JPH0427428A - Catalyst for contact reduction of nitrogen oxide - Google Patents

Abstract

PURPOSE:To effect contact reduction of nitrogen oxide by using hydrocarbon as a reducing agent in the exhaust gas temp. range from 200 to 500 deg.C by preparing a catalyst containing (a), and a specified catalytic component selected from each group of (b) and (c) described below. CONSTITUTION:TiO2 (a) and metal oxide (b) are preliminarily mixed, molded by a proper method (e.g. extrusion molding, punching into tablets, or forming into spheres), and then calcined at 300-800 deg.C. The calcined product is then immersed in an aq. soln. of soluble salt of metal selected from Ru, Rh, Pd, Ag and Pt or metal oxide of these (c), dried and calcined at 300-800 deg.C. Further, if required, the product is calcined in a reductive atmosphere to obtain a selective reduction catalyst for nitrogen oxides. As for the preferable source material of metal oxide (b) in the form of precursors, water-soluble salt such as hydroxides, nitrate, sulfate, chloride, etc., can be used.

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.

(1ml!I which the prior art and the invention try to solve)
Conventionally, nitrogen oxides contained in exhaust gas have been treated by two methods: (1) oxidizing the nitrogen oxides and then absorbing them in alkali; (2) NH
It has been removed by methods such as converting it into NZ using reducing agents such as i, Hz, and Co.

However, in the case of the method (■), it is necessary to treat alkaline wastewater to prevent pollution, and when an alkaline agent such as NHz is used as a reducing agent in the method (■), this may react with SOx in the exhaust gas. There has been a problem in that salts are produced, resulting in a decrease in the reducing activity of the reducing agent. Furthermore, when H2 and CO1 hydrocarbons are used as reducing agents, they react with 02, which is present in higher concentrations, than with NOX, which is present in lower concentrations, so NO
A large amount of reducing agent was required to reduce x.

For this reason, a method has recently been proposed in which nitrogen oxides are directly decomposed using a catalyst without using a reducing agent.
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. The present invention provides a catalyst for catalytic reduction of nitrogen oxides using hydrocarbons, which can efficiently reduce nitrogen oxides.

(Means for Solving the Problems) A selective reduction catalyst (catalytic reduction catalyst) for nitrogen oxides according to the present invention for achieving the above object includes .TiO2(a),
At least one metal oxide selected from the group consisting of Adz Ox, S I C'z, and Z r 02 (b)
and at least one metal selected from the group consisting of Ru, RhS Pd, Ag, and Pt and/or its metal oxide (c).

The catalyst for selectively reducing nitrogen oxides using hydrocarbons according to the present invention is manufactured, for example, by each of the following manufacturing methods (1), (2), or (3).

(1) First, TiO□ (a) and metal oxide (b) are mixed in advance, molded by an appropriate molding method (extrusion molding, tablet molding, spherical molding, etc.), and then heated at 300 to 800°C. The fired product obtained by firing is treated with Ru, Rh, Pd, Ag and pt.
After being immersed in an aqueous solution of a soluble salt of a metal and/or its metal oxide (c) selected from the group consisting of
Bake at 0-800°C.

If necessary, it may be further fired in a reducing atmosphere.

(2) T i 02 (a) and metal oxide (b)
The salt was dissolved in aqueous solution, and an alkali such as ammonia or sodium hydroxide was added thereto as a precipitant to form a precipitate. After drying the precipitate, it was calcined at 300 to 800°C. The fired product is pulverized and molded by an appropriate molding method (extrusion molding, tablet molding, spherical molding, etc.).Then, after firing at 300 to 800°C as necessary, the molded product is treated with Ru, Rh. , a metal selected from the group consisting of Pd, Ag and pt and/or its metal oxide (c)
300 to 800 after drying.
Bake at °C. If necessary, it may be further fired in a reducing atmosphere.

(3) Dissolve the Ti salt, the metal salt of the metal oxide (b), and the metal salt of the metal and/or its metal oxide (c) in water, etc., and add ammonia, sodium hydroxide, etc. Add an alkali as a precipitant to form a precipitate, dry the precipitate, and then sinter at 300 to 800°C. Then, if necessary, it may be fired at 300 to 800''C, and in some cases, it may be fired in a reducing atmosphere.

Note that (1) to (3) above are examples of methods for preparing the catalyst according to the present invention, and the catalyst according to the present invention may be prepared by methods other than the above-mentioned method. Of course, if the catalyst components are substantially the same, products with equivalent effects can be obtained.

Precursors of Ti01 in the present invention include titanium sulfate, titanium chloride, titanic acid, and the like. As these precipitants, alkali agents such as ammonia or sodium hydroxide are preferable.

Precursors that are preferred raw materials for the metal oxide Φ) in the present invention include water-soluble salts such as hydroxides, nitrates, sulfates, and chlorides. Furthermore, examples of precursors that are preferable raw materials for the metal or metal oxide (c) 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 chikunia, alumina, and silica, molding aid components such as clay, and reinforcing components such as glass fiber may be added. The total amount of these components is 5% of the catalyst components.
It is preferably 0% or less.

The preferred composition ratio of (a)(bl (c1) in the present invention is (a):(b):(c) in atomic ratio of 90 to 5.
0:5-50:0.01-10, more preferably 90-75:10-25:0.1-5. Although the contribution of each of these to the reaction rate is unclear, the results showed the highest reducing properties at these atomic ratios.

Examples of the hydrocarbon in 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 l-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 to be added varies depending on the type of hydrocarbon, but the molar ratio to the concentration of nitrogen oxides is 0.
It is about 1 to 2 times. 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 reducing agent and catalyst type used, but is usually 100°C.
~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 200 to 500°C.

As described above, the catalyst according to the present invention has (a) and (b)
and a catalyst component selected from each group (c), thereby making it possible to catalytically reduce nitrogen oxides using hydrocarbons as a reducing agent in an exhaust gas temperature range of 200 to 500°C. It is.

〔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) Titanium sulfate and aluminum nitrate were each prepared at a concentration of 90% on an oxide basis.
9g was weighed out and dissolved in 11 ion-exchanged water. Ammonia was blown into this aqueous solution with sufficient stirring and added until the pH reached 7.0 to complete the neutralization reaction (neutralization time 1 hour). After that, after aging for 30 minutes, filtering, washing with water, and drying at 100 ° C for 18 hours,
It was baked for 3 hours in SO'C. This baked product was pulverized in a sample mill with a screen of 0.5 φ. 50 g of this pulverized material was poured into 20 Od of water and thoroughly stirred, resulting in a slurry with a porosity of 81% and a pitch of 4 m.
A corrugated honeycomb made of ceramic fiber was immersed, and TiO2-A1203 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 product was immersed in a chloroplatinic acid aqueous solution (33 g/l as pt, dried with ventilation at room temperature, dried at 100°C for 18 hours, and then calcined at 500°C for 3 hours to form a catalyst (AI).
I got it.

(Example 2) Aluminum nitrate and zirconium oxychloride were weighed in an amount of 50 g and 50 g, respectively, based on the oxide, and dissolved in 11 ion-exchanged water. Ammonia was blown into this aqueous solution with sufficient stirring to complete the neutralization reaction (neutralization time: 1 hour) to obtain p) I'7.0. Afterwards, after aging for 30 minutes, filtering, washing with water, and 100° After drying at C for 18 hours, it was fired at 600°C for 3 hours. This fired product was pulverized in a sample mill with a screen having a diameter of 0.5 mm. 50 g of this pulverized material and 50 g of Ti0□ obtained by firing titanium hydroxide at 500"C for 1 hour were put into 400 d of water and pulverized for 30 minutes in a planetary mill. In this slurry, the porosity A ceramic fiber corrugated honeycomb of 81% and pitch 41Il was immersed in Ti(h
AI! , z (h Zr0z was supported on the honeycomb. The supporting rate was 156%. Hereinafter, a catalyst (A-2) was obtained in the same manner as in Example 1.

(Example 3) In Example 2, the concentration of the chloroplatinic acid aqueous solution was 165 g/j as Pt! A catalyst (A-3) was obtained in the same manner as in Example 2, except for the following.

(Example 4) A catalyst was obtained in the same manner as in Example 2, except that a palladium chloride aqueous solution was used in place of the chloroplatinic acid aqueous solution. Two days later, the concentration was 16 g/l, 3
3g/j! , 66 g/j! Each catalyst (A-4-
1), (A-4-2), and (A-4-3) were obtained.

(Example 5) Catalyst (A-5) was prepared in the same manner as in Example 2, except that a ruthenium chloride aqueous solution (33 g/j of Ru was used in place of the chloroplatinic acid aqueous solution). Obtained.

(Example 6) A catalyst (A-6) was obtained in the same manner as in Example 2, except that a rhodium chloride aqueous solution (33 g/l as Rh was used in place of the chloroplatinic acid aqueous solution). .

(Example 7) Catalyst (A-7) was obtained in the same manner as in Example 2, except that a silver nitrate aqueous solution (71 g/j as AgzO) was used in place of the chloroplatinic acid aqueous solution. Ta.

(Example 8) Weighed 50g and 50g of metatitanic acid sol (metatatitanic acid peptized with nitric acid) manufactured by Kakuto Kagaku Co., Ltd. in terms of oxides, mixed them thoroughly, and then heated them at 100°C.
The mixture was dried for 18 hours at 700° C. and then fired for 3 hours at 700°C. This fired product was pulverized in the same manner as in Example 1. Using this pulverized product, a catalyst (A-8) was obtained in the same manner as in Example 1.

(Example 9) A catalyst (A-9) was obtained in the same manner as in Example 8, except that an aqueous palladium chloride solution was used in place of chloroplatinic acid.

(Example 10) Catalysts (A to 10) were obtained in the same manner as in Example 8, except that an aqueous rhodium nitrate solution was used in place of chloroplatinic acid.

(Example 11) In Example 8, except that Snowtex O and metatitanic acid sol were 30 g and 70 g in terms of oxide,
A catalyst (A11) was obtained in the same manner as in Example 8.

(Example 12) In Example 8, except that Snowtex 0 and metatitanic acid sol were set to log 90g in terms of oxide,
A catalyst (A-12) was obtained in the same manner as in Example 8.

(Comparative Example 1) Calcium carbonate was calcined at 65''O<0>C for 1 hour to prepare 100 g of calcia, and then 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 thereafter, the same procedure as in Example 1 was carried out to obtain a catalyst (B-2).

(Comparative Example 3) In a beaker, add 3°1 of A1(NOx)i 9H20.
Add 3 g of tetrapropylammonium bromide and 100 d of water and stir with a magnetic stirrer to dissolve. 0
．． 60 g of an aqueous solution containing 0.3% by weight) were added.

This solution was then added with 3.5% sodium hydroxide. A solution of 12 g of 407 in water was gradually added with stirring. This mixed solution was placed in an autoclave and stirred at 160°C for 72 hours to crystallize it.

After solid-liquid separation of this product, the solid material was washed with water and dried, and sodium-type ZSM-5 zeolite (
SiCh/Al2O3=70) was obtained.

This zeolite was placed in an aqueous solution of 0.05 mol/l copper acetate, stirred day and night, 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).

10 Evaluation Test Examples 1 to 12 and Comparative Examples 1 to 3 Catalysts A-1 to A-
For No. 12 and B-1 to B-3, nitrogen oxide catalytic reduction of the nitrogen oxide-containing gas was performed under the following test conditions,
The conversion rate of nitrogen oxides to N2 was calculated by quantifying N2 by gas chromatography.

(Test conditions) (1) Gas composition NO1 volume %02 10 volume % Reduction side 1 volume % He balance (2) Space velocity 1000 1/Hr (3) Reaction temperature 200°C1300°C1400°C or 500°C Show the results Shown below.

(Hereinafter, 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-12) 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 NZ 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.

Claims (1)

[Claims] 1. TiO_2(a), Al_2O_3, SiO_2
, at least one metal oxide selected from the group consisting of ZrO_2 (b), and at least one metal selected from the group consisting of Ru, Rh, Pd, Ag, and Pt and/or its metal oxide (c) A catalyst for catalytic reduction of nitrogen oxides using hydrocarbons.