JP3580136B2 - Catalyst production method - Google Patents

Description

【００４３】
上記表１より知られるごとく，耐久試験前における触媒成分としてのＰｔは，いずれの貴金属担持触媒においても，Ｘ線回折によって感知できる大きさ以下の微細粒径であった。
しかし，上記耐久試験後においては，比較例では粒成長のためにＰｔ粒径が１１０ｎｍと大きくなっている。これに対して，本例にかかる実施例１，２においては，粒成長が極めて少ないことが分る。
【００４４】
【発明の効果】
本発明によれば，担体に対して貴金属等の触媒成分が高分散配置されており，かつ耐久性の優れた触媒の製造方法を提供ことができる。
【図面の簡単な説明】
【図１】実施形態例１における，貴金属担持触媒の製造方法の工程を示す説明図。
【符号の説明】
１．．．基材，
１１．．．表面，
２．．．貴金属，
３．．．担体物質，[0001]
【Technical field】
The present invention relates to a method for producing a catalyst in which a catalyst component such as a noble metal is highly dispersed and which has excellent durability.
[0002]
[Prior art]
As a noble metal-supported catalyst, a large number of catalysts in which a porous carrier material having an acid point such as zeolite is impregnated or ion-exchanged by using a solution of a noble metal salt have been reported.
However, in the case of zeolite, which has many acid sites, that is, many ion exchange sites, the hydrothermal durability test shows that the crystal structure of the carrier material due to the removal of Al (4 coordination in the zeolite structure becomes 6 coordination) There is a problem in that the noble metal supported on the carrier substance easily grows as a result of the destruction of the particles.
Thus, for example, Japanese Patent Application Laid-Open No. 4-176337 discloses an exhaust gas purifying catalyst in which a noble metal is supported on a high silica zeolite carrier material having a Si / Al ratio of 40 to less than 1,000. Zeolite having a large Si / Al ratio suppresses the growth of noble metal particles based on the removal of Al.
[0003]
[Problem to be solved]
However, in the case of zeolites having a large Si / Al ratio, it is difficult to support the noble metal in a highly dispersed state because the noble metal is concentrated on a small number of ion exchange sites. In addition, since the noble metal easily moves on zeolite, particle growth is likely to occur, and it is hard to say that the durability is excellent.
[0004]
The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a method for producing a catalyst in which a catalyst component such as a noble metal is highly dispersed in a carrier and which has excellent durability.
[0005]
[Means for solving the problem]
The invention of claim 1, relative to precursor fluid obtained by dissolving the reaction precursor of the catalyst component in the supercritical fluid, by contacting a substrate which contains a reaction initiator, above the surface of the substrate A catalyst component attaching step of dispersing and attaching the catalyst component or its precursor;
A carrier coating step of coating a carrier material on the catalyst component or its precursor;
Thereafter, a substrate removing step of removing the substrate is performed.
A method for producing a catalyst, characterized in that a catalyst comprising the above-mentioned catalyst component supported on the above-mentioned carrier substance is obtained.
[0006]
Further, the invention according to claim 2 is to contact a porous base material containing a reaction initiator with a precursor fluid obtained by dissolving a reaction precursor of a noble metal as a catalyst component in a supercritical fluid, and a noble metal deposition step of the noble metal or a precursor thereof in the hole wall surface of the porous substrate is dispersed deposited,
A carrier coating step of coating a carrier substance on the noble metal or its precursor;
Thereafter, a substrate removing step of removing the porous substrate is performed,
A method for producing a noble metal-supported catalyst, characterized in that a noble metal-supported catalyst comprising the noble metal supported on the carrier substance is obtained.
Further, the invention according to claim 3 is a catalyst component adhering step of dispersing and adhering the catalyst component on the surface of the base material by a CVD method of vapor deposition under reduced pressure;
A carrier coating step of coating a carrier material on the catalyst component;
Thereafter, a substrate removing step of removing the substrate is performed.
A method for producing a catalyst, characterized in that a catalyst comprising the above-mentioned catalyst component supported on the above-mentioned carrier substance is obtained.
Further, the invention of claim 4 provides a noble metal attaching step of dispersing and attaching a noble metal as a catalyst component to the surface of the porous substrate by a CVD method of vapor deposition under reduced pressure;
A carrier coating step of coating a carrier substance on the noble metal,
Thereafter, a substrate removing step of removing the porous substrate is performed,
A method for producing a noble metal-supported catalyst, characterized in that a noble metal-supported catalyst comprising the noble metal supported on the carrier substance is obtained.
[0007]
The most remarkable point of the invention is that the catalyst component is dispersed and adhered to the surface of the substrate, and then the carrier material is coated thereon, and then the substrate is removed.
[0008]
Next, the operation and effect of the present invention will be described.
In the present invention, in order to disperse and attach the catalyst component to the substrate surface, the catalyst component is highly dispersed and arranged as a catalyst component having a small particle size. Then, a carrier material is coated thereon. Therefore, the catalyst component is in a state of being substantially uniformly, densely and highly dispersed in a granular form on the surface of the carrier material. Therefore, the catalyst obtained according to the present invention has high catalytic activity.
[0009]
In addition, as shown in FIG. 1 described later, since the rear part of the particles of the catalyst component is embedded in the carrier material, the interaction between the catalyst component and the carrier material is strong, and the movement of the catalyst component is restricted. Therefore, sintering in which the catalyst components are combined to grow grains hardly occurs. Therefore, the catalyst obtained according to the present invention has excellent durability.
Further, by repeating the noble metal-adhering step, the carrier coating step, and the noble metal-forming and carrier-forming step on the obtained noble metal-supported catalyst, a more highly active catalyst can be obtained.
[0010]
Next, first, the catalyst component attaching step will be described.
In the present invention, a porous substrate is particularly effective as a substrate. The porous substrate refers to a substrate having a large number of pores on the surface.
Examples of such a porous base material include porous carbon such as activated carbon, porous metal such as porous aluminum and porous tantalum, porous silica, porous alumina, porous alumina silica, porous ruthenium oxide, and porous ruthenium oxide. Porous body made of conductive oxide of metal and / or metalloid such as porous vanadium oxide, porous indium oxide, porous tin oxide and porous nickel oxide, or polymer foam such as polyolefin and polyurethane Can be used.
[0011]
Among them, activated carbon is particularly preferable because it has a high specific surface area and can disperse and adhere a large amount of noble metal. The substrate is preferably one that can be easily removed by heat treatment, acid / base treatment, or the like. In particular, activated carbon is more preferable because it can be easily removed by firing or the like.
[0012]
Next, examples of the catalyst component include a noble metal or a co-catalyst such as CeO ₂ . As the noble metal, Pt, Rh, Pd, Ir, Ru, or the like can be used depending on the use of the noble metal-supported catalyst.
As a noble metal deposition step for dispersing and depositing a catalyst component such as a noble metal on the surface of the substrate, for example, a CVD coating method or a supercritical coating method described later can be used. Particularly, the supercritical coating method is more preferable since a uniform catalyst component layer can be formed in a short time.
[0013]
The CVD method is a method in which a catalyst component such as the noble metal is deposited on the surface under reduced pressure .
[0014]
Further, the supercritical coating method comprises a dissolving step of preparing a precursor fluid by dissolving a reaction precursor of a catalyst component in a supercritical fluid, and a base material containing a reaction initiator with respect to the precursor fluid. And causing the precursor to react with the reaction initiator, and coating the surface of the substrate with a catalyst component such as a noble metal as a reaction product or a precursor thereof.
[0015]
The supercritical fluid generally refers to a fluid placed at a temperature and pressure higher than the critical point of a substance. However, the supercritical fluid in the present invention is a fluid at least at the temperature of the critical point, and the pressure does not need to be in the range defined above. The fluid in this state is a substance having the same dissolving power as a liquid, and diffusivity and viscosity similar to a gas. Therefore, a large amount of the reaction precursor can be easily and quickly carried into the micropores. The above dissolving ability can be adjusted by temperature, pressure, entrainer (additive) and the like.
[0016]
Examples of the supercritical fluid include hydrocarbons such as methane, ethane, propane, butane, ethylene, and propylene, methanol, ethanol, propanol, iso-propanol, butanol, iso-butanol, sec-butanol, tert-butanol, and the like. Alcohol, acetone, ketones such as methyl ethyl ketone, carbon dioxide, water, ammonia, chlorine, chloroform, freons and the like can be used.
[0017]
In order to adjust the solubility of the reaction precursor in the supercritical fluid, alcohols such as methanol, ethanol and propanol, ketones such as acetone and ethyl methyl ketone, and aromatic hydrocarbons such as benzene, toluene and xylene are used. It can be used as an entrainer.
[0018]
As a reaction precursor of the above-mentioned noble metal, a noble metal alkoxide, a noble metal acetyl acetate, a noble metal organic acid salt, a noble metal nitrate, a noble metal oxychloride, a noble metal chloride, or a mixture of two or more kinds thereof Can be used.
[0019]
As the above-mentioned reaction initiator, there is water as for the above-mentioned reaction precursor. Surface functional groups of the porous substrate such as OH groups can be used as the reaction initiator.
[0020]
Examples of a method for incorporating the above-mentioned reaction initiator into the above-mentioned substrate include a gas layer contact method and a liquid layer contact method. When the base material has pores, the reaction initiator can be easily contained by contact with a gas or liquid containing the reaction initiator.
The coating thickness of the reaction product noble metal layer can be adjusted from a cluster to a layer by adjusting the amount of the reaction initiator and / or the amount of the reaction precursor.
[0021]
For example, when the reaction initiator is a surface functional group of a base material such as water and / or an OH group and the base material is activated carbon, the amount of water in the activated carbon can be adjusted by adjusting the amount of water in an atmosphere in contact with the activated carbon. It can be adjusted based on data such as the surface area of activated carbon and the isotherm adsorption line. Also, the amount of surface functional groups of activated carbon such as OH groups can be adjusted by optimizing the activated carbon activation conditions.
In this way, it is possible to design a predetermined noble metal from a cluster of several atoms to various thicknesses.
[0022]
Heretofore, as a method of supporting a noble metal on the surface of a porous substrate, there has been proposed a method of dissolving a noble metal salt in a solvent such as water or ethanol and coating the same on the surface of the porous substrate.
However, in such a solution coating method using a liquid as a solvent, the solvent does not sufficiently enter the pores of the porous substrate due to the high surface tension of the liquid, and the coat layer blocks the pores of the substrate. May be lost.
Therefore, in this method, although the porous substrate itself has a large specific surface area, it is difficult to make full use of this surface to disperse and adhere the noble metal.
[0023]
Next, the carrier coating step will be described.
In this step, the carrier material is coated on the noble metal as a catalyst component dispersed and attached to the pore wall surface of the porous substrate as described above. The carrier material is formed, for example, so as to cover the entire surface of the pore wall surface.
Examples of the carrier material include metal oxides, metal nitrides, metal carbides, metals, and organic polymers. Examples of the metal oxide include Al ₂ O ₃ , SiO ₂ , Fe ₂ O ₃ , ZrO ₂ , SnO ₂ , and TiO ₂ .
[0024]
Examples of the metal nitride include silicon nitride, aluminum nitride, boron nitride, and carbon nitride. Examples of the metal carbide include calcium carbide, silicon carbide, tungsten carbide, iron carbide, sodium carbide, boron carbide, and manganese carbide.
As the organic polymer, various organic polymers such as foamed polymers such as polyolefin and polyurethane can be used as carriers.
As a method of coating the carrier material, there are a CVD coating method and a supercritical coating method described in the above-mentioned noble metal deposition step. There is also a solution immersion method.
The solution immersion method is a method of immersing the base material in a solution such as an aqueous solution of a noble metal salt (for example, platinum chloride salt).
[0025]
In the above-mentioned supercritical coating method, a reaction precursor composed of a raw material for a carrier substance such as the metal oxide (for example, a compound of a metal such as Al or Si) is dissolved in a supercritical fluid to prepare a precursor fluid. A dissolving step, a reaction initiator is contained in the precursor fluid, and the substrate on which the noble metal is dispersed and adhered is brought into contact with the precursor fluid to cause the precursor and the reaction initiator to react with each other; A coating step of coating the surface with a carrier material which is a reaction product.
[0026]
Examples of the reaction precursor include a metal or / and metalloid alkoxide, a metal or / and metalloid acetyl acetate, a metal or / and metalloid organic acid salt, and a metal / metalloid alkoxide constituting the metal oxide and metal nitride. And / or metalloid nitrate, metal or metalloid oxychloride, metal or metalloid chloride and the like.
Further, it is possible to use an organic monomer, an organic dimer, an organic trimer, an organic tetramer, or the like that constitutes the organic polymer.
And a compound consisting of one or more of these compounds and / or a mixture consisting of one or more of these compounds can be used.
Further, by repeating the coating step as needed, a sturdy carrier can be produced.
[0027]
Next, in the substrate removing step, when the substrate is porous carbon such as activated carbon, the substrate is heated in an oxidizing atmosphere to oxidize the carbon and decompose to carbon monoxide and / or carbon dioxide. There is a method of removing. At the time of this heating, the above-mentioned carrier material raw material is changed into a carrier material such as a metal oxide.
In addition, the reaction precursor of the noble metal used in the supercritical coating method or the noble metal salt used in the solution immersion method changes into a noble metal as a catalyst component during the heating.
[0028]
When the substrate is a porous metal, the substrate can be removed by dissolving with an acid such as hydrochloric acid or hydrofluoric acid or an alkali such as an aqueous solution of sodium hydroxide.
In this case, it is preferable that the raw material of the carrier material is changed into the carrier material before the step of removing the base material by heating or adding a polymerization accelerator.
The noble metal salt is converted into a noble metal by a treatment such as heating or light irradiation before or after the removal of the base material.
[0029]
In particular, when the carrier material is an organic polymer, it is not preferable to remove the substrate by heating in an oxidizing atmosphere, but it is preferable to dissolve and remove the substrate using the acid, alkali or organic solvent.
Through the above steps, a catalyst in which a catalyst component such as a noble metal is supported on a carrier material is obtained.
[0030]
The catalyst obtained by the present invention can be used for various purposes such as exhaust gas purification, petrochemical industry, flue gas purification, organic matter decomposition, etc. by selecting a noble metal or the like as a catalyst component.
[0031]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1
A method for producing a noble metal supported catalyst according to an embodiment of the present invention will be described with reference to FIG.
The manufacturing method of this example includes a noble metal attaching step of dispersing and attaching the noble metal 2 to the surface 11 of the substrate 1 (FIGS. 1A and 1B) and a carrier coating step of coating the noble metal 2 with the carrier substance 3 (FIG. C), and thereafter, a base material removing step of removing the base material 1 (FIGS. 1C and 1D).
Thus, a noble metal-supported catalyst 20 in which the noble metal 2 is supported on the carrier material 3 is obtained (FIG. 1D).
[0032]
According to this example, the noble metal 2 is dispersed and adhered to the surface 11 of the base material 1, so that the noble metal 2 is highly dispersed as a catalyst component having a small particle size. Then, the carrier substance 3 is coated thereon. Therefore, the noble metal 2 is in a state of being substantially uniformly, densely and highly dispersed in the form of particles on the surface of the carrier material 3. Therefore, the noble metal supported catalyst has high catalytic activity.
[0033]
Further, as shown in FIG. 1D, since the rear part of the particles of the noble metal 2 is embedded in the carrier material 3, the interaction between the noble metal 2 and the carrier material 3 is strong, and the movement of the noble metal 2 is restricted. Is done. Therefore, the effect of suppressing sintering, in which the two noble metals bond and grow grains, is large. Therefore, the noble metal-supported catalyst 20 obtained from this example has excellent durability.
[0034]
Embodiment 2
Next, examples and comparative examples will be described.
(Example 1)
In this example, the noble metal deposition step and the carrier coating step were performed by a supercritical coating method.
That is, in a high-pressure reactor, a platinum diacetylacetonato complex {Pt (acac) 2 ↓} as a reaction precursor of a noble metal was dissolved in the presence of an activated carbon fiber (Osaka Gas, Renoves A) as a base material. An acetone solution (0.7 g / l) was dissolved in supercritical carbon dioxide (150 ° C., 345 atm).
This state was maintained for 3 hours. Thereafter, the supercritical carbon dioxide was removed under reduced pressure and dried at room temperature for 10 hours to obtain a precursor A (precious metal deposition step).
[0035]
Next, in the presence of the precursor A, 2 ml of tetraethyl orthosilicate (TEOS) as a carrier material as a reaction precursor was dissolved in supercritical carbon dioxide (150 ° C., 345 atm). This state was maintained for 3 hours.
Thereafter, the supercritical carbon dioxide was removed under reduced pressure (carrier coating step).
[0036]
Thereafter, after drying at room temperature for 10 hours, heat treatment is performed in air at 500 ° C. for 2 hours to remove the porous substrate and oxidize the TEOS to obtain a carrier material composed of SiO ₂ (substrate removing step). ).
Further, by the heating, the platinum diacetylacetonato complex becomes Pt as a catalyst component.
[0037]
As a result, a noble metal-supported catalyst in which Pt was supported on a carrier material of SiO ₂ was obtained.
[0038]
(Example 2)
In this example, the supercritical coating method was used for the noble metal deposition step, and the solution dipping method was used for the carrier coating step.
In the same manner as in Example 1, an acetone solution (0.7 g / l) in which a platinum diacetylacetonato complex {Pt (acac) 2 ↓} was dissolved was supercritical dioxide-oxidized in the presence of activated carbon fiber (Osaka Gas Renoves A). It was dissolved in carbon (150 ° C., 345 atm). This state was maintained for 3 hours. Thereafter, the supercritical carbon dioxide was removed under reduced pressure and dried at room temperature for 10 hours to obtain a precursor A (precious metal deposition step).
[0039]
Next, the precursor A was immersed in tetraethylorthosilicate (TEOS) at room temperature. Then, after removing excess TEOS by filtration, the resultant was dried at room temperature for 10 hours. Next, a heat treatment was performed in air at 500 ° C. for 2 hours to obtain a noble metal-supported catalyst in which Pt was supported on a SiO ₂ support in the same manner as in Example 1.
[0040]
(Comparative Example 1)
An aqueous solution of dinitrodiammineplatinum salt was quantitatively added to 1 g of the porous body made of silica so that Pt became 2 g with respect to 120 g of the porous body, stirred for 1 hour at room temperature, heated, and evaporated to dryness. .
This was heat-treated in air at 500 ° C. for 2 hours to convert the platinum salt into Pt, thereby obtaining a noble metal-supported catalyst having Pt supported on the porous body.
[0041]
"Evaluation method"
A durability test was performed on each of the noble metal-supported catalysts by performing a heat treatment in air at 900 ° C. for 5 hours.
Then, the particle size of each Pt was determined by X-ray diffraction. Table 1 shows the results.
[0042]
[Table 1]

[0043]
As known from Table 1 above, Pt as a catalyst component before the durability test had a fine particle size smaller than a size detectable by X-ray diffraction in any of the noble metal-supported catalysts.
However, after the endurance test, the Pt particle size in the comparative example was as large as 110 nm due to grain growth. On the other hand, in Examples 1 and 2 according to this example, it can be seen that the grain growth is extremely small.
[0044]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the catalyst components, such as a noble metal, are highly disperse | distributed and arrange | positioned with respect to a support | carrier, and the manufacturing method of the catalyst excellent in durability can be provided.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing steps of a method for producing a noble metal-supported catalyst in a first embodiment.
[Explanation of symbols]
1. . . Base material,
11. . . surface,
2. . . Precious metal,
3. . . Carrier material,

Claims (4)

Respect precursor fluid obtained by dissolving the reaction precursor of the catalyst component in the supercritical fluid, by contacting a substrate which contains a reaction initiator, the catalyst component or its precursor on the surface of the substrate A catalyst component attaching process for dispersing and attaching;
A carrier coating step of coating a carrier material on the catalyst component or its precursor;
Thereafter, a substrate removing step of removing the substrate is performed.
A method for producing a catalyst, comprising obtaining a catalyst comprising the above-mentioned catalyst component supported on the above-mentioned carrier substance. Respect precursor fluid obtained by dissolving the reaction precursor of the noble metal as a catalyst component in the supercritical fluid, contacting the porous substrate which contains a reaction initiator, pore wall surface of the porous substrate and a noble metal deposition step of dispersing attaching the noble metal or its precursor,
A carrier coating step of coating a carrier substance on the noble metal or its precursor;
Thereafter, a substrate removing step of removing the porous substrate is performed,
A method for producing a noble metal-supported catalyst, comprising obtaining a noble metal-supported catalyst in which the noble metal is supported on the carrier substance. A catalyst component attaching step of dispersing and attaching the catalyst component on the surface of the base material by a CVD method of vapor deposition under reduced pressure;
  A carrier coating step of coating a carrier material on the catalyst component;
  Thereafter, a base material removing step of removing the base material is performed,
  A method for producing a catalyst, comprising obtaining a catalyst comprising the above-mentioned catalyst component supported on the above-mentioned carrier substance. A noble metal deposition step of dispersing and depositing a noble metal as a catalyst component on the surface of the porous substrate by a CVD method of vapor deposition under reduced pressure;
  A carrier coating step of coating a carrier substance on the noble metal,
  Thereafter, a substrate removing step of removing the porous substrate is performed,
  A method for producing a noble metal-supported catalyst, comprising obtaining a noble metal-supported catalyst in which the noble metal is supported on the carrier substance.

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