Method for photocatalysis by light / dark cycles

Abstract

The present invention relates to a photocatalysis method carried out in the gas phase and / or in the liquid phase, comprising the following steps: a) bringing a feedstock comprising a molecule selected from CO2, H2O, NH3 and a photodegradable organic compound, alone or as a mixture, into contact with a photocatalyst, and forming a reaction medium; b) irradiating the reaction medium with at least one irradiation source producing at least one wavelength of between 280 and 2500 nm, for n cycles of a duration t1 of between 1 and 60 minutes, n being greater than or equal to 2, the n cycles being spaced apart from one another by a duration t2 of between 1 and 60 minutes during which the reaction medium is not irradiated.

Description

[0001] PHOTOCATALYSIS PROCESS BY LIGHT / DARK CYCLES

[0002] TECHNICAL FIELD

[0003] The technical field is that of photocatalysis and its application for:

[0004] - Photoconversion of CO2 into liquid phase and / or gas phase;

[0005] - The production of dihydrogen H2, for example by photoconversion of water into the liquid phase and / or into the gas phase;

[0006] - Photooxidation of pollutants in a gaseous environment such as volatile organic compounds (VOCs) and / or pollutants in a liquid environment.

[0007] PRIOR TECHNIQUE

[0008] The process of using solar energy to convert carbon dioxide is of major interest because it allows solar energy to be stored in the form of solar fuel and / or other recoverable platform molecules. Moreover, since all the carbon atoms present in these solar fuels come from gaseous CO2, the process is considered carbon neutral in terms of its footprint.

[0009] Corma et al. WO2012168355A1 "Direct Photoconversion of Carbon Dioxide to Liquid Products" described, among other things, a photocatalytic process for the reduction of carbon dioxide and water. The process comprises the reactants: carbon dioxide (CO2) and water (H2O) in the presence of a photocatalyst which is exposed to electromagnetic radiation having a wavelength in the range of 200 to 700 nm.

[0010] The use of a light source to convert CO2 was first reported in 1978 in the work of Inoue et al. (Nature 1979, 277, 637-638). Since then, different photocatalytic materials (Li et al. Chem. Rev. 2019, 119, 3962) have been used under variable operating conditions in terms of CO2 concentration, H2O, CO2 / H2O ratio, presence of C>2, temperature, pressure. However, the result in the majority of studies is that the efficiency of the process remains low to date for various reasons mentioned in the literature (Protti et al. Phys. Chem. Chem. Phys., 2014, 16, 19790):

[0011] - Low absorption of light (solar spectrum) by the semiconductor (such as TiC>2, ZnO, WO3, BiVO4...);

[0012] - Low charge separation;

[0013] - Low solubility of CO2 in water (liquid phase conditions);

[0014] - Presence of reverse reactions during CO2 reduction; - Competition between CO2 reduction to solar fuel and H2O to H2.

[0015] The conditions of use of photocatalysts need to be optimized.

[0016] Thompson et al. (ACS Sustainable Chem. Eng. 2020, 8, 12, 4677) discloses a loss of activity when the photocatalyst operates in continuous flow, probably related to deactivation following the formation of reaction intermediates.

[0017] Document US5439652A "Use of controlled periodic illumination for an improved method of photocatalysis and an improved reactor design" by Sczechowski et al. also demonstrates that it was possible to improve the efficiency of a photocatalytic process for converting formates into CO2 and H2O by periodically irradiating a slurry-type photoreactor. The cycles described are very short, on the order of a few seconds.

[0018] It is potentially possible to improve the performance of photocatalysis processes by modifying, in particular, various parameters of these processes. The applicant has surprisingly demonstrated that alternating light / dark cycles of respective durations of between 1 and 60 minutes in a photocatalysis process makes it possible to significantly increase the production of photocatalysis products per unit of irradiation time and catalyst mass compared to a photocatalysis process by continuous irradiation.

[0019] SUMMARY OF THE INVENTION

[0020] The present invention relates to a photocatalysis process carried out in the gas phase and / or in the liquid phase comprising the following steps: a) bringing a feedstock comprising a molecule chosen from CO2, H2O, NH3 and a photodegradable organic compound, alone or as a mixture, into contact with a photocatalyst, and forming a reaction medium; b) irradiating the reaction medium with at least one irradiation source producing at least one wavelength between 280 and 2500 nm, for n cycles of a duration t1 between 1 and 60 minutes, preferably between 5 and 45 minutes, preferably between 10 and 30 minutes, n being greater than or equal to 2, the n cycles being spaced apart by a duration t2 between 1 and 60 minutes, preferably between 5 and 45 minutes, preferably between 15 and 45 minutes during which the reaction medium is not irradiated.

[0021] DETAILED DESCRIPTION OF THE INVENTION

[0022] According to the present invention, the expression "between ... and ..." and "between .... and ..." are equivalent and mean that the limit values ​​of the interval are included in the described range of values. If this is not the case and the limit values ​​are not included in the described range, such clarification will be provided by the present invention. For the purposes of the present invention, the different parameter ranges for a given step such as pressure ranges and / or temperature ranges can be used alone or in combination. For example, for the purposes of the present invention, a preferred pressure value range can be combined with a more preferred temperature value range.

[0023] In the following, particular embodiments of the invention may be described. They may be implemented separately or combined with each other, without limitation of combinations when technically feasible.

[0024] The following terms are defined within the scope of the present invention for better understanding:

[0025] The term "photodegradable organic compound" means a molecule comprising at least one carbon-hydrogen (CH) bond and which is capable of being degraded by the action of photons. Degradation means a reduction in its molecular weight.

[0026] The term "sacrificial compound" corresponds to an oxidizable compound, in gaseous or liquid form.

[0027] The groups of chemical elements correspond to those of the CAS classification (CRC Handbook of Chemistry and Physics, publisher CRC press, editor-in-chief DR Lide, 81st 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.

[0028] The textural and structural properties of the support and catalyst described below are determined by characterization methods known to those skilled in the art.

[0029] The total pore volume and pore distribution are determined by nitrogen porosimetry as described in the book “Adsorption by powders and porous solids. Principles, methodology and applications” written by F. Rouquérol, J. Rouquérol and K. Sing, Academic Press, 1999.

[0030] The term "specific surface area" means the BET specific surface area (SBET in m2 / g) determined by nitrogen adsorption in accordance with ASTM D 3663-78 established from the BRUNAUER-EMMETT-TELLER method described in the periodical "The Journal of American Society", 1938, 60, 309.

[0031] The maximum wavelength absorbable by a semiconductor is calculated using the following equation: With Δmax the maximum wavelength 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 forbidden band width or "bandgap" according to the Anglo-Saxon terminology of the semiconductor (in eV).

[0032] The term “reaction medium” means the mixture formed by the charge, the possible sacrificial compound and the photocatalyst.

[0033] According to European Council Directive 1999 / 13 / EC, "volatile organic compounds (VOCs)" means any compound containing at least the element carbon and one or more of the following elements: hydrogen, halogen, oxygen, sulfur, phosphorus, silicon or nitrogen, with the exception of carbon dioxide, and having a vapor pressure of 0.01 kPa or more at a temperature of 273.15 K.

[0034] Step a) of contact

[0035] The present invention comprises a step a) of bringing into contact a filler comprising a molecule chosen from CO2, H2O, NH3 and a photodegradable organic compound, alone or in a mixture, with a photocatalyst, and forming a reaction medium.

[0036] The charge

[0037] The process is carried out in gaseous, liquid or biphasic, gaseous and liquid phase, meaning respectively that the feedstock treated according to the process is in gaseous, liquid or biphasic, gaseous and liquid form.

[0038] When the process is carried out in the gas phase, with a feedstock in gaseous form, the molecule chosen from CO2, H2O, NH3 and a photodegradable organic compound is also in gaseous form.

[0039] A diluting fluid such as N2 or Ar may be present in the reaction medium when the process is carried out in the gas phase. The presence of a diluting fluid is not required for carrying out the invention, however it may be useful to add one to the feedstock to ensure the dispersion of the feedstock and / or the photocatalyst in said medium, the control of the adsorption of the reactants / products on the surface of the photocatalyst, the control of the absorption of photons by the photocatalyst, the dilution of the products to limit their recombination and other parasitic reactions of the same order. The presence of a diluting fluid also allows the control of the temperature of the reaction medium, thus being able to compensate for the possible exo / endothermicity of the photocatalyzed reaction. The nature of the diluting fluid is chosen in such a way that its influence is neutral on the reaction medium or that its possible reaction does not harm the achievement of the desired application.When the process is carried out in the liquid phase, with a charge in liquid form, this can be in ionic, organic or aqueous form. The charge in liquid form is preferably aqueous.

[0040] Optionally, and in order to modulate the pH of the aqueous liquid feedstock, a basic or acidic agent may be added to the feedstock. The basic agent may be chosen from alkali or alkaline earth hydroxides, organic bases, for example amines or ammonia. The acidic agent may be chosen from inorganic acids, for example nitric, sulfuric, phosphoric, hydrochloric, hydrobromic acid or organic acids such as carboxylic or sulfonic acids.

[0041] Optionally, when the liquid charge is aqueous, it can contain in any quantity any solvated ion, such as for example K + , Li + , N / A + , That 2+ , Mg2 + , SO42 CI; F; NCh 2 '.

[0042] When the desired application is the production of H2 in the gas phase, the molecule is chosen from H2O, NH3, and a photodegradable organic compound chosen from CH4 and an alcohol, alone or in a mixture.

[0043] When the desired application is the production of H2 in liquid phase, the molecule is chosen from H2O, NH3, and a photodegradable organic compound being an alcohol, alone or in a mixture.

[0044] When the desired application is the photoconversion of CO2 into the gas phase, the molecule is CO2 in gaseous form.

[0045] When the desired application is the photoconversion of CO2 in the liquid phase, the molecule is CO2 solubilized in the form of aqueous CO2, hydrogen carbonate or carbonate.

[0046] Advantageously, when the desired application is the production of H2 or the photoconversion of CO2, and the process is carried out in the gas phase, the feedstock and the photocatalyst are also brought into contact with at least one gaseous sacrificial compound which is an oxidizable compound chosen from H2O, NH3, H2, CH4 and an alcohol, alone or in a mixture. Preferably, the at least one gaseous sacrificial compound is chosen from H2O, H2 and an alcohol, alone or in a mixture.

[0047] Advantageously, when the desired application is the production of H2 or the photoconversion of CO2, and the process is carried out in the liquid phase, the feedstock and the photocatalyst are also brought into contact with at least one sacrificial compound which is a liquid or solid oxidizable compound soluble in the liquid feedstock chosen from H2O, NH3, an alcohol, an aldehyde, a carboxylic acid and an amine, alone or in combination. Preferably, the sacrificial compound is H2O or an alcohol. The pH is generally between 2 and 12, preferably between 3 and 10. Generally, the sacrificial compound is advantageously present to allow the reduction reactions (for example the reduction of CO2 or the reduction of H2O)

[0048] When the desired application is the photooxidation of pollutants in a gaseous medium, the molecule is a photodegradable organic compound being a volatile organic compound (VOC).

[0049] Advantageously, the at least one volatile organic compound is chosen from halogenated hydrocarbons, aromatic hydrocarbons, alkanes, alkenes, alkynes, aldehydes, ketones, alone or as a mixture.

[0050] When the desired application is the photooxidation of pollutants in a liquid medium, the molecule is a photodegradable organic compound solubilized in aqueous form.

[0051] Advantageously, the at least one solubilized photodegradable organic compound is chosen from halogenated hydrocarbons, aromatic hydrocarbons, alkanes, alkenes, alkynes, aldehydes, ketones, alone or as a mixture.

[0052] The photocatalyst

[0053] The photocatalyst is advantageously composed of one or more inorganic, organic or organic-inorganic semiconductors, and / or one or more transition metal complexes. The maximum wavelength of the photons absorbable by said photocatalysts is between 280 nm and 2500 nm (i.e. a forbidden band width generally between 0.50 and 4.43 eV).

[0054] According to a first variant, the semiconductor is chosen from inorganic semiconductors. The inorganic semiconductors may be chosen from one or more elements of group IVA, such as silicon, germanium, silicon carbide or silicon-germanium.They can also be composed of elements from groups A and VA, such as GaP, GaN, InP and InGaAs, or elements from groups IIB and VIA, such as CdS, ZnO and ZnS, or elements from groups IB and VIIA, such as CuCl and AgBr, or elements from groups IVA and VIA, such as PbS, PbO, SnS and PbSnTe, or elements from groups VA and VIA, such as Bi2Te3 and Bi2O3, or elements from groups IIB and VA, such as CdsP2, ZnsP2 and ZnsAs2, or elements from groups IB and VIA, such as CuO, CU2O and Ag2S, or elements from groups VII IB and VIA, such as CoO, PdO, Fe2O3 and NiO, or elements from groups VI B and VIA, such as M0S2 and WO3, or elements from groups VB and VIA, such as V2O5 and Nb20s, or elements from groups IVB and VIA, such as TiO2 and HfS2, or elements from groups II IA and VIA, such as ln2O3 and 10283, or elements from groups VIA and lanthanides, such as Ce2O3, Pr2O3, 801283, Tb2Ss and La2Ss, or elements from groups VIA and actinides, such as UO2 and UO3.Preferably, the semiconductor is chosen from TiO2, SiC, Bi2S3, Bi2O3, CdO, CdS, Ce2O3, CeO2, CeAIOs, CoO, CU2O, Fe2O3, FeTiOs, In2O3, In(OH)3, NiO, PbO, ZnO, Ag2S, CdS, Ce2S3, Cu2S, CulnS2, In2S3, MOS2, ZnFe2O3, ZnS, ZnO, WO3, ZnFe2O4 and ZrS2, alone or as a mixture.

[0055] According to another variant, the semiconductor is chosen from organic semiconductors. Said organic semiconductors may be chosen from tetracene, anthracene, polythiophene, polystyrene sulfonate, phosphyrenes, fullerenes and carbon nitrides.

[0056] According to another variant, the semiconductor is chosen from organic-inorganic semiconductors. Among organic-inorganic semiconductors, we can cite crystalline solids of the MOF type (for Metal Organic Frameworks according to the Anglo-Saxon terminology). MOFs are made up of inorganic subunits (transition metals, lanthanides, etc.) and connected to each other by organic ligands (carboxylates, phosphonates, imidazolates, etc.), thus defining crystallized hybrid networks, sometimes porous.

[0057] According to another variant, the transition metal complexes are in the form of a metal center of varying oxidation state and organic ligands having the following formula M(L)n, with M the metallic element and the n organic ligands L. The metallic element M is included in the transition metals of the periodic table of elements, preferably the metallic element M is Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Ir. When the transition metal complex is bimetallic (or binuclear), then the formula becomes M1M2(L)n. The L ligands can be monodentate (H2O, OH NH3, CH3OH, Cl; NCS; CN; CO, ...), bidentate (oxalate, 1,2-diaminoethane, ...), polydentate (EDTA, ...) and macrocyclic (crown ether, ...) ligands. When n>1, then the L ligands can be the same or different.

[0058] Preferably, the photocatalyst is composed of one or more inorganic semiconductors.

[0059] The semiconductors constituting said photocatalyst may optionally be doped with one or more ions chosen from metal ions, such as for example ions of V, Ni, Cr, Mo, Fe, Sn, Mn, Co, Re, Nb, Sb, La, Ce, Ta, Ti, non-metallic ions, such as for example C, N, S, F, P, or by a mixture of metal and non-metallic ions.

[0060] The semiconductors constituting said photocatalyst may contain particles comprising one or more element(s) in the metallic state chosen from an element of groups IVB, VB, VIB, VI IB, VI II B, IB, II B, I HA, IVA and VA of the periodic table of elements. Said particles comprising one or more element(s) in the metallic state are in direct contact with said semiconductor. Said particles may be composed of a single element in the metallic state or of several elements in the metallic state which may form an alloy. The term "element in the metallic state" (not to be confused with "metallic element") means an element belonging to the family of metals, said element being in the zero oxidation state (and therefore in the form of metal).Preferably, the element(s) in the metallic state are chosen from a metallic element from groups VIIB, VIIIB, IB and IIB of the periodic table of elements, and particularly preferably from platinum, palladium, gold, nickel, cobalt, ruthenium, silver, copper, rhenium or rhodium. Said particles comprising one or more element(s) in the metallic state are preferably in the form of particles with sizes between 0.5 nm and 1000 nm, preferably between 0.5 nm and 100 nm and even more preferably between 1 and 20 nm.

[0061] The semiconductors constituting said photocatalyst can be surface-sensitized with any organic molecules capable of absorbing photons.

[0062] The method of preparing the photocatalyst may be any preparation method known to those skilled in the art and suitable for the desired photocatalyst.

[0063] The photocatalyst used in the process according to the invention can be in different forms (nanometric powder, nanoobjects with or without cavities, etc.) or shaped (films, monolith, micrometric or millimetric sized beads, etc.). The photocatalyst is advantageously in the form of nanometric powder.

[0064] Contacting

[0065] The contacting of the charge comprising a molecule chosen from CO2, H2O, NH3 and a photodegradable organic compound, alone or in a mixture, can be done by any means known to those skilled in the art.

[0066] The contacting of said charge can advantageously be carried out in a fixed crossed bed, in a fixed licking bed or in suspension (also called "slurry" according to Anglo-Saxon terminology). The photocatalyst can also be deposited directly on optical fibers.

[0067] When the contact is in a fixed crossed bed, the photocatalyst is preferably deposited in a layer on a porous support, for example of the ceramic or metallic sintered type, and the charge is sent through the photocatalytic bed.

[0068] When the contact is in a fixed licking bed, the photocatalyst is preferably deposited in a layer on a non-porous support of the ceramic or metallic type, and the charge is sent to the photocatalytic bed.

[0069] When the contact is in suspension, the photocatalyst is preferably in the form of particles suspended in a liquid or liquid-gas charge comprising the molecule chosen from CO2, H2O, NH3 and a photodegradable organic compound, alone or in a mixture. In suspension, the implementation can be done in a closed reactor or continuously.

[0070] Step b) irradiation of the reaction medium

[0071] The method according to the invention comprises a step b) of irradiating the reaction medium with at least one irradiation source producing at least one wavelength between 280 and 2500 nm, preferably between 280 and 1100 nm, preferably between 315 nm and 800 nm, for n cycles of a duration t1 between 1 and 60 minutes, preferably between 5 and 45 minutes, preferably between 10 and 30 minutes, n being greater than or equal to 2, the n cycles being spaced apart by a duration t2 between 1 and 60 minutes, preferably between 5 and 45 minutes, preferably between 15 and 45 minutes during which the reaction medium is not irradiated.

[0072] The durations t1 and t2 can be equal or different.

[0073] Advantageously, the duration t2 is greater than or equal to the duration t1, preferably the duration t2 is greater than the duration t1. In this embodiment, the quantity of photocatalysis products obtained is increased, the applicant has demonstrated that the use of a dark time of duration t2 greater than or equal to the duration t1 during which the reaction medium is irradiated allows more efficient recharging of the surface of the photocatalyst.

[0074] In one embodiment n is greater than or equal to 3.

[0075] In one embodiment n is greater than or equal to 4.

[0076] In one embodiment n is greater than or equal to 5.

[0077] In one embodiment n is greater than or equal to 6.

[0078] A photocatalyst is advantageously composed of one or more semiconductors, and / or one or more transition metal complexes, which can be activated by the absorption of at least one photon.

[0079] In the case of semiconductors, absorbable photons are those whose energy is greater than the band gap. In other words, photocatalysts can be activated by at least one photon of a wavelength corresponding to the energy associated with the band gaps of the semiconductors constituting the photocatalyst or of a shorter wavelength.

[0080] Any irradiation source emitting at least one wavelength suitable for activating said photocatalyst present in the reaction medium, i.e. absorbable by said photocatalyst, can be used according to the invention. The irradiation source can be either natural by solar irradiation or artificial such as laser, Hg, incandescent lamp, fluorescent tube, plasma or light-emitting diode (LED). Preferably, the irradiation source is natural by solar irradiation.

[0081] The irradiation source produces radiation of which at least some of the wavelengths are lower than the maximum absorbable wavelength (λmax) by the semiconductors constituting the photocatalyst. When the irradiation source is solar irradiation, it generally emits in the ultraviolet, visible and infrared spectrum, that is to say it emits a wavelength range from 280 nm to 2500 nm (according to ASTM G173-03 standard).

[0082] The irradiation source provides a flux of photons 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.

[0083] When the irradiation source is natural, for example by solar irradiation, the irradiation source is located outside the reactor and the interface between the two can be an optical window made of pyrex, quartz, organic glass or any other interface allowing the photons absorbable by the photocatalyst according to the invention to diffuse from the external environment into the reactor.

[0084] The realization of the photocatalysis reaction is conditioned by the supply of photons adapted to the photocatalyst for the envisaged reaction and therefore is not limited to specific pressure or temperature ranges outside those allowing the stability of the product to be ensured.

[0085] Advantageously, the temperature range used for the photocatalysis reaction according to the invention is generally between -10 and +200°C, preferably between 0 and 150°C, and very preferably between 0 and 50°C.

[0086] Advantageously, the pressure range used for the photocatalysis reaction according to the invention is generally between 0.01 and 70 MPa (0.1 to 700 bar), preferably between 0.1 and 5 MPa (1 to 50 bar) and very preferably between 0.1 and 2 MPa (1 to 20 bar).

[0087] The following examples illustrate the invention without limiting its scope.

[0088] DESCRIPTION OF FIGURES

[0089] Figure 1 shows the cumulative amount of methane in arbitrary units produced as a function of time in minutes for a continuous CO2 photoconversion process over a 3-hour test period. The bottom right inset shows the amount of methane in arbitrary units produced as a function of time in minutes (analyzed by mass spectroscopy, m / z = 15).

[0090] Figure 2 represents the cumulative quantity of methane in arbitrary units produced as a function of time in minutes over 6 hours of testing including 3 hours of cumulative irradiation by light / dark cycles for a CO2 photoconversion process according to an embodiment of the invention, t1 = 30 min, t2 = 30 min, n = 6. The bottom right inset represents the quantity of methane in arbitrary units produced as a function of time in minutes (analyzed by mass spectroscopy, m / z = 15). It is observed that at a similar irradiation time, the CO2 photoconversion process according to an embodiment of the invention allows increased methane production compared to a conventional continuous irradiation process.

[0091] EXAMPLES

[0092] Example 1: Catalyst based on TiO2 and impregnated with 1% weight of Pt

[0093] The photocatalyst is a commercial TiO2-based semiconductor (CristalACTiV™ PC-500, Tronox, anatase, purity > 99 wt%). The particle size of the photocatalyst measured by X-ray diffraction (XRD) is 6 nm and the specific surface area measured by BET method is 393 m 2 / g. Reduced platinum particles were deposited by photodeposition, average particle size: 3 nm.

[0094] The sample is subjected to a gas-phase photocatalytic CO2 reduction test in a continuous flow-through reactor equipped with a quartz optical window with a surface area of ​​5.3.10' 4 m 2 and a porous sintered filter placed in front of the optical window on which the photocatalytic solid is deposited.

[0095] The tests are carried out at room temperature of 23°C under atmospheric pressure of 1 atm. A CO2 flow rate of 5 cc / min passes through a water saturator (allowing the carrier gas to be loaded at a level of 20,000 ppm H2O) before being distributed into the reactor.

[0096] After 3 hours of continuous irradiation or by n=6 cycles of a duration t1= 30 min with a period of darkness (absence of irradiation) of a duration t2 = 30 minutes also between each cycle, the analysis of the output products shows that much more methane is produced in the case of the cyclic scheme according to an embodiment of the invention compared to continuous irradiation.

[0097] The results are presented in the following table:

[0098]

[0099] We observe a gain of 1.8 for the production of methane (photoconversion of CO2) and of 1.2 for the production of dihydrogen (photoconversion of H2O).

[0100] Example 2: Catalyst based on TiO2 only

[0101] The photocatalyst is a commercial TiO2-based semiconductor (CristalACTiV™ PC-500, Tronox, anatase, purity > 99 wt%). The particle size of the photocatalyst measured by X-ray diffraction (XRD) is 6 nm and the specific surface area measured by BET method is 393 m 2 / g.

[0102] The sample is subjected to a gas-phase photocatalytic CO2 reduction test in a continuous flow-through reactor equipped with a quartz optical window with a surface area of ​​5.3.10 -4 m 2 and a porous sintered filter placed in front of the optical window on which the photocatalytic solid is deposited.

[0103] The tests are carried out at room temperature of 23°C under atmospheric pressure of 1 atm. A CO2 flow rate of 5 cc / min passes through a water saturator (allowing the carrier gas to be loaded at a level of 20,000 ppm H2O) before being distributed into the reactor.

[0104] After 1 h of continuous irradiation or by n=2 cycles of a duration t1= 30 min with a period of darkness (absence of irradiation) of a duration t2 = 30 minutes also between the two cycles, the analysis of the output products shows that much more methane is produced in the case of the cyclic scheme for a CO2 photoconversion process according to an embodiment of the invention compared to continuous irradiation.

[0105] The results are presented in the following table:

[0106] A gain of 1.2 is also observed for the production of dihydrogen (photoconversion of H2O).

Claims

CLAIMS 1 Photocatalysis process carried out in the gas phase and / or in the liquid phase comprising the following steps: a) bringing a feedstock comprising a molecule chosen from CO2, H2O, NH3 and a photodegradable organic compound, alone or in a mixture, into contact with a photocatalyst, and forming a reaction medium; b) irradiating the reaction medium with at least one irradiation source producing at least one wavelength between 280 and 2500 nm, for n cycles of a duration t1 of between 1 and 60 minutes, preferably between 5 and 45 minutes, preferably between 10 and 30 minutes, n being greater than or equal to 2, the n cycles being spaced apart by a duration t2 of between 1 and 60 minutes, preferably between 5 and 45 minutes, preferably between 15 and 45 minutes during which the reaction medium is not irradiated. 2 Method according to claim 1 in which the duration t2 is greater than or equal to the duration t1, preferably the duration t2 is greater than the duration t1. 3 Method according to any one of the preceding claims wherein said at least one wavelength is between 280 and 1100 nm, preferably between 315 nm and 800 nm. 4 Method according to any one of the preceding claims in which the photocatalyst is composed of one or more inorganic, organic or organic-inorganic semiconductors, and / or one or more transition metal complexes. 5 Method according to claim 4 wherein the semiconductor is chosen from TiC>2, SiC, Bi2Sa, Bi20s, CdO, CdS, Ce2C>3, CeC>2, CeAICh, CoO, CU2O, Fe2C>3, FeTiOs, I^Ch, I' I n(OH)s, NiO, PbO, ZnO, Ag2S, CdS, Ce2S3, CU2S, CulnS2, ln2S3, M0S2, ZnFe2C>3, ZnS, ZnO, WO3, ZnFe2O4 and ZrS2, alone or in a mixture. 6 Method according to claim 4 in which the semiconductor is an organic semiconductor chosen from tetracene, anthracene, polythiophene, polystyrene sulfonate, phosphyrenes, fullerenes and carbon nitrides. 7 Method according to claim 4 wherein the semiconductor is an organic-inorganic semiconductor such as a crystalline solid of the MOF type. 8 Method according to any one of the preceding claims in which the contacting of the load is carried out in a fixed crossed bed, in a fixed licking bed or in suspension. 9 Method according to any one of the preceding claims in which the source of irradiation is natural by solar irradiation. 10 Method according to any one of claims 1 to 9 in which the molecule is chosen from H2O, NH3, and a photodegradable organic compound chosen from CH4 and an alcohol, alone or as a mixture. 11 Method according to any one of claims 1 to 9 in which the molecule is chosen from H2O, NH3, and a photodegradable organic compound being an alcohol, alone or in a mixture. 12 Method according to any one of claims 1 to 9 in which the molecule is CO2 in gaseous form. 13 Method according to any one of claims 1 to 9 in which the molecule is CO2 solubilized in the form of aqueous CO2, hydrogen carbonate or carbonate. 14 Method according to any one of claims 1 to 9 in which the molecule is a photodegradable organic compound being a volatile organic compound. 15 Method according to any one of claims 1 to 9 in which the molecule is a photodegradable organic compound solubilized in aqueous form chosen from halogenated hydrocarbons, aromatic hydrocarbons, alkanes, alkenes, alkynes, aldehydes, ketones, alone or in a mixture.

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