Chemistry of inorganic compounds – Oxygen or compound thereof – Peroxide
Reexamination Certificate
1998-04-30
2001-03-27
Langel, Wayne (Department: 1754)
Chemistry of inorganic compounds
Oxygen or compound thereof
Peroxide
C502S174000, C502S177000, C502S178000, C502S182000, C502S183000, C502S185000, C502S240000, C502S242000, C502S251000, C502S252000, C502S262000, C502S263000, C502S300000, C502S328000, C502S333000, C502S339000, C502S340000, C502S341000, C502S349000, C502S350000, C502S351000, C502S355000
Reexamination Certificate
active
06207128
ABSTRACT:
The present invention relates to a method of producing a catalyst comprising a porous support and a catalytically active metal deposited thereon. The method involves electroless deposition of the active metal on the support. The invention also relates to a catalyst obtainable by the method and a process of producing hydrogen peroxide.
Catalysts made of a porous support and a catalytically active metal deposited thereon are used in numerous chemical processes. A porous support involves the advantage of achieving a high specific surface area and efficient utilisation of the active metal. Such a catalyst can, for example, be used for hydrogenation of alkylated anthraquinones in the anthraquinone process of producing hydrogen peroxide or for production of hydrogen peroxide by direct reaction between hydrogen and oxygen.
In the anthraquinone process of producing hydrogen peroxide alkylated anthraquinones dissolved in suitable organic solvents, a so called working solution, are treated with hydrogen in the presence of a catalyst to form the corresponding hydroquinones. The hydroquinones are then oxidised to quinones with oxygen (usually air) with simultaneous formation of hydrogen peroxide which is extracted with water while the quinones are returned with the working solution to the hydrogenation step.
The hydrogenation is the most important step in modem hydrogen peroxide production and different methods of performing this step efficiently are described in the literature. For example, U.S. Pat. No. 3,009,782 discloses use of a fixed bed of catalyst particles, U.S. Pat. Nos. 4,552,748 and 5,063,043 disclose use of a monolithic fixed bed catalyst, and U.S. Pat. No. 5,071,634 discloses use of a catalyst coated static mixer.
In most cases the catalytically active metals are precious metals such as platinum or palladium. The catalysts are normally produced by impregnating a porous support with a solution of a salt of the metal and then treating the impregnated support with a reducing agent such as hydrogen gas. Such processes are described in, for example, U.S. Pat. No. 4,521,531, U.S. Pat. No. 4,240,933 and GB 933979. Although the efficiency of prior art catalysts normally is acceptable, there is always a demand for catalysts having improved activity. As chemical processes like hydrogen peroxide production are performed in large scale even a small enhancement of the catalyst activity can be crucial for the economy of the process.
Many metals can be deposited on various surfaces by electroless or autocatalytic deposition which is described in, for example, W. Goldie, “Metallic Coating of Plastic, Electrochemical Publications Ltd 1969, p 39-52, 55-58, 99-110; F. A. Lowenheim, “Modern Electroplating, John Wiliey & Sons, inc. 1974, p 710-711, 738-745; and J. L Vossen, W. Kern, “Thin Film Processes, Academic Press 1978, p 212-221.
J. R. Kosak (DuPont), “A Novel Fixed Bed Catalyst for the Direct Combination of H
2
and O
2
to H
2
O
2
”, Chem. Ind. (Dekker), 1995, Vol., p 115-125, 62, Catalysis of Organic Reactions, describes preparation of a catalyst by electroless deposition of palladium on a base metal support.
The present invention intends to solve the problem of providing an improved catalyst comprising a porous support and a catalytically active metal deposited thereon. It is also an object of the intention to provide an improved process of producing hydrogen peroxide. According to the invention it has surprisingly been found that the activity of a metal catalyst on a porous support is significantly increased if the catalytically active metal is deposited thereon by electroless deposition.
Electroless deposition refer to methods of depositing metals on catalytic surfaces by the action of a chemical reducing agent in a solution to reduce metallic ions to metal, i.e. autocatalytic deposition.
Thus, the invention concerns a method of preparing a catalyst comprising a porous support and a catalytically active metal deposited thereon comprising the step of treating the porous support with a preferably aqueous solution of a salt of the catalytically active metal and a reducing agent to achieve electroless deposition of the catalytically active metal on the support. Thus, a salt of the catalytically active metal and a reducing agent appear in the same solution during the deposition.
The catalytically active metal may, for example, be any of nickel, palladium, platinum, rhodium, ruthenium, gold, silver, or mixtures thereof. Preferred metals are nickel, palladium, platinum and gold, of which palladium or mixtures comprising at least 50 wt % palladium are particularly preferred. Any water soluble salt of the catalytically active metal can be used. Examples of useful salts are chlorides and nitrates such as PdCl
2
, (NH
3
)
4
PdCl
2
, H
2
PtCl
6
and Pd(NO
3
)
2
.
The porous support may be in the form of discrete particles or fiber cloth or, which is particularly preferred, be arranged in the form of a monolithic structure which, for example, may form substantially parallel channels coated with the support or a static mixer. A monolithic structure may be made of the porous support as such or of another material such as ceramic, metallic or polymeric materials or glass which has been coated with a porous support. Suitable materials for a porous support may, for example, be silica, silicate, alumina, carbon, aluminium silicate such as zeolite, carbonates of alkaline earth metals such as magnesium, calcium, barium or strontium, oxides of magnesium, aluminium, titanium or zirconium, or carbides of magnesium, silicon, aluminium, titanium or zirconium. Silica and alumina are particularly preferred. Preferably the support has a specific surface area from about 0.3 to about 500 m
2
/g, most preferably from about 1 to about 200 m
2
/g, particularly from about 10 to about 100 m
2
/g.
The reducing agent may, for example, be any of formic acid, formaldehyde, hydrazine, salts of hypophosphite or borohydride, or derivatives thereof, or a reducing gas such as hydrogen. Preferred reducing agents are salts of hypophosphite, particularly alkali metal salts such as sodium hypophosphite.
The solution of the salt of the catalytically active metal preferably also contains additional substances, such as stabilisers, particularly complexing agents such as ammoniac or derivatives thereof like ammonium chloride, EDTA, DTPA, or mixtures thereof, of which ammoniac and ammonium chloride are particularly preferred. It is advantageous if the solution contains a sufficient amount of stabilizers to avoid spontaneous precipitation of the catalytically active metal.
The treatment can be performed by contacting the porous support with a solution containing the salt of the catalytically active metal, the reducing agent and any other optional ingredients such as stabilisers, for example by immersing the support into the solution or pumping the solution through a body of a support for a time sufficient to achieve electroless deposition of a desired amount of the metal thereon which normally is from about 0.1 to about 10 g catalytically active metal per 100 g of the support. Normally a suitable contact time is from about 30 seconds to about 2 hours, preferably from about 1 to about 60 minutes. A longer contact time is not detrimental but does not involve any significant advantages. The temperature is not critical and may for example be from the freezing point to the boiling point of the solution, preferably from about 5 to about 70° C. The concentration of the solution is not critical and may, for instance, be from about 0.0001 g catalytically active metal/liter solution up to saturation, for example up to about 50 g metal/liter or more. The amount of reducing agent is suitably sufficient for precipitating substantially all the catalytically active metal onto the support. Preferably the reducing agent is added in stochiometric excess and the solution in contact with the support may, for instance, contain up to 100 g/liter or more of the reducing agent, although it is preferred to maintain a concentration below about 50 g/liter for avo
Nystrom Mats
Sellin Annicka
Akzo Nobel N.V.
Langel Wayne
Serbin David J.
LandOfFree
Method of producing a catalyst does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of producing a catalyst, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of producing a catalyst will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2442007