JPH04310240A - Catalyst for reducing nitrogen oxide - Google Patents

Abstract

PURPOSE:To reduce efficiently nitrogen oxide of low concentration in an exhaust gas by using a catalyst for reducing nitrogen oxide which is prepared by loading a specified metal oxide on zeolite ion-exchanged with a specific metal ion. CONSTITUTION:An ion M in zeolite expressed by the molecular formula Ma {(AlO2)X(SiO2)y}.ZH2O, where M is alkali metal, alkaline earth metal, or hydrogen, and nA=X ((n) is a valency of M), Y1X>=5}, is partly or totally ion-exchanged for a metal ion selected from Ti<4+>, Zr<4+>,and Sn<4+>. Separately, an aqueous solution of a metal salt, the metal of which is selected from V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, and W, is prepared. The ion-exchanged zeolite, after being immersed in the metal salt aqueous solution to carry the metal salt, is dried and calcinated to obtain the catalyst for reducing nitrogen oxide with NH3.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a catalyst for catalytic reduction of nitrogen oxides when NH3 is used as a reducing agent, and more specifically, the present invention relates to a catalyst for catalytic reduction of nitrogen oxides when NH3 is used as a reducing agent. The present invention relates to a catalyst for catalytic reduction of nitrogen oxides using NH3, which is suitable for use in reducing and removing substances. In particular, the present invention relates to a catalyst for the catalytic reduction of nitrogen oxides with NH3 of low concentration nitrogen oxides.

[Prior art and problems to be solved by the invention] Conventionally,
Nitrogen oxides contained in exhaust gas can be treated by: ■ oxidizing the nitrogen oxides and then absorbing them into alkali; ■ NH3, H
2. It has been removed by methods such as converting it into N2 using a reducing agent such as CO. However, in the case of the method (■), alkali drainage treatment is required to prevent pollution, and the method (2) using NH3 as a reducing agent has high reaction selectivity with nitrogen oxides and generates large-sized fixed substances. It has been put into practical use at power sources (thermal power plants, etc.).
However, there is a problem in that when the concentration of nitrogen oxides in the exhaust gas is less than 100 ppm, the reduction rate decreases. Furthermore, when H2, CO, and hydrocarbons are used as ring agents, they react with O2, which is present in higher concentrations, than with NOX, which is present in low concentrations, so a large amount of reducing agent is required to reduce NOX. I needed it. The present invention has been made in view of the above circumstances, and its purpose is to reduce the low concentration of nitrogen oxides in exhaust gas by using NH3 as a reducing agent. An object of the present invention is to provide a catalyst for catalytic reduction of nitrogen oxides using NH3, which can efficiently reduce nitrogen oxides.

[Means for Solving the Problems] The catalyst for selective reduction of nitrogen oxides (catalytic reduction catalyst) according to the present invention for achieving the above object has the following compositional formula (1): V, Cr, Mn, F to zeolite (A) obtained by ion-exchanging some or all of with metal ions selected from the group consisting of Ti4+, Zr4+ and Sn4+.
oxide of at least one metal selected from the group consisting of e, Co, Ni, Cu, Zn, Nb, Mo and W (B
). MA [(AlO2)X(SiO2)Y]・ZH2O...
(1) [Wherein, ion M is an alkali metal ion, alkaline earth metal ion or hydrogen ion, nA=X (n: valence of ion M), Y/X≧5. ]N according to the present invention
The nitrogen oxide selective reduction catalyst using H3 is produced, for example, as follows. That is, first, using a commercially available zeolite represented by the above formula (1) as a precursor, some or all of the alkali metal ions, alkaline earth metal ions, or hydrogen ions M contained therein are removed by a conventionally known method. , a zeolite (A) represented by the following compositional formula (2) is prepared by ion exchange with a specific metal ion M'. MAM'B [(AlO2)X(SiO2)Y]・ZH2
O...(2) [wherein M' is a metal ion selected from the group consisting of Ti4+, Zr4+ and Sn4+, n1A+
n2B=X (n1, n2: valence of ion M and metal ion M', respectively), Y/X≧5, and B≠0. ] Typical commercial products of the precursor zeolite represented by the above formula (1) include NM-100P (sodium type mordenite, Y/X=8, manufactured by Nippon Kagaku Co., Ltd., trade name), HM
-100P (sodium type mordenite, Y/X=12
, manufactured by Nippon Kagaku Co., Ltd. (trade name), and ZSM-5 (sodium type, Y/X=35, manufactured by Nippon Mobil Shokubai Co., Ltd.). Thus, in the present invention, the raw material zeolite with Y/X≧5 is used because if Y/X<5, the amount of SiO2 in the raw material zeolite is too small, resulting in poor acid resistance and resistance to Ti4+ etc. This is because ion exchange treatment becomes difficult. The zeolite (A) in the present invention includes Ti4+,
It is obtained by ion-exchanging part or all of the ion M with at least one kind of metal ion M' selected from Zr4+ and Sn4+. This ion exchange treatment involves converting the zeolite into predetermined concentrations of Ti4+, Zr4+ and/or Sn4+.
This is done by immersing the sample in an aqueous solution containing it, stirring it for a predetermined period of time, filtering it out, and washing it. By repeating this process an appropriate number of times, ions M in commercially available zeolite can be obtained.
can be ion-exchanged with metal ion M' in a predetermined amount. Instead of the above zeolite (A), the zeolite (A)
Alternatively, Ti
Zeolite (C) supported on at least one metal oxide selected from O2, ZrO2 and SnO2 may be used. Such zeolite (C) contains a predetermined amount of Ti.
The raw material zeolite represented by the above formula (1) is immersed in an aqueous solution of these metal salts containing at least one of Zr4+, Zr4+, and/or Sn4+, and while stirring, NH
3. The precipitate produced by dropping an aqueous alkali solution such as NaOH is filtered, washed, dried, and then calcined at 300 to 700°C. The catalyst thus obtained differs depending on the timing of addition of NH3 and the reaction temperature, but most of the supported metals are supported as metal hydroxides, and upon calcination, they become metal oxides. others,
After impregnating zeolite with the aqueous solution of the metal salt and repeating the drying operation an appropriate number of times,
It can also be obtained by thermally decomposing the above metal salt by firing at 0°C. In the catalyst obtained by this method, most of the supported metals are supported as metal salts, and upon calcination, they become metal oxides. Preferred methods for preparing zeolite (C) include water-soluble titanium salts such as titanium tetrachloride, titanyl sulfate, and titanium sulfate; water-soluble zirconium salts such as zirconium tetrachloride and zirconium sulfate; and water-soluble zirconium salts such as tin tetrachloride and tin sulfate. Zeolite (
Examples include a method in which A) is charged and hydrolyzed by heating to produce precipitates of titanic acid, zirconic acid, and stannic acid within the pores. The most suitable water-soluble metal salts for this method are sulfates such as titanium sulfate, zirconium sulfate, and tin sulfate. This is thought to be due to the fact that when sulfate is used, the solid acidity becomes extremely high. In this way, the zeolite in the present invention is
Since the zeolite contains at least one of Ti4+, Zr4+, and Sn4+ and a metal oxide, its effect as a carrier is fully expressed. The preferred amount of metal oxide supported by these methods is 0 as the metal.
．． It is 1 to 20% by weight. If it exceeds 20% by weight, the activity decreases because the pores of the catalyst are blocked, and if it exceeds 0.1% by weight.
If the amount is less than
Although the details are unknown, it is clear from acid solubility tests and FT-IR analysis that Ti ion exchange is occurring. However, the quantitative ratio is unknown. The above zeolite (A) or (C) contains V, Cr, Mn,
An oxide of at least one metal selected from the group consisting of Fe, Co, Ni, Cu, Zn, Nb, Mo and W (
By supporting B), the catalyst for catalytic reduction of nitrogen oxides using NH3 as a reducing agent according to the present invention can be obtained. A suitable total amount of the metal oxide (B) supported is 0.1 to 20% by weight. Even if it exceeds 20% by weight, the added effect corresponding to the increase in amount cannot be obtained and it is uneconomical, and if it is less than 0.1% by weight, sufficient activity cannot be obtained. The catalyst for catalytic reduction of nitrogen oxides using NH3 as a reducing agent according to the present invention can be formed into various shapes such as a honeycomb shape and a spherical shape by a conventionally known forming method. It may be supported on the previous powdered zeolite (A) or (C), it may be kneaded with the zeolite (A) or (C) during molding, or it may be supported on the zeolite (A) or (C) after molding.
C) may be impregnated. During molding, molding aids, molded body reinforcements, inorganic fibers, organic binders, etc. may be appropriately blended. The preferable addition amount of NH3 varies depending on the nitrogen oxide removal rate and the leaked ammonia concentration, but is about 0.1 to 2 times the molar ratio to the nitrogen oxide concentration. If it is less than 0.1 times, sufficient activity cannot be obtained, and if it exceeds 2 times, the amount of unreacted NH3 discharged increases, which requires post-treatment. The optimal temperature at which the catalyst for selective reduction of nitrogen oxides by NH3 according to the present invention exhibits reduction activity toward nitrogen oxides is as follows:
Although it varies depending on the catalyst type, it is usually 100 to 800 °C,
In this temperature range, the space velocity (SV) is 500-5
It is preferable to allow the exhaust gas to flow through the exhaust gas at a temperature of about 0,000. Note that a more suitable operating temperature range is 300 to 600°C.

[Examples] The present invention will be explained in more detail based on examples below, but the present invention is not limited to the following examples in any way, and can be practiced with appropriate modifications within the scope of the gist thereof. It is possible. (I) Preparation of catalyst (Example 1) Compositional formula: NaX [(AlO2)X・(Si
A commercial product of sodium type mordenite represented by O2)Y]・ZH2O (manufactured by Nippon Kagaku Co., Ltd., product name "NM-100P")
”, Y/X=8) 100g with 0.025 mol/l of Ti
The mixture was immersed in 1 liter of Cl4 aqueous solution and stirred for 24 hours to ion-exchange Na with Ti, followed by filtration and washing with water to obtain a zeolite cake. Then, after drying this cake, 65
It was baked at 0°C for 4 hours. The amount of Ti in the obtained zeolite was 0.4% by weight in terms of TiO2. 50 g of this zeolite was added to 500 ml of a 15.2 g/l copper (II) nitrate aqueous solution, stirred and mixed thoroughly, and then an aqueous sodium hydroxide solution was added until the pH of the solution reached 8 to form a precipitate. I let it happen. This precipitate was filtered, washed with water, dried, and then calcined at 500°C for 3 hours to obtain the catalyst (A-1).
I got it. (Example 2) The catalyst (
A-2) was obtained. (Example 3) In Example 2, instead of NM-100P, composition formula: HX [(AlO2)X・(SiO2)Y]
・Commercial product of hydrogen type mordenite represented by ZH2O (manufactured by Nippon Kagaku Co., Ltd., product name "HM-100P", Y/X = 12
) was used in the same manner as in Example 2 except that the catalyst (A
-3) was obtained. The amount of Ti in the obtained zeolite is Ti
As O2, it was 2.8% by weight. (Example 4) Example 1 except that a TiOSO4 aqueous solution was used in place of the TiCl4 aqueous solution in Example 1.
A catalyst (A-4) was obtained in the same manner as above. The amount of Ti in the obtained zeolite was 0.7% by weight as TiO2. (Example 5) The catalyst (A- 5
) was obtained. (Example 6) Catalyst (A-6) was prepared in the same manner as in Example 3 except that a 18.2 g/l cobalt nitrate aqueous solution was used in place of the copper(II) nitrate aqueous solution. Obtained. (Example 7) Catalyst (A-7) was prepared in the same manner as in Example 3 except that a 19.5 g/l nickel nitrate aqueous solution was used in place of the copper(II) nitrate aqueous solution. Obtained. (Example 8) Catalyst (A-8) was prepared in the same manner as in Example 3 except that a 18.2 g/l manganese nitrate aqueous solution was used in place of the copper(II) nitrate aqueous solution. Obtained. (Example 9) Catalyst (A-9) was prepared in the same manner as in Example 3 except that a 18.3 g/l zinc nitrate aqueous solution was used in place of the copper(II) nitrate aqueous solution. Obtained. (Example 10) Catalyst (A-10) was prepared in the same manner as in Example 3 except that a 26.3 g/l chromium nitrate aqueous solution was used in place of the copper(II) nitrate aqueous solution.
I got it. (Example 11) Zeolite 5 obtained in the same manner as Example 3
0g was immersed in an aqueous solution of vanadyl oxalate containing 142g/l of vanadyl oxalate in terms of V2O5, and after removing the excess aqueous solution, it was dried, and then soaked at 500°C for 3
The catalyst (A-11) was obtained by firing for a period of time. (Example 12) The procedure was repeated in the same manner as in Example 11, except that in Example 11, an ammonium metatungstate aqueous solution containing 142 g/l of ammonium metatungstate in terms of WO3 was used instead of the vanadyl oxalate aqueous solution. , catalyst (A-12) was obtained. (Example 13) In the same manner as in Example 11, except that in Example 11, an ammonium molybdate aqueous solution containing 142 g/l of ammonium molybdate in terms of NoO3 was used instead of the vanadyl oxalate aqueous solution.
A catalyst (A-13) was obtained. (Example 14) The catalyst was prepared in the same manner as in Example 11 except that a niobium oxalate aqueous solution containing 142 g/l of niobium oxalate in terms of Nb2O5 was used in place of the vanadyl oxalate aqueous solution. (A-14) was obtained. (Example 15) In Example 3, instead of the 15.2 g/l copper(II) nitrate aqueous solution, 7.6 g/l copper nitrate (I
I) Same as Example 3 except that an aqueous solution was used,
A catalyst (A-15) was obtained. (Example 16) The procedure was the same as in Example 3 except that 30.4 g/l of copper(II) nitrate aqueous solution was used instead of 15.2 g/l of copper(II) nitrate aqueous solution. Thus, a catalyst (A-16) was obtained. (Example 17) In Example 3, except that an aqueous solution containing 7.6 g/l of copper nitrate and 9.1 g/l of cobalt nitrate was used instead of the 152 g/l aqueous solution of copper(II) nitrate. A catalyst (A-17) was obtained in the same manner as in Example 3. (Example 18) In Example 2, 0.075 mol/liter of TiCl4 aqueous solution was replaced with 0.025 mol/liter of TiCl4 aqueous solution.
A TiO2-supported zeolite was obtained in the same manner as in Example 2, except that 1 liter of TiCl4 aqueous solution was used. The amount of Ti in the obtained zeolite was 7.3% by weight as TiO2. Hereinafter, the catalyst (
A-18) was obtained. (Example 19) Example 2 except that a 0.15 mol/liter TiCl4 aqueous solution was used in place of the 0.025 mol/liter TiCl4 aqueous solution in Example 2.
A zeolite cake was obtained in the same manner. The amount of Ti in the obtained zeolite was 16.7% by weight as TiO2. Hereinafter, the catalyst (A-1
9) was obtained. (Example 20) A zeolite cake was obtained in the same manner as in Example 2, except that a 0.025 mol/liter ZrCl4 aqueous solution was used in place of the TiCl4 aqueous solution. The amount of Zr in the obtained zeolite is Zr
It was 2.9% by weight as O2. Thereafter, a catalyst (A-20) was obtained in the same manner as in Example 2. (Example 21) A zeolite cake was obtained in the same manner as in Example 2, except that a 0.075 mol/liter ZrCl4 aqueous solution was used in place of the TiCl4 aqueous solution. The amount of Zr in the obtained zeolite is Zr
It was 8.1% by weight as O2. Thereafter, a catalyst (A-21) was obtained in the same manner as in Example 2. (Example 22) A zeolite cake was obtained in the same manner as in Example 2, except that a 0.025 mol/liter SnCl4 aqueous solution was used in place of the TiCl4 aqueous solution. The amount of Sn in the obtained zeolite is Sn
It was 3.2% by weight as O2. Thereafter, a catalyst (A-22) was obtained in the same manner as in Example 2. (Example 23) Composition formula: NaX [(AlO2)X・(S
A commercial product of sodium mordenite represented by iO2)Y]・ZH2O (manufactured by Nippon Mobil Co., Ltd., product name "ZSM-
5'', Y/X=35) was immersed in 1 liter of 0.025 mol/liter TiOSO4 aqueous solution and thoroughly stirred. This was heated in an autoclave at a rate of 100°C/hour with stirring and held at 125°C for 1 hour to hydrolyze TiOSO4 and ion exchange Na with Ti, followed by filtration and washing with water. and obtained a zeolite cake. Next, after drying this cake, it was heated at 650°C for 4 hours.
Baked for an hour. The amount of Ti in the obtained zeolite is Ti
It was 2.4% by weight as O2. Thereafter, a catalyst (A-23) was obtained in the same manner as in Example 11. (Comparative example) 100 g of anatase-type titanium oxide with a specific surface area of 85 m2/g and 5 g of vanadyl oxalate aqueous solution in terms of V2O5 were mixed, thoroughly kneaded, dried at 100°C for 15 hours, and then heated at 450°C. After firing for 3 hours, the catalyst (
B-1) was obtained. (II) Evaluation Test For catalysts A-1 to A-23 and B-1 obtained in Examples 1 to 23 and Comparative Example 1, nitrogen oxide catalytic reduction of nitrogen oxide-containing gas was performed under the following test conditions. The removal rate of nitrogen oxides was determined using the following formula. (Test conditions) ■ Gas composition NO 50pp
mNH3 50ppm SO2 100ppm O2 10% H2O 5% N2 Balance ■ Reaction temperature 300℃, 350℃, 40
The 0°C results are shown in Table 1.

Effects of the Invention As explained in detail above, the catalyst for catalytic reduction of nitrogen oxides according to the present invention can efficiently catalytically reduce nitrogen oxides in exhaust gas in the presence of NH3, etc. has excellent unique effects.

Claims (1)

[Claims] Claim 1: Some or all of the ions M in the zeolite represented by the following compositional formula are replaced by Ti4+, Zr4+ and S
Zeolite (A) formed by ion exchange with metal ions selected from the group consisting of n4+, V, Cr, Mn, Fe,
A catalyst for catalytic reduction of nitrogen oxides by NH3, characterized in that it supports an oxide (B) of at least one metal selected from the group consisting of Co, Ni, Cu, Zn, Nb, Mo and W. MA [(AlO2)X(SiO2)
Y]・ZH2O [where ion M is an alkali metal ion, alkaline earth metal ion or hydrogen ion, nA=X
(n: valence of ion M), Y/X≧5. [Claim 2] A zeolite represented by the following compositional formula or a part or all of the ions M in the zeolite are replaced by Ti4+, Zr
Zeolite (A) formed by ion exchange with metal ions selected from the group consisting of 4+ and Sn4+, TiO2,
Zeolite (C
), V, Cr, Mn, Fe, Co, Ni, Cu, Zn
A catalyst for catalytic reduction of nitrogen oxides by NH3, characterized in that it supports at least one metal oxide (B) selected from the group consisting of , Nb, Mo and W. MA [
(AlO2)X(SiO2)Y]・ZH2O [wherein, M
is an ion selected from the group consisting of alkali metal ions, alkaline earth metal ions and hydrogen ions, nA=X(
n: valence of ion M), Y/X≧5. ]