JPH0429747A - Catalyst for nitrogen oxide contact reduction - Google Patents

Abstract

PURPOSE:To obtain a catalyst which is for nitrogen oxide contact reduction and useful for removal of harmful nitrogen oxide in waste gas from a plant, an automobile, etc., by carrying one metal oxide selected from Cr, Fe, etc., on a specified zeolite which is ion-exchanged by a metal ion such as Ti<4+>, and Zr<4+>. CONSTITUTION:A catalyst for nitrogen oxide contact reduction is prepared by either a method of carrying at least one oxide (B) of a group selected from V, Cr, Mn, Co, Ni, Cu, Zn, Nb, Mo, and W on a zeolite (A) which has a composi tion formula I [ion M stands for alkali metal ions, alkaline earth metal ions, or hydrogen ions, nA=X ((n) stands for valence of ions, M), Y/X>=5] and of which a part or the whole of ions, M is ion-exchanged by metal ions selected from a group of Ti<4+>, Zr<4+>, and Sn<4+> or another method of carrying at least one metal oxide of TiO2, ZrO2, and SnO2 on the above-mentioned A component and then carrying B component.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a catalyst for catalytic reduction of nitrogen oxides when hydrocarbons are used as reducing agents, and more specifically, the present invention relates to catalysts for catalytic reduction of nitrogen oxides when hydrocarbons are used as reducing agents. The present invention relates to a catalyst for catalytic reduction of nitrogen oxides using hydrocarbons, which is suitable for use in reducing and removing harmful nitrogen oxides contained in nitrogen oxides.

[Problems to be solved by conventional techniques and inventions] Conventionally,
Nitrogen oxides contained in exhaust gas can be treated by: (1) oxidizing the nitrogen oxides and then absorbing them into an alkali; (2) N H3;
It has been removed by methods such as converting it into N2 using reducing agents such as H2 and CO.

However, when using the method (2), it is necessary to treat alkaline waste liquid to prevent pollution, and when using an alkaline agent such as NH2 as a reducing agent in the method (2), this may react with SOX in the exhaust gas. There is a problem in that salts are produced and the reducing activity of the reducing agent is reduced as a result. In addition, when H2, Co, and hydrocarbons are used as reducing agents, they react with 02, which is present at a higher concentration, than Not, which is present at a lower concentration, so NO
A large amount of reducing agent was required to reduce x.

For this reason, recently, methods have been proposed in which nitrogen oxides are directly decomposed by catalysts without using reducing agents.
Since the nitrogen oxide decomposition activity was low, there was a problem that it could not be put to practical use.

The present invention has been made in view of the above circumstances, and
The purpose of this is that when hydrocarbons are used as reducing agents, nitrogen oxides react selectively with hydrocarbons even in the presence of oxygen. An object of the present invention is to provide a catalyst for catalytic reduction of nitrogen oxides using hydrocarbons, which can efficiently reduce nitrogen oxides.

[Means to solve the problem]

The nitrogen oxide selective reduction catalyst (catalytic reduction catalyst) according to the present invention for achieving the above object converts some or all of the ions M in the zeolite represented by the following compositional formula (1),
Zeolite (A) obtained by ion exchange with metal ions selected from the group consisting of Ti4+, Zr4+ and Sn4+
, V, Cr, Mn, Fe5CoSNiSCu, Zn,
At least one metal oxide (B) selected from the group consisting of NbSMo and W is supported.

Mn [(Af!0x)x (S i Chh l
・ZHz 0-(1) [In the formula, ion M is an alkali metal ion, alkaline earth metal ion or hydrogen ion,
nAxX (n: valence of ion M), Y/X≧5.

), the nitrogen oxide selective reduction catalyst using hydrocarbons according to the present invention 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'.

MA M' * [(Aj!Oth+ (S 1ox)
y] -Z)IzO-...(2) (wherein, M' is a metal ion selected from the group consisting of Ti", ZS" and Sn4+, n+A+nzB=χ(n
+, nz: ion M and metal ion M, respectively
"' valence), Y/X≧5, and B≠0.

A typical commercially available product of the raw material zeolite represented by the above formula (1), which is a precursor, is NM-100PC sodium type mordenite, Y/X = 8, manufactured by Nippon Kagaku Co., Ltd., product name L H
M-100P (sodium type mordenite, Y/X=
12, manufactured by Nippon Kagaku Co., Ltd. (trade name), ZSM-5 (+) rhium type, Y/X=35, manufactured by Nippon Mobil Shokubai Co., Ltd.), and the like.

In this way, in the present invention, the raw material zeolite with Y/X≧5 is used because if Y/X<5, the amount of 5i02 in the raw material zeolite is too small and the acid resistance is poor, and Ti
This is because ion exchange treatment becomes difficult.

The zeolite (A) in the present invention contains at least one metal ion M selected from Ti"Zr'° and Sn".
It can be obtained by ion-exchanging part or all of the ions M with .

This ion exchange treatment converts zeolite into Ti' with a predetermined concentration.
This is carried out by immersing in an aqueous solution containing Zr" and/or Sn", stirring for a predetermined period of time, filtering, and washing. By repeating this process an appropriate number of times, a predetermined amount of ions M in commercially available zeolite can be ion-exchanged with metal ions M°.

The above zeolite) (A) in place of the zeolite (A)
Alternatively, Ti
Zeolite (C) supported on at least one metal oxide selected from O2, Zr0z and SnO2 may be used.

Such zeolite (C) is obtained by immersing the raw material zeolite represented by the above formula (1) in an aqueous solution of these metal salts containing a predetermined amount of at least one of Ti, Zr" and Sn", and stirring the mixture. The precipitate produced by dropping an alkaline aqueous solution such as , NH2, NaOH, etc. is filtered, washed, dried, and then calcined at 300 to 700°C. The catalyst thus obtained differs depending on the time of addition of N 2 H2 and the reaction temperature, but most of the supported metals are supported as metal hydroxides, and upon calcination, they become metal oxides.

In addition, after impregnating zeolite with the aqueous solution of the metal salt and drying it an appropriate number of times,
It can also be obtained by thermally decomposing the above metal salt by firing at 0 to 700°C. The catalyst obtained by this method is
Most of the supported metals are supported as metal salts, and upon firing, they become metal oxides.

As described above, the zeolite of the present invention exhibits a sufficient effect as a carrier because at least one of Ti'°, Zr'' and Sn'' and a metal oxide are present in the zeolite.

The preferred amount of metal oxide supported by these methods is 0.1 to 20% by weight of the metal. When O exceeds 2% by weight, the activity decreases because the pores of the catalyst are blocked, and when O is less than 1% by weight, the effect of the metal oxide is not fully expressed. Although the details of the supported state of Tf and the like are unknown, it has been revealed from acid solubility tests and FT-IR analysis that ion exchange of Ti is occurring. However, the quantitative ratio is unknown.

In the above zeolite (A) or (C), V, Cr, Mn
5Fe, Co, Nj, Cu, Zn, Nb.

By supporting the oxide (B) of at least one metal selected from the group consisting of Mo and W, the catalyst for catalytic reduction of nitrogen oxides using a hydrocarbon as a reducing agent according to the present invention can be obtained.

A preferable total amount of the metal oxide (B) supported is 0°1 to 2
O% by weight. Even if it exceeds 20% by weight, the addition 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 a hydrocarbon as a reducing agent according to the present invention can be formed into various shapes such as a honeycomb shape or a spherical shape by a conventionally known forming method, and the metal oxide (B) can be formed into various shapes such as a honeycomb shape or a spherical shape. The zeolite may be supported on powdered zeolite (A) or (C) before molding, and zeolite (A) may be supported during molding.
) or (C), or further impregnated into zeolite (A) or (C) after molding.

During molding, molding aids, molded body reinforcements, inorganic fibers, organic binders, etc. may be blended as appropriate.

Hydrocarbons 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 increases in the order of alkynes, alkenes, aromatic hydrocarbons, and alkanes. Furthermore, in similar hydrocarbons, the temperature decreases as the number of carbon atoms increases.

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 preferred amount of the hydrocarbon added varies depending on the type of hydrocarbon, but the molar ratio is 0.1 to the concentration of nitrogen oxides.
~2 times as much. If it is less than 0.1 times, it will not be possible to obtain sufficient activity, and if it exceeds 2 times, the amount of unreacted hydrocarbons will increase, so post-treatment is required to deal with this. Become.

The optimal temperature at which the catalyst for selective reduction of nitrogen oxides by hydrocarbons according to the present invention exhibits reducing activity for nitrogen oxides varies depending on the reduction side and catalyst type used, but is usually 100%
~800°C, and in this temperature range, it is preferable to flow the exhaust gas at a space velocity (SV) of about 500 to 50,000. A more suitable working temperature range is 300 to 600″C.

〔Example〕

Hereinafter, the present invention will be explained in more detail based on examples, 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.

(1) Preparation of catalyst (Example 1) Compositional formula: Naz ((AfCh)x ・(SiCh
)7] ・Commercial product of sodium type mordenite represented by ZH2O (manufactured by Nippon Kagaku Co., Ltd., trade name rNM-100P
J, Y/X=8) 100g is 0.025 mol/! of Ti
The Na
After ion-exchanging with Ti, the mixture was filtered and washed with water to obtain a zeolite cake.

This cake was then dried and then baked at 650°C for 4 hours.

The amount of TiO in the obtained zeolite was 0.0 in terms of TiO2.
It was 4% by weight. 50g of this zeolite, 15.2
The mixture was added to 500 g/N of copper nitrate (It) aqueous solution and stirred and mixed thoroughly, and then an aqueous sodium hydroxide solution was added thereto until the pH of the solution reached 8 to form a precipitate. This precipitate was filtered, washed with water, dried, and then heated at 500°C for 3
The catalyst (A-1) was obtained by firing for a period of time.

(Example 2) In Example 1, the catalyst (A-2 ) was obtained.

(Example 3) In Example 2, instead of NM-100P, the composition formula:
Hz ((Aj!0x)x ・(SiCh)
Commercially available hydrogen-type mordenite represented by
Catalyst (A-3) was obtained in the same manner as in Example 2 except that -12) was used.

(Example 4) In Example 1, instead of Ti (44 aqueous solution), Ti
A catalyst (A-4) was obtained in the same manner as in Example 1 except that the OS Oa aqueous solution was used.

(Example 5) In Example 3, instead of copper nitrate (n) aqueous solution, 25
．． A catalyst (A5) was obtained in the same manner as in Example 3, except that a 3 g/l iron nitrate (■) aqueous solution was used.

(Example 6) In Example 3, in place of the copper nitrate (It) aqueous solution, 1
A catalyst (A6) was obtained in the same manner as in Example 3 except that an 8.2 g/l aqueous cobalt nitrate solution was used.

(Example 7) In Example 3, in place of the copper nitrate (It) aqueous solution, 1
A catalyst (A-7) was obtained in the same manner as in Example 3 except that a 9.5 g/l aqueous nickel nitrate solution was used.

(Example 8) In Example 3, instead of copper nitrate (Il) aqueous solution, 1
A catalyst (A8) was obtained in the same manner as in Example 3, except that an 8.2 g/ffi manganese nitrate aqueous solution was used.

(Example 9) In Example 3, in place of the copper nitrate (I[) aqueous solution, 1
8.3g#! A catalyst (A-9) was obtained in the same manner as in Example 3, except that the aqueous zinc nitrate solution was used.

(Example 10) In Example 3, instead of copper nitrate (Il) aqueous solution, 2
A catalyst (A-10) was obtained in the same manner as in Example 3 except that a 6.3 g/l aqueous chromium nitrate solution was used.

(Example 11) 50 g of zeolite obtained in the same manner as in Example 3 was
The catalyst (A-11 ) was obtained.

(Example 12) Same as Example 11 except that in Example 11, an ammonium metatungstate aqueous solution containing 142 g/l of ammonium metatungstate in terms of W O2 was used instead of the vanadyl oxalate aqueous solution. and
A 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 MoO3 conversion was used instead of the vanadyl oxalate aqueous solution. Catalyst (-A-1
3) was obtained.

(Example 14) The same procedure as in Example 11 was carried out except that in Example 11, an aqueous solution of niobium oxalate containing 142 g of niobium oxalate (NbzOs conversion) was used instead of the aqueous solution of vanadyl oxalate. Thus, a catalyst (A-14) was obtained.

(Example 15) Same as Example 3 except that in Example 3, 7.6 g/l copper nitrate (I [) aqueous solution was used instead of 15.2 g/f copper nitrate (n) aqueous solution. and the catalyst (A-15
) was obtained.

(Example 16) In Example 3, 15.2 g/f! copper(II) nitrate
The catalyst (A
-16) was obtained.

(Example 17) In Example 3, 15.2 g/j! copper(II) nitrate
Instead of an aqueous solution, copper nitrate was added at 7.68/f and cobalt nitrate was added at 9.1 g//! A catalyst (A-17) was obtained in the same manner as in Example 3, except that an aqueous solution containing the above was used.

(Comparative Example 1) Calcium carbonate was calcined at 650° C. for 1 hour to prepare calcia log, and thereafter, the same procedure as in Example 1 was carried out to obtain a catalyst (B-1).

(Comparative Example 2) Magnesium hydroxide was calcined at 650°C for 1 hour to prepare 100 g of magnesia, and then the same procedure as in Example 1 was carried out to obtain a catalyst (B-2).

(Comparative Example 3) Aj! in a beaker. (NOzh ・9H2O 3゜1
Add 3g of tetrapropylammonium bromide and an aqueous silica sol solution (SiCh: 31% by weight, Na2O: 0.4% by weight, Alz Oh:
60 g of an aqueous solution containing 0.03% by weight) were added.

Next, 3.12 g of sodium hydroxide was added to this solution.
A solution of OLI& in water was slowly added with stirring. Pour this mixture into an autoclave and heat it to 160°C.
The mixture was stirred for 72 hours for crystallization.

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

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

After repeating the above operation three times in total, it was washed with pure water five times and then dried at 110°C overnight to obtain a catalyst (B-3).

(It) Catalyst AI-A-1 obtained in Evaluation Test Examples 1 to 17 and Comparative Examples 1 to 3
7 and B-1 to B-3, the nitrogen oxide-containing gas was subjected to nitrogen oxide catalytic reduction under the following test conditions, and the conversion rate of nitrogen oxides to N2 was determined by quantifying N2 by gas chromatography. Calculated.

(Test conditions) (1) Gas composition N○ 1% by volume○2 1
0% by volume Reducing agent 1% by volume He Balance (2) Space velocity 1000 1/Hr (3) Reaction temperature 300'C2400°C1500°C or 600°C The results are shown in the table.

(The following is a blank space) From the table, it can be seen that the catalysts for catalytic reduction of nitrogen oxides using hydrocarbons according to the present invention (A-1 to A-17) all have a high conversion rate to N2, whereas the conventional catalysts have a high conversion rate to N2. (B-1 to B-3)
It can be seen that the conversion rate to N2 is generally low at any reaction temperature.

〔Effect of the invention〕

As described above in detail, the catalyst for catalytic reduction of nitrogen oxides using hydrocarbons according to the present invention has excellent and unique properties, such as being able to efficiently catalytically reduce nitrogen oxides in exhaust gas. be effective.

Patent applicant: Sakai Chemical Industry Co., Ltd. Agent Patent Attorney Tomo Matsu Otomo Procedural Amendment (spontaneous) March 15, 1991

Claims (1)

[Claims] 1. Some or all of the ions M in the zeolite represented by the following compositional formula are replaced by Ti^4^+, Zr^4^+ and S
Zeolite (A) formed by ion exchange with metal ions selected from the group consisting of n^4^+, V, Cr, Mn, F
oxide of at least one metal selected from the group consisting of e, Co, Ni, Cu, Zn, Nb, Mo and W (B
) is supported on a catalyst for catalytic reduction of nitrogen oxides by a hydrocarbon. M_A[(AlO_2)_X(SiO_2)_Y]・Z
H_2O [where ion M is an alkali metal ion, alkaline earth metal ion or hydrogen ion, nA=X (n:
valence of ion M), and Y/X≧5. ] 2. Zeolite represented by the following compositional formula or a part or all of the ions M in the zeolite, Ti^4^+, Z
Zeolite (A) obtained by ion exchange with metal ions selected from the group consisting of r^4^+ and Sn^4^+,
V, Cr, Mn, Fe, Co,
A catalyst for catalytic reduction of nitrogen oxides by hydrocarbons, characterized in that it supports an oxide (B) of at least one metal selected from the group consisting of Ni, Cu, Zn, Nb, Mo and W. M_A[(AlO_2)_X(SiO_2)_Y]・Z
H_2O [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
It is. ]