JP5979422B2 - Exhaust gas purification catalyst and method for producing the same - Google Patents

Description

  The present invention relates to an exhaust gas purifying catalyst and a method for producing the same.

  Conventionally, silver is supported on a metal oxide carrier made of alumina, titania, silica, zirconia, ceria, etc. as an exhaust gas purifying catalyst having a catalytic action for oxidizing hydrocarbon (HC), carbon monoxide (CO), and the like. Catalysts are known. As a method for producing such a catalyst, for example, in WO 2007/011062 (Patent Document 1), a precipitate of a nitrate solution containing cerium (Ce) and silver (Ag) is calcined. A method for obtaining a catalyst comprising an aggregate composed of silver particles having an average primary particle diameter of 10 to 100 nm and ceria covering the periphery of the silver particles is disclosed in Japanese Patent Application Laid-Open No. 2000-218163 (Patent Document 2). ) Discloses a method in which nickel (Ni) is supported on an alumina base material, heated in a non-oxidizing atmosphere, then silver is supported and heated in a non-acidic atmosphere. However, the exhaust gas purifying catalyst obtained by the methods described in Patent Documents 1 and 2 has a problem that the average primary particle diameter of silver particles is large and sufficient oxidation catalyst activity is not exhibited.

  On the other hand, as a method of obtaining ultrafine particles of silver, a method of adding amines, sodium borohydride, hydrazine, citric acid, etc. as a reducing agent to a silver compound, polyvinylpyrrolidone, polyvinyl alcohol, multiple A method of adding an organic polymer such as an acid is known. For example, in JP 2011-225974 A (Patent Document 3), silver nitrate is reduced with citric acid in the presence of a hydrophilic polymer compound such as polyvinylpyrrolidone and an amine compound, and the average particle size is about 3.0 to 20 nm. Japanese Patent Application Laid-Open No. 2010-37574 (Patent Document 4) discloses a method for obtaining an aqueous dispersion of silver nanoparticles in the presence of a protective colloid comprising a specific amine and a carboxylic acid. Reduction to obtain silver colloid particles having an average particle diameter of about 6.3 nm comprising silver nanoparticles and protective colloids covering the silver nanoparticles, or sintering the metal nano paste containing the silver colloid particles A method for obtaining a fine line pattern is disclosed.

  JP 2009-102716 A (Patent Document 5) discloses that an average particle diameter of 20 nm or less is obtained by reducing a silver compound dissolved in a primary amine having an unsaturated bond in a molecular weight of 200 to 400 with an alcohol amine. A method for precipitating silver particles is disclosed, and Japanese Patent Application Laid-Open No. 2007-217794 (Patent Document 6) uses a multiple acid such as polyacrylic acid as a stabilizer and reduces the silver compound to obtain an average particle size of 5 A method of obtaining ˜100 nm silver particles is disclosed.

  However, in the silver particle dispersion or colloidal solution obtained by the production methods described in Patent Documents 3 to 4, the particle diameter of the silver particles is not yet sufficiently small, and described in Patent Documents 5 to 6 Since silver particles obtained by the above production method tend to aggregate when dispersed in water and the particle diameter tends to increase, a catalyst produced using these particles has a problem that sufficient oxidation catalytic activity is not exhibited. Was.

  Therefore, for the purpose of reducing the particle size of colloidal particles containing silver, Japanese Patent Application Laid-Open No. 2004-33901 (Patent Document 7) describes silver with a reducing compound such as an amine in the presence of a polymer pigment dispersant. It has been disclosed to use a microreactor in reducing the compound. However, even in such a method, the average particle diameter of the obtained colloidal particles was not yet sufficiently small, about 3.9 to 6.3 nm.

  Moreover, as a method of obtaining a colloid solution using an apparatus such as the microreactor, for example, in JP-A-2011-144420 (Patent Document 8) and JP-A-2011-144421 (Patent Document 9), reduction is performed. A method of obtaining a noble metal-based colloidal solution by homogeneously mixing a solution containing a noble metal compound and a solution containing a polymer dispersant at a high shear rate in the presence of an agent is disclosed.

International Publication No. 2007/011062 JP 2000-218163 A JP 2011-225974 A JP 2010-37574 A JP 2009-102716 A JP 2007-217794 A JP 2004-33901 A JP 2011-144420 A JP 2011-144421 A

  However, in the methods described in Patent Documents 8 to 9, when a silver compound is used instead of the noble metal compound, the reduction reaction does not proceed sufficiently, and it is difficult to obtain ultrafine particles containing silver. The present inventors have found out.

  In addition, when a catalyst is produced by supporting a silver-containing particle on a carrier using a colloidal solution in which silver-containing colloidal particles are dispersed, an organic substance such as a dispersant or a protective agent contained in the colloidal solution is baked. However, in the conventional colloidal solution containing silver, an organic polymer such as polyvinylpyrrolidone, polyvinyl alcohol, oleylamine, multiple acid, polyalkyleneimine is used as the dispersant or protective agent. When the organic polymer is baked and removed, an abnormal overheating state occurs on the catalyst surface, and ultrafine particles on the catalyst surface grow, resulting in a problem that the activity of the resulting catalyst is lowered. Found.

  The present invention has been made in view of the above-described problems of the prior art, can prevent abnormal overheating during firing, and has a high level of catalytic activity in which ultrafine particles containing silver are stably held. It is an object of the present invention to provide a method for producing an exhaust gas purifying catalyst capable of obtaining a catalyst, and an exhaust gas purifying catalyst obtained by the method.

  As a result of intensive studies to achieve the above object, the inventors of the present invention specified a first raw material solution containing silver ions and a second raw material solution containing a water-soluble amine while heating. Introducing directly into the shear rate region and mixing homogeneously, the mass ratio of carbon and silver atoms (carbon atoms / silver atoms) determined from the specified inductively coupled plasma emission analysis is in a specific range. It was found that a silver-based colloidal solution is obtained in which the average particle size of colloidal particles containing silver is within a specific range.

  Further, the inventors of the present invention provide a method for producing an exhaust gas purifying catalyst comprising a metal oxide support and ultrafine particles containing silver supported on the metal oxide support, and using the silver-based colloidal solution, A catalyst having a high level of catalytic activity in which ultra-fine particles containing silver are stably held can be prevented by supporting the ultra-fine particles containing silver on the metal oxide support. The inventors have found that it is possible to obtain the present invention and have completed the present invention.

That is, the method for producing the exhaust gas purifying catalyst of the present invention comprises:
A method for producing an exhaust gas purification catalyst comprising a metal oxide support and ultrafine particles supported on the metal oxide support and containing silver,
The first raw material solution containing silver ions and the second raw material solution containing a water-soluble amine are placed in a region having a shear rate of 1,000 to 50,000 sec ^{−1 at} 40 to 95 ° C. A step of obtaining a silver-based colloidal solution in which colloidal particles containing silver are dispersed by directly introducing and independently mixing independently;
The step of contacting the silver-based colloidal solution with the metal oxide support, followed by firing in the atmosphere at 300 to 600 ° C. to obtain the exhaust gas purification catalyst,
The component ratio of carbon to silver in the silver-based colloidal solution is inductively coupled plasma after alumina powder is mixed with the silver-based colloidal solution and dried under reduced pressure at 300 torr or less and then heated at 120 ° C. for 12 hours in the air. The mass ratio of carbon atoms to silver atoms (carbon atom / silver atom) determined by emission analysis is in the range of 0.17 to 2.5, and the average particle size of the colloidal particles is 1.0 to Within the range of 3.5 nm,
It is characterized by.

  In the method for producing an exhaust gas purification catalyst of the present invention, the average primary particle diameter of the ultrafine particles after the reduction treatment is performed at 500 ° C. in a reducing atmosphere with respect to the exhaust gas purification catalyst is 5.0. It is preferable to be within a range of ˜20 nm.

  Further, in the step of obtaining the silver-based colloidal solution, the molar ratio of the silver ions contained in the first raw material solution and the water-soluble amine contained in the second raw material solution (silver ion moles: water-soluble). It is preferable to introduce the first raw material solution and the second raw material solution so that the number of amine moles) is 1: 4 to 1: 100.

  In the method for producing an exhaust gas purifying catalyst of the present invention, the water-soluble amine is preferably ethylenediamine. Further, in the step of obtaining the exhaust gas purifying catalyst, the metal oxide support with respect to 100 parts by mass of the metal oxide carrier. It is preferable that the silver-based colloidal solution is brought into contact with the metal oxide support so that the supported amount of ultrafine particles is 0.5 to 20 parts by mass in terms of metal.

  The reason why the production method of the present invention can prevent abnormal overheating at the time of firing and can provide a catalyst having a high level of catalytic activity in which ultrafine particles containing silver are stably maintained is not necessarily the reason. Although not certain, the present inventors speculate as follows. That is, in a conventional colloidal solution containing silver, an organic polymer such as polyvinylpyrrolidone, polyvinyl alcohol, oleylamine, multiple acid, polyalkyleneimine is usually added as a dispersant or protective agent to silver particles or silver compound particles. Although it adsorbs and suppresses its agglomeration, if the organic polymer is baked and removed during the production of a catalyst using such a colloidal solution, an abnormal overheating state occurs on the catalyst surface, resulting in a super Fine particles grow. This is because silver particles and silver compound particles, which are active species activated during calcination, promote the combustion of the organic polymer, and as a result, the surface of the catalyst is exposed to an abnormal overheating state above the calcination temperature. The present inventors speculate that silver particles and silver compound particles grow and the activity of the catalyst decreases.

  In contrast, in the production method of the present invention, an amount necessary for protecting silver particles and silver compound particles by obtaining a silver colloid solution using a low molecular weight water-soluble amine under specific conditions. Only the organic substance is adsorbed on the fine particles containing silver, and colloidal particles having a sufficiently small particle diameter are obtained. Therefore, ultrafine particles containing silver can be uniformly dispersed on the metal oxide support, and furthermore, abnormal overheating of the catalyst surface at the time of firing and removing the organic matter is prevented, so that particle growth and catalyst activity decrease. The present inventors speculate that this is suppressed.

  According to the present invention, it is possible to produce an exhaust gas purifying catalyst that can prevent abnormal overheating at the time of firing and can obtain a catalyst having a high level of catalytic activity in which ultrafine particles containing silver are stably held. It becomes possible to provide a method and an exhaust gas purifying catalyst obtained by the method.

It is a schematic longitudinal cross-sectional view which shows suitable one Embodiment of the manufacturing apparatus of the colloidal solution which concerns on this invention. FIG. 2 is an enlarged longitudinal sectional view showing a tip portion (stirring portion) of the homogenizer 10 shown in FIG. 1. It is a side view of the inner side stator 13 shown in FIG. It is a cross-sectional view of the inner stator 13 shown in FIG. 2 is a transmission electron microscope (TEM) photograph of the colloidal particles obtained in Example 1. FIG.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

The method for producing the exhaust gas purifying catalyst of the present invention comprises:
A method for producing an exhaust gas purification catalyst comprising a metal oxide support and ultrafine particles supported on the metal oxide support and containing silver,
The first raw material solution containing silver ions and the second raw material solution containing a water-soluble amine are placed in a region having a shear rate of 1,000 to 50,000 sec ^{−1 at} 40 to 95 ° C. A step of obtaining a silver-based colloidal solution in which colloidal particles containing silver are dispersed by directly introducing and independently mixing independently;
The step of contacting the silver-based colloidal solution with the metal oxide support, followed by firing in the atmosphere at 300 to 600 ° C. to obtain the exhaust gas purification catalyst,
The component ratio of carbon to silver in the silver-based colloidal solution is inductively coupled plasma after alumina powder is mixed with the silver-based colloidal solution and dried under reduced pressure at 300 torr or less and then heated at 120 ° C. for 12 hours in the air. The mass ratio of carbon atoms to silver atoms (carbon atom / silver atom) determined by emission analysis is in the range of 0.17 to 2.5, and the average particle size of the colloidal particles is 1.0 to Within the range of 3.5 nm,
Is a manufacturing method characterized by

[Colloid solution preparation process]
In the production method of the present invention, first, a first raw material solution containing silver ions and a second raw material solution containing a water-soluble amine are mixed at 40 to 95 ° C. for 1,000 to 50,000 sec ^−. A silver-based colloidal solution in which silver-containing colloidal particles are dispersed is obtained by directly directly introducing into a region having a shear rate of ¹ and homogeneously mixing them (colloidal solution preparation step).

  The first raw material solution containing silver ions is silver; silver salt (acetate, nitrate, chloride, sulfate, sulfite, inorganic complex salt, etc.), silver oxide, silver hydroxide, etc. It is obtained by dissolving the compound in a solvent. Among these, it is preferable to use a silver salt, and it does not produce a corrosive solution such as HCl as a by-product, and does not contain sulfur as a performance deterioration component in the obtained exhaust gas purification catalyst. From the viewpoint, it is more preferable to use acetate or nitrate.

  Moreover, as a silver ion concentration in a 1st raw material solution, it is preferable that it is 0.01-1.5 mol / L, and it is more preferable that it is 0.025-0.5 mol / L. When the silver ion concentration is within the above range, the crystallites of silver or silver compound are dispersed in the liquid as it is or in the form of uniform aggregates with a small diameter to obtain a colloidal solution having excellent storage stability. There is a tendency to be able to. On the other hand, when the silver ion concentration is less than the lower limit, the yield of colloidal particles tends to decrease. On the other hand, when the upper limit is exceeded, aggregation occurs and the average particle size of the colloidal particles tends to increase.

  The second raw material solution containing a water-soluble amine can be obtained by dissolving the water-soluble amine in a solvent. The water-soluble amine preferably has a weight average molecular weight of 60 to 200, and more preferably 60 to 150. When the weight average molecular weight is less than the lower limit, the function as a protective agent tends to be reduced. On the other hand, when the upper limit is exceeded, the temperature on the catalyst surface at the time of calcination increases and the catalyst surface There is a tendency that the particles supported on the particles grow and the activity of the resulting catalyst is lowered. In the present invention, the weight average molecular weight is determined by gel permeation chromatography (GPC) (device name: molecular weight distribution measurement system (manufactured by Shimadzu Corporation), solvent: THF, column: GPC-80M, temperature: 40 ° C., speed: 1 ml / min) and is a value converted with a standard substance (trade name: shodex STANDARD, manufactured by Showa Denko KK).

  Examples of such water-soluble amines include diamines such as ethylenediamine, propylenediamine, tetramethylenediamine, and hexamethylenediamine; ethanolamines such as N, N-dimethylethanolamine; and monoamines such as hexylamine. From the standpoint that abnormal overheating during firing is further suppressed and removal of excess amine tends to be easy, ethylenediamine is preferred.

  Moreover, as a water-soluble amine density | concentration in a 2nd raw material solution, it is preferable that it is 0.11-10 mol / L, and it is more preferable that it is 0.25-5 mol / L. If the water-soluble amine concentration is less than the lower limit, the average particle size of the colloidal particles tends to be large. On the other hand, if the upper limit is exceeded, it is difficult to remove excess amine and the mixture tends to be overheated during firing.

  In the production method of the present invention, the solvent used in the first raw material solution and the second raw material solution is water, a water-soluble organic solvent (methanol, ethanol, propanol, isopropanol, butanol, acetone, acetonitrile, etc.), water and the above-mentioned Examples thereof include a mixed solvent with a water-soluble organic solvent.

In the colloidal solution preparation step according to the present invention, the first raw material solution and the second raw material solution are directly and independently introduced into a region having a shear rate of 1,000 to 50,000 sec ⁻¹ to be homogeneous. Mix. By such homogeneous mixing, even in a solvent such as water in which silver and silver compound crystallites are likely to aggregate, the crystallites are dispersed in the liquid in the same state or in a uniform aggregate state with a smaller diameter. Is possible.

  As an apparatus used for such a mixing method, for example, the apparatus shown in FIG. Hereinafter, a preferred embodiment of an apparatus for producing a colloidal solution according to the present invention will be described in detail with reference to the drawings. In the following description and drawings, the same or corresponding elements are denoted by the same reference numerals, and duplicate descriptions are omitted.

  The manufacturing apparatus shown in FIG. 1 includes a homogenizer 10 as a stirring device, and a front end portion (stirring portion) of the homogenizer 10 is disposed in the reaction vessel 20. As shown in FIG. 2, the front end of the homogenizer 10 includes a concave outer stator 12 disposed so that a predetermined gap region is formed between the concave rotor 11 and the outer periphery of the rotor 11, and the rotor. 11 and a convex inner stator 13 arranged so that a predetermined gap region is formed between the inner periphery of the inner stator 11 and the inner periphery. Further, the rotor 11 is connected to a motor 15 via a rotating shaft 14 and has a structure capable of rotating.

  In the manufacturing apparatus shown in FIG. 1, a plurality of nozzles, that is, a nozzle 16 </ b> A for introducing the raw material solution A and a nozzle 16 </ b> B for introducing the raw material solution B are opposed to the rotor 11 in the inner stator 13. It is provided on each surface. Further, a supply device (not shown) for the raw material solution A is connected to the nozzle 16A via a flow path 17A, and a supply device (not shown) for the raw material solution B is connected to the nozzle 16B via a flow path 17B. The raw material solution A and the raw material solution B can be directly and independently introduced into the region between the rotor 11 and the inner stator 13.

  Further, in the manufacturing apparatus shown in FIG. 1, as shown in FIGS. 3 and 4, the nozzle 16 </ b> A and the nozzle 16 </ b> B are orthogonal to the rotation axis X of the rotor 11 on the surface facing the rotor 11 in the inner stator 13. The predetermined surfaces Y are alternately provided in the outer peripheral direction.

  3 and 4, 12 nozzles 16A and 12 nozzles 16B are provided (24-hole type), but the numbers of nozzles 16A and nozzles 16B are not particularly limited. Therefore, one nozzle 16A and one nozzle 16B may be provided (two-hole type), but the time from when the raw material solution A and the raw material solution B are introduced into the region until homogeneous mixing is further reduced. From the viewpoint of being able to do so, the number of nozzles 16A and 16B is preferably 10 or more, and more preferably 20 or more. On the other hand, the upper limit of the number of each of the nozzles 16A and 16B is not particularly limited and varies depending on the size of the device, but from the viewpoint of more reliably preventing nozzle clogging, the alternately arranged nozzles 16A. It is preferable that the diameter of the opening of the nozzle 16B can take a dimension of about 0.1 mm or more. As described above, the diameter of the opening of the nozzle is not particularly limited and varies depending on the size of the apparatus, but is preferably about 0.1 to 1 mm from the viewpoint of more reliably preventing nozzle clogging. .

  3 and 4, the nozzles 16 </ b> A and the nozzles 16 </ b> B are alternately provided in a row in the outer peripheral direction of one surface Y orthogonal to the rotation axis X of the rotor 11. It may be provided alternately in a plurality of rows in the outer circumferential direction.

In the manufacturing apparatus shown in FIG. 1 described above, regions where the raw material solution A and the raw material solution B are respectively introduced from the nozzle 16A and the nozzle 16B, that is, the inner periphery of the rotor 11 and the inner stator 13 in FIGS. in the region between the outer periphery of, but the shear rate is set to be 1,000～50,000Sec ^-1, it is particularly preferred to be set so that 1,000～20,000Sec ^-1 . When the shear rate in this region is less than the lower limit, the aggregates of crystallites of silver and silver compounds are not broken, and the average particle size of the colloidal particles is increased. On the other hand, when the shear rate in this region exceeds the above upper limit, the water-soluble amine as a protective agent is destroyed and sufficient repulsive force cannot be imparted to the colloidal particles, and the aggregation of the colloidal particles proceeds and the particle size increases. growing.

  Conditions for achieving such a shear rate are affected by the rotational speed of the rotor and the size of the gap between the rotor and the stator. There is a need to. The specific rotation speed of the rotor 11 is not particularly limited and varies depending on the size of the apparatus. For example, the outer diameter of the inner stator 13 is 12.0 mm, and the gap between the rotor 11 and the outer stator 12 is 0. In the case of 2 mm, a gap of 0.5 mm between the rotor 11 and the inner stator 13, and an inner diameter of the outer stator 12 of 18.8 mm, the rotational speed of the rotor 11 is preferably 2,000 to 20,000 rpm, more preferably The shear rate can be achieved by setting the speed to 3,000 to 15,000 rpm.

  Further, the size of the gap between the rotor 11 and the outer stator 12 and the gap between the rotor 11 and the inner stator 13 are not particularly limited, and may vary depending on the size of the device. It is preferable that it is 2-1.0 mm. By adjusting the rotational speed of the rotor 11 in response to the change in the size of the gap, it becomes possible to achieve the shear speed in the above range. When these gaps are less than the lower limit, clogging of the gaps tends to occur, and when the upper limit is exceeded, effective shearing force cannot be applied.

  In the manufacturing apparatus shown in FIG. 1, the raw material solution A and the raw material solution B respectively supplied from the nozzle 16A and the nozzle 16B are introduced into the region within 1.0 msec (particularly preferably within 0.5 msec). It is preferable that the nozzle 16A and the nozzle 16B are arranged so as to be homogeneously mixed. Here, the time from when the raw material solution is introduced into the region until it is homogeneously mixed is the nozzle 16B adjacent to the raw material solution A (or raw material solution B) introduced from the nozzle 16A (or nozzle 16B). (Or nozzle 16A) The time until it reaches the position of the nozzle and is mixed with the raw material solution B (or raw material solution A) introduced from the nozzle 16B (or nozzle 16A).

  The apparatus suitably used in the present invention has been described above. However, in the present invention, the first raw material solution can be used as the raw material solution A and the second raw material solution can be used as the raw material solution B. There may be. Further, the present invention is not limited to the method using the manufacturing apparatus shown in FIG. For example, in the manufacturing apparatus shown in FIG. 1, the nozzle 16 </ b> A and the nozzle 16 </ b> B are respectively provided on the surface facing the rotor 11 in the inner stator 13, but the nozzle 16 </ b> A and the nozzle 16 </ b> B are respectively rotors in the outer stator 12. 11 may be provided respectively on the surface facing 11. If comprised in that way, it will become possible to introduce the raw material solution A and the raw material solution B directly into the area | region between the rotor 11 and the outer side stator 12, respectively independently. Note that the shear rate in that region needs to be set so as to satisfy the above condition.

  The feed rate of each raw material solution in the first raw material solution and the second raw material solution is not particularly limited, but is preferably 1.0 to 30 ml / min. If the feed rate of the raw material solution is less than the lower limit, the production efficiency of colloidal particles containing silver tends to be reduced. On the other hand, if the upper limit is exceeded, the average particle diameter of the colloid particles tends to increase.

  In the colloidal solution preparation step according to the present invention, the molar ratio of silver ions contained in the first raw material solution to the water-soluble amine contained in the second raw material solution (silver ion moles: water-soluble amine moles). It is preferable to introduce the first raw material solution and the second raw material solution so that the number) is 1: 4 to 1: 100 (more preferably 1:10 to 1:30). If the amount of the water-soluble amine with respect to silver ions is less than the lower limit, the average particle size of the colloidal particles tends to increase. On the other hand, if the amount exceeds the upper limit, excess amine is difficult to remove and tends to be overheated during firing. .

  In the colloidal solution preparation step according to the present invention, the first raw material solution and the second raw material solution are directly and independently introduced into the shear rate region at 40 to 95 ° C. and homogeneously mixed. When the temperature at the time of mixing is less than the lower limit, it becomes difficult to obtain colloidal particles containing silver. On the other hand, when the upper limit is exceeded, the average particle size of the colloidal particles becomes large, and it becomes difficult to obtain a catalyst having a high level of catalytic activity in which ultrafine particles containing silver are stably held. Moreover, as a temperature at the time of mixing a 1st raw material solution and a 2nd raw material solution from a viewpoint that the colloidal particle with a sufficiently small average particle diameter tends to be obtained with a higher yield, it is 50-90. It is particularly preferable that the temperature is C. In addition, it does not restrict | limit especially as a method of carrying out homogeneous mixing within such a temperature range, For example, in the above-mentioned manufacturing apparatus, the method of heating the raw material solution A and the raw material solution B, or heating the reaction container 20 A method is mentioned.

  Through such a colloid solution preparation step, a silver-based colloid solution in which colloidal particles containing silver are dispersed can be obtained. Examples of the colloidal particles include colloidal particles containing fine particles containing at least one kind of silver selected from the group consisting of silver particles and silver compound particles, and the water-soluble amine. Examples of the silver crystallites or aggregates of the silver compound particles include the aforementioned crystallites or aggregates of the silver compound.

  In the silver-based colloidal solution according to the present invention, the component ratio of carbon to silver in the colloidal solution is mixed with alumina powder in the silver-based colloidal solution and dried under reduced pressure at 300 torr or less. The mass ratio of carbon atoms to silver atoms (carbon atoms / silver atoms) determined by inductively coupled plasma optical emission spectrometry after heating for 12 hours must be in the range of 0.17 to 2.5. When the mass ratio (carbon atom / silver atom) is less than the lower limit, the average primary particle diameter of the fine particles containing silver obtained by increasing the average particle diameter of the colloidal particles is increased, while the upper limit is set. In the case of exceeding the temperature, the temperature on the catalyst surface at the time of calcination rises, and the particles supported on the catalyst surface grow and the activity of the resulting catalyst decreases. Moreover, from the viewpoint that carbon derived from a water-soluble amine that protects silver particles tends to be difficult to remove, the mass ratio (carbon atom / silver atom) is particularly preferably 0.5 to 1.50. .

More specifically, the mass ratio of carbon atoms to silver atoms (carbon atom / silver atom) is more specifically determined by using alumina (Al ₂ O ₃ ) powder with respect to 5 parts by mass of the silver-based colloidal solution in terms of metal. After adding 100 parts by mass and stirring and removing the solvent under a reduced pressure of 300 torr (40,000 Pa), the colloidal particles composed of organic matter and silver-containing fine particles are kept at 120 ° C. for 12 hours in the atmosphere. The supported alumina powder was obtained, and then the obtained powder was subjected to ICP emission analysis using an inductively coupled plasma (ICP) light emitting device (CIROS 120EOP, manufactured by Rigaku Corporation), and carbon present on the alumina powder was obtained. It can obtain | require by quantifying the containing mass of an atom (C) and a silver atom (Ag), and calculating the ratio. Although it does not restrict | limit especially as said alumina, It is preferable that an average primary particle diameter is 5-100 nm, and it is preferable that it is a porous body whose specific surface area is 50-300 m < ² > / g.

  In the silver-based colloidal solution according to the present invention, the colloidal particles containing silver must have an average particle diameter in the range of 1.0 to 3.5 nm. When the average particle diameter of the colloidal particles is less than the lower limit, the colloidal particles are oxidized into an oxide. On the other hand, when the average particle diameter exceeds the upper limit, the catalytic activity of the resulting catalyst is lowered. Further, from the viewpoint that the catalytic activity of the catalyst obtained by increasing the active sites tends to be further improved, the average particle diameter of the colloidal particles is preferably 1.0 to 3.0 nm. In the present invention, the average particle size of the colloidal particles is determined by observing the colloidal solution with a transmission electron microscope (TEM: “JEM-2100F” manufactured by JEOL Ltd.), and particles of any 50 or more colloidal particles. It can be obtained by measuring and averaging the diameters.

[Catalyst preparation step]
In the production method of the present invention, the silver-based colloidal solution obtained in the colloidal solution preparation step is brought into contact with a metal oxide support, and then calcined in the atmosphere at 300 to 600 ° C. to obtain the exhaust gas purification catalyst.

  The metal oxide carrier is not particularly limited, and a carrier made of a metal oxide such as silica, titania, ceria, zirconia, alumina, alumina-ceria-zirconia, ceria-zirconia can be appropriately used. Among these, as the metal oxide, alumina is preferable from the viewpoint of having a large specific surface area and excellent heat resistance.

  The form of the metal oxide carrier is not particularly limited, but when it is particulate, the average primary particle diameter is preferably 5 to 100 nm. When the average primary particle diameter of the metal oxide support particles is less than the lower limit, the metal oxide support particles tend to aggregate when subjected to a high-temperature treatment such as a heat treatment or a reduction treatment, and when the upper limit is exceeded, the specific surface area tends to decrease. is there. In the present invention, the average primary particle diameter of the metal oxide carrier particles is the transmission particle microscope (TEM: manufactured by JEOL Ltd., “JEM- 2100F "), and the average value can be obtained. Further, such a particle diameter means the maximum diameter of the cross section of the particle, and when the cross section of the particle is not circular, the diameter is the maximum circumscribed circle of the cross section of the particle.

Further, such a metal oxide support may be a non-porous body or a porous body, but is preferably a porous body. Moreover, when it is a porous body, it is preferable that a specific surface area is 50-300 m < ² > / g. When the specific surface area is less than the lower limit, the degree of dispersion of the supported fine particles serving as active points tends to be lowered, and when the upper limit is exceeded, the heat resistance tends to be lowered. In the present invention, the specific surface area of the porous body can be calculated as the BET specific surface area from the adsorption isotherm using the BET isotherm adsorption formula.

  A method for producing the metal oxide support is not particularly limited, and a known method can be appropriately employed. Moreover, as such a metal oxide support, a commercially available product may be used.

  The method for bringing the silver-based colloid solution into contact with the metal oxide support is not particularly limited, and the silver-type colloid solution is impregnated with the metal-oxide support such as a method of impregnating the silver-type colloid solution with the metal-oxide support. A known method that can be adsorbed and supported on a carrier can be appropriately employed.

  Further, when the silver-based colloidal solution is brought into contact with the metal oxide support in this way, ultrafine particles containing silver derived from the silver-based colloidal solution are added to 100 parts by mass of the metal oxide support. It is preferable that the loading is 0.5 to 20 parts by mass in terms of metal, more preferably 2.0 to 15 parts by mass, and more preferably 5.0 to 10 parts by mass. It is more preferable to make it contact. If the supported amount of ultrafine particles is less than the lower limit, it tends to be difficult to exhibit sufficient catalytic activity. On the other hand, if it exceeds the upper limit, a decrease in catalytic activity due to sintering is caused. It tends to be.

  As the heating conditions for the firing, in the present invention, it is necessary to be within a temperature range of 300 to 600 ° C. in the atmosphere. In the present invention, even when heated within such a temperature range, abnormal overheating on the catalyst surface can be prevented, so that a catalyst having a high level of catalytic activity in which ultrafine particles containing silver are stably held. Can be obtained. If the heating temperature is less than the lower limit, the sintering is not completed, so that the sintering progresses when the catalyst is used and the catalyst performance is significantly lowered. On the other hand, if the upper limit is exceeded, the initial activity of the catalyst obtained by growing the ultrafine particles supported on the metal oxide support is lowered. Such a heating temperature is preferably within a temperature range of 300 to 500 ° C. from the viewpoint that the protective agent such as the water-soluble amine tends to be sufficiently removed. Further, the heating time in the baking is not generally known because it depends on the heating temperature, but it is preferably 3 to 50 hours.

[Exhaust gas purification catalyst]
By such a production method, the exhaust gas-purifying catalyst of the present invention can be produced. In the silver-based colloidal solution, colloidal particles containing silver and having a sufficiently small average particle diameter are dispersed, and the component ratio of carbon and silver is within a specific range. On the purification catalyst surface, fine particles containing silver are supported on the metal oxide carrier in a sufficiently dispersed state.

  In such an exhaust gas purifying catalyst of the present invention, the average primary particle diameter of the ultrafine particles after reduction treatment at 500 ° C. in a reducing atmosphere is 5 to 20 nm (more preferably 5 to 10 nm). And a high level of catalytic activity can be exhibited. When the average primary particle size of the ultrafine particles is less than the lower limit, it tends to be easily oxidized to an oxide. On the other hand, when the upper limit is exceeded, the active sites are reduced and sufficient catalytic activity is exhibited. There is a tendency not to be.

In the present invention, the average primary particle size of the ultrafine particles is determined by using an X-ray diffractometer (trade name “RINT-2200” manufactured by Rigaku Corporation), scan step 0.01 °, divergence and scattering slit 1 deg, light receiving slit. Based on the half-value width of the diffraction peak derived from the (1,1,1) plane, measured by the conditions of 0.15 mm, CuKα ray, 40 kV, 20 mA, scan speed of 1 ° / min, Scherrer's formula:
D = 0.9λ / βcos θ
(In the formula, D represents the crystallite diameter, λ represents the used X-ray wavelength, β represents the half width of the XRD measurement sample, and θ represents the diffraction angle)
It can obtain | require by calculating using.

  Moreover, as said reducing atmosphere, it is preferable that reducing gas concentration is 0.1 volume% or more, and it is more preferable that it is 0.1-10 volume%. Examples of such reducing gas include hydrogen, carbon monoxide, hydrocarbons, and the like. One of these may be used alone, or two or more may be used in combination.

  The form of the exhaust gas purifying catalyst of the present invention is not particularly limited, and for example, a form in which the exhaust gas purifying catalyst is fixed to a base material corresponding to the intended use can be adopted. Examples of such a form include a honeycomb form and a pellet form. Further, the substrate is not particularly limited and is appropriately selected depending on the intended use of the catalyst, but more preferably a DPF substrate, a monolith substrate, a pellet substrate, a plate substrate, etc. It can be used suitably. Furthermore, the material of such a base material is not particularly limited, but a base material made of ceramics such as cordierite, silicon carbide, mullite, or a base material made of metal such as stainless steel including chromium and aluminum is more preferably used. be able to. Further, in the case of using such a base material, a method in which the metal oxide carrier is coated on the base material by a method such as a wash coat method and then the ultrafine particles are supported thereon is adopted. Can do.

  Further, the exhaust gas purifying catalyst of the present invention may further contain a noble metal, a transition metal, an alloy thereof, and the like within a range that does not impair the effects of the present invention.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example. The component ratio measurement in the colloidal solution obtained in each example and each comparative example, the average particle diameter measurement of the colloidal particles, the average primary particle diameter measurement of the ultrafine particles in the obtained catalyst, and the catalytic activity evaluation are as follows. It carried out according to the method shown.

<Measurement of component ratio of colloidal solution>
First, alumina powder (average primary particle size: 100 nm, specific surface area: 100 m ² / g, 100 parts by mass) was added to the obtained colloidal solution (5 parts by mass in terms of metal), and after stirring for 1 hour, 300 torr (40, The solvent was removed under a reduced pressure of 000 Pa), and the mixture was kept in the atmosphere for 12 hours at a temperature of 120 ° C. Next, an inductively coupled plasma (ICP) light emitting device (CIROS 120EOP, manufactured by Rigaku Corporation) was used for the powder after the solvent removal. ICP emission analysis is carried out, and the contained mass (mass%) of carbon atoms (C) and silver atoms (Ag) present on the powder is quantified, and the mass ratio of carbon atoms to silver atoms (C / Ag) In order to clarify the background level of carbon contamination, the IC powder was similarly applied to the alumina powder before the colloidal solution was added. Was quantified initial content by weight of carbon atoms (C) (mass%) was conducted emission analysis, it was 0.15 wt%.

<Measurement of average particle size of colloidal particles>
The obtained colloid solution was observed with a transmission electron microscope (TEM: trade name “JEM-2100F” manufactured by JEOL Ltd.), and the particle size of any 50 colloidal particles was observed with a transmission electron microscope (TEM). The average particle diameter of the colloidal particles was determined by measuring and averaging each.

<Measurement of average primary particle size of ultrafine particles>
First, the obtained catalyst was subjected to reduction treatment by being held at a temperature of 500 ° C. for 1 hour in a mixed gas stream of 1 vol% hydrogen and 99 vol% nitrogen (N ₂ ). Next, with respect to the catalyst after the reduction treatment, an X-ray diffraction (XRD) pattern was measured using an X-ray diffractometer (trade name “RINT-2200” manufactured by Rigaku Corporation), scan step 0.01 °, divergence and scattering slit 1 deg. The average of ultrafine particles containing silver based on diffraction peaks derived from the (1,1,1) plane, measured under conditions of a light receiving slit of 0.15 mm, CuKα ray, 40 kV, 20 mA, scanning speed of 1 ° / min. The primary particle diameter was determined, and the diffraction peak derived from the (1,1,1) plane overlaps with the diffraction peak derived from the (2,2,1) plane and the (1,1,4) plane of alumina. Therefore, the waveform was separated and analyzed.

<Catalyst activity evaluation>
First, 1.0 g of the obtained catalyst was filled in a quartz reaction tube having an inner diameter of 15 mm, and installed in an atmospheric pressure fixed bed flow type reactor (manufactured by Vest Sokki), CO (0.7 vol% (6998 ppm)), C ₃ H ₆ (0.16 vol% (1600 ppm)), NO (0.12 vol% (1200 ppm)), O ₂ (0.65 vol% (6460 ppm)), CO ₂ (10 vol%), H ₂ A model gas composed of O (5% by volume) and N ₂ (remainder) was supplied at a flow rate of 7000 mL / min, and kept at a temperature of 500 ° C. for 10 minutes for pre-heating treatment. Next, the temperature of the model gas (entry gas) supplied to the catalyst is increased from 100 ° C. to 500 ° C. at a rate of 15 ° C./min, and the CO concentration and C ₃ H ₆ concentration of the catalyst-containing gas, and the catalyst output The CO concentration and C ₃ H ₆ concentration of the gas are measured, the CO conversion rate and the THC conversion rate are respectively calculated from the difference, and the temperature at which the CO conversion rate and the THC conversion rate become 50% is set to 50% purification temperature. It was. It is recognized that the lower the 50% purification temperature, the higher the oxidation activity of the catalyst.

Example 1
[Colloid solution preparation process]
First, 0.63 g of silver nitrate was dissolved in 131.2 g of ion-exchanged water to prepare a first raw material solution containing silver ions. This addition amount corresponds to a silver ion concentration of 0.028 mol / L. Next, 3.755 g of ethylenediamine (EDA) was dissolved in 131.2 g of ion-exchanged water to prepare a second raw material solution. This addition amount corresponds to an ethylenediamine concentration of 0.48 mol / L.

  Next, a colloidal solution in which colloidal particles were dispersed was prepared using the manufacturing apparatus (super agitation reactor) shown in FIG. As the inner stator 13, a 48-hole type in which 24 nozzles 16A and 24 nozzles 16B are provided, respectively, is used. As shown in FIG. 1, the inside of the 100 ml beaker 20 in which the tip of the homogenizer 10 is held at 60 ° C. The first raw material solution and the second raw material solution, each heated to 60 ° C. while rotating the rotor 11 in the homogenizer 10 at a rotational speed of 3400 rpm, were supplied at a feed rate of 12.5 ml / min. Then, using a tube pump (not shown), liquid was fed from the nozzle 16A and nozzle 16B to the area between the rotor 11 and the inner stator 13 and mixed to prepare a colloidal solution. At this time, the molar ratio of the silver ions contained in the first raw material solution and the water-soluble amine contained in the second raw material solution (number of silver ions mole: number of moles of water-soluble amine) was 1: 17.1. It was.

The outer diameter of the rotor 11 is 18.0 mm, the inner diameter of the outer stator 12 is 18.8 mm, the gap between the rotor 11 and the outer stator 12 is 0.4 mm, and the shear rate in the region between them is 8 1,000 sec ⁻¹ . Further, the inner diameter of the rotor 11 is 12.2 mm, the outer diameter of the inner stator 13 is 11.8 mm, the gap between the rotor 11 and the inner stator 13 is 0.2 mm, and the shear rate in the region between them is 11 1,000 sec ⁻¹ . Further, the time from when the first raw material solution and the second raw material solution were introduced into the region until they were homogeneously mixed was 0.37 msec.

[Catalyst preparation step]
First, a colloidal solution preparation step in the resulting colloidal solution of alumina powder (average primary particle diameter: 100 nm, specific surface area: 100m ² / g) impregnated was calcined by holding for 30 hours at a temperature 300 ° C. in air. The fired powder was molded at 1000 kgf / cm ² using a cold isostatic press, and then pulverized to a particle size of 0.5 to 1 mm to obtain a pellet-shaped catalyst. In addition, in the obtained catalyst, the supported amount of the silver compound in terms of metal was 0.25 part by mass with respect to 5 parts by mass of the alumina powder.

(Example 2)
A catalyst was obtained in the same manner as in Example 1 except that the heating temperature of the first raw material solution and the second raw material solution and the heating temperature of the beaker 20 were set to 50 ° C.

(Example 3)
A catalyst was obtained in the same manner as in Example 1 except that the heating temperature of the first raw material solution and the second raw material solution and the heating temperature of the beaker 20 were set to 90 ° C.

Example 4
A catalyst was obtained in the same manner as in Example 1 except that the mass of ethylenediamine dissolved in the second raw material solution was 0.939 g, which was 1/4 of that in Example 1. This addition amount corresponds to an ethylenediamine concentration of 0.12 mol / L. In the colloidal solution preparation step, the molar ratio of silver ions to water-soluble amine (silver ion moles: water-soluble amine moles) was 1: 4.3.

(Comparative Example 1)
A catalyst was obtained in the same manner as in Example 1 except that the mass of ethylenediamine dissolved in the second raw material solution was 0.751 g which was 1/5 of that in Example 1. This addition amount corresponds to an ethylenediamine concentration of 0.10 mol / L. In the colloidal solution preparation step, the molar ratio of silver ions to water-soluble amine (silver ion moles: water-soluble amine moles) was 1: 3.6.

(Comparative Example 2)
As Example 2 except that a solution obtained by dissolving 3.755 g of ethylenediamine and 3.401 g of polyvinylpyrrolidone (PVP, weight average molecular weight 10,000) in 131.2 g of ion-exchanged water was used as the second raw material solution. A catalyst was obtained in the same manner.

(Comparative Example 3)
The same as Example 1 except that the first raw material solution, the second raw material solution, and the beaker 20 were not heated and the mixing temperature of the first raw material solution and the second raw material solution was set to room temperature (25 ° C.). Thus, a catalyst was obtained.

(Comparative Example 4)
A catalyst was obtained in the same manner as in Example 1 except that the heating temperature of the first raw material solution and the second raw material solution and the heating temperature of the beaker 20 were set to 100 ° C.

(Comparative Example 5)
A catalyst was obtained in the same manner as in Example 1 except that an aqueous silver nitrate solution in which 0.39 g of silver nitrate was dissolved in 220 g of ion-exchanged water was used instead of the colloidal solution.

(Comparative Example 6)
Instead of the colloidal solution, the same procedure as in Example 1 was used except that a solution obtained by dissolving 0.25 g of commercially available silver nanoparticles (manufactured by Dowa Electronics Co., Ltd., average primary particle size 20 nm) in 220 g of ion-exchanged water was used. A catalyst was obtained.

  Table 1 shows the compositions of the colloidal solutions obtained in Examples 1 to 4 and Comparative Examples 1 to 6, and Table 2 shows the average primary particle size measurement and catalytic activity evaluation of the ultrafine particles in the obtained catalysts. Results are shown. In Comparative Examples 3, 5, and 6, colloidal particles were not obtained, and in Comparative Example 3, ultrafine particles were not obtained. FIG. 5 shows a TEM photograph of the colloidal particles obtained in Example 1 among the transmission electron microscope (TEM) photographs taken in the measurement of the average particle diameter of the colloidal particles.

  As is apparent from the results shown in Table 1 and FIG. 5, it was confirmed that the colloidal particles were stably dispersed in a fine state in the silver-based colloid solution obtained by the production method of the present invention. When a low molecular weight water-soluble amine such as ethylenediamine is used as in the silver-based colloidal solution according to the present invention, the component ratio of carbon and silver in the colloidal solution (carbon atom mass / silver atom mass (C / Ag )) Was within the range of 0.18 to 2.2, and the average particle size of the colloidal particles was confirmed to be within the range of 1.0 to 3.5 nm. Furthermore, the catalyst of the present invention obtained by using such colloidal particles has a high level of catalytic activity because the ultrafine particles are uniformly dispersed and stably held on the metal oxide support. Was confirmed.

  As described above, according to the present invention, abnormal overheating during firing can be prevented, and a catalyst having a high level of catalytic activity in which ultrafine particles containing silver are stably maintained can be obtained. It becomes possible to provide a method for producing an exhaust gas purifying catalyst and an exhaust gas purifying catalyst obtained by the method.

  DESCRIPTION OF SYMBOLS 10 ... Homogenizer, 11 ... Rotor, 12 ... Outer stator, 13 ... Inner stator, 14 ... Rotating shaft, 15 ... Motor, 16A, 16B ... Nozzle, 17A, 17B ... Flow path (supply pipe), 20 ... Reaction vessel, A , B ... reaction solution, X ... rotation axis, Y ... surface perpendicular to the rotation axis X.

Claims (5)

A method for producing an exhaust gas purification catalyst comprising a metal oxide support and ultrafine particles supported on the metal oxide support and containing silver,
The first raw material solution containing silver ions and the second raw material solution containing a water-soluble amine are placed in a region having a shear rate of 1,000 to 50,000 sec ^{−1 at} 40 to 95 ° C. A step of obtaining a silver-based colloidal solution in which colloidal particles containing silver are dispersed by directly introducing and independently mixing independently;
The step of contacting the silver-based colloidal solution with the metal oxide support, followed by firing in the atmosphere at 300 to 600 ° C. to obtain the exhaust gas purification catalyst,
The component ratio of carbon to silver in the silver-based colloidal solution is inductively coupled plasma after alumina powder is mixed with the silver-based colloidal solution and dried under reduced pressure at 300 torr or less and then heated at 120 ° C. for 12 hours in the air. The mass ratio of carbon atoms to silver atoms (carbon atom / silver atom) determined by emission analysis is in the range of 0.17 to 2.5, and the average particle size of the colloidal particles is 1.0 to Within the range of 3.5 nm,
A method for producing an exhaust gas purifying catalyst.   The average primary particle diameter of the ultrafine particles after subjecting the exhaust gas-purifying catalyst to reduction treatment at 500 ° C. in a reducing atmosphere is in the range of 5.0 to 20 nm. The manufacturing method of the catalyst for exhaust gas purification as described in any one of.   In the step of obtaining the silver-based colloidal solution, the molar ratio of the silver ions contained in the first raw material solution and the water-soluble amine contained in the second raw material solution (silver ion moles: water-soluble amine moles) 3. The method for producing an exhaust gas purifying catalyst according to claim 1, wherein the first raw material solution and the second raw material solution are introduced so as to be 1: 4 to 1: 100.   The said water-soluble amine is ethylenediamine, The manufacturing method of the catalyst for exhaust gas purification as described in any one of Claims 1-3 characterized by the above-mentioned.   In the step of obtaining the exhaust gas purifying catalyst, the silver-based colloidal solution is added to the metal oxide so that the supported amount of the ultrafine particles with respect to 100 parts by mass of the metal oxide support is 0.5 to 20 parts by mass in terms of metal. The method for producing an exhaust gas purifying catalyst according to any one of claims 1 to 4, wherein the catalyst is brought into contact with a carrier.