JPH1110002A - Exhaust gas purifying catalyst layer, exhaust gas purifying catalyst-coated structural body, and exhaust gas purifying method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas purifying catalyst layer, a catalyst-coated structural body and an exhaust gas purifying method for efficiently removing NOx in a lean combustion exhaust gas. SOLUTION: This exhaust gas purifying catalyst layer is constituted of a catalyst A formed by incorporating silver and rhodium or further tin on an alumina and a catalyst B formed by incorporating silver and >=0.01 wt.% to <=5 wt.% silica or titania on the alumina. The alumina has the fine pore structure that Y is >=70% of X and Z is <=20% of X in the relation between the fine pore radius and fine pore volume measured by gaseous nitrogen absorption method when the total value of the fine pore volume occupied by the pore having <=300 Åfine pore radius is X, the total value of the fine pore volume occupied by the pore having >=25 Å to <100 Å fine pore radius is Y and the total value of the fine pore volume occupied by the fine pore having 100-300 Åfine pore radius is Z. The catalyst A is arranged in the preceding stage and the catalyst B is arranged in the post stage.

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 a purifying catalyst coating 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 water oxides and carbon dioxide as combustion products, as well as nitrogen oxides (NOx) such as nitrogen monoxide and nitrogen dioxide. include. ΝOx 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 removing NOx 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 the unreacted reducing agent, and furthermore uses odorful and harmful ammonia, which is particularly dangerous for exhaust gas denitration technology from mobile sources such as automobiles. Not applicable.

[0006] In recent years, it has been reported that the use of unburned hydrocarbons remaining in a lean combustion exhaust gas in an oxygen-excess atmosphere as a reducing agent can accelerate the NOx reduction reaction. 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, N
An example in which alumina or silica-alumina containing i and V is used as a ΝOx reduction catalyst has been reported.

Further, when a catalyst in which Pt 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. JP-A-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 a large amount of が₂ O, which is one of the substances causing global warming, is by-produced. , it is made to proceed the reduction reaction of the harmless N ₂ selectively 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, similar ΝOx reduction and removal techniques using a catalyst containing silver are disclosed in JP-A-4-354536, JP-A-5-92124, and JP-A-5-9212.
No. 5, JP-A-6-277454 and the like.

[0009]

However, the alumina-supported silver catalysts described in these conventional publications are not suitable for SOx.
In addition, there is a problem that the denitration performance in the coexistence of steam is still insufficient for practical use.

SUMMARY OF THE INVENTION 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 capable of efficiently removing NOx in lean combustion exhaust gas. An object of the present invention is to provide a coating structure and an exhaust gas purifying method for purifying NOx in lean combustion 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 a catalyst coating structure having high denitration performance in a lean burn region where SOx and water vapor coexist, and an exhaust gas purifying structure using them. As a result of intensive studies on the method, it was found that alumina having a specific pore structure in the flow direction of the exhaust gas, silver and rhodium or, if necessary, catalyst A containing tin in advance, the specific pore The inventors have found that the above problems can be solved by arranging catalyst B containing a small amount of silver and silica or titania on alumina having a structure so as to be located at a later stage, and have completed the present invention.

That is, a first embodiment of the present invention for solving the above-mentioned problems is a catalyst A comprising alumina containing silver and rhodium or silver, tin and rhodium.
And a catalyst B comprising alumina and 0.01% by weight or more and less than 5% by weight of silica or titania, wherein the alumina has a pore radius measured by a nitrogen gas adsorption method. The relationship between the pore volumes is that the pore radius is 30.
The total value of the pore volume occupied by pores of 0 Å or less is defined as Χ, and 10
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.
An exhaust gas purifying catalyst having a pore structure in which Y is 70% or more of Χ and Ζ is 20% or less of Χ, where 合計 is the total value of pore volumes occupied by pores of 00 Å or less. Characterized by layers. 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, a support substrate having an integral structure made of a refractory material having a large number of through holes, and the above-mentioned catalyst layer provided on at least the inner surface of the through hole in the support substrate. The present invention is characterized by an exhaust gas purifying catalyst-coated structure that is separately coated.

Still further, a third embodiment of the present invention provides:
A method for removing NOx in exhaust gas using a hydrocarbon as a reducing agent, comprising contacting combustion 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 An exhaust gas purifying method, which is the catalyst layer according to the first embodiment or the catalyst coated structure according to the second embodiment, is characterized by the catalyst A contained in the exhaust gas purifying catalyst layer in the flow direction of the exhaust gas. Is characterized by an exhaust gas purification method in which a catalyst B is disposed in a former stage and a catalyst B is disposed in a latter stage.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention and its operation will be described more specifically below. (Catalyst Structure and Method for Producing the Same) Alumina, which is one of the main components of the catalysts A and B in the exhaust gas purifying catalyst layer of the present invention, is, for example, boehmite, pseudoboehmite, vialite or norstrandite in terms of mineralogy A powder or gel of aluminum hydroxide classified as is heated and dehydrated in air or vacuum at 300 to 800 ° C., preferably 400 to 900 ° C., thereby crystallographically obtaining γ-type and η-
It is preferable from the viewpoint of denitration performance that the phase transition is made to alumina classified into type, δ-type, 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 has a pore diameter measured by a nitrogen gas adsorption method having a pore radius of 300 angstroms or less and a total pore volume of 容積.
When the total value of the pore volume occupied by pores of 5 Å or more and less than 100 Å 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 Ζ,
Alumina must have a pore structure in which Y is 70% or more of Χ and Ζ is 20% or less of Χ. In the case where alumina having a pore structure not satisfying the above conditions is used as a carrier in the catalyst layer of the present invention, the exhaust gas purifying catalyst layer constituted by the alumina denitration of exhaust gas in the presence of SOx and steam. Performance was inadequate.
Therefore, it can be said that alumina having the above-mentioned crystal structure and pore characteristics is appropriate as the alumina effective as the catalyst component of the present invention.

The exhaust gas purifying catalyst layer of the present invention is the following catalyst. The catalyst layer according to the present invention comprises: a catalyst A comprising alumina containing silver and rhodium or silver, tin and rhodium; and alumina containing 0.01% by weight or more and less than 5% by weight of silica or titania with silver. Alumina is characterized by having the above-mentioned crystal structure and pore characteristics. In the catalyst A, the states of silver, tin, and rhodium contained in alumina are not particularly limited, and examples thereof include a metal state, an oxide state, an alloy state, and a mixed state thereof. The state of silver and silica or titania contained in alumina in the catalyst B is not particularly limited. For example, in the case of silver, an oxide state, a metal state, and a mixed state thereof are used, and in the case of silica or titania, an oxidation state is used. Physical condition,
Local composite oxide state and a mixed state thereof are included. In particular, since the composition of the combustion exhaust gas of an internal combustion engine such as a lean-burn gasoline-powered vehicle changes depending on operating conditions, the catalyst layer is exposed to a reducing atmosphere and an oxidizing atmosphere.
It is assumed that the state of the active metal forming the catalyst layer changes depending on the atmosphere. The starting materials of silver for catalysts A and B, rhodium (and tin) for catalyst A, and silica or titania for catalyst B are not particularly limited.

[0018] The alumina in the catalyst A according to the present invention contains silver, tin and rhodium;
The method for incorporating silver and silica or titania into the alumina in the catalyst B is not particularly limited, and conventionally used methods, for example, an adsorption method, a pore filling method, an incipient wetness method, an evaporation to dryness method, and a spray method Any known method such as an impregnation method, a kneading method, a physical mixing method, and a combination thereof can be arbitrarily adopted. In this case, in the catalyst A, a silver source and a rhodium source or a silver source, a tin source and a rhodium source may be simultaneously supported on alumina or an alumina precursor substance, and then dried and calcined, or a silver source and a rhodium source or After the silver source, the tin source and the rhodium source are successively supported, drying and firing may be performed. On the other hand, in the catalyst B, the silver source and the silica source or the titania source are simultaneously supported on the alumina or the alumina precursor material and dried, and then dried and calcined, or the silver source and the silica source or the titania source are successively added. After being supported, drying and baking may be performed. 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 in Catalyst A,
After mixing an alcohol solution of a silver source and a rhodium source or a silver source, a tin source and a rhodium source, and in the catalyst B, an alcohol solution of an aluminum alkoxide and various alcohol solutions of a silver source and a silica source or a titania source,
The alkoxide method of heating and hydrolyzing the catalyst, the catalyst A in an aqueous solution of an aluminum source, a silver source and a rhodium source or a silver source, a tin source and a rhodium source, and the catalyst B in an aluminum source, an silver source and a silica source or a titania A coprecipitation method in which an alkali is added to an aqueous solution mixed with a source to cause precipitation is also applicable.

The contents of silver, tin and rhodium in terms of metal with respect to the catalyst A are not particularly limited, but are each 0.1% in terms of denitration performance. 1 to 10% by weight, 0.01 to 5% by weight,
It is preferably from 0001 to 1% by weight. Further, the content of silver in terms of metal relative to catalyst B is not particularly limited, but is preferably 0.1 to 10% by weight. On the other hand, the content of silica or titania in terms of oxide is 0.01
It is necessary to be not less than 5% by weight and not less than 5% by weight. When the content of silica or titania is 5% by weight or more, the performance of silver is not exhibited, and the denitration performance is reduced. If the content is less than 0.01% by weight, the synergistic effect of the addition of silica or titania is not sufficiently exhibited, so that the content needs to be in the above range.

The drying temperature of the catalyst A and the catalyst B is not particularly limited, and drying is usually performed at about 80 to 120 ° C. The firing temperature is 300 to 1000 ° C., preferably 400 to 1000 ° C.
About 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. The catalyst-coated structure referred to here has a structure in which at least the inner surface of the through-hole is divided and coated with the above-described catalyst layer on a support substrate having an integral structure 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 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 layer is coated at least on the inner surface of the through hole, but may be coated on the end face or side face 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 coating method of the catalyst layer on the support substrate is as follows: the catalyst of the present invention, sized to a fixed particle size, is divided into at least the inner surface of the through hole of the support substrate with or without a binder. So-called ordinary wash coat method and sol-gel method can be applied. Alternatively, the support substrate may be coated with alumina in advance, and then the catalyst active layer of the present invention may be subjected to a treatment to form a catalyst coating layer. The amount of the catalyst layer coated on the supporting substrate is not particularly limited, but may be 50 to 50 per unit volume of the supporting substrate.
About 250 g / l, preferably 100 to 200 g / l.
More preferably, the amount is about g / liter.

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:
By using the catalyst layer of the first embodiment and the catalyst-coated structure of the second embodiment, CO, ΗC and Η in the exhaust gas are used.
By _two such reducing component contacting a flue gas containing excess oxygen from the stoichiometry near required to complete oxidation with oxidizing components such as NOx and O _2,
NOx is reduced and decomposed to N ₂ and { ₂ O}
Reducing agent such as C are also intended to be oxidized to Eta _{2 O} and CΟ _2.

In the present invention, the catalyst A is placed before the catalyst B,
The reason for disposing in the subsequent stage is to prevent coking at the catalyst inlet portion, and the ratio between the catalyst A and the catalyst B may be appropriately selected according to the required performance.

When the ΗC / NOx ratio of the exhaust gas itself is low, such as the exhaust gas of a diesel engine, the fuel ΗC having a methane conversion concentration of about several hundreds to several thousands ppm in the exhaust gas.
If the system for contacting with the catalyst layer of the present invention is used after additionally adding, a sufficiently high NOx removal rate can be achieved.
Here, ΗC 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.

[0029] not particularly limited gas space velocity (SV) is the time for purifying combustion exhaust gas of an internal combustion engine is operated in the region of the lean air-fuel ratio using the catalyst layer according to the present invention but, SV5,000h ^- 200,000h ^{-1 for 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 ΔC. In the case of using the catalyst layer of the present invention, for example, C _{2 to} C ₆ paraffin,
4 for olefins and C ₆ -C ₉ aromatic ΔC
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 exhibit a high denitrification rate, it is necessary to set the catalyst layer inlet temperature at 100 ° C. or higher to 700 ° C. or lower, preferably at 200 ° C. to 600 ° C.

[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 In order to select an alumina carrier to be used, a variety of γ-type aluminas having a specific surface area and a pore distribution as shown in Table 1 are used. Yes, d
To g are aluminas outside the scope of the present invention. In addition, the pore distribution of alumina of a to g was measured by a soapmatic manufactured by Carlo Elba.

[0032]

[Table 1] ─────────────────────────────── Alumina specific surface area pore distribution (m ² / g) Y / Χ (%) Ζ / 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 A preparation example for preparing a catalyst for constituting the catalyst layer of the present invention is shown below as a reference example. (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 mixed with 16.1 g of silver nitrate and silica sol (SiO ₂ : 20% by weight) 12 After immersion in 500 ml of an aqueous solution containing 0.5 g, the mixture was heated with stirring to evaporate water. This was dried by ventilation at 110 ° C., and then calcined in air at 550 ° C. for 3 hours to obtain Catalyst 1. The contents of Ag in terms of metal and SiO ₂ in terms of oxide in the catalyst 1 were 4.5% by weight and 1.1% by weight, respectively, based on the entire catalyst.

Reference Example 2 to Reference Example 18 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) were obtained. Reference Example 1
Catalyst 8 (Reference Example 8) and Catalyst 9 (Catalyst 1) except that the silver content was 0%, 2%, 3%, and 8% by weight when preparing Catalyst 1. Reference Example 9), Catalyst 10 (Reference Example 10), Catalyst 11 (Reference Example 11), and silica contents of 0% by weight, 0.002% by weight, 0.1%
Catalyst 12 (Reference Example 1) in the same manner as in Reference Example 1 except that the content was changed to 1.6%, 1.6%, 3%, and 5% by weight.
2), catalyst 13 (Reference Example 13), catalyst 14 (Reference Example 1)
4), catalyst 15 (Reference Example 15), catalyst 16 (Reference Example 1)
6) The catalyst 17 (Reference Example 17) was replaced by a titania sol (TiO ₂ : 30% by weight) 8.3 instead of the silica sol.
Catalyst 18 (Reference Example 18) was obtained in the same manner as in Reference Example 1, except that g was used.

(B) Preparation of catalyst A: [Reference Examples 19 to 25] γ-type alumina a in Table 1
Was immersed in a 500 ml aqueous solution containing 16.1 g of silver nitrate, and heated with stirring to evaporate water. This one
After ventilation drying at 10 ° C., the mixture was calcined in air at 550 ° C. for 3 hours to obtain a catalyst b. Next, 100 g of the catalyst b was immersed in 500 ml of an aqueous solution containing 0.16 g of an aqueous rhodium nitrate solution (Rh concentration 5%) and 0.3 g of stannic chloride pentahydrate. And catalyst 19
(Reference Example 19) was obtained. The contents of Ag, Rh and Sn in terms of metal in the catalyst 19 were 4.5% by weight, 0.008% by weight and 0.1% by weight, respectively, based on the entire catalyst. Also, in preparing catalyst 19 of Reference Example 19, each of Catalysts 20 (Reference Example 20) was prepared in the same manner as Reference Example 19 except that the rhodium content was 0.004% by weight, 0.05% by weight, and 2% by weight. ), Catalyst 21 (Reference Example 2)
1) and Catalyst 22 (Reference Example 22), except that the tin content was 0% by weight and 0.3% by weight in the same manner as in Reference Example 19, respectively. Example 2
Catalyst 25 (Reference Example 25) was obtained in the same manner as in Reference Example 19 except that γ-type alumina f in Table 1 was used.

(C) Preparation of honeycomb catalyst: [Reference Examples 26 and 27] 6 of the above powder catalyst 1
0 g of alumina sol (Al ₂ O ₃ solid content 20% by weight)
5 g and 120 ml of water were charged into a ball mill pot and wet-pulverized to obtain a slurry. In this slurry, a commercially available 400 cpsi (cell / inch ² )
A cylindrical core having a diameter of 1 inch and a length of 2.5 inches penetrated from a cordierite honeycomb substrate was immersed and pulled up, and then excess slurry was removed by air blow and dried. Thereafter, the mixture was fired at 500 ° C. for 30 minutes, and coated with 150 g of solid content in terms of dry weight per liter of honeycomb to obtain a honeycomb catalyst 26 (Reference Example 26).

Also, 60 g of the above-mentioned powder catalyst 19 was mixed with 5 g of alumina sol (Al ₂ O ₃ solid content of 20% by weight).
And 120 ml of water were charged into a ball mill pot and wet-pulverized to obtain a slurry. A cylindrical core having a diameter of 1 inch and a length of 2.5 inches penetrated from a commercially available 400 cpsi (cell / inch ² ) cordierite honeycomb substrate is immersed in the slurry, and the excess slurry is air blown. And dried.
Then, it was baked at 500 ° C. for 30 minutes, and coated with 150 g of solid content in terms of dry weight per liter of honeycomb to obtain a honeycomb catalyst 27 (Reference Example 27).

Hereinafter, the results of evaluating the denitration performance of the exhaust gas purifying catalyst layer formed using the catalysts of Reference Examples 1 to 27 under various conditions will be described. Example 1 Catalyst 19 of Reference Example 19 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 19
Was filled in a stainless steel reaction tube having an inner diameter of 15 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 of catalyst 19 to catalyst 1 was 1:10.

[Performance Evaluation Example 1] The temperature of the exhaust gas in the reaction tube was maintained at 425 ° C.
Ο: 750 ppm, kerosene (C ₁ ): 4500 ppm, O
_{2: 10%, Η 2 O} : 10%, the balance: was a mixed gas consisting of _{N 2} was passed at a space velocity (SV) 78,000h ^-1. In the analysis of the gas composition at the outlet of the reaction tube, NO and NO ₂
Was measured with a chemiluminescent NOx meter, and N ₂ O
The concentration was measured using a gas chromatograph / thermal conductivity detector equipped with a Ρorapack Q column. The denitration rate was defined by the following equation (1). Further, N ₂ O and NO ₂ were hardly generated in any of the catalyst layers of the present invention.

[0040]

(Equation 1)

Examples 2 to 14 and Comparative Examples 1 to 10
Catalysts 2 of Reference Examples 2, 3, 9 to 11, 14 to 16, and 18,
3, 9-11, 14-16, 18 and Reference Examples 4-8,
Using the catalysts 4 to 8, 12, 13, and 17 of 12, 13, and 17 instead of the catalyst 1 of Example 1, respectively, a catalyst layer similar to the above was formed, and a model gas evaluation test was performed in the same manner. . The catalyst layers using catalysts 2, 3, 9 to 11, 14 to 16, and 18 were referred to as Examples 2 to 10, respectively.
The catalyst layers using 8, 12, 13, and 17 were Comparative Examples 1 to 8, respectively. Further, instead of the catalyst 19 of Example 1,
Catalysts 20, 21, 2 of Reference Examples 20, 21, 23, 24
Using catalysts 3 and 24 and catalysts 22 and 25 of Reference Examples 22 and 25, a catalyst layer was formed in the same manner as in Example 19, and a model gas evaluation test was performed in the same manner. Catalysts 20, 21, 23,
A model gas evaluation test was performed in the same manner as described above, using the catalyst layers using 24 as Examples 11 to 14 and the catalyst layers using catalysts 22 and 25 as Comparative Examples 9 and 10, respectively. Table 2 below shows the initial activity of each catalyst layer as a result.

Performance Evaluation Example 2 (Example 15) In Performance Evaluation Example 1, the honeycomb catalyst 26 of Reference Example 26
5 mm, length 32 mm, the honeycomb catalyst 2 of Reference Example 27
7 was processed into a cylindrical shape with a diameter of 15 mm and a length of 3.2 mm,
The honeycomb catalyst 27 is arranged at the front stage in the flow direction of the exhaust gas,
A stainless steel reaction tube having an inner diameter of 15 mm was filled so that the honeycomb catalyst 26 was located at a later stage. Space velocity (SV) of gas fed to the catalyst layer of the honeycomb catalyst 26
The evaluation test was performed using the same model gas as in Performance Evaluation Example 1 except that the ^value was changed to 13,000 h ^−1, and the results are shown in Table 2 together with the results of Performance Evaluation Example 1.

[0043]

[Table 2]

As shown in Table 2, Examples 1 to 15 and Comparative Example 6
Comparative Examples 1 to 8 have an initial activity of 60% or more.
-5, 9 and 10 showed higher activity than the catalyst layers.

[Performance Evaluation Example 3] Performance evaluation example 1 was applied to the catalyst layers of Examples 1, 8 and Comparative Examples 6 to 8.
A durability test using a model gas similar to that of Performance Evaluation Example 1 was performed except that a gas in which 10 ppm of SO ₂ was further coexisted with the gas composition of Example 1 was fed. Table 3 shows the values at the time when the activity of each catalyst layer was stabilized.

[0046]

[Table 3] 活性 Activity after catalyst endurance First stage Second stage (%) ───────── ───────────────── Example 1 Catalyst 19 + Catalyst 1 64 Example 8 Catalyst 19 + Catalyst 15 60 Comparative Example 6 Catalyst 19 + Catalyst 12 51 Comparative Example 7 Catalyst 19 + Catalyst 13 50 Comparison Example 8 Catalyst 19 + Catalyst 17 51 ──────────────────────────

As can be seen from Table 3, the catalyst layers of Examples 1 and 8 exhibited an activity of 60 % or more even after running.

[0048]

As described above, according to the exhaust gas purifying catalyst layer and the exhaust gas purifying catalyst coating structure of the present invention, and the exhaust gas purifying method using the same, water vapor is contained in the coexisting lean combustion exhaust gas. Since nitrogen oxides can be reduced and purified with a high denitration rate and exhibit excellent durability in the presence of SOx, they are useful for purification of nitrogen oxides in combustion exhaust gas of an internal combustion engine.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI B01D 53/36 102H (72) Inventor Atsushi Katakei 3-18-5 Chugoku, Ichikawa, Chiba Sumitomo Metal Mining Co., Ltd. On-site (72) Inventor Masaki Funabiki 678 Ipponmatsu, Numazu City, Shizuoka Prefecture. Echem Cat Co., Ltd. Numazu Factory

Claims (6)

[Claims] 1. A catalyst A comprising alumina containing silver and rhodium, and a catalyst B comprising alumina containing 0.01% by weight or more and less than 5% by weight of silica or titania. The alumina has a relationship between a pore radius and a pore volume measured by a nitrogen gas adsorption method, wherein the total pore volume occupied by pores having a pore radius of 300 Å or less is X, and the pore radius is When the total value of the pore volume occupied by pores of 25 Å or more and less than 100 Å 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 Ζ, Y is 70% of X
The exhaust gas purifying catalyst layer having a pore structure wherein Z is 20% or less of X. 2. The exhaust gas purifying catalyst layer according to claim 1, wherein the catalyst A further comprises tin in alumina. 3. A catalyst substrate according to claim 1 or 2, wherein at least the inner surface of the through-hole in a support substrate having a unitary structure made of a refractory material having a large number of through-holes is divided and coated. An exhaust gas purifying catalyst-coated structure. 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 purification method comprising the exhaust gas purification catalyst layer according to Item 1 or 2. 5. A method for purifying exhaust gas using a hydrocarbon as a reducing agent, comprising contacting combustion 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 Item 4. An exhaust gas purifying method comprising the exhaust gas purifying catalyst coating structure according to Item 3. 6. The catalyst according to claim 4, 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.