JPH0362459B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for controlling the particle size of a metal on a carrier in the preparation of a so-called supported metal catalyst in which a metal is supported on a carrier. (Prior Art) Supported metal catalysts are widely used in various industries and are of great importance. It is also known that the activity etc. are greatly influenced by the size of metal particles present on the carrier, and it is desired to control the metal particle size. As methods for controlling the particle size of the supported metal, there are two known methods: (a) changing the concentration of the supported metal; and (b) treating the supported catalyst once prepared at high temperature to cause agglomeration and increase the particle size. be. (Problems to be Solved by the Invention) However, in the method (a) above, it is necessary to change the concentration of the metal that essentially affects the reaction;
The disadvantage of this method is that once the metal particles have been formed, they must be treated at high temperatures, which carries the risk of essentially changing the properties of the catalyst. (Means for Solving the Problems) The present inventors have conducted various studies in order to find a method for controlling the particle size of catalyst metal that overcomes the above-mentioned drawbacks, and as a result, the pore diameter and pore volume of the support are It was discovered that this has a large effect on the particle size, and based on this knowledge, the present invention was completed. That is, according to the present invention, there is provided a particle size control method characterized by changing the pore size of the carrier when impregnating the carrier with a metal. In the present invention, various metal salts soluble in water and various solvents can be used as the metal salts used as catalyst preparation raw materials, and there are no particular limitations. In the method of the present invention, a so-called impregnation method is employed in which the metal salt solution is brought into contact with the carrier. In this case, control will proceed favorably if the amount of solution used is close to the pore volume of the carrier. As the carrier used in the present invention, silica, alumina, silica-alumina, etc., which do not easily react with metal salts, are employed. A preferred carrier is silica. Various types of pore volumes and pore diameters can be applied to these carriers, but considering the ease of predicting control results, pore volumes of 0.2 ml/g to 2 ml/g and pore diameters of 30 Å are recommended.
~700 Å is preferred. (Effects of the Invention) In the present invention, unlike conventional methods, it is possible to change the particle size of the metal and its distribution state while keeping the supported concentration of the catalyst metal, which has a large effect on the reaction rate and products, constant. Furthermore, it is not necessary to heat the metal particles once generated at high temperatures, and there is no risk of changing the properties or state of the catalyst. (Example) Next, the invention will be explained in more detail with reference to Examples. Example 1 Pore volume range of 1.0 to 1.1G10ml/g, pore diameter 70
Add 0.4 g of chloroplatinic acid hexahydrate dissolved in 2.4 ml of water to 2.0 g of silica selected from the range of ~507 Å.
After standing for a period of time, using a rotary evaporator under reduced pressure at 80℃ for 1.5 hours, at 110℃ for 1 hour, at 050℃ for 1.5 hours.
Dry for an hour. Next, the temperature was raised to 400°C at a rate of 4.5°C/min in a hydrogen stream, and then heated at 400°C for an additional 2 hours to obtain a catalyst with a platinum concentration of 8.29 (W/W)%. The particle size of this catalyst was measured by the line broadening method of X-ray diffraction, and the results are shown in Table 1.

[Table] Example 2 A catalyst was prepared in the same manner as in Example 1 by adding 0.24 g of rhodium chloride trihydrate dissolved in 2.4 ml of water to 2.0 g of silica with a pore volume of 1.0 to 1.10 ml/g and a pore diameter of 70 Å. did. Note that the final hydrogen treatment was performed at 450°C. The particle size of the obtained catalyst was measured in the same manner as in Example 1, and the results are shown in Table 2.

[Table] From the results shown in Tables 1 and 2, it can be seen that the method of changing the pore size of the carrier is very effective in controlling the particle size of the supported metal. Furthermore, from the results in Table 2, it can be seen that metals having the required particle size can be prepared on the carrier by combining the method with a method that allows the concentration of the metal to be supported to be obtained. Furthermore, it is clear from these results that changing the pore volume of the carrier changes the absolute amount of impregnated metal salt solution, and therefore changes the concentration of the supported metal.

Claims (1)

[Claims] 1. A method for controlling particle size, which comprises changing the pore size of the carrier when impregnating and supporting a metal on the carrier. 2. The method according to claim 1, wherein the carrier is silica.