FR3156337A1 - Method for the organic preparation of a catalyst in the presence of an additive - Google Patents

Abstract

The present invention relates to a method for preparing a catalyst, comprising: a) a step of preparing an organic solution comprising: a metal precursor of a metallic element selected from elements in groups 3, 4, and 5 of the periodic table, an additive, which is a multifunctionalized acidic organic compound, a multifunctionalized ketone compound, a beta-multifunctionalized ester compound, a hydrogen halide, a hydrogen halide precursor, or a mixture thereof, said metal precursor and said additive being present in the organic solution in amounts such that the additive/metal molar ratio is greater than 2; b) a step of depositing said metal precursor on an oxide matrix, by bringing the organic solution into contact with said oxide matrix; then c) a heat treatment step. The present invention also relates to the catalyst obtained and its use for converting a feedstock comprising ethanol into butadiene.

Description

Method for the organic preparation of a catalyst in the presence of an additive

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 organic solution of at least one precursor of said metallic element, said organic solution also containing an additive. 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.

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 (SiO ₂ ), alumina (Al ₂ O ₃ ), titanium (TiO ₂ ), zirconia (ZrO ₂ ), 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 also have utility in photocatalysis or electrocatalysis.

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, in particular 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 chosen from the elements of group 3, 4 and/or 5.

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 (BB Corson, at al. Butadiene form 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 Ta ₈ (μ ₃ -O) ₂ (μ-O) ₈ (μ-OEt) ₆ (OEt) ₁₄ . 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 PN, Mehrotra RC, Organic Compounds of Niobium and Tantalum. IV. Reactions of niobium and tantalum pentaethoxides with β-diketones. J. Less-Common Metals , 8 (1965) 339-346),

- ketoesters (cf. Mehrotra RC, Kapoor PN, Organic Compounds of Tantalum. Reactions of tantalum pentaethoxide with β-ketoesters. J. Less-Common Metals , 7 (1964) 453-457),

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

- glycols (see Mehrotra RC, Kapoor PN, Organic Compounds of Tantalum. I. Reactions of tantalum pentaethoxide with glycols. J. Less-Common Metals , 10 (1965) 237-245),

- acyl halides (cf. R Mehrotra RC, Kapoor PN, 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.

The objective of the present invention is 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 an improvement 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.

The present invention thus relates to a method for preparing a catalyst, comprising:

a) a step of preparing at least one organic solution comprising:

at least one metallic precursor of at least one metallic element chosen from the elements of groups 3, 4 and 5 of the periodic table,

at least one additive, said at least one additive being a multifunctionalized organic acid compound, a multifunctionalized ketone compound, a beta-multifunctionalized ester compound, a hydrogen halide, a hydrogen halide precursor, or a mixture thereof,

said at least one metallic precursor and said at least one additive being present in the organic solution in quantities such that the additive/metal molar ratio between the number of moles of said at least one additive and the number of moles of the metallic element(s) provided by said at least one metallic precursor is greater than 2;

b) a step of depositing said at least one metallic precursor on an oxide matrix, by bringing the 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 the 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. Another advantage of the process according to the invention lies in the fact that extensive drying of the support and/or the compounds involved, such as the additive and/or the organic solvent, is not necessary to prepare a catalyst having good catalytic performances. The process according to the invention therefore has the advantage of making it possible to alleviate the handling constraints during the preparation of the catalyst which would be linked to the need to have dry products or those having a low residual water content.

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.

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.

According to the invention, the term hydroxy acid means any compound having a carboxylic acid function and a hydroxyl function preferably in the alpha, beta or gamma position (very preferably in alpha or beta), or their derivatives, the term derivatives here meaning their oligomers comprising in particular between 2 and 20 repeating units, possibly in cyclic form (i.e. in lactone form). Indeed, hydroxy acids are known to have a tendency to oligomerize, i.e. to condense in the form of oligomers, linear or cyclic, in particular when they are in concentrated solution. For example, lactic acid oligomerizes to form lactic acid oligomers comprising between 2 and 20 and more particularly between 2 and 10, when the concentration of lactic acid in aqueous solution increases (cf. Vu DT, et al., Oligomer distribution in concentrated lactic acid solutions, Fluid Phase Equilibria , 236 (2005) 125–135). Lactic acid can also dimerize and cyclize to form dilactide. Thus, the hydroxy acids as possibly envisaged as additive in the process according to the invention can be in the form of monomeric compounds of a hydroxy acid whose hydroxyl function is preferably in the alpha, beta or gamma position, or oligomeric compounds of said hydroxy acid, in cyclic (for example dillactide) or linear form. In this description, the terms "hydroxy acids" and "alpha-hydroxy acids", "beta-hydroxy acids", "gamma-hydroxy acids", are therefore to be understood as "hydroxy acids and their derivatives" and "alpha-hydroxy acids and their derivatives", "beta-hydroxy acids and their derivatives", "gamma-hydroxy acids and their derivatives", respectively. Similarly, the various specific hydroxy acids cited in this description, for example lactic acid, tartaric acid, malic acid, mandelic acid, correspond to said specific acids in monomeric form and their oligomeric derivatives, for example respectively lactic acid and its derivatives, tartaric acid and its derivatives, malic acid and its derivatives, mandelic acid and its derivatives.

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, the following steps:

a) a step of preparing at least one organic solution which comprises at least one metallic precursor of at least one metallic element chosen from the elements of groups 3, 4 and 5 of the periodic table, at least one additive preferably chosen from hydroxy acids and their anhydrides, keto acids and their anhydrides, polyacids (for example diacids and triacids), and their anhydrides, hydroketones, diketones, beta-hydroxyesters, beta-ketoesters, hydrogen halides, hydrogen halide precursors, and mixtures thereof, and optionally an organic solvent,

said at least one metallic precursor and said at least one additive being present in the organic solution in quantities such that the molar ratio (additive/metal) between the number of moles of said at least one additive and the number of moles of the metallic element(s) provided by said at least one metallic precursor is greater than 2, preferably between 2.1 and 30, preferentially between 2.5 and 20, preferably between 5 and 15;

b) a step of depositing said at least one metallic precursor on an oxide matrix, by bringing the organic solution prepared in step a) into contact with said oxide matrix, to obtain a solid,

b’) possibly a maturation stage of the solid obtained at the end of stage b),

c) a step of heat treatment of the solid resulting from step b) of deposition or possibly b') of maturation, preferably comprising drying or drying followed by calcination,

the drying being advantageously carried out at a temperature between 50 and 200°C and preferably between 80 and 150°C, for a duration 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) possibly 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 organic solution which comprises at least one metal precursor, preferably which comprises one or two metal precursor(s), and very particularly a metal precursor, comprising at least one metal element chosen from the elements of groups 3, 4 and 5 of the periodic table, that is to say 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, preferably one or two, and very particularly one, metal precursor(s) of at least one element of group 3, group 4 and/or group 5. Preferably, the or each metal precursor comprises a metal element chosen from the elements of groups 3, 4 and 5 of the periodic table. The or each metal precursor may optionally comprise another element chosen from 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 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 metallic element from group n of the periodic table, n being an integer equal to 3, 4 or 5, preferably M is Ta or Nb or Zr, 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 metallic precursors of tantalum are tantalum pentachloride (TaCl ₅ ) and tantalum pentaethanoate (Ta(OC ₂ H ₅ ) ₅ or Ta(OEt) ₅ ) which can be used with most organic solvents. The metallic precursor of niobium can be chosen from niobium pentachloride (NbCl ₅ ) and niobium pentaethanoate (Nb(OC ₂ H ₅ ) ₅ or Nb(OEt) ₅ ). The metal precursor of zirconium may be chosen from zirconium tetrachloride (ZrCl ₄ ) and zirconium tetraethanoate (Zr(OC ₂ H ₅ ) ₄ or Zr(OEt) ₄ ). According to a very preferred embodiment of the invention, said at least one metal precursor is tantalum pentachloride (TaCl ₅ ) or tantalum pentaethanoate (Ta(OC ₂ H ₅ ) ₅ or Ta(OEt) ₅ ), optionally combined with a metal precursor of the element niobium and/or a metal precursor of the element zirconium.

The 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 additive and optionally an organic solvent.

Said additive may be a multifunctionalized organic acid compound, a multifunctionalized ketone compound, a beta-multifunctionalized ester compound, a hydrogen halide, a hydrogen halide precursor, or a mixture thereof. According to the invention, a multifunctionalized acidic organic compound is an organic compound comprising a carboxylic acid function, or a carboxylic acid-generating function (i.e. an acid anhydride capable of generating an acid, in particular in an alcoholic medium), and at least one second chemical function, advantageously oxygenated (for example a carbonyl and/or hydroxyl group), nitrogenous (for example an amine or amide group) or sulfurous, preferably in position 1 (alpha position, i.e. on the carbon directly adjacent to the carbon of the acid function), in position 2 (beta position, i.e. on the second carbon adjacent to the carbon of the acid function) or position 3 (gamma position, i.e. on the third carbon adjacent to the carbon of the acid function). In the same way, a multifunctionalized ketone compound is an organic compound comprising a ketone function and at least one second chemical function, advantageously oxygenated (for example a carbonyl or hydroxyl group), nitrogenous (for example an amine or amide group) 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). Finally, a beta-multifunctionalized ester compound is an organic compound comprising an ester function and at least one second chemical function, advantageously oxygenated (for example a carbonyl or hydroxyl group), nitrogenous (for example an amine or amide group) or sulfurous, in position 2 (beta position, i.e. on the second carbon adjacent to the carbon of the ketone function). Preferably, said at least one additive is chosen from hydroxy acids and their anhydrides, keto acids and their anhydrides, polyacids (for example diacids and triacids), and their anhydrides, hydroxyketones, diketones, beta-hydroxyesters, beta-ketoesters, hydrogen halides, hydrogen halide precursors, and mixtures thereof.

Preferably, the hydroxy acids, keto acids and polyacids are chosen from alpha-hydroxy acids, beta-hydroxy acids, alpha-keto acids, beta-keto acids, alpha-diacids, beta-diacids, their anhydrides, and their mixtures, and more particularly from pyruvic acid, lactic acid, tartaric acid, malic acid, citric acid, oxalic acid, glycolic acid, salicylic acid, mandelic acid, α-ketoglutaric acid and β-ketoglutaric acid, their anhydrides, and their mixtures. Preferably, the hydroxy acids, keto acids and polyacids are chosen from alpha-hydroxy acids, alpha-keto acids, alpha-diacids, such as pyruvic acid, lactic acid, tartaric acid, malic acid, citric acid, oxalic acid, glycolic acid, mandelic acid, their anhydrides and their mixtures.

Preferably, the hydroxyketones and diketones are chosen from alpha-hydroxyketones, beta-hydroxyketones, beta-diketones, and mixtures thereof, for example from 3-hydroxybutanone (or acetoin), pentane-2,4-dione (or acetylacetone), and mixtures thereof.

Preferably, the beta-hydroxyesters and the beta-ketoesters are chosen from ethyl acetoacetate, ethyl 2-oxocyclopentanecarboxylate, diethyl malonate, and mixtures thereof, preferably ethyl acetoacetate, ethyl 2-oxocyclopentanecarboxylate, and mixtures thereof.

Preferably, the hydrogen halide is chosen from hydrogen chloride, hydrogen bromide, hydrogen iodide and mixtures thereof, and preferably hydrogen chloride. It can, for example, be introduced into the organic solution, by bubbling gaseous hydrogen halide into the organic solution, or into the organic solvent prior to step a); at least a portion of the gaseous hydrogen halide is then advantageously dissolved in the organic solvent.

Very advantageously, the hydrogen halide precursors are compounds comprising at least one halide and in which said at least one halide is labile. The hydrogen halide precursors are therefore advantageously capable of releasing at least one halide ion which can react with the organic solvent to form a hydrogen halide. Preferably, the hydrogen halide precursors are chosen from acyl halides (R-COHa, with Ha the halide i.e. fluoride, chloride, bromide or iodide), alcohol hydrohalides (ROH-HHa, with Ha the halide i.e. fluoride, chloride, bromide or iodide, and ROH said alcohol preferably chosen from methanol, ethanol, propanol, isopropanol, butanol, isobutanol, tert-butanol and mixtures thereof), and mixtures thereof. Very preferably, the hydrogen halide precursors are chosen from acyl halides such as formyl chloride, acetyl chloride, propionyl chloride, butyryl chloride, and mixtures thereof, and preferably acetyl chloride.

Preferably, said at least one additive is chosen from pyruvic acid, lactic acid, tartaric acid, malic acid, citric acid, oxalic acid, glycolic acid, mandelic acid and their anhydrides, 3-hydroxybutanone, pentane-2,4-dione, ethyl acetoacetate, ethyl 2-oxocyclopentanecarboxylate, diethyl malonate, hydrogen chloride, hydrogen bromide, hydrogen iodide, formyl chloride, acetyl chloride, propionyl chloride, butyryl chloride, and mixtures thereof.

Preferably, the organic solution prepared in step a) comprises one or two additive(s) and preferably one additive, as defined in the present description above.

The organic solution may also comprise an organic solvent, to enable a so-called homogeneous organic solution to be obtained as explained later in this description. Preferably, the 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 it is present in the organic solution, the organic solvent is very advantageously chosen from organic compounds in which said at least one additive and said at least one metal precursor are soluble. Advantageously, when it is present, the organic solvent of the organic solution prepared in step a) comprises, preferably consists of, at least one organic compound and preferably an oxygenated or hydrocarbon organic compound. Said organic solvent may optionally also comprise water. More particularly, the organic solvent is chosen from alcohols, carboxylic acids, ethers, esters, ketones, hydrocarbon compounds, 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 in the organic solution. The alcohols that 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 that 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 that 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 that 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 that can be used as organic solvent are preferably esters of C2-C6 carboxylic acid, preferably C2-C4, and of C1-C6 alcohol, preferably C1-C4, in particular linear, branched or cyclic, advantageously non-aromatic, such as methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, ethyl propanoate. The ketones optionally used as organic solvent are chosen from diketones, for example acetylacetone. The hydrocarbon compounds which can be used as organic solvent are preferably aliphatic, cyclic or aromatic hydrocarbon compounds, having between 5 and 10 carbon atoms (i.e. C5-C10), preferably between 6 and 8 carbon atoms (i.e. C6-C8), and in particular having 6, 7 or 8 carbon atoms, for example chosen from hexane isomers, heptane isomers, octane isomers and mixtures thereof. For example, the organic solvent comprises, preferably consists of, at least one 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, acetylacetone, hexane, heptane, and mixtures thereof, in particular from methanol, ethanol, propanol, isopropanol, isobutanol, tert-butanol, acetic acid, propionic acid, isopropyl acetate, hexane, heptane, 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 organic solution, said at least one alcohol optionally being mixed with acetic acid and/or propionic acid.

The metal precursor(s) of at least one element from group 3, 4 and/or 5 and the additive(s) are present in the organic solution in quantities such that the molar ratio (additive/metal) of the number of moles of 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 2 (i.e. strictly greater than 2), preferably between 2.1 and 30, preferentially between 2.5 and 20, more preferably between 5 and 15. When the additive/metal molar ratio is less than or equal to 2, the catalytic performances of the catalyst obtained, in particular in terms of selectivity and productivity, in particular during the conversion of a feedstock comprising ethanol into butadiene, are not or only slightly improved compared to prior art catalysts, in particular those prepared without additives. From a certain additive/metal molar ratio, for example between 10 and 15, the catalytic performance of the catalyst obtained, in particular in terms of selectivity and productivity, particularly during the conversion of a feedstock comprising ethanol into butadiene, are significantly improved and seem to have reached a plateau (they no longer change or change very little). Thus, an additive/metal molar ratio above 30 can lead to excessive consumption of additive without any additional effect on the catalytic performance of the catalyst obtained.

The metal precursor(s) and the additive(s) 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 additive(s) are distributed uniformly in the organic solution at the end of step a). The organic solution may then be said to be homogeneous.

In step a), several organic solutions, for example two or three organic solutions, can be prepared. The organic solutions then prepared can each advantageously contain a metal precursor identical or different between said organic solutions, of an element from group 3, group 4 and/or group 5 identical or different between the organic solutions prepared, and at least one additive identical or different between them. In the case where several 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 organic solutions prepared into contact at least once with the oxide matrix (or support).

Preferably, step a) of preparing the 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 organic solution very advantageously comprises mixing said at least one metal precursor and said at least one additive, optionally with the organic solvent.

Step a) thus makes it possible to prepare at least one 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 additive very advantageously chosen from hydroxy acids and their anhydrides, keto acids and their anhydrides, hydroketones, diketones, beta-hydroxyesters, beta-ketoesters, hydrogen halides, hydrogen halide precursors, and mixtures thereof, optionally in an organic solvent, in particular oxygenated.

Said 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 specific surface area S _BET of at least 250 m²/g, preferably between 250 m²/g and 700 m²/g and even more preferably between 400 m²/g and 600 m²/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 B.E.T. specific surface area (S_BETin m²/g) determined by nitrogen adsorption in accordance with ASTM D 3663-78 established from the BRUNAUER-EMMETT-TELLER method described in the periodical “The Journal of American 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 obtained according to the BJH model is described in the periodical «The Journal of 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/P⁰ _maxof the nitrogen adsorption-desorption isotherm. The nitrogen adsorption volume is the volume measured for P/ P⁰ _max = 0.99, pressure for which it is assumed that nitrogen has filled all the pores. The diameter of the mesopores ϕ of the material tested, in particular of the oxide matrix, is determined by the formula 4000.V/S_BET.

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 500°C, more particularly between 100 and 300°C, or even between 100 and 250°C, for example for 1 to 24 hours, in particular for 2 to 16 hours. Advantageously, the oxide matrix which is brought into contact with the 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, relative to the total weight of the oxide matrix. However, the oxide matrix may optionally comprise traces of water, for example at a content greater than or equal to 0.5% by weight, or even between 0.5 and 2.5% 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 envisaged in particular without particular 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.

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 organic solution prepared in step a) into contact with the oxide matrix such that said volume of organic solution can correspond to the total or partial pore volume of said oxide matrix, and impregnating the 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 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 of 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 organic solutions are prepared in step a) as explained above in this description, etc. When the preparation method comprises a repetition step d), the 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 organic solution (step a) can also be repeated if necessary);

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

- a step c) of heat treatment advantageously comprising drying or drying then calcination;

then n times the succession of: a step b) of deposition, optionally followed by a step b') of maturation, followed by a step c) of heat treatment advantageously comprising drying or drying then 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 of 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.

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, preferentially from the element tantalum, the element niobium, the element zirconium, and mixtures thereof, preferentially 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 a silica-based oxide matrix 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, preferably between 300 and 360°C, at a pressure of between 0.05 and 2.00 MPa, preferably between 0.05 and 1.50 MPa, preferably between 0.08 and 1.00 MPa, and preferably at a space velocity of between 0.2 and 10 h ^-1 , preferably between 0.5 and 5 h ^-1 , preferably between 1 and 4 h ^-1 .

When the feedstock 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/SiO catalysts ₂

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:

Characteristic Unit Value BET surface m²/g 450 Porous volume ml/g 1.0 Porous diameter nm 10.4 Average ball size* mm 2

(*: 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, an additive is introduced into a volume V _EtOH of ethanol (which can contain up to 1% volume of water), to form an ethanolic solution. In other cases, no additive is introduced into said volume of ethanol V _EtOH . The volume of ethanol V _EtOH 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 pentaethanoate (Ta(OEt) ₅ ), is then introduced and diluted in a volume V _EtOH of ethanol (references) or in the ethanolic solution containing the additive, at a concentration corresponding to a targeted additive/Ta molar ratio. The organic solution is then homogenized with stirring.

The resulting organic solution 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 shown in Table 2.

Catalyst According to the invention Metallic precursor Additive Additive type Additive/Ta ratio (mol/mol) HAS No Ta(OEt) ₅ - - - B No Ta(OEt) ₅ pyruvic acid β-ketoacid 1 C Yes Ta(OEt) ₅ pyruvic acid β-ketoacid 7 D Yes Ta(OEt) ₅ lactic acid α-hydroxy acid 7 E No Ta(OEt) ₅ acetylacetone β-diketone 1 F Yes Ta(OEt) ₅ acetylacetone β-diketone 7 G Yes Ta(OEt) ₅ acetoin α-hydroxy ketone 7 H Yes Ta(OEt) ₅ 2-oxocyclopentane ethyl carboxylate β-ketoester 7 I No Ta(OEt) ₅ Acetyl chloride Precursor of HCl 1 I Yes Ta(OEt) ₅ Acetyl chloride Precursor of HCl 2.5 K Yes Ta(OEt) ₅ Acetyl chloride Precursor of HCl 5 L Yes Ta(OEt) ₅ Acetyl chloride Precursor of HCl 10 M Yes Ta(OEt) ₅ Acetyl chloride Precursor of HCl 20

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 and mass transfer problems. 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 M 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).

Catalyst According to the invention Additive Additive/Ta ratio (mol/mol) Gain in selectivity
(+/- uncertainty)
(% weight/weight) Productivity gain
(+/- uncertainty)
(%) HAS No - 0 - - B No pyruvic acid 1 + 0.2 (+/- 0.6) + 9% (+/- 4%) C Yes pyruvic acid 7 + 4.8 (+/- 0.6) + 39% (+/- 4%) D Yes lactic acid 7 + 3.8 (+/- 0.6) + 36% (+/- 4%) E No acetylacetone 1 + 0.6 (+/- 0.6) + 2% (+/- 4%) F Yes acetylacetone 7 + 4.4 (+/- 0.6) + 36% (+/- 4%) G Yes acetoin 7 + 2.1 (+/- 0.6) + 18% (+/- 4%) H Yes 2-oxocyclopentane ethyl carboxylate 7 + 4.7 (+/- 0.6) + 36% (+/- 4%) I No Acetyl chloride 1 + 0.9 (+/- 0.6) + 9% (+/- 4%) I Yes Acetyl chloride 2.5 + 2.8 (+/- 0.6) + 25% (+/- 4%) K Yes Acetyl chloride 5 + 3.5 (+/- 0.6) + 32% (+/- 4%) L Yes Acetyl chloride 10 + 4.2 (+/- 0.6) + 29% (+/- 4%) M Yes Acetyl chloride 20 + 4.2 (+/- 0.6) + 36% (+/- 4%)

Table 3 shows that the butadiene selectivity and the carbon productivity are definitely improved (i.e. beyond the uncertainty) when the conversion reaction is carried out in the presence of a catalyst in accordance with the invention, i.e. prepared in the presence of a sufficient quantity of an additive, in particular of the ketoacid, hydroxyacid, hydroxyketone, diketone, beta-multifunctionalized ester, or hydrogen halide type, compared to a conversion in the presence of a non-compliant catalyst prepared without additive (catalyst A) or with an insufficient quantity of additive (catalysts B, E, I).

Claims (15)

Method of preparing a catalyst, comprising:
a) a step of preparing at least one organic solution comprising:
at least one metallic precursor of at least one metallic element chosen from the elements of groups 3, 4 and 5 of the periodic table,
at least one additive, said at least one additive being a multifunctionalized organic acid compound, a multifunctionalized ketone compound, a beta-multifunctionalized ester compound, a hydrogen halide, a hydrogen halide precursor, or a mixture thereof,
said at least one metallic precursor and said at least one additive being present in the organic solution in quantities such that the additive/metal molar ratio between the number of moles of said at least one additive and the number of moles of the metallic element(s) provided by said at least one metallic precursor is greater than 2;
b) a step of depositing said at least one metallic precursor on an oxide matrix, by bringing the 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). Method according to claim 1, wherein the additive/metal molar ratio in step a) is between 2.1 and 30, preferably between 2.5 and 20, more preferably between 5 and 15. Method according to claim 1 or 2, 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. Method according to one of claims 1 to 3, wherein said at least one metallic precursor is tantalum pentachloride or tantalum pentaethanoate, optionally combined with a metallic precursor of the element niobium and/or with a metallic precursor of the element zirconium. Method according to one of claims 1 to 4, in which the additive is chosen from hydroxy acids and their anhydrides, keto acids and their anhydrides, polyacids and their anhydrides, hydroketones, diketones, beta-hydroxyesters, beta-ketoesters, hydrogen halides, hydrogen halide precursors, and mixtures thereof, The method of claim 5, wherein the additive is selected from pyruvic acid, lactic acid, tartaric acid, malic acid, citric acid, oxalic acid, glycolic acid, mandelic acid and their anhydrides, 3-hydroxybutanone, pentane-2,4-dione, ethyl acetoacetate, ethyl 2-oxocyclopentanecarboxylate, diethyl malonate, hydrogen chloride, hydrogen bromide, hydrogen iodide, formyl chloride, acetyl chloride, propionyl chloride, butyryl chloride, and mixtures thereof. Method according to one of claims 1 to 6, in which the organic solution of step a) comprises an organic solvent. Method according to one of claims 1 to 7, in which the oxide matrix comprises silica, preferably at least 90% by weight of silica relative to the total mass of the oxide matrix. Method according to one of claims 1 to 8, in which step c) of heat treatment comprises drying, the drying preferably being carried out at a temperature between 50 and 200°C for a duration between 1 and 24 hours, preferably under a gas flow. Method according to claim 9, in which step c) of heat treatment comprises calcination following said drying, the calcination being carried out under gas flow, at a temperature between 350 and 700°C, for a duration between 1 and 6 h. 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. Catalyst according to claim 11, wherein 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, more preferably between 0.5 and 5% by weight of metallic element(s) relative to the weight of the oxide matrix. 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, at a pressure between 0.05 and 2.00 MPa. 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 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. Conversion process according to claim 14, wherein the feed comprises ethanol and acetaldehyde, preferably in a molar ratio of ethanol to acetaldehyde of between 1 and 5.