JPH10128070A - Exhaust gas purifying catalyst layer, exhaust gas purifying catalyst coated structure and exhaust gas purifying method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas purifying catalyst layer and a catalyst coating structure capable of efficiently removing NOx in a lean combustion exhaust gas, and a lean combustion exhaust gas using the same. An exhaust gas purification method for purifying NOx with high efficiency and high reliability is provided. SOLUTION: Alumina is made of magnesium, calcium,
A catalyst A containing at least one selected from the group consisting of strontium and barium;
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 angstroms is Z, the alumina carrier having a pore structure in which Y is 70% or more of X and Z is 20% or less of X is added to silver. And an exhaust gas purifying catalyst layer comprising: a catalyst B containing:

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, 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 a novel exhaust gas purifying catalyst layer and an exhaust gas 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 nitrogen oxides (NOx) such as nitric oxide and nitrogen dioxide together with water and carbon dioxide as combustion products. Have been. NOx not only adversely affects the human body, particularly the respiratory system, but also becomes 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.

However, since the three-way catalyst system has an absolute condition that the engine is operated at a stoichiometric ratio, it 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 not only requires a special device for the recovery treatment of the unreacted reducing agent, but also uses ammonia, which has a strong odor and is harmful. Not applicable due to danger.

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.

[0007] Further, Japanese Patent Application Laid-Open No. 4-267946 discloses that 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.
JP-A-5-68855 and JP-A-5-103949
No., etc. However, when these supported precious metal catalysts are used, the combustion reaction of hydrocarbons as a reducing agent is excessively promoted, and a large amount of N ₂ O, which is one of the substances causing global warming, is produced as a by-product. Harmless
However, it had a drawback that it was difficult to selectively advance the reduction reaction to ₂ .

One of the present applicants has previously found that the use of a catalyst containing silver with a hydrocarbon as a reducing agent under an oxygen-excess atmosphere causes the NOx reduction reaction to proceed selectively. -281844. Even after the disclosure, similar 類似 Ox 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 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 and a catalyst coating structure capable of efficiently removing NOx in lean combustion exhaust gas. An object of the present invention is to provide an exhaust gas purifying method for purifying NOx in lean combustion exhaust gas with high efficiency and high reliability by 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 intensive studies on the exhaust gas purification method, the catalyst A comprising at least one selected from the group consisting of magnesium, calcium, strontium and barium in alumina with respect to the flow direction of the exhaust gas, The inventors have found that the above problems can be solved by arranging the catalyst B containing silver on alumina having a specific pore structure so as to be located at a later stage, thereby completing the present invention.

That is, a first embodiment of the present invention for solving the above-mentioned problems comprises a catalyst A comprising alumina containing at least one selected from the group consisting of magnesium, calcium, strontium and barium;
The relationship between the pore radius and the pore volume measured by the nitrogen gas adsorption method is such that the total pore volume occupied by pores having a pore radius of 300 Å or less is X, and the pore radius is 25 Å or more and less than 100 Å. Let Y be the total value of the pore volume occupied by pores having a pore radius of 100 Å or more and 300 Å or less, and let Z be 7
0% or more and a catalyst B comprising silver contained in an alumina carrier having a pore structure in which Z is 20% or less of X
And an exhaust gas purifying catalyst layer 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.

Further, a third embodiment of the present invention relates to a method of removing NOx in exhaust gas by bringing combustion exhaust gas of an internal combustion engine operated at a lean air-fuel ratio into contact with a catalyst-containing layer. The catalyst contained is the catalyst layer in the first embodiment or the catalyst-coated structure in the second embodiment, and is divided such that the catalyst A is at the front stage and the catalyst B is at the rear stage in the flow direction of the exhaust gas. The method is characterized by an exhaust gas purification method arranged in the manner described above.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention and its operation will be more specifically described below. (Catalyst Structure and Method for Producing the Same) Alumina, which is one of the main components of the catalyst A and the catalyst B in the exhaust gas purifying catalyst layer of the present invention, is, for example, boehmite, pseudo-boehmite,
Vialite or aluminum hydroxide powder or gel classified as norstrandite is placed in air or vacuum at 300 to 800 ° C, preferably 400 to 900 ° C.
By heating and dehydration, crystallographically γ-type, 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.

Particularly, the alumina of the catalyst B is defined as X, where X is the total pore volume occupied by pores having a pore radius of 300 angstroms or less measured by a nitrogen gas adsorption method, and 100 when the pore radius is 25 angstroms or more. When the total value of the pore volume occupied by pores smaller than Angstroms is Y, and the total value of the pore volume occupied by pores having a radius of 100 Å or more and 300 Å or less is Z, Y is 70 of Χ. % Or more and Z must be 20% or less of X. In the case where alumina having a pore structure not satisfying the above-mentioned 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, it can be said that alumina having the above-mentioned crystal structure and pore characteristics is suitable as the alumina effective as a component of the catalyst B 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 is on alumina,
A catalyst A containing at least one selected from the group consisting of magnesium, calcium, strontium and barium; and a catalyst B containing silver in alumina having the above-mentioned crystal structure and pore characteristics. Things. The state of magnesium, calcium, strontium and barium contained in the alumina of the catalyst A is not particularly limited. In addition, the state of silver contained in the alumina of the catalyst B is not particularly limited, for example, a metal state,
An oxide state and a mixed state thereof are exemplified.
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 materials of magnesium, calcium, strontium and barium in the catalyst A and silver in the catalyst B are not particularly limited.

The method of causing the alumina in the catalyst A to contain at least one selected from the group consisting of magnesium, calcium, strontium and barium, and the method of causing the alumina in the catalyst B to contain silver are not particularly limited. Commonly used techniques such as adsorption, pore filling, incipient wetness, evaporation to dryness, impregnation such as spraying, kneading, physical mixing, and combinations thereof. A known method can be arbitrarily adopted.

In the case of the catalyst A, alumina or a precursor material of alumina is made to contain at least one selected from the group consisting of a magnesium source, a calcium source, a strontium source and a barium source, and then dried and calcined. Further, a method for producing a catalyst comprising at least one selected from the group consisting of a magnesium source, a calcium source, a strontium source and a barium source when producing an alumina carrier,
For example, an alkoxide method of mixing an alcohol solution of an aluminum alkoxide and an alcohol solution containing at least one selected from the group consisting of a magnesium source, a calcium source, a strontium source and a barium source, followed by heating and hydrolysis, a magnesium source, A coprecipitation method in which an alkali is added to a mixed aqueous solution of an aluminum source and at least one selected from a calcium source, a strontium source, and a barium source to precipitate the solution, can also be applied.

In the case of the catalyst B, a silver source is supported on alumina or an alumina precursor material, and then dried and calcined. In addition, 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, mixing an alcohol solution of aluminum alkoxide and an alcohol solution of silver source, followed by heating and adding water An alkoxide method of decomposing or a coprecipitation method of adding an alkali to an aqueous solution of an aluminum source or a silver source for precipitation is also applicable.

The content of at least one selected from the group consisting of magnesium, calcium, strontium and barium in the catalyst A is not particularly limited, and can be arbitrarily selected according to the required performance. On the other hand, the content of silver in terms of metal with respect to alumina in the catalyst B is not particularly limited, but is preferably in the range of 0.1 to 10% by weight, and particularly preferably in the range of 2 to 8% by weight in terms of denitration performance. If the amount of silver supported is less than 0.1% by weight, the effect is not sufficiently exhibited,
If it exceeds 10% by weight, the combustion reaction of the hydrocarbon as the reducing agent proceeds preferentially, and the NOx removal characteristics deteriorate.

The drying temperature is not particularly limited, and it is usually dried at about 80 to 120 ° C. The firing temperature is 3
The temperature is about 00 to 1000C, preferably about 400 to 900C. 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 the catalyst layer for purifying exhaust gas is formed, the above-mentioned catalyst is formed into a predetermined shape or is kept in a powdery state in a certain space where the target exhaust gas flows. Fill. When forming the catalyst layer into a molded body, the shape is not particularly limited, for example, spherical,
Various shapes such as 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. The shape may be a conventional one such as a honeycomb or a foam, but a preferable one is a honeycomb-shaped support substrate made of cordierite or stainless steel.

As a method for coating the support substrate with a catalyst,
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 coated on the inner surface of the support substrate with or without a binder, 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 coating amount of the catalyst layer on the supporting substrate is not limited, but is preferably about 50 to 250 g / l per unit volume of the supporting substrate, and
More preferably, it is about 0 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
Reducing agents such as C are also oxidized to CO ₂ and H ₂ O.

In the present invention, the catalyst A is arranged at the front stage and the catalyst B is arranged at the rear stage.
This is for improving the Ox durability. 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 about 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 region 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. When the catalyst layer of the present invention is used, for example, C _{2 to} 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 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. or higher to 600 ° C. or lower.

[0033]

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 an alumina carrier to be used for catalyst B, a to c of the present invention are used in various γ-type aluminas having specific surface areas and pore distributions as shown in Table 1. And 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.

[0034]

[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 will be shown as reference examples. (A) Production 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 900 ml of an 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. The content of Ag in the catalyst 1 in terms of metal was 4.5% by weight based on alumina.

Reference Example 2 to Reference Example 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) were obtained. Reference Example 1
Catalyst 8 (Reference Example 8) and Catalyst 9 were prepared in the same manner as in Reference Example 1 except that the silver content was changed to 0% by weight, 1% by weight, 3% by weight, and 8% by weight. (Reference Example 9), Catalyst 10 (Reference Example 10), Catalyst 11 (Reference Example 1)
1) was obtained.

(B) Production of catalyst A: [Reference Example 12] 55.3 g of alumina hydrate and calcium hydroxide 7 which are precursors of γ-type alumina a in Table 1
9.3 g was added to 300 ml of ion-exchanged water, and
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 Ca content of the catalyst 12 in terms of metal was 43% by weight based on alumina.

Reference Examples 13 to 18 Reference Example 1 above
Catalyst 12 (Reference Example 1) was prepared in the same manner as in Reference Example 12 except that magnesium, strontium, and barium were used in place of calcium in preparing Catalyst 12.
3), catalyst 14 (Reference Example 14), catalyst 15 (Reference Example 1)
Catalyst 16 (Reference Example 16) was obtained in the same manner as in Reference Example 12 except that the content of 5) was changed to 48% by weight of calcium. Also, a catalyst 17 (Reference Example 17) was obtained in the same manner as in Reference Example 12, except that alumina hydrate which was a precursor substance of the γ-type alumina f in Table 1 was used. Further, a catalyst composed of only commercially available silica was designated as Catalyst 18 (Reference Example 18).

(C) Production of honeycomb catalyst: [Reference Examples 19 and 20] 60 g of the above powdered catalyst 1
To 8 g of alumina sol (Αl ₂ O ₃ solid content 10% by weight)
And 120 ml of water in a ball mill pot,
The slurry was obtained by wet pulverization. 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. afterwards,
Baking at 500 ° C. for 30 minutes, and covering 150 g of solid content in terms of dry weight per liter of honeycomb, 4.5% Αg /
A honeycomb catalyst 19 of Reference Example 19 having a composition of Αl ₂ O ₃ was obtained. Also, except that catalyst 12 was used instead of catalyst 1,
The honeycomb catalyst 20 of Reference Example 20 was prepared by the same preparation method as described above.
I got

The results of evaluating the denitration performance of the catalyst layers for purifying exhaust gas formed using the catalysts of Reference Examples 1 to 20 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 is 1: 1.

[Performance Evaluation Example 1] In this catalyst layer, NO: 750 ppm and kerosene (C ₁ ): 450 as model exhaust gas
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. Further, N ₂ O and NO ₂ were hardly produced by any of the catalysts of the present invention.

[0042]

(Equation 1)

[Examples 2 to 11 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,
The catalyst layers using the catalysts 9 to 11 are referred to as Examples 2 to 6, and the catalyst layers using the catalysts 4 to 8 are referred to as Comparative Examples 1 to 5, respectively.
It was set to 5. Further, the catalysts 13 to 17 of Reference Examples 13 to 17 and the catalyst 18 of Reference Example 18 were respectively replaced with the catalyst 1 of Example 1.
A catalyst layer similar to that described above was formed in place of Sample No. 2, and an evaluation test using a model gas was performed in the same manner. Catalyst 13
The catalyst layers using the catalysts 18 to 17 were referred to as Examples 7 to 11, respectively, and the catalyst layer using the catalyst 18 was referred to as Comparative Example 6. Table 2
The denitration rate C ₄₂₅ (%) at the catalyst layer temperature of 425 ° C. for the catalyst layers of the above Examples and Comparative Examples is shown below. The catalyst layers of Examples of the present invention and Comparative Example 6 exhibited higher denitration performance of 80% or more than the catalyst layers of Comparative Examples 1 to 5.

Performance Evaluation Example 2 (Example 12) In Performance Evaluation Example 1, the honeycomb catalyst 19 of Reference Example 19 and the honeycomb catalyst 20 of Reference Example 20 were each 1.5 cm in diameter.
It was processed into a cylindrical shape having a length of 3.2 cm, and filled in a stainless steel reaction tube having an inner diameter of 15 mm so that the honeycomb catalyst 20 was at the front stage and the honeycomb catalyst 19 was at the rear stage in the flow direction of the exhaust gas (Example 12). . An evaluation test was performed on the latter catalyst layer using the same model gas as in Performance Evaluation Example 1 except that the space velocity of the gas to be fed was 13,000 h ⁻¹ , and the results are shown in Table 2. From Table 2, it can be seen that even the catalyst layer composed of the honeycomb shows high denitration performance of 70% or more.

[0045]

[Table 2] ─────────────────────────── Catalyst layer First stage Second stage Denitration rate (%) ───────── ────────────────── Example 1 Catalyst 12 Catalyst 1 91.8 Example 2 Catalyst 12 Catalyst 2 90.9 Example 3 Catalyst 12 Catalyst 3 88.5 Comparative Example 1 Catalyst 12 Catalyst 4 20.0 Comparative Example 2 Catalyst 12 Catalyst 5 2.9 Comparative Example 3 Catalyst 12 Catalyst 6 30.9 Comparative Example 4 Catalyst 12 Catalyst 7 25.9 Comparative Example 5 Catalyst 12 Catalyst 8 35.5 Example 4 Catalyst 12 Catalyst 9 87.0 Example 5 Catalyst 12 Catalyst 10 94.9 Example 6 Catalyst 12 Catalyst 11 82.1 Example 7 Catalyst 13 Catalyst 1 88.9 Example 8 Catalyst 14 Catalyst 1 93.0 Example 9 Catalyst 15 Catalyst 1 91.6 Example 10 Catalyst 16 Catalyst 1 83.8 Example 11 Catalyst 17 Catalyst 88.5 Comparative Example 6 Catalyst 18 Catalyst 1 86.8 Example 12 Catalyst 20 Catalyst 19 78.3 ───────────────────────────

[Performance Evaluation Example 3] The catalyst layers of Example 1, Example 7, Example 10 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. Was. Table 3 shows the catalyst layer temperature 42 after one hour.
The denitration rate C ₄₂₅ (%) of each catalyst at 5 ° C. is shown. The catalyst of the example of the present invention maintained 70% or more of the activity as compared with the catalyst of the comparative example. The catalyst of Comparative Example 6 has high initial performance,
The durability in an O ₂ coexisting gas is low.

[0047]

[Table 3] 評 価 Catalyst performance evaluation example 3 ─────────────── Example 1 81.9 Example 7 79 .8 Example 10 74.8 Comparative Example 6 43.6

[0048]

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 with a high denitration rate and has SOx durability, it is useful for purifying nitrogen oxides in combustion exhaust gas of an internal combustion engine.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ Identification code FI B01J 35/10 301 B01D 53/36 ZABC 102A 102C (72) Inventor Atsushi Katakei 3-18-5, Chugoku, Ichikawa-shi, Chiba Inside the Central Research Laboratory, Sumitomo Metal Mining Co., Ltd. (72) Inventor Ken Ito 2-4-1 Hamamatsucho, Minato-ku, Tokyo Inside N-Echemcat Co., Ltd. (72) Inventor Yukio Ozaki 678 Ipponmatsu 678, Ipponmatsu, Numazu, Shizuoka Prefecture Cat Corporation Numazu Plant (72) Inventor Makoto Nagata 3-19-3, China, Ichikawa City, Chiba Prefecture

Claims (5)

[Claims] 1. A catalyst A comprising alumina containing at least one member selected from the group consisting of magnesium, calcium, strontium and barium, and a catalyst having a pore radius and a pore volume measured by a nitrogen gas adsorption method. In the relationship, X is the total pore volume occupied by pores having a pore radius of 300 Å or less, and Y is the total pore volume occupied by pores having a pore radius of 25 Å or more and less than 100 Å. When 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 X.
And a catalyst B comprising silver contained in an alumina carrier having a pore structure in which Z is 20% or less of X. 2. A catalyst-coated structure for purifying an exhaust gas, wherein at least the inner surface of the through-hole is coated with the catalyst according to claim 1 in a support substrate having an integral structure made of a refractory material having a large number of through-holes. . 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 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.
The exhaust gas purifying method according to the above.