Method for preparing an inorganic monolith with multi-scale porosity

Abstract

The present invention relates to a method for preparing an inorganic monolith with multi-scale porosity, comprising: a) a step of emulsification of an oily phase in an acidic aqueous phase, wherein: a1) the aqueous phase comprises at least one acid, at least one surfactant and at least one inorganic precursor; a2) the oily phase is added to the mixture obtained in step a1); a3) the mixture obtained in step a2) is subjected to mechanical rotary stirring, preferably at a rotational speed of more than 100 revolutions per minute, in order to obtain an emulsion; b) a step of polycondensation of the emulsion obtained in step a3), preferably for 1 day to 20 days, in order to obtain a gel; c) a step of drying the gel obtained in step b); d) a first step of calcination at a temperature of between 160°C and 200°C, with a heating rate of between 0.5 and 3°C / min, the plateau being maintained for a period of 2 to 6 hours, preferably 3 hours; and e) a second step of calcination at a temperature of between 300°C and 900°C, preferably between 400°C and 800°C, with a heating rate of between 0.5 and 2°C / min, the plateau being maintained for 3 to 8 hours, preferably 7 hours.

Description

[0001] Process for preparing an inorganic monolith with multi-scale porosity

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention relates to a new method for preparing an inorganic monolith with multi-scale porosity.

[0004] For over 20 years, inventors have been developing processes for preparing numerous inorganic monoliths with multiscale porosity, of particular interest in the fields of catalysis and decontamination (French patent application FR 0303774; F. Cam et al. J. Mat. Chem. 2004, 14, 1370). The synthesis of these monoliths, called Si(HIPE) (High Internal Phase Emulsion), relies on a combination of sol-gel chemistry and the physical chemistry of complex fluids, involving concentrated direct emulsions and lyotropic mesophases. Since then, numerous inorganic monoliths with varied morphologies and properties have been developed. Among these monolithic materials, the inventors have developed porous silica monoliths comprising titanium oxide nanoparticles of the TiO2@Si(HIPE) type (FR2113537) or monolithic nanoparticulate metallo-oxides (FR3114317).All these monoliths are prepared from an emulsion comprising an oil phase and an aqueous phase (surfactant and silica precursor). This emulsification step is carried out using a mortar and pestle. The resulting emulsion then undergoes a polycondensation (or maturation) step for approximately one week until gels are obtained. These gels are then dried, for example in a desiccator, for about one month. The monoliths can then be heat-treated to release the mesoporosity (through CO2 production) and sinter the silica matrix.

[0005] Current synthesis processes present challenges in terms of reproducibility, complicating their application on an industrial scale.

[0006] The emulsification step is particularly sensitive to operating conditions, such as the diameter of the pestle and the force applied by the operator. Furthermore, during emulsion formation, the incorporation of air leads to expansion, characterized by the presence of air bubbles within the oil droplets. This situation accentuates the polydispersity of the macropores.

[0007] Therefore, there is a need to develop reproducible and controllable processes suitable for industrial-scale use. It is in this context that inventors have developed a process for synthesizing inorganic monoliths with multi-scale porosity.

[0008] One aim of the present invention is to provide a method for preparing these materials which is reproducible, simple, rapid, while maintaining a homogeneous structure of the monolith, particularly at the level of macroporous structures.

[0009] DESCRIPTION OF THE INVENTION

[0010] The present invention thus relates as its first object to a method for preparing an inorganic monolith with multi-scale porosity comprising:

[0011] (a) an emulsification step of an oily phase in an acidic aqueous phase, wherein: a1) the aqueous phase comprises at least one acid, at least one surfactant and at least one inorganic precursor; a2) the oily phase is added to the mixture obtained in step a1); a3) the mixture obtained in step a2 is subjected to mechanical rotary agitation, preferably at a rotational speed greater than 100 revolutions per minute, in order to obtain an emulsion;

[0012] (b) a polycondensation step of the emulsion obtained in step a3), preferably for 1 to 20 days, in order to obtain a gel; and

[0013] (c) a drying step of the gel obtained in step b);

[0014] (d) a first calcination stage at a temperature between 160°C and 200°C, with a heating rate between 0.5 and 3°C / min, the plateau being maintained for a period of 2 to 6 hours, preferably 3 hours; and

[0015] (e) a second calcination stage at a temperature between 300°C and 900°C, preferably between 400°C and 800°C, with a heating rate between 0.5 and 2°C / min, the tray being maintained for 3 to 8 hours, preferably for 7 hours.

[0016] A "monolith" is defined as a solid object with a smallest dimension of at least 1 mm. Monoliths are easy to shape (columns, films, spheres) due to their lack of dust. Such a monolith is self-supporting; in other words, it possesses sufficient mechanical strength to be used as is, i.e., without support.

[0017] An "inorganic monolith" is defined as a continuous structure (matrix) made of inorganic (porous) materials. "Multi-scale porosity" refers to a material with a hierarchical structure, including macropores, mesopores, and micropores.

[0018] The different pore size classes are determined according to the IUPAC nomenclature (in English, for International Union of Pure and Applied Chemistry).

[0019] Macropores can be identified by scanning electron microscopy (SEM), and their junction windows can be quantified by mercury intrusion measurements. The implementation of the mercury intrusion technique demonstrates the good mechanical strength of the resulting monoliths, which withstand the mercury pressures to which they are subjected during measurements.

[0020] Mesoporosity can be identified by transmission electron microscopy (TEM). The vermicular texture of the mesoporosity can be identified by small-angle X-ray diffraction (SAXS), a technique also used to quantify the pore-to-pore distance. Mesoporosity and microporosity can be quantified and segregated by a nitrogen adsorption-desorption technique, the results of which are analyzed by the BET calculation method, which aggregates mesoporosity and microporosity (Brunauer, Emmett and Teller model or BET method (S. Brunauer, PH Emmet, E. Teller, Journal of the American Chemical Society, vol 60(2), pages 309-319 (1938)) and by the BJH calculation method (Barrett, Joyner and Halenda (1951) Journal of the American Chemical Society, 73, 373-380), according to which the segregation between microporosity and mesoporosity becomes effective, the BJH method considering only pores greater than 1.5 angstroms.

[0021] By "acidic aqueous phase" is meant an aqueous phase having a pH below the isoelectric point of silica, i.e. below 2.1, and preferably between 0.01 (Hammet acidity) and 1. The strong acid used to adjust the pH of the aqueous surfactant solution is preferably hydrochloric acid, for example at a concentration between 30% and 40% by mass.

[0022] It should be noted that within the framework of the present invention, and unless otherwise stipulated, the ranges of values ​​indicated are understood to include the limits.

[0023] In an advantageous embodiment of the invention, the inorganic precursor is a silica precursor, preferably a silicon alkoxide selected from tetraethyl orthosilicate (TEOS), (3-mercaptopropyl)trimethoxyxilane, (3-aminopropyl)triethoxysilane, N-(3-trimethoxysilylpropyl)pyrrole, 3-(2,4-dinitrophenylamino)propyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, phenyltriethoxysilane, methyltriethoxysilane, sodium silicate solutions, or mixtures thereof. TEOS is particularly advantageous.

[0024] A mixture of silicon alkoxide precursors in which TEOS remains predominant can also be considered.

[0025] The concentration of silica precursor is preferably greater than 10% by mass relative to the total mass of the aqueous phase, to obtain total mineralization of the monolith and good mechanical strength.

[0026] Advantageously, an inorganic precursor such as aluminum oxide is added to the silica precursor, at a Si / Al molar ratio preferably between 1 and 35. Thus, in association with the silica precursor, the precursor forms a matrix cooxide (mixed oxide), i.e. a monolith in the form of a mixed oxide.

[0027] According to an advantageous embodiment of the invention, the aqueous phase further comprises at least one metal salt precursor of metal oxide M and / or nanoparticles of at least one metal oxide M, where M represents a metal or metalloid selected from the following metals and metalloids: Cr, Co, Mn, Ni, Ce, V, Y, W, Nb, Mo, Fe, Zn, Ta, Sn, Cd, Cu, In, Ti, Zr, Al, Nb, Pt, Pd, Au, Hg.

[0028] In an advantageous embodiment of the invention, the metal salts used as precursors of metal oxides (i.e., metal oxides M) are selected from chlorides and nitrides. Such metal salts used as precursors of metal oxide M are, for example, described in patent application WO2022 / 058449. These metal salts used as precursors of metal oxide M are transformed during the process into metal oxide M nanoparticles.

[0029] For the purposes of the present invention, nanoparticles of a metal oxide M are understood to mean an oxide having at least one dimension less than or equal to approximately 500 nm, preferably less than or equal to 200 nm, and particularly preferably less than or equal to 100 nm.

[0030] The metal oxide M preferably has at least one dimension greater than 10 nm, and preferably greater than 50 nm.

[0031] Advantageously, the M / Si molar ratio is between 0.01 and 1, preferably between 0.05 and 0.5.

[0032] According to the present invention, the molar ratios refer to those present in the oil-in-water emulsion obtained at the end of step a). This molar ratio remains substantially constant during steps a), b) and c). Advantageously, the concentration of metal oxide M in the aqueous solution varies preferably from 1 g 1-1 to 100 g 1-1, preferably from 2 g 1-1 to 50 g I-1.

[0033] Thus, in association with at least one inorganic precursor, the nanoparticles form a nanoparticulate co-oxide (mixed oxide), i.e. a monolith in the form of a mixed oxide.

[0034] According to an advantageous embodiment of the invention, the surfactant is a cationic surfactant selected from quaternary ammonium compounds having at least 8 carbon atoms. Examples include tetradecyltrimethylammonium bromide (TTAB), dodecyltrimethylammonium bromide, and cetyltrimethylammonium bromide.

[0035] According to another advantageous embodiment of the invention, the surfactant is a non-ionic surfactant.

[0036] The presence of a nonionic surfactant enhances the mesoporosity of the monolith obtained at the end of the process. In this case, the nonionic surfactant is preferably chosen from among ethoxylated surfactants and nonylphenols. Among such surfactants, ethylene glycol and propylene glycol block copolymers, sold for example under the trade names Pluronic® P123, Pluronic® P125, and Pluronic® F127 by BASF, are particularly noteworthy.

[0037] Advantageously, the nonionic surfactant is mixed with at least one salt such as ammonium sulfate, sodium chloride, magnesium chloride or sodium sulfate.

[0038] The concentration of surfactant used in step a1) preferably varies from 20 to 40% by mass.

[0039] According to an advantageous embodiment of the invention, the oily phase used in step a2) consists of one or more compounds selected from linear and branched alkanes having at least 9 carbon atoms. Even more advantageously, the linear alkanes comprise between 10 and 12 carbon atoms. Examples include decane and dodecane.

[0040] Advantageously, in step a2), the oily phase is added entirely at once to the aqueous phase.

[0041] Then, the mixture obtained in step a2) is subjected to mechanical rotary agitation, preferably at a higher rotation speed of between 100 revolutions per minute and 2500 revolutions per minute, even more preferably between 200 revolutions per minute and 2000 revolutions per minute, in order to obtain an emulsion.

[0042] The term "mechanical rotary stirring" refers to any device (or mixer) that applies mechanical rotation, regardless of the type of rotary motion. This device may include, for example, simple rotary motion or motions combining rotation and revolution. The term explicitly excludes any manual stirring, such as stirring with a mortar and pestle or any other hand-operated tool.

[0043] According to the invention, units expressed in "revolutions per minute" are used interchangeably with the unit expressed in English, namely "revolutions per minute" or "rpm".

[0044] Advantageously, step a3) is carried out for a duration of between 1 minute and 15 minutes, preferably between 3 minutes and 7 minutes.

[0045] Advantageously, mechanical rotary agitation is achieved by a planetary mixer, combining rotational and revolutional movements, or a high shear mixer with or without turbulence and / or in laminar regime, such as an Ultra-Turrax®, Rayneri® or Dispermat® mixer.

[0046] Unlike manual stirring, this step a3) of mechanical rotary stirring allows precise control of the porous structure: the rotation speed allows adjustment of the size of the macropores, the thickness of the walls and the distribution of the pores.

[0047] According to an advantageous embodiment of the invention, the process includes a pre-emulsification step before step a3), preferably manually or under mechanical agitation, preferably for a period of between 30 seconds and 5 minutes, even more preferably between 30 seconds and 1 minute.

[0048] According to the present invention, step b) of polycondensation (or maturation) is preferably carried out at room temperature, in particular for a period of at least 1 day, preferably from 2 to 8 days.

[0049] At the end of step b), a gel is obtained, which can also be described as a solid material (solidified emulsion).

[0050] Since step b) is carried out in an acidic medium, only the silica precursor hydrolyzes and polycondenses.

[0051] The process according to the invention may further include, after step b) of polycondensation, a step b') of removal of the oily phase, by treatment with at least one organic solvent such as tetrahydrofuran, dichloromethane, or chloroform.

[0052] By "treatment with at least one organic solvent" is meant a washing of the gel obtained in step b) with an organic solvent, preferably carried out by several successive baths, preferably between one and three successive baths.

[0053] Advantageously, step b') of removing the oily phase by an organic solvent preferably lasts about 24 hours, even more preferably about one night.

[0054] Advantageously, when mixed oxides are prepared, dichloromethane is used during step b') of removing the oily phase.

[0055] Advantageously, to avoid evaporation of the washing solvent, the washing step is carried out under a desiccator.

[0056] Advantageously, this step b') allows the elimination of organic residues from the oily phase which are found mainly in the macropores.

[0057] According to the present invention, a drying step of the gel obtained in step b) is carried out, preferably under atmospheric conditions, for example using a desiccator.

[0058] Drying consists of removing the continuous liquid phase from the solid network. This step is particularly crucial for preparing monolithic materials.

[0059] Advantageously, step c) of drying is carried out over a period of between 1 week and 2 months, preferably between 2 weeks and 1 month.

[0060] Advantageously, the gels are dried slowly in a desiccator with absorbent paper inside, which is changed every two days, for approximately one to two months. Once the paper no longer absorbs solvent, the materials are removed from the desiccator to complete the drying process for one week at room temperature.

[0061] When gels are dried under atmospheric conditions, they are called xerogels. In this case, the gel shrinks to the volume previously occupied by the liquid after it has flowed out of the network. As this happens, the silanol groups within the internal structure move closer together and form new siloxane bonds. The network thus becomes increasingly rigid. Capillary forces increase, and the pore radii decrease accordingly. Eventually, the network becomes sufficiently rigid to the point where it can no longer shrink.

[0062] According to the present invention, the process comprises, after step c) of drying, a calcination comprising:

[0063] - A first stage at a temperature between 160°C and 200°C, with a heating rate between 0.5 and 3°C / min, the plate being maintained for a period of 2 to 6 hours, preferably 3 hours; and

[0064] - A second stage at a temperature between 300°C and 900°C, preferably between 400°C and 800°C, with a heating rate between 0.5 and 2°C / min, the plate being maintained for 3 to 8 hours, preferably for 7 hours.

[0065] The first stage allows the physisorbed water to be eliminated first, then the chemisorbed water in a second stage.

[0066] The second platform, meanwhile, allows for the elimination of residual surfactant molecules, but also for sintering the silica framework to densify the monoliths, and thus give the monolith better mechanical strength, thanks to the sintering of the silica.

[0067] Another object of the present invention is to provide an inorganic monolith with multi-scale porosity, obtained or obtainable by the process as described above.

[0068] According to an advantageous embodiment of the invention, the monolith according to the present invention comprises macropores, having an average diameter of 0.5 to 60 micrometers, mesopores having an average diameter of 2 to 10 nanometers and micropores having an average diameter of less than 2 nm, said pores being interconnected.

[0069] According to an advantageous embodiment of the invention, the monolith has a specific surface area between 700 m2 g-1 and 1500 m2 g-1, preferably between 780 m2 g-1 and 1100 m2 g-1. This makes it possible to obtain a monolith with optimal adsorption properties.

[0070] According to the present invention, the specific surface area is determined by methods well known to those skilled in the art, and in particular by the BET method, preferably using nitrogen as the gas. Advantageously, the monolith has a porosity greater than 80%, preferably between 80% and 99%, over the total volume of the monolith.

[0071] Advantageously, the monolith according to the invention has a density between 0.06 g cm-3 and 0.3 g cm-3, preferably between 0.07 g cm-3 and 0.25 g cm-3.

[0072] The present invention also relates to the use of an inorganic monolith with multi-scale porosity, particularly as a catalyst, specifically as a photo-activated catalyst (gaseous or liquid phases) or a thermo-activated catalyst (gaseous or liquid phases), for water or air treatment, as well as for capturing carbon dioxide (CO2) or volatile organic compounds (VOCs). This capture can be achieved passively (simple capture) or actively (capture and decomposition activated by heat or light).

[0073] BRIEF DESCRIPTION OF THE FIGURE

[0074] Other features and advantages of the invention will become apparent in the following illustrative examples, with reference to:

[0075] [Fig.1] Figure 1 represents a photograph of (Si(HIPE)) monoliths obtained in Example 1, from left to right: Si(HIPE)2000, Si(HIPE)1500, Si(HIPE)1000, Si(HIPE)500 and Si(HIPE)200 (in all figures, these designations are used to define a (Si(HIPE)) monolith obtained by stirring at a revolution speed of, respectively, 2000 rpm, 1500 rpm, 1000 rpm, 500 rpm and 200 rpm during the emulsification step).

[0076] [Fig.2] Figure 2 represents scanning electron microscopy images of the monoliths obtained in Example 1: A: Si(HIPE)200, B: Si(HIPE)500, C: Si(HIPE)1000, D: Si(HIPE)1500 and E, F) Si(HIPE)2000.

[0077] [Fig. 3] Figure 3 represents the pore size distribution (pm) obtained by mercury intrusion porosimetry of monoliths obtained in Example 1 at different revolution speeds, 2000 rpm, 1500 rpm, 1000 rpm, 500 rpm and 200 rpm, during the emulsification step.

[0078] [Fig. 4] Figure 4 shows two curves, A: evolution of volumes (cm 3 ) of the monoliths obtained in example 1, as a function of the applied rotation speed (Q [rpm]) and B: evolution of the apparent densities (θ [g / cm³] 3 ]) monoliths obtained in example 1, as a function of the applied rotation speed (Q [rpm]).

[0079] [Fig. 5] Figure 5 represents transmission electron microscopy (TEM) images of monoliths obtained in Example 1 at different revolution speeds of 2000 rpm, 1500 rpm, 1000 rpm, 500 rpm and 200 rpm, during the emulsification step: A: Si(HIPE)200, B: Si(HIPE)500, C: Si(HIPE)1000, D: Si(HIPE)1500 and E: Si(HIPE)2000.

[0080] [Fig. 6] Figure 6 represents the nitrogen adsorption / desorption isotherms of the monoliths obtained in example 1 (Si(HIPE)200, Si(HIPE)500, Si(HIPE)100, Si(HIPE)1500, Si(HIPE)2000).

[0081] [Fig. 7] Figure 7 shows two scanning electron microscopy (SEM) images (A and B illustrate the structure of Si(HIPE)2000 and Si(HIPE)1000 monoliths, respectively, and show some representative thicknesses "5"); C, D, and E illustrate the wall thickness distributions (nm), and F shows two curves (mean wall thickness (nm) and mean macrocell diameter (pm)) correlated with the emulsification rate (rpm). The data were obtained using Image! software.

[0082] EXAMPLES

[0083] The raw materials used in the examples are listed below:

[0084] - Dodecane, purity > 99%, density of 0.75 g / mL, Sigma-Aldrich,

[0085] - Hydrochloric acid (HCl), 37% by mass, Sigma-Aldrich,

[0086] - Tetradecyltrimethylammonium bromide (TTAB), 35% by mass, Alfa-Aesar,

[0087] - Tetraethyl orthosilicate (TEOS), purity > 99%, Sigma-Aldrich,

[0088] - Tetrahydrofuran (THF), Sigma-Aldrich,

[0089] - Deionized water, obtained using a Milli-Q type water purification system.

[0090] The planetary mixer used is the SK-300SII model from the Kakuhunter brand.

[0091] Unless otherwise stated, all materials were used as received from the manufacturers.

[0092] Example 1: A method for preparing an inorganic monolith according to the present invention

[0093] - Emulsification stage

[0094] The emulsification step includes an aqueous phase composed of a 35% (16 g) concentrated surfactant solution (tetradecyltrimethylammonium bromide). This concentration, significantly higher than the critical micelle concentration of the surfactant, was chosen to ensure the presence of a sufficient number of micelles to contribute to mesostructure formation. The concentrated surfactant solution is acidified by adding 5 g of 37% (at room temperature) concentrated hydrochloric acid. The pH of the reaction medium is then close to 0.01. Next, 5 g of a silicic precursor, tetraethyl orthosilicate (TEOS), are incorporated into the aqueous phase and subjected to magnetic stirring for approximately 5 minutes to initiate precursor hydrolysis. Finally, 37 g of dodecane are added entirely to the aqueous phase.The mixture is then subjected to a pre-emulsification step under manual stirring for a few seconds (approximately 30 seconds). The pre-emulsified mixture is then subjected to mechanical rotary stirring in a planetary mixer at different stirring speeds, both rotating and revolutionally.

[0095] The applied rotational speeds were 200 rpm, 500 rpm, 1000 rpm, 1500 rpm, and 2000 rpm. These rotational speeds corresponded to 40% of the applied rotational speed. These monoliths were designated Si(HIPE) followed by a number corresponding to the rotational speed (X) at which they were synthesized using a planetary mixer, and designated "Si(HIPE)X". The mechanical rotary stirring step was performed for 5 minutes at each of the applied speeds.

[0096] - Polycondensation stage (or maturation)

[0097] The resulting emulsion is poured into appropriate containers (here, hemolysis tubes) and left to mature for one week to form gels. The quantities used in this synthesis yield approximately ten gels.

[0098] - Oil phase removal stage

[0099] The gels obtained after seven days are washed in a solvent bath, tetrahydrofuran (THF), overnight.

[0100] - Drying stage

[0101] The gel is then left to dry in a desiccator for 1 month.

[0102] - Heat treatment (or calcination) stage

[0103] The gel is then subjected to an air calcination step at a first plateau of 180 °C for 10 hours (with a temperature rise rate of 2 °C / min). This first plateau allows for the removal of physisorbed water initially, followed by chemisorbed water. A second temperature increase is then carried out to a plateau of 700 °C for 7 hours (with a temperature rise rate of 1 °C / min), eliminating residual surfactant molecules and also sintering the silica framework to densify the monoliths and thus improve their mechanical properties.

[0104] Example 2: Characterization of inorganic monoliths prepared by the process according to the present invention

[0105] - Characterization techniques

[0106] The monoliths obtained in example 1 were characterized at all scales (macroscopic, microscopic and mesoscopic).

[0107] Macroporosity was qualitatively characterized by scanning electron microscopy (SEM) using a Hitachi TM-1000 scanning electron microscope operating at 15kV. The samples were coated under a gold / palladium plasma prior to characterization.

[0108] Macroporosity was also quantified by mercury intrusion measurements at room temperature, using a device marketed under the name Autopore IV from Micromeretics, to achieve the characteristics of the macroscopic cells composing the skeleton of the monolith.

[0109] Mesoporosity and microporosity were characterized by small-angle X-ray scattering (SAXS). This analysis allows for the study of the size, shape, and organization of the monoliths. SAXS enables the characterization of structures and the acquisition of dimensions on the order of nanometers, with object sizes ranging from 0.5 nm to 100 nm.

[0110] Scattering experiments were performed on a XEUSS 2.0 (XENOCS) equipped with a GeniX3D system (XENOCS copper anode coupled to a FOX3D single-reflecting mirror), delivering an 8 keV monochromatic beam (Cu Ka, Å = 0.15418 nm). Powder samples were placed in thin glass capillaries (optical path length of approximately 1.5 mm). Data were collected by a DECTRIS PILATUS-300k two-dimensional detector positioned at a sample-to-detector distance of 1635 mm. It should be noted that the XEUSS 2.0 device provides a flight path entirely under vacuum, from the downstream end of the mirror to a few centimeters before the detector, including the samples. 1D diffractograms (intensity / vs q) were obtained by processing the detector images with FOXTROT software.

[0111] Mesoscopic characterizations were performed using nitrogen adsorption / desorption (physisorption) techniques to obtain information on pore size distribution and specific surface area. The monoliths obtained in Example 1 were prepared using a Smart VacPrep and then analyzed using a Micromeretics 3Flex. Before measurements, the samples were activated under vacuum at 110°C for 12 hours.

[0112] Mesoporosity was also qualitatively characterized using transmission electron microscopy (TEM). The method employed involved ultrathin sectioning of a sample observed with a JEOL JEM-1400+ (with an accelerating voltage of 120 kV). Regarding sample preparation, a 1x1x4 mm sample was first taken and embedded in Agarl OO resin. Next, an ultrathin 60 nm section was prepared on a Leica UC7 ultramicrotome using a TRIM cutter and a diatomaceous earth cut. Finally, the section was transferred to a copper grid for analysis. This method minimizes the stacking effect of silica layers, resulting in much clearer observation and delineation of the arrangements.

[0113] Example 2.1: Macroscopic scale characterization

[0114] Figure 1 shows the monoliths obtained in Example 1. These silica monoliths have a tubular shape, attributable to the geometry of the container in which polycondensation took place. In addition to their appearance, a reduction in the average volume of the ceramics is observed as a function of the emulsification rate.

[0115] Figure 2 shows scanning electron microscopy (SEM) images of the monoliths obtained in Example 1 as a function of their speed. This figure illustrates, in particular, how the rotation speed and emulsification conditions influence the porous structure, contraction, and characteristics of the silica monoliths.

[0116] Indeed, a higher rotational speed produces smaller oil droplets, resulting in smaller diameter pores, a larger interfacial surface area, and thinner silica walls. The oil-water interface acts as a heterogeneous nucleation site for silica, promoting nucleation and reducing the associated enthalpy.

[0117] The emulsification speed also influences the monolith's contraction, which is more pronounced with a higher oil volume fraction and accentuated at high speeds (2000 rpm). At this speed, in addition to the main macroporosity structure (aggregated hollow spheres), distinct silica sphere domains are observed. These monoliths, exhibiting hierarchical porosity, were also analyzed by mercury intrusion to evaluate the size distribution of the junction windows connecting two spheres, as shown in Figure 3. Figure 3 shows that the pore size distribution changes as a function of the rotational speed applied during the emulsification step.

[0118] For each monolith, a generally bimodal pore size population is observed. Small pore sizes correspond to connections between adjacent cells induced by coalescence during synthesis, while large sizes correspond to inter-cell spaces (walls surrounding the pores). Overall, a general decrease in pore size is noted with increasing shear. Indeed, Si(HIPE)1500 and Si(HIPE)2000 exhibit a majority of small pore sizes. However, for Si(HIPE)200, Si(HIPE)500, and Si(HIPE)1000, these predominant populations are those with the largest sizes. With the decrease in oil droplet diameter, the emulsions become more stable due to a higher surface energy, thereby limiting the coalescence phenomena that destabilize the emulsions.

[0119] Mercury intrusion measurements also provide information on skeleton density, bulk density, and percentage porosity, as shown in Table 1 below:

[0120] [Table 1]

[0121] * If (HIPE) does not conform to the present invention. This material was obtained by a conventional mixing step (mortar and pestle) during the emulsification step.

[0122] Table 1: Skeletal density, apparent density and porosity, obtained by mercury intrusion, of monoliths obtained in example 1 and of a silica monolith not in accordance with the present invention.

[0123] The density of the skeleton corresponds to that of the siliceous walls forming the edges of the Plateau. This density, as well as the apparent density, increases with the rotation speed, while the porosity decreases slightly, remaining at acceptable levels.

[0124] Furthermore, the volume and density of the monoliths obtained in Example 1 were analyzed and are shown in Figure 4. This figure shows the evolution of the volumes of the monoliths obtained in Example 1 (Figure 4 A) and the evolution of their densities (Figure 4 B), as a function of the applied rotation speed.

[0125] It is observed that the volume decreases with increasing rotation speed. This volume variation is correlated with an overall density that increases with rotation speed. This volume variation phenomenon is influenced by the initial droplet size, which is kept constant for a given oil volume fraction, or by a fixed droplet size with a variable oil volume fraction (M. Destribats et al., Tailored Silica Macrocellular Foams: Combining Limited Coalescence-Based Pickering Emulsion and Sol-Gel Process. Advanced Functional Materials, 22(12):2642-2654, 2012).

[0126] This variation is attributed to the amount of oil-water interface, which depends both on the droplet size, which decreases as the rotational speed increases, and on the oil volume fraction. Smaller droplets and / or a higher volume fraction increase the elasticity and viscosity of the emulsion.

[0127] Thus, depending on the desired density or volume, it is possible to control the final structure of the monolith by varying the rotation speed of the mixer.

[0128] Example 2.2: Characterization at the microscopic and mesoscopic scales

[0129] Transmission electron microscopy (TEM) was performed to study the mesoscopic scale of the monoliths obtained in example 1.

[0130] Figure 5 shows TEM images of the different monoliths obtained in Example 1 at different rotation speeds. Mesoscopic organization is observed within the monoliths. There is very little difference in the mesoscopic organization between the different monoliths.

[0131] This mesostructure was organized from the cationic surfactant used to stabilize the oil-water interfaces of the concentrated direct emulsion. Following washing and heat treatment, these surfactant molecules were extracted by combustion and generated a mesoscopic organization within the final monolith.

[0132] Physisorption measurements were performed to complete the characterization of the different monoliths and are shown in Figure 6. The isotherms in Figure 6 are characteristic of strong nitrogen adsorption at low relative pressure, indicating microporosity of the monoliths (type I isotherms as described in the IUPAC nomenclature) (Thommes, K. Kaneko, AV Neimark, JP Olivier, F. Rodriguez-Reinoso, J. Rouquerol, and KSW Sing. Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Report). Pure and Applied Chemistry, 87(9-10): 1051–1069, 2015).), followed by a spreading plateau at medium relative pressure and a final set at high relative pressure, where a weak hysteresis loop can be observed only for the Si(HIPE)2000 and Si(HIPE)1500 monoliths (mixed type I and H3 isotherms), indicating both microporosity and a very wide mesoscopic pore size distribution. The strong set at high relative pressure (close to 1.0) foreshadows macroporosity for all monoliths.

[0133] The isotherms obtained for the different monoliths, as well as the specific surface areas, were determined from the BET and BJH models. The BJH surface area was determined from the adsorption isotherm. The BET (SBET) and BJH (SBJH) surface areas are presented in Table 2 below:

[0134] [Table 2]

[0135] * If (HIPE) does not conform to the present invention. This material was obtained by a conventional mixing step (mortar and pestle) during the emulsification step.

[0136] Table 2: Specific surface areas calculated from the BET and BJH models for the monoliths obtained in example 1.

[0137] The specific surfaces (BET and BJH) are comparable to that of a traditional Si(HIPE) monolith obtained manually using a mortar and pestle as emulsification tools.

[0138] These microporous and mesoporous surfaces are primarily located at the walls (plateau boundaries) with thicknesses on the nanometer scale. This is particularly important because it minimizes limitations related to diffusion or kinetics when used as heterogeneous catalysts. Indeed, the continuous nanometer-thick walls extend over millimeter lengths, which improves the efficiency of catalytic processes.

[0139] Figure 7 shows two scanning electron microscopy images and some representative thicknesses of "5" (Figure 7 A and B). Figure 7 C, D, and E highlight an increase in the thickness of the Plateau 5 edges and a broadening of the size populations with decreasing shear rate. The mean Plateau edge thicknesses are correlated with the mean macrocell diameters as a function of the applied rotation speed (Figure 7 F).

[0140] The use of a planetary mixer offers numerous advantages in the synthesis of Si(HIPE) monoliths. This method allows for better control over the uniformity of oil droplets during emulsification, thus reducing the diversity of macrocell sizes obtained post-synthesis. Furthermore, by varying the speeds, and therefore the shear rate, it is possible to modify the macrostructure according to the desired end result. Macroscopically, with increasing shear, whether by SEM or mercury intrusion, a general decrease in the size of the shells, characteristic of monoliths, as well as in their connection windows and overall volume, is observed.

[0141] At the mesoscopic scale, on the one hand, TEM still shows the same vermicular appearance, resulting from the degradation of the surfactant used to structure the walls. On the other hand, physisorption measurements also reveal stable specific surface areas.

[0142] The examples described above demonstrate that the process according to the invention makes it possible to obtain, in a reproducible manner, self-supporting inorganic monoliths exhibiting controlled hierarchical porosity. Mechanical rotary agitation, using for example a planetary mixer, provides precise control of the internal morphology, in particular the size of the macrocells, the dimension of the interconnected pores (openings), and the thickness of the silica walls. It is particularly evident that the applied rotational speed is a determining parameter for fine-tuning the porous structure.

[0143] The resulting monoliths exhibit high porosities, typically on the order of 80 to 95% by volume, while retaining significant specific surface areas (between approximately 800 and 970 m²). 2 g -1 The wall thickness is on the nanoscale and remains adjustable depending on the emulsification conditions, which contributes both to the self-supporting nature of the materials and to a reduced diffusion path within the mesoporous structure. The process according to the invention thus constitutes an efficient and industrializable approach for the preparation of inorganic monoliths with multi-scale porosity, exhibiting adjustable structural characteristics suitable for numerous applications, particularly in the fields of catalysis, separation, and fluid processing.

Claims

DEMANDS 1. A process for preparing a multi-scale porosity inorganic monolith comprising: a) an emulsification step of an oily phase in an acidic aqueous phase, wherein: a1) the aqueous phase comprises at least one acid, at least one surfactant and at least one inorganic precursor; a2) the oily phase is added to the mixture obtained in step a1); a3) the mixture obtained in step a2 is subjected to mechanical rotary agitation, preferably at a rotational speed greater than 100 revolutions per minute, in order to obtain an emulsion; b) a polycondensation step of the emulsion obtained in step a3, preferably for 1 to 20 days, in order to obtain a gel; c) a drying step of the gel obtained in step b); d) a first calcination stage at a temperature between 160°C and 200°C, with a heating rate between 0.5 and 3°C / min, the tray being maintained for a period of 2 to 6 hours, preferably for 3 hours;and e) a second calcination stage at a temperature between 300°C and 900°C, preferably between 400°C and 800°C, with a heating rate between 0.5 and 2°C / min, the tray being maintained for 3 to 8 hours, preferably for 7 hours.

2. A process according to claim 1, characterized in that it comprises a pre-emulsification step before step a3), preferably manually or under mechanical stirring, preferably for a period of between 30 seconds and 5 minutes.

3. A method according to any one of claims 1 or 2, characterized in that the mechanical rotary agitation is achieved by a planetary mixer or a high shear mixer with or without turbulence and / or in laminar flow.

4. A method according to any one of claims 1 to 3, characterized in that the rotation speed is between 100 revolutions per minute and 2500 revolutions per minute, preferably between 200 revolutions per minute and 2000 revolutions per minute.

5. A method according to any one of claims 1 to 4, characterized in that step a3) is carried out for a duration of between 1 minute and 15 minutes, preferably between 3 minutes and 7 minutes.

6. A process according to any one of claims 1 to 5, characterized in that the surfactant is a cationic surfactant selected from quaternary ammoniums having at least 8 carbon atoms.

7. A process according to any one of claims 1 to 6, characterized in that the inorganic precursor is a silica precursor, preferably a silicon alkoxide selected from tetraethyl orthosilicate (TEOS), (3-mercaptopropyl)trimethoxyxilane, (3-aminopropyl)triethoxysilane, N-(3-trimethoxysilylpropyl)pyrrole, 3 (2,4-dinitrophenylamino)propyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, phenyltriethoxysilane, methyltriethoxysilane, sodium silicate solutions or mixtures thereof.

8. A process according to any one of claims 1 to 7, characterized in that at step a1) at least one metal salt precursor of metal oxide M and / or nanoparticles of a metal oxide M are added, where M represents a metal or metalloid selected from the following metals and metalloids: Cr, Co, Mn, Ni, Ce, V, Y, W, Nb, Mo, Fe, Zn, Ta, Sn, Cd, Cu, In, Ti, Zr, Al, Nb, Pt, Pd, Au and Hg.

9. A process according to claim 8, characterized in that the metal salt precursor of metal oxide M is selected from chlorides and nitrides.

10. A method according to any one of claims 1 to 9, characterized in that step c) of drying is carried out under atmospheric conditions.

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