JPH07114965B2 - Nitrogen oxide catalytic reduction catalyst - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a catalyst for catalytic reduction of nitrogen oxides when a hydrocarbon is used as a reducing agent, more specifically, in exhaust gas emitted from factories, automobiles, etc. The present invention relates to a catalyst for catalytic reduction of nitrogen oxides with hydrocarbons, which is suitable for use in reducing and removing harmful nitrogen oxides contained in.

[Problems to be Solved by Prior Art and Invention]

Conventionally, the nitrogen oxide contained in the exhaust gas is a method of oxidizing the nitrogen oxide and then absorbing it in an alkali.
It has been removed by a method of converting to N ₂ using a reducing agent such as H ₃ , H ₂ and CO.

However, in the case of the method of (1), it is necessary to perform drainage treatment of alkali for the prevention of pollution, and in the case of using an alkali agent such as NH ₃ as a reducing agent in the method of ( ₃₎ , this reacts with SO _X in the exhaust gas. As a result, salts are produced, and as a result, the reducing activity of the reducing agent is reduced. Moreover, H _2, CO, when using a hydrocarbon as a reducing agent, since they will react with O ₂ present in higher concentration than NO _X present in low concentrations, a large amount in order to reduce the NO _X Needed a reducing agent.

Therefore, recently, a method of directly decomposing nitrogen oxides by a catalyst without using a reducing agent has been proposed,
Since the activity of decomposing nitrogen oxides is low, there is a problem that it cannot be put to practical use.

The present invention has been made in view of the above circumstances,
The purpose is that when a hydrocarbon is used as a reducing agent, nitrogen oxides selectively react with the hydrocarbon even in the coexistence of oxygen, so that a large amount of hydrocarbon in the exhaust gas is not used. It is intended to provide a catalyst for catalytic reduction of nitrogen oxides by hydrocarbons, which can efficiently reduce nitrogen oxides.

[Means for Solving the Problems]

A selective reduction catalyst for nitrogen oxides (catalytic reduction catalyst) according to the present invention for achieving the above object is a part or all of the ions M in the zeolite represented by the following composition formula (1):
Ti ^4+, the Zr ⁴⁺ and Sn consisting ⁴⁺ formed by ion exchange in a more selected metal ion group zeolite (A), V, Cr,
An oxide (B) of at least one metal selected from the group consisting of Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo and W is carried.

M _A [(AlO ₂ ) _X (SiO ₂ ) _Y ] .ZH ₂ O (1) [wherein, the ion M is an alkali metal ion, an alkaline earth metal ion or a hydrogen ion, nA = X (n: ion) The valence of M), and Y / X ≧ 5. The nitrogen oxide selective reduction catalyst with hydrocarbon according to the present invention is produced, for example, as follows.

That is, first, a commercially available zeolite represented by the above formula (1) is used as a precursor, and a part or all of alkali metal ions, alkaline earth metal ions or hydrogen ions M contained therein are contained by a conventionally known method. Then, the zeolite (A) represented by the following composition formula (2) is prepared by ion-exchange with a specific metal ion M ′.

M _A M ′ _B [(AlO ₂ ) _X (SiO ₂ ) _Y ] · ZH ₂ O (2) [In the formula, M ′ is selected from the group consisting of Ti ⁴⁺ , Zr ⁴⁺ and Sn ^4+. Metal ions, n ₁ A + n ₂ B = X (n ₁ and n ₂ : valences of the ion M and the metal ion M ′, respectively), Y / X ≧ 5, B ≠
It is 0. As a typical commercially available product of the raw material zeolite represented by the above formula (1) which is a precursor, 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), ZSM-5 (sodium type, Y / X = 35, manufactured by Nippon Mobil Catalyst Co., Ltd.) and the like.

Thus, in the present invention, to use a raw material zeolite Y / X ≧ 5, Y / X <intended 5, the amount of SiO ₂ in the raw material zeolite is too low acid resistant bad Ti ⁴⁺ This is because it becomes difficult to perform the ion exchange treatment on the above.

Zeolite (A) in the present invention includes Ti ⁴⁺ , Zr ⁴⁺ and
It can be obtained by ion exchanging a part or all of the ion M with at least one metal ion M ′ selected from Sn ⁴⁺ .

This ion-exchange treatment uses zeolite with a predetermined concentration of Ti ⁴⁺ ,
It is carried out by immersing in an aqueous solution containing Zr ⁴⁺ and / or Sn ⁴⁺ , stirring for a predetermined time, and then filtering and washing. The ion M in the commercially available zeolite can be exchanged with the metal ion M ′ by a predetermined amount by repeating this treatment an appropriate number of times.

Instead of the above zeolite (A), the zeolite (A) or a commercially available zeolite represented by the above formula (1) may be added with TiO ₂ ,
At least one metal oxide selected from ZrO ₂ and SnO ₂ may be used zeolite (C) composed by supporting a.

Such zeolite (C) contains a certain amount of Ti ⁴⁺ , Zr ⁴⁺ and
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 Sn ⁴⁺ ,
While stirring, a precipitate formed by dropwise addition of an aqueous alkaline solution such as NH ₃ or NaOH is filtered, washed, and dried, then 300 to 7
Obtained by firing at 00 ° C. The catalyst thus obtained varies depending on the time of introduction of NH _{3 and the} like and the reaction temperature, but most of the supported metals are supported as metal hydroxides, and upon firing, they become metal oxides.

In addition, after the zeolite is impregnated with the aqueous solution of the metal salt, the drying operation is repeated an appropriate number of times, and then 300
It can also be obtained by firing at ~ 700 ° C to thermally decompose the metal salt. In the catalyst obtained by this method, most of the supported metals are supported as metal salts, and upon firing, they become metal oxides.

Suitable methods for preparing zeolite (C) include water-soluble titanium salts such as titanium tetrachloride, titanyl sulfuric acid and titanium sulfate; water-soluble zirconium salts such as zirconium tetrachloride and zirconium sulfate; water-soluble tin tetrachloride and tin sulfate. Zeolite (A) is put into an aqueous solution of water soluble tin salt,
It is hydrolyzed by heating, and titanic acid, zirconic acid, etc.
A method of producing a precipitate of stannic acid can be mentioned. The most suitable water-soluble metal salt in this method is a sulfate such as titanium sulfate, zirconium sulfate, tin sulfate. It is considered that the solid acidity becomes extremely high when the sulfate is used.

As described above, in the zeolite of the present invention, since at least one of Ti ⁴⁺ , Zr ⁴⁺ and Sn ⁴⁺ and the metal oxide are present in the zeolite, the effect as a carrier is sufficiently exhibited.

The preferable loading amount of the metal oxide supported by these methods is 0.1 to 20% by weight as a metal. If it exceeds 20% by weight, the pores of the catalyst are clogged to lower the activity, and if it is less than 0.1% by weight, the effect of the metal oxide is not sufficiently exhibited. The supported state of supported Ti and the like is not known in detail, but an acid solubility test, FT-
IR analysis reveals that Ti ion exchange is taking place. However, the amount ratio is unknown.

V, Cr, Mn, F in the above zeolite (A) or (C)
Nitrogen oxidation using the hydrocarbon according to the present invention as a reducing agent by supporting an oxide (B) of at least one metal selected from the group consisting of e, Co, Ni, Cu, Zn, Nb, Mo and W. A catalyst for material catalytic reduction is obtained.

The preferable total supported amount of the metal oxide (B) is 0.1 to 20% by weight. If it exceeds 20% by weight, it is uneconomical because the effect of addition according to the increase is not obtained, and if it is less than 0.1% by weight, sufficient activity cannot be obtained.

The catalyst for catalytic reduction of nitrogen oxides using the hydrocarbon according to the present invention as a reducing agent can be molded into various shapes such as a honeycomb shape and a spherical shape by a conventionally known molding method, and the metal oxide (B) is It may be supported on powdery zeolite (A) or (C) before molding, may be kneaded with zeolite (A) or (B) at the time of molding, and further, zeolite (A) or (C) after molding. ) May be impregnated.

At the time of molding, a molding aid, a molded body reinforcing material, an inorganic fiber, an organic binder and the like may be appropriately mixed.

Examples of the hydrocarbon used in the practice of the present invention include aliphatic hydrocarbons such as alkanes, alkenes and alkynes, aromatic hydrocarbons and the like.

The temperature at which the selective reduction reaction occurs is higher in the order of alkyne <alkene <aromatic hydrocarbon <alkane. Further, in the same type of hydrocarbon, the temperature becomes lower as the carbon number becomes larger.

Examples of suitable hydrocarbons include lower alkynes such as acetylene, methylacetylene and 1-butyne, lower alkenes such as ethylene, propylene, isobutylene, 1-butene and 2-butene, and lower dienes such as butadiene and isoprene.

The suitable addition amount of the above-mentioned hydrocarbon varies depending on the kind of the hydrocarbon, but is 0.1 to 0.1 by molar ratio with respect to the concentration of nitrogen oxides.
It is about twice. If it is less than 0.1 times, sufficient activity cannot be obtained, and if it exceeds 2 times, the amount of unreacted hydrocarbons discharged becomes large, so post-treatment for treating this is required.

The optimum temperature at which the catalyst for selective reduction of nitrogen oxides by hydrocarbons according to the present invention exhibits reduction activity with respect to nitrogen oxides varies depending on the reducing agent and catalyst species used, but is usually 100.
~ 800 ℃, in this temperature range space velocity (S
V) It is preferable to let the exhaust gas flow at about 500 to 50,000. A more suitable operating temperature range is 300 to 600 ° C.

〔Example〕

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to the following examples and can be carried out by appropriately changing the scope without changing the gist thereof. Is.

(I) Preparation of catalyst (Example 1) Compositional formula: Na _X [(AlO ₂ ) _X. (SiO ₂ ) _Y ] .ZH ₂ O A commercially available sodium-type mordenite (manufactured by Nippon Kagaku Co., Ltd.,
Product name "NM-100P", Y / X = 8) 100 g of 0.025 mol /
It was immersed in a TiCl ₄ aqueous solution 1 and stirred for 24 hours to ion exchange Na with Ti, then filtered and washed with water to obtain a cake of zeolite.

Next, the cake was dried and then baked at 650 ° C. for 4 hours.

The amount of Ti in the obtained zeolite is 0.4% by weight in terms of TiO _2.
Met. 50 g of this zeolite was mixed with 15.2 g / copper nitrate (I
I) The mixture was placed in 500 ml of an aqueous solution and thoroughly mixed with stirring, and then an aqueous solution of sodium hydroxide was added thereto until the pH of the liquid reached 8, to form a precipitate. The precipitate was filtered, washed with water, dried and then calcined at 500 ° C. for 3 hours to obtain the catalyst (A-1).
Got

(Example 2) Example 1, after the ion exchange, an excess of Ti was neutralized with aqueous ammonia, except that is 2 wt% on the TiO ₂ in the same manner as in Example 1, the catalyst (A- 2) was obtained.

(Example 3) In Example 2, instead of NM-100P, a composition formula: H _X [(A
lO ₂ ) _X · (SiO ₂ ) _Y ] · ZH ₂ O A commercial product of hydrogen-type mordenite (manufactured by Nippon Kagaku Co., Ltd., trade name “HM-100P”,
In the same manner as in Example 2 except that Y / X = 12) was used,
A catalyst (A-3) was obtained.

The amount of Ti in the obtained zeolite was 2.8% by weight as TiO _2.
Met.

(Example 4) A catalyst (A) was obtained in the same manner as in Example 1 except that an aqueous TiOSO ₄ solution was used instead of the aqueous TiCl ₄ solution.
-4) was obtained.

The amount of Ti in the obtained zeolite is 0.7% by weight as TiO _2.
Met.

(Example 5) In Example 3, instead of the copper (II) nitrate aqueous solution, 25.3
A catalyst (A-5) was obtained in the same manner as in Example 3 except that a g / iron (III) nitrate aqueous solution was used.

(Example 6) In Example 3, instead of the copper (II) nitrate aqueous solution, 18.2
Example 3 except that a g / cobalt nitrate aqueous solution was used.
A catalyst (A-6) was obtained in the same manner as in.

(Example 7) In Example 3, instead of the copper (II) nitrate aqueous solution, 19.5
Example 3 except that an aqueous solution of nickel nitrate of g / was used.
A catalyst (A-7) was obtained in the same manner as in.

(Example 8) In Example 3, instead of the copper (II) nitrate aqueous solution, 18.2
Example 3 except that a g / manganese nitrate aqueous solution was used.
A catalyst (A-8) was obtained in the same manner as in.

(Example 9) In Example 3, instead of the copper (II) nitrate aqueous solution, 18.3
A catalyst (A-9) was obtained in the same manner as in Example 3 except that a g / zinc nitrate aqueous solution was used.

(Example 10) In Example 3, instead of the copper (II) nitrate aqueous solution, 26.3
A catalyst (A-10) was obtained in the same manner as in Example 3 except that an aqueous g / chromium nitrate solution was used.

(Example 11) 50 g of zeolite obtained in the same manner as in Example 3 was immersed in an aqueous vanadyl oxalate solution containing 142 g / vanadyl oxalate in terms of V ₂ O ₅ to remove excess aqueous solution, and then dried. And then calcined at 500 ° C. for 3 hours to give the catalyst (A-1
1) got.

Example 12 In Example 11, instead of the vanadyl oxalate aqueous solution,
A catalyst (A-12) was obtained in the same manner as in Example 11 except that an ammonium metatungstate aqueous solution containing 142 g / mole ammonium metatungstate in terms of WO ₃ was used.

(Example 13) In Example 11, instead of the vanadyl oxalate aqueous solution,
A catalyst (A-13) was obtained in the same manner as in Example 11 except that an aqueous ammonium molybdate solution containing 142 g / ammonium molybdate in terms of MoO ₃ was used.

(Example 14) In Example 11, instead of the vanadyl oxalate aqueous solution,
A catalyst (A-14) was obtained in the same manner as in Example 11 except that an aqueous niobium oxalate solution containing 142 g / niobium oxalate in terms of Nb ₂ O ₅ was used.

(Example 15) In the same manner as in Example 3 except that instead of 15.2 g / copper (II) nitrate aqueous solution, 7.6 g / copper (II) nitrate aqueous solution was used, a catalyst ( A-15) was obtained.

(Example 16) In the same manner as in Example 3 except that 30.4 g / copper (II) nitrate aqueous solution was used instead of 15.2 g / copper (II) nitrate aqueous solution, the catalyst ( A-16) was obtained.

Example 17 Example 3 was repeated except that an aqueous solution containing 7.6 g / copper nitrate and 9.1 g / cobalt nitrate was used in place of the 15.2 g / copper (II) nitrate aqueous solution. Similarly, a catalyst (A-17) was obtained.

Example 18 A TiO ₂ -supporting zeolite was obtained in the same manner as in Example 2, except that the 0.025 mol / liter TiCl ₄ aqueous solution was used in place of the 0.075 mol / liter TiCl ₄ aqueous solution. .

The amount of Ti in the obtained zeolite was 7.3% by weight as TiO _2.
Met.

Then, a catalyst (A-18) was obtained in the same manner as in Example 2.

(Example 19) Example 2, in place of TiCl ₄ aqueous solution of 0.025 mole / liter, except for using TiCl ₄ aqueous solution of 0.15 mol / l to obtain a zeolite cake in the same manner as in Example 2.

The amount of Ti in the obtained zeolite was 16.7% by weight as TiO _2.
Met.

Then, a catalyst (A-19) was obtained in the same manner as in Example 2.

(Example 20) Example 2, in place of TiCl ₄ aqueous solution, 0.025 mol /
A zeolite cake was obtained in the same manner as in Example 2 except that 1 liter of ZrCl ₄ aqueous solution was used.

The amount of Zr in the obtained zeolite was 2.9% by weight as ZrO _2.
Met.

Then, a catalyst (A-20) was obtained in the same manner as in Example 2.

(Example 21) Example 2, in place of TiCl ₄ aqueous solution, 0.075 mol /
A zeolite cake was obtained in the same manner as in Example 2 except that 1 liter of ZrCl ₄ aqueous solution was used.

The amount of Zr in the obtained zeolite was 8.1% by weight as ZrO _2.
Met.

Then, a catalyst (A-21) was obtained in the same manner as in Example 2.

(Example 22) Example 2, in place of TiCl ₄ aqueous solution, 0.025 mol /
A zeolite cake was obtained in the same manner as in Example 2 except that 1 liter of SnCl ₄ aqueous solution was used.

The amount of Sn in the obtained zeolite was 3.2% by weight as SnO _2.
Met.

Then, a catalyst (A-22) was obtained in the same manner as in Example 2.

(Example 23) Compositional formula: Na _X [(AlO ₂ ) _X · (SiO ₂ ) _Y ] · ZH ₂ O A sodium-type mordenite commercial product (manufactured by Nippon Mobile Co., Ltd., trade name “ZSM-5”). , Y / X = 35) 100 g 0.025 mol /
It was immersed in 1 liter of an aqueous TiOSO ₄ solution and sufficiently stirred. 10 while stirring in an autoclave
The temperature is raised at a heating rate of 0 ° C / hour and held at 125 ° C for 1 hour.
After OSO ₄ was hydrolyzed and Na was ion-exchanged with Ti, it was filtered and washed with water to obtain a zeolite cake. Next, the cake was dried and then baked at 650 ° C. for 4 hours.

The amount of Ti in the obtained zeolite was 2.4% by weight as TiO _2.
Met.

Then, a catalyst (A-23) was obtained in the same manner as in Example 2.

(Comparative Example 1) Calcium carbonate was calcined at 650 ° C for 1 hour to calcia 100.
g, and thereafter, in the same manner as in Example 1, the catalyst (B-
1) was obtained.

(Comparative Example 2) Magnesia (100 g) was prepared by calcining magnesium hydroxide at 650 ° C for 1 hour. Thereafter, in the same manner as in Example 1, a catalyst (B-2) was obtained.

(Comparative Example 3) beaker, _{Al (NO 3) 3 · 9H} 2 O and 3.13g and water 100ml
While stirring and dissolving with a magnetic stirrer, 7.98 g of tetrapropylammonium bromide and an aqueous solution of silica sol (SiO ₂ : 31% by weight, Na ₂ O: 0.4% by weight, Al ₂ O ₃ : 0.0
60 g of an aqueous solution containing 3% by weight) was added.

Then, a solution of 3.12 g of sodium hydroxide in 40 ml of water was gradually added to this solution while stirring. This mixed solution was charged into an autoclave and stirred at 160 ° C. for 72 hours for crystallization.

After solid-liquid separation of this product, the solid was washed with water and dried to obtain a ZSM-5 zeolite with Y / X = 35 as a base.

This ZSM-5 zeolite was placed in an aqueous solution of 0.05 mol / liter of copper acetate, stirred for 24 hours, and then centrifuged.

The above operation was repeated 3 times in total, washed with pure water 5 times, and then dried at 110 ° C. overnight to obtain a catalyst (B-3).

Comparative Example 4 A zeolite cake was obtained in the same manner as in Example 2 except that the 0.025 mol / liter TiCl ₄ aqueous solution was used in place of the 0.50 mol / liter TiCl ₄ aqueous solution.

The amount of Ti in the obtained zeolite was 31.4% by weight as TiO _2.
Met.

Hereinafter, a catalyst (B-4) was obtained in the same manner as in Example 2.

Comparative Example 5 A zeolite cake was obtained in the same manner as in Example 2 except that the 0.025 mol / liter TiCl ₄ aqueous solution was used in place of the 0.50 mol / liter ZrCl ₄ aqueous solution.

The amount of Zr in the obtained zeolite was 37.1% by weight as ZrO _2.
Met.

Hereinafter, a catalyst (B-5) was obtained in the same manner as in Example 2.

(II) Evaluation test Catalysts A-1 to A-23 obtained in Examples 1 to 23 and Comparative Examples 1 to 5
For B-1 to B-5, the nitrogen oxide-containing gas was subjected to nitrogen oxide catalytic reduction under the following test conditions, and the conversion rate of nitrogen oxide to N ₂ was measured by gas chromatography.
N ₂ was quantified and calculated.

(Test conditions) (1) Gas composition NO 1 volume% O ₂ 10 volume% Reducing agent 1 volume% He balance (2) Space velocity 1000 1 / Hr (3) Reaction temperature 300 ℃, 400 ℃, 500 ℃ or 600 ℃ The results are shown in the table.

From the table, all of the catalysts for catalytic reduction of nitrogen oxides by hydrocarbons (A-1 to A-23) according to the present invention have a high conversion rate to N ₂ , whereas the conventional catalyst (B-1 ~ B-5) is
It can be seen that the conversion rate to N ₂ is generally low at any reaction temperature.

〔The invention's effect〕

As described above in detail, the catalyst for catalytic reduction of nitrogen oxides by hydrocarbons according to the present invention is capable of efficiently catalytically reducing nitrogen oxides in exhaust gas. Produce an effect.

Claims (2)

[Claims] 1. A part or all of the ion M in the zeolite represented by the following composition formula is ion-exchanged with a metal ion selected from the group consisting of Ti ⁴⁺ , Zr ⁴⁺ and Sn ^4+. Zeolite (A) with V, Cr, Mn, Fe, Co, Ni, Cu, Zn, N
A catalyst for catalytic reduction of nitrogen oxides by hydrocarbons, which comprises an oxide (B) of at least one metal selected from the group consisting of b, Mo and W. M _A [(AlO ₂ ) _X (SiO ₂ ) _Y ] ZH ₂ O [wherein, the ion M is an alkali metal ion, an alkaline earth metal ion or a hydrogen ion, nA = X (n: the valence of the ion M) , Y / X ≧ 5. ] 2. A zeolite represented by the following composition formula or a part or all of the ions M in the zeolite are ^replaced with Ti ⁴⁺ and Zr.
Zeolite (A) formed by ion-exchange with a metal ion selected from the group consisting of ⁴⁺ and Sn ^{4+ is added} to TiO ₂ , ZrO ₂ and
Zeolite (C) carrying at least one metal oxide selected from the group consisting of SnO _{2 is} mixed with V, Cr, Mn,
Nitrogen oxide catalytic reduction by hydrocarbons, characterized in that it carries an oxide (B) of at least one metal selected from the group consisting of Fe, Co, Ni, Cu, Zn, Nb, Mo and W. Catalyst. M _A [(AlO ₂ ) _X (SiO ₂ ) _Y ] .ZH ₂ O [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 the ion M), Y / X ≧ 5. ]