JP2005081180A - Method for carrying metal particle in fin pore - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for uniformly carrying a metal, particularly a noble metal particle in a fine pore of a porous body. <P>SOLUTION: A solution containing a metal ion, a complex-forming agent and a reducing agent is made to permeate only into the fine pore of the porous body and the metal is precipitated and carried on a surface in the fine pore by a reduction reaction. The metal ion is preferably the noble metal ion; the complex-forming agent is preferably EDTA, NTA (nitrilotriacetic acid), an aliphatic oxy acid, formic acid, ammonia or salts thereof; the reducing agent is preferably a sugar, hydrazine, tartaric acid, a boronated compound, aldehyde, hypophosphorous acid, phosphinic acid, phosphonic acid or a salt thereof; and the solvent is preferably an alcohols, glycol, ether, ketone, ester or water. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for uniformly supporting metal particles inside pores, particularly inside pores of a porous carrier. The method of the present invention is useful for preparing, for example, a metal-supported catalyst having a large surface area and excellent gas permeability, especially a noble metal-supported catalyst.

  Metals, especially precious metals, are known to be catalysts that promote reactions in various chemical industrial processes and increase product selectivity, but there has been a strong demand to increase their surface area. Attempts have been made to support metals on a carrier such as ceramic (see Patent Document 1). However, due to the finer particles, the gas permeation rate of the column packed with particles decreases, and the amount of metal required increases.

  In general, it is well known to form a metal film by carrying out electroless plating on a ceramic surface to carry metal particles (see Patent Documents 2 to 5). However, even if this method is applied to the porous ceramic as it is, the surface of the support is covered with a metal film and the pores are blocked, and it is difficult to uniformly carry the metal only on the inner surface of the pores. It is. In addition, physical metal film formation methods such as chemical vapor deposition (CVD) and vacuum deposition are effective techniques for forming a metal thin film on the surface of a non-conductive material, but the apparatus is large and expensive. In addition, when it is applied to a porous body, its surface is covered with metal, and the intended performance cannot be obtained.

On the other hand, it is also known that electroless plating is performed on the surface of a ceramic material having holes or grooves, such as a through-hole ceramic substrate (see Patent Documents 6 and 7), but both methods immerse the material in the solution. However, no special knowledge has been given to the fact that a metal is supported inside the pore without blocking the micron-sized pore.
On the other hand, it is also known that a metal-containing solution is impregnated inside a porous body, and further, metal particles are precipitated inside the pores by a technique such as drying, thermal decomposition, hydrogen reduction or the like (Patent Documents 8 to 8). 9), these methods cannot control the state of precipitation in the pores of the metal, and inevitably suffer from problems such as clogging due to solid precipitation and reduction in air permeability.

JP 63-93872 A (Claims and others) JP-A-52-790 (Claims and others) JP-A-57-42114 (Claims and others) JP-A-57-180434 (Claims and others) JP-A-58-36634 (Claims and others) Japanese Patent Laid-Open No. 3-21286 (Claims and others) JP-A-6-17256 (Claims and others) JP 52-151690 A (claims and others) JP 55-114347 A (claims and others)

  An object of the present invention is to uniformly support particles of metal, particularly noble metal, in the pores of the porous body under such circumstances.

  According to the present invention, by using a solution containing a metal to be supported as a metal ion together with a reducing agent and a complexing agent, this solution is impregnated only in the pores of the porous body, and a reduction reaction is performed. The metal particles are deposited and supported on the inner surfaces of the pores of the porous body, which is difficult to support the metal particles.

That is, the present invention is as follows.
(1) A metal particle characterized by impregnating only a pore of a porous body with a solution containing a metal ion, a complexing agent and a reducing agent, and depositing and supporting the metal on the surface of the pore by a reduction reaction. In-pore support method.
(2) The method according to (1) above, wherein the metal ion is a noble metal ion and the metal is a noble metal.
(3) The method according to (1) or (2) above, wherein the complexing agent is at least one selected from EDTA, NTA, aliphatic oxyacid, formic acid and ammonia or a salt thereof.
(4) The above (1) to (3), wherein the reducing agent is at least one selected from saccharides, hydrazine, tartaric acid, boride, aldehydes, hypophosphorous acid, phosphinic acid and phosphonic acid, or a salt thereof. The method in any one of.
(5) The method according to any one of (1) to (4), wherein the solvent in the solution is at least one selected from alcohol, glycol, ether, ketone, ester and water.
(6) The method according to any one of (1) to (5), wherein the metal ion concentration in the solution is 0.002 to 3M.
(7) The method according to any one of (2) to (6), wherein the metal ion is a noble metal ion, and the concentration of the noble metal ion in the solution is 0.002 to 3M.
(8) The method according to any one of (1) to (7), wherein the concentration of the complexing agent in the solution is 0.002 to 10M.
(9) The method according to any one of (1) to (8), wherein the reducing agent concentration in the solution is 0.002 to 3M.
(10) The method according to any one of (1) to (9), wherein the porous body is made of ceramic or sintered metal.
(11) The method according to any one of (1) to (10), wherein the porous body has a pore diameter of 20 microns or less.

In the method of the present invention, the solution impregnated in the pores of the porous body (hereinafter sometimes referred to as impregnation liquid) includes a metal ion, a complexing agent, a reducing agent, and a solvent.
The metal ion is not particularly limited as long as it can be reduced to a metal by a reducing agent, but is easily reduced with a low ionization tendency, and ions of noble metals such as gold, silver, palladium, and platinum having high catalytic activity. preferable. Metal ions are provided in the form of metal salts that are soluble in the solvent.
The metal salt is preferably a noble metal salt. Examples of the noble metal salt include silver salts such as silver nitrate and silver sulfate, palladium salts such as palladium acetate, palladium chloride, palladium nitrate and palladium sulfate, platinum chloride, platinum hydroxide and hexachloroplatinum. Examples thereof include platinum compounds such as chloroplatinic acid such as acids.

The complexing agent is not particularly limited as long as it can stably dissolve the metal salt and maintain the stability of the impregnating liquid. Examples of such a complexing agent include chelating agents and ammonia. . Examples of chelating agents include EDTA, NTA (nitrilotriacetic acid), aliphatic oxyacids such as citric acid and tartaric acid, formic acid and their salts.
The complexing agent preferably includes at least one selected from EDTA, NTA, aliphatic oxyacid, formic acid and ammonia or a salt thereof.

The reducing agent is not particularly limited as long as it can reduce the coexisting metal ion to a metal, but in terms of having an appropriate reducing power and easy to control the reaction, saccharides, hydrazine, tartaric acid, boride, Preference is given to at least one selected from aldehydes, hypophosphorous acid, phosphinic acid and phosphonic acid or salts thereof.
Examples of the boride include tetrahydroborate such as sodium tetrahydroborate, amine boranes such as trimethylamine borane and dimethylamine borane, and aldehydes include formalin and acetaldehyde.

  The solvent is not particularly limited as long as it can be dissolved uniformly without precipitating all components. Examples of such solvents include alcohols such as methanol, ethanol and isopropanol, ethylene glycol, and propylene glycol. Such as glycol, ethylene glycol monomethyl ether, ketone such as acetone, ester such as ethyl acetate, water, etc. Among them, ethylene glycol, methanol, ethanol, isopropanol, water, and these mixed liquids It is preferable because the solubility of the ionic component is high.

  The content ratio of each component in the impregnation liquid is not particularly limited as long as the concentration of metal ions is within the solubility range, and is usually 0.002 to 3M, preferably 0.005 to 2M, more preferably 0. The amount of metal that can be supported in pores having a small internal volume is reduced especially when the concentration of metal ions is low, so that a certain level of high concentration, preferably 0.1 to 1 M is selected. It is selected in the range of 1M.

The complexing agent is selected in the range of usually 0.002 to 10M, preferably 0.005 to 2M, more preferably 0.01 to 1M, although it depends on the type of metal.
The concentration of the reducing agent is usually 0.002 to 3M, preferably 0.005 to 2M, more preferably 0.01 to 1M.
The solvent is selected in the range of usually 0.01 to 10M, preferably 0.1 to 3M, although it depends on the type of metal.

  In the method of the present invention, the temperature of the impregnation liquid used for the impregnation treatment is usually in the range of 0 ° C. to 90 ° C., but maintains a reaction rate of a certain level or more, and transpiration of volatile substances such as ammonia or chemicals The range of 20 to 50 ° C. is preferable from the viewpoint of reducing the decomposition of. The treatment time after impregnation is in the range of 1 minute to 3 hours, preferably 2 to 90 minutes, more preferably 3 to 60 minutes, although it depends on the temperature of the liquid for impregnation, the treatment temperature and the pore diameter after the impregnation. .

  Since the impregnating solution containing a high concentration of metal ions becomes unstable, the impregnating solution is prepared by mixing the reducing agent alone (this may be referred to as pre-impregnating solution) and the reducing agent. It is good to do. The pre-impregnation solution does not contain a reducing agent and does not cause a reaction with metal ions, and therefore is easy to store. For handling the liquid for impregnation and the liquid for pre-impregnation, it is preferable to use a chemically inert resin container or pipette.

  Since the reduction rate of metal ions, and thus the deposition rate of metal, shows temperature dependence, it is preferable to set the temperature conditions so as to obtain an appropriate reduction rate. In general, the higher the temperature, the more the reduction reaction is promoted, and the metal deposition rate is increased. By lowering the set temperature, the reduction reaction is suppressed, the deposition rate of the metal is delayed, and the deposited metal is better dispersed and deposited on the inner surface of the pore. Can be more uniformly carried.

  The reducing agent needs to have sufficient reducing power to sufficiently reduce metal ions, but if the reducing power is too strong, the reaction proceeds too quickly, and if the reducing power is too weak or insufficient, precipitation of metal particles may occur. May be insufficient. Moreover, since the reduction rate increases as the concentration of the reducing agent increases, it is desirable to adjust the deposition rate with a complexing agent or the like, particularly under conditions where the metal ion concentration is high. As the reducing agent, glucose, tartaric acid or a salt thereof are preferably used for silver ions, and hydrazine is preferably used for palladium ions. As the complexing agent, formate, ethylenediaminetetraacetic acid or a salt thereof is preferably used.

  The porous body for supporting the metal particles is not particularly limited as long as it has an affinity for the particles and water permeability and can stably support the metal particles, but is stable to heat and chemical substances and is compatible with water. Of these, ceramics such as alumina, mullite and zirconia, stainless sintered filters and the like are preferably used. The shape is preferably a flat plate or tube.

  The pore diameter of the porous carrier is not particularly limited as long as it is large enough to be impregnated with the impregnating solution, but is preferably 20 μm or less, and more preferably 0.01 to 10 μm. Further, when the impregnating liquid does not permeate naturally, it is effective to perform press-fitting or vacuum suction from the opposite side of the impregnating liquid. However, it should be noted that if the impregnating solution is left on the surface of the carrier after impregnation with the impregnating solution, the pore inlet may be blocked.

  According to the present invention, metal particles can be efficiently deposited and supported on the surface of a porous body, which has conventionally been difficult to support uniform metal particles. The method of the present invention is useful, for example, as a method for producing a catalyst having a large surface area and excellent gas permeability in the production process of a noble metal catalyst.

  The method of the present invention is suitable for supporting noble metals, especially silver, palladium, platinum, only in the pores. For this purpose, noble metal salts, EDTA, NTA, citric acid, tartaric acid, formic acid and the like are used as impregnation liquids. It is preferable to use a precious metal chelating agent, a reducing agent such as glucose, hydrazine, and formalin, and a solvent mainly composed of alcohol, glycol, ether, ketone, ester, water, and a mixture thereof. The phrase “mainly contains ...” means “consisting of ... or mainly containing ..., preferably in a proportion of 80% by mass or more”.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
In each example, M means molar concentration (mol / liter).

5 ml of an aqueous solution (Trens reagent) containing silver nitrate 0.55M, ammonia 2.3M and sodium hydroxide 0.7M and 5 ml 0.83M glucose (glucose) aqueous solution are mixed at room temperature. Was prepared.
If this mixed solution is divided into two and one is left as it is, a silver plate in the solution is precipitated within a few minutes, and the other is activated by a hydrochloric acid solution containing 0.53M stannous chloride. When it was brought into contact with silver, silver was deposited on the glass surface. Therefore, it is desirable to store the torence reagent containing silver at a high concentration without mixing with a reducing agent, and it should be used immediately after mixing, that is, a group whose surface is activated immediately after mixing. It has been found that application to the material is desirable for depositing silver on the surface of the substrate.

0.5 ml of aqueous solution containing 0.35M silver nitrate, 1.7M ammonia, 0.7M sodium hydroxide, 0.17M ethylenediaminetetraacetic acid disodium salt, and 0.83M glucose (glucose) aqueous solution 0.5 ml was mixed at room temperature to prepare a mixed solution. When 7 μl of this mixed solution was injected so as to be sandwiched between two glass plates having an area of 3.8 cm ² facing each other at an interval of 18 μm, silver in the solution was deposited on the glass surface within 1 minute at room temperature. It was confirmed. From this, it was found that it is possible to carry a metal such as silver in a narrow area.

7 μl of an aqueous solution containing 0.25 M silver nitrate, 1.1 M ammonia, 0.38 M sodium hydroxide, and 0.42 M glucose (glucose) was prepared as a test solution. The test solution was sandwiched between two glass plates with an area of 3.8 cm ² , which were activated at a test temperature of 5 ° C. and 22 ° C. with a 0.53 M stannous chloride solution and opposed at an interval of 18 μm. Then, a silver precipitation test was conducted. The relationship between the elapsed time from the start of the test and the amount of silver deposited on the glass surface is shown in a graph in FIG. In the figure, the X-axis is the test time, that is, the time (minutes) when the test solution was brought into contact with the glass, and the Y-axis is obtained by the mass on the glass by the test (on), that is, the test on the glass before the test. The increased mass (μg) of glass and the estimated film thickness (nm) of silver are shown respectively. Moreover, in the figure, a diagram indicated by-□-is a graph when the test temperature is 5 ° C, and a diagram indicated by-◯-is a graph when the test temperature is 22 ° C. From this, it can be seen that the amount of silver deposited increases with the passage of time, and the increased mass is almost flat at around 200 μg. Since the estimated increased mass when all the silver in the solution is deposited is 190 μg, this result suggests that the silver in the solution is completely deposited on the glass surface.

  An aqueous solution containing 0.5M silver nitrate, 1.9M ammonia, 0.75M tetramethylammonium hydroxide, and 0.5M ammonium formate, and 0.83M glucose (glucose) aqueous solution are mixed in the same volume. 7 μl of the mixed solution was prepared as a test solution. A silver precipitation test using this test solution was conducted in the same manner as in Example 3 at a test temperature of 22 ° C. It was found that the increase in mass due to silver precipitation remained at 33 μg even 10 minutes after the start of the test, and the reduction reaction rate was suppressed by formate ions.

  An anodized alumina filter (diameter 21 mm, thickness 60 μm, pore diameter 0.1 μm) is immersed in a 0.53 M stannous chloride solution to activate the inner surface of the filter, then washed with water, dried and activated. Preparation filter was prepared. In addition, an aqueous solution containing silver nitrate of 0.5M, ammonia of 2.4M, and tetramethylammonium hydroxide at a concentration of 0.82M and a 0.83M glucose (glucose) aqueous solution are mixed in the same volume to obtain 40 μl of a mixed solution. Prepared as a test solution. This test solution was added onto the activated filter. The test solution was immediately impregnated inside the filter, and the entire white filter gradually turned brown. Scanning electron micrographs of the surface and cross-section of this processing filter are shown in FIGS. 2A and 2B, respectively. Most of the holes on the surface were not blocked, and no solid deposition or pore clogging was observed inside the pores.

  In the same manner as in Example 5, a treatment filter impregnated with the test solution and discolored was prepared and embedded in a methacrylic acid methyl ester resin. About the cross section of this sample, the X-ray analysis of silver was performed in the depth direction, and the distribution state of the silver particle was investigated. The results are shown graphically in FIG. In the sample cross section of about 20 to 80 μm, the amount of silver tended to increase slightly at the center of the sample, but it was confirmed that it was spread throughout the sample.

  After coating the side surface of the porous alumina filter (diameter 25 mm, thickness 2 mm, pore diameter 0.1-1 μm) with glass, the pressure inside the filter is reduced to replace the air inside the filter with water, and then the filter is taken out. After heating to 70 ° C. in pure water, 0.53M stannous chloride solution was passed through the pores to activate the pore inner surfaces. Also, an aqueous solution containing silver nitrate 0.5M, ammonia 2.4M, tetramethylammonium hydroxide 0.55M and ammonium formate 0.25M in each concentration was mixed with 0.83M glucose aqueous solution of the same volume. A mixed solution was prepared as a test solution. When this test solution was sucked from the back side of the activated filter with a vacuum pump and 0.5 ml of the test solution was impregnated inside the filter, the entire white filter gradually turned brown. This treated filter was confirmed to allow water to pass through, and there was an 8.3 mg increase in mass compared to the filter before treatment with the test solution, and it was estimated that 0.36% by mass of silver was supported.

The filter prepared in the same manner as in Example 7 was dried and then fixed to a stainless steel filter holder, and argon gas was allowed to flow through the filter. FIG. 4 is a graph showing the relationship between gas pressure, gas permeability, and permeate gas flow rate. In the figure, the X-axis represents the pressure (MPa) of argon gas, and the Y-axis represents the permeability of argon gas (10 ⁻³ mol min ⁻¹ cm ⁻² ) and the permeate gas flow rate (cm ³ min ⁻¹ ). In the figure, -o- indicates a diagram in the case of using a filter before carrying silver, and-●-indicates a diagram in the case of using a filter after carrying silver. The degree of decrease in gas permeability before and after loading was about 10%, and it was found that sufficient gas permeability was maintained after loading.

  A 0.53M stannous chloride solution and a hydrochloric acid solution containing 1 gram / liter of palladium chloride were passed through the pores of a porous alumina filter (diameter 25 mm, thickness 2 mm, pore size 0.1 to 1 μm). The surface inside the pores was activated. In addition, 0.4 ml of an aqueous solution containing 0.5 M of palladium chloride, 1.0 M of ethylenediaminetetraacetic acid disodium salt, and 9 M of ammonia is mixed with 0.1 ml of 2 M hydrazine aqueous solution, and the mixed solution is used as a test solution. Prepared. This test solution was aspirated from the back side of the activated filter with a vacuum pump, and 0.5 ml of the test solution was impregnated inside the filter. After 6 minutes, it was possible to wash with water, and it was confirmed that this treated filter allowed water to pass through. The filter was dried at 110 ° C. overnight and weighed. Compared to the filter before treatment with the test solution, the mass increased by 9 mg, and it is estimated that 0.4 mass% palladium was supported.

The graph which shows the relationship between the elapsed time in the silver precipitation test of Example 3, and the amount of silver precipitation. The scanning electron micrograph of the surface and cross section of the process filter of Example 5. FIG. The graph which shows the distribution state of the silver in the depth direction of the cross section of the sample of Example 6. FIG. The graph which shows the relationship between the gas pressure about the gas permeation | transmission test of the filter in Example 8, gas permeability, and permeate gas flow rate.

Claims (11)

Metal particle pores characterized by impregnating only a pore of a porous body with a solution containing a metal ion, a complexing agent and a reducing agent, and depositing and supporting the metal on the surface of the pore by a reduction reaction Inner loading method. The method according to claim 1, wherein the metal ion is a noble metal ion and the metal is a noble metal. The method according to claim 1 or 2, wherein the complexing agent is at least one selected from EDTA, NTA, aliphatic oxyacid, formic acid and ammonia or a salt thereof. 4. The reducing agent according to claim 1, wherein the reducing agent is at least one selected from saccharides, hydrazine, tartaric acid, boride, aldehydes, hypophosphorous acid, phosphinic acid and phosphonic acid, or a salt thereof. Method. The method according to any one of claims 1 to 4, wherein the solvent in the solution is at least one selected from alcohol, glycol, ether, ketone, ester and water. The method according to claim 1, wherein the metal ion concentration in the solution is 0.002 to 3M. The method according to any one of claims 2 to 6, wherein the metal ions are noble metal ions, and the concentration of the noble metal ions in the solution is 0.002 to 3M. The method according to any one of claims 1 to 7, wherein the concentration of the complexing agent in the solution is 0.002 to 10M. The method according to any one of claims 1 to 8, wherein the concentration of the reducing agent in the solution is 0.002 to 3M. The method according to claim 1, wherein the porous body is made of ceramic or sintered metal. The method according to any one of claims 1 to 10, wherein the porous body has a pore diameter of 20 microns or less.