JPH02187131A - Method for removing nitrogen oxide - Google Patents

Abstract

PURPOSE:To reductively decompose nitrogen oxides in a waste gas into N2 and O2 and remove in high efficiency by adding CO as a reducing agent to a catalyst and bringing the waste gas into contact with the catalyst in the co-existence of sulfur dioxide. CONSTITUTION:CO as a reducing agent is added to a catalyst, such as a ZSM-5 whose alkali metal is substituted with Cu<+2>, containing nitrogen oxides present in a waste gas. The nitrogen oxides can be reductively decomposed into N2 and O2 by bringing nitrogen oxides-containing waste gas into contact with the catalyst in the co-existence of sulfur dioxide.

Description

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

(Prior art) Nitrogen oxides contained in exhaust gas have been conventionally treated by: ■ oxidizing nitrogen oxides and absorbing alkali; ■ converting nitrogen oxides to NH3
, N2, CO, and other reducing agents. These methods require wastewater treatment in the case of ①, and require a reducing agent such as NH3 in the case of ①, resulting in high treatment costs.In particular, when NH3 is used as the reducing agent, activity decreases due to salt formation due to reaction with SOx. There have been some problems. Further, when CO is used as a reducing agent, the above-mentioned problems do not occur, but there is a problem that in the coexistence of oxygen, CO reacts with 02 and the sending reaction does not occur efficiently.

(Problems to be Solved by the Invention) The present invention solves the above drawbacks by adding a reducing agent CO,
The present invention relates to a method capable of highly efficiently reductively decomposing nitrogen oxides in the presence of oxygen.

(Means for Solving the Problem) The method according to the present invention uses a catalyst having nitrogen oxides contained in a gas, for example: (1) (a) A1.03,5in2. Zr09゜Fe2
O3, wo3. MoO3, Sn 021 B' 203 * Z n O2, T i
02, Nb2O, and (b) Cub, Nip, Cr20a+ Ag2O, Co
3O4, MnO2, Ru.

Catalyst (2) characterized in that it consists of a metal oxide or metal selected from Rh, Pd, Pt, and Au (a) C0304, Cu2O, Cr2O3Mn-
203, Ni01pbo, B1°03, MoO2, and (b) one or more metals or metal oxides selected from Ru, Rh, Ag, Pt, Au. Catalyst (3) whose main components are represented by the composition formula F(A(Ml)B(N
2). C(AIO□)X・(S t O2) Y]-2
H20 (where M, N2 are metals, n1n2 are respective valences. A+n I B+n 2 C=X), (a) Mt is an alkali metal and/or alkaline earth metal (b) N2 Ru, Rh, PdSAg5PtAu, Co
, Cu1Cr, and Ni.

(4) (a) Compositional formula HAMB [(AlO2)X(Si0
2),] - Zeolite (also known as mordenite) which is composed of 2H20 (where M is a metal and n is its valence; A+nB =X), and is characterized in that M is an alkali metal and/or an alkaline earth metal. include).

(b) Ru, Rh, Pd, Ag, Pt, Au, Co5C
A catalyst comprising a metal or metal oxide selected from u, Cr, and Ni.

(5) L a bxS r XB O3La2. X,
AX, Cu1-y, B↓04YBa2Cu30. A catalyst comprising a velorskite compound represented by .

However, B is one or more elements selected from Co, Mn, Fe, N, Cu, Zr, and AI, and A is Sr, Ce,
B' is one or more elements selected from Zr and Al, and satisfies 0≦X≦0.6.0≦xl≦0°2 and O≦y'≦0°2.

(6) By adding CO as a reducing agent to the catalyst in which the alkali metal in ZSM-5 has been replaced with Cu+2 and bringing it into contact in the coexistence of sulfur dioxide, nitrogen oxides can be converted into N2 with high efficiency.
This method allows reductive decomposition into 02 and 02.

Although it is not clear why the reductive decomposition reaction of nitrogen oxides by CO is promoted in the presence of sulfur dioxide, the present inventors think as follows.

The reaction of reductive decomposition of NOx by CO is NO + CO → N
In the coexistence of oxygen, the CO used in the reaction of 2+CO, is consumed by the reaction of co+”o□→COQ, and becomes NO.
However, since sulfur dioxide adsorbs to the oxygen catalyst adsorption site, CO+HO
In order to suppress the reaction of 2→CO9, NO+CO→N
This is thought to be because 2+C02 reacts selectively.

The preferred reaction temperature for the reaction of the present invention varies depending on the catalyst, but 1
00°C to 800°C. Further, more preferable reaction temperatures are 200°C to 600°C for catalysts (1) to (5), (
In the case of the catalyst 6), the temperature is 400°C to 600°C.

The role of sulfur dioxide in the present invention is as described above, but the temperature of the sulfur dioxide coexisting in the present invention is such that sulfur dioxide prevents oxygen coexisting in the exhaust gas from being adsorbed onto the catalyst, and NO and CO selectively reacts even in the presence of oxygen, and N.

reacts with so2, NO+SO2−+HN 2 +SO
Since a portion of NO is converted to N2 by 0, the concentration is preferably high in order to increase the conversion rate of NO to N2 under conditions of high oxygen concentration. However, it is undesirable to add a large amount of SO9 concentration to exhaust gas because it is harmful.
The content should be 110,000 ppm or less, preferably 1,000 ppm or less.

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.

(Preparation of catalyst) Example 1 Nitrate steel and zinc nitrate were each 6.4g and 30g in terms of oxides.
Ammonia gas was blown into the aqueous solution containing 6 g (solution amount: 250 mK) while sufficiently stirring the solution until the pH reached 7.5 to perform a neutralization precipitation reaction. This regression, water washing, and repulping were performed three times to sufficiently remove free salts. This was dried at 100°C for 18 hours and then fired at 600°C for 3 hours. This baked product was pulverized in a sample mill, 30 g of this pulverized product was weighed, and 100 g of water was added thereto and thoroughly stirred.

A ceramic fiber corrugated honeycomb with a porosity of 81% and a pitch of 4 mm was immersed in this slurry.
An O-ZnO catalyst was supported. At this time, the loading rate was 145%. This was dried with ventilation at room temperature, then dried at 100°C for 18 hours, and then calcined in an air atmosphere at 500°C for 3 hours to obtain a catalyst.

Example 2 Nippon Kagaku mordenite (NM-100P) was heated at 90°C.
Acid treatment was performed under 5N-HCl conditions for 20 hours. After this, filtration, water washing, and repulping were performed three times to sufficiently remove free salts and obtain acid type mordenite. This was weighed in an amount of 30 gfiP, and water was added thereto and thoroughly stirred. The honeycomb used in Example 1 was immersed in this slurry to obtain a mordenite supporting carrier. The loading rate at this time was 158%.

This was immersed in a chloroplatinic acid aqueous solution (12.5 g/gL), dried at room temperature, 100°C for 18 hours, and then 500°C for 3 hours.
Baked for an hour.

Example 3 Weighed 40 g of anatase-type titanium oxide with a specific surface area of 98 d/g and 2.0 g of ruthenium chloride as RuO2, added water thereto, dried with steam, and heated at 500° in air.
It was fired for 13 hours. Grind this in a sample mill,
30g of this pulverized material was weighed and the same procedure as in Example 1 was carried out to obtain a catalyst. At this time, the loading rate was 116%.

Example 4 Iron nitrate and nickel nitrate were each 5°4g in terms of oxide, 3
A catalyst was obtained in the same manner as in Example 1 using an aqueous solution containing 0.6 g (solution amount: 500 -).

At this time, the loading rate was 144%.

Example 5 5.4 g of cobalt nitrate as Co3O4 was weighed out, and 50 J of water was added thereto to obtain a solution. Also, ammonium molybdate is 30.6g1 as MoO2? 100 mft of aqueous ammonia was added to the Pfik to obtain a solution. Ammonium molybdate l'a solution was added to the cobalt nitrate solution to form a precipitate. Thereafter, a catalyst was obtained in the same manner as in Example 1. At this time, the carrier ratio wave was 153%.

Example 6 Ruthenium chloride and chloroauric acid were each weighed in an amount of 0.63 g, and dissolved in a solution containing 200 mL of ethyl alcohol water containing 800+ aK, and while stirring this solution, the titanium oxide used in Example 3 was added. Thoroughly dispersed. This slurry was irradiated with ultraviolet rays with a wavelength of 350 nm for 20 hours at room temperature to precipitate Ru-Au on TiO□. This slurry was filtered, washed with water, and repulped to remove free salts.
After drying at 18°C for 18 hours, the mixture was calcined at 500°C for 3 hours, and the same procedure as in Example 1 was carried out to obtain a catalyst.

Ta.

(1) Gas composition No. 200ppm 02 10% Co 200ppm SO2 ■Oppm ■1100pp ■250pp
m ■1000ppm N2 Balance (2) SV 1000 Hr' (3) Reaction temperature 300℃, 400℃, 600℃, 6
00°C The test results are shown in Table 1.

The values in Table 1 indicate the conversion rate to N2.

Claims (1)

[Claims] A method for removing nitrogen oxides, characterized in that in a method of reductively decomposing nitrogen oxides in gas using CO, sulfur dioxide is allowed to coexist and react in exhaust gas.