JPH11226403A - Catalyst layer for purification of exhaust gas, catalyst-coated structure for purification of exhaust gas, and purifying method of exhaust gas using that - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst layer in a purifying device of exhaust gas which purifies NOx in lean burnt exhaust gas in a high efficiency and which high reliability. SOLUTION: This catalyst layer consists of a catalyst (A) containing iridium and at least one kind selected from among alkali metals and alkaline earth metals on a porous inorg. oxide carrier in the preceding stage, and a catalyst (B) described below in the succeeding stage. The catalyst (B) contains silver and >=0.05 wt.% and <5 wt.% of silica or titania in an alumina carrier. This alumina carrier has a pore structure with such a relation of the pore radius and the pore volume that the total X of th pore volume of pores having <=300 Åpore radius, the total Y the pore volume of pores having >=25 Å and <100 Åpore radius, and the total Z of the pore volume of pores having 100 Å to 300 Å pore radius satisfy Y>=70%×X and Z<=20% × X.

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 has an adverse effect on the human body, particularly on 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.
This is combustion at a stoichiometric ratio controlled around 4.7. For exhaust gas treatment, an alumina catalyst mainly containing platinum, rhodium, palladium and ceria mainly containing carbon monoxide, hydrocarbons and NOx in the exhaust gas. A three-way catalyst system has been adopted in which harmful three components are simultaneously removed by contact with a catalyst.

However, this three-way catalyst system cannot be applied to exhaust gas purification of a lean burn gasoline engine operated at a lean air-fuel ratio because it is an absolute condition that the engine is operated at a stoichiometric ratio. . 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 not only a special device for collecting and processing the unreacted reducing agent, but also uses 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, Δn, Ni, V
NOx containing alumina or silica-alumina containing
An example of use as a 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.
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 a large amount of N ₂ O, which is said to be one of the substances causing global warming, is produced as a by-product, resulting in harmlessness. a _{N 2}
However, it has a drawback that it is difficult to selectively advance the reduction reaction to.

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 NOx reduction and removal technique using a silver-containing catalyst was disclosed in JP-A-4-3545.
No. 36, JP-A-5-92124, JP-A-5-92124
No. 92125 and JP-A-6-277454.

[0009]

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

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 efficiently remove NOx from lean combustion exhaust gas and to purify the exhaust gas with excellent durability. It is an object of the present invention to provide an exhaust gas purifying method for purifying NOx in lean combustion exhaust gas with high efficiency and high reliability by using the catalyst layer for exhaust gas and the catalyst coated structure for exhaust gas purification.

[0011]

The present inventors have developed an exhaust gas purifying catalyst layer and an exhaust gas purifying catalyst exhibiting high denitration performance and excellent durability in a lean burn region where SOx and steam coexist. As a result of intensive studies on the body and the exhaust gas purification method using the same, a catalyst A comprising iridium and an alkali metal and / or an alkaline earth metal in a porous inorganic oxide carrier was provided at the front stage. It has been found that the above-mentioned problems can be solved by arranging catalyst B, which contains silver and a small amount of silica or titania in an alumina carrier having a specific pore structure, separately in the latter stage. The invention has been completed.

That is, a first embodiment of the present invention for solving the above problems is a catalyst comprising a porous inorganic oxide carrier containing iridium and at least one of an alkali metal and an alkaline earth metal. A, and the relationship between the pore radius and the pore volume measured by the nitrogen gas adsorption method is such that when the total value of the pore volume occupied by pores having a pore radius of 300 Å or less is X, the pore radius is 25 Å or more. When the total value of the pore volume occupied by pores smaller than 100 Å 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 Ζ, Y is 70 of X. % Or more and Ζ is 20% or less of X on an alumina support having a pore structure, and 0.05% by weight or more and less than 5% by weight of silica or titanium. An exhaust gas purifying catalyst layer comprising a catalyst B containing tania. 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, 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. The present invention is characterized by an exhaust gas purifying catalyst-coated structure coated with the catalyst.

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

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention and its operation will be described more specifically below. (Production of Catalyst and Production Method Thereof) The porous inorganic oxide carrier of the catalyst A in the exhaust gas purifying catalyst layer of the present invention is not particularly limited, and examples thereof include alumina, silica, titania, zirconia, zeolite, and composite oxides thereof. Can be On the other hand, alumina, which is one of the main components of the catalyst B, is obtained by converting aluminum hydroxide powder or gel classified as boehmite, pseudoboehmite, vialite or norstrandite in mineralogy, for example, in air or vacuum.
By heating and dehydrating at 0 to 800 ° C, preferably 400 to 900 ° C, crystallographically, γ-type, η-type, δ-
It is preferable from the viewpoint of denitration performance that a phase transition is made to alumina classified into a type, a χ-type or a mixed type thereof. Alumina having another crystal structure, for example, α-type alumina, is unsuitable as the catalyst component of the present invention because of its extremely small specific surface area and poor solid acidity.

The alumina as a main component of the catalyst B has a pore radius X of pores having a pore radius of 300 angstroms or less as measured by a nitrogen gas adsorption method. 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 Z, It is necessary that the alumina has a pore structure such that Y is 70% or more of X and Ζ 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 B of the present invention, the exhaust gas purifying catalyst constituted thereby has a denitration performance of exhaust gas in the coexistence of steam and SOx. It was not enough. 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 comprises a catalyst A comprising a porous inorganic oxide carrier containing iridium and at least one of an alkali metal or an alkaline earth metal; and an alumina having the above-mentioned crystal structure and pore characteristics. The catalyst B comprises silver and 0.05% by weight or more and less than 5% by weight of silica or titania in the carrier. The alkali metal contained in the catalyst A is not particularly limited, but includes, for example, sodium and potassium. The alkaline earth metal is not particularly limited, and includes, for example, barium, calcium, strontium, and the like.

Further, the state of iridium and at least one of the alkali metal and the alkaline earth metal contained in the catalyst A is not particularly limited.
Examples include a composite oxide state and a mixed state thereof. Further, the state of silver and silica or titania contained in the catalyst B is not particularly limited. For example, in the case of silver, a metal state, an oxide state, a mixed state thereof, and the like can be mentioned, and in the case of silica or titania, Is the oxide state,
A local complex 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 a lean burn gasoline automobile changes each time depending on the operating conditions, and therefore, 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 materials of at least one of iridium and an alkali metal or an alkaline earth metal in the catalyst A, and the starting materials of silver, silica, or titania in the catalyst B are not particularly limited.

In the present invention, the porous inorganic oxide carrier of the catalyst A contains iridium and at least one of an alkali metal and an alkaline earth metal, and the catalyst B contains alumina, silica, or titania. The method of containing is not particularly limited, and conventionally performed methods such as an adsorption method, a pore filling method, an incipient wetness method, an evaporation to dryness method, an impregnation method such as a spray method, a kneading method, and a physical method. Any known method such as a mixing method and a combination thereof can be arbitrarily adopted.

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

The content of iridium in terms of metal with respect to the catalyst A is not particularly limited.
It is 2% by weight, preferably 0.005 to 1% by weight. The content of the alkali metal in terms of metal with respect to the catalyst A is not particularly limited, but is 0.01 to 20% by weight, preferably 0.05 to 15% by weight, and the content of the alkaline earth metal is also particularly preferable. Although not limited, it is 0.3 to 30% by weight, preferably 0.5 to 20% by weight. On the other hand, catalyst B
The content of silver in terms of metal is not particularly limited, but is 0.1 to 10% by weight, preferably 1 to 8% in terms of denitration performance.
% By weight. The content of silica or titania,
It is necessary to be 0.05% by weight or more and less than 5% by weight, preferably 0.1 to 3% by weight in terms of oxide. If the content of silica or titania is 5% by weight or more, the durability performance in the presence of SOx and water vapor decreases, while 0.05% by weight
If it is less than 10, the synergistic effect due to the addition of silica or titania is not sufficiently exerted, so that the above range is required.

The drying temperature of the catalyst A and the catalyst B is not particularly limited, and is usually dried at about 80 to 120 ° C. The firing temperature is 300-1000 ° C., preferably 4
It is about 00 to 900 ° C. 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. Further, 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. The term "catalyst-coated structure" as used herein means that the above-mentioned catalyst A and catalyst B are separately coated on at least the inner surface of the through-hole of a monolithic supporting substrate made of a refractory material having many through-holes. It has the following structure.

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%. Where the number is one square inch (5.
30 to 700, preferably 200 to 0.6 cm ² )
There are 600. The catalyst 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 support 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 preferred one is a cordierite or stainless steel honeycomb supporting substrate.

As a method for coating the support substrate with a catalyst,
A so-called ordinary washcoat 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 support substrate together with or without a binder, that is, a so-called wash-gel method can be applied. Alternatively, the support substrate may be coated with alumina in advance, and the catalyst support layer of the present invention may be subjected to the treatment to form a catalyst coating layer. The coating amount of the catalyst layer on the support substrate is not particularly limited, but is preferably about 50 to 250 g / L, more preferably about 100 to 200 g / L per unit volume of the support substrate.

Next, an exhaust gas purifying method according to a third embodiment of the present invention will be described. The third embodiment of the present invention uses the catalyst layer of the first embodiment and the catalyst-coated structure of the second embodiment to combine CO, HC and H _{2 in} exhaust gas.
By contacting the exhaust gas containing excess oxygen reducing component from stoichiometry near required to complete oxidation with oxidizing components such as NOx and O _2, such as, N
Ox is reduced and decomposed to N ₂ and H ₂ O,
And the like are also oxidized to CO ₂ and H ₂ O.

In the present invention, the reason why the catalyst A is disposed in the former stage and the catalyst B is disposed in the latter stage is that the catalyst A in the former stage burns a part of the reducing agent to raise the reaction gas inlet temperature of the latter catalyst B. This is because the coking deterioration and the sulfur poisoning deterioration of the catalyst B at the subsequent stage are suppressed, and the catalyst life in the total catalyst system is improved. The ratio between the catalyst A and the catalyst B may be appropriately 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 HC has a concentration of about several hundreds to several thousands ppm in terms of methane 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 here refers to paraffinic hydrocarbons, olefinic hydrocarbons and aromatic hydrocarbons, alcohols,
It means those containing oxygen-containing organic compounds such as aldehydes, ketones, and ethers, gasoline, kerosene, light oil, and heavy oil A.

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 the catalyst and the type of HC. When the catalyst layer of the present invention is used, for example, C _{2 to} C ₆ paraffin, olefin and olefin. 45 for C ₆ -C ₉ aromatic HC
0-600 ° C., 350-550 ° C. for C ₆ -C ₉ paraffins and olefins, and 250-500 ° C. for C ₁₀ -C ₂₅ paraffins and olefins. It is appropriate that the temperature be 100 ° C or higher and 700 ° C or lower, preferably 200 ° C or higher and 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. Of the catalyst B, 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] ───────────────────────────── Alumina specific surface area pore distribution (m ² / g) Y / X ( %) Z / X (%) ─────────────────────────────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 mixed with 16.1 g of silver nitrate and 9 g of silica sol (SiO ₂ : 20% by weight). Including 50
After immersion in a 0 ml aqueous solution, the mixture was heated with stirring to evaporate water. This was air-dried at 110 ° C. and then calcined in air at 550 ° C. for 3 hours to obtain Catalyst 1 (Reference Example 1). The content of Ag in the catalyst 1 in terms of metal is:
4.5% by weight of the total catalyst, SiO in oxide conversion
The content of ₂ was 0.8% by weight.

Reference Examples 2 to 17 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), Catalyst 7 (Reference Example 7) I got In preparing Catalyst 1 of Reference Example 1, the silver content was set to 0% by weight,
Catalyst 8 (Reference Example 8), Catalyst 9 (Reference Example 9), and Catalyst 10 (Reference Example 10) were prepared in the same manner as Reference Example 1 except that the content of silica was 0% by weight and 8% by weight, respectively.
Catalyst 11 (Reference Example 11) and Catalyst 11 (Reference Example 11) in the same manner as in Reference Example 1 except that the weight%, 0.02%, 0.1%, 1.2%, 3% and 5% by weight were used. 12 (Reference Example 12), Catalyst 13 (Reference Example 13), Catalyst 14 (Reference Example 14), Catalyst 15 (Reference Example 15), Catalyst 16 (Reference Example 16), and a titania sol (TiO ₂ : Reference Example 1 except that 6 g was used.
Catalyst 17 (Reference Example 17) was obtained in the same manner as described above.

(B) Production of catalyst A: [Reference Example 18] After impregnating 50 g of commercially available γ-type alumina in a 200 ml aqueous solution containing 0.049 g of iridium tetrachloride hydrate and 8 g of barium nitrate. The mixture was heated with stirring to evaporate water. This is dried by ventilation at 110 ° C., and calcined at 550 ° C. for 3 hours in the air to obtain a catalyst 18.
(Reference Example 18) was obtained. The contents of Ir and Ba in terms of metal in the catalyst 18 were 0.05% by weight and 8.4% by weight with respect to alumina, respectively.

[Reference Examples 19 to 23] In preparing catalyst 18 of Reference Example 18, the contents of iridium were reduced to 0%, 0.01%, 0.02%, 1% and 3% by weight. Catalyst 19 (Reference Example 19), Catalyst 20 (Reference Example 20),
Catalyst 21 (Reference Example 21), Catalyst 22 (Reference Example 22), and Catalyst 23 (Reference Example 23) were obtained.

[Reference Examples 24 to 28] In the preparation of the catalyst 18 of Reference Example 18, the barium content was 0% by weight,
0.42 wt%, 4.2 wt%, 20 wt% and 35
Catalyst 24 (Reference Example 24), Catalyst 25 (Reference Example 25), Catalyst 26 (Reference Example 26), Catalyst 27 (Reference Example 27), and Catalyst 28 ( Reference Example 28) was obtained.

[Reference Examples 29 to 32] In the same manner as in Reference Example 18, except that silica, titania, zirconia and β-type zeolite were used instead of alumina in preparing the catalyst 18 of Reference Example 18, Catalyst 29 (Reference Example 29), Catalyst 30 (Reference Example 30), Catalyst 31 (Reference Example 31), and Catalyst 32 (Reference Example 32) were obtained, respectively.

REFERENCE EXAMPLES 33-34 Reference Example 1 was repeated except that calcium nitrate and strontium nitrate were used instead of barium nitrate in the preparation of catalyst 18 of Reference Example 18.
In the same manner as in Example 8, catalyst 33 (Reference Example 33) and catalyst 34 (Reference Example 34) were obtained.

Reference Examples 35 to 36 The procedure of Reference Example 18 was repeated, except that 2.6 g of sodium nitrate and 3 g of potassium acetate were used instead of 8 g of barium nitrate in the preparation of catalyst 18 of Reference Example 18. Catalyst 35 (Reference Example 35) and Catalyst 36 (Reference Example 36) were obtained, respectively.

[Reference Example 37] In preparing catalyst 18 of Reference Example 18, barium nitrate 4 was used instead of barium nitrate 8 g.
Catalyst 37 (Reference Example 37) was obtained in the same manner as in Reference Example 18, except that g and 1.5 g of potassium acetate were used.

(C) Production of honeycomb catalyst: [Reference Examples 38 to 39] 60 g of the above-mentioned powdered catalyst 1
With alumina sol (Al ₂ O ₃ solid content: 10% by weight) 8
g and 120 ml of water were charged into a ball mill pot and wet-pulverized to obtain a slurry. 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 mixture is baked at 500 ° C. for 30 minutes, and is coated with 150 g of solid content in terms of dry weight per 1 liter of the honeycomb to 4.5.
% Ag / _Al 2 _{O 3} composition of the honeycomb catalyst 38 (Reference Example 3
8) was obtained. Further, in the same manner as in Reference Example 38 except that the powder catalyst 18 was used instead of the powder catalyst 1, 0.05% Ir
/8.4%Ba/Al ₂ O ₃ composition honeycomb catalyst 39
(Reference Example 39) was obtained.

Hereinafter, the results of evaluating the denitration performance of the exhaust gas purifying catalyst layer formed using the catalysts of Reference Examples 1 to 39 under various conditions will be described. (Example 1) Catalyst 18 of Reference Example 18 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 18
Is filled in a stainless steel reaction tube having an inner diameter of 15 mm so that the catalyst 1 is placed in the former stage to form a catalyst layer, and the catalyst is attached to an atmospheric fixed bed flow reactor. 1: 3.

[Performance Evaluation Example 1] The temperature of the exhaust gas in the reaction tube was maintained at 400 ° C.
O: 750 ppm, kerosene (C ₁ ): 4500 ppm, O
₂ : 10%, SO ₂ : 1 ppm, H ₂ O: 10%, balance: N ₂ with a space velocity of 75,000 h
^-1 . In the analysis of the gas composition at the outlet of the reaction tube, the concentrations of NO and NO ₂ were measured with a chemiluminescence NOx meter, and the N ₂ O concentration was measured with a gas chromatograph / thermal conductivity detector equipped with a Porapak 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.

[0047]

(Equation 1)

Examples 2 to 24 and Comparative Examples 1 to 9 Catalysts 2 of Reference Examples 2, 3, 9, 10, 13 to 15 and 17
3, 9, 10, 13 to 15, 17 and Reference Examples 4 to 8,
11, 12, 16 catalysts 4-8, 11, 12, 16
A catalyst layer similar to that described above was formed using each of the catalysts 1 of Example 1 and an evaluation test was performed using a model gas in the same manner. Catalysts 2, 3, 9, 10, 13 to 15, 1
The catalyst layers using Examples 7 to 9 were used as Examples 2 to 9, and the catalyst layers using Catalysts 4 to 8, 11, 12, and 16 were used as Comparative Examples 1 to 8, respectively. Further, a catalyst layer similar to that of Example 1 was formed using Catalysts 19 to 37 of Reference Examples 19 to 37 in place of the catalyst 18 of Example 1, and an evaluation test was performed using a model gas in the same manner. Catalysts 20-22, 25-2
Catalyst layers using Examples 7 and 29 to 37 were prepared in Examples 10 to 24.
The catalyst layers using the catalysts 19, 23, 24, and 28 were Comparative Examples 9 to 12, respectively. Table 2 shows that the above Examples 1 to
24 shows the initial denitration ratio (%) for the catalyst layers of 24 and Comparative Examples 1 to 12.

[Performance Evaluation Example 2 (Example 25)] In the performance evaluation example 1, the honeycomb catalyst 38 of Reference Example 38 was replaced with a diameter 1
The honeycomb catalyst 39 of Reference Example 39 was processed into a cylindrical shape having a diameter of 15 mm and a length of 8 mm, and the honeycomb catalyst 39 was processed into a cylindrical shape having a diameter of 15 mm and a length of 8 mm.
Was filled in a stainless steel reaction tube having an inner diameter of 15 mm such that the honeycomb catalyst 38 was provided in the first stage and the honeycomb catalyst 38 was provided in the second stage. A model gas evaluation test was performed in the same manner as in the performance evaluation example 1 except that the space velocity of the gas to be fed was set to 13,000 h ^−1, and this was designated as Example 25. The results are shown in Table 2 together with the results of Performance Evaluation Example 1.

[0050]

[Table 2]

As is clear from Table 2, Examples 1 to 25 and Comparative Examples 6 to 9, 11, and 12 had an initial denitration performance of 70%.
% Or more, showing superior performance as compared with Comparative Examples 1 to 5 and Comparative Example 10.

[Performance Evaluation Example 3] Performance evaluation example 1 for the catalyst layers of Examples 1 and 7 and Comparative Examples 6 to 9, 11, and 12
A 10-hour endurance test was carried out with the same gas composition as in the above. Table 3
Figure 10 shows the change over time after 10 hours. The rate of change with time was defined by the following equation 2.

[0053]

(Equation 2)

[0054]

[Table 3] 率 After 10 hours of endurance catalyst Change over time (%) First stage Second stage ──── ────────────────────── Example 1 Catalyst 18 + Catalyst 1 3.9 Example 7 Catalyst 18 + Catalyst 14 1.0 Comparative Example 6 Catalyst 18 + Catalyst 115 7.7 Comparative Example 7 Catalyst 18 + Catalyst 12 26.0 Comparative Example 8 Catalyst 18 + Catalyst 16 23.4 Comparative Example 9 Catalyst 19 + Catalyst 1 20.9 Comparative Example 11 Catalyst 24 + Catalyst 19.8 Comparative Example 12 Catalyst 28 + Catalyst 1 15.7 通 り As is clear from Table 3, Examples 1 and 7 are Comparative Examples 6 to
It was found that the rate of change with time after 10 hours of durability was smaller than that of 9, 11, and 12, indicating high durability.

[0055]

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. Nitrogen oxides contained therein can be reduced and purified at a high denitration rate, and exhibit excellent durability in the presence of SOx, so that they are useful for purifying nitrogen oxides in combustion exhaust gas of an internal combustion engine.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Atsushi Katakei 3-18-5, Chugoku, Ichikawa-shi, Chiba Sumitomo Metal Mining Co., Ltd. Central Research Laboratory (72) Inventor Masaki Funabiki 678 Ichihonmatsu, Numazu-shi, Shizuoka N・ Echem Cat Co., Ltd. Numazu Plant

Claims (6)

[Claims] 1. A porous inorganic oxide carrier comprising: iridium;
The relationship between the catalyst A containing at least one of an alkali metal and an alkaline earth metal and the pore radius and pore volume measured by the nitrogen gas adsorption method is as follows.
Let X be the total value of the pore volume occupied by pores of not more than 00 Å, and 1
When the total value of the pore volume occupied by pores less than 00 Å 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 Ζ, Y is 70 of X. % Or more,
A catalyst layer for purifying exhaust gas, comprising: a catalyst B containing silver and silica or titania in an alumina carrier having a pore structure such that X is 20% or less of X. 2. The exhaust gas purifying catalyst layer according to claim 1, wherein the content of silica or titania in terms of oxide with respect to the catalyst B is 0.05% by weight or more and less than 5% by weight. 3. A catalyst substrate according to claim 1 or 2, 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 coated separately. Exhaust gas purification catalyst coated structure. 4. 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 the catalyst-containing layer, wherein the catalyst contained in the catalyst-containing layer is 3. An exhaust gas purifying method comprising the exhaust gas purifying catalyst layer according to 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 the catalyst-containing layer, wherein the catalyst contained in the catalyst-containing layer is An exhaust gas purifying method comprising the exhaust gas purifying catalyst-coated structure according to claim 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.