Classifications

• • 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
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
  • B01J35/39—Photocatalytic properties
• • 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—Ultraviolet light
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  • 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
• • 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
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/19—Catalysts containing parts with different compositions
• • 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
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
  • B01J35/33—Electric or magnetic properties
• • 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
• • 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
  • B01J2235/00—Indexing scheme associated with group B01J35/00, related to the analysis techniques used to determine the catalysts form or properties
• • 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 .

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