JP4112933B2 - Exhaust gas treatment catalyst and exhaust gas treatment method - Google Patents

Description

【００４５】
以上の結果、実施例１〜６および参考例１〜４では、比較例１〜２に比べて、ＣＯ酸化率（ＣＯ除去率）およびアセトアルデヒド除去率のいずれについても優れた性能が発揮できることが確認された。
【００４６】
【発明の効果】
本発明にかかる排ガス処理触媒は、金属酸化物に対する貴金属粒子の全担持量のうち７０重量％以上を、触媒の表面から深さ１００μｍの領域に偏在させておくことで、排ガスの処理効率を格段に向上させることができる。
特に、一酸化炭素や未燃の揮発性有機化合物などを含む燃焼排ガスに対して、一酸化炭素と未燃の揮発性有機化合物とを同時に効率的に除去できる。
【図面の簡単な説明】
【図１】 本発明の実施形態を表す触媒の断面図（ａ）、拡大断面図（ｂ）および貴金属濃度グラフ（ｃ）。
【図２】 実施例１のＥＰＭＡ断面線分析グラフ。
【図３】 参考例２のＥＰＭＡ断面線分析グラフ。
【符号の説明】
１０ 排ガス処理触媒
１１ 担体
１２ 担持領域
１３ 排ガス通路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas treatment catalyst and an exhaust gas treatment method, and more particularly, to a catalyst for efficiently treating harmful substances contained in combustion exhaust gas discharged from a boiler, a gas turbine, a diesel engine, a gas engine, and the like. It is intended for an exhaust gas treatment method using a catalyst.
[0002]
[Prior art]
As an exhaust gas treatment catalyst, a catalyst in which noble metal particles are supported on a metal oxide is known.
An exhaust gas treatment catalyst made of such a noble metal-supported metal oxide is formed in a plate shape, a honeycomb shape, or the like, or is supported on another metal structure, and is disposed in the exhaust gas passage. The exhaust gas in circulation comes into contact with the catalyst, and harmful substances in the exhaust gas are catalyzed to be converted into harmless substances or substances that are easily detoxified or removed by subsequent treatment.
[0003]
Compared to catalysts composed of metal oxides only, catalysts made of noble metal-supported metal oxides can perform efficient exhaust gas treatment or treatment because the metal oxide and noble metal exhibit a complex catalytic action. There is an advantage that the range of ingredients that can be expanded.
Specifically, an exhaust gas purification catalyst in which Pt, Pd or the like is supported on a binary complex oxide such as a Ti—Si complex oxide or a ternary complex oxide is known (for example, Patent Documents). 1).
[0004]
[Patent Document 1]
JP 53-146991 A
[0005]
[Problems to be solved by the invention]
The above-mentioned noble metal-supported oxide catalyst has a higher processing efficiency than a catalyst composed only of a normal metal oxide, but may still fail to exhibit the required performance. In addition, since noble metals are used, the processing performance may not be sufficiently improved if the cost is high.
In the noble metal-supported oxide catalyst, it is expected that the catalyst function will be improved if the amount of the noble metal supported is increased. Moreover, SO in the exhaust gas _X Is included, SO ₂ → SO _Three The conversion rate increases and SO _Three Problems such as pipe corrosion due to
[0006]
Accordingly, an object of the present invention is to further improve the processing efficiency of the above-described noble metal-supported metal oxide catalyst. In particular, high processing efficiency can be achieved without increasing the amount of noble metal supported.
[0007]
[Means for Solving the Problems]
The exhaust gas treatment catalyst according to the present invention is a combustion exhaust gas. Volatile organic compounds and carbon monoxide A catalyst for treating Ti, -To a honeycomb formed body made of a metal oxide containing a Si composite oxide, At least one noble metal particle selected from the group consisting of Pt, Pd, Rh, Ru, Ir and Au, By chemisorption 70% by weight or more of the total supported amount of the noble metal particles with respect to the metal oxide is unevenly distributed in a region from the surface of the catalyst to a depth of 100 μm.
[Combustion exhaust gas]
It can be applied to combustion exhaust gas discharged from ordinary various industrial devices and facilities. Specific examples include boilers, gas turbines, diesel engines, gas engines, heating furnaces, and other various industrial process combustion exhaust gases.
[0008]
The gas component contained in the combustion exhaust gas and subject to exhaust gas treatment differs depending on the supply source, and also varies depending on environmental conditions such as emission standards. Specifically, as gas components that adversely affect the environment, carbon monoxide CO, nitrogen oxide NO _X Etc. In particular, in the case of combustion exhaust gas, unburned volatile compounds that are components derived from fuel but have not been burned are included, and adverse effects on the environment are a problem. The exhaust gas treatment catalyst of the present invention is effective for treatment of exhaust gas containing harmful substances such as carbon monoxide and unburned volatile compounds.
The combustion exhaust gas may be subjected to various exhaust gas treatments before the treatment process using the exhaust gas treatment catalyst of the present invention. Therefore, the components of the combustion exhaust gas at the stage discharged from the supply source and the combustion exhaust gas at the stage of exhaust gas treatment with the exhaust gas treatment catalyst of the present invention may be different.
[0009]
The temperature condition and speed of the combustion exhaust gas change depending on the discharge condition from the supply source and the history until the exhaust gas treatment is performed.
[Catalyst material]
Basically, the catalyst material can be selected from materials common to ordinary exhaust gas treatment catalysts.
<Metal oxide>
As a metal oxide, metals, such as Ti, Al, Si, Zr, can be included. These metals can be used alone or in combination. Among them, those containing Ti are preferable. Further, a combination of two or more elemental components such as a combination of Ti and Si, Ti and Zr, or Ti and Al is preferable. When combining Ti and other components, the Ti content is preferably 5 to 95 mol% of the entire metal oxide. More preferably, it is 20-95 mol%.
[0010]
Ti-Si composite oxide is SO ₂ Low oxidation rate, strong solid acidity, and advantageous for supporting noble metals by chemisorption.
Furthermore, by combining the metal oxide with a metal such as V, W, Mo, or Ce, the catalytic activity can be enhanced or a denitration function can be provided. Metals such as Fe, Cu, Mn, Cr, Co, Ni, Sn, and La can also be combined.
For the production of a metal oxide, a production technique of a metal oxide that is a normal catalyst material is applied. For example, a method in which a metal alkoxide is hydrolyzed by adding water to an alcohol solution containing a metal alkoxide, and the resulting metal oxide precursor is dried and fired as necessary to obtain a metal oxide; a soluble metal compound A method in which an aqueous solution containing is heated at a temperature of 80 ° C. to its boiling point to thermally hydrolyze the metal compound, and the obtained metal oxide precursor is dried and fired as necessary to obtain a metal oxide; A method of obtaining a metal oxide by hydrolyzing chloride in an oxygen-hydrogen flame; adding a basic substance to a solution containing a soluble metal compound to hydrolyze the metal compound, and then obtaining a metal oxide precursor Examples of the method include obtaining a metal oxide by drying and baking as necessary. Among these, a method of obtaining a metal oxide by adding a basic substance to a solution containing a soluble metal compound, hydrolyzing the metal compound, and drying and firing the obtained metal oxide precursor as necessary. Are preferably used. The basic substance is not particularly limited, and specific examples include amines such as ammonia, urea, dimethylamine, and trimethylamine, tetramethylammonium hydroxide, sodium hydroxide, sodium bicarbonate, and the like. be able to. The preparation of the Ti—Si composite oxide can be performed by the same means as that of a normal Ti—Si composite oxide, and examples thereof include the technique disclosed in Japanese Patent Laid-Open No. 53-146991. In particular, a technique disclosed in Japanese Patent Application No. 2000-99593 filed previously by the applicant of the present patent application is cited as a preferred technique.
[0011]
In addition to using a metal oxide prepared in advance as a raw material for supplying a metal oxide, a material that generates an oxide by firing can be used. Specifically, any of inorganic and organic compounds may be used. For example, hydroxides, ammonium salts, ammine complexes, oxalates, halides, sulfates, nitrates, carbonates, alkoxides containing a predetermined metal, etc. Can be used.
<Precious metal>
As the noble metal, Pt, Pd, Rh, Ru, Ir, Au, or the like can be used. A plurality of these noble metals can be combined. By using these noble metals, incombustible volatile compounds can be efficiently treated simultaneously with carbon monoxide contained in the combustion exhaust gas.
[0012]
[Supporting precious metals]
The noble metal is supported on the metal oxide in the form of particles. As the particle shape, a spherical shape or other shapes can be adopted. The noble metal particles preferably have an average particle size of 30 nm or less. More preferably, the average particle size is 20 nm or less. The smaller the noble metal particle size and the higher the dispersion state, the higher the activity.
As means for supporting the noble metal particles on the metal oxide, basically, the same means as that for a normal noble metal-supported metal oxide catalyst can be employed. In the process of supporting the noble metal particles on the metal oxide, the supporting means and the supporting conditions are selected so that the noble metal particles can be unevenly distributed on the surface of the metal oxide catalyst as much as possible.
[0013]
Specifically, a technique in which noble metal particles are supported by chemical adsorption on a metal oxide compact prepared in advance can be preferably applied. According to chemical adsorption, noble metal particles can be intensively and firmly supported on the surface layer of the metal oxide as compared with other supporting techniques such as physical adsorption. The precious metal can be finely dispersed in a finely dispersed state and unevenly distributed on the catalyst surface.
In the case of physical adsorption, the movement of noble metal particles on the metal oxide and the associated aggregation and deterioration of dispersibility of the noble metal particles are likely to occur with only a little energy (heating etc.). You may not be able to do enough.
[0014]
In the case of chemical adsorption, the noble metal particles are supported on the surface of the metal oxide by chemical bonding, and thus the movement of the noble metal particles from the metal oxide is much less likely to occur compared to physical adsorption. As a result, the exhaust gas treatment ability on the catalyst surface is stabilized and the treatment efficiency is improved, so that it becomes a preferred noble metal supporting means in the present invention.
As a specific means of chemical adsorption, when a metal oxide is impregnated with a solution containing a noble metal component in a heated state, chemical adsorption is efficiently performed, and precious metal particles are easily distributed and supported on the surface of the metal oxide. . Specifically, the temperature of the solution containing the noble metal component is preferably heated to 40 ° C. or higher, more preferably 50 ° C. or higher, 60 ° C. or higher, 70 ° C. or higher, 80 ° C. or higher, or 90 ° C. or higher. If the temperature of the solution is too low, chemical adsorption hardly occurs and the object of the present invention cannot be achieved.
[0015]
As the noble metal source, materials used for ordinary catalysts can be used. Specific examples include nitrates, halides, ammonium salts, and ammine complexes. When a basic complex such as an ammine complex is used, chemical adsorption can be performed efficiently.
The precious metal particles are distributed in a region from the surface of the catalyst to a depth of 100 μm in an amount of 70% by weight or more of the total supported amount of the metal oxide. Preferably, 90% by weight or more, more preferably 95% by weight or more of the total supported amount is unevenly distributed in a region from the surface of the catalyst to a depth of 100 μm.
[0016]
The catalytic reaction is considered to occur in the surface layer portion of the catalyst. Even if the loading amount of the noble metal is the same, the exhaust gas treatment efficiency by the catalyst is increased by increasing the noble metal concentration in the surface layer portion. If the noble metal can be supported while being unevenly distributed in the surface layer portion, the amount of the noble metal supported can be reduced while maintaining high efficiency. Cost can be reduced and SO ₂ The oxidation rate is also lowered.
The amount of the noble metal particles supported on the metal oxide varies depending on the combination of materials and the processing conditions of the supporting treatment, but usually the range of 0.01 to 5.0% by weight of the noble metal with respect to the total amount of the catalyst, Preferably it is used in the range of 0.05 to 1% by weight. If the amount of noble metal supported is too small, the catalytic activity is lowered. Even if the amount of noble metal supported is too large, the catalyst activity cannot be improved so much and the material cost is high. If too much precious metal is loaded, SO ₂ The oxidation rate may become too high, or the dispersibility of the noble metal particles may be deteriorated and the catalytic activity may be decreased instead.
[0017]
A catalyst made of a metal oxide supporting noble metal particles has a porous structure having fine pores. The amount of pores affects the flow of exhaust gas and the loading of noble metal particles. Usually, the total pore volume is 0.2-0.8cm ^Three A range of / g (mercury intrusion method) is appropriate. If the pore volume is too small, the catalytic activity is lowered. When there are too many pore volumes, the mechanical strength of a catalyst will become low.
The specific surface area of the catalyst also affects performance. Usually, specific surface area 30-250m ² / G (BET method) range is adopted, 40-200m ² / G is preferred. If the specific surface area is too small, the catalytic activity is not sufficient. If the specific surface area is too large, the catalyst activity is not improved so much, but there are problems such as an increase in accumulation of catalyst poisoning components and a decrease in catalyst life.
[0018]
[Usage form of catalyst]
The catalyst shape is not particularly limited, and a desired shape selected from a plate shape, a corrugated plate shape, a net shape, a honeycomb shape, a columnar shape, a cylindrical shape, and the like can be adopted. A fine catalyst having a granular shape, a rod shape, a spherical shape, a ring shape, a cylindrical shape, or the like can be used in a state where the container is filled or deposited.
The catalyst is usually used by being housed in a container-shaped catalyst reactor made of metal or the like. The catalyst reactor is provided with an exhaust gas inlet and an exhaust port so that the exhaust gas can efficiently come into contact with the catalyst accommodated therein.
[0019]
[Exhaust gas treatment method]
Basically, an exhaust gas treatment technique using a normal noble metal-supported metal oxide catalyst is applied.
Usually, a catalyst reactor in which a catalyst is accommodated is installed in the middle of a combustion exhaust gas discharge path. When the combustion exhaust gas passes through the catalytic reactor, it comes into contact with the surface of the catalyst to receive a predetermined catalytic action.
The catalyst of the present invention can simultaneously treat incombustible volatile organic compounds and carbon monoxide contained in combustion exhaust gas.
[0020]
By appropriately setting conditions such as the temperature and space velocity of the combustion exhaust gas, the efficiency of exhaust gas treatment with a catalyst is improved. For example, gas temperature 250 ° C to 500 ° C, space velocity 30,000H ^-1 ~ 1,000,000H ^-1 It is preferable to treat the combustion exhaust gas. More preferably, a gas temperature of 300 ° C. to 450 ° C. can be adopted, and a space velocity of 50,000H. ^-1 ~ 500,000H ^-1 Can be adopted. Further, LV = 0.1 m / s (Normal) or more, or dust 10 mg / m ^Three (Normal) The following processing conditions are preferred.
Another exhaust gas treatment process may be combined before or after the exhaust gas treatment process using the catalyst of the present invention. As another exhaust gas treatment step, a step capable of efficiently treating components that are difficult to treat with the catalyst of the present invention is preferable. For example, if an exhaust gas treatment process using a denitration catalyst is combined before an exhaust gas treatment process using the catalyst of the present invention, the exhaust gas after efficiently treating nitrogen oxides with the denitration catalyst is used as an exhaust gas treatment process using the catalyst of the present invention. In addition, carbon monoxide and unburned volatile organic compounds can be efficiently treated.
[0021]
As the exhaust gas treatment technology using the above-described denitration catalyst, the technology disclosed in Japanese Patent Application Laid-Open No. 10-235206 previously filed by the applicant of this patent can be applied. The denitration catalyst used in this technology has a structure in which a catalyst component A (titanium oxide) and a catalyst component B (metal oxide made of vanadium or tungsten) are combined, and the catalyst component B is supported on the catalyst component A. Have.
The treatment of nitrogen oxides in exhaust gas with a denitration catalyst is carried out in the presence of a reducing agent such as ammonia, urea and hydrazine, at a gas temperature of 250 to 600 ° C., and a space velocity of 200 to 100,000 H. ^-1 Under the following conditions. The amount of the reducing agent used is not particularly limited and may be appropriately adjusted so as to obtain a desired denitration rate, but the molar ratio of the reducing agent to nitrogen oxide (reducing agent / nitrogen oxide) is less than 2. It is preferable to supply in a range, more preferably less than 1.5, still more preferably less than 1.2. When the molar ratio is 2 or more, a large amount of reducing agent remains in the gas after the denitration treatment, which is not preferable.
[0022]
Known exhaust gas treatment methods described in JP-A-53-146991, JP-A-62-65721, JP-B-6-4126, and the like can be combined with the exhaust gas treatment method of the present invention.
In the present invention, as the noble metal-supported metal oxide catalyst used as the exhaust gas treatment catalyst, a catalyst in which the majority of the noble metal particles are unevenly distributed in a narrow region of the surface of the metal oxide, the activity on the catalyst surface is extremely high. To be high. As a result, it becomes a very effective method as a method for effectively treating exhaust gas having a large space velocity, such as exhaust gas treatment of a gas turbine.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
The exhaust gas treatment catalyst 10 shown in FIG. 1 (a) has a honeycomb structure with a cross section having a lattice shape.
The catalyst 10 is formed by supporting noble metal particles such as Pt on a carrier 11 composed of a Ti—Si composite oxide or the like. Exhaust gas treatment is performed by circulating the exhaust gas to be treated through a large number of through rectangular passages 13 provided in the carrier 11 having a lattice shape.
As shown in FIG. 1B, in the catalyst 10, the noble metal particle supporting region 12 is unevenly distributed at a certain depth within the carrier 11 from the surface facing the exhaust gas passage 13.
[0024]
The graph shown in FIG. 1C schematically shows the concentration distribution at each position of the noble metal particles supported on the support 11 in the transverse direction of FIG.
In the wall of the carrier 11, the noble metal concentration rapidly increases from the surface positions on both sides toward the inside, and then rapidly decreases after reaching the maximum concentration in the middle of the supporting region 12. It goes down to a very low concentration, almost near zero. The central region of the carrier 11 located inside the support region 12 contains only a very small amount of noble metal and is substantially free of noble metal. The inner edge position of the carrier region 12 is arranged on the surface side from the surface of the carrier 11 with a depth of 100 μm. The area below the concentration graph represents the amount of noble metal supported. Therefore, if the ratio of the lower area of the concentration graph in the range from the surface on both sides to the position of 100 μm on the inner side with respect to the lower area of the entire concentration graph is calculated, the ratio of the noble metal existing between the surface and the position of 100 μm is obtained. Desired. In FIG. 1C, 90% by weight or more of the total supported amount of the noble metal particles supported on the carrier 11 exists in a region from the surface to a depth of 100 μm. The noble metal concentration in the present invention is a concentration obtained by EPMA cross-sectional line analysis that provides a concentration graph as shown in FIG.
[0025]
The exhaust gas treatment catalyst 10 having the above-described structure is disposed in the middle of a combustion exhaust gas discharge path in a gas turbine or the like. The exhaust gas having a relatively high temperature and a high speed passes through the exhaust gas passage 13 of the catalyst 10 and contacts the catalyst 10 on the inner wall surface of the exhaust gas passage 13.
Since the inner wall surface of the exhaust gas passage 13 of the catalyst 10 is the carrying region 12 having a high precious metal concentration, the exhaust gas is efficiently catalyzed and the exhaust gas treatment is performed. Although the high-speed exhaust gas has a short contact time with the catalyst 10, the exhaust gas is reliably processed by the above-described efficient catalytic action.
[0026]
Combustion exhaust gas such as a gas turbine contains unburned volatile organic compounds, such as aldehydes, as well as carbon monoxide as a component to be treated. In the catalyst 10, these carbon monoxide and the volatile organic compound can be treated simultaneously to remove any components.
Next, the result of manufacturing the exhaust gas treatment catalyst of the present invention specifically, treating the exhaust gas using the catalyst, and evaluating the treatment performance will be described.
[0027]
【Example】
Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to these examples.
Examples below Reference examples The conditions of composition analysis and EPMA cross-sectional analysis of the catalysts produced in the comparative examples are shown below.
<Composition analysis of catalyst>
The analysis of the catalyst composition was performed under the following conditions by fluorescent X-ray analysis.
Analyzer: Rigaku Corporation, product name: RIX2000
Sample atmosphere during analysis: vacuum
Sample spin speed: 60 rpm
X-ray source: Rh tube
<EPMA cross section analysis>
Analyzer: manufactured by Shimadzu Corporation, product name: EPMA-1610
X-ray beam diameter: 1 μm
Acceleration voltage: 15 kV
Sample current: 0.1 μA
Measurement interval: 1 μm
Measurement time: 1 second / point
-Exhaust gas treatment catalyst-
<Example 1>
A honeycomb formed body made of a Ti—Si composite oxide was produced as a carrier by the method described in (Example 2) of Japanese Patent Application No. 2000-99593.
[0028]
Preparation of Ti-Si composite oxide:
Snowtex-20 (Nissan Chemical Co., Ltd. silica sol, about 20 wt% SiO ₂ Containing) 21.3 kg, stirring and mixing, titanyl sulfate in sulfuric acid solution (TiO 2) ₂ (125 g / liter, sulfuric acid concentration 550 g / liter) was gradually added dropwise with stirring. The obtained gel was allowed to stand for 3 hours, filtered, washed with water, and then dried at 150 ° C. for 10 hours. This was baked at 500 ° C. and further pulverized using a hammer mill to obtain a powder. TiO in powder X-ray diffraction chart ₂ And SiO ₂ Thus, it was confirmed by a broad diffraction peak that it was a complex oxide of titanium and silicon (Ti-Si complex oxide) having an amorphous fine structure.
[0029]
Manufacture of honeycomb molded body:
Add 1 kg of phenolic resin (Bellepearl (trade name), Kanebo Co., Ltd.) and 0.5 kg of starch as a molding aid to 20 kg of the above Ti-Si composite oxide, and mix them with a kneader while adding an appropriate amount of water. After kneading well, it was formed into a honeycomb shape having an external shape of 80 mm square, an aperture of 2.1 mm, a wall thickness of 0.4 mm, and a length of 500 mm with an extruder. Next, after drying at 80 ° C., firing was performed in an air atmosphere at 450 ° C. for 5 hours to obtain a honeycomb formed body.
The honeycomb formed body has a lattice-like structure as shown in FIG. 1 (a), and the opening of each exhaust gas passage is 2.1 mm and the wall thickness of the lattice wall is 0.4 mm.
[0030]
Production of noble metal supported composite oxide catalyst:
The honeycomb formed body was impregnated with a boiled dinitrodiammine platinum solution, and Pt was chemisorbed and dried. Next, it was fired in an air atmosphere at 450 ° C. for 2 hours to obtain a catalyst A in which Pt as noble metal particles was supported on a support made of a honeycomb formed body.
When the composition of the obtained catalyst A was analyzed, it was Ti—Si composite oxide: Pt = 99.7: 0.3 (weight ratio).
The catalyst A was subjected to Pt EPMA cross section analysis, and the results are shown in FIG. From this result, it was confirmed that 90% by weight or more of Pt was present in the region from the surface of the catalyst A to a depth of 100 μm.
[0031]
The average particle diameter of Pt measured using a transmission electron microscope was less than 5 nm.
<Example 2>
In Example 1, Catalyst B was obtained in the same process as in Example 1 except that a hexaammine platinum hydroxide solution was used instead of the dinitrodiammine platinum solution.
The composition of the catalyst B was Ti—Si composite oxide: Pt = 99.7: 0.3 (weight ratio). As a result of the EPMA cross-sectional line analysis of Pt, it was confirmed that 90% by weight or more of the total supported amount of Pt exists in a region from the surface to a depth of 100 μm. From the measurement result of the transmission electron microscope, the average particle diameter of Pt was less than 5 nm.
[0032]
< reference Example 1 >
In Example 1, as a metal oxide, a commercially available titanium oxide powder (made by Millennium, trade name DT-51) was used instead of the Ti—Si composite oxide, and a titanium oxide honeycomb molded body was obtained. In the same manner as in Example 1, Catalyst C was obtained.
The composition of catalyst C is TiO ₂ : Pt = 99.7: 0.3 (weight ratio). As a result of the EPMA cross-sectional line analysis of Pt, it was confirmed that 90% by weight or more of Pt in the total supported amount was present in the region from the surface to a depth of 100 μm. From the measurement result of the transmission electron microscope, the average particle diameter of Pt was less than 5 nm.
[0033]
< reference Example 2 >
Al ₂ O ₃ Was used as a material, and a honeycomb formed body having the same shape and structure as in Example 1 was produced and used as a carrier.
Except that the honeycomb formed body was impregnated with a dinitrodiammine platinum solution at room temperature, Pt was supported in the same process as in Example 1 to obtain Catalyst D.
The composition of catalyst D is Al ₂ O ₃ : Pt = 99.6: 0.4 (weight ratio).
For catalyst D, an EPMA cross-sectional analysis of Pt was performed, and the results are shown in FIG. From this result, it was confirmed that 80% by weight of the total supported amount of Pt exists in a region from the surface to a depth of 100 μm.
[0034]
The average particle diameter of Pt measured using a transmission electron microscope was less than 5 nm.
< reference Example 3 >
Preparation of titanium oxide:
Sulfuric acid solution of titanyl sulfate (TiO2) in 1000 liters of 10 wt% ammonia water ₂ (125 g / liter, sulfuric acid concentration 550 g / liter) was gradually added dropwise with stirring. The obtained gel was allowed to stand for 3 hours, filtered, washed with water, and then dried at 150 ° C. for 10 hours. This was baked at 500 ° C. and further pulverized using a hammer mill to obtain titanium oxide powder.
[0035]
Manufacture of honeycomb molded body:
Add 1 kg of phenolic resin (Bellepearl (trade name), Kanebo Co., Ltd.) and 0.5 kg of starch as a molding aid to 20 kg of the above titanium oxide powder and mix well. Mix well with a kneader while adding an appropriate amount of water. After kneading, it was molded into a honeycomb shape having an external shape of 80 mm square, an aperture of 2.1 mm, a wall thickness (lattice wall thickness) of 0.4 mm, and a length of 500 mm by an extruder. Next, after drying at 80 ° C., firing was performed at 450 ° C. in an air atmosphere for 5 hours to obtain a honeycomb formed body of titanium oxide.
Production of noble metal supported titanium oxide catalyst:
The honeycomb formed body was impregnated with a boiled dinitrodiammine platinum solution, and Pt was chemisorbed and dried. Subsequently, it was fired in an air atmosphere at 450 ° C. for 2 hours to obtain a catalyst E in which Pt as noble metal particles was supported on a support made of a honeycomb formed body.
[0036]
When the composition of the obtained catalyst E was analyzed, TiO ₂ : Pt = 99.7: 0.3 (weight ratio).
When an EPMA cross-sectional analysis of Pt was performed on catalyst E, it was confirmed that 90% by weight or more of the total supported amount of Pt was present in the region from the surface of catalyst E to a depth of 100 μm.
The average particle diameter of Pt measured using a transmission electron microscope was less than 5 nm.
< reference Example 4 >
reference Example 3 In, except that the honeycomb formed body was impregnated with a dinitrodiammine platinum solution at room temperature, reference Example 3 The catalyst F was obtained by supporting Pt in the same process as in Example 1.
[0037]
The composition of catalyst F is TiO ₂ : Pt = 99.7: 0.3 (weight ratio). As a result of the EPMA cross-sectional analysis of Pt, it was confirmed that 80% by weight of Pt in the total supported amount was present in the region from the surface to a depth of 100 μm. The average particle diameter of Pt measured using a transmission electron microscope was less than 5 nm.
<Comparative Example 1>
reference Example 3 Except that the honeycomb molded body was impregnated with a chloroplatinic acid solution at room temperature, reference Example 3 In the same process as described above, Pt was supported and Catalyst G was obtained.
The composition of catalyst G is TiO ₂ : Pt = 99.7: 0.3 (weight ratio). As a result of the EPMA cross-sectional line analysis of Pt, it was confirmed that Pt was present in the region from the surface of the catalyst G to a depth of 100 μm and less than 70% by weight of the total supported amount. The average particle diameter of Pt measured using a transmission electron microscope was less than 5 nm.
[0038]
<Example 3 >
In Example 1, except that the honeycomb formed body was impregnated with a dinitrodiammine platinum solution at room temperature, Pt was supported and Catalyst H was obtained in the same process as in Example 1.
The composition of the catalyst H was Ti—Si composite oxide: Pt = 99.7: 0.3 (weight ratio). As a result of the EPMA cross-sectional line analysis of Pt, it was confirmed that 80% by weight of the total supported amount of Pt was present in the region from the surface to a depth of 100 μm. The average particle diameter of Pt measured using a transmission electron microscope was less than 5 nm.
<Comparative example 2>
reference Example 3 In place of titanium oxide powder, Al ₂ O ₃ Except for using powder and impregnating the honeycomb molded body with chloroplatinic acid solution at room temperature, reference Example 3 In the same manner as described above, Pt was supported and Catalyst I was obtained.
[0039]
The composition of catalyst I is Al ₂ O ₃ : Pt = 99.7: 0.3 (weight ratio). As a result of the EPMA cross-sectional line analysis of Pt, it was confirmed that Pt was present in the region from the surface of the catalyst I to a depth of 100 μm and less than 70% by weight of the total supported amount. The average particle diameter of Pt measured using a transmission electron microscope was less than 5 nm.
<Example 4 >
The Ti—Si composite oxide honeycomb formed body prepared in Example 1 was impregnated with a cerium nitrate solution, dried, and then fired at 450 ° C. for 2 hours in an air atmosphere. Furthermore, this cerium-supported honeycomb formed body was impregnated with a boiled ruthenium nitrate solution, dried, and then fired at 450 ° C. for 2 hours in an air atmosphere to support Ru and Ce, whereby catalyst J was obtained. .
[0040]
The composition of the catalyst J was Ti—Si composite oxide: Ce: Ru = 94.4: 5: 0.6 (weight ratio). As a result of EPMA cross-sectional line analysis of Ru, it was confirmed that 90% by weight or more of Ru was present in the region from the surface to a depth of 100 μm.
<Example 5 >
In Example 1, except that a mixed solution of hexaammine platinum hydroxide and tetraammine palladium hydroxide was used instead of the dinitrodiammine platinum solution, Pt and Pd were supported in the same process as in Example 1, Catalyst K was obtained.
[0041]
The composition of the catalyst K was Ti—Si composite oxide: Pt: Pd = 99.6: 0.2: 0.2 (weight ratio). As a result of EPMA cross-sectional line analysis of Pt and Pd, it was confirmed that 90% by weight or more of the total supported amount of Pt and Pd was present in the region from the surface to a depth of 100 μm.
<Example 6 >
The honeycomb formed body of Ti—Si composite oxide prepared in Example 1 was impregnated with a tungstic acid solution, dried, and then fired at 450 ° C. for 2 hours in an air atmosphere. Further, this tungsten-supported honeycomb formed body was impregnated with a boiled hexaneammineplatinum hydrochloride solution, dried, and then fired at 450 ° C. for 2 hours in an air atmosphere to support Pt and W. L was obtained.
[0042]
The composition of the catalyst L was Ti—Si composite oxide: W: Pt = 97.2: 2.5: 0.3 (weight ratio). As a result of the EPMA cross-sectional line analysis of Pt, it was confirmed that 90% by weight or more of the total supported amount of Pt exists in a region from the surface to a depth of 100 μm.
-Treatment of exhaust gas-
Example 1 6, Reference Examples 1-4 In addition, the “catalysts A to L” produced in Comparative Examples 1 and 2 were treated by contacting an exhaust gas having the following composition, and the CO oxidation rate (CO removal rate) and the acetaldehyde removal rate were measured.
[0043]
<Processing conditions>
Exhaust gas composition: CO = 20ppm, CH _Three CHO = 20 ppm, O ₂ = 12%
H ₂ O = 8%, N ₂ = Balance.
Exhaust gas temperature: 350 ° C
Space velocity: 100,000H ^-1 (STP)
<Measurement item>
CO oxidation rate (CO removal rate) (%) =
[{(Reactor inlet CO concentration)-(Reactor outlet CO concentration)}}
/ (Reactor inlet CO concentration)] × 100
Acetaldehyde removal rate (%) =
[{(Reactor inlet acetaldehyde concentration)
-(Reactor outlet acetaldehyde concentration)}
/ (Reactor inlet acetaldehyde concentration)] × 100
The results of the above exhaust gas treatment are summarized in Table 1 below.
[0044]
[Table 1]

[0045]
As a result, Examples 1 to 6 and Reference Examples 1-4 Then, compared with Comparative Examples 1-2, it was confirmed that the outstanding performance can be exhibited about both CO oxidation rate (CO removal rate) and acetaldehyde removal rate.
[0046]
【The invention's effect】
In the exhaust gas treatment catalyst according to the present invention, exhaust gas treatment efficiency is remarkably increased by unevenly distributing 70% by weight or more of the total supported amount of the noble metal particles to the metal oxide in a region having a depth of 100 μm from the surface of the catalyst. Can be improved.
In particular, carbon monoxide and unburned volatile organic compounds can be efficiently removed simultaneously from combustion exhaust gas containing carbon monoxide and unburned volatile organic compounds.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view (a), an enlarged cross-sectional view (b), and a noble metal concentration graph (c) of a catalyst representing an embodiment of the present invention.
2 is an EPMA sectional line analysis graph of Example 1. FIG.
[Fig. 3] reference Example 2 EPMA sectional line analysis graph.
[Explanation of symbols]
10 Exhaust gas treatment catalyst
11 Carrier
12 Loading area
13 Exhaust gas passage

Claims (6)

A catalyst for treating volatile organic compounds and carbon monoxide contained in combustion exhaust gas,
At least one noble metal particle selected from the group consisting of Pt, Pd, Rh, Ru, Ir and Au is supported by chemical adsorption on a honeycomb formed body made of a metal oxide containing a Ti— Si composite oxide ,
70% by weight or more of the total supported amount of the noble metal particles with respect to the metal oxide is unevenly distributed in a region from the surface of the catalyst to a depth of 100 μm.
An exhaust gas treatment catalyst characterized by that. The noble metal particles are supported by the chemical adsorption by impregnating the honeycomb molded body with a solution containing a noble metal component heated to 40 ° C. or higher, and adsorbing the noble metal component on the surface layer of the honeycomb molded body and then firing in an air atmosphere. in are those that are made, the metal 90 wt% or more of the total supported amount of the noble metal particles to the oxide are unevenly distributed in the area to a depth of 100μm from the surface of the catalysts, according to claim 1 Exhaust gas treatment catalyst.   The metal oxide further comprises at least one metal selected from the group consisting of V, W, Mo, Fe, Cu, Mn, Cr, Co, Ni, Sn, La, and Ce. The exhaust gas treatment catalyst as described.   The exhaust gas treatment catalyst according to any one of claims 1 to 3, wherein the noble metal particles have an average particle diameter of 30 nm or less. A method for treating volatile organic compounds and carbon monoxide contained in combustion exhaust gas,
The step (a) of bringing a combustion exhaust gas having a gas temperature of 250 ° C. to 500 ° C. and a space velocity of 30,000 H ^{−1 to} 1,000,000 H ⁻¹ into contact with the exhaust gas treatment catalyst according to claim 1. including,
An exhaust gas treatment method characterized by that.   The exhaust gas treatment method according to claim 5, further comprising a step (-a) of bringing the combustion exhaust gas into contact with a denitration catalyst before the step (a).

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