FR3038893A1 - AMORPHOUS AMORPHOUS ACIDIC AND / OR BASIC MIXED OXIDE COMPRISING SILICON - Google Patents

Abstract

An amorphous mesoporous acidic and / or basic mixed oxide comprising silicon and at least one metal M selected from the group consisting of niobium, tantalum, magnesium, tin and mixtures thereof. Said metal represents at most 20% of the weight of the mixed oxide according to the invention. Said mixed oxide is highly mesoporous, that is to say it is characterized by a specific surface area of at least 400 m 2 / g and a pore volume of at least 0.45 ml / g. Said mixed oxide is also homogeneous at least on the micron scale and contains M-O-Si bonds, which gives it specific acidic and / or basic properties. This mixed oxide is obtained by a particular preparation process.

Description

The present invention relates to the field of acidic and / or basic amorphous mesoporous materials of mixed oxide type based on silicon and at least one metal. It also relates to the preparation of these materials which are obtained according to the "non-hydrolytic sol-gel" methodology. The textural and acid-base properties make them particularly suitable for applications allowing the specific transformation of oxygenated compounds such as biomass and / or its transformation products. State of the art

The energy and environmental challenges of the 21st century involve finding alternatives to fossil fuels. In the specific areas of refining and petrochemicals, the success of this energy transition requires the development of new processes using renewable resources. To achieve this objective, one of the possible lines of research focuses on improving or developing heterogeneous catalysts. This aspect is particularly critical when using biomass-type renewable resources, the difference in composition of the latter compared to fossil resources requiring a considerable adaptation of the properties of the usual heterogeneous catalysts, particularly in terms of the acid-base properties of biomass. area. Indeed, the biomass, as well as the products of lower molecular weight obtained after a first transformation of the latter, are characterized by the presence of oxygen functions in a significant amount. The elimination of this excess of oxygen, necessary to obtain products used as fuel bases or as monomeric reagents for petrochemical applications, requires catalysts having a specific reactivity allowing the occurrence of the following chemical reactions: dehydrogenation, dehydration, aldolisation, condensation, etherification, esterification, etc. In addition, the presence of water as a solvent and / or produced chemical reactions involved requires the use of heterogeneous catalysts hydrothermally stable under the conditions of the processes considered. This last point makes the use of heterogeneous catalysts based on delicate alumina and excludes in fact a large number of usual catalysts associated with the transformations of fossil resources.

In this context, the development of mesoporous mixed oxides based on transition metals and silicon ("M-Si") is particularly interesting because of the multiple acid-base properties and hydrothermal resistance they present (K. Tanabe , T. Sumiyoshi, K. Shibata, T. Kiyoura, J. Kitagawa, Bulletin of the Chemical Society of Japan, 1974, 47, 1064, M. Ziolek, Catalysis Today, 2003, 78, 2003, p47). In order to maximize the catalytic performance of these oxides, it is recommended to best control the textural properties of the catalyst, so as to ensure a good diffusion of the reagents and products of the reaction, as well as the surface reactivity (nature, force and many of the active sites) simultaneously playing on the chemical composition and the degree of homogeneity of the material (preferred formation of MO-Si bonds, with M = metal, 0 = oxygen and Si = silicon). Consequently, the preferred synthetic routes for obtaining these solids generally use "sol-gel" chemistry, based on chemical reactions of hydrolysis and condensation of molecular precursors (often alkoxides), most often carried out at atmospheric pressure. and ambient temperature in an aqueous or aquo-organic medium. Indeed, this methodology of synthesis, compared to other conventional ways, allows to better control the purity, the chemical composition, the homogeneity and the texture of mesoporous oxides. However, and despite these numerous advantages, obtaining mixed oxides as desired is not trivial, especially in terms of homogeneity of the solid obtained and therefore indirectly of surface reactivity. Different kinetics associated with the hydrolysis and condensation reactions of the various precursors are, among other things, at the origin of these difficulties (in particular between transition metal precursors and silicic precursors). Several synthetic methodologies have been proposed to overcome these problems but are often complex, costly and time consuming (B, Yoldas E., Mater J. Sci, 1986, 21, 1086, C. Sanchez J. Livage, M. Henry, F. Babonneau, J. Non-Cryst Solids, 1988, 100, 65). An elegant alternative is to use so-called "non-hydrolytic" so-called "sol-gel" synthesis methodologies (SGNH) where the constituent oxygen donor of the solid network is not water but an organic molecule (alkoxide, ether , alcohol, etc.) carried out in an anhydrous organic medium. The specific condensation reactions inherent in this "waterless" chemistry have an impact on the intrinsic properties of texture, homogeneity and surface reactivity of the mixed oxides thus obtained. In particular, a lesser variation in the kinetics of reactions associated with the molecular precursors involved is usually observed, which leads to mixed oxides which are often more homogeneous than their homologues obtained according to standard sol-gel methods. In the particular case of mixed oxides based on silicon, it also proves possible to catalyze the condensation reactions of silicic precursors (and thus increase their kinetics) by the very presence of the precursors of the metals. Some homogeneous Μ-Si oxides at least on the micron scale have thus been obtained. In addition, these non-hydrolytic methodologies can make it possible to avoid the loss of well-known porosity related to a collapse of the porous network during the steps of drying gels under conventional conditions. The SGNH is therefore a method of choice for generating various mixed oxides (Ti-Si, Zr-Si, W-Si, Al-Si, etc.), highly porous and homogeneous, as evidenced by the recently available journals in the Literature (DP Debecker, PH Mutin, Chem Soc Rev., 2012, 41, 3624, PH Mutin, A. Vioux, J. Mater Chem A, 2013, 1, 11504 DP Debecker, V. Hulea, PH Mutin, Applied Catalysis A. General, 2013, 451, 192). On the other hand, the method must be adjusted each time that the metal M of the mixed oxide is changed, leading to finding for each precursor the good operating conditions, the good solvents, the good proportions, making the generalization of the method possible. a metal M any non trivial. The targeted catalytic reactions are numerous such as epoxidation, photocatalysis, metathesis, selective oxidation, selective reduction of nitrogen oxides, etc.

Mixed oxides "M-Si" with M = Nb, Ta, Mg, Sn and their mixtures are particularly interesting candidates for catalyzing part of the chemical reactions involved in the transformation of biomass or its transformation products (oxygenated molecules such as alcohols, etc.). Indeed, their potential acidity and / or basicity properties make it possible to envisage dehydration, dehydrogenation, aldolisation, condensation, etc. reactions, or to modulate the importance of one of these chemical reactions with respect to another . Few, or no,) studies concern obtaining these families of mixed oxides by SGNH, reflecting the difficulty of synthesizing mixed oxides with a final solid developing an interesting porosity. A single publication mentions the synthesis of a Ta-Si oxide by autogenous pressure thermal decomposition in an anhydrous organic medium of a specific non-commercial reagent (1PrO) 2Ta [OSi (OtBu) 3] 3. The resulting mixed oxides are rich in tantalum element with at least 23% weight of metal relative to the final solid and are not very mesoporous (R, L, Bratchey, CG Lugmair, L. O, Schebaum, T, D. Tilley, J. Catal., 2005, 229, 72). No Nb-Si mixed oxide has been identified in the literature, although a Nb-V-Si ternary system has been obtained by reacting precursor chlorides and / or alkoxides of the various elements (so-called "alkoxides"). The mixed oxide thus obtained is nevertheless very slightly porous (SB and not exceeding 150 m 2 / g) (Moggi P., Devillers M., Ruiz P., Predieri G., Cauzzi D., Morselli S., O. Ligabue, Catalysis Today, 2003, 81, 77, F. Barbieri, D. Cauzzi, F. De Smet, M. Devillers, P. Moggi, Predieri G., P. Ruiz, Catalysis Today, 2000, 61, 353). Similarly, a publication indirectly deals with a mixed Mg-Si oxide, the latter being obtained according to the SGNH "alkoxides" and also developing little porosity (from 2 to 254 m2 / g) ((JR Caresani, RM Lattuada , C. Radtke, IHZ dos Santos, Powder Technology, 2014, 252, 56) Finally, few studies concern the production of mixed Sn-Si oxides, the latter being again little porous and developed only via a single channel. The invention relates to an amorphous acidic and / or basic mixed oxide comprising amorphous acid and / or basic mixed oxide, comprising: silicon and at least one metal M selected from the group consisting of the elements niobium, tantalum, magnesium, tin and mixtures thereof, the mass of said metal M being between 0.1 and 20% of the weight of the mixed oxide, said mixed oxide having a surface area of at least 400 m2 / g and a pore volume of at least 0.45 ml / g, said mixed oxide being homogeneous at least on the micron scale and containing MO-Si bonds, said mixed oxide being prepared according to at least the steps of: a) mixing in organic solution of at least one halide precursor of the element Si of formula SiX4, with X = Cl, Br, I and F, of at least one halide precursor of the metal M of formula MXn, with X = Cl, Br, I and F and n = 2 for M = Mg and Sn, n = 4 for M = Sn and n = 5 for M = Nb and Ta, of at least one dialkyl ether oxygen donor ROR, R being a linear or branched alkyl and optionally of at least one surfactant, the mixture in solution of the various precursors and the oxygen donor being produced under an inert atmosphere; b) heating said solution obtained in step a); c) optional washing of the precursor gel of the mixed oxide according to the invention obtained during step b) of the preparation process according to the invention and d) heat treatment of the gel obtained in step b) or gel washed from step c) optional so as to obtain said mixed oxide. The invention relates to an amorphous acidic and / or basic mixed oxide comprising silicon and at least one metal M selected from the group consisting of niobium, tantalum, magnesium, tin and their mixtures, prepared by a synthesis method "sol non-hydrolytic gel "involving halogenated metal and silicic precursors and an ether-type oxygen donor. Said metal represents at most 20% of the weight of the mixed oxide according to the invention. Said mixed oxide is highly mesoporous, that is to say it is characterized by a specific surface area of at least 400 m 2 / g and a pore volume of at least 0.45 ml / g. Said mixed oxide is also homogeneous at least on the micron scale and contains M-O-Si bonds, which gives it specific acidic and / or basic properties. This homogeneity and these specific acidic and / or basic properties are the product of the specific preparation process of the mixed oxide according to the invention.

Interest of the invention

The present invention proposes for the first time the production of mesoporous mixed oxides, homogeneous (presence of numerous MO-Si bonds), with specific acidic and / or basic properties, comprising silicon and at least one metal M chosen from the group. constituted by the elements niobium, tantalum, magnesium, tin and their mixtures, these properties being due to the composition of said mixed oxide and to its preparation process.

SUMMARY OF THE INVENTION The invention relates to an amorphous acidic and / or basic mixed oxide comprising silicon. By mixed oxides are meant solids resulting from the combination of oxygen atoms with at least two other different elements of the latter. The mixed oxides considered according to the invention comprise at least the silicon element as the first additional element to oxygen. The second additional element considered is a metal M selected from the group consisting of niobium, tantalum, magnesium and tin elements and mixtures thereof. The presence of silicon and a metal selected from the above list define so-called "binary" mixed oxides called Ta-Si, Nb-Si, Mg-Si and Sn-Si in the rest of the text of the present invention. It is also possible to combine at least two metals M as defined above so as to obtain mixed oxides with three elements (ternary), four elements, etc. Preferably, the metal M is selected from the group consisting of tantalum and niobium and mixtures thereof.

Advantageously, the mixed oxide according to the invention comprising the silicon element and at least the metal M as described above may also comprise a metal M ', different from M, chosen from the group consisting of Ni, Co , Cu, Zn, Zr, Ti, Mo and W and mixtures thereof. Preferably, the metal M 'is selected from the group consisting of Ni, Zr and W and mixtures thereof.

Even more preferably, the ternary mixed oxides envisaged are Ta-Nb-Si, Ni-Mg-Si, Zn-Ta-Si, Zr-Ta-Si and Zr-Mg-Si systems. That is to say, advantageously, the following metals are associated: M = Ta and Nb; M = Mg and M '= Ni; M = Ta and M '= Zn; M = Ta and M '= Zr; M = Mg and M '= Zr. The mixed oxide prepared according to the invention comprises a mass of metal M between 0.1 and 20% of the mass of the mixed oxide prepared according to the invention, preferably between 0.3 and 10% of the mass, preferably between 0.5 and 5% of the mass. The mixed oxide according to the invention advantageously comprises a mass of metal M 'of between 0.1 and 20%, of the mass of the mixed oxide prepared according to the invention, preferably between 0.3 and 10% of the mass, preferably between 0.5 and 5% of the mass. The mixed oxide is mesoporous, that is to say that it is characterized by the presence of pores whose size varies between 2 and 50 nm according to the classification of Γ IUP AC (KSW Sing, Everett DH, RA Haul, L. Moscow, J. Pierotti, J. Rouquerol, T. Siemieniewska, Pure Appl. Chem., 1985, 57, 603). In addition to being mesoporous, said material may be mesostructured (that is to say have mesopores of uniform size and periodically distributed in said matrix) or hierarchically porous (presence of micropores and / or macropores additional to mesopores). In a preferred manner, the mixed oxide according to the invention is mesoporous with unorganized porosity without micropores. The mixed oxide can be considered highly mesoporous, i.e. it is characterized by a surface area of at least 400 m 2 / g and a pore volume of at least 0.45 ml / g.

The aforementioned textural parameters are determined by the so-called "nitrogen volumetric" analysis technique which corresponds to the physical adsorption of nitrogen molecules in the porosity of the material via a progressive increase in pressure at a constant temperature. By specific surface is meant the specific surface B.E.T. (SBet in m2 / g) determined by nitrogen adsorption according to ASTM D 3663-78 established from the method BRUNAUER-EMMETT-TELLER described in the journal "The Journal of American Society", 1938, 60, 309 The representative porous distribution of a mesopore population is determined by the Barrett-Joyner-Halenda model (BJH). The nitrogen adsorption-desorption isotherm according to the model B JH thus obtained is described in the periodical "The Journal of the American Society", 1951, 73, 373, written by E. P. Barrett, L. G. Joyner and P. P. Halenda. The pore volume V is defined as the value corresponding to the volume observed for the partial pressure P / P ° max of the nitrogen adsorption-desorption isotherm. In the following description, the diameter of the mesospores φ of the mixed oxide according to the invention is determined by the formula 4000.V / SBet-

Said mixed oxide is also homogeneous at least on the micron scale and contains M-O-Si bonds, which gives it specific acidic and / or basic properties. The homogeneity at the micron scale means that the mixed oxide according to the invention does not comprise micron-sized domains which are very rich in M metal and poor in Si element, the others very rich in Si element. and poor in M elements (which would translate a phase separation). This characteristic is determined by microprobe analysis (EDX = Energy Dispersive X-ray spectrometry) or by comparison of the values of the molar ratio Μ / Si determined by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy, overall chemical composition) and XPS (X -ray Photoelectron Spectrometry, surface chemical composition). The qualitative proof of the existence of Si-OM bonds can also be provided for example by the presence of vibration bands on the corresponding infrared or Raman spectra, by the detection of mixed species of MxSiyOz type (cationic or anionic) in ToF. -SIMS (Time-of-Flight Secondary Ion Mass Spectroscopy), by displacements of binding energies in XPS, or by Nuclear Magnetic Resonance,

The acidic and / or basic properties of the mixed oxide according to the invention are evaluated via the catalytic model reaction of hydrogen transfer between cyclopentanol and cyclohexanone to yield cyclopentanone and cyclohexanol (chemical reaction known as name Meerwein-Pondorff-Verley or Oppenauer). This chemical reaction is particularly suitable for evaluating the presence of basic sites or acid-base pairs. In parallel, the possible reaction of dehydration of cyclopentanol with cyclopentene informs about the presence of acidic sites. The comparison of the catalytic results obtained for the mixed oxides according to the invention with their homologues obtained according to conventional "sol-gel" methodologies confirms a specific reactivity for the mixed oxides according to the invention, reactivity directly related to the textural and homogeneity properties. claimed.

The present invention also relates to the process for preparing the mixed oxide according to the invention. Said method comprises: a) mixing in organic solution at least one precursor of the element Si, at least one precursor of the metal M, at least one organic oxygen donor and optionally at least one surfactant, b) the heating (for example in autoclave under autogenous pressure) of said solution obtained in step a), c) the optional washing of the precursor gel of the mixed oxide according to the invention obtained in step b ) of the preparation process according to the invention and d) the heat treatment of the gel obtained in step b) or the washed gel resulting from the optional step c) so as to obtain the mixed oxide according to the invention.

According to step a) of the preparation process according to the invention, the precursor of the silicon element is a halide of formula SiX 4, with X = Cl, Br, I and F. Preferably, X is chosen from chlorine. and bromine. The precursor of the metal M is a halide of formula MX ", with X chosen from the group consisting of Cl, Br, I and F and n = 2 for M = Mg and Sn, n = 4 for M = Sn and n = 5 for M = Nb and Ta. Preferably, X is CL. The oxygen donor is a dialkyl ether R-O-R, where R is a linear or branched alkyl with preferably 1 to 6 carbon atoms, preferably 2 to 4 carbon atoms. The R groups of the dialkyl ether may be the same or different. The solution mixture of the various precursors and the oxygen donor according to step a) of the preparation process according to the invention is carried out under an inert atmosphere. The solvent (s) used is (are) dried (s) at reflux and distilled (s) before use. This (s) last (s) is (are) any solvent in which the precursors, oxygen donors and the possible surfactants are soluble, for example dichloromethane. When certain precursors used are liquid, they can serve as solvent, possibly hot, for the other precursors and for the intermediate products obtained. Likewise, the ethers which can be used as oxygen donor agents are liquids and can be used as solvents. In addition, some of the chlorides used in the preparation process of the invention are liquids in which the other reagents can be soluble, possibly hot. Step b) of heating the solution obtained in step a) of the preparation process according to the invention may be autoclaving. The autoclaving process, well known to those skilled in the art, consists of treating said solution resulting from step a) via a controlled temperature and autogenous pressure confinement. The autoclaving temperature is between 50 and 300 ° C, preferably between 100 and 250 ° C and even more preferably between 100 and 200 ° C. The duration of this step is from a few hours to a few days, depending on the conditions of implementation. A duration of 1 to 6 days is generally adequate. It is also possible to achieve such a temperature heating at atmospheric pressure via the introduction of a reflux. Any other experimental device allowing said heating of the solution obtained in step a) of the preparation process according to the invention is also conceivable.

Steps a) and b) of the preparation process according to the invention are critical for obtaining a mixed oxide according to the invention. Indeed, during step a), it is necessary to solubilize as much as possible the precursors of the silicon element and the metal M, an essential condition for controlling the chemical composition and the homogeneity of the mixed oxide according to the invention. invention. Similarly, step b) must lead to the formation of a homogeneous gel attesting to the homogeneity of the oxide network formed. These two points need to pay particular attention to the order of addition and purity of the various reagents used to constitute the solution and then the gel in accordance with steps a) and b) of the preparation process according to the invention. The proportion of the various reagents and the optimization of the solvent (s) for each system studied are also critical parameters.

According to the optional step c) of the preparation process according to the invention, the washing of the gel is carried out according to the conventional methods and known to those skilled in the art. This step can be carried out under air or under an inert atmosphere. An inert atmosphere is preferred.

According to step d) of the process for preparing the material according to the invention, the heat treatment applied may be chosen from the following treatments: drying, calcination (under air or inert atmosphere), steaming (calcination in the presence of water ) or a combination of said treatments mentioned. Preferably, the treatment of the washed gel resulting from stage c) of the preparation process according to the invention consists of drying followed by calcination. Preferably, the drying is carried out under inert or under vacuum at a temperature between 15 ° C and 200 ° C, preferably from T = 50 ° C to T = 150 ° C and even more preferably at room temperature and at 120 ° C (from T = 100 ° C to T = 130 ° C) for a period of less than 72 hours, preferably less than 24 hours and even more preferably for 1 hour and 4 hours, respectively. Preferably, the calcination is carried out under air at a temperature of between 200 ° C. and 1000 ° C., preferably from T = 300 ° C. to T = 700 ° C. and even more preferably from T = 400 ° C. to T = 600 ° C for a period of less than 12 hours and preferably less than 6 hours. The mixed oxide according to the invention may be used in powder form or advantageously shaped in a step e), in the form of pelletized and crushed powder, beads, pellets, granules, monoliths or extrudates ( hollow cylinders or not, multilobed cylinders with 2, 3, 4 or 5 lobes for example, twisted cylinders), or rings, other shaping known to those skilled in the art that can be performed, these operations of implementation form being made by conventional techniques known to those skilled in the art. Advantageously, said mixed oxide prepared according to the invention is shaped in the form of beads, pellets, granules, monoliths or extrudates.

During the possible shaping step e), the mixed oxide according to the invention may optionally be mixed with at least one porous oxide material having the role of binder so as to generate physical properties of the final material compatible with its use as a potential catalyst in various processes (mechanical strength, attrition resistance, etc.).

Said binder is preferably a porous oxide material selected from the group consisting of silica, magnesia, clays, titanium oxide, lanthanum oxide, cerium oxide, boron phosphates and a mixture of at least two of the oxides mentioned above. It is also possible to use titanates, for example titanates of zinc, nickel or cobalt. It is still possible to use simple, synthetic or natural clays of 2: 1 dioctahedral phyllosilicate or 3: 1 trioctahedral phyllosilicate such as kaolinite, antigorite, chrysotile, montmorillonite, beidellite, vermiculite, talc. , hectorite, saponite, laponite. These clays can be optionally delaminated. The various mixtures using at least two of the compounds mentioned above are also suitable for acting as binder.

When using a binder, the latter is, preferably, of silicic nature. For example and non-exhaustively, said silicic binder may be in the form of powders or colloidal solutions.

When using a binder, the latter preferably represents from 2 to 60% by weight of the final material and preferably from 2 to 20% and even more preferably from 2 to 10% by weight.

Very preferably, step e) of shaping the mixed oxide according to the invention is carried out without the addition of binder. Optionally, at least one organic adjuvant is also mixed during said forming step e). The presence of said organic adjuvant facilitates extrusion shaping. Said organic adjuvant may advantageously be chosen from methylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, carboxymethylcellulose and polyvinyl alcohol. The proportion of said organic adjuvant is advantageously between 0 and 20% by weight, preferably between 0 and 10% by weight and preferably between 0 and 7% by weight, relative to the total weight of said shaped material.

In the case where the mixed oxide according to the invention comprises, in addition to the elements Si and M, at least one metal M 'as defined above, the latter may be introduced in the form of a precursor (s) molecular (s) at all stages of synthesis of the mixed oxide according to the invention. Thus, the latter may be introduced in the form of halogenated precursor during step a) of the process for preparing the mixed oxide according to the invention provided that said precursor solubilizes and does not affect the obtaining of a homogeneous gel following step b) of the preparation process according to the invention. The deposition of at least one molecular precursor of the metal M 'on the surface of the mixed oxide obtained after synthesis, or even after the step e) of shaping, is also possible via the use of well-known synthetic methods. those skilled in the art such as dry impregnation, excess impregnation, CVD (Chemical Vapor Deposition), CLD (Chemical Liquid Deposition), deposition-precipitation (DP), etc. Advantageously, said metal M 'is introduced after synthesis of said mixed oxide, preferably after shaping, by a method selected from the group consisting of dry impregnation, excess impregnation, CVD (chemical vapor deposition, or Chemical Vapor Deposition according to English terminology), CLD (Chemical Liquid Deposition, or Chemical Liquid Deposition), deposition-precipitation (DP). Finally, the metal M 'can also be introduced directly during the shaping steps. The invention is illustrated by means of the following examples.

Examples

Example 1. Nb-Si mixed oxdef comprising 4.7%. enBO_ids.de metalNo ...... comreceptor to lamas ^ JoMeJeJ.iMyde mixture obtained by SGNH according to I.procedure of .preparation confome..toJlinÿ £ niion ·

Under an inert atmosphere and at ambient temperature, a mass of 0.25 g of NbCl5 is solubilized in 6.5 ml of SiCl4, 23.3 ml of dichloromethane and 17.1 ml of diisopropyl ether. The mixture is at 110 ° C. for 4 days under autogenous pressure conditions. The gel obtained is dried under vacuum at ambient temperature for 1 h and at 120 ° C. for 4 h. The powder obtained is calcined at 500 ° C. for 5 h under a stream of dry air. The mixed oxide obtained is characterized by the following textural data: SBet = 813 m 2 / g, Vp = 0.61 ml / g, and φ = 3.0 nm.

EXAMPLE 2 Nb-Si mixed oxide comprising 7.0% by weight of Nb metal with respect to the mass of entrained silica obtained by SGNH according to the preparation method according to the invention.

Under an inert atmosphere and at room temperature, a mass of 0.72 g of NbCl5 is solubilized in 6.5 ml of SiCl4, 23.3 ml of dichloromethane and 17.1 ml of diisopropyl ether. The mixture is maintained at 110 ° C. for 4 days under autogenous pressure conditions. The gel obtained is dried under vacuum at ambient temperature for 1 h and at 120 ° C. for 4 h. The powder obtained is calcined at 500 ° C. for 5 hours under a stream of dry air. The mixed oxide obtained is characterized by the following textural data: SBet = 791 m 2 / g, Vp = 0.73 ml / g, and φ = 3.7 nm.

EXAMPLE 3 Mixed Ta-Si oxvde comprising 8.2% by weight of Ta metal by mixed recovery obtained by SGNH according to the preparation method according to the invention.

Under an inert atmosphere and at room temperature, a mass of 0.57 g of TaCfi is solubilized in 6.0 ml of SiClt, 23.3 ml of dichloromethane and 15.3 ml of diisopropyl ether. The mixture is maintained at 110 ° C. for 4 days under autogenous pressure conditions. The gel obtained is dried under vacuum at ambient temperature for 1 h and at 120 ° C. for 4 h. The powder obtained is calcined at 500 ° C. for 5 h under static air. The mixed oxide obtained is characterized by the following textural data: SBet = 556 m2: g, Vp = 1.83 ml / g, and φ = 13 nm.

EXAMPLE 4 Mixed Oxygen Mg-Si Comprising 6% by Weight of Metal ..... Mg Bar Compared to the ...... Weight of Mixed Oxide Obtained by SGNH According to preparation process according to the invention.

Under an inert atmosphere and at room temperature, a mass of 0.83 g of MgCl 2 synthesized in situ is solubilized in 6.0 ml of SiCl 4, 23.3 ml of dichloromethane and 16.0 ml of diisopropyl ether. The mixture is maintained at 110 ° C. for 4 days under autogenous pressure conditions. The gel obtained is dried under vacuum at ambient temperature for 1 h and at 120 ° C. for 4 h. The powder obtained is calcined at 500 ° C. for 5 h under static air. The mixed oxide obtained is characterized by the following textural data: SBet = 506 m 2 / g, Vp = 0.82 ml / g, and φ = 6 nm.

EXAMPLE 5 Sn-Si mixed oxvde comprising 9.5% by weight of Sn metal relative to the total weight of the mixed oxide obtained by SGNH according to the preparation method according to the invention.

Under an inert atmosphere and at room temperature, a mass of 0.21 g of SnCl 4 is solubilized in 1.7 ml of SiCl 4 and 4.5 ml of diisopropyl ether. The mixture is maintained at 110 ° C. for 4 days under autogenous pressure conditions. The gel obtained is dried under vacuum at ambient temperature for 1 h and at 120 ° C. for 4 h. The powder obtained is calcined at 500 ° C. for 5 h under static air. The mixed oxide obtained is characterized by the following textural data: SBet = 606 m 2 / g, Vp = 1.1 ml / g, and φ = 7.2 nm.

Example 6 Nb-Si mixed oxvde comprising 4.7% by weight of metal Nb relative to the mass of the oxide. mixed mixture obtained by conventional sol-gel not in accordance with the invention of the invention of ......... rartisiejj

Kvisle. A. Aguero, R. P. A. Sneeden. Applied Catalvsis. 1988, 43, 117. To a solution containing 55 ml of tetraethylorthosilicate (TEOS, Si (OCH2CH3) 4) and 150 ml of ethanol are added 12.5 ml of a solution of nitric acid at 68% (volumetric) to ambient temperature. The whole is left stirring for 30 min. 2.67 g of niobium ethoxide (Nb (OCH2CH3) 5) are then added to the taste to taste in conditions inert to the previous mixture. 50 ml of a solution of ammonia at 14% (volume) are then added. The system becomes cloudy and a gel is formed. 19 ml of ethanol are then added to allow additional stirring for 3 hours. The final gel is filtered, washed with ethanol and then dried at 100 ° C. for 24 hours. The Nb-SiO 2 powder obtained is then calcined under air at 550 ° C. for 4 hours. The mixed oxide obtained is characterized by the following textural data: SBet = 579 m 2 / g, Vp = 0.92 ml / g, and φ = 6.4 nm.

Example 7: Ta-Si mixed oxvde comprising 8.9% by weight Tajar metal relative to the total ..... of mixed oxide obtained by conventional sol-gel not according to the invention on the basis of ...... .du ....... erotoçole of ..... FartjdeJI · ..... Kvisle ^ .A,

Aeuero. R. P. Sneeden. Applied Catalvsis. To a solution containing 55 ml of tetraethylorthosilicate (TEOS, Si (OCH2CH3) 4) and 150 ml of ethanol are added 12.5 ml of a solution of 68% nitric acid (volume). ) at room temperature. The whole is left stirring for 30 min. 3.71 g of tantalum ethoxide (Ta (OCH 2 CH 3) 5) are then added to the taste to taste in conditions inert to the previous mixture. 50 ml of a solution of ammonia at 14% (volume) are then added. The system becomes cloudy and a gel is formed. 19 ml of ethanol are then added to allow additional stirring for 3 hours. The final gel is filtered, washed with ethanol and then dried at 100 ° C. for 24 hours. The Ta-Si powder obtained is then calcined in air at 550 ° C. for 4 hours. The mixed oxide obtained is characterized by the following textural data: SBet = 720 m2 / g, Vp = 1.06 ml / g and φ = 5.9 nm.

EXAMPLE 8 Comparison of the Molar Percentages of M with respect to Si Nominelle et Emerimgnatine Gqres .. By ICP-AES for Examples 1.2 and 6

Table 1: Comparison of Nominal and Experimental Nb Levels

The samples obtained via the SGNH method have overall Nb contents very close to the nominal content, respectively 0.85 and 0.28% difference for Examples 1 and 2. The sample obtained via SGH comprises 42.74% difference between its nominal and global Nb percentage. The SGNH synthesis method therefore makes it possible, for the grades studied, to have better control of the composition.

EXAMPLE 9 Comparison of the Acidic and the Hydrogen Properties and the Model of the Transfer of Hydrogen Between Cytopentanol and Cydohexapoxide

Figure 1 represents the overall scheme of the cyclopentanol / cyclohexanone mixture transformation (S. Carre, N.S. Gnep, R. Revel, P.Magnoux, Applied Catalysis A: General, 2008, 348, 71).

This catalytic probe test allows us to detect acidic properties responsible for the dehydration (DES) of alcohols and the basic properties responsible for hydrogen transfer (TH) reactions between an alcohol and a ketone. In addition, it allows to probe catalytic materials in real conditions, which allows to evaluate their stability, or to observe their tendency to deactivation.

Table 2: Catalytic activity of Nb-Si mixed oxides (200 ° C, contact time of 0.005 h)

Two samples with overall levels measured by similar ICP-AES are compared; Example 2 and Example 6 having respectively 4.84 and 4.57 at% Nb (Table 1). Both solids have acidic and basic properties (Table 2). Example 2 obtained by SGNH has a higher yield for dehydration than Example 6 obtained by SGH after 3, 15 and 100 minutes of reaction. The mixed oxide obtained by SGNH is more acidic than that obtained by SGNH. The basic properties of the two solids are similar, in addition, the yields of dehydration and hydrogen transfer vary less over time for Example 2. The mixed oxide obtained by SGNH is therefore more stable under the conditions of the test. catalytic than that obtained by SGH.

Claims (10)

1. An amorphous acidic and / or basic mixed amorphous oxide comprising silicon and at least one metal M selected from the group consisting of niobium, tantalum, magnesium, tin and their mixtures, the mass of said metal M being between 0.1 and 20% by weight of the mixed oxide, said mixed oxide having a specific surface area of at least 400 m 2 / g and a pore volume of at least 0.45 ml / g, said mixed oxide being homogeneous at least at the micron scale and containing MO-Si bonds, said mixed oxide being prepared according to at least the steps of: a) mixing in organic solution of at least one halide precursor of the Si element of formula SiX4, with X = Cl, Br, I and F, of at least one halide precursor of the metal M of formula MX ", with X = Cl, Br, I and F and n = 2 for M = Mg and Sn, n = 4 for M = Sn and n = 5 for M = Nb and Ta, of at least one dialkyl ether oxygen donor ROR, R being a linear or branched alkyl and optionally at least one surfactant, the mixture in solution of the various precursors and the oxygen donor being produced under an inert atmosphere; b) heating said solution obtained in step a); c) optional washing of the precursor gel of the mixed oxide according to the invention obtained during step b) of the preparation process according to the invention and d) heat treatment of the gel obtained in step b) or gel washed from step c) optional so as to obtain said mixed oxide. 2. The mixed oxide of claim 1 wherein said metal M is selected from the group consisting of tantalum and niobium and mixtures thereof. 3. Mixed oxide according to one of claims 1 or 2 also comprising a metal M ', different from M, selected from the group consisting of Ni, Co, Cu, Zn, Zr, Ti, Mo and W and mixtures thereof, the mass of metal M 'being between 0.1 and 20%, of the mass of the mixed oxide. 4. Mixed oxide according to claim 3 wherein said metal M 'is selected from the group consisting of Ni, Zr and W and mixtures thereof. 5. Mixed oxide according to one of claims 3 to 4 wherein said metal M 'is introduced in the form of halogenated precursor in step a) of the process for preparing the mixed oxide. 6. Mixed oxide according to one of claims 3 to 4 wherein said metal M 'is introduced after synthesis of said mixed oxide, by a method selected from the group consisting of dry impregnation, impregnation in excess, the deposit chemical vapor phase, chemical deposition liquid phase, deposition-precipitation. 7. Mixed oxide according to one of claims 1 to 6 wherein X is Cl. 8. Mixed oxide according to one of claims 1 to 7 wherein said heating step b) is autoclaving in a confined medium at a temperature between 50 and 300 ° C, a duration of between 1 and 6 days and autogenous pressure . 9. Mixed oxide according to one of claims 1 to 8 wherein said step d) heat treatment is drying followed by calcination, said drying being carried out under inert or under vacuum at a temperature between 15 ° C and 200 ° G, for a duration of less than 72 hours, said calcination being carried out under air, at a temperature of between 200 ° C. and 1000 ° C., for a duration of less than 12 hours. 10. Mixed oxide according to one of claims 1 to 9 shaped in the form of beads, pellets, granules, monoliths or extrudates.