JP4058503B2 - Exhaust gas purification catalyst layer, exhaust gas purification catalyst coating structure, and exhaust gas purification method using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification catalyst layer used for purification of combustion exhaust gas, particularly nitrogen oxide contained in combustion exhaust gas of mobile and stationary internal combustion engines such as automobiles, boilers, gas engines, gas turbines, ships, etc., and exhaust gas purification More specifically, a catalyst layer for exhaust gas purification and exhaust gas capable of purifying nitrogen oxide in exhaust gas discharged from an internal combustion engine operated in a lean combustion region at high space velocity and with high efficiency The present invention relates to a purification catalyst covering structure and an exhaust gas purification method using these.
[0002]
[Prior art]
Various combustion exhaust gases discharged from internal combustion engines including automobiles contain nitrogen oxides (NOx) such as nitrogen monoxide and nitrogen dioxide together with water and carbon dioxide as combustion products. NOx not only adversely affects the human body, particularly the respiratory system, but is also one of the causes of acid rain that is regarded as a problem from the viewpoint of protecting the global environment. Therefore, development of a denitration technique that efficiently removes nitrogen oxides from these various exhaust gases is desired.
[0003]
On the other hand, lean combustion internal combustion engines have attracted attention in recent years from the viewpoint of preventing global warming. Conventional automobile gasoline engines burn at a stoichiometric ratio controlled near an air-fuel ratio (A / F) = 14.7. For the exhaust gas treatment, carbon monoxide and hydrocarbons in the exhaust gas are used. A three-way catalyst system in which NOx is contacted with an alumina catalyst mainly containing platinum, rhodium, palladium and ceria to remove harmful three components simultaneously has been adopted.
[0004]
However, since this three-way catalyst system is an absolute condition that the engine is operated at a stoichiometric ratio, it cannot be applied to exhaust gas purification of a lean combustion gasoline engine operated at a lean air-fuel ratio. Diesel engines are inherently lean combustion engines, but strict regulations are about to be imposed on both the suspended particulate matter and NOx for the exhaust gas.
[0005]
Conventionally, as a method for reducing and removing soot Ox in an oxygen-excess atmosphere, NH is selectively adsorbed on the catalyst even with a small amount as a reducing gas. ₃ The technology to use is already established. This technology has been industrialized as a method for denitrating exhaust gas from boilers and diesel engines, which are so-called fixed sources, but this method requires special equipment for the recovery of unreacted reducing agent, and odors. However, because it uses strong and harmful ammonia, it is dangerous and cannot be applied particularly as an exhaust gas denitration technology from mobile sources such as automobiles.
[0006]
In recent years, since it has been reported that an unburned hydrocarbon remaining in a lean combustion exhaust gas in an oxygen-rich atmosphere can be used as a reducing agent, a NOx reduction reaction can be promoted, and thus a catalyst for promoting this reaction. 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. In addition, JP-A-4-284848 reports an example in which alumina or silica-alumina containing 0.1 to 4% by weight of Cu, Fe, Cr, Zn, Ni, V is used as a soot Ox reduction catalyst. Yes.
[0007]
Further, when a catalyst in which Ρt is supported on alumina is used, the NOx reduction reaction proceeds in a low temperature range of about 200 to 300 ° C. Japanese Patent Laid-Open Nos. 4-267946, 5-68855, and 5- No. 103949 and the like. However, when these supported noble metal catalysts are used, the combustion reaction of hydrocarbon as a reducing agent is excessively promoted, and N is said to be one of the causative substances of global warming. ₂ A lot of O by-product, harmless moth ₂ However, it was difficult to selectively proceed the reduction reaction.
[0008]
One of the present applicants has previously found that when a catalyst containing silver with hydrocarbon as a reducing agent is used in an oxygen-excess atmosphere, the NOx reduction reaction proceeds selectively, and this technique is disclosed in JP-A-4-281844. It was disclosed in the publication. Even after this disclosure has been made, similar soot Ox reduction and removal techniques using a silver-containing catalyst are disclosed in JP-A-4-354536, JP-A-5-92124, JP-A-5-92125 and JP-A-5-92125. It is disclosed in Japanese Patent Laid-Open No. 6-277454.
[0009]
[Problem to be Solved by the Invention]
However, the alumina-supported silver catalysts described in these conventional publications still have practically insufficient denitration performance in the presence of SOx and water vapor.
[0010]
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 purification catalyst layer and an exhaust gas purification catalyst coating capable of efficiently removing NOx in a lean combustion exhaust gas. An object of the present invention is to provide a structure and an exhaust gas purification method for purifying NOx in lean combustion exhaust gas using these with high efficiency and high reliability.
[0011]
[Means for Solving the Problems]
The present inventors have conducted extensive research on exhaust gas purification catalyst layers and exhaust gas purification catalyst coating structures having high denitration performance in a lean combustion region in which SOx and water vapor coexist, and exhaust gas purification methods using these. As a result, the catalyst A containing at least one of silica and calcium and, if necessary, at least one of sulfate radicals, alumina and zirconia in the flow direction of the exhaust gas, has a specific pore structure. The inventors have found that the above-mentioned problems can be solved by arranging the catalyst B containing silver on the support so as to be arranged in the subsequent stage, and have completed the present invention.
[0012]
That is, in order to solve the above-mentioned problem, the first embodiment of the present invention includes a catalyst A containing silica, calcium and alumina or zirconia, and 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 angstroms or less, and Y is the total pore volume occupied by pores having a pore radius of 25 angstroms or more and less than 100 angstroms. A pore structure in which Y is 70% or more of X and Z is 20% or less of X, where Z is the total pore volume occupied by pores having a pore radius of 100 angstrom or more and 300 angstrom or less On an alumina carrier having 0.1 to 10% by weight in terms of metal And a catalyst layer for purifying exhaust gas, which is composed of a catalyst B containing silver, and is arranged so that the catalyst A is divided into the front stage and the catalyst B is divided into the rear stage with respect to the exhaust gas flow direction. Is.
Another first embodiment of the present invention is characterized by an exhaust gas purifying catalyst layer in which the catalyst A further contains a sulfate group. The catalyst layer is preferably arranged in the exhaust gas circulation space in a powdered or molded state.
[0013]
Further, the second embodiment of the present invention is a support substrate having a monolithic structure made of a refractory material having a large number of through holes, and the above catalyst on the inner surface of at least the through holes in the support substrate. A and B are arranged in such a manner that the catalyst A is divided into the front stage and the catalyst B is divided into the rear stage with respect to the exhaust gas flow direction. An exhaust gas purifying catalyst-coated structure formed by coating is characterized.
[0014]
Still further, a third embodiment of the present invention is a method for removing NOx in exhaust gas using hydrocarbon as a reducing agent, comprising contacting a combustion exhaust gas of an internal combustion engine operated at a lean air-fuel ratio with a catalyst-containing layer. The catalyst contained in the catalyst-containing layer is the exhaust gas purification catalyst layer in the first embodiment or the exhaust gas purification catalyst coating structure in the second embodiment. Toss Is.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the details of the present invention and the operation thereof will be described more specifically.
(Catalyst structure and production method)
Alumina, which is one of the main components of catalyst B and one of the optional components of catalyst A in the exhaust gas purifying catalyst layer of the present invention, is, for example, mineralized boehmite, pseudoboehmite, vialite, or norstrandite. The powder and gel of aluminum hydroxide classified into the following are crystallographically γ-type, η-type, δ by dehydrating in air or in vacuum at 300 to 800 ° C, preferably 400 to 900 ° C. In view of the denitration performance, a phase transition to alumina classified into a -type, a χ-type, or a mixed type thereof is preferable. Alumina having another crystal structure, such as α-type alumina, is extremely unsuitable as a catalyst component of the present invention because of its extremely small specific surface area and poor solid acidity.
[0016]
In addition, the alumina of the catalyst B is a fine value having a pore radius of 25 angstroms or more and less than 100 angstroms, where X is the total pore volume occupied by pores having a pore radius of 300 angstroms or less measured by the nitrogen gas adsorption method. When the total value of the pore volume occupied by pores is Y, and the total value of the pore volume occupied by pores having a pore radius of 100 angstroms or more and 300 angstroms or less is Z, Y is 70% or more of the soot. , It is necessary to be an alumina having a pore structure such that Z is 20% or less of X. When alumina whose pore structure does not satisfy the above-described conditions is used as the carrier in the catalyst B of the present invention, the denitration performance of the exhaust gas in the presence of SOx and water vapor of the exhaust gas purification catalyst constituted thereby is not good. It was enough. Therefore, it can be said that alumina having the above-described crystal structure and pore characteristics is appropriate as an effective alumina as the main component of the catalyst B of the present invention.
[0017]
The exhaust gas purifying catalyst layer of the present invention is the following catalyst.
The catalyst layer according to the present invention includes a catalyst A containing at least one selected from the group consisting of silica and calcium, and optionally sulfate group, alumina and zirconia, and the crystal structure and pores described above. It is comprised from the catalyst B which contains silver in the alumina which has a characteristic. The state of calcium contained in the silica of catalyst A, and at least one state selected from the group consisting of sulfate radical, alumina, and zirconia are also not particularly limited. On the other hand, the state of silver contained in the alumina in the catalyst B is not particularly limited, and examples thereof include a metal state, an oxide state, and a mixed state thereof. In particular, the combustion exhaust gas composition of an internal combustion engine such as a lean-burn gasoline automobile changes each time depending on the operating state, so that 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 varies depending on the atmosphere. The starting material for calcium in catalyst A is not particularly limited, but calcium hydroxide is preferred in terms of durability. In addition, when the catalyst A contains a sulfate group, it is preferable to use sulfuric acid, calcium sulfate, or the like as a starting material for the sulfate group. The silver starting material in the catalyst B is not particularly limited.
[0018]
There is no particular limitation on the method for containing silica in the catalyst A according to the present invention with at least one selected from the group consisting of calcium, sulfate, alumina, and zirconia, and the method for containing silver in the alumina with the catalyst B. For example, adsorption methods, pore filling methods, incipient wetness methods, evaporative drying methods, impregnation methods such as spray methods, kneading methods, physical mixing methods, and combinations thereof are usually employed. Any known method can be employed.
[0019]
The calcium content relative to the catalyst A is not particularly limited, but is preferably 10 to 80% by weight in terms of CaO. When the calcium content is less than 10% by weight in terms of CaO, the initial denitration performance is excellent, but since the SOx absorption performance of the catalyst A is poor, the activity is lowered early. On the other hand, if it exceeds 80% by weight, the dispersibility of calcium decreases, so the SOx absorption performance decreases, leading to an early decrease in denitration activity. Next, the weight of at least one selected from the group consisting of sulfate, alumina and zirconia contained in catalyst A is not particularly limited, but alumina and zirconia are particularly preferably less than 30% by weight in terms of SOx absorption performance. . On the other hand, the metal content in terms of metal relative to the catalyst B is not particularly limited, but is preferably 0.1 to 10% by weight. If the supported amount of silver is less than 0.1% by weight, the effect is not exhibited, and if it exceeds 10% by weight, the combustion reaction of hydrocarbon as a reducing agent preferentially proceeds, and the NOx removal characteristics are deteriorated.
[0020]
The drying temperature of the catalyst A is about 80 to 120 ° C. The firing temperature is about 200 to 800 ° C, preferably about 400 to 600 ° C.
If the firing temperature exceeds 800 ° C., it is not preferable because the specific surface area of silica is reduced and the dispersibility of calcium is also lowered. 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 about 300 to 1000 ° C, preferably about 400 to 900 ° C. When 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 air, inert gas, or oxygen may be appropriately selected according to the catalyst composition. Moreover, you may change each atmosphere alternately for every fixed time.
[0021]
In the first embodiment of the present invention, when forming a catalyst layer for exhaust gas purification, the catalyst layer is molded into a predetermined shape or in a fixed space in which the target exhaust gas flows in a powder state. To fill.
When the catalyst layer is formed into a molded body, the 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 employed. These shapes, sizes, etc. may be arbitrarily selected according to the use conditions.
[0022]
Next, the exhaust gas purifying catalyst coating structure of the second embodiment of the present invention will be described. The catalyst-coated structure here has a structure in which at least the inner surface of the through-hole of a monolithic support substrate made of a refractory material having a large number of through-holes is coated with the above-mentioned catalyst being divided. It is.
[0023]
The support substrate is provided with a large number of through holes along the flow direction of the exhaust gas. In the cross section perpendicular to the flow direction, the porosity is usually 60 to 90%, preferably 70 to 90%. The number is 1 square inch (5.06 cm) ² ) 30 to 700, preferably 200 to 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 supporting substrate.
[0024]
As the material for the refractory support substrate, ceramics such as α-type alumina, mullite, cordierite and silicon carbide, and metals such as austenitic and ferritic stainless steel are used. Conventional shapes such as honeycombs and foams can be used, but cordierite or stainless steel honeycomb support substrates are preferred.
[0025]
As a method of coating the catalyst on the support substrate, the catalyst of the present invention, which has been sized to a certain particle size, is coated with at least the inner surface of the through hole of the support substrate with or without a binder. A so-called normal washcoat method or sol-gel method can be applied. Alternatively, the support substrate may be coated with alumina in advance, and a catalyst coating layer may be formed thereon by carrying the catalyst active substance according to the present invention. The coating amount of the catalyst layer on the support substrate is not limited, but is preferably about 50 to 250 g / liter, more preferably about 100 to 200 g / liter per unit volume of the support substrate.
[0026]
Next, an exhaust gas purification method of the 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 coating structure of the second embodiment described above, and CO, HC and H in the exhaust gas. ₂ Reducing components such as ΝOx and O ₂ By contacting exhaust gas containing excess oxygen from near the stoichiometric amount required for complete oxidation with an oxidizing component such as ₂ And nephew ₂ At the same time as reductive decomposition to O, reducing agents such as HC are also CO. ₂ And H ₂ It is oxidized to O.
[0027]
In the present invention, the reason why the catalyst A is arranged at the front stage and the catalyst B is arranged at the rear stage is that SOx is adsorbed and removed by the catalyst A at the front stage, thereby improving the SOx durability performance in the total catalyst system. The ratio of the catalyst A and the catalyst B may be arbitrarily selected according to the SOx durability performance and the NOx removal performance.
[0028]
When the HC / NOx ratio of the exhaust gas itself is low, such as the exhaust gas of a diesel engine, after adding fuel soot C of about several hundred to several thousand ppm in terms of methane in the exhaust gas, the catalyst-containing layer of the present invention A sufficiently high NOx removal rate can be achieved by adopting a system for contacting with NO. The term “HC” as used herein includes paraffinic hydrocarbons, olefinic hydrocarbons and aromatic hydrocarbons, oxygen-containing organic compounds such as alcohols, aldehydes, ketones and ethers, gasoline, kerosene, light oil, A heavy oil, and the like. Means something.
[0029]
The gas space velocity (SV) at the time of purifying combustion exhaust gas of an internal combustion engine operated in a lean air-fuel ratio region using the catalyst-containing layer according to the present invention is not particularly limited, but is SV5,000h. ^-1 200,000h for the above ^-1 The following is preferable.
[0030]
The denitration rate when the gas composition is constant depends on the type of catalyst and the type of HC, but when the catalyst layer of the present invention is used, for example, C ₂ ~ C ₆ Paraffins, olefins and C ₆ ~ C ₉ 450 to 600 ° C. for aromatic HC ₆ ~ C ₉ 350-550 ° C. for C ₁₀ ~ C ₂₅ In order to show a high denitration rate at 250 to 500 ° C. for paraffins and olefins, the catalyst layer inlet temperature must be 100 ° C. or higher and 700 ° C. or lower, preferably 200 ° C. or higher and 600 ° C. or lower.
[0031]
[Example]
Examples and Reference examples, The present invention will be described in more detail with reference to comparative examples.
However, the present invention is not limited to the following examples.
(1) Selection of alumina
For the selection of the alumina support to be used for catalyst B, in various γ-type aluminas having specific surface areas and pore distributions as shown in Table 1, a to c fall within the scope of the present invention, and d ~ G is alumina outside the scope of the present invention.
In addition, the pore distribution of the alumina of ag was measured by the soapomatic by the Carlo Elba company.
[0032]
[Table 1]
[0033]
(2) Preparation of catalyst layer
In the following, preparation examples for the preparation of each catalyst for constituting the catalyst layer of the present invention sample As shown.
(A) Production of catalyst B:
[ sample 1]
100 g of alumina hydrate, which is a precursor material of γ-type alumina a in Table 1, was immersed in a 300 ml aqueous solution containing 5.36 g of silver nitrate for 10 hours, and then evaporated to dryness at 80 ° C. This was dried by ventilation at 110 ° C. and then calcined in air at 550 ° C. for 3 hours to obtain Catalyst 1. In addition, the content of Ag in terms of metal in the catalyst 1 was 4.5% by weight with respect to the whole catalyst.
[0034]
[ sample 2 to sample 12]
Similarly, except for using alumina hydrate which is a precursor material from which γ-type alumina b to g shown in Table 1 are obtained, sample 1 in the same way as catalyst 1 ( sample 2), catalyst 3 ( sample 3), catalyst 4 ( sample 4), catalyst 5 ( sample 5), catalyst 6 ( sample 6), catalyst 7 ( sample 7) was obtained.
Also, sample 1 except that the content of silver was 0% by weight, 2% by weight, 3% by weight, 8% by weight and 12% by weight. sample 1 and catalyst 8 ( sample 8), catalyst 9 ( sample 9), catalyst 10 ( sample 10), catalyst 11 ( sample 11) and catalyst 12 ( sample 12) was obtained.
[0035]
(B) Production of catalyst A:
[ sample 13 ~ sample 19]
20 g of commercially available silica and 40 g of calcium hydroxide are stirred and mixed in 200 ml of pure water, evaporated to dryness at 80 ° C., dried at 110 ° C. and calcined at 550 ° C. to form catalyst 13 ( sample 13) was prepared. SiO at this time ₂ And Ca (OH) ₂ The weight ratio was 1: 2. In addition, SiO ₂ And Ca (OH) ₂ Having a mixing ratio of 15: 1, 3: 1, 1: 5 and 1:10 were prepared in the same manner, and catalysts 14 to 17 ( sample 14-17). In addition, a catalyst composed only of commercially available calcium oxide is replaced with catalyst 18 ( sample 18) A catalyst composed only of commercially available silica is designated as catalyst 19 ( sample 19).
[0036]
[ sample 20 and sample 36]
the above sample 13, calcium sulfate (hemihydrate gypsum) is further added, and the weight ratio of silica, calcium hydroxide, and calcium sulfate is 2: 4: 3, 8: 1: 1, 4: 1: 1, 1: 4: 3. And 1: 8: 5 sample 13 to catalyst 20 to 24 ( sample 20-24), and commercially available alumina is added so that the weight ratio of silica, calcium hydroxide and alumina is 2: 4: 1, 8: 16: 1, 4: 8: 1 and 1: 2: 1. Except for being prepared in sample In the same manner as in FIG. sample 25-28), and a catalyst made only of commercially available alumina is the catalyst 29 ( sample 29) except that zirconia was added and the weight ratio of silica, calcium hydroxide and zirconia was 2: 4: 3, 8: 16: 1, 4: 8: 1 and 1: 2: 1. Is sample 13 to catalyst 30 to 33 ( sample 30 to 33), and a catalyst composed only of commercially available zirconia is designated as catalyst 34 ( sample 34).
Also above sample 13 except that commercially available alumina and zirconia were further added so that the weight ratio of silica, calcium hydroxide, alumina and zirconia was 8: 16: 3: 1 and 8: 16: 1: 3. sample 13 and catalyst 35 and 36 ( sample 35, 36).
[0037]
(C) Manufacturing of honeycomb catalyst:
[ sample 37 and 38]
60 g of the catalyst 13 was mixed with alumina sol (Αl ₂ O ₃ A ball mill pot was prepared together with 5 g of solid content (20 wt%) and 120 ml of water, and wet pulverized to obtain a slurry. In this slurry, a commercially available 400 cpsi (cell / inch ² ) A cylindrical core having a diameter of 1 inch and a length of 2.5 inches punched from the cordierite honeycomb substrate was immersed, and after lifting, excess slurry was removed by air blow and dried.
Thereafter, it was fired at 500 ° C. for 30 minutes, and coated with 150 g of a solid content in dry conversion per liter of honeycomb, and Ca (OH) ₂ -SiO ₂ Honeycomb catalyst 37 ( sample 37) was obtained.
[0038]
In addition, 60 g of the above powder catalyst 1 was added to alumina sol (Αl ₂ O ₃ A ball mill pot was prepared together with 8 g of solid content (10 wt%) and 120 ml of water, and wet pulverized to obtain a slurry. In this slurry, a commercially available 400 cpsi (cell / inch ² ) A cylindrical core having a diameter of 1 inch and a length of 2.5 inches punched from the cordierite honeycomb substrate was immersed, and after lifting, excess slurry was removed by air blow and dried.
After that, it was fired at 500 ° C. for 30 minutes, and coated with 150 g of a solid content per liter of honeycomb and coated with 4.4% Αg / Αl. ₂ O ₃ Honeycomb catalyst 38 ( sample 38) was obtained.
[0039]
As described above sample The results of evaluating the NOx removal performance under various conditions for the exhaust gas purifying catalyst layer formed using 1 to 38 catalysts 1 to 38 will be described.
[ Reference example 1]
sample 13 catalysts 13 and sample Each of the catalyst 1 was pressure-molded and then pulverized to adjust the particle size to 350 to 500 μm. A reaction tube was filled to form a catalyst layer, which was attached to an atmospheric pressure fixed bed flow reactor. The weight ratio of catalyst 13 to catalyst 1 was 1: 1.
[0040]
[Example of performance evaluation 1]
In this catalyst layer, the exhaust gas temperature in the reaction tube is kept at 425 ° C., and NO: 750 ppm as model exhaust gas, kerosene (C ₁ ): 4500 ppm, O ₂ : 10%, H ₂ O: 10%, SO ₂ : 50 ppm, balance: N ₂ A mixed gas consisting of ^-1 It was passed through.
In the analysis of the reaction tube outlet gas composition, NO and NO ₂ The concentration of N was measured with a chemiluminescent NOx meter, and N ₂ The O concentration was measured using a gas chromatograph / thermal conductivity detector equipped with a Ρorapack Q column. The denitration rate was defined by the following formula.
In any catalyst layer of the present invention, N ₂ O and NO ₂ Hardly formed.
[0041]
[Formula 1]
Reaction tube inlet NO concentration-Reaction tube outlet Ν Ox concentration
Denitration rate (%) ＝ ──────────────────── × 100
Reaction tube inlet NO concentration
[0042]
[ Reference Examples 2-11, Examples 12-21, And Comparative Examples 1 to 14]
sample 2, 3, 9-11 catalysts 2, 3, 9-11 and sample 4-8, 12 catalysts 4-8, 12 respectively Reference example 1 was used in place of the catalyst 1 to form a catalyst layer similar to the above, and an evaluation test using a model gas was performed in the same manner. The catalyst layers using the catalysts 2, 3, 9 to 11 are respectively Reference example 2 to 6, and the catalyst layers using the catalysts 4 to 8 and 12 were referred to as Comparative Examples 1 to 6, respectively.
Also, sample 15, 16, 20, 22, 23, 25-28, 30-33, 35, 36 catalyst 15, 16, 20, 22, 23, 25-28, 30-33, 35, 36 and sample 14, 17-19, 21, 24, 29, 34 catalyst 14, 17-19, 21, 24, 29, 34 Reference example A catalyst layer similar to the above was formed using the catalyst 13 instead of the catalyst 13 and an evaluation test using a model gas was performed in the same manner. Catalyst layers using catalysts 15, 16, 20, 22, 23, 25-28, 30-33, 35, 36, respectively Reference example 7 to 11, and catalyst layers using the catalysts 14, 17 to 19, 21, 24, 29, and 34 were referred to as Comparative Examples 7 to 14, respectively.
Table 2 shows the above Reference Examples 1-11, Examples 12-21 The initial denitration performance and the denitration performance 8 hours after the start of the reaction are shown for the catalyst layers of Comparative Examples 1-14.
[0043]
[Performance evaluation example 2 ( Reference example 22)]
In performance evaluation example 1, sample 37 honeycomb catalyst 37 and sample Each of the 38 honeycomb catalysts 38 is processed into a cylindrical shape having a diameter of 15 mm and a length of 32 mm. Filled the tube ( Reference example 22). The space velocity of the gas to be fed to the catalyst layer of the honeycomb catalyst 38 is 13,000 h. ^-1 Except for the above, an evaluation test using the same model gas as in the performance evaluation example 1 was performed, and the initial denitration performance and the denitration performance 8 hours after the start of the reaction are shown in Table 2 together with the results of the performance evaluation example 1.
[0044]
[Table 2]
[0045]
From Table 2, Reference Examples 1 to 11, 22, Examples 12 to 21 and Comparative Examples 7 to 14 had an initial denitration performance of 75% or more, and showed superior performance as compared with Comparative Examples 1 to 6. Examples 12 to 21 are ,ratio Even after 8 hours of reaction under the coexistence conditions of 50 ppm SOx as compared with Comparative Examples 7 to 14, high denitration performance of at least 61% was maintained.
[0046]
【The invention's effect】
As described above, according to the exhaust gas purifying catalyst layer and the exhaust gas purifying catalyst coating structure according to the present invention, and the exhaust gas purifying method using these, nitrogen oxides contained in the lean combustion exhaust gas in which SOx and water vapor coexist are obtained. Since it can be reduced and purified at a high denitration rate, it is useful for the purification of nitrogen oxides in the combustion exhaust gas of an internal combustion engine.

Claims (5)

The relationship between the catalyst A containing silica, calcium and alumina or zirconia and the pore radius and pore volume measured by the nitrogen gas adsorption method is the pore volume occupied by pores having a pore radius of 300 angstroms or less. The total value of the pore volume occupied by pores having a pore radius of 25 angstroms or more and less than 100 angstroms is defined as Y, and the total value of the pore volume occupied by pores having a pore radius of 100 angstroms or more and 300 angstroms or less. When the total value is Z , 0.1 to 10% by weight of silver in terms of metal is added to an alumina support having a pore structure in which Y is 70% or more of X and Z is 20% or less of X. And the catalyst B is arranged in the front stage and the catalyst B is divided in the rear stage with respect to the exhaust gas flow direction. Gas purification catalyst layer.  The exhaust gas purification catalyst layer according to claim 1, wherein the catalyst A further contains a sulfate group. The catalyst A and B according to claim 1 or 2 on at least the inner surface of the through-hole in a monolithic support substrate made of a refractory material having a large number of through-holes , the catalyst A being in the preceding stage with respect to the exhaust gas flow direction, An exhaust gas purifying catalyst coating structure, wherein the catalyst B is disposed and coated in a subsequent stage .  3. The exhaust gas purification method using a hydrocarbon as a reducing agent, which comprises contacting combustion exhaust gas of an internal combustion engine operated at a lean air-fuel ratio with a catalyst-containing layer, and the catalyst contained in the catalyst-containing layer is defined in claim 1 or 2. An exhaust gas purification method, which is an exhaust gas purification catalyst layer.  The exhaust gas purification method using hydrocarbon as a reducing agent, which comprises contacting combustion exhaust gas of an internal combustion engine operated at a lean air-fuel ratio with a catalyst-containing layer, and the catalyst contained in the catalyst-containing layer is the exhaust gas purification according to claim 3. An exhaust gas purification method comprising a catalyst-coated structure for use.