Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
  • B01J35/39—Photocatalytic properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
  • B01D53/86—Catalytic processes
  • B01D53/8671—Removing components of defined structure not provided for in B01D53/8603 - B01D53/8668
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
  • B01D53/86—Catalytic processes
  • B01D53/88—Handling or mounting catalysts
  • B01D53/885—Devices in general for catalytic purification of waste gases
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
  • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
  • B01J21/063—Titanium; Oxides or hydroxides thereof
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
  • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
  • B01J21/08—Silica
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/40—Catalysts, in general, characterised by their form or physical properties characterised by dimensions, e.g. grain size
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
  • B01J35/51—Spheres
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/0201—Impregnation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/207—Transition metals
  • B01D2255/20707—Titanium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/80—Type of catalytic reaction
  • B01D2255/802—Photocatalytic
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2257/00—Components to be removed
  • B01D2257/50—Carbon oxides
  • B01D2257/504—Carbon dioxide

Definitions

• Catalytic bed comprising a particulate photocatalytic catalyst
• the present invention relates to the field of photocatalysis, aimed at treating liquid or gaseous phases by bringing them into contact with a photocatalytic material, which is irradiated with a source emitting in an appropriate wavelength range. It relates more particularly to a new type of photocatalytic material, its method of obtaining and its applications.
• Photocatalysis is based on the principle of activation of a semiconductor acting as a photocatalyst using the energy provided by irradiation.
• a semiconductor is characterized by its forbidden band (or "bandgap" according to the Anglo-Saxon terminology), i.e. by the energy difference between its conduction band and its valence band, which is specific to it.
• Photocatalysis can be defined as the absorption of a photon, the energy of which is greater than the forbidden band width, or "bandgap", between the valence band and the conduction band, which induces the formation of a electron-hole pair in the case of a semiconductor. We therefore have the excitation of an electron at the level of the conduction band, and the formation of a hole on the valence band.
• This electron-hole pair will allow the formation of free radicals which will either react with compounds present in the medium in order to initiate oxidation-reduction reactions, or else recombine according to various mechanisms. Any photon with an energy greater than its band gap can be absorbed by the semiconductor. Any photon with energy below its band gap cannot be absorbed by the semiconductor.
• Photocatalysis can thus be used to operate the decontamination of gaseous media, in particular to convert by oxidation compounds of the VOC type (acronym for Volatile Organic Compounds), or to treat liquid media, containing for example toluene, benzene, ethanol or acetone.
• Photocatalysis can also be used to convert the CO2 of a gaseous medium by reduction, in order to convert it into valuable compounds, in particular with 1 carbon or more, such as CO, methane, methanol, carboxylic acids, ketones or others.
• alcohols we thus actively convert the CO2, rather than capturing and storing it to reduce its content in the atmosphere.
• titanium oxide titanium oxide
• one or two refractory oxides with in addition a particular porosity leading to photocatalytic performances superior to those which would be obtained with a material entirely made up of titanium oxide.
• the object of the invention is therefore the development of an improved photocatalytic material, in particular in terms of further improved photocatalytic performance, and, alternatively, of improved implementation and/or production.
• the invention firstly relates to a catalytic bed comprising a particulate photocatalytic catalyst, said bed comprising structuring particles of mineral material b associated with at least one semiconductor material a with photocatalytic properties, the association being made
• the structuring particles b being essentially spherical in shape and with an average diameter of between 22 nm and 8.0 ⁇ m, and preferably between 30 nm and 7.5 ⁇ m.
• the mineral material targeted by the invention is of the electrical insulating type, therefore essentially inert with respect to photocatalysis: it is a material whose forbidden band ("band gap") is greater than 6 e.v.
• this catalytic bed is intended to be a fixed bed (as opposed, in particular, to a fluidized bed).
• the invention has therefore chosen to disperse the semiconductor material in a mineral material which is not, by calibrating the size of the particles of this mineral material as a function of the range of wavelengths targeted for the irradiation of the material.
• semiconductor allowing the creation of electron-hole pairs and thus the desired photocatalytic reactions.
• irradiation sources are chosen in the field of IIV-A, IIV-B and/or the visible field, which define a wavelength range capable of activating conventional semiconductor materials such as titanium oxide.
• the invention by choosing particles, called here structuring, in mineral material that are both spherical and of specific average diameter, exploits what is known under the term Mie scattering, by causing optimal scattering of the radiation, preferentially in the direction of the incident radiation: Mie scattering is directly linked to the wavelength of the incident radiation and designates the preferential scattering of the radiation in its incident axis for spherical particles whose radius is between 0.1 and 10 times the wavelength in question.
• the structuring particles of the invention will thus amplify the effectiveness of the irradiation in the domain from the IIV-A to the visible domain: they will diffuse the radiation mainly in the incident direction from the surface of the catalytic bed, and thus considerably increase the possibilities that the semiconductor material is irradiated, thus increasing its photocatalytic capacities. Indeed, the depth of penetration of the incident radiation within the catalytic bed will be greater, the radiation then being able to reach areas of semiconductor material that are otherwise difficult to reach by the radiation.
• the photocatalytic performances of the material could be increased by a factor of 2, even 3 or 4, even in the most favorable configurations by a factor of 10 and more compared to a material composed in the same way but with particles outside this diameter range and/or non-spherical, which gives a great deal of flexibility in the implementation of the invention.
• the invention proposes two alternative or cumulative variants for constituting the material, and they both have their advantages:
• the variant with two types of particles, the structuring ones and the semiconductor ones, is interesting because it is simple to does not seek to unite the two types of material, and that the preparation is just based on a mixture of the two powders, without chemical reaction, heat treatment etc...
• This variant also makes it possible to adapt very easily to any shape and any catalytic bed dimensions. It makes it possible to form the bed in situ, directly in the reactor in which the bed is to be placed, without prior pre-conditioning, by easily adapting, on a case-by-case basis, the proportion between the two types of particles in particular, except to provide suitable tools to ensure as homogeneous a mixture as possible between the two types of particles. It is also possible to condition the mixture beforehand, so as to have only one product to be deposited to form the bed.
• the other variant consisting in chemically/physico-chemically depositing the semiconductor on the structuring particles, also has advantages: it ensures a controlled distribution of the semiconductor with respect to the particles, a connection between the two materials favoring their interactions, in particular here vis-à-vis the radiation scattered by the particles. It thus offers a “ready-to-use” product to build catalytic beds in reactors.
• the structuring particles can be completely or only partially covered by the semiconductor. It should also be noted that according to this variant, provision can also be made for a certain proportion of the structuring particles to remain devoid of deposit of semiconductor material.
• the structuring particles are (essentially) spherical and solid: that they are solid gives them better mechanical properties, better mechanical resistance, resistance to abrasion, to attrition, etc.
• all of the particles within the bed are arranged in a disorganized manner. It turned out, surprisingly, that this disorganization was beneficial in terms of the photocatalytic performance of the material.
• “Disorganized” means the fact that the particles of the material are not arranged in an orderly fashion, do not form layers of particles aligned in three dimensions.
• the material according to the invention therefore has inter-grain spaces of non-uniform sizes and locations, randomly arranged within the material. These spaces are also different depending on whether we have either the variant of mixtures of particles (of different size and shape), or the variant with only one particle type (the structuring particles covered at least partially with semiconductor)
• the bed contains the semiconductor material a in the form of particles
• said particles have an average dimension of at most 100 nm, in particular at most 50 nm and at least 5 nm, preferably between 10 and 30 nm. It should be noted that, in this case, these particles are not spherical, or not necessarily, and their average size is not conditioned by the wavelength of the irradiation radiation.
• the catalytic bed according to the invention has a void ratio equal to the ratio of the void volume in the photocatalytic bed to the total volume of the bed composed of void and particles, of at least 40%, preferably of at most 80% and in particular between 40 and 70%.
• This void ratio is, indirectly, an indication of the disorganized arrangement of the material mentioned above. Indeed, the void content is minimal when dealing with perfectly organized spheres, and the void content according to the invention is greater than this minimum content.
• the catalytic bed according to the invention has a "dilution rate" equal to the ratio of the volume occupied by structuring particles of mineral material b to the volume occupied by the sum of the semiconductor material(s) a, a' and structuring particles of mineral material b, of at most 80%, in particular between 5% and 70%, and preferably between 10 and 50%.
• This dilution rate of at most 80% is chosen in particular in the case of a chemical or physico-chemical deposition of the semiconductor material a on the structuring particles of mineral material b, but can naturally apply to the two variants of the invention.
• dilution rate is used to reflect the proportion of the active material (the semiconductor) in relation to the structuring particles, which, a priori, are little or not at all. The higher this dilution rate, the higher the quantity of structuring particles. From the examples set out later, it will be seen that this degree of dilution can be increased without reducing, or even increasing, the photocatalytic performances of the material as a whole. It is more judicious to reason in dilution rate by volume than by mass, insofar as the density of materials, in particular of the semiconductor, can vary widely from one semiconductor to another.
• the catalytic bed may comprise (at least) two distinct semiconductor materials, a first material a, and a second material a′. It can be done:
• the bed contains, in addition, a certain proportion of structuring particles not covered with semiconductor material, in the variant where the semiconductors are deposited on their surface.
• the structuring particles of mineral material b can be chosen from metal oxide(s), in particular oxides of metals from groups IIIA and IVA of the periodic table, and preferably chosen from aluminum oxide, l silicon oxide a mixture of aluminum and silicon oxides.
• the/at least one of the semiconductor material(s) a, a' can be chosen from inorganic semiconductors.
• the inorganic semiconductors can be selected from one or more group IVA elements, such as silicon, germanium, silicon carbide or silicon-germanium.
• They can also be composed of elements of groups IIIA and VA, such as GaP, GaN, InP and InGaAs, or of elements of groups IIB and VIA, such as CdS, ZnO and ZnS, or of elements of groups IB and VI IA, such as CuCl and AgBr, or elements from groups IVA and VIA, such as PbS, PbO, SnS and PbSnTe, or elements from groups VA and VIA, such as Bi 2 Te3 and Bi 2 O 3 , or elements from groups IIB and VA, such as Cd 3 P 2 , Zn 3 P 2 and Zn 3 As 2 , or elements from groups IB and VIA, such as CuO, Cu 2 O and Ag 2 S, or elements from groups VI II B and VIA, such as CoO, PdO, Fe 2 O 3 and NiO, or elements from groups VI B and VIA, such as MoS 2 and WO 3 , or elements from groups VB and VIA, such as V 2 Os and Nb 2
• they comprise at least one of the following metal oxides: titanium oxide, tungsten oxide, cerium oxide, bismuth oxide, zinc oxide, copper oxide, vanadium oxide, iron oxide, cadmium oxide, and preferably is chosen from TiO 2 , Bi 2 O 3 , CdO, Ce 2 O 3 , CeO 2 , CeAIO 3 , CuO, Fe 2 O 3 , FeTiO 3 , ZnFe 2 O 3 , V 2 O5, ZnO, WO 3 and ZnFe 2 O4, alone or in a mixture.
• metal oxides titanium oxide, tungsten oxide, cerium oxide, bismuth oxide, zinc oxide, copper oxide, vanadium oxide, iron oxide, cadmium oxide, and preferably is chosen from TiO 2 , Bi 2 O 3 , CdO, Ce 2 O 3 , CeO 2 , CeAIO 3 , CuO, Fe 2 O 3 , FeTiO 3 , ZnFe 2 O 3 , V 2 O5, ZnO, WO 3
• The/at least one of the semiconductor material(s) a, a' can be doped with one or more ions chosen from metal ions, in particular ions of V, Ni, Cr, Mo, Fe, Sn, Mn, Co, Re, Nb, Sb, La, Ce, Ta, Ti, or from non-metallic ions, in particular C, N, S, F, P, or by a mixture of metallic and non-metallic ions.
• metal ions in particular ions of V, Ni, Cr, Mo, Fe, Sn, Mn, Co, Re, Nb, Sb, La, Ce, Ta, Ti
• non-metallic ions in particular C, N, S, F, P, or by a mixture of metallic and non-metallic ions.
• The/at least one of the semiconductor material(s) a, a' may also comprise one or more element(s) in the metallic state chosen from an element of groups I VB, VB, VIB, VI IB , VI II B, IB, II B, II IA, IVA and VA of the periodic table of the elements and preferably in direct contact with said semiconductor material. It is preferentially a metal among platinum, palladium, gold, nickel, cobalt, ruthenium, silver, copper, rhenium or rhodium.
• group VIII according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IIIPAC classification.
• the catalytic bed according to the invention may have a thickness of at most 1 cm, in particular of at most 5 mm, and in particular of at least 10 ⁇ m. Preferably, its thickness is at least 100 or 200 microns. This thickness depends in particular on the depth of penetration of the radiation from the irradiation source into the bed.
• a subject of the invention is also a process for obtaining the catalytic bed as defined above, where one mixes, on the one hand, the structuring particles of mineral material b, on the other hand, the particles of semiconductor material a, so as to achieve a homogeneous distribution of the two types of particles within the bed.
• the invention also relates to a process for obtaining the catalytic bed as defined above, where the or at least one of the semiconductor materials a, a' is deposited on the structuring particles of mineral material b by impregnation of said structuring particles by a solution of at least one precursor of the semiconductor material, or by ion exchange, or by electrochemical means of the type, in particular with molten salts, then drying and optional calcination.
• CVD chemical vapor deposition
• spray-drying spray-drying
• ALD atomic layer deposition
• a subject of the invention is also any photocatalytic feed treatment reactor in gaseous and/or liquid form and which comprises at least one photocatalytic bed as defined above and which is fixedly mounted in said reactor. Indeed, it is when the bed is fixed (for as opposed to moving bed reactors) that the benefits of Mie scattering on the structuring particles can be best exploited.
• the invention also relates to a process for the photocatalytic treatment of a charge in gaseous or liquid form, such as:
• At least one photocatalytic bed defined above is placed in a fixed manner in a reactor
• the photocatalytic bed is irradiated during contact with at least one radiation source emitting in the range of LIVA-A, and/IIV-B and/or the visible range, in particular in the length range of wave between 220 and 800 nm, preferably in the range between 300 and 750 nm.
• the invention also relates to such a process, where the photocatalytic treatment is:
• Figure 1 shows a schematic re-emission pattern of a beam incident on particles according to Rayleigh-type scattering and Mie-type scattering.
• FIG. 2 represents a transmission electron microscopy (TEM) image of the titanium oxide semiconductor particles used according to one embodiment of the photocatalytic material according to the invention.
• TEM transmission electron microscopy
• FIG. 3 represents an image by scanning electron microscopy (SEM) of the structuring particles in silicon oxide used according to an embodiment of the photocatalytic material according to the invention.
• FIG. 4 represents a simplified diagram of an installation aiming to measure the performance of a photocatalytic material according to the invention.
• FIG. 5 represents a graph quantifying the photocatalytic performances of two examples of material according to the invention, with, on the abscissa, the volume fraction of titanium oxide semiconductor of the material of the invention comprising this semiconductor and structuring particles in silicon oxide, and, along the ordinate, the overall consumption of electrons for 20 hours per square meter, expressed in pmol/m 2 .
• the invention relates to the composition of a photocatalytic bed with mineral structuring particles, here solid, which are calibrated according to the wavelength of the radiation emitted by a light source to activate a semiconductor material, so that that the radiation scatters largely preferentially in the direction of the incident radiation at the surface of these spheres by exploiting Mie scattering.
• Figure 1 simply schematizes the phenomenon of MIE scattering mentioned above: on the left is symbolically represented a light source S emitting radiation at a given wavelength A.
• a spherical P1 particle whose diameter is not calibrated according to the invention, and which is less than 0.1 ⁇ , will re-emit the incident radiation quite equally in all directions, this is Rayleigh scattering.
• a P2 particle whose diameter is calibrated to be between 0.1 ⁇ and 10 ⁇ will re-emit the radiation in a privileged way according to the direction of the incident radiation, this is the diffusion of MIE: this is what the invention uses, so that the calibrated particles “bring” more radiation into the depth of the catalytic bed, that it facilitates its propagation, and that the semiconductor material is thus better exploited.
• the photocatalytic material a1 is titanium oxide: it is TiC>2 available under the trade name Aeroxide® P25 from the company Aldrich, with a purity of 99.5%. Titanium oxide is in the form of fine particles. Its particle size measured by transmission electron microscopy (TEM) is 21 nm. Its specific surface measured by the BET method is 52 m 2 /g. BET is an abbreviated term: it is the method Brunauer, Emmett, Tellert as defined in S. Brunauer, PH Emmett, E. Teller, J. Am. Chem. Soc., 1938, 60 (2), pp 309-319).
• this titanium oxide is in the form of a mixture of rutile and anatase.
• Figure 2 is a representation obtained by TEM of these titanium oxide particles: we see that they are of irregular shape and that they tend to agglomerate.
• the photocatalytic material a2 is titanium oxide with the addition of metallic platinum particles prepared by photo-deposition as follows:
• H 2 PtCl6.6H2O (37.5% by mass of metal) is introduced into 500 ml of distilled water. 50 ml of this solution are withdrawn and inserted into a jacketed glass reactor.
• the mixture is then left with stirring and under UV radiation for two hours.
• the lamp used to supply the UV radiation is a 125 W HPKTM mercury vapor lamp.
• the mixture is then centrifuged for 10 minutes at 3000 revolutions per minute in order to recover the solid.
• Two washes with water are then carried out, each of the washes being followed by centrifugation.
• the recovered powder is finally placed in an oven at 70° C. for 24 hours.
• the photocatalytic material a2 is then obtained.
• the Pt element content is measured by plasma source atomic emission spectrometry (or “inductively coupled plasma atomic emission spectroscopy “ICP-AES” according to the English terminology) at 0.99% by mass.
• the a3 photocatalytic material is a semiconductor based on commercial WO3 (available from Sigma Aldrich, having a particle size of less than 100 nm).
• the specific surface measured by the BET method is equal to 20 m 2 /g.
• the photocatalytic material particle size measured by X-ray diffractometry (Debye-Scherrer method) is 50 ⁇ 5 nm.
• the a4 photocatalytic material is a mixture of titanium and copper oxides, with particles of platinum Cu 2 O/Pt/TiO2. It is prepared as follows:
• a Cu(NOs)2 solution is prepared by dissolving 0.125 g of Cu(NOs)2.3H2O (Sigma-AldrichTM, 98%) in 50 ml of a 50/50 isopropanol/H 2 O mixture, i.e. a concentration in Cu 2+ of 10.4 mmol/L.
• Into the reactor were introduced: 0.20 g of the photocatalytic material a2 25 ml of distilled water and finally 25 ml of isopropanol.
• the system is purged in the dark under a flow of argon (100 ml/min) for 2 hours.
• the reactor is thermostated at 25° C. throughout the synthesis.
• the argon flow is then slowed down to 30 ml/min and the irradiation of the reaction mixture starts.
• the lamp used to provide the UV radiation is a 125 W HPKTM mercury vapor lamp.
• the 50 ml of copper nitrate solution are added to the mixture.
• the mixture is left for 10 hours with stirring and irradiation.
• the mixture is then centrifuged for 10 minutes at 3000 revolutions per minute in order to recover the solid. Two washes with water are then carried out, each of the washes being followed by centrifugation.
• the recovered powder is finally placed in an oven at 70° C. for 24 hours.
• the photocatalytic material a4 Cu 2 O/Pt/TiO2 is then obtained.
• the Cu element content is measured by ICP-AES at 2.2% by mass.
• XPS measurement (“X-Ray Photoelectron Spectrometry” according to the English terminology), and copper oxide phases at 67% Cu 2 O and 33% CuO.
• the structuring particles b1 chosen in some of the following examples are spherical particles in silicon oxide based on commercial SiO 2 , which can be obtained from the company Alfa Aesar (CAS: 7631-86-9): these are balls with a purity greater than 99.9%, and whose average diameter measured by laser granulometry is 0.4 ⁇ m.
• Figure 3 is a representation obtained by SEM of these balls, which can be seen to be very homogeneous in their size and shape.
• the structuring particles b2 chosen in other examples are silicon oxide particles based on commercial SiO 2 , which can be obtained from the company Sigma Aldrich, under the commercial reference Davisil Grade 710, 10-14 ⁇ m : these are beads with a purity greater than 99%, and whose mean dimension measured by laser granulometry is 12.7 ⁇ m (distribution by volume).
• the semiconductor particles a1 to a4 and the structuring particles b1 (SiO 2 powder) or b2 (SiO 2 powder with a particle size greater than that of b1) are mixed mechanically with a dilution rate varying from 0 to 75% by volume , so as to obtain a homogeneous distribution of the two types of particles in the material. It is recalled that within the meaning of the present invention the “dilution rate” is equal to the ratio of the volume occupied by the structuring particles of mineral material to the volume occupied by the sum of the semiconductor material(s) and the structuring particles. Then, as represented in FIG.
• each sample 3 of photocatalytic material of each example is subjected to a test of photocatalytic reduction of CO2 in the gas phase in the following way:
• a reactor 1 is used, which operates continuously, with a bed 2 stationary arranged horizontally in its cavity, bed comprising a frit 4 on which the sample 3 is placed.
• the reactor 1 has in its upper wall a quartz optical window 5, facing which the sample 3 is located. above the reactor, and facing the window 5 is arranged a source of UV-visible irradiation 6.
• reactor 1 is supplied via an inlet in the upper part with a flow of 7 gaseous CO2, which is bubbled beforehand in a container/saturator filled with water 8.
• Flow 7 passes through sample 3 then is discharged through an outlet in the lower part in the form of a flow 9 which is analyzed online by a gas analyzer 10 of the gas phase micro-chromatograph type.
• the UV-visible irradiation source 6 is a xenon lamp, available from Asahi under the trade name MAX 303.
• samples 3 weighing between 45 and 70 mg, their weight varying according to their chosen dilution rate, the thickness of the catalytic bed 2, that of sample 3 therefore, remaining fixed and equal to 0.3 mm .
• the operating conditions are as follows:
• - irradiation power of the xenon lamp 6 kept constant at 80 W/m 2 measured for a wavelength range between 315 and 400 nm.
• the targeted CO2 conversion corresponds to the following reaction:
• the measurement of the photocatalytic performances of the samples is done by microchromatography with the device 10, by following the production of H2, CH4 and CO resulting from the reduction of CO2 and H2O, by an analysis every 6 minutes: Reduction products of CO2 are identified, such as CO, methane or even ethane.
• the average photocatalytic activities are expressed in pmol of photogenerated electrons which are consumed by the reaction over the duration of the test and per square meter of irradiated catalyst surface. Examples
• example 9 thus achieves an impressive level of photocatalytic activity.
• FIG. 5 represents in the form of a graph the results of Examples 2 and 3.
• the abscissa shows the volume fraction of the TiO2 particles, the ordinate shows the overall consumption of electrons over 20 hours per square meter: From this figure, we see that example 3 with the b2 structuring particles of too large a size gives results (the diamonds on the graph) that are much worse than with example 2 using the b1 structuring particles (the circles on the graph) whose size was calibrated to promote Mie diffusion.
• This calibration of the structuring particles is simple to choose, to obtain, and much simpler than having to refine other more complex parameters to control of the macro- or microporosity type of the material.
• the invention is very flexible in its implementation: depending on the desired level of performance, depending on the equipment and the chosen reactor, we will be able to adapt the composition of the material according to the invention by playing on the choice of materials, on the dilution rate, and on the way in which the mixing between the two materials will be carried out (mechanical mixing, chemical or physico-chemical solidarity, etc.).

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