JP4335583B2 - Exhaust gas purification catalyst and production method thereof - Google Patents

Description

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【表２】

【００３４】
【発明の効果】
請求項１〜５記載の発明によれば、酸化チタンを主成分とする耐熱性および低温活性を併せ持つ排ガス浄化用触媒が得られる。
請求項６記載の発明によれば、例えばシンプルサイクルガスタービン発電設備、ディーゼルエンジン、ガスエンジンを用いる車や発電設備からの排ガス中のＮＯｘの、尿素やＮＨ_３による還元除去を効率よく行うことができる。
【図面の簡単な説明】
【図１】本発明の触媒の使用をモデル的に説明する説明図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification catalyst, and more particularly to a novel denitration catalyst having both activity and heat resistance that can efficiently remove NOx in all exhaust gases such as internal combustion engines and external combustion engines from low temperatures, and a method for producing the same.
[0002]
[Prior art]
In the United States, so-called simple cycle gas turbine power generation, in which a gas turbine is constructed and operated independently, is increasing in order to make up for power shortages and to cope with peak power consumption. Since the equipment used for these is constructed in the suburbs of the city, it is necessary to decompose and purify NOx in the exhaust gas at a high rate, and a denitration method using ammonia (NH ₃ ) as a reducing agent is adopted. In recent years, the number of vehicles and stationary power generation facilities using diesel engines (DE) with high energy utilization efficiency to prevent global warming has increased, and a large amount of NOx generated from them has been reduced to urea and ammonia (NH ₃ ). A method of purifying as a reducing agent is being taken.
[0003]
In these facilities, the denitration device is often installed immediately after the exit of the combustor or engine, and the denitration catalyst is exposed to a high temperature of 450 ° C. to 600 ° C., and thus requires high heat resistance. In particular, in the denitration of DE exhaust gas, the temperature of the catalyst may exceed 600 ° C. when unburned oil or soot in the exhaust gas is burned, and the catalyst must have higher heat resistance. In addition, since these facilities are mounted in the suburbs of the city, in the city, or in vehicles traveling in the city area, it is desired to denitrate from the start-up time when the exhaust gas temperature is low, and it is also necessary to have low-temperature activity.
[0004]
As a highly active catalyst from low temperature, there is a titanium oxide-vanadium oxide catalyst widely used for denitration of boiler exhaust gas around 350 ° C, but thermal deterioration cannot be used remarkably in the above high temperature range. . For this reason, many devices and inventions relating to catalysts that are unlikely to deteriorate at high temperatures have been made, and in particular, it is known that a catalyst containing cerium (Ce) as an active component exhibits relatively high performance even at high temperatures (Patent Document 1 and 2). In Patent Document 1, soluble titanium (Ti), tungsten (W), and cerium (Ce) compounds are obtained by coprecipitation method, and Ce compounds are highly dispersed in titania to aim for stabilization and high activation. It is. In Patent Document 2, Ce ions are dispersed in the zeolite pores by an exchange method to achieve high activation and stabilization. The present inventors have invented a catalyst in which Ce oxide is highly dispersed and stabilized and highly activated, and have applied for a patent (Japanese Patent Application No. 2002-56240), but the viewpoint that the catalyst has heat resistance. However, in the viewpoint of the catalyst having both heat resistance and low temperature activity, which the present inventors aim at, the point to be improved has been left.
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 08-257402 [Patent Document 2]
Japanese Patent Laid-Open No. 08-27408 [Patent Document 3]
Japanese Patent Laid-Open No. 08-229407
[Problems to be solved by the invention]
Among the above-described conventional techniques, the method of precipitating a soluble compound of Ti, W, and Ce by a coprecipitation method has the following problems.
(1) Ti and Ce are the same tetravalent atom, and both compounds tend to be uniformly dispersed. For this reason, the Ce compound (oxide) is buried in the titanium compound (oxide), and the excellent activity of the Ce compound cannot be sufficiently extracted. This can be seen from the fact that it is difficult to separate them from each other, and Ce oxide often remains as an impurity in the titanium oxide for industrial use.
(2) In the case of using Ce ions substituted with Ce ions in a highly dispersed manner, an extremely high initial performance can be obtained, but the so-called aluminum is separated from the zeolite structure into the pores. Degraded easily due to dealumination. In particular, since the dealumination phenomenon is accelerated by the presence of temperature and water vapor, it is difficult to maintain high denitration activity over a long period of time when exposed to high temperature exhaust gas containing 5 to 10% water vapor. .
(3) In addition, the catalyst based on the idea of supporting the CeO ₂ sol in fine pores similar to zeolite from TiO ₂ and WO ₃ that is the present inventor is excellent not only in heat resistance but also in activity. In order to perform denitration of low temperature exhaust gas at the start of the internal combustion engine at 200 to 250 ° C., there is room for improving low temperature activity.
[0007]
In view of the problems of the prior art as described above, the object of the present invention is to prevent the Ce oxide from being buried in the Ti oxide and realize high dispersion similar to that of ion-exchanged zeolite on the surface of titanium oxide. An object of the present invention is to provide a catalyst capable of preventing phenomena such as titanium sintering and deterioration of zeolite due to water vapor and exhibiting activity from a low temperature. It is another object of the present invention to provide the above highly active catalyst that facilitates reduction of NOx by urea or NH _{3 in} exhaust gas from a simple cycle gas turbine power generation facility, a diesel engine, a vehicle using a gas engine, or a power generation facility.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, the invention claimed in the present application is as follows.
(1) A catalyst for reducing and purifying nitrogen oxide in exhaust gas discharged from the outlet of a combustor or engine using ammonia or urea as a reducing agent, and a close mixed oxide of titanium oxide and tungsten oxide as a first component Or an intimate mixed oxide of titanium oxide, tungsten oxide and silicon oxide, cerium dioxide (CeO ₂ ) as the second component, and niobium pentoxide (Nb ₂ O ₅ ) as the third component. The ratio of the second component to the first component is greater than 0 to 40% by weight, the ratio of the third component to the first component is greater than 0 to 6% by weight, and the intimate mixed oxide comprises titanium oxide particles to but tungsten trioxide particles and / or fine holes formed by oriented aggregation across the silicon dioxide particles, particles of cerium and niobium pentoxide particles dioxide responsible Purifying catalyst of the nitrogen oxides in the exhaust gas, characterized in that it is.
[0009]
(2) The first component dries the intimate mixed oxide obtained by mixing the oxyacid or its salt of tungsten (W) with the slurry containing hydrous titanium oxide or its dried product, or the colloid containing titanium oxide . Or the catalyst according to (1), wherein the catalyst is calcined after drying.
(3) The catalyst according to (1) or (2), wherein a sol or organosilicic acid compound containing water of silicon dioxide as a dispersion medium is added.
[0011]
( 4 ) A cerium dioxide sol as a second component raw material and a niobium pentoxide sol as a third component raw material are added to the first component powder, and then kneaded, dried and fired. A method for preparing the catalyst according to any one of (1) to (3).
( 5 ) Exhaust gas purification characterized by using a honeycomb catalyst carrying the catalyst according to any one of (1) to (3) and detoxifying nitrogen oxides in the exhaust gas in the presence of a reducing agent. Method.
[0012]
The inventors of the present invention have intensively studied to develop a catalyst having titanium oxide as a main component and having improved heat resistance and low temperature activity, and as a result, have come to the following conclusion.
(1) As oxides having high performance at high temperatures, there are CeO ₂ and Nb ₂ O ₅ , which are adsorbed on titanium oxide and act as a titanium oxide crystal accelerator. For this reason, means for preventing these oxides from being adsorbed on titanium oxide, or making the crystallization difficult to proceed even if adsorbed is effective in improving the heat resistance.
(2) To achieve high dispersion, when Ti and Ce and Nb compounds are mixed in an easily mixable state, Ce and Nb compounds are adsorbed on titanium oxide, resulting in a composite of Ce and Nb oxides. In addition to being inhibited, Ce or Nb compounds are buried in the titanium oxide, and contact with the gas is inhibited. Therefore, in order to obtain a highly active catalyst, a means capable of preventing the above-described Ce and Nb compounds from being adsorbed and buried in TiO ₂ is necessary.
(3) In order to obtain a catalyst having high activity from a low temperature, it is necessary to promote the formation of oxygen lattice defects by adding Nb ₂ O ₅ oxide to CeO ₂ and controlling the valence. For that purpose, a mixing method in which CeO ₂ and Nb ₂ O ₅ can contact with each other preferentially is effective.
[0013]
From this point of view, when titanium oxide having a hydroxyl group on the surface and tungstic acid or a salt thereof are mixed in the presence of water, the hydroxyl group of TiO ₂ and tungstic acid are condensed to form a bridge between TiO ₂ crystals, Focusing on the fact that fine pores of 50 mm or less comparable to the zeolite pores are formed when this is fired (Japanese Patent Laid-Open No. 08-229407), TiO ₂ and WO ₃ prepared in advance, or these and SiO ₂ Incorporation of CeO ₂ and Nb ₂ O ₅ sols in the intimate mixed oxide with the catalyst, a catalyst satisfying the requirements (1) to (3) was realized.
[0014]
Specifically, it looks like the advance of TiO ₂ and WO ₃ were prepared, or in FIG. 1 when the state of intimate mixing oxides of these with SiO ₂ illustrates schematically (a), TiO ₂ is WO ₃ and / or oriented and aggregated across the SiO ₂ oxide forming fine pores, the stable catalyst pores even at a high temperature to prevent contact of the TiO ₂ crystals together inhibit the growth of the TiO ₂ crystals by heat Form.
[0015]
Further, when CeO ₂ and Nb ₂ O ₅ sol are further supported on the intimate mixed oxide, as shown in FIG. 1 (b), the valence of TiO ₂ is controlled by Nb ₂ O ₅ in the gap of TiO _2. Active CeO ₂ will be present in a highly dispersed manner. As a result, not only the supported CeO ₂ is effectively used as an active component, but also the combination of CeO ₂ and Nb ₂ O ₅ (generation of Ce-Nb oxide) preferentially proceeds, and high heat resistance and High low temperature activity is realized.
[0016]
The first component used in the catalyst of the present invention includes a slurry of hydrous titanium oxide such as metatitanic acid and orthotitanic acid, or a dried product thereof, or a colloid containing titanium oxide such as titania sol, an oxo acid of tungsten (W) or Add the salt and, if necessary, a sol using silicon dioxide water as a dispersion medium or an organic silicate compound such as ethyl silicate, mix or knead, then dry, or continue drying to a temperature of 300 ° C or higher. It is obtained by firing with The titanium oxide raw material used here may be any material as long as it has a hydroxyl group on the surface of titanium oxide. For example, a hydrous titanium oxide, a titanium oxide sol, or a dried product thereof may be used. it can. For example, it may be one containing a sulfate radical as an impurity like a dried product of metatitanic acid obtained by the sulfuric acid method. As the W raw material, an oxygen acid or heteropolyacid containing an MO ₄ type ion (M: W) of the corresponding metal, or an ammonium salt such as ammonium meta or tungstate can be used. The addition amount of tungsten (W) is ₁ to 50 wt%, preferably 5 to 30 wt% as an oxide with respect to TiO ₂ . If the added amount of W is small, the heat resistance is deteriorated, and if it is too large, the ratio of titanium oxide holding the active ingredient is decreased and the activity is lowered. Furthermore, as the silicon dioxide to be added as needed, organosilicon compounds such as ethyl silicate and colloidal silica of several to several tens of nm can be used, and the amount added to TiO ₂ is within 0 to ₂₀ wt% as SiO ₂ . It is good to suppress it. Too much addition will form an aggregate of only the added silica and lower the activity.
[0017]
On the other hand, cerium oxide, the second component added to the first component, is preferably a sol-like product in which CeO ₂ is dispersed in water contained in an organic alkali, acid, or stabilizer, and is commercially available as an ultraviolet absorber or coating agent. You may use what is. The addition amount with respect to titania is 0 to 50 wt%, preferably 5 to 40 wt%. When the addition amount is small, it is difficult to obtain high activity, and when it is too large, it tends to cause a decrease in activity at 500 ° C. or higher. Also, niobium pentoxide, the third component, can be used by dispersing Nb ₂ O ₅ oxide in water containing organic alkali, acid, and stabilizer, as with CeO ₂ sol. A sol-like material that forms a film can be used. The addition amount is selected from the range of more than 0 to 10 wt%, usually 1 to 6 wt%. When the addition amount is small, the degree of improvement in low-temperature activity is small. When the addition amount is large, the increase in low-temperature activity becomes remarkable, but the denitration performance at 450 ° C. or higher tends to be low.
[0018]
The second component and the third component may be added to the first component at the same time, but after the first component and the second component are mixed in advance, dried and / or calcined at 500 ° C. or lower, the third component is added. It is easier to obtain better results by adding ingredients.
[0019]
The intimate mixture of the first to third components obtained as described above is dried and calcined at 300 to 600 ° C., pulverized into powder, added to water to form a slurry or paste, and then used in a well-known manner. Molded into catalyst shape. Specifically, the intimate mixture powder of the first component to the third component is added with a binder such as water or silica sol, and then made into a slurry or paste (hereinafter referred to as catalyst slurry or catalyst paste) inorganic fiber. Honeycomb carrier with corrugated sheet, nonwoven fabric carrier made of inorganic fiber, ceramic honeycomb carrier such as cordierite and alumina, meshes such as wire mesh and metal lath, and nets woven from inorganic fiber yarns such as E-glass fibers For example, a method of impregnating or coating an object or the like, or applying it by rolling so as to fill the eyes of a net-like substance, followed by drying and baking.
[0020]
The carrier supporting the catalyst slurry or paste containing the above compound includes a honeycomb carrier obtained by corrugating an inorganic fiber sheet as described above, an inorganic fiber nonwoven fabric, a net such as a wire net or a metal lath, and an inorganic such as E-glass fiber. A net-like material woven from a fiber yarn is used. These are reinforced with a known reinforcing agent, or provided with a coating layer for the purpose of preventing an increase in adhesion of a catalyst component and oxidation of a metal substrate. Also good.
[0021]
Any supporting method may be used, but in an inorganic fiber corrugated honeycomb, ceramic nonwoven fabric, ceramic honeycomb carrier, etc., it is immersed in a slurry having a catalyst component of 30 to 50 wt% so as to be in the fiber gap or on the surface. A method of coating the catalyst slurry is suitable. On the other hand, when using a metal or ceramic mesh, in addition to the coating method described above, a catalyst paste with a moisture content of 30-35% is added with inorganic fibers so that the mesh is filled with a roller. The method of apply | coating can be taken.
[0022]
By the above method, a catalyst slurry or catalyst paste supported on various substrates is subjected to treatments such as cutting, molding and deformation as necessary, and then dried by a known means such as air drying or hot air drying. Later, it is calcined at 500 to 700 ° C. and used as a catalyst.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
【Example】
Hereinafter, the present invention will be described in detail using specific examples.
Example 1
Low-temperature dry titanium oxide (G5 manufactured by Millennium, surface area 275 m2 / g) 100 g, ammonium metatungstate aqueous solution ((NH ₄ ) ₆ • H ₂ W ₁₂ O ₄₀ • xH ₂ O, WO ₃ containing 50 wt%), After mixing 5 g of succinic acid and 50 g of silica sol (manufactured by Nissan Chemical Industries, OS sol, concentration 20 wt%), the water was evaporated by a heating kneader to obtain a viscous product having a water content of about 38 wt%. This was formed into a 3φ columnar shape by extrusion granulation, dried in a fluid bed dryer, fired at 500 ° C. for 2 hours, and pulverized with a hammer mill to obtain a first component raw material powder.
[0024]
100 g of the obtained first component is 120 g of CeO ₂ sol (manufactured by Taki Chemical Co., CeO ₂ content 30 wt%) as the _second component, and Nb ₂ O ₅ sol (manufactured by Taki Chemical Co., Nb _{2 is used} as the third component). 55 g of O ₅ content (10 wt%) was added, and a viscous product having a water content of about 38 wt% was obtained while further evaporating water with a heating kneader. This was formed into a 3φ columnar shape by extrusion granulation, dried by a fluidized bed dryer, calcined at 600 ° C. for 2 hours, and pulverized by a hammer mill to obtain a catalyst powder.
[0025]
60 g of water was added to 30 g of the catalyst powder, and 7.5 g of SiO ₂ sol (OS-sol) was added as a binder to obtain a catalyst slurry. A cordierite honeycomb (manufactured by Hitachi Metals, number of cells: 400 cells / square inch, wall pressure: 6 mil) was immersed in this slurry and then dried to obtain a supported catalyst having a supported amount of 180 g / liter. This was further dried and calcined at 600 ° C. for 2 hours to obtain the desired catalyst.
[0026]
Example 2
Titanium oxide used in the preparation method of the first component in Example 1 was added to 330 g of hydrolyzed slurry of titanium sulfate (Ishihara Sangyo Co., Ltd., TiO ₂ content 30 wt%, sulfuric acid 8 wt%), and ammonium metatungstate aqueous solution (( NH ₄ ) ₆ • H ₂ W ₁₂ O ₄₀ • xH ₂ O, containing 50 wt% as WO ₃ ) 64g is replaced with 18g, silica sol is replaced with ethyl silicate (Si (OC ₂ H ₅ ) ₄ ), and kneaded with a heating kneader While the ethyl silicate was hydrolyzed with sulfuric acid to generate a silica sol, the other components were obtained in the same manner. Using this, a honeycomb catalyst containing CeO ₂ and Nb ₂ O ₅ was prepared in the same manner as in the example.
[0027]
Example 3
The first component of Example 1 was replaced with a commercially available TiO ₂ —WO ₃ —SiO ₂ compound (DT58 manufactured by Millennium, WO ₃ : 8.5 wt%, SiO ₂ : 9.7 wt%), and the catalyst was prepared in the same manner as others. did.
Example 4
The first component was prepared without adding the SiO ₂ sol in the first component preparation method of Example 1, and a catalyst was obtained in the same manner as the other components.
Examples 5 and 6
A catalyst was prepared in the same manner as in Example 1 except that the amount of the second component added was changed to 72 g and 24 g, respectively.
Examples 7-9
The addition amount of the second component and the third component in the catalyst of Example 4 was changed to 72 g and 55 g, 72 g and 18.5 g, and 24 g and 18.5 g, respectively.
[0028]
Comparative Example 1
The CeO ₂ sol and Nb ₂ O ₅ in Example 1 were replaced with cerium nitrate (Ce (NO ₃ ) ₃ .6H ₂ O) 90 g and niobic acid (Nb ₂ O ₅ content 75.5%) 7.3 g. A catalyst was obtained in the same manner.
Comparative Example 2
A catalyst was obtained in the same manner except that the first component in Example 1 was replaced with commercially available TiO ₂ powder (MC90, manufactured by Ishihara Sangyo Co., Ltd.).
Comparative Example 3
7.5 g of vanadyl sulfate (VOSO ₄ xH ₂ O, VOSO ₄ content 83%) is added to 100 g of the TiO ₂ —WO ₃ —SiO ₂ oxide used in Example 4, and water is added to heat knead and extrusion. After forming into a 3φ columnar shape with grains, it was dried with a fluid bed dryer, calcined at 500 ° C. for 2 hours, and further pulverized with a hammer mill to obtain a first component raw material powder. Subsequent preparation methods were the same as in Example 4 to prepare a TiO ₂ —WO ₃ —SiO ₂ —V ₂ O ₅ catalyst.
Comparative Examples 4 and 5
In Example 1, a catalyst without the addition of the second component and a catalyst without the addition of the third component were prepared.
[0029]
In order to evaluate the low-temperature activity, high-temperature activity, and heat resistance of the catalysts of Examples 1 to 9 and Comparative Examples 1 to 5, the prepared honeycomb catalyst was cut into a rectangular parallelepiped of 6 cells long × 6 cells wide × 50 mm long, and steam was removed. A heat resistance test was carried out in air containing 10% at 600 ° C. for 50 hours (hours), and the denitration performance of the catalyst before and after that was measured under the exhaust gas conditions shown in Table 1. Of the obtained results, the measurement results of the denitration rate at 250 ° C. and 450 ° C. before and after the durability test are summarized as shown in Table 2.
[0030]
In Table 2, Comparative Example 3 which is a Ti-WV catalyst with high initial performance used for normal denitration and Comparative Example 2 using only titanium oxide as the first component caused a significant decrease in activity in the heat resistance test. The performance after the test is extremely low. On the other hand, the catalyst which becomes Example 1-9 of this invention maintains high performance after a heat test, and it is clear that it is an excellent catalyst.
[0031]
In addition, Comparative Examples 4 and 5 in which the third component or the second component was not added, Comparative Example 1 in which soluble salts were used for the second and third components, and the catalyst according to the example of the present invention had heat resistance and It is clear that a preparation method that is excellent in low-temperature activity and that selectively combines the second component and the third component in a sol form is excellent in realizing a practical catalyst.
[0032]
[Table 1]

[0033]
[Table 2]

[0034]
【The invention's effect】
According to invention of Claims 1-5, the catalyst for exhaust gas purification which has heat resistance which has a titanium oxide as a main component, and low-temperature activity is obtained.
According to the invention described in claim 6, for example, NOx in exhaust gas from a simple cycle gas turbine power generation facility, a diesel engine, a car using a gas engine, or a power generation facility can be efficiently reduced and removed by urea or NH _3. it can.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory diagram that schematically illustrates use of a catalyst of the present invention.

Claims (5)

A catalyst for reducing and purifying nitrogen oxides in exhaust gas discharged from the outlet of a combustor or engine using ammonia or urea as a reducing agent, and a close mixed oxide of titanium oxide and tungsten oxide as a first component, or oxidation An intimate mixed oxide of titanium, tungsten oxide and silicon oxide, a composition having three components of cerium dioxide (CeO ₂ ) as a second component and niobium pentoxide (Nb ₂ O ₅ ) as a third component, The ratio of the second component to the component is more than 0 to 40% by weight, the ratio of the third component to the first component is more than 0 to 6% by weight, and the intimate mixed oxide has titanium oxide particles trioxide the tungsten particles and / or fine holes formed by oriented aggregation across the silicon dioxide particles, particles of cerium and niobium pentoxide particles dioxide is carried Purifying catalyst of the nitrogen oxides in the exhaust gas, characterized in that there. The first component is a dried intimate mixed oxide obtained by mixing a hydrated titanium oxide slurry or dried product thereof or a colloid containing titanium oxide with an oxo acid of tungsten (W) or a salt thereof; or The catalyst according to claim 1, wherein the catalyst is calcined after drying. 3. The catalyst according to claim 1 or 2, wherein a sol or organosilicic acid compound containing water of silicon dioxide as a dispersion medium is added. A cerium dioxide sol as a second component raw material and a niobium pentoxide sol as a third component raw material are added to the first component powder, and then kneaded, dried and fired. A method for preparing the catalyst according to any one of 1 to 3. A method for purifying exhaust gas, comprising using the honeycomb catalyst carrying the catalyst according to any one of claims 1 to 3 and detoxifying nitrogen oxides in the exhaust gas in the presence of a reducing agent.

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