Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Inorganic carbon containing
Patent
1981-10-19
1983-10-11
Shine, W. J.
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Inorganic carbon containing
502150, 502263, 502261, 502313, 502325, 502301, 502327, B01J 2118, B01J 2342, B01J 2344, B01J 2346
Patent
active
044091290
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of manufacturing a catalyst. More specifically, the present invention relates to a method of producing a catalyst suitable for an electrode of a fuel cell, such as a platinum black catalyst.
BACKGROUND ART
As the method of manufacturing a platinum black catalyst used for a fuel cell, there have heretofore been mainly adopted the following two methods. According to one method, a platinum ingot is mechanically pulverized, and this method is ordinarily called "a dispersing method". This dispersing method is defective in that the size of platinum particles is large and the particle size distribution is broad and not uniform.
According to the other method, a solution of a platinum salt is reacted with a reducing agent to precipitate platinum. This method is ordinarily called "a flocculation method". A formalin reducing method is most popular as the flocculation method, and according to this method, a solution of chloroplatinic acid is reacted with formalin, an alkali metal hydroxide is added to the reaction mixture under cooling and formed platinum black is separated. Secondary cohesion takes place in the obtained platinum black particles because of the hydrophobic force thereof, and the average particle size is relatively large and several thousand angstroms and the surface area is scores of square meters per gram.
The larger is the specific surface area, the higher is the activity of the catalyst, and a smaller particle size of particles is more effective for increasing the specific surface area. Accordingly, development of a method of manufacturing a catalyst composed of fine particles is of great significance.
DISCLOSURE OF THE INVENTION
It is a primary object of the present invention to provide a method of manufacturing a catalyst in which fine particles having a larger specific surface area than that of particles obtained by the conventional methods are obtained.
In accordance with the present invention, there is provided a method of manufacturing a catalyst, which comprises the step of reducing a solution containing at least two metal ions or complex ions differing in the oxidation-reduction potential to precipitate metal particles and the step of dissolving out particles of at least one metal from the precipitated metal particles.
As an example of the solution containing at least two metal ions or complex ions, there can be mentioned a solution containing a platinum ion and a metal or complex ion as a second element different from platinum in the oxidation-reduction potential. It has been found by the electron microscope observation that the size of particles formed by secondary cohesion of platinum particles and second metal particles is as small as several hundred angstroms because of a certain action of fine platinum particles and second metal particles. If the metal as the second element is dissolved out from the precipitated particles, the platinum particles are rendered porous and the specific surface area of the platinum particles becomes as large as about 70 to about 100 m.sup.2 /g.
The present invention can be applied to not only a platinum black catalyst but also all the catalysts where the above-mentioned combination of metal ions is possible.
Incidentally, by the term "platinum black" is meant a fine particle of platinum. Although a metal has a peculiar inherent color, as the metal is powdered to a fine particle, with reduction of the particle size the color grows black. Therefore, a fine particle of platinum is ordinarily called "platinum black".
Metal particles may be precipitated in the form supported on a carrier. In this case, it is necessary to insert the carrier in the solution. By dissolving out particles of a metal having a lower reduction potential from metal particles supported on the carrier, there can be obtained a carrier-supported catalyst. As the carrier, there can be used alumina, silica, titania, active carbon, graphite, carbon black, diatomaceous earth, chromium oxide, zirconia, tungsten oxide and porous poly
REFERENCES:
patent: 3380934 (1968-04-01), Batzold
patent: 4192907 (1980-03-01), Jalan et al.
patent: 4255247 (1981-03-01), Oda et al.
Matsuda Shimpei
Takeuchi Seizi
Hitachi , Ltd.
Shine W. J.
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