JPH11104492A - Exhaust gas purifying catalyst layer, exhaust gas purifying catalyst coated structure, and exhaust gas purifying process using the layer and the structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas purifying and catalytic process for purifying NOx in dilute combustion exhaust gas with high efficiency and high reliability. SOLUTION: An exhaust gas purifying catalyst layer is composed of a catalyst A containing alumina and/or alumina and at least one kind selected from alkaline earth metals and a catalyst B composed of an alumina carrier containing silver or silver and silica or titanium and having a pore structure in which the relation between the pore radius and the pore volume measured by the nitrogen gas adsorption method, is satisfied as: Y is 70% or more of X and Z is 20% or less of X when the total value of pore volume occupied by pores of pore radius of 300 angstrom or less is set as X, the total value of pore volume occupied by pores of pore radius of >=25 angstrom to <=100 angstrom is set as Y and the total value of pore volume occupied by pores of pore radius of >=100 angstrom or larger to <=300 angstrom is set as 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, 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. Have been. NOx not only adversely affects the human body, especially 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.

[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 not only a special device for the recovery treatment of the unreacted reducing agent, but also the use of ammonia, which has a strong odor and is harmful. It is dangerous and cannot be applied.

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 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, 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 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 a 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 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 diligent research on exhaust gas purification methods for alumina, alumina and / or alkaline earth metals (magnesium,
Calcium, strontium, barium), and before the catalyst A containing at least one selected from the group consisting of alumina having a specific pore structure, and silver containing silver or a trace amount of silica or titania. The inventors have found that the above-mentioned problems can be solved by arranging the catalyst B separately in the latter stage so that the present invention has been completed.

That is, a first embodiment of the present invention for solving the above-mentioned problems is to provide a catalyst A containing at least one selected from alumina and / or an alkaline earth metal, and a nitrogen gas adsorption method. The relationship between the pore radius and the pore volume measured by the following formula is defined as X, where the total value of the pore volumes occupied by pores having a pore radius of 300 Å or less is X, and pores having a pore radius of 25 Å or more and less than 100 Å are obtained. Assuming that the total value of the pore volume occupied by 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% or more of X, and Z is A catalyst B comprising silver contained in an alumina carrier having a pore structure not more than 20% of X. The alumina support medium B, and further contain silica or titania is characterized by comprising, additionally alkaline earth metal of the catalyst A, magnesium,
It is characterized by an exhaust gas purifying catalyst layer comprising calcium, strontium and barium. The catalyst layer is preferably disposed in a flow space of the exhaust gas in a powdered or molded state.

According to a second embodiment of the present invention, at least the inner surface of the through-hole in a support substrate having an integral structure made of a refractory material having a large number of through-holes is coated with the above-mentioned catalyst in a divided manner. It is characterized by an exhaust gas purifying catalyst-coated structure.

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 A catalyst layer according to one embodiment or a catalyst coating structure according to a second embodiment,
The method is characterized by an exhaust gas purifying method in which the catalyst A is disposed in the front stage and the catalyst B is disposed in the rear stage with respect to the flow direction of the exhaust gas.

[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.

The alumina of the catalyst B has a total pore volume occupied by pores having a pore radius of 300 angstroms or less measured by a nitrogen gas adsorption method as X, and a pore radius of 25 angstroms or more and 100 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 preferable that the alumina is a alumina having a pore structure in which Z is 20% or less of X. When alumina having a pore structure not satisfying the above-mentioned conditions is used as a carrier in the catalyst of the present invention, the exhaust gas purifying catalyst layer constituted by the alumina has water vapor and SO 2.
The denitration performance of exhaust gas in the presence of x was insufficient.
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 has a catalyst A containing at least one selected from the group consisting of alumina and / or alkaline earth metals such as magnesium, calcium, strontium and barium, and has the above-mentioned crystal structure and pore characteristics. The catalyst comprises alumina or silver and silver and a small amount of silica or titania. At least one state selected from the group consisting of alkaline earth metals, particularly magnesium, calcium, strontium and barium, which are one component of catalyst A, is not particularly limited. Further, the state of silver or silica or titania contained in the alumina of the catalyst B is not particularly limited. For example, in the case of silver, a metal state, an oxide state, and a mixed state thereof can be mentioned. In the case of silica or titania, An oxide state, a local composite oxide state, a mixed state thereof, and the like can be given. In particular, since the composition of the combustion exhaust gas of an internal combustion engine such as a lean burn gasoline automobile changes depending on the operating conditions, 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 depending on the atmosphere. The starting material of the catalyst A is at least one selected from the group consisting of alumina and / or alkaline earth metal, particularly magnesium, calcium, strontium and barium, and the starting material of silver and silica or titania in the catalyst B is not particularly limited.

The method of adding at least one selected from the group consisting of alumina and / or alkaline earth metals (magnesium, calcium, strontium and barium) in the catalyst A according to the present invention, and silver in the alumina in the catalyst B Alternatively, the method for containing silver and silica or titania is not particularly limited, and conventionally used methods such as an adsorption method, a pore filling method, an incipient wetness method, an evaporation to dryness method, and an impregnation method such as a spray method. Any known method, such as a kneading method, a physical mixing method, or a combination thereof, may be used.

For example, when the catalyst A is composed of alumina and at least one selected from the group consisting of magnesium, calcium, strontium and barium as alkaline earth metals, alumina and a magnesium source, a calcium source, a strontium After mixing at least one selected from the group consisting of a source and a barium source, the mixture is dried and fired. Further, at the time of manufacturing the alumina carrier, at least one selected from the group consisting of a magnesium source, a calcium source, a strontium source, and a barium source.
A method for producing a catalyst containing seeds, for example, mixing an alcohol solution of aluminum alkoxide with 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 Alternatively, a coprecipitation method in which an alkali is added to an aqueous solution of a mixture of an alkoxide method and an alumina source and at least one selected from a magnesium source, a calcium source, a strontium source, and a barium source to cause precipitation, can be applied.

Next, in the case of the catalyst B, a silver source or a silver source and a silica source or a titania source may be simultaneously supported on alumina or an alumina precursor material, and then dried and calcined. After sequentially supporting the titania source, drying and firing 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, a silver source or a silver source and a silica source or a titania source An alkoxide method in which an alcohol solution is mixed and then heated and hydrolyzed, or a coprecipitation method in which an alkali is added to an aluminum source, a silver source, or a mixed aqueous solution of a silver source and a silica source or a titania source to cause precipitation, can be applied.

The content of at least one selected from alumina and / or alkaline earth metals (magnesium, calcium, strontium and barium) in the catalyst A is not particularly limited, and can be arbitrarily selected according to required performance. In particular, the content of one selected from the group consisting of magnesium, calcium, strontium and barium is preferably 10 to 80% by weight in terms of SOx absorption performance. The silver content of the catalyst B in terms of metal with respect to alumina in the catalyst B is not particularly limited.
A range of 1 to 10% by weight is preferred, and a range of 2 to 8% by weight is particularly preferred. Further, the content of silica or titania in terms of oxide with respect to the entire catalyst was 0.05% in terms of denitration performance.
The range is preferably 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 denitration performance is reduced. If the content is less than 0.05% by weight, the synergistic effect due to the addition of silica or titania is not sufficiently exhibited, so that the content is preferably in the above range.

The drying temperature of the catalyst A is not particularly limited, and it is usually dried at about 80 to 120 ° C. The firing temperature is 200 to 900 ° C, preferably 400 to 800.
It is about ° C. When the firing temperature exceeds 900 ° C., the specific surface area of alumina decreases, and magnesium, calcium,
The dispersibility of at least one selected from the group consisting of strontium and barium also decreases, which is not preferable. On the other hand, the drying temperature of the catalyst B is not particularly limited and is usually dried at about 80 to 120 ° C. The firing temperature is 300 to 1000 ° C, preferably 400 to 900 ° C.
It is about. 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 forming a catalyst layer for purifying exhaust gas, the catalyst layer is formed by molding the above-mentioned catalyst into a predetermined shape or in a powdered state to allow a target exhaust gas to flow therethrough. 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 separately coated on at least the inner surface of the through-hole, but may be separately 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 separately coated on the inner surface of the supporting 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,
The amount is preferably about 50 to 250 g / L, more preferably about 100 to 200 g / L, per unit volume of the supporting substrate.

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 _{N 2} until Eta 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. to 600 ° C.

[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 alumina of type γ-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 Catalyst 1 was 4.5% by weight based on the entire catalyst.

Reference Example 2 to Reference Example 16 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) is the same as the reference except that silica sol (SiO ₂ : 20% by weight) was added so that the silica content was 0.1%, 0.8%, 1.2%, and 5% by weight. Catalyst 12 (Reference Example 12), Catalyst 1
3 (Reference Example 13), Catalyst 14 (Reference Example 14), Catalyst 15
(Reference Example 15) was prepared in the same manner as in Reference Example 13 except that titania sol (TiO ₂ : 30% by weight) was used instead of silica sol in preparing Catalyst 13 of Reference Example 13.
(Reference Example 16) was obtained.

(B) Production of Catalyst A: [Reference Example 17] Catalyst 17 (Reference Example 17) was obtained by calcining alumina hydrate, which is a precursor of γ-type alumina a in Table 1, in air at 550 ° C. for 3 hours. Example 17) was obtained.

REFERENCE EXAMPLE 18 In 300 ml of ion-exchanged water, 55.3 g of alumina hydrate, which is a precursor of γ-type alumina a shown in Table 1, and 79.times. Of calcium hydroxide.
3 g was added, and the mixture was stirred at room temperature for 1 hour. After stirring, the mixture was heated to evaporate water. After drying this at 110 ° C with ventilation,
The catalyst 18 was calcined at 550 ° C. for 3 hours in the air (Reference Example 1).
8) was obtained. The metal in the catalyst 18 in terms of Ca
Is 43% by weight with respect to the alumina.

Reference Examples 19 to 26 Reference Example 1 above
In the same manner as in Reference Example 18, except that the content of Ca in terms of metal in Example 8 was changed to 48% by weight based on alumina, water was used instead of the catalyst 19 (Reference Example 19) and the calcium hydroxide of Reference Example 18. Catalyst 20 (Reference Example 20), Catalyst 21 (Reference Example 21), Catalyst 22 (Reference Example 22), and Reference Example 18 in the same manner as in Reference Example 18 except that magnesium oxide, strontium hydroxide, and barium hydroxide were used. In the preparation of Catalyst 21 of No. 21, a catalyst composed only of strontium oxide without using alumina was designated as Catalyst 23 (Reference Example 23),
The catalyst composed of commercially available silica alone was replaced with Catalyst 24 (Reference Example 2).
4). Further, a catalyst 25 (Reference Example 25) was obtained in the same manner as in Reference Example 18 except that alumina hydrate which was a precursor substance of γ-type alumina f in Table 1 was used. Further, instead of the alumina hydrate which is the precursor substance of the γ-type alumina a in Reference Example 18, the alumina hydrate which is the precursor substance of the γ-type alumina f in Table 1 was used and only alumina was used. Catalyst 26 was prepared in the same manner as in Reference Example 17 except that the catalyst was constituted.
(Reference Example 26) was obtained.

(C) Production of honeycomb catalyst: [Reference Examples 27 and 28] 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 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.
Thereafter, the resultant was baked at 500 ° C. for 30 minutes, and was coated with 150 g of solid content in terms of dry weight per liter of honeycomb to obtain a honeycomb catalyst 27 of Reference Example 27. Further, a honeycomb catalyst 28 of Reference Example 28 was obtained by the same preparation method as described above except that the catalyst 18 of Reference Example 18 was used instead of the catalyst 1.

The results of evaluating the denitration performance of the catalyst layers for purifying exhaust gas formed using the catalysts of Reference Examples 1 to 28 under various conditions will be described below. Example 1 Catalyst 17 of Reference Example 17 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 17
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 17 and the catalyst 1 was 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 generated in any of the catalyst layers of the present invention.

[0043]

(Equation 1)

Examples 2 to 20 and Comparative Examples 1 to 8 Catalysts 2, 3, 9 to 14 of Reference Examples 2, 3, 9 to 14 and 16
Using the catalysts 4 to 8 and 15 of Reference Examples 4 to 8 and 15 in place of the catalyst 1 of Example 1, a catalyst layer similar to the above was formed, and an evaluation test using a model gas was performed in the same manner. went. The catalyst layers using catalysts 2, 3, 9 to 14, and 16 were referred to as Examples 2 to 10, respectively, and catalysts 4 to 8, 1
The catalyst layers using No. 5 were Comparative Examples 1 to 6, respectively. Further, Catalyst 1 of Reference Examples 18 to 23, 25, 26 and 24
8 to 23, 25, 26, and 24 were each used in place of the catalyst 17 of Example 1, a catalyst layer similar to the above was formed, and an evaluation test using a model gas was performed in the same manner. The catalyst layers using catalysts 18 to 23, 25, and 26 were Example 11 and Examples 14 to 20, respectively, and the catalyst layer using catalyst 24 was Comparative Example 7. Further, the same catalyst layer as that described above was formed by using the catalyst layer of Reference Example 13 alone using the catalyst 13 alone in Comparative Example 8, using the catalyst 18 as the former stage, and using the catalysts 9 and 10 in place of the catalyst 1 in Example 1, respectively. Similarly, an evaluation test using a model gas was performed. The catalyst layers using the catalysts 9 and 10 were referred to as Example 12 and Example 13, respectively. Table 2 shows the denitration ratio C ₄₂₅ (%) at the catalyst layer temperature of 425 ° C. for the catalyst layers of the above Examples and Comparative Examples. The catalyst layers of Examples 1 to 20 and Comparative Examples 6 to 8 of the present invention
Compared to the catalyst layers of Comparative Examples 1 to 5, the denitration performance was 70% or higher.

Performance Evaluation Example 2 (Example 21) In Performance Evaluation Example 1, the honeycomb catalyst 27 of Reference Example 27 and the honeycomb catalyst 28 of Reference Example 28 were each
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 such that the honeycomb catalyst 28 was at the front stage and the honeycomb catalyst 27 was at the rear stage in the flow direction of the exhaust gas (Example 21). . 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. Table 2 shows that the honeycomb catalyst layer also exhibits high denitration performance of 70% or more.

[0046]

[Table 2] Catalyst layer Catalyst layer First stage Second stage Denitration rate First stage Second stage denitration rate (%) (%) ─────────────────────────────────── Example 1 Catalyst 17 Catalyst 177.8 Example 10 Catalyst 17 Catalyst 16 70.5 Example 2 Catalyst 17 Catalyst 2 74.9 Example 11 Catalyst 18 Catalyst 1 91.8 Example 3 Catalyst 17 Catalyst 3 74.2 Example 12 Catalyst 18 Catalyst 9 87.0 Comparative Example 1 Catalyst 17 Catalyst 4 17.6 Example 13 Catalyst 18 Catalyst 10 94.9 Comparative Example 2 Catalyst 17 Catalyst 5 2.5 Example 14 Catalyst 19 Catalyst 1 83.8 Comparative Example 3 Catalyst 17 Catalyst 6 27.1 Example 15 Catalyst 20 Catalyst 1 88.9 Comparative Example 4 Catalyst 17 Catalyst 7 23.1 Example 16 Catalyst 21 Catalyst 1 93.0 Comparative Example 5 Catalyst 17 Catalyst 8 33.7 Example 17 Catalyst 22 Catalyst 1 91.6 Example 4 Catalyst 17 Catalyst 9 83.1 Example 18 Catalyst 23 Catalyst 1 88.0 Example 5 Catalyst 17 Catalyst 10 87.3 Comparative Example 7 Catalyst 24 Catalyst 1 86.8 Example 6 Catalyst 17 Catalyst 11 75.9 Example 19 Catalyst 25 Catalyst 1 74.2 Example 7 Catalyst 17 Catalyst 12 70.1 Example 20 Catalyst 26 Catalyst 1 88.5 Example 8 Catalyst 17 Catalyst 13 80.3 Comparative Example 8 Catalyst 13 87.7 Example 9 Catalyst 17 Catalyst 14 79.7 Example 21 Catalyst 28 Catalyst 27 70.1 Comparative Example 6 Catalyst 17 Catalyst 15 73.0 ──────────────────

[Performance Evaluation Example 3] For the catalyst layers of Example 1, Example 8, Example 9, Example 11, Example 15, Example 18, and Comparative Examples 6 to 8, the gas of Performance Evaluation Example 1 was used. An endurance test was carried out in the presence of 50 ppm of SO ₂ in the composition. Table 3 shows that the catalyst layer temperature of each catalyst after one hour was 425 ° C.
Shows the denitration rate C ₄₂₅ (%) of each catalyst in FIG. The activity values of the catalyst layers of Examples 1, 8, 9, 11, 15, and 18 of the present invention are all 50% or more, while Comparative Examples 6 to
The catalyst layer of No. 8 was less than 50%.

[0048]

[Table 3] ────────────────── Catalyst NOx removal rate C ₄₂₅ (%) 実 施 Implementation Example 1 61.6 Example 8 72.3 Example 9 73.2 Example 11 81.9 Example 15 79.8 Example 18 53.4 Comparative Example 6 40.8 Comparative Example 7 43.6 Comparative Example 8 31.4 ──────────────────

[0049]

As described above, according to the exhaust gas purifying catalyst layer, the exhaust gas purifying catalyst coating structure and the exhaust gas purifying method using the same according to the present invention, the lean flue gas in which steam and SOx coexist is contained in the lean flue gas. Since it is possible to reduce and purify nitrogen oxides contained therein at a high denitration rate and has excellent SOx durability, 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 35/10 301 F01N 3/24 C F01N 3/24 B01D 53/36 102H (72) Inventor Atsushi Katakei Ichikawa, Chiba 3-18-5 China Sumitomo Metal Mining Co., Ltd. Central Research Laboratory (72) Inventor Masaki Funabiki 678 Ichihonmatsu, Numazu City, Shizuoka Prefecture N-Chem Cat Co., Ltd. Numazu Plant

Claims (7)

[Claims] 1. The relationship between a catalyst A containing at least one selected from alumina and / or alkaline earth metal and a pore radius and a pore volume measured by a nitrogen gas adsorption method, X is the total value of the pore volume occupied by pores having a radius of 300 Å or less, and a pore radius of 25
The total value of the pore volume occupied by pores of not less than 100 Å and not less than 100 Å is defined as Y, and the pore radius is 10
When the total value of the pore volume occupied by the pores of 0 Å to 300 Å is Z, Y has a pore structure in which 70% or more of X and Z is 20% or less of X. An exhaust gas purifying catalyst layer comprising: a catalyst B comprising silver contained in an alumina carrier. 2. The exhaust gas purifying catalyst layer according to claim 1, wherein the alumina carrier of the catalyst B further contains silica or titania. 3. The exhaust gas purifying catalyst layer according to claim 1, wherein the alkaline earth metal of the catalyst A is magnesium, calcium, strontium and barium. 4. The catalyst according to claim 1, wherein at least the inner surface of the through-hole in the integral support substrate made of a refractory material having a large number of through-holes is separately coated. An exhaust gas purifying catalyst-coated structure characterized by the above-mentioned. 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 layer according to any one of Items 1 to 3. 6. 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 5. An exhaust gas purifying method comprising the exhaust gas purifying catalyst-coated structure according to Item 4. 7. The catalyst according to claim 5, 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.
An exhaust gas purifying method as described in the above.