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

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 comprising a support based on alumina or silica or silica-alumina and nanoparticles of molybdenum sulfide or of tungsten sulfide having a bandgap greater than 2.3 eV, said process comprising the following steps:

• a) bringing a feedstock containing carbon dioxide and at least one sacrificial compound into contact with said photocatalyst,
• b) irradiating the photocatalyst with at least one irradiation source producing at least one wavelength smaller than the bandgap of said photocatalyst so as to reduce the carbon dioxide and to oxidize the sacrificial compound in the presence of said photocatalyst activated by said irradiation source, in such a way as to produce an effluent containing, at least partly, C1 or above carbon-based molecules other than CO2,
• wherein
• the photocatalyst is prepared according to a process comprising the following successive steps:
• i) a step of impregnation by bringing a solution comprising an organic solvent A and at least one mononuclear precursor based on Mo or on W, denoted M, in their monomeric or dimeric form, having at least one M═O or M—OR bond or at least one M═S or M—SR bond where R═CxHy where x≥1 and (x−1)≤y≤(2x+1), into contact with a support based on alumina or silica or silica-alumina, advantageously previously calcined under vacuum or under an inert gas stream to remove the water possibly physisorbed on said support,
• ii) a maturing step,
• iii) a step of drying the impregnated support, at a temperature below 200° C., under an anhydrous atmosphere or under vacuum or under an inert gas stream,
• iv) a sulfurization step.

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 comprising a support based on alumina or silica or silica-alumina and nanoparticles of molybdenum sulfide or of tungsten sulfide having a bandgap greater than 2.3 eV, said process comprising the following steps:

• a) bringing a feedstock containing carbon dioxide and at least one sacrificial compound into contact with said photocatalyst,
• b) irradiating the photocatalyst with at least one irradiation source producing at least one wavelength smaller than the bandgap of said photocatalyst so as to reduce the carbon dioxide and to oxidize the sacrificial compound in the presence of said photocatalyst activated by said irradiation source, in such a way as to produce an effluent containing, at least partly, C1 or above carbon-based molecules other than CO2,
• wherein
• the surface density which corresponds to the amount of molybdenum Mo atoms or of tungsten W atoms, deposited per unit surface area of support, is between 0.5 and 12 atoms of Mo or W per square nanometer of support;
• or
• the molybdenum precursor is selected from the following compounds:
• Mo(OEt)5, Mo(OEt)6, Mo(═O)(OEt)4, Mo(═S)(OEt)4, Mo(═S)(SEt)4, Mo(═O)2(OEt)2, Mo(OC6H5)6, Mo(SEt)5, Mo(SEt)6, Mo(OEt)(SEt)4, Mo(OEt)2(SEt)3, Mo(OEt)3(SEt)2, Mo(OEt)4(SEt), Mo(═O)(OEt)3(acac) with Et=CH2CH3 (ethyl group) and acac=(CH3COCHCOCH3)— (acetylacetonate) in their monomeric or dimeric form;
• or
• the tungsten precursor is selected from the following compounds:
• W(OEt)5, W(OEt)6, W(═O)(OEt)4, W(═S)(OEt)4, W(═S)(SEt)4, W(═O)2(OEt)2, W(OC6H5)6, W(SEt)5, W(SEt)6, W(OEt)4(SEt), W(OEt)3(SEt)2, W(OEt)2(SEt)3, W(OEt)(SEt)4, W(═O)(OEt)3(acac) with Et=CH2CH3 (ethyl group) and acac=(CH3COCHCOCH3)— (acetylacetonate), in their monomeric or dimeric form.