JPH08168640A - Catalyst for removing nitrogen oxide and manufacture thereof - Google Patents

Abstract

PURPOSE: To provide a catalyst for removing a titanium-vanadium nitrogen oxide which has a high activity and whose activity will not be affected by sintering at the time of preparation of catalyst or in its use. CONSTITUTION: A mixture, in the form of paste, comprising oxides or hydration oxides of titanium and smectite clayey minerals is dried and solidified, and then crushed to prove catalyst carriers, and vanadium compounds are supported on the carriers by a wet method thereby to manufacture the catalyst. Other wise a mixture thereof, in the form of paste, comprising oxides or hydration oxides of titanium, smectite clayey minerals, and vanadium compounds are dried, solidified, and crushed to prepare a catalyst for removing nitrogen oxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to a catalyst and method of its manufacture removing nitrogen oxides, in particular thermally has a stable structure, and NO _X (nitrogen oxide) removal rate of high nitrogen oxide The present invention relates to a catalyst for removing substances and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, air pollution has progressed on a global scale, and interest in environmental problems such as effects on the human body and destruction of forests has been further increased. In order to suppress atmospheric concentrations of pollutants such as nitrogen oxides and sulfur oxides, emission regulations of the sources of these substances are becoming stricter year by year.

The dry reduction method using ammonia, which is one of the methods for removing nitrogen oxides, is carried out by reacting exhaust gas into which ammonia is injected on a plate-shaped or honeycomb-shaped catalyst containing titanium oxide as a main component. , NO _x (nitrogen oxide)
Is reduced to N ₂ . This method is a relatively simple system that uses a catalyst and can efficiently treat exhaust gas. Therefore, this method is mainly applied to the treatment of a large amount of exhaust gas emitted from a fixed emission source such as a thermal power plant.

In the above method, the nitrogen oxide removal rate (hereinafter, simply referred to as activity) is closely related to the physical properties and shape of the catalyst and the operating conditions of the reactor. Among them, the selection of the composition of the catalyst and the method of preparation thereof, which are related to the physical properties of the catalyst, have a great influence on the activity, and are important as the basis of this technique. Currently, a catalyst based on a highly active titania-vanadium composition is predominant. Usually, this catalyst is used in the form of supporting vanadium on the surface of titania particles by several to ten and several percent (for example, JP-B-53-28).
148, Japanese Patent Publication No. 55-23086).

The activity of the titania-vanadium catalyst is
It depends largely on the surface area of titania and the amount of vanadium supported, and if a sufficient amount of vanadium is supported on titania having a high specific surface area, a catalyst with high performance can be obtained. However, when vanadium is originally supported on titania, which has low heat resistance, the sintering is further promoted, so during the thermal decomposition process of the vanadium raw material during catalyst preparation, or when using actual equipment, titania with a large amount of supported vanadium has a specific surface area Under the present circumstances, the decrease is remarkable and the activity corresponding to the supported amount cannot be obtained. Therefore, in order to improve the activity, establishment of a technique for preventing titania sintering is of utmost importance.

Various techniques for preventing the sintering of titania have been studied so far, and the present inventors have also examined a method of using a clay mineral as a shielding material.
In this method, a smectite clay mineral and a titania sol are kneaded while shearing, a clay layer shields the contact between titania particles, a porous carrier is prepared, and vanadium is supported thereon to catalyze. .

[0007]

When a clay mineral and a titania sol are kneaded, a clay layer having a shape close to a scaly is separated from an interlayer portion where the bond is weak and dispersed in the titania sol. When dried in this state, the clay layer has a structure in which it covers the fine titania particles. The state up to this point is schematically shown until the step of kneading the clay mineral and the titania sol and then drying and firing. From a macroscopic view of the catalyst of the prior invention, it can be inferred that the surface is occupied by a clay layer, and fine particles of titania are incorporated therein. In the catalyst having such a structure, when the reaction gas containing nitrogen oxide is passed, the clay layer may hinder the diffusion of the reaction gas.

According to the experimental results of the present inventors, it has been found that the activity is extremely low even when vanadium is supported on the clay mineral, and vanadium is contained in the mixed system of titania and clay mineral as in the above porous carrier. It is presumed that the part of titania carrying is responsible for the activity. Therefore, if the diffusion of the reaction gas is inhibited during the reaction, the vanadium-supported titania in the carrier will not be used effectively,
It is considered that the activity becomes low relative to the specific surface area. In particular, the reaction temperature when treating boiler exhaust gas is usually 35
The temperature is 0 to 400 ° C., and under this condition, the diffusion of the reaction gas in the catalyst pores becomes the rate-determining step of the denitration reaction, and thus the shielding of the clay mineral further causes the activity to decrease. .

The object of the present invention is to eliminate the above-mentioned problems of the prior art and to facilitate the diffusion of reaction gas in a catalyst in which vanadium is supported on a titania / clay mineral type porous carrier having excellent heat resistance. According to the structure, a highly active catalyst for removing nitrogen oxides and a method for producing the same are proposed.

[0010]

In order to achieve the above object, the invention claimed in the present application is as follows. (1) In a catalyst for removing nitrogen oxides by ammonia reduction in which a vanadium compound is supported on titanium oxide, titanium oxide particles are interposed between scale-like clay layers, and the scale-like clay layer is destroyed. A catalyst for removing nitrogen oxides, characterized in that the titanium oxide particles carry a vanadium compound. (2) In a method for producing a catalyst for removing nitrogen oxides by ammonia reduction in which a vanadium compound is supported on titanium oxide, after drying and solidifying a pasty mixture of titanium oxide or hydrated oxide and smectite clay mineral A method for producing a catalyst for removing nitrogen oxides, which comprises carrying out a pulverization treatment to obtain a catalyst carrier, and supporting a vanadium compound thereon by a wet method. (3) In a method for producing a catalyst for nitrogen oxide removal by ammonia reduction in which a vanadium compound is supported on titanium oxide, a paste-like mixture of titanium oxide or hydrated oxide, a smectite clay mineral, and a vanadium compound is dried, A method for producing a catalyst for removing nitrogen oxides, which comprises firing and then pulverizing.

[0011]

After the clay mineral and the titania raw material are wet-kneaded as in the present invention, once dried, the structure becomes relatively brittle against impact like a brittle material. The scale-like clay layer peeled off from the part is further broken and subdivided within the layer. This state is schematically shown in the portion of the catalyst of the present invention in FIG.

By the pulverization, the passage of the reaction gas inside the catalyst is increased, and the vanadium supported on the titania is exposed on the surface, so that the reaction gas is easily contacted and the activity is improved. In addition, it can be expected that vanadium, which is not supported on titania, comes into contact with titania during the pulverization process to form new active sites and contribute to the activity improvement.

As in the prior art, just by wet-kneading the clay mineral and the titania raw material, the clay layer is peeled from the portion where the bonding strength between the layers is weak, and the structure of the dried body is a scale-like clay layer. The titania particles are sandwiched between them, and in this state, the diffusion of the reaction gas is not easy at the time of activity measurement, and the activity does not become high relative to the specific surface area. Therefore, as in the present invention, it is effective to improve the activity by drying the carrier or the catalyst once and then pulverizing it.

As described above, a carrier having titania and clay minerals or a catalyst carrying vanadium is dried, solidified and then pulverized to obtain a highly active catalyst which makes use of the feature of high specific surface area. . Titanium oxides or hydrated oxides and smectite clay minerals (generic term for swelling clay that expands in volume when water is included) dispersed in water are used, if necessary, with mineral acids such as nitric acid and hydrochloric acid or organic acids. A viscous paste is prepared by mixing with an acid, and is kneaded while being sheared, dried and solidified, washed with water if necessary, and calcined at an appropriate temperature to first make a porous carrier. Next, the catalyst of the present invention can be obtained by mixing this porous carrier and a water-soluble vanadium raw material such as metavanadic acid dissolved in water, drying and solidifying, pulverizing once, and then calcining at an appropriate temperature. .

In addition to the above, when kneading the above-mentioned titania raw material and clay mineral, vanadium is added at the same time and dried and then crushed, or after crushing the above-mentioned porous carrier,
A method of supporting vanadium may be used. In short, what is important in the present invention is that the clay mineral and the titania raw material are wet-kneaded, then once subjected to a drying operation, and then pulverized.

As the vanadium raw material, ammon metavanadate, which is an industrial raw material, may be used, and vanadyl sulfate or the like may be used. In this case, since it is desirable that vanadium penetrates into the porous body as much as possible, it is preferable to use a water-soluble raw material rather than a powder raw material. The crushing treatment may use either a wet method or a dry method, and the apparatus and method are not particularly limited.

[0017]

EXAMPLES The present invention will be described in detail below with reference to specific examples. Example 1 Titania sol peptized with hydrochloric acid (solid content concentration: 29 wt%) 70
87 g of montmorillonite containing 10.5 wt% of water and 3 wt% of Na ₂ O was added to 0 g of the montmorillonite, and the mixture was kneaded while being sheared with a kneader for 30 minutes. 15 after air-drying the kneading paste
Gel at 0 ° C, then soak in a large amount of water, stir well, discard the supernatant, dry the remaining precipitate, and finally add 5
It was calcined at 50 ° C. for 2 hours to obtain a catalyst carrier.

Next, the above catalyst carrier obtained was added to an aqueous solution in which 21.3 g of ammonium metavanadate was dissolved, and the mixture was mixed while heating at 150 ° C. with a stirrer, and finally after evaporating all the water. It was baked at 550 ° C. for 2 hours. Then, the fired body was pulverized with a hammer mill to obtain a catalyst of Example 1. Example 2 In Example 1, the catalyst whose particle size was adjusted to 10 to 20 mesh for activity measurement was recalcined at 500 ° C. for 2 hours to obtain a catalyst of Example 2. Example 3 The catalyst of this Example 3 was prepared in the same manner as in Example 1 except that 40.3 g of vanadyl sulfate (VOSO ₄ ) having a solid content concentration of 73.7% was used as the vanadium raw material. Example 4 In Example 1, the catalyst carrier was mixed with 21.3 g of ammonium metavanadate dissolved in water in a kneader.
After thoroughly kneading and pulverizing, the mixture was dried and then calcined at 550 ° C. for 2 hours to prepare a catalyst of this Example 4. Example 5 700 g of the titania sol peptized with hydrochloric acid used in Example 1 and 21.3 g of ammonium metavanadate were mixed, and 91 g of montmorillonite containing 14.2% of water and 0.2 wt% of Na ₂ O was added in a wet process. Kneaded Subsequently, the kneaded product was dried, calcined at 550 ° C. for 2 hours, and then pulverized with a hammer mill to obtain a catalyst of Example 5.

Comparative Example 1 A catalyst of Comparative Example 1 was prepared in the same manner as in Example 1 except that the grinding with a hammer mill was omitted in the method of Example 1. Comparative Example 2 A catalyst of Comparative Example 2 was prepared in the same manner as Comparative Example 1 except that the kneading time of the clay mineral and the titania sol was 60 minutes when the catalyst carrier was prepared. Comparative Example 3 A catalyst of Comparative Example 3 was prepared in the same manner as in Example 1 except that V ₂ O ₅ powder was used as the vanadium raw material by the method of Example 1. Comparative Example 4 2h calcination at 550 ° C., T and ground in a hammer mill _i /
Example 5 with 200 g of catalyst powder of V = 95/5 (atomic ratio)
The catalyst of Comparative Example 4 was prepared by mixing 90 g of the montmorillonite used in 1 above with water to form a paste, kneading well with a kneader for 30 minutes, drying the mixture, and then calcining at 550 ° C. for 2 hours.

As for the activity, NH ₃ /NO=1.2 and SV = 120,0 were obtained by sizing the above catalysts to 10 to 20 mesh.
The measurement was carried out under the conditions of 00 h ⁻¹ and a reaction temperature of 350 ° C., and the value was calculated according to the following formula.

[0021]

[Equation 1] The results are shown in Table 1. The catalyst of Example 1 is obtained by crushing the catalyst of Comparative Example 1. As described above, it is clear that the activity of the catalyst containing the clay mineral is improved by pulverization.

[0022]

[Table 1] The catalyst of Example 2 was pulverized in Example 1 and then re-calcined. The reason why the activity of the catalyst of Example 2 was higher than that of the catalyst of Example 1 was that vanadium not supported on titania was contacted with titania by pulverization and then re-calcined so that vanadium was deposited on the titania. It is considered that the number of active points increased after moving to.

In the catalyst of Example 3, vanadyl sulfate was used as the vanadium raw material instead of ammonium metavanadate. The performances of Example 1 and Example 3 were almost the same, and the water-soluble vanadium raw material was used. For example, the effect of the present invention can be obtained similarly. The catalyst of Comparative Example 3 was powdered V ₂ O.
Incorporating No. ₅ , the invasion of vanadium into the carrier is greatly suppressed compared to the water-soluble raw material, so even if it is pulverized, its effect hardly appears, and the activity is extremely low.

In Example 4, the catalyst carrier and ammon metavanadate were kneaded in a paste in a kneader, and even with such a method, activity improvement was recognized. In Example 5, all the catalyst components were kneaded at once, dried and calcined, and finally dry-milled. Even in such a simplified process, by providing the drying and milling steps, the activity can be easily activated. A catalyst with high efficiency can be obtained.

The specific surface area of the catalysts of Examples 1 to 5 is 100 m ^2.
It is about / g, and it can be seen that a catalyst with high activity is obtained in a state where the addition of clay mineral increases the specific surface area. In Comparative Example 2, the kneading time of the clay mineral and titania was lengthened, and even in this case, the activity was almost the same as that of Comparative Example 1 in which the kneading time was short. In Comparative Example 4, the clay mineral was added to the catalyst powder and the mixture was wet-kneaded, and the clay mineral was not sufficiently pulverized by such a preparation method, and thus the activity was low. From these results, even if the clay mineral is not solidified together with the titania fine particles, even if the clay mineral is kneaded for a certain time or more in a wet state, the clay mineral is crushed only to the extent that it separates between the layers, so that the inhibition of the diffusion of the reaction gas is alleviated. It is speculated that it will not reach.

As described above, in the carrier composed of clay mineral and titania, or in the catalyst in which vanadium is supported on the carrier, it is important for the catalyst to be dried and then pulverized to improve the activity. Without being limited thereto, the same effects as those of the present invention can be obtained through such processing steps.

[0027]

According to the present invention, a sufficient amount of vanadium oxide is supported on titanium oxide having a high specific surface area, and the sintering of the catalyst due to heat during catalyst preparation or use is prevented, so that the catalyst can be used for a long period of time. Thus, a highly active ammonia reduction denitration catalyst can be obtained.

[Brief description of drawings]

FIG. 1 schematically illustrates the structures of a catalyst of the present invention and a conventional catalyst.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 21/06 ZAB A 23/22 A B01D 53/36 102 C

Claims (3)

[Claims] 1. A catalyst for removing nitrogen oxides by ammonia reduction in which a vanadium compound is supported on titanium oxide, wherein titanium oxide particles are sandwiched between scale-like clay layers, and the scale-like clay layer is formed. A catalyst for removing nitrogen oxides, characterized in that it is broken and fragmented, and that the titanium oxide particles carry a vanadium compound. 2. A method for producing a catalyst for removing nitrogen oxides by reducing ammonia, which comprises supporting a vanadium compound on titanium oxide, by drying and solidifying a pasty mixture of titanium oxide or hydrated oxide and smectite clay mineral. After that, pulverization treatment is performed to obtain a catalyst carrier, and a vanadium compound is supported on the catalyst carrier by a wet method, which is a method for producing a catalyst for removing nitrogen oxides. 3. A method for producing a catalyst for removing nitrogen oxides by reducing ammonia, which comprises supporting a vanadium compound on titanium oxide, wherein a paste-like mixture of titanium oxide or hydrated oxide, smectite clay mineral and vanadium compound is used. A method for producing a catalyst for removing nitrogen oxides, which comprises drying, firing, and then pulverizing.