JP3423703B2 - Nitrogen oxide removal catalyst - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a catalyst for removing nitrogen oxides. For details, internal combustion engines such as automobile engines,
For example, the present invention relates to a catalyst for removing nitrogen oxides in exhaust gas discharged from a gasoline engine, a diesel engine, a boiler, an industrial plant, etc. in an oxygen excess atmosphere .

[0002]

2. Description of the Related Art In recent years, the exhaust gas discharged from internal combustion engines of automobiles, boilers, industrial plants, etc. contains harmful components of nitrogen oxides (hereinafter sometimes referred to as NOx), which cause air pollution, It causes acid rain. Therefore, the removal of NOx has been studied from various aspects.

Conventionally, three-way catalysts have been used to remove nitrogen oxides in the exhaust gas of automobiles, and hydrocarbons (HC) are used.
Also, NOx is removed together with carbon monoxide (CO). This method is introduced with an amount of air sufficient to completely burn the fuel. However, since this method decomposes NOx in a reducing atmosphere, the A / F
Is lean (A / F; when air / fuel has a large amount of air), it is comfortable to purify HC and CO in the exhaust gas, but excessive oxygen causes to purify NOx. , NOx cannot be reduced and removed.

Further, among internal combustion engines, in the case of diesel engines, boilers, etc., methods of removing NOx using a reducing agent of ammonia, hydrogen or carbon monoxide are used, but these methods are unreacted. There is a problem that a special device is required for the recovery and treatment of the reducing agent.

Further, to cite general literature, as a method for reducing nitrogen oxides by hydrocarbons, a method using a catalyst in which platinum and barium are supported on activated alumina (JP-A-55-67334), platinum, A method using a catalyst in which rhodium and tungsten, and chlorides of sodium and / or potassium are supported on alumina (Japanese Patent Publication No. S58-58).
No. 45288) is disclosed, but none of these methods is sufficient to remove nitrogen oxides when a large excess of oxygen is contained in the exhaust gas.

Further, a method of removing nitrogen oxides by reacting NOx with hydrocarbons using a copper-containing catalyst in the presence of hydrocarbons in an oxidizing atmosphere (JP-A-63-1009).
No. 19) is disclosed, but this method has a high temperature at which nitrogen oxides can be removed, and cannot effectively remove nitrogen oxides at a low temperature.

[0007]

[SUMMARY OF THE INVENTION Accordingly, under oxygen excess Kiri囲<br/> gas, efficiently from low-temperature up to the high temperature, the development of the catalyst is desired to be used for the removal of nitrogen oxides ing.

[0008]

As a result of earnest research, the present inventors have found the following catalyst and method as a method for solving the above problems, and completed the invention.

The present invention relates to (A) an integral structure of a refractory inorganic oxide having a BET surface area of 50 to 200 m ² / g, which is loaded with 0.5 to 10% by weight of platinum based on the refractory inorganic oxide. And (B) then the monolithic structure is immersed in at least one aqueous solution selected from the group consisting of sodium and / or potassium nitrates, carbonates or hydroxides, and (C) dried and baked. To remove nitrogen oxides in an oxygen-rich atmosphere characterized by being obtained by
Is a catalyst used in .

Examples of the sodium and / or potassium source include nitrates, carbonates, and hydroxides. Each salt or compound other than these does not obtain preferable activity.

Sodium and / or potassium is preferably 1% by weight to 20% by weight in terms of each metal element, based on the refractory inorganic oxide. More preferably from 5% by weight
It is 10% by weight. When it is less than 1% by weight, the NOx removal efficiency decreases in the high temperature range, and when it exceeds 20% by weight, the NOx purification efficiency in each temperature range decreases.

The refractory inorganic oxide may be any one as long as it is usually used as a catalyst carrier, and examples thereof include α-alumina, activated alumina such as γ, δ, η and θ, titania, or zirconia. Alternatively, composite oxides of these, for example, alumina titania, alumina zirconia, titania zirconia, etc. can be used,
Activated alumina is preferable.

Also, these refractory inorganic oxides are BET
A refractory inorganic oxide having a surface area of 50 to 200 m ² / g is preferable.

As the platinum source, water-soluble salts such as chloroplatinic acid, dinitrodiamine platinum, potassium platinate, or sodium platinate are preferably used. The amount of platinum carried is
0.5 wt% to 10 wt% based on the refractory inorganic oxide
Is preferred, and more preferably 2 wt% to 5
% By weight. When the amount is less than 1% by weight, the NOx removal efficiency is lowered in each temperature range, and even when the amount is more than 10% by weight, the activity suitable for supporting and using cannot be obtained.
Further, it is preferable that platinum is supported on a refractory inorganic oxide.

The monolithic structure is usually used as a carrier for a catalyst, that is, an inorganic oxide honeycomb monolith such as cordierite, a metal honeycomb monolith, a corrugate, a plug honeycomb, etc. are preferably used. It is a monolith.

[0016] The method for preparing the catalyst according to the present invention are shown below, a platinum resistance fire resistant inorganic oxide supported in a conventional manner, after it has been slurried, immersing an integral structure, the redundant slurry After removing and drying and firing, the monolithic structure was then dipped in a predetermined sodium aqueous solution to remove excess liquid, dried and fired to obtain a finished catalyst . Of this preparation procedure, drying is preferably from 30 minutes to 3 hours at 80 ° C. to 150 DEG ° C., firing is 1 hour to 5 hours is preferable at 300 ° C. to 600 ° C..

[0017]

The hydrocarbon may be a saturated or unsaturated chain, cyclic or aromatic hydrocarbon, but is preferably an unsaturated chain hydrocarbon, such as ethylene, propylene or butene. Can be given.

The content of nitrogen oxides and hydrocarbons (converted to methane) in the exhaust gas is preferably 0.5 to 0.02 in terms of molar ratio. If it exceeds 0.5, the hydrocarbon reacts preferentially to make it difficult for the reaction with NOx to occur, so that the NOx removal efficiency decreases, and if it is less than 0.02, the hydrocarbon concentration is reduced. Even if it is higher than this, it is difficult to recognize the NO removing effect corresponding to it.

Although hydrocarbons are usually contained in the exhaust gas, for example, diesel engine exhaust gas may have a low hydrocarbon content and may not be in the above range of the ratio of hydrocarbon to nitrogen oxide. In such a case, in order to sufficiently remove the nitrogen oxides, it is necessary to newly add hydrocarbons to the catalyst from the exhaust gas inlet side for the lack thereof.

[0021]

The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto unless it goes against the gist of the present invention.

EXAMPLE 1 Activated alumina 10 having a BET surface area of 100 m / g ^2.
An aqueous solution of dinitrodiammine platinum having 5 g of platinum was added to 0 g, mixed, dried at 120 ° C. for 2 hours, and calcined at 500 ° C. for 2 hours. The obtained powder is wet-milled by a ball mill to obtain an aqueous slurry, and a commercially available cordierite honeycomb carrier (manufactured by Nippon Insulators Co., Ltd., with 400 gas distribution cells having a cross section of 1 inch square). After dipping it, the diameter was 33 mmφ, the length was 76 mm, and the volume was 65 ml), and then the excess slurry was blown off by compressed air. Then, dry at 120 ° C for 2 hours and at 500 ° C for 2 hours.
Firing was performed for a time to obtain a honeycomb carrier coated with platinum-supported alumina powder.

Further, the obtained honeycomb carrier was immersed in a 4.3 mol / liter sodium nitrate aqueous solution,
Blow off excess solution with compressed air and remove it at 120 ° C.
Completed catalyst (A)
Got This catalyst contains 5 platinum on activated alumina.
% By weight, and 10% by weight of sodium were supported.

Example 2 A finished catalyst was prepared in the same manner as in Example 1 except that a 2.1 mol / liter sodium nitrate aqueous solution was used instead of the 4.3 mol / liter sodium nitrate aqueous solution. B) was obtained. This catalyst had 5% by weight of platinum and 5% by weight of sodium supported on activated alumina.

Example 3 A completed catalyst (C) was prepared in the same manner as in Example 2 except that the aqueous solution of dinitrodiammine platinum containing 5 g of platinum was replaced with the aqueous solution of dinitrodiammine platinum containing 1 g of platinum. Got This catalyst had 1% by weight of platinum and 5% by weight of sodium supported on activated alumina.

Example 4 A finished catalyst (D) was prepared in the same manner as in Example 1 except that a 2.5 mol / liter potassium carbonate aqueous solution was used instead of the 4.3 mol / liter sodium nitrate aqueous solution. ) Got. This catalyst had 5% by weight of platinum and 10% by weight of potassium supported on activated alumina.

Example 5 A finished catalyst (E) was prepared in the same manner as in Example 1 except that a 4.3 mol / liter sodium nitrate aqueous solution was used instead of the 4.3 mol / liter sodium nitrate aqueous solution. ) Got. This catalyst had 5% by weight of platinum and 10% by weight of sodium supported on activated alumina.

Example 6 A finished catalyst was prepared in the same manner as in Example 1 except that a 4.3 mol / liter sodium nitrate aqueous solution was used instead of the 4.3 mol / liter sodium nitrate aqueous solution. F) was obtained. This catalyst had 5% by weight of platinum and 10% by weight of sodium supported on activated alumina.

Comparative Example 1 A finished catalyst (G) was prepared in the same manner as in Example 1 except that a 4.3 mol / liter sodium nitrate aqueous solution was used instead of the 4.3 mol / liter sodium nitrate aqueous solution. ) Got. This catalyst had 5% by weight of platinum and 10% by weight of sodium supported on activated alumina.

Comparative Example 2 An aqueous dinitrodiammine platinum solution containing 5 g of platinum and an aqueous solution containing 36.9 g of sodium nitrate were added to 100 g of the activated alumina used in Example 1 and mixed, followed by drying at 120 ° C. for 2 hours and at 500 ° C. It was baked for 2 hours. The obtained powder was wet pulverized with a ball mill to obtain an aqueous slurry. The same honeycomb carrier as that used in Example 1 was immersed in this slurry, and then the excess slurry was blown off by compressed air. Then, dry at 120 ℃ for 2 hours, 500 ℃
It was calcined for 2 hours to obtain a finished catalyst (H). This catalyst had 5% by weight of platinum and 10% by weight of sodium supported on activated alumina.

Comparative Example 3 An aqueous solution of dinitrodiammine platinum containing 5 g of platinum was added to the activated alumina used in Example 1 and mixed, and then 12
It was dried at 0 ° C. for 2 hours and calcined at 500 ° C. for 2 hours. An aqueous solution containing 36.9 g of sodium nitrate was added to and mixed with this powder, which was then dried at 120 ° C for 2 hours and then at 500 ° C.
It was baked for 2 hours. The obtained powder was wet pulverized with a ball mill to obtain an aqueous slurry, the same honeycomb carrier as that used in Example 1 was immersed in this slurry, and then the excess slurry was blown off by compressed air. Then 12
It was dried at 0 ° C. for 2 hours and calcined at 500 ° C. for 2 hours to obtain a finished catalyst (I). This catalyst had 5% by weight of platinum and 10% by weight of sodium supported on activated alumina.

Comparative Example 4 An aqueous solution containing 36.9 g of sodium nitrate was prepared in Example 1.
After adding and mixing to the activated alumina used in 1., 120 ℃
And dried at 500 ° C. for 2 hours. An aqueous solution of dinitrodiammineplatinum containing 5 g of platinum was added to and mixed with the powder, and then dried at 120 ° C. for 2 hours.
Calcination was carried out for 2 hours. This powder was wet pulverized with a ball mill to obtain an aqueous slurry, the same honeycomb carrier as used in Example 1 was immersed in this slurry, and then the excess slurry was blown off by compressed air. Then 120
Drying was carried out at 0 ° C for 2 hours and firing was carried out at 500 ° C for 2 hours to obtain a finished catalyst (J). This catalyst had 5% by weight of platinum and 10% by weight of sodium supported on activated alumina.

Comparative Example 5 A method for preparing ZSM-5 type zeolite is described in the literature (Rapid).
onal Crystallizing Method, P
roseceing 8th International
al Congress on Catalysis,
Berlin, 1984, Vol. 3, P569). It was confirmed by X-ray diffraction that the obtained zeolite was a ZSM-5 type zeolite.

400 g of pure water was added to 100 g of ZSM-5 type zeolite obtained by the above procedure, stirred at 98 ° C. for 2 hours, and 0.2 mol / liter of copper ammine complex aqueous solution was slowly added dropwise at 80 ° C. After the dropping was completed, the mixture was heated and stirred at 80 ° C. for 12 hours for ion exchange. Further, the ion-exchanged zeolite was filtered and further thoroughly washed until nitrate ions were not detected. The ion-exchanged zeolite was dried at 120 ° C. for 24 hours. The obtained powder was wet pulverized with a ball mill to obtain an aqueous slurry, and the same cordierite honeycomb carrier as that used in Example 1 was immersed in the aqueous slurry, and then the excess slurry was blown off by compressed air. .

Then, it is dried at 120 ° C. for 2 hours and then 500
Calcination was performed at 0 ° C. to obtain a finished catalyst (K). This catalyst has
The loading rate of copper is 5.8 with respect to ZSM-5 type zeolite.
% By weight.

Example 7 Catalysts (A) prepared in Examples 1-6 and Comparative Examples 1-5
For (K), a catalyst activity test was conducted under the following conditions. A stainless steel reaction tube having a diameter of 34.5 mm and a length of 300 mm was filled with a catalyst, and NO was used as a reaction gas.
Is 750 ppm, propylene is 1000 ppm (in terms of methane), CO is 0.2% by volume, steam is 10% by volume, carbon dioxide is 13.5% by volume, oxygen is 2.0% by volume, and the balance is nitrogen. Was introduced under the condition of 20000 / hr. The catalyst inlet temperature was evaluated in the range of 200 ° C to 400 ° C, and the results are shown in Table 1.

The reaction gas of the above catalyst evaluation is oxygen 2.
Change 0% by volume to 10% by volume and perform the same catalyst evaluation,
The results are shown in Table 2.

Example 8 Example 8 was repeated, except that the catalyst for evaluation was changed to the catalyst (A) obtained in Example 1 and the propylene concentration and NO concentration were changed to the respective concentrations shown in Table 3. The catalyst was evaluated in the same manner as in Example 7, and the results are shown in Table 3.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI F01N 3/10 F01N 3/28 301P 3/28 301 B01D 53/36 102B ZAB 102H (72) Inventor Tomohisa Ohata Hibashi, Himeji-shi, Okohama, Hyogo Prefecture 1 992 Nishi-oki, Japan Catalysis Research Institute, Inc. (56) Reference JP-A-2-157042 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B01J 21/00- 38/74 B01D 53/86, 53/94 F01N 3/28

Claims (2)

(57) [Claims] 1. (A) 0.5 with respect to the refractory inorganic oxide
-10 wt% platinum supported BET surface area is 50-2
The monolithic structure is coated with a refractory inorganic oxide of 00 m ² / g, and (B) the monolithic structure is then at least one selected from the group consisting of sodium and / or potassium nitrate, carbonate and hydroxide. (C)
An acid characterized by being obtained by drying and baking
It is used to remove nitrogen oxides under oxygen-rich atmosphere
That catalyst. 2. The catalyst according to claim 1, wherein the refractory inorganic oxide is activated alumina.