JP2921517B2 - Nitrogen oxide decomposition catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a catalyst for decomposing and removing nitrogen oxides contained in exhaust gas.

[0002]

2. Description of the Related Art Conventionally, nitrogen oxides contained in exhaust gas are obtained by oxidizing the nitrogen oxides and then absorbing them into an alkali, or by using a reducing agent such as ammonia, hydrogen or carbon monoxide to remove the nitrogen oxides. , Nitrogen and the like. However, according to the former method,
Wastewater treatment is required, while the latter method
Since a reducing agent such as ammonia is required, there are problems such as a high processing cost and a reduction in catalytic activity due to generation of salts due to reaction with these sulfur oxides.
Therefore, catalysts capable of directly decomposing nitrogen oxides without adding a reducing agent have been proposed, but such catalysts known in the past have low nitrogen oxide decomposition activity. Therefore, there is a problem that it cannot be put to practical use.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has as its object to efficiently reduce nitrogen oxides without adding a reducing agent. To provide a catalyst that can be directly decomposed.

[0004]

According to the present invention, there is provided a catalyst for decomposing and removing nitrogen oxides by contacting with an exhaust gas containing nitrogen oxides, wherein (a) magnesia and (b) Al
_At least one metal oxide selected from the group consisting of ₂ O ₃ , SiO ₂ , ZrO ₂ , Fe ₂ O ₃ and TiO ₂ , and (c) Ru, R
It is composed of at least one metal or metal oxide selected from h, Pd, Ag, Pt, and Au, and has a composition ratio of (a) :( b) group: (c) group of 90 to 50: 5-50:
It is characterized by being 0.01 to 10.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The nitrogen oxide decomposition catalyst according to the present invention is prepared by using a catalyst component or a precursor selected from the above (a), (b) and (c) by a conventionally known method. Can be prepared. For example, (1) (a)
Gnesia and an oxide selected from the group (b) are mixed in advance, molded by an arbitrary molding method such as extrusion molding, tablet molding, or spherical molding, and then fired at a temperature of 300 ° C to 800 ° C. Then, this is immersed in an aqueous solution of a metal salt selected from the group (c) and, if necessary, fired in a reducing atmosphere.

(2) A magnesia of (a) and a metal salt selected from (b) are dissolved in water or the like, and ammonia,
A precipitant such as an alkali such as sodium hydroxide is added to form, which is dried, fired at a temperature of 300 ° C. to 800 ° C., then pulverized, extruded, tableted, or spherically shaped. And, if necessary, firing at a temperature of 300 ° C. to 800 ° C., immersing this in an aqueous solution of a metal salt selected from the group (c), drying, It is fired at a temperature of 800 ° C. and, if necessary, fired in a reducing atmosphere.

[0007] The above is an example of a method for preparing a catalyst according to the present invention, and the present invention is not limited thereto.

[0008] Magne that can be used in the present invention
Examples of the shear precursor include water-soluble salts such as magnesium hydroxide and magnesium nitrate. still,
As these precipitants, alkalis such as sodium carbonate and sodium hydroxide are preferable. The magnesia (a) may contain an alkali metal oxide such as sodium oxide.

The metal oxides of the group (b) which can be used in the present invention are Al ₂ O ₃ , SiO ₂ , ZrO
_{2, Fe} 2 _{O 3,} and is at least one metal oxide selected from TiO _2. Preferred precursors of the metal oxides of group (b) include, for example, water-soluble salts such as hydroxides and nitrates. Further, as the metal or metal oxide of group (c), it is preferable to use a precursor, such as ruthenium chloride, rhodium nitrate, palladium chloride, silver nitrate, chloroplatinic acid, chloroauric acid and the like. Can be exemplified. In addition to these components, titania, alumina, conventionally known carrier components such as silica, molding aid components such as clay,
An auxiliary material such as glass fiber may be added. However, the total amount of these components is preferably not more than 50% of the catalyst components.

The catalyst according to the present invention comprises the groups (a), (b) and (c).
Atomic ratio of (a) :( b) group: (c) group is 90-50: 5
~ 50: 0.01 to 10, more preferably 90 to
75:10 to 25: 0.1 to 5.

[0011] Nitrogen oxides according to the present inventors, elementary reactions of catalytic cracking of NOx is ^{2NO + 2e → 2NO - (1} ) 2NO - → N 2 + 2O (2) 2O → O 2 + 2e (3) O 2 → O consists ₂ ↑ (4), involved respectively in the reaction of (a) is (1) and the reaction of (2), (b) group to the reaction of (3), (c) group (4) It is thought that there is. Although the contribution of each of these to the reaction rate is not clear, the results showing the highest decomposition activity at the above atomic ratio were obtained.

The temperature at which the catalyst according to the invention exhibits a cracking activity is in the range from 300 ° C. to 800 ° C. In particular, a preferred temperature is in the range of 400-600C. At such a temperature range, the catalyst according to the invention has a space velocity (S
V) can be suitably used in the range of 500 to 50,000 hr ^-1 .

[0013]

As described above, according to the present invention,
(A) using a catalyst component containing a catalyst component selected from the groups (b) and (c) to add a reducing agent to the exhaust gas in a temperature range of 300 ° C to 800 ° C; In addition, nitrogen oxides in exhaust gas can be decomposed and removed.

[0014]

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

Example 1 Magnesium nitrate and aluminum nitrate were weighed in an amount of 90 g and 9 g in terms of oxide, respectively, and dissolved in 1 L of ion-exchanged water. While sufficiently stirring the aqueous solution, sodium carbonate was added until the pH became 7.0,
The neutralization reaction was completed. The time required for neutralization was 1 hour.

After aging for 30 minutes, the solid content was filtered, washed with water, dried at 100 ° C. for 18 hours, and then calcined at 500 ° C. for 3 hours. The fired product obtained is screened at 0.
It was pulverized by a sample mill having a diameter of 5 mm. 50 g of the pulverized material is put into 200 mL of water and sufficiently stirred, and thus the obtained slurry has a porosity of 81% and a pitch of 4 mm.
The corrugated honeycomb was immersed ceramic fibers, it was supported _MgO-Al 2 _{O 3} in the honeycomb.
Its loading was 143%.

After drying this with ventilation at room temperature,
Dried for hours. The obtained dried product is chlorauric acid aqueous solution (Au
33 g / L), and air-dry at room temperature.
Dry at 00 ° C for 18 hours, bake at 500 ° C for 3 hours,
A catalyst was obtained.

Example 2 Aluminum nitrate and titanyl nitrate were each weighed in an amount of 50 g in terms of oxide, and dissolved in 1 L of ion-exchanged water. Ammonia was blown into the aqueous solution with sufficient stirring to adjust the pH to 7.0, and the neutralization reaction was terminated. The time required for neutralization was 1 hour.

After aging for 30 minutes, the solid content was filtered, washed with water, dried at 100 ° C. for 18 hours, and then calcined at 600 ° C. for 3 hours. The fired product obtained is screened at 0.
It was pulverized by a sample mill having a diameter of 5 mm. 50 g of this pulverized material and 50 g of magnesia (specific surface area: 53 m ² / g) obtained by calcining magnesium hydroxide at 650 ° C. for 1 hour were put into 400 mL of water, and wet pulverized by a planetary mill for 30 minutes. Thus, the resulting porosity of 81% to the slurry, was immersed a corrugated honeycomb made of a pitch 4mm ceramic fibers, it was supported _{MgO-Al 2} O 3 -TiO 2 in the honeycomb. Its loading was 156%.
Thereafter, a catalyst was obtained in the same manner as in Example 1.

Example 3 In Example 2, MgO and Al ₂ O ₃ —TiO ₂ were respectively 75 g and 25 g (Example 3-1) and 25 g and 75 g (Example 3-2) in terms of oxide.

Example 4 In Example 2, the concentration of the aqueous solution of chloroauric acid was set to 1 as Au.
It was 65 g / L.

Example 5 In Example 2, a chloroplatinic acid aqueous solution was used instead of the chloroauric acid aqueous solution. Here, the Pt concentration was set to 16 g / L (Example 5-1), 33 g / L (Example 5-2) or 66 g / L.
/ L (Example 5-3).

Example 6 In Example 2, a ruthenium chloride aqueous solution (Ru: 33 g / L) was used in place of the chloroauric acid aqueous solution.

Example 7 In Example 2, an aqueous silver nitrate solution (71 g / L as Ag ₂ O) was used in place of the aqueous chloroauric acid solution.

[0025]

[0026]

[0027]

Example 8 A catalyst was obtained in the same manner as in Example 1 except that iron nitrate was used instead of aluminum nitrate.

Example 9 In Example 1, an aqueous solution of chloroauric acid containing sodium (33 g / L as Au,
A catalyst was obtained in the same manner using 3 g / L of Na).

Example 10 The catalyst obtained in Example 4 was replaced with nitrogen-hydrogen (volume ratio 1:
It processed at 400 degreeC in reducing gas of 1) for 1 hour.

Reference Example 1 50 g of ZSM-5 manufactured by Mobil Oil was immersed in a 0.1 N aqueous cupric chloride solution and stirred at 90 ° C. to 100 ° C. for 12 hours in a three-necked flask equipped with a reflux condenser. And filtered. The same operation is repeated using the obtained cake,
The replacement amount of copper was 4.8% by weight. Thereafter, a catalyst was obtained in the same manner as in Example 1.

(Reduction of Nitrogen Oxide)10as well as
Using the catalyst obtained in Reference Example 1, exhaustion was performed under the following test conditions.
A reduction test of nitrogen oxides in the gas was performed. Table 1 shows the results
Show. (1) Gas composition NO 200 ppm O₂ 2% H₂O 10% N₂ Balance (2) SV 1000hr^-1  (3) Reactor temperature 300 ° C, 400 ° C, 500 ° C

[0033]

[Table 1]

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B01D 53/94 B01J 23/58 B01J 23/66 B01J 23/89

Claims (1)

(57) [Claims] Claims: 1. Contacting an exhaust gas containing nitrogen oxides,
In the catalyst for decomposing and removing nitrogen oxides (a) magnesium
And _{A, (b) Al 2 O 3} , SiO 2, ZrO 2, Fe 2
At least one metal or metal oxide selected from O ₃ and TiO ₂ and (c) Ru, Rh, Pd, Ag, Pt and Au
And (a): (b) group: (c) group is 9 in atomic ratio of at least one metal or metal oxide selected from
0-50: 5-50: 0.01-10
Nitrogen oxide decomposition catalyst.