JPH09299763A - Denitration catalyst layer and denitrating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a denitration catalyst layer capable of efficiently removing NOx in exhaust gas discharged from an internal combustion engine operated in the range from a stoichiometric region to a lean burning region at a sufficiently high gas space velocity of >=10,000h<-1> and to provide a denitrating method using the catalyst layer by which NOx in exhaust gas is efficiently removed with high reliability. SOLUTION: This denitration catalyst layer consists of a catalyst (A) obtd. by incorporating Ag, Zn and P into alumina, a catalyst (B) obtd. by incorporating Au, Zn and P into alumina and a catalyst (C) obtd. by incorporating Ce and one or more selected from among Pt, Pd, Rh and Ir into alumina. A flow of exhaust gas discharged from an internal combustion engine operated in a lean air-fuel ratio is brought into contact with this catalyst layer to carry out denitration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst used for purifying exhaust gas of an internal combustion engine, particularly nitrogen oxide in exhaust gas discharged from an internal combustion engine such as a stationary engine or an automobile engine. More specifically, a denitration catalyst layer and a denitration catalyst layer capable of purifying nitrogen oxides in exhaust gas discharged from an internal combustion engine in a stoichio region to a lean burn region with high space velocity and high efficiency were used. The present invention relates to a method for denitration of exhaust gas.

[0002]

2. Description of the Related Art Various combustion exhaust gases emitted from internal combustion engines such as automobile engines contain nitrogen oxides (NOx) such as nitric oxide and nitrogen dioxide together with water and carbon dioxide which are combustion products. Has been. NOx not only affects the human body and increases the respiratory disease morbidity, but it is also one of the causes of acid rain, which is regarded as a problem from the viewpoint of global environment conservation. Therefore, development of a denitration technique for efficiently removing nitrogen oxides from these various exhaust gases is desired.

On the other hand, from the viewpoint of preventing global warming, a lean-burn internal combustion engine has recently attracted attention. A conventional gasoline engine for an automobile has an air-fuel ratio (A / F) = 1.
Combustion is performed with a stoichiometric amount of oxygen in the vicinity of 4.7, and carbon monoxide and hydrocarbons (hereinafter referred to as HC) in the exhaust gas are treated for the exhaust gas treatment.
A three-way catalyst system has been adopted in which the harmful three components are simultaneously removed by bringing Al and Ox into contact with an alumina catalyst containing mainly platinum, rhodium, palladium and cerium.

However, the exhaust gas purification method using the three-way catalyst system is an exhaust gas of a lean-burn engine operated at a lean air-fuel ratio because the absolute condition is that the engine be operated at a stoichiometric ratio. Not applicable for gas purification. Further, although the diesel engine is a lean burn engine by nature, strict regulations are being imposed on both exhaust particulate matter and NOx with respect to its exhaust gas.

Conventionally, as a method for reducing and removing NOx in an oxygen-excess atmosphere, a technique has already been established in which NH ₃ which is selectively adsorbed by a catalyst even in a small amount as a reducing gas is used. This technology has been industrialized as a denitration method for exhaust gas from a fixed source such as a boiler or a diesel engine. However, this method requires a special device for recovering unreacted reducing agent, and uses ammonia, which has a strong odor and is harmful. Therefore, exhaust gas denitration technology for mobile sources such as automobiles for transportation of human body is required. As it is dangerous, it cannot be applied.

In recent years, by using HC remaining in the lean combustion gas in an oxygen excess atmosphere as a reducing agent, NOx
It has been reported that the reduction reaction can be promoted. Since then, various catalysts for promoting this reaction have been developed and reported. For example, many reports have been made that a catalyst in which a transition metal is supported on alumina or a silica-alumina carrier is effective for a NOx reduction reaction using HC as a reducing agent. In addition, JP-A-4-28484
No. 8 discloses that 0.1 to 4% by weight of Cu, Fe, Cr,
Alumina or silica containing Zn, Ni, V, etc.
An example of using an alumina catalyst as a NOx 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.
It is reported in JP-A-5-68855 and JP-A-5-103949. However, when these noble metal-supported catalysts are used, the combustion reaction of HC, which is a reducing agent, is excessively promoted, and a large amount of N ₂ O, which is said to be one of the causative substances of global warming, is produced, which is harmless. There was a drawback when it became difficult to selectively proceed the reduction reaction to N ₂ .

The applicant of the present invention has previously reported that when using a catalyst containing silver as a reducing agent with HC as an reducing agent under an oxygen-rich atmosphere,
It was found that the Ox reduction reaction selectively proceeded, and this was disclosed in JP-A-4-281844. However, this catalyst certainly shows a good NOx reduction performance in an oxygen excess atmosphere, but when this is applied to the exhaust gas emitted from the lean burn engine in an actual running state,
The combustion conditions of the lean burn engine are the air-fuel ratio (A /
Since F) continuously changes from near stoichio, which is the theoretical ratio, to the lean burn region under oxygen excess, durability performance against aging in the stoichio region (hereinafter referred to as stoichio durability performance) is insufficient and long-term use There is a drawback that it becomes difficult.

It is considered that such deterioration of the silver-alumina catalyst occurring in the stoichio region is caused by agglomeration of silver supported in the catalyst, caulking of the alumina carrier and the like. That is, the above-mentioned catalyst is a catalyst that can exhibit high denitration performance only in the lean burn region, and as a catalyst for gasoline lean burn vehicles that require high denitration performance in a wide range from the stoichio region to the lean burn region. Was insufficient.

[0010]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No. 4-281 is disclosed.
Even after the disclosure of an alumina catalyst using silver according to Japanese Patent No. 844, a NOx reduction / removal technique similar to the technique described in the Japanese Patent Laid-Open No. 4-354536, Japanese Patent Laid-Open No. 5-92124, Japanese Patent Laid-Open No. 5-91212
No. 5 and Japanese Patent Application Laid-Open No. 6-277454. However, the alumina-supported silver catalysts described in these publications have not only practically insufficient denitration performance in the coexistence of water, but the disclosure thereof is only evaluated for performance under oxygen excess conditions. Nothing is said about stoichio durability, and of course, these catalysts are catalysts that can show performance only in the lean burn region, and are gasoline lean burn vehicles that can cover from the stoichio region to the lean burn region. It was not a catalyst for use.

Furthermore, in JP-A-7-80306, there is disclosed a catalyst in which an inorganic oxide carries at least one element selected from the group consisting of silver and gold, and Ρd, Ru, Rh and Ir. Although disclosed
The catalyst described in the publication has a problem that the catalytic activity of gold and silver supported during the stoichio durability is deteriorated, so that the denitration performance in the lean burn region after the stoichio durability is deteriorated.

Generally, a catalyst using alumina as a carrier has a passing gas flow rate per unit volume of the catalyst, that is, a gas space velocity (hereinafter, referred to as space velocity, indicated by symbol SV).
It is known that there is a high dependence on. That is, SV
At a low space velocity of about 1,000 to 10,000 h ⁻¹ , sufficient NOx reduction performance can be exhibited, but for example, “Catalyst”, Vol. 33, Item 61 (1991).
SV 10,000 h
There has been a problem that the NOx purification performance is obviously deteriorated at a high space velocity of ^-1 or more.

Generally, a catalyst used for purifying exhaust gas of a moving internal combustion engine of an automobile or the like is required to be a relatively compact device corresponding to its exhaust amount.
As described above, a catalyst that functions only at an SV of less than 10,000 h ^-1 requires a large volume disproportionately larger than the engine displacement as a catalyst layer, and therefore becomes too large in terms of equipment and impractical. I have to say that.

The present invention has been made to solve the above-mentioned drawbacks of the prior art. The object of the present invention is to exhaust gas emitted from an internal combustion engine operated in the range from the stoichio region to the lean burn region. NOx in 1
Provided is a denitration catalyst layer that can be efficiently removed by operating with a sufficiently high gas hourly space velocity of 20,000 h ⁻¹ or more, and at the same time, use the catalyst layer to efficiently and reliably detect NOx in exhaust gas. It is to provide a highly denitrifying method.

[0015]

Means for Solving the Problems The present inventors have conducted various studies on a catalyst layer having high denitration performance in the range from the stoichio region to the lean burn region, and a denitration method using the catalyst layer, and as a result, A catalyst containing silver, zinc and phosphorus in alumina, a catalyst containing gold, zinc and phosphorus in alumina, and at least one selected from the group consisting of platinum, palladium, rhodium and iridium in alumina. The inventors have found that the above-mentioned problems can be solved by forming a catalyst layer by using a catalyst containing cerium and cerium in combination, and completed the present invention.

That is, the first embodiment of the present invention for achieving the above object is to use a catalyst A containing alumina, silver, zinc and phosphorus, and alumina containing gold, zinc and phosphorus. And a catalyst C containing cerium and at least one selected from the group consisting of platinum, palladium, rhodium and iridium in alumina, and a catalyst layer for denitration. is there.

In the catalyst layer of the present invention, the contents of silver, zinc and phosphorus in catalyst A are 0.1 to 10% by weight, 0.1 to 10% by weight and 0.01% in terms of metal based on alumina. The content of gold, zinc and phosphorus in the catalyst B is preferably 0.1 to 10% by weight, and 0.1% to 0.
It is preferably 1 to 10% by weight and 0.01 to 7% by weight, and at least 1 selected from the group consisting of platinum, palladium, rhodium and iridium in the catalyst C.
The content of seeds or more and cerium is 0.05 to 10% by weight and 1 to 50% by weight, respectively, in terms of metal based on alumina.
It is preferable that

Further, the second embodiment of the present invention is a method for denitrifying exhaust gas, which comprises contacting a flow of exhaust gas discharged from an internal combustion engine operated at a lean air-fuel ratio with a catalyst layer, It is characterized by a denitration method using the denitration catalyst layer according to the first embodiment as a layer. In the second embodiment, are the catalyst A, the catalyst B, and the catalyst C forming the denitration catalyst layer arranged in the order of the catalyst A, the catalyst B, and the catalyst C from the preceding stage in the flow direction of the exhaust gas? It is preferable that the catalyst A and the catalyst B are mixed and arranged before the catalyst C, but the mixed catalyst of the catalyst A and the catalyst B is in the front stage, the mixed catalyst of the catalyst A and the catalyst C is in the rear stage, Alternatively, the mixed catalyst of the catalyst A and the catalyst B may be arranged in the front stage, and the mixed catalyst of the catalyst B and the catalyst C may be arranged in the rear stage. Further, in the second embodiment, the gas space velocity of the exhaust gas passing through the denitration catalyst layer is 10,000.
it is appropriate to 200,000 ^-1 or less in the range in h ^-1 or more.

According to the denitration catalyst layer and the denitration method of the present invention as described above, excellent denitration performance and stoichio durability can be exhibited even in an oxygen excess atmosphere in which water vapor coexists and even at a high space velocity. Therefore, it is possible to extremely effectively remove NOx in the exhaust gas from the internal combustion engine operated in the stoichio region to the lean burn region.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. First, the denitration catalyst layer according to the first embodiment of the present invention will be described. The denitration catalyst layer comprises a catalyst A, a catalyst B and a catalyst C. It is composed of Alumina, which is one of the main constituent components of the catalyst constituting the denitration catalyst of the present invention, is, for example, a powder or gel of aluminum hydroxide which is classified into boehmite, cohesive boehmite, vialite, or norstrandite in mineralogy. 300-80 in air or vacuum
By heat dehydration at 0 ° C., preferably 400 to 700 ° C., a phase transition to alumina which is crystallographically classified as γ-type, η-type, δ-type, χ-type or a mixed type thereof is performed. Those that are preferred are. Alumina having another crystal structure, such as α-type alumina, has an extremely small specific surface area and is poor in solid acidity, and is therefore unsuitable as the catalyst component of the present invention.

The catalyst A is the above alumina containing silver, zinc and phosphorus. The state of silver, zinc and phosphorus contained in alumina is not particularly limited, and for example,
Examples thereof include a metal state, an alloy state, an oxide state and a complex oxide state. Also, each starting material is not limited, but it is particularly preferable to use a water-soluble salt.

The catalyst B is the above alumina containing gold, zinc and phosphorus, and the catalyst C is the above alumina containing at least one selected from the group consisting of platinum, palladium, rhodium and iridium and cerium. However, strontium, zirconium, lanthanum, etc. may be contained depending on the required performance.
The state of gold, zinc, phosphorus, platinum, palladium, rhodium, iridium and cerium contained in these aluminas is not particularly limited, and may be the same as that of the catalyst A. Also, each starting material is not particularly limited as in the case of the catalyst A, but it is particularly preferable to use a water-soluble salt.

Then, in the catalyst A, a method of adding silver, zinc and phosphorus to the alumina, in the catalyst B, a method of adding gold, zinc and phosphorus to the alumina, and in the catalyst C, the alumina is platinum, palladium, rhodium, iridium and cerium. The method of incorporating the is not particularly limited, methods that have been conventionally performed in the production of this catalyst species, such as adsorption method, pore filling method, incipient wetness method, evaporation dryness method, impregnation method such as spray method and It is possible to achieve this by incorporating these elements into the above-mentioned alumina or alumina hydrate that is a precursor of alumina by employing a commonly known method such as a kneading method and a physical mixing method. it can.

In the present invention, the catalyst A, the catalyst B and the catalyst C containing the catalytically active substance in alumina as described above are dried and calcined, but the drying temperature is not particularly limited, and the usual drying temperature, For example, the drying is performed at a temperature of about 80 to 120 ° C. Further, the baking after the completion of drying is 30
It is carried out at a temperature in the range of 0 to 1000 ° C, preferably 400 to 900 ° C. If the firing temperature is less than 300 ° C,
Alumina does not have a desired crystal form, and when it exceeds 1000 ° C., alumina is transformed into another undesirable crystal form, which is not preferable.

The contents of silver, zinc and phosphorus in catalyst A are not particularly limited, but are 0.1 to 10% by weight, 0.1 to 10% by weight and 0.01 to 7% by weight in terms of metal, respectively, based on alumina. % Is preferable. Further, the content of gold, zinc and phosphorus in the catalyst B is not limited, but is 0.1 to 1 in terms of metal with respect to alumina.
It is preferably 0% by weight, 0.1 to 10% by weight, and 0.01 to 7% by weight. Moreover, the content of at least one or more of platinum, palladium, rhodium, and iridium in the catalyst C and the content of cerium are also not limited, but are 0.05 to 10% by weight and 1 to 50% by weight with respect to alumina, respectively. % Is preferable.

The catalyst layer for denitration of the present invention comprises catalyst A and catalyst B.
And catalyst C to form a catalyst layer, which is used for denitration of exhaust gas. The ratio of the catalyst A and the catalyst B is not particularly limited and can be arbitrarily changed according to the required performance. Further, the ratio of the catalyst C to the catalyst A is not particularly limited and can be arbitrarily changed according to the required performance. The form of the denitration catalyst layer is not particularly limited. For example, the catalyst layer for denitration is formed of these catalyst A, catalyst B, and catalyst C.
The above three kinds of catalysts may be packed in the space in which the exhaust gas is circulated in the powder state in the above-described arrangement, and these denitration catalysts may be molded into a catalyst molded body using a molding machine. Good. The shape of such a catalyst molded body is not particularly limited, and for example, powdery, spherical, cylindrical, honeycomb, spiral,
Various shapes such as a granular shape, a pellet shape, and a ring shape can be adopted. The shape, size, etc. of these molded products can be arbitrarily selected according to the usage conditions.

Further, as another mode of the catalyst layer for denitration, the above catalyst is coated on the inner surface of the through hole of the supporting substrate having an appropriate through hole made of ceramics or metal to form a catalyst structure. It may be used by forming a body. Especially when it is used for purifying exhaust gas of automobile engine,
Since the exhaust gas has a high gas space velocity, in order to minimize the pressure loss, a catalyst is coated on the inner surface of a refractory monolithic support substrate having a large number of through holes in the exhaust gas flow direction. A catalyst structure having a catalyst layer is suitable.
The through holes preferably have an opening ratio of 60 to 90%, optimally 70 to 90% in a cross section perpendicular to the exhaust gas flow direction, and the number thereof is 30 per square inch (5.06 cm ² ). It is preferable to provide ~ 700, optimally 200-600.

The denitration catalyst coated on the surface of the supporting substrate may be coated not only on the inner surface thereof but also on the end faces and side faces.
As the coating method, the powder of the denitration catalyst of the present invention, which has been sized to a certain particle size, may be used with or without a binder by using a known coating method such as a washcoat method or a sol-gel method. it can. Also,
The ceramic material used for the supporting substrate is α
-Alumina, mullite, cordierite, silicon carbide, and the like, and examples of the metal material include austenitic or ferritic stainless steel. Further, the shape of the supporting substrate may be a conventional shape such as a honeycomb shape or a foam shape.

Next, an exhaust gas denitration method using the denitration catalyst layer of the present invention will be described. The catalyst layer of the present invention has excess oxygen in the vicinity of the stoichiometric amount that completely oxidizes CO, HC and H ₂ and reducing components in exhaust gas with NOx and O ₂ and oxidizing components. It is applied to the purification of NOx in the exhaust gas, that is, the exhaust gas of the internal combustion engine in the range up to the lean air-fuel ratio.

By bringing such exhaust gas into contact with the denitration catalyst layer of the present invention, NOx is reduced to N ₂ and H ₂ O by a reducing agent present in a small amount in the exhaust gas such as HC, and at the same time. , HC and other reducing agents are also CO ₂ and H ₂ O.
Is oxidized. When the HC / NOx ratio (molar ratio) of the exhaust gas itself is low, like the exhaust gas of a diesel engine, after adding several hundred to several thousand ppm of fuel HC in methane conversion concentration to the exhaust gas, If a system for contacting the catalyst layer of the present invention is adopted, sufficient N
Ox removal rate can be achieved. In addition, HC here means paraffinic hydrocarbons, olefinic hydrocarbons and aromatic hydrocarbons, alcohols, aldehydes,
Oxygen-containing organic compounds such as ketones and ethers, gasoline,
It means anything including light lots, light lots, heavy lots, etc.

The gas space velocity for purifying the exhaust gas of the internal combustion engine operated with the air-fuel ratio in the range from the stoichiometric region to the lean burn region using the catalyst layer according to the present invention is particularly limited. However, if the internal combustion engine is a moving internal combustion engine such as an automobile engine,
As described above, the space velocity is preferably 10,000 h ^-1 or more. In addition, the upper limit of space velocity is about 2 in consideration of the performance of the internal combustion engine such as the current automobile engine.
A ^value of 0,000 h ^-1 is suitable.

Then, using the catalyst layer for denitration of the present invention, the space velocity as described above is 10,000 h ⁻¹ to 200,
In order to efficiently perform purification of NOx by HC in an oxygen-excess atmosphere at a high space velocity of 000 h ⁻¹ , the catalyst layer inlet temperature is 100 ° C. or higher and 700 ° C. or lower, and optimally 200 ° C. or higher and 600 ° C. or lower. Is preferred.

[0033]

The following examples and comparative examples of the present invention
The present invention will be described in more detail. However, the present invention is not limited to the following examples.

First, the preparation of each denitration catalyst for forming the denitration catalyst layers according to the examples and comparative examples of the present invention will be described. Reference example 1: a. Preparation of catalyst A 300 g of commercially available boehmite powder (structure water 27.7%)
Was immersed in an aqueous solution of 500 ml in which 8.8 g of silver nitrate, 70 g of zinc nitrate hexahydrate and 2 g of phosphoric acid were dissolved for 24 hours, and then heated with stirring to evaporate water.
Next, this was air-dried at 110 ° C. and then calcined in air at 700 ° C. for 3 hours to obtain a catalyst A1. The contents of silver, zinc and phosphorus in terms of metal in the catalyst A1 were 2.5 wt%, 6.6 wt% and 0. It is 3% by weight.

B. Preparation of Catalyst B Commercially available boehmite powder 150 g (structure water 27.7%)
Γ obtained by firing at 700 ° C. for 3 hours
100 g of mono-alumina (specific surface area of 169 m ² / g) was dissolved in a 200 ml aqueous solution of 2.1 g of chloroauric acid, 32.3 g of zinc nitrate hexahydrate and 0.9 g of phosphoric acid.
After soaking for 4 hours, it was heated with stirring to evaporate the water content. Next, after air-drying this at 110 ° C., 700 in air
The catalyst was calcined at 3 ° C. for 3 hours to obtain a catalyst B1. The contents of gold, zinc and phosphorus in terms of metal in the catalyst B1 are 1% by weight, 6.6% by weight and 0.3% by weight, respectively, based on alumina.

C. Preparation of Catalyst C γ-alumina (specific surface area 174 m ² // obtained by calcining commercially available boehmite powder at 600 ° C. for 3 hours
g) 100 g was impregnated with an aqueous cerium nitrate solution so that the cerium content was 10% by weight, dried at 110 ° C. for 3 hours, and then calcined at 600 ° C. for 2 hours. Next, the cerium-containing alumina carrier was adjusted in concentration so that the contents of platinum and rhodium in γ-alumina were 0.5% by weight and 0.1% by weight, respectively, in terms of metal, and chloroplatinic acid and rhodium chloride were adjusted. The catalyst C1 was obtained by impregnating it with the mixed aqueous solution of 1), drying at 110 ° C. for 3 hours, and then calcining at 500 ° C. for 2 hours.

Reference Examples 2 and 3: Catalyst A1 of Reference Example 1 was prepared in the same manner as in Reference Example 1 except that the silver content was changed to 1.5% by weight and 3.6% by weight, respectively.
2 (reference example 2) and catalyst A3 (reference example 3) were obtained.

Reference Example 4: In the catalyst C1 of Reference Example 1,
The contents of platinum, rhodium and cerium are 1.
A catalyst C2 (Reference Example 4) was obtained in the same manner as in Reference Example 1 except that 5% by weight, 1% by weight and 25% by weight were used.

Reference Example 5: In the catalyst C2 of Reference Example 4,
A catalyst C3 (Reference Example 5) was obtained in the same manner as in Reference Example 1 except that palladium was used instead of platinum.

Reference Example 6: In the catalyst A1 of Reference Example 1,
A catalyst A4 (Reference Example 6) was obtained in the same manner as in Reference Example 1 except that the contents of zinc and phosphorus were 0% by weight.

Reference Example 7: Instead of the catalyst A1 of Reference Example 1,
Catalyst A5 was prepared based on the technique described in Example 9 of JP-A-6-277454. That is, zinc nitrate hexahydrate 46 g and alumina nitrate nonahydrate 280 g
It was dissolved in liter of water, and 650 g of 7% by weight aqueous ammonia solution was added to this aqueous solution with vigorous stirring, and the resulting precipitate was aged for about one day and night, and then filtered and washed. Dry at temperature for about 1 day and then 6
A catalyst carrier was obtained by calcining at 00 ° C for 6 hours. The composition of the obtained carrier was ZnO: A1 ₂ 0 ₃ = 25: 75.
(Weight ratio, converted to oxide). And this carrier 38
g to 200 ml of an aqueous solution containing 1.26 g of silver nitrate, evaporated to dryness and then baked to obtain 2% by weight of silver.
A supported catalyst A5 (Reference Example 7) was obtained. The catalyst A5 is
The contents of silver and zinc are 2% by weight and 21% by weight, respectively, and the catalyst does not contain phosphorus.

The results of evaluating the denitration performance under various conditions by forming a denitration catalyst layer using each of the catalysts of the above-mentioned reference examples will be described below. Example 1: Catalyst A1, catalyst B1 and catalyst C of Reference Example 1
1 After each pressure molding, crushed to a particle size of 250-5
The particle size was adjusted to 00 μm, and the weight ratio of the catalyst A1 and the catalyst B1 was 1:
The catalyst mixed so as to be 1 was added to the front stage, and the front stage catalyst A1
Catalyst C1 such that the ratio of catalyst C1 to
Was filled in a stainless steel reaction tube having an inner diameter of 21 mm to form a catalyst layer, and the catalyst layer was attached to an atmospheric fixed bed reactor. [Performance Evaluation Example 1] Denitration performance of a catalyst layer composed of a fresh catalyst in a lean atmosphere; N0: 5 was used as a model exhaust gas in this catalyst layer.
_{00ppm, C 3 H 6: 500ppm} , O 2: 5%, H
₂ O: 10%, mixed gas consisting of balance N ₂ with space velocity 3
It was passed at 10,000 h ^-1 .

[0043] In the test, analysis of the reaction tube exit gas composition, the concentration of NO and NO ₂ is measured by the Thermo Electron Corporation chemiluminescence NOx meter (model number _{12), N} 2 O
The concentration was measured using a gas chromatograph / thermal conductivity detector equipped with a Polarak Q column. The catalyst layer inlet temperature was set to a predetermined temperature of 100 to 700 ° C., and the denitration rate was calculated from the following formula 1 using the value at the time when the reaction tube outlet gas composition became stable at each predetermined temperature. Almost no generation of N ₂ O and NO ₂ could be confirmed using any of the catalyst layers of the present invention.

[0044]

(Equation 1)

Examples 2 and 3 and Comparative Examples 1 and 2: Using the catalysts A2 to A5 of Reference Examples 2, 3, 6, and 7 instead of the catalyst A1 of Example 1, a catalyst layer similar to the above was formed. After being formed, an evaluation test with a model gas was performed in the same manner. A catalyst layer formed by using the catalysts A2 to A3 was used in Examples 2 to 3
And a catalyst layer formed by using the catalysts A4 to A5.
~ 2. The catalyst layer inlet temperature of each catalyst layer is 420 ° C in Table 1.
Shows the denitration rate at. From the results in Table 1, it is understood that the catalyst layers of the present invention of Examples 1 to 3 exhibit much higher denitration performance than the catalyst layers of Comparative Examples 1 and 2.

Example 4 and Example 5: Using the catalysts C2 and C3 of Reference Examples 4 and 5 respectively instead of the catalyst C1 of Example 1, a catalyst layer similar to that of Example 1 was formed, Similarly, an evaluation test using model gas was performed.
A catalyst layer was formed using the catalysts C2 to C3, and examples 4 to 5 were obtained. Table 1 shows the NOx removal rate at each catalyst layer inlet temperature of 420 ° C. From the results in Table 1, it can be seen that the catalyst layers of the present invention of Examples 4 and 5 exhibit much higher denitration performance than the catalyst layers of Comparative Examples 1 and 2.

Comparative Example 3 and Comparative Example 4: A catalyst layer comprising only the catalyst B1 and the catalyst C1 of Reference Example 1 (Comparative Example 3),
Alternatively, a catalyst layer (Comparative Example 4) composed of only the catalyst A1 and the catalyst B1 was formed, and an evaluation test using a model gas was performed in the same manner. Table 1 shows the NOx removal rate at each catalyst layer inlet temperature of 420 ° C. From the results shown in Table 1, it can be seen that the catalyst layer of Comparative Example 3 has low activity, but the catalyst layer of Comparative Example 4 exhibits high performance equivalent to or higher than the denitration performance of Example.

Example 6 A catalyst layer was prepared in the same manner as in Example 1 except that the catalysts A1 and B1 that had been subjected to sizing were filled in the former stage of the catalyst A1 and the latter stage of the catalyst B1 in the flow direction of the model gas. The denitration rate was evaluated. Table 1 shows the NOx removal rate at a catalyst layer inlet temperature of 420 ° C. From the results in Table 1, it can be seen that the catalyst layers arranged according to the arrangement order of the present invention exhibit high denitration performance.

Comparative Example 5: The catalyst C1 of Example 1 was used in the preceding stage,
The denitration rate of the catalyst layer was evaluated in the same manner as in Example 1 except that the mixed catalyst of the catalysts A1 and B1 was placed in the latter stage. Table 1 shows the NOx removal rate at a catalyst layer inlet temperature of 420 ° C. When the catalyst C1 was arranged in the former stage, the denitration performance was lowered.

[0050]

[Table 1] ─────────────────────────────────── Catalyst layer Denitration rate (%) ──── ─────────────────────────────── Example 1 First Stage [Catalyst A1 + Catalyst B1] + Second Stage [Catalyst C1] 75.8 Example 2 First Stage [Catalyst A2 + Catalyst B1] + Second Stage [Catalyst C1] 75.1 Example 3 First Stage [Catalyst A3 + Catalyst B1] + Second Stage [Catalyst C1] 68.5 Comparative Example 1 Previous Stage [Catalyst A4 + Catalyst B1] + 2nd stage [catalyst C1] 56.5 Comparative example 2 1st stage [catalyst A5 + catalyst B1] + 2nd stage [catalyst C1] 41.6 Example 4 1st stage [catalyst A1 + catalyst B1] + 2nd stage [catalyst C2] 76.1 Example 5 1st stage [Catalyst A1 + Catalyst B1] + Last stage [Catalyst C3] 74.9 Comparative Example 3 [Catalyst B1 + Catalyst C1] 19.2 Comparative Example 4 [Catalyst A1 + Catalyst B1] 84.1 Example 6 First stage [catalyst A1] Middle stage [catalyst B1] Second stage [catalyst C1] 78.1 Comparative Example 5 First stage [catalyst C1] + Last stage [catalyst A1 + catalyst B1] 7.2 ────── ──────────────────────────────

[Performance Evaluation Example 2] Denitration performance of a catalyst layer composed of a fresh catalyst in stoichio; using the catalyst layers of Example 1, Example 4, Example 5 and Comparative Example 4, the stoichiogas composition shown in Table 2 was used. The denitration rate of the catalyst layer was evaluated in the same manner as in Performance Evaluation Example 1 except that the gas was flown. Table 3 shows the NOx removal rate at a catalyst layer inlet temperature of 420 ° C. From the results in Table 3, it can be seen that when the catalyst layer according to the present invention is used, high denitration performance is exhibited even under stoichiometric conditions.

[0052]

[Table 2] ────────────────────────── (gas composition) NO: 2000 ppm C ₃ H ₆ : 1000 ppm O ₂ : 0.9% _{H 2: 1% H 2 O} : 10% N 2: balance (aeration) gas space velocity (SV): 30,000 h ^-1 the catalyst layer inlet Rogasu temperature: 700 ° C. treatment time: 3 hours ────── ────────────────────

[0053]

[Table 3] ──────────────────── Catalyst layer denitration rate (%) ─────────────────── -Example 1 96.5 Example 4 95.0 Example 5 94.0 Comparative Example 4 10.0 ------------------------------------------------------------------------------------------------------------------------

[Performance Evaluation Example 3] Lean atmosphere denitration performance of the catalyst layer after stoichio durability; Performance evaluation example except that the catalyst layer of Example 1, the catalyst layer of Comparative Example 1 and the catalyst layer of Comparative Example 2 were used, respectively. A catalyst layer was formed in the same manner as in 1, and each catalyst layer was exposed to a stoichiometric gas atmosphere in Table 2 at 700 ° C. for 3 hours, and then the denitration rate of the catalyst layer was evaluated by the model gas in the same manner as in Performance Evaluation Example 1. I went. Maximum denitration rate Cmax in each catalyst layer when the gas catalyst layer inlet temperature is changed to 100 to 700 ° C
(%) Is shown in Table 4. From the results of Table 4, the catalyst layer formed by the catalyst of the present invention exhibits higher denitration performance even after being exposed to the stoichiometric atmosphere, that is, the stoichiometric durability, as compared with the catalyst layer formed by the catalyst of the comparative example. It is understood that there is a nature.

[0055]

[Table 4] ──────────────────── Catalyst layer denitration rate (%) ─────────────────── Example 1 70.3 Comparative Example 1 30.2 Comparative Example 2 30.1 ────────────────────

[Performance Evaluation Example 4] Space velocity dependency: The performance of the catalyst layer formed in Example 1 was evaluated in the same manner as in Performance Evaluation Example 1 except that the space velocity was set to 90,000 h ^-1 . Table 5 shows the maximum denitration rate Cmax (%) at the above space velocity of the catalyst layer. The catalyst layer according to the present invention showed very good denitration performance even at higher space velocities.

[0057]

[Table 5] ────────────────────── Gas space velocity Denitration rate (h ⁻¹ ) Cmax (%) of Performance Evaluation Example 4 ───── ───────────────── 90,000 76.1 ───────────────────────

[0058]

As described above, according to the catalyst layer for denitration and the denitration method of the present invention, since it has stoichiometric durability in an oxygen excess atmosphere in which water vapor coexists and even at a high space velocity, it has a wide range. It is possible to purify the nitrogen oxides in the exhaust gas discharged from the internal combustion engine that is operated with the air-fuel efficiency, at a high conversion rate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyuki Ikeda 3-18-5 Chugoku, Ichikawa, Chiba Prefecture Central Research Laboratory, Sumitomo Metal Mining Co., Ltd. (72) Masao Wakabayashi 3-18-5 Chugoku, Ichikawa, Chiba 5 Sumitomo Metal Mining Co., Ltd. Central Research Laboratory (72) Inventor Yukio Kozaki 3-16 Takashimahonmachi, Numazu City, Shizuoka Prefecture Lions Takashima No.901 (72) Inventor Makoto Nagata Ichikawa City, Chiba Prefecture 3-11-1 Maison Do・ Grace No. 203 (72) Inventor Ken Ito 2-4 B507, Minamiono, Ichikawa-shi, Chiba

Claims (6)

[Claims] 1. A catalyst A made of alumina containing silver, zinc and phosphorus, a catalyst B made of alumina containing gold, zinc and phosphorus, and platinum containing palladium and palladium.
A catalyst layer for denitration, comprising at least one or more selected from the group consisting of rhodium and iridium and a catalyst C containing cerium. 2. The contents of silver, zinc and phosphorus in catalyst A are each 0.1 to 100 in terms of metal based on alumina.
10% by weight, 0.1 to 10% by weight and 0.01 to 7% by weight, and the contents of gold, zinc and phosphorus in the catalyst B are 0.1 to 1 in terms of metal based on alumina.
0% by weight, 0.1 to 10% by weight and 0.01 to 7% by weight, and the content of at least one of platinum, palladium, rhodium, and iridium and cerium in the catalyst C is different from that of the alumina. Converted to 0.05-
The denitration catalyst layer according to claim 1, which is 10% by weight and 1 to 50% by weight. 3. A denitration method for exhaust gas, which comprises contacting a flow of exhaust gas discharged from an internal combustion engine operated at a lean air-fuel ratio with a denitration catalyst layer, wherein the denitration catalyst layer comprises the denitration catalyst layer. A denitration method using the catalyst layer for denitration of 1. 4. The catalyst A, the catalyst B, and the catalyst C contained in the denitration catalyst layer are arranged in the order of the catalyst A, the catalyst B, and the catalyst C from the previous stage in the flow direction of the exhaust gas, The denitration method according to claim 3, wherein the catalyst A and the catalyst B are mixed and arranged before the catalyst C. 5. The space velocity of the exhaust gas passing through the catalyst layer for denitration is 10,000 h ⁻¹ or more and 200,000 h.
^-1 or less, The denitration method of Claim 3 or 4 characterized by the above-mentioned. 6. The inlet temperature of the denitration catalyst layer is 100 to 100.
The denitration method according to any one of claims 3 to 5, wherein the temperature is 700 ° C.