JPS6156019B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a novel supported noble metal catalyst exhibiting high catalytic activity. Supported noble metal catalysts are most commonly used because they contain a large metal surface area and are easy to recover and handle. However, methods for producing metal catalysts in this form include activated carbon, silica gel, A solid with a large specific surface area, such as diatomaceous earth, is impregnated with or adsorbed with a metal salt serving as a catalyst, and then molecular hydrogen or an appropriate reducing agent is applied to the solid to reduce the metal salt and form metal fine particles. There are known methods to generate it. However, in this method, since the reduction of the metal salt occurs on the surface of the carrier, the shape of the resulting metal fine particles is not constant, and the reproducibility of the catalytic activity is often a problem. Furthermore, when the density of the metal salt on the surface of the carrier is low, this reduction reaction is significantly slowed down, and therefore, strict conditions are generally required to produce a metal catalyst with a low loading rate. On the other hand, when metal salts are reduced in an aqueous or alcoholic solution, the reaction proceeds at a sufficient speed even at low concentrations, and all of the metal salts can be easily converted into the corresponding metal fine particles. The powdered metal obtained in this way is also effective as a catalyst, but depending on the reaction conditions, the metal particles may agglomerate to form a lumpy precipitate, reducing the effective surface area and significantly reducing the catalytic activity, or conversely, the metal particles There are many operational difficulties compared to supported metal catalysts, such as if the particles are too fine, it becomes difficult to recover them after the reaction. The present inventors aimed to overcome the drawbacks of conventional supported precious metal catalysts and powdered precious metal catalysts, maintain a large effective surface area over a long period of time, and obtain a precious metal catalyst with constant reproducibility. As a result of extensive research, we have found that if a precious metal catalyst is formed into fine particles and then supported on a predetermined solid, the catalyst particles prepared to have a fixed particle size and shape will be able to maintain their particle size and shape. If noble metal fine particles prepared by reduction in a lower alcohol are brought into contact with a solid anion exchange resin having a quaternary ammonium group, the surface of the resin can be easily formed. We have discovered that redispersion occurs, and based on these findings, we have accomplished the present invention. That is, in the present invention, a salt of a noble metal selected from rhodium, platinum, and silver is reduced in a lower alcohol to precipitate the noble metal, and then,
The present invention provides a method for producing an ion-exchange resin-supported noble metal catalyst, which comprises bringing the catalyst into contact with a solid anion-exchange resin having a quaternary ammonium group and dispersing the catalyst on the resin. In the method of the present invention, it is first necessary to precipitate the precious metal as fine particles, which makes it easy to adjust the particle size and shape of the catalyst. This can be carried out by a known method in which a solution is treated with an alcohol-soluble reducing agent such as sodium borohydride or hydrazine. As noble metal salts, rhodium chloride, chloroplatinic acid, silver nitrate, etc. are used, and as lower alcohols as solvents,
Alcohols having 1 to 3 carbon atoms such as methanol, ethanol, and propanol are used. The operation for forming the noble metal is carried out at 0°C to the boiling point of the lower alcohol, and is usually carried out at around room temperature.
At this time, if the precious metal precipitate coagulates and becomes a large lump, the time required for supporting it will be extremely long.
It is desirable to form a well-dispersed precipitate. In the present invention, a solid anion exchange resin having a quaternary ammonium group is used as a carrier. Most commercially available anion exchange resins are of the chlorine ion type, but hydroxide ions can be obtained by washing with water to remove impurities, or by contacting them with an excessive amount of sodium hydroxide, sodium sulfate, etc. Anion exchange resins such as type and sulfate ion type can be used. The supporting operation is carried out by adding an anion exchange resin to a lower alcohol suspension containing the noble metal precipitate and stirring the mixture. At this time, the anion exchange resin changes from its initial white to pale yellow color to black or gray, and the black precious metal precipitate decreases accordingly and finally disappears. Carrying operation is 0
℃ to the boiling point of the lower alcohol, and the time required for this is within 5 hours when the temperature is around room temperature, and within 30 minutes when the reaction is carried out under normal pressure under reflux. A commercially available anion exchange resin used as a carrier is powdered or granular Amberlite.
Examples include IRA-938, Amberlite CG-400, Amberlite A-26, Amberlite IRA-904, etc., but if the loading rate is high, a powdered resin with a larger surface area is suitable. The amount of ion exchange resin used is 20 to 1000 times, preferably 100 to 500 times the weight of the total amount of noble metals to be supported. The obtained suspension containing the supported noble metal catalyst can be directly subjected to a liquid phase reaction using a lower alcohol as a solvent, but usually the solid catalyst is dispersed by filtration or the like, washed with alcohol, etc.
It is used for practical use by drying or keeping it in a wet state. According to the present invention, it is possible to easily and efficiently obtain a solid catalyst supporting fine precious metal particles, and the obtained solid catalyst can be used for liquid phase reactions and gas phase reactions, and at the same time, it can be easily recovered. The reproducibility of catalyst activity is also good. Next, the present invention will be explained in more detail with reference to Examples. Example 1 50 μmol of rhodium chloride (Rhcl _{3.3H 2} O) was dissolved in 95 ml of ethanol, and 5 ml of an ethanol solution of 200 μmol of sodium borohydride was added dropwise at room temperature with stirring. A suspension containing a fine black precipitate of metal was obtained. Separately, chlorine ion type anion exchange resin (manufactured by Rohm and Haas, Amberlite CG-400)
The mold (200 to 400 mesh) was washed three times with 20 times the amount of pure water, filtered, and then dried at 70°C for 6 hours. 1.00 g of the resin thus obtained was added to the suspension of rhodium metal and stirred at room temperature for 4 hours. During this time, the resin turned gray and the black precipitate of rhodium metal disappeared.
After filtering this resin, it was dried under reduced pressure to obtain a supported rhodium catalyst in the form of gray fine particles. 20mg of this supported rhodium catalyst (Rhodium 1μ
(containing g-atoms) in a 50 ml eggplant-shaped flask,
After replacing the inside with hydrogen, add 20ml of ethanol from which dissolved oxygen has been removed, and heat at 30℃ under 1 atm of hydrogen for about 15 minutes.
Stir for a minute to saturate with hydrogen. When 0.25 mmol of cyclohexene was added dropwise to this, hydrogen absorption started immediately, and after about 30 minutes, hydrogen absorption stopped and cyclohexane was obtained. The initial hydrogenation rate at this time is 0.45 mol/atom per gram of rhodium.
It was hot in sec. Example 2 A supported rhodium catalyst was prepared in the same manner as in Example 1 by changing the solvent for the rhodium chloride () reduction reaction and the carrier resin. The initial hydrogenation rate of cyclohexene in hydrogenation at 30° C. and 1 atm using the catalyst thus obtained is shown below.

[Table] (Sulfate ion type)
Ethanol Amberlight 0.23
CG〓400
(Hydroxy ion type)

Claims (1)

[Claims] 1 A salt of a noble metal selected from rhodium, platinum, and silver is reduced in a lower alcohol to precipitate the noble metal, and then brought into contact with a solid anion exchange resin having a quaternary ammonium group. A method for producing an ion-exchange resin-supported noble metal catalyst, which comprises dispersing and supporting the catalyst on a resin.