JPH09108571A - Catalyst layer for denitration, denitration catalyst structure and denitration method by then same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove NOx in exhaust gas efficiently at an adequately high gas space velocity by constituting a denitration catalyst layer from a catalyst in which silver, zinc, and phosphorus are incorporated into activated alumina and a catalyst in which gold, zinc and phosphorus are incorporated into activated alumina. SOLUTION: A denitration catalyst layer is composed of a catalyst A and a catalyst B, the catalyst A is prepared by incorporating silver, zinc, and phosphorus into activated alumina having crystal structure of γ-type, η-type, etc., and the catalyst B is made by incorporating gold, zinc, and phosphorus into activated alumina having similar crystal structure. The denitration catalyst layer, with the molded catalysts mixed, is placed in the space of an exhaust gas passage, or the catalyst layers are arranged separately in the direction of an exhaust gas passage. The exhaust gas of an internal combustion engine operated in a lean air-fuel ratio is contacted with the denitration catalyst layer to remove NOx in the exhaust gas efficiently. In this process, the exhaust gas is contacted with the catalyst layer at a gas space velocity of 10,000hr<-1> or more.

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 in a combustion apparatus, in particular, nitrogen oxide in exhaust gas of an internal combustion engine such as an automobile engine. The present invention relates to a denitration catalyst device capable of purifying nitrogen oxides in exhaust gas discharged from an internal combustion engine in a burn region with high space velocity and high efficiency, and an exhaust gas denitration method using the same.

[0002]

2. Description of the Related Art In various kinds of combustion exhaust gas discharged from a combustion device, especially an internal combustion engine such as an automobile engine, there are produced water, carbon dioxide (CO ₂ ) and nitric oxide (NO). It contains nitrogen oxides (NOx) such as nitrogen dioxide (NO ₂ ). NOx affects the human body,
Not only does it increase the prevalence of respiratory diseases, but it is also one of the causes of acid rain, which is a problem from the viewpoint of global environmental protection. Therefore, efficient removal of nitrogen oxides from these various exhaust gases has become an important issue.

For example, there is a process for detoxifying exhaust gas of an automobile gasoline engine that burns at a controlled stoichiometric ratio near an air-fuel ratio (A / F) = 14.7. In this process, the exhaust gas is mainly platinum (Pt), rhodium (R
h), a three-way catalyst system in which carbon monoxide (CO), hydrocarbons (HC) and NOx in exhaust gas are simultaneously removed by contacting with an alumina catalyst containing palladium (Pd) and ceria (CeO ₂ ). To be adopted.

By the way, in recent years, a lean-burn internal combustion engine has been attracting attention from the viewpoint of preventing global warming. Then, with respect to the exhaust gas of the diesel engine, which is originally a lean-burn engine, the suspended particulate matter and N
Strict restrictions are about to be imposed on both Ox.

However, since the exhaust gas of these lean-burn type internal combustion engines contains excess oxygen and water, in recent years, unburned hydrocarbons remaining in the lean-burn gas in an oxygen-excess atmosphere are left unburned. Since it was reported that the reduction reaction of NOx proceeded as a reducing agent, various catalysts for promoting this reaction have been proposed. For example, alumina and catalysts in which various transition metals are supported on alumina have been proposed, and these catalysts use NO using hydrocarbon as a reducing agent.
There are many reports that it is effective for the x reaction.

Further, in JP-A-4-284848, 0.1 to 4% by weight of Cu, Fe, Cr, Zn,
An example has been reported in which alumina containing Ni, V, or the like, or silica-alumina is used as a NOx reduction catalyst. Furthermore, when a catalyst in which Pt is supported on alumina is used,
The fact that the NOx reduction reaction proceeds in a low temperature region of about 200 to 300 ° C. is disclosed in JP-A-4-267946 and JP-A-5-26946.
-68855, JP-A-5-103949 and the like. However, when these noble metal-supported catalysts are used, the combustion reaction of hydrocarbons, which should be a reducing agent, is excessively promoted, and a large amount of N ₂ O, which is said to be one of the ozone depleting substances, is generated, and NOx of NOx is generated. It has a drawback that it becomes difficult to selectively proceed the reduction reaction to N ₂ .

[0007] One of the applicants has previously found that the NOx reduction reaction selectively proceeds when a catalyst containing silver as a reducing agent is used as a hydrocarbon in an oxygen excess atmosphere.
This is disclosed in Japanese Patent Laid-Open No. 4-281844. However, this catalyst does have good NOx in an oxygen-rich atmosphere.
Although it shows a reducing ability, it was found that sufficient performance cannot be obtained when this is used in an atmosphere assuming actual traveling conditions. This is because the combustion condition of the lean burn engine in the actual running state continuously changes from near stoichio where the air-fuel ratio (A / F) is the theoretical ratio to the lean burn region under excess oxygen. However, this is because the catalyst disclosed in the above publication is insufficient in durability performance against exhaust gas in the combustion state in the stoichio region (hereinafter referred to as stoichio durability performance).

After the disclosure of the above publication, a NOx reduction and removal technology similar to the technology described in the publication is disclosed in Japanese Patent Laid-Open No. 4-35453.
No. 6, JP-A-5-92124, and JP-A-5-9.
No. 2125 and Japanese Patent Laid-Open No. 6-277454. However, these techniques are also based on a conventional catalyst in which silver is supported as an active metal on an alumina carrier, and the denitration performance in the presence of water vapor in exhaust gas is insufficient, and the denitration performance is Is performed only under oxygen excess conditions, and there is no description about stoichio durability.

Further, Japanese Patent Laid-Open No. 6-319997 discloses a catalyst for denitration which seems to utilize these techniques. That is, in this publication, a catalyst in which silver is supported on a porous inorganic oxide, Pt, Pd on a porous inorganic oxide,
There is a description of a catalyst in combination with a catalyst supporting at least one selected from the group consisting of Ru, Rh and Ir. However, in the catalyst described in the publication, the catalyst in which silver is supported on the porous inorganic oxide deteriorates when used in the stoichio region, so that the denitration performance in the lean burn region after using in the stoichio region deteriorates. There is a problem that it ends up.

Further, Japanese Patent Application Laid-Open No. 7-96187 discloses a catalyst in which gold is fixed to one of metal oxides such as aluminum oxide, titanium oxide, magnesium oxide or zinc oxide. However, it cannot be said that the catalyst described in this publication has sufficient denitration performance, and the stoichio durability was insufficient.

It is generally known that a catalyst using alumina as a carrier has a high dependency on the amount of passing gas per unit volume of the catalyst, that is, the gas space velocity (hereinafter referred to as space velocity and represented by symbol SV). There is. That is, SV is 1,
At a low space velocity of about 000 to 10,000 hr ^-1 ,
Exhibits sufficient NOx reduction performance, but SV is 10,000
When the space velocity is higher than 0 hr ^-1, there is a problem that the NOx purification performance obviously deteriorates. The high space velocity dependence of the catalyst using alumina as the carrier is, for example, “Catalyst” 33, 61 (1991).
It is already known as reported in (1).

[0012] 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.
The above-mentioned catalyst that functions only when the SV is less than 10,000 hr ⁻¹ requires a catalyst layer that is disproportionately large in volume as compared with the engine displacement, and therefore is too large in terms of equipment and is not practical.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks of the prior art. The problem is that the exhaust gas emitted from an internal combustion engine driven in the lean burn region is exhausted. NOx 10,000 hr ^-1
It is an object of the present invention to provide a catalyst device that uses a catalyst that can be efficiently removed at a sufficiently high gas space velocity, and a method for removing NOx in exhaust gas using this catalyst device.

[0014]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors
The inventors have found that the above problems can be solved by using a catalyst containing zinc and phosphorus in combination with a catalyst containing gold, zinc and phosphorus in alumina, and completed the present invention.

That is, the first aspect of the present invention for achieving the above object is to provide a catalyst A comprising activated alumina containing silver, zinc and phosphorus, and activated alumina comprising gold, zinc and phosphorus. Is a catalyst layer for exhaust gas denitration. The catalyst layer may be arranged in the exhaust gas flow space in a state of mixing the molded catalysts, or may be arranged separately in the exhaust gas flow direction.

A second invention of the present invention is to provide a supporting substrate made of a refractory material having a large number of through holes, and the above-mentioned catalyst A and catalyst B on at least the inner surface of the through holes in the supporting substrate. Alternatively, it is a catalyst coating structure coated with a mixture of catalyst A and catalyst B.

Furthermore, a third invention of the present invention is a method for removing NOx in exhaust gas by bringing exhaust gas of an internal combustion engine operated at a lean air-fuel ratio into contact with a NOx removal catalyst layer, The denitration method is characterized in that the catalyst layer according to the first invention or the catalyst coating structure according to the second invention is contacted at a gas space velocity of exhaust gas of 10,000 hr ⁻¹ or more.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. First, the denitration catalyst layer according to the first aspect of the present invention will be described. The denitration catalyst layer is composed of the catalyst A and the catalyst B as described above. Activated alumina, which is one of the main constituents of the denitration catalyst layer of the present invention, is an aluminium hydroxide powder or gel classified into boehmite, pseudo-boehmide, vialite or norstrandalite in the air, for example. By heating and dehydration in the temperature range of 300 to 800 ° C., preferably 400 to 700 ° C., to cause a phase transition to activated alumina having a crystal structure which is crystallographically classified as γ-type, η-type or a mixed type thereof. 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 a catalyst layer component of the present invention.

The catalyst A is made by adding silver, zinc and phosphorus to the activated alumina having the above crystal structure. The states of silver, zinc and phosphorus contained are not particularly limited, and examples thereof include a metal state, an alloy state, an oxide state and a complex oxide state. Also, each starting material is not particularly limited, but it is particularly preferable to use a water-soluble salt.

On the other hand, the catalyst B is formed by adding gold, zinc and phosphorus to the activated alumina having the above crystal structure. The state of the gold, zinc, phosphorus contained and the starting materials are not particularly limited, and the conditions similar to those of the catalyst A may be used.

The method of adding silver, zinc and phosphorus to the activated alumina in the catalyst A and the method of adding gold, zinc and phosphorus to the activated alumina in the catalyst B are not particularly limited. Methods that are performed, for example, adsorption method, pore filling method, incipient wetness method, evaporation dryness method, impregnation method such as spraying method, kneading method and physical mixing method, etc. It can be realized.

As described above, the catalyst A and the catalyst B in which the catalytic active substance is contained in the activated alumina are dried,
Although firing is performed, the drying temperature is not particularly limited, and the drying is performed at a normal drying temperature, for example, a temperature of about 80 to 120 ° C. Moreover, the firing after the completion of drying is 300 to 800 ° C.,
It is preferably carried out at a temperature in the range of 400 to 700 ° C.
When the firing temperature is lower than 300 ° C., the alumina does not have a desired crystal form, and when the firing temperature is higher than 800 ° C., the alumina is phase-transformed into another undesirable crystal form, which is not preferable.

The contents of silver, zinc and phosphorus in the catalyst A are not limited, but are 0.1 to 10% by weight, 0.1 to 10% by weight and 0.01 to 7% in terms of metal based on the total amount of the catalyst A, respectively. It is preferably in the weight%. Also catalyst B
The content of gold, zinc and phosphorus in is not particularly limited, but is 0.05 to 10% by weight with respect to the total amount of the catalyst B,
It is preferably 0.1 to 10% by weight and 0.01 to 7% by weight.

In the first aspect of the present invention, when the catalyst A and the catalyst B are combined to form a catalyst layer for denitration,
The catalyst layer is formed by molding each of the catalyst A and the catalyst B into a predetermined shape, and mixing and filling the molded catalyst A and the catalyst B in a certain space where the target exhaust gas flows, Either of the method of forming the catalyst layer by connecting the filled catalyst A and the catalyst B in parallel to each other in the exhaust gas flow passage or in the front and back of the exhaust gas is formed. When forming the catalyst layer into a molded body, its shape is not particularly limited, for example, powder, spherical, cylindrical, honeycomb,
Various shapes such as a spiral shape, a ring shape, and a pellet shape can be adopted. These shapes, sizes, etc. may be arbitrarily selected according to usage conditions.

Next, the denitration catalyst coating structure of the second invention will be described. The catalyst-coated structure referred to here is
In a supporting substrate having an integral structure made of a refractory material having a large number of through holes, at least the inner surface of the through holes has a structure coated with a catalyst. In the catalyst coating structure for denitration according to the second aspect of the present invention, the catalyst coating structure is mixed with the catalyst A and the catalyst B in a powder state to coat the surface of the supporting substrate, or exhaust gas of the supporting substrate. The catalyst A and the catalyst B are divided into two regions in the front-back direction in the flow direction of the above, and the catalyst A and the catalyst B are coated at predetermined positions on the surface of the supporting substrate. in this case,
It is preferable to coat the A catalyst in the front area and the B catalyst in the rear area with respect to the direction in which the exhaust gas flows. Further, without using the catalyst coating structure alone, the catalyst A coating structure coated with the catalyst A and the catalyst B coating structure coated with the catalyst B are separately manufactured, and each catalyst coating structure is provided with exhaust gas. It is also possible to arrange the catalyst A coating structure in the front stage and the catalyst B coating structure in the rear stage with respect to the flow direction, or to arrange them in parallel.

The through holes in the refractory support substrate have an opening ratio of 60 to 60 in a cross section perpendicular to the exhaust gas flow direction.
90%, preferably 70-90%, the number being 1
30 to 700 pieces per square inch (6.45 cm ² ),
The number is preferably 200 to 600. The catalyst is coated on at least the inner surface of the through hole, but may be coated on the end surface or side surface of the supporting substrate.

As the material of the refractory support substrate, ceramics such as α-alumina, mullite, cordierite and silicon carbide, and austenitic and ferritic stainless steels and the like are used. As for its shape, a conventional one such as a honeycomb structure can be used.
The most preferable of these is a honeycomb structure made of cordierite or stainless steel.

As a method for coating the catalyst on the supporting substrate, a so-called wash coat is used in which the catalyst of the present invention, which has been sized to a certain particle size, is coated on the inner surface of the supporting substrate with or without a suitable binder. Known techniques such as a method and a sol-gel method can be applied. Further, the above-mentioned supporting substrate may be coated with activated alumina in advance, and the catalytically active substance of the present invention may be supported thereon to form a catalyst coating layer. The coating amount of the catalyst layer on the supporting substrate is not limited, but is 50 to 250 g per unit volume of the supporting substrate.
/ L, preferably about 100 to 200 g / l.

Next, the denitration method of the third invention of the present invention will be described. The third aspect of the present invention uses the catalyst layer of the first aspect of the invention and the catalyst-coated structure of the second aspect of the invention to apply CO and H
The reducing component such as C and H ₂ is brought into contact with the exhaust gas having excess oxygen in the vicinity of the stoichiometric amount required to completely oxidize the reducing component with the oxidizing component such as NOx and O _2. N in exhaust gas
Ox is reductively decomposed into N ₂ and H ₂ O, and at the same time H
Reducing agents such as C are also oxidized to CO ₂ and H ₂ O.

Like the exhaust gas of a diesel engine,
When the HC / NOx ratio (molar ratio) of the exhaust gas itself is low, several hundred to several thousand pp in methane conversion concentration in the exhaust gas
A sufficient NOx removal rate can be achieved by adopting a system in which after adding about m of fuel HC, the system is brought into contact with the catalyst layer of the present invention.

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, it is preferable to set the SV to 10,000 hr ⁻¹ , but the upper limit is about 200,000 hr ⁻¹ from the performance of the current automobile engine. Then, in order to efficiently proceed with the removal of NOx in the exhaust gas in the range from the stoichio region to the lean burn region at the high space velocity as described above, the catalyst layer temperature is 100 to 700 ° C, preferably 200 to 600 ° C. Need to

According to the denitration method of the present invention as described above,
In an oxygen-excess atmosphere in which water vapor coexists, high stoichiometric durability is achieved even at high space velocity, and NOx in exhaust gas in the lean burn region can be efficiently removed.

[0033]

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

(A) Production of catalyst A and catalyst B (a) Production of catalyst A; 300 g of commercially available boehmite powder
(Structured water 27.7%), silver nitrate 8.8g, zinc nitrate 6
It was immersed in a 500 ml aqueous solution containing 70 g of the hydrate and 2 g of phosphoric acid for 24 hours, and then heated with stirring to evaporate the water content. Next, this is air-dried at 110 ° C.
It was calcined at 00 ° C. for 3 hours to obtain a catalyst A1. The catalyst A
The contents of Ag, Zn and P in terms of metal of 1 are 2.5%, 6.6% and 0.3% with respect to alumina, respectively.
Is

Next, except that the addition concentrations of silver nitrate, zinc nitrate and phosphoric acid were changed, the respective contents of Ag, Zn and P in terms of metal were 1.5 to alumina, respectively, by the same procedure as above. %, 6.6% and 0.3% of catalyst A2, and the respective contents of Ag, Zn and P in terms of metal are 3.6%, 6.6% and 0.3% based on alumina. The content of certain catalyst A3, Ag, Zn, and P in terms of metal is 10.0% with respect to alumina, respectively.
6.6% and 0.3% of catalyst A4, and catalyst A5 in which the respective contents of Ag, Zn and P in terms of metal are 2.5%, 0.5% and 0.3% based on alumina. ,
Catalyst A6 in which the contents of Ag, Zn, and P in terms of metal are 2.5%, 10.0%, and 0.3%, respectively, based on alumina, and the contents of Ag, Zn, and P in terms of metal Are 2.5%, 6.6% and 0.05% of alumina, respectively, and catalyst A7, Ag and Zn in terms of metal
And P content is 2.5 for alumina
%, 6.6% and 7.0% of catalyst A8, and catalysts in which the contents of Ag, Zn and P in terms of metal are 2.5%, 0.0% and 0.0% of alumina, respectively. A9
I got

Furthermore, based on the technique described in Example 9 of JP-A-6-277454, 46 g of zinc nitrate hexahydrate and 280 g of aluminum nitrate nonahydrate were added to 1.
It was dissolved in 5 liters 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, then filtered and washed, and this was washed at a temperature of 110 ° C. Dry for about 1 day at 600 ℃
After a catalyst support was obtained by firing for 6 hours (the composition of the obtained support was ZnO: Al ₂ O ₃ = 25: 75 (weight ratio, oxide conversion)), 38 g of the support was added to silver nitrate. A catalyst A1 carrying 2% by weight of silver was added to 200 ml of an aqueous solution containing 1.26 g, evaporated to dryness and then calcined.
0 was obtained.

(B) Preparation of catalyst B: γ obtained by calcining commercially available boehmite powder at 700 ° C. for 3 hours
-100 g of alumina (specific surface area 169 m ² / g) is
-Alumina was immersed in a 200 ml aqueous solution containing 2.1 g of chloroauric acid, 32.3 g of zinc nitrate hexahydrate and 0.9 g of phosphoric acid, and heated with stirring to evaporate water. Next, after air-drying this at 110 ° C. for 3 hours, 70
A catalyst B1 was obtained by calcining at 0 ° C. for 3 hours. The contents of Au, Zn, and P in terms of metal of the catalyst B1 are 1.0%, 6,6%, and 0.3% with respect to alumina, respectively.

Next, except that the concentrations of chloroauric acid, zinc nitrate, and phosphoric acid were changed, the contents of Au, Zn, and P in terms of metal were 1.5 to alumina, respectively, by the same procedure as above. %, 6.6% and 0.3% Catalyst B
2. Catalyst B3 in which the contents of Au, Zn, and P in terms of metal are 3.6%, 6.6%, and 0.3% of alumina, respectively, and the contents of Au, Zn, and P in terms of metal Are 10.0%, 6.6% and 0.3% respectively with respect to alumina, and the contents of Au, Zn and P in terms of metal are 2.5% with respect to alumina, respectively.
Catalyst B5 containing 0.5% and 0.3%, and Catalyst B containing Au, Zn and P in terms of metal of 2.5%, 10.0% and 0.3% of alumina, respectively.
6. The contents of Au, Zn and P in terms of metal are 2.5%, 6.6% and 0.05 based on alumina, respectively.
% Of the catalyst B7, the content of Au, Zn and P in terms of metal is 2.5%, 6.6% and 7.0% of the alumina, respectively, and the catalyst B8, Au and Zn in terms of the metal.
And P content is 2.5% with respect to alumina,
Catalyst B9 was obtained which was 0.0% and 0.0%.

[Performance Evaluation Example 1] (Examples 1 to 3 and Comparative Examples 1 to 5) Next, the above A1 and A
2, A3, A9 and A10 catalysts and B1 and B9 catalysts were respectively pressure-molded and then ground to a particle size of 250.
The particle size is adjusted to ˜500 μm, and as shown in Table 1, A series catalyst and B series catalyst are mixed in a weight ratio of 1: 1 and mixed, and these mixed catalysts are filled in a stainless steel reaction tube having an inner diameter of 21 mm. Then, a catalyst layer for denitration was formed, and this was attached to an atmospheric fixed bed reactor.

Next, NO 500 was used as model exhaust gas.
ppm, C ₃ H ₆ 500 ppm, O ₂ 5%, H ₂ O
The denitration performance was measured by passing a mixed gas consisting of 10% and the balance N ₂ through the above atmospheric pressure fixed bed reactor at a space velocity of 30,000 hr ⁻¹ .

In the test, the catalyst layer inlet temperature was set to 100.
The denitrification rate was determined by the following equation 1 by using the analytical value at the time when the reaction tube outlet gas composition became stable at each predetermined temperature set to a predetermined temperature in the range of up to 600 ° C. Table 1 shows the maximum denitration rate Cmax (%) in each case. When determining the composition of the gas at the outlet of the reaction tube, the concentrations of NO and NO ₂ were measured by a chemiluminescence type NOx meter, and the N ₂ O concentration was determined by Polarak Q.
The measurement was performed using a gas chromatograph and a thermal conductivity detector equipped with a column. Almost no generation of N ₂ O and NO ₂ could be confirmed when any of the catalyst layers of the present invention was used.

[0042]

(Equation 1)

[0043]

[Table 1] ─────────────────────────────────── No catalyst layer Remarks ─────── ─────────────────────────── A series catalyst (%) B series catalyst (%) ───────── ───────────────────────── Catalyst Ag Zn P Catalyst Au Zn P ───────────────── ───────────────── 1 A 1 2.5 6.6 0.3 B 1 1.0 6.6 0.3 Example 1 2 A 2 1.5 6.6 0.3 B 1 1.0 6.6 0.3 〃 2 3 A 3 3.6 6.6 0.3 B 1 1.0 6.6 0.3 〃 3 4 A 1 2.5 6.6 0.3----Comparative example 1 5----B 1 1.0 6.6 0.3 〃 2 6 A 9 2.5 0.0 0.0 B 1 1.0 6.6 0.3 〃 3 7 A 1 2.5 6.6 0.3 B 9 2.5 0.0 0.0 〃 4 8 A10 2.0 21.0 0.0----〃 5 ─────────────────────────────── ─── The results according to the examples of the present invention shown in Table 1 are shown in FIG. , Also shows the results of Comparative Example 2. Both of these drawings show the relationship of the denitration rate to the catalyst layer temperature.
As can be seen by comparing FIGS. 1 and 2, the catalyst of the present invention exhibits higher denitration performance in a wider temperature range than the catalyst of the comparative example.

[Performance Evaluation Example 2] (Example 4) Except that the A1 catalyst and the B1 catalyst were arranged and packed in the front stage and the rear stage of the model gas flow passage without mixing the A1 catalyst and the B1 catalyst. The relationship between the catalyst layer temperature and the denitration rate was obtained in the same manner as in Performance Evaluation Example 1 (Example 4). The measurement result is shown in FIG. From the results of FIG. 3, it can be seen that even when the A series catalyst and the B series catalyst are simply arranged in series without being mixed as in the present catalyst layer, high denitration performance is exhibited in a wide temperature range.

[Performance Evaluation Example 3] (Example 5 and Comparative Example 6) Each of the catalyst layers of Example 1 and Comparative Example 3 shown in Table 1 was exposed to the stoichiometric conditions shown in Table 2 and then subjected to the above-mentioned performance. The denitration performance was determined in the same manner as in Evaluation Example 1 (Example 5 and Comparative Example 6). The obtained results are shown in FIG.

[0046]

TABLE 2 (gas _{composition) NO: 2,000ppm C 3 H 6} : 1,000ppm O 2: 0.9% H 2: 1% H 2 O: 10.0% balance: N ₂ (operating conditions) Gas Space velocity SV: 30,000 hr ⁻¹ Catalyst layer inlet gas temperature: 700 ° C. Gas passage time: 5 hours From the result of FIG. 4, the catalyst layer of Example 5 according to the present invention is more than the catalyst layer of Comparative Example 6. It can be seen that, even after exposure to stoichio conditions, high denitration performance is exhibited in a wide temperature range.

[Performance Evaluation Example 4] (Example 6) The space velocity of the distribution model gas was 90,000.
The denitration performance of the catalyst layer of Example 1 was evaluated in the same manner as in Performance Evaluation Example 1 except that it was hr ⁻¹ (Example 6). Table 3
The Cmax (%) obtained is shown in FIG. From the results of Table 3, it can be seen that the catalyst layer of the present invention exhibits extremely high denitration performance even under a higher space velocity.

[0048]

[Table 3] ─────────────────────── Catalyst performance Space velocity (hr ⁻¹ ) Denitration rate Cmax (%) of Performance Evaluation Example 4 ─ ────────────────────── 90,000 85.9 ─────────────────────── ─

(Examples 7 to 19) The above A4, A5, A
6, A7 and A8 catalysts and B2, B3, B4, B5,
Each of the catalysts B6, B7 and B8 was pressure-molded and then pulverized to adjust the particle size to 250 to 500 μm.
Performance Evaluation Example 1 except that the A-series catalyst and the B-series catalyst were combined and mixed in a weight ratio of 1: 1 as described above.
The denitration performance of each catalyst layer was evaluated in the same manner as in. From the obtained results, it was found that the catalyst layer of the present invention exhibits high denitration performance over a wide temperature range as in FIG.

[0050]

[Table 4] ─────────────────────────────────── No Catalyst layer Remarks ────── ───────────────────────────── A series catalyst (%) B series catalyst (%) ─────── ──────────────────────────── Catalyst Ag Zn P Catalyst Au Zn P ─────────────── ───────────────────── 9 A 3 3.6 6.6 0.3 B 1 1.0 6.6 0.3 Example 7 10 A 4 10.0 6.6 0.01 B 1 1.0 6.6 0.3 〃 8 11 A 5 2.5 0.5 7.0 B 1 1.0 6.6 0.3 〃 9 12 A 6 2.5 10.0 0.0 B 1 1.0 6.6 0.3 〃 10 13 A 7 2.5 6.6 0.0 B 1 1.0 6.6 0.3 〃 11 14 A 8 2.5 6.6 0.3 B 1 1.0 6.6 0.3 〃 12 15 A 1 2.5 6.6 0.3 B 2 1.5 6.6 0.3 〃 13 16 A 1 2.5 6.6 0.3 B 3 3.6 6.6 0.3 〃 14 17 A 1 2.5 6.6 0.3 B 4 10.0 6.6 0.3 〃 15 18 A 1 2.5 6.6 0.3 B 5 2.5 0.5 0.3 〃 16 19 A 1 2.5 6.6 0.3 B 6 2.5 10.0 0.3 〃 1 7 20 A 1 2.5 6.6 0.3 B 7 2.5 6.6 0.05 〃 18 21 A 1 2.5 6.6 0.3 B 8 2.5 6.6 7.0 〃 19 ──────────────────────── ─────────────

[Performance Evaluation Example 5] (Examples 20 and 21) Example 1 except that the ratio of the A1 catalyst to the B1 catalyst was 1: 4 (Example 20) and 4: 1 (Example 21). A catalyst layer was obtained by the same procedure as above, and the denitration performance was evaluated in the same manner as in Performance Evaluation Example 1. The obtained results all showed the same tendency as in FIG. 1, and showed excellent denitration performance over a wide temperature range.

[Performance Evaluation Example 7] (Example 22) The above-mentioned A1 catalyst and B1 catalyst were respectively pressure-molded and then pulverized to adjust the particle size to 250 to 500 μm to obtain powder catalyst A1 and powder catalyst B1. Got 60 g of this powder catalyst A1 was added to alumina sol (Al ₂ O ₃ solid content 1
(0 wt%) 6 g and 120 ml of water were charged into a ball pot mill and wet-milled to obtain a slurry. Commercially available 400 cpsi (cell / inch ² ) in this slurry
2cm diameter made from cordierite honeycomb material
This was immersed by using a cylindrical core having a length of 4 cm as a support substrate, pulled up, and then excess slurry was removed by air blow and dried. Then, it was fired at 500 ° C. for 30 minutes, and 100 g of the solid content in dry conversion was coated per liter of the honeycomb to obtain a catalyst A-coated honeycomb AA1. Similarly, a catalyst B coated honeycomb BB1 with a B1 catalyst
I got

Next, a catalyst A-coated honeycomb AA1 is arranged in the front stage in the gas flow direction and a catalyst B-coated honeycomb BB1 is arranged in the rear stage in a stainless steel atmospheric pressure fixed reaction tube having an inner diameter of 21 mm to form a denitration catalyst layer, This was attached to a fixed pressure fixed bed reactor. Then, the denitration performance was evaluated in the same manner as in Performance Evaluation Example 1 (Example 22). The obtained results show the same tendency as in FIG. 1 and show high denitration performance over a wide temperature range. I understood.

[0054]

As described above, according to the denitration catalyst and the denitration method of the present invention, even in an oxygen-excess atmosphere in which water vapor coexists, and even at a high space velocity, high stoichio durability and a relatively low temperature are obtained. The nitrogen oxide can be purified at a high conversion rate in a wide temperature range including the temperature range.

[Brief description of the drawings]

FIG. 1 is a correlation diagram between catalyst temperature and denitration performance by a catalyst layer of the present invention in denitration performance evaluation example 1.

FIG. 2 is a correlation diagram between the catalyst temperature and the denitration performance of the catalyst layer of the comparative example in the denitration performance evaluation example 1.

FIG. 3 is a correlation diagram between the catalyst temperature and the denitration performance of the catalyst layer of the present invention and the catalyst layer of the comparative example in the denitration performance evaluation example 2.

FIG. 4 is a correlation diagram between catalyst temperature and denitration performance by the catalyst layer of the present invention in denitration performance evaluation example 3.

 ─────────────────────────────────────────────────── ─── 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 3-6-14 Nitta, Ichikawa City, Chiba Excel No. 2 Building 303 (72) Makoto Nagata 3-11-1 Chugoku, Ichikawa City, Chiba Prefecture Maison de Grace No. 203 (72) Inventor Ken Ito 2-4, Minamiono, Ichikawa-shi, Chiba B507

Claims (14)

[Claims] 1. A denitration catalyst comprising a catalyst A made of activated alumina containing silver, zinc and phosphorus and a catalyst B made of activated alumina containing gold, zinc and phosphorus. layer. 2. The denitration catalyst layer according to claim 1, wherein the catalyst A and the catalyst B are mixed. 3. The denitration catalyst layer according to claim 2, wherein the mixing ratio of the catalyst A and the catalyst B is 1: 4 to 4: 1 by weight. 4. Activated alumina is a mineralogy boehmite,
At least one powder or gel selected from pseudo-boehmite, vialite, and aluminum hydroxide classified into norstrandalite, or gel in air or in vacuum 30
The denitration catalyst layer according to any one of claims 1 to 3, which is obtained by heating and dehydrating at 0 to 800 ° C. 5. The contents of silver, zinc and phosphorus in the catalyst layer A are 0.1 to 10% by weight, 0.1 to 10% by weight and 0.0% in terms of metal, respectively, based on activated alumina.
1 to 7% by weight, and the contents of gold, zinc and phosphorus in the catalyst B are 0.05 to 10% by weight, 0.1 to 10% by weight and 0.01% by metal, respectively, based on activated alumina. ~ 7% by weight of claim 1.
A catalyst for denitration according to claim 4. 6. A NOx removal method comprising coating a mixture of the catalyst A and the catalyst B according to claim 1 on at least the inner surface of the through-hole in a monolithic supporting substrate made of a refractory material having a large number of through-holes. Catalyst coated structure. 7. A catalyst A coating structure comprising the catalyst A according to claim 1 coated on at least the inner surface of the through-hole in a support substrate having a monolithic structure made of a refractory material having a large number of through-holes, and a large number. 2. A catalyst B coating structure comprising the catalyst B according to claim 1 coated on at least the inner surface of the through hole in a monolithic support substrate made of a refractory material having the through hole. A catalyst coating structure for denitration. 8. The catalyst coating structure for denitration according to claim 7, wherein the catalyst A coating structure and the catalyst B coating structure are arranged in parallel with respect to the exhaust gas flow direction. 9. The catalyst A-coated structure and the catalyst B-coated structure are arranged in series with respect to the exhaust gas flow direction so that the catalyst A-coated structure is in the front stage and the catalyst B-coated structure is in the rear stage. The catalyst coating structure for denitration according to claim 7, wherein 10. The through holes in the support substrate have an opening ratio of 60 to 90% in a cross section in the exhaust gas flow direction, and
30 to ⁷ per square inch (6.45 cm ² ).
It is 00 pieces, The claim 6 thru | or 10 characterized by the above-mentioned.
The catalyst-coated structure for denitration according to any one of 1. 11. The through holes in the supporting substrate have an opening ratio of 70 to 90% in a cross section in the flow direction of exhaust gas, and the number of through holes is 200 to 600 per square inch (6.45 cm ² ). Claim 6 thru | or Claim 1 characterized by the above-mentioned.
The catalyst coating structure for denitration according to any one of 0. 12. Exhaust gas of an internal combustion engine operated at a lean air-fuel ratio is brought into contact with a NOx removal catalyst to contact NOx in the exhaust gas.
In the method for removing nitrogen, the denitration catalyst is the denitration catalyst layer according to claim 1 or any one of claims 6 to 9.
An exhaust gas denitration method, which is the catalyst-coated structure according to the above item. 13. The denitration method for exhaust gas according to claim 6, wherein the gas space velocity of the exhaust gas passing through the denitration catalyst layer is set to 10,000 hr ⁻¹ or more. 14. The denitration method for exhaust gas according to claim 12, wherein the catalyst layer temperature is set in the range of 100 to 700 ° C.