JPS63126560A - Catalyst for catalytic reduction of nox - Google Patents

Abstract

PURPOSE:To prevent the degradation in activity by catalyst poisons, more particularly SOx and arsenic in an exhaust gas by depositing a catalytically active component consisting of titanium and transition metal on zeolite having specific component ratios. CONSTITUTION:The catalytically active component (e.g., copper, V, Mo, W, iron consisting of the titanium and transition metal is deposition on the zeolite having >=10 (SiO2/Al2O3) ratio to form the catalyst for removing the Nox in the exhaust gas. As a result, the catalyst which is less deteriorated by the catalyst poisons, more particularly SOx and arsenic in the exhaust gas is obtd. Denitrsation of the exhaust gas contg. a large amt. of the co-existing volatile catalyst poisons such as arsenic and selenium compd. and SOx with which the deterioration in the catalyst activity if unavoidable in long-period use in the case of the conventional zeolite catalyst deposited with the transition metal element is thus permitted in the state of maintaining the stable catalyst activity for a long period of time.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention deals with nitrogen oxides (hereinafter referred to as NOx) in exhaust gas.
The present invention relates to a catalyst for removing nitrogen oxides (denitrification catalyst), and particularly to a catalyst for removing nitrogen oxides (denitrification catalyst) that is not easily deteriorated by catalyst poisonous substances in exhaust gas.

(Prior Art) Since NOx emitted from power plants, sintering furnaces, various chemical factories, automobiles, etc. is considered to be a causative agent of photochemical smog, an effective means for treating it is desired. Conventionally, many (
Among the proposed flue gas denitrification methods, the NOx catalytic reduction method uses NH3 as a reducing agent because NH3 selectively reacts with NOx even if the flue gas contains 1% or more of 02 by volume. This method is considered advantageous in that it requires less.

As catalysts used in this method, catalysts in which a transition metal compound is supported on a carrier such as activated alumina, silica gel, alumina, zeolite, or titanium oxide are known.

Among these, those currently in practical use are
The main component is titanium oxide as typified by No. 0-51966 and JP-A-52-122293, and vanadium (■
), molybdenum (Mo), tungsten (W), etc. These catalysts are excellent in that they are not affected by sulfur oxides in exhaust gas. Deterioration caused by oxides such as krillam and arsenic was not taken into account.For this reason, coal containing a large amount of minerals and crude oil produced in China are used as fuel, and when the concentration of the volatile substances in the exhaust gas increases, the catalyst A problem arose in that the activity of

This kind of deterioration can be alleviated to some extent by using a zeolite-based catalyst that allows active ingredients to be introduced into the micropores while preventing the volatile oxidizing substances from diffusing. Patent applications have been filed (Japanese Patent Application No. 172508/1982, Japanese Patent Application No. 1725/1983)
No. 09, etc.).

Additionally, among zeolite catalysts, those with a low Si○z/Al2O3 ratio (10 or less) may have the problem that their catalytic activity is reduced by acidic substances (especially sulfur oxides 5Ox) contained in coal. Do you get it. This is thought to be because the acidic substance reacts with the aluminum compound in the zeolite and destroys its structure. On the other hand, 5i02
It was found that those with a high /Al2O3 ratio (10 or more) were less likely to be degraded by acidic substances, and the present inventors found that 5i02/
A catalyst using zeolite with an Al103 ratio of 10 or more has been investigated. The catalysts disclosed in the above two applications have extremely high durability against volatile oxidizing substances such as arsenic.
It is also a zeolite-based catalyst that exhibits little deterioration with respect to SOx.

(Problem to be solved by the invention) However, it has been found that even if such a zeolite catalyst is used, a decrease in catalytic activity is unavoidable when exposed to SOx generated during combustion for a long time. . This is considered to be because SOx coats the catalyst surface or reacts with the catalytically active metal. Therefore, in order to prevent a decrease in activity due to SOx, it is necessary to use a catalyst that has active sites that are difficult for SOx to enter or be coated with, or that are difficult to react with SOx.

An object of the present invention is to develop a zeolite-based catalyst that has high resistance to SOx while maintaining high resistance to volatile oxidizing substances (particularly arsenic oxide) in order to prevent a decrease in activity due to SOx.

(Means for Solving the Problems) The present inventors have found that the above problems can be solved by making zeolite support titanium and a metal element that is a catalytically active component. That is, in a catalyst that removes nitrogen oxides from exhaust gas, S i02 /AJz 0
Zeolite with a ratio of 3 to 10 or more is combined with titanium (typically titanium oxide) and transition metals (copper, copper, etc.) that are catalytically active components.
It is characterized by supporting one or more elements selected from vanadium, molybdenum, tungsten, and iron.

The zeolite used in the present invention is one that has a high silica composition (S io2/A1z Oa ratio of 10 or more) and exists stably. Examples include mordenite, ferrierite, and the conventionally known ZSM-5 published by Mopil Oil.

On the other hand, titanium compounds include titanate esters such as methyl titanate, ethyl titanate, and propyl titanate;
Alternatively, titanium chloride such as titanium trichloride and titanium tetrachloride can be used.

In addition, copper (Cu), vanadium (
■), molybdenum (Mo), tungsten (W), iron (
The transition metal compounds (Fe) can be used alone or in combination. Examples of the transition metal compounds include oxides, acidic oxide salts, nitrates, sulfates, halides, hydroxides, organic acid salts, alcoholades, and the like.

To prepare the catalyst, first, if titanium is to be introduced into the zeolite, titanate ester or titanium chloride is introduced into the zeolite by ion exchange, impregnation, or vacuum fujiguri, and if necessary, it is placed in a closed, constant humidity container. hydrolyzed inside. After that, 1
After gradually drying at a temperature of about 00°C or lower, and then sufficiently drying at a temperature of about 200°C or lower, under an inert gas or air atmosphere, below 800°C, preferably from 300°C In the range of 700℃, usually 1
Zeolite into which titanium (Ti) is introduced (hereinafter abbreviated as Ti-zeolite) is obtained by firing for 1 to 10 hours. The above-mentioned transitional total bending compound, which is an active ingredient, is added to the Ti-zeolite thus obtained by a method such as ion exchange or impregnation, and after thoroughly drying at a temperature of about 200°C or lower, inert gas, or under an air atmosphere, below 800°C, preferably from 300°C to 700°C
A zeolite catalyst can be obtained by firing within a range of 1 to 10 hours, usually for 1 to 10 hours.

The zeolite catalyst prepared in this way can be directly used as
Alternatively, molding is performed after adding a binder such as TiO2. The shape of the molded product can be arbitrarily selected such as granule, pellet, granule, honeycomb, plate, etc., and a molding machine suitable for each shape, such as an extrusion molding machine, a tablet machine, and a transfer granulation machine, can be used. It is molded using a machine.

The molded product molded as described above is then heat-treated. Although the strength of the molded product can be improved by simply drying the molded product by heating it to a temperature of about 100° C. or lower, it is effective to heat the molded product at an even higher temperature.

That is, the heat treatment is usually performed under an inert gas or air atmosphere at a temperature of less than 800°C, preferably from 300°C to 70°C.
The temperature is appropriately selected within the range of 00°C.

Calcination time also affects the physical properties and strength of the catalyst, but
Usually, it can be carried out suitably for 1 to 10 hours.

In order to reduce NOx in exhaust gas using a catalyst manufactured by such a method, a mixed gas of exhaust gas and ammonia gas may be passed through the catalyst at a temperature of 300° C. or higher.

Using the catalyst of the present invention, NOx in the presence of ammonia
When it is reductively decomposed, not only can a high NOx decomposition rate be obtained, but it can also maintain high activity for a long time without being degraded by catalyst poisons in exhaust gas.

Zeolite supporting transition metal elements such as Cu, ■, MO, etc. shows extremely high resistance to volatile oxidizing substances such as arsenic oxide and selenium oxide for a long period of time, but it is resistant to acidic substances,
In particular, when exposed to SOx for a long time, the activity decreases. However, when TiO2, which is known to be highly resistant to SOX, is mixed with other active ingredients (Cu, ■, M
This catalyst introduced into the micropores of zeolite together with transition metal elements such as O) exhibits extremely high resistance to SOx while maintaining high resistance to volatile oxidants. TiO2 previously supported on zeolite and CusV introduced as an active ingredient
It is thought that transition metal elements such as sMo form active sites in the micropores of the zeolite, forming a metal -Ti02), which not only plays a role in the denitrification reaction but also exhibits extremely high SOx resistance.

In addition, TiO2 in the microbore is an active component of Cu.
It is thought that this prevents a reaction between a transition metal element such as V or MO and SOx, or prevents the transition metal element from being coated with SOx and being deactivated.

Next, the present invention will be explained using specific examples.

(Example) In Examples and Comparative Examples, durability tests were conducted using a simulated gas simulating combustion exhaust gas of coal with a high mineral content. The catalyst poison component is sulfur dioxide (S
O3) and arsenic trioxide (AS203) were vaporized and added to the gas.

Gas composition: oxygen 3% by volume, carbon dioxide 12% by volume,
Water 12% by volume, NOx 200ppm, ammonia 240ppm, sulfur dioxide 500ppm, 303
16 ppm, AS203 21) pm, remainder nitrogen. In this test, the above mixed gas was added to 2 ml of the catalyst, which had been molded, calcined, and sieved into 10 to 20 meshes, at a space velocity of 12.
The experiment was carried out by circulating at 0,000 h-1.

The denitrification catalyst performance was measured before and after the above durability test. The NOx content is measured using a chemiluminescent NOx meter.
The NOx decomposition rate (denitrification rate) is N.

The concentration of X was measured before and after addition of ammonia, and calculated using the following formula.

The specific surface area and pore distribution were determined by taking 0.5 g of the calcined and molded catalyst and sifting it into 10 to 20 sieves.
It was measured using a CHROME AUTO3ORI3-1 type gas adsorption test device.

The specific surface area has a relative pressure (P/Po) of 0.025 to 0.
Calculated by the B, E, T multi-point method in 3.

In addition, H-type mordenite is TSZ- manufactured by Toyo Soda Kogyo ■.
650XOA was used.

H-type mordenite, H-type mordenite supported with a titanium compound (vacuum evaporation method - Q with Ti as TiO2,
Table 1 shows the specific surface areas of 4 wt % (containing 4 wt %) and 3 wt % copper (Cu). Mordenite supporting titanium also exhibits a decrease in specific surface area, similar to mordenite supporting copper. From this, titanium (Ti
) is also considered to be contained within the micropores like copper (Cu).

Table 1 Example 1 Titanium trichloride aqueous solution (Ti concentration 3.0 g/1) 11,
H-type Mordenai with an average particle size of 60 mesh) (S i
02 /A1203 = 23, pore size 7 people) 100g
is added and stirred at 80° C. for 24 hours under a nitrogen atmosphere to perform sufficient ion exchange. After that, filter and wash with water,
After drying at ℃, it was fired at 500℃ for 2 hours in an air atmosphere to produce mordenite containing titanium (Ti) (hereinafter referred to as Ti-
Abbreviated as mordenite. ) was obtained. The TiO2 content was 0.3 wt%.

Next, take 10g of this Ti-mordenite and
After drying, this was formed into a cylindrical shape of 10φ×3L using a press molding machine, and then fired at 500° C. for 2 hours in an air atmosphere. Crush this and make 10-2
The material sieved to 0 mesh was used as a catalyst. The Cu content was 3 wt%.

Example 2 H-type mordenite (Si02
/ A1203-23, pore size 7) was gradually dried while kneading 100 g of titanium tetrachloride aqueous solution (Tj concentration 8 pm). Then, after drying at 180°C for 3 hours, at 500°C for 2 hours in an air atmosphere. Ti-mordenite was obtained by sintering at the bottom, and the TiO2 content was 15 wt%.

Next, this Ti-mordenite was catalyzed by the same method as in Example 1.

Examples 3 to 5 In place of the titanium tetrachloride aqueous solution in Example 2, 2-propertool solutions of methyl titanate, ethyl titanate, and propyl titanate (Tt concentration 88 g/l) were used, respectively. The catalyst was prepared by the method.

Examples 6 to 7 Catalysts were prepared in the same manner as in Example 1 except that mordenite was replaced with ferrierite and conventionally known ZSM-5.

Example 8 H-type mordenite (Si02
/A12 03 =23, pore diameter 7) After deaerating 100 g of the sample to 3 Q mTorr or less using a vacuum deaerator, titanium tetrachloride vapor is introduced at room temperature. After leaving it for 24 hours, take out the mordenite and leave it in a sealed constant humidity container for 24 hours.
Sufficiently hydrolyze titanium tetrachloride. After that, 180
Ti-mordenite was obtained by drying at 500° C. for 3 hours and firing at 500° C. for 2 hours in an air atmosphere. The TiO2 content was 0.7 wt%.

Next, this Ti-mordenite was catalyzed by the same method as in Example 1.

Example 9 A catalyst was prepared in the same manner as in Example 8 except that titanium tetrachloride was replaced with ethyl titanate.

Examples 10 to 13 1 in Example 4. 1 4 g of copper nitrate, 0
.

44g vanadyl sulfate, 0. 5 5 g ammonium molybdate, 0.43 g ammonium tungstate, 1. Using the same method instead of 4 5 g of iron(III) chloride, 1, 3, and 3.3 wt of metal components were added, respectively.
% supported catalyst was prepared.

Example 14 H-type mordenite (S io
z /Aj'z 03 = 23, pore size 7 people) 100g
was impregnated with 11.4 g of copper nitrate, dried, and fired in an air atmosphere at 500° C. for 2 hours to produce mordenite supporting copper (CU) (hereinafter abbreviated as Cu-mordenite).

) was obtained. The content of Cu was 3 wt%.

Next, take 10 g of this Cu-mordenite and impregnate it with 7.15 g of ethyl titanate by diluting it with 2-propatool, and then leave it in a sealed constant humidity container for 24 hours to sufficiently add ethyl titanate. Let it break down.

After that, it was dried at 180℃ for 3 hours, and then dried at 500℃ for 2 hours.
The catalyst was prepared by calcination under air atmosphere.

The content of TiO2 was 15 wt%.

Example 15 Cu-mordenite 1 obtained in the same manner as Example 14
Titanium tetrachloride was vapor-deposited on 0 g of the H-type mordenite in the same manner as in Example 8 to prepare a catalyst. Ti
The O2 content was Q, 5 wt%.

Comparative Example 1 A catalyst was prepared in the same manner as in Example 14 by impregnating copper nitrate into H-type mordenite (S io2/AJz 03 =23, pore size 7) having an average particle diameter of 60 meso. The content of Cu was 3 wt%.

Comparative Example 2 10g of powder obtained by drying a slurry of titanium oxide obtained by hydrolyzing and neutralizing titanium sulfate at 180°C
It was taken, impregnated with 1.14g of copper nitrate, and molded at 500°C.
The catalyst was prepared by calcination under air atmosphere for 3 hours. The content of Cu was 3 wt%.

Comparative Example 3 A titanium oxide slurry obtained in the same manner as Comparative Example 2 was
Take 10g of the powder obtained by drying at 0°C,
A catalyst was prepared by impregnating the catalyst with 100 g of vanadyl sulfate and calcining it at 500° C. for 3 hours in an air atmosphere after molding.

The content of (2) was 1 wt%.

Experimental Example 1 FIG. 1 is a plot of the change in denitrification rate versus durability test time for the catalysts of Example 1 and Comparative Examples 1 and 3. As is clear from the figure, the catalyst of the present invention not only has high initial activity but also has high resistance to catalyst poisons such as As2O3 and SOx.

Experimental Example 2 A durability test was conducted on the catalysts of Examples 1 to 15 and Comparative Examples 1 to 3. The results are summarized in Table 2. In addition,
As in Examples 14 and 15, instead of first supporting a transition metal as an active ingredient on zeolite and then supporting titanium, as in other Examples, titanium was supported on zeolite in advance and then titanium was supported as an active ingredient. It is more effective to support certain transition metals.

From the above results, the catalyst of the present invention has significantly better durability against SOx than the conventional zeolite-based catalyst that simply supports the transition metal element.

Table 2 (Effects of the Invention) According to the present invention, a catalyst can be obtained that is less likely to be degraded by catalyst poisons in exhaust gas, particularly SOX and arsenic. Therefore, with conventional zeolite-based catalysts supporting transition metal elements, denitrification of exhaust gas containing a large amount of volatile catalyst poisons such as arsenic and selenium compounds and SOX is required for a long time, which inevitably causes deterioration of catalytic activity after long-term use. This is possible while maintaining stable catalytic activity over a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the initial properties and activity after a durability test of the catalysts of Example 1 and Comparative Examples 1 and 3. Agent Patent Attorney Takenaga Kawakita Figure 1 Time (h)

Claims (2)

[Claims] (1) In a catalyst that removes nitrogen oxides from exhaust gas,
A catalyst for catalytic reduction of nitrogen oxides, characterized in that a catalytically active component consisting of titanium and a transition metal is supported on zeolite having a silicon oxide/alumina (SiO_2/Al_2O_3) ratio of 10 or more. (2) The catalyst according to claim 1, wherein the active component consisting of a transition metal is one or more transition metal elements selected from copper, vanadium, molybdenum, tungsten, and iron. Catalyst for catalytic reduction of oxides.