JPH02122830A - Catalyst for removal of nitrogen oxide - Google Patents

Abstract

PURPOSE:To permit an efficient cleavage of nitrogen oxides in a gas in the presence of CO by forming a catalyst of the baked product of (a) the oxides of alkali metal (b) Al2O3, SiO2, etc., and (c) platinum group metal or its oxide. CONSTITUTION:A mixture of alkali metal or the oxides of alkaline earth metal and a metallic oxide selected from Al2O3, SiO2, ZrO2, Fe2O3, TiO2, etc., after formation by extrusion molding, is baked at a temperature of 300-800 deg.C. Such baked product is immersed in the water-soluble salt of any one of Ru, Rh, Pd, Ag, Pt and Au and, after drying, is baked at a temperature of 300-800 deg.C and baked again, as required, in a reducing atmosphere to form a catalyst. This catalyst can effect the reductive cleavage of nitrogen oxides for removal from exhaust gases with the addition of a reducing agent CO thereto at the gas temperature of 300-800 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Application Decomposition The present invention relates to a method for removing nitrogen oxides contained in exhaust gas.

Nitrogen oxides contained in exhaust gas from conventional laboratories can be removed by: ■ oxidizing nitrogen oxides and absorbing alkali; ■ converting nitrogen oxides to NH3
, [■2, CO and other reducing agents have been used to remove N2. These methods require wastewater treatment in the case of (■), and require a reducing agent such as NH3 in the case of (■), resulting in high treatment costs.In particular, there are problems such as a decrease in activity due to the formation of salts due to the reaction between NH3 and SOx. I have had it. In addition, when CO is used as a reducing agent, these problems do not occur, but in the coexistence of 0□, CO and 02 react, making it impossible to reduce efficiently.

Problems due to 11' The present invention solves the above-mentioned drawbacks and relates to a catalyst that can selectively decompose nitrogen oxides with high efficiency by adding a reducing agent CO.

The catalyst according to the present invention converts nitrogen oxides contained in exhaust gas into (a) alkali metal and/or alkaline earth metal oxides and (b) A I 203.5in2, ZrO2, Fe2O
3, TiO2, WO3, MoO3, 51102, B1□
03, one or more metal oxides selected from ZnO, and (c) RuSRh, Pd, Ag, Pt, Au
This is a catalyst that can decompose nitrogen oxides into N2 and 002 when brought into contact with a catalyst consisting of one or more metals or metal oxides selected from the following.

The present catalyst can be prepared by a known method using a catalyst component selected from (a), (b) and (C) or a precursor thereof.

For example, (1) an alkaline earth metal oxide (magnesia, calcia, strontium oxide, etc.) and an oxide selected from group (b) are mixed in advance, and any molding method (extrusion molding, tablet molding, spherical molding, etc.) is used. ) and then molded at 300℃~8
This is baked at a temperature of 300°C to 800°C, immersed in an aqueous solution of metal and/or alkali metal salt selected from group (C), and dried at a temperature of 300°C to 800°C. Further, if necessary, it is fired in a reducing atmosphere.

(2) Dissolve an alkaline earth metal salt and a salt of a metal selected from group (b) in water, etc., and add alkali (ammonia,
A precipitant such as sodium hydroxide is added to form a precipitate, which is dried, then calcined and pulverized at a temperature of 300°C to 800°C. etc.), and if necessary, 3
It is fired at a temperature of 00°C to 800°C.
It is immersed in a metal and/or alkali metal salt aqueous solution selected from group C), dried, and then fired at a temperature of 300°C to 800°C. Further, if necessary, it is fired in a reducing atmosphere.

(3) Dissolving an alkali metal salt, a metal salt selected from group (b), and a metal salt selected from group (C) in water or the like,
Add to this an alkali (ammonia, sodium hydroxide, etc.)
A precipitant such as the like is added to form a precipitate, which is dried and then calcined at a temperature of 300°C to 800°C. This is crushed and molded by any molding method (extrusion molding, tablet molding, spherical molding, etc.), and further heated to 300°C to 800°C as necessary.
Fired at a temperature of 0°C. Furthermore, depending on the case, this may be fired in a reducing atmosphere.

These methods are illustrative of methods for preparing the catalyst of the present invention, and are not limited thereto, and equivalent effects can be obtained if the catalyst components are the same.

The metal oxides of group (a) that can be used in the present invention are magnesium oxide, calcium oxide, and strontium oxide, and the precursors of group (a) are magnesium hydroxide, calcium hydroxide, strontium hydroxide, and barium hydroxide. Hydroxides such as nitrate, sium, calcium nitrate, strontium nitrate, barium nitrate, and water-soluble salts. The precipitating agent is preferably an alkali such as carbonate or sodium hydroxide.

Further, metal oxides of group (b) that can be used in the present invention include Al2O3, SiO, , ZrO□, Fe, 0
3. TiO2, WO3, MoO3, SnO2, B12O
Precursors of group (b), which are one or more metal oxides selected from 3. ZnO and are preferred raw materials, include water-soluble salts such as hydroxides and nitrates.

Furthermore, as the metal or metal oxide of group (C), it is preferable to use a precursor, and examples thereof include water-soluble salts such as ruthenium chloride, rhodium nitrate, palladium chloride, silver nitrate, chloroplatinic acid, and chloroauric acid. In addition to these components, known carrier components such as titania, alumina, and silica, molding aid components such as clay, and reinforcing agents such as glass fiber may be added.

The total amount of these components is preferably 50% or less in the catalyst components.

The catalyst according to the present invention comprises group (a), group (b) and group (c).
The preferred composition ratio of these groups is (a
) group: (b) group: (C) group is 90-50:5-50:0
．． 01-10, more preferably 90-75:10
25:0.1-5. The present inventors found that the elementary reaction of catalytic decomposition of NOx is 2NO+2e −+ 2NO−(1)2NO−+
CO+ N,,+2CO'-(2)2CO--Co
□+2e (3) CO2→ CO2↑ (4) Group (a) is the reaction of (1) (2), (b)
We believe that group (c) is involved in reaction (3) and group (c) is involved in reaction (4). Although the contribution of each of these to the reaction rate is unclear, the results showed the highest reductive decomposition activity at these atomic ratios.

The temperature at which the catalyst of the present invention exhibits reductive decomposition activity is 300°C to 8°C.
It is 00°C. The preferred temperature is 400-600℃
It is. At this temperature, the catalyst of the present invention has a voltage of 5V=500
~50,000 can be used.

As described above, according to the present invention, group (a), group (b), and group (c)
By using a catalyst containing a catalyst component selected from the group, it has become possible to reduce and decompose nitrogen oxides in the exhaust gas temperature range of 300°C to 800°C by adding a reducing agent CO. be.

The present invention will be explained below by giving Examples and Comparative Examples, but the present invention is not limited to these Examples in any way.

Example 1 Magnesium nitrate and aluminum nitrate were weighed in an amount of 90 g and 9 g, respectively, based on their oxides, and dissolved in 1 cup of ion-exchanged water. Sodium carbonate was added to this aqueous solution with sufficient stirring until the pH reached 7.0 to complete the neutralization reaction. (Neutralization time: 1 hour) Thereafter, the mixture was aged for 30 minutes, washed with water, dried at 100°C for 18 hours, and then calcined at 500°C for 3 hours. This fired product was pulverized using a sample mill with a screen of 0.5 mmφ. 50g of this crushed material, 20g of water
A corrugated honeycomb made of ceramic fibers with a porosity of 81% and a pitch of 4 mm was immersed in the slurry that had been poured into a slurry of Mg O-Al 203 and thoroughly stirred.
was supported on the honeycomb. The loading rate was 143%. This was air-dried at room temperature and then dried at 100° C. for 18 hours.

This dried material was dissolved in an aqueous solution of chloroauric acid (33 g/view as Au).
After drying at room temperature with ventilation, drying at 100°C for 18 hours,
It was fired at 500°C for 3 hours.

Example 2 Aluminum nitrate and titanyl nitrate were each 5
0g and 50g were weighed out and dissolved in ion-exchanged water. Ammonia was blown into this aqueous solution with sufficient stirring to adjust the pH to 7.0 and complete the neutralization reaction.

(Neutralization time: 1 hour) Thereafter, the mixture was aged for 30 minutes, washed with water, dried at 100°C for 18 hours, and then fired at 600°C for 3 hours. This fired product was pulverized using a sample mill with a screen of 0.5 mmφ. 50 g of this pulverized material and 50 g of magnesia (specific surface area 53 m2/g) obtained by calcining magnesium hydroxide at 650°C for 1 hour were added to 400 J of water and pulverized for 30 minutes in a planetary mill. Immerse a corrugated honeycomb made of ceramic fiber with a ratio of 81% and a pitch of 4 mm, Mg0-Al2O2
-Ti02 was supported on the honeycomb. Its carrying rate is 15
It was 6%. A catalyst was prepared in the same manner as in Example I.

Example 3 In the method of Example 2, MgO and A1203-TiO
75g and 25g of 2 on an oxide basis (Example 3-1)
and 25g and 75g (Example 3-2).

Example 4 In the method of Example 2, the concentration of aqueous chloroauric acid α was changed to
IG5g/Q, closed.

Example 5 In the method of Example 2, a chloroplatinic acid aqueous solution was used in place of the chloroauric acid aqueous solution. At this time, the Pt concentration was reduced to 16g/min (
Example 55-1) 33/min (Example 55-2) 66/min (Example 5-3).

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

Example 7 In the method of Example 2, a silver nitrate aqueous solution (71 g/stu as A g 20) was used in place of the chloroplatinic acid aqueous solution.

Example 8 Aqueous solutions of zirconium hydroxide and metatungsten ammonium (85 g and 15 g) were weighed in terms of oxide, water was added, and the mixtures were sufficiently kneaded, dried at 100°C for 18 hours, and fired at 700°C for 3 hours. This fired product was pulverized using a sample mill with a screen of 0.5 mmφ. A catalyst was obtained in the same manner as in Example 2 using 50 g of this pulverized material and the magnesia used in Example 2.

Example 9 Weighed 50g of Snowtex O manufactured by 8 San Kagaku and metatitanic acid sol (metatatitanic acid peptized with nitric acid) in terms of oxide, mixed thoroughly, dried at 100°C for 18 hours, and then heated to 700°C. It was baked for 3 hours. This fired product was pulverized in the same manner as in Example 2. Calcia (specific surface area: 4
A catalyst was obtained in the same manner as in Example 2 using 50 g of 6m2/g).

Example 10° In the method of Example 9, an aqueous palladium chloride solution was used in place of chloroplatinic acid.

Example 11 In the method of Example 9, an aqueous rhodium nitrate solution was used in place of chloroplatinic acid.

Example 12゜ Bismuth nitrate aqueous solution and ammonia molybdate aqueous solution: α
50 g and 50 g in terms of oxide were weighed out, and an aqueous ammonium molybdate ammonia solution was added to an aqueous bismuth nitrate solution to perform a neutralization reaction. (Final pH=7.0) A catalyst was obtained in the same manner as in Example 2.

Example 13 - Zinc nitrate was used in place of aluminum nitrate in the method of Example 2.

Example 14 In the method of Example 2, tin(II) chloride was used in place of aluminum nitrate.

Example 15 In the method of Example 1, iron nitrate was used instead of aluminum nitrate.

Example 16 In the method of Example 2, a chloroauric acid aqueous solution containing Na (33 g/in terms of Au, 3 g/α as Na) was used in place of the chloroauric acid aqueous solution.

Example 17 The catalyst obtained in Example 4 was treated with a reducing gas of N2-N2 (1:1) at 400°C for 1 hour.

(1) Gas composition No. 200ppm 02 2% N20 1O% Co2 200ppm N2 Balance (2) SV 1000 (3) Reaction temperature 300.400.500°C The test results are shown in Table 1.

Claims (1)

[Claims] Contacting a gas containing nitrogen oxides in the coexistence of CO,
In a catalyst that decomposes and removes nitrogen oxides, (a) an alkali metal and/or alkaline earth metal oxide and (b) A1_2O_3, SiO_2, ZrO_2, Fe
_2O_3, TiO_2, WO_3, MoO_3, Sn
Consisting of one or more metal oxides selected from O_2, Bi_2O_3, and ZnO and (c) one or more metals or metal oxides selected from Ru, Rh, Pd, Ag, Pt, and Au. Features of nitrogen oxide decomposition catalyst