Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Patent
1981-11-05
1984-01-10
Shine, W. J.
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
106 121, 252313R, 502527, B01J 1300, B01J 2340
Patent
active
044252617
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a liquid suspension of particles of a metal belonging to the platinum group, and a method for the manufacture of such a suspension. The suspension of the invention is useful, for example, for manufacturing catalysts by depositing the metal particles on a carrier. The platinum group comprises ruthenium, rhodium, palladium, osmium, iridium, and platinum.
BACKGROUND ART
It is well known to prepare a suspension of platinum particles by reducing a platinum salt in an aqueous solution with hydrogen, for example. The platinum particles thus produced usually have an average size of at least 10 nm. The suspension, however, contains particles of various sizes, which is due to the fact that small particles have a tendency to unite to form bigger particles during the reduction. This is a disadvantage if the particles are to be used for catalytic purposes, because in this case small particles of approximately the same size are desired. It is another inconvenience that the suspension referred to is not quite stable. The particles have a tendency to settle.
DISCLOSURE OF INVENTION
The invention aims at eliminating said inconveniences. The suspension of the invention is characterized in that the liquid in which the metal particles are suspended consists of a microemulsion. The invention also relates to a method for manufacturing the suspension. The method is characterized by reducing a metal salt dissolved in a microemulsion.
Microemulsions have been known for about three decades. They consist of transparent, thermodynamically stable solutions of water and hydrocarbons, stabilized by a surfactant and, if desired, a second substance having a carbon chain of medium length and a polar end group, for example an aliphatic alcohol or a fatty acid. When used in the present invention the surfactant should be a non-ionic compound soluble in the hydrocarbon. The non-ionic compound shall not react with the reducing agent, meaning that it shall not contain double bonds or other characteristic groups which can be reduced (hydrated). The non-ionic compound shall not, for example, have aromatic groups in the hydrocarbon chain. This demand is met by non-ionic surfactants having been synthesized by reacting ethyleneoxide oligomers with high aliphatic alcohols so that they are bonded to the hydrocarbon chain with an ether bond, for example pentaethyleneglycol dodecylether and its homologs. The non-ionic compounds shall be insoluble in the solvents present in the microemulsion. These demands eliminate several classes of non-ionic surfactants, for example those having been formed by an esterification process, because they are reduced by, or form a precipitation with, hydrazine. We prefer to use polyethyleneglycol alkylethers, preferably containing 12-14 carbon atoms in the carbon chain, and 2-8 ethyleneoxide units in the polyethyleneglycol chain, for example tetraethyleneglycol dodecylether. The hydrocarbon shall not react chemically with the other components of the solution, or with the reducing agents, which are very reactive. This demand eliminates, for example, aromatic hydrocarbons which react with the reducing agents. The boiling temperature of the hydrocarbon shall not be close to the temperature at which the metal particles are precipitated, because this would result in a heavy evaporation of the hydrocarbon when gaseous reaction products leave the microemulsion. The following types of hydrocarbons are useful, fiz: Aliphatic non-cyclic hydrocarbons, for example the homologous series hexane-hexadecane, including branched isomers; aliphatic cyclic hydrocarbons, for example cyclohexane, methyl-cyclohexane, dimethyl-cyclohexanes and other cyclohexane derivatives, decahydronaphtalene. If the particles are to be deposited on a carrier it is preferred to use readily volatile alkanes (6-10 carbon atoms).
The metal salt shall be soluble in the microemulsion. The salt can be dissolved in a small quantity of water, and the aqueous solution thus produced may be mixed into a mixture of the surfactan
REFERENCES:
patent: 3835066 (1974-09-01), Davies et al.
patent: 3992331 (1976-11-01), Petrow et al.
Boutonnet Magali
Kizling Jerzy
Stenius Per
Shine W. J.
Ytkemiska Institutet
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