JP2506598B2 - Nitrogen oxide removal method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is, in oxidizing conditions as a whole an excess of oxygen and water vapor is present, the exhaust gas, in the presence of methanol, is contacted with a specific catalyst,
The present invention relates to a method for removing nitrogen oxides that removes nitrogen oxides in the exhaust gas.

[0002]

2. Description of the Related Art Nitrogen oxides in various exhaust gases (hereinafter referred to as
Since "NOx") is harmful to health and can cause photochemical smog and acid rain, it is desired to develop an effective removal method therefor.

Conventionally, as a method for removing NOx, several methods for reducing NOx in exhaust gas using a catalyst have already been put to practical use. For example, (a) a three-way catalytic method in a gasoline vehicle, and (b) a selective catalytic reduction method using ammonia for exhaust gas from a large facility discharge source such as a boiler. As another proposed method, (c) NOx in exhaust gas using hydrocarbon
As a removal method, there is a method of contacting a gas containing NOx in the presence of hydrocarbon with a hydrophobic zeolite carrying a metal as a catalyst (Japanese Patent Laid-Open No. 63-283727).

[0004]

SUMMARY OF THE INVENTION The method (a) is
Hydrocarbon components and carbon monoxide contained in automobile flue gas are made into water and carbon dioxide by a catalyst, and at the same time NOx
Is reduced to nitrogen, but is burned so that the amount of oxygen contained in NOx and the amount of oxygen required to oxidize hydrocarbon components and carbon monoxide are stoichiometrically equal. Must be adjusted, and there is a serious problem in that it cannot be applied in principle in a system such as a diesel engine in which excess oxygen exists.

In the method (b), ammonia is used which is very toxic and which must be handled as a high-pressure gas in many cases. In particular, it is extremely difficult to apply to mobile sources, and it is not economical.

On the other hand, the method (c) is mainly applied to gasoline automobiles, and it is difficult to apply it under the exhaust gas conditions of a diesel engine, and the catalyst activity is insufficient, which is economically disadvantageous.

The inventors of the present invention also filed Japanese Patent Application No. 3-3522.
Although various methods are disclosed in No. 3, etc., the activity of the catalyst was lowered in some cases in the presence of water vapor.

The present invention has been made as a result of studying various problems existing in the above-mentioned prior art. In the oxidizing atmosphere, various kinds of equipment including exhaust gas from not only gasoline engines but also diesel engines are used. It is an object of the present invention to propose a method for removing nitrogen oxides, which is capable of efficiently removing NOx in exhaust gas containing generated steam.

[0009]

Means and Actions for Solving the Problems The inventors of the present invention have conducted extensive studies to achieve the above object, and as a result, by using a specific catalyst and a reducing agent, the exhaust gas in the presence of water vapor Also, they have found that NOx can be efficiently removed without causing a decrease in catalyst activity, and have completed the present invention.

[0010] That is, the gist of the present invention, in an oxidizing atmosphere an excess of oxygen and water vapor are present, in the presence of methanol, proton-type zeolite, alumina, spinel type metal aluminate and the fourth period transition metal and alumina The method for removing nitrogen oxides comprises contacting one or more catalysts selected from the group with exhaust gas containing nitrogen oxides at a reaction temperature of 200 to 550 ° C.

The details of the method of the present invention will be described below together with the operation. The catalyst that can be used in the method of the present invention includes ZSM-5, mordenite, proton-type zeolite such as Y-zeolite, alumina (aluminum oxide), and spinel-type metal adduct of the fourth period transition metal and alumina.
It is one or more selected from luminates .

Among these catalysts, the proton-type zeolite has a Cavern ratio (ratio of SiO ₂ to Al ₃ O ₂ formula) of
Although not particularly limited, it is preferably relatively high in view of stability against heat and steam, etc., more preferably about 5 to 200, further preferably about 10 to 100.

These zeolites can be produced by a known method. Silica, silica sol, silica source such as sodium silicate, alumina gel, alumina sol, alumina source such as sodium aluminate, sodium hydroxide, sodium silicate. A raw material mixture containing an alkali source such as water, water and optionally an organic base such as amine is hydrothermally synthesized, and the product is separated, washed with water, dried and ion-exchanged to obtain a proton-type zeolite. be able to.
For example, the alkali metal type zeolite prepared by the above hydrothermal synthesis is treated with an ammonium chloride or ammonium nitrate aqueous solution to form an ammonium type zeolite,
Then, it can be calcined in a temperature range of about 400 to 700 ° C. to obtain a proton-type zeolite. By using proton type zeolite, NOx is much more efficient.
Can be decomposed and removed.

Further, in the present invention, alumina having acidity similar to zeolite can also be used. The type of alumina is not particularly limited in its crystal structure, but it is preferable that the specific surface area is larger in view of the nature of the reaction using these catalysts. Therefore, as long as it is heat resistant within the temperature range used, it has a high surface area. γ-type alumina is effective.

Further, depending on the use conditions such as reaction temperature, SV, and amount of water vapor, the oxidation activity of alumina itself may cause insufficient reaction rate. It is effective to carry a metal.

[0016] The fourth period transition metals, chromium, manganese, iron, cobalt, nickel, copper, zinc, etc., the form of these metals, on alumina, metals and composite oxide of aluminum Existing in the form of MAl ₂ O ₄ (many of the structures are spinel type, and if the fourth-period transition metal is represented by M, they can be represented by MAl ₂ O ₄ in the general formula). Metal aluminates having a structure other than spinel, for example, perovskite, also complex oxide with aluminum having a structure of delafossite type,
Although effective as a catalyst , a spinel type is required in the present invention.
Exist, and perovskites, delafossite types, etc.
It may coexist with the flannel type .

The method of supporting the fourth period transition metal on alumina is such that a metal aluminate having a spinel structure is obtained.
Usually impregnation method used that, coprecipitation, precipitation, or by any mixing method. For example, in the impregnation method, activated alumina that is normally used is used as alumina,
It can be obtained by impregnating the alumina with a solution containing a compound of the fourth period transition metal, drying and calcining in air. As the compound of the fourth period transition metal, various inorganic acid salts such as nitrates, sulfates and halides, and various organic acid salts such as acetates and oxalates are suitable. In the precipitation method, a precipitate obtained by dropping a solution of a suitable basic precipitating agent into a mixed solution of transition metal and aluminum can be obtained by washing, drying and air-baking.

[0018] Thus, when using contain a fourth period transition metal on an alumina supported amount of metals contained in the form of a metal aluminate, based on total catalyst weight, usually from about 0.01 -40 wt%, preferably about 0.05-30w
t%. About no effect for improving the reduction activity of the NOx is less than 0.01 wt%, there is a possibility that oxidation of methanol to be used as a reducing agent of greater than about 40 wt% is given priority, effective for the selective reduction of NOx It will not work on.

The optimum temperature for air calcination varies depending on the type of transition metal used, but generally it is about 4
A temperature of 00 to 900 ° C, preferably about 500 to 800 ° C is suitable. Air firing temperature, in order to form a metal aluminate, requires a relatively high temperature, since the catalytic activity is lowered too high surface area is reduced, the upper limit of the
As described above, the temperature is about 900 ° C, preferably about 800 ° C.

The above-mentioned catalyst can be used in the form of powder, granules, pellets, honeycombs, or any other shape, and the shape and structure thereof are not particularly limited. When the catalyst is molded and used, a binder that is usually used at the time of molding, that is, silica sol, polyvinyl alcohol, or the like, or a lubricant, that is, graphite, wax, fatty acid salt, carbon wax, or the like can be used.

The NOx-containing gas to be treated by the method of the present invention includes diesel engine exhaust gas such as diesel automobiles and stationary diesel engines, gasoline engine exhaust gas such as gasoline automobiles, nitric acid production facilities, various combustion facilities, etc. Exhaust gas can be mentioned, and the exhaust gas containing water vapor can also be targeted.

That is, the exhaust gas generally contains about 2 to about 2.
Since about 15 vol% of water vapor is contained, in the conventional method, when water vapor is present in the exhaust gas, the activity of the catalyst is reduced. On the other hand, according to the method of the present invention, NOx in the exhaust gas containing water vapor can be effectively removed.

[0023] Removal of NOx of the exhaust gas, using the above catalyst, to the catalyst in an oxidizing atmosphere present water vapor, in the presence of methanol, the reaction temperature from 200 to 5
It is carried out by contacting exhaust gas at 50 ° C.

[0024] Here, the oxidizing atmosphere, the carbon monoxide contained in exhaust gas, and hydrogen and hydrocarbons, and a reducing substance of methanol to be added in advance how the present invention, fully oxidized water An atmosphere that contains more oxygen than the amount of oxygen required to convert it to carbon dioxide. For example, in the case of exhaust gas emitted from an internal combustion engine such as an automobile, the air-fuel ratio is large (lean region). Is usually the atmosphere of
The excess oxygen rate is about 20 to 200%. During this oxidizing atmosphere, the above catalyst, even in the presence of water vapor in the exhaust gas, than the reaction between methanol and oxygen, preferentially promotes the reaction of a meta <br/> no le and NOx NOx
Is removed by reductive decomposition.

The amount of methanol be present is not particularly limited, for example when the required low NOx removal rate,
In some cases, the amount may be less than the theoretical amount required for reductive decomposition of NOx. However, since the reduction reaction proceeds more when the amount exceeds the required theoretical amount, it is generally preferable to add the amount excessively. Typically, the amount of methanol is about 20 to 2,000% of the theoretical amount required for the reduction decomposition of the NOx excessive, thereby preferably about 30～1,500% excess is present.

[0026] Here, the theoretical amount of methanol needed,
Since oxygen in the reaction system is present, in the method of the present invention, which is defined as a main <br/> Tano Le amount necessary for reductive decomposition of nitrogen dioxide (NO _2), for example, with methanol The theoretical amount of methanol for reductive decomposition of 1,000 ppm of nitric oxide (NO) in the presence of oxygen is about 66.
It becomes 7 ppm. In general, depending on the amount of NOx in the exhaust gas, the amount of methanol be present is about in terms of methane 5
It is about 0 to 10,000 ppm.

In the method of the present invention, N
As a reducing substance for reducing Ox, theoretically, any substance can be used as long as it is a flammable oxygen-containing compound, but the reaction proceeds to some extent, but an effective catalyst used here is an acidic catalyst such as zeolite or alumina. from composed character on a metal oxide having a particularly methanol is preferably used.
For example, when an alcohol such as 2-propanol or 2-butanol that easily causes a dehydration reaction on the above-mentioned catalyst is used, it is easily dehydrated to become an olefin and the original alcohol (2-propanol or 2-butanol) is used. Since it is more flame-retardant than that of (butanol, etc.), the reduction reaction may not proceed unless it is at a high temperature, or there may be difficulties such as the reaction being greatly inhibited by water vapor.

Further, the reducing substance may be a solid or liquid substance from the viewpoint of supply to the catalyst layer, and may be vaporized at the reaction temperature from the viewpoint of reaction. It is more preferable that it is liquid at room temperature, and from the viewpoint of safety, it is more preferable that it is compatible with water, kerosene, light oil, etc. to some extent. Accordingly, methanol is not only reactive surface,
It can be said that it is also suitable in terms of operation safety.

The dilution of the methanol by water, vary with use, not particularly limited, typically, methanol concentration in the aqueous solution is about 5% to 90%, preferably about 60-80% It is a degree.

The methanol in the present invention, use of safety and handling surface for avoiding the danger of explosion, the water than other diluent (e.g., kerosene, gas oil, hydrocarbons such as heavy oil) is mixed with You may.

The reaction to prepare the reactor disposed above catalyst, in an oxidizing atmosphere present water vapor, methanol
The be present, carried out by passing the NOx-containing exhaust gases. The reaction temperature at this time is about 200 to 550 ° C., preferably about 2 although it depends on the removal rate of NOx in the exhaust gas.
It is 50 to 450 ° C, particularly preferably about 300 to 400 ° C. The present invention is characterized in that a higher NOx removal rate can be achieved at a lower temperature as compared with the case where a hydrocarbon such as propane is used as a reducing agent.

The reaction pressure is not particularly limited, and the reaction proceeds under pressure or under reduced pressure, but it is convenient to introduce the exhaust gas into the catalyst layer at a normal exhaust pressure to proceed the reaction. The space velocity is determined by the type of catalyst, other reaction conditions, the required NOx removal rate, etc., and is not particularly limited, but generally about 500 to 10
10,000 Hr ^-1 , preferably about 1,000 to 70,
It is in the range of 000 Hr ^-1 . In the method of the present invention, when treating exhaust gas from an internal combustion engine, it is preferable that the catalyst be disposed downstream of the exhaust manifold.

When the exhaust gas is treated by the method of the present invention, depending on the treatment conditions, incomplete combustion products such as unburned hydrocarbons and carbon monoxide which cause pollution are discharged into the treated gas. There is a case. As a countermeasure in such a case, a method in which the gas treated with the above-mentioned catalyst (hereinafter, referred to as “reduction catalyst”) is brought into contact with the oxidation catalyst can be adopted.

As the oxidation catalyst which can be used in the method of the present invention, generally, any substance can be used as long as it completely burns the above-mentioned incomplete combustion product, but activated alumina, silica, zirconia and the like can be used. Noble metals such as platinum, palladium and ruthenium, base metal oxides such as lanthanum, cerium, copper, iron and molybdenum, perovskite type crystal structures such as lanthanum trioxide trioxide, lanthanum trioxide trioxide and cobalt strontium trioxide, etc. The catalyst components such as the above may be used alone or in combination of two or more. The supported amount of these catalyst components is about 0.01 to 2 wt% with respect to the carrier for the noble metal, and about 5 to 70 wt% for the base metal oxide or the like. Of course,
In particular, a base metal oxide or the like can be used without being supported on a carrier.

The additives added for the purpose of the shape of the oxidation catalyst, molding, etc. are the same as those in the case of the reduction catalyst, and various kinds can be used.

The use ratio of the above reduction catalyst and oxidation catalyst,
The amount of the catalyst component supported on the oxidation catalyst can be appropriately selected depending on the required performance. Particularly, when the substance to be oxidized and removed is a hydrocarbon intermediate oxide such as carbon monoxide, the reduction catalyst and the oxidation catalyst Although it is possible to use a mixture with a catalyst, it is possible to arrange the reduction catalyst on the exhaust gas upstream side and the oxidation catalyst on the exhaust gas downstream side in general.

In the method of the present invention, as a specific example of purifying exhaust gas by using these catalysts, a reactor in which a reduction catalyst is arranged is an exhaust gas introduction section (first stage), and a reactor in which an oxidation catalyst is arranged is an exhaust gas discharge section. The method of arranging in (the latter stage), 1
There is a method of disposing each catalyst in one reactor at a ratio according to the required performance.

The ratio of the reduction catalyst (A) to the oxidation catalyst (B) is generally expressed by (A) / (B) and is about 0.5 to 9.5.
/9.5 to 0.5.

The use temperature of the oxidation catalyst may not be the same as the use temperature of the reduction catalyst, but in general, it is possible to select one that can be used within the range of the use temperature of the above-mentioned reduction catalyst. It is preferable because no special equipment is required.

[0040]

EXAMPLES Next, examples of the method of the present invention will be described, but the method of the present invention is not limited to these examples. Example 1 [Evaluation of reducing activity by model gas] (Preparation of H-ZSM-5) In an aqueous solution in which 957 g of sodium silicate was dissolved in 1200 g of water, 41 g of aluminum sulfate, 80 g of concentrated sulfuric acid and 360 g of sodium chloride were added to 1600 g of water. The aqueous solution in which was dissolved was added and mixed with gradual stirring for 30 minutes. Further, 120 g of tetrapropylammonium bromide was added to adjust the pH to 10. This mixed solution was charged into an autoclave and stirred at 165 ° C. for 16 hours to crystallize. After the product was separated, it was washed with water and dried to obtain a pentasil-type ZSM-5 zeolite with SiO ₂ / Al ₂ O ₃ = 62.7 as a base.

(Preparation of proton-type pentasil-type zeolite) 500 ml of a 1 mol / l ammonium nitrate solution
To the above, 20 g of the above pentasil-type zeolite was added, and the mixture was refluxed with stirring for 24 hours and then centrifuged. This was washed 5 times with pure water and air-baked at 110 ° C. for 3 hours to prepare a proton type ZSM-5.

(NOx removal reaction) 0.1 g of the zeolite catalyst thus prepared was filled in an atmospheric flow reactor, and 1000 ppm of nitric oxide (hereinafter referred to as NO) and 10% oxygen were added. Water containing 1 helium gas was introduced into the system at a flow rate of 60 ml per minute.
2.88 g of methanol (3.5 vol% ) in 00 ml
An aqueous solution containing, by using a micro-feeder pump, the reaction was carried out by introducing at a rate of 5 [mu] l. Therefore, the total gas flow rate in the system is about 66 ml / min, and the concentrations of water and methanol are about 8.5 vol% and about 13%, respectively.
The reaction was evaluated under the condition of 70 ppm and the reduction rate was investigated. Space velocity (SV) is about 20,000 Hr ^-1 , reaction temperature is 2
It evaluated in the range of 50-500 degreeC. The analysis of the reaction gas is
It was performed using a NOx analyzer and a gas chromatograph. The reductive decomposition rate of NO was determined from the yield of generated nitrogen, and the results are shown in Table 1 as Example 1.

Example 2 (Preparation of proton-stabilized Y-zeolite) Proton-stabilized Y-zeolite commercially available as zeolite (SiO 2
₂ / Al ₂ O ₃ = 49.7) except that 1.0 g was used, and methanol was used in the same manner as in Example 1 and SV = 2.
The decomposition rate of NO was examined under the condition of 000 Hr ⁻¹ . The results are shown in Table 1 as Example 2.

Example 3 (Preparation of Alumina Catalyst) Pelletized alumina (3 × 3 mmφ, surface area 244 mm ² / g) was crushed as a catalyst, and 1.0 g of coarse-grained alumina prepared in 12 to 50 mesh was used. and have <br/> use Le, in the same manner as in example 1, was examined reduction rate of NO under the conditions of SV = 2000 hr ^-1. Also, for reference,
A system in which methanol was used and no water vapor was present was also evaluated. The results are shown in Table 1 as Example 3.

Example 4 (Preparation of Co / alumina catalyst) A 0.42 mol / l solution of commercially available cobalt acetate was added to 4 m.
1g was prepared, 5 g of the same coarse-grained alumina as used in Example 3 was added, and the mixture was left standing at room temperature for 3 hours to impregnate and carry cobalt, and dried at 100 ° C. for one day and night.
It was baked at 00 ° C. for 3 hours. Further, this was calcined in a muffle furnace at 800 ° C. for 3 hours to obtain a catalyst (with a spinel structure).
A high content Co aluminate) was prepared. 2 wt% of cobalt metal was supported. Using 1.0 g of this catalyst, the reduction rate of NO was examined under the conditions of SV = 2000 Hr ^{−1 in} the same manner as in Example 1. The results are shown in Example 4.
Is shown in Table 1.

Example 5 (Preparation of Ni / alumina catalyst) A commercially available 0.43 mol / l solution of nickel nitrate was added to 4 m.
1g, 5g of the same alumina pellets as used in Example 3 was added, and left to stand at room temperature for 3 hours to impregnate and carry nickel, and dried at 100 ° C for a whole day and night, in an air stream,
Calcination at 630 ° C for 3 hours was followed by catalyst (many spinel type structures
Containing Ni aluminate) was prepared. Nickel metal
It was carried by 2 wt%. Using 1.0 g of this catalyst and methanol as a reducing agent, the reduction rate of NO was examined under the conditions of SV = 2000 Hr ^{−1 in} the same manner as in Example 1. The results are shown in Table 1 as Example 5.

Example 6 (Preparation of Proton Mordenite) Ammonium Nitrate 1
In 500 ml of a mol / l solution, 20 g of commercially available sodium mordenite (SiO ₂ / Al ₂ O ₃ = 20.1) was added.
Was charged, and the mixture was refluxed with stirring for 24 hours and then centrifuged. This was washed with pure water 5 times, dried at 110 ° C. overnight, and air dried at 500 ° C. for 3 hours to prepare a proton-type mordenite.

(Preparation of Alumina / Proton-type Mordenite Catalyst) The catalyst was prepared by uniformly mixing 5 g of the proton-type mordenite obtained above and 5 g of powder obtained by grinding the same alumina pellets as used in Example 4. .

(NO removal reaction) Using 0.1 g of this catalyst and methanol as a reducing agent, the reduction ratio of NO was examined under the conditions of SV = 20,000 Hr ^{−1 in} the same manner as in Example 1. The results are shown in Table 1 as Example 6.

Comparative Example 1 (Preparation of copper-supported zeolite) 0.05 m of commercially available copper acetate
An ol / l solution was prepared, the base ZSM-5 prepared in the same manner as in Example 1 was added, and the mixture was stirred at room temperature for 24 hours, refluxed, and then centrifuged. This operation was repeated 3 times, and finally, washed with pure water 5 times and dried overnight at 110 ° C. to prepare a copper-supported zeolite. Copper metal is 3.2 wt%
It was carried.

(NOx removing reaction) 0.1 g of the copper-supported zeolite thus prepared was used, methanol was used as the reducing agent in the same manner as in Example 1, and SV = 20000 Hr.
The reduction rate of NO was examined under the condition of ^-1 . The results are shown in Table 1 as Comparative Example 1.

[0052]

[Table 1]

Table 1 shows the results in the presence of 8.5 vol% of water, and the numerical values in parentheses of Example 3 in Table 1 are
The results of the system in the absence of water vapor are shown. As apparent from Table 1, by using methanol as the reducing agent, even in the presence of steam, without reducing activity of the catalyst is reduced, and it can be seen that the high activity at low temperature region.
Further, in the comparative example in which the copper is supported on the proton-type zeolite, the NO reduction rate is significantly inferior to the respective examples, and the effectiveness of the proton-type zeolite containing no metal employed in the method of the present invention can be seen.

Comparative Examples 2 to 4 In the same manner as in Example 1 except that propane (340 ppm) was used as the reducing agent, the effect of water vapor on the NO reduction reaction was examined for each catalyst. The amount of water vapor was 1.6 on the catalyst layer using a micro feeder pump.
They were prepared and added so that the concentrations would be vol% and 8.5 vol%, respectively. The results are shown in Table 2 as Comparative Examples 2 to 4.

[0055]

[Table 2]

As is clear from Table 2, when a hydrocarbon such as propane is used as a reducing agent, the NO reduction reaction effectively proceeds on the catalyst in a system in which water vapor does not exist, but water vapor is 1.6 vol. It can be seen that the presence of even a small amount of% hinders the reaction, and the reduction rate of any catalyst decreases as the amount of steam increases. Although the reduction rates of the alumina, Co / alumina, and Ni / alumina catalysts do not decrease so much in the high temperature range of 500 ° C. or higher, the reduction rates in the actual gas exhaust temperature range of about 400 ° C. significantly decrease.

[0057] As for the Anoremina catalyst has been investigated NO reduction rate in the same manner as in Example 1 using 2-propanol (about 510 ppm) as a reducing agent, methanol
The effect of improving the catalytic activity in the low temperature range of 400 ° C. or lower as seen in No. 2 is not seen so much. Regarding this, since the production of propylene was observed in the reaction product gas, 2
-It is assumed that the dehydration reaction of propanol occurs and the activity is not improved due to the inhibition of water vapor.

Examples 7 to 9 [Evaluation of reduction activity using actual gas] (Preparation of catalyst) The same pelletized alumina of 3 mmφ as used in Example 3 was calcined in air at 630 ° C for 3 hours to obtain an actual gas. It was used as an alumina test catalyst for evaluation. Further, in the same manner as in Example 4, 2% of cobalt metal was loaded on the pellet-shaped alumina, and a Co / alumina test catalyst for actual gas evaluation (spine
Co-aluminate) containing a large amount of le-type structure . The cobalt metal was analyzed by XMA (X-ray microanalyzer) and used after confirming that it was uniformly supported inside.

(NOx removal reaction) 120 ml of the catalyst prepared as described above was filled in a normal pressure flow reactor (inner diameter: 2 inches), and a predetermined amount of reducing agent was mixed with the exhaust gas generated from the diesel engine. The product was fed into a catalyst layer kept at 400 ° C. at a flow rate of 20 liters per minute to carry out a reaction. In Example 7, the exhaust gas (composition: NO; 505 ppm, water; 6.0 vol) using an alumina catalyst.
%), Methanol as a reducing agent was added to the inlet of the catalyst layer at 40 μl / min, and an active life test was performed for 200 hours. The NOx in the exhaust gas and the reaction gas is chemiluminescence type N
It analyzed by the Ox analyzer and calculated the NOx removal rate. The results are shown in Table 3 as Example 7.

In Example 8, alumina and Co / alumina (Co aluminate containing a large amount of spinel type structure)
Example 7 using both of the above catalysts and the above exhaust gas.
In the same manner as above for 100 hours, when the activity of the catalyst is almost stabilized, the amount of methanol added is 20 to 120.
By changing it in the range of μl (500 to 3000 ppm),
The effect of the amount of methanol added on the reduction rate was investigated. The results are shown in Table 4 as Example 8.

Furthermore, in Example 9, after the alumina catalyst was allowed to stand for 100 hours in the same manner as in Example 8,
The engine conditions were changed to produce exhaust gas with a NO concentration of 1710 ppm, and the effect of the reducing agent on the reducing activity under high NO concentration conditions was investigated in the temperature range of 300 to 650 ° C. using propylene and methanol, respectively. The results are shown in Table 5 as Example 9.

The operating conditions of the diesel engine and the composition of the exhaust gas are shown in Table 6.

[0063]

[Table 3]

[0064]

[Table 4]

[0065]

[Table 5]

[0066]

[Table 6]

As is clear from the life test in Table 3, the reduction rate tends to slightly decrease immediately after the start of the reaction even in an actual gas atmosphere in which water vapor and SOx coexist.
It can be seen that after 4 hours, it stabilizes immediately, and thereafter it changes with almost no decrease. Further, as is clear from Table 4, the reduction rate of both catalysts increased with an increase in the addition amount of methanol, and the Co / alumina catalyst supporting the fourth period transition metal (spinel type
It can be seen that Co-aluminate containing a large amount of structure acts more effectively. Furthermore, as is clear from Table 5, it is found that the low-temperature reducing activity is significantly improved when methanol is used as the reducing agent.

[0068]

As described in detail above, according to the method of the present invention, NOx in exhaust gas can be efficiently removed in an oxidizing atmosphere in which water vapor and oxygen are excessively present. This catalyst proton-type zeolite in the present invention method, in the presence of methanol, NOx and methanol
This is because it preferentially promotes the reaction with the le . As described above, the method of the present invention efficiently removes N from exhaust gas containing steam from various facilities including diesel engine exhaust gas.
Ox can be removed and the industrial value is extremely high.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/74 ZAB B01D 53/34 129B 23/75 B01J 23/74 311A 23/755 321A (72) Inventor, Kazuaki Kaneda, 1-1, Higashi 1-chome, Tsukuba-shi, Ibaraki Institute of Industrial Science and Technology (72) Inventor Hideaki Hamada 1-1-chome, Higashi, Tsukuba, Ibaraki (72) Inventor, Takehiko Ito Higashi 1-1-chome, Tsukuba-shi, Ibaraki Institute of Chemical Technology, Institute of Industrial Technology (72) Inventor, Moto Sasaki Ic-chome 1-chome, Tsukuba, Ibaraki, Institute of Chemical Technology (72) Inventor Fujio Suganuma Katsushika-kita, Saitama 228-16 (72) Inventor Tomohiro Yoshinari 3-32-25-201 Motomachi, Urawa City, Saitama Prefecture (72) Inventor Tada Mitsunori Hata 1134-2, Gongendo, Satte City, Saitama Prefecture (72) Inventor, Hiroshi Tsuchida 2-24-6-408, Kyomachi, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture (72) Tadao Nakatsuji, 5-1, Hinoshima-cho, Sakai City, Osaka Prefecture Sakai Chemical Industry Co., Ltd. Central Research Institute (72) Inventor Hiromitsu Shimizu 5-1, Ebishima-cho, Sakai City, Osaka Prefecture Sakai Chemical Industry Co., Ltd. Central Research Laboratory (72) Inventor, Ritsu Yaskawa 5 Ebishima-cho, Sakai City, Osaka Prefecture D. No. 1 Sakai Chemical Industry Co., Ltd. Central Research Laboratory Examiner Yoshio Ishii (56) Reference JP 4-156922 (JP, A) JP 3-181321 (JP, A) JP 2-149317 ( JP, A) JP-A-2-233124 (JP, A)

Claims (1)

(57) [Claims] 1. A in an oxidizing atmosphere an excess of oxygen and water vapor are present, in the presence of methanol, proton-type zeolite, alumina, and the fourth period transition metal and alumina
One or more catalysts selected from spinel-type metal aluminates and exhaust gas containing nitrogen oxides at a reaction temperature of 200-
A method for removing nitrogen oxides, which comprises contacting at 550 ° C.