JPH07155599A - Catalyst for removal of nox in water gas and its production - Google Patents

Abstract

PURPOSE:To prevent the reduction of the activity of an active component due to the sintering of titanium oxide and to obtain a high activity catalyst having high heat resistance. CONSTITUTION:Silica granules 2 or a silica compact 2 as a carrier substrate is coated with titanic ester and dried in a steam-contg. atmosphere at beta300 deg.C Cto form a thin film or filmlike fine particles of a titanium compd. on the silica substrate 2 and this substrate 2 is prefired at 200-700 deg.C in the air to obtain a catalyst carrier with a film and/or filmlike particles of titania 1 on the surface of the silica 2. One or more kinds of catalytically active components 3 selected from among V, W, Mo, Cu and Fe are carried on the carrier, dried and fired at 200-7004oC. The reduction of the activity of the active components 3 due to the sintering of the titania 1 can be prevented and the objective denitration catalyst having high activity even at a relatively high temp. is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for removing nitrogen oxides in exhaust gas and a method for producing the same, and particularly in a catalyst using titania as a carrier, the heat resistance of the catalyst is not lowered by the sintering of titania. The present invention relates to a highly active catalyst for removing nitrogen oxides and a method for producing the same.

[0002]

2. Description of the Related Art A denitration method as shown in FIG. 6 is currently used for treating nitrogen oxides in combustion exhaust gas. According to this method, the denitration device 12 having the denitration catalyst built-in in an appropriate temperature range around 400 ° C. of the flue of the boiler 11
Is provided and by injecting ammonia from the ammonia introduction part 13, nitrogen oxide (almost NO, but also NO ₂ , N ₂ O and other components are present as a reducing agent using the ammonia (NH ₃ ), so NO _x is present. Is decomposed into nitrogen (N ₂ ) and water vapor (H ₂ O) and then discharged from the exhaust gas stack 14. At this time, a denitration catalyst is used to improve the reaction rate and reaction rate in the above reaction. Generally, a method for producing a denitration catalyst has a high specific surface area (about 10
(0 m ² / g or more) The oxide is supported on the oxide and then baked. At this time, a more highly active catalyst can be obtained by uniformly dispersing the active ingredient in the carrier, particularly in titania. Therefore, for example, in the case of vanadium pentoxide, the dispersibility is improved by dissolving vanadate in oxalic acid and then mixing it with titania slurry containing sulfate.

[0003]

However, in the above catalyst, when the active component acts to promote the sintering of the carrier, particularly titania, and the specific surface area of the carrier decreases to about 30-40 m ² / g. However, the effect was not always sufficient. On the other hand, when silica is used as the carrier, the heat resistance as the carrier is very excellent, but there is a problem that the activity as much as the titania carrier is not exhibited even when the active ingredient is carried.

It is also effective to use a titania-silica binary oxide as a carrier (Japanese Patent Publication No. 57-3).
According to the results of the study by the present inventor, it is particularly effective in preventing the sintering. However, in this method, since the active component is supported on both surfaces of silica and titania, it is necessary to support a larger amount of the catalytic active component than the catalyst carrier containing only titania. The object of the present invention is to solve the above-mentioned problems of the prior art, (1) the carrier is difficult to sinter when the active ingredient is carried on the surface of the carrier, and (2) the raw material is inexpensive and the manufacturing process is simple. It is an object of the present invention to provide a denitration catalyst that can easily realize the above two points and a method for producing the same.

[0005]

In order to achieve the above object, the invention claimed in the present application is as follows. (1) In a catalyst for catalytic reduction removal of nitrogen oxides in exhaust gas with ammonia, a catalyst carrier having a silica surface having a high specific surface area as a carrier substrate is coated with thin layered or particulate titania, vanadium, tungsten,
A catalyst for removing nitrogen oxides in exhaust gas, which is loaded with a catalytically active compound composed of one or more of molybdenum, copper and iron. (2) In the method for producing a catalyst in which nitrogen oxides in exhaust gas are catalytically reduced and removed with ammonia, silica powder and titanic acid ester are mixed and dried in an atmosphere in which water vapor is present, whereby one surface of the silica powder is removed. After covering part or all with a titanic acid film and / or particles, 20
Vanadium (V), tungsten (W), molybdenum (M _O ), copper (C _u ), and iron (F) were formed on the surface of the catalyst carrier obtained by pre-calcination at 0 ° C. or higher and 700 ° C. or lower.
_e ) supporting one or more metals, oxides or sulphates consisting of one or more of the above as active ingredients, and at 200 ° C or higher 70
A method for producing a catalyst for removing nitrogen oxides in exhaust gas, which comprises calcination at 0 ° C. or lower. (3) Nitrogen in the exhaust gas according to the above (2), characterized in that silica powder and titanic acid ester are mixed so that the atomic ratio of S _i / T _i is between 8/2 and 5/5. A method for producing a catalyst for removing oxides. (4) The method for producing a catalyst for removing nitrogen oxides in exhaust gas according to (2) above, wherein the active ingredient is added together with sulfate or sulfuric acid. (5) In the method for producing a catalyst in which nitrogen oxides in exhaust gas are catalytically reduced and removed with ammonia, a silica molded body is impregnated with a titanic acid ester and dried in an atmosphere in which steam is present to remove the surface of the silica powder. After covering a part or all with a titanic acid film and / or particles, 2
Vanadium (V), tungsten (W), molybdenum (M _O ), copper (C _u ) and iron (F) are formed on the surface of the catalyst carrier obtained by pre-baking at a temperature of 00 ° C. or higher and 700 ° C. or lower.
_e ) One or more metals, oxides or sulphates consisting of one or more of the above) are supported as active components on silicon and titanium atoms in a ratio of 0.5 / 99.5 or more and 40/60 or less, and 200 to 700 ° C. A method for producing a catalyst for removing nitrogen oxides in exhaust gas, which comprises firing as follows.

[0006]

[Function] High specific surface area (100
m ² / g or more) silica is used as a carrier substrate, and its surface is coated with titania. At that time, by using a titanate ester (Ti (OR) ₄ : R is an alkyl group or an aryl group) which is an industrial raw material as a titania coating raw material, the titanate ester can be obtained by low temperature drying containing steam at 300 ° C. or lower. Hydrolyzes and condenses. Depending on the viscosity of the titanate ester, it may be diluted with alcohol or ketone. Drying temperature is over 20 ℃ 3
It may be 00 ° C or lower, but 50 ° C or higher and 200 ° C or lower is desirable. This is due to the hydrolysis of titanate ester,
This is because if the temperature is low, the reaction rate becomes slow and the treatment time becomes long, and if the temperature is too high, the reaction rate becomes too fast and only particulate titania is produced. By drying, large molecules of titanium compound thin film-shaped and / or film-shaped fine particles containing an alkyl group or an aryl group are formed on the silica surface. But after this,
When the alkyl group or the aryl group is decomposed by baking at a drying temperature or higher and 200 ° C. to 700 ° C., preferably 350 ° C. or higher and 550 ° C. or lower, the molecule adheres to silica and has a sufficient volume of fine particles. It becomes a titania with various pores. According to the experiments of the present inventor, the titania thus dispersed on silica exhibits a characteristic that it is difficult to sinter even if it carries an active ingredient and is fired. Although the cause is unknown, as shown in FIG. 7, since the titania in the catalyst of the present invention is present as a film and / or film-like particles on the surface of the silica, it causes selective mass transfer in the plane direction. It is considered that a thermal change is less likely to occur as compared with the case where the sintering by the three-dimensional mass transfer such as the above-mentioned titania carrier has progressed.

The present invention is directed to vanadium (having a function of decomposing into nitrogen oxides such as NO and NO ₂ generated when burning fossil fuels into N ₂ and H ₂ O by using NH ₃ as a reducing agent. V), tungsten (W), molybdenum (M _O ), copper (C _u ), tin (S _n ), iron (F _e ), and nickel (N _i ), a metal or oxide composed of at least one atom. Further, the present invention relates to a catalyst in which an active ingredient comprising one or more sulfates is supported on a titania film on silica and / or particles and a method for producing the same.

In any of the cases, the present invention uses a silica powder having a high specific surface area as silica and a titanate ester as a titania raw material for kneading when a titania film and / or particles are placed on a silica substrate. The subsequent drying process is performed in an atmosphere containing water vapor. At this time, the higher the water vapor concentration, the faster the progress of hydrolysis, but even if the water vapor concentration is low, the same effect can be obtained by prolonging the treatment time.

Further, the higher the pre-calcination temperature and the calcination temperature, the more the thermal stability increases, but the sintering phenomenon of the carrier occurs,
Since the specific surface area may decrease, it is usually preferably 350 ° C or higher and 550 ° C or lower. After supporting the active ingredient, the water content may be dried at a temperature not higher than the firing temperature. In the following examples, high specific surface area silica (initial specific surface area 200 m ² / g) powder as a carrier raw material and titanic acid tetraisopropoxide (hereinafter referred to as TTI) as a titanate ester.
However, in the present invention, the silica raw material does not have to be a powder, and even if a fired body having various shapes such as a honeycomb, a granular shape, or a plate shape or silica gel is used as long as the specific surface areas are the same, Are the same, and the titanate ester may be another one such as tetrastearyl titanate or tetrabutyl titanate. However, since the titanic acid ester having a large molecular weight also has a high melting point, it is necessary to set the drying temperature above the melting point.

As for the active ingredient, those other than those containing vanadium can be used because they express the activity. Furthermore, the activity can be further enhanced by using a sulfate as an active ingredient and / or adding sulfuric acid. In addition, the more the active ingredient is added to the same amount of the carrier, the higher the activity is.However, if it is added above a certain amount, the ratio of the carrier is decreased and the interaction between the carrier and the active ingredient is decreased. Will fall. In the present invention, the ratio of the active ingredient to the carrier atom is 0.5 / 99.5 or more and 40/60 or less, preferably 1 /
99 to 20/80.

[0011]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples.
explain. FIG. 1 shows the catalyst particle breakage prepared according to the present invention.
It is a schematic diagram of a surface. Titania 1 has high specific surface area with pores
The transparent silica 2 is covered with a thin layer or particles. That
The active ingredient 3 is carried on the surface, but most of the surface
Since Titania 1 covers most of the active ingredients,
It is carried on the titania 1. Example 1 The manufacturing process is shown in FIG. First, an electric furnace as shown in FIG.
10% water generated by air pump 5 and evaporator 6 inside 4
Supply steam. At this time, water is transferred to the evaporator 6 by the metering pump 7.
The absolute humidity of the supply gas 8 to 10% by supplying
Controlled to be. Approximately 10 times the electric furnace to prevent condensation
After heating to 0 ℃, after the internal humidity became constant,
High specific surface area silica powder and TTIP S_i/ T_iAtomic ratio is
Put the raw materials kneaded to 7/3 into the crucible 9,
Stir sample 10 for 2 hours at 150 ° C in an electric furnace.
It was dried with stirring. Then, in the air at 550 ° C for 2 hours
After pre-baking, the carrier powder obtained and
V / (S _i+ T_i) Atomic ratio is 15/8
Water to 5 (30 wt% for all raw powders)
%) And kneading with φ10 × 5^tAfter molding, 150
After drying in air at ℃ for 2 hours, at 550 ℃ in air for 2 hours
Fired for a while. Example 2 Using the same apparatus as in Example 1, the pre-firing and firing temperatures were changed.
The test was conducted under exactly the same conditions except that the temperature was 200 ° C.

Example 3 Using the same apparatus as in Example 1, the pre-firing and firing temperatures were changed.
The test was conducted under exactly the same conditions except that the temperature was 700 ° C. Example 4 The same apparatus as in Example 1 was used and the internal humidity during drying was 100%.
% Same as steam except that the drying time was 30 minutes
The test was conducted under the conditions. Example 5 Using the same apparatus as in Example 1, ammonium paratungstate
Aqueous solution with atomic ratio W / (S_i+ T_i) = 15/85 live
Test under exactly the same conditions except that it was added as a sex ingredient
It was. Example 6 Using the same apparatus as in Example 1, ammonium molybdate aqueous solution
Liquid atomic ratio M_O/ (S _i+ T_i) = 15/85 activated
The test was conducted under exactly the same conditions except that the minutes were set. Example 7 Using the same apparatus as in Example 1, an aqueous solution of copper sulfate was used with an atomic ratio of C._u
/ (S_i+ T_i) = 15/85 except the active ingredient
The test was conducted under exactly the same conditions. Example 8 Using the same apparatus as in Example 1, iron sulfate was added to atomic ratio F_e/ (S
_i+ T_i) = 15/85, except that it was the active ingredient
The test was conducted under the same conditions. Example 9 As a carrier substrate, high specific surface area silica pellets (specific surface area
About 150m²/ G, φ10 x 5^t, 350 ℃ baked product)
The test was conducted under exactly the same conditions as in Example 1 except that it was present.

Example 10 A test was conducted under exactly the same conditions as in Example 1 except that an oxalic acid solution of ammonium metavanadate was used as the active ingredient. Example 11 A test was conducted under exactly the same conditions as in the example except that the S _i / T _i atomic ratio for the carrier was 5/5. Example 12 The addition amount of the active ingredient was 0.5 in terms of V / (S _i + T _i ) atomic ratio.
The test was carried out under exactly the same conditions as in the example except that it was /99.5. Example 13 The addition amount of the active ingredient was 40 / in terms of V / (S _i + T _i ) atomic ratio.
The test was conducted under the same conditions as in the example except that the value was 60.

Comparative Example 1 Treatment was carried out under the same conditions as in Example 1 except that nitrogen was sent instead of 10% steam during drying. Comparative Example 2 Treatment was carried out under the same conditions as in Example 1 including drying in steam except that only the high specific surface area silica powder was used as the catalyst carrier. Comparative Example 3 Treatment was carried out under the same conditions as in Example 1 including drying in steam except that only TTIP was used as the catalyst carrier. Comparative Example 4 Treatment was carried out under the same conditions as in Example 1 including drying in steam except that silicon tetrachloride and titanium tetrachloride were used as catalyst carrier raw materials and a mixture by an ammonia coprecipitation method was used. Comparative Example 5 The addition amount of the active ingredient was 50 / in terms of V / (S _i + T _i ) atomic ratio.
The test was conducted under the same conditions as in Example 1 except that the value was 50. Comparative Example 6 The addition amount of the active ingredient was 0.1 in terms of V / (S _i + T _i ) atomic ratio.
The test was performed under exactly the same conditions as in Example 1 except that the value was /99.9. Comparative Example 7 Treatment was performed under the same conditions as in Example 1 except that the pre-baking temperature was 750 ° C. Comparative Example 8 Treatment was performed under the same conditions as in Example 1 except that the firing temperature was 750 ° C.

FIG. 4 shows comparative values of the relative activities of Example 1 and Comparative Examples 1-8. For the measurement, an experiment was conducted using simulated combustion exhaust gas. The composition of the exhaust gas is CO _2: 500 ppm, NO _X
The concentration was 200 ppm, the O ₂ concentration was 3.0%, and the balance was nitrogen gas. The denitration experiment was performed at a temperature of 350 ° C and a gas flow rate of 17 m.
/ h condition, the NH ₃ / NO _x ratio at the catalyst inlet is 1
It was carried out in. It can be seen that in each case, the activity of Example 1 is clearly superior to that of Comparative Example, which is two times or more. In particular, the difference between Comparative Example 4 and Example 1 shows that the carrier of the present invention is superior to the binary oxide when the amount of the active ingredient supported per unit weight of the carrier is the same. Further, the low activity of Comparative Examples 2 and 3 means that, in the catalyst carrier of the present invention, one of the carrier components does not exhibit the effect,
It is shown that it becomes effective only after being compounded.

On the other hand, Examples 1 to 13 were also measured by the above denitration rate measuring method and compared. Results are shown in FIG. All of them were superior in the activity side as compared with the comparative example shown in FIG. 4, and were 85% or more as compared with the denitration rate of Example 1. When calcined at a high temperature, the catalytic activity is rather low, but the thermal stability increases, so it can be used when the operating temperature is high. Further, comparing Examples 1 and 10, the activity is improved when a sulfate is used as an active ingredient, but when the sulfate is added, the SO ₂ oxidation rate in the exhaust gas is slightly increased. In that case (SO ₂ Exhaust gas with a large content) needs to use a metal- or oxide-based active component that does not contain sulfuric acid.

[0017]

According to the present invention, a relatively inexpensive high specific surface area silica substrate coated with titania can be used as a catalyst carrier for a denitration catalyst.
Further, the obtained denitration catalyst is highly active and has a long life even under a relatively high temperature use condition of 450 ° C. or higher, and thus can be suitably used as a high temperature denitration catalyst.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a basic structure of a denitration catalyst of the present invention.

FIG. 2 is a diagram showing a manufacturing process of the catalyst of the present invention.

FIG. 3 is a schematic view showing an apparatus for producing a catalyst of Example 1.

FIG. 4 is a diagram comparing the catalytic activities of Example 1 and Comparative Examples 1-8.

FIG. 5 is a diagram showing the catalytic activity of Examples 1 to 13.

FIG. 6 is a schematic view showing a conventional denitration device.

FIG. 7 is a schematic view showing a sintering prevention mechanism in the present invention.

[Explanation of symbols]

1 ... titania, 2 ... silica, 3 ... active ingredient, 4 ... electric furnace, 5 ... air pump, 6 ... evaporator, 7 ... water metering pump, 8 ... supply gas, 9 ... crucible, 10 ... sample, 11 ... boiler , 12 ... Denitration device, 13 ... Ammonia introduction part, 14
… Exhaust gas chimney.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location B01J 23/22 ZAB A 9342-4G 23/28 ZAB A 9342-4G 23/30 ZAB A 9342-4G 23/72 ZAB A 9342-4G 23/74 ZAB 9342-4G 23/745 27/053 ZAB A 9342-4G 9342-4G B01J 23/74 301 A

Claims (5)

[Claims] 1. In a catalyst for catalytically reducing nitrogen oxides contained in exhaust gas by ammonia, a silica carrier having a high specific surface area as a carrier substrate is coated with a thin layered or particulate titania catalyst carrier, vanadium, A catalyst for removing nitrogen oxides in exhaust gas, which is loaded with a catalytically active compound composed of one or more of tungsten, molybdenum, copper and iron. 2. A method for producing a catalyst for catalytically reducing nitrogen oxides contained in exhaust gas with ammonia, wherein silica powder and titanic acid ester are mixed and dried in an atmosphere in which steam is present to obtain a surface of the silica powder. Was covered with a titanic acid film and / or particles, and then pre-calcined at 200 ° C. or higher and 700 ° C. or lower on the surface of the catalyst carrier to obtain vanadium (V), tungsten (W), molybdenum (M _O ), copper (C _u ), and iron (F _e ), at least one of which is a metal, an oxide, or a sulfate, which is carried as an active ingredient, and is baked at 200 ° C. or higher and 700 ° C. or lower. To produce a catalyst for removing nitrogen oxides in exhaust gas. 3. The exhaust gas according to claim 2, wherein the silica powder and the titanate ester are mixed so that the atomic ratio of S _i / T _i is between 8/2 and 5/5. A method for producing a catalyst for removing nitrogen oxides. 4. The method for producing a catalyst for removing nitrogen oxides in exhaust gas according to claim 2, wherein the active ingredient is added together with sulfate or sulfuric acid. 5. A method for producing a catalyst for catalytically reducing nitrogen oxides contained in exhaust gas with ammonia, the silica powder being obtained by impregnating a silica molded product with a titanate ester and drying in an atmosphere containing water vapor. Vanadium (V), tungsten (W), molybdenum (molybdenum (V), tungsten (W), and molybdenum ( M _O ), copper (C _u ), and iron (F _e ), at least one of which is a metal, oxide or sulfate of 0.5 or more and 99.5 or more as an active ingredient. A method for producing a catalyst for removing nitrogen oxides in exhaust gas, which comprises supporting the catalyst at a ratio of / 60 or less and calcining at 200 ° C or more and 700 ° C or less.