Patent Application
20080274037
The present invention is related to a method for preparing X-ray amorphous or weakly crystalline metal oxide fluoride, a catalyst comprising an X-ray amorphous or weakly crystalline metal oxide fluoride, a method for preparing such catalyst and uses of said catalyst.
Metal oxides, metal fluorides and metal oxide fluorides are of great importance to the chemical, pharmaceutical and, e. g., ceramics industry. In particular, inorganic materials having high surface areas are of great interest for, e. g., heterogeneous catalysis where the activity of a catalyst depends largely on its surface.
Metal oxides with very high surface areas can be prepared via sol-gel routes, by freeze-drying or under supercritical conditions as xerogels (c. f. Advanced Catalysts and Nanostructured Materials, editor W. R. Moser: Chapter 2—The Role of Prehydrolysis in the Preparation of Zr—Si Aerogels by J. B. Miller and E. I. Ko, Academic Press, San Diego, 1996) or aerogels.
A particularly preferred metal fluoride catalyst is aluminium trifluoride, which is used as a Lewis acidic catalyst for industrial fluorination. The synthesis, characteristics and uses of such aluminium fluorides are described in E. Kemnitz and D.-H. Menz, Prog. Solid St. Chem. 26 (1998), p. 97-153. Aluminium fluoride based catalysts such as AlF3 exhibit an octahedral arrangement of fluorine atoms, the aluminium atoms of which are thus saturated in a coordinative manner. Because of this arrangement these AlF3 species exhibit a comparatively low Lewis acidity. In addition, the crystalline structure goes along with a limited specific surface of, e. g., 0.5 to 30 m2/g which is disadvantageous as the activity of a solid phase or heterogeneous catalyst strongly depends on its specific surface area. Aluminium fluorides can be produced using wet-chemical synthesis and subsequent controlled dehydration. Alternatively, non-wet-chemical synthesis routes are reported. Ziegler, K. and Köster, R., Liebigs Ann. Chem. 608 (1957) 1-7 describe the synthesis of aluminium trifluoride using aluminium trialkyl and boron trifluoride as starting materials. DE 4041771 describes the fluorination of aluminium chloride using anhydrous hydrogen fluoride. U.S. Pat. No. 5,157,171 discloses the fluorination of AlCl3 using chlorofluorocarbons. Both methods result in an AlClxF3−x which still contains chlorine.
This residual chlorine is responsible for both the observed high acidity and the high hygroscopicity. The product resulting from both methods is also referred to as aluminium chlorofluoride, ACF. Because of its hygroscopicity ACF is extremely difficult to be used in technical applications. Also, ACF is rapidly deactivated upon, e. g., contacting H containing organic solvents such as ethers, alcohols and the like. In addition, the particular fluorination process cannot be transferred to other metal chlorides as only the particular reaction provides the gain in energy required for the conversion of AlCl3 into AlF3.
By none of the abovementioned synthetic routes metal oxide fluorides can be obtained.
Surface fluorinated aluminium oxide has been prepared by (A. Hess and E. Kemnitz, J. Catal. 1994, 149, 449-457) and (P. J. Chupas, M. F. Ciraolo, J. C. Hanson and C. P. Grey, J. Am. Chem. Soc. 2001, 123, 1694-1702) by fluorination of aluminium oxide with chlorodifluoromethane at higher temperatures. However, by this method no defined fluorination degree throughout the material can be obtained, and the method cannot be applied to magnesium oxide fluoride, a preferred compound of the present invention.
The basic considerations in relation to and the limitations of metal oxide fluoride catalysts as described above, also apply for doped metal oxide fluoride catalysts. Doped metal oxide fluoride catalysts can be particularly advantageous as it is known that in metal oxide as well as metal fluoride based catalysts a partial replacement of host metal atoms by doping metal atoms has a strong influence on the activity and/or selectivity of the respective catalyst.
The problem underlying the present invention is thus to provide a method for preparing an amorphous or weakly crystalline metal oxide fluoride, preferably an X-ray amorphous metal oxide fluoride, having a high active surface and preferably being catalytically active. It is a further problem underlying the present invention to provide a metal oxide fluoride based catalyst which has a high specific surface and is moisture resistant, i. e. it may be handled in open air without becoming irreversibly deactivated.
According to the present invention the problem is solved in a first aspect by a method for preparing an X-ray amorphous or weakly crystalline metal oxide fluoride of a composition represented by the formula Ma+ObFc comprising the steps of
In an embodiment, the organic acid anion is selected from the group comprising formic acid, acetic acid, propionic acid and butyric acid, each in its divers forms such its iso form.
In an embodiment the conversion in step b) is performed
In a further embodiment the precursor contains a metal oxygen bond. Preferably such metal oxygen bond is established between the metal moiety and another moiety selected from the group comprising alkoxides, enolates, nitrates and salts of organic acids, each as defined herein. Hydrolysis is preferred in case the oxygen containing precursor is or comprises an alkoxide or an enolate.
In an embodiment the reaction conditions for the thermal treatment are 150° C. to 800° C., preferably 250° C. to 450° C.
In an embodiment the hydrolysis is carried out using a water containing fluid, whereby the water containing fluid is preferably selected from the group comprising water, aqueous systems and mixtures of water and at least one organic solvent. It is also within the present invention that the organic solvent is the same as the organic solvent referred to and defined herein as “L”.
In an embodiment the precursor is mixed with another hydrolysable metal compound M′E, whereby M′ is different from M and E is a group or an anion selected from the group comprising alkoxide, enolate, alkyl, chloride, bromide and iodide, whereby preferably the hydrolysis is carried out such that the final product contains the M′ as an oxide. This can be achieved by hydrolysis using reaction parameters as disclosed herein for any hydrolysis reaction and subsequent calcinations using reaction parameters as disclosed herein for any calcinations process. More preferably, M′ is selected from the same group as defined herein for M.
In an embodiment the amount of water added for hydrolysis is about 5 to 50 mol % of the metal content of the precursor.
In an embodiment the temperature for the calcinating step is from about 100° C. to about 700° C., preferably from about 250° C. to about 450° C. More preferably, the heating is performed under ambient pressure. The preferred reaction vessel is a flow reactor. Even more preferably, the reaction is run under a flow of gas, whereby the gas is preferably an inert gas and whereby the gas is preferably selected from the group comprising helium, argon, nitrogen, oxygen and any mixture of any of these gases.
In an embodiment the precursor and/or the metal oxide fluoride comprises two or more different metals. Preferably, both the precursor and the metal oxide fluoride comprise two or more different metal.
In an embodiment B is selected from the group comprising alkoxides, enolates and salts of carboxylic acid whereby each and any of the groups preferably have a length of 1 to 5 C atoms. This preferred length applies to any of these groups as used herein, irrespective of whether the individual group is related to B. As used herein the term “a length of 1 to 5 C-atoms” means 1, 2, 3, 4, or 5 C-atoms.
In an embodiment B is selected from alkoxides.
In an embodiment the precursor is made from a compound of the formula
Ma+BaLx
whereby
In an embodiment the precursor is prepared by
In an embodiment the precursor, the starting material for the precursor, or the fluorinating agent for the preparation of the precursor is present in or introduced into an anhydrous organic solvent.
In a preferred embodiment the anhydrous organic solvent is preferably selected from the group comprising alcohols, ethers, ketones, formic acid, acetic acid and propionic acid.
In an embodiment the metal oxide fluoride is MgOdF2−2d, wherein d is 0.01 to 0.5, more preferred 0.05 to 0.2.
In an embodiment the X-ray amorphous or weakly crystalline metal oxide fluoride is a catalyst, preferably a heterogenous catalyst.
According to the present invention the problem is solved in a second aspect by a method for the manufacture of a catalyst comprising an X-ray amorphous or weakly crystalline metal oxide fluoride of the formula Ma+ObFc,
whereby
According to the present invention the problem is solved in a third aspect by an X-ray amorphous or weakly crystalline metal oxide fluoride obtainable by a method according to the first aspect of the present invention.
According to the present invention the problem is solved in a fourth aspect by a catalyst obtainable by a method according to the first aspect of the present invention.
According to the present invention the problem is solved in a fifth aspect by a catalyst comprising an X-ray amorphous or weakly crystalline metal oxide fluoride of the formula Ma+ObFc,
whereby
According to the present invention the problem is solved in a sixth aspect by an industrially producible catalyst, preferably a catalyst according to the fourth and fifth aspect of the present invention, containing an X-ray amorphous or weakly crystalline metal oxide fluoride of the formula Ma+ObFc.
whereby
In an embodiment of the catalyst according to the fourth to the sixth aspect of the present invention, M is selected from the group comprising Zn, Sn, Cu, Fe, Cr, V, Mg and Al, whereby preferably M has a charge of +2 or +3.
In an embodiment of the catalyst according to the fourth to the sixth aspect of the present invention, any of M is used as Mx+Fx−δ, as guest component or as host component.
In an embodiment of the catalyst according to the fourth to the sixth aspect of the present invention, the catalyst comprises two different M, whereby a first M is part of the host component and a second M is part of the guest component.
In an embodiment of the catalyst according to the fourth to the sixth aspect of the present invention, any of M is used as Mx+Fx−δ, as host component to accommodate a metal oxide M′yOz with M′≠M, wherein said metal oxide is bound via a M′-O-M bond.
In an embodiment of the catalyst according to the fourth to the sixth aspect of the present invention, any M is used in the form of Mx+Fx−δ, as host component to accommodate a metal oxide M′yOz with M′ being different from M.
In an embodiment of the fourth to the sixth aspect of the present invention, the catalyst is to be used as solid catalyst for oxidation processes.
In an embodiment of the fourth to the sixth aspect of the present invention, the catalyst is to be used as solid acid or solid base catalyst.
The present inventors have surprisingly found that an X-ray amorphous or weakly crystalline metal oxide fluoride preferably having a highly distorted lattice can be prepared by using distinct classes of a precursor molecule and subjecting said precursor molecule to either thermal treatment or hydrolysis. Such metal oxide fluorides have a high surface area, are an X-ray amorphous or weakly crystalline solid of a strongly distorted solid state structure. Additionally, the irregularities and disorder of the structural arrangement result in a mesoporous surface. Metal oxide fluorides are less strong Lewis acids in case of Lewis acidic metals than the respective metal fluorides. Rather the metal oxide fluorides as disclosed herein have a certain degree of basicity compared to metal fluorides the extent of which can be modulated so as to provide different metal oxide fluorides having different basicity. These effects attribute to tailored catalytic properties for a variety of reactions, such as, e.g., halogen exchange reactions, dismutations and isomerisations of CFCs/HCFCs as well as Friedel-Crafts alkylations acylations, and oxidations respectively.
Such amorphous metal oxide fluoride which is referred to herein as the metal oxide fluoride according to the present invention, has the general formula
Ma+ObFc,
whereby a is any integer of 1, 2, 3, 4, 5 or 6, preferably 2 or 3; and b and c are any numbers obeying the formula b/2+c=a, and c is 0.1b to 10b.
As used herein and if not indicated to the contrary, amorphous or weakly crystalline metal oxide fluoride is the same as highly distorted metal oxide fluoride. The amorphous metal oxide fluoride according to the present invention is X-ray amorphous. X-ray amorphous, as described herein, preferably means that the X-ray diffraction pattern shows no peaks. Weakly crystalline, as described herein, preferably means that the X-ray diffraction pattern shows at least one peak the intensity of which is, however, nearly as low as the background is. Without wishing to be bound by any theory, it seems that the highly distorted structure of the metal oxide fluoride is critical to the observed catalytic activity.
It is to be noted that, in principle, the metal oxide fluoride may also be a mixed metal oxide fluoride such that the catalyst is a doped catalyst. The metal component of the metal oxide fluoride and the catalyst, respectively, is preferably any divalent or trivalent metal and transition metal, respectively. Preferably, the metal component is selected from the group comprising Zn, Sn, Cu, Fe, Cr, V, Mg, and Al, whereby any of said metals may either alone or in combination be used as the independent fluoride compound, as guest component or as host component and respective compound. In a further preferred embodiment, the metal component may be Fe, Cr, V, Mg or Al, whereby any of said metals may either alone or in combination be used as the independent metal fluoride, as the guest compound or the host compound. In any of these embodiments, Mg is a preferred host compound in case of doped catalysts. In a further preferred embodiment the metal component is Mg, either as independent metal fluoride or preferably as a host component for other metal fluorides, preferably those mentioned herein. In a further embodiment Al is used as an independent metal fluoride or as host component or as guest component. Most preferably the metal component is Al, either as an independent fluoride or as host component or as guest component as used in connection with the catalyst according to the present invention. As used herein the term independent metal oxide fluoride is meant to be the catalytically active metal fluoride, the guest compound or guest component is meant to be the doped component or compound of a doped catalyst and the host compound or host component is meant to be the matrix for the guest compound or guest component in case of doped catalysts, whereby the host compound or host component can be either an inert or a catalytically active matrix.
The catalytically active metal oxide fluorides according to the present invention are applicable in any reaction where the metal fluorides of the state of the art may be used. Such reactions comprise, however are not limited to halogen exchange reactions, dismutations and isomerisations of CFCs/HCFCs as well as Friedel-Crafts alkylations acylations, and oxidations respectively. Also, the catalytically active metal fluorides may be used in any catalysis where a Lewis acid or a Lewis base catalyst is used.
Further, the metal oxide fluorides of the present invention can be used for glass coatings and for manufacture of ceramics and optical devices.
The invention is now further illustrated by the examples from which further features, embodiments and advantages may be taken.
24.3 g (1 mol) magnesium chips are reacted in 500 ml dry methanol to magnesium methylate. 240 ml of 5 M solution of hydrogen fluoride in ether (1.2 mol) are added thereto under steering and cooling. Subsequently 28.8 ml (1.6 mol) water are added. All volatile components are removed under vacuo after 2 hours, whereby a white powder is obtained.
The powder is calcinated under an argon atmosphere at 350° C. for 3 hours. The thus obtained MgO0.4F1.2 has a specific surface of 363 m2/g and a fluoro content of 28.1% corresponding to MgO0.64F0.72 as well as a carbon content of 2.86% and H 1.57%.
1.6 g (22.5 mmol) methylvinyl ketone, 1.9 g (15 mmol) 2-methyl cyclohexane-1,3-dione, 0.7 g dimethylphthalate (internal standard) and 10 ml methanol are steered in a 50 ml flask at room temperature, whereupon 0.225 g of the catalyst as manufactured in example 1 are added. After 2 hours the reaction is terminated, the catalyst removed by centrifugation and methanol as well as remaining methylvinylketon removed by distillation. 1H-NMR analysis based on the integrates of the methyl group of dimethylphthalate and of 2-(γ-oxobutyl)-2-methyl cyclohexane-1,3-dione of the product mixture dissolved in DMSO-d6 result in a yield of 1.62 g (55%) of 2-(γ-oxobutyl)-2-methylcyclohexane-1,3-dione.
Aluminium isopropylate is dissolved in excessive isopropanol under gentle warming and stirring. The solution is cooled to about 0° C. in an ice bath, than hydrofluoric acid dissolved in diethyl ether is added under stirring in an amount that the molar ratio of Al:F is 1:2. The mixture is stirred further for about 20 min, followed by addition of 10 mol % with respect to Al of VO(OiPr)3 and such an amount of water that the molar ratio is as follows:
n(Al(OiPr)3):n(HF):n(H2O)=1:2:1
This mixture is stirred another 2 hrs and then kept over night to allow aging. Next day the isopropanol is removed under vacuum at about 70° C. and the resulting solid is calcined in a flow system under air (20 ml/min) as follows:
Heating rate 5° C./min; 1 hr at 150° C., 1 h at 200° C., 1 h at 250° C., 1 h at 300° C. and 5 h at 350° C.
The catalyst as prepared in example 3 was used for oxidative dehydrogenation of propane to propene. In a tube-type reactor 100 mg catalyst was heated for 1 h at 500° C. under nitrogen followed by by a mixture of 20 vol % N2, 50 vol % O2 and 30 vol % propane (35.5 ml/min).
Under these conditions, 35.6% of the propane was converted yielding 12.5% propene corresponding to a selectivity for propene of 35.1%.
Similar to example 1, 24.3 g (1 mol) magnesium chips are reacted in 1000 ml dry methanol to magnesium methylate. 240 ml of 5 M solution of hydrogen fluoride in dry methanol (1.2 mol) are added thereto under stirring and cooling. Subsequently, 28.8 ml (1.2 mol) water is added. The obtained clear, somewhat viscous liquid is suitable to prepare coatings on different supports. Thus, it is pressed through the thoroughly dried channels of a micro-reactor made of stainless steel leaving a thin film of magnesium hydroxide/oxide fluoride on the inner surface of the micro-reactor. The reactor is then heated under argon passing through (about 2 ml/min) up to 350° C. for 3 hours whereby a magnesium oxide fluoride layer is formed on the inner wall of the micro-reactor.
The features of the present invention disclosed in the specification, the claims and/or the drawings may both separately and in any combination thereof be material for realizing the invention in various forms thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 04028672.6 | Dec 2004 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP05/13026 | 12/5/2005 | WO | 00 | 7/12/2007 |
