WO2025125054A1 - Method for organically preparing a catalyst in the presence of a multifunctional ketone additive - Google Patents

Abstract

The present invention relates to a method for preparing a catalyst, comprising: • a) a step of preparing an acidified organic solution comprising: • a metal precursor of a metal element chosen from the elements of groups 3, 4 and 5 of the periodic table, such as tantalum, and • a multifunctional ketone additive, • the metal precursor and the multifunctional ketone additive being present in the acidified organic solution in amounts such that the additive/metal molar ratio is greater than or equal to 1; • b) a step of depositing the metal precursor on an oxide matrix, by placing the acidified organic solution in contact with the oxide matrix; and then • c) a thermal treatment step. The present invention also relates to the catalyst obtained and to the use thereof for converting a feedstock comprising ethanol into butadiene.

Description

METHOD FOR THE ORGANIC PREPARATION OF A CATALYST IN THE PRESENCE OF A MULTIFUNCTIONALIZED KETONE ADDITIVE

Technical field

The present invention relates to a method for manufacturing a supported metal oxide catalyst of a group 3, 4 and/or 5 element having improved performance. More particularly, the present invention relates to a method for preparing a heterogeneous catalyst comprising at least one metallic element chosen from the elements of groups 3, 4 and 5 of the periodic table, deposited on an oxide matrix by bringing said oxide matrix into contact with an acidified organic solution of at least one precursor of said metallic element, said acidified organic solution also comprising a multifunctionalized ketone additive and advantageously at least one acidifying agent. The present invention also relates to the catalyst obtained by said preparation method and the use of this catalyst for the conversion into butadiene of a feedstock comprising at least ethanol. The present invention also relates to a method for converting into butadiene a feedstock comprising at least ethanol, comprising in particular a step corresponding to the method for preparing a heterogeneous catalyst according to the invention.

Prior art

Supported metal oxides are a class of heterogeneous catalysts that comprise one or more metal oxide species charged and deposited on the surface of a support material, such as silica (SiCh), alumina (AI2O3), titanium (TiCh), zirconia (ZrCh), magnesium oxide (MgO), and mixtures thereof. Examples of commonly used metal oxides include Group 3–10 metal oxides because they are capable of forming numerous catalysts that are used to synthesize a wide variety of chemicals. For example, supported tantalum oxide catalysts have active sites with diverse properties (acid-base and redox) and are therefore capable of catalyzing many chemical reactions relevant to industry, including the production of 1,3-butadiene (which may also be referred to in this description as butadiene) from ethanol, the decomposition of methyl-t-butyl ether into isobutene and methanol, the Beckmann rearrangement, the epoxidation of olefins. They are also useful in photocatalysis or electrocatalysis.

Patent US2421361, for example, describes the use of niobium or tantalum-based catalysts in a process for converting a mixture of ethanol and acetaldehyde into butadiene, the catalysts being prepared in particular by contacting silica with aqueous citric acid solutions comprising a precursor of niobium or tantalum. As with any catalyst composed of a metallic element deposited on a support, a particular dispersion and a specific distribution of the metallic element, for example tantalum, can be sought to characterize the catalyst. The dispersion of the metallic element at the atomic level is known to affect the selectivity and activity of the catalyst, via the modulation of the nature of the active site. Completely independently, the control of the distribution of the metallic element in a support particle is another parameter to explore to manage problems of intra-granular diffusional limitations when these exist. In the absence of intergranular diffusional limitations, it is generally known to use the entire available surface and volume, particularly for catalytic performance considerations.

There is still a need to improve the catalytic performance, for example the selectivity, of a heterogeneous catalyst comprising in particular a metallic element selected from the elements of group 3, 4 and/or 5, and possibly to improve the distribution of the metallic element on the catalytic support.

In the case of the preparation of catalysts comprising the element tantalum, the use of commercial tantalum precursors, soluble in organic medium such as tantalum alcoholates or halides, is widely described, as in application WO2017/009107 or in the 1950 article by Corson (B. B. Corson, at al. Butadiene from Ethyl Alcohol. Catalysis in the One- and Two-Step Processes. Industrial And Engineering Chemistry. 1950, 42 (2), 359-373). However, tantalum alcoholate precursors or halides may have the disadvantage of being extremely sensitive to hydrolysis. The formation of a tantalum hydroxide function results in the formation of tantalum clusters and can therefore lead to a modification or even a limitation of the catalytic performances (cf. Ambreen, S. et al., Characterization and photocatalytic study of tantalum oxide nanoparticles prepared by the hydrolysis of tantalum oxo-ethoxide Ta8(p3-O)2(p-O)8(p-OEt)6(OEt)i4. Beilstein J. Nanotechnol. 2014, 5, 1082-1090).

To limit the hydrolysis phenomenon, it therefore seems necessary to limit the quantity of water present in the support, for example by extensive drying of the support, in particular at temperatures above 100°C, preferably at 150°C for several hours. To further limit the hydrolysis phenomenon of tantalum or niobium precursors (which are group 5 elements), it is possible to modify said precursors by adding additives. The literature is full of various complexing agents with varying success. For example, there are studies on the reaction of group 5 elements, particularly tantalum and niobium, with compounds such as:

- diketones, such as acetylacetone (cf. Kapoor P. N., Mehrotra R.C., Organic Compounds of Niobium and Tantalum. IV. Reactions of niobium and tantalum pentaethoxides with p-diketones. J. Less-Common Metals, 8 (1965) 339-346),

- ketoesters (cf. Mehrotra R.C., Kapoor P.N., Organic Compounds of Tantalum. Reactions of tantalum pentaethoxide with p-ketoesters. J. Less-Common Metals, 7 (1964) 453-457),

- hydroxyesters (see Narula A.K., et al., Some Aliphatic and Aromatic Hydroxy Ester Derivatives of Niobium and Tantalum. Transition Met. Chem. 7 (1982) 325-330),

- glycols (cf. Mehrotra R.C., Kapoor P.N., Organic Compounds of Tantalum. I. Reactions of tantalum pentaethoxide with glycols. J. Less-Common Metals, 10 (1965) 237-245),

- acyl halides (cf. R Mehrotra R.C., Kapoor P.N., Organic Compounds of Niobium. I. Reactions of niobium penta-alkoxides with acyl halides. J. Less-Common Metals, 10 (1966) 348-353).

While these documents detail the reactions and properties of the complexes formed, they do not specify the effect and use of such Ta or Nb complexes in the preparation of heterogeneous catalysts. Application WO2022/165190 describes the use of acetylacetone in the preparation of a tantalum-based catalyst deposited on silica. Patent application CN115364844 describes the preparation of a tantalum- and silica-based catalyst by contacting a silica with a solution comprising a tantalum precursor and anhydrous citric acid in absolute ethanol.

The present invention aims to prepare a heterogeneous catalyst comprising at least one metallic element, in particular chosen from the elements of groups 3, 4 and 5, which exhibits good catalytic performance, or even a gain in performance compared to catalysts of the state of the art, in particular in terms of selectivity and productivity, and in particular during the conversion into butadiene of a feedstock comprising ethanol, and preferably which exhibits a better distribution (or distribution) of the metallic element over the entire support.

Summary of the invention

The present invention thus relates to a method for preparing a catalyst, comprising: a) a step of preparing at least one acidified organic solution comprising: at least one metal precursor of at least one metallic element chosen from the elements of groups 3, 4 and 5 of the periodic table, at least one multifunctionalized ketone additive, said at least one metal precursor and said at least one multifunctionalized ketone additive being present in the acidified organic solution in quantities such that the additive/metal molar ratio between the number of moles of said at least one multifunctionalized ketone additive and the number of moles of the metallic element(s) provided by said at least one metal precursor is greater than or equal to 1; b) a step of depositing said at least one metal precursor on an oxide matrix, by bringing the acidified organic solution prepared in step a) into contact with said oxide matrix, to obtain a solid; c) a step of heat treatment of the solid obtained at the end of step b).

Such a process makes it possible to obtain a catalyst whose catalytic performances, in particular in terms of selectivity and productivity, during the reaction for converting a feedstock comprising ethanol into butadiene, are satisfactory or even improved compared to catalysts of the state of the art, in particular prepared by organic means. The present invention therefore has the advantage of allowing the simple preparation of catalysts with satisfactory or even improved performances, for reasonable production costs. A process according to the present invention can also allow a better distribution of the metallic elements in the particles of the support (i.e. of the oxide matrix), so as to limit the risks of losses of activity of the catalyst due to attrition during its use.

The invention also relates to the catalyst obtained by the preparation process according to the invention, and which comprises at least one metallic element chosen from the group of elements of group 3, group 4 and group 5 of the periodic table, preferably chosen from yttrium, zirconium, hafnium, niobium, tantalum and their mixtures, preferentially from the element tantalum, the element niobium and/or the element zirconium, preferably the element tantalum, and an oxide matrix preferably based on silica.

The present invention also relates to the use of said catalyst for converting a feedstock comprising ethanol into butadiene, at a temperature of between 250 and 450°C, at a pressure of between 0.05 and 2.00 MPa.

Finally, the present invention relates, according to another aspect, to a process for converting a feedstock comprising at least ethanol into butadiene, which comprises:

A) the preparation of a catalyst according to the preparation method according to the invention; B) a step of converting the feedstock comprising ethanol into butadiene, carried out in the presence of the catalyst prepared in step A), at a temperature between 250 and 450°C, at a pressure between 0.05 and 2.00 MPa.

Description of the embodiments

According to the invention, the expressions “between ... and ...” and “between .... and ...” are equivalent and mean that the limit values of the interval are included in the range of values described. If this is not the case and the limit values are not included in the range described, such clarification will be provided by the present description.

In the present description, the different parameter ranges for a given step, such as pressure ranges and temperature ranges, may be used alone or in combination. For example, in the present description, a range of preferred pressure values may be combined with a range of more preferred temperature values.

In the following, particular embodiments of the invention are described. They can be implemented separately or combined with each other, without limitation of combinations when technically feasible.

According to the present invention, the pressures are absolute pressures and are given in absolute MPa (or MPa abs.).

According to the invention, the times and durations are expressed in hours (h), minutes (min) and/or seconds (sec).

In the present description, the term "ambient temperature (Tamb)" corresponds to a temperature typically of 20°C ± 5°C (the acronym "±" meaning "more or less", "20°C ± 5°C" means between 15 and 25°C), and the term "atmospheric pressure" means a pressure of approximately 0.1 MPa, i.e. between 0.05 MPa and 0.15 MPa, preferably between 0.08 MPa and 0.12 MPa, and generally a pressure of 0.101325 MPa.

The terms “upstream” and “downstream” are to be understood in relation to the general flow of the fluid(s) or flow(s) in question in the process.

The present invention relates to a method for preparing a catalyst, called a heterogeneous catalyst, which comprises at least one metallic element chosen from the elements of groups 3, 4 and 5 of the periodic table, preferably from yttrium, zirconium, hafnium, niobium, tantalum, and mixtures thereof, preferentially zirconium, niobium, tantalum, and mixtures thereof, very preferentially tantalum, and an oxide matrix, preferably based on silica. The preparation method according to the invention comprises, very particularly consists of, the following steps: a) a step of preparing at least one acidified organic solution which comprises at least one metal precursor of at least one metal element chosen from the elements of groups 3, 4 and 5 of the periodic table, at least one multifunctionalized ketone additive, very advantageously chosen from hydroxyketones, diketones, and mixtures thereof, preferably an acidifying agent, and optionally an organic solvent, said at least one metal precursor and said at least one multifunctionalized ketone additive being present in the acidified organic solution in amounts such that the molar ratio (additive/metal) between the number of moles of said at least one multifunctionalized ketone additive and the number of moles of the metal element(s) provided by said at least one metal precursor is greater than or equal to 1, preferably greater than or equal to 2, preferentially between 2 and 20, more preferably between 5 and 15; b) a step of depositing said at least one metal precursor on an oxide matrix, by bringing the acidified organic solution prepared in step a) into contact with said oxide matrix, to obtain a solid, b') optionally a step of maturing the solid obtained at the end of step b), c) a step of heat treatment of the solid resulting from step b) of deposition or optionally b') of maturing, preferably comprising drying or drying followed by calcination, the drying being advantageously carried out at a temperature of between 50 and 200°C and preferably between 80 and 150°C, for a period of between 1 and 24 hours, advantageously under a gas flow, preferably under an air flow; the calcination, when integrated into step c), being advantageously carried out under a gas flow, preferably under a gas flow comprising oxygen, at a temperature of between 350 and 700°C, preferably between 450 and 600°C, for a duration of between 1 and 6 h, preferably between 2 and 4 h; and d) optionally the repetition of the succession of steps b) of deposition and c) of heat treatment, or optionally of the succession of step b) of deposition, followed by step b') of maturation then by step c) of heat treatment.

Advantageously, step a) of the preparation method makes it possible to prepare at least one acidified organic solution which comprises at least one metallic precursor, preferably which comprises one or two metallic precursor(s), and very particularly a metallic precursor, comprising at least one metallic element chosen from among the elements of groups 3, 4 and 5 of the periodic table, i.e. at least one metallic precursor of at least one metallic element chosen from among the elements of groups 3, 4 and 5 of the periodic table, preferably one or two, and very particularly one, metallic precursor(s) of at least one element of group 3, group 4 and/or group 5. Preferably, the or each metallic precursor comprises a metallic element chosen from among the elements of groups 3, 4 and 5 of the periodic table. The or each metallic precursor may optionally comprise another element chosen from among the elements of a group of the periodic table other than those of groups 3, 4 and 5.

Said at least one metallic precursor of at least one metallic element chosen from the elements of group 3, group 4 and/or group 5 of the periodic table is advantageously a metallic precursor of at least one metallic element chosen in particular from yttrium (Y), zirconium (Zr), hafnium (Hf), niobium (Nb), tantalum (Ta), and mixtures thereof, preferably from zirconium (Zr), niobium (Nb), tantalum (Ta), and mixtures thereof, very preferably tantalum. According to a very preferred embodiment of the invention, said at least one metallic precursor is a metallic precursor of the element tantalum, optionally combined with a metallic precursor of the element niobium and/or with a metallic precursor of the element zirconium.

Advantageously, a metal precursor of at least one metal element chosen from the elements of group 3, 4 and/or 5, for example a metal precursor of the element tantalum, is any compound comprising said at least one element respectively of group 3, 4 and/or 5, for example tantalum, and capable of releasing this element in solution in reactive form. The metal precursors used are thus organic or inorganic compounds comprising said metal element of group 3, 4 and/or 5, and which are advantageously soluble at least partially, preferably entirely, in the acidified organic solution, and in particular in the organic solvent when an organic solvent is used, under the temperature and pressure conditions implemented during step a) and step b) of the preparation method. The organic or inorganic compounds are in particular chosen from the group consisting of halides, nitrates, sulfates, phosphates, hydroxides, carbonates, carboxylates, alcoholates, diketonates, amines, cyclopentadienyl, of said metal element from group 3, 4 and/or 5, and combinations of two or more thereof, more preferably chosen from the group consisting of chlorides, nitrates, carboxylates, alcoholates, diketonates, of said metal element from group 3, 4 and/or 5, and combinations of two or more thereof. The alcoholate precursors have for example the formula M(OR) _n where M is a metal element n of the periodic table, n being an integer equal to from group 3, 4 or 5, preferably M is Ta or Nb or Zr, of very preferably Ta, and R is a group chosen from alkyls such as ethyl, isopropyl, n-butyl, s-butyl, t-butyl groups. For example, the preferred metal precursors of tantalum are tantalum pentachloride (TaCls) and tantalum pentaethanoate (Ta(OC2Hs)s or Ta(OEt)s), very preferably tantalum pentachloride (TaCls). The metal precursor of niobium may be chosen from niobium pentachloride (NbCls) and niobium pentaethanoate (Nb(OC2Hs)s or Nb(OEt)s very preferably niobium pentachloride (NbCls),). The metal precursor of zirconium may be chosen from zirconium tetrachloride (ZrCL) and zirconium tetraethanoate (Zr(OC2Hs)4 or Zr(OEt)4), very preferably zirconium pentachloride (ZrCL). According to a very preferred embodiment of the invention, said at least one metal precursor is tantalum pentachloride (TaCls) or tantalum pentaethanoate (Ta(OC2Hs)s or Ta(OEt)s), very preferably tantalum pentachloride (TaCls), optionally combined with a metal precursor of the element niobium and/or a metal precursor of the element zirconium.

The acidified organic solution prepared in step a) of the method according to the invention comprises, in addition to said at least one metallic precursor of at least one element from group 3, 4 and/or 5 of the periodic table, at least one multifunctionalized ketone additive and optionally an organic solvent.

Said multifunctionalized ketone additive is advantageously an organic compound comprising a ketone (or carbonyl) function, and at least one second chemical function, advantageously oxygenated, nitrogenous or sulfurous, preferably in position 1 (alpha position, i.e. on the carbon directly adjacent to the carbon of the ketone function), in position 2 (beta position, i.e. on the second carbon adjacent to the carbon of the ketone function) or position 3 (gamma position, i.e. on the third carbon adjacent to the carbon of the ketone function). Said multifunctionalized ketone additive is preferably an organic compound comprising a ketone function and at least one hydroxyl or ketone function preferably located in position 1 (alpha position, i.e. on the carbon directly adjacent to the carbon of the first ketone function), in position 2 (beta position, i.e. on the second carbon adjacent to the carbon of the first ketone function) or position 3 (gamma position, i.e. on the third carbon adjacent to the carbon of the first ketone function). Said at least one multifunctionalized ketone additive is thus preferentially chosen from hydroxyketones, diketones, and mixtures thereof, preferably chosen from alpha-hydroxyketones, beta-hydroxyketones, gamma-hydroxyketones, alpha-diketones, beta-diketones, gamma-diketones, and mixtures thereof, very preferentially from alpha-hydroxyketones, beta-hydroxyketones, beta-diketones, and mixtures thereof. For example, the multifunctionalized ketone additive may be selected from 3-hydroxybutanone (or acetoin), pentane-2,4-dione (or acetylacetone), and mixtures thereof.

The metal precursor(s) of at least one element from group 3, 4 and/or 5 and the multifunctionalized ketone additive(s) are present in the acidified organic solution in amounts such that the molar ratio (additive/metal) of the number of moles of multifunctionalized ketone additive(s) relative to the number of moles of the metal element(s), i.e. total number of moles of elements from groups 3, 4 and 5 (for example the element tantalum), provided by the metal precursor(s) is greater than or equal to 1, preferably greater than or equal to 2, preferentially between 2 and 20, more preferably between 5 and 15.

Preferably, the acidified organic solution prepared in step a) comprises one or two multifunctionalized ketone additive(s) and preferably one multifunctionalized ketone additive, advantageously as defined in the present description above. Said acidified organic solution may optionally comprise, in addition to said at least one multifunctionalized ketone additive, another additive.

The acidified organic solution may also comprise an organic solvent, to enable a so-called homogeneous acidified organic solution to be obtained as explained later in this description. Preferably, the acidified organic solution comprises an organic solvent, preferably at least 5% by weight of organic solvent, or even at least 20% by weight of organic solvent, and for example up to 90% by weight or 75% by weight of organic solvent, the percentages being given by weight of organic solvent relative to the total weight of the organic solution. When present in the organic solution, the organic solvent is very advantageously chosen from organic compounds in which said at least one multifunctionalized ketone additive and said at least one metal precursor are soluble. Advantageously, when present, the organic solvent of the acidified organic solution prepared in step a) comprises, preferably consists of, at least one organic compound and preferably an oxygenated organic compound (called oxygenated organic solvent). More particularly, the organic solvent of the acidified organic solution prepared in step a) is chosen from alcohols, carboxylic acids, ethers, esters and mixtures thereof. Preferably, the organic solvent comprises at least one alcohol, preferably at least 10% by weight (and up to 100% by weight), in particular at least 50% by weight (and up to 100% by weight), or even at least 90% by weight (and up to 100% by weight), of at least one alcohol, the percentages being given relative to the total weight of organic solvent of the acidified organic solution. The alcohols which can be used as organic solvent are preferably monoalcohols having between 1 and 6 carbon atoms (i.e. C1-C6), preferably between 1 and 4 carbon atoms (i.e. C1-C4) and in particular having 1, 2, 3 or 4 carbon atoms, in particular linear, branched or cyclic, advantageously non-aromatic. The alcohols which can be used as organic solvent are for example chosen from methanol, ethanol, propanol, isopropanol, butanol, isobutanol, tert-butanol and mixtures thereof. Preferably, the carboxylic acids which can be used as organic solvent are preferably carboxylic acids having between 2 and 4 carbon atoms (i.e. C2-C4), in particular linear, branched or cyclic, advantageously non-aromatic. The carboxylic acids which can be used as organic solvent are for example chosen from acetic acid, propionic acid, butyric acid. The ethers optionally used as organic solvent are preferably C4-C8 ethers, in particular linear, branched or cyclic, advantageously non-aromatic, for example tetrahydrofuran (THF), diethyl ether, diisopropyl ether. The esters which can be used as organic solvent are preferably esters of C2-C6, preferably C2-C4, carboxylic acid and C1-C6, preferably C1-C4 alcohol, in particular linear, branched or cyclic, advantageously non-aromatic, such as methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, ethyl propanoate. For example, the organic solvent comprises, preferably consists of, at least one oxygenated organic compound selected from methanol, ethanol, propanol, isopropanol, butanol, isobutanol, tert-butanol, acetic acid, propionic acid, butyric acid, tetrahydrofuran (THF), diethyl ether, diisopropyl ether, methyl acetate, ethyl acetate, isopropyl acetate, ethyl propanoate, and mixtures thereof, in particular from methanol, ethanol, propanol, isopropanol, isobutanol, tert-butanol, acetic acid, propionic acid, isopropyl acetate and mixtures thereof. According to a very preferred embodiment, the organic solvent comprises, preferably consists of, at least one alcohol, preferably at least 10% by weight (and up to 100% by weight), in particular at least 50% by weight (and up to 100% by weight), or even at least 90% by weight (and up to 100% by weight), of at least one alcohol preferably chosen from methanol, ethanol, propanol, isopropanol, butanol, isobutanol, tert-butanol or mixtures thereof, and in particular from ethanol, isopropanol, tert-butanol, and mixtures thereof, the percentages being given relative to the total weight of organic solvent of the acidified organic solution, said at least one alcohol optionally being mixed with acetic acid and/or propionic acid.

The organic solution is acidified, which means that the organic solution advantageously comprises at least one acidifying agent. Said acidifying agent (also called acidifying compound or acidifying agent) is advantageously an organic or inorganic acidic compound or capable of generating at least one acid in the acidified organic solution. The expression "compound capable of generating at least one acid in the acidified organic solution" means more particularly that said compound is capable of generating an acid in the presence of an organic solvent which comprises in particular at least one alcohol, for example chosen from methanol, ethanol, propanol, isopropanol, butanol, isobutanol, tert-butanol. Said acidifying agent advantageously makes it possible to acidify the organic solution. Preferably, the acidified organic solution has a pH of less than 7.0, preferably less than or equal to 5.0, more preferably less than or equal to 3.0.

More particularly, said at least one acidifying agent is chosen from:

- carboxylic acids, in particular monocarboxylic acids such as acetic acid, propionic acid, butanoic acid; hydroxy acids, keto acids and polyacids (in particular di- and tri-acids) such as pyruvic acid, lactic acid, tartaric acid, malic acid, citric acid, oxalic acid, glycolic acid, mandelic acid;

- inorganic acids, such as sulfuric acid, nitric acid, hydrogen halides such as hydrogen chloride, hydrogen bromide, hydrogen iodide;

- hydrogen halide precursors, which are advantageously organic or inorganic halide compounds and capable of releasing at least one halide ion in an organic solvent which in particular comprises an alcohol, to form a hydrogen halide, the hydrogen halide precursors preferably being chosen from metal halide salts, preferably halide salts of a metal element chosen from elements of groups 3, 4 and 5, preferably from tantalum, niobium, zirconium; acyl halides;

- and their mixtures.

Preferably, said at least one acidifying agent is chosen from hydrogen halides such as hydrogen chloride (HCl), metal halide salts and preferably salts of chloride and of a metal element chosen from elements of groups 3, 4 and 5, such as tantalum pentachloride (TaCls), niobium pentachloride (NbC ), zirconium tetrachloride (ZrCl); acyl halides such as formyl chloride, acetyl chloride, propionyl chloride, butyryl chloride, preferably acetyl chloride; and mixtures thereof. Said at least one acidifying agent may thus be identical to or different from said metal precursor of at least one metal element.

Preferably, said at least one acidifying agent is present in the acidified organic solution, in an amount such that the pH of the acidified organic solution is less than 7, preferably less than or equal to 5, very preferably less than or equal to 3. Very preferably, said at least one acidifying agent is present in the acidified organic solution in an amount adjusted so as to have an acidifying/metal molar ratio of the number of moles of said acidifying agent relative to the number of moles of said at least one metallic element provided by said at least one metallic precursor greater than 0.0, preferably greater than or equal to 0.1, preferably greater than or equal to 1.0, and very advantageously less than or equal to 20, or even less than or equal to 15.

Thus, according to a preferred embodiment of the invention, the acidified organic solution prepared in step a) of the process according to the invention comprises, in particular consists of:

- at least tantalum pentachloride (TaCl5), niobium pentachloride (NbCl5) and/or zirconium tetrachloride (ZrCl4), preferably tantalum pentachloride (TaCl5),

- a multifunctionalized ketone additive chosen from hydroxyketones and/or diketones, very preferably from 3-hydroxybutanone (or acetoin), pentane-2,4-dione (or acetylacetone), and their mixtures,

- optionally an organic solvent comprising at least one alcohol, preferably at least 10% by weight (and up to 100% by weight), in particular at least 50% by weight (and up to 100% by weight), or even at least 90% by weight (and up to 100% by weight), of at least one alcohol, the percentages being given relative to the total weight of organic solvent of the acidified organic solution, said at least one alcohol being preferentially chosen from methanol, ethanol, propanol, isopropanol, butanol, isobutanol, tert-butanol and mixtures thereof.

The metal precursor(s) and the multifunctionalized ketone additive(s), and advantageously said acidifying agent, may be dissolved, diluted and/or in advantageously colloidal suspension, in the organic solution prepared in step a). Whatever their form, the metal precursor(s) and the multifunctionalized ketone additive(s), and advantageously said acidifying agent, are distributed uniformly in the acidified organic solution at the end of step a). The acidified organic solution may then be said to be homogeneous.

In step a), several acidified organic solutions, for example two or three acidified organic solutions, may be prepared. The acidified organic solutions then prepared may each advantageously contain a metal precursor identical or different between said acidified organic solutions, of an element from group 3, group 4 and/or group 5 identical or different between the acidified organic solutions prepared, and at least one multifunctionalized ketone additive identical or different between them, or even advantageously an acidifying agent identical or different between them. In the case where several acidified organic solutions are prepared, the method for preparing a catalyst advantageously comprises a step d) of repeating at least steps b) of deposition and c) of heat treatment, so as to bring each of the acidified organic solutions prepared into contact at least once with the oxide matrix (or support).

Preferably, step a) of preparing the acidified organic solution is carried out at a temperature between room temperature and 80°C, and at a pressure between atmospheric pressure and 3.0 MPa. Step a) of preparing the acidified organic solution very advantageously comprises mixing said at least one metal precursor and said at least one multifunctionalized ketone additive, optionally with the organic solvent.

Step a) thus makes it possible to prepare at least one acidified organic solution comprising at least one metallic precursor of at least one element from group 3, group 4 and/or group 5 of the periodic table, and at least one multifunctionalized ketone additive advantageously chosen from hydroxyketones, diketones, and their mixtures, advantageously at least one acidifying agent, and optionally in an organic solvent, in particular oxygenated.

Said acidified organic solution obtained at the end of step a) can then be brought into contact with an oxide matrix to obtain a solid. This contacting step corresponds to step b) of the preparation method according to the invention which is a step of depositing said metallic precursor(s) on said oxide matrix.

Said oxide matrix may also be called a support and is typically in the form of particles. Preferably, the oxide matrix comprises silica; said oxide matrix may then be called a silica-based oxide matrix. It preferably comprises at least 90% by weight (i.e. between 90% and 100% by weight), preferably at least 95% by weight (i.e. from 95% up to 100%), more preferably at least 98% by weight (i.e. from 98% up to 100%) and even more preferably at least 99.5% by weight (i.e. from 99.5% up to 100%) of silica relative to the total mass of oxide matrix. Said oxide matrix very advantageously comprises pores, in particular mesopores. The average pore diameter (or pore size) of the oxide matrix, in particular based on silica, is preferably at least 4 nm, preferably between 4.5 and 50 nm and even more preferably between 4.5 and 20 nm. Preferably, the pore volume of the oxide matrix, in particular based on silica, is in particular between 0.4 and 1.8 ml/g, and in particular between 0.5 and 1.5 ml/g. Preferably, the oxide matrix has a SBET specific surface area of at least 250 m ² /g, preferably between 250 m ² /g and 700 m ² /g and even more preferably between 400 m ² /g and 600 m ² /g.

The above-mentioned textural parameters are determined by the analysis technique known as “Nitrogen Volumetry” which corresponds to the physical adsorption of nitrogen molecules in the porosity of the material via a progressive increase in pressure at constant temperature. According to the invention, the specific surface area in particular of the oxide matrix corresponds to the BET specific surface area (SBET in m ² /g) determined by nitrogen adsorption in accordance with the ASTM D 3663-78 standard established from the BRUNAUER-EMMETT-TELLER method described in the periodical “The Journal of the American Chemical Society”, 1938, 60, 309. The representative pore distribution of a mesopore population is determined by the Barrett-Joyner-Halenda (BJH) model. The nitrogen adsorption-desorption isotherm according to the BJH model obtained is described in the periodical "The Journal of the American Chemical Society", 1951, 73, 373, written by EP Barrett, LG Joyner and PP Halenda. The pore volume V is defined as the value corresponding to the volume observed for the partial pressure P/P° _ma x of the nitrogen adsorption-desorption isotherm. The nitrogen adsorption volume is the volume measured for P/P° _ma x = 0.99, pressure for which it is assumed that nitrogen has filled all the pores. The diameter of the mesopores <|) of the tested material, in particular of the oxide matrix, is determined by the formula 4000. /SBET.

The oxide matrix may optionally include traces of water, for example at a content greater than or equal to 0.5% by weight, relative to the total weight of the oxide matrix. The presence of traces of water in the support does not seem to affect the quality of the heterogeneous catalyst obtained, in particular its catalytic performances, such as selectivity and productivity, in particular during the reaction of converting a feedstock comprising ethanol into butadiene. Thus, as the requirement to work with dry materials is relaxed, handling constraints can be reduced, for example: prior drying of the oxide matrix can be avoided or reduced (for example, drying the oxide matrix at 100°C for 2 hours may be sufficient); storage of the oxide matrix can be considered, in particular without special humidity conditions; handling of the oxide matrix in a dry atmosphere can be avoided; drying of the organic solvent is not necessary. Thus, the process according to the invention makes it possible to reduce energy consumption and the cost of the preparation process.

Optionally, the oxide matrix may be dried, prior to step b), for example in a fixed or circulating oven, at a temperature typically less than or equal to 600°C, more particularly between 100 and 350°C, or even between 150 and 300°C, for example for 10 minutes to 24 hours, in particular for 1 to 16 hours. Advantageously, the oxide matrix which is brought into contact with the acidified organic solution in step b) has a water content preferably less than or equal to 5% by weight, preferably less than or equal to 2.5% by weight, or even between 0.5 and 2.5% by weight, relative to the total weight of the oxide matrix.

The oxide matrix, in particular silica-based, may be commercially available or custom-synthesized using methods known to those skilled in the art. The oxide matrix, in particular silica-based, may be used directly in powder form or already shaped, in particular in the form of pelletized, crushed and sieved powder, beads, pellets, granules, or extrudates (hollow or non-hollow cylinders, multi-lobed cylinders with 2, 3, 4 or 5 lobes for example, twisted cylinders), or rings, etc., these shaping operations being carried out using conventional techniques known to those skilled in the art. For example, said oxide matrix, in particular silica-based, is in the form of beads or extrudates, optionally spheronized, preferably of a size between 0.5 and 10 mm, preferably between 1.0 and 5 mm.

The contacting in step b), i.e. the deposition of said at least one metal precursor on said oxide matrix, can be carried out by any methods known to those skilled in the art. For example, and in a non-exhaustive manner, the methods known as dry impregnation, excess impregnation, CVD (Chemical Vapor Deposition), CLD (Chemical Liquid Deposition), etc. can be used. For example, step b) of the method for preparing the catalyst according to the invention comprises, preferably consists of: bringing a volume of acidified organic solution prepared in step a) into contact with the oxide matrix such that said volume of acidified organic solution can correspond to the total or partial pore volume of said oxide matrix, and impregnating the acidified organic solution on the surface of said oxide matrix, so as to ensure the dispersion of said at least one metal precursor over the entire surface of the oxide matrix. Very advantageously, the contacting and the impregnation are carried out at a temperature between room temperature and 80°C and at a pressure between atmospheric pressure and 3.0 MPa.

The deposition step b) may optionally be followed by a step b') of maturation of the solid obtained, so as to further promote the dispersion and distribution of said at least one metal precursor over the entire surface of the oxide matrix. For example, the maturation step may be carried out between room temperature and 80°C and at a pressure between atmospheric pressure and 3.0 MPa, for a duration of between 1 and 5 h, in particular for 2 hours. The method for preparing the catalyst according to the invention also comprises a step c) of heat treatment of the solid obtained at the end of step b) of deposition or possibly of step b') of maturation.

Preferably, step c) of heat treatment comprises, preferably consists of, drying or drying followed by calcination, preferably drying followed by calcination. The drying is very advantageously carried out at a temperature of between 50 and 200°C and preferably between 80 and 150°C, for a duration of between 1 and 24 hours, advantageously under a gas flow, preferably under an air flow, for example in an oven. The calcination, when carried out in step c) of the method for preparing the catalyst, is advantageously carried out under a gas flow, preferably under a gas flow comprising oxygen, for example under an air flow, at a temperature of between 350 and 700°C, preferably between 450 and 600°C, for a duration of between 1 and 6 h and preferably between 2 and 4 h.

Optionally, steps b) of deposition and c) of heat treatment, or optionally steps b), b') then c), may be repeated n times, n being an integer between 1 and 10, preferably between 1 and 5. Thus, the method for preparing the catalyst may comprise a step d) of repetition, for example in the case where the targeted catalyst comprises several metallic elements from group 3, group 4 and/or group 5, for example the element Nb and the element Ta or the element Ta and the element Zr; or so as to achieve the targeted content of the metallic element (or metallic elements) in the prepared catalyst; or in the case where several acidified organic solutions are prepared in step a) as explained above in this description, etc. When the preparation method comprises a repetition step d), the acidified organic solution is then brought into contact with the solid heat-treated in step c) during the first repetition, or with the solid heat-treated in the (i-1) ^th heat treatment step during the ^ith repetition, i being an integer between 2 and n. When it comprises a repetition step d), i.e. the repetition n times of steps b) and c), or possibly b), b') and c), the method for preparing the catalyst therefore comprises:

- at least one step a) of preparation of an acidified organic solution (step a) can also be repeated if necessary);

- a deposit step b), possibly followed by a maturation step b’), then

- a heat treatment step c) advantageously comprising drying or drying then calcination; then n times the succession of: a deposit step b), optionally followed by a maturation step b'), followed by a heat treatment step c) advantageously comprising drying or drying followed by calcination, the last heat treatment (i.e. the ^nth heat treatment) preferably comprising drying followed by calcination.

The catalyst obtained at the end of step c) or possibly step d) is a heterogeneous catalyst, comprising at least one metallic element from group 3, group 4 and/or group 5, deposited on a support (or oxide matrix) in particular based on silica.

The preparation method may optionally further comprise a step of shaping the catalyst obtained, optionally followed by a heat post-treatment, in particular in the case where the oxide matrix used in step b) is in the form of an unshaped powder. Thus, during this optional shaping step, at the end of step c) or optionally of step d), the catalyst may be shaped in the form of pelletized, crushed, sieved powder, beads, pellets, granules, or extrudates (hollow or non-hollow cylinders, multi-lobed cylinders with 2, 3, 4 or 5 lobes for example, twisted cylinders), or rings, etc., these shaping operations being carried out by conventional techniques known to those skilled in the art. Preferably, said catalyst is shaped in the form of extrudates of a size between 1 and 10 mm, optionally spheronized. During this optional shaping step, the catalyst may optionally be mixed with at least one porous oxide material acting as a binder so as to generate the appropriate physical properties of the catalyst (mechanical strength, attrition resistance, etc.). The porous oxide material, which acts as a binder, is preferably chosen from the group formed by silica, magnesia, clays (such as kaolinite, antigorite, chrysotile, montmorillonnite, beidellite, vermiculite, talc, hectorite, saponite, laponite), titanium oxide, titanates (for example zinc, nickel, cobalt titanates), lanthanum oxide, cerium oxide, boron phosphates and mixtures thereof. Very preferably, the binder used is of silicic nature, and preferably at a content of between 5 and 60% by weight, and preferably between 10 and 30% by weight of binder relative to the total mass of the final shaped and optionally heat-post-treated catalyst. The heat post-treatment when carried out is of the same nature and follows the operating conditions of the heat treatment of step c).

The catalyst obtained at the end of step c) or optionally at the end of step d), or even at the end of the optional shaping step, comprises at least one metallic element chosen from the elements of group 3, group 4 and group 5, preferably from yttrium, zirconium, hafnium, niobium, tantalum, and mixtures thereof, preferentially from the element tantalum, the element niobium, the element zirconium and mixtures thereof, very preferentially the element tantalum, and preferably at a content of between 0.1 and 30% by weight, preferably between 0.3 and 10% by weight, preferably between 0.5 and 5% by weight of metallic element(s) relative to the weight of the oxide matrix. Very advantageously, the catalyst obtained can be loaded into any type of catalytic reactor known to those skilled in the art, in particular a reactor in axial, radial mode or a tubular reactor, with or without heat exchange, with or without multiple injection.

The present invention thus also relates to the catalyst obtained by the preparation method according to the invention, which comprises at least one metallic element chosen from the group of elements of group 3, group 4 and group 5 of the periodic table, preferably chosen from yttrium, zirconium, hafnium, niobium, tantalum, and mixtures thereof, preferentially from the element tantalum, the element niobium, the element zirconium and mixtures thereof, very preferentially the element tantalum, and an oxide matrix, preferably based on silica. Preferably, said metallic element(s) is (are) present at a content of between 0.1 and 30% by weight, preferably between 0.3 and 10% by weight, preferably between 0.5 and 5% by weight of metallic element(s) relative to the weight of the oxide matrix. According to a highly preferred embodiment, the catalyst comprises a silica-based oxide matrix and between 0.5 and 5% by weight of tantalum relative to the weight of the oxide matrix. According to another embodiment, the catalyst comprises a silica-based oxide matrix and between 0.3 and 10% by weight, in particular between 0.5 and 5% by weight, of zirconium relative to the weight of the oxide matrix. According to another embodiment, the catalyst comprises a silica-based oxide matrix and between 0.3 and 10% by weight, in particular between 0.5 and 5% by weight, of niobium relative to the weight of the oxide matrix.

The method for preparing a catalyst, according to the invention, advantageously makes it possible to obtain, in a simple and inexpensive manner, a heterogeneous catalyst comprising at least one metallic element from group 3, group 4 and/or group 5, in particular the element Nb and/or Ta and/or Zr, very preferably the element Ta, having catalytic performances, in particular selectivity and productivity during the reaction for converting a feedstock comprising ethanol into butadiene, which are very satisfactory or even improved compared to the catalysts of the state of the art prepared organically. Such a preparation method can also possibly make it possible to ensure good dispersion of the metallic elements from group 3, group 4 and/or group 5 over the entire surface of the oxide matrix (i.e. good distribution of the metallic elements in the support particles).

The present invention also relates to the use for the conversion of a feedstock comprising at least ethanol into butadiene, of a catalyst obtained by the preparation method according to the invention, and which comprises at least one metallic element chosen from the group of elements of groups 3, 4 and 5 of the periodic table, preferably from yttrium, zirconium, hafnium, niobium, tantalum, and mixtures thereof, preferably from the element tantalum, the element niobium, the element zirconium, and mixtures thereof, preferably the element tantalum, and an oxide matrix preferably based on silica, preferably at a content between 0.1 and 30% by weight, preferably between 0.3 and 10% by weight, preferably between 0.5 and 5% by weight of metallic element(s) relative to the weight of the oxide matrix. According to a preferred embodiment, the catalyst used comprises an oxide matrix based on silica and between 0.5 and 5% by weight of tantalum relative to the weight of the oxide matrix. The use of the catalyst obtained, for the conversion of a feedstock comprising at least ethanol into butadiene, then results in improvements in catalytic performance, particularly in terms of selectivity and productivity. The operating conditions for the conversion reaction are preferably a temperature between 250 and 450°C, preferably between 270°C and 380°C, preferentially between 300 and 360°C, a pressure between 0.05 and 2.00 MPa, preferably between 0.05 and 1.50 MPa, preferentially between 0.08 and 1.00 MPa, and preferably a space velocity between 0.2 and 10 h' ¹ , preferentially between 0.5 and 5 h ^-1 and preferably between 1 and 4 h' ¹ . The space velocity is defined as the ratio between the mass flow rate of feedstock and the mass of catalyst. When the treated feedstock also comprises acetaldehyde, the ethanol/acetaldehyde molar ratio is between 1 and 5, preferably between 2 and 4.

The present invention also relates, according to another aspect, to a process for converting into butadiene a feedstock comprising ethanol and optionally acetaldehyde, which comprises at least:

A) the preparation of a catalyst according to the preparation method according to the invention;

B) a step of converting the feedstock comprising ethanol, preferably ethanol and acetaldehyde, into butadiene, preferably in a molar ratio of ethanol to acetaldehyde of between 1 and 5, preferably between 2 and 4, the conversion step being carried out in the presence of the catalyst prepared in step A), and at a temperature of between 250 and 450°C, preferably between 270 and 380°C, preferentially between 300 and 360°C, at a pressure of between 0.05 and 1.5 MPa, preferably between 0.05 and 1.50 MPa, preferentially between 0.08 and 1.00 MPa, and preferably at a space velocity of between 0.2 and 10 h' ¹ , preferentially between 0.5 and 5 h ^-1 , preferably between 1 and 4 h' ¹ .

When the feed comprises ethanol and acetaldehyde, the catalyst prepared in step A) very preferably comprises the tantalum element and a silica-based oxide matrix, the tantalum element content of the catalyst prepared in A) preferably being between 0.3 and 10%, and in particular between 0.5 and 5% by weight relative to the weight of the silica-based oxide matrix.

The following examples illustrate the invention, in particular particular embodiments of the invention, without limiting its scope.

Examples

Catalysts are prepared according to the methods described in Example 1. The catalysts are then tested: they are used to convert a feedstock comprising ethanol and acetaldehyde as described in Example 2.

Example 1: Preparation of 3% Ta/SiO2 catalysts

Catalysts are prepared with 3% by weight of tantalum on silica beads (also called silica support), the percentage of tantalum being given by weight of tantalum element relative to the weight of silica beads. For each of the catalysts, the preparation method is as follows:

The silica support used for the impregnation step has the following characteristics:

Table 1

(*: the average size of the beads corresponds to an average diameter in number of the silica beads.)

Before impregnation, the support is dried in an oven at 100°C for 2 hours. After drying, the water content in the silica beads is 1.5% by weight (determined by weight loss of a 50 g sample of silica beads).

In some cases, a multifunctional ketone additive, acetoin (α-hydroxy-ketone) or acetylacetone (β-diketone), is introduced into a VEtOH volume of ethanol, to form an ethanolic solution. In the reference case, no additive or acidifying agent is introduced into said VEtOH ethanol volume, the organic solution is not an acidified organic solution. The volume of VEtOH ethanol is proportional to the pore volume of the silica support and equal to the total pore volume of the silica support used. A tantalum precursor, tantalum pentachloride (TaCls) (which is also an acidifying compound) or tantalum pentaethanoate (Ta(OEt)s), is then introduced and diluted in a VROH volume of ethanol (references) or in the ethanolic solution containing the multifunctionalized ketone additive at a concentration corresponding to an additive/Ta molar ratio of 7. An acidifying agent, other than tantalum pentachloride (TaCls), may also be introduced into the organic solution: said acidifying agent, other than TaCls, is acetyl chloride (AcCl). In the case where an acidifying agent, TaCls or AcCl, is introduced into the organic solution, the latter is an acidified organic solution. The acidification of the organic solution is therefore carried out either by reaction of tantalum pentachloride or acetyl chloride with ethanol:

TaCIs + x EtOH TaCI(5-x)(OEt) _x + x HCl (1)

CH3COCI + EtOH CH ₃ COOEt + HCl (2)

The organic solution, acidified or not, is then homogenized while stirring.

The organic solution obtained, acidified or not, is quickly added dropwise and mixed with the silica support until wettability of the surface of the latter is observed (dry impregnation). The solid is then placed in an atmosphere saturated with ethanol for 3 hours. The solid is then dried at 100°C for 24 hours in an oven, then calcined in air at 550°C for 4 hours, to obtain a catalyst.

The prepared catalysts and preparation parameters are presented in Table 2. The distribution coefficient of tantalum (also called partition) in silica beads is also presented in Table 2.

The distribution coefficient of an element (in this case, the tantalum element) in a support particle (in this case, the silica bead) is calculated from a profile measured by Castaing microprobe and represents the ratio of the concentrations of the element (i.e. tantalum) at the core of the support particle (in particular the silica bead) compared to the edge of this same support particle (cf. L. Sorbier, Determining the Distribution of Metal by Electron Probe Micro Analysis, in: H. Toulhoat, P. Raybaud (Eds.), Catalysis by Transition Metal Sulphides, Ed. Technip, Paris, 2013, pp. 407-411 and references cited). A value of this coefficient close to 1 indicates a homogeneous distribution of the element in the support particle (i.e. of Ta in the silica bead); a value approaching 0 is significant of a distribution of the element on the surface of the support particle and called crust. Table 2

According to Table 2, the distribution of tantalum in the silica beads appears to be more uniform for catalysts C, D and E, in accordance with the invention, prepared in the presence of an α-hydroxy ketone additive (acetoin) or β-diketone (acetylacetone) in combination with an acidifying agent, capable of releasing hydrogen chloride (HCl) by reaction with the ethanol solvent, compared to non-compliant catalysts A and B and prepared respectively without an acidifying agent or even without a multifunctionalized ketone additive and without an acidifying agent. Indeed, the distribution coefficients are 0.65+/-0.14, 0.63+/-0.18 and 0.85+/-0.19 respectively for the compliant catalysts C, D and E, whereas they are equal to 0.50+/-0.08 and 0.48+/-0.06 for the non-compliant catalysts A and B respectively. These distribution coefficients are significant of a presence of the tantalum element in a non-negligible proportion at the heart of the silica beads in the case of catalysts C, D and E in accordance with the invention, unlike the non-compliant catalysts A and B.

Example 2: Use of the prepared catalysts to convert an ethanol-acetaldehyde feedstock into butadiene

Description of the catalytic test unit

The reactor used consists of a 20 cm long, 10 mm diameter stainless steel tube. The reactor is first charged with carborundum, then with the catalyst diluted in carborundum, and finally with carborundum. Carborundum is inert to the charge and does not affect the catalytic results; it allows the catalyst to be positioned in the isothermal zone of the reactor and limits the risk of heat transfer problems. heat and matter. The reactor temperature is controlled with a three-zone heating tube furnace.

The liquid feed (ethanol and acetaldehyde mixture) is injected via a dual-piston HPLC pump. The liquid stream is vaporized in the tracer-heated lines before entering the reactor and is homogenized by passing through a static mixer.

At the reactor outlet, the products formed during the reaction are kept in the vapor phase to be analyzed online by gas chromatography (PONA capillary column) to allow the most precise identification of the hundreds of products formed. The catalyst is activated in situ under nitrogen at the test temperature.

For each test, the Ethanol/Acetaldehyde ratio of the feed is set at 2.6 (mol/mol), the temperature at 350°C and the pressure at 0.15 MPa.

For each catalyst tested, the carbon productivity value is measured at iso-feed rate (constant pph of 250g/gTa/h, i.e. a space velocity of 7.5 h ^-1 ) while the butadiene selectivity measurement is determined at iso-conversion (feed conversion at 40%). The carbon productivity (which is generally expressed in % weight/weight per hour) corresponds to the mass flow rate of butadiene (in g/h), measured at the reactor outlet, per unit mass of Ta element, for a pph of the feed of 250 g/gTa/h. The butadiene selectivity (which is expressed in % weight/weight) measured is a carbon selectivity and corresponds to the butadiene flow rate measured at the reactor outlet relative to the sum of the flow rates of the carbon products formed (unconverted ethanol and acetaldehyde are not taken into account in the selectivity calculation).

The results obtained in terms of butadiene selectivity and carbon productivity, with catalysts A to E prepared as described in Example 1, are presented in Table 3, in the form of gain in butadiene selectivity compared to the reference catalyst A (i.e. gain in selectivity = [selectivity obtained with the catalyst] - [selectivity obtained with catalyst A], gain expressed in points or % weight/weight) and in the form of gain in carbon productivity expressed relative to the productivity measured for the corresponding reference catalyst A (i.e. gain in productivity = ([productivity obtained with the catalyst] - [productivity obtained with catalyst A]) / [productivity obtained with catalyst A], expressed in % weight/weight). Table 3

Table 3 shows that even if they are improved when the catalyst (catalyst B) is prepared in the presence of a hydroxyketone additive, the butadiene selectivity and the carbon productivity are even more improved when the conversion reaction is carried out in the presence of a catalyst in accordance with the invention, that is to say prepared in the presence of a hydroxyketone or diketone additive in an acidified medium, in particular in a medium also containing an acidifying agent, in particular tantalum pentachloride TaCls or acetyl chloride AcCl, (catalysts C, D and E). The selectivity is in fact improved by +4.4 to +4.8 points and the productivity between +36% and +43% for catalysts C, D and E in accordance with the invention compared to the non-compliant reference catalyst (catalyst A) prepared without additive or acidifier, while the non-compliant catalyst B, prepared in the presence of ketone additive but without acidifier, has a butadiene selectivity of only +2.1 points and a carbon productivity of +18% compared to the reference catalyst A.

Claims

Claims 1. Method for preparing a catalyst, comprising: a) a step of preparing at least one acidified organic solution comprising: at least one metal precursor of at least one metallic element chosen from the elements of groups 3, 4 and 5 of the periodic table, at least one multifunctionalized ketone additive, said at least one metal precursor and said at least one multifunctionalized ketone additive being present in the acidified organic solution in amounts such that the additive/metal molar ratio between the number of moles of said at least one multifunctionalized ketone additive and the number of moles of the metallic element(s) provided by said at least one metal precursor is greater than or equal to 1; b) a step of depositing said at least one metal precursor on an oxide matrix, by bringing the acidified organic solution prepared in step a) into contact with said oxide matrix, to obtain a solid; c) a step of heat treatment of the solid obtained at the end of step b). 2. Method according to claim 1, in which the metallic element is chosen from yttrium, zirconium, hafnium, niobium, tantalum and their mixtures, preferably from tantalum, niobium, zirconium and their mixtures, preferentially the element tantalum. 3. Method according to one of claims 1 to 2, in which the multifunctionalized ketone additive is chosen from alpha-hydroxyketones, beta-hydroxyketones, beta-diketones, and mixtures thereof, preferably from 3-hydroxybutanone, pentane-2,4-dione, and mixtures thereof. 4. Method according to one of claims 1 to 3, in which the additive/metal molar ratio in step a) is greater than or equal to 2, preferably between 2 and 20, more preferably between 5 and 15. 5. Method according to one of claims 1 to 4, in which the acidified organic solution comprises at least one acidifying agent, in particular an acidic compound or one capable of generating at least one acid in the acidified organic solution, preferably chosen from carboxylic acids such as monocarboxylic acids, hydroxy acids, keto acids and polyacids; inorganic acids, such as sulfuric acid, nitric acid, hydrogen halides; hydrogen halide precursors such as metal halide salts, acyl halides; and mixtures thereof. 6. Method according to claim 5, wherein said at least one acidifying agent is chosen from hydrogen halides, such as hydrogen chloride; salts metal halide salts, such as chloride salts of a metallic element selected from elements of groups 3, 4 and 5, such as tantalum pentachloride, niobium pentachloride, zirconium tetrachloride, or mixtures thereof; acyl halides such as formyl chloride, acetyl chloride, propionyl chloride, butyryl chloride, preferably acetyl chloride; and mixtures thereof. 7. Method according to one of claims 1 to 6, in which the organic solution of step a) comprises an organic solvent. 8. Method according to claim 7, in which the organic solvent comprises at least one alcohol, preferably at least 10% by weight (and up to 100% by weight), in particular at least 50% by weight (and up to 100% by weight), or even at least 90% by weight (and up to 100% by weight), of at least one alcohol, the percentages being given relative to the total weight of organic solvent of the acidified organic solution. 9. Method according to one of claims 1 to 8, in which the oxide matrix comprises silica, preferably at least 90% by weight of silica relative to the total mass of the oxide matrix. 10. Method according to one of claims 1 to 9, in which step c) of heat treatment comprises drying, the drying preferably being carried out at a temperature of between 50 and 200°C for a duration of between 1 and 24 hours, preferably under a gas flow, said drying preferably being followed by calcination carried out under a gas flow, at a temperature of between 350 and 700°C, for a duration of between 1 and 6 hours. 11. Catalyst obtained by the preparation method according to one of claims 1 to 10, and which comprises at least one metallic element chosen from the group of elements of group 3, group 4 and group 5 of the periodic table, preferably chosen from yttrium, zirconium, hafnium, niobium, tantalum and their mixtures, preferentially from the element tantalum, the element niobium and/or the element zirconium, preferably the element tantalum, and an oxide matrix preferably based on silica. 12. Catalyst according to claim 11, in which said at least one metallic element is present at a content of between 0.1 and 30% by weight, preferably between 0.3 and 10% by weight, preferably between 0.5 and 5% by weight of metallic element(s) relative to the weight of the oxide matrix. 13. Use of the catalyst according to claim 11 or 12 for converting a feedstock comprising ethanol into butadiene, at a temperature between 250 and 450°C, a pressure between 0.05 and 2.00 MPa. 14. A process for converting a feedstock comprising ethanol into butadiene, which comprises: A) the preparation of a catalyst according to the preparation method according to one of claims 1 to 10; B) a step of conversion into butadiene of the feedstock comprising ethanol, carried out in the presence of the catalyst prepared in step A), at a temperature between 250 and 450°C, a pressure between 0.05 and 2.00 MPa. 15. Conversion process according to claim 14, in which the feedstock comprises ethanol and acetaldehyde, preferably in a molar ratio of ethanol to acetaldehyde of between 1 and 5.