermined temperature in the range of 100 to 700 ° C., and the value at the time when the gas composition at the outlet of the reaction tube became stable at each predetermined temperature was used to define the denitration rate by the following equation. N _{2 O} and NO ₂ at any of the catalysts of the present invention did not produce little.

[0040]

(Equation 1)

[Examples 2 to 9 and Comparative Examples 1 to 6] The catalysts 2, 3, and 9 to 11 of Reference Examples 2, 3, and 9 to 11 and the catalysts 4 to 8 of Reference Examples 4 to 8 were used in Example 1 respectively. A catalyst layer similar to the above was formed using the catalyst 1 in place of the above-described catalyst 1, and an evaluation test using a model gas was performed in the same manner. Catalysts 2, 3, 9
The catalyst layers using Nos. 1 to 11 are Examples 2 to 6, respectively.
The catalyst layers using catalysts 4 to 8 were Comparative Examples 1 to 5, respectively. Further, the catalysts 13 to 16 of Reference Examples 13 to 16 and the catalyst 17 of Reference Example 17 were each used instead of the catalyst 12 of Example 1 to form a catalyst layer similar to the above, and similarly evaluated with a model gas. The test was performed. Catalyst 13-1
The catalyst layers using the catalyst No. 6 were referred to as Examples 7 to 10, and the catalyst layer using the catalyst 17 was referred to as Comparative Example 6. Table 2 shows the catalyst layer temperature of 425 for the catalyst layers of the above Examples and Comparative Examples.
The denitration rate C ₄₂₅ (%) at ° C. is shown. The catalyst layers of Examples of the present invention and Comparative Example 6 exhibited a high denitration performance of 70% or more as compared with the catalyst layers of Comparative Examples 1 to 5.

[Performance Evaluation Example 2] In the performance evaluation example 1,
Each of the honeycomb catalyst 18 of Reference Example 18 and the honeycomb catalyst 19 of Reference Example 19 was 1.5 cm in diameter and 3.2 cm in length.
And filled in a stainless steel reaction tube having an inner diameter of 15 mm so that the honeycomb catalyst 18 was at the front stage and the honeycomb catalyst 18 was at the rear stage in the flow direction of the exhaust gas (Example 11). The space velocity of the gas to be fed to the catalyst layer of the subsequent honeycomb catalyst 18 is 13,000 h ^-1.
An evaluation test was performed using the same model gas as in Performance Evaluation Example 1 except that the evaluation was made, and the results are shown in Table 2 together with the results of Performance Evaluation Example 1.
Table 2 shows that the honeycomb catalyst layer also shows high denitration performance of 70% or more.

[0043]

[Table 2]

[Performance Evaluation Example 3] The catalyst layers of Examples 1, 8 and Comparative Example 6 were reacted for 1 hour in the gas composition of Performance Evaluation Example 1 in the presence of 50 ppm of SO ₂ . Table 3 shows the denitration ratio C ₄₂₅ (%) of each catalyst at a catalyst layer temperature of 425 ° C. after one hour. Embodiment 1 of the present invention
The catalyst layers of Nos. 8 and 8 maintained 70% or more of the activity as compared with the catalyst layer of Comparative Example 6.

[0045]

[Table 3] 評 価 Catalyst performance evaluation example 3 ─────────────── Example 1 77.5 Example 8 76 .9 Comparative Example 6 43.6───────────────

[0046]

As described above, according to the exhaust gas purifying catalyst layer, the exhaust gas purifying catalyst coated structure and the exhaust gas purifying method using the same according to the present invention, the nitrogen contained in the lean combustion exhaust gas in which water vapor coexists. Since it is possible to reduce and purify oxides at a high denitration rate and has SOx durability performance, it is useful for purifying nitrogen oxides in combustion exhaust gas of an internal combustion engine.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01J 23/50 ZAB F01N 3/10 A 35/10 301 3/28 J F01N 3/10 301C 3/28 B01D 53/36 ZAB 301 102A 102H 102C (72) Inventor Atsushi Katakei 3-18-5, China, Ichikawa, Chiba Sumitomo Metal Mining Co., Ltd. Central Research Laboratory (72) Inventor Kunihide Chino 678 Ipponmatsu 678, Numazu, Shizuoka Prefecture Numazu Plant

Claims (5)

[Claims] Claims 1. A relationship between silica, a catalyst A comprising at least one selected from the group consisting of magnesium, strontium and barium, and a relationship between a pore radius and a pore volume measured by a nitrogen gas adsorption method is as follows. The total value of the pore volume occupied by pores having a radius of 300 Å or less is defined as X, the total value of the pore volume occupied by pores having a radius of 25 Å or more and less than 100 Å is defined as Y, and a pore radius of 100 Å or more is defined. Is the total value of the pore volume occupied by pores of 300 Å or less in Z
, Y is 70% or more of X, and Z is 20% of X.
%. The catalyst layer for purifying exhaust gas, comprising an alumina carrier having a pore structure of not more than 0.1% and a catalyst B made of silver. 2. An exhaust gas purifying method, wherein at least an inner surface of a through-hole in a monolithic supporting substrate made of a refractory material having a large number of through-holes is coated with the catalyst according to claim 1 separately. Catalyst-coated structure. 3. A method for purifying exhaust gas using a hydrocarbon as a reducing agent, which comprises contacting flue gas of an internal combustion engine operated at a lean air-fuel ratio with a catalyst-containing layer, wherein the catalyst contained in the catalyst-containing layer is Item 7. An exhaust gas purifying method comprising the exhaust gas purifying catalyst layer according to Item 1. 4. A method for purifying exhaust gas using a hydrocarbon as a reducing agent, which comprises contacting flue gas from an internal combustion engine operated at a lean air-fuel ratio with a catalyst-containing layer, wherein the catalyst contained in the catalyst-containing layer is Item 3. An exhaust gas purifying method comprising the exhaust gas purifying catalyst-coated structure according to Item 2. 5. The exhaust gas purifying catalyst layer according to claim 3, wherein the catalyst A contained in the exhaust gas purifying catalyst layer is disposed at a front stage and the catalyst B is disposed at a rear stage in a flow direction of the exhaust gas. Exhaust gas purification method.