Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Inorganic carbon containing
Reexamination Certificate
2002-04-02
2004-10-19
Bell, Mark L. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Inorganic carbon containing
C502S162000, C502S164000, C502S167000, C502S169000, C502S172000, C502S184000, C502S224000, C502S230000, C502S330000
Reexamination Certificate
active
06806224
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing a supported metal catalyst which comprises a metal more highly dispersed than that in conventional supported catalysts.
2. Description of the Related Arts
As the process for producing a supported metal catalyst, a process in which an inert support material is impregnated with or allowed to adsorb a salt of a metal used as the catalyst, the metal salt is reduced by treating the resultant product with a reducing agent such as hydrogen gas and fine particles of the metal are formed on the surface of the support material, has been known. However, in accordance with this process, it is necessary that the treatment of reduction be conducted at a high temperature since the entire amount of the metal salt on the support material must be reduced into fine particles of the metal. The treatment at a high temperature causes sintering of the fine particles of the metal and, as the result, it is difficult that a catalyst in which the metal is highly dispersed is obtained.
As another process, a process in which colloidal particles of a metal dispersed in a liquid are fixed on a support material has been known. Since colloidal particles of a metal tend to aggregate with each other and precipitate, in general, a protective colloid is formed by adding a macromolecular compound or a surfactant so that the dispersion is stabilized. In general, for preparation of a supported metal catalyst using colloidal particles of a metal, the colloidal particles of a metal is stabilized as a protective colloid using the above method, then a support material is added to the stabilized colloidal fluid and the resultant colloidal fluid is destabilized by heating or the like method (for example, Japanese Patent Application Laid-Open No. Showa 56(1981)-155645). However, this process has drawbacks in that the process for the preparation requires many steps and that the amount of the metal supported on the support material decreases due to the stabilization of the colloid of the metal as the protective colloid by the addition of a macromolecular compound or a surfactant and the process is disadvantageous with respect to cost, in particular, When a supported noble metal catalyst is prepared.
As still another process for preparing a supported metal catalyst using a colloidal fluid, Nakao et al. introduced a process for supporting a metal without using a protective colloid (Japanese Patent Application Publication Heisei 3(1991)-60534). Although this process may be considered to be advantageous with respect to cost since no protective colloid is used, an expensive salt of boron hydride is used for reduction of the metal salt and this process is disadvantageous with respect to cost. Moreover, when an alkali metal salt of boron hydride which is most stable and most easily available among salts of boron hydride is used, the alkali metal component tends to remain in the catalyst and unexpected side reactions frequently take place in the actual reaction system. Therefore, the above process is not preferable.
For producing a supported metal catalyst in accordance with the so-called ion exchange process, the surface treatment of the support material, repeated exchange reactions of functional groups at the surface of the support material with the metal ion and the treatment of reduction must be conducted and it takes a long time for the preparation. Moreover, since the amount of the supported metal is limited by the ion-exchange capacity of the support material (Petrotech, Volume 17, 1994, Page 331), it is difficult that a supported metal catalyst having a great amount of the supported metal is prepared. The above process has a further drawback in that the obtained supported metal catalyst does not always exhibit a high activity since sintering of the metal particles occasionally takes place during the treatment of reduction.
As the process for producing a metal black, the process of Feulgen et al. has been known for a long time (Ber., 54, 360 (1921)). However, when the process of Feulgen et al. is applied to preparation of a supported metal catalyst, an alkali metal is mixed into the catalyst since an alkali metal compound is used in a step of the preparation. Therefore, this process is not preferable. When the obtained catalyst is washed with a great amount of water to remove the alkali metal, a drawback arises in that, since a portion of the metal intended to be supported on the support material flows away as colloidal particles, the metal is not fixed to the support material in the prescribed amount and the portion of the metal which has flowed away must be recovered.
SUMMARY OF THE INVENTION
The object of present invention is to provide an industrially advantageous process for producing a supported metal catalyst which comprises the metal component supported in the highly dispersed condition and exhibits high activity.
As the result of intensive studies by the present inventors to overcome the above drawbacks on the process for preparing a supported metal catalyst, it was found that a supported metal catalyst which comprises the metal component supported in the highly dispersed condition could be obtained by using an inexpensive metal halide as the raw material and reducing the metal component in the liquid phase in the presence of an organic base. The present invention has been completed based on this knowledge.
The present invention provides a process for producing a supported metal catalyst which comprises reducing a metal halide in a liquid phase in a presence of a support material, an organic base and a reducing agent.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the process for producing a supported metal catalyst of the present invention, a metal halide is used as the precursor.
As the metal component, various metals which can be used as the catalyst can be used. Gold, silver, platinum, rhodium, palladium, ruthenium, osmium and iridium are preferable. The metal component is used as a halide such as fluoride, chloride, bromide and iodide.
The metal halide may be used singly or as a mixture of two or more. When a metal halide having poor solubility in water is used as the precursor, it is necessary that the metal halide is dissolved into a dilute hydrochloric acid or a dilute nitric acid so that an aqueous solution is prepared and the prepared aqueous solution is used for the process.
For producing a supported metal catalyst of the present invention, various support materials usually used for supported metal catalysts may be used. Examples of the support materials include carbon black, activated carbon, alumina and silica.
As the organic base used in the process for producing a supported metal catalyst of the present invention, quaternary ammonium hydroxides represented by general formula (1), quaternary ammonium hydroxides represented by general formula (2), tertiary alkylamines represented by general formula (3) and triethylenediamine (1,4-diazabicyclo[2,2,2]octane) are preferably used. The organic base may be used singly or as a mixture.
In general formula (1), R
1
, R
2
, R
3
and R
4
each represent an alkyl group having 1 to 4 carbon atoms.
In general formula (2), R
5
, R
6
and R
7
each represent an allyl group having 1 to 4 carbon atoms and R
8
—OH represents a hydroxyalkyl group having 1 to 4 carbon atoms.
In general formula (3), R
9
, R
10
and R
11
each represent an alkyl group having 1 to 6 carbon atoms.
Among the organic bases represented by the above general formulae, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide and choline are preferable and tetramethylammonium hydroxide is more preferable.
When sodium hydroxide is used as the base without using the organic base, the supported metal flows away as a colloid during washing of the obtained catalyst to remove the alkali metal and a catalyst having the metal in the desired amount cannot be obtained. When ammonia is used as the base, a stable ammine complex is
Maeshima Kazuaki
Motoi Takashi
Yoshihara Jun
Antonelli Terry Stout & Kraus LLP
Bell Mark L.
Hailey Patricia L.
Mitsubishi Gas Chemical Company Inc.
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