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

Abstract

The present invention relates to the use of TiO2 particles bearing 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 bearing a metal and / or a metal oxide.

Description

Title of the invention: USE OF TITANIUM DIOXIDE PARTICLES CARRYING A METAL OR A METAL OXIDE FOR THE OBTAINING OF ALKENES BY PHOTOCATALYSIS

[0001] The present invention relates to the use of TiO2 particles bearing 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 bearing 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 numerous 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 widely used organic molecule in the world. A cornerstone of the petrochemical industry, its global market represents over $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 primarily 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 relies on the cracking of naphtha (an intermediate between gasoline and kerosene, produced by fractional distillation of petroleum) or hydrocarbons such as ethane, usually heated to between 750 and 950°C. Ethylene yields vary, approximately 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 limitations of fossil fuels and the climate challenge, it has become essential to develop new low-energy and low-cost ethylene synthesis processes using renewable resources.

[0005] In view of these challenges, numerous research projects have been undertaken to find an alternative to the cracking of petroleum derivatives for the production of ethylene.

[0006] One of these alternative technologies consists of the catalytic dehydration of Ethanol is converted into ethylene. This can be, for example, bioethanol, a renewable resource produced at low cost without the use 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 to ethylene at high temperatures. Thus, the operating temperature and pressure significantly affect the ethylene yield. Consequently, these technologies generally allow for high ethylene yields, but the temperatures (typically 300 to 550°C) and pressures (generally between 0.3 and 4 MPa) used remain high, and therefore energy-intensive and expensive.And generally, when operating temperatures are lower, a significant amount of by-product is formed, with a limited percentage of ethanol conversion and still high pressures. Furthermore, the acid catalysts typically used to lower the operating temperature have a limited lifespan because they tend to deactivate through coking (the formation of a coke deposit on the surfaces of a system subjected to high temperatures by thermal cracking, resulting in reduced performance), and high-temperature regeneration reactions lead to high costs and a significant loss of catalytic efficiency.

[0007] Other technologies, based on the production of ethylene by photocatalysis, have subsequently been developed, notably using CuCl2 as a catalyst. These methods are attractive because they replace the use of thermal energy and high pressure with the use of light energy. However, the CuCl2 catalyst becomes inactive very quickly, typically in less than an hour, and therefore must be regularly regenerated under air.

[0008] In addition to ethanol, carboxylic acids, particularly propanoic acid (CH3CH2COOH), are of considerable interest because they can be used as renewable resources within biomass to produce liquid fuels and other molecules of interest to 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 glycerol fermentation, as well as from the fermentation of industrial wastewater, for example, from rapeseed oil extraction or potato waste.

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

[0010] The present invention aims to provide a process for obtaining alkenes, in particular ethylene, by a photocatalytic reaction which avoids the aforementioned disadvantages.

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

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

[0013] Another object of the invention is to provide a process for obtaining alkenes, in particular ethylene, with excellent selectivity, particularly 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 made of or comprising TiO2 bearing on at least a 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, 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) Ra-COOH, and / or at least one alcohol of formula (II) Rb-OH, wherein Ra and Rb are independently selected from linear, branched or cyclic alkyl groups, in particular linear, branched or cyclic C2 to C6 alkyl groups, more particularly linear, branched or cyclic C2 to C6 alkyl groups, said alkyl groups being optionally substituted by at least one group X selected from the arenas, 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, notably by measuring size by counting, for example via the ImageJ software, on transmission electron microscopy (TEM) images.

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

[0018] Particles made up 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 having an anatase / rutile ratio of 0.80 to 2.33, in particular from 1.00 to 2.00.

[0020] According to a particular embodiment, the particles made of or comprising TiO2 have a specific surface area ranging from 10 to 500 m² / g, in particular from 30 to 150 m² / g. These specific surface area ranges may correspond to the specific surface area of ​​the particles made of or comprising TiO2, excluding the surface area corresponding to the metal M and / or metal oxide M. These specific surface area ranges may also correspond to the total specific surface area of ​​the particles made of or comprising TiO2 carrying the metal M and / or metal oxide M.

[0021] According to a particular embodiment, 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.

[0022] According to a particular embodiment, the particles made of or comprising TiO2 bearing on at least a 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.

[0023] According to a more particular embodiment, the majority of the metal M and / or the metal oxide M of the particles made up of or comprising TiO2 is present on the surface of said particles.

[0024] According to another more 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 the metal oxide M of the particles made up of or comprising TiO2 is present on the surface of said particles. This can be measured by any technique known to those skilled in the art, for example by comparing measurements made by inductively coupled plasma spectrometry (ICP), which makes it possible to quantify the total metal content of a material, with those made by X-ray photoelectron spectrometry (XPS), which allows the quantity of surface elements of the material to be measured.

[0025] According to a particular embodiment, the metal M and / or the metal oxide M are present, at least on the surface of the particles made up of or comprising TiO2, in the form of particles whose largest dimension average by number of particles is from 0.1 to 50 nm, in particular from 0.5 to 10 nm, more particularly from 1 to 3 nm.

[0026] According to a particular embodiment, particles made 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, possibly followed by annealing, in particular in air, in particular at a temperature of 300 to 500°C, in particular from 400 to 500°C, for example at a temperature of about 450°C, and / or in particular for 3 hours, in particular from 3 to 6 hours.

[0027] 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.

[0028] 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.

[0029] According to a particular embodiment, at least one alkene is ethylene.

[0030] According to a particular embodiment, the invention relates to a method of obtaining ethylene from propanoic acid.

[0031] 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) Ra-COOH, and / or at least one alcohol of formula (II) Rb-OH, wherein Ra and Rb are 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 made up of or comprising particles made up of or comprising TiO2 bearing on at least a 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, and more particularly from the group comprising Cu, Zn, Fe, and Ni.

[0032] 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, notably by measuring size by counting, for example via the ImageJ software, on transmission electron microscopy (TEM) images.

[0033] According to a particular embodiment, the particles made of or comprising TiO2 are spherical, spheroidal, rod-shaped, wire-shaped, tube-shaped, and / or plate-shaped. These include, in particular, nanospheres, nanospheroids, nanorods, nanowires, nanotubes, and / or nanoplatelets.

[0034] Particles made up of or comprising TiO2, in particular in one of the forms described above, may optionally be organized into chains, in particular nanochains.

[0035] 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 having an anatase / rutile ratio of 0.80 to 2.33, in particular from 1.00 to 2.00.

[0036] According to a particular embodiment, the particles made of or comprising TiO2 have a specific surface area ranging from 10 to 500 m² / g, in particular from 30 to 150 m² / g. These specific surface area ranges may correspond to the specific surface area of ​​the particles made of or comprising TiO2, excluding the surface area corresponding to the metal M and / or metal oxide M. These specific surface area ranges may also correspond to the total specific surface area of ​​the particles made of or comprising TiO2 carrying the metal M and / or metal oxide M.

[0037] According to a particular embodiment, 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.

[0038] According to a particular embodiment, the particles made of or comprising TiO2 bearing on at least a 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.

[0039] According to a more particular embodiment, the majority of the metal M and / or the metal oxide M of the particles made up of or comprising TiO2 is present on the surface of said particles.

[0040] According to another more 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 the metal oxide M of the particles made of or comprising TiO2 is present on the surface of said particles. This can be measured by any technique known to those skilled in the art, for example by comparing measurements made by inductively coupled plasma spectrometry (ICP), which makes it possible to quantify the total metal content of a material, with those made by X-ray photoelectron spectrometry (XPS), which allows the quantity of surface elements of the material to be measured.

[0041] According to a particular embodiment, the metal M and / or the metal oxide M are present, at least on the surface of the particles made up of or comprising TiO2, in the form of particles whose largest dimension average by number of particles is from 0.1 to 50 nm, in particular from 0.5 to 10 nm, more particularly from 1 to 3 nm.

[0042] According to a particular embodiment, particles made 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, possibly followed by annealing, in particular under air, then possibly under dihydrogen, in particular at a temperature of 300 to 500°C, in particular from 400 to 500°C, for example at a temperature of about 450°C, and / or in particular for 3 hours, in particular from 3 to 6 hours.

[0043] Laser pyrolysis and impregnation are, for example, carried out according to operating procedures well known to those skilled in the art.

[0044] According to a more particular embodiment, laser pyrolysis is carried out by bringing an aerosol of a liquid composition comprising at least one precursor of TiO2, at least one precursor of metal M and / or of metal oxide M, and optionally an organic solvent, into contact with a laser beam.

[0045] According to another more particular embodiment, the impregnation is carried out by contacting TiO2, for example obtained by laser pyrolysis, with a precursor of the metal M and / or of the oxide of metal M, the impregnation being optionally followed by annealing, in particular under air, then optionally under dihydrogen, in particular at a temperature of 300 to 500°C, in particular from 400 to 500°C, for example at a temperature of about 450°C, and / or in particular for 3 hours, in particular from 3 to 6 hours.

[0046] When TiO2 or TiO2 bearing on at least part of its surface a metal M and / or a metal oxide M is obtained by laser pyrolysis, annealing is carried out, under air, then possibly under dihydrogen.

[0047] When the TiO2 is commercial and intended to be impregnated as defined above, annealing under air is optional but preferential, which can advantageously be followed by annealing under dihydrogen.

[0048] By "annealing under dihydrogen," we mean in particular annealing under pure dihydrogen or dihydrogen diluted in an inert gas, such as, for example, argon or dinitrogen. Such annealing is capable of limiting, if necessary, the presence of oxide on the surface of the metal M.

[0049] According to a particular embodiment, the invention relates to a method of obtaining of 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.

[0050] 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.

[0051] According to a particular embodiment, at least one alkene is ethylene.

[0052] According to a particular embodiment, the invention relates to a method of obtaining ethylene from propanoic acid.

[0053] According to a particular embodiment, step (i) is carried out under an inert gas atmosphere, in particular under an atmosphere of nitrogen, helium and / or argon, more particularly under an argon atmosphere.

[0054] 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.

[0055] According to a particular embodiment, step (i) is carried out under a continuous flow of inert gas, in particular under an atmosphere of nitrogen, helium and / or argon, 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 that can be described as dynamic.

[0056] 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 that can be described as static. Also 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 step (i) is carried out.

[0057] According to a particular embodiment, 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.

[0058] According to another particular embodiment, at least one carboxylic acid and / or at least one alcohol is not in the presence of a solvent.

[0059] According to a particular embodiment, 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 the at least one carboxylic acid and / or the less an alcohol, at a concentration of 0.01 to 50 g / L, for example about 0.5 g / L.

[0060] According to a particular embodiment, 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.

[0061] 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.

[0062] According to a particular embodiment, the invention relates to a process comprising a step (ii), following step (i), of recovery of the alkene(s), this step (ii) being optionally followed by a step (iii) of isolation of the alkene(s).

[0063] Step (ii) can be carried out by any technique known to a person skilled in the art, in particular by recovery of the headspace of the photocatalytic device used.

[0064] Step (iii) can be carried out by any technique known to those skilled in the art, in particular by distillation, especially 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 to a distillation column. The liquid is gradually heated, which allows the gases to be separated according to their boiling points.

[0065] Step (iii) can also be carried out using absorption-based techniques. The 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 highest 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.

[0066] Step (iii) can also be carried out by membrane separation, again based on the principle of gas affinity for a membrane, allowing the gases to infiltrate more or less rapidly through the membrane. The 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 across the membrane separating the retentate from the permeate. DEFINITIONS

[0067] As used in this description, the term "approximately" refers to a range of values ​​within ±10% of a specific value. For example, the expression "approximately 20" includes values ​​within 20 ±10%, that is, values ​​from 18 to 22.

[0068] For the purposes of this description, percentages refer to percentages by mass relative to the total mass of the formulation, unless otherwise stated.

[0069] As understood here, value ranges in the form 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" denotes the integers 1, 2, 3, 4, and 5. Preferred embodiments include each integer taken individually within 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.

[0070] As used herein, the term "alkyl" refers to a linear or branched alkyl group having the number of carbon atoms indicated before the term, in particular 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, an expression such as "C1-C4 alkyl" refers to an alkyl radical containing 1 to 4 carbon atoms. The same applies to the term "alkane".

[0071] Cycloalkyls are in particular alkyls (as defined above) comprising a ring. An example is cyclohexyl.

[0072] As used herein, the term "arene" refers to a mono- or bicyclic, substituted or unsubstituted, aromatic hydrocarbon cyclic system having 6 to 10 carbon atoms in the ring. Examples include benzene and naphthalene. Preferred arenes include unsubstituted and substituted benzene and naphthalene. The definition of "arene" also includes condensed cyclic systems, including, for example, cyclic systems in which an aromatic ring is condensed to a cycloalkyl ring. Examples of such condensed cyclic systems include, for example, indane, indene, and tetrahydronaphthalene. FIGURES

[0073] Figure 1 shows an example of a photocatalytic device capable of enabling the implementation of a use or process according to the present invention.

[0074] 1. UV lamp;

[0075] 2. Photocatalytic reactor;

[0076] 3. Bubbler;

[0077] 4. Coolant water inlet;

[0078] 5. Coolant water outlet;

[0079] 6. Solution containing the photocatalyst and the alcohol and / or acid precursor(s) carboxylic(s);

[0080] 7. Headspace containing the gases produced during photocatalysis;

[0081] 8. Injector connected to a gas chromatography (GC) apparatus;

[0082] 9. Mechanical agitator;

[0083] 10. Isolation valve;

[0084] 11. Mass flow regulator;

[0085] 12. Gas supply;

[0086] 13. Valve;

[0087] 14. Gas chromatography (GC) apparatus coupled with a flame ionization detector (FID) and a helium ionization detector (PDHID for "Pulsed Discharge Helium ionization Detector").

[0088] Fig. 2 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 TiO2 nanoparticles (reference outside invention) and Cu / TiO2 (invention) synthesized by laser pyrolysis.

[0089] Fig. 3 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 invention) synthesized by laser pyrolysis and Cu1MP / TiO2 (invention) obtained by impregnation of the TiO2 support. EXAMPLES

[0090] Example 1: Example of a photocatalytic device enabling the implementation of a use or process according to the invention

[0091] The photocatalytic device ([Fig. 1]) consists of an airtight Pyrex reactor with a volume of 250 mL, comprising 100 mL of aqueous solution, 150 mL of headspace, a glass mechanical stirrer, and a bubbler (also made of glass) providing a supply of neutral gas. The neutral gas can be helium (He), nitrogen (N2), or preferably argon (Ar).

[0092] An 18W Phillips UVA PLL lamp, delivering a surface power of 4.8 mW.cm2, was used as the light source centered at 370 nm. The emitted wavelengths were between 350 and 400 nm.

[0093] The concentration of alcohol(s) or carboxylic acid(s) in the solution is The concentration of the photocatalyst (metal oxide) / TiO2 is between 0.01 and 100% by volume, preferably 1.00%. Alcohol and / or carboxylic acid compounds may be introduced as a mixture or not. The concentration of the photocatalyst (metal oxide) / TiO2 is between 0.01 and 50 g / L, preferably 0.5 g / L.

[0094] After complete purging of ambient air from the reactor by bubbling with neutral gas, the aqueous suspension comprising one or more alcohols and / or one or more carboxylic acids and the photocatalyst is irradiated by UVA. The photocatalytic reaction can be carried out under a continuous flow of neutral gas (dynamic mode) or in static mode (without a flow of neutral gas), preferably in static mode. Typically, the flow of neutral gas during purging and / or under irradiation is between 1 and 500 mL / min, preferably between 50 and 70 mL / min.

[0095] The gases produced in the reactor headspace during photocatalysis are analyzed by gas chromatography using a flame ionization detector (FID) and a plasma helium ionization detector (PDHID). In the case of a dynamic reaction, the gases are carried by the neutral gas flow; in the case of a static reaction, the gases are transported by pumping.

[0096] Example 2: preparation of a catalyst enabling the implementation of a use or process according to the invention

[0097] The metal and / or metal oxide can be brought into contact with the surface of the TiO2 particles by any technique known to those skilled in the art. This could, for example, be a laser pyrolysis or impregnation technique.

[0098] Synthesis by laser pyrolysis:

[0099] 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.

[0100] A liquid mixture comprising 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 isopropylate (TTIP); the copper precursor may be, for example, copper acetylacetonate Cu(acac)2. Optionally, the copper precursor may be pre-dissolved in one or more organic solvents such as an o-xylene / ethyl acetate mixture in a 6.5:3.5 volume ratio.

[0101] 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.

[0102] [Tables 1] Material TTIP Cu(acac)2 o-xylene / ethyl acetate (6.5:3.5) TiO2 (excluding invention) 175 g - 150 mL Cu / TiO2 175 g 4.134 g 150 mL

[0103] Composition of the precursor mixture for laser pyrolysis

[0104] The liquid precursor mixture is converted into an aerosol by actuation of the piezoelectric pellet. Optionally, the mixture may be heated throughout the synthesis, over a range of 10 to 100°C. Preferably, the mixture is heated to 30°C.

[0105] The resulting aerosol is then conveyed to a confined reaction chamber under a neutral atmosphere via a carrier gas, which may be helium (He), argon (Ar), or nitrogen (N2). Similarly, the confinement gas in the reaction chamber may 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 cm³ / min*, preferably 0 cm³ / min for confinement at the chimney and 3000 cm³ / min for confinement at the visibility windows. The entrainment gas flow rate is between 50 and 10,000 cm³ / min*, preferably 2000 cm³ / min*.

[0106] Within the reaction chamber, a CO2 infrared 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, which is carried in the form of fine droplets. Ideally, the laser power delivered in the reaction zone is between 100 and 900 W, and on the order of 670 W for the synthesis of TiO2 and Cu / TiO2. A laser radiation-absorbing gas, preferably ethylene C2H4, can also be added at a flow rate ranging from 0 to 5,000 cm³.min*. In the present example, the flow rate of this gas is set at 800 cm³.min*. 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 ethylene gas allows the growth of nanoparticles collected on the surface of a filter barrier containing nanopores.Note that the use of ethylene for synthesis is optional and that it is possible to synthesize TiO2 and Cu / TiO2 materials without using it.

[0107] The nano-powders synthesized by said process are then calcined in a tubular furnace via an air reactor to remove the amorphous carbon from the pre sliders and possibly 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 1 for a duration of 3 to 6 hours - until almost total or even total elimination of the amorphous carbon, here, for example, 6 hours.

[0108] The main physico-chemical characteristics of the TiO2 and Cu / TiO2 photocatalysts synthesized by laser pyrolysis are shown in the following Table 2.

[0109] [Tables2] Material Copper content (%mICP) Sbet (m2.g1) %m Anatase %m Rutile TiO2 (excluding invention) - 81 72 28 Cu / TiO2 1.91 40 53 47

[0110] Physico-chemical characteristics of photocatalysts synthesized by laser pyrolysis

[0111] It should be noted that the copper content in the Cu / TiO2 material synthesized by laser pyrolysis, determined by inductively coupled plasma spectrometry (ICP), is 1.91% by mass, which is very similar to the percentage introduced into the pyrosol (2.00% by mass).

[0112] Transmission electron microscopy (TEM) images of TiO2 and Cu / TiO2 nanoparticles obtained according to the present document show that the size of the nanoparticles is between 5 and 25 nm for TiO2 and between 10 and 70 nm for Cu / TiO2.

[0113] 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.

[0114] Synthesis by impregnation on TiO2 support:

[0115] The metal (oxide) / TiO2 photocatalysts of the invention can also be synthesized by metal impregnation via a metallic precursor onto a TiO2 support. This TiO2 support can be commercially available or obtained by laser pyrolysis, such as the TiO2 described above. An example is given below using copper as the metal.

[0116] 500 mg of TiO2 obtained by laser pyrolysis were dissolved in 50 mL of distilled water to which 43.3 mg (2.00 wt%) of a copper precursor, copper acetylacetonate Cu(acac)2 (purity = 97%), was added. 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 may be added, and the precursors are dispersed in a bath at ultrasound. Once the precursors have completely dissolved, the mixture is transferred to a 50 mL flat-bottom flask and heated in a water bath at 70°C. The stirred mixture is evaporated over 12 hours using a magnetic stir bar, and the residual powder is dried in an oven at 120°C.

[0117] 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*.

[0118] The main physico-chemical characteristics of the TiO2 support obtained by laser pyrolysis are recalled and those of the Cu1MP / TiO2 photocatalyst synthesized by impregnation are presented in the following Table 3.

[0119] [Tables3] Material Copper content (%mICP) Sbet (m2.g1) %m Anatase %m Rutile TiO2 (excluding invention) - 81 72 28 Cu1MP / TiO2 2.15 37 66 34

[0120] Physico-chemical characteristics of TiO2 and Cu1MP / TiO2 photocatalysts

[0121] It should be noted that the copper content in the Cu / TiO2 material synthesized by im Pregnation, determined by inductively coupled plasma spectrometry (ICP), is 2.15%m, which is very similar to the percentage (2.00%m) introduced into the balloon for impregnation of the TiO2 support. Example 3: Photocatalysis of propanoic acid

[0122] The TiO2 (reference not given) and Cu / TiO2 (Example 2, Part 1) photocatalysts were introduced into the aforementioned photocatalytic reactor ([Fig. 1]) at a concentration of 0.5 g L⁻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 collected from the reactor headspace and sent to the GC / FID and GC / PDHID.

[0123] Figure 2 shows the ethylene produced from propanoic acid (1 vol% in H₂O). 2O) for 910 minutes under UVA irradiation centered at 370 nm with the photocatalysts TiO2 and Cu / TiO2. The 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.

[0124] Table 4 below shows the hourly gas productions obtained for this reaction as well as the selectivities, calculated according to the quotient [compound] / E[CxHyOz] with x and y > 1 after 910 minutes of irradiation.

[0125] [Tables4] Material Synthesis c2h4 (ppmv / h), selectivity (%) c2h6 (ppmv / h), selectivity (%) c4h10 (ppmv / h), selectivity (%) TiO2 (not part of the invention) Laser pyrolysis 2 (1%) 163 (96%) 3 (2%) Cu / TiO2 Laser pyrolysis 214 (91%) 18 (8%) 2 (1%)

[0126] Hourly production (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

[0127] The yield of ethylene, 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 a molecule of ethylene or ethane, is 1.0% for TiO2 and 85.0% for Cu / TiO2 after 910 minutes of irradiation.

[0128] In a completely analogous way, photocatalysis was carried out using impregnated photo-calysers (example 2, second part).

[0129] The Cu1MP / TiO2 impregnated photocatalyst was introduced into the aforementioned photocatalytic reactor ([Fig. 1]) at a concentration of 0.5 g L⁻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.

[0130] Figure 3 shows the 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 irradiation) and Cu₁MP / TiO₂ (obtained by impregnation of the aforementioned TiO₂ support, for 3,250 minutes, i.e., more than 54 hours of irradiation). The ethylene synthesized by photocatalysis with TiO₂ reaches a production rate of 2 ppmv / h, and 218 ppmv / h with Cu₁MP / TiO₂. This production is linear, and the photocatalyst does not lose activity during the 3,250 minutes of irradiation.

[0131] Table 5 below shows the hourly gas productions obtained for this reaction as well as the selectivities, calculated according to the quotient [compound] / E[CxHyOz] with x and y > 1 after 910 minutes of irradiation.

[0132] [Tables5] Material Synthesis c2h4 (ppmv / h), selectivity (%) c2h6 (ppmv / h), selectivity (%) c4h10 (ppmv / h), selectivity (%) TiO2 (not part of the invention) Laser pyrolysis 2 (1%) 163 (96%) 3 (2%) Cu / TiO2 Impregnation 218 (92%) 16 (7%) 2 (1%)

[0133] Hourly production (ppmv / h) and selectivities (%) in photo-produced gases from 1 vol% of propanoic acid under argon by TiO2 synthesized by laser pyrolysis and Cu^p / TiO2

[0134] The yield of ethylene is 1.0% for TiO2 and 86.5% for Cu1MP / TiO2 after 910 minutes of irradiation.

Claims

Demands

1. 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 selected 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) Ra-COOH, wherein Ra is 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.

2. A process for obtaining at least one alkene from at least one carboxylic acid of formula (I) Ra-COOH, wherein Ra is 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 in the presence of a catalyst consisting of or comprising particles consisting of or comprising TiO2 bearing on at least a 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.

3. 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, the measurement of said largest number-average dimension being carried out by size measurement by counting on transmission electron microscopy images; 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.

4. A method 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.

5. A method 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; and / or - the metal M and / or metal oxide M are present, at least on the surface of the particles made of or comprising TiO2, in the form of particles having the largest number-average dimension of the particles from 0.1 to 50 nm, in particular from 0.5 to 10 nm, more particularly from 1 to 3 nm, the measurement of said largest number-average dimension being carried out by size measurement by counting on transmission electron microscopy images.

6. 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 phenyl-propanoic acid, in particular 2-phenylpropanoic acid, n-butyric acid, n-valeric acid, or pivalic acid, more particularly propanoic acid, and / or at least one alkene is ethylene.

7. A method according to any one of claims 2 to 6, wherein step (i) is carried out: - under an atmosphere of inert gas, in particular under an atmosphere of nitrogen, 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 nitrogen, 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.

8. A method according to any one of claims 2 to 7, wherein at least one carboxylic acid is present in a composition further comprising a solvent, in particular in solution in a solvent, the solvent preferably being water, the concentration of 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 in which at least one carboxylic acid is not in the presence of a solvent.

9. 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 the solvent, or, in the absence of solvent, in at least one carboxylic acid, at a concentration of 0.01 to 50 g / L, for example about 0.5 g / L.

10. 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 irradiation, in particular UV-A, in particular at a wavelength of 350 to 400 nm.

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