Catalyst bed containing granular photocatalytic catalyst

Abstract

The present invention relates to a catalyst bed containing a specific photocatalytic catalyst, which comprises structured particles b made of inorganic material in combination with at least one semiconductor material a having photocatalytic properties, the combination being produced by: mixing the structured particles b made of inorganic material with the semiconductor material a in particulate form and / or by chemical or physicochemical deposition of the semiconductor material a on the structured particles b made of inorganic material, the structured particles b being substantially spherical in shape and having an average diameter between 22 nm and 8.0 μm.

Description

Technical Field

[0001] The present invention relates to the field of photocatalysis, aims to treat a liquid phase or a gas phase by contacting with a photocatalytic material, and will be irradiated with a light source that emits light in an appropriate wavelength range. More specifically, the present invention relates to a new type of photocatalytic material, a method for preparing the same, and its uses.

Background Art

[0002] Photocatalysis is based on the principle of activation of a semiconductor acting as a photocatalyst using the energy provided by light irradiation. A semiconductor is characterized by its band gap, that is, the energy difference between its conduction band and its valence band, and this energy difference is specific to the semiconductor. Photocatalysis can be defined as the absorption of photons, the energy of which is greater than the band gap width between the valence band and the conduction band, which in the case of a semiconductor induces the formation of electron-hole pairs. There is excitation of electrons to the conduction band and formation of holes in the valence band. This electron-hole pair enables the formation of free radicals, which react with compounds present in the medium to initiate an oxidation / reduction reaction or also recombine according to various mechanisms. Any photon having an energy greater than the band gap can be absorbed by the semiconductor. Photons having an energy lower than its band gap cannot be absorbed by the semiconductor.

[0003] The application areas are vast: photocatalysis can therefore be used to manipulate the decontamination of gaseous media, particularly to convert VOC (Volatile Organic Compounds) type compounds by oxidation, or to treat liquid media (e.g., those containing toluene, benzene, ethanol, or acetone). Photocatalysis can also be used to convert CO2 in gaseous media by reduction, converting it into upgradeable compounds, especially those having one or more carbon atoms, such as CO, methane, methanol, carboxylic acids, ketones, or other alcohols: CO2 is therefore actively converted rather than being captured and stored to reduce its content in the atmosphere. It is also possible to carry out the photolysis of water in liquid or gaseous media to produce upgradeable hydrogen (H2), particularly as a low-carbon energy source.

[0004] A photocatalytic material in the form of a porous monolith is known from Patent Document 1. This photocatalytic material contains 20% to 70% by weight of TiO2 relative to the total weight of the monolith, and 30% to 80% by weight of a refractory oxide selected from silica, alumina, or silica-alumina relative to the total weight of the monolith, has a bulk density of less than 0.19 g / mL, and has a specific degree of porosity, particularly with respect to macroporosity and mesoporosity. This relates to a material that, therefore, combines a semiconductor (titanium dioxide), which is the source of its photocatalytic properties, with one or two types of refractory oxides, and further has a specific degree of porosity that results in a photocatalytic performance quality superior to that which could be obtained from a material composed entirely of titanium dioxide.

[0005] The subject of this invention is therefore the development of improved photocatalytic materials, in particular, in which the performance quality of the photocatalyst is further improved, and in which the implementation and / or manufacture is further improved. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2018 / 197432 [Overview of the Initiative] [Means for solving the problem]

[0007] (Summary of the invention) The present invention relates, firstly, to a catalyst bed containing a granular photocatalytic catalyst, wherein the bed contains structured particles b made from a mineral material, and these structured particles are combined with at least one semiconductor material a having photocatalytic properties, and this combination is as follows: - Mixing structured particles b made from mineral material with semiconductor material a in particle form, and / or - Chemical or physicochemical deposition of semiconductor material a on structured particles b made from mineral material. Caused by, The structured particles b are essentially spherical and have an average diameter of 22 nm to 8.0 μm, preferably 30 nm to 7.5 μm.

[0008] The mineral materials targeted by this invention are of the electrical insulating type and are therefore intrinsically inert to photocatalysis: they are materials with a band gap greater than 6 eV.

[0009] Preferably, this catalyst bed is intended to be a fixed bed (in contrast to a fluidized bed).

[0010] Therefore, the present invention has chosen to disperse a semiconductor material in a non-semiconductor mineral material by calibrating the particle size of the mineral material, depending on the range of wavelengths to which the semiconductor material is irradiated, which enables the generation of electron-hole pairs and thus enables the desired photocatalytic reaction. This is because, conventionally in the field of photocatalysis, the irradiation source is selected in the UV-A, UV-B and / or visible range, which defines the range of wavelengths that can activate conventional semiconductor materials, such as titanium dioxide.

[0011] In fact, the present invention utilizes what is known under the term Mie scattering by selecting spherical particles (referred to here as structured particles) made from a mineral material having a specific average diameter, thereby causing optimal scattering of radiation preferentially in the direction of the incident radiation: Mie scattering is directly related to the wavelength of the incident radiation and exhibits preferential scattering of radiation in its incident axis for spherical particles whose radius is 0.1 to 10 times the wavelength in question. The structured particles of the present invention have their appropriately tuned diameters and therefore amplify the effectiveness of irradiation in the range from UV-A to the visible range: they scatter radiation mainly in the incident direction from the surface of the catalyst bed, thus greatly increasing the likelihood that semiconductor materials are irradiated, and thus improving their photocatalytic activity. This is because the penetration depth of the incident radiation into the catalyst bed becomes greater, allowing radiation to reach areas of the semiconductor material that are difficult for radiation to reach.

[0012] It has been found that, compared to materials with a similar configuration but containing particles outside this diameter range and / or non-spherical particles, the photocatalytic performance quality of the material can be improved by two, actually three or four, and even more actually, by more than ten times in the most preferred configuration, providing great flexibility in implementing the present invention. Thus, depending on whether catalyst performance quality or cost is prioritized, it is possible to choose to amplify the material's performance quality as much as possible while keeping the semiconductor amount the same, amplify it to a lesser extent, or reduce the amount of semiconductor in the material and maintain it at a minimum level identical.

[0013] The present invention provides two alternative or cumulative modifications for constructing a material, both of which have their advantages; The advantage of using two types of particles, structured particles and semiconductor particles, is that they are easy to manufacture, do not require the integration of the two types of materials, and preparation is based solely on mixing the two powders without chemical reactions or heat treatment. This deformation also allows for very easy adaptation of catalyst beds to any shape and dimensions. This makes it possible to form the bed in situ, directly within the reactor where the bed must be placed, without prior adjustments, and by easily adjusting the ratio between the two types of particles on a case-by-case basis, except for providing a device suitable for ensuring the most uniform mixing possible between the two types of particles. It is also possible to pre-prepare the mixture to deposit only one type of product and form the bed.

[0014] Other variations involving the chemical / physicochemical deposition of semiconductors on structured particles also offer advantages: it ensures a controlled distribution of semiconductors, integration between them that works favorably for the interaction of the two materials, and especially with respect to radiation scattered by the particles in this case. In this way, it provides a “ready-to-use” product for forming a catalyst bed in the reactor. It should be noted that the structured particles may be covered only completely or partially by the semiconductor. It should also be noted that this variation may also provide for a certain proportion of structured particles in which no semiconductor material deposition remains.

[0015] Advantageously, structured particles are (essentially) spherical and solid: their solidity gives them better mechanical properties, better mechanical strength, wear resistance, abrasion resistance, etc.

[0016] Preferably, all particles in the substrate are arranged in a disordered manner. This is because, surprisingly, this disorder has been found to be beneficial with respect to the photocatalytic performance quality of the material. The term "disordered" is understood to mean the fact that the particles of the material are not neatly arranged and do not form layers of three-dimensionally aligned particles. The material according to the present invention thus exhibits interparticle spaces of non-uniform size and position randomly distributed within the material. Furthermore, these spaces differ depending on whether the deformation involves a mixture of particles (of different sizes and shapes) or a deformation having only one type of particle (structured particles at least partially covered by a semiconductor).

[0017] Preferably, if the floor contains semiconductor material a in the form of particles, the particles have an average size of up to 100 nm, particularly up to 50 nm, and at least 5 nm, preferably 10 to 30 nm. In this case, it should be noted that these particles are not, or not necessarily, spherical, and their average size is not adjusted by the wavelength of the irradiating radiation.

[0018] Preferably, the catalyst bed according to the present invention exhibits a porosity equal to the ratio of the void volume to the total volume of the bed composed of voids and particles in the photocatalytic bed: a minimum of 40%, preferably a maximum of 80%, and particularly 40% to 70%. This porosity is indirectly an indicator of the disordered arrangement of the materials described above. This is because the porosity is minimal in the case of a perfectly organized sphere, and the porosity according to the present invention is greater than this minimum ratio.

[0019] Preferably, the catalyst bed according to the present invention exhibits a “dilution ratio” equal to the ratio of the volume occupied by structured particles b made from mineral material to the total volume occupied by semiconductor material (one or more types) a, a' and structured particles b made from mineral material: up to 80%, particularly 5% to 70%, preferably 10% to 50%. This dilution ratio of up to 80% is particularly selected when semiconductor material a is chemically or physicochemically deposited on structured particles b made from mineral material, but of course, it can be applied to both variations of the present invention.

[0020] The term "dilution rate" is used empirically to reflect the ratio of the active material (semiconductor) to structured particles that are not at all active or are hardly active. The higher this dilution rate, the greater the amount of structured particles. From the examples described below, it will be seen that this dilution rate can actually be increased while improving, rather than decreasing overall, the photocatalytic performance quality of the material. As long as the density of the materials, particularly semiconductors, can vary greatly from semiconductor to semiconductor, it is wiser to infer the dilution rate by volume rather than by mass.

[0021] In one embodiment of the present invention, the catalyst bed can comprise a first material a and a second material a', which are (at least) two different semiconductor materials. It can be produced as follows: - Mixing structured particles b made from mineral materials, respectively, with semiconductor material(s) in the form of particles of the first material a and particles of the second material a'; and / or, - Chemical or physicochemical deposition of semiconductor materials a, a' on carrier particles b; deposition of both the first semiconductor material a and the second semiconductor material a' on structured particles b, or deposition of the first semiconductor material a on a first part of the structured particles b and deposition of the second semiconductor material a' on a second part of the structured particles b.

[0022] Therefore, there are either three powders of the three different materials a, a' and b to be mixed, namely, two powders b + a and b + a' (structured particles covered by either the first semiconductor or the second semiconductor), or a single powder b + a + a' (structured particles covered by both the first and the second semiconductors).

[0023] Of course, based on the same principle, it is possible to use more than two different semiconductor materials. Also, in the variant where the semiconductors are deposited on their surfaces, there remains the option of a bed that further contains specific parts of the structured particles not covered by the semiconductor material.

[0024] Advantageously, the structured particles b made of mineral material can be made from one or more metal oxides, particularly oxides of metals of groups IIIa and IVa of the periodic table, preferably selected from aluminum oxide, silicon oxide, and mixtures of aluminum oxide and silicon oxide.

[0025] Advantageously, at least one of the semiconductor materials a, a' and the semiconductor materials a, a' can be selected from inorganic semiconductors. The inorganic semiconductor can be selected from one or more elements of group IVa, such as silicon, germanium, silicon carbide or silicon-germanium. They can also be elements of groups IIIa and Va, such as GaP, GaN, InP and InGaAs, or elements of groups IIb and VIa, such as CdS, ZnO and ZnS, or elements of groups Ib and VIIa, such as CuCl and AgBr, or elements of groups IVa and VIa, such as PbS, PbO, SnS and PbSnTe, or elements of groups Va and VIa, such as Bi2Te3 and Bi2O3, or elements of groups IIb and Va, such as Cd3P2, Zn3P2 and Zn3As2, or elements of groups Ib and VIa, such as CuO, Cu2O and Ag2S, or elements of groups VIIIb and VIa, such as CoO, PdO, Fe2O3 and NiO, or elements of groups VIb and VIa, such as MoS2 and WO3, or elements of groups Vb and VIa, such as V2O5 and Nbr2O5, or elements of groups IVb and VIa, such as TiO2 and HfS2, or elements of groups IIIa and VIa, such as In2O3 and In2S3, or elements of group VIa and lanthanide elements, such as Ce2O3, Pr2O3, Sm2S3, Tb2S3 and La2S3, or elements of group VIa and actinide elements, such as UO2 and UO3.

[0026] Preferably, they include at least one of the following metal oxides: titanium oxide, tungsten oxide, cerium oxide, bismuth oxide, zinc oxide, copper oxide, vanadium oxide, iron oxide, and cadmium oxide, and are preferably selected individually or in mixtures from TiO2, Bi2O3, CdO, Ce2O3, CeO2, CeAlO3, CuO, Fe2O3, FeTiO3, ZnFe2O3, V2O5, ZnO, WO3, and ZnFe2O4.

[0027] Semiconductor materials a, a', or at least one of semiconductor materials a, a', can be doped with one or more ions selected from metal ions, particularly V, Ni, Cr, Mo, Fe, Sn, Mn, Co, Re, Nb, Sb, La, Ce, Ta, Ti, or nonmetal ions, particularly C, N, S, F, P, or a mixture of metal and nonmetal ions.

[0028] The semiconductor material a, a', or at least one of the semiconductor materials a, a', may also include one or more elements in a metallic state selected from the elements of groups IVb, Vb, VIb, VIIb, VIIIb, Ib, IIb, IIIa, IVa, and Va of the periodic table, preferably in direct contact with the semiconductor material. These elements are preferably metals from platinum, palladium, gold, nickel, cobalt, ruthenium, silver, copper, rhenium, or rhodium.

[0029] It should be noted that throughout this specification, the groups of chemical elements are given according to the CAS IUPAC classification (CRC Handbook of Chemistry and Physics, CRC Press, 81st edition, 2000-2001), not the new classification. For example, Group VIII according to the CAS classification corresponds to the metals of Groups 8, 9, and 10 according to the new IUPAC classification.

[0030] The catalyst bed according to the present invention can have a thickness of up to 1 cm, particularly up to 5 mm, and especially at least 10 μm. Preferably, the thickness is at least 100 or 200 microns. This thickness is particularly dependent on the depth of radiation penetration from the irradiation source to the bed.

[0031] Another subject of the present invention is a method for obtaining the catalyst bed defined above, which involves mixing structured particles b of a mineral material and particles a of a semiconductor material to produce a uniform distribution of the two types of particles within the bed. Screw mixer / mill type devices exist at both laboratory and industrial scales to ensure uniform mixing.

[0032] Another subject of the present invention is a method for obtaining a catalyst bed as defined above, wherein the deposition of semiconductor material a, a' or at least one of the mineral materials a, a' on structured particles b of semiconductor material a, a' is carried out by impregnating the structured particles with a solution of at least one precursor of the semiconductor material, or by ion exchange, or by an electrochemical route of a type particularly using a molten salt, followed by drying and optional calcination. It is also possible to choose chemical vapor deposition (CVD), spray drying, or atomic layer deposition (ALD), or any other technique known to experts in this type of deposition.

[0033] Another subject of the present invention is any reactor for photocatalytic treatment of feedstocks in gaseous and / or liquid form, comprising at least one photocatalytic bed as defined above, which is mounted in a fixed manner within the reactor. This is because the advantages of Mie scattering on structured particles can be best utilized when the bed is fixed (as opposed to a moving-bed reactor).

[0034] Another subject of the present invention is a method for photocatalytic treatment of a feedstock in gaseous or liquid form, the method comprising: - At least one photocatalytic bed as defined above is placed in the reactor in a fixed manner. - The supply material is brought into contact with the catalyst bed in the reactor, and - The photocatalytic bed is irradiated during the contact operation by at least one irradiation source that emits in the UVA-A range and / or the UV-B range and / or the visible range, particularly in the wavelength range of 220 to 800 nm, preferably in the wavelength range of 300 to 750 nm.

[0035] Another subject of the present invention is a method in which the photocatalytic treatment is performed as follows: - Photo-oxidation of components present in liquid or gaseous feedstock, specifically for the purpose of decontamination / removal of feedstock, or - Photocatalytic reduction of CO2 in liquid or gaseous raw materials, - Photolysis of liquid or gaseous water in the feedstock for the purpose of generating H2.

[0036] (List of drawings) Figure 1 shows schematic re-emission patterns of an incident beam on a particle due to Rayleigh scattering and Mie scattering.

[0037] Figure 2 shows a transmission electron microscopy (TEM) image of semiconductor particles made from titanium dioxide used in an embodiment of the photocatalytic material according to the present invention.

[0038] Figure 3 shows a scanning electron microscopy (SEM) image of structured particles made from silicon dioxide used in an embodiment of the photocatalytic material according to the present invention.

[0039] Figure 4 shows a simplified diagram of equipment intended for measuring the performance quality of the photocatalytic material according to the present invention.

[0040] Figure 5 shows a graph quantifying the photocatalytic performance quality of two examples of materials according to the present invention, with the horizontal axis representing the fraction by volume of the semiconductor made from titanium oxide of the material according to the present invention, and the material according to the present invention includes this semiconductor particle and structured particle made from silicon oxide, with the vertical axis representing μmol / m 2 It has the total electron consumption per square meter over 20 hours, represented by [formula]. [Modes for carrying out the invention]

[0041] (Description of the embodiment) The present invention relates to a composition for a photocatalytic bed having mineral-structured particles. In this case, the mineral-structured particles are solid and are calibrated according to the wavelength of radiation emitted by a light source to activate a semiconductor material, and the radiation is large and preferentially scattered in the direction of radiation incident on the surface of these spheres by utilizing Mie scattering.

[0042] Therefore, Figure 1 schematically illustrates the Mie scattering phenomenon described above: on the left, a light source S emitting radiation of a given wavelength λ is symbolically represented. The diameter of the spherical particle P1 is not calibrated according to the present invention and is less than 0.1λ. The spherical particle P1 re-emits the incident radiation fairly uniformly in all directions; this is Rayleigh scattering. On the other hand, the diameter of particle P2 is calibrated to be between 0.1λ and 10λ, and particle P2 re-emits radiation favorably along the direction of the incident radiation; this is Mie scattering. This is what the present invention uses, and as a result, the calibrated particles "guide" more radiation to the depth of the catalyst bed, facilitating its propagation, thus allowing semiconductor materials to be used more effectively.

[0043] Semiconductor materials combined with these particles then experience a remarkable increase in their photocatalytic activity. This activity can be utilized in all known areas of photocatalytic activity of liquid and / or gaseous fluids. This could include the reduction of CO2, the photocatalytic production of H2 by the photoconversion of water (also expressed in the term "water splitting"), and even photocatalytic decontamination of air (conversion of VOCs) or water.

[0044] The present invention will be illustrated below by non-limiting examples using different photocatalytic materials and different structured particles.

[0045] (Photocatalytic materials) Photocatalytic material a1. Photocatalytic material a1 is titanium dioxide: it is TiO2 available from Aldrich under the trade name Aeroxide® P25, with a purity of 99.5%. The titanium dioxide is in the form of fine particles. Its particle size is 21 nm, measured by transmission electron microscopy (TEM). Its specific surface area is 52 m², measured by the BET method. 2 The value is / g. BET is an abbreviation: it is the Brunauer-Emmett-Teller method as defined in S. Brunauer, P.H. Emmett and E. Teller, J. Am. Chem.S oc., 1938, 60(2), pp 309-319.

[0046] Crystallographically, this titanium dioxide exists in the form of a mixture of rutile and anatase forms.

[0047] Figure 2 shows the TEM results obtained from these titanium oxide particles: it can be seen that they have an irregular shape and that they tend to aggregate.

[0048] Photocatalytic material a2. Photocatalytic material a2 is titanium oxide to which platinum metal particles, prepared by photodeposition using the following method, have been added: 0.0712 g of H2PtCl6·6H2O (37.5 wt% metal) is introduced into 500 mL of distilled water. 50 mL of this solution is taken out and placed in a jacketed glass reactor. Then, 3 mL of methanol is added, followed by 250 mg of a1 type TiO2 (Aeroxide® P25, Aldrich®, purity >99.5%), while stirring, to form a suspension.

[0049] Next, the mixture is left under UV irradiation for 2 hours while being stirred. The lamp used to supply the UV radiation is a 125W HPK® mercury vapor lamp. Subsequently, the mixture is centrifuged at 3000 rpm for 10 minutes to recover the solid. Then, it is washed twice with water, with centrifugation performed after each wash. Finally, the recovered powder is placed in an oven at 70°C for 24 hours.

[0050] This yields photocatalytic material a2. The Pt element content is measured to be 0.99 wt% by inductively coupled plasma-atomic emission spectroscopy (ICP-AES).

[0051] Photocatalytic material a3. Photocatalytic material a3 is a commercially available semiconductor based on WO3 (available from Sigma-Aldrich, exhibiting a particle size of less than 100 nm). The specific surface area was measured by the BET method and was 20 m². 2 It is equal to / g. The particle size of the photocatalytic material is 50±5 nm, measured by X-ray diffraction (Debye-Scherr method).

[0052] Photocatalytic material a4. Photocatalytic material a4 is a mixture of titanium dioxide and copper oxide with platinum Cu2O / Pt / TiO2 particles. It is prepared by the following method: The Cu(NO3)2 solution is prepared by dissolving 0.125 g of Cu(NO3)2·3H2O (Sigma-Aldrich®, 98%) in 50 mL of a 50 / 50 isopropanol / H2O mixture, i.e., a solution with a Cu2+ concentration of 10.4 mmol / L.

[0053] The following were introduced into the reactor: 0.20 g of photocatalytic material a2, 25 mL of distilled water, and finally 25 mL of isopropanol. The system was purged in the dark under a flow of argon (100 mL / min) for 2 hours. The reactor was thermostat-controlled to 25°C throughout the entire synthesis.

[0054] Next, the argon flow is reduced to 30 mL / min, and irradiation of the reaction mixture is started. The lamp used to provide UV radiation is a 125 W HPK® mercury vapor lamp. Then, 50 mL of copper nitrate solution is added to the mixture. The mixture is left under irradiation for 10 hours while being stirred. Next, the mixture is centrifuged at 3000 rpm for 10 minutes to recover the solid. Then, two washing operations with water are performed, followed by centrifugation after each washing operation. Finally, the recovered powder is placed in an oven at 70°C for 24 hours.

[0055] Photocatalytic material a4, Cu2O / Pt / TiO2, is obtained here. The content of element Cu is measured as 2.2 wt% by ICP-AES. By XPS (X-ray Photoelectron Spectrometry), the copper oxide phase is found to be 67% Cu2O and 33% CuO.

[0056] (Structured particles) Structured particles b1. The structured particles b1 selected in some of the following examples are spherical particles made from commercially available SiO2-based silicon dioxide, which can be obtained from Alfa Aesar (CAS: 7631-86-9): these are beads with a purity of over 99.9%, and their average diameter is 0.4 μm, as measured by laser particle size analysis.

[0057] Figure 3 shows the SEM images of these beads, which clearly demonstrate their remarkable uniformity in size and shape.

[0058] Structured particles b2. The structured particles b2 selected in other examples are particles made from commercially available SiO2-based silicon dioxide, which can be obtained from Sigma-Aldrich under the commercial reference name Davisil Grade 710, 10-14 μm: these are beads with a purity of over 99%, and their average size, measured by laser particle size analysis, is 12.7 μm (distributed by volume).

[0059] Semiconductor particles a1-a4 and structured particles b1 (SiO2 powder) or b2 (SiO2 powder having a particle size larger than that of b1) are mechanically mixed at a dilution ratio that varies between 0 vol% and 75 vol% to obtain a uniform distribution of the two types of particles in the material. In the sense of the present invention, "dilution ratio" is thought to be equal to the ratio of the volume occupied by structured particles made from mineral material to the total volume occupied by the semiconductor material (one or more types) and structured particles.

[0060] Next, as shown in Figure 4, each sample (3) of the photocatalytic material of each embodiment is subjected to a test of photocatalytic reduction of CO2 in the gas phase in the following manner: a continuously operating reactor (1) is used, with a fixed bed (2) placed horizontally in its cavity, the bed containing a sintered material (4), and the sample (3) is placed on the sintered material (4). The reactor (1) has a quartz optical window (5) on its upper wall, to which the sample (3) faces. Above the reactor, facing the window (5), a UV-visible irradiation source (6) is positioned.

[0061] During operation, the reactor (1) is supplied with a stream (7) of gaseous CO2 through an inlet at the top, which is pre-bubbled in a container / saturator filled with water (8). The stream (7) passes through the sample (3) and is then discharged in the form of a stream (9) through an outlet at the bottom, which is analyzed in-line by a microgas chromatograph type gas analyzer (10).

[0062] The UV-visible light source (6) is a xenon lamp available from Asahi under the product name MAX303.

[0063] The test was performed on samples (3) in amounts of 45-70 mg, the weight of which varied according to the selected dilution ratio, while the thickness of the catalyst bed (2), and therefore the thickness of the sample (3), remained fixed and equal to 0.3 mm.

[0064] The operating conditions are as follows: - Ambient temperature - Atmospheric pressure - Flow rate of CO2 passing through the water saturator (8) (7): 18 mL / h - Duration of testing for each sample: 20 hours - Irradiation output of xenon lamp (6): 80W / m 2 It is maintained at a constant level and measured in the wavelength range of 315-400 nm.

[0065] The target conversion of CO2 corresponds to the following reactions.

[0066] [ka]

[0067] The photocatalytic performance quality of the sample is measured by microchromatography with device (10), and the production of H2, CH4, and CO resulting from the reduction of CO2 and H2O is monitored by analysis every 6 minutes. Products of CO2 reduction, such as CO, methane, and even ethane, are identified. The average photocatalytic activity is expressed as the number of photogenerated electrons in μmol per square meter of irradiated catalyst surface area consumed by the reaction over the duration of the test.

[0068] (Examples) All of the implemented examples and their results are shown in Table 1 below.

[0069] [Table 1]

[0070] From this table, it can be seen that the photocatalytic activity of the "mixed" material, which combines the semiconductor material and structured particles according to the present invention, is significantly higher than that of a material consisting only of the semiconductor material that causes the photocatalytic activity of the material.

[0071] Comparing the results of Example 1 (Comparative Example) and Example 2, it can be seen that when the semiconductor material is 25% less (Example 2), the photocatalytic activity jumps up to 4.5 times. Starting with a different semiconductor (materials a2, a3, a4), the initial photocatalytic activity is higher for the material made of 100% semiconductor, and the present invention can increase this by at least 4 times by combining it with structured particles: Example 9 thus achieves an excellent level of photocatalytic activity.

[0072] Figure 5 shows the results for Examples 2 and 3 in graph form. The horizontal axis shows the volume fraction of particles made from TiO2, and the vertical axis shows the total electron consumption per square meter over 20 hours. From this figure, it can be seen that Example 3 (diamond shape in the graph), in which the size of structured particle b2 is too large, shows far inferior results to Example 2 (circle in the graph), which uses structured particle b1 whose size is calibrated to favor Mie scattering.

[0073] This calibration of structured particles is straightforward in terms of selection and acquisition, and significantly simpler than when other parameters must be refined, which are more complex in controlling the macro or microporosity of the material type.

[0074] The present invention is understood to be highly flexible in its implementation: it will be possible to adapt the composition of the materials according to the present invention by changing the choice of materials, the dilution ratio, and the method by which the mixing of the two materials will be carried out (mechanical mixing, chemical or physicochemical integration, etc.) depending on the desired level of performance, the type of equipment, and the reactor chosen. [Brief explanation of the drawing]

[0075] [Figure 1] This shows schematic re-emission patterns of an incident beam on a particle due to Rayleigh scattering and Mie scattering. [Figure 2] The image shows a transmission electron microscope (TEM) image of semiconductor particles made from titanium dioxide used in an embodiment of the photocatalytic material according to the present invention. [Figure 3] The image shows a scanning electron microscopy (SEM) image of structured particles made from silicon dioxide used in an embodiment of the photocatalytic material according to the present invention. [Figure 4] This diagram shows a simplified view of equipment intended for measuring the performance quality of the photocatalytic material according to the present invention. [Figure 5] The graph shows the quantitative photocatalytic performance quality of two examples of materials according to the present invention, with the horizontal axis representing the fraction by volume of the semiconductor made from titanium oxide of the material according to the present invention, and the vertical axis representing the total electron consumption per square meter over 20 hours, expressed in μmol / m2.

Claims

1. A catalyst bed containing a granular photocatalytic catalyst, wherein the bed contains structured particles b made from a mineral material, and these structured particles are combined with at least one semiconductor material a having photocatalytic properties, and this combination is as follows: - Mixing of structured particles b made from mineral material with semiconductor material a in particle form, and / or - Chemical or physicochemical deposition of semiconductor material a on structured particles b made from mineral material Caused by, Structured particles b are essentially spherical and have an average diameter of 22 nm to 8.0 μm, preferably 30 nm to 7.5 μm. The "dilution ratio," which is equal to the ratio of the volume occupied by structured particles b made from mineral materials to the total volume occupied by one or more types of semiconductor materials a, a' and structured particles b made from mineral materials, reaches a maximum of 80%. A catalyst bed characterized by the following features.

2. The catalyst bed according to claim 1, characterized in that all particles within the bed are arranged in a disordered manner.

3. The catalyst bed according to claim 1 or 2, characterized in that when the bed contains semiconductor material a in the form of particles, the particles a have an average size of up to 100 nm, particularly up to 50 nm, and at least 5 nm, preferably 10 to 30 nm.

4. The catalyst bed according to any one of claims 1 to 3, characterized in that the porosity in the photocatalytic bed is equal to the ratio of the void volume to the total volume of the photocatalytic bed composed of voids and particles: at least 40%, preferably at most 80%, and particularly 40% to 70%.

5. The catalyst bed according to any one of claims 1 to 4, characterized in that, in the case of chemical or physicochemical deposition of semiconductor material a on structured particles b made from mineral material, it exhibits a "dilution ratio" equal to the ratio of the volume occupied by structured particles b made from mineral material to the total volume occupied by one or more types of semiconductor materials a, a' and structured particles b made from mineral material: 5% to 70%, preferably 10% to 50%.

6. A catalyst bed according to any one of claims 1 to 5, comprising at least two distinct semiconductor materials, a first material a and a second material a', and manufactured by the following: - A mixture of structured particles b made from mineral materials with one or more semiconductor materials, each in the form of particles of a first material a and a second material a', and / or - Chemical or physicochemical deposition of semiconductor materials a, a' on carrier particles b; deposition of both the first semiconductor material a and the second semiconductor material a' on structured particles b, or deposition of the first semiconductor material a on a first portion of structured particles b and deposition of the second semiconductor material a' on a second portion of structured particles b.

7. The catalyst bed according to any one of claims 1 to 6, characterized in that the structured particles b made from mineral material are made from one or more metal oxides, particularly from oxides of metals in Group IIIa and Group IV of the periodic table, and are preferably selected from aluminum oxide, silicon oxide, and a mixture of aluminum and silicon oxides.

8. The catalyst bed according to any one of claims 1 to 7, wherein the semiconductor material a, a' or at least one of the semiconductor materials a, a' comprises at least one of the following metal oxides: titanium oxide, tungsten oxide, cerium oxide, bismuth oxide, zinc oxide, copper oxide, vanadium oxide, iron oxide, and cadmium oxide, and is preferably selected individually or as a mixture from TiO2, Bi2O3, CdO, Ce2O3, CeO2, CeAlO3, CuO, Fe2O3, FeTiO3, ZnFe2O3, V2O5, ZnO, WO3, and ZnFe2O4.

9. The catalyst bed according to any one of claims 1 to 8, characterized in that semiconductor material a, a' or at least one of semiconductor material a, a' is doped with one or more ions selected from metal ions, particularly V, Ni, Cr, Mo, Fe, Sn, Mn, Co, Re, Nb, Sb, La, Ce, Ta, Ti, or nonmetal ions, particularly C, N, S, F, P, or a mixture of metal and nonmetal ions.

10. The catalyst bed according to any one of claims 1 to 9, wherein the semiconductor material a, a' or at least one of the semiconductor materials a, a' includes one or more elements in a metallic state selected from elements of groups IVb, Vb, VIb, VIIb, VIIIb, Ib, IIb, IIIa, IVa, and Va of the periodic table, and is in direct contact with the semiconductor material, preferably selected from platinum, palladium, gold, nickel, cobalt, ruthenium, silver, copper, rhenium, or rhodium.

11. A method for obtaining a catalyst bed according to any one of claims 1 to 10, characterized by mixing one, structured particles b of the mineral material, with the other, particles of the semiconductor material a, to create a uniform distribution of two types of particles in the bed.

12. A method for obtaining a catalyst bed according to any one of claims 1 to 10, characterized in that the deposition of structured particles b of semiconductor material a, a' or at least one mineral material of semiconductor material a, a' is carried out by chemical vapor deposition, spray drying or atomic layer deposition by impregnating the structured particles with a solution of at least one precursor of the semiconductor material, by ion exchange, or by an electrochemical route in particular of the type using a molten salt, followed by drying and optional calcination.

13. A reactor (1) for photocatalytic treatment of a feedstock in gaseous or liquid form, comprising at least one photocatalytic bed (2) according to any one of claims 1 to 10, and mounted in a manner fixed within the reactor.

14. A method for photocatalytic treatment of a feed material (7) in gaseous and / or liquid form, characterized by the following: - At least one photocatalytic bed (2) according to any one of claims 1 to 10 is arranged in a manner that is fixed inside the reactor (1). - The supply material (7) is brought into contact with the catalyst bed (2) in the reactor, and - The photocatalytic bed (2) is irradiated during the contact operation with at least one irradiation source (6) that emits light in the UVA-A range and / or the UV-B range and / or the visible range, particularly in the wavelength range of 220 to 800 nm, preferably in the wavelength range of 300 to 750 nm.

15. The method according to 14, characterized in that the photocatalytic treatment is as follows: - Photo-oxidation of components present in liquid or gaseous raw materials, specifically for the purpose of decontamination / removal of contaminants from the raw materials, or - Photocatalytic reduction of CO2 in liquid or gaseous raw materials, - Photolysis of water, a liquid or gaseous feedstock, for the purpose of generating H2.

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