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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 a strategy is 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 as methanol, ethanol, formic acid or even methane and all the hydrocarbons in Ci + can find an energy utility directly,.
• Carbon monoxide CO can also be energetically valorised in admixture with hydrogen for the formation of fuels by Fischer-Tropsch synthesis.
• the molecules of carboxylic acids, aldehydes, ketones or different alcohols can find applications in chemical or petrochemical processes. All these molecules are therefore of great interest from an industrial point of view.
• Halmann et al. (Solar Energy, 31, 4, 429-431, 1983) evaluated the performances of three semiconductors (Ti0 2 , SrTi0 3 and CaTiO 3 ) for the photocatalytic reduction of CO 2 in an aqueous medium. They notice the production of formaldehyde, formic acid and methanol.
• TiO 2 photocatalysts on which platinum nanoparticles are deposited are known for converting into a methane a mixture of CO 2 and H 2 O in the gas phase (QH, Zhang et al., Catal.Text, 148, p 335-340, 2009).
• Photocatalysts based on TiO 2 loaded with gold nanoparticles are also known from the literature for the photocatalytic reduction of CO 2 in the gas phase (SC Roy et al., ACS Nano, 4, 3, pp. 1259-1278, 2010) and in the aqueous phase (W. Hou et al., ACS Catal., 1, pp. 929-936, 201 1).
• Liou et al. (Energy Sci., 4, pp. 1487-1494, 201 1) have used NiO doped photocatalysts 4 with NiO to reduce CO 2 to CH 3 OH.
• the object of the invention is to propose a new, sustainable and more efficient way of producing carbon molecules that are valorized by photocatalytic conversion of carbon dioxide using an electromagnetic energy, using a photocatalyst in the form of monoliths. porous material containing at least one semiconductor.
• a patent application WO2015 / 1 1072 describes the use of a material based on N-TiO 2 in the form of a porous monolith as a photocatalyst for the degradation of pollutants in air or in water under radiation in the visible spectrum or for the cracking of water in H 2 under radiation in the visible spectrum.
• the document FR 2975309 describes a mode of preparation of porous monolith containing TiO 2 and its use as a photocatalyst for the degradation of pollutants in air or in water under irradiation.
• the present invention relates to a process for photocatalytic reduction of carbon dioxide carried out in the liquid phase and / or in the gas phase under irradiation using a photocatalyst in the form of a porous monolith containing at least one semiconductor.
• Said method more particularly comprises the following steps: a) a filler containing carbon dioxide and at least one sacrificial compound is contacted with a photocatalyst in the form of a porous monolith having a bulk density of less than or equal to 0.25 g / mL; 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 .
• the apparent density is calculated by making the ratio between the mass of catalyst and its geometric volume.
• the sacrificial compound is a gaseous compound chosen from water, ammonia, hydrogen, methane and an alcohol.
• the sacrificial compound is a compound that is soluble in the liquid phase 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.
• said photocatalyst in the form of a porous monolith has a mesoporous volume, whose pore diameter is greater than 0.2 nm and less than or equal to 50 nm, of between 0.01 and 1 ml / g, preferably between 0.05 and 0.5 ml / g.
• said photocatalyst in the form of a porous monolith has a macroporous volume of type I, ie a macroporous volume whose pore diameter is greater than 50 nm and less than or equal to 1000 nm (1 ⁇ ), between 0.1 at 3 ml / g, preferably between 0.2 and 2.5 ml / g.
• said photocatalyst in the form of a porous monolith has a macroporous volume of type II, ie a macroporous volume whose pore diameter is greater than 1 ⁇ and less than or equal to 10 ⁇ , of between 0.1 to 8 ml / for a diameter, preferably between 0.5 and 8 ml / g.
• said photocatalyst in the form of a porous monolith has a mesoporosity and / or a macroporosity of type I and / or a macroporosity of type II.
• said photocatalyst in the form of a porous monolith also has a macroporous volume, whose pore diameter is greater than 10 ⁇ , less than 0.5 ml / g.
• said photocatalyst in the form of a porous monolith has a bulk density of between 0.05 and 0.5 g / ml.
• the macroporous and mesoporous volumes are measured by mercury intrusion porosimetry according to ASTM D4284-83 at a maximum pressure of 4000 bar, using a surface tension of 484 dyne / cm and a contact angle of 140 °.
• said photocatalyst in the form of a porous monolith has a specific surface area (measured according to the ASTM D 3663-78 standard established from the Brunauer method, Emmett, Teller, the BET method, as defined in S.Brunauer, PHEmmett , E.Teller, J. Am. Chem Soc., 1938, 60 (2), pp 309-319.) Of between 10 and 1000 m 2 / g, preferably between 50 and 600 m 2 / g.
• said photocatalyst in the form of a porous monolith comprises at least one semiconductor diluted within at least one inorganic phase that does not absorb energy photons higher than 4 eV.
• the inorganic phase contains silica or alumina.
• the photocatalyst in the form of a monolith is constituted by the semiconductor.
• said photocatalyst in the form of a porous monolith comprises at least one semiconductor dispersed within at least one inorganic phase which does not absorb energy photons higher than 4 eV
• the semiconductor content is between 5 and 70% by weight relative to the total weight of the photocatalyst.
• said photocatalyst may contain at least one element M chosen from an element of the groups VIIIB, IB and NIA of the periodic classification of the elements in the metallic state.
• the content of element (s) M in the metallic state is between 0.001 and 20% by weight relative to the total weight of the photocatalyst.
• the semiconductor of said photocatalyst is selected from TiO 2 , ZnO, Cu 2 O, CuO, Ce 2 O 3 , CeO 2 , Nn 2 O 3 , SiC, ZnS, and Nn 2 S 3. , alone or in mixture.
• group VIII according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IUPAC classification.
• 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 C0 2 containing one or more carbon atoms, with the exception of C0 2 .
• 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.
• micropores means pores whose diameter is less than 2 nm; mesopores pores whose diameter is greater than 2 nm and less than or equal to 50 nm and macropores pores whose diameter is greater than 50 nm, and more particularly macropores type I pores whose diameter is greater than 50 nm and less or equal to 1000 nm (1 ⁇ ), and type II macropores pores whose diameter is greater than 1 ⁇ and less than or equal to 10 ⁇ .
• the subject of the present invention is a process for the photocatalytic reduction of carbon dioxide carried out in the liquid phase and / or in the gaseous phase under irradiation, using a photocatalyst in the form of a porous monolith containing at least one semiconductor, which process comprises the following steps:
• a filler containing carbon dioxide and at least one sacrificial compound is contacted with a photocatalyst in the form of a porous monolith comprising a bulk density of less than or equal to 0.25 g / ml;
• 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.
• 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.
• 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 CO 2 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 CO 2 In an aqueous medium, the CO 2 is then solubilized in the form of aqueous carbonic acid (H 2 CO 3 ), hydrogen carbonate or carbonate.
• the sacrificial compounds are liquid or solid oxidizable compounds soluble in the liquid charge, such as water (H 2 0) , alcohols, aldehydes, amines. 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 ⁇ , CI “ , F “ , N0 3 2 ⁇ .
• any solvated ion such as for example K + , Li + , Na + , Ca 2+ , Mg 2+ , S0 4 2 ⁇ , CI “ , 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 the production. the desired reduction of carbon dioxide.
• nitrogen can 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 photocatalyst in the form of a porous monolith comprises at least one semiconductor.
• the constituent semiconductor (s) of said photocatalyst are independently selected from inorganic, organic or organic-inorganic semiconductors.
• the bandgap of inorganic, organic or hybrid organic-inorganic semiconductors is generally between 0.1 and 4.0 eV.
• an inorganic semiconductor may be chosen from one or more elements of group IVA, such as silicon, germanium, silicon carbide or silicon-germanium. They may also be composed of elements of the NIA and VA groups, such as GaP, GaN, InP and InGaAs, or elements of groups MB and VIA, such as CdS, ZnO and ZnS, or elements of groups IB and VI IA, such as CuCl and AgBr, or elements of groups IVA and VIA, such as PbS, PbO, SnS and PbSnTe, or elements of groups VA and VIA, such as Bi 2 Te 3 and Bi 2 0 3 or elements of groups MB and VA, such as Cd 3 P 2 , Zn 3 P 2 and Zn 3 As 2 , or elements of groups IB and VIA, such as CuO, Cu 2 0 and Ag 2 S, or elements of groups VI I IB and VIA, such as CoO, PdO, Fe 2 O 3 and NiO,
• a semiconductor is selected from TiO 2 , ZnO, Cu 2 O, CuO, Ce 2 O 3 , CeO 2 , In 2 0 3 , SiC, ZnS, and Nn. 2 S 3 , alone or in mixture
• the semiconductor may optionally be doped with one or more elements chosen from metallic elements, such as for example elements V, Ni, Cr, Mo, Fe, Sn, Mn, Co, Re, Nb, Sb, La, Ce , Ta, Ti, non-metallic elements, such as for example C, N, S, F, P, or by a mixture of metallic and non-metallic elements.
• metallic elements such as for example elements V, Ni, Cr, Mo, Fe, Sn, Mn, Co, Re, Nb, Sb, La, Ce , Ta, Ti
• non-metallic elements such as for example C, N, S, F, P, or by a mixture of metallic and non-metallic elements.
• a semiconductor is chosen from organic semiconductors.
• Said organic semiconductors may be tetracene, anthracene, polythiophene, polystyrene sulphonate, phosphyrenes and fullerenes.
• a semiconductor is chosen from organic-inorganic semiconductors.
• organic-inorganic semiconductors mention may be made of crystalline solids of MOF type (for Metal Organic Frameworks according to the English terminology).
• the MOFs consist of inorganic subunits (transition metals, lanthanides, etc.) connected to each other by organic ligands (carboxylates, phosphonates, imidazolates, etc.), thus defining crystallized hybrid networks, sometimes porous.
• a semiconductor may be surface-sensitized with any organic molecules capable of absorbing photons.
• said photocatalyst in the form of a porous monolith is constituted by the semiconductor in the form of a monolith.
• said photocatalyst in the form of a porous monolith comprises at least one semiconductor dispersed in at least one inorganic phase that does not absorb energy photons higher than 4 eV.
• the inorganic dilution phase contains silica or alumina.
• said photocatalyst in the form of a porous monolith comprises at least one semiconductor diluted within at least one inorganic phase which does not absorb energy photons higher than 4 eV
• the semiconductor content is between 5 and 70% by weight relative to the total weight of the photocatalyst.
• said photocatalyst may contain at least one element M chosen from an element of the groups VIIIB, IB and NIA of the periodic classification of the elements in the metallic state.
• element in the metallic state means an element being at the zero oxidation state (and therefore in the form of metal).
• the content of element (s) M in the metallic state is between 0.001 and 20% by weight relative to the total weight of the photocatalyst.
• said photocatalyst in the form of a porous monolith has a mesoporous volume, whose pore diameter is greater than 0.2 nm and less than or equal to 50 nm, of between 0.01 and 1 ml / g, preferably between 0.05 and 0.5 ml / g.
• said photocatalyst in the form of a porous monolith has a macroporous volume of type I, ie a macroporous volume whose pore diameter is greater than 50 nm and less than or equal to 1000 nm (1 ⁇ ), between 0.1 at 3 ml / g, preferably between 0.2 and 2.5 ml / g.
• said photocatalyst in the form of a porous monolith has a macroporous volume of type II, ie a macroporous volume whose pore diameter is greater than 1 ⁇ and less than or equal to 10 ⁇ , of between 0.1 to 8 ml / for a diameter, preferably between 0.5 and 8 ml / g.
• said photocatalyst in the form of a porous monolith has a mesoporosity and / or a macroporosity of type I and / or a macroporosity of type II.
• said photocatalyst in the form of a porous monolith also has a macroporous volume, whose pore diameter is greater than 10 ⁇ , less than 0.5 ml / g.
• said photocatalyst in the form of a porous monolith has a bulk density of between 0.05 and 0.5 g / ml.
• the apparent density is calculated by making the ratio between the mass of catalyst and its geometric volume.
• said photocatalyst in the form of a porous monolith has a BET surface area of between 10 and 1000 m 2 / g, preferably between 50 and 600 m 2 / g.
• the process for preparing the photocatalyst can be any preparation method known to those skilled in the art and adapted to the desired photocatalyst. According to one variant, the process for preparing the photocatalyst comprises the following steps: 1) mixing a solution containing a surfactant with an acidic solution;
• step 2) adding to the solution obtained in step 1) at least one soluble precursor of inorganic carrier not absorbing photons of energy higher than 4 eV or an inorganic semiconductor precursor absorbing photons of energy between 0 , 1 and 4 eV; 3) optionally, is added to the solution obtained in step 2) at least one liquid organic compound, immiscible with the solution obtained in step 2) to form an emulsion;
• step 4 the solution obtained in step 2) or the emulsion obtained in step 3) is allowed to mature in the wet state in order to obtain a gel;
• step 5) the gel obtained in step 4) is washed with an organic solution; 6) the gel obtained in step 5) is dried and calcined to obtain a porous monolith;
• a solution comprising at least one semiconductor soluble precursor is impregnated into the porosity of the porous monolith obtained in step 6) when in step 2) at least one precursor is added to the solution obtained in step 1) soluble inorganic carrier that does not absorb energy photons higher than 4 eV, or optionally impregnates a solution comprising at least one soluble semiconductor precursor in the porosity of the porous monolith obtained in step 6) when at step 2) to the solution obtained in step 1) is added at least one inorganic semiconductor precursor absorbing energy photons between 0.1 and 4 eV, said precursor being identical to or different from said molecular precursor introduced at step 2);
• step 8) optionally, the product obtained in step 7) is dried and calcined to obtain a porous monolith.
• Step 1 Step 1
• step 1) of the process for preparing the photocatalyst a solution containing a surfactant is mixed with an acidic aqueous solution to obtain an acidic aqueous solution comprising a surfactant.
• the surfactant may be anionic, cationic, amphoteric or nonionic, more preferably the surfactant is poly (ethylene glycol), cetyl trimethylammonium bromide, or myristyltrimethylammonium bromide.
• the acidic agent is preferably selected from inorganic acids such as nitric, sulfuric, phosphoric, hydrochloric or hydrobromic acid or organic acids such as carboxylic or sulphonic acids, alone or as a mixture.
• the pH of the mixture is preferably less than 4. 2nd step)
• step 2) of the process for preparing the photocatalyst at least one soluble precursor of inorganic support not absorbing photons of energy higher than 4 eV is added or an inorganic semiconductor precursor absorbing photons of energy included between 0.1 and 4 eV
• an alcoholate-type precursor is chosen, preferably from aluminum isopropoxide, aluminum tert-butylate, tetraethylorthosilicate or tetramethylorthosilicate, alone or in admixture.
• an alcoholate precursor is preferably selected from titanium isopropoxide or tetreethylorthotitanate, alone or as a mixture.
• the precursor carrier alcoholate and / or inorganic semiconductor it is possible to add to the precursor carrier alcoholate and / or inorganic semiconductor, another inorganic semiconductor precursor ionic type or colloidal sol.
• the precursor mass / surfactant ratio is between 0.1 and 10.
• step 3 at least one liquid organic compound immiscible with the solution obtained in step 2) is added to the solution obtained in step 2) to form an emulsion.
• the liquid organic compound is a hydrocarbon or a mixture of hydrocarbons having 5 to 15 carbon atoms.
• the liquid organic compound / solution ratio obtained in step 2) is between 0.2 and 5.
• step 4 the solution obtained in step 2) or the emulsion obtained in step 3) is allowed to mature in the wet state in order to obtain a gel;
• the maturation is carried out at a temperature between 5 and 80 ° C.
• the maturation is carried out for 1 to 30 days.
• step 5 the gel obtained in step 4) is washed with an organic solution.
• the organic solution is acetone, ethanol, methanol, isopropanol, tetrahydrofuran, ethyl acetate or methyl acetate, alone or as a mixture.
• the washing step is repeated several times.
• step 6 the gel obtained in step 5) is dried and calcined to obtain a porous monolith.
• the drying is carried out at a temperature between 5 and 80 ° C. Preferably, the drying is carried out for 1 to 30 days.
• paper towels can be used to accelerate the drying of the materials.
• the calcination is carried out in two stages: a first temperature stage of between 120 and 250 ° C. for 1 to 10 hours, then a second temperature stage of between 300 and 950 ° C. for 2 to 24 hours.
• step 7 a solution comprising at least one semiconductor soluble precursor in the porosity of the porous monolith obtained in step 6) is impregnated when in step 2) is added to the solution obtained in step 1) at least one soluble precursor of inorganic support not absorbing energy photons higher than 4 eV, or optionally impregnating a solution comprising at least one soluble semiconductor precursor in the porosity of the porous monolith obtained in step 6 ) when in step 2) at least one energy-absorbing photon absorbing inorganic semiconductor precursor of between 0.1 and 4 eV is added to the solution obtained in step 1), said precursor being identical to or different from said precursor introduced in step 2).
• a maturation step is carried out in a humid atmosphere after the impregnation.
• a drying step is then carried out at a temperature of between 5 and 80 ° C. and for 0.5 to 30 days.
• a calcination step under air is then carried out with a first temperature stage of between 80 and 150 ° C. for 1 to 10 hours, then a second temperature stage of between 150 and 250 ° C. for 1 to 10 hours. and finally a third temperature stage of between 300 and 950 ° C for 0.5 to 24 hours.
• step 8 the product obtained in step 7) is dried and calcined to obtain a porous monolith.
• the precursor may be in the solubilized state in solution or in the form of a colloidal sol.
• a drying step is then carried out at a temperature of between 5 and 120 ° C. and for 0.5 to 2 days.
• a calcination step under air is then carried out with a first temperature stage of between 120 and 250 ° C. for 0.5 to 10 hours, then a second temperature stage of between 300 and 950 ° C. for 0, 5 to 24 hours.
• a reduction step is then carried out under a flow of hydrogen at a temperature of between 100 and 600 ° C. for 0.5 to 24h.
• the photocatalyst is irradiated with at least one irradiation source producing at least one wavelength less than the band gap width of said photocatalyst so as to reduce carbon dioxide. and oxidizing 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 .
• 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 forbidden 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: hxc
• 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 produces a radiation of which at least a portion of the wavelengths is less than the maximum absorbable wavelength (A max ) by the constituent semiconductor or semiconductors of the photocatalyst according to the invention.
• the irradiation source is solar irradiation, it generally emits in the ultraviolet, visible and infrared spectrum, that is, it emits a wavelength range of about 280 nm to about 2500 nm ( 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 the photocatalytic reduction of the carbon dioxide containing feedstock is generally -10 ° C to + 200 ° C, preferably 0 to 150 ° C, and very preferably preferred of 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.
• the following examples illustrate the invention without limiting its scope.
• a photocatalyst is a semiconductor-based shopping Ti0 2 in powder form (Aeroxide ® P25, Aldrich TM, purity> 99.5%).
• the particle size of the photocatalyst is 21 nm and its specific surface area is 52 m 2 / g.
• Photocatalyst B is a commercial Ce0 2 semiconductor in powder form (Aldrich TM 99.95% purity).
• the particle size of the photocatalyst is less than 50 nm and its specific surface area is 30 m 2 / g.
• the mixture is then poured into a 5.5 cm internal diameter Petri dish, which is installed in a saturator for 7 days for gelation.
• the gel obtained is then washed with isopropanol (Aldrich TM, purity> 99.5%) twice in succession and then dried at room temperature for 2 days.
• the gel is finally calcined in air in muffle furnace at 180 ° C for 2h, then at 350 ° C for 6h.
• Photocatalyst C is then obtained in the form of a porous monolith based on TiO 2 .
• Photocatalyst C has a mesoporous volume of 0.16 ml / g, a type I marcoporous volume of 0.19 ml / g and a macroporous volume of type II of 2.3 ml / g.
• Photocatalyst C has a specific surface area of 64 m 2 / g.
• Photocatalyst C has a bulk density of 0.23 g / ml.
• the emulsion is then poured into a petri dish of 5.5 cm internal diameter, which is installed in a saturator for 7 days for gelation.
• the gel obtained is then washed a first time with anhydrous tetrahydrofuran (Aldrich TM, purity> 99%), then with a mixture of anhydrous tetrahydrofuran / acetone (VWR TM, ACS grade) at 70/30 by volume twice in succession.
• Aldrich TM anhydrous tetrahydrofuran
• VWR TM a mixture of anhydrous tetrahydrofuran / acetone
• the gel is then dried at room temperature for 7 days.
• the gel is finally calcined in air in muffle furnace at 180 ° C for 2h, then at 800 ° C for 5h.
• the photocatalyst D is then obtained in the form of a porous monolith comprising Ti0 2 in an Si0 2 matrix.
• Photocatalyst D has a mesoporous volume of 0.1 1 ml / g, a Marc I volume of 0.74 ml / g and a macroporous volume of type II of 6.4 ml / g. Photocatalyst D has a specific surface area of 82 m 2 / g.
• the Ti element content measured by ICP-AES is 9.18% by weight, which is equivalent to 15.3% by weight of the TiO 2 semiconductor in the photocatalyst D.
• Photocatalyst D has a bulk density of 0.1 g / ml.
• the emulsion is then poured into a petri dish of 5.5 cm internal diameter, which is installed in a saturator for 7 days for gelation.
• the gel obtained is then washed a first time with anhydrous tetrahydrofuran (Aldrich, purity> 99%), then with a mixture of anhydrous tetrahydrofuran / acetone (VWR TM, ACS grade) at 70/30 by volume 2 times in succession.
• the gel is then dried at room temperature for 7 days.
• the gel is finally calcined in air in a muffle furnace at 180 ° C. for 2 hours, then at 650 ° C. for 5 hours.
• a porous monolith based on SiO 2 is then obtained.
• a solution containing 34 mL of distilled water, 44.75 mL of isopropanol (Aldrich TM, purity> 99.5%), 10.74 mL of hydrochloric acid (37% by weight, Aldrich TM, purity 97%) and 10.50 mL of titanium isopropoxide (Aldrich TM, 97% purity) is prepared with stirring. Part of this solution corresponding to the pore volume is impregnated in the porosity of the monolith, then left to mature for 12 hours. The monolith is then dried under ambient atmosphere for 24 hours. The step is repeated a second time.
• the monolith is finally calcined in air in muffle furnace at 120 ° C for 2 hours, then at 180 ° C for 2 hours and finally at 400 ° C for 1 hour.
• a porous monolith comprising TiO 2 in an SiO 2 matrix is then obtained.
• Photocatalyst E has a mesoporous volume of 0.20 ml / g, a macroporous volume of type I of 1.15 ml / g and a macroporous volume of type II of 5.8 ml / g.
• Photocatalyst E has a surface area of 212 m 2 / g.
• the content of Ti element measured by ICP-AES is 27.35% by weight, which is equivalent to 52.1% by weight of TiO 2 in the photocatalyst E.
• the photocatalyst E has a bulk density of 0.14 g / ml.
• the emulsion is then poured into a petri dish of 5.5 cm internal diameter, which is installed in a saturator for 7 days for gelation.
• the gel obtained is then washed a first time with anhydrous tetrahydrofuran (Aldrich TM, purity> 99%), then with a mixture of anhydrous tetrahydrofuran / acetone (VWR TM, ACS grade) at 70/30 by volume twice in succession.
• the gel is then dried at room temperature for 7 days.
• the gel is finally calcined in air in a muffle furnace at 180 ° C. for 2 hours, then at 650 ° C. for 5 hours.
• a porous monolith based on SiO 2 is then obtained.
• cerium nitrate hexahydrate (Aldrich TM, purity 99%) are dissolved in 95 ml of distilled water with stirring. Part of this solution corresponding to the pore volume is impregnated in the porosity of the monolith, then left to mature for 12 hours.
• the monolith is then dried under ambient atmosphere for 24 hours.
• the monolith is finally calcined in air in muffle furnace at 120 ° C for 2 hours, then at 180 ° C for 2 hours and finally at 450 ° C for 1 hour.
• a porous monolith comprising CeO 2 in an SiO 2 matrix is then obtained.
• Photocatalyst F has a mesoporous volume of 0.30 ml / g, a type I marcoporous volume of 1.34 ml / g and a macroporous volume of type II of 6.7 ml / g.
• Photocatalyst F has a specific surface area of 257 m 2 / g.
• the Ce element content measured by ICP-AES is 13.03% by weight, which is equivalent to 16.0% by weight of CeO 2 in the photocatalyst F.
• Photocatalyst F has a bulk density of 0.14 g / ml.
• the photocatalysts A, B, C, D, E and F 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 frit. face of the optical window on which the photocatalytic solid is deposited.
• photocatalysts A and B For photocatalysts A and B, a sufficient quantity of powder is deposited on the sinter so as to cover the entire irradiated surface of the reactor.
• photocatalysts C, D, E and F the monoliths are just placed on the sinter, their diameter being equal to the diameter of the reactor.
• the irradiated surface for all photocatalysts is 8.042477.10 "04 m 2. The tests were performed at room temperature under atmospheric pressure.
• the UV-Visible irradiation source is provided by a Xe-Hg lamp (Asahi TM, MAX302 TM) .
• the irradiation power is always maintained at 80 W / m 2 for a range of wavelength between 315 and 400 nm
• the duration of the test is 20 hours.
• the photocatalytic activities are expressed in ⁇ of dihydrogen and 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 implementation of the solids according to the invention systematically has the best photocatalytic performance and particularly better selectivities towards the photocatalytic reduction of C0 2 .

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