JPH07275708A - Denox catalyst and its production, and denitrification method - Google Patents

Abstract

PURPOSE:To efficiently remove, at a sufficiently high space velocity (sufficiently short contact time), NOx in a exhaust gas from an internal combustion engine operated at a dilute air-fuel ratio. CONSTITUTION:Copper or cesium and silver are deposited on an activated alumina in which a volume of fine pores having <=50Angstrom fine pore radius measured by a gaseous nitrogen adsorption method and the volume of fine pores having 100-300Angstrom fine pore radius are >=30% and <=15% respectively per volume of fine pores having <=300Angstrom fine pore radius.

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, particularly nitrogen oxides in the exhaust gas of internal combustion engines such as automobiles, and more particularly, to a lean air-fuel ratio internal combustion engine. The present invention relates to a denitration catalyst capable of purifying nitrogen oxides in exhaust gas in an engine with high space velocity and high efficiency, a method for producing the same, and a denitration method using the catalyst.

[0002]

2. Description of the Related Art In various combustion exhaust gases discharged from internal combustion engines such as automobile engines, nitric oxide (NO) and nitrogen dioxide (NO) along with water and carbon dioxide (CO ₂ ) which are combustion products. ₂ ) Nitrogen oxides (NO _x ) are included. NO _X affects the human body, not only increases the respiratory disease morbidity, has become one of the causes of acid rain, which is problematic from the top of the global environment. for that reason,
Development of a denitration technology for efficiently removing nitrogen oxides from these various exhaust gases is desired.

An ideal method for removing NO in NO _X is to utilize the direct decomposition reaction of NO shown in Formula 1. Equation 1 is overwhelmingly advantageous to the right-hand side generator in terms of equilibrium.

[0004]

[Formula 1] 2NO ---> N ₂ + O ₂

Japanese Patent Application Laid-Open No. Sho 60 (1994) discloses that it is based on this reaction.
There is a denitration technology described in Japanese Patent No. 125250. This denitration technique uses a catalyst in which Cu is supported on zeolite by an ion exchange method, and this catalyst promotes a direct decomposition reaction of NO.

However, in this denitration technique, oxygen generated by the reaction of the formula 1 is preferentially adsorbed on the catalytic active site. As a result, there arises a problem that the denitration efficiency gradually decreases. Further, there is a drawback that the reaction of the formula 1 is completely inhibited under the condition that excess oxygen exists in the reaction system (oxygen excess atmosphere).

On the other hand, the conventional gasoline engine for automobiles burns with a controlled stoichiometric ratio in the vicinity of the air-fuel ratio λ = 1, and the carbon monoxide (CO ), Hydrocarbons (HC) and NO _x , mainly platinum (pt), rhodium (Rh), palladium (P
A three-way catalyst system has been adopted in which the harmful three components are simultaneously removed by contacting with an alumina catalyst containing d) and ceria (CeO ₂ ).

However, this three-way catalyst system is operated under a stoichiometric ratio as an absolute condition. Therefore, from the viewpoint of preventing global warming, a lean-burn internal combustion engine, such as, for example, It cannot be applied to the exhaust gas purification of lean-burn gasoline engine operated with lean air-fuel ratio. Moreover, although the diesel engine is a lean burn engine by nature, the exhaust gas emits suspended particulate matter and NO.
Strict regulations are about to be applied to both _X.

Conventionally, as a method of reducing and removing NO _x in an oxygen-rich atmosphere, a technique of using NH ₃ which selectively adsorbs a small amount of a reducing gas on a catalyst has already been established, and so-called fixed generation is performed. It has been industrialized as a method for denitration of exhaust gas from a boiler or diesel engine, which is the source. However, this method is not suitable for reducing the unreacted reducing agent (NH ₃ ).
Since special equipment is required for the recovery treatment of the above, and ammonia, which has a strong odor and is harmful, is used, it is dangerous and cannot be applied to the technology for denitration of exhaust gas from mobile sources such as automobiles.

In recent years, since it was reported that the NO _x reduction reaction proceeds using unburned hydrocarbons (HC) remaining in the exhaust gas from lean combustion in an oxygen excess atmosphere as a reducing agent,
Various catalysts that accelerate the NO _x reduction reaction have been proposed.
For example, there are many reports that alumina or a catalyst in which a transition metal is supported on alumina is effective for the NO _x reduction reaction using hydrocarbon as a reducing agent. JP-A-4-908
In the example of Japanese Patent No. 26, the powdered alumina for FCC is NO.
An example of use as an _X reduction catalyst has been reported. Also,
JP The 4-284848 discloses 0.1-4 wt% of Cu, Fe, Cr, Zn, Ni, alumina or silica-containing V - example alumina was used as the NO _X reduction catalysts have been reported .

Further, when a catalyst in which Pt is supported on alumina is used, the NO _x reduction reaction proceeds in a low temperature range of about 200 to 300 ° C. in JP-A-4-267946 and JP-A-5-68855. JP-A-5-1039
It is reported in Japanese Patent Publication No. 49 and the like. However, when these Pt-supported alumina catalysts are used, the combustion reaction of hydrocarbons that should remain as a reducing agent is promoted and the catalytic function is poor, or a large amount of N ₂ O is generated, and the selectivity of the NO _X reduction reaction is increased. It had the drawback of being scarce.

The present applicants previously noted that when a catalyst containing silver was used in a NO _x reduction reaction using a hydrocarbon as a reducing agent in an oxygen excess atmosphere, the production of N ₂ O was suppressed and the NO _x reduction was performed. It was found that the reaction selectively proceeded, and the present technique was disclosed in Japanese Patent Application Laid-Open No. 4-281844. After this disclosure
A similar NO _x reduction and removal technique using a catalyst containing silver is disclosed in JP-A-4-354536 and JP-A-5-92124.
It has been disclosed in Japanese Laid-Open Patent Publication No. 5-92125. Also, `` Applied Catalysis B: Environme
ntal ”(1993, Vol. 2, pp. 199-205) describes a catalyst in which silver is supported on γ-alumina by a usual impregnation method.
It has been reported that it is superior to the alumina catalyst supporting o, Cu, V, and Cr in the NO _x reduction performance in the presence of water vapor.

[0013] However, silver-supported alumina catalyst using conventional alumina carrier under steam coexistence, as the NO _X reduction catalyst by hydrocarbon activity was still insufficient.

Further, it has been conventionally known that a catalyst using alumina as a carrier has a large space velocity dependency. That is, SV: 1000 to 10000 h ^-1 shows a sufficient NO _x reduction performance at a low space velocity, but SV: 10000 h ^-1 as reported in "Catalyst" (Vol. 33, p. 61, 1991). It has been reported that the NO _x reduction and removal performance is significantly reduced at the above high space velocities.
Such a phenomenon was also common sense in the field. For example, in the exhaust gas treatment method disclosed in JP-A-5-92124, the contact time between the exhaust gas and the catalyst is 0.03 g. s
ec / cm ³ or more, more preferably 0.1 g. sec
This is the reason why it is limited to / cm ³ or more.

However, in the exhaust gas treatment of a lean burn engine for vehicles such as automobiles, which is a typical internal combustion engine operated at a lean air-fuel ratio, another performance which is practically indispensable is a catalyst layer or a catalyst. The required space and weight of a structure (hereinafter, referred to as a catalyst-containing layer in the present specification) composed of a supporting substrate coated with. This is because it is not practical to load the catalyst-containing layer with a capacity of several times or more the engine displacement in consideration of the engine displacement and work.

Therefore, it is usually preferable that the capacity of the catalyst-containing layer is equal to or less than the engine displacement. This means that in order to construct a practical catalyst-containing layer, the space velocity of the exhaust gas passing through the catalyst-containing layer is high (corresponding to a very short contact time), that is, 7,000 h ⁻¹ or more, preferably Means that it is required to be 10,000 h ⁻¹ or more. The contact time was 0.03 g. sec
/ Cm ^3, less than 0.02 g. sec / cm ³
It roughly corresponds to the following.

However, the conventional silver-supported alumina catalyst produced by using alumina has an insufficient denitration performance for exhaust gas at such a high space velocity (short contact time) in which water vapor coexists.

[0018]

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art, and an object thereof is to reduce NO _X in exhaust gas in an internal combustion engine of a lean air-fuel ratio. Provided is a denitration catalyst which can be efficiently removed at a sufficiently high gas space velocity (sufficiently short contact time), a method for producing such a catalyst, and an exhaust gas of an internal combustion engine having a lean air-fuel ratio using such a denitration catalyst. An object of the present invention is to provide a method for denitrifying NO _x in gas with high efficiency and high reliability.

[0019]

DISCLOSURE OF THE INVENTION The inventors of the present invention have made a denitration catalyst, a method for producing the same, and a denitration method in which a NO _x reduction reaction by hydrocarbon (CH) progresses with high efficiency even in an oxygen excess atmosphere in which water vapor coexists. As a result of earnest research on the method, it is possible to solve the above problems by using a denitration catalyst in which copper or cesium and silver and / or silver oxide are supported on activated alumina having specific pores. The present invention has been completed and the present invention has been completed.

That is, the first NOx removal catalyst of the present invention for removing nitrogen oxides in exhaust gas in an internal combustion engine operated at a lean air-fuel ratio has a pore radius of 50 A (angstrom) measured by a nitrogen gas adsorption method. The pore volume and the pore volume with a pore radius of 100 to 300 A below are 30% or more and 15% or less of the pore volume of the pore radius of 300 A or less, respectively, and the denitration catalyst is copper supported on activated alumina.

The method for producing the denitration catalyst is as follows.
As the activated alumina precursor having the specific pores as described above, a pore radius of 50 A or less and a pore radius of 1 or less measured by a nitrogen adsorption method by firing at 300 to 800 ° C.
After using an alumina hydrate having a pore volume of 00 to 300 A of 50% or more and 10% or less of the pore volume of 300 A or less, respectively, after supporting a copper salt on the alumina hydrate, A method for producing a denitration catalyst is characterized by drying and firing.

Further, in the exhaust gas denitration method comprising contacting exhaust gas of an internal combustion engine operated at a lean air-fuel ratio with the catalyst containing layer, the denitration catalyst contained in the catalyst containing layer is the first denitration catalyst. And a temperature of exhaust gas is 350 to 450 ° C. at the inlet of the catalyst-containing layer.

On the other hand, the second aspect of the present invention for removing nitrogen oxides in exhaust gas in an internal combustion engine operated at a lean air-fuel ratio
The denitration catalyst of No. 1 has a pore volume of 50 A or less and a pore radius of 100 to 300 A measured by a nitrogen gas adsorption method.
With a denitration catalyst comprising activated alumina having a pore volume of 30% or more and 15% or less of a pore volume of 300 A or less, and cesium and silver and / or silver oxide supported on the activated alumina. is there.

Further, regarding the method for producing the denitration catalyst,
A method for producing a denitration catalyst is characterized in that activated carbon having specific pores as described above is loaded with silver and / or silver oxide and then cesium is sequentially loaded.

Further, in the exhaust gas denitration method comprising contacting the exhaust gas of an internal combustion engine operated at a lean air-fuel ratio with the catalyst containing layer, the denitration catalyst contained in the catalyst containing layer is the second denitration catalyst. And the temperature of the exhaust gas is 400 to 550 ° C. at the inlet of the catalyst-containing layer.

According to the above method of the present invention, even if the space velocity of the exhaust gas passing through the denitration-containing layer is 10,000 h ^-1 or more, the NO _x reduction removal of the exhaust gas can be sufficiently performed.

According to the denitration catalyst, the method for producing the same, and the denitration method of the present invention, NO _X in exhaust gas can be effectively removed in a low temperature region even in an oxygen excess atmosphere in which water vapor coexists.

The present invention will be described in more detail below.

[0029]

The activated alumina, which is the carrier of the denitration catalyst of the present invention, has a pore radius of 50 A measured by the nitrogen gas adsorption method.
Pore volume and pore radius of less than (angstrom) 10
The pore volume of 0 to 300 A has a pore radius of 300 A, respectively.
It is 30% or more and 15% or less of the following pore volume, and the alumina hydrate is 300 to 8 in air or vacuum.
By dehydration by heating at a temperature of 00 ° C., preferably 300 to 700 ° C., it undergoes a phase transition to activated alumina which is crystallographically classified as γ-type, η-type or a mixed type thereof. For example, it is a powder or gel of aluminum hydroxide that is classified into boehmite, pseudo-boehmite, vialite, or norstrandalite in mineralogy,
Preferred are boehmite and pseudo-boehmite.

Alumina having another crystal structure, for example, α-
Alumina is extremely unsuitable as the catalyst carrier of the present invention because it has an extremely small specific surface area and poor solid acidity. Also,
δ-alumina also has a small specific surface area of 100 m ² / g and does not reach γ-alumina or η-alumina as a carrier for the denitration catalyst. In addition, β-alumina and χ-alumina are also unsuitable as the denitration catalyst carrier of the present invention.

As activated alumina, the pore volume with a pore radius of 50 A or less is 30% of the pore volume with a pore radius of 300 A or less.
The following alumina and alumina having a pore volume of 100 to 300 A in pore diameter of 15% or more of the pore volume of 300 A or less in pore radius had insufficient denitration activity in the presence of water vapor. That is, activated alumina that is effective as a carrier for the copper-supported alumina catalyst and the cesium / silver-supported alumina catalyst of the present invention has a pore volume of 50 A or less and a pore volume of 100 to 300 A, respectively. Hole radius 30
It was limited to alumina having physical properties of 30% or more and 15% or less of the pore volume of 0 A or less.

The method for producing a copper-supported alumina catalyst of the present invention uses an activated alumina precursor substance at 300 to 800 ° C.
The pore volume and the pore radius of 100 to 3 having a pore radius of 50 A or less measured by the nitrogen gas adsorption method by firing in
Alumina hydrate to be activated alumina having a pore volume of 00A of 50% or more and 10% or less of the pore volume of a pore radius of 300 A or less is used, and a water-soluble copper salt is added to the alumina hydrate. Is carried and dried and fired. The activated alumina having specific pores as described above may be prepared by supporting a copper salt, but it is preferable to use the alumina hydrate as an activated alumina precursor substance from the viewpoint of denitration performance. In the method for producing a cesium / silver-supported alumina catalyst, it is preferable to support silver and / or silver oxide in advance on activated alumina having the above-described specific pores and then support cesium.

The method of supporting copper, cesium and silver is not particularly limited, but for example, an impregnation method or a kneading method such as an adsorption method, a pore filling method, an incipient wetness method, an evaporation dryness method, a spray method, or the like, or Combinations of these are applicable. The cesium and silver may be loaded by loading silver on activated alumina in advance and then sequentially loading cesium.

The copper loading in terms of metal is preferably in the range of 1 to less than 6% by weight with respect to the activated alumina of the present invention. If it is less than 1% by weight, satisfactory denitration activity cannot be obtained,
If it is 6% by weight or more, the combustion reaction of the reducing agent (hydrocarbon) is excessively promoted, and the activity and selectivity of the denitration reaction decrease.

The loading rate of cesium and silver in terms of metal is
0.01% by weight to the activated alumina of the present invention
It is preferably in the range of not less than 2% by weight and not less than 1% by weight and less than 6% by weight. If the loading rate of cesium is less than 0.01% by weight, the effect of adding cesium is not exhibited, and if it is 2% by weight or more, the denitration performance is deteriorated due to excessive poisoning of acid sites. On the other hand, when the loading ratio of silver is less than 1% by weight, a satisfactory denitration activity cannot be obtained, and when it is 6% by weight or more, the combustion reaction of the reducing agent hydrocarbon is excessively promoted and the activity and selectivity of the denitration reaction decrease. .

The drying temperature is not particularly limited,
Usually dried at about 80-120 ℃, then 300-800
A method of firing at a temperature of about 400 ° C., preferably about 400 to 600 ° C. is used. If the firing temperature exceeds 800 ° C., phase transformation of alumina occurs, which is not preferable.

The shape of the denitration catalyst of the present invention is not particularly limited, such as spherical shape, cylindrical shape, honeycomb shape, spiral shape, and granular shape, and the shape, size and the like can be arbitrarily selected according to the use conditions. it can. In particular, in the case of purifying exhaust gas of an automobile engine, since the gas space velocity is high, in order to minimize pressure loss, a fireproof integral structure having a large number of through holes in the exhaust gas flow direction is used. A support substrate having a channel surface coated with the denitration catalyst is preferably used.

The denitration catalyst of the present invention is used for CO in exhaust gas,
Exhaust gas containing oxygen in excess of the stoichiometric amount required to completely oxidize reducing components such as HC and H _{2 with} oxidizing components such as NO _x and O ₂ , specifically, exhaust gas of an internal combustion engine with a lean air-fuel ratio It is applied to the purification of NO _x inside.

By bringing such exhaust gas into contact with the denitration catalyst of the present invention, NO _x is reduced and decomposed to N ₂ by a reducing agent such as HC existing in a trace amount, and at the same time H
The reducing agent such as C is also oxidized to CO ₂ and H ₂ O. HC of exhaust gas itself like exhaust gas of diesel engine
/ If NO _X ratio is low, after adding addition of several hundreds to several thousands ppm of about fuel methane concentration in terms (HC) in the exhaust gas, sufficient to employ a system of contacting with denitration catalyst of the present invention A high NO _x removal rate can be achieved.

In order to efficiently proceed with NO _x purification by hydrocarbons in an oxygen excess atmosphere at such a high space velocity (short contact time) using the denitration catalyst produced by the production method of the present invention, a copper-supported alumina catalyst is used. Then, the inlet temperature of the catalyst-containing layer must be 350 ° C. or higher, and that of the cesium- and silver-supported alumina catalyst must be 400 ° C. or higher. In order for the copper-supported alumina catalyst, cesium- and silver-supported alumina catalyst obtained by the present invention to exhibit the denitration performance, the amount of each is 35
It is necessary to have a temperature of 0 ° C or higher and 400 ° C or higher, since hydrocarbons are not sufficiently activated at a temperature lower than 350 ° C in the case of a copper-supported alumina catalyst and at a temperature lower than 400 ° C in the case of a cesium- and silver-supported alumina catalyst. is there. Further, when the catalyst layer inlet temperature is higher than 450 ° C for the copper-supported alumina catalyst and higher than 550 ° C for the cesium- and silver-supported alumina catalyst, the combustion of hydrocarbons, which is a side reaction, becomes predominant and the NO _x reduction activity decreases. To do.

[0041]

The present invention will be described in more detail with reference to Reference Examples, Examples and Comparative Examples below. However, the present invention is not limited to the following examples.

[Example 1] In the pore structure after firing, the volume of pores having a radius of 50 A (angstrom) or less and the volume of pores having a radius of 100 to 300 A were 300 A or less, respectively. Alumina hydrate of 86.1% and 5.5% (referred to as alumina precursor A) was immersed in an aqueous solution of copper nitrate and heated at 100 to 110 ° C with stirring to evaporate water. Further, it was calcined in air at 500 ° C. for 3 hours to obtain a Cu / Al ₂ O ₃ catalyst (1). The alumina was γ-alumina. Note that the metal-supported rate of Cu was 3% with respect to alumina.

[Example 2] In the pore structure after firing, the pore volume having a pore radius of 50 A or less and the pore radius of 100 to 30
The pore volume of 0A is 300A or less
Alumina hydrate of 9.5% and 5.1% (referred to as alumina precursor B) was immersed in an aqueous solution of copper nitrate and heated at 100 to 110 ° C with stirring to evaporate water. further,
It was calcined in air at 500 ° C. for 3 hours to obtain a Cu / Al ₂ O ₃ catalyst (2). The alumina was γ-alumina. The loading rate of Cu in terms of metal is 3 with respect to alumina.
%.

[Example 3] In the pore structure after firing, the pore volume of 50 A or less and the pore radius of 100 to 30
The pore volume of 0A is 5 of the pore volume of 300A or less.
Alumina hydrate of 4.2% and 8.2% (referred to as alumina precursor C) was immersed in a copper nitrate aqueous solution and heated at 100 to 110 ° C. with stirring to evaporate water. further,
It was calcined in air at 500 ° C. for 3 hours to obtain a Cu / Al ₂ O ₃ catalyst (3). The alumina was γ-alumina. The loading rate of Cu in terms of metal is 3 with respect to alumina.
%.

[Example 4] In the pore structure after firing, the pore volume is 50 A or less and the pore radius is 100 to 30.
The pore volume of 0A is 300A or less
Alumina hydrate of 8.1% and 2.5% (referred to as alumina precursor D) was immersed in an aqueous solution of copper nitrate and heated at 100 to 110 ° C. with stirring to evaporate water. further,
It was calcined in air at 500 ° C. for 3 hours to obtain a Cu / Al ₂ O ₃ catalyst (4). The alumina was γ-alumina. The loading rate of Cu in terms of metal is 3 with respect to alumina.
%.

[Comparative Example 1] In the pore structure after firing, the pore volume of 50 A or less and the pore radius of 100 to 30.
The pore volume of 0 A is 3 A of the pore volume of 300 A or less, respectively.
Alumina hydrate of 5.5% and 32.5% (referred to as alumina precursor E) was immersed in a copper nitrate aqueous solution and heated at 100 to 110 ° C. with stirring to evaporate water. Further, it was calcined in air at 500 ° C. for 3 hours to obtain a Cu / Al ₂ O ₃ catalyst (5). The alumina was γ-alumina. The loading rate of Cu in terms of metal is 3 with respect to alumina.
%.

[Comparative Example 2] In the pore structure after firing, the pore volume of 50 A or less and the pore radius of 100 to 30.
The pore volume of 0 A is 3 A of the pore volume of 300 A or less, respectively.
Alumina hydrate of 1.0% and 22.7% (referred to as alumina precursor F) was immersed in an aqueous solution of copper nitrate and heated at 100 to 110 ° C. with stirring to evaporate water. Further, it was calcined in air at 500 ° C. for 3 hours to obtain a Cu / Al ₂ O ₃ catalyst (6). The alumina was γ-alumina. The loading rate of Cu in terms of metal is 3 with respect to alumina.
%.

[Comparative Example 3] In the pore structure after firing, the pore volume is 50 A or less and the pore radius is 100 to 30.
The pore volume of 0 A is 3 A of the pore volume of 300 A or less, respectively.
Alumina hydrate of 9.7% and 39.8% (referred to as alumina precursor G) was immersed in an aqueous solution of copper nitrate and heated at 100 to 110 ° C. with stirring to evaporate water. Further, it was calcined in air at 500 ° C. for 3 hours to obtain a Cu / Al ₂ O ₃ catalyst (7). The alumina was γ-alumina. The loading rate of Cu in terms of metal is 3 with respect to alumina.
%.

[Comparative Example 4] A γ-Al ₂ O ₃ catalyst (8) was obtained in the same manner as in Example 4 except that it was not immersed in an aqueous solution of copper nitrate.

[Performance Evaluation Example 1] After the catalyst of Example 1 was pressure-molded, it was crushed and sized to a particle size of 250 to 500 μm, and the catalyst was filled in a stainless steel reaction tube having an inner diameter of 12 mm and fixed at atmospheric pressure. Attached to the floor reactor. NO 1000 ppm, propylene 1000 as model exhaust gas in this catalyst layer
A mixed gas consisting of ppm, O ₂ 5%, H ₂ O 8% and the balance N ₂ was passed at a space velocity of 15,000 h ⁻¹ .

Regarding the composition of the gas at the outlet of the reaction tube, NO and NO ₂
Measured by chemiluminescent NO _X meter for the concentration, N ₂ O concentration is a gas chromatograph equipped with a Porapack Q column -
It measured using the thermal conductivity detector. The catalyst layer inlet temperature is 2
The temperature was set to a predetermined temperature in the range of 00 to 600 ° C., and the value at the time when the reaction tube outlet gas composition became stable at each predetermined temperature was used.
Although NO in the reaction gas is converted into NO ₂ , N ₂ O and / or N ₂ by passing the model exhaust gas through the catalyst, N ₂ O is hardly produced when passing through the catalyst of the present invention. Since it has been clarified, the denitration rate is defined by the following equation 2 in the specification of the present invention. However, in the formula, x includes 1.

[0052]

[Formula 2] NO conversion rate = (reaction tube inlet NO _X concentration−reaction tube outlet NO _X concentration) / (reaction tube inlet NO concentration) × 100

Model gas evaluations were also conducted on the catalysts of Examples 2-4 and Comparative Examples 1-4.

Table 1 shows the denitration rate, that is, the NO conversion rate (%), at each of the catalyst layer inlet temperatures of 350 ° C. to 450 ° C. for each of the catalysts (1) to (8). Examples 1 to 4 of the present invention
Catalysts (1) to (4) of Comparative Examples 1 to 4 are catalysts (5) to
Compared to (8), it showed excellent denitration performance in a lower temperature range.

[Performance Evaluation Example 2] Space velocity 50000h ^-1
The performance of the catalyst (1) of Example 1 was evaluated in the same manner as in Performance Evaluation Example 1 except that the catalyst (1) and 70,000 h ^-1 were used.

Table 2 shows the maximum denitration rate Cm of the catalyst (1) at the above space velocity at the catalyst inlet temperature of 200 to 600 ° C.
The ax (%) and the temperature Tmax (° C.) at that time are shown. The catalyst (1) of the example of the present invention showed excellent denitration performance even at a higher space velocity (shorter contact time).

[0057]

[Table 1] Catalytic activity Active catalytic activity Lumina Denitration rate (%) of Performance Evaluation Example 1 Precursor 350 ° C 400 ° C 450 ° C Example 1 3% Cu / Al ₂ O ₃ (1) A 18.8 31 .2 26 Example 2 3% Cu / Al ₂ O ₃ (2) B 17 28.2 23.5 Example 3 3% Cu / Al ₂ O ₃ (3) C 15.5 27.9 22 Example 4 3% Cu / Al ₂ O ₃ (4) D 16.7 28 23.6 Comparative Example 1 3% Cu / Al ₂ O ₃ (5) E 4.2 10.3 15.8 Comparative Example 2 3% Cu / Al ₂ O ₃ (6) F 5.8 9.7 15.3 Comparative Example 3 3% Cu / Al ₂ O ₃ (7) G 9.9 15.5 12.5 Comparative Example 4 3% Cu / Al ₂ O ₃ (8) D 2.1 3 4.3

[0058]

[Table 2] Denitration activity of performance evaluation example 2 Space velocity (h ^-1 ) Cmax (%) Tmax (° C) 50,000 32.2 350 7,000 33.1 350

[Embodiment 5] Pore radius of 50 A (angstrom) or less and pore radius of 100 to 300 A.
Has a pore volume of 40.4% and 4.4% of the pore volume of 300 A or less, respectively.
100) while being immersed in an aqueous solution of silver nitrate and stirred.
Heated at ˜110 ° C. to evaporate water. Further, it was calcined in air at 500 ° C. for 3 hours to obtain an Ag / Al ₂ O ₃ catalyst.
Next, this catalyst was immersed in a cesium acetate aqueous solution, and a Cs / Ag / Al ₂ O ₃ catalyst (9) was obtained by the same method. The loadings of Cs and Ag in terms of metal are 0.1% and 3%, respectively, with respect to alumina.

[Example 6] The volume of pores having a radius of 50 A or less and the volume of pores having a radius of 100 to 300 A are 74.7% and 2.4% of the volume of pores of 300 A or less, respectively.
-Alumina (referred to as Alumina I) was immersed in a silver nitrate aqueous solution and heated at 100 to 110 ° C with stirring to evaporate water. Furthermore, it was calcined in air at 500 ° C. for 3 hours to obtain Ag.
A / Al ₂ O ₃ catalyst was obtained. Next, this catalyst was immersed in an aqueous solution of cesium acetate, and Cs / Ag / Al ₂ O ₃ was added by the same method.
A catalyst (10) was obtained. The loadings of Cs and Ag in terms of metal are 0.1% and 3%, respectively, with respect to alumina.

[Embodiment 7] The pore volume of 50 A or less and the pore volume of 100 to 300 A are 57.8% and 3.9%, respectively, of the pore volume of 300 A or less.
-Alumina (referred to as Alumina J) was immersed in an aqueous silver nitrate solution and heated at 100 to 110 ° C with stirring to evaporate water. Furthermore, it was calcined in air at 500 ° C. for 3 hours to obtain Ag.
A / Al ₂ O ₃ catalyst was obtained. Next, this catalyst was immersed in an aqueous solution of cesium acetate, and Cs / Ag / Al ₂ O ₃ was added by the same method.
A catalyst (11) was obtained. The loadings of Cs and Ag in terms of metal are 0.1% and 3%, respectively, with respect to alumina.

[Embodiment 8] The volume of pores having a radius of 50 A or less and the volume of pores having a radius of 100 to 300 A are 32.1% and 10.8% of the pore volume of 300 A or less, respectively. Alumina (referred to as alumina K) was immersed in an aqueous silver nitrate solution and heated at 100 to 110 ° C. with stirring to evaporate water. Furthermore, it is fired in air at 500 ° C. for 3 hours to give A
A g / Al ₂ O ₃ catalyst was obtained. Next, this catalyst was immersed in an aqueous cesium acetate solution, and Cs / Ag / Al ₂ was added by the same method.
O ₃ catalyst (12) was obtained. The loadings of Cs and Ag in terms of metal are 0.1% and 3%, respectively, with respect to alumina.
Is.

[Example 9] The loading rate of cesium was set to 0.05.
% Cs / Ag /
An Al ₂ O ₃ catalyst (13) was obtained.

[Example 10] The supporting rate of cesium was set to 1.0.
% Cs / Ag /
An Al ₂ O ₃ catalyst (14) was obtained.

[Comparative Example 5] The volume of pores having a radius of 50 A or less and the volume of pores having a radius of 100 to 300 A are 14.0% and 45.9% of the volume of 300 A or less, respectively. Alumina (referred to as alumina L) was immersed in a silver nitrate aqueous solution and heated at 100 to 110 ° C. with stirring to evaporate water. Furthermore, it is fired in air at 500 ° C. for 3 hours to give A
A g / Al ₂ O ₃ catalyst was obtained. Next, this catalyst was immersed in an aqueous solution of cesium acetate, and Cs / Ag / Al was processed by the same method.
_{A 2} O ₃ catalyst (15) was obtained. The loadings of Cs and Ag in terms of metal are 0.1% and 3%, respectively, with respect to alumina.
Is.

[Comparative Example 6] Alumina H used in Example 5
Was immersed in a mixed aqueous solution of cesium acetate and silver nitrate and heated at 100 to 110 ° C. with stirring to evaporate water.
Furthermore, it is fired in air at 500 ° C. for 3 hours to obtain Cs / Ag /
An Al ₂ O ₃ catalyst (16) was obtained. The loadings of Cs and Ag in terms of metal are 0.1% for alumina,
3%.

[Comparative Example 7] A Cs / Al ₂ O ₃ catalyst (17) was obtained in the same manner as in Example 5 except that silver nitrate was not used.

[Comparative Example 8] An Ag / Al ₂ O ₃ catalyst (18) was prepared in the same manner as in Example 5 except that cesium acetate was not used.
Got

[Performance Evaluation Example 3] With respect to Examples 5 to 10 and Comparative Examples 5 to 8, model gas evaluation was performed in the same manner as in Performance Evaluation Example 1.

Table 3 shows the denitration rate, that is, the NO conversion rate (%), for each of the catalysts (9) to (18) at a catalyst layer inlet temperature of 400 to 550 ° C. The catalysts (9) to (14) of the examples of the present invention are the catalysts (15) to (18) of Comparative Examples 5 to 8.
It showed a very high denitration performance compared to

[Performance Evaluation Example 4] Space velocity 50000h ^-1
And except that the 70000H ^-1 evaluated the performance of the catalyst (9) in Example 5 in the same manner as in Performance Evaluation Example 1.

Table 4 shows the maximum denitration rate Cm of the catalyst (9) at the above space velocity at the catalyst inlet temperature of 300 to 600 ° C.
The ax (%) and the temperature Tmax (° C.) at that time are shown. The catalyst (9) of the example of the present invention showed excellent denitration performance even at higher space velocity (shorter contact time).

[0073]

[Table 3] Catalytic activity Active catalytic activity Lumina Denitration rate of performance evaluation example 1 (%) Precursor 400 ℃ 450 ℃ 500 ℃ 550 ℃ 5 0.1% Cs / 3% Ag / Al ₂ O ₃ (9) H 33 55.3 79.5 41.7 Actual 6 0.1% Cs / 3% Ag / Al ₂ O ₃ (10) I 40 62 86.2 46 Application 7 0.1% Cs / 3% Ag / Al ₂ O ₃ (11) J 38 60 83.1 43.9 Example 8 0.1% Cs / 3% Ag / Al ₂ O ₃ (12) K 33.5 56.2 79 42.3 9 0.05% Cs / 3% Ag / Al ₂ O ₃ (13) H 25 59 83.1 43.5 10 1% Cs / 3% Ag / Al ₂ O ₃ (14) H 29 55.7 73 40.7 Ratio 5 0.1% Cs / 3% Ag / Al ₂ O ₃ (15) L 7 29 61 67.5 Comparison 6 0.1% Cs / 3% Ag / Al ₂ O ₃ (16 ) H 10 26.1 62.5 44 Example 7 0.1% Cs / Al ₂ O ₃ (17) H 3 4 10 7 8 3% Ag / Al ₂ O ₃ (18) H 8 58.3 80.3 42.1

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[Table 4] Denitration activity of Performance Evaluation Example 3 Space velocity (h ^-1 ) Cmax (%) Tmax (° C) 50000 89 450 70000 86 86 450

Tables 5 to 6 summarize the cell volume ratios in the above Examples and Comparative Examples.

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[Table 5]

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[Table 6]

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INDUSTRIAL APPLICABILITY As described above, according to the denitration catalyst, the method for producing the same, and the denitration method according to the present invention, a high space velocity (short contact time) is achieved in an oxidizing excess atmosphere in which water vapor coexists.
However, it can be reduced to nitrogen gas with a high conversion rate in a lower temperature range.

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Claims (8)

[Claims] 1. A pore volume of 50 A or less and a pore radius of 100 to 300 A measured by a nitrogen gas adsorption method.
The denitration catalyst comprises activated alumina having a pore volume of 30% or more and 15% or less of the pore volume having a pore radius of 300 A or less, and copper supported on the activated alumina. 2. The method for producing a denitration catalyst according to claim 1, wherein calcination at 300 to 800 ° C. is performed, and a pore volume and a pore radius of 100 A to 300 A each having a pore radius of 50 A or less measured by a nitrogen gas adsorption method. Of 50% or more and 10% or more of the pore volume of the pore radius of 300 A or less, respectively.
%, A method for producing a denitration catalyst, comprising supporting a copper salt on an alumina hydrate to be activated alumina having a content of not more than%, followed by drying and firing. 3. A denitration method for exhaust gas, which comprises contacting exhaust gas of 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 according to claim 1. Moreover, the exhaust gas has a temperature of 350 to 450 ° C. at the inlet of the denitration catalyst layer, which is a denitration method. 4. The denitration method according to claim 3, wherein the space velocity of the exhaust gas passing through the denitration catalyst layer is 10,000 h ⁻¹ or more. 5. A pore volume of 50 A or less and a pore radius of 100 to 300 A measured by a nitrogen gas adsorption method.
Denitration catalyst comprising activated alumina having a pore volume of 30% or more and 15% or less of a pore volume of 300A or less, and cesium and silver and / or silver oxide supported on the activated alumina. . 6. The method for producing a NOx removal catalyst according to claim 5, wherein the pore radius is 50 as measured by a nitrogen gas adsorption method.
The pore volume of A or less and the pore volume of 100 to 300 A are 3 times the volume of pores of 300 A or less, respectively.
0% or more and 15% or less of activated alumina, silver and /
Alternatively, a method for producing a denitration catalyst, which comprises supporting silver oxide and then supporting cesium. 7. A denitration method for exhaust gas, which comprises contacting exhaust gas of 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 according to claim 5. Further, the denitration method is characterized in that the exhaust gas has a temperature of 400 to 550 ° C. at the inlet of the denitration catalyst layer. 8. The denitration method according to claim 7, wherein the space velocity of the exhaust gas passing through the denitration catalyst layer is 10,000 h ⁻¹ or more.