JP2010094623A - Method for preparing catalyst for removing nitrogen oxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly durable denitrification catalyst which is not deteriorated by coexistence gases such as steam or SO<SB>2</SB>, and which possesses a high initial activity, as a method for improving poisoning-resistance against catalyst poison components such as P or As. <P>SOLUTION: In the method for preparing a catalyst for removing nitrogen oxides, a first component of a composition prepared by pre-burning a V component and an Mo component carried on a Ti oxide and a second component of a mesoporous silica are wet-crushed in the presence of water, then formed, dried and burned. The mesoporous silica possesses tight and uniform mesopores of a porous structure of a pore diameter of 2-5 nm. Reactant gases can enter mesopores but a catalyst poisoning phosphorous compound cannot intrude. The secondary particles of mesoporous silica are made minute while the mesopores are maintained by wet-crushing and mixing a catalyst powder and the mesoporous silica, and such a structure that the mesoporous silica present around TiO<SB>2</SB>carrying the active components is achieved. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a catalyst for purifying nitrogen oxides in exhaust gas, and in particular, prevents deterioration of the denitration catalyst due to catalyst poison components (P, As, etc.) contained in a large amount in exhaust gas from coal-fired boilers, etc. The present invention relates to a method for producing a catalyst for removing nitrogen oxides, which can perform good exhaust gas purification.

  In exhaust gas from a coal-fired boiler or the like, components that are regarded as catalyst poisons for denitration catalysts such as phosphorus (P) compounds and arsenic (As) compounds are included. In general, the deterioration of a denitration catalyst by a phosphorus (P) compound is caused by the adsorption or chemical reaction of the phosphorus (P) compound to the active component, so the active component on the catalyst surface is likely to be poisoned. It has been. In the future, the number of boilers using low-grade subbituminous coal and bituminous coal as fuel will increase, and the amount of catalyst poison contained in the exhaust gas is increasing. For this reason, a catalyst having high denitration performance and high toxicity resistance is required, and many studies have been conducted on methods for preventing catalyst deterioration.

The method for preventing the deterioration of the catalyst includes (1) a chemical deterioration preventing method for suppressing the adsorption of the catalyst poison to the active component, and (2) a molecule in which the active component is supported in a specific pore. There is a physical deterioration prevention method in which contact with the catalyst poison is physically prevented by a sieving effect. Among these, in the method (1), the composition comprising titanium oxide and an oxide of one or more elements selected from vanadium, copper, iron, and manganese is added to one or more selected from molybdenum, tungsten, and tin. In the method of catalytic catalytic reduction denitration that adsorbs / supports elemental oxide (Patent Document 1) and (2), a catalyst using zeolite as a substance having specific pores (Patent Documents 2 and 3) In addition to zeolite, research on catalysts using nano-sized pores has also made use of mesoporous silica, and in this method, for example, pores of existing mesoporous silica are disclosed. The catalyst around which the catalyst component is supported (Patent Documents 4 and 5, Non-Patent Documents 1 and 2), and a silicate and a titanium compound such as sodium silicate are used around the titanium oxide. Such catalysts to form a porous silica (Patent Document 6, 7, 8) can be mentioned.
JP-A 64-70144 JP 63-12348 A JP-A-63-91142 JP 2005-152725 A JP-A-9-299794 JP 2006-151753 A JP-A-2005-314208 JP 2005-162596 A Xueguaug Wang, J. of Catal., 222 (2004), p565-571 98th CATSJ Meeting abstracts, No.1 A 10

However, in the above-described prior art, there is still room for improvement in that the chemical degradation prevention method (1) cannot completely prevent the degradation of poisonous substances. On the other hand, the method (2) for preventing the entry of a specific substance (component that becomes a catalyst poison) into the pores by the molecular sieving effect is highly effective because it prevents contact between the catalyst poison component and the active component. However, among these, the physical deterioration prevention method using a zeolite catalyst still has improvements such as being easily deteriorated by a coexisting gas such as water vapor or SO ₂ .

  Furthermore, a catalyst in which a denitration catalyst is supported in a mesopore of mesoporous silica having a number of mesopores having a diameter that cannot be penetrated by a catalyst poison, such as a phosphorus (P) compound, is a catalyst having excellent acid resistance. As a result, the inlet of the pores is blocked or narrowed, so the diffusion rate of the denitration reaction in the pores is slow, and high performance is difficult to obtain, and the amount of catalyst components supported is reduced to avoid this There is still room for improvement, such as initial performance cannot be improved.

The problem of the present invention is to solve the above-mentioned problems of the prior art, and as a method for improving the toxicity resistance from catalytic poison components such as phosphorus (P) and arsenic (As), deterioration due to coexisting gases such as water vapor and SO ₂ And providing a highly durable denitration catalyst having high initial activity.

The above-mentioned problems of the present invention are solved by the following means.
According to the first aspect of the present invention, a composition obtained by pre-calcining an active component of molybdenum and vanadium on titanium oxide is preliminarily calcined as a first component, mesoporous silica as a second component, and the first component and The second component is a method for producing a catalyst for removing nitrogen oxides, which is subjected to wet pulverization in the presence of water, followed by molding, drying, and firing.

According to a second aspect of the present invention, the pre-baking temperature after supporting the active components of vanadium and molybdenum on the titanium oxide is 250 ° C. or higher and 600 ° C. or lower (preferably 300 ° C. or higher and 500 ° C. or lower). 2. The method for producing a catalyst for removing nitrogen oxides according to claim 1, wherein the weight ratio of the two components (catalyst powder / SiO ₂ ) is 0.2 to 1.5 (preferably 0.5 to 1.0).

  The invention according to claim 3 is the method for producing a catalyst for removing nitrogen oxide according to claim 1, wherein the wet pulverization is performed in the presence of water using a planetary ball mill pulverizer.

(Function)
As shown in FIG. 2, the mesoporous silica 1 has uniform mesopores 2 having a firm pore structure having a pore diameter of 2 to 5 nm in addition to the macropores 3. Further, as a result of the study by the present inventors, it has been clarified that the reaction gas 5 can enter the mesopores 2 as shown in FIG. 1, but the phosphorus compound 6 or the like, which is a catalyst poison, cannot enter. .

  FIG. 5 shows the pore distribution after mesoporous silica and mesoporous silica are loaded with phosphorus. Even after phosphorus is supported, the mesopores 2 of the mesoporous silica 1 are hardly decreased, and it can be seen that the phosphorus (P) compound does not enter the mesopores 2. Therefore, in order to realize a catalyst having dramatically enhanced toxicity resistance using the mesopores 2, the present inventors can diffuse the reaction gas 5 but cannot enter the catalyst poison component such as the phosphorus compound 6. The inventors considered that it would suffice to realize a catalyst having a structure as shown in FIG. As a result, the present invention has been achieved.

In the present invention, as means for realizing the catalyst having the structure shown in FIG. 1, mesoporous silica containing catalyst powder and commercially available secondary particles having a particle size of 50 to 70 μm (aggregates of primary particles) is used. It is important to mix while wet grinding. By doing so, the secondary particles of the mesoporous silica 1 are refined while maintaining the mesopores 2, and the structure shown in FIG. 1 in which the mesoporous silica 1 exists around the TiO ₂ 4 supporting the active component is realized. it can. In the pulverization method or mixing method that does not involve pulverization of the secondary particles of the mesoporous silica 1, the macropores 3 of the mesoporous silica 1 that is the second component are not destroyed, and thus a catalyst as shown in FIG. 1 cannot be obtained.

  In order to ensure high denitration performance, it is important that the mesopores 2 of the mesoporous silica 1 do not carry a catalyst component so as not to reduce the diffusibility of the reaction gas 5 into the pores of the catalyst. . As a means for obtaining the above catalyst, the catalyst component 4 is a powder in which an active component is previously supported and fired on titanium oxide. By doing this, it is possible to obtain a highly active powder in which a denitration active component is supported on titanium oxide, stabilize the oxide structure, and easily change the oxide structure even in the presence of water. The effect | action which prevents and the effect which increases the particle diameter of catalyst powder can be acquired.

  On the other hand, in the catalyst using the porous silica 7, as shown in FIG. 3, the phosphorus (P) compound 6 comes into contact with the denitration catalyst component 4 and the poisoning proceeds, and as shown in FIG. P) In a catalyst having a dense structure in which the compound 6 does not come into contact with the denitration catalyst component 4, gas diffusibility is lowered, so that both denitration activity and toxicity resistance cannot be achieved.

  According to the present invention, a denitration catalyst is supported between secondary particles of mesoporous silica so that it becomes a highly active catalyst, and further, it is possible to suppress deterioration due to catalyst poisons such as phosphorus (P) and arsenic (As). Become.

Embodiments of the present invention will be described with reference to the drawings.
The catalyst component of this embodiment is preferably an oxide mainly composed of molybdenum and vanadium as a titanium raw material excellent in catalytic reduction denitration reaction using ammonia as a reducing agent, but is particularly a catalyst having normal denitration catalytic activity. There is no limitation. Moreover, the raw material used for a denitration catalyst may be a raw material normally used for a denitration catalyst, and is not specifically limited. For example, as titanium raw material, hydrous titanium oxide powder, titanium oxide slurry, TiO ₂ sol, etc., as Mo raw material, ammonium molybdate, molybdenum trioxide, Mo composite oxide, etc., as V raw material, ammonium metavanadate, When vanadyl sulfate, vanadyl nitrate, a composite oxide of Mo and V (for example, JP 2000-308832 A) or the like is used, good results are easily obtained. Alternatively, a tungsten (W) component may be added. As the W raw material, ammonium metatungstate, W composite oxide, or the like is used.

  The method of supporting the vanadium oxide on the titanium raw material powder, the method of supporting the tungsten oxide and the molybdenum oxide are not particularly limited, but a method of kneading with water, a method of impregnating the titanium oxide with an active ingredient, etc. The method is not particularly limited as long as the active component is supported on the catalyst carrier. After loading the active ingredient, a drying process is performed and a baking process is performed. The baking temperature is 250 ° C. or higher and 600 ° C. or lower, and 300 ° C. to 500 ° C. is particularly preferable. When the calcining temperature is less than 250 ° C., when the prepared catalyst component and mesoporous silica are pulverized and mixed in the next step, the denitration catalyst component is eluted in water and supported in the mesopores of the mesoporous silica. Therefore, it is not preferable. On the other hand, when the temperature exceeds 600 ° C., sintering occurs in an oxide such as titanium oxide, which causes an adverse effect on the denitration activity.

  In the present invention, it is important to mix the first component, which is the catalyst component, and the mesoporous silica, which is the second component, while pulverizing in a wet manner. By grinding under wet conditions, the particles of the first and second components can be mixed while being ground. As a means for pulverizing under wet conditions, a medium stirring pulverizer is preferable, and a planetary ball mill is suitable. The wet pulverization conditions such as the particle size of the balls and the pulverization time vary depending on the performance of the pulverizer, and thus cannot be generally described. The average particle size of the particles obtained after pulverization is preferably 2 to 30 μm. When the average particle size is less than 2 μm, the residual ratio of mesopores is low, and when it exceeds 30 μm, the intended mixture cannot be obtained due to insufficient pulverization.

  Further, the weight ratio of the catalyst component to the mesoporous silica is such that the supported amount of titanium oxide is 0.2 to 1.5, more preferably 0.5 to 1.0, and the supported amount of titanium oxide is silica. When the weight ratio to the weight ratio is less than 0.2, sufficient activity cannot be obtained, and when the weight ratio exceeds 1.5, the catalyst component is supported on the surface of the secondary particles of mesoporous silica, resulting in lower durability. In addition, the diffusion of the reaction gas into the catalyst is also inhibited.

  As the mesopores of this catalyst, uniform pores having a small pore size distribution of 2 to 5 nm are suitable, and if it is less than 2 nm, high activity cannot be obtained due to diffusion resistance of the reaction gas, and if it exceeds 5 nm, the catalyst The poisonous phosphorus (P) compound is likely to enter the mesopores, and high durability cannot be obtained.

Example 1
Hereinafter, the present invention will be described in detail using specific examples.
JP-A-2000-308832 describes a powder obtained by evaporating and drying a titania sol (manufactured by Ishihara Sangyo Co., Ltd., CS-N, particle size d50 = 50 nm) on a sand bath, followed by baking at 500 ° C. for 2 hours. A solution containing the active ingredient represented by the formula NH ₄ 3Mo ₂ V ₃ O _15, which was prepared by dissolving by the above method, was impregnated under the condition that Ti / V = 84/16 in terms of atomic ratio, and on a sand bath After evaporation to dryness, drying was performed at 150 ° C. for 1 hour, followed by baking at 500 ° C. for 2 hours to obtain a carrier sample 1. TiO ₂ and mesoporous silica carrier sample 1 (Chemical Industry, MCM-41, the average pore size 4 nm, average particle size 50 [mu] m) weight ratio of SiO ₂ is TiO a _2: SiO ₂ = 1: planetary ball mill in one condition ( Using Puluerisette (manufactured by FRITSCH Co. Ltd), add about 7 times the amount of water to the weight of mesoporous silica (MPS), and put alumina balls (diameter 20 mm and 5 mm) to the extent that this mesoporous silica slurry is hidden. The slurry pulverized and mixed for a minute was evaporated to dryness on a sand bath. At this time, the average particle size of the slurry obtained after the wet pulverization and mixing is about 2 μm. This was calcined at 500 ° C. for 2 hours to obtain Catalyst 1.

(Examples 2 to 6)
The weight ratios of the carrier sample 1 and mesoporous silica in Example 1 were TiO ₂ : SiO ₂ = 0.2: 1, 0.5: 1, 1.5: 1, 0.1: 1, 2.0: Catalysts 2, 3, 4, 5, and 6 were obtained in the same manner as in Example 1 except that the conditions were changed to 1.

(Examples 7 to 9)
Catalysts 7, 8, and 9 were obtained in the same manner as in Example 1 except that the calcination temperature of the carrier sample 1 in Example 1 was changed to 250, 300, and 600 ° C., respectively.

(Example 10)
In Example 1, a catalyst 10 was obtained in the same manner as in Example 1 except that the titanium raw material of the carrier sample 1 was changed to G5 (Millennium) conditions.

(Comparative Example 1)
In Example 1, catalyst 11 was obtained in the same manner as in Example 1 except that carrier sample 1 and mesoporous silica were changed to the conditions for evaporation to dryness while stirring with a stirring rod on a sand bath.

(Comparative Example 2)
In Example 1, the catalyst 12 was prepared in the same manner as in Example 1 except that the mixed slurry of the carrier sample 1 and mesoporous silica was changed to a condition in which the slurry was ground using a planetary ball mill until the average particle diameter of the slurry became about 1 μm. Got.

(Comparative Example 3)
In Example 1, the catalyst 13 was prepared in the same manner as in Example 1 except that the carrier sample 1 and silica (manufactured by Tomita Pharmaceutical Co., Ltd., microcomputer F) were changed to TiO ₂ : SiO ₂ = 1: 1 by weight. Got.

(Comparative Example 4)
In Example 1, the catalyst was prepared in the same manner as in Example 1 except that the carrier sample 1 and silica sol (Nissan Chemical Co., Ltd., OS sol) were changed to a TiO ₂ : SiO ₂ = 0.5: 1 condition by weight ratio. 14 was obtained.

(Comparative Example 5)
A catalyst 15 was obtained in the same manner as in Example 1 except that the liquid containing the active ingredient represented by titania sol and the formula NH ₄ 3Mo ₂ V ₃ O ₁₅ and mesoporous silica were mixed and ground at the same time.

(Comparative Example 6)
A catalyst 16 was obtained in the same manner as in Example 1 except that the calcination temperature of the carrier sample 1 in Example 1 was changed to 700 ° C.

The powders of the catalysts 1 to 16 were pressure-molded by a hydraulic press and then crushed and sized to 8 to 17 μm (10 to 20 mesh). Using this, the initial denitration performance was measured under the conditions shown in Table 2. Further, as a representative of the accelerated deterioration test using a phosphorus (P) compound, after impregnating a 4 wt% phosphoric acid aqueous solution in terms of P ₂ 2O ₅ , firing was performed at 350 ° C. for 1 hour, and the denitration performance after the deterioration test was measured. The test results are summarized in Table 1. Moreover, the average particle diameter of the powder of Example 1 and Comparative Examples 1 and 2 was measured with a particle measuring device (Mastersizer: manufactured by Sysmex Corporation) using a laser diffraction / scattering method. The measurement results are summarized in Table 3.

The denitration rate was calculated according to the following formula (1).
The calculation of k / k0, which is the reaction rate constant ratio between the phosphorus (P) accelerated deterioration test and the initial denitration rate, was calculated according to equation (2).

From Table 1, the k / k0 value indicating durability by the phosphorus (P) compound is as in Examples 1 to 4, that is, the weight ratio of the carrier sample 1 to the mesoporous silica is TiO ₂ : SiO ₂ = 1: 1 (( Example 1)), 0.2: 1 (Example 2), 0.5: 1 (Example 3), 1.5: 1 (Example 4) It is clear that This is suggested to be the result that the effect of the present invention was fully exhibited.

On the other hand, according to Examples 5 and 6, when the weight ratio of the carrier sample 1 and mesoporous silica is TiO ₂ : SiO ₂ = 0.1: 1 (Example 5), the initial activity is 10% and the denitration activity is low. When the weight ratio of the carrier sample 1 to the mesoporous silica is TiO ₂ : SiO ₂ = 2: 1 (Example 6), the contribution of the effect of the present invention is small, ie, the k-k0 = 0.6. It is suggested that

On the other hand, in the example using silica raw material instead of mesoporous silica as in Comparative Example 3, it is clear that the toxicity resistance obtained with mesoporous silica cannot be obtained, and this is the same with the silica sol of Comparative Example 4. is there. In Examples 1 to 4, the mesoporous silica mesopores suppress the phosphorous (P) compound poisoning. As shown in FIG. 3, the silicas of Comparative Examples 3 and 4 are used. This is because, in the structure of the catalyst covering the periphery of the denitration catalyst component, the phosphorus (P) compound is brought into contact with the denitration catalyst, so that the toxicity resistance is not expressed.
Moreover, about the influence by the calcination temperature of Examples 7-9, since the initial stage performance and toxicity resistance equivalent to Example 1 were obtained in the preliminary calcination by 250 degreeC, 300 degreeC, and 600 degreeC, activity by the calcination temperature in the meantime We think that there is no decline.

On the other hand, in the example in which the pre-baking temperature of Comparative Example 6 is 700 ° C., it is apparent that the initial performance is degraded due to sintering of the catalyst component.
Furthermore, from Example 10, it is clear that the initial activity and durability can be secured in the same manner even if the raw material of titanium oxide is changed.

  On the other hand, in Comparative Example 1 which is an example of drying and firing without performing pulverization and mixing according to the present invention, and in an example using a raw material in which the mesoporous structure of mesoporous silica is destroyed, no toxicity resistance is expressed. Is suggested. Similarly, in Comparative Example 5, which is an example in which the effect of the pre-baking of the present invention is eliminated and the raw materials are pulverized and mixed at one time, it is suggested that no toxicity resistance is exhibited. These suggest that mesoporous silica is not sufficiently present around the catalyst component, and the catalyst component dispersed on the surface is poisoned by the P compound.

  The exhaust gas generated from a coal-fired boiler contains a component that becomes a catalyst poison in a denitration catalyst such as P or As, and the present invention that solved the catalyst's toxicity resistance (durability) is industrially applicable. Is expensive.

1 shows a structural diagram of a catalyst according to the present invention. The conceptual diagram of mesoporous silica is shown. The structural diagram of the catalyst using silica is shown. The structural diagram of the catalyst using silica is shown. B. of BET apparatus for mesoporous silica after accelerated degradation test with mesoporous silica and P compound J. et al. The measurement result of pore diameter distribution by H method is shown.

Explanation of symbols

1 Mesoporous silica 2 Mesopores
3 Macropore 4 Catalyst component 5 Reaction gas 6 Phosphorus (P) compound 7 Silica

Claims (3)

  A composition obtained by pre-sintering molybdenum and vanadium active components on titanium oxide and then pre-baking the composition as the first component, mesoporous silica as the second component, and the first component and the second component in the presence of water. A method for producing a catalyst for removing nitrogen oxides, characterized in that, after wet pulverization, molding, drying and firing are sequentially performed. The pre-baking temperature after supporting the active components of vanadium and molybdenum on the titanium oxide is 250 ° C. or more and 600 ° C. or less, and the weight ratio of the first component to the second component (catalyst powder / SiO ₂ ) is 0.2 to 1. The method for producing a catalyst for removing nitrogen oxides according to claim 1, wherein   2. The method for producing a catalyst for removing nitrogen oxides according to claim 1, wherein the wet pulverization is performed by using a planetary ball mill pulverizer in the presence of water.

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