Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2002-02-12
2004-03-16
Dunn, Tom (Department: 1725)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C502S150000, C502S158000, C502S243000, C502S261000, C502S262000, C502S325000, C502S339000, C502S344000, C502S313000, C502S317000, C502S350000
Reexamination Certificate
active
06706902
ABSTRACT:
The present invention relates to a process for the continuous production of nano-scale precious metal particles on SiH-containing support materials and the use of these precious metal-containing compositions as catalysts. Specifically, the process according to the invention comprises: a) impregnating support materials; b) drying the support material by spraying or by fluidized bed technology leads to form compositions that are after thermal activation active in the catalysis of oxidation reactions. The catalytically active precious metal-containing compositions exhibit high selectivities and productivities and very long catalyst service lives without deactivation. The present invention also relates to a process for the oxidation of hydrocarbons in the presence of oxygen and a reducing agent.
Processes for depositing gold particles on support materials are known. Such methods are disclosed in, for example, U.S. Pat. No. 5,623,090, WO-
98/00413-
A1, WO-98/00415-A1, WO-98/00414-A1, WO-00/59632-A1, WO-99/43431-A1, and EP-A1-0 827 779. These references discloses the following processes for depositing gold particles on support materials: deposition-precipitation; co-precipitation; impregnation in solution; incipient wetness; colloid processes; sputtering; chemical vapor deposition (“CVD”), physical vapor deposition (“PVD”), and microemulsion. These references also disclose processes relating to heterogeneously catalyzed gaseous phase oxidations of propene to propene oxide with molecular oxygen in the presence of hydrogen.
Preferably, the deposition-precipitation method is used. With this method, gold particles are precipitated from corresponding gold precursor compounds onto inorganic titanium dioxides, preferably anatase, or inorganic titanium dioxide-containing silicon dioxides. Active catalysts can be obtained by impregnating purely inorganic silicon dioxide surfaces with titanium precursor compounds in solution followed by gold coating by deposition-precipitation and subsequent calcination in an air atmosphere of the resultant materials. These active catalysts nonetheless have relatively low propene conversions, deactivate extremely rapidly (typical half-life times are 10-100 hrs.) and thus cannot be used in large-scale industrial operations.
A disadvantage of the deposition-precipitation process is the fact that the process uses large amounts of solvents. Additionally, a pH adjustment to 7.5-10, using bases, is necessary. Only a fraction of the gold compound used is deposited as catalytically active species on the support material. In addition, production is carried out batchwise and, especially when catalyst supports based on silicon dioxide are used, results in undesirable broad particle size distributions of the precious metal (4 to >>50 nm). Such precious metals must then be precipitated on the support matrix. Typically, only gold particles of <10 nm are catalytically active. The deposition-precipitation method, therefore, is not an efficient process for generating gold particles of a catalytically active size.
Incipient wetness and solvent impregnation methods for generating precious metal particles on support materials carrying SiH groups are disclosed in DE 199 59 525 and DE 100 23 717. The expression “incipient wetness” is used to refer to the process of adding a solution containing soluble gold and/or silver compounds to a support material (impregnation), the volume of the solution on the support being less than, equal to or slightly higher than the pore volume of the support. The solution is rapidly removed after impregnation. DE 199 59 525 and DE 100 23 717, however, do not disclose details of the advantageous limits of the contact times during the coating of the support material.
WO-00/59633-A1 discloses a process for the synthesis of gold particles on support materials. In this reference, inorganic support materials are impregnated with a soluble reducing agent and then with a gold precursor compound. Reducing agents such as acetic acid, lactic acid, citric acid, acetates, alcohols or amines are disclosed.
The catalysts produced according to WO-00/59633-A1 exhibit relatively low activities in the gaseous phase oxidation of hydrocarbons in the presence of hydrogen. Catalysts produced in this way deactivate relatively quickly over reaction time and have broad gold particle size distributions on the support materials.
DE-A1-197 09 101 and EP-A1-0 469 662 disclose a method for the production of gold or precious metal-containing titanium silicalites. The titanium silicalites are impregnated with a gold solution or precious metal compound and then dried. The need to restrict the impregnation time and the influence on the size of the metal particles is not disclosed. Also, the supports of these references do not contain any SiH groups.
The known processes for preparing catalyst preparation are thus extremely unsatisfactory with regard to the methods used for the production of the nano-scale precious metal particles. Additionally, huge reactors are required for industrial processes using relatively inactive catalysts. Also, short catalyst service lives lead to production breakdowns during the regeneration phase or require redundant, costly production paths.
One object of the present invention is to provide an industrial process for the continuous production of nano-scale precious metal particles having homogeneous size distributions on a support material.
Another object of the present invention is to develop new catalysts for the oxidation of hydrocarbons, wherein the precious metal content should be the minimum amount necessary to achieve high catalyst activity. A further object of the present invention is to provide a catalyst available on an industrial scale for the oxidation of alkenes.
Yet a further object of the present invention is to eliminate disadvantages of the known processes for the production of nano-scale metal particles on support materials.
These objects are achieved by using a process wherein support materials comprising precious metal particles having a diameter in the range from 0.01-10 nm are produced by bringing a support material which has SiH groups into contact with at least one precious metal compound and/or precious metal particles for a time span of less than 2 hours and then immediately drying the drying the support material.
Precious metals useful in the present invention include gold, silver or mixtures of gold and silver, palladium, platinum or ruthenium. Preferably, gold is used in the process. Several precious metals may be used simultaneously in the process.
The size distribution of the precious metal particles obtained by the process according to the invention is very narrow. 50% of the particles, preferably 60% of the particles and most preferably 65% of the particles are smaller than 10 nm.
Support materials useful in the invention are purely inorganic materials or organic-inorganic hybrid materials. Preferably, organic-inorganic hybrid materials (hybrid support materials) are used. Amorphous as well as crystalline support materials are also suitable for use in the invention.
The composition of the support materials according to the invention may vary widely. In one preferred embodiment of the invention, the support materials are based on silicon oxide and/or silicon dioxide.
Organic-inorganic hybrid materials useful in the invention are organically modified glasses that preferably form soluble precursor compounds in sol-gel processes via hydrolysis and condensation reactions and that contain non-hydrolysable terminal and/or bridging organic groups in the network. These materials and their production are disclosed, for example, in DE 199 59 525 and DE 100 23 717.
The organic-inorganic and inorganic support materials containing SiH units are preferably produced via sol-gel processes. This is carried out for example by mixing suitable, soluble compounds, the hydrolysis and condensation reaction being initiated by adding water and optionally catalysts (e.g. acids, bases and/or organometallic compounds and/or electrolytes and/or
Stürmann Martin
Wegener Gerhard
Weisbeck Markus
Zbrozek Frank
Bayer Aktiengesellschaft
Dunn Tom
Gil Joseph C.
Ildebrando Christina
Mrozinski, Jr. John E.
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