Process for the preparation of catalysts by organic methods in the presence of polyfunctional acid additives

Abstract

This invention relates to a method for preparing a catalyst, comprising: a) preparing an organic solution comprising: at least one metal precursor selected from elements of Groups 3, 4, and 5 of the periodic table, such as tantalum and zirconium; and at least one polyfunctional acid additive, preferably selected from hydroxy acids, keto acids, polybasic acids, their anhydrides, and mixtures thereof; wherein the metal precursor and the polyfunctional acid additive are present in the organic solution in an amount such that the acid / metal molar ratio between the polyfunctional acid additive and the metal element provided by the metal precursor is greater than 1; b) depositing the metal precursor onto the oxide matrix by contacting the organic solution with the oxide matrix; and then c) heat treatment. The invention also relates to the obtained catalyst and its use in converting a feedstock containing ethanol into butadiene.

Description

Technical Field

[0001] This invention relates to a method for manufacturing supported metal oxide catalysts of Group 3, 4, and / or 5 elements with improved performance. More particularly, this invention relates to a method for preparing a heterogeneous catalyst comprising at least one metal element selected from Group 3, 4, and 5 elements of the periodic table deposited on an oxide matrix by contacting the oxide matrix with an organic solution containing at least one precursor of the metal element, wherein the organic solution further contains a multifunctional acid additive. This invention also relates to the catalyst obtained by the aforementioned preparation method and the use of the catalyst for converting a feedstock containing at least ethanol into butadiene. This invention further relates to a method for converting a feedstock containing at least ethanol into butadiene, particularly comprising steps corresponding to the method for preparing a heterogeneous catalyst according to the invention. Existing technology

[0002] Supported metal oxides are a class of heterogeneous catalysts comprising one or more types of charged metal oxides deposited on the surface of a support material, such as silica (SiO2), alumina (Al2O3), titanium dioxide (TiO2), zirconium oxide (ZrO2), magnesium oxide (MgO), and mixtures thereof. Examples of commonly used metal oxides include those from groups 3 to 10, as they are capable of forming numerous catalysts for the synthesis of a wide variety of chemicals. For example, supported tantalum oxide catalysts possess diverse active sites (acid-base and redox), thus enabling them to catalyze many industrially relevant chemical reactions, including the production of 1,3-butadiene (also referred to as butadiene in this specification) from ethanol, the decomposition of methyl tert-butyl ether into isobutene and methanol, the Beckmann rearrangement, and olefin epoxidation. Similarly, they can be used for photocatalysis and electrocatalysis.

[0003] For example, US Patent 2,421,361 describes the use of niobium-based or tantalum-based catalysts in a method for converting a mixture of ethanol and acetaldehyde into butadiene, the catalysts being prepared, in particular, by contacting silica with an aqueous solution of citric acid containing niobium or tantalum precursors.

[0004] For any catalyst composed of metal elements deposited on a support, a specific dispersion and distribution of the metal element, such as tantalum, can be pursued as a characteristic of the catalyst. The atomic-level dispersion of metal elements is known to influence the selectivity and activity of the catalyst by modulating the properties of the active sites. Completely independently, controlling the distribution of metal elements within the support particles is another parameter explored to manage intraparticle diffusion limitations in the presence of such limitations. In the absence of interparticle diffusion limitations, it is generally known to utilize the entire available surface area and volume, especially for catalytic performance considerations.

[0005] There is still a need to improve the catalytic performance, such as selectivity, of heterogeneous catalysts containing metals selected from Groups 3, 4 and / or 5, and optionally improve the distribution of the metals on the catalyst support.

[0006] In the preparation of catalysts containing elemental tantalum, the use of commercial tantalum precursors soluble in organic media, such as tantalum alkoxides or tantalum halides, is widely described, for example in patent application WO 2017 / 009107 or in Corson's 1950 article (BB Corson et al., Butadiene from Ethyl Alcohol. Catalysis in the One- and Two-Step Processes). Industrial and Engineering Chemistry. In 1950, 42 (2), 359-373). However, tantalum alkoxide or halide precursors may have the disadvantage of being extremely sensitive to hydrolysis. The formation of tantalum hydroxide functional groups leads to the formation of tantalum clusters, and may therefore lead to changes in or even limitation of catalytic performance (see Ambreen, S. et al., Characterization and photocatalytic study of tantalum oxide nanoparticles prepared by the hydrolysis of tantalum oxo-ethoxide Ta8(μ3-O)2(μ-O)8(μ-OEt)6(OEt). 14 . Beilstein J. Nanotechnol. 2014, 5, 1082–1090).

[0007] To limit hydrolysis, it appears necessary to limit the amount of water present in the support, for example, by rigorous drying of the support, especially at temperatures above 100°C, preferably at 150°C for several hours. To further limit the hydrolysis of the tantalum or niobium precursor (which is a Group 5 element), the precursor can be modified by adding additives.

[0008] The literature contains a wide range of complexing agents, with varying degrees of success. For example, studies exist on the reactions of Group 5 elements, particularly tantalum and niobium, with the following compounds: - Diketones, such as acetylacetone (see 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). - Keto esters (see Mehrotra RC, Kapoor PN, Organic Compounds of Tantalum. Reactions of tantalum pentaethoxide with β-keto esters. J. Less- Common Metals , 7 (1964) 453-457). - Hydroxy esters (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 (see 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).

[0009] While these documents detail the reactions and properties of the formed complexes, they do not specify the effects and uses of such Ta or Nb complexes in the preparation of heterogeneous catalysts. Patent application WO 2022 / 165190 describes the use of acetylacetone in the preparation of tantalum-based catalysts deposited on silica. Patent application CN115364844 describes the preparation of tantalum-silica catalysts by contacting silica with an organic solution containing a tantalum precursor and anhydrous citric acid.

[0010] The present invention aims to prepare heterogeneous catalysts containing at least one metal element, particularly metal elements selected from Groups 3, 4 and 5, which exhibit good catalytic performance, or even performance gains, compared with prior art catalysts, especially in terms of selectivity and productivity, and particularly in the conversion of ethanol-containing feedstocks into butadiene, and preferably exhibit better metal element distribution throughout the support. Summary of the Invention

[0011] This invention therefore relates to a method for preparing a catalyst, comprising: a) The step of preparing at least one organic solution, said organic solution comprising: At least one metallic precursor selected from at least one metallic element in Groups 3, 4, and 5 of the periodic table. At least one multifunctional acid additive. The at least one metal precursor and the at least one polyfunctional acid additive are present in an organic solution such that the acid / metal molar ratio between the number of moles of the at least one polyfunctional acid additive and the number of moles of the metal element from the at least one metal precursor is greater than 1. b) A step of depositing the at least one metal precursor onto the oxide matrix to obtain a solid by contacting the organic solution prepared in step a) with the oxide matrix; c) The step of heat-treating the solid obtained in step b).

[0012] This method enables the production of catalysts with satisfactory or even improved catalytic performance (particularly in terms of selectivity and productivity) during the conversion of ethanol-containing feedstocks to butadiene. The present invention therefore has the advantage of enabling the simple preparation of catalysts with satisfactory or even improved performance at a reasonable production cost. The method according to the invention also allows for better distribution of the metal element within the particles of the support (i.e., the oxide matrix), limiting the risk of catalyst activity loss due to wear during use.

[0013] The present invention also relates to a catalyst obtained by the preparation method according to the invention, and comprising elements selected from Groups 3, 4 and 5 of the periodic table, preferably selected from yttrium, zirconium, hafnium, niobium, tantalum and mixtures thereof, preferably selected from elemental tantalum, elemental niobium and / or elemental zirconium, preferably at least one metallic element of elemental tantalum, and preferably an oxide matrix based on silica.

[0014] The present invention also relates to the use of the catalyst in converting a feedstock containing ethanol into butadiene at a temperature between 250 and 450°C and a pressure between 0.05 and 2.00 MPa.

[0015] Finally, according to another aspect, the present invention relates to a method for converting a feedstock containing at least ethanol into butadiene, the method comprising: The step of converting a feedstock containing ethanol into butadiene is carried out in the presence of a catalyst prepared according to the preparation method, at a temperature between 250 and 450°C and at a pressure between 0.05 and 2.00 MPa.

[0016] Description of the implementation plan According to the present invention, the expressions "of between ... and ..." and "...to ..." are equivalent and refer to the fact that the limit values ​​of the interval are included within the described numerical range. If this is not the case and if the limit values ​​are not included within the described range, this will be indicated in this specification.

[0017] In this specification, various ranges of parameters for a given step, such as pressure ranges and temperature ranges, can be used individually or in combination. For example, in this specification, a preferred range of pressure values ​​can be combined with a more preferred range of temperature values.

[0018] Specific embodiments of the invention are described below. They may be implemented individually or in combination, and there is no limitation on the combination where technically feasible.

[0019] According to the present invention, the pressure is absolute pressure and is given in absolute MPa (or MPa abs).

[0020] According to the present invention, time and duration are expressed in hours (h), minutes (min) and / or seconds (sec).

[0021] In this specification, the term "room temperature (T)" is used. room "" corresponds to a temperature of 20°C ± 5°C (the abbreviation "±" means "addition or subtraction", and "20°C ± 5°C" means between 15 and 25°C), and the term "atmospheric pressure" refers to a pressure of approximately 0.1 MPa, that is, between 0.05 MPa and 0.15 MPa, preferably between 0.08 MPa and 0.12 MPa, and typically 0.101325 MPa.

[0022] The terms “upstream” and “downstream” should be understood in accordance with the general flow of the fluid or material flow considered in this method.

[0023] The present invention relates to a method for preparing a catalyst, the catalyst being called a heterogeneous catalyst, comprising at least one metallic element selected from elements of Groups 3, 4 and 5 of the periodic table, preferably selected from yttrium, zirconium, hafnium, niobium, tantalum and mixtures thereof, more preferably zirconium, niobium, niobium and mixtures thereof, and very preferably tantalum, and an oxide matrix, preferably a silica-based matrix.

[0024] The preparation method according to the present invention comprises the following steps, and very specifically consists of the following steps: a) The step of preparing at least one organic solution, said organic solution comprising at least one metallic precursor of at least one metallic element selected from elements of Groups 3, 4 and 5 of the periodic table, at least one polyfunctional acid additive very advantageously selected from hydroxy acids, keto acids, polybasic acids (e.g., diacids and tricids), their anhydrides and mixtures thereof, and optionally an organic solvent. The at least one metal precursor and the at least one polyfunctional acid additive are present in an organic solution such that the (acid / metal) molar ratio between the number of moles of the at least one polyfunctional acid additive and the number of moles of the metal element from the at least one metal precursor is greater than 1, preferably greater than or equal to 2, preferably between 2 and 20, and more preferably between 5 and 15. b) A step of depositing the at least one metal precursor onto the oxide matrix by contacting the organic solution prepared in step a) with the oxide matrix to obtain a solid. b') Optionally, the maturation step of the solid obtained in step b) c) A step of heat-treating the solid obtained in deposition step b) or optional aging step b'), preferably including drying or drying followed by calcination. Drying is advantageously carried out at a temperature between 50°C and 200°C, preferably between 80°C and 150°C, for a time between 1 and 24 hours, advantageously under a gaseous flow, preferably under an air flow; When combined with step c), calcination is advantageously carried out in a gaseous stream, preferably an oxygen-containing gaseous stream, at a temperature between 350°C and 700°C, preferably between 450°C and 600°C, for a time between 1 and 6 hours, preferably between 2 and 4 hours; and d) Optionally repeat the sequence of deposition step b) and heat treatment step c), or optionally repeat the sequence of deposition step b), subsequent ripening step b') and then heat treatment step c).

[0025] Advantageously, step a) of the preparation method allows for the preparation of at least one organic solution containing at least one metal precursor, preferably one or two metal precursors, and very particularly one metal precursor containing at least one metal element selected from Groups 3, 4, and 5 of the periodic table, i.e., at least one metal precursor of at least one metal element selected from Groups 3, 4, and 5 of the periodic table, preferably one or two of at least Group 3, Group 4, and / or Group 5 elements, and very particularly one metal precursor. Preferably, the metal precursor or each metal precursor contains a metal element selected from Groups 3, 4, and 5 of the periodic table. The metal precursor or each metal precursor may optionally contain another element selected from groups other than Groups 3, 4, and 5 of the periodic table.

[0026] The at least one metallic precursor, selected from at least one metallic element of Group 3, Group 4, and / or Group 5 of the periodic table, is advantageously selected particularly 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, with tantalum being very preferred. According to a highly preferred embodiment of the invention, the at least one metallic precursor is a metallic precursor of element tantalum, optionally combined with a metallic precursor of element niobium and / or a metallic precursor of element zirconium.

[0027] Advantageously, the metal precursor selected from at least one metallic element of Groups 3, 4, and / or 5, such as tantalum, is any compound containing at least one element of Groups 3, 5, and / or 4, such as tantalum, and capable of releasing the element in a reactive form in solution. Therefore, the metal precursor used is an organic or inorganic compound containing the metal element of Groups 3, 4, and / or 5, and is advantageously at least partially and preferably completely soluble in an organic solution under the temperature and pressure conditions used, particularly in steps a) and b) of the preparation method. The organic or inorganic compound is particularly selected from halides, nitrates, sulfates, phosphates, hydroxides, carbonates, carboxylates, alkoxides, diketones, amines, and cyclopentadienyl groups of the metal element of Groups 3, 4, and / or 5, and combinations of two or more thereof, more preferably from chlorides, nitrates, carboxylates, alkoxides, and diketones of the metal element of Groups 3, 4, and / or 5, and combinations of two or more thereof. For example, an alkoxide precursor has the formula M(OR). nIn this system, M is a group n metallic element of the periodic table, n is an integer equal to 3, 4, or 5, preferably M is Ta, Nb, or Zr, very preferably Ta, and R is a group selected from alkyl groups, such as ethyl, isopropyl, n-butyl, sec-butyl, or tert-butyl. For example, preferred tantalum metal precursors are tantalum pentachloride (TaCl5) and tantalum pentaethoxy (Ta(OC2H5)5 or Ta(OEt)5), which can be used with most organic solvents. Niobium metal precursors can be selected from niobium pentachloride (NbCl5) and niobium pentaethoxy (Nb(OC2H5)5 or Nb(OEt)5). Zirconium metal precursors can be selected from zirconium tetrachloride (ZrCl4) and zirconium tetraethoxy (Zr(OC2H5)4 or Zr(OEt)4). According to a highly preferred embodiment of the invention, the at least one metal precursor is tantalum pentachloride (TaCl5) or tantalum pentaethoxylate (Ta(OC2H5)5 or Ta(OEt)5), which is optionally combined with a metal precursor of element niobium and / or a metal precursor of element zirconium.

[0028] The organic solution prepared in step a) of the method according to the invention contains, in addition to at least one metal precursor of at least one element of Group 3, 4 and / or 5 of the periodic table, at least one polyfunctional acid additive and optional organic solvent.

[0029] The at least one polyfunctional acid additive may also optionally be referred to as a polyfunctional acid compound. The polyfunctional acid additive is advantageously an organic compound comprising a carboxylic acid or carboxylic acid generating function (i.e., an acid anhydride capable of generating an acid, particularly in an alcoholic medium) and at least a second chemical function, which is advantageously oxidized, nitrided, or sulfided, preferably at position 1 (α position, i.e., on the carbon directly adjacent to the acid-functional carbon), at position 2 (β position, i.e., on the second carbon adjacent to the acid-functional carbon), at position 3 (γ position, i.e., on the third carbon adjacent to the acid-functional carbon), or at position 4 (δ position, i.e., on the fourth carbon adjacent to the acid-functional carbon). The polyfunctionalized acid additive is preferably an organic compound comprising a carboxylic acid or carboxylic acid-forming function (i.e., an anhydride capable of forming an acid, particularly in an alcoholic medium), and at least one hydroxyl and / or carbonyl function, preferably located at position 1 (α position, i.e., on the carbon directly adjacent to the carbon of the acid function), position 2 (β position, i.e., on the second carbon adjacent to the carbon of the acid function), position 3 (γ position, i.e., on the third carbon adjacent to the carbon of the acid function), or position 4 (δ position, i.e., on the fourth carbon adjacent to the carbon of the acid function). The polyfunctionalized acid additive may include a plurality of second chemical functions, particularly oxidized ones, such as a plurality of hydroxyl and / or carbonyl functions, like tartaric acid, which, in addition to the first carboxylic acid function, includes one carbonyl function and three hydroxyl functions (particularly one carboxylic acid function and two hydroxyl functions).

[0030] The at least one multifunctional acid additive is preferably selected from hydroxy acids, keto acids, polybasic acids (e.g., diacids and tricids), their anhydrides, and mixtures thereof. According to the invention, the term "hydroxy acid" refers to any compound, or a derivative thereof, preferably having carboxylic acid and hydroxyl functionalities at the α, β, γ, or δ positions (very preferably at the α or β positions), and the term "derivative" herein refers to its oligomers, particularly containing 2 to 20 repeating units, optionally in a cyclic form (i.e., lactone form). Specifically, hydroxy acids are known to have an oligomerization tendency, i.e., condensation into linear or cyclic oligomers, particularly when they are in concentrated solutions. For example, as the concentration of lactic acid in an aqueous solution increases, lactic acid oligomers form lactic acid oligomers containing 2 to 20 repeating units, more particularly 2 to 10 repeating units (see 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 dilactides. Therefore, in the method according to the invention, the hydroxy acid that can be conceived as a polyfunctionalized acid additive can be in the form of a monomeric compound of a hydroxy acid whose hydroxyl function is preferably at the α, β, γ or δ position, or in the form of an oligomer of said hydroxy acid in a cyclic (e.g., dilactide) or linear form. Therefore, in this specification, the terms “hydroxy acid” and “α-hydroxy acid”, “β-hydroxy acid”, “γ-hydroxy acid” and “δ-hydroxy acid” should be understood as “hydroxy acid and its derivatives” and “α-hydroxy acid and its derivatives”, “β-hydroxy acid and its derivatives”, “γ-hydroxy acid and its derivatives” and “δ-hydroxy acid and its derivatives”, respectively. Similarly, the various specific hydroxy acids mentioned in this specification, such as lactic acid, tartaric acid, malic acid, mandelic acid, and levulinic acid, correspond to the specific acids in the form of monomers and their oligomeric derivatives, such as lactic acid and its derivatives, tartaric acid and its derivatives, malic acid and its derivatives, mandelic acid and its derivatives, and levulinic acid and its derivatives, respectively.

[0031] Preferably, the at least one polyfunctional acid additive is selected from α-hydroxy acids, β-hydroxy acids, γ-hydroxy acids, δ-hydroxy acids, α-keto acids, β-keto acids, γ-keto acids, δ-keto acids, α-diacids, β-diacids, γ-diacids, δ-diacids, their anhydrides, and mixtures thereof. For example, the polyfunctional acid additive may be selected from pyruvic acid, lactic acid, tartaric acid, malic acid, acetoacetic acid, citric acid, oxalic acid, glycolic acid, salicylic acid, mandelic acid, benzoylcarboxylic acid, α-ketoglutaric acid and β-ketoglutaric acid, succinic acid, levulinic acid, maleic acid, their anhydrides, and mixtures thereof. Preferably, the at least one polyfunctional acid additive is selected from α-hydroxy acids, β-hydroxy acids, α-keto acids, β-keto acids, α-diacids, β-diacids, their anhydrides, and mixtures thereof. More specifically, the at least one polyfunctional acid additive is selected from pyruvate, 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 mixtures thereof. Preferably, the at least one polyfunctional acid additive is selected from α-hydroxy acids, α-keto acids, α-diacids, their anhydrides and mixtures thereof, such as pyruvate, lactic acid, tartaric acid, malic acid, citric acid, oxalic acid, glycolic acid, mandelic acid, their anhydrides and mixtures thereof.

[0032] Preferably, the organic solution prepared in step a) contains one or two polyfunctional acid additives, preferably one polyfunctional acid additive, advantageously as defined above in this specification. In addition to the at least one polyfunctional acid additive, the organic solution may optionally contain another additive, for example selected from diketones (such as acetylacetone), hydroxy esters, keto esters (especially β-keto esters), hydroxy ketones, hydrogen halides, or hydrogen halide precursors, which are capable of releasing dissolved hydrogen halide (such as acyl halides, for example acetyl chloride) in the organic solvent of the organic solution.

[0033] The organic solution may also contain an organic solvent to provide a “homogeneous” organic solution, as explained later in this specification. Preferably, the organic solution contains an organic solvent, preferably at least 5% by weight, or even at least 20% by weight, and for example, up to 90% by weight or 75% by weight, the percentages being by weight of the organic solvent relative to the total weight of the organic solution. When present in the organic solution, the organic solvent is very advantageously selected from organic compounds, wherein the at least one polyfunctional acid additive and at least one metal precursor are soluble. Advantageously, when present, the organic solvent of the organic solution prepared in step a) contains at least one organic compound, preferably consisting of at least one organic compound, and preferably an oxygen-containing organic compound (referred to as an oxidizing organic solvent). More particularly, the organic solvent is selected from alcohols, carboxylic acids, ethers, esters, ketones, and mixtures thereof. The organic solvent may optionally contain water. Alcohols that can be used as organic solvents preferably contain between 1 and 6 carbon atoms (i.e., C1-C6), more preferably between 1 and 4 carbon atoms (i.e., C1-C4), and particularly monohydric alcohols containing 1, 2, 3, or 4 carbon atoms, especially straight-chain, branched, or cyclic, and preferably non-aromatic alcohols. Alcohols that can be used as organic solvents are selected from, for example, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, tert-butanol, and mixtures thereof. Preferably, carboxylic acids that can be used as organic solvents are carboxylic acids containing between 2 and 4 carbon atoms (i.e., C2-C4), especially straight-chain, branched, or cyclic, and preferably non-aromatic carboxylic acids. Carboxylic acids that can be used as organic solvents are selected from, for example, acetic acid, propionic acid, and butyric acid. Ethers optionally used as organic solvents are preferably C4-C8 ethers, especially straight-chain, branched, or cyclic, and preferably non-aromatic ethers, such as tetrahydrofuran (THF), ethylene glycol, or diisopropyl ether. The esters that can be used as organic solvents are preferably C1-C6, preferably C2-C6 of C1-C4 alcohols, and preferably C2-C4 carboxylic acid esters, especially straight-chain, branched, or cyclic esters. Non-aromatic esters are advantageous, such as methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, ethyl propionate, or ethyl acetoacetate. Preferably, the ketones optionally used as organic solvents are selected from diketones, such as acetylacetone. For example, the organic solvent comprises at least one oxygen-containing organic compound, preferably composed of at least one oxygen-containing 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 propionate, acetylacetone, and mixtures thereof, particularly selected from methanol, ethanol, propanol, isopropanol, isobutanol, tert-butanol, acetic acid, propionic acid, isopropyl acetate, and mixtures thereof. When the multifunctional acid additive is an anhydride (i.e., a keto acid, a hydroxy acid, or a dianhydride), the organic solution contains an organic solvent, and the organic solvent contains at least one alcohol, preferably at least 10% by weight, and more preferably at least 50% by weight.

[0034] The metal precursor of at least one element of Group 3, 4 and / or 5 and the polyfunctional acid additive are present in an organic solution such that the molar number of the polyfunctional acid additive relative to the molar number of the metal element from the metal precursor, i.e., the total molar number of Group 3, 4 and 5 elements (e.g., element tantalum), is greater than 1, preferably greater than or equal to 2, preferably between 2 and 20, and more preferably between 5 and 15.

[0035] The metal precursor and the polyfunctional acid additive can be dissolved, diluted, and / or suspended (advantageously in colloidal form) in the organic solution prepared in step a). Regardless of their form, the metal precursor and the polyfunctional acid additive are uniformly distributed in the organic solution at the end of step a). The organic solution can then be said to be homogeneous.

[0036] During step a), multiple organic solutions, such as two or three organic solutions, can be prepared. The prepared organic solutions may then advantageously each contain the same or different metal precursors from Group 3, Group 4, and / or Group 5 elements, which are the same or different among the prepared organic solutions, and at least one polyfunctional acid additive, which is the same or different among them. In the case of preparing multiple organic solutions, the method of preparing the catalyst advantageously includes repeating step d) at least the deposition step b) and the heat treatment step c) in such a way that each prepared organic solution is contacted with the oxide matrix (or support) at least once.

[0037] 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 advantageously includes mixing the at least one metal precursor and the at least one polyfunctionalized acid additive optionally with an organic solvent.

[0038] Therefore, step a) allows the preparation of at least one organic solution comprising at least one metal precursor of at least one element of Group 3, Group 4 and / or Group 5 of the periodic table, and at least one polyfunctional acid additive, very advantageously selected from hydroxy acids, keto acids, polybasic acids, their anhydrides and mixtures thereof, optionally, in particular, an oxygen-containing organic solvent.

[0039] The organic solution obtained in step a) can then be contacted with the oxide matrix to obtain a solid. This contacting step corresponds to step b) of the preparation method according to the invention, which is the step of depositing the metal precursor onto the oxide matrix.

[0040] The oxide matrix, also referred to as a carrier, is typically in particle form. Preferably, the oxide matrix comprises silica; the oxide matrix is ​​thus referred to as a silica-based oxide matrix. It preferably contains at least 90% by weight (i.e., between 90% and 100% by weight), more preferably at least 95% by weight (i.e., 95% to 100%), more preferably at least 98% by weight (i.e., 98% to 100%), and even more preferably at least 99.5% by weight (i.e., 99.5% to 100%) silica relative to the total mass of the oxide matrix. The oxide matrix advantageously contains pores, particularly mesopores. The average pore diameter (or average pore size) of the oxide matrix, particularly the silica-based oxide matrix, 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, particularly the silica-based matrix, is between 0.4 and 1.8 ml / g, and especially between 0.5 and 1.5 ml / g. Preferably, the oxidizing matrix has an S content of at least 250 m² / g, more preferably between 250 m² / g and 700 m² / g, and even more preferably between 400 m² / g and 600 m² / g. BET Specific surface area.

[0041] The aforementioned structural parameters were determined using an analytical technique known as "nitrogen volumetry," which corresponds to the physical adsorption of nitrogen molecules into the pores of the material by gradually increasing pressure at a constant temperature. According to the invention, the specific surface area, particularly the specific surface area of ​​the oxide matrix, corresponds to the area determined by the journal "..." The Journal of the American Chemical Society The standard ASTM D 3663-78, established by the Brunauer-Emmett-Teller method described in 1938, 60, 309, measures the BET specific surface area (in m²) by nitrogen adsorption, as determined by nitrogen adsorption. 2 S in g BET The pore distribution, representing the mesoporous population, was determined using the Barrett-Joyner-Halenda (BJH) model. Nitrogen adsorption-desorption isotherms derived from the BJH model are described in the journal "..." by EP Barrett, LG Joyner, and PP Halenda. The Journal of the American Chemical Society In 1951, 73, 373, the pore volume V was defined as the partial pressure P / P corresponding to the nitrogen adsorption-desorption isotherm. 0 max The observed volume value. The nitrogen adsorption volume is at P / P 0 max= 0.99, the volume measured at this pressure assuming nitrogen fills all pores. The mesopore diameter ϕ of the tested material, particularly the oxide matrix, is obtained using the formula ϕ = 4000.V / S BET Measurement.

[0042] Optionally, the oxide matrix may contain trace amounts of water, for example, greater than or equal to 0.5% by weight relative to the total weight of the oxide matrix. The presence of trace amounts of water in the support does not appear to affect the quality of the obtained heterogeneous catalyst, particularly its catalytic performance, such as selectivity and productivity, especially during the reaction of converting a feedstock containing ethanol to butadiene. Therefore, operational limitations can be mitigated by relaxing the requirements for operating with dry materials, for example: pre-drying of the oxide matrix can be avoided or reduced (e.g., drying the oxide matrix at 100°C for 2 hours may be sufficient); storage of the oxide matrix can be considered, in particular, without any specific humidity conditions; handling the oxide matrix in a dry atmosphere can be avoided; drying of the organic solvent is not necessary. Therefore, the method according to the invention can reduce the energy consumption and cost of the preparation process.

[0043] Optionally, the oxide matrix may be dried, for example, in a stationary or circulating furnace 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 10 minutes to 24 hours, particularly 1 to 16 hours, prior to step b). Advantageously, the oxide matrix in contact with the organic solution in step b) has a water content preferably less than or equal to 5% by weight relative to the total weight of the oxide matrix, preferably less than or greater than 2.5% by weight, or even between 0.5% by weight and 2.5% by weight.

[0044] The oxide matrix, particularly a silica-based matrix, can be commercially available or synthesized according to methods known to those skilled in the art. The oxide matrix, particularly a silica-based matrix, can be used directly in powder form or pre-formed, particularly in the form of granulated, crushed, and sieved powders, beads, pellets, granules, or extrusions (hollow or filled cylinders, multi-leaved cylinders with, for example, 2, 3, 4, or 5 leaves, twisted cylinders), or rings, etc. These forming operations are performed using conventional techniques known to those skilled in the art. For example, the oxide matrix, particularly a silica-based matrix, is optionally in the form of spherical beads or extrusions, preferably having a size between 0.5 and 10 mm, more preferably between 1.0 and 5 mm.

[0045] The contact in step b), namely the deposition of the at least one metal precursor onto the oxide matrix, can be performed using any method known to those skilled in the art. For example, but not exhaustively, methods such as dry impregnation, over-impregnation, CVD (chemical vapor deposition), CLD (chemical liquid deposition), etc., can be used. For example, step b) of the method for preparing a catalyst according to the invention preferably includes, preferably, contacting a certain volume of the organic solution prepared in step a) with the oxide matrix such that the volume of organic solvent corresponds to all or part of the pore volume of the oxide matrix, and impregnating the organic solution onto the surface of the oxide matrix to ensure that the at least one metal precursor is dispersed across the entire surface of the oxide matrix. Most advantageously, the contact and impregnation are performed at a temperature between room temperature and 80°C and at a pressure between atmospheric pressure and 3.0 MPa.

[0046] Optionally, step b') of aging the obtained solid can be performed after deposition step b) to further promote the dispersion and distribution of the at least one metal precursor on the entire surface of the oxide matrix. For example, the aging step can be carried out for a duration of 1 to 5 hours, particularly 2 hours, at a pressure between atmospheric and 3.0 MPa, between room temperature and 80°C.

[0047] The method for preparing the catalyst according to the present invention further includes step c) of heat treatment of the solid obtained in the deposition step b) or optionally the ripening step b').

[0048] Preferably, heat treatment step c) includes, preferably, drying or drying followed by calcination, preferably drying followed by calcination. Drying is very advantageously carried out at a temperature between 50 and 200°C, and preferably between 80 and 150°C, for a period of 1 to 24 hours, advantageously under a gaseous feed, preferably under an air feed, for example in an oven. Calcination, when carried out in step c) of the catalyst preparation method, is advantageously carried out under a gaseous feed, preferably under a gaseous feed containing oxygen, for example under an air feed, at a temperature between 350 and 700°C, preferably between 450 and 600°C, for a period of 1 to 6 hours, and preferably between 2 and 4 hours.

[0049] Optionally, the deposition step b) and the heat treatment step c), or optionally steps b), b'), and then c), can be repeated n times, where n is an integer between 1 and 10, preferably an integer between 1 and 5. Therefore, the catalyst preparation method may include repeating step d), for example, in the case where the target catalyst contains multiple metal elements of Group 3, Group 4, and / or Group 5, such as element Nb and element Ta or element Ta and element Zr; or to achieve a target content of metal elements in the prepared catalyst; or in the case of preparing multiple organic solutions as explained above in step a), etc. When the preparation method includes repeating step d), the organic solution is then contacted with the heat-treated solid in step c) during the first repetition, or with the heat-treated solid in the (i-1)th heat treatment step during the i-th repetition, where i is an integer between 2 and n. When it includes repeating step d), i.e., repeating steps b) and c) n times, or optionally b), b'), and c), the method for preparing the catalyst therefore includes: - At least one step a) of preparing the organic solution (if necessary) may also be repeated; - Deposition step b), optionally followed by ripening step b'), and then - Heat treatment step c), which advantageously includes drying or drying followed by calcination; Then the following sequence is repeated n times: deposition step b), optionally followed by ripening step b'), followed by heat treatment step c), which advantageously includes drying or drying followed by calcination, and a final heat treatment (i.e. the nth heat treatment), which preferably includes drying followed by calcination.

[0050] The catalyst obtained in step c) or optionally step d) is a heterogeneous catalyst containing at least one Group 3, Group 4 and / or Group 5 metal element deposited on a support (or oxide matrix), particularly silica-based.

[0051] The preparation method may optionally include a step of shaping the obtained catalyst, which may subsequently undergo thermal post-treatment, particularly when the oxide matrix used in step b) is in unshaped powder form. Thus, in this optional shaping step, at the end of step c) or possibly step d), the catalyst may be shaped into granulated, crushed, sieved powder, beads, pellets, granules, or extrusions (hollow or filled cylinders, multi-lobed cylinders with, for example, 2, 3, 4, or 5 lobes, twisted cylinders), or rings, etc., these shaping operations being performed using conventional techniques known to those skilled in the art. Preferably, the catalyst is shaped into extrusions with a size between 1 and 10 mm, which are optionally spherical. During this optional shaping step, the catalyst may optionally be mixed with at least one porous oxide material acting as a binder to produce suitable physical properties of the catalyst (mechanical strength, abrasion resistance, etc.). The porous oxide material serving as the binder is preferably selected from silica, magnesium oxide, clay (such as kaolinite, serpentine, chrysotile, montmorillonite, bedecitex, vermiculite, talc, hydropyrite, soapstone, lithium soapstone), titanium oxide, titanates (e.g., zinc, nickel, or cobalt titanates), lanthanum oxide, cerium oxide, boron phosphate, and mixtures thereof. Very preferably, the binder used is essentially silicic and preferably does not comprise 5% to 60% by weight, more preferably 10% to 30% by weight, relative to the total mass of the catalyst to be finalized and optionally heat-treated. When heat-treated, its properties are similar, exhibiting properties similar to those of the heat treatment in step c) and following its operating conditions.

[0052] The catalyst obtained in step c) or possibly in step d), or even in an optional molding step, comprises at least one metallic element selected from Group 3, Group 4 and Group 5 elements, preferably selected from yttrium, zirconium, hafnium, niobium, tantalum and mixtures thereof, preferably selected from elemental tantalum, elemental niobium, elemental zirconium and mixtures thereof, very preferably tantalum, and preferably has a metallic element content of between 0.1 wt% and 30 wt% relative to the oxide matrix, preferably between 0.3 wt% and 10 wt%, preferably between 0.5 wt% and 5 wt%.

[0053] Advantageously, the obtained catalyst can be loaded into any type of catalytic reactor known to those skilled in the art, particularly axial, radial or tubular reactors, with or without heat exchange, and with or without multiple injections.

[0054] Therefore, the present invention also relates to a catalyst obtained by the preparation method according to the invention, comprising at least one metallic element selected from Groups 3, 4, and 5 of the periodic table, preferably selected from yttrium, zirconium, hafnium, niobium, tantalum, and mixtures thereof, preferably selected from elemental tantalum, elemental niobium, elemental zirconium, and mixtures thereof, very preferably elemental tantalum, and an oxide matrix, preferably a silica-based matrix. Preferably, the metallic element is present in an amount between 0.1 wt% and 30 wt%, preferably between 0.3 wt% and 10 wt%, more preferably between 0.5 wt% and 5 wt% relative to the oxide matrix. According to a highly preferred embodiment, the catalyst comprises a silica-based oxide matrix and tantalum in an amount between 0.5 wt% and 5 wt% relative to the oxide matrix. According to another embodiment, the catalyst comprises a silica-based oxide matrix and zirconium in an amount between 0.3 wt% and 10 wt% relative to the oxide matrix, particularly between 0.5 wt% and 5 wt%. According to another embodiment, the catalyst comprises a silica-based oxide matrix and niobium at a weight ratio of 0.3% to 10% relative to the oxide matrix, particularly between 0.5% and 5% by weight.

[0055] The method for preparing the catalyst according to the invention advantageously enables the simple and inexpensive acquisition of a heterogeneous catalyst comprising at least one Group 3, Group 4, and / or Group 5 metal element, particularly Nb and / or Ta and / or Zr, with Ta being very preferred. This catalyst provides highly satisfactory or even improved catalytic performance, particularly in selectivity and productivity, during the conversion of ethanol-containing feedstocks to butadiene, compared to prior art organically prepared catalysts. Such a method also ensures good dispersion of the Group 3, Group 4, and / or Group 5 metal element across the entire surface of the oxide matrix (i.e., good distribution of the metal element within the support particles).

[0056] The present invention also relates to the use of a catalyst obtained by the preparation method according to the invention for converting a feedstock containing at least ethanol into butadiene, wherein the catalyst comprises at least one metallic element selected from elements of Groups 3, 4, and 5 of the periodic table, preferably selected from yttrium, zirconium, hafnium, niobium, tantalum, and mixtures thereof, preferably selected from elemental tantalum, elemental niobium, elemental zirconium, and mixtures thereof, and preferably elemental tantalum, with the content of the metallic element preferably between 0.1 wt% and 30 wt% relative to the oxide matrix, preferably between 0.3 wt% and 10 wt%, more preferably between 0.5 wt% and 5 wt%. According to a preferred embodiment, the catalyst used comprises a silica-based oxide matrix and tantalum between 0.5 wt% and 5 wt% relative to the oxide matrix. The use of the obtained catalyst for converting a feedstock containing at least ethanol into butadiene is subsequently reflected in improvements in catalytic performance, particularly in selectivity and productivity. The operating conditions for the conversion reaction are preferably between 250 and 450°C, preferably between 270 and 380°C, preferably between 300 and 360°C, at a temperature 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 between 0.2 and 10 h⁻¹. -1 Between 0.5 and 5 h is preferred. -1 Between and preferably within 1 to 4 hours -1 The space velocity is defined as the flow rate ratio between the mass of the feedstock and the mass of the catalyst. When the processed feedstock also contains acetaldehyde, the ethanol / acetaldehyde molar ratio is between 1 and 5, preferably between 2 and 4.

[0057] According to another aspect, the present invention also relates to a method for converting a feedstock comprising ethanol and optionally acetaldehyde into butadiene, the method comprising at least: The step of converting a feedstock containing ethanol, preferably ethanol and acetaldehyde, into butadiene, wherein the molar ratio of ethanol to acetaldehyde is preferably between 1 and 5, more preferably between 2 and 4, wherein the conversion step is carried out in the presence of a catalyst prepared according to the above preparation method, and at a temperature between 250 and 450°C, preferably between 270 and 380°C, more preferably between 300 and 360°C, at a pressure between 0.05 and 2.00 MPa, more preferably between 0.05 and 1.50 MPa, more preferably between 0.08 and 1.00 MPa, and more preferably for 0.2 to 10 h. -1 Between 0.5 and 5 h is preferred. -1 Between, more preferably 1 to 4 hours -1 It is carried out at airspeed.

[0058] When the feedstock contains ethanol and acetaldehyde, the catalyst preferably contains elemental tantalum and a silica-based oxide matrix, wherein the content of tantalum in the catalyst is preferably between 0.3% by weight and 10% by weight relative to the silica-based oxide matrix, and particularly between 0.5% by weight and 5% by weight.

[0059] The following examples illustrate the present invention, particularly specific embodiments thereof, but do not limit its scope. Example

[0060] Catalysts were prepared according to the method described in Example 1. The catalysts were then tested: they were used to convert feedstocks containing ethanol and acetaldehyde, as described in Example 2.

[0061] Example 1: Preparation of 3% Ta / SiO2 catalyst Catalysts containing 3% by weight tantalum were prepared on silica beads (also known as silica supports), where the percentage of tantalum is given as the weight of elemental tantalum relative to the weight of the silica beads. The preparation methods for each catalyst are as follows: The silica support used in the impregnation step has the following characteristics: [Table 1] feature unit value BET surface area m² / g 450 Pore ​​volume ml / g 1.0 aperture nm 10.4 Average bead size* mm 2 (*: Average bead size corresponds to the number-average diameter of silica beads).

[0062] Before impregnation, the carrier was dried at 100°C for 2 hours. After drying, the water content in the silica beads was 1.5% by weight (determined by the weight loss of a 50 g silica bead sample).

[0063] In some cases, the additive is introduced into volume V EtOH In ethanol, to form an ethanol solution. In other cases (see reference), not to the volume V EtOH Additives are introduced into ethanol. Volume V EtOH The ethanol content is proportional to the pore volume of the silica support and equal to the total pore volume of the silica support used.

[0064] Then, the tantalum precursor, tantalum pentachloride (TaCl5) or tantalum pentaethoxylate (Ta(OEt)5), is introduced and diluted to a concentration corresponding to an additive / Ta molar ratio of 7 or 1 in volume V. EtOH The organic solution is prepared in ethanol (reference) or in an ethanol solution containing additives, and the ethanol content in the prepared organic solution is at least 65% by weight. The organic solution is then homogenized under stirring.

[0065] The obtained organic solution was rapidly added dropwise and mixed with the silica support until wettability of the support surface was observed (dry impregnation). The solid was then placed in an ethanol-saturated atmosphere for 3 hours. The solid was then dried in an oven at 100°C for 24 hours, and then calcined in air at 550°C for 4 hours to obtain the catalyst.

[0066] The prepared catalysts and preparation parameters are shown in Table 2 for the TaCl5 precursor and in Table 3 for the Ta(OEt)5 precursor. The distribution coefficient (also known as the distribution) of tantalum in the silica beads is also shown in Tables 2 and 3.

[0067] The distribution coefficient of the element (in this case, tantalum) in the carrier particle (in this case, silica beads) is calculated from the distribution map obtained by Castaing microprobe and represents the concentration ratio of the element (i.e., tantalum) in the core of the carrier particle (especially silica beads) relative to the concentration at the edge of the same carrier particle (see L. Sorbier, Determining the Distribution of Metal by Electron Probe Micro Analysis, in: H. Toulhoat and P. Raybaud (Eds.), Catalysis by Transition Metal Sulphides, Ed. Technip, Paris, 2013, pp. 407-411, and the references cited therein). A value of this coefficient close to 1 indicates that the element is uniformly distributed in the carrier particle (i.e., Ta in silica beads); a value close to 0 indicates that the element is distributed on the surface of the carrier particle and is referred to as being in the shell.

[0068] [Table 2] catalyst According to the present invention Metal precursor additive Additive types Additive / Ta (mol / mol) Distribution coefficient A no <![CDATA[TaCl5]]> - - 0 0.65 + / - 0.14 B yes <![CDATA[TaCl5]]> Mandelic acid α-hydroxy acid 7 nd* C yes <![CDATA[TaCl5]]> lactic acid α-hydroxy acid 7 0.77 + / - 0.18 D yes <![CDATA[TaCl5]]> Pyruvic acid α-Keto acids 7 nd* E yes <![CDATA[TaCl5]]> tartaric acid Di-α-hydroxy acid 7 nd* *nd = Not determined.

[0069] According to Table 2, compared with a reference catalyst prepared with the same tantalum precursor TaCl5 without additives (distribution of 0.65+ / -0.14 in the case of catalyst A), the tantalum distribution in silica beads of the catalyst according to the present invention prepared in an organic solution containing tantalum precursor TaCl5 appears to be more uniform in the presence of α-hydroxy acid additives, particularly lactic acid (distribution of 0.77+ / -0.18 in the case of catalyst C).

[0070] [Table 3] *nd = Not determined.

[0071] In the case of precursor Ta(OEt)5, it is also clear that when catalysts are prepared in the presence of hydroxy acid, keto acid, or polybasic acid type multifunctionalized acid additives, tantalum is more uniformly distributed in silica beads (0.58+ / -0.12 and 0.74+ / -0.17 in the presence of lactic acid (catalyst G) and pyruvic acid (catalyst H), respectively, compared to the catalyst prepared without additives (0.45+ / -0.02 in the case of catalyst F). However, when catalysts are prepared with additives other than hydroxy acid, keto acid, or polybasic acid type additives, such as α-keto esters (0.35+ / -0.02 in the case of catalyst J) or ethylene glycol (0.35+ / -0.01 in the case of catalyst L), the distribution is more uniform.

[0072] Furthermore, it can be seen that when catalysts are prepared in the presence of multifunctional acid additives (especially in the presence of citric acid) and the molar ratio of additive to Ta is 7 (i.e., greater than 1), tantalum is more uniformly distributed in the silica beads. In contrast, catalysts prepared in the presence of the same multifunctional acid additive (i.e., citric acid) but with a molar ratio of 1 (the distribution coefficient of catalyst N is 0.37 + / - 0.02), and an additive / Ta molar ratio of 7 (i.e., greater than 1) (the distribution coefficient of catalyst O is 0.51 + / - 0.10), therefore, the impact of wear on the catalytic performance of catalyst O is smaller compared to catalyst N, which exhibits a shell distribution.

[0073] Furthermore, it can be seen that, compared to the catalyst prepared with the same multifunctional acid additive (i.e., citric acid) but at a molar ratio of 1 (catalyst N, with a distribution coefficient of 0.37 + / - 0.02), when the catalyst is prepared in the presence of a multifunctional acid additive (especially citric acid) with a molar ratio of additive / Ta of 7 (i.e., greater than 1), tantalum is more uniformly distributed in the silica beads (catalyst O, with a distribution coefficient of 0.51 + / - 0.10). Therefore, the effect of wear on the catalytic performance of catalyst O will be less than its effect on the catalytic performance of catalyst N, and catalyst N exhibits a shell distribution.

[0074] Example 2: Application of the prepared catalyst in the conversion of ethanol-acetaldehyde feedstock to butadiene. Description of the catalytic testing unit The reactor used consisted of stainless steel tubes 20 cm long and 10 mm in diameter. The reactor was first filled with silicon carbide, then with catalyst diluted in the silicon carbide, and finally with silicon carbide again. Silicon carbide is inert to the feedstock and does not affect the catalytic results; it allows the catalyst to be positioned within the isothermal zone of the reactor and limits the risk of heat and material transfer problems. A tubular furnace with three heating zones was used to control the reactor temperature.

[0075] The liquid feedstock (a mixture of ethanol and acetaldehyde) is injected via a dual-piston HPLC pump. The liquid stream is vaporized in a heated line before entering the reactor and homogenized by passing through a static mixer.

[0076] At the reactor outlet, the products formed during the reaction are retained in the gas phase for online analysis by gas chromatography (PONA capillary column), enabling the most accurate identification of the hundreds of products formed. The catalyst is activated in situ under nitrogen at the test temperature.

[0077] For each test, the ethanol / acetaldehyde ratio of the raw material was set to 2.6 (mol / mol), the temperature was set to 350°C, and the pressure was set to 0.15 MPa.

[0078] For each catalyst tested, the carbon productivity value was obtained at an equivalent feed flow rate (250 g / g Ta / h at a constant pph, i.e., 7.5 h). -1 The carbon productivity (usually expressed as weight / weight percentage / hour) is measured at the reactor outlet at a feed pph of 250 g / g Ta / h, while the butadiene selectivity is determined at an equivalent conversion rate (40% feed conversion). The measured butadiene selectivity (expressed as weight / weight percentage) is the carbon selectivity and corresponds to the butadiene flow rate measured at the reactor outlet relative to the total flow rate of the carbon-based products formed (excluding unconverted ethanol and acetaldehyde in the selectivity calculation).

[0079] The results obtained using catalysts A to E and F to M prepared as described in Example 1 in terms of butadiene selectivity and carbon productivity are shown in Tables 4 and 5 as butadiene selectivity gain relative to reference catalyst A or F (i.e., selectivity gain = [selectivity obtained with the catalyst] - [selectivity obtained with the corresponding reference catalyst], with gains expressed in points or weight / weight percentage), and as carbon productivity gain relative to the productivity measured with the corresponding reference catalyst A or F (i.e., productivity gain = ([productivity obtained with the catalyst] - [productivity obtained with the corresponding reference catalyst]) / [productivity obtained with the corresponding reference catalyst], with gains expressed in weight / weight percentage).

[0080] [Table 4] The catalyst being tested According to the present invention Metal precursor additive Selective gain (weight / weight%) Productivity gain (%) A no <![CDATA[TaCl5]]> - - - B yes <![CDATA[TaCl5]]> Mandelic acid + 2.6 + 31% C yes <![CDATA[TaCl5]]> lactic acid + 4.1 + 46% D yes <![CDATA[TaCl5]]> Pyruvic acid + 3.7 + 42% E yes <![CDATA[TaCl5]]> tartaric acid + 3.2 + 42%

[0081] [Table 5] The catalyst being tested According to the present invention Metal precursor additive Selective gain (weight / weight%) Productivity gain (%) F no <![CDATA[Ta(OEt)5]]> - - - G yes <![CDATA[Ta(OEt)5]]> lactic acid + 3.8 + 36% H yes <![CDATA[Ta(OEt)5]]> Pyruvic acid + 4.8 + 39% I yes <![CDATA[Ta(OEt)5]]> tartaric acid + 3.2 + 36% J no <![CDATA[Ta(OEt)5]]> Ethyl pyruvate + 2.3 + 7% K no <![CDATA[Ta(OEt)5]]> Ethyl lactate - 1.1 - 7% L no <![CDATA[Ta(OEt)5]]> 1,3-Propanediol - 0.2 + 7% M no <![CDATA[Ta(OEt)5]]> Pyruvic acid + 0.2 + 9% N no <![CDATA[Ta(OEt)5]]> Citric acid + 2.3 + 25 O yes <![CDATA[Ta(OEt)5]]> Citric acid + 3.7 + 38

[0082] Tables 4 and 5 clearly demonstrate that, compared to the conversion in the presence of incompatible catalysts (refer to catalysts A and F) prepared without additives, butadiene selectivity and carbon productivity are significantly improved when the conversion reaction is carried out in the presence of the catalyst according to the present invention (i.e., prepared in the presence of polyfunctional acid additives such as keto acids or hydroxy acids), regardless of whether the metal precursor used to prepare the catalyst is TaCl5 or Ta(OEt)5.

[0083] As can be further seen from Table 5, compared with catalysts J, K, L and M prepared in the presence of pyruvate (β-keto acid) at an additive / Ta molar ratio of 1 (which do not conform to the present invention), when the catalyst used is according to the present invention (catalysts G, H, I), butadiene selectivity and carbon production are better when prepared in an organic solution containing precursor Ta(OEt)5 with keto acid or hydroxy acid additives.

[0084] Furthermore, as shown in Table 5, compared to the catalyst prepared in the presence of citric acid with an additive / Ta molar ratio of 1 (catalyst N), the catalyst prepared in the presence of citric acid with an additive / Ta molar ratio of 7 (catalyst O) exhibits higher productivity and selectivity. In addition, as explained in Example 1, catalyst O has a better distribution of tantalum in the silica beads; therefore, when using these catalysts, the performance of catalyst O will be less affected by wear than that of catalyst N.

[0085] Example 3: Preparation and Use of Zr / Silica Catalyst A catalyst with 3% zirconium by weight on silica beads was prepared in the same manner as the catalyst with tantalum by weight on silica beads in Example 1 (the same silica beads as in Example 1). The difference is that the precursor used was tetraethoxyzirconium (Zr(OEt)4), catalyst P was prepared without additives, while catalyst Q was prepared in the presence of pyruvate at an additive / Zr molar ratio of 7.

[0086] As explained in Example 1, the coefficient distribution of the prepared catalyst Zr / silica was measured. The results are presented in Table 6.

[0087] The prepared catalyst, having 3% by weight zirconium on silica, was tested in the same catalytic unit as described in Example 2 and under the same operating conditions as described in Example 2.

[0088] The results obtained in terms of butadiene selectivity and carbon productivity are presented in Table 6. They are presented in the same manner as in Example 2, with catalyst P as the reference catalyst. In other words, the results are expressed as the butadiene selectivity gain relative to reference catalyst P (i.e., selectivity gain = [selectivity obtained with catalyst] - [selectivity obtained with reference catalyst], the gain being expressed in points or weight / weight percentage), and as the carbon productivity gain relative to the productivity measured with reference catalyst P (i.e., productivity gain = ([productivity obtained with catalyst] - [productivity obtained with reference catalyst]) / [productivity obtained with reference catalyst], expressed in weight / weight percentage).

[0089] [Table 6] catalyst According to the present invention Metal precursor additive Additive / Zr (mol / mol) Coefficient distribution Selective gain (wgt / wgt %) Productivity gain (%) P no <![CDATA[Zr(OEt)4]]> - - 0.42 + / - 0.02 - - Q yes <![CDATA[Zr(OEt)4]]> Pyruvic acid 7 0.80 + / - 0.03 + 5.2 + 34

[0090] Table 6 clearly shows that when the zirconium-based catalyst is the catalyst according to the present invention, i.e., compared with the catalyst without additives prepared not according to the present invention (catalyst P), the catalyst prepared in the presence of multifunctional acid additives (catalyst Q) has significantly improved butadiene selectivity and carbon production.

Claims

1. A method for preparing a catalyst, comprising: a) The step of preparing at least one organic solution, said organic solution comprising: At least one metallic precursor selected from at least one metallic element in groups 3, 4, and 5 of the periodic table. At least one multifunctional acid additive. The at least one metal precursor and the at least one polyfunctional acid additive are present in an organic solution such that the acid / metal molar ratio between the number of moles of the at least one polyfunctional acid additive and the number of moles of the metal element from the at least one metal precursor is greater than 1. b) A step of depositing the at least one metal precursor onto the oxide matrix to obtain a solid by contacting the organic solution prepared in step a) with the oxide matrix; c) The step of heat-treating the solid obtained in step b).

2. The method according to claim 1, wherein the metallic element is selected from yttrium, zirconium, hafnium, niobium, tantalum and mixtures thereof, preferably selected from tantalum, niobium, zirconium and mixtures thereof, and preferably tantalum.

3. The method according to claim 1 or 2, wherein the at least one multifunctional acid additive comprises at least one carboxylic acid or carboxylic acid generating function and a second chemical function located at the α position, β position, γ position or δ position.

4. The method according to any one of claims 1 to 3, wherein the at least one polyfunctional acid additive is selected from hydroxy acids, keto acids, polybasic acids, their anhydrides, and mixtures thereof.

5. The method according to any one of claims 1 to 4, wherein the polyfunctional acid additive is selected from α-hydroxy acids, α-keto acids, α-diacids, their anhydrides and mixtures thereof, such as pyruvic acid, lactic acid, tartaric acid, malic acid, citric acid, oxalic acid, glycolic acid, mandelic acid, their anhydrides and mixtures thereof.

6. The method according to any one of claims 1 to 5, wherein the acid / metal molar ratio in step a) is greater than or equal to 2, preferably between 2 and 20, and more preferably between 5 and 15.

7. The method according to any one of claims 1 to 6, wherein the organic solution in step a) comprises an organic solvent.

8. The method according to any one of claims 1 to 7, wherein the oxide matrix comprises silicon dioxide, preferably at least 90% by weight of silicon dioxide relative to the total mass of the oxide matrix.

9. The method according to any one of claims 1 to 8, wherein the heat treatment step c) comprises drying, the drying preferably being carried out at a temperature between 50 and 200°C for a time between 1 and 24 hours, preferably under a gaseous flow.

10. The method of claim 9, wherein the heat treatment step c) comprises calcining after drying, the calcination being carried out under a gaseous flow at a temperature between 350 and 700°C for a period between 1 and 6 hours.

11. The catalyst obtained by the preparation method according to any one of claims 1 to 10, wherein it comprises elements selected from Groups 3, 4 and 5 of the periodic table, preferably selected from yttrium, zirconium, hafnium, niobium, tantalum and mixtures thereof, preferably selected from elemental tantalum, elemental niobium and / or elemental zirconium, preferably at least one metallic element of elemental tantalum, and preferably an oxide matrix based on silica.

12. The catalyst according to claim 11, wherein the at least one metal element is present in an amount between 0.1 wt% and 30 wt%, preferably between 0.3 wt% and 10 wt%, more preferably between 0.5 wt% and 5 wt%, relative to the oxide matrix.

13. The use of the catalyst according to claim 11 or 12 for converting a feedstock containing ethanol into butadiene at a temperature between 250 and 450°C and a pressure between 0.05 and 2.00 MPa.

14. A method for converting a feedstock containing ethanol into butadiene, comprising: The step of converting a feedstock containing ethanol into butadiene is carried out in the presence of a catalyst prepared by the preparation method according to any one of claims 1 to 10, at a temperature between 250 and 450°C and a pressure between 0.05 and 2.00 MPa.

15. The conversion method according to claim 14, wherein the raw materials comprise ethanol and acetaldehyde, preferably in a molar ratio of ethanol to acetaldehyde between 1 and 5.

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