EP3710162A1 - Method for the photocatalytic reduction of carbon dioxide implementing a supported photocatalyst made from molybdenum sulfide or tungsten sulfide - Google Patents

Method for the photocatalytic reduction of carbon dioxide implementing a supported photocatalyst made from molybdenum sulfide or tungsten sulfide

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Publication number
EP3710162A1
EP3710162A1 EP18796073.7A EP18796073A EP3710162A1 EP 3710162 A1 EP3710162 A1 EP 3710162A1 EP 18796073 A EP18796073 A EP 18796073A EP 3710162 A1 EP3710162 A1 EP 3710162A1
Authority
EP
European Patent Office
Prior art keywords
oet
photocatalyst
carbon dioxide
support
alumina
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP18796073.7A
Other languages
German (de)
French (fr)
Inventor
Antoine Fecant
Audrey BONDUELLE-SKRZYPCZAK
Ranin ATWI
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
IFP Energies Nouvelles IFPEN
Original Assignee
IFP Energies Nouvelles IFPEN
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Publication date
Application filed by IFP Energies Nouvelles IFPEN filed Critical IFP Energies Nouvelles IFPEN
Publication of EP3710162A1 publication Critical patent/EP3710162A1/en
Pending legal-status Critical Current

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    • B01J35/39—
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
    • B01J19/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
    • B01J19/12—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor employing electromagnetic waves
    • B01J19/122—Incoherent waves
    • B01J19/123—Ultra-violet light
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
    • B01J19/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
    • B01J19/12—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor employing electromagnetic waves
    • B01J19/122—Incoherent waves
    • B01J19/127—Sunlight; Visible light
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
    • B01J27/02—Sulfur, selenium or tellurium; Compounds thereof
    • B01J27/04—Sulfides
    • B01J27/047—Sulfides with chromium, molybdenum, tungsten or polonium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
    • B01J27/02—Sulfur, selenium or tellurium; Compounds thereof
    • B01J27/04—Sulfides
    • B01J27/047—Sulfides with chromium, molybdenum, tungsten or polonium
    • B01J27/051—Molybdenum
    • B01J35/19—
    • B01J35/30—
    • B01J35/33—
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/0201—Impregnation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/0201—Impregnation
    • B01J37/0203—Impregnation the impregnation liquid containing organic compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/0236—Drying, e.g. preparing a suspension, adding a soluble salt and drying
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/20—Sulfiding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
    • B01J37/341—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation
    • B01J37/344—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation of electromagnetic wave energy
    • B01J37/345—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation of electromagnetic wave energy of ultraviolet wave energy
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C1/00—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon
    • C07C1/02—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon from oxides of a carbon
    • C07C1/12—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon from oxides of a carbon from carbon dioxide with hydrogen
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C2521/00—Catalysts comprising the elements, oxides or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium or hafnium
    • C07C2521/02—Boron or aluminium; Oxides or hydroxides thereof
    • C07C2521/04—Alumina
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C2527/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
    • C07C2527/02—Sulfur, selenium or tellurium; Compounds thereof
    • C07C2527/04—Sulfides
    • C07C2527/047—Sulfides with chromium, molybdenum, tungsten or polonium
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C2527/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
    • C07C2527/02—Sulfur, selenium or tellurium; Compounds thereof
    • C07C2527/04—Sulfides
    • C07C2527/047—Sulfides with chromium, molybdenum, tungsten or polonium
    • C07C2527/051—Molybdenum

Definitions

  • the field of the invention is that of the photocatalytic reduction of carbon dioxide (CO 2 ) under irradiation by the use of a photocatalyst.
  • Fossil fuels such as coal, oil and natural gas
  • their combustion produces carbon dioxide emissions which are considered to be the main cause of global warming.
  • C0 2 emissions there is a growing need to mitigate C0 2 emissions, either by capturing it or by transforming it.
  • CSC carbon capture and sequestration
  • Such active strategies are based on the reduction of carbon dioxide into valuable products.
  • the reduction of carbon dioxide can be carried out biologically, thermally, electrochemically or photocatalytically.
  • photocatalytic C0 2 reduction is gaining increased attention as it can potentially consume alternative forms of energy, for example by exploiting solar energy, which is abundant, cheap, and ecologically clean and safe.
  • C1 carbonaceous molecules or more such as CO, methane, methanol, ethanol, formaldehyde, formic acid or other molecules such as carboxylic acids, aldehydes, ketones or different alcohols.
  • These molecules, such methanol, ethanol, formic acid or even methane and all C 1 + hydrocarbons can find an energy utility directly.
  • Carbon monoxide CO can also be energetically recovered in admixture with hydrogen for the formation of Fischer-Tropsch synthesis fuels.
  • the molecules of carboxylic acids, aldehydes, ketones or different alcohols can be used in chemical or petrochemical processes. All these molecules are therefore of great interest from an industrial point of view.
  • the photocatalytic reduction of carbon dioxide requires the use of semiconductors, which are capable of absorbing photons and initiating redox reactions.
  • a semiconductor is characterized by its bandgap (also called bandgap according to the English terminology).
  • the band gap is the difference in energy between the valence and conduction bands of the materials. Any photon of energy greater than its forbidden band can be absorbed by the semiconductor. Any photon of energy below its forbidden band can not be absorbed by the semiconductor.
  • the band gap of semiconductors in the form of particles varies according to the size of these particles.
  • the semiconductor gap is increasing for nanoparticle sizes that decrease to the nanometer scale. This known physical phenomenon is called the quantum size effect.
  • Tu et al. (Nanoscale, 9 (26), pp. 9065-9070, 2017) propose a hybrid compound M0S2-T1O2 for the photocatalytic reduction of CO2 to methanol.
  • the molybdenum sulphide phase acts as a co-catalyst and does not participate in the absorption of photons allowing the reduction of C0 2 due to the low bandgap of this material.
  • Only Ti0 2 acts as a semiconductor and thus involves photon absorption only in the ultraviolet range.
  • Zang et al. (Journal of Energy Chemistry, 25 (3), pp. 500-506, 2016) propose a solid hybrid based on M0S3-T1O2.
  • the molybdenum sulphide phase acts as a cocatalyst and is not capable of absorbing photons effective for the reduction of CO 2 because of the low bandgap of this material, it is still the T1O2 which plays this role with the further constraint of only absorbing photons in the ultraviolet range.
  • nanoparticles of molybdenum sulphide having a bandgap greater than that of a molybdenum sulphurized mass are known from the prior art.
  • Wilcoxon et al. proposes the synthesis of colloidal suspensions of MoS 2 nanoparticles having a forbidden band of 2.25 eV for average nanoparticle sizes of 4 nm, whereas M0S2 nanoparticles for sizes greater than 10 nm have a band gap well below 2.25 eV.
  • These sulphurised molybdenum nanoparticles have been used for the oxidation of organic compounds. Nevertheless, the colloidal suspensions suffer from problems of stability and high production cost.
  • the object of the invention is to propose a new, sustainable and more efficient way of producing carbon molecules which can be upgraded by photocatalytic conversion of carbon dioxide by means of electromagnetic energy, using a photocatalyst comprising a support for base of alumina or silica or silica-alumina and nanoparticles of molybdenum sulphide or tungsten sulphide having a bandgap greater than 2.3 eV.
  • a photocatalyst comprising a support for base of alumina or silica or silica-alumina and nanoparticles of molybdenum sulphide or tungsten sulphide having a bandgap greater than 2.3 eV.
  • the invention describes a process for photocatalytic reduction of carbon dioxide carried out in the liquid phase and / or in the gaseous phase under irradiation using a photocatalyst comprising a support based on alumina or silica or silica-alumina and nanoparticles of molybdenum sulphide or tungsten sulphide having a band gap greater than 2.3 eV, said process comprising the steps following:
  • a charge containing carbon dioxide and at least one sacrificial compound is contacted with said photocatalyst; b) the photocatalyst is irradiated with at least one irradiation source producing at least one wavelength less than the width of the photocatalyst; forbidden band of said photocatalyst so as to reduce the carbon dioxide and oxidize the sacrificial compound in the presence of said photocatalyst activated by said irradiation source, so as to produce an effluent containing at least partly C1 carbonaceous molecules or more, different from the CO2 .
  • the nanoparticles of molybdenum sulphide or tungsten sulphide having a band gap greater than 2.3 eV advantageously absorb part of the visible spectrum of solar irradiation while allowing the reduction of carbon dioxide by appropriate band levels, that the sulphide phases of molybdenum or tungsten in the form of larger nanoparticles having a band gap of less than 2.3 eV are not possible.
  • the implementation of said photocatalyst for the photocatalytic reduction of C0 2 thus makes it possible to enhance the visible part of the solar spectrum since it can absorb all the photons with a wavelength of less than 620 nm (compared to 400 nm for a conventional photocatalyst of the type Ti0 2 ).
  • these supported nanoparticles have the advantage of better stability vis-à-vis the colloidal suspensions.
  • the sacrificial compound is a gaseous compound chosen from water, ammonia, hydrogen, methane and an alcohol.
  • the sacrificial compound is a liquid compound chosen from water, ammonia, an alcohol, an aldehyde or an amine.
  • a diluent fluid is present in steps a) and / or b).
  • the irradiation source is a source of artificial or natural irradiation. According to one variant, the irradiation source emits at least in a wavelength range greater than 280 nm.
  • the porous support does not absorb energy photons higher than 4 eV.
  • the content of molybdenum sulphide or of tungsten sulphide of the photocatalyst is between 4 and 50% by weight relative to the total weight of the photocatalyst.
  • the surface density which corresponds to the quantity of molybdenum Mo atoms or tungsten W atoms deposited per unit area of support is between 0.5 and 12 atoms of Mo or W per square nanometer of support.
  • the photocatalyst is prepared according to a process comprising the following successive steps:
  • a step of drying the impregnated support at a temperature below 200 ° C, under an anhydrous atmosphere or under vacuum or under an inert gas stream, iv) a sulphurization step.
  • group VIII according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IUPAC classification.
  • Photocatalysis is based on the principle of activating a semiconductor or a set of semiconductors such as the photocatalyst used in the process according to the invention, using the energy provided by the irradiation .
  • Photocatalysis can be defined as the absorption of a photon whose energy is greater than or equal to the bandgap or "bandgap" according to the English terminology between the valence band and the conduction band, which induces the formation of an electron-hole pair in the semiconductor.
  • This electron-hole pair will allow the formation of free radicals that will either react with compounds present in the medium or then recombine according to various mechanisms.
  • Each semiconductor has a difference in energy between its conduction band and its valence band, or "bandgap", which is its own.
  • a photocatalyst composed of one or more semiconductors can be activated by the absorption of at least one photon.
  • Absorbable photons are those whose energy is greater than bandgap, semiconductor.
  • the photocatalysts can be activated by at least one photon of a wavelength corresponding to the energy associated with the bandgap widths of the semiconductors constituting the photocatalyst or of a lower wavelength.
  • the maximum wavelength absorbable by a semiconductor is calculated using the following equation:
  • the value of the forbidden band of semiconductor materials is measured by diffuse reflection absorption spectroscopy as described by the Tauc method (J. Tauc, R. Grigorovici, and A. Vancu, Phys Status Solidi, 1966, 15, p 627, J. Tauc, "Optical Properties of Solids", F. Abeles ed., North Holland, 1972, EA Davis and NF Mott, Philos Mag., 1970, 22 p 903).
  • the invention describes a method for photocatalytic reduction of carbon dioxide carried out in the liquid phase and / or in the gas phase under irradiation using a photocatalyst comprising a support based on alumina or silica or silica-alumina and nanoparticles.
  • a photocatalyst comprising a support based on alumina or silica or silica-alumina and nanoparticles.
  • molybdenum sulphide or tungsten sulphide having a band gap greater than 2.3 eV said method comprising the steps of:
  • the photocatalyst is irradiated with at least one irradiation source producing at least one wavelength less than the forbidden band width of said photocatalyst so as to reduce the carbon dioxide and oxidize the sacrificial compound in the presence of said photocatalyst activated by said irradiation source, so as to produce an effluent containing at least partly carbon molecules C1 or more, different from CO2 .
  • a feedstock containing said carbon dioxide and at least one sacrificial compound is contacted with said photocatalyst.
  • sacrificial compound is meant an oxidizable compound.
  • the sacrificial compound may be in gaseous or liquid form.
  • C1 carbonaceous molecules or more means molecules resulting from the reduction of CO2 containing one or more carbon atoms, with the exception of CO2.
  • Such molecules are, for example, CO, methane, methanol, ethanol, formaldehyde, formic acid or other molecules such as hydrocarbons, carboxylic acids, aldehydes, ketones or various alcohols.
  • the process according to the invention can be carried out in the liquid phase and / or in the gas phase.
  • the filler treated according to the process is in gaseous, liquid or biphasic gas and liquid form.
  • C0 2 When the feedstock is in gaseous form, C0 2 is present in its gaseous form in the presence of any gaseous sacrificial compounds alone or as a mixture.
  • the gaseous sacrificial compounds are oxidizable compounds such as water (h 2 O) , hydrogen (H 2 ), methane (CH 4 ) or alcohols.
  • the gaseous sacrificial compounds are water or hydrogen.
  • the CO2 and the sacrificial compound may be diluted with a gaseous diluent fluid such as N 2 or Ar.
  • the filler When the filler is in liquid form, it may be in the form of an ionic liquid, organic or aqueous.
  • the charge in liquid form is preferably aqueous.
  • the CO2 In an aqueous medium, the CO2 is then solubilized in the form of aqueous carbonic acid (H2CO3), hydrogen carbonate or carbonate.
  • the sacrificial compounds are liquid oxidizable compounds, possibly obtained by solubilization of a solid, in the liquid feed, such as water (hhO) , alcohols, aldehydes, amines, ammonia. In a preferred manner, the sacrificial compound is water.
  • the pH When the liquid charge is an aqueous solution, the pH is generally between 1 and 9, preferably between 2 and 7.
  • a basic or acidic agent may be added to the charge.
  • a basic agent is preferably selected from alkali or alkaline earth hydroxides, organic bases such as amines or ammonia.
  • an acidic agent is introduced, it is preferably selected from inorganic acids such as nitric, sulfuric, phosphoric, hydrochloric or hydrobromic acid or organic acids such as carboxylic or sulphonic acids.
  • the liquid charge when it is aqueous, it may contain in any quantity any solvated ion, such as for example K + , Li + , Na + , Ca 2+ , Mg 2+ , S0 4 2 , Cl, F, N0 3 2 .
  • any solvated ion such as for example K + , Li + , Na + , Ca 2+ , Mg 2+ , S0 4 2 , Cl, F, N0 3 2 .
  • a diluent fluid which may be liquid or gaseous, may be present in the reaction medium.
  • a diluent fluid is not required for the realization of the invention, however it may be useful to add to the charge to ensure the dispersion of the charge in the medium, the dispersion of the photocatalyst, a control the adsorption of the reagents / products on the surface of the photocatalyst, a control of the absorption of photons by the photocatalyst, the dilution of the products to limit their recombination and other similar parasitic reactions.
  • a diluent fluid also makes it possible to control the temperature of the reaction medium, thus being able to compensate for the possible exo / endothermicity of the photocatalyzed reaction.
  • the nature of the diluent fluid is chosen such that its influence is neutral on the reaction medium or that its possible reaction does not interfere with achieving the desired reduction of carbon dioxide.
  • nitrogen or argon may be selected as the gaseous diluent fluid.
  • the contacting of the charge containing the carbon dioxide and the photocatalyst can be done by any means known to those skilled in the art.
  • the contacting of the carbon dioxide feedstock and the photocatalyst is in fixed bed traversed or in fixed licking bed.
  • said photocatalyst is preferably fixed within the reactor, and the feedstock containing the carbon dioxide to be converted into gaseous and / or liquid form is sent through the photocatalytic bed.
  • the photocatalyst is preferably fixed within the reactor and the feed containing the carbon dioxide to be converted into gaseous and / or liquid form is sent to the photocatalytic bed.
  • the implementation When the implementation is in fixed bed or in bed licking, the implementation can be done continuously.
  • the photocatalytic process according to the invention uses a photocatalyst comprising a support and nanoparticles of molybdenum sulphide or tungsten sulphide having a bandgap greater than 2.3 eV.
  • the content of molybdenum sulphide or of tungsten sulphide of the photocatalyst is between 4 and 50% by weight relative to the total weight of the photocatalyst, and preferably between 5 and 25% by weight.
  • the surface density which corresponds to the quantity of molybdenum Mo atoms or tungsten W atoms deposited per unit area of support is advantageously between 0.5 and 12 atoms of Mo or W per square nanometer of support, and preferably between 1 and 7 atoms of Mo or W per square nanometer of support.
  • the photocatalyst according to the invention comprises a support based on alumina or silica or silica-alumina.
  • the porous support does not absorb energy photons higher than 4 eV.
  • the support of said catalyst is based on alumina, it contains more than 50% of alumina and, in general, it contains only alumina or silica-alumina as defined below.
  • the support of said catalyst is a silica-alumina containing at least 50% by weight of alumina.
  • the silica content in the support is at most 50% by weight, most often less than or equal to 45% by weight, preferably less than or equal to 40%.
  • the support of said catalyst is based on silica, it contains more than 50% by weight of silica and, in general, it contains only silica.
  • the support consists of alumina, silica or silica-alumina.
  • the support is based on alumina, and particularly preferably the support is made of alumina.
  • the alumina may be a transition alumina, for example an alpha phase alumina, a delta phase alumina, a gamma phase alumina or a mixture of alumina of these different phases.
  • the support has a specific surface area (measured according to the ASTM D 3663-78 standard established from the Brunauer, Emmett, Teller method, ie the BET method, as defined in S. Brunauer, PH Emmett, E.Teller J. Am. Chem. Soc., 1938, 60 (2), pp. 309-319) between 10 and 1000 m 2 / g, preferably between 50 and 600 m 2 / g.
  • a step of drying the impregnated support at a temperature below 200 ° C, under an anhydrous atmosphere or under vacuum or under an inert gas stream, iv) a sulphurization step.
  • the process for preparing the photocatalyst makes it possible to obtain nanoparticles of molybdenum sulphide or of tungsten sulphide having a band gap greater than 2.3 eV, this band gap value corresponds to particle sizes of less than 3.5 nm.
  • the photocatalyst may also comprise nanoparticles of molybdenum oxysulfides or tungsten oxysulfides. These nanoparticles are defined by their raw formula MoO y S z such that 0 ⁇ y + z ⁇ 5 with y and z are strictly positive integers.
  • Step i) said contacting the solution and the support is an impregnation.
  • Impregnations are well known to those skilled in the art.
  • the impregnation method according to the invention is chosen from dry impregnation, impregnation in excess, successive impregnations. The so-called dry impregnation method is advantageously used.
  • the organic solvent A used in step i) is generally an alkane, an alcohol, an ether, a ketone, a chlorinated solvent or an aromatic compound. Cyclohexane and n-hexane are preferably used.
  • R ' Cx'Hy' where x '> 1 and (x'-1) ⁇ y' ⁇ (2x '+ 1),
  • ligands well known to those skilled in the art and of the THF type, dimethyl ether, dimethylsulfide, P (CH3) 3, allyl, aryl halogenated (chosen from fluorinated, chlorinated, brominated, amine, acetate, acetylacetonate, halide, hydroxide, -SH, ....
  • the ligands are chosen from acetylacetonate, THF and dimethyl ether.
  • the precursors according to the invention do not contain ligand (L1), (L2), (L3), (L4) and (L5).
  • the molybdenum precursor is Mo (OEt) s.
  • the tungsten precursors according to the invention are W (OEt) 5 or W (OEt) 6 .
  • Stage ii) is a maturation stage intended to allow the species to spread to the core of the support. It is advantageously carried out under anhydrous atmosphere (without water), preferably between 30 minutes and 24 hours at room temperature. The atmosphere must preferably be anhydrous in order not to polycondense the previously impregnated precursors.
  • the drying carried out during step iii) is intended to evacuate the impregnating solvent A.
  • the atmosphere should preferably be anhydrous (without water) in order not to polycondense said precursors previously impregnated.
  • the temperature must not exceed 200 ° C to keep intact said precursors grafted or deposited on the surface of the support. Preferably, the temperature will not exceed 120 ° C.
  • the drying is carried out under vacuum, at room temperature. This step can be carried out alternately by the passage of an inert gaseous flow.
  • Step iv) of sulfurization may advantageously be carried out using a gaseous mixture H 2 S / H 2 or H 2 S / N 2 containing at least 5% by volume of H 2 S in the mixture at a temperature equal to or greater than ambient temperature, at a total pressure equal to or greater than 1 bar (0.1 MPa) for at least 2 hours.
  • the sulfurization temperature is less than 350 ° C.
  • the sulfurization temperature is below 200 ° C.
  • the sulfurization step iv) is intended to obtain the photocatalyst based on molybdenum sulphide or tungsten.
  • the photocatalyst is irradiated with at least one irradiation source producing at least photons with a wavelength of less than 540 nm or with energy greater than 2.3 eV (the minimum forbidden band of the photocatalyst), so as to reduce the carbon dioxide and oxidize the sacrificial compound in the presence of said photocatalyst activated by said irradiation source, so as to produce an effluent containing at least in part C1 carbonaceous molecules or more, different from C0 2 .
  • any irradiation source emitting at least one wavelength suitable for activating said photocatalyst, that is to say absorbable by the photocatalyst, can be used according to the invention.
  • irradiation source emitting at least one wavelength suitable for activating said photocatalyst, that is to say absorbable by the photocatalyst.
  • the irradiation source is solar irradiation.
  • the irradiation source is solar irradiation, it generally emits in the ultraviolet spectrum, visible and infra-red, that is to say it emits a wavelength range of 280 nm to 2500 nm about (according to ASTM G173-03).
  • the source emits at least in a wavelength range greater than 280 nm, very preferably 315 nm to 800 nm, which includes the UV spectrum and / or the visible spectrum.
  • the irradiation source provides a photon flux that irradiates the reaction medium containing the photocatalyst.
  • the interface between the reaction medium and the light source varies depending on the applications and the nature of the light source.
  • the irradiation source is located outside the reactor and the interface between the two may be an optical window pyrex, quartz, organic glass or any other interface allowing photons absorbable by the photocatalyst according to the invention to diffuse external medium within the reactor.
  • the realization of the photocatalytic reduction of carbon dioxide is conditioned by the provision of photons adapted to the photocatalytic system for the reaction envisaged and therefore is not limited to a specific pressure or temperature range apart from those allowing ensure the stability of the product (s).
  • the temperature range employed for photocatalytic reduction of the carbon dioxide containing feedstock is generally -10 ° C to + 200 ° C, preferably 0 to 150 ° C, and most preferably 0 and 100 ° C.
  • the pressure range employed for the photocatalytic reduction of the carbon dioxide containing feedstock is generally from 0.01 MPa to 70 MPa (0.1 to 700 bar), more preferably from 0.1 MPa to 2 MPa (1 to 20 bar).
  • the effluent obtained after the photocatalytic reduction reaction of the carbon dioxide contains on the one hand at least one molecule at C1 or more, different from the carbon dioxide resulting from the reaction and secondly from the unreacted charge, as well as the possible diluent fluid, but also products of parallel reactions such as for example the dihydrogen resulting from the photocatalytic reduction of H 2 0 when this compound is used as a sacrificial compound.
  • Photocatalyst A is a commercially available MoS 2 semiconductor in powder form (Aldrich TM, 99% purity). The band gap of photocatalyst A is measured by diffuse reflection absorption spectrometry at 1.71 eV.
  • Photocatalyst B is a semiconductor based on commercial WS 2 in powder form (Aldrich TM 99% purity).
  • the band gap of photocatalyst A is measured by diffuse reflection absorption spectrometry at 1.56 eV.
  • alumina carrier y (y-AI 2 0 3) is loaded into a quartz reactor and calcined for 6 hours at 300 ° C with a temperature increase ramp of 5 ° C / min, then placed under vacuum (10 5 mbar) at the same temperature for 16h. Then, the dehydroxylated carrier is removed from the vacuum line and cooled to 140 ° C and stored in a glove box.
  • the specific surface area of the alumina support is 284 m 2 / g.
  • the precursor of molybdenum is molybdenum pentaethoxide Mo (OC2H 5) 5 (Gelest TM, 90%). Dry and degassed cyclohexane is used as the solvent.
  • the amount of molybdenum is adjusted to obtain about 1.7 Mo / nm 2, ie a mass content of 8% Mo.
  • the extrudates were dried in vacuo (10 -5 mbar) for 2 hours at room temperature.
  • the solid is subjected to 2 drying cycles under vacuum at room temperature, firstly by the Schlenk line ( ⁇ 8.10 2 mbar) for 1 h and then by the vacuum line pushed to 10 5 mbar for 1 hour.
  • the solid undergoes a sulphurization step carried out at 100 ° C. with a gas flow H 2 S / H 2 (15/85 vol) of 2 L / h / g.
  • XPS analysis shows that 60% of the molybdenum is surrounded by sulfur.
  • the bandgap of the photocatalyst C is measured by diffuse reflection absorption spectrometry at 3.18 eV.
  • Photocatalyst D is prepared identically to photocatalyst C, only the sulfurization step differs with a treatment temperature of 200 ° C.
  • XPS analysis gives a molybdenum sulphidation of 87%.
  • the bandgap of the photocatalyst D is measured by diffuse reflection absorption spectrometry at 2.49 eV.
  • An alumina carrier y (Y-Al2O3) is loaded into a quartz reactor and calcined for 6 hours at 300 ° C with a temperature increase ramp of 5 ° C / min, then placed under vacuum (10 -5 mbar) to the same temperature for 16h. Then, the dehydroxylated carrier is removed from the vacuum line and cooled to 140 ° C and stored in a glove box.
  • the specific surface area of the alumina support is 284 m 2 / g.
  • the treated alumina support (y-Al 2 O 3 ) and a liquid precursor of tungsten pentaethoxide (V) -W (OEt) 5 (Gelest TM, 90%) are inserted into Schlenk flasks. separated. The flasks were then sealed and transferred to the Schlenk line.
  • the tungsten precursor is diluted with dried and degassed cyclohexane to obtain an impregnating solution. This organic solution is prepared so as to obtain a loading rate in W of 1.7 atoms / nm 2 , a mass content in W of 5.5%.
  • the impregnation of this precursor on the support is done using the needle.
  • the solid After a maturation of 16 h, the solid is subjected to 2 drying cycles under vacuum at room temperature, firstly by the Schlenk line ( ⁇ 8.10 2 mbar) for 1 h and then by the vacuum line pushed to 10 5 mbar for 1 hour. Finally, the solid undergoes a sulphurization step carried out at 150 ° C. with a gas flow H 2 S / H 2 (15/85 vol) of 2 L / h / g. XPS analysis gives a 75% tungsten sulfuration. The band gap of the photocatalyst E is measured by diffuse reflection absorption spectrometry at 2.71 eV.
  • the photocatalysts A, B, C, D and E are subjected to a photocatalytic CO 2 gas phase reduction test in a continuous steel through-bed reactor equipped with a quartz optical window and a sintered glass opposite. the optical window on which the photocatalytic solid is deposited.
  • Sufficient powder is deposited on the sinter so as to cover the entire irradiated surface of the reactor (about 100 mg).
  • the irradiated geometric area for all the photocatalysts is 8.042477.10 04 m 2 .
  • the tests are carried out at ambient temperature under atmospheric pressure.
  • a CO 2 flow rate of 0.3 ml / min passes through a water saturator before being dispensed into the reactor.
  • the production of CH 4 from the reduction of carbon dioxide is monitored by an analysis of the effluent every 6 minutes by gas chromatography.
  • the UV-Visible irradiation source is provided by an Xe-Hg lamp (Asahi TM, MAX302 TM).
  • the irradiation power is always maintained at 80 W / m 2 for a range of wavelengths between 315 and 400 nm.
  • the duration of the test is 20 hours. Photocatalytic activities are expressed in micromoles (pmol) of methane produced per hour per irradiated m 2 . These are average activities over the entire duration of the tests. The results are reported in Table 1 (below)
  • the activity values show that the use of the solids according to the invention allows the photocatalytic reduction of carbon dioxide to CH 4 .

Abstract

The invention concerns a method for the photocatalytic reduction of carbon dioxide carried out in the liquid phase and/or in the gas phase under irradiation using a photocatalyst comprising a support made from alumina or silica or silica-alumina and nanoparticles of molybdenum sulfide or tungsten sulfide having a band gap greater than 2.3 eV, said method comprising the following steps: a) bringing a feedstock containing carbon dioxide and at least one sacrificial compound into contact with said photocatalyst, b) irradiating the photocatalyst with at least one source of irradiation producing at least one wavelength smaller than the width of the band gap of said photocatalyst so as to reduce the carbon dioxide and oxidise the sacrificial compound in the presence of said photocatalyst activated by said source of irradiation, in such a way as to produce an effluent containing, at least in part, C1 or above carbon-containing molecules, different from CO2.

Description

PROCEDE DE REDUCTION PHOTOCATALYTIQUE DU DIOXYDE DE CARBONE METTANT EN ŒUVRE UN PHOTOCATALYSEUR A BASE DE SULFURE DE MOLYBDENE OU DE SULFURE DE TUNGSTENE SUPPORTE  METHOD FOR PHOTOCATALYTIC REDUCTION OF CARBON DIOXIDE IMPLEMENTING A PHOTOCATALYST BASED ON MOLYBDENE SULFIDE OR TUNGSTEN SULFIDE SUPPORTED
Domaine technique de l’invention Technical field of the invention
Le domaine de l'invention est celui de la réduction photocatalytique du dioxyde de carbone (C02) sous irradiation par l'emploi d'un photocatalyseur. The field of the invention is that of the photocatalytic reduction of carbon dioxide (CO 2 ) under irradiation by the use of a photocatalyst.
Etat de la technique  State of the art
Les combustibles fossiles, comme le charbon, le pétrole et le gaz naturel, sont les principales sources d'énergie conventionnelles dans le monde en raison de leur disponibilité, de leur stabilité et de leur densité d'énergie élevée. Cependant leur combustion produit des émissions de dioxyde de carbone qui sont considérées comme la principale cause du réchauffement climatique. Ainsi, il existe un besoin croissant pour atténuer les émissions de C02, soit en le captant, soit en le transformant. Fossil fuels, such as coal, oil and natural gas, are the world's leading conventional sources of energy because of their availability, stability and high energy density. However, their combustion produces carbon dioxide emissions which are considered to be the main cause of global warming. Thus, there is a growing need to mitigate C0 2 emissions, either by capturing it or by transforming it.
Bien que la capture et séquestration « passives » du carbone (CSC) soient généralement considérées comme un procédé efficace pour réduire les émissions de C02, d’autres stratégies peuvent être envisagées, notamment des stratégies « actives » de conversion du C02 en produits ayant une valeur économique, tels que les carburants et produits chimiques industriels. Although "passive" carbon capture and sequestration (CSC) is generally considered to be an effective method for reducing C0 2 emissions, other strategies may be considered, including "active" C0 2 conversion strategies into products. having economic value, such as fuels and industrial chemicals.
De telles stratégies actives se basent sur la réduction du dioxyde de carbone en produits valorisables. La réduction du dioxyde de carbone peut être réalisée par voie biologique, thermique, électrochimique ou encore photocatalytique.  Such active strategies are based on the reduction of carbon dioxide into valuable products. The reduction of carbon dioxide can be carried out biologically, thermally, electrochemically or photocatalytically.
Parmi ces options, la réduction photocatalytique du C02 gagne une attention accrue car elle peut potentiellement consommer des formes alternatives d'énergie, par exemple en exploitant l'énergie solaire, qui est abondante, bon marché, et écologiquement propre et sûre. Among these options, photocatalytic C0 2 reduction is gaining increased attention as it can potentially consume alternative forms of energy, for example by exploiting solar energy, which is abundant, cheap, and ecologically clean and safe.
La réduction photocatalytique du dioxyde de carbone permet d’obtenir des molécules carbonées en C1 ou plus, telles que le CO, le méthane, le méthanol, l’éthanol, le formaldéhyde, l’acide formique ou encore d’autres molécules telles que les acides carboxyliques, les aldéhydes, les cétones ou différents alcools. Ces molécules, telles le méthanol, l’éthanol, l’acide formique ou encore le méthane et tous les hydrocarbures en Ci+ peuvent trouver une utilité énergétique directement. Le monoxyde de carbone CO peut également être valorisé énergétiquement en mélange avec de l’hydrogène pour la formation de carburants par synthèse Fischer- Tropsch. Les molécules d’acides carboxyliques, d’aldéhydes, de cétones ou de différents alcools quant à elles peuvent trouver des applications dans les procédés de chimie ou de pétrochimie. Toutes ces molécules présentent donc un grand intérêt d'un point de vue industriel. The photocatalytic reduction of carbon dioxide makes it possible to obtain C1 carbonaceous molecules or more, such as CO, methane, methanol, ethanol, formaldehyde, formic acid or other molecules such as carboxylic acids, aldehydes, ketones or different alcohols. These molecules, such methanol, ethanol, formic acid or even methane and all C 1 + hydrocarbons can find an energy utility directly. Carbon monoxide CO can also be energetically recovered in admixture with hydrogen for the formation of Fischer-Tropsch synthesis fuels. The molecules of carboxylic acids, aldehydes, ketones or different alcohols can be used in chemical or petrochemical processes. All these molecules are therefore of great interest from an industrial point of view.
La réduction photocatalytique du dioxyde de carbone nécessite l’emploi de semi- conducteurs, lesquels sont capables d’absorber des photons et d’initier les réactions redox. Un semi-conducteur est caractérisé par sa bande interdite (aussi appelée bandgap selon la terminologie anglo-saxonne). La bande interdite correspond à la différence d’énergie entre les bandes de valence et de conduction des matériaux. Tout photon d’énergie supérieure à sa bande interdite peut être absorbé par le semi- conducteur. Tout photon d’énergie inférieure à sa bande interdite ne peut pas être absorbé par le semi-conducteur. The photocatalytic reduction of carbon dioxide requires the use of semiconductors, which are capable of absorbing photons and initiating redox reactions. A semiconductor is characterized by its bandgap (also called bandgap according to the English terminology). The band gap is the difference in energy between the valence and conduction bands of the materials. Any photon of energy greater than its forbidden band can be absorbed by the semiconductor. Any photon of energy below its forbidden band can not be absorbed by the semiconductor.
D’autre part, il est connu de l’homme du métier que la bande interdite des semi- conducteurs sous forme de particules varie en fonction de la taille de ces particules. La bande interdite de semi-conducteur augmente pour des tailles de nanoparticules qui diminuent jusqu’à l’échelle du nanomètre. Ce phénomène physique connu est appelé effet quantique de taille. On the other hand, it is known to those skilled in the art that the band gap of semiconductors in the form of particles varies according to the size of these particles. The semiconductor gap is increasing for nanoparticle sizes that decrease to the nanometer scale. This known physical phenomenon is called the quantum size effect.
Des procédés de réduction photocatalytique du dioxyde de carbone en présence d’un photocatalyseur contenant une phase sulfurée de molybdène sont connus dans l’état de l’art. Methods of photocatalytic reduction of carbon dioxide in the presence of a photocatalyst containing a molybdenum sulphide phase are known in the state of the art.
Tu et al. (Nanoscale, 9(26), p. 9065-9070, 2017) proposent un composé hybride M0S2-T1O2 pour la réduction photocatalytique du CO2 en méthanol. Cependant, la phase sulfurée de molybdène joue le rôle de co-catalyseur et ne participe pas à l’absorption des photons permettant la réduction du C02 en raison de la faible bande interdite de ce matériau. Seul Ti02 joue ce rôle de semi-conducteur et implique ainsi une absorption de photons uniquement dans la gamme des ultraviolets. Zang et al. (Journal of Energy Chemistry, 25(3), p. 500-506, 2016) proposent quant à eux un solide hybride à base de M0S3-T1O2. Ici également, la phase sulfurée de molybdène joue le rôle de co-catalyseur et n’est pas capable d’absorber des photons efficaces pour la réduction du C02 en raison de la faible bande interdite de ce matériau, c’est encore le T1O2 qui joue ce rôle avec encore la contrainte de n’absorber que les photons dans la gamme de l’ultraviolet. Tu et al. (Nanoscale, 9 (26), pp. 9065-9070, 2017) propose a hybrid compound M0S2-T1O2 for the photocatalytic reduction of CO2 to methanol. However, the molybdenum sulphide phase acts as a co-catalyst and does not participate in the absorption of photons allowing the reduction of C0 2 due to the low bandgap of this material. Only Ti0 2 acts as a semiconductor and thus involves photon absorption only in the ultraviolet range. Zang et al. (Journal of Energy Chemistry, 25 (3), pp. 500-506, 2016) propose a solid hybrid based on M0S3-T1O2. Here too, the molybdenum sulphide phase acts as a cocatalyst and is not capable of absorbing photons effective for the reduction of CO 2 because of the low bandgap of this material, it is still the T1O2 which plays this role with the further constraint of only absorbing photons in the ultraviolet range.
D’autre part, des nanoparticules de molybdène sulfuré présentant une bande interdite supérieure à celle d’un molybdène sulfuré massique sont connus de l’art antérieur. On the other hand, nanoparticles of molybdenum sulphide having a bandgap greater than that of a molybdenum sulphurized mass are known from the prior art.
En effet, Wilcoxon et al. (The Journal of physical Chemistry B, 103, p.11 -17, 1999) propose la synthèse de suspensions colloïdales de nanoparticules de MoS2 ayant une bande interdite de 2,25 eV pour des tailles moyennes de nanoparticules de 4 nm, alors que les nanoparticules de M0S2 pour les tailles supérieures à 10 nm possèdent une bande interdite bien inférieure à 2,25 eV. Ces nanoparticules de molybdène sulfurées ont été mises en œuvre en oxydation photoassistée de composés organiques. Néanmoins, les suspensions colloïdales souffrent de problèmes de stabilité et de coût de production élevé. Indeed, Wilcoxon et al. (The Journal of Physical Chemistry B, 103, p.11 -17, 1999) proposes the synthesis of colloidal suspensions of MoS 2 nanoparticles having a forbidden band of 2.25 eV for average nanoparticle sizes of 4 nm, whereas M0S2 nanoparticles for sizes greater than 10 nm have a band gap well below 2.25 eV. These sulphurised molybdenum nanoparticles have been used for the oxidation of organic compounds. Nevertheless, the colloidal suspensions suffer from problems of stability and high production cost.
Objets de l’invention Objects of the invention
L’objet de l’invention est de proposer une voie nouvelle, durable et plus performante de production de molécules carbonées valorisables par conversion photocatalytique du dioxyde de carbone à l’aide d’une énergie électromagnétique, mettant en œuvre un photocatalyseur comprenant un support à base d'alumine ou de silice ou de silice- alumine et des nanoparticules de sulfure de molybdène ou de sulfure de tungstène présentant une bande interdite supérieure à 2,3 eV. La mise en œuvre de ce type de photocatalyseurs pour la réduction photocatalytique de C02 permet d’atteindre des performances améliorées par rapport aux photocatalyseurs connus pour cette réaction. The object of the invention is to propose a new, sustainable and more efficient way of producing carbon molecules which can be upgraded by photocatalytic conversion of carbon dioxide by means of electromagnetic energy, using a photocatalyst comprising a support for base of alumina or silica or silica-alumina and nanoparticles of molybdenum sulphide or tungsten sulphide having a bandgap greater than 2.3 eV. The implementation of this type of photocatalyst for the photocatalytic reduction of C0 2 makes it possible to achieve improved performances compared with known photocatalysts for this reaction.
Plus particulièrement, l'invention décrit un procédé de réduction photocatalytique du dioxyde de carbone effectué en phase liquide et/ou en phase gazeuse sous irradiation mettant en œuvre un photocatalyseur comprenant un support à base d'alumine ou de silice ou de silice-alumine et des nanoparticules de sulfure de molybdène ou de sulfure de tungstène présentant une bande interdite supérieure à 2,3 eV, ledit procédé comprenant les étapes suivantes : More particularly, the invention describes a process for photocatalytic reduction of carbon dioxide carried out in the liquid phase and / or in the gaseous phase under irradiation using a photocatalyst comprising a support based on alumina or silica or silica-alumina and nanoparticles of molybdenum sulphide or tungsten sulphide having a band gap greater than 2.3 eV, said process comprising the steps following:
a) on met en contact une charge contenant le dioxyde de carbone et au moins un composé sacrificiel avec ledit photocatalyseur, b) on irradie le photocatalyseur par au moins une source d'irradiation produisant au moins une longueur d'onde inférieure à la largeur de bande interdite dudit photocatalyseur de manière à réduire le dioxyde de carbone et oxyder le composé sacrificiel en présence dudit photocatalyseur activé par ladite source d'irradiation, de manière à produire un effluent contenant au moins en partie des molécules carbonées en C1 ou plus, différentes du CO2. a) a charge containing carbon dioxide and at least one sacrificial compound is contacted with said photocatalyst; b) the photocatalyst is irradiated with at least one irradiation source producing at least one wavelength less than the width of the photocatalyst; forbidden band of said photocatalyst so as to reduce the carbon dioxide and oxidize the sacrificial compound in the presence of said photocatalyst activated by said irradiation source, so as to produce an effluent containing at least partly C1 carbonaceous molecules or more, different from the CO2 .
Les nanoparticules de sulfure de molybdène ou de sulfure de tungstène présentant une bande interdite supérieure à 2,3 eV absorbent avantageusement une partie du spectre visible de l’irradiation solaire tout en permettant la réduction du dioxyde de carbone par des niveaux de bandes adaptés, ce que ne permet pas les phases sulfures de molybdène ou de tungstène sous forme de nanoparticules de plus grande taille présentant une bande interdite inférieure à 2,3 eV. La mise en œuvre dudit photocatalyseur pour la réduction photocatalytique du C02 permet ainsi de valoriser la partie visible du spectre solaire puisqu’il peut absorber tous les photons de longueur d’onde inférieure à 620 nm (contre 400 nm pour un photocatalyseur classique de type Ti02). The nanoparticles of molybdenum sulphide or tungsten sulphide having a band gap greater than 2.3 eV advantageously absorb part of the visible spectrum of solar irradiation while allowing the reduction of carbon dioxide by appropriate band levels, that the sulphide phases of molybdenum or tungsten in the form of larger nanoparticles having a band gap of less than 2.3 eV are not possible. The implementation of said photocatalyst for the photocatalytic reduction of C0 2 thus makes it possible to enhance the visible part of the solar spectrum since it can absorb all the photons with a wavelength of less than 620 nm (compared to 400 nm for a conventional photocatalyst of the type Ti0 2 ).
De plus, ces nanoparticules supportées présentent l’avantage d’une meilleure stabilité vis-à-vis des suspensions colloïdales.  In addition, these supported nanoparticles have the advantage of better stability vis-à-vis the colloidal suspensions.
Selon une variante, et lorsque le procédé est effectué en phase gazeuse, le composé sacrificiel est un composé gazeux choisi parmi l’eau, l’ammoniac, l’hydrogène, le méthane et un alcool. According to a variant, and when the process is carried out in the gas phase, the sacrificial compound is a gaseous compound chosen from water, ammonia, hydrogen, methane and an alcohol.
Selon une variante, et lorsque le procédé est effectué en phase liquide, le composé sacrificiel est un composé liquide choisi parmi l’eau, l’ammoniaque, un alcool, un aldéhyde ou une amine. Selon une variante, un fluide diluant est présent dans les étapes a) et/ou b). According to a variant, and when the process is carried out in the liquid phase, the sacrificial compound is a liquid compound chosen from water, ammonia, an alcohol, an aldehyde or an amine. Alternatively, a diluent fluid is present in steps a) and / or b).
Selon une variante, la source d’irradiation est une source d’irradiation artificielle ou naturelle. Selon une variante, la source d’irradiation émet à au moins dans une gamme de longueurs d'ondes supérieure à 280 nm.  According to one variant, the irradiation source is a source of artificial or natural irradiation. According to one variant, the irradiation source emits at least in a wavelength range greater than 280 nm.
Selon une variante, le support poreux n’absorbe pas de photons d’énergie supérieure à 4 eV.  According to one variant, the porous support does not absorb energy photons higher than 4 eV.
Selon une variante, la teneur en sulfure de molybdène ou en sulfure de tungstène du photocatalyseur est comprise entre 4 et 50% poids par rapport au poids total du photocatalyseur.  According to one variant, the content of molybdenum sulphide or of tungsten sulphide of the photocatalyst is between 4 and 50% by weight relative to the total weight of the photocatalyst.
Selon une variante, la densité surfacique qui correspond à la quantité d'atomes de molybdène Mo ou d’atomes de tungstène W, déposés par unité surfacique de support est comprise entre 0,5 et 12 atomes de Mo ou de W par nanomètres carré de support.  According to one variant, the surface density which corresponds to the quantity of molybdenum Mo atoms or tungsten W atoms deposited per unit area of support is between 0.5 and 12 atoms of Mo or W per square nanometer of support.
Selon une variante, le photocatalyseur est préparé selon un procédé comprenant les étapes successives suivantes :  According to a variant, the photocatalyst is prepared according to a process comprising the following successive steps:
i) une étape d'imprégnation par mise en contact d'une solution comprenant un solvant organique A et au moins un précurseur mononucléaire à base de Mo ou de W, noté M, sous leur forme monomérique ou dimérique, présentant au moins une liaison M=0 ou M-OR ou au moins une liaison M=S ou M-SR où R = CxHy où x > 1 et (x-1 ) < y < (2x+1 ), avec un support à base d'alumine ou de silice ou de silice-alumine, avantageusement préalablement calciné sous vide ou sous flux de gaz inerte pour évacuer l'eau éventuellement physisorbée sur ledit support, i) a step of impregnation by bringing into contact a solution comprising an organic solvent A and at least one mononuclear precursor based on Mo or W, denoted M, in their monomeric or dimeric form, having at least one M bond = 0 or M-OR or at least one M = S or M-SR bond where R = C x H y where x> 1 and (x-1) <y <(2x + 1), with a d-based support alumina or silica or silica-alumina, advantageously previously calcined under vacuum or under an inert gas flow to evacuate the water possibly physisorbed on said support,
ii) une étape de maturation,  ii) a ripening stage,
iii) une étape de séchage du support imprégné, à une température inférieure à 200°C, sous atmosphère anhydre ou sous vide ou sous flux de gaz inerte, iv) une étape de sulfuration.  iii) a step of drying the impregnated support, at a temperature below 200 ° C, under an anhydrous atmosphere or under vacuum or under an inert gas stream, iv) a sulphurization step.
Selon cette variante, le précurseur de molybdène est choisi parmi les composés suivants : Mo(OEt)5, Mo(OEt)6, Mo(=0)(OEt)4, Mo(=S)(OEt)4, Mo(=S)(SEt)4, Mo(=0)2(OEt)2, MO(OC6H5)6, Mo(SEt)5, Mo(SEt)6, Mo(OEt)(SEt)4, Mo(OEt)2(SEt)3, Mo(OEt)3(SEt)2, Mo(OEt)4(SEt), Mo(=0)(OEt)3(acac) avec Et = CH2CH3 (groupement éthyle) et acac = (CH3COCHCOCH3)- (acétylacétonate) sous leur forme monomérique ou dimérique. According to this variant, the molybdenum precursor is chosen from the following compounds: Mo (OEt) 5 , Mo (OEt) 6 , Mo (= O) (OEt) 4 , Mo (= S) (OEt) 4 , Mo (= S (SEt) 4 , Mo (= O) 2 (OEt) 2 , MO (OC 6 H 5 ) 6 , Mo (SEt) 5 , Mo (SEt) 6 , Mo (OEt) (SEt) 4 , Mo ( OEt) 2 (SEt) 3 , Mo (OEt) 3 (SEt) 2 , Mo (OEt) 4 (SEt), Mo (= O) (OEt) 3 (acac) with Et = CH 2 CH 3 (group ethyl) and acac = (CH 3 COCHCOCH 3 ) - (acetylacetonate) in their monomeric or dimeric form.
Selon cette variante, le précurseur de tungstène est choisi parmi les composés suivants : W(OEt)5, W(OEt)6> W(=0)(0Et)4, W(=S)(OEt)4, W(=S)(SEt)4,According to this variant, the tungsten precursor is chosen from the following compounds: W (OEt) 5 , W (OEt) 6> W (= O) (OEt) 4 , W (= S) (OEt) 4 , W (= S) (SEt) 4 ,
W(=0)2(0Et)2, W(OC6H5)6, W(SEt)5, W(SEt)6, W(OEt)4(SEt), W(OEt)3(SEt)2, W(OEt)2(SEt)3, W(OEt)(SEt)4, W(=0)(0Et)3(acac) avec Et = CH2CH3 (groupement éthyle) et acac = (CH3COCHCOCH3)- (acétylacétonate), sous leur forme monomérique ou dimérique. W (= O) 2 (OEt) 2 , W (OC 6 H 5 ) 6 , W (SEt) 5 , W (SEt) 6 , W (OEt) 4 (SEt), W (OEt) 3 (SEt) 2 , W (OEt) 2 (SEt) 3 , W (OEt) (SEt) 4 , W (= O) (OEt) 3 (acac) with Et = CH 2 CH 3 (ethyl group) and acac = (CH 3 COCHCOCH 3 ) - (acetylacetonate), in their monomeric or dimeric form.
Dans la suite, les groupes d'éléments chimiques sont donnés selon la classification CAS (CRC Handbook of Chemistry and Physics, éditeur CRC press, rédacteur en chef D.R. Lide, 81 ème édition, 2000-2001 ). Par exemple, le groupe VIII selon la classification CAS correspond aux métaux des colonnes 8, 9 et 10 selon la nouvelle classification IUPAC.  In the following, the groups of chemical elements are given according to the classification CAS (CRC Handbook of Chemistry and Physics, publisher CRC press, editor-in-chief D. R. Lide, 81 st edition, 2000-2001). For example, group VIII according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IUPAC classification.
Description détaillée de l’invention Detailed description of the invention
La photocatalyse repose sur le principe d'activation d'un semi-conducteur ou d’un ensemble de semi-conducteurs tel que le photocatalyseur utilisé dans le procédé selon l’invention, à l'aide de l'énergie apportée par l'irradiation. La photocatalyse peut être définie comme l'absorption d'un photon, dont l'énergie est supérieure ou égale à la largeur de bande interdite ou "Bandgap" selon la terminologie anglo-saxonne entre la bande de valence et la bande de conduction, qui induit la formation d'une paire électron-trou dans le semi-conducteur. On a donc l'excitation d'un électron au niveau de la bande de conduction et la formation d'un trou sur la bande de valence. Cette paire électron-trou va permettre la formation de radicaux libres qui vont soit réagir avec des composés présents dans le milieu ou alors se recombiner suivant divers mécanismes. Chaque semi-conducteur possède une différence d'énergie entre sa bande de conduction et sa bande de valence, ou "bandgap", qui lui est propre.  Photocatalysis is based on the principle of activating a semiconductor or a set of semiconductors such as the photocatalyst used in the process according to the invention, using the energy provided by the irradiation . Photocatalysis can be defined as the absorption of a photon whose energy is greater than or equal to the bandgap or "bandgap" according to the English terminology between the valence band and the conduction band, which induces the formation of an electron-hole pair in the semiconductor. We therefore have the excitation of an electron at the level of the conduction band and the formation of a hole on the valence band. This electron-hole pair will allow the formation of free radicals that will either react with compounds present in the medium or then recombine according to various mechanisms. Each semiconductor has a difference in energy between its conduction band and its valence band, or "bandgap", which is its own.
Un photocatalyseur composé d’un ou plusieurs semi-conducteurs peut être activé par l'absorption d'au moins un photon. Les photons absorbables sont ceux dont l'énergie est supérieure à la largeur de bande interdite, au "bandgap", des semi- conducteurs. Autrement dit, les photocatalyseurs sont activables par au moins un photon d'une longueur d'onde correspondant à l'énergie associée aux largeurs de bande interdite des semi-conducteurs constituant le photocatalyseur ou d'une longueur d'onde inférieure. On calcule la longueur d'onde maximale absorbable par un semi-conducteur à l'aide de l'équation suivante : A photocatalyst composed of one or more semiconductors can be activated by the absorption of at least one photon. Absorbable photons are those whose energy is greater than bandgap, semiconductor. In other words, the photocatalysts can be activated by at least one photon of a wavelength corresponding to the energy associated with the bandgap widths of the semiconductors constituting the photocatalyst or of a lower wavelength. The maximum wavelength absorbable by a semiconductor is calculated using the following equation:
Avec Amax la longueur l'onde maximale absorbable par un semi-conducteur (en m), h la constante de Planck (4,13433559.10 15 eV.s), c la vitesse de la lumière dans le vide (299 792 458 m.s 1) et Eg la largeur de bande interdite ou "bandgap" du semi- conducteur (en eV). With A max the length the maximum wave absorbable by a semiconductor (in m), h the Planck constant (4,13433559.10 15 eV.s), c the speed of light in vacuum (299,792,458 ms 1 ) and Eg the bandgap bandwidth of the semiconductor (in eV).
On mesure la valeur de la bande interdite de matériaux semi-conducteurs par spectroscopie d’absorption en réflexion diffuse tel que décrit par la méthode de Tauc (J. Tauc, R. Grigorovici, and A. Vancu, Phys. Status Solidi, 1966, 15, p 627 ; J. Tauc,”Optical Properties of Solids”, F. Abeles ed., North-Holland, 1972 ; E.A. Davis and N. F. Mott, Philos. Mag., 1970, 22 p 903).  The value of the forbidden band of semiconductor materials is measured by diffuse reflection absorption spectroscopy as described by the Tauc method (J. Tauc, R. Grigorovici, and A. Vancu, Phys Status Solidi, 1966, 15, p 627, J. Tauc, "Optical Properties of Solids", F. Abeles ed., North Holland, 1972, EA Davis and NF Mott, Philos Mag., 1970, 22 p 903).
L'invention décrit un procédé de réduction photocatalytique du dioxyde de carbone effectué en phase liquide et/ou en phase gazeuse sous irradiation mettant en œuvre un photocatalyseur comprenant un support à base d'alumine ou de silice ou de silice- alumine et des nanoparticules de sulfure de molybdène ou de sulfure de tungstène présentant une bande interdite supérieure à 2,3 eV, ledit procédé comprenant les étapes suivantes : The invention describes a method for photocatalytic reduction of carbon dioxide carried out in the liquid phase and / or in the gas phase under irradiation using a photocatalyst comprising a support based on alumina or silica or silica-alumina and nanoparticles. molybdenum sulphide or tungsten sulphide having a band gap greater than 2.3 eV, said method comprising the steps of:
a) on met en contact une charge contenant le dioxyde de carbone et au moins un composé sacrificiel avec ledit photocatalyseur,  a) a filler containing carbon dioxide and at least one sacrificial compound is contacted with said photocatalyst,
b) on irradie le photocatalyseur par au moins une source d'irradiation produisant au moins une longueur d'onde inférieure à la largeur de bande interdite dudit photocatalyseur de manière à réduire le dioxyde de carbone et oxyder le composé sacrificiel en présence dudit photocatalyseur activé par ladite source d'irradiation, de manière à produire un effluent contenant au moins en partie des molécules carbonées en C1 ou plus, différentes du CO2. Etape a) du procédé b) the photocatalyst is irradiated with at least one irradiation source producing at least one wavelength less than the forbidden band width of said photocatalyst so as to reduce the carbon dioxide and oxidize the sacrificial compound in the presence of said photocatalyst activated by said irradiation source, so as to produce an effluent containing at least partly carbon molecules C1 or more, different from CO2 . Step a) of the process
Selon l’étape a) du procédé selon l’invention, on met en contact une charge contenant ledit dioxyde de carbone et au moins un composé sacrificiel avec ledit photocatalyseur. On entend par composé sacrificiel un composé oxydable. Le composé sacrificiel peut être sous forme gazeuse ou liquide. According to step a) of the process according to the invention, a feedstock containing said carbon dioxide and at least one sacrificial compound is contacted with said photocatalyst. By sacrificial compound is meant an oxidizable compound. The sacrificial compound may be in gaseous or liquid form.
On entend par « molécules carbonées en C1 ou plus » des molécules issues de la réduction du CO2 contenant un ou plus d’atome de carbone, à l’exception du CO2. De telles molécules sont par exemple le CO, le méthane, le méthanol, l’éthanol, le formaldéhyde, l’acide formique ou encore d’autre molécules telles que des hydrocarbures, des acides carboxyliques, les aldéhydes, les cétones ou différents alcools. The term "C1 carbonaceous molecules or more" means molecules resulting from the reduction of CO2 containing one or more carbon atoms, with the exception of CO2. Such molecules are, for example, CO, methane, methanol, ethanol, formaldehyde, formic acid or other molecules such as hydrocarbons, carboxylic acids, aldehydes, ketones or various alcohols.
Le procédé selon l'invention peut être effectué en phase liquide et/ou en phase gazeuse. La charge traitée selon le procédé se présente sous forme gazeuse, liquide ou biphasique gazeuse et liquide. The process according to the invention can be carried out in the liquid phase and / or in the gas phase. The filler treated according to the process is in gaseous, liquid or biphasic gas and liquid form.
Lorsque la charge se présente sous forme gazeuse, le C02 est présent sous sa forme gazeuse en présence de tous composés sacrificiels gazeux seuls ou en mélange. Les composés sacrificiels gazeux sont des composés oxydables tels que l’eau (h^O), l’hydrogène (H2), le méthane (CH4) ou encore les alcools. De manière préférée, les composés sacrificiels gazeux sont l’eau ou l’hydrogène. Lorsque la charge se présente sous forme gazeuse, le CO2 et le composé sacrificiel peuvent être dilués par un fluide diluant gazeux tel que N2 ou Ar. When the feedstock is in gaseous form, C0 2 is present in its gaseous form in the presence of any gaseous sacrificial compounds alone or as a mixture. The gaseous sacrificial compounds are oxidizable compounds such as water (h 2 O) , hydrogen (H 2 ), methane (CH 4 ) or alcohols. Preferably, the gaseous sacrificial compounds are water or hydrogen. When the charge is in gaseous form, the CO2 and the sacrificial compound may be diluted with a gaseous diluent fluid such as N 2 or Ar.
Lorsque la charge se trouve sous forme liquide, celle-ci peut être sous forme d’un liquide ionique, organique ou aqueux. La charge sous forme liquide est préférentiellement aqueuse. En milieu aqueux, le CO2 est alors solubilisé sous forme d’acide carbonique aqueux (H2CO3), d’hydrogénocarbonate ou de carbonate. Les composés sacrificiels sont des composés oxydables liquides, possiblement obtenu par solubilisation d’un solide, dans la charge liquide, tels que l’eau (hhO), les alcools, les aldéhydes, les amines, l’ammoniaque. De manière préférée, le composé sacrificiel est l’eau. Lorsque la charge liquide est une solution aqueuse, le pH est généralement compris entre 1 et 9, de préférence entre 2 et 7. Eventuellement, et afin de moduler le pH de la charge liquide aqueuse, un agent basique ou acide peut être ajouté à la charge. Lorsqu’un agent basique est introduit il est sélectionné de préférence parmi les hydroxydes d’alcalins ou d’alcalinoterreux, les bases organiques telles que des amines ou de l’ammoniaque. Lorsqu’un agent acide est introduit il est sélectionné de préférence parmi les acides inorganiques tels que l’acide nitrique, sulfurique, phosphorique, chlorhydrique, bromhydrique ou les acides organiques tels que des acides carboxyliques ou sulfoniques. When the filler is in liquid form, it may be in the form of an ionic liquid, organic or aqueous. The charge in liquid form is preferably aqueous. In an aqueous medium, the CO2 is then solubilized in the form of aqueous carbonic acid (H2CO3), hydrogen carbonate or carbonate. The sacrificial compounds are liquid oxidizable compounds, possibly obtained by solubilization of a solid, in the liquid feed, such as water (hhO) , alcohols, aldehydes, amines, ammonia. In a preferred manner, the sacrificial compound is water. When the liquid charge is an aqueous solution, the pH is generally between 1 and 9, preferably between 2 and 7. Optionally, and in order to modulate the pH of the aqueous liquid charge, a basic or acidic agent may be added to the charge. When a basic agent is introduced it is preferably selected from alkali or alkaline earth hydroxides, organic bases such as amines or ammonia. When an acidic agent is introduced, it is preferably selected from inorganic acids such as nitric, sulfuric, phosphoric, hydrochloric or hydrobromic acid or organic acids such as carboxylic or sulphonic acids.
Eventuellement, lorsque la charge liquide est aqueuse, celle-ci peut contenir en toute quantité tout ion solvaté, tels que par exemple K+, Li+, Na+, Ca2+, Mg2+, S04 2 , CI , F , N03 2 . Optionally, when the liquid charge is aqueous, it may contain in any quantity any solvated ion, such as for example K + , Li + , Na + , Ca 2+ , Mg 2+ , S0 4 2 , Cl, F, N0 3 2 .
Lorsque le procédé est effectué en phase liquide ou en phase gazeuse, un fluide diluant, respectivement liquide ou gazeux, peut être présent dans le milieu réactionnel. La présence d'un fluide diluant n'est pas requis pour la réalisation de l'invention, cependant il peut être utile d'en adjoindre à la charge pour assurer la dispersion de la charge dans le milieu, la dispersion du photocatalyseur, un contrôle de l'adsorption des réactifs/produits à la surface du photocatalyseur, un contrôle de l’absorption des photons par le photocatalyseur, la dilution des produits pour limiter leur recombinaison et autres réactions parasites du même ordre. La présence d’un fluide diluant permet aussi le contrôle de la température du milieu réactionnel pouvant ainsi compenser l'éventuelle exo/endo-thermicité de la réaction photocatalysée. La nature du fluide diluant est choisie de telle façon que son influence soit neutre sur le milieu réactionnel ou que son éventuelle réaction ne nuise pas à la réalisation de la réduction souhaitée du dioxyde de carbone. A titre d'exemple, on peut choisir de l'azote ou l’argon en tant que fluide diluant gazeux. When the process is carried out in the liquid phase or in the gas phase, a diluent fluid, which may be liquid or gaseous, may be present in the reaction medium. The presence of a diluent fluid is not required for the realization of the invention, however it may be useful to add to the charge to ensure the dispersion of the charge in the medium, the dispersion of the photocatalyst, a control the adsorption of the reagents / products on the surface of the photocatalyst, a control of the absorption of photons by the photocatalyst, the dilution of the products to limit their recombination and other similar parasitic reactions. The presence of a diluent fluid also makes it possible to control the temperature of the reaction medium, thus being able to compensate for the possible exo / endothermicity of the photocatalyzed reaction. The nature of the diluent fluid is chosen such that its influence is neutral on the reaction medium or that its possible reaction does not interfere with achieving the desired reduction of carbon dioxide. For example, nitrogen or argon may be selected as the gaseous diluent fluid.
La mise en contact de la charge contenant le dioxyde de carbone et du photocatalyseur peut se faire par tout moyen connu de l'homme du métier. De manière préférée, la mise en contact de la charge de dioxyde de carbone et du photocatalyseur se fait en lit fixe traversé ou en lit fixe léchant. Lorsque la mise en œuvre est en lit fixe traversé, ledit photocatalyseur est préférentiellement fixé au sein du réacteur, et la charge contenant le dioxyde de carbone à convertir sous forme gazeuse et/ou liquide est envoyée à travers le lit photocatalytique. The contacting of the charge containing the carbon dioxide and the photocatalyst can be done by any means known to those skilled in the art. Preferably, the contacting of the carbon dioxide feedstock and the photocatalyst is in fixed bed traversed or in fixed licking bed. When the implementation is in fixed bed traversed, said photocatalyst is preferably fixed within the reactor, and the feedstock containing the carbon dioxide to be converted into gaseous and / or liquid form is sent through the photocatalytic bed.
Lorsque la mise en œuvre est en lit fixe léchant, le photocatalyseur est préférentiellement fixé au sein du réacteur et la charge contenant le dioxyde de carbone à convertir sous forme gazeuse et/ou liquide est envoyée sur le lit photocatalytique.  When the implementation is fixed bed licking, the photocatalyst is preferably fixed within the reactor and the feed containing the carbon dioxide to be converted into gaseous and / or liquid form is sent to the photocatalytic bed.
Lorsque que la mise en œuvre est en lit fixe ou en lit léchant, la mise en œuvre peut se faire en continu.  When the implementation is in fixed bed or in bed licking, the implementation can be done continuously.
Le procédé photocatalytique selon l’invention met en œuvre un photocatalyseur comprenant un support et des nanoparticules de sulfure de molybdène ou sulfure de de tungstène présentant une bande interdite supérieure à 2,3 eV. The photocatalytic process according to the invention uses a photocatalyst comprising a support and nanoparticles of molybdenum sulphide or tungsten sulphide having a bandgap greater than 2.3 eV.
La teneur en sulfure de molybdène ou en sulfure de tungstène du photocatalyseur est comprise entre 4 et 50% poids par rapport au poids total du photocatalyseur, et de manière préférée entre 5 et 25% poids. The content of molybdenum sulphide or of tungsten sulphide of the photocatalyst is between 4 and 50% by weight relative to the total weight of the photocatalyst, and preferably between 5 and 25% by weight.
La densité surfacique qui correspond à la quantité d'atomes de molybdène Mo ou d’atomes de tungstène W, déposés par unité surfacique de support est avantageusement comprise entre 0,5 et 12 atomes de Mo ou de W par nanomètres carré de support, et de manière préférée entre 1 et 7 atomes de Mo ou de W par nanomètres carré de support. The surface density which corresponds to the quantity of molybdenum Mo atoms or tungsten W atoms deposited per unit area of support is advantageously between 0.5 and 12 atoms of Mo or W per square nanometer of support, and preferably between 1 and 7 atoms of Mo or W per square nanometer of support.
Le photocatalyseur selon l’invention comprend un support à base d'alumine ou de silice ou de silice-alumine. Selon une variante, le support poreux n’absorbe pas les photons d’énergie supérieure à 4 eV. The photocatalyst according to the invention comprises a support based on alumina or silica or silica-alumina. According to one variant, the porous support does not absorb energy photons higher than 4 eV.
Lorsque le support dudit catalyseur est à base d'alumine, il contient plus de 50 % d'alumine et, de façon générale, il contient uniquement de l'alumine ou de la silice- alumine telle que définie ci-dessous.  When the support of said catalyst is based on alumina, it contains more than 50% of alumina and, in general, it contains only alumina or silica-alumina as defined below.
Dans un autre cas préféré, le support dudit catalyseur est une silice-alumine contenant au moins 50 % poids d'alumine. La teneur en silice dans le support est d'au plus 50% poids, le plus souvent inférieure ou égale à 45% poids, de préférence inférieure ou égale à 40%. In another preferred case, the support of said catalyst is a silica-alumina containing at least 50% by weight of alumina. The silica content in the support is at most 50% by weight, most often less than or equal to 45% by weight, preferably less than or equal to 40%.
Lorsque le support dudit catalyseur est à base de silice, il contient plus de 50 % poids de silice et, de façon générale, il contient uniquement de la silice.  When the support of said catalyst is based on silica, it contains more than 50% by weight of silica and, in general, it contains only silica.
Selon une variante particulièrement préférée, le support est constitué d’alumine, de silice ou de silice-alumine.  According to a particularly preferred variant, the support consists of alumina, silica or silica-alumina.
De préférence, le support est à base d’alumine, et de manière particulièrement préférée le support est constitué d’alumine.  Preferably, the support is based on alumina, and particularly preferably the support is made of alumina.
L’alumine peut être une alumine de transition, par exemple une alumine phase alpha, une alumine phase delta, une alumine phase gamma ou un mélange d'alumine de ces différentes phases.  The alumina may be a transition alumina, for example an alpha phase alumina, a delta phase alumina, a gamma phase alumina or a mixture of alumina of these different phases.
Selon une variante, le support possède une surface spécifique (mesurée selon la norme ASTM D 3663-78 établie à partir de la méthode Brunauer, Emmett, Teller, i.e. méthode BET, telle que définie dans S. Brunauer, P. H. Emmett, E.Teller, J. Am. Chem. Soc., 1938, 60 (2), pp 309-319.) comprise entre 10 et 1000 m2/g, de manière préférée entre 50 et 600 m2/g. According to one variant, the support has a specific surface area (measured according to the ASTM D 3663-78 standard established from the Brunauer, Emmett, Teller method, ie the BET method, as defined in S. Brunauer, PH Emmett, E.Teller J. Am. Chem. Soc., 1938, 60 (2), pp. 309-319) between 10 and 1000 m 2 / g, preferably between 50 and 600 m 2 / g.
Le photocatalyseur comprenant un support et des nanoparticules de sulfure de molybdène ou de sulfure de tungstène présentant une bande interdite supérieure à 2,3 eV est préparé par le procédé décrit dans les documents FR 3 004 967 (pour le Mo) et FR 3 004 968 (pour le W) et comprend les étapes successives suivantes : i) une étape d'imprégnation par mise en contact d'une solution comprenant un solvant organique A et au moins un précurseur mononucléaire à base de Mo ou de W, noté M, sous leur forme monomérique ou dimérique, présentant au moins une liaison M=0 ou M-OR ou au moins une liaison M=S ou M-SR où R = CxHy où x > 1 et (x-1 ) < y < (2x+1 ), avec un support poreux, avantageusement préalablement calciné sous vide ou sous flux de gaz inerte pour évacuer l'eau éventuellement physisorbée sur ledit support, The photocatalyst comprising a support and nanoparticles of molybdenum sulphide or tungsten sulphide having a band gap greater than 2.3 eV is prepared by the method described in documents FR 3,004,967 (for Mo) and FR 3,004,968 (for W) and comprises the following successive steps: i) an impregnation step by bringing into contact a solution comprising an organic solvent A and at least one mononuclear precursor based on Mo or W, denoted by M, under their monomeric or dimeric form, having at least one M = O or M-OR bond or at least one M = S or M-SR bond where R = C x H y where x> 1 and (x-1) <y < (2x + 1), with a porous support, advantageously previously calcined under vacuum or under an inert gas flow to evacuate the water possibly physisorbed on said support,
ii) une étape de maturation,  ii) a ripening stage,
iii) une étape de séchage du support imprégné, à une température inférieure à 200°C, sous atmosphère anhydre ou sous vide ou sous flux de gaz inerte, iv) une étape de sulfuration. Le procédé de préparation du photocatalyseur permet d’obtenir des nanoparticules de sulfure de molybdène ou de sulfure de tungstène présentant une bande interdite supérieure à 2,3 eV, cette valeur de bande interdite correspond à des tailles de particules inférieures à 3,5 nm. iii) a step of drying the impregnated support, at a temperature below 200 ° C, under an anhydrous atmosphere or under vacuum or under an inert gas stream, iv) a sulphurization step. The process for preparing the photocatalyst makes it possible to obtain nanoparticles of molybdenum sulphide or of tungsten sulphide having a band gap greater than 2.3 eV, this band gap value corresponds to particle sizes of less than 3.5 nm.
Les nanoparticules de sulfure de molybdène ou de sulfure tungstène se définissent par leur formule brute : MoSx tel que x = 2 ou 3. The nanoparticles of molybdenum sulphide or of tungsten sulphide are defined by their empirical formula: MoS x such that x = 2 or 3.
Le photocatalyseur peut également comprendre des nanoparticules d’oxysulfures de molybdène ou d’oxysulfures de tungstène. Ces nanoparticules se définissent par leur formule brute MoOySz tel que 0 < y+z <5 avec y et z des entiers strictement positifs. The photocatalyst may also comprise nanoparticles of molybdenum oxysulfides or tungsten oxysulfides. These nanoparticles are defined by their raw formula MoO y S z such that 0 <y + z <5 with y and z are strictly positive integers.
L’étape i) dite de mise en contact de la solution et du support est une imprégnation. Les imprégnations sont bien connues de l’Homme de l’art. La méthode d’imprégnation selon l’invention est choisie parmi l’imprégnation à sec, l’imprégnation en excès, les imprégnations successives. La méthode dite d'imprégnation à sec est avantageusement utilisée. Step i) said contacting the solution and the support is an impregnation. Impregnations are well known to those skilled in the art. The impregnation method according to the invention is chosen from dry impregnation, impregnation in excess, successive impregnations. The so-called dry impregnation method is advantageously used.
Le solvant organique A utilisé à l'étape i) est généralement un alcane, un alcool, un éther, une cétone, un solvant chloré ou un composé aromatique. Le cyclohexane et le n-hexane sont utilisés de manière préférée. The organic solvent A used in step i) is generally an alkane, an alcohol, an ether, a ketone, a chlorinated solvent or an aromatic compound. Cyclohexane and n-hexane are preferably used.
Le précurseur mononucléaire à base de Mo ou de W (noté M), utilisé sous sa forme monomérique ou dimérique, selon l'invention a avantageusement pour formule M(=0)n(=S)n'(0R)a(SR')b(L1)c(L2)d(L3)e(L4)f(L5)g  The mononuclear precursor based on Mo or W (denoted M), used in its monomeric or dimeric form, according to the invention advantageously has the formula M (= O) n (= S) n '(OR) a (SR' ) b (L1) v (L2) d (L3) e (L4) f (L5) g
où R = CxHy où x > 1 et (x-1 ) < y < (2x+1 ),  where R = CxHy where x> 1 and (x-1) <y <(2x + 1),
où R' = Cx'Hy' où x' > 1 et (x'-1) < y' < (2x'+1),  where R '= Cx'Hy' where x '> 1 and (x'-1) <y' <(2x '+ 1),
où 0 < h+h' < 2 et 0 < n < 2 et 0 < h' < 2,  where 0 <h + h '<2 and 0 <n <2 and 0 <h' <2,
où, si n = h' = 0, alors (a¹0 ou b¹0) et [(a+b+c+d+e+f+g = 6et0£a<6, 0<b <6, 0 < c < 6, 0 < d < 6, 0 < e < 6, 0 £ f £ 6, 0 < g < 6, ou (a+b+c+d+e+f+g = 5 et0£a<5, 0<b<5, 0<c<5, 0<d<5, 0<e<5, 0<f <5, 0<g<5), ou (a+b+c+d+e+f+g = 4et0£a<4, 0<b<4, 0<c<4, 0<d<4, 0<e<4, 0<f < 4, 0 < g < 4)] où, si [(n=1 et h' = 0) ou (h' = 1 et n = 0)], alors [a+b+c+d+e+f+g = 4 et 0 < a < 4, 0 < b < 4, 0 < c < 4, 0 < d < 4, 0 < e < 4, 0 < f < 4, 0 < g £ 4)] ou [(a+b+c+d+e+f+g = 3et0£a<3, 0<b<3, 0<c<3, 0<d<3, 0<e<3, 0<f < 3, 0 < g < 3)] where, if n = h '= 0, then (a¹0 or b¹0) and [(a + b + c + d + e + f + g = 6 and 0 <6, 0 <b <6, 0 <c <6 , 0 <d <6, 0 <e <6, 0 £ f £ 6, 0 <g <6, or (a + b + c + d + e + f + g = 5 and0 <5, 0 < b <5, 0 <c <5, 0 <d <5, 0 <e <5, 0 <f <5, 0 <g <5), or (a + b + c + d + e + f + g = 4 and 0 to <4, 0 <b <4, 0 <c <4, 0 <d <4, 0 <e <4, 0 <f <4, 0 <g <4)] where, if [(n = 1 and h '= 0) or (h' = 1 and n = 0)], then [a + b + c + d + e + f + g = 4 and 0 <a <4 , 0 <b <4, 0 <c <4, 0 <d <4, 0 <e <4, 0 <f <4, 0 <g 4)] or [(a + b + c + d + e + f + g = 3 and 0 <<3 <0 <e <3, 0 <f <3, 0 <g <3)]
où, si [n+n'=2 et 0 < n < 2 et 0 < h' < 2], alors (a+b+c+d+e+f+g = 2 et 0 < a < 2, 0<b<2, 0<c<2, 0<d<2, 0<e<2, 0<f<2, 0<g<2). avec (L1), (L2), (L3), (L4) et (L5), des ligands bien connus de l'Homme du métier et de type THF, dimethyl ether, dimethylsulfure, P(CH3)3, allyl, aryl, halogénés (choisis parmi les fluorés, les chlorés, les bromés, amine, acétate, acétylacétonate, halogénure, hydroxyde, -SH,... De manière préférée, les ligands sont choisis parmi l'acétylacétonate, le THF et le dimethyl ether.  where, if [n + n '= 2 and 0 <n <2 and 0 <h' <2], then (a + b + c + d + e + f + g = 2 and 0 <a <2, 0 <b <2, 0 <c <2, 0 <d <2, 0 <e <2, 0 <f <2, 0 <g <2). with (L1), (L2), (L3), (L4) and (L5), ligands well known to those skilled in the art and of the THF type, dimethyl ether, dimethylsulfide, P (CH3) 3, allyl, aryl halogenated (chosen from fluorinated, chlorinated, brominated, amine, acetate, acetylacetonate, halide, hydroxide, -SH, .... Preferably, the ligands are chosen from acetylacetonate, THF and dimethyl ether.
De manière préférée, les précurseurs selon l'invention ne contiennent pas de ligand (L1), (L2), (L3), (L4) et (L5). Preferably, the precursors according to the invention do not contain ligand (L1), (L2), (L3), (L4) and (L5).
De manière préférée, les précurseurs de molybdène selon l'invention sont choisis parmi les composés suivants : Mo(OEt)5, Mo(OEt)6, Mo(=0)(OEt)4, Mo(=S)(OEt)4, Mo(=S)(SEt)4, Mo(=0)2(OEt)2, Mo(OC6H5)6, Mo(SEt)5, Mo(SEt)6, Mo(OEt)(SEt)4, Mo(OEt)2(SEt)3, Mo(OEt)3(SEt)2, Mo(OEt)4(SEt), Mo(=0)(OEt)3(acac) avec Et = CH2CH3 (groupement éthyle) et acac = (CH3COCHCOCH3)- (acétylacétonate) sous leur forme monomérique ou dimérique. Preferably, the molybdenum precursors according to the invention are chosen from the following compounds: Mo (OEt) 5 , Mo (OEt) 6 , Mo (= O) (OEt) 4 , Mo (= S) (OEt) 4 , Mo (= S) (SEt) 4 , Mo (= O) 2 (OEt) 2 , Mo (OC 6 H 5 ) 6 , Mo (SEt) 5 , Mo (SEt) 6 , Mo (OEt) (SEt) 4 , Mo (OEt) 2 (SEt) 3 , Mo (OEt) 3 (SEt) 2 , Mo (OEt) 4 (SEt), Mo (= O) (OEt) 3 (acac) with Et = CH 2 CH 3 (ethyl group) and acac = (CH 3 COCHCOCH 3 ) - (acetylacetonate) in their monomeric or dimeric form.
De manière encore plus préférée, le précurseur de molybdène est le Mo(OEt)s.  Even more preferably, the molybdenum precursor is Mo (OEt) s.
De manière préférée, les précurseurs de tungstène selon l'invention sont choisis parmi les composés suivants : W(OEt)5, W(OEt)6, W(=0)(OEt)4, W(=S)(OEt)4, W(=S)(SEt)4, W(=0)2(0Et)2, W(OC6H5)6, W(SEt)5, W(SEt)6, W(OEt)4(SEt), W(OEt)3(SEt)2, W(OEt)2(SEt)3, W(OEt)(SEt)4, W(=0)(OEt)3(acac) avec Et = CH2CH3 (groupement éthyle) et acac = (CH3COCHCOCH3)- (acétylacétonate), sous leur forme monomérique ou dimérique. Preferably, the tungsten precursors according to the invention are chosen from the following compounds: W (OEt) 5 , W (OEt) 6 , W (= O) (OEt) 4 , W (= S) (OEt) 4 , W (= S) (SEt) 4 , W (= O) 2 (OEt) 2 , W (OC 6 H 5 ) 6 , W (SEt) 5 , W (SEt) 6 , W (OEt) 4 (SEt) ), W (OEt) 3 (SEt) 2 , W (OEt) 2 (SEt) 3 , W (OEt) (SEt) 4 , W (= O) (OEt) 3 (acac) with Et = CH 2 CH 3 (ethyl group) and acac = (CH 3 COCHCOCH 3 ) - (acetylacetonate), in their monomeric or dimeric form.
De manière très préférée, les précurseurs de tungstène selon l'invention sont W(OEt)5 ou W(OEt)6. L'étape ii) est une étape de maturation destinée à laisser diffuser les espèces à cœur du support. Elle est réalisée avantageusement sous atmosphère anhydre (sans eau), de préférence entre 30 minutes et 24h à température ambiante. L'atmosphère doit être de préférence anhydre afin de ne pas polycondenser les précurseurs préalablement imprégnés. Very preferably, the tungsten precursors according to the invention are W (OEt) 5 or W (OEt) 6 . Stage ii) is a maturation stage intended to allow the species to spread to the core of the support. It is advantageously carried out under anhydrous atmosphere (without water), preferably between 30 minutes and 24 hours at room temperature. The atmosphere must preferably be anhydrous in order not to polycondense the previously impregnated precursors.
Le séchage réalisé au cours de l'étape iii) est destiné à évacuer le solvant A d'imprégnation. L'atmosphère doit être de préférence anhydre (sans eau) afin de ne pas polycondenser lesdits précurseurs préalablement imprégnés. La température ne doit pas excéder 200°C afin de garder intacts lesdits précurseurs greffés ou déposés à la surface du support. De préférence, la température n'excédera pas 120°C. De manière très préférée, le séchage s'effectue sous vide, à température ambiante. Cette étape peut s’effectuer alternativement par le passage d’un flux gazeux inerte. The drying carried out during step iii) is intended to evacuate the impregnating solvent A. The atmosphere should preferably be anhydrous (without water) in order not to polycondense said precursors previously impregnated. The temperature must not exceed 200 ° C to keep intact said precursors grafted or deposited on the surface of the support. Preferably, the temperature will not exceed 120 ° C. Very preferably, the drying is carried out under vacuum, at room temperature. This step can be carried out alternately by the passage of an inert gaseous flow.
L'étape iv) de sulfuration peut être réalisée avantageusement à l'aide d'un mélange gazeux H2S/H2 ou H2S/N2 contenant au moins 5% volumique d'H2S dans le mélange à une température égale ou supérieure à la température ambiante, sous une pression totale égale ou supérieure à 1 bar (0,1 MPa) pendant au moins 2h. De manière préférée, la température de sulfuration est inférieure à 350°C. De manière très préférée, la température de sulfuration est inférieure à 200°C. L’étape iv) de sulfuration est destinée à obtenir le photocatalyseur à base de sulfure de molybdène ou de tungstène. Step iv) of sulfurization may advantageously be carried out using a gaseous mixture H 2 S / H 2 or H 2 S / N 2 containing at least 5% by volume of H 2 S in the mixture at a temperature equal to or greater than ambient temperature, at a total pressure equal to or greater than 1 bar (0.1 MPa) for at least 2 hours. Preferably, the sulfurization temperature is less than 350 ° C. Very preferably, the sulfurization temperature is below 200 ° C. The sulfurization step iv) is intended to obtain the photocatalyst based on molybdenum sulphide or tungsten.
Etape b) du procédé Step b) of the process
Selon l’étape b) du procédé selon l’invention, on irradie le photocatalyseur par au moins une source d'irradiation produisant au moins des photons de longueur d'onde inférieure à 540 nm ou d’énergie supérieure à 2,3 eV (soit la bande interdite minimum du photocatalyseur), de manière à réduire le dioxyde de carbone et oxyder le composé sacrificiel en présence dudit photocatalyseur activé par ladite source d'irradiation, de manière à produire un effluent contenant au moins en partie des molécules carbonées en C1 ou plus, différentes du C02. Toute source d'irradiation émettant au moins une longueur d'onde adaptée à l'activation dudit photocatalyseur, c'est-à-dire absorbable par le photocatalyseur, peut être utilisée selon l'invention. On peut par exemple utiliser l'irradiation solaire naturelle ou une source d'irradiation artificielle de type laser, Hg, lampe à incandescence, tube fluorescent, plasma ou diode électroluminescente (DEL, ou LED en anglais pour Light-Emitting Diode). De manière préférée, la source d'irradiation est l’irradiation solaire. According to step b) of the process according to the invention, the photocatalyst is irradiated with at least one irradiation source producing at least photons with a wavelength of less than 540 nm or with energy greater than 2.3 eV ( the minimum forbidden band of the photocatalyst), so as to reduce the carbon dioxide and oxidize the sacrificial compound in the presence of said photocatalyst activated by said irradiation source, so as to produce an effluent containing at least in part C1 carbonaceous molecules or more, different from C0 2 . Any irradiation source emitting at least one wavelength suitable for activating said photocatalyst, that is to say absorbable by the photocatalyst, can be used according to the invention. For example, it is possible to use natural solar irradiation or an artificial irradiation source of the laser, Hg, incandescent lamp, fluorescent tube, plasma or light emitting diode (LED) type (LED or Light-Emitting Diode). Preferably, the irradiation source is solar irradiation.
La source d'irradiation produit un rayonnement dont au moins une partie des longueurs d'onde est inférieure à la longueur d'onde maximale absorbable (Amax=540 nm) par les nanoparticules de sulfure de molybdène ou de sulfure de tungstène constitutives du photocatalyseur selon l’invention. Lorsque la source d’irradiation est l’irradiation solaire, elle émet généralement dans le spectre ultra-violet, visible et infra-rouge, c'est-à-dire elle émet une gamme de longueur d'onde de 280 nm à 2500 nm environ (selon la norme ASTM G173-03). De préférence, la source émet à au moins dans une gamme de longueurs d'ondes supérieure à 280 nm, de manière très préférée de 315 nm à 800 nm, ce qui inclut le spectre UV et/ou le spectre visible.The irradiation source produces a radiation of which at least a portion of the wavelengths is less than the maximum absorbable wavelength (A max = 540 nm) by the nanoparticles of molybdenum sulphide or of tungsten sulphide constituting the photocatalyst according to the invention. When the irradiation source is solar irradiation, it generally emits in the ultraviolet spectrum, visible and infra-red, that is to say it emits a wavelength range of 280 nm to 2500 nm about (according to ASTM G173-03). Preferably, the source emits at least in a wavelength range greater than 280 nm, very preferably 315 nm to 800 nm, which includes the UV spectrum and / or the visible spectrum.
La source d'irradiation fournit un flux de photons qui irradie le milieu réactionnel contenant le photocatalyseur. L'interface entre le milieu réactionnel et la source lumineuse varie en fonction des applications et de la nature de la source lumineuse. Dans un mode préféré lorsqu’il s’agit d’irradiation solaire, la source d'irradiation est localisée à l'extérieur du réacteur et l’interface entre les deux peut être une fenêtre optique en pyrex, en quartz, en verre organique ou toute autre interface permettant aux photons absorbables par le photocatalyseur selon l’invention de diffuser du milieu extérieur au sein du réacteur. The irradiation source provides a photon flux that irradiates the reaction medium containing the photocatalyst. The interface between the reaction medium and the light source varies depending on the applications and the nature of the light source. In a preferred mode when it is solar irradiation, the irradiation source is located outside the reactor and the interface between the two may be an optical window pyrex, quartz, organic glass or any other interface allowing photons absorbable by the photocatalyst according to the invention to diffuse external medium within the reactor.
La réalisation de la réduction photocatalytique du dioxyde de carbone est conditionnée par la fourniture de photons adaptés au système photocatalytique pour la réaction envisagée et de ce fait n’est pas limitée à une gamme de pression ou de température spécifique en dehors de celles permettant d’assurer la stabilité du ou des produit(s). La gamme de température employée pour la réduction photocatalytique de la charge contenant le dioxyde de carbone est généralement de -10°C à + 200°C, de manière préférée de 0 à 150°C, et de manière très préférée de 0 et 100 °C. La gamme de pression employée pour la réduction photocatalytique de la charge contenant le dioxyde de carbone est généralement de 0,01 MPa à 70 MPa (0,1 à 700 bar), de manière préférée de 0,1 MPa à 2 MPa (1 à 20 bar). The realization of the photocatalytic reduction of carbon dioxide is conditioned by the provision of photons adapted to the photocatalytic system for the reaction envisaged and therefore is not limited to a specific pressure or temperature range apart from those allowing ensure the stability of the product (s). The temperature range employed for photocatalytic reduction of the carbon dioxide containing feedstock is generally -10 ° C to + 200 ° C, preferably 0 to 150 ° C, and most preferably 0 and 100 ° C. The pressure range employed for the photocatalytic reduction of the carbon dioxide containing feedstock is generally from 0.01 MPa to 70 MPa (0.1 to 700 bar), more preferably from 0.1 MPa to 2 MPa (1 to 20 bar).
L'effluent obtenu après la réaction de réduction photocatalytique du dioxyde de carbone contient d'une part au moins une molécule en C1 ou plus, différente du dioxyde de carbone issue de la réaction et d'autre part de la charge non réagie, ainsi que l'éventuel fluide diluant, mais aussi des produits de réactions parallèles tel que par exemple le dihydrogène résultant de la réduction photocatalytique d’H20 lorsque ce composé est utilisé en tant que composé sacrificiel. The effluent obtained after the photocatalytic reduction reaction of the carbon dioxide contains on the one hand at least one molecule at C1 or more, different from the carbon dioxide resulting from the reaction and secondly from the unreacted charge, as well as the possible diluent fluid, but also products of parallel reactions such as for example the dihydrogen resulting from the photocatalytic reduction of H 2 0 when this compound is used as a sacrificial compound.
L’emploi du photocatalyseur dans un procédé de réduction photocatalytique de C02 permet d’absorber la partie visible du spectre solaire, et ainsi de valoriser une proportion importante de l’énergie solaire incidente. The use of the photocatalyst in a photocatalytic C0 2 reduction process makes it possible to absorb the visible part of the solar spectrum, and thus to recover a significant proportion of the incident solar energy.
Les exemples suivants illustrent l'invention.  The following examples illustrate the invention.
EXEMPLES EXAMPLES
Exemple 1 : Photocatalyseur A (non-conforme à l’invention) MoS2 Example 1 Photocatalyst A (not in accordance with the invention) MoS 2
Le photocatalyseur A est un semi-conducteur à base de MoS2 commercial sous forme de poudre (Aldrich™, pureté 99%). La bande interdite du photocatalyseur A est mesurée par spectrométrie d’absorption en réflexion diffuse à 1 ,71 eV. Photocatalyst A is a commercially available MoS 2 semiconductor in powder form (Aldrich ™, 99% purity). The band gap of photocatalyst A is measured by diffuse reflection absorption spectrometry at 1.71 eV.
Exemple 2 : Photocatalyseur B (non-conforme à l’invention) WS2 Example 2 Photocatalyst B (not in accordance with the invention) WS 2
Le photocatalyseur B est un semi-conducteur à base de WS2 commercial sous forme de poudre (Aldrich™ pureté 99%). La bande interdite du photocatalyseur A est mesurée par spectrométrie d’absorption en réflexion diffuse à 1 ,56 eV. Photocatalyst B is a semiconductor based on commercial WS 2 in powder form (Aldrich ™ 99% purity). The band gap of photocatalyst A is measured by diffuse reflection absorption spectrometry at 1.56 eV.
Exemple 3 : Photocatalyseur C (conforme à l’invention) MoSx/AI203 Example 3 Photocatalyst C (in accordance with the invention) MoSx / Al 2 O 3
Un support d’alumine y (y-AI203) est chargé dans un réacteur en quartz et calciné pendant 6h à 300 °C avec une rampe de montée en température de 5 °C/min, puis placé sous vide (105 mbar) à la même température pendant 16h. Ensuite, le support déshydroxylé est retiré de la ligne de vide et est refroidi à 140 °C puis stocké en boîte à gants. La surface spécifique du support d’alumine est de 284 m2/g. Le précurseur du molybdène est le pentaéthoxyde de molybdène Mo(OC2H5)5 (Gelest™, 90%). Du cyclohexane sec et dégazé est utilisé comme solvant. 1 ,96 mL de solution d'imprégnation, préparée à partir de 0,67 g de précurseur et de cyclohexane, sont imprégnés sur 2,58 g de support sec sur une rampe de synthèse utilisant des schlenks. L'imprégnation du support par la solution d’imprégnation se fait à l'aide d’une aiguille d’un schlenk à l’autre. An alumina carrier y (y-AI 2 0 3) is loaded into a quartz reactor and calcined for 6 hours at 300 ° C with a temperature increase ramp of 5 ° C / min, then placed under vacuum (10 5 mbar) at the same temperature for 16h. Then, the dehydroxylated carrier is removed from the vacuum line and cooled to 140 ° C and stored in a glove box. The specific surface area of the alumina support is 284 m 2 / g. The precursor of molybdenum is molybdenum pentaethoxide Mo (OC2H 5) 5 (Gelest ™, 90%). Dry and degassed cyclohexane is used as the solvent. 1.96 ml of impregnating solution, prepared from 0.67 g of precursor and cyclohexane, are impregnated on 2.58 g of dry support on a synthesis ramp using schlenks. The impregnation of the support with the impregnating solution is done using a needle from one schlenk to the other.
La quantité de molybdène est ajustée de façon à obtenir environ 1 ,7 Mo/nm2 soit une teneur massique en Mo de 8 %. Après une maturation de 15 heures, les extrudés sont séchés sous vide (105 mbar) durant 2 heures, à température ambiante. Après une maturation de 16 h, le solide est soumis à 2 cycles de séchage sous vide à température ambiante, d'abord par la ligne Schlenk (~ 8.102 mbar) pendant 1 h et ensuite par la ligne de vide poussé à 105 mbar pendant 1 h. Enfin le solide subit une étape de sulfuration effectuée à 100 °C avec un débit de gaz H2S/H2 (15/85 vol) de 2 L/h/g. L'analyse XPS montre que 60% du molybdène est entouré de soufre. La bande interdite du photocatalyseur C est mesurée par spectrométrie d’absorption en réflexion diffuse à 3,18 eV. The amount of molybdenum is adjusted to obtain about 1.7 Mo / nm 2, ie a mass content of 8% Mo. After maturing for 15 hours, the extrudates were dried in vacuo (10 -5 mbar) for 2 hours at room temperature. After a maturation of 16 h, the solid is subjected to 2 drying cycles under vacuum at room temperature, firstly by the Schlenk line (~ 8.10 2 mbar) for 1 h and then by the vacuum line pushed to 10 5 mbar for 1 hour. Finally, the solid undergoes a sulphurization step carried out at 100 ° C. with a gas flow H 2 S / H 2 (15/85 vol) of 2 L / h / g. XPS analysis shows that 60% of the molybdenum is surrounded by sulfur. The bandgap of the photocatalyst C is measured by diffuse reflection absorption spectrometry at 3.18 eV.
Exemple 4 : 2O3 Example 4 2O3
Le photocatalyseur D est préparé de manière identique au photocatalyseur C, seule l’étape de sulfuration diffère avec une température de traitement à 200 °C.  Photocatalyst D is prepared identically to photocatalyst C, only the sulfurization step differs with a treatment temperature of 200 ° C.
L'analyse XPS donne une sulfuration de molybdène de 87%. La bande interdite du photocatalyseur D est mesurée par spectrométrie d’absorption en réflexion diffuse à 2,49 eV.  XPS analysis gives a molybdenum sulphidation of 87%. The bandgap of the photocatalyst D is measured by diffuse reflection absorption spectrometry at 2.49 eV.
Exemple 5 : 2O3 Example 5 2O3
Un support d’alumine y (Y-AI2O3) est chargé dans un réacteur en quartz et calciné pendant 6h à 300 °C avec une rampe de montée en température de 5 °C/min, puis placé sous vide (105 mbar) à la même température pendant 16h. Ensuite, le support déshydroxylé est retiré de la ligne de vide et est refroidi à 140 °C puis stocké en boîte à gants. La surface spécifique du support d’alumine est de 284 m2/g. An alumina carrier y (Y-Al2O3) is loaded into a quartz reactor and calcined for 6 hours at 300 ° C with a temperature increase ramp of 5 ° C / min, then placed under vacuum (10 -5 mbar) to the same temperature for 16h. Then, the dehydroxylated carrier is removed from the vacuum line and cooled to 140 ° C and stored in a glove box. The specific surface area of the alumina support is 284 m 2 / g.
Le support d’alumine traitée (y -Al203) et un précurseur liquide de pentaéthoxyde de tungstène(V) - W(OEt)5 (Gelest™, 90%) sont insérés dans des flacons de Schlenk séparés. Les flacons ont ensuite été scellés et transférés sur la ligne Schlenk. Le précurseur de tungstène est dilué avec du cyclohexane séché et dégazé pour obtenir une solution d’imprégnation. Cette solution organique est préparée de manière à obtenir un taux de chargement en W de 1 ,7 atomes/nm2, soit une teneur massique en W de 5,5 %. L'imprégnation de ce précurseur sur le support se fait à l'aide de l'aiguille. The treated alumina support (y-Al 2 O 3 ) and a liquid precursor of tungsten pentaethoxide (V) -W (OEt) 5 (Gelest ™, 90%) are inserted into Schlenk flasks. separated. The flasks were then sealed and transferred to the Schlenk line. The tungsten precursor is diluted with dried and degassed cyclohexane to obtain an impregnating solution. This organic solution is prepared so as to obtain a loading rate in W of 1.7 atoms / nm 2 , a mass content in W of 5.5%. The impregnation of this precursor on the support is done using the needle.
Après une maturation de 16 h, le solide est soumis à 2 cycles de séchage sous vide à température ambiante, d'abord par la ligne Schlenk (~ 8.102 mbar) pendant 1 h et ensuite par la ligne de vide poussé à 105 mbar pendant 1 h. Enfin le solide subit une étape de sulfuration effectuée à 150 °C avec un débit de gaz H2S/H2 (15/85 vol) de 2 L/h/g. L'analyse XPS donne une sulfuration de tungstène de 75%. La bande interdite du photocatalyseur E est mesurée par spectrométrie d’absorption en réflexion diffuse à 2,71 eV. After a maturation of 16 h, the solid is subjected to 2 drying cycles under vacuum at room temperature, firstly by the Schlenk line (~ 8.10 2 mbar) for 1 h and then by the vacuum line pushed to 10 5 mbar for 1 hour. Finally, the solid undergoes a sulphurization step carried out at 150 ° C. with a gas flow H 2 S / H 2 (15/85 vol) of 2 L / h / g. XPS analysis gives a 75% tungsten sulfuration. The band gap of the photocatalyst E is measured by diffuse reflection absorption spectrometry at 2.71 eV.
Exemple 6 : Mise en œuyre des photocatalyseurs en réduction photocatalytique duExample 6: Implementation of photocatalysts in photocatalytic reduction of
C02 en phase gazeuse C0 2 in the gas phase
Les photocatalyseurs A, B, C, D et E sont soumis à un test de réduction photocatalytique du C02 en phase gazeuse dans un réacteur continu à lit traversé en acier muni d’une fenêtre optique en quartz et d’un fritté en face de la fenêtre optique sur lequel est déposé le solide photocatalytique. The photocatalysts A, B, C, D and E are subjected to a photocatalytic CO 2 gas phase reduction test in a continuous steel through-bed reactor equipped with a quartz optical window and a sintered glass opposite. the optical window on which the photocatalytic solid is deposited.
Une quantité suffisante de poudre est déposée sur le fritté de manière à recouvrir l’ensemble de la surface irradiée du réacteur (environ 100 mg). La surface géométrique irradiée pour tous les photocatalyseurs est de 8,042477.1004 m2. Les tests sont réalisés à température ambiante sous pression atmosphérique. Un débit de C02 de 0,3 ml/min traverse un saturateur d’eau avant d’être distribué dans le réacteur. On suit la production de CH4 issu de la réduction du dioxyde de carbone, par une analyse de l’effluent toutes les 6 minutes par micro chromatographie en phase gazeuse. La source d'irradiation UV-Visible est fournie par une lampe Xe-Hg (Asahi™ , MAX302™ ). La puissance d’irradiation est toujours maintenue à 80 W/m2 pour une gamme de longueur d’onde comprise entre 315 et 400 nm. La durée du test est de 20 heures. Les activités photocatalytiques sont exprimées en micromoles (pmol) de méthane produit par heure et par m2 irradié. Il s’agit d’activités moyennes sur l’ensemble de la durée des tests. Les résultats sont reportés dans le tableau 1 (ci-après) Sufficient powder is deposited on the sinter so as to cover the entire irradiated surface of the reactor (about 100 mg). The irradiated geometric area for all the photocatalysts is 8.042477.10 04 m 2 . The tests are carried out at ambient temperature under atmospheric pressure. A CO 2 flow rate of 0.3 ml / min passes through a water saturator before being dispensed into the reactor. The production of CH 4 from the reduction of carbon dioxide is monitored by an analysis of the effluent every 6 minutes by gas chromatography. The UV-Visible irradiation source is provided by an Xe-Hg lamp (Asahi ™, MAX302 ™). The irradiation power is always maintained at 80 W / m 2 for a range of wavelengths between 315 and 400 nm. The duration of the test is 20 hours. Photocatalytic activities are expressed in micromoles (pmol) of methane produced per hour per irradiated m 2 . These are average activities over the entire duration of the tests. The results are reported in Table 1 (below)
Tableau 1 : Performances des photocatalvseurs relatives à leur activité moyenne pour la production de méthane à partir d’un mélange CO? et HpO en phase gazeuse Table 1: Photocatalyst performance for their average activity for methane production from a mixture CO? and HpO in the gas phase
Les valeurs d'activité montrent que la mise en œuvre des solides selon l'invention permet la réduction photocatalytique du dioxyde de carbone en CH4. The activity values show that the use of the solids according to the invention allows the photocatalytic reduction of carbon dioxide to CH 4 .

Claims

REVENDICATIONS
1. Procédé de réduction photocatalytique du dioxyde de carbone effectué en phase liquide et/ou en phase gazeuse sous irradiation mettant en œuvre un photocatalyseur comprenant un support à base d'alumine ou de silice ou de silice- alumine et des nanoparticules de sulfure de molybdène ou de sulfure de tungstène présentant une bande interdite supérieure à 2,3 eV, ledit procédé comprenant les étapes suivantes : 1. Process for the photocatalytic reduction of carbon dioxide carried out in the liquid phase and / or in the gas phase under irradiation using a photocatalyst comprising a support based on alumina or silica or silica-alumina and nanoparticles of molybdenum sulphide or tungsten sulphide having a band gap greater than 2.3 eV, said method comprising the following steps:
a) on met en contact une charge contenant le dioxyde de carbone et au moins un composé sacrificiel avec ledit photocatalyseur,  a) a filler containing carbon dioxide and at least one sacrificial compound is contacted with said photocatalyst,
b) on irradie le photocatalyseur par au moins une source d'irradiation produisant au moins une longueur d'onde inférieure à la largeur de bande interdite dudit photocatalyseur de manière à réduire le dioxyde de carbone et oxyder le composé sacrificiel en présence dudit photocatalyseur activé par ladite source d'irradiation, de manière à produire un effluent contenant au moins en partie des molécules carbonées en C1 ou plus, différentes du C02. b) the photocatalyst is irradiated with at least one irradiation source producing at least one wavelength less than the forbidden band width of said photocatalyst so as to reduce the carbon dioxide and oxidize the sacrificial compound in the presence of said photocatalyst activated by said irradiation source, so as to produce an effluent containing at least partly C1 carbonaceous molecules or more, different from C0 2.
2. Procédé selon la revendication 1 , dans lequel, lorsqu’il est effectué en phase gazeuse, le composé sacrificiel est un composé gazeux choisi parmi l’eau, l’ammoniac, l’hydrogène, le méthane et un alcool.  The process according to claim 1, wherein, when carried out in the gas phase, the sacrificial compound is a gaseous compound selected from water, ammonia, hydrogen, methane and an alcohol.
3. Procédé selon la revendication 1 , dans lequel, lorsqu’il est effectué en phase liquide, le composé sacrificiel est un composé liquide choisi parmi l’eau, l’ammoniaque, un alcool, un aldéhyde et une amine. The method of claim 1 wherein, when carried out in the liquid phase, the sacrificial compound is a liquid compound selected from water, ammonia, an alcohol, an aldehyde and an amine.
4. Procédé selon l’une des revendications 1 à 3, dans lequel un fluide diluant est présent dans les étapes a) et/ou b). 4. Method according to one of claims 1 to 3, wherein a diluent fluid is present in steps a) and / or b).
5. Procédé selon l’une des revendications 1 à 4, dans lequel la source d’irradiation est une source d’irradiation artificielle ou naturelle. 5. Method according to one of claims 1 to 4, wherein the source of irradiation is a source of artificial or natural irradiation.
6. Procédé selon l’une des revendications 1 à 5, dans lequel la source d’irradiation émet à au moins dans une gamme de longueurs d'ondes supérieure à 280 nm. 6. Method according to one of claims 1 to 5, wherein the irradiation source emits at least in a wavelength range greater than 280 nm.
7. Procédé selon l’une des revendications 1 à 6, dans lequel le support poreux n’absorbe pas de photons d’énergie supérieure à 4 eV. 7. Method according to one of claims 1 to 6, wherein the porous support does not absorb energy photons greater than 4 eV.
8. Procédé selon l’une des revendications 1 à 7, dans lequel la teneur en sulfure de molybdène ou en sulfure de tungstène du photocatalyseur est comprise entre 4 et 50% poids par rapport au poids total du photocatalyseur.  8. Method according to one of claims 1 to 7, wherein the content of molybdenum sulfide or tungsten sulfide photocatalyst is between 4 and 50% by weight relative to the total weight of the photocatalyst.
9. Procédé selon l’une des revendications 1 à 8, dans lequel la densité surfacique qui correspond à la quantité d'atomes de molybdène Mo ou d’atomes de tungstène W, déposés par unité surfacique de support, est comprise entre 0,5 et 12 atomes de Mo ou de W par nanomètres carré de support. 9. Method according to one of claims 1 to 8, wherein the surface density which corresponds to the amount of Mo molybdenum atoms or tungsten W atoms, deposited per unit area support, is between 0.5 and 12 atoms of Mo or W per square nanometer of support.
10. Procédé selon l’une des revendications 1 à 9, dans lequel le photocatalyseur est préparé selon un procédé comprenant les étapes successives suivantes : 10. Method according to one of claims 1 to 9, wherein the photocatalyst is prepared according to a method comprising the following successive steps:
i) une étape d'imprégnation par mise en contact d'une solution comprenant un solvant organique A et au moins un précurseur mononucléaire à base de Mo ou de W, noté M, sous leur forme monomérique ou dimérique, présentant au moins une liaison M=0 ou M-OR ou au moins une liaison M=S ou M-SR où R = CxHy où x > 1 et (x-1 ) < y < (2x+1 ), avec un support à base d'alumine ou de silice ou de silice-alumine, avantageusement préalablement calciné sous vide ou sous flux de gaz inerte pour évacuer l'eau éventuellement physisorbée sur ledit support, i) a step of impregnation by bringing into contact a solution comprising an organic solvent A and at least one mononuclear precursor based on Mo or W, denoted M, in their monomeric or dimeric form, having at least one M bond = 0 or M-OR or at least one M = S or M-SR bond where R = C x H y where x> 1 and (x-1) <y <(2x + 1), with a d-based support alumina or silica or silica-alumina, advantageously previously calcined under vacuum or under an inert gas flow to evacuate the water possibly physisorbed on said support,
ii) une étape de maturation,  ii) a ripening stage,
iii) une étape de séchage du support imprégné, à une température inférieure à 200°C, sous atmosphère anhydre ou sous vide ou sous flux de gaz inerte, iv) une étape de sulfuration.  iii) a step of drying the impregnated support, at a temperature below 200 ° C, under an anhydrous atmosphere or under vacuum or under an inert gas stream, iv) a sulphurization step.
11. Procédé selon la revendication 10, dans lequel le précurseur de molybdène est choisi parmi les composés suivants : Mo(OEt)5, Mo(OEt)6, Mo(=0)(OEt)4, Mo(=S)(OEt)4, Mo(=S)(SEt)4, Mo(=0)2(OEt)2, Mo(OC6H5)6, Mo(SEt)5, Mo(SEt)6, Mo(OEt)(SEt)4, Mo(OEt)2(SEt)3, Mo(OEt)3(SEt)2, Mo(OEt)4(SEt), Mo(=0)(OEt)3(acac) avec Et = CH2CH3 (groupement éthyle) et acac = (CH3COCHCOCH3)- (acétylacétonate) sous leur forme monomérique ou dimérique. The process according to claim 10, wherein the molybdenum precursor is selected from the following compounds: Mo (OEt) 5 , Mo (OEt) 6 , Mo (= O) (OEt) 4 , Mo (= S) (OEt) ) 4 , Mo (= S) (SEt) 4 , Mo (= O) 2 (OEt) 2 , Mo (OC 6 H 5 ) 6 , Mo (SEt) 5 , Mo (SEt) 6 , Mo (OEt) ( SEt) 4 , Mo (OEt) 2 (SEt) 3 , Mo (OEt) 3 (SEt) 2 , Mo (OEt) 4 (SEt), Mo (= O) (OEt) 3 (acac) with Et = CH 2 CH 3 (ethyl group) and acac = (CH 3 COCHCOCH 3 ) - (acetylacetonate) in their monomeric or dimeric form.
12. Procédé selon la revendication 10, dans lequel le précurseur de tungstène est choisi parmi les composés suivants : W(OEt)s, W(OEt)6, W(=0)(0Et)4, W(=S)(OEt)4, W(=S)(SEt)4, W(=0)2(0Et)2, W(OC6H5)6, W(SEt)5, W(SEt)6, W(OEt)4(SEt), W(OEt)3(SEt)2, W(OEt)2(SEt)3, W(OEt)(SEt)4, W(=0)(0Et)3(acac) avec Et = CH2CH3 (groupement éthyle) et acac = (CH3COCHCOCH3)- (acétylacétonate), sous leur forme monomérique ou dimérique. The process according to claim 10, wherein the tungsten precursor is selected from the following compounds: W (OEt) s, W (OEt) 6 , W (= O) (OEt) 4 , W (= S) (OEt) ) 4 , W (= S) (SEt) 4 , W (= O) 2 (OEt) 2 , W (OC 6 H 5 ) 6 , W (SEt) 5 , W (SEt) 6 , W (OEt) 4 (SEt), W (OEt) 3 (SEt) 2 , W (OEt) 2 (SEt) 3 , W (OEt) (SEt) 4 , W (= O) (OEt) 3 (acac) with Et = CH 2 CH 3 (ethyl group) and acac = (CH 3 COCHCOCH 3 ) - (acetylacetonate), in their monomeric or dimeric form.
EP18796073.7A 2017-11-15 2018-11-07 Method for the photocatalytic reduction of carbon dioxide implementing a supported photocatalyst made from molybdenum sulfide or tungsten sulfide Pending EP3710162A1 (en)

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