FR3026965A1 - METHOD FOR PHOTOCATALYTIC REDUCTION OF CARBON DIOXIDE USING COMPOSITE PHOTOCATALYST. - Google Patents

Abstract

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 containing a first semiconductor SC1, particles comprising one or more element (s) M to the metallic state, and a second semiconductor SC2, said method being carried out by contacting a charge containing CO2 and at least one sacrificial compound with said photocatalyst, and then the photocatalyst is irradiated so as to reduce the CO 2 and oxidize the sacrificial compound so as to produce an effluent containing at least partly C1 carbonaceous molecules or more, different from CO2.

Description

The field of the invention is that of the photocatalytic reduction of carbon dioxide (CO2) under irradiation by the use of a particular photocatalyst, preferably containing a supported core-layer type architecture. Fossil fuels, such as coal, oil and natural gas, are the world's leading conventional sources of energy because of their availability, stability and high energy density. However, combustion produces carbon dioxide emissions which are considered to be the main cause of global warming. Thus, there is a growing need to mitigate CO2 emissions, either by capturing it or by transforming it. Although carbon capture and sequestration (CCS) is generally considered to be an effective process for reducing CO2 emissions, other strategies need to be considered, including strategies for converting CO2 into products with economic value, such as fuels and industrial chemicals. Such a strategy is the reduction of carbon dioxide into valuable products. The reduction of carbon dioxide can be carried out biologically, thermally, electrochemically or photocatalytically.

Among these options, the photocatalytic reduction of CO2 is gaining increased attention as it can potentially consume alternative forms of energy by harnessing solar energy, which is plentiful, cheap, and ecologically clean and safe. The photocatalytic reduction of carbon dioxide makes it possible to obtain carbon molecules in Cl 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 can find an energy utility directly, such as methanol, ethanol, formic acid or methane and all hydrocarbons in C1 ±. Carbon monoxide CO can also be energetically valorised in admixture with hydrogen for the formation of fuels by FischerTropsch synthesis. The carboxylic acid molecules, aldehydes, ketones or different alcohols for their part can find applications in the chemical or petrochemical processes. All these molecules are therefore of great interest from an industrial point of view. PRIOR ART Methods of photocatalytic reduction of carbon dioxide in the presence of a sacrificial compound are known in the state of the art. Halmann et al. (Solar Energy, 31, 4, 429-431, 1983) evaluated the performance of three semiconductors (TiO2, SrTiO3 and CaTiO3) for the photocatalytic reduction of CO2 in an aqueous medium. They notice the production of formaldehyde, formic acid and methanol.

Anpo et al. (J. Phys Chem B 101, pp. 2632-2636, 1997) investigated the photocatalytic reduction of CO2 with water vapor on TiO 2 photocatalysts anchored in micropores of zeolites. These showed a very high selectivity in methanol gas. TiO2-based photocatalysts on which platinum nanoparticles are deposited are known to convert a mixture of CO 2 and H 2 O to the gas phase into methane (QH, Zhang et al., Catal.Text, 148, 335). 340, 2009). Photocatalysts based on TiO 2 loaded with gold nanoparticles are also known from the literature for the photocatalytic reduction of CO2 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, 2011). Wang et al. (J. Phys., Lett., 1, pp. 48-53, 2010) conducted a study on CO2 photoreduction with H2O in visible light catalyzed by CdSe-based heterostructured materials deposited on a solid composed of platinum nanoparticles. on the surface of TiO2. This type of implementation, however, differs from the invention in that the platinum metal is not at the heart of CdSe or TiO2 nanoparticles. Indeed, as demonstrated in the publication by transmission electron microscopy and XPS analyzes, the solid is composed of CdSe particles on the one hand and platinum metal particles on the other hand, both types of particles being deposited. on the same TiO2 semiconductor medium.

It is also known that the photocatalytic reduction of CO2 in methanol, formic acid and formaldehyde in aqueous solution can be carried out using different semiconductors such as ZnO, CdS, GaP, SiC or WO3 (T Noue et al., Nature, 277, 637-638, 1979). Liou et al. (Energy Environ, Sci., 4, pp. 1487-1494, 2011) used NiO doped InTaO4 photocatalysts to reduce CO2 to CH3OH.

Sato et al. (JACS, 133, pp. 15240-15243, 2011) have studied a hybrid system combining a p-type InP semiconductor and a ruthenium-complexed polymer in order to achieve a selective reduction of CO2. Finally, a review and a book chapter from the open literature provide a comprehensive review of the photocatalysts employed in photocatalytic carbon dioxide reduction: M. Tahir, N. S. Amin, Energy Conv. Manag., 76, p. 194-214, 2013 on the one hand, and Photocatalysis, Topics in current chemistry 303C.A. Bignozzi Editor, Springer, p. 151-184,2011 on the other hand. 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 using an electromagnetic energy, using a photocatalyst containing a first semiconductor SC1 in direct contact with particles comprising one or more elements M in the metallic state chosen from an element of Groups IVB, VB, VIB, VIIB, VIIIB, IB, IIB, IIIA, IVA and VA of the periodic classification of the elements, said particles being in direct contact with a second semiconductor SC2 so that the second semiconductor SC2 covers at least 50% of the surface of the particles comprising one or more element (s) M to the metallic state. The use of this type of photocatalyst for the photocatalytic reduction of CO2 makes it possible to achieve improved performances compared to known photocatalysts for this reaction. Photocatalysts containing semiconductors, in particular photocatalysts composed of core-layer particles on the surface of a semiconductor substrate are known in the state of the art. C. Li et al (J. Hydrogen Energy, 37, pp. 6431-6437, 2012) have unveiled the synthesis of TiO2 nanotube-based solids on which are deposited in a photo-assisted manner oxidized metallic copper particles in their surface.

H. Lin et al. (Comm.Comm., 21, pp. 91-95, 2012) propose a composite prepared by coprecipitation composed of AgBr / Ag / Agl, AgBr and Agl both being semiconductors. C. Wang et al. (Chem Eng J., 237, p.29-37, 2014) prepared by successive impregnations a material having contacts between WO3 and Pt on the one hand and Pt and TiO2 on the other hand. Finally, H. Tada (Nature Materials, 5, pp. 782-786, 2006) proposes a solid based on hemispherical particles having a layer of CdS around an Au core, which particles are deposited on the semiconductor TiO2. It is also known from the open literature (Ding et al., Int.J. Hydrogen Energy, 38, pp. 8244-8253, 2013) to carry out, in photocatalytic conversion of H 2 O to H 2, a solid exhibiting the CdS-Au-TiO2 structure, CdS and Au being constitutive of nanoparticles such that the CdS is in the form of a layer around an Au core, these nanoparticles being deposited on a TiO2 support.

However, none of these documents discloses the use of a photocatalyst containing a first semiconductor SC1 in direct contact with particles comprising one or more element (s) M in the metallic state chosen from an element of groups IVB , VB, VIB, VIIB, VIIIB, IB, IIB, IIIA, IVA and VA of the Periodic Table of Elements, said particles being in direct contact with a second SC2 semiconductor in a photocatalytic carbon dioxide reduction process. More particularly, the invention describes 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 containing a first semiconductor SC1, particles comprising one or more elements ( s) M in the metallic state selected from an element of groups IVB, VB, VIB, VIIB, VIIIB, IB, IIB, IIIA, IVA and VA of the periodic table of elements, and a second semiconductor SC2, said first semiconductor conductor SC1 being in direct contact with said particles having one or more element (s) M in the metallic state, said particles being in direct contact with said second semiconductor SC2 so that the second semiconductor SC2 overlaps with less than 50% of the surface area of the particles comprising one or more elements M in the metallic state, said process comprising the following steps: aact a feedstock containing carbon dioxide and at least one sacrificial compound with said photocatalyst, b) the photocatalyst is irradiated with at least one irradiation source producing at least one wavelength less than the band gap width of said photocatalyst in order to reduce the carbon dioxide and to 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 the CO2. According to a variant, and when the process is carried out in the gas phase, the sacrificial compound is a gaseous compound chosen from water, ammonia, hydrogen, methane and an alcohol. Alternatively, and when the process is carried out in the liquid phase, the sacrificial compound is a soluble liquid or solid compound selected from water, ammonia, an alcohol, an aldehyde or an amine. Alternatively, a diluent fluid is present in steps a) and / or b). According to one variant, the irradiation source is a source of artificial or natural irradiation.

According to a preferred variant, the first semiconductor SC1 is in direct contact with the second semiconductor SC2. According to a preferred variant, said first semiconductor SC1 forms a support, said support contains at its surface core-layer type particles, said layer being formed by said semiconductor SC2, said core being formed by said particles comprising a or more element (s) M in the metallic state. According to one variant, the respective content of semiconductors SC1 or SC2 is between 0.01 and 50% by weight relative to the total weight of the photocatalyst. According to one variant, 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.

According to one variant, the element M in the metallic state is chosen from platinum, palladium, gold, nickel, cobalt, ruthenium, silver, copper, rhenium or rhodium. Alternatively, the semiconductors SC1 and SC2 are independently selected from inorganic, organic or organic-inorganic semiconductor. According to one variant, the semiconductor SC1 is chosen from TiO2, ZnO, WO3, Fe2O3, and ZnFe2O4. According to one variant, the semiconductor SC2 is chosen from Cu2O, Ce203, In203, SiC, ZnS, and In2S3.

According to a variant, the photocatalyst comprises a support composed of a semiconductor SC1 chosen from TiO2, ZnO, WO3, Fe2O3, ZnFe2O4 containing on its surface core-layer particles, said core consisting of one or more element (s) M in the metallic state selected from platinum, palladium, gold, nickel, cobalt, ruthenium, silver, copper, rhenium or rhodium, said layer consisting of a semiconductor SC2, selected from Cu2O, Ce203, In203. In the following, groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, publisher CRC Press, editor in chief D.R. 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. DETAILED DESCRIPTION OF THE INVENTION The invention describes 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 containing a first semiconductor SC1, particles comprising one or more a plurality of metallic M element (s) selected from an element of groups IVB, VB, VIB, VIIB, VIIIB, IB, IIB, IIIA, IVA and VA of the periodic table of elements, and a second semiconductor SC2 said first semiconductor SC1 being in direct contact with said particles having one or more metal element (s) M, said particles being in direct contact with said second semiconductor SC2 so that the second semiconductor SC2 covers at least 50% of the surface area of the particles comprising one or more metal M-element (s), said process comprising the following steps: 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 bandwidth said photocatalyst is inhibited 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 a portion of the C1 carbonaceous molecules or more, different from the CO2. According to step a) of the process according to the invention, a feedstock containing said carbon dioxide and at least one sacrificial compound is contacted with said photocatalyst. By sacrificial compound is meant an oxidizable compound. The sacrificial compound may be in gaseous or liquid form. The term "carbon-containing molecules in Cl 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 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.

When the feed is in gaseous form, the CO2 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 (H2O), ammonia (NH3), hydrogen (H2), methane (CH4) or alcohols. Preferably, the gaseous sacrificial compounds are water or hydrogen. When the charge is in gaseous form, the CO2 and the sacrificial compound may be diluted by a gaseous diluent fluid such as N 2 or Ar. When the charge is in liquid form, it may be in the form of a liquid. ionic, organic or aqueous. The charge in liquid form is preferably aqueous. In an aqueous medium, the CO2 is then solubilized in the form of aqueous CO2, hydrogen carbonate or carbonate. The sacrificial compounds are oxidizable liquid or solid compounds soluble in the liquid charge, such as water (H2O), ammonia (NH3), alcohols, aldehydes, amines. In a preferred manner, the sacrificial compound is water. When the liquid charge is an aqueous solution, the pH is generally between 2 and 12, preferably between 3 and 10. Optionally, and in order to modulate the pH of the aqueous liquid charge, a basic or acidic agent may be added to load. When a basic agent is introduced it is preferably selected from alkali or alkaline earth hydroxides, organic bases such as amines or ammonia.

When an acidic agent is introduced it is preferably selected from inorganic acids such as nitric, sulfuric, phosphoric, hydrochloric, hydrobromic acid or organic acids such as carboxylic or sulfonic acids. Optionally, when the liquid charge is aqueous, it may contain in any quantity any solvated ion, such as, for example, K +, Li +, Na +, Ca 2 +, mg 2 +, s0 42-, Cl-, F-, NO 2. is carried out in the liquid phase or in the gas phase, a diluent fluid, respectively liquid or gaseous, may be present in the reaction medium. The presence of a diluent fluid is not required for carrying out the invention, however it may be useful to add to the charge to ensure dispersion of the charge in the medium, the dispersion of the photocatalyst, a control of the adsorption of the reagents / products on the surface of the photocatalyst, a control of the absorption of photons by the photocatalyst, the dilution of the products to limit their recombination and other similar parasitic reactions. The presence of a diluent fluid also makes it possible to control the temperature of the reaction medium, thus being able to compensate for the possible exo / endothermicity of the photocatalyzed reaction. The nature of the diluent fluid is chosen such that its influence is neutral on the reaction medium or that its possible reaction does not interfere with achieving the desired reduction of carbon dioxide. For example, nitrogen 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. Preferably, the contacting of the carbon dioxide feedstock and the photocatalyst is in fixed bed traversed, fixed bed licking or suspended (also called "slurry" in the English terminology). The photocatalyst can also be deposited directly on optical fibers. When the implementation is in fixed bed traversed, the photocatalyst is preferentially layered on a porous support, for example of ceramic or metallic sintered type, and the charge containing the carbon dioxide to be converted into gaseous and / or liquid form. is sent through the photocatalytic bed. When the implementation is in a fixed licking bed, the photocatalyst is preferably deposited in a layer on a support and the feedstock containing the carbon dioxide to be converted into gaseous and / or liquid form is sent to the photocatalytic bed. When the implementation is in suspension, the photocatalyst is preferably in the form of particles suspended in a liquid or liquid-gas feed containing carbon dioxide. In suspension, the implementation can be done in batch and continuously. The photocatalyst comprises a first semiconductor SC1 in direct contact with particles comprising one or more element (s) M in the metallic state chosen from an element of Groups IVB, VB, VIB, VIIB, VIIIB, IB, IIB, IIIA. , IVA and VA of the periodic table of elements, said particles being in direct contact with a second semiconductor SC2. Preferably, the photocatalyst consists of a first semiconductor SC1, particles comprising one or more element (s) M in the metallic state 30 selected from an element of groups IVB, VB, VIB, VIIB, VIIIB, IB, IIB, IIIA, IVA and VA of the periodic table of elements, and a second semiconductor SC2.

According to an important aspect of the invention, the first semiconductor SC1 is in direct contact with particles comprising one or more element (s) M in the metallic state, said particles being in direct contact with a second semiconductor SC2. so that the second semiconductor SC2 covers at least 50% of the surface of the particles having one or more element (s) M in the metallic state. Preferably, the first semiconductor SC1 is also in direct contact with the second semiconductor SC2. According to a preferred variant of the invention, the photocatalyst used in the process 10 according to the invention has a supported core-layer architecture. More particularly, said first semiconductor SC1 forms a support, said support contains on its surface core-layer type particles, said layer being formed by said semiconductor SC2, said core being formed by said particles comprising one or more element (s) M in the metallic state. The photocatalyst 15 thus comprises a support containing a semiconductor SC1 containing at its surface core-layer type particles, said core comprising one or more of said element (s) M in the metallic state, said layer comprising a semiconductor SC2, said core being in direct contact with said semiconductor SC1 of the support and the layer covers said core so that the layer covers at least 50% of the surface of the particles comprising one or more element (s) M in the state metallic. The use of this type of photocatalyst in a photocatalytic reduction reaction of CO2 surprisingly makes it possible to obtain improved photocatalytic performance compared with known photocatalysts of the state of the art not containing the core-type architecture. layer supported. The layer covers a surface greater than 50% of the metal core, and preferably greater than 60% and very preferably greater than 75%. The layer has a thickness of 1 nm to 1000 nm, preferably 1 nm to 500 nm, and particularly preferably 2 to 50 nm.

The semiconductors SC1 and SC2 are independently selected from inorganic, organic or organic-inorganic semiconductors. The bandgap width of inorganic, organic or organic-inorganic hybrid semiconductors is generally between 0.1 and 5.5 eV. The semiconductors SC1 and SC2 may be identical or different in the photocatalyst used in the process according to the invention. Preferably, the semiconductor SC1 is different from the semiconductor SC2 in the photocatalyst used in the process according to the invention. According to a first variant, the semiconductors SC1 and SC2 are independently selected from inorganic semiconductors. The inorganic semiconductors may be selected from one or more Group IVA elements, such as silicon, germanium, silicon carbide or silicon germanium. They may also be composed of elements of groups IIIA and VA, such as GaP, GaN, InP and InGaAs, or elements of groups IIB and VIA, such as CdS, ZnO and ZnS, or elements of groups IB and VIIA, 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 Bi2Te3 and Bi203, or elements of groups IIB and VA, such as Cd3P2, Zn3P2 and Zn3As2, or elements of groups IB and VIA, such as CuO, Cu2O and Ag2S, or elements of groups VIIIB and VIA, such as CoO, PdO, Fe2O3 and NiO or elements of groups VIB and VIA, such as MoS2 and WO3, or elements of groups VB and VIA, such as V205 and Nb2O5, or elements of groups IVB and VIA, such as TiO2 and HfS2, or elements of groups IIIA and VIA, such as In203 and In253, or elements of groups VIA and lanthanides, such as Ce203, Pr203, Sm253, Tb2S3 and La2S3, or elements of groups VIA and actinides,such as UO2 and UO3. In a preferred manner, the semiconductors SC1 and SC2 are independently selected from TiO2, SiC, Bi2S3, Bi203, CdO, Ce203, CeO2, CoO, Cu2O, Fe2O3, FeTiO3 In203, In (OH) 3, NiO, PbO, ZnO, Ag2S, CdS, Ce2S3, Cu2S, CuInS2, In2S3, ZnFe2O3, ZnS, ZnO, W03, ZnFe2O4 and ZrS2. Particularly preferably, the semiconductor SC1 is selected from TiO2, ZnO, WO3, Fe2O3, and ZnFe2O4. Particularly preferably, the semiconductor SC2 is selected from Ce203, In203, Cu2O, SiC, ZnS, and In2S3.

In another variant, the semiconductors SC1 and SC2 are chosen from organic semiconductors. Said organic semiconductors may be tetracene, anthracene, polythiophene, polystyrene sulphonate, phosphyrenes and fullerenes.

According to another variant, the semiconductors SC1 and SC2 are chosen from organic-inorganic semiconductors. Among the 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.) and are connected between them by organic ligands (carboxylates, phosphonates, imidazolates, etc.), thus defining crystallized hybrid networks, sometimes porous. The semiconductors SC1 and SC2 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 a mixture of metal and non-metallic ions. According to another variant, the semiconductors SC1 and SC2 may be surface-sensitized with any organic molecules capable of absorbing photons. The semiconductors SC1 and SC2 can be respectively in different forms (nanometric powder, nanoobjects with or without cavities, etc.) or shaped (films, monolith, beads of micrometric or millimetric size, etc.) . The respective content of semiconductors SC1 or SC2 is generally between 0.01 and 50% by weight, preferably between 0.5 and 20% by weight relative to the total weight of the photocatalyst, it being understood that the sum of respective contents of semiconductors SC1 or SC2 and particles comprising one or more element (s) M in the metallic state has 100% of the photocatalyst when it consists of these 3 components.

The photocatalyst also comprises particles comprising one or more elements M in the metallic state chosen from an element of Groups IVB, VB, VIB, VIIB, VIIIB, IB, IIB, IIIA, IVA and VA of the Periodic Table. elements.

These particles comprising one or more element (s) M are in direct contact with said semiconductor SC1 and SC2 respectively. Said particles can be composed of a single element in the metallic state or of several elements in the metallic state that can form an alloy.

The term "element in the metallic state" means an element belonging to the family of metals, said element being at the zero oxidation state (and therefore in the form of metal). Preferably, the element or elements M in the metallic state are chosen from a metal element of 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) M in the metallic state are preferably in the form of particles of sizes between 0.5 nm and 1000 nm, very preferably between 0.5 nm and 100 nm. The content of element (s) M in the metallic state is between 0.001 and 20% by weight, preferably between 0.01 and 10% by weight relative to the total weight of the phtocatalyst. The photocatalyst used in the process according to the invention may be in different forms (nanometric powder, nanoobjects with or without cavities, etc.) or shaped (films, monolith, beads of micrometric or millimetric size, etc. .). The photocatalyst is advantageously in the form of a nanometric powder. Preferably, the photocatalyst comprises a support composed of a semiconductor SC1 containing on its surface core-layer type particles, said core consisting of one or more of said element (s) M in the metallic state, said layer consisting of a semiconductor SC2. Particularly preferably, the photocatalyst consists of a support composed of a semiconductor SC1 containing on its surface core-layer type particles, said core consisting of one or more of said element (s) M to the metallic state, said layer consisting of a semiconductor SC2. According to an even more preferred embodiment, the photocatalyst used according to the method of the invention comprises, and preferably consists of a support consisting of a semiconductor SC1 selected from TiO2, ZnO, WO3, Fe2O3 and ZnFe2O4, containing on its surface core-layer type particles, said core consisting of one or more element (s) M in the metallic state chosen from platinum, palladium, gold, nickel , cobalt, ruthenium, silver, copper, rhenium or rhodium, said layer consisting of a semiconductor SC2 selected from Cu2O, Ce203, In203, SiC. ZnS and In2S3. The process for preparing the photocatalyst can be any preparation method known to those skilled in the art and adapted to the desired photocatalyst. Preferably, the photocatalyst is prepared by successive photodepositions or by precipitation-deposition under irradiation. These preparation methods are known in the state of the art. According to step b) of the process according to the invention, 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 the carbon dioxide of the photocatalyst. carbon 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. 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 the forbidden bandgap or "bandgap" according to the English terminology between the valence band and the conduction band, which induces the forming an electron-hole pair in the semiconductor. There is therefore the excitation of an electron at the level of the conduction band and the formation of a hole on the valence band. This electron-hole pair will allow the formation of free radicals that will either react with compounds present in the medium or then recombine according to various mechanisms. Each semiconductor has a difference in energy between its conduction band and its valence band, or "bandgap", which is its own.

A photocatalyst composed of one or more semiconductors may be activated by the absorption of at least one photon. Absorbable photons are those whose energy is greater than bandgap, semiconductor.

In other words, the photocatalysts can be activated by at least one photon of a wavelength corresponding to the energy associated with the bandgap widths of the semiconductors constituting the photocatalyst or of a lower wavelength. The maximum wavelength absorbable by a semiconductor is calculated using the following equation: ## EQU1 ## With A max the maximum wavelength absorbable by a semiconductor (in m), h the Planck constant (4). , 13433559.10-15 eV. $), C the speed of light in vacuum (299,792,458 ms-1) and Eg the band gap or "bandgap" of the semiconductor (in eV). Any irradiation source emitting at least one wavelength suitable for activating said photocatalyst, that is to say absorbable by the photocatalyst can be used according to the invention. For example, it is possible to use natural solar radiation or an artificial irradiation source of the laser, Hg, incandescent lamp, fluorescent tube, plasma or light emitting diode (LED) type (LED or Light-Emitting Diode). Preferably, the irradiation source is solar irradiation. The irradiation source produces a radiation of which at least a portion of the wavelengths is less than the maximum absorbable wavelength (λmax) by the constituent semiconductors of the photocatalyst according to the invention. When the irradiation source is solar irradiation, it generally emits in the ultraviolet spectrum, visible and infra-red, that is to say it emits a wavelength range of 280 nm to 2500 nm about (according to ASTM G173-03). Preferably, the source emits at least one wavelength range greater than 280 nm, most 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.

In a preferred mode in the case of solar irradiation, the irradiation source is located outside the reactor and the interface between the two may be an optical pyrex quartz window. 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 thus 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 feed is generally -10 ° C to + 200 ° C, more preferably 0 to 150 ° C, most preferably 0 to 50 ° 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 in C1 or more, different from the carbon dioxide resulting from the reaction and on the other hand 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 O when this compound is used as a sacrificial compound. The following examples illustrate the invention without limiting its scope. EXAMPLES Example 1: Solid A (not in accordance with the invention) TiO 2 Photocatalyst A is a commercial TiO 2 semiconductor (Aeroxide® P25, Aldrich ™, purity> 99.5%). The particle size of the photocatalyst is 21 nm and the specific surface area measured by BET method is equal to 52 m 2 / g. Example 2: Solid B (not in accordance with the invention) Pt / TiO 2 0.0712 g of H 2 PtCl 6 6H 2 O (37.5% by weight of metal) is inserted in 500 ml of distilled water. 50 ml of this solution are taken and inserted into a double glass reactor. 3 ml of methanol then 250 mg of TiO2 (P25, DegussaTM) are then added with stirring to form a suspension. The mixture is then left stirring and under UV radiation for two hours. The lamp used to provide the UV radiation is a 125W mercury vapor HPKTM lamp. The mixture is then centrifuged for 10 minutes at 3000 rpm to recover the solid. Two washings with water are then carried out, each washing being followed by centrifugation. The recovered powder is finally placed in an oven at 70 ° C. for 24 hours.

The solid B Pt / TiO 2 is then obtained. The content of Pt element is measured by plasma emission atomic emission spectrometry (or inductively coupled plasma atomic emission spectroscopy "ICP-AES" according to the English terminology) at 0.93% by mass.

Example 3: Solid C (according to the invention) Cu2O / Pt / T102 0.0712 g of H2PtC16.6H2O (37.5% by weight of metal, AldrichTM) is inserted into 500 ml of distilled water. 50 ml of this solution are taken and inserted into a double jacketed glass reactor. 3 ml of methanol then 250 mg of TiO2 (P25, DegussaTM) are then added with stirring to form a suspension.

The mixture is then left stirring and under UV radiation for two hours. The lamp used to provide the UV radiation is a mercury vapor HPKTM lamp of 125 W. The mixture is then centrifuged for 10 minutes at 3000 rpm to recover the solid. Two washings with water are then carried out, each of the washings being followed by centrifugation. The recovered powder is finally placed in an oven at 70 ° C. for 24 hours. A solid C 'Pt / TiO 2 is then obtained. The content of Pt element is measured by ICPAES 0.93% by mass. A solution of Cu (NO3) 2 is prepared by dissolving 0.125 g of Cu (NO3) 2, 3H20 (Sigma-AldrichTM, 98%) in 50 ml of 50/50 isopropanol / H 2 O, a concentration of Cu 2+ 10.4 mmol / L.

In the reactor were introduced: 0.20 g of the solid C ', 25 ml of distilled water and finally 25 ml of isopropanol. The system is purged in the dark under a stream of argon (100 ml / min) for 2 hours. The reactor is thermostated at 25 ° C. throughout the synthesis. The argon flow is then slowed down to 30 ml / min and the irradiation of the reaction mixture starts. The lamp used to provide the UV radiation is a mercury vapor HPKTM lamp of 125 W. Then the 50 ml of copper nitrate solution is added to the mixture. The mixture is left stirring for 10 hours and irradiation. The mixture is then centrifuged for 10 minutes at 3000 rpm to recover the solid. Two washings with water are then carried out, each of the 10 washings being followed by centrifugation. The recovered powder is finally placed in an oven at 70 ° C. for 24 hours. The solid C Cu 2 O / Pt / TiO 2 is then obtained. The content of Cu element is measured by ICP-AES at 2.2% by mass. By measurement XPS (X-Ray Photoelectron Spectrometry according to the English terminology), a platinum particle coating greater than 77% and copper oxide phases were measured at 67% Cu 2 O and 33% CuO. Transmission electron microscopy measured a 5 nm thick copper oxide layer thickness around the metal particles. Example 4: Solid D (in accordance with the invention) Cu 2 O / Au / TiO 2 0.0470 g of HAuCl 4, xH 2 O (52% by weight of metal, AldrichTM) is inserted into 500 ml of distilled water. 50 ml of this solution are taken and inserted into a double jacketed glass reactor. 3 mL of methanol then 250 mg of TiO2 (P25, DegussaTM) are then added with stirring to form a suspension. The mixture is then left stirring and under UV radiation for two hours. The lamp used to provide UV radiation is a 125W Mercury vapor HPKTM lamp. The mixture is then centrifuged for 10 minutes at 3000 rpm to recover the solid. Two washings with water are then carried out, each washing being followed by centrifugation. The recovered powder is finally placed in an oven at 70 ° C for 24 hours. An Au / TiO 2 solid is then obtained. The content of element Au is measured by ICPAES at 0.96% by mass.

A Cu (NO 3) 2 solution is prepared by dissolving 0.125 g of Cu (NO 3) 2, 3H 2 O (Sigma-AldrichTM, 98%) in 50 ml of 50/50 isopropanol / H 2 O, a concentration of Cu2 + of 10.4 mmol / L. In the reactor were introduced: 0.20 g of the solid D ', 25 ml of distilled water and finally 25 ml of isopropanol. The system is purged in the dark under a stream of argon (100 ml / min) for 2 hours. The reactor is thermostated at 25 ° C. throughout the synthesis. The argon flow is then slowed down to 30 ml / min and the irradiation of the reaction mixture starts. The lamp used to provide UV radiation is a 125W Mercury vapor HPKTM lamp. Then, the 50 ml of copper nitrate solution is added to the mixture. The mixture is left stirring for 10 hours and irradiation. The mixture is then centrifuged for 10 minutes at 3000 rpm to recover the solid. Two washings with water are then carried out, each washing being followed by centrifugation. The recovered powder is finally placed in an oven at 70 ° C. for 24 hours.

The solid D Cu 2 O / Au / TiO 2 is then obtained. The content of Cu element is measured by ICP-AES at 2.3% by weight. By XPS measurement, an overlap of platinum particles greater than 79% and phases of copper oxides at 76% in Cu 2 O and 24% in CuO are measured. Transmission electron microscopy measured a mean copper oxide layer thickness of 7 nm around the metal particles. Example 5: Solid E (in accordance with the invention) Cu 2 O / Pt / ZnO 0.0714 g of H 2 PtCl 6 6H 2 O (37.5% by weight of metal, AldrichTM) is inserted into 500 ml of distilled water. 50 ml of this solution are taken and inserted into a double jacketed glass reactor. 3 ml of methanol then 250 mg of ZnO (Lotus SynthesisTM, specific surface area 50 m 2 / g) are then added with stirring to form a suspension. The mixture is then left stirring and under UV radiation for six hours. The lamp used to provide the UV radiation is a 125 W mercury vapor HPKTM lamp. The mixture is then centrifuged for 10 minutes at 3000 rpm to recover the solid. Two washings with water are then carried out, each washing being followed by centrifugation. The recovered powder is finally placed in an oven at 70 ° C. for 24 hours.

A solid E 'Pt / ZnO is obtained. The content of Pt element is measured by ICPAES at 0.77% by weight. A solution of Cu (NO3) 2 is prepared by dissolving 0.125 g of Cu (NO3) 2, 3H2O (Sigma-AldrichTM, 98%) in 50 ml of a 50/50 isopropanol / H 2 O mixture, ie a Cu 2+ concentration. 10.4 mmol / L. In the reactor were introduced: 0.20 g of the solid E ', 25 ml of distilled water and finally 25 ml of isopropanol. The system is purged in the dark under a stream of argon (100 ml / min) for 2 hours. The reactor is thermostated at 25 ° C. throughout the synthesis. The argon flow is then slowed down to 30 ml / min and the irradiation of the reaction mixture starts. The lamp used to provide the UV radiation is a mercury vapor HPKTM lamp of 125 W. Then the 50 ml of copper nitrate solution is added to the mixture. The mixture is left stirring for 10 hours and irradiation. The mixture is then centrifuged for 10 minutes at 3000 rpm to recover the solid. Two washings with water are then carried out, each of the 15 washes being followed by centrifugation. The recovered powder is finally placed in an oven at 70 ° C. for 24 hours. The solid E Cu 2 O / Pt / ZnO is then obtained. The content of Cu element is measured by ICP-AES at 1.9% by weight. By XPS measurement, platinum platinum coverage greater than 83% was measured and copper oxide phases were 79% Cu 2 O and 21% CuO. Transmission electron microscopy measured an average copper oxide layer thickness of 4 nm around the metal particles. Example 6: Solid F (according to the invention) Ce 2 O 3 / Pt / TiO 2 0.0712 g of H 2 PtCl 6 H 2 O (37.5% by weight of metal) is inserted into 500 ml of distilled water. 50 ml of this solution are taken and inserted into a double jacketed glass reactor. 3 ml of methanol then 250 mg of TiO2 (P25, DegussaTM) are then added with stirring to form a suspension. The mixture is then left under stirring and under UV radiation for two hours. The lamp used to provide UV radiation is a 125W Mercury vapor HPKTM lamp. The mixture is then centrifuged for 10 minutes at 3000 rpm to recover the solid. Two washings with water are then carried out, each of which is followed by centrifugation. The recovered powder is finally placed in an oven at 70 ° C. for 24 hours. The solid F 'Pt / TiO 2 is then obtained. The content of Pt element is measured by ICPAES at 0.93% by mass.

A solution of Ce (NO3) 3 is prepared by dissolving 0.05 g of Ce (NO3) 3, 6H2O (Sigma-AldrichTM, 99%) in 50 ml of H2O. In the reactor were introduced: 0.10 g of the solid F ', 25 ml of distilled water and finally 25 ml of isopropanol. The system is purged in the dark under a stream of argon (100 ml / min) for 2 hours. The reactor is thermostated at 25 ° C. throughout the synthesis.

The argon flow is then slowed down to 30 ml / min and the irradiation of the reaction mixture starts. The lamp used to provide the UV radiation is a mercury vapor HPKTM lamp 125 W. Then, 5 ml of the cerium nitrate solution is added to the mixture. The mixture is left for 1 hour with stirring and irradiation. 1 ml of a 30% solution of NH3 is then added. The mixture is again left for 1 hour with stirring and irradiation. The mixture is then centrifuged for 10 minutes at 3000 rpm to recover the solid. Two washings with water are then carried out, each washing being followed by centrifugation. The recovered powder is finally placed in an oven at 70 ° C. for 24 hours.

The solid F Ce 2 O 3 / Pt / TiO 2 is then obtained. The content of element Ce is measured by ICP-AES at 1.7% by weight. By XPS measurement, a lapse of platinum particles greater than 83% and cerium oxide phases are measured at 74% Ce 2 O 3 and 26% CeO 2. By transmission electron microscopy, an average layer thickness of cerium oxide of 4 nm was measured around the metal particles. Example 7: Solid G (in accordance with the invention) In 2 O 3 / Pt / TiO 2 0.0712 g of H 2 PtCl 6 6H 2 O (37.5% by weight of metal) is inserted in 500 ml of distilled water. 50 ml of this solution are removed and inserted into a double reactor glass envelope. 3 ml of methanol then 250 mg of TiO2 (P25, DegussaTM) are then added with stirring to form a suspension.

The mixture is then left stirring and under UV radiation for two hours. The lamp used to provide UV radiation is a 125W Mercury vapor HPKTM lamp. The mixture is then centrifuged for 10 minutes at 3000 rpm to recover the solid. Two washings with water are then carried out, each washing being followed by centrifugation. The recovered powder is finally placed in an oven at 70 ° C. for 24 hours. The solid G 'Pt / TiO 2 is then obtained. The content of Pt element is measured by ICPAES at 0.93% by mass.

A solution of In (NO3) 3 is prepared by dissolving 0.05 g of In (NO3) 3, xH2O (Sigma-AldrichTM, 99.9%) in 50 ml of H2O. In the reactor were introduced: 0.10 g of the solid G ', 25 ml of distilled water and finally 25 ml of isopropanol. The system is purged in the dark under a stream of argon (100 ml / min) for 2 hours. The reactor is thermostated at 25 ° C. throughout the synthesis.

The argon flow is then slowed down to 30 ml / min and the irradiation of the reaction mixture starts. The lamp used to provide the UV radiation is a 125 W mercury vapor HPKTM lamp. Then, 5 ml of the indium nitrate solution is added to the mixture. The mixture is left for 1 hour with stirring and irradiation. 1 ml of a 30% solution of NH3 is then added. The mixture is again left for 1 hour with stirring and irradiation. The mixture is then centrifuged for 10 minutes at 3000 rpm to recover the solid. Two washings with water are then carried out, each washing being followed by centrifugation. The recovered powder is finally placed in an oven at 70 ° C. for 24 hours.

The solid In203 / Pt / TiO2 is then obtained. The content of element In is measured by ICP-AES at 1.9% by weight. By XPS measurement, a recovery of platinum particles greater than 79% is measured. Transmission electron microscopy measured an average layer thickness of 5 nm indium oxide around the metal particles.

EXAMPLE 8 Use of Solids in Photocatalytic CO2 Reduction in Liquid Phase Solids A, B, C, D, E, F and G are subjected to a photocatalytic reduction test of CO2 in the liquid phase in a liquid phase. Pyrex stirred semi-open reactor equipped with a quartz optical window and a jacket to regulate the test temperature. 100 mg of solid are suspended in 60 ml of an aqueous solution of potassium carbonate at 0.15 mol / l. The pH of the solution is 9. The tests are carried out at 25 ° C. under atmospheric pressure with an argon flow rate of 300 ml / h to entrain the gaseous products. The production of dihydrogen gas produced from the undesirable photocatalytic reduction of water is monitored and analyzed every 6 minutes by gas chromatography. The photocatalytic reduction of CO2 is followed by the production of formic acid by taking samples of liquid every 30 minutes which are analyzed by HPLC chromatography equipped with a UV detector. The UV-Visible irradiation source is provided by an Xe-Hg lamp (AsahiTM, MAX302TM). The irradiation power is always maintained at 100%. The duration of the test is 20 hours.

The photocatalytic activities are expressed in moles of dihydrogen and formic acid produced per hour and per gram of photocatalyst. The results are reported in Table 1. The activity values show that the use of the solids according to the invention systematically has the best photocatalytic performance and particularly better selectivities towards the photocatalytic reduction of CO2.

Photocatalyst Activity Activity Initial SC1 / M / SC2 Initial HCOOH H2 (pmol / h / g) (pmol / hr / g) Solid A (non-compliant) TiO2 n.e.

12 Solid B (non-compliant) Pt / TiO2 n.e.

4230 Solid C (in accordance) Cu20 / Pt / ZnO 207 5 Solid D (compliant) Cu2O / Au / TiO2 289 6 Solid E (compliant) Cu20 / Pt / ZnO 146 2 Solid F (compliant) Ce203 / Pt / TiO2 102 nd Solid G (consistent) In203 / Pt / TiO2 137 ndnd: not determined Table 1: Initial activity solids performance for the production of dihydrogen or formic acid from an aqueous solution of potassium carbonate Example 9: Implementation The solids in photocatalytic reduction of CO2 in the gas phase The solids A, B, C, D, E, F and G are subjected to a photocatalytic reduction test of CO2 in the gas phase in a continuous reactor with a crossed bed of steel provided with of a quartz optical window and a sinter in front of the optical window on which the photocatalytic solid is deposited. 100 mg of solid are deposited on the sinter. The tests are carried out at ambient temperature under atmospheric pressure. An argon flow rate of 300 ml / h and CO2 of 10 ml / hr passes through a water saturator before being dispensed into the reactor. The production of dihydrogen gas produced from the undesirable photocatalytic reduction of the water entrained in the saturator and CH4 resulting from the reduction of the carbon dioxide is monitored by an analysis of the effluent every 6 minutes by micro-chromatography in phase. gas. The UV-Visible irradiation source is provided by an Xe-Hg lamp (Asahi ™, MAX302 ™). The irradiation power is always maintained at 100%. The duration of the test is 20 hours. The photocatalytic activities are expressed in moles of dihydrogen and methane produced per hour per gram of photocatalyst. The results are reported in Table 1. The activity values show that the use of the solids according to the invention systematically has the best photocatalytic performance and particularly better selectivities towards the photocatalytic reduction of CO.sub.2. Photocatalyst Activity Activity SC1 / M / SC2 Initial initial CH4 H2 (pmol / h / g) (pmol / h / g) Solid A (non-compliant) TiO2 26 7 Solid B (non-compliant) Pt / TiO2 45 216 Solid C (compliant) Cu20 / Pt / ZnO 489 29 Solid D (compliant) Cu2O / Au / TiO2 630 36 Solid E (compliant) Cu20 / Pt / ZnO 402 16 Solid F (compliant) Ce203 / Pt / TiO2 396 nd Solid G (compliant) ) In203 / Pt / TiO2 560 ndnd: not determined Table 1: Initial activity solids performances for the production of dihydrogen or methane from a gas phase CO2 and H2O mixture

Claims (14)

REVENDICATIONS1. Process for the photocatalytic reduction of carbon dioxide carried out in the liquid phase and / or in the gas phase under irradiation using a photocatalyst containing a first semiconductor SC1, particles comprising one or more selected metal element (s) M from an element of groups IVB, VB, VIB, VIIB, VIIIB, IB, IIB, IIIA, IVA and VA of the periodic table of elements, and a second semiconductor SC2, said first semiconductor SC1 being in direct contact with said particles comprising one or more elements M in the metallic state, said particles being in direct contact with said second semiconductor SC2 so that the second semiconductor SC2 covers at least 50% of the surface of the particles comprising one or more elements M in the metallic state, said process comprising the following steps: a) contacting a filler containing carbon dioxide and at least one n sacrificial compound with said photocatalyst, 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 compound sacrificial 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. 2. The method of claim 1, wherein, when carried out in the gas phase, the sacrificial compound is a gaseous compound selected from water, ammonia, hydrogen, methane and an alcohol. The process according to claim 1, wherein when carried out in the liquid phase, the sacrificial compound is a soluble liquid or solid compound selected from water, ammonia, an alcohol, an aldehyde and an amine. 4. Method according to one of claims 1 to 3, wherein a diluent fluid is present in steps a) and / or b). 5. Method according to one of claims 1 to 4, wherein the source of irradiation is a source of artificial or natural irradiation. 3026965 27 6. Method according to one of claims 1 to 5, wherein the first semiconductor SC1 is in direct contact with the second semiconductor SC2. 7. Method according to one of claims 1 to 6, wherein said first semiconductor SC1 forms a support, said support contains on its surface core-layer type particles, said layer being formed by said semiconductor SC2, said core being formed by said particles having one or more element (s) M in the metallic state. The method according to one of claims 1 to 7, wherein the respective content of the semiconductors SC1 or SC2 is between 0.01 and 50% by weight relative to the total weight of the photocatalyst. 9. Method according to one of claims 1 to 8, wherein 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. 10. Method according to one of claims 1 to 9, wherein the element M in the metal state is selected from platinum, palladium, gold, nickel, cobalt, ruthenium, silver , copper, rhenium and rhodium. 11. Method according to one of claims 1 to 10, wherein the semiconductors SC1 and SC2 are independently selected from an inorganic semiconductor, organic or organic-inorganic. 20 12. The method of claims 1 to 11, wherein the semiconductor SC1 is selected from TiO2, ZnO, WO3, Fe2O3, and ZnFe2O4. 13. The method of claims 1 to 12, wherein the semiconductor SC2 is selected from Cu2O, Ce203, In203, SiC, ZnS, In2S3. 14. Method according to one of claims 1 to 13, wherein the photocatalyst 25 comprises a support composed of a semiconductor SC1 selected from TiO2, ZnO, WO3, Fe2O3, and ZnFe2O4, containing on its surface core-layer type particles, said core consisting of one or more element (s) M in the metallic state selected from platinum, palladium, gold, nickel, cobalt, ruthenium, silver, copper, rhenium or rhodium, said layer consisting of a semiconductor SC2 selected from Cu2O, Ce203 and In203.