Use of particles of titanium dioxide bearing a metal or a metal oxide for obtaining alkenes by photocatalysis

Abstract

The present invention relates to the use of particles of TiO2 bearing a metal and / or a metal oxide for obtaining alkanes by photocatalysis. The present invention also relates to a method for obtaining alkanes by photocatalysis of carboxylic acids and / or of alcohols in the presence of a catalyst based on particles of TiO2 bearing a metal and / or a metal oxide.

Description

USE OF TITANIUM DIOXIDE PARTICLES CARRYING A METAL OR A METAL OXIDE FOR OBTAINING ALKENES BY PHOTOCATALYSIS

[0001] The present invention relates to the use of TiO2 particles carrying a metal and / or a metal oxide for obtaining alkenes by photocatalysis. The present invention also relates to a process for obtaining alkenes by photocatalysis of carboxylic acids and / or alcohols in the presence of a catalyst based on TiO2 particles carrying a metal and / or a metal oxide.

[0002] Generally produced during the refining of crude oil, alkenes are compounds widely used in the chemical industry, for many and varied applications, notably as raw materials for the production of polymers, for example plastics or lacquers, but also in the synthesis of alcohols, surfactants and fuels.

[0003] Among alkenes, ethylene is the most produced and used organic molecule in the world. The basis of the petrochemical industry, its global market represents more than $130 billion annually, with consumption exceeding 150 million tons per year. These high tonnages are explained by the fact that ethylene is the basic monomer for the production of more than 75% of petrochemical products. It is mainly used in the synthesis of plastics such as polyethylene (PET), or in the synthesis of chemical surfactants such as ethylene oxide and ethylene glycol.

[0004] Currently, 99% of industrial ethylene production is based on the cracking of naphtha (an intermediate between gasoline and kerosene, produced by fractional distillation of petroleum) or hydrocarbons such as ethane, usually heated between 750 and 950°C. Ethylene yields vary, around 35% from naphtha and 80% from ethane. However, in addition to being very energy-intensive, this synthesis is polluting and dependent on petroleum resources. Thus, with the limitation of fossil fuels and the climate challenge, it has become essential to develop new low-energy and low-cost ethylene synthesis processes from renewable resources.

[0005] Given these challenges, much research has been carried out to find an alternative to the cracking of petroleum derivatives for the production of ethylene.

[0006] One of these alternative technologies is the catalytic dehydration of ethanol to ethylene. This can, for example, be bioethanol, a renewable resource produced at low cost in the absence of toxic reagents. Ethanol dehydration uses acid catalysts such as monofunctional oxides, typically alumina γ-Al2O3, or "molecular sieves" such as zeolite structures like ZSM-5 (Zeolite Socony Mobil-5). However, despite the use of acid catalysts, the ethanol dehydration reaction remains highly endothermic and is only shifted towards ethylene at high temperatures. Thus, the working temperature and pressure significantly affect the ethylene yield.Therefore, these technologies generally achieve high ethylene yields, but the temperatures (typically 300 to 550°C) and pressures (generally between 0.3 and 4 MPa) employed remain high, and therefore energy-intensive and costly. And generally, when operating temperatures are lower, the formation of a significant amount of by-product is observed, with a limited ethanol conversion percentage and pressures remaining high. In addition, the acid catalysts typically used to lower the operating temperature have a limited lifetime because they tend to deactivate by coking (formation by thermal cracking of a coke deposit on the surfaces of a system subjected to high temperatures, resulting in reduced performance), and high-temperature regeneration reactions result in high costs and a significant loss of catalytic efficiency.

[0007] Other technologies based on the production of ethylene by photocatalysis were subsequently developed, the catalyst used being CuCl2. These methods are interesting because the use of light energy replaces the use of thermal energy and high pressure. However, the CuCl2 catalyst becomes inactive very quickly, typically in less than an hour, and must therefore be regularly regenerated, in air.

[0008] In addition to ethanol, carboxylic acids, particularly propanoic acid (CH3CH2COOH), are of particular interest because they can be used as renewable resources within biomass to produce liquid fuels and other molecules of interest in the energy sector. Propanoic acid is a volatile fatty acid found as a pollutant in domestic wastewater. It can also be obtained from biomass by fermentation of glycerol, as well as from the fermentation of industrial waters such as rapeseed oil extraction or potato waste.

[0009] Processes for the decarboxylation of propanoic acid into alkanes by photocatalysis using TiO2 powders, possibly platinized, have been developed in this context. Ethylene can also be formed using these processes, but only in trace amounts, following secondary reactions. Furthermore, the platinum present in some processes is a noble platinum metal, which makes it an expensive material to produce and therefore not very suitable for development on an industrial scale.

[0010] The aim of the present invention is to provide a process for obtaining alkenes, in particular ethylene, by a photocatalysis reaction which avoids the aforementioned drawbacks.

[0011] Thus, one aim of the invention is to provide a process for producing alkene(s), in particular ethylene, which does not require fossil resources and does not require significant heating (i.e. typically above 200°C), or even the supply of thermal energy. None of the solutions currently proposed makes it possible to obtain both a good yield and / or good selectivity for alkene(s), in particular ethylene, under ambient temperature and pressure conditions, and in particular on volumes compatible with the industrial scale of alcohol or acid solution which can be synthesized from biomass.

[0012] Another aim of the invention is to provide a method that is simple to implement, stable over time (for example for at least 50 hours) and inexpensive. Indeed, certain approaches of the prior art propose the use of expensive photocatalysts based on noble metals and / or which deactivate quickly under irradiation and therefore require regeneration, generating additional costs.

[0013] Another aim of the invention is to provide a process for obtaining alkenes, in particular ethylene, with excellent selectivity, in particular at ambient temperature and pressure, under simple UV / visible irradiation.

[0014] Thus, according to a first aspect, the invention relates to the use of particles consisting of or comprising TiO2 bearing on at least part of their surface a metal M and / or a metal oxide M, M being chosen from the group comprising Cu, Zn, Fe, Mo, W and Ni, and more particularly from the group comprising Cu, Zn, Fe, and Ni, for obtaining at least one alkene by photocatalysis from at least one carboxylic acid of formula (I) R a -COOH, and / or at least one alcohol of formula (II) R b -OH, in which R a and R b are independently selected from linear, branched or cyclic alkyl groups, in particular C2 to C alkyl groups 18 linear, branched or cyclic, more particularly linear, branched or cyclic C2 to C6 alkyl groups, said alkyl groups being optionally substituted by at least one group X chosen from arenes, X being in particular a phenyl group.

[0015] By "photocatalysis" we mean in particular a reaction catalyzed by the action of light rays on the surface of a catalyst called a photocatalyst.

[0016] According to a particular embodiment, the largest number-average dimension of the particles is from 1 to 100 nm, in particular from 5 to 70 nm. The measurement of the largest number-average dimension can be carried out by any technique known to man, in particular by size measurement by counting, for example via ImageJ software, on transmission electron microscopy (TEM) images.

[0017] According to a particular embodiment, the particles consisting of or comprising TiO2 are spherical, spheroidal, rod-shaped, wire-shaped, tube-shaped, and / or plate-shaped. These are therefore in particular nanospheres, nanospheroids, nanorods, nanowires, nanotubes, and / or nanoplatelets.

[0018] The particles consisting of or comprising TiO2, in particular in one of the forms described above, may optionally be organized into chains, in particular nanochains.

[0019] According to a particular embodiment, the TiO2 is in the form of anatase, rutile and / or brookite, in particular in the form of anatase, rutile, or a mixture of anatase and rutile, more particularly in the form of a mixture of anatase and rutile whose anatase / rutile ratio is from 0.80 to 2.33, in particular from 1.00 to 2.33, in particular from 1.00 to 2.00.

[0020] According to a particular embodiment, the particles consisting of or comprising TiO2 have a specific surface area of ​​from 10 to 500 m 2 / g, especially from 30 to 150 m 2 / g. These specific surface area ranges may correspond to the specific surface area of ​​particles consisting of or comprising TiO2, excluding the surface area corresponding to the metal M and / or metal oxide M. These specific surface area ranges may correspond to the total specific surface area of ​​particles consisting of or comprising TiO2, bearing the metal M and / or the metal oxide M.

[0021] According to a particular embodiment, the content of metal M and / or metal oxide M relative to the TiO2 is from 0.01 to 50% by mass, in particular from 0.1 to 5% by mass, for example approximately 2% by mass, or more than 0.01% and less than 2% by mass.

[0022] According to a particular embodiment, the content of metal M and / or metal oxide M relative to the TiO2 is from 0.01 to 1.0; 1.2; 1.4; 1.6; 1.8 or 1.9% by mass, in particular from 0.1 to 1.0; 1.2; 1.4; 1.6; 1.8 or 1.9% by mass.

[0023] According to a particular embodiment, the particles consisting of or comprising TiO2 bearing on at least part of their surface a metal M and / or a metal oxide M, also comprise, within them, the metal M and / or the metal oxide M.

[0024] According to a particular embodiment, the majority of the metal M and / or the metal oxide M of the particles consisting of or comprising TiO2 is present on the surface of said particles.

[0025] According to another particular embodiment, more than 50% by mass, in particular more than 60, 70, 75, 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98 or 99% by mass of the metal M and / or of the metal oxide M of the particles consisting of or comprising TiO2 is present on the surface of said particles. This can be measured by any techniques known to those skilled in the art, for example by comparing the measurements carried out by inductively coupled plasma spectrometry (ICP), which make it possible to quantify the total metal content of a material, with those carried out by X-ray photoelectron spectrometry (XPS), which make it possible to measure the quantity of surface elements of the material.

[0026] According to a particular embodiment, the metal M and / or the metal oxide M are present, at least on the surface of the particles consisting of or comprising TiO2, in the form of particles whose largest number-average particle size is from 0.1 to 50 nm, in particular from 0.5 to 10 nm, more particularly from 1 to 3 nm.

[0027] According to a particular embodiment, the particles consisting of or comprising TiO2 bearing on at least part of their surface a metal M and / or a metal oxide M are obtained by laser pyrolysis or by impregnation, optionally followed by annealing, in particular in air, in particular at a temperature of 300 to 500°C, in particular 400 to 500°C, for example at a temperature of approximately 450°C, and / or in particular for 3 hours, in particular 3 to 6 hours.

[0028] According to a particular embodiment, the particles of the invention do not comprise gold.

[0029] According to a particular embodiment, the invention relates to a process for obtaining at least one alkene from at least one carboxylic acid, which is in particular propanoic acid, acetic acid, a phenylpropanoic acid, in particular 2-phenylpropanoic acid, n-butyric acid, n-valeric acid, or pivalic acid, more particularly propanoic acid.

[0030] According to a particular embodiment, the invention relates to a process for obtaining at least one alkene from at least one alcohol, which is in particular ethanol, or cyclohexanol, more particularly ethanol.

[0031] According to a particular embodiment, the at least one alkene is ethylene.

[0032] According to a particular embodiment, the invention relates to a process for obtaining ethylene from propanoic acid.

[0033] According to another aspect, the invention also relates to a process for obtaining at least one alkene from at least one carboxylic acid of formula (I) R a -COOH, and / or at least one alcohol of formula (II) R b -OH, in which R a and R b are independently chosen from linear, branched or cyclic alkyl groups, optionally substituted by at least one group X chosen from arenes, X being in particular a phenyl group, comprising a step (i) of photocatalysis by UV and / or visible irradiation of at least one carboxylic acid and / or at least one alcohol in the presence of a catalyst consisting of or comprising particles consisting of or comprising TiO2 bearing on at least part of their surface a metal M and / or a metal oxide M, M being chosen from the group comprising Cu, Zn, Fe, Mo, W and Ni, and more particularly from the group comprising Cu, Zn, Fe, and Ni.

[0034] According to a particular embodiment, the largest number-average dimension of the particles is from 1 to 100 nm, in particular from 5 to 70 nm. The measurement of the largest number-average dimension can be carried out by any technique known to man, in particular by size measurement by counting, for example via ImageJ software, on transmission electron microscopy (TEM) images.

[0035] According to a particular embodiment, the particles consisting of or comprising TiO2 are spherical, spheroidal, rod-shaped, wire-shaped, tube-shaped, and / or plate-shaped. These are therefore in particular nanospheres, nanospheroids, nanorods, nanowires, nanotubes, and / or nanoplatelets.

[0036] The particles consisting of or comprising TiO2, in particular in one of the forms described above, may optionally be organized into chains, in particular nanochains.

[0037] According to a particular embodiment, the TiO2 is in the form of anatase, rutile and / or brookite, in particular in the form of anatase, rutile, or a mixture of anatase and rutile, more particularly in the form of a mixture of anatase and rutile whose anatase / rutile ratio is from 0.80 to 2.33, in particular from 1.00 to 2.33, in particular from 1.00 to 2.00.

[0038] According to a particular embodiment, the particles consisting of or comprising TiO2 have a specific surface area of ​​from 10 to 500 m 2 / g, especially from 30 to 150 m 2 / g. These specific surface area ranges may correspond to the specific surface area of ​​particles consisting of or comprising TiO2, excluding the surface area corresponding to the metal M and / or metal oxide M. These specific surface area ranges may correspond to the total specific surface area of ​​particles consisting of or comprising TiO2, bearing the metal M and / or the metal oxide M.

[0039] According to a particular embodiment, the content of metal M and / or metal oxide M relative to the TiO2 is from 0.01 to 50% by mass, in particular from 0.1 to 5% by mass, for example approximately 2% by mass, or more than 0.01% and less than 2% by mass.

[0040] According to a particular embodiment, the content of metal M and / or metal oxide M relative to the TiO2 is from 0.01 to 1.0; 1.2; 1.4; 1.6; 1.8 or 1.9% by mass, in particular from 0.1 to 1.0; 1.2; 1.4; 1.6; 1.8 or 1.9% by mass.

[0041] According to a particular embodiment, the particles consisting of or comprising TiO2 bearing on at least part of their surface a metal M and / or a metal oxide M, also comprise, within them, the metal M and / or the metal oxide M.

[0042] According to a particular embodiment, the majority of the metal M and / or the metal oxide M of the particles consisting of or comprising TiO2 is present on the surface of said particles.

[0043] According to another particular embodiment, more than 50% by mass, in particular more than 60, 70, 75, 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98 or 99% by mass of the metal M and / or of the metal oxide M of the particles consisting of or comprising TiO2 is present on the surface of said particles. This can be measured by any techniques known to those skilled in the art, for example by comparing the measurements carried out by inductively coupled plasma spectrometry (ICP), which make it possible to quantify the total metal content of a material, with those carried out by X-ray photoelectron spectrometry (XPS), which make it possible to measure the quantity of surface elements of the material.

[0044] According to a particular embodiment, the metal M and / or the metal oxide M are present, at least on the surface of the particles consisting of or comprising TiO2, in the form of particles whose largest number-average particle size is from 0.1 to 50 nm, in particular from 0.5 to 10 nm, more particularly from 1 to 3 nm.

[0045] According to a particular embodiment, the particles consisting of or comprising TiO2 bearing on at least part of their surface a metal M and / or a metal oxide M are obtained by laser pyrolysis or by impregnation, optionally followed by annealing, in particular in air, then optionally in dihydrogen, in particular at a temperature of 300 to 500°C, in particular 400 to 500°C, for example at a temperature of approximately 450°C, and / or in particular for 3 hours, in particular 3 to 6 hours.

[0046] Laser pyrolysis and impregnation are, for example, carried out according to operating methods well known to those skilled in the art.

[0047] According to a more particular embodiment, the laser pyrolysis is carried out by bringing an aerosol of a liquid composition comprising at least one TiO2 precursor, at least one precursor of the metal M and / or the metal oxide M, and optionally an organic solvent, into contact with a laser beam.

[0048] According to another more particular embodiment, the impregnation is carried out by bringing TiO2, for example obtained by laser pyrolysis, into contact with a precursor of the metal M and / or the oxide of metal M, the impregnation being optionally followed by annealing, in particular in air, then optionally in dihydrogen, in particular at a temperature of 300 to 500°C, in particular 400 to 500°C, for example at a temperature of approximately 450°C, and / or in particular for 3 hours, in particular 3 to 6 hours.

[0049] When the TiO2 or the TiO2 bearing on at least part of its surface a metal M and / or an oxide of metal M is obtained by laser pyrolysis, the annealing is carried out, in air, then possibly in dihydrogen.

[0050] When the TiO2 is commercial and intended to be impregnated as defined above, annealing in air is optional but preferential, which can be advantageously followed by annealing in dihydrogen.

[0051] By "annealing under dihydrogen" is meant in particular annealing under pure dihydrogen or diluted in an inert gas, such as for example argon, or nitrogen. Such annealing is likely to make it possible, if necessary, to limit the presence of oxide on the surface of the metal M.

[0052] According to a particular embodiment, the invention relates to a process for obtaining at least one alkene from at least one carboxylic acid, which is in particular propanoic acid, acetic acid, a phenylpropanoic acid, in particular 2-phenylpropanoic acid, n-butyric acid, n-valeric acid, or pivalic acid, more particularly propanoic acid.

[0053] According to a particular embodiment, the invention relates to a process for obtaining at least one alkene from at least one alcohol, which is in particular ethanol, or cyclohexanol, more particularly ethanol.

[0054] According to a particular embodiment, the at least one alkene is ethylene.

[0055] According to a particular embodiment, the invention relates to a process for obtaining ethylene from propanoic acid.

[0056] According to a particular embodiment, step (i) is carried out under an atmosphere comprising by volume less than 1% of dioxygen, in particular less than 0.1% of dioxygen,

[0057] in particular less than 0.01% of oxygen, more particularly less than 0.001% of oxygen.

[0058] According to a particular embodiment, step (i) is carried out under an inert gas atmosphere, in particular under a nitrogen, helium and / or argon atmosphere, more particularly under an argon atmosphere.

[0059] According to a more particular embodiment, the inert gas atmosphere is obtained by purging using a flow of inert gas, the flow being in particular from 1 to 500 mL / min, preferably from 50 to 70 mL / min.

[0060] According to a particular embodiment, step (i) is carried out under a continuous flow of inert gas, in particular under a nitrogen, helium and / or argon atmosphere, more particularly under an argon atmosphere, the flow being more particularly from 1 to 500 mL / min, preferably from 50 to 70 mL / min. In this case, it is a mode which can be described as dynamic.

[0061] According to another particular embodiment, step (i) is carried out in the absence of a continuous flow of inert gas. In this case, it is a mode which can be described as static. Still in this case, step (i) is carried out under an inert gas atmosphere. In particular, a purge as defined above is carried out prior to step (i). This purge is then stopped before carrying out step (i).

[0062] According to a particular embodiment, the at least one carboxylic acid and / or the at least one alcohol is present within a composition further comprising a solvent, in particular in solution in a solvent, the solvent preferably being water, the concentration of alcohol(s) and / or carboxylic acid(s) in the composition being in particular greater than or equal to 0.0001% by volume, in particular greater than or equal to 0.01% by volume, and / or less than 100% by volume, for example approximately 1.00% by volume.

[0063] According to another particular embodiment, the at least one carboxylic acid and / or the at least one alcohol is not in the presence of a solvent.

[0064] According to a particular embodiment, the catalyst is present in the composition comprising the at least one carboxylic acid and / or the at least one alcohol and the solvent, or, in the absence of solvent, in the at least one carboxylic acid and / or the at least one alcohol, at a concentration of from 0.01 to 50 g / L, for example approximately 0.5 g / L.

[0065] According to a particular embodiment, step (i) is carried out at a temperature of from 10 to 200°C, in particular at a temperature of from approximately 20 to approximately 40°C, or at a temperature of from 40 to 200°C, in particular from 40 to 150°C, or even from 40 to 100°C.

[0066] According to a particular embodiment, step (i) is carried out at a temperature of from 60 to 200°C, in particular at a temperature of from 60 to 150°C, in particular from 60 to 100°C.

[0067] According to a particular embodiment, the irradiation is UV-A, UV-B, UV-C, and / or visible irradiation, in particular UV-A, in particular at a wavelength of 350 to 400 nm.

[0068] According to a particular embodiment, the invention relates to a process comprising a step (ii), following step (i), of recovering the alkene(s), this step (ii) being optionally followed by a step (iii) of isolating the alkene(s).

[0069] Step (ii) can be carried out by any technique known to those skilled in the art, in particular by recovering the headspace of the photocatalytic device used.

[0070] Step (iii) can be carried out by any technique known to those skilled in the art, in particular by distillation, in particular by cryogenic distillation. This purification technique, based on the fact that each gas has its own boiling point, consists of separating a gas mixture by varying the pressure and temperature of the gas storage medium. The gas mixture is first cooled to a low temperature (usually T < -50°C). Following cooling, the gases are liquefied and then conveyed into a distillation column. The liquid is gradually reheated, which makes it possible to separate the gases according to their boiling point.

[0071] Step (iii) can also be performed using absorption-based techniques. Separation is based on the principle that each gas has a particular affinity for absorbents such as zeolites, alumina, or activated carbon, or for solvents such as methanolamine (MEA). The Pressure Swing Absorption (PSA) method best illustrates this technique. Separation occurs when the gas mixture comes into contact with the absorbent / solvent in a reservoir that is subsequently pressurized. The gas with the best affinity for the absorbent is trapped while the other gaseous species pass through the system. The reservoir is regenerated by returning to atmospheric pressure, releasing the previously trapped gas.

[0072] Step (iii) can also be carried out by membrane separation, still based on the principle of gas affinity for a membrane, allowing gases to infiltrate more or less quickly through the membrane. Membrane materials frequently encountered in the literature are varied, such as microporous organic polymers, zeolites and ceramic or metal-based materials. Thus, within a first reservoir, the gas mixture is brought into contact with a membrane located at the interface of a second reservoir. The different gases diffuse into the second reservoir using a pressure gradient, promoting mass transport through the membrane separating the retentate from the permeate.

[0073] According to a particular embodiment, the molar selectivity for alkene, in particular for ethylene, is greater than or equal to 40%, in particular greater than 45%, more particularly greater than 50%.

[0074] According to a more particular embodiment, the molar selectivity for alkene, in particular ethylene, obtained from at least one carboxylic acid of formula (I) R a -COOH, is greater than or equal to 50%, in particular greater than 60%, more particularly greater than 70, 80 or 90%.

[0075] According to another more particular embodiment, the molar selectivity for alkene, in particular ethylene, obtained from at least one alcohol of formula (II) R b -OH, is greater than or equal to 40%, in particular greater than 45%, more particularly greater than 50%.

[0076] According to a particular embodiment, acetone and / or ethyl acetate is not formed at the end of the process.

[0077] According to a particular embodiment, the molar selectivity for by-product chosen from acetone and / or ethyl acetate is less than 1%, in particular less than 0.1%, more particularly less than 0.01%. DEFINITIONS

[0078] As used herein, the term "about" refers to a range of values ​​within ± 10% of a specific value. For example, the term "about 20" includes values ​​of 20 ± 10%, or values ​​from 18 to 22.

[0079] For the purposes of this description, percentages refer to percentages by mass relative to the total mass of the formulation, unless otherwise indicated.

[0080] As used herein, the value ranges of "xy" or "from x to y" or "between x and y" include the bounds x and y as well as the integers between these bounds. For example, "1-5", or "from 1 to 5" or "between 1 and 5" denote the integers 1, 2, 3, 4 and 5. Preferred embodiments include each individual integer in the value range, as well as any subcombination of these integers. For example, preferred values ​​for "1-5" may include the integers 1, 2, 3, 4, 5, 1-2, 1-3, 1-4, 1-5, 2-3, 2-4, 2-5, etc.

[0081] As used herein, the term "alkyl" means a straight or branched chain alkyl group having the number of carbon atoms indicated before said term, especially 2 to 6 carbon atoms, such as ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isoamyl, neopentyl, 1-ethylpropyl, 3-methylpentyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, hexyl, etc. Thus, a term such as "C1-C4 alkyl" means an alkyl radical containing from 1 to 4 carbon atoms. The same is true for the term "alkane".

[0082] Cycloalkyls are in particular alkyls (as defined above) comprising a ring. This is for example cyclohexyl.

[0083] As used herein, the term "arene" means a mono- or bicyclic, substituted or unsubstituted, hydrocarbon aromatic ring system having 6 to 10 carbon atoms in the ring. Examples include benzene and naphthalene. Preferred arenes include unsubstituted or substituted benzene and naphthalene. Included within the definition of "arene" are fused ring systems, including, for example, ring systems in which an aromatic ring is fused to a cycloalkyl ring. Examples of such fused ring systems include, for example, indane, indene, and tetrahydronaphthalene. FIGURES

[0084] This presents an example of a photocatalytic device capable of enabling the implementation of a use or a method according to the present invention.

[0085] 1. UV lamp;

[0086] 2. Photocatalytic reactor;

[0087] 3. Bubbler;

[0088] 4. Refrigerant water inlet;

[0089] 5. Refrigerant water outlet;

[0090] 6. Solution containing the photocatalyst and the alcohol(s) and / or carboxylic acid(s) precursor(s);

[0091] 7. Headspace containing the gases produced during photocatalysis;

[0092] 8. Injector connected to a gas chromatography (GC) apparatus;

[0093] 9. Mechanical agitator;

[0094] 10. Isolation valve;

[0095] 11. Mass flow regulator;

[0096] 12. Gas inlet;

[0097] 13. Valve;

[0098] 14. Gas chromatography (GC) apparatus coupled with a flame ionization detector (FID) and a helium ionization detector (PDHID for “Pulsed Discharge Helium Ionization Detector”).

[0099] This is a graph representing the production of ethylene according to example 3, under argon from the degradation of propanoic acid (1 vol%) under UVA with nanoparticles of TiO2 (reference outside the invention) and Cu / TiO2 (invention) synthesized by laser pyrolysis.

[0100] The figure relates to a graph representing the production of ethylene according to example 3 under argon from the degradation of propanoic acid (1 vol%) under UVA with TiO2 nanoparticles (reference outside the invention) synthesized by laser pyrolysis and Cu IMP / TiO2 (invention) obtained by impregnation of the TiO2 support.

[0101] The products obtained by photo-oxidation of ethanol (1%m) under UVA are shown, depending on the irradiation time, according to example 4.

[0102] Describes the molar selectivities in C products x H y O z as obtained by photo-oxidation of ethanol (1% m) under UVA, according to example 4. EXAMPLES

[0103] Example 1: Example of a photocatalytic device allowing the implementation of a use or a method according to the invention

[0104] The photocatalytic device () is composed of an airtight Pyrex reactor with a volume of 250 mL including 100 mL of aqueous solution, 150 mL of headspace, a glass mechanical stirrer and a bubbler (also made of glass) ensuring an inlet of neutral gas. The neutral gas can be helium He, nitrogen N2 or preferably argon Ar.

[0105] An 18W Phillips PLL UVA lamp, delivering a surface power of 4.8 mW.cm -2 was used as a light source centered at 370 nm. The emitted wavelengths were between 350 and 400 nm.

[0106] The concentration of alcohol(s) or carboxylic acid(s) in the solution is between 0.01 and 100% by volume, preferably 1.00%. The alcohol and / or carboxylic acid compounds may or may not be introduced in the form of a mixture. The concentration of metal (oxide) / TiO2 photocatalyst is between 0.01 and 50 g / L, preferably 0.5 g / L.

[0107] After complete purging of ambient air in the reactor via bubbling of neutral gas, the aqueous suspension comprising one or more alcohol(s) and / or one or more carboxylic acid(s) and the photocatalyst is irradiated by UVA. The photocatalytic reaction can be carried out under a continuous flow of neutral gas (dynamic mode) or statically (without neutral gas flow), preferably statically. Typically, the neutral gas flow during purging and / or under irradiation is between 1 and 500 mL / min, preferably 50 and 70 mL / min.

[0108] The gases produced in the reactor headspace during photocatalysis are analyzed by gas chromatography via a flame ionization detector (FID) and a helium plasma detector (PDHID). In the case of a dynamic mode reaction, the gases are transported by the neutral gas flow; in the case of static mode, the gases are transported by pumping.

[0109] Example 2: preparation of a catalyst allowing the implementation of a use or a process according to the invention

[0110] The metal and / or metal oxide may be brought into contact with the surface of the TiO2 particles by any technique known to those skilled in the art. This may, for example, be a laser pyrolysis or impregnation technique.

[0111] Synthesis by laser pyrolysis:

[0112] The TiO2 (outside the invention) and (oxide of) metal / TiO2 photocatalysts of the invention can be synthesized by the laser pyrolysis technique, an example of which is given below with copper as the metal.

[0113] A liquid mixture comprising the titanium and copper precursors is inserted into a chamber called a "pyrosol" comprising a cooling device, a drive gas inlet and a piezoelectric pellet. Typically, the titanium precursor is titanium isopropoxide (TTIP); the copper precursor may be, for example, copper acetylacetonate Cu(acac)2. Optionally, the copper precursor may be dissolved beforehand in one or more organic solvents such as a mixture of o-xylene / ethyl acetate in a proportion of 6.5:3.5 by volume.

[0114] The composition of said mixture is indicated in Table 1 below for a target copper content of 2.00 wt% relative to the mass of TiO2.

[0115] MaterialTTIPCu(acac)2o-xylene / ethyl acetate (6.5:3.5)TiO2(not in the invention)175 g-150 mLLCu / TiO2175 g4.134 g150 mL

[0116] Composition of the precursor mixture for laser pyrolysis

[0117] The liquid precursor mixture is converted into an aerosol by actuating the piezoelectric pellet. Optionally, the mixture can be heated throughout the synthesis, over a range of 10 to 100°C. Preferably, the mixture is heated to 30°C.

[0118] The aerosol obtained is then conveyed into a confined reaction chamber under a neutral atmosphere via a carrier gas which can be helium He, argon Ar or nitrogen N2. Similarly, the confinement gas in the reaction chamber can be helium He, argon Ar or nitrogen N2. Preferably, the entrainment and confinement gases (chimney, reactor windows) are argon Ar. The confinement flow rates are between 0 and 5000 cm 3 .min -1 , preferably 0 cm 3 .min -1 for containment at the chimney level and 3,000 cm 3 .min -1 for containments at the visibility windows. The entrainment gas flow rate is between 50 and 10,000 cm 3 .min -1 , preferably 2,000 cm 3 .min -1 .

[0119] Within the reaction chamber, an infrared CO2 laser beam with a wavelength of 10.6 μm and a power of up to 2,800 W is emitted orthogonally to the precursor mixture, carried in the form of fine droplets. Ideally, the laser power delivered to the reaction zone is between 100 and 900 W and around 670 W for the synthesis of TiO2 and Cu / TiO2. A laser radiation absorbing gas, preferably ethylene C2H4, can also be added in a flow rate range of 0 to 5,000 cm 3 .min -1 . In this example, the flow rate of this gas is set at 800 cm 3 .min -1. In this case, the laser power absorbed by the precursor aerosol listed in Table 1 is 276 W for TiO2, and 250 W for Cu / TiO2. The interaction between the laser beam, the precursor aerosol and possibly the ethylene gas allows the growth of nanoparticles collected on the surface of a filter barrier comprising nanopores. Note that the use of ethylene for the synthesis is optional and that it is possible to synthesize the TiO2 and Cu / TiO2 materials without using it.

[0120] The nanopowders synthesized by the said process are then calcined in a tubular furnace via an air reactor to remove the amorphous carbon from the precursors and possibly from the ethylene gas if ethylene is used. The heat treatment applied is for example a temperature of 450°C under an air flow of 100 mL.min -1for a period of 3 to 6 hours - until almost total or even total elimination of amorphous carbon, here, for example, 6 hours.

[0121] The main physicochemical characteristics of TiO2 and Cu / TiO2 photocatalysts synthesized by laser pyrolysis are shown in the following Table 2.

[0122] MaterialCopper content (%m ICP)S BET (m 2 .g -1 )%m Anatase%m RutileTiO2(excluding invention)-817228Cu / TiO21.91405347

[0123] Physicochemical characteristics of photocatalysts synthesized by laser pyrolysis

[0124] It is noteworthy that the copper content in the Cu / TiO2 material synthesized by laser pyrolysis, determined by inductively coupled plasma (ICP) spectrometry, is 1.91% by mass, which is very similar to the percentage introduced into the pyrosol (2.00% by mass).

[0125] Transmission electron microscopy (TEM) images of TiO2 and Cu / TiO2 nanoparticles obtained according to the present invention show that the size of the nanoparticles is between 5 and 25 nm for TiO2 and between 10 and 70 nm for Cu / TiO2.

[0126] Images obtained by scanning transmission electron microscopy (STEM) and EDX of Cu / TiO2 nanoparticles of the invention highlighting copper / copper oxide clusters on the surface of the TiO2, with a diameter between 1 and 3 nm.

[0127] Synthesis by impregnation on TiO2 support:

[0128] The metal (oxide) / TiO2 photocatalysts of the invention can also be synthesized by impregnation of metal via a metal precursor on a TiO2 support. This TiO2 support can be commercial or obtained by laser pyrolysis such as for example the TiO2 described above. An example is given below with copper as the metal.

[0129] 500 mg of TiO2 obtained by laser pyrolysis were dissolved in 50 mL of distilled water to which was added 43.3 mg (2.00 wt%) of a copper precursor, copper acetylacetonate Cu(acac)2 (purity = 97%). The metallic precursor, in the case of copper, is not limited to this compound and can be, for example, copper acetate (anhydrous or hydrated) or copper nitrate. Optionally, one or more organic solvents such as ethanol can be added and the precursors are dispersed in an ultrasonic bath. Once the precursors are completely dissolved, the mixture is transferred to a 50 mL flat-bottomed flask and heated in a water bath at 70°C. The evaporation of the stirred mixture via a magnetic bar takes place over a period of 12 hours and the residual powder is dried in an oven at 120°C.

[0130] The impregnated powder is then calcined at 450°C for 6 hours in a reactor in a tubular furnace under an air flow of 100 mL.min-1 .

[0131] The main physicochemical characteristics of the TiO2 support obtained by laser pyrolysis are recalled as well as those of the Cu photocatalyst IMP / TiO2 synthesized by impregnation are presented in the following Table 3.

[0132] MaterialCopper content (%m ICP)S BET (m 2 .g -1 )%m Anatase%m RutileTiO2(excluding invention)-817228Cu IMP / TiO22,15376634

[0133] Physicochemical characteristics of TiO2 and Cu photocatalysts IMP / TiO2

[0134] It is noted that the copper content in the Cu / TiO2 material synthesized by impregnation, determined by inductively coupled plasma (ICP) spectrometry, is 2.15%m which is very similar to the percentage (2.00%m) introduced into the balloon for the impregnation of the TiO2 support. Example 3: Photocatalysis of propanoic acid

[0135] The photocatalysts TiO2 (reference outside the invention) and Cu / TiO2 (example 2, first part) were introduced into the aforementioned photocatalytic reactor () at a level of 0.5 gL -1 with 1 vol% propanoic acid in 100 mL of aqueous solution. An argon flow set at 70 mL / min for 6 hours was used to expel the air from the photocatalytic reactor and replace it with a neutral argon atmosphere. After complete purging, the argon flow was stopped and the photocatalytic reactor was isolated. The photo-produced gaseous compounds were sampled from the reactor headspace to be sent to the GC / FID and GC / PDHID.

[0136] Ethylene produced from propanoic acid (1 vol% in H2O) is presented for 910 minutes under UVA irradiation centered at 370 nm with TiO2 and Cu / TiO2 photocatalysts. Ethylene obtained by photocatalysis with TiO2 reaches a production rate of 2 ppmv / h, and 214 ppmv / h with Cu / TiO2. This production is linear and the photocatalyst does not lose activity during the 910 minutes of irradiation.

[0137] Table 4 below shows the hourly gas productions obtained for this reaction as well as the selectivities, calculated according to the quotient [compound] / ∑[C x H y O z ] with x and y ≥ 1 after 910 minutes of irradiation.

[0138] MaterialSynthesisC2H4(ppmv / h), selectivity (%)C2H6(ppmv / h), selectivity (%)C4H 10 (ppmv / h), selectivity (%)TiO2(outside invention)Laser pyrolysis2 (1%)163 (96%)3 (2%)Cu / TiO2Laser pyrolysis214 (91%)18 (8%)2 (1%)

[0139] Hourly productions (ppmv / h) and selectivities (%) in photo-produced gases from 1 vol% of propanoic acid under argon by TiO2 and Cu / TiO2 synthesized by laser pyrolysis

[0140] The ethylene yield, calculated by the ratio [C2H4 / CO2] considering that a photo-degraded propanoic acid molecule forms an ethane radical and a CO2 molecule and that an ethane radical can form an ethylene or ethane molecule, is 1.0% for TiO2 and 85.0% for Cu / TiO2 after 910 minutes of irradiation.

[0141] In a completely analogous way, photocatalysis was carried out using impregnated photocatalyzers (example 2, second part).

[0142] The Cu-impregnated photocatalyst IMP / TiO2 was introduced into the aforementioned photocatalytic reactor () at a rate of 0.5 gL-1 with 1 vol% propanoic acid in 100 mL of aqueous solution. The synthesis of ethylene by photocatalysis was carried out under the same conditions as described above.

[0143] Ethylene produced from propanoic acid (1 vol% in H2O) under UVA irradiation centered at 370 nm with the photocatalysts TiO2 (obtained by laser pyrolysis, 910 min of irradiation) and Cu IMP / TiO2 (obtained by impregnation of the aforementioned TiO2 support, for 3,250 minutes, i.e. more than 54 hours of irradiation). Ethylene synthesized by photocatalysis with TiO2 reaches a production rate of 2 ppmv / h, and 218 ppmv / h with Cu IMP / TiO2. This production is linear and the photocatalyst does not lose activity during the 3,250 minutes of irradiation.

[0144] Table 5 below shows the hourly gas productions obtained for this reaction as well as the selectivities, calculated according to the quotient [compound] / ∑[C x H y O z ] with x and y ≥ 1 after 910 minutes of irradiation.

[0145] MaterialSynthesisC2H4(ppmv / h), selectivity (%)C2H6(ppmv / h), selectivity (%)C4H 10 (ppmv / h), selectivity (%)TiO2(outside invention)Laser pyrolysis2 (1%)163 (96%)3 (2%)Cu / TiO2Impregnation218 (92%)16 (7%)2 (1%)

[0146] Hourly productions (ppmv / h) and selectivities (%) in photo-produced gases from 1 vol% of propanoic acid under argon by TiO2 synthesized by laser pyrolysis and Cu IMP / TiO2

[0147] The ethylene yield is 1.0% for TiO2 and 86.5% for Cu IMP / TiO2 after 910 minutes of irradiation. Example 4: Photocatalysis of ethanol

[0148] An ethanol concentration of 1% by mass (i.e. 1.27% by volume) was used. The 2%Cu / TiO2 catalyst was introduced at 0.5 g cat / L in the resulting 100 mL solution, under an inert atmosphere (argon). Still under an inert atmosphere, UV irradiation (UVA centered at 370 nm) took place for approximately 650 min at room temperature (20-25°C). The monitoring of the gaseous products was carried out as in Example 3, i.e. with kinetic monitoring by GC-FID and GC-PDHID, as well as with identification and calibration of the products from standards. Results :

[0149] After 600 minutes of irradiation, H2, CO2, ethylene C2H4, acetaldehyde CH3CHO, methane CH4, as well as traces of CO and ethane were obtained.

[0150] This shows the formation of these species during the irradiation time, and the selectivities obtained.

[0151] The results show excellent selectivity of ethylene over other C products x H y O z (x, y ≥ 1). Thus, the molar selectivity to ethylene and acetaldehyde is 51% and 38%, respectively. Ethylene is therefore the product C x H y O z (x, y ≥ 1) majority.

[0152] Additionally, no acetone or ethyl acetate was detected.

Claims

Use of particles made of or comprising TiO2 bearing on at least part of their surface a metal M and / or a metal oxide M, M being chosen from the group comprising Cu, Zn, Fe, Mo, W and Ni, for obtaining at least one alkene by photocatalysis from at least one carboxylic acid of formula (I) R a -COOH, and / or at least one alcohol of formula (II) R b -OH, in which R a and R b are independently chosen from linear, branched or cyclic alkyl groups, optionally substituted by at least one group X chosen from arenes, X being in particular a phenyl group. Process for obtaining at least one alkene from at least one carboxylic acid of formula (I) R a -COOH, and / or at least one alcohol of formula (II) R b -OH, in which R a and R bare independently selected from linear, branched or cyclic alkyl groups, optionally substituted by at least one group X selected from arenes, X being in particular a phenyl group, comprising a step (i) of photocatalysis by UV and / or visible irradiation of at least one carboxylic acid and / or at least one alcohol in the presence of a catalyst consisting of or comprising particles consisting of or comprising TiO2 bearing on at least part of their surface a metal M and / or a metal oxide M, M being selected from the group comprising Cu, Zn, Fe, Mo, W and Ni. A method according to claim 2, wherein: the largest number-average dimension of the particles made of or comprising TiO2 is from 1 to 100 nm, in particular from 5 to 70 nm; and / or the particles made of or comprising TiO2 are spherical, spheroidal, rod-shaped, wire-shaped, tube-shaped, and / or plate-shaped, the particles optionally being arranged in chains. A process according to any one of claims 2 to 3, wherein the TiO2 is in the form of anatase, rutile and / or brookite, in particular in the form of anatase, rutile, or a mixture of anatase and rutile, more particularly in the form of a mixture of anatase and rutile having an anatase / rutile ratio of 0.80 to 2.33, in particular 1.00 to 2.

00. A process according to any one of claims 2 to 4, wherein: the content of metal M and / or metal oxide M relative to TiO2 is from 0.01 to 50% by mass, in particular from 0.1 to 5% by mass, for example about 2% by mass, or more than 0.01% and less than 2% by mass; and / or metal M and / or metal oxide M are present, at least on the surface of particles made of or comprising TiO2, in the form of particles whose largest number-average dimension is from 0.1 to 50 nm, in particular from 0.5 to 10 nm, more particularly from 1 to 3 nm. A process according to any one of claims 2 to 5, of obtaining at least one alkene from at least one carboxylic acid, which is in particular propanoic acid, acetic acid, a phenylpropanoic acid, in particular 2-phenylpropanoic acid, n-butyric acid, n-valeric acid, or pivalic acid, more particularly propanoic acid, or from at least one alcohol, which is in particular ethanol, or cyclohexanol, more particularly ethanol, and / or at least one alkene is ethylene. A method according to any one of claims 2 to 6, wherein step (i) is carried out: under an atmosphere comprising by volume less than 1% of dioxygen, in particular less than 0.1% of dioxygen, in particular less than 0.01% of dioxygen, more particularly less than 0.001% of dioxygen; under an atmosphere of inert gas, in particular under an atmosphere of dinitrogen, helium and / or argon, more particularly under an atmosphere of argon; and / or under a continuous flow of inert gas, in particular under an atmosphere of dinitrogen, helium and / or argon, more particularly under an atmosphere of argon, the flow being more particularly from 1 to 500 mL / min, preferably from 50 to 70 mL / min; or in the absence of a continuous flow of inert gas. A process according to any one of claims 2 to 7, wherein at least one carboxylic acid and / or at least one alcohol is present in a composition further comprising a solvent, in particular in solution in a solvent, the solvent preferably being water, the concentration of alcohol(s) and / or carboxylic acid(s) in the composition being in particular greater than or equal to 0.0001% by volume, in particular greater than or equal to 0.01% by volume, and / or less than 100% by volume, for example about 1.00% by volume, or wherein the at least one carboxylic acid and / or at least one alcohol is not in the presence of a solvent. A process according to any one of claims 2 to 8, wherein the catalyst is present in the composition comprising at least one carboxylic acid and / or at least one alcohol and the solvent, or, in the absence of solvent, in at least one carboxylic acid and / or at least one alcohol, at a concentration of 0.01 to 50 g / L, for example about 0.5 g / L. A method according to any one of claims 2 to 9, wherein: step (i) is carried out at a temperature of 10 to 200°C, in particular at a temperature of about 20 to about 40°C, or at a temperature of 40 to 200°C, in particular from 40 to 150°C, or even from 40 to 100°C; and / or the irradiation is UV-A, UV-B, UV-C, and / or visible, in particular UV-A, in particular at a wavelength of 350 to 400 nm.

Images