FR2836070A1 - MESOSTRUCTURE MATERIALS INCLUDING PARTICLES OF NANOMETRIC DIMENSIONS LINKED BETWEEN THEM BY A SILICA MATRIX INTEGRATING ALUMINUM OR TITANIUM CATIONS IN TETRAEDRIC POSITION - Google Patents

Abstract

The present invention relates to a mesostructured material, with a high specific surface area, comprising nanometric particles (p) based on cerium oxide, zirconium oxide or titanium oxide, linked together by a mineral matrix (m). based on a silica containing cations of a metal M chosen from aluminum or titanium. The invention also relates to a process for obtaining such a material, as well as the uses of this type of material, in particular as heterogeneous acid-base or redox catalysts.

Description

<Desc / Clms Page number 1>

 The present invention relates to thermally stable mesostructured or mesoporous or ordered mesoporous materials, useful in particular as heterogeneous acid-base or redox catalysts.

 Within the meaning of the present description, a so-called "structured" material is a material having an organized structure, that is to say, within the meaning of the invention, a structure which has at least one diffusion peak in a flow diagram. radiation scattering obtained when said structure is subjected to radiation scattering (usually X-rays or neutrons). Examples of obtaining such diffusion diagrams are for example described in Small Angle X-Rays Scattering (Glatter and KratkyAcademic Press London-1982). The diffusion peak observed in the diffusion diagram obtained for a given structured material can be associated with a repetition distance characteristic of the material considered.

This characteristic repetition distance will be designated in the remainder of this description by the term "spatial repetition period" of the structured system.

 By "mesostructured material" is meant, within the meaning of the present invention, a structured material having a spatial repetition period of between 2 and 50 nm. The organized structure present in such a material will be designated here by the term "mesostructure".

 The so-called "ordered mesoporous" materials constitute a special case of mesostructured materials. These are mesoporous materials, that is to say solids having pores, called "mesopores", with an average diameter of between 2 and 50 nm, said mesopores typically having an organized spatial arrangement.

 Most often, and in particular in the case of ordered mesoporous materials, the existence of a spatial period of repetition results, for a mesostructured material, by the existence of a repetition distance within the mesostructure, understood between 2 and 50 nm, this distance being generally observable on photographs of the mesostructured material in electron microscopy.

<Desc / Clms Page number 2>

 The family of materials of generic designation "M41S", in particular described by Kresge et al. in Nature, vol. 359, pp. 710-712 (1992) or by Q. Huo et al. in Nature, vol. 368, pp. 317-321 (1994) is the best known example of ordered mesostructured and mesoporous materials: they are silicas or aluminosilicates whose structure is formed of two or three-dimensional channels ordered in a hexagonal arrangement (MCM-41 ) or cubic (MCM-48), or which have a vesicular or lamellar structure (MCM-50). Although they consist of a structure presenting channels and not mesopores, the so-called MCM-41 and MCM-48 compounds are often described in the literature as being ordered mesoporous materials. Fengxi Chen et al, for example, describe in Chemicals Materials, vol. 9, No 12, p. 2685 (1997), the channels present within these structures as "two- or three-dimensional mesopores". On the other hand, materials with a vesicular or lamellar structure of the MCM-50 type cannot be assimilated to mesoporous structures, insofar as their porous parts cannot be considered as mesopores. Such structures will therefore only be designated by the term "mesostructures" in the following description.

 As additional examples of particular mesostructures, mention may also be made of so-called "MSU" materials, which are for example described by Bagshaw et al. in Science, volume 269, pp. 1242-1244 (1995). These mesostructures, sometimes called "vermicular", are schematically made up of a three-dimensional network of channels of substantially constant diameter.

 The ordered mesostructured and mesoporous materials such as M41S are generally obtained by a process called "texturing by liquid crystals", usually designated by the initials "LCT" corresponding to the English expression "Liquid Crystal Templating". This "LCT" process consists in forming a mineral matrix such as a silica or aluminosilicate gel in the presence of amphiphilic compounds of surfactant type.

<Desc / Clms Page number 3>

 The term "liquid crystal texturing" comes from the fact that it can be schematically considered that the liquid crystal structure initially adopted by the surfactant molecules imprints on the mineral matrix its final form.

 Thus, it can be considered that within the liquid crystal structure, the mineral precursors are localized on the hydrophilic parts of the amphiphilic compounds before condensing between them, which gives the mineral matrix obtained in fine a spatial arrangement modeled on that liquid crystal. By elimination of the surfactant, in particular by heat treatment or entrainment with a solvent, an ordered mesostructured or mesoporous material is obtained, which in a way constitutes the imprint of the initial liquid crystal structure. Beck et al. thus explain in the Journal of American Chemical Society (vol. 114, p. 10834; 1992) the formation of the honeycomb structure of MCM-41 by the initial organization of the surfactant molecules in the form of a crystal phase hexagonal liquid.

 It seems, however, as Davis et al. in Microporous Materials, vol. 2, p. 27 (1993), that the mechanism involved is a little more complex. In fact, it would first pass through the formation of composite species consisting of micelles covered with mineral precursors which are organized, in a second step, into a hexagonal, cubic or lamellar network. The fact remains, however, that the final arrangement of the mineral matrix obtained is well governed by the initial shape of the micelles formed by the amphiphilic molecules used, which justifies the designation "LCT" and the fact that generally used the term "texturing agent" to denote the amphiphilic compounds of surfactant type used during this process.

 Whatever their exact method of production, ordered mesostructured or mesoporous materials are of very great interest, in particular in the field of catalysis, especially given their high specific surface and their particular ordered structure.

 However, attempts have been made to further improve the properties of these materials to make them even better suited for use in catalysis.

<Desc / Clms Page number 4>

 In this context, it has in particular been recently discovered that it is possible to synthesize ordered mesostructured or mesoporous materials, according to a route analogous to the conventional texturing process by liquid crystals, but with the additional presence of particles of nanometric dimensions in the texturing medium. This type of process, described in particular in patent application WO 01/32558, makes it possible to obtain mesostructures which integrate, within their walls, at least part of the particles of nanometric dimensions introduced into the texturing medium, linked between them by a mineral phase (binder matrix), this mineral phase generally being based on silica, and often essentially consisting of silica.

 The integration of particles of nanometric dimensions within the walls of the mesostructure as described in WO 01/32558 makes it possible to obtain mesostructured materials with increased thermal stability compared to that, generally weak, of mesostructures of the type of M41 S.

In addition, by choosing suitable starting nanometric particles, it is possible to modulate to a fairly large extent the catalytic properties of thermally stable materials obtained at the end of a process such as that described in WO 01/32558. Thus, according to the teaching of WO 01/32558, it is in particular possible to synthesize mesostructured materials whose walls of the mesostructure incorporate particles based on cerium oxide of zirconium or titanium, these specific materials being able in particular to be useful as heterogeneous redox and / or acid-base catalysts.

 Unexpectedly, the inventors have now discovered that it is possible to further improve the catalytic properties of the mesostructured materials of WO 01/32558 which comprise, within their walls, particles of nanometric dimensions based on cerium oxide. , zirconium or titanium, linked together by a mineral phase based on silica.

 More specifically, the inventors have discovered that by introducing an adequate concentration into the porous parts of the mesostructure of

<Desc / Clms Page number 5>

 these materials an aluminum or titanium compound (such as a salt or alkoxide, in particular), then by subjecting the solid to a heat treatment under suitable temperature conditions, it is observed, within the mineral phase to silica base, a quantitative integration of aluminum ions (respectively of titanium) in a tetrahedral position, which is reflected in particular by the quantitative formation of particular catalytic sites which have a pronounced Bronsted acid character and / or particular redox properties.

 Given the additional presence of cerium, zirconium or titanium oxide, these catalytic species can also be used to produce heterogeneous catalysts of the "multifunctional" type, that is to say using several types of acid-base and / or redox functionality. In this context, the work of the inventors has indeed made it possible to highlight that, unexpectedly, the quantitative integration of aluminum or titanium within the mineral matrix based on silica can be carried out without deteriorating the activity. catalytic of particles based on cerium oxide, zirconium or titanium.

 In a particularly surprising manner, the inventors have further demonstrated that, despite the imposed heat treatment and the structural modifications induced during the above-mentioned process, it is possible to obtain materials having, in addition to their particular catalytic properties, both a high specific surface and good thermal stability.

 The inventors have also demonstrated that the particularly advantageous catalytic properties of the materials obtained can be further improved or modulated, by introducing, into their mesostructure, other compounds based on metallic elements, such as salts or alkoxides. , at suitable concentrations, and then subjecting the material to a controlled heat treatment. The inventors have demonstrated that such a post-treatment can in particular make it possible to make the materials suitable as supports for catalytic species (in particular of metallic species of noble metals type) or else as

<Desc / Clms Page number 6>

 heterogeneous catalysts having, in addition to an acid Brônsted and / or redox, other specific catalytic properties.

 On the basis of these discoveries, the present invention aims to provide mesostructured materials having a high specific surface and good thermal stability, and also having a pronounced Bronsted acid character and / or a specific redox functionality.

 Another object of the invention is to provide solid catalysts or supports for solid, mesostructured catalytic species, of an acidic nature, and / or having a redox functionality.

 The invention also aims to provide solids useful as heterogeneous catalysts and having a double catalytic functionality, namely a functionality of Brônsted acid catalysis, associated with another catalytic functionality, and in particular a redox functionality.

 Thus, according to a first aspect, the present invention relates to mesostructured materials, with BET specific surface greater than or equal to 400 m2 per cm3, comprising particles (p) of nanometric dimensions based on a metal oxide chosen from an oxide of cerium, a zirconium oxide or a titanium oxide, said particles (p) being linked to one another by an inorganic matrix (m), said matrix being based on a silica containing cations of a metal M chosen from l aluminum or titanium, at least part of these cations being integrated in a tetrahedral position within said silica, and in which: (i) the amount of metal M present in the state of cations in a tetrahedral position within silica represents at least 10 mol% of the total amount of metallic element M present in the material, this total amount of metallic element M present in the material itself being such that the molar ratio overall M / Si within the material is greater than or equal to 5%;

<Desc / Clms Page number 7>

 (ii) the metal cations M present in the silica are distributed in the mineral matrix (m) with a decreasing concentration gradient from the surface to the core; and (iii) the particles (p) present in the material have a partially accessible surface.

 The term "BET specific surface", as used in the present description, designates the specific surface of a material as determined according to the "Brunauer-Emmet-Teller" method described in the Journal of the American Chemical Society , flight. 60, page 309 (February 1938). The mesostructured materials of the invention typically have a relatively high BET specific surface, namely generally between 400 and 2300 m2 per cm3 of material, this BET specific surface is preferably at least equal to 600 m2 per cm3 of material, advantageously at least equal to 1000 m2 per cm3 of material and even more preferably at least equal to 1500 m2 per cm3 of material. Expressed in unit area per unit mass, this BET specific surface area is, as a general rule, between 100 and 600 m2 / g, preferably at least equal to 150 m2 / g and more advantageously at least equal to 200 m2 / g .

 By “metal cations M integrated in a tetrahedral position within a silica” is meant, within the meaning of the present invention, aluminum and / or titanium cations in 4-coordination within a silica phase, namely integrated in tetrahedra of type M04, with oxygen atoms as nearest neighbors, the tetrahedra M04 can schematically be considered as analogues of the tetrahedra Si04 present elsewhere in silica, and where the silicon is substituted by the metal M. These cations metallic metals integrated in a tetrahedral position within the silica of the mineral matrix (m) advantageously represent at least 15%, and preferably at least 20% of the total amount of metallic element M present in the material. Preferably, this total quantity of metallic element M present in a material according to the invention is such that the overall molar ratio M / Si at

<Desc / Clms Page number 8>

 within the material is greater than or equal to 10%, this ratio advantageously being at least equal to 15%.

 The mineral matrix (m) of the mesostructured material of the present invention, which binds the particles (p) together, constitutes an amorphous to partially crystalline phase. This matrix (m) is at least partially made up of a silica integrating cations of the metal M in a tetrahedral position as defined above, and it is most often made up mainly of such silica, that is to say that the matrix mineral (m) is generally made up of at least 60% by mass, and preferably at least 70% by mass, of silica.

 Characteristically, in the materials of the present invention, the metal cations M which are present within the matrix (m) are distributed within said matrix with a decreasing concentration gradient from the surface to the core, and these cations are thus mainly located on the surface of the matrix, that is to say near the porous zones of the mesostructure. In this context, it is preferred that at least 50%, preferably at least 60%, of metal cations M which are integrated within the matrix (m) are located in the zones located less than 2 nm below the level from the surface. The cations specifically present in the tetrahedral position generally have the same type of distribution within the matrix (m), with a decreasing concentration gradient from the surface to the core. In this regard, it is preferable that these tetrahedral species are present in large quantities on the surface of the material. More generally, it is advantageous for at least 10% of the cation species M in a tetrahedral position within the matrix (m) (preferably at least 20% of these species, advantageously at least 30% of these species, and even more advantageously at least 40% of these species, or even at least 50% of these species) is accessible, which gives the material of the invention an effective acid character and / or sufficiently marked redox properties, useful in particular in applications in catalysis.

<Desc / Clms Page number 9>

 According to a first variant, the materials of the invention specifically comprise aluminum cations in a tetrahedral position within the silica of their mineral matrix (m), in combination or not with titanium cations.

 The specific presence of aluminum cations in a tetrahedral position within the mineral matrix (m) can then be demonstrated in particular by subjecting said materials to an analysis of nuclear magnetic resonance (NMR) of aluminum (27AI). The presence of aluminum cations in a tetrahedral position is then reflected on the spectrum obtained by the appearance of a peak at a chemical displacement around 50 ppm.

An NMR analysis of 27 AI on a material according to the invention also makes it possible to highlight the possible presence of other types of aluminum cations. Thus, on the NMR 27 AI spectrum of a material according to the invention having aluminum cations in a tetrahedral position within the silica of its mineral matrix, we generally observe other peaks than the peak at 50 ppm, namely, most often, a peak around 25 ppm, corresponding to so-called aluminum cations "with pentahedral environment", and a peak around 0 ppm, corresponding to so-called aluminum cations "with octahedral environment".

 In general, when the materials of the invention comprise the aluminum element, this element is present in the form of cations distributed in the three populations of cations with tetrahedral, pentahedral or octahedral environments mentioned above. In a material according to the invention incorporating aluminum cations in the tetrahedral position, the molar ratio of the quantity of aluminum cations in the tetrahedral position relative to the total quantity of aluminum cations present in the material is most often at least equal to 20% in mole. Preferably, this ratio is at least 25% by mole, and it is advantageously greater than or equal to 30% by mole, this ratio possibly reaching in certain cases values greater than or equal to 35%.

This ratio most often remains less than or equal to 80%.

 Within a material according to the invention comprising aluminum cations in a tetrahedral position within its mineral matrix (m), the ratio

<Desc / Clms Page number 10>

 AI / Si molar of the total amount of aluminum present compared to the total amount of silicon present is generally between 5% and 50%. Preferably, this ratio is greater than 10%, and more advantageously greater than 15%.

 According to another variant, the materials of the invention can specifically comprise titanium cations in a tetrahedral position within the silica of their mineral matrix (m), possibly in combination with aluminum cations. The additional presence of aluminum as a doping cation is generally indicated when the particles (p) are based on titanium oxide. In the case where a material according to the invention comprises only titanium cations within its matrix (m), excluding aluminum cations, the particles (p) are most often particles which are not solely based titanium oxide.

 The presence, within a material according to the invention, of titanium cations in a tetrahedral position can in particular be demonstrated by an analysis of the material by X-ray spectroabsorption (spectrometry known as EXAFS).

 In the materials of the invention which comprise the titanium element, the titanium is generally present in the form of cations of which only a part is found integrated in tetrahedral form within the silica of the matrix (m). Most often, the molar ratio of the quantity of titanium cations in the tetrahedral position relative to the total quantity of titanium cations present in the material is greater than or equal to 10% by mole, this ratio preferably being at least 15% in mole. In a material according to the invention, this ratio generally remains less than or equal to 80%.

 Within a material according to the invention comprising titanium cations in a tetrahedral position within its mineral matrix (m), the Ti / Si molar ratio of the total amount of titanium present compared to the total amount of silicon present is generally between 5% and 80%. Preferably, this ratio is greater than 10%.

<Desc / Clms Page number 11>

 It is generally advantageous for a material according to the invention to comprise, in a tetrahedral position within the silica of the matrix (m), both aluminum cations and titanium cations. Indeed, the inventors have found that, in most cases, the combined presence of the two types of cations within the matrix (m) results in an improvement in the thermal stability of the mesostructure.

 In this regard, it should be emphasized that, in the most general case, it is preferred that the mesostructured material of the invention, intended in general for use in catalysis, is thermally stable. Thus, it is preferred that a material according to the invention retains a mesostructured character when it is subjected to a heat treatment at a temperature of 4000C for a period of 6 hours, which is generally the case. Preferably, the material according to the invention retains this mesostructured character even when it is subjected, for the same duration, to a temperature of 5000C, and preferably to a higher temperature, which can advantageously go up to 6000C, or even up to at 7000C, and even, in certain particular cases, up to 800 C, and even more preferably up to 9000C.

 With regard to the thermal stability of the materials of the invention, it should be remembered that, in the most general case, the exposure of mesostructured materials to high temperatures generally leads to embrittlement of these materials, in particular due to reducing the thickness of the walls of their mesostructure, which can lead to a collapse of said structure. The present invention surprisingly provides compounds which are very stable in temperature.

 In general, when the material is subjected to a 6 hour heat treatment at the aforementioned temperatures, in addition to the preservation of the mesostructured character, a relatively good maintenance of the specific surface is observed, that is to say, following this type of heat treatment, the BET specific surface of said material does not generally vary by a factor exceeding 60%, this factor preferably remaining less than or equal to 50%, advantageously less than or equal to 40%, and even more preferably less than 30%. The variation factor of the BET surface to which it is made

<Desc / Clms Page number 12>

 reference is calculated by the ratio (Si-Sf) / (Si), where "Si" denotes the BET specific surface area measured before heat treatment; and where "Sf" denotes the BET specific surface area measured after the heat treatment. A material according to the invention is generally such that, if it is treated at 400 ° C. for 6 hours, then it is treated again for 6 hours at a temperature T of 500 C, the specific surface S400 measured after the heat treatment at 400 C and the specific surface ST measured after the heat treatment at 5000C are such that the ratio (S400-ST) / S400 is less than or equal to 60% , preferably less than or equal to 50%, and advantageously less than or equal to 40% Preferably, this ratio remains lower than the above values if the second heat treatment is carried out at a temperature T of 600 C, preferably even when T = 700 C, advantageously even when T = 800 C, even when T = 900 C.

 In parallel, it is most often found that the porous distribution of the material, determined by the BET method, is substantially the same before and after a heat treatment of 6 hours at the aforementioned temperatures.

 Most often, a material according to the invention is such that, following a heat treatment for 6 hours at 400 ° C., its BET specific surface remains at least equal to 900 m2 per cm 3 of material, this BET specific surface typically being between 1000 and 2300 m2 per cm3 of material (and most often, between 200 and 400 m2 / g), this specific surface is advantageously at least equal to 1200 m2 per cm3 of material.

 Furthermore, if a material according to the invention is subjected to a heat treatment for 6 hours at 800 ° C., its BET specific surface generally remains at least equal to 400 m2 per cm 3 of material, this BET specific surface preferably remaining at least equal to 750 m2 per cm3.

 Advantageously, the mesostructured materials of the present invention are solids having, at least at a local level, one or more mesostructure (s) chosen from:

<Desc / Clms Page number 13>

 - mesoporous mesostructures of three-dimensional hexagonal symmetry P63 / mmc, two-dimensional hexagonal symmetry P6mm, three-dimensional cubic symmetry la3d, Im3m or Pn3m; or - mesostructures of the vesicular or lamellar type; or - vermicular type mesostructures.

 With regard to the definition of these different symmetries and structures, reference may be made, for example, to the articles in Chemical Materials, vol. 9, No 12, pp. 2685-2686 (1997), of Nature, vol. 398, pp. 223-226 (1999), or Science, vol. 269, pp. 1242-1244 (1995).

 The particles (p) "of nanometric dimensions" which are present in the materials of the invention are, typically, particles based on cerium oxide, zirconium oxide or titanium oxide. Preferably, the particles (p) comprise one of these three oxides as the majority constituent, that is to say that the mass of zirconium oxide, cerium oxide or titanium oxide represents at least 50% of the total mass of the particles (p), the particles (p) advantageously being particles essentially based on cerium oxide, essentially based on zirconium oxide, or essentially based on titanium. According to a specific mode, the particles (p) can comprise, as a mixture, at least two of the oxides chosen from cerium oxide, zirconium oxide and titanium oxide. Thus, it can in particular be a mixture of particles based on zirconium oxide and particles based on cerium oxide, a mixture of particles based on titanium oxide and particles based cerium oxide, a mixture of particles based on titanium oxide and particles based on zirconium oxide or a mixture of these three types of particles.

 Preferably, the particles (p) present in the matrix (m) are particles of spherical or isotropic morphology, of which at least 50% of the population has an average diameter of between 1 and 10 nm,

<Desc / Clms Page number 14>

 advantageously less than 6 nm, with a particle size distribution of these advantageously monodisperse particles.

 It should be emphasized that the mineral matrix (m) present in the materials of the invention plays a characteristic role of binder between the particles of nanometric dimensions (p). Thus, the particles (p) are specifically located within this binding phase (m), that is to say within the walls of the mesoporous structure. It should therefore be emphasized that the materials according to the invention are in particular to be distinguished from mesoporous materials including particles in the internal space of their pores.

 Furthermore, typically, in the materials of the invention, at least part of the particles (p) integrated in the binder mineral phase is in contact with the porous parts constituting the accessible internal space of the material. Therefore, the material according to the invention is in particular a material where the mineral phase plays an effective role of interarticular binder, but where said matrix (m) does not completely cover the particles of nanometric dimensions which it contains.

 It is however important to carefully consider the primordial role of inter-particle consolidation of the mineral phase. Indeed, in order to favor the formation of a structure where the particles are partially exposed, one would be tempted a priori to strongly reduce the molar ratio of the mineral binding matrix (m) / particles (p). However, it appears that the stability of the structure is generally not ensured when the molar ratio (m) / (p) (namely, in general, the molar ratio Si02 / (Ce02 + Zr02 + Ti02) within the material , that is to say, most often, the Si / (Ce + Zr + Ti) molar ratio is below the proportion of 20:80. The Si02 / (Ce02 + Zr02 + Ti02) molar ratio within of the material of the invention is therefore generally between 20: 80 and 99.5: 0.5, and it is advantageously between 40: 60 and 95: 5. Even more preferably, this molar ratio is understood between 40: 60 and 92: 8.

 Typically, in a material according to the invention, the oxide-based particles (p) which are linked together by the matrix (m) are particles from which at least part of the surface is accessible. We hear

<Desc / CRUD Page number 15>

 thereby that within a material according to the invention, some of the particles (p) (preferably at least 20%, and advantageously at least 40%, or even at least 50% of these particles) have a part of their surface in direct contact with the porous space of the mesostructure, so that their constituent oxide (cerium, zirconium or titanium oxide) can react with reactive chemical species (molecules (especially in the form of gas or in solution) ), ions, radicals ...) of sufficiently small size to penetrate inside the mesostructure of the material.

 Thus, it should in particular be emphasized that, in a material according to the invention, the particles (p) cannot all be continuously covered by a layer of one or more materials other than cerium oxide, zirconium and / or titanium oxide. Therefore, it is in particular excluded that the particles (p) are all completely encapsulated by the matrix (m), and it is preferable, in general, that the free surfaces of the particles (p), i.e. -to say the surfaces which are not in contact with the matrix (m), are not covered by a layer of one or more materials other than cerium oxide, zirconium oxide or titanium oxide, or then only partially, and preferably discontinuously if necessary. In any event, continuous covering of the particle-free surfaces (p) with a layer of one or more materials other than cerium oxide, zirconium oxide or titanium oxide is prohibited.

 When the particles (p) are based on cerium oxide, the accessible nature of said particles (p) can in particular be demonstrated by the fact that the materials have a reducible character, that is to say that they have a ability to reduce in a reducing atmosphere (especially in the presence of hydrogen) and to reoxidize in an oxidizing atmosphere.

 More precisely, this "reducibility" of a material according to the invention can be demonstrated by treating the material with hydrogen and by analyzing the conversion rate of cerium in the oxidation state IV

<Desc / Clms Page number 16>

initially present, in cerium in the oxidation state i! in the material obtained after treatment, according to the overall reaction below:
2Ce02 + H2 Ce203 + H2O
The reducible nature of a material according to the invention incorporating particles (p) based on cerium oxide can thus in particular be quantified by the conversion rate measured at the end of one according to the so-called "TPR" protocol, set out below: - In an AMI-1 Altamira type device fitted with a silica reactor, a 100 mg sample of the solid to be tested is placed at ambient temperature (generally between 15 ° C. and 25 ° C.) under a flow gaseous mixture of hydrogen / argon at 10% hydrogen by volume, at a flow rate of
30 mL per minute.

 - A temperature rise is carried out up to 900 ° C. at the rate of a constant temperature rise gradient of 10 ° C. per minute. Using a thermal conductivity detector at 70mA, the quantity of hydrogen captured by the material is determined from the missing surface of the hydrogen signal from the baseline at room temperature to the baseline. at 900 C.

 At the end of such a test, a conversion rate of the cerium IV species initially present is generally measured which is at least 20%, this conversion rate advantageously being at least 30%, more preferably at least equal to 40%, and even more advantageously 50% or more. In general, this conversion rate remains below 90%.

 Furthermore, the particles (p) of nanometric dimensions based on cerium oxide, zirconium oxide or titanium oxide which are present in the material of the invention are advantageously particles at least partially crystalline, at in which the cerium oxide, zirconium oxide or titanium oxide has, if necessary, a degree of crystallinity preferably ranging from 30 to 100% by volume. The rate of

<Desc / Clms Page number 17>

 volume crystallinity of a metal oxide present in the particles of nanometric dimensions of the material of the invention, can be calculated by the ratio of the area of the same diffraction peak obtained for a sample of said material according to the invention, relative to the area of a diffraction peak obtained for a control sample of said oxide in the fully crystallized state, these areas being, if necessary, corrected for the absorption factors of the oxides present.

 The presence of such partially crystallized particles within the mineral phase then gives the mesostructured materials of the invention, in addition to an ordered arrangement of their pore network, an overall crystallinity rate generally at least equal to 10% by volume. , and preferably greater than 30% by volume, this "overall volume crystallinity rate" being calculated by multiplying the volume crystallinity rate determined experimentally for the particles, according to the method described above, by the fraction of volume of the material which is occupied by said particles.

 By “degree of crystallinity of a mesostructured material” is meant within the meaning of the invention, the degree of crystallinity proper to the walls of the structure, which globally takes into account both the possible crystallinity of the binder mineral phase and the crystallinity of particles of nanometric dimensions included in this binding phase. On this subject, it must therefore be emphasized that the crystallinity of the material, within the meaning of the invention, corresponds to a microscopic organization detectable in particular by diffraction (for example by X-ray diffraction at large angles), which is to be distinguished in particular of the order presented, at a more macroscopic level, by the mesostructure of the material.

 When the particles (p) are particles based on a metal oxide (cerium, zirconium or titanium oxide) at least partially crystalline, it is often preferable that said at least partially crystalline oxide comprise at least one metallic element M1 (said "dopant" element), in cationic form, in solid solution within its crystal lattice, generally in solid solution for insertion and / or substitution.

 The materials of the invention comprising particles of cerium, zirconium or titanium thus doped are generally

<Desc / Clms Page number 18>

 particularly suitable as supports for catalytic species, in particular for metallic species of the noble metal type (platinum for example). The use of these particular materials as a support for catalytic species constitutes another object of the present invention. Yet another object of the invention is the catalysts capable of being obtained by supporting catalytic species (in particular of the noble metal type) on such a material.

 By "cations present in solid solution within a metal oxide" is meant cations present, by way of insertion and / or substitution cations, within said crystalline metal oxide which typically plays the role of a host crystal lattice, said cations being most often in the minority compared to the cations constituting the metal oxide where they are integrated in solid solution, that is to say generally representing strictly less than 50% by mole of the total quantity of metal cations present in the oxide, the content of said cations being able however to reach 50% in certain cases. A crystalline oxide integrating cations in solid solution retains the structure of the crystalline oxide in the pure state, slight modifications of the mesh parameters which can however be observed, for example in accordance with Vegard's law. A crystalline oxide integrating cations in solid solution therefore generally has an X-ray diffraction diagram similar to that of pure mixed oxide, with a possible offset of the peaks, more or less significant.

 Preferably, when the particles (p) of the materials of the invention are "doped" with cations of the metallic element M 1 in solid solution, the quantity of cations M1 in solid solution (or all of the doping cations in solid solution (including the cations M1), when several dopants are present) represents at least 0.2% by mole of the total amount of metal cations present in the oxide, advantageously at least 0.5% by mole, and again more advantageously at least 1 mol%. In general, it is most often preferred that the content of “doping” cations (cations of the element M1, possibly in combination with other doping cations) is as high as possible. Thus, when it is possible, in particular

<Desc / Clms Page number 19>

 taking into account the nature of the doping element (s) and of the oxide within which they are introduced in solid solution, it is preferred that the content of "doping" cations is at least equal to 5%, of preferably at least equal to 20%, and even more advantageously at least equal to 30%, or even at least equal to 40%.

 The exact nature of the metal cations M 1, the presence of which can be envisaged in solid solution within the particles (p) depends on the nature of the metal oxide within which it is integrated in solid solution.

 Thus, when the particles (p) of nanometric dimensions integrated in the mineral binder phase of the materials of the invention are particles based on a cerium oxide at least partially crystalline, the element M1 present in the cationic state in solid solution can, in general, be chosen from rare earths other than cerium, the transition metals capable of being able to be integrated in cationic form in solid solution within a cerium oxide (in particular zirconium or, manganese), or alternatively among the alkaline earth metals (in particular barium, calcium, or strontium), said metal M1 preferably designating a rare earth other than cerium (advantageously lanthanum, yttrium, neodymium, praseodymium, dysprosium or europium), or zirconium.

The quantity of cations of metal M which can be introduced in solid solution within a cerium oxide depends on the nature of said metal M1. When the doping metal M1 represents zirconium or a rare earth other than cerium, the quantity of cations of the metal M1 which can be integrated in solid solution can represent up to 50% by mole of the total quantity of metal cations present in doped oxide.

 When the particles (p) of nanometric dimensions integrated in the mineral binder phase of the materials of the invention are particles based on an zirconium oxide at least partially crystalline, the metal M1 which may be present in the cationic state in solid solution can be chosen from cerium, rare earths other than cerium, transition metals capable of being able to be incorporated in cationic form in solid solution

<Desc / Clms Page number 20>

 within a zirconium oxide, or alternatively among alkaline earth metals (in particular barium, calcium, or strontium), said metal M preferably designating a rare earth (advantageously cerium, lanthanum, yttrium, neodymium, praseodymium, dysprosium or europium). When the doping metal M1 represents cerium or another rare earth, the quantity of cations of the metal M1 which can be integrated in solid solution can represent up to 50% by mole of the total quantity of metal cations present in the oxide dope.

 Furthermore, when the particles (p) of nanometric dimensions integrated in the mineral binder phase of the materials of the invention are particles based on an at least partially crystalline titanium oxide, the element M1 present in the cationic state in solid solution can, in general, be chosen from rare earths, the transition metals capable of being able to be integrated in cationic form in solid solution within a titanium oxide, or alternatively among alkaline earth metals ( in particular barium, calcium, or strontium), said metal M1 preferably being a formative element of a phase of rutile or anatase type. Advantageously, in particles based on titanium oxide, the metal M1 "doping" is a rare earth, or else manganese, tin, vanadium, niobium, molybdenum or antimony.

 In addition to the silica-based mineral phase and the particles of nanometric dimensions possibly doped above, the materials of the invention most often comprise crystallites based on hydroxide or oxy-hydroxide of the metal M (for example, crystallites based on aluminum oxyhydroxide, in particular of the y-AIOOH type or else based on titanium oxide, preferably with anatase structure where appropriate).

When present, these crystallites are generally included in the mineral phase and / or located on its surface. Where appropriate, it is preferred that these crystallites have an average size less than or equal to 500 nm, and more preferably less than or equal to 200 nm. In general, these crystallites have an average size at least equal to 2 nm.

<Desc / Clms Page number 21>

 When the particles (p) are particles based on an at least partially crystalline metal oxide "doped" with cations of a metal M1 in solid solution, as defined above, the mineral matrix (m) can comprise compounds based on said doping element M1, in particular metal cations of the metal M1 or clusters based on the metal M1, dispersed, preferably homogeneously within the binder matrix (m). By “cluster” based on the metal M1, is meant a polyatomic entity of dimension less than 2 nm, preferably less than 1 nm, comprising at least atoms of the metal M1, in the oxidation state 0 or in a state of higher oxidation (typically, these are clusters based on oxide and / or hydroxide species of the metal M, for example polyatomic entities within which several atoms of the metal M are linked together by -0or- bridges OH-, each of the atoms of the metal M possibly being linked to one or more groups -0- or -OH). The matrix (m) of the materials of the invention can, moreover, advantageously comprise on its surface such metal cations of the element Ml and / or clusters based on the metal M 1. This can in particular be the case when the metal M1 is zirconium, manganese, or even a rare earth (in particular lanthanum, yttrium, neodymium, praseodymium, dysprosium or europium). According to an advantageous variant, the mineral phase of the materials of the invention comprises metal cations of the element M 1 and / or clusters based on the metal M1, both dispersed within said mineral phase and on the surface of said mineral phase. This variant can be particularly advantageous when the metal M1 denotes zirconium, manganese, barium, or a rare earth such as lanthanum, yttrium, neodymium, praseodymium, dysprosium or europium).

 More generally, whether or not the particles (p) are particles based on an at least partially crystalline metal oxide "doped" with cations of a metal M1 in solid solution, the materials of the invention advantageously comprise cations of at least one metal M2 or clusters based on said metal M2, this metal M2, which may be one of the metals of type M 1 mentioned above, being chosen from alkali or alkaline earth metals (in particular barium, strontium, calcium, potassium or sodium),

<Desc / Clms Page number 22>

terres rares (en particulier le lanthane, l'yttrium, le néodyme, le praséodyme, le dysprosium ou l'europium), ou bien le manganèse. Le cas échéant, ces cations et/ou clusters sont généralement présents notamment en surface de la matrice (m) et/ou sous forme dispersée au sein de la matrice (m). Avantageusement, ils sont présents à la fois sous forme dispersée au sein de la matrice et en surface de ladite matrice.

rare earths (in particular lanthanum, yttrium, neodymium, praseodymium, dysprosium or europium), or manganese. Where appropriate, these cations and / or clusters are generally present in particular on the surface of the matrix (m) and / or in dispersed form within the matrix (m). Advantageously, they are present both in dispersed form within the matrix and on the surface of said matrix.

In the most general case, it is also often advantageous that the materials of the invention comprise crystallites based on oxide, hydroxide, oxy-hydroxide, carbonate or hydroxy-carbonate of an element metallic of a metal of the type of metals M1 or M2 defined above. Where appropriate, these crystallites are generally included in the matrix and / or present on its surface. When present, it is preferred that these crystallites have a size less than or equal to 700 nm, and preferably less than or equal to 500 nm. Thus, in a particularly advantageous manner, these crystallites have a size of between 2 nm and 200 nm. It is particularly advantageous for these crystallites to be based on zirconium oxide, hydroxide and / or manganese oxide and / or hydroxide and / or oxide of at least one rare earth.

Clusters and / or crystallites, of the type of those which are potentially present within and / or on the surface of the matrix (m), can also be present, in certain cases, within and or on the surface of the particles ( p) which are dispersed within this phase. The presence of these clusters and / or crystallites can give the material increased catalytic properties. However, it should be emphasized that, typically in a material according to the invention, the crystallites and / or clusters possibly present on the surface of the particles (p) are such that they do not prevent the accessibility of the particles (p) by reducing agents such as hydrogen. Therefore, when they are present, the crystallites and / or clusters on the surface of the particles (p) are preferably individual crystallites and / or clusters which do not completely cover the surface of the particles (p). In general, it is preferred that such crystallites and / or clusters occupy less than 50%,

<Desc / Clms Page number 23>

 advantageously less than 30%, even more advantageously less than 20%, preferably less than 10% and even more preferably less than 5% of the portion of the surface of the particles (p) which is not in contact with the binding matrix .

 According to a particularly preferred variant, a material according to the invention incorporates lanthanum compounds, preferably at least in the form of lanthanum cations and / or lanthanum-based clusters within its matrix (m) and / or at the surface of this matrix (m). Materials with this type of mineral phase incorporating lanthanum often have increased thermal stability, generally associated with advantageous catalytic properties, in particular acid-base and / or redox properties, which can for example make them suitable for the heterogeneous catalysis of oxidation or basic catalysis reactions at high temperature, especially for the heterogeneous catalysis of hydrocarbon oxidation reactions (alkanes, aromatics, etc.). The use of these specific compounds for this particular application constitutes another object of the present invention.

 In general, when a material according to the invention comprises, within its matrix and / or on the surface of this matrix, cations and / or clusters based on lanthanum, it is often advantageous that it also contains a metallic element chosen from manganese or alkali or alkaline earth metals, preferably from barium, strontium, calcium, potassium or sodium, and advantageously from barium, potassium or manganese. Preferably in this case, said metallic element (alkaline or alkaline earth or manganese), is present at least in part in the form of crystallites of oxide and / or hydroxide, or even small clusters salts (sulfates, carbonates or nitrates, for example, sulfates and carbonates being preferred).

 A family of materials according to the present invention which proves to be particularly advantageous consists of materials comprising:

<Desc / Clms Page number 24>

 (1) particles (p) of cerium oxide or zirconium, doped with a metallic doping element M1 of the aforementioned type, advantageously particles of cerium oxide doped with zirconium or with a rare earth other than cerium; and (2) a matrix (m) comprising cations and / or clusters based on lanthanum (generally dispersed within it and / or present on the surface, and advantageously at least present on the surface).

 A particularly advantageous class of this family of materials is constituted by materials further comprising: (3) an alkaline or alkaline-earth element (preferably, barium, strontium, calcium, potassium or sodium), manganese or a mixture of an alkaline or alkaline earth element and manganese, this alkali or alkaline earth metal and / or this manganese then being generally present at least in part in the form of oxide crystallites and / or hydroxide or mass of salts of the aforementioned type.

 The specific materials comprising the aforementioned components (1), (2) and (3) appear to be particularly suitable as absorption catalysts, of nitrogen oxides, in particular in an oxidizing atmosphere, and in particular for the absorption of the so-called compounds. NOx (NO, N02, N20 in particular) which are present for example in certain industrial gaseous effluents, or in automobile exhaust gases. The use of these specific compounds for this particular application constitutes another object of the present invention.

 In general, in a material according to the invention, the overall thickness of the walls of the mesostructure, which integrate the particles (p), and the aforementioned clusters and / or crystallites, is preferably between 3 and 12 nm, and preferably between 4 and 10 nm.

 In the case of an ordered mesoporous structure, the diameter of the pores is generally between 2 and 8 nm, this diameter generally being less than 6 nm.

<Desc / Clms Page number 25>

 According to another aspect, the present invention also relates to a process for preparing the mesostructured material as defined above. This process is characterized in that it comprises the successive stages consisting in: (a) producing a mineral mesostructure integrating, within its walls, particles of nanometric dimensions based on a cerium oxide, an oxide of zirconium or a titanium oxide, linked together by a mineral matrix based on silica, said matrix not completely covering said particles; (b) introducing into the mesoporous structure thus obtained a compound of element M (preferably said metal M in cationic form, optionally complexed, or alternatively an alkoxide of metal M), the total content of element M introduced into within the structure, related to the total surface developed by the mesostructure, being less than 5 micromoles of cation per m2 of surface; and (c) subjecting the mesostructure thus produced to a temperature at least equal to 300 C, and not greater than 1000 C, whereby at least part of the metal M is integrated in the form of cations in a tetrahedral position within the mineral phase based on silica.

 Step (a) of the process of the invention can be carried out by any means known to those skilled in the art. However, this step (a) is preferably carried out by implementing the method which is the subject of patent application WO 01/32558, that is to say by implementing the steps consisting in: (a1) forming an initial medium, preferably aqueous or hydroalcoholic, advantageously of pH less than 4, comprising a texturing agent, namely an amphiphilic compound of surfactant type, in particular a copolymer, preferably not loaded under the conditions for carrying out the process , and capable of forming micelles in the reaction medium (in particular a nonionic surfactant of the copolymer type

<Desc / Clms Page number 26>

 block, and more preferably a poly (ethylene oxide) -poly (propylene oxide) -poly (ethylene oxide) triblock copolymer; (a2) add in the middle of step (a1) a colloidal dispersion of particles of nanometric dimensions, preferably based on a metal oxide, advantageously in the crystalline state, and preferably chosen from a cerium oxide, an oxide of zirconium, or a titanium oxide, preferably with a hydrodynamic diameter of at least 50% of the population of the colloidal particles between 1 and 15 nm, and a preferential monodisperse particle size distribution of these colloidal particles; (a3) forming, by adding in the medium a mineral precursor of the alkaline silicate type (sodium silicate for example) or else silicon alkoxide, a mesostructured mineral phase, at least partially (preferably essentially) consisting of silica, said mineral phase then integrating, within its mesostructured walls, at least part of the particles of nanometric dimensions introduced during step (a2); and (a4) removing the texturing agent, in particular by heat treatment or else entrainment with a solvent, these steps being optionally followed by one or more steps of washing, drying, and / or calcination, optionally followed by a partial chemical attack. controlled in the mineral phase (for example by NH40H, NaOH or HF) in particular in the case where, in the structure obtained at the end of step (4), the binder matrix completely covers the oxide particles.

 In any event, it is generally preferable for the mesoporous structure obtained at the end of step (a) to have the highest BET specific surface possible, this surface most often being at least equal to 1500 m2 per cm 3 of material, preferably at least equal to 1600 m2 per cm3 of material, and even more advantageously of the order of 2100 m2 per cm3 of material, that is to say, in general, between 1800 and 2500 m2 per cm3 of

<Desc / Clms Page number 27>

 material. It is also preferred that this mesostructure produced during step (a) has a pore volume at least equal to 0.2 crr / g for its pores of dimensions less than or equal to 20 nm.

 Typically, in the material obtained at the end of step (a), it is necessary that the particles based on cerium oxide, zirconium oxide and / or titanium oxide are not completely covered by the silica-based binding matrix. In other words, these particles must be at least partially in contact with the internal space of the pores of the mesostructure. This property can be verified by carrying out for the mesostructured material a curve of evolution of the electrophoretic potential as a function of the pH (in particular by zetametry), in particular when the material comprises particles based on cerium oxide.

 When the particles present are specifically based on cerium oxide, another means of verifying the accessible nature of the oxide particles within the material produced in step (a) consists in establishing the reducible character of the material by a treatment with hydrogen and measurement of the rate of conversion of cerium IV into cerium ttt, in particular according to the above-mentioned "TPR" procedure. It is preferred that the rate of conversion of cerium IV into cerium Ht measured according to the TPR procedure is at least 25%, preferably at least 35%, this conversion rate being advantageously at least equal to 50%.

 In all cases, if it is desired to improve the accessibility of the oxide particles, it is possible to carry out a partial chemical attack on the mineral phase based on silica, for example with NH40H, NaOH or HF. In this context, it is naturally necessary to carry out this partial chemical attack under controlled conditions, so as not to harm the stability of the material.

 Whatever the exact mode of implementation of step (a), the nanometric particles which are immobilized within the mineral mesostructure are preferably cerium oxide particles of the type described in particular in patent applications

<Desc / Clms Page number 28>

 FR 2 416 867, EP 0 206 906 or EP 208 580, zirconium oxide particles as described in the Journal of Gel Science Technology, vol. 1, p. 223 (1994), and / or titanium oxide particles of the type described in Chemical Materials, vol. 10, pp. 3217-3223 (1998).

 More generally, the metal oxide particles used can also be any particles based on cerium oxide, zirconium oxide and / or titanium oxide, obtained in particular by acid treatment, washing or else by dispersion of ultrafine powders obtained for example by high temperature synthesis methods of the type of combustion of metal chlorides in a flame known to those skilled in the art.

 Step (b) of the method consists in impregnating at least part of the porous zones of the mesostructure produced in step (a) with a compound of the element M which it is desired to introduce at least part in the form of cations in a tetrahedral position within the silica of the binding matrix of the mesostructure obtained at the end of step (a).

Generally, this impregnation is carried out by introducing said compound of the element M into the mesostructure, by dispersing it within a vector phase, liquid or gas, this vector phase preferably being a liquid medium, generally a medium aqueous or hydro-alcoholic, or alternatively an organic solvent medium.

 Thus, step (b) most often consists in impregnating at least part of the porous zones of the mesostructure produced in step (a) with a solution, generally aqueous, of a salt of cation of the metal M, preferably of a nitrate, oxy-nitrate, oxalate, and / or acetate of the metal M, or else with an aqueous or hydro-alcoholic solution comprising cations of the metal M in the complexed state, or else also with a solution, generally in an anhydrous organic solvent medium, comprising an alkoxide of the metal M. However, according to particular modes of implementation, it is also possible to envisage in step (b) the use of dispersions of clusters based on metal M (in particular clusters based

<Desc / Clms Page number 29>

 of oxide and / or hydroxides of the metal M), or alternatively a gas phase comprising a compound of the metal (this gas phase then generally being constituted by said compound in the gaseous state).

 In the specific case where the metal M denotes aluminum, the compound based on the metal M of step (b) is preferably introduced: - in the form of an aqueous (or optionally hydroalcoholic) solution comprising at least one aluminum salt, preferably an aluminum salt with the lowest possible tendency to hydrate. In this context, aluminum can be introduced in the form of a solution comprising an aluminum nitrate, an aluminum acetate, an aluminum sulphate, or a mixture of these salts, and advantageously in the form of a solution comprising an aluminum nitrate or acetate, or an aluminum acetate / aluminum nitrate mixture; - in the form of a solution, generally aqueous or hydroalcoholic, comprising aluminum cations in complexed form, for example in the form of polynuclear aluminum complexes, of type AI (OH) x (N03) 3-x (where x goes 1 to 2.5); - In the form of an aqueous dispersion comprising clusters based on an aluminum compound, preferably clusters of aluminum oxides and / or hydroxide, in particular clusters of type A) is.

 In this context, it is generally preferred that aluminum is introduced in the form of species having a positive overall charge. Thus, according to a particularly preferred embodiment, the introduction of aluminum during step (b) is carried out by impregnating the structure of step (a) with an aqueous solution comprising an aluminum salt (of preferably a nitrate and / or an acetate) at a pH between 1 and 6, and preferably less than or equal to 5.5.

 The introduction of aluminum is naturally not limited to the introduction of the solutions and dispersions envisaged above, the implementation of which constitutes only a preferred embodiment of the invention. Thus, this introduction of aluminum can alternatively be carried out using a

<Desc / Clms Page number 30>

 solution, generally in an organic solvent medium, of an aluminum alkoxide, such as, for example, aluminum butylate A! (OBu) s. According to another variant, the introduction of aluminum into the mesostructure obtained at the end of step (a) can also be carried out by subjecting said mesostructure to a flow of AICI3 in a gaseous medium.

 In the specific case where the metal M denotes titanium, the compound based on the metal M of step (b) is generally introduced: - in the form of an aqueous solution (or optionally hydroalcoholic) comprising at least one salt of titanium, preferably chosen from titanium acetate, or TiOCI2; - In the form of a solution of a titanium alkoxide, said titanium alkoxide preferably having the general formula Ti (OR) 4, where R denotes a hydrocarbon group, linear or branched, saturated or unsaturated, and preferably a alkyl group having from 1 to 6 carbon atoms.

 In this context, it is also preferred, as a general rule, for the titanium to be introduced in the form of species having a positive overall charge. Thus, according to a particularly preferred embodiment, the introduction of titanium during step (b) is carried out by impregnating the structure of step (a) with a hydroalcoholic solution, preferably concentrated, comprising an alkoxide of titanium in combination with an acid with an H + / Ti ratio in the hydroalcoholic medium generally ranging from 0.1 to 4.

 Generally, in step (b), whether the metal M designates aluminum or titanium, it is necessary that the overall concentration of element M introduced into the porous zones is relatively low, in particular so as not to observe an excessive reduction in the specific surface of the material, or even a clogging of the pores, following the heat treatment of step (c). This overall concentration is such that the total content of cations of said element M, relative to the total surface developed by the mesostructure, remains, as a general rule, less than 5 micromoles of cation per m 2 of surface. Preferably, this content remains at

<Desc / Clms Page number 31>

 less than 1 micromole of cation per m2 of surface. The “total surface of the mesostructured material” to which reference is made here is calculated by multiplying the BET specific surface, measured in m2 / g for the mesostructured material obtained at the end of step (a), by the mass of said material.

 In most cases, it is preferred that, during step (b), the compounds based on the metal M are introduced into the mesostructure in the form of a solution, in an aqueous or hydro-alcoholic medium, or much still in an organic solvent. In this context, in order to be placed under the aforementioned concentration conditions, the overall concentration C in cations M within the medium which is found incorporated in the mesostructure at the end of step (b) is generally less than 2 mol / L and it is preferably between 0.1 mol / L and 1.5 mol / L, this concentration being advantageously less than or equal to 1 mol / L. It should be noted that, in the context of the present process, it is possible to impregnate with relatively concentrated solutions, the concentration C possibly being greater than 0.5 mol / L, or even 0.7 mol / L in the most cases. To achieve the incorporation of a solution having such a concentration C within the mesostructured material resulting from step (a), step (b) can be carried out in different possible ways.

 Thus, according to a first possible variant, step (b) can be carried out by immersing the mesostructured material obtained at the end of step (a) in a solution comprising the element M at a concentration of l order of the concentration C (generally between 0.1 and 1.5 mol / L, and advantageously between 0.2 and 1 mol / L), then by filtering the medium obtained. The impregnated solid collected after filtration then effectively comprises within its porous zones a solution comprising a compound of metal M, with the desired content of metal M.

 According to another possible variant, step (b) can also be carried out by immersing the mesostructured material obtained at the end of step (a) in a solution comprising the element M at a concentration close to the concentration C (in general at a concentration advantageously understood

<Desc / Clms Page number 32>

 between 0.2 and 1.5 mol / L, and preferably between 0.4 and 1.2 mol / L), then subjecting the medium obtained to centrifugation. Provided that the centrifugation is not carried out under excessively high conditions (typically, the centrifugation is carried out, at a rate of 2000 to 5000 revolutions per minute, for a duration generally not exceeding 30 minutes), the centrifugation pellet obtained is a impregnated solid which comprises, within its porous zones, a solution comprising the element M at the desired concentration.

 According to another conceivable variant, step (b) can also be carried out by adding to the mesostructured material obtained at the end of step (a) a volume V of a solution comprising the element M, said volume V being of the order of the pore volume developed by the material, whereby a paste is obtained. The mixing is generally carried out by kneading. The paste obtained is then subjected to evaporation of the solvent, preferably slowly. In this case, almost all of the element M introduced at the start is found within the mesostructure. In this context, it is generally preferred to conduct step (b) by adding to the mesostructured material obtained at the end of step (a) a volume of solution representing between 0.2 and 3 times the volume of the material (and preferably represents at most 2 times the volume of the material), said solution comprising the element M at a concentration generally between 0.1 and 2 mol / L, then evaporating the solvent in the mixture obtained.

 Whatever the exact mode of implementation of step (b), the impregnated solid obtained at the end of this step is then subjected to a step (c) of heat treatment. This step (c) generally comprises a treatment of the material at a temperature at least equal to 300 ° C., this temperature being preferably at least equal to 350 ° C., higher temperatures being generally not required as regards integration of the cations of the element M in tetrahedral form within the silica of the mineral matrix of the mesostructure produced in step (a).

<Desc / Clms Page number 33>

 However, in certain cases, it may be advantageous to carry out the heat treatment of step (c) at a temperature at least equal to 400 C, or even at least equal to 500 C, in particular so as to improve certain physical characteristics. and / or chemical of the material (concentrations in active catalytic sites, specific catalytic activities, etc.), which generally does not excessively affect the specific surface of the material. However, in order not to jeopardize the stability of the mesostructure, the temperature of the heat treatment must generally not exceed 1000 C, and, preferably, it remains below 950 C, advantageously less than or equal to 900 C, and even more preferably less than or equal to 850 C.

 Optionally, in particular in the case where the metal M is introduced in step (b) in the form of a solution, step (c) may comprise a drying step, prior to the heat treatment. In this case, this preliminary drying is generally carried out in the slowest possible way, in particular so as to favor the ionic exchanges. To this end, the drying is most often carried out at a temperature between 15 and 800C, preferably at a temperature below 50 C, or even 400C, and advantageously at room temperature. This drying can be carried out under an inert atmosphere (nitrogen, argon) or under an oxidizing atmosphere (air, oxygen) depending on the compounds present in the material. In the case where the metal M is introduced into the material in the form of an alkoxide, the drying is advantageously carried out under a water-free atmosphere.

 Particularly advantageously, step (c) can be carried out by subjecting the solid to a temperature gradient, from an initial temperature between 15 and 95 C, at a final temperature between 350 C and 1000 C, advantageously with a rise in temperature of between 0.5 ° C. per minute and 2 ° C. per minute, and with one or more successive stages of maintenance at intermediate temperatures, preferably between 350 and 6000 ° C., for variable durations, generally between 1 hour and 24 hours.

<Desc / Clms Page number 34>

According to a particularly advantageous embodiment, the method of the invention can comprise, following the impregnation / heat treatment process of steps (b) and (c), one or more subsequent cycles of impregnation / heat treatment using stages of type (b) and (c), carried out on the solid obtained at the end of the preceding cycle. By implementing this type of process with several successive impregnation / heat treatment cycles, it is possible to achieve very good incorporation of the element M within the silica of the binder matrix of the mesostructure produced in step (at). One can also envisage the implementation of several impregnation / heat treatment cycles using for some aluminum as the metal M, and for others titanium, whereby one can obtain materials integrating with the both titanium and aluminum cations within their binding matrix. In this context, it is generally preferable for the first impregnation / heat treatment cycle to be carried out using aluminum as the metal M.

It should be noted that the impregnation process (s) / heat treatment used may lead, in parallel to an integration of the element M in a tetrahedral position within the matrix, to the formation of crystallites based on a compound. metal M, in particular of the oxide, hydroxide, oxy-hydroxide, carbonate or hydroxy-carbonate type, on the surface of the binder phase, and / or at least partially integrated therein. We can also observe in some cases the formation of clusters or crystallites on the surface and / or within the particles of cerium, zirconium or titanium oxides.

According to an even more specific embodiment, the material obtained at the end of the impregnation cycle (s) / heat treatment using steps of type (b) and (c), can still be modified. In this context, the method of the invention can thus additionally comprise one or more subsequent cycles of impregnation / heat treatment similar to steps of type (b) and (c) previously described, but using an impregnation by a compound of a metal other than metal M.

<Desc / Clms Page number 35>

Le procédé comporte alors en général, des étapes (b') et (c'), postérieures aux étapes (b) et (c), et consistant à : (b') introduire, au sein d'au moins une partie des zones poreuses du matériau, un composé d'un métal M'différent du métal M (généralement ledit métal M'sous forme cationique, éventuellement complexée, ou un alcoxyde dudit métal M'), la teneur en ledit élément M'introduit au sein de la structure, rapportée à la surface totale développée par la mésostructure, étant inférieure à 5 micromole de cation par m2 de surface ; et (c') soumettre le matériau ainsi imprégné à une température au moins égale à 300 C, et non supérieure à 10000C.

The method then generally comprises steps (b ') and (c'), subsequent to steps (b) and (c), and consisting in: (b ') introducing, into at least part of the zones porous of the material, a compound of a metal M 'different from the metal M (generally said metal M' in cationic form, possibly complexed, or an alkoxide of said metal M '), the content of said element M' Introduces into the structure, related to the total surface developed by the mesostructure, being less than 5 micromole of cation per m2 of surface; and (c ') subjecting the material thus impregnated to a temperature at least equal to 300 C, and not higher than 10000C.

In the most general case, steps (b ') and (c') can advantageously be carried out under the conditions described above for steps (b) and (c), subject to any necessary adaptations, in particular if the compound based on the metal M ′ used in step (b ′) exhibited a specific physicochemical nature. In most cases, the different modes of impregnation envisaged for the compounds of the metal M are generally transposable to the impregnation of a compound of a metal M ', in particular as regards the concentrations to be used. The conditions of the heat treatment to be implemented for step (c ') are, as a general rule, the same as those used in step (c) defined above.

According to a particularly advantageous embodiment, the impregnation / heat treatment cycle of steps (b ') and (c') can be implemented when it is desired to integrate lanthanum compounds within the material, in particular in the form of cations and / or lanthanum-based clusters within its matrix and / or on the surface of this matrix, which in particular leads to an increase in the thermal stability of the material obtained. In this case, the metal M 'denotes the lanthanum. Generally, the lanthanum compound used in step (b ') is preferably a salt

<Desc / Clms Page number 36>

 lanthanum, for example nitrate or lanthanum acetate, and step (b ′) can typically consist in impregnating the material with a solution of the lanthanum salt, the pH of said solution being preferably less than 8 and advantageously less than 7. When the metal M 'used in steps (b') and (c ') is lanthanum, we generally observe, in addition to an integration of lanthanum in the form of cations and / or of lanthanum-based clusters within its matrix and / or on the surface thereof, the formation of lanthanum-based crystallites, which generally locate on the surface of the material. Most often, part of the lanthanum is also found integrated within the particles of cerium or zirconium oxides.

 According to another embodiment, usable when the particles of cerium oxide, zirconium or titanium present within the material are at least partially crystalline, the impregnation / heat treatment cycle of steps (b ') and (c ') can advantageously be used to integrate cations in solid solution within the crystal lattice of the oxide of said particles. In this case, the metal M 'used in steps (b') and (c ') can, in general, be chosen from any metal capable of being able to be incorporated in the cationic state in solid solution in an oxide. of cerium or of zirconium or of titanium, namely a metal corresponding to the definition of the doping elements M1 of these oxides as defined above in the present description. Preferably, the metal M 'denotes a metal chosen from cerium (in particular when the material comprises particles based on at least partially crystalline zirconium oxide or at least partially crystalline titanium oxide), zirconium (especially when the material comprises particles based on cerium oxide at least partially crystalline), or a rare earth other than cerium. Whatever its exact nature, this metal M is generally introduced into the material during step (b) in the form of a salt, for example a nitrate or an acetate, and step (b) can typically consist in carrying out an impregnation of the material with a solution of this salt, the pH of said solution preferably being between 0 and 8, this pH advantageously being less than 7. In the context of this embodiment

<Desc / Clms Page number 37>

 specific, the impregnation / heat treatment process of steps (b ') and (c') can lead, in parallel to the integration of the element M 'in solid solution within the oxide particles, to an integration of this element in cationic form or in the form of a cluster within and / or on the surface of the mineral binding matrix based on silica. In addition, at the end of a heat treatment step of type (c '), the formation of crystallites often based on a compound of metal M', in particular of the oxide, hydroxide, oxyhydroxide, carbonate or hydroxy-carbonate, at the surface of the binder phase, and / or at least partially integrated therein. One can also observe the formation of the aforementioned clusters or crystallites on the surface and / or within the oxide particles.

 Steps (b ') and (c') defined above can also be used to integrate within the material of the invention a compound of an alkali or alkaline earth metal. In this case, the metal M is an alkali or alkaline earth metal, preferably barium or potassium, and the compound of the metal M 'used is generally a salt, preferably a nitrate, a sulfate or a carbonate. , and preferably a sulfate or a carbonate, which is generally introduced in step (b ') in the form of an aqueous solution, the pH of said solution preferably being between 0 and 8.5, this pH advantageously being less than 8.

 Steps (b ') and (c') can also be advantageously used to integrate manganese within the material. In this case, the metal M 'denotes manganese, and the compound of the metal M' used is generally a salt, preferably a nitrate, which is generally introduced in step (b ') in the form of an aqueous solution of pH preferably less than 8.

 It is generally advantageous to conduct several successive cycles using steps of the type of steps (b ') and (c') defined above, the nature of the metal M'implemented being able to be identical or not during each of these cycles. It should however be noted that in the process of

<Desc / Clms Page number 38>

 the invention, it is often preferable to limit the number of impregnation / heat treatment cycles of the type of steps (b) and (c) or (b ') and (c'). Thus, in particular so as not to affect the mesostructure of the material, it is often preferable that the number of these cycles remains less than or equal to 5.4 and preferably less than or equal to 3.

 Furthermore, the order of integration of the various elements of type M 'introduced during these successive cycles is sometimes decisive, in particular as regards the quantities of metallic elements that can be introduced into the material. Thus, for example, if it is desired to synthesize a material according to the invention comprising (1) particles of cerium oxide doped with a metallic element of the cerium, zirconium or rare earth type, (2) a silica-based matrix comprising cations and / or clusters based on lanthanum and optionally (3) an alkaline or alkaline earth element and / or manganese, the respective integration steps of the dopant (zirconium or rare earth), lanthanum, alkali metal or alkaline earth, and manganese are preferably carried out in the following order: 10- integration of lanthanum; 2 "-integration of the dopant; 30- if necessary, integration of manganese; and 40-if necessary, integration of the alkali or alkaline-earth metal.

 In general, in the process of the present invention, the various heat treatment steps, of the type of steps (c) and (c '), which are implemented in the successive impregnation / heat treatment processes do not require in general the use of temperatures above 500 C. This can in particular be used when it is desired to integrate certain metallic compounds in the form of salts within the material, which can for example allow the integration of sulfate or alkali or alkaline earth metal carbonate within the material of the invention, the presence of which may prove to be particularly useful, in particular for certain catalytic applications such as the absorption, in an oxidizing atmosphere, of nitrogen oxides, such as the so-called compounds NOx. On the other hand, it is also possible, when desired for other catalytic applications, to

<Desc / Clms Page number 39>

 conduct the heat treatment steps at temperatures above 500 ° C., whereby the formation of metal oxides or hydroxides is generally observed, most often in the form of crystallites. Thus, the process of the present invention makes it possible to modulate to a fairly large extent the catalytic properties of the materials capable of being obtained according to the invention. The present invention thus makes it possible to obtain a very wide range of catalysts and functionalized supports for catalytic species.

 It should also be emphasized that, surprisingly, despite the impregnation / heat treatment steps imposed during the process of the invention, the solids obtained in the most general case have a BET specific surface which remains relatively high. , and which generally represents at least 50%, advantageously at least 60%, and even more preferably at least 75% of the BET specific surface of the mesostructured material obtained at the end of step (a).

 It should also be noted that the various stages of impregnation / heat treatment imposed during the process of the invention do not lead to a consequent reduction in accessibility to the particles compared to the accessibility to the particles presented in the mesostructure. performed in step (a). Thus, when the oxide particles introduced during step (a) are specifically based on cerium oxide, the reducibility of the material obtained following the various stages of impregnation / heat treatment is generally similar to that of the mesostructure. obtained at the end of step (a). Thus, if we denote by ta the conversion rate of cerium IV into cerium H! measured according to the above-mentioned "TPR" operating mode for the mesostructure carried out in step (a), and by tf the rate of conversion of cerium IV into cerium! t measured according to the above-mentioned "TPR" operating mode for the material obtained at the end of the various impregnation / heat treatment stages imposed during the process, the tf / ta ratio generally remains greater than or equal to 40%, this ratio being the more often at least equal to 50%, advantageously at least equal to 70%, and preferably at least equal to 80%.

<Desc / Clms Page number 40>

 Given their high specificity and their particular properties in terms of acid-basicity, associated with a reducible character, the materials of the present invention prove, in general, particularly useful as heterogeneous catalysts, in particular as heterogeneous acid-base or redox catalysts.

 These different uses constitute another object of the present invention.

 The characteristics and advantages of the present invention will appear even more clearly in the light of the illustrative examples set out below.

<Desc / Clms Page number 41>

Exemple 1 : Préparation d'un matériau mésostructuré intégrant, au sein d'une matrice minérale liante de silice, des particules nanométriques d'oxyde de cérium, la matrice liante de silice comprenant des cations aluminium en position tétraédrique 1-1. Préparation d'une dispersion colloïdale aqueuse (D) de particules d'oxyde de cérium On a obtenu une dispersion aqueuse de colloïdes cristallisés d'oxyde de cérium Ce02, de diamètre centré sur 5 nm, selon les étapes suivantes : - on a d'abord préparé un précipité à base de CeOz suivant le procédé de thermo-hydrolyse à 100 C d'une solution de nitrate cérique partiellement neutralisée décrit dans la demande de brevet EP 208 580.

Example 1: Preparation of a mesostructured material integrating, within a mineral silica-binding matrix, nanometric particles of cerium oxide, the silica-binding matrix comprising aluminum cations in tetrahedral position 1-1. Preparation of an aqueous colloidal dispersion (D) of cerium oxide particles An aqueous dispersion of crystallized colloids of cerium oxide CeO2, with a diameter centered on 5 nm, was obtained according to the following steps: First prepared a CeOz-based precipitate following the thermo-hydrolysis process at 100 C of a partially neutralized ceric nitrate solution described in patent application EP 208 580.

250 g of the thermohydrolysis precipitate obtained, 68.6% of CeO 2, were then dispersed in 200 g of demineralized water, then the mixture was left to stand overnight at ambient temperature. It was centrifuged at 4500 rpm for 15 minutes, then the supernatant phase was washed and concentrated, by ultrafiltration on a 3 KD membrane.

The concentration of the colloidal dispersion obtained was 43% by weight, ie 4.15 M in CeO2.

1-2. Preparation of a mesostructured Si02 / Ce02 compound (1) In a reactor, at room temperature, 2 g of Pluronics P123 (POE (2o) -PPO (7o) -POE (2o) copolymer) from the company were added BASF and 58, 1 g of demineralized water. 16.9 g of a 2 mol / liter HCl solution were then added. The mixture was stirred using a magnetic bar. The medium thus obtained was maintained at 37 C.

<Desc / Clms Page number 42>

 (2) Was added, with stirring and instantaneously, 4 g of the colloidal dispersion (D) previously prepared.

 (3) 2.08 g of TEOS (tetra-ethyl ortho-silicate, MW = 208 g) were then added at constant rate over one hour using a pump (KDS syringe pump).

The molar ratio (Si02 / Ce02) introduced is 50: 50
The reaction assembly was stirred at 37 ° C for 20 hours. The dispersion obtained was then transferred to a closed enclosure, then it was placed in the oven at 80 ° C. overnight.

 The solid product was recovered by centrifugation at 4500 rpm and then washed with a volume of demineralized water equivalent to the initial volume of the reaction assembly.

 After separation by centrifugation, the solid product was allowed to dry at room temperature under an air atmosphere.

 (4) The product was then calcined at temperature (5000C) for 6 hours. The temperature rise used was 1 C per minute.

 By BET adsorption measurements with nitrogen, the specific surface area measured for the mesostructured compound obtained is 380 m2 / g and the pore volume is 0.37 ml / g. The size of the mesopores is 4 nm.

 By transmission electron microscopy on samples subjected to an ultramicrotomy, an ordered texture of the material is observed.

 In the mesoporous structure observed in FIG. 3, the center-to-center distance of the pores determined is of the order of 14 nm.

analyse chimique localisée, on montre que ces particules de Ce02 sont parfaitement dispersées au sein des parois de Si02. At high resolution, we can distinguish perfectly crystallized particles of Ce02, inserted into the walls of the mesoporous structure. Through

localized chemical analysis, we show that these CeO2 particles are perfectly dispersed within the walls of SiO2.

<Desc / Clms Page number 43>

1-3. Impregnation and doping of the mesostructure obtained
2 g of the mesostructured material obtained in step 1-2 were introduced into 50 ml of a 0.25 mol / L aluminum nitrate solution in aluminum. This medium was placed under stirring for one hour at 25 C.

 The dispersion produced was then subjected to centrifugation at 4500 rpm for 15 minutes.

 The centrifugation pellet was collected and then dried, leaving it in the open air at 25 ° C. for 16 hours.

 The solid obtained was then placed in an oven at 800C for 8 hours.

 The solid was then gradually brought to 4000C, at the rate of a temperature rise of 10C per minute. The solid was then left at 400 C for 6 hours, then the temperature was allowed to gradually decrease to 25 C.

 The impregnation / heat treatment operation (immersion in 50 mL of a 0.25 mol / L aluminum nitrate solution in aluminum, stirring for one hour, centrifugation at 4,500 rpm for 15 minutes, drying of 16 hours at 25 C, 8 hours oven at 80 C, gradual rise in temperature 1 C per minute to 400 C, maintenance at 4000C for 6 hours and slow decrease in temperature) was renewed three times on solid obtained.

By fluorescence analysis under X-rays, the following molar proportions of the Ce, Si and AI cations are determined within the material obtained following these various steps: (Si: Ce: Al) = (46%: 46%: 8 %)
By BET analysis, the specific surface of the product obtained is measured equal to 271 m2 / g, and the porous distribution observed is centered on 4 to 5 nm.

<Desc / Clms Page number 44>

 By X-ray diffraction, we observe a spectrum attributable to pure cerium oxide.

 By solid NMR 27 AI, three well identified lines are observed corresponding to chemical shifts at 50 ppm, 25 ppm and 0 ppm. The percentage of aluminum in tetrahedral form (which corresponds to the peak at 50 ppm) is 40% compared to total aluminum.

Example 2 Preparation of a Mesostructured Material Integrating, Within a Mineral Silica Binding Matrix, Nanometric Cerium Oxide Particles, the Silica Binding Matrix Comprising Aluminum Cations in the Tetrahedral Position
2 g of a mesostructured material as obtained in step 1-2 of Example 1 were introduced into 50 mL of a 1.5 mol / L aluminum nitrate solution in aluminum. This medium was placed under stirring for one hour at 25 C.

 The dispersion produced was then subjected to centrifugation at 4500 rpm for 15 minutes.

 The centrifugation pellet was collected and then dried, leaving it in the open air at 25 ° C. for 16 hours.

 The solid obtained was then placed in an oven at 80 ° C. for 8 hours.

 The solid was then gradually brought to 400 ° C., at the rate of a temperature rise of 1 ° C. per minute. The solid was then left at 400 C for 6 hours, then the temperature was allowed to gradually decrease to 25 C.

 By fluorescence analysis under X-rays, the following molar proportions of the Ce, Si and AI cations are determined within the material obtained following these various steps: (Si: Ce: AI) = (45%: 45%: 10 %)

<Desc / Clms Page number 45>

By BET analysis, the specific surface of the product obtained was measured equal to 296 m2 / g, and the porous distribution observed is centered on 4 to 5 nm.

 By X-ray diffraction, we observe a spectrum attributable to pure cerium oxide.

 By solid NMR 27 AI, three well identified lines are observed corresponding to the chemical displacements 50 ppm, 25 ppm and 0 ppm. The percentage of aluminum in tetrahedral form (peaks at 50 ppm) is 35% compared to total aluminum.

Example 3: Preparation of a mesostructured material integrating, within a mineral silica-binding matrix, nanometric particles of cerium oxide, the silica-binding matrix comprising aluminum cations in tetrahedral position. Additional doping with lanthanum
20 g of the mesostructured material as obtained in step 1-2 of Example 1 were introduced into 200 ml of a 1.5 mol / L aluminum nitrate solution in aluminum. This medium was placed under stirring for one hour at 25 C.

 The dispersion produced was then subjected to centrifugation at 4500 rpm for 15 minutes.

 The centrifugation pellet was collected and then dried, leaving it in the open air at 250C for 16 hours.

 The solid obtained was then placed in an oven at 800C for 8 hours.

 The solid was then gradually brought to 400 ° C., at the rate of a temperature rise of 10 ° C. per minute. The solid was then left at 4000C for 6 hours, then the temperature was allowed to gradually decrease to 25 C.

<Desc / Clms Page number 46>

 The solid thus obtained was immersed in 200 ml of a lanthanum nitrate solution at 1 mol / L in lanthanum. This medium was placed under stirring for one hour at 25 C.

 The dispersion produced was then subjected to centrifugation at 4500 rpm for 15 minutes.

 The centrifugation pellet was collected and then dried, leaving it in the open air at 25 ° C. for 16 hours.

 The solid obtained was then placed in an oven at 800C for 8 hours.

 The solid was then gradually brought to 400 ° C., at the rate of a temperature rise of 10 ° C. per minute. The solid was then left at 400 C for 6 hours, then the temperature was allowed to gradually decrease to 25 C.

 By Solid NMR 27AI, three well identified lines are observed corresponding to the chemical displacements 50 ppm, 25 ppm and 0 ppm. The percentage of aluminum in tetrahedral form (peaks at 50 ppm) compared to total aluminum is estimated to be around 35%.

 The solid was then brought to 800 C at the rate of a temperature rise of 1 C per minute. The solid was then left at 8000C for 6 hours, then the temperature was allowed to gradually decrease to 25 C.

By X-ray fluorescence analysis, the following molar proportions of the Ce, Si and AI cations are determined within the material obtained following these various steps:

By BET analysis, the specific surface of the product obtained is measured equal to 120 m2 / g, and the porous distribution observed is centered on 5 to 6 nm.

<Desc / Clms Page number 47>

 By X-ray diffraction, we observe a spectrum slightly shifted towards the great inter reticular distances compared to the spectrum of a pure cerium oxide.

 By solid NMR 27 AI, three well identified lines are observed corresponding to the chemical displacements 50 ppm, 25 ppm and 0 ppm. The percentage of aluminum in tetrahedral form (peaks at 50 ppm) compared to total aluminum is 35%.

Example 4 Preparation of a Mesostructured Material Integrating, Within a Mineral Silica Binding Matrix, Nanometric Cerium Oxide Particles, the Silica Binding Matrix Comprising Titanium Cations in the Tetrahedral Position
20 g of the mesostructured material as obtained in step 1-2 of Example 1 were introduced into a solution of acidified butyl titanate Ti (OBu) 4, obtained by dissolving 68.2 g of butyl titanate in 200 mL of ethanol and 33 mL of 15N nitric acid. This medium was stirred for one hour at 25 C.

 The dispersion produced was then subjected to centrifugation at 4500 rpm for 15 minutes.

 The centrifugation pellet was collected and then dried, leaving it in the open air at 25 ° C. for 16 hours.

 The solid obtained was then placed in an oven at 80 ° C. for 8 hours.

 The solid was then gradually brought to 400 ° C., at the rate of a temperature rise of 10 ° C. per minute. The solid was then left at 4000C for 6 hours, then the temperature was allowed to gradually decrease to 25 C.

<Desc / Clms Page number 48>

By fluorescence analysis under X-rays, the following molar proportions of the Ce, Si and Ti cations are determined within the material obtained following these various steps:

By BET analysis, the specific surface of the product obtained is measured equal to 249 m2 / g, and the porous distribution observed is centered on 5 to 6 nm.

 By X-ray diffraction, we observe a spectrum attributable to pure cerium oxide.

 By Solid NMR 27 Si, a reduction in the intensity of the line is observed corresponding to the chemical displacement of the species Q4 silicon towards -110 ppm, in comparison with a reference spectrum produced on the initial sample Si02-Ce02, as obtained in step 1-2 of Example 1.

 The solid was then gradually brought to 800 ° C., at the rate of a temperature rise of 10 ° C. per minute. The solid was then left at 800 C for 6 hours, then the temperature was allowed to gradually decrease to 25 C.

 By BET analysis, the specific surface of the product obtained is measured equal to 120 m2 / g, and the porous distribution observed is centered on 5 to 6 nm.

 By X-ray diffraction, we observe a spectrum of lines attributable to pure cerium oxide and the presence of lines attributable to titanium oxide of anatase structure.

<Desc / Clms Page number 49>

Example 5 Preparation of a Mesostructured Material Integrating, Within a Mineral Silica Binding Matrix, Nanometric Cerium Oxide Particles, the Silica Binding Matrix Comprising Titanium Cations and Aluminum Cations in the Tetrahedral Position
20 g of the mesostructured material as obtained in step 1-2 of Example 1 were introduced into 200 ml of a 1.5 mol / L aluminum nitrate solution in aluminum. This medium was placed under stirring for one hour at 25 C.

 The dispersion produced was then subjected to centrifugation at 4500 rpm for 15 minutes.

 The centrifugation pellet was collected and then dried, leaving it in the open air at 25 ° C. for 16 hours.

 The solid obtained was then placed in an oven at 80 ° C. for 8 hours.

 The solid was then gradually brought to 400 ° C., at the rate of a temperature rise of 1 ° C. per minute. The solid was then left at 400 C for 6 hours, then the temperature was allowed to gradually decrease to 25 C.

 The solid obtained was then immersed in 200 ml of a solution of acidified butyl titanate obtained by dissolving 68.2 g of butyl titanate in 200 ml of ethanol and 26.6 ml of 15 N nitric acid. placed this medium under stirring for one hour at 25 C.

 The dispersion produced was then subjected to centrifugation at 4500 rpm for 15 minutes.

 The centrifugation pellet was collected and then dried, leaving it in the open air at 25 ° C. for 16 hours.

<Desc / Clms Page number 50>

 The solid obtained was then placed in an oven at 800C for 8 hours.

 The solid was then gradually brought to 400 ° C., at the rate of a temperature rise of 10 ° C. per minute. The solid was then left at 400 C for 6 hours, then the temperature was allowed to gradually decrease to 25 C.

 The solid is then again calcined at 800 C at the rate of a temperature rise of 1 C per minute. The solid was then left at 8000C for 6 hours, then the temperature was allowed to gradually decrease to 25 C.

 By BET analysis, the specific surface of the product obtained is measured equal to 90 m2 / g, and the porous distribution observed is centered on 5 to 6 nm.

 By X-ray diffraction, we observe a spectrum of lines attributable to pure cerium oxide and the presence of lines attributable to titanium oxide of anatase structure.

Claims (37)

 CLAIMS 1. Mesostructured material, with BET specific surface area greater than or equal to 400 m2 per cm3, comprising particles (p) of nanometric dimensions based on a metal oxide chosen from a cerium oxide, a zirconium oxide or an oxide of titanium, said particles (p) being linked to one another by an inorganic matrix (m), said matrix being based on a silica containing cations of a metal M chosen from aluminum or titanium, with at least one part of these cations in a tetrahedral position within said silica, and in which: (i) the quantity of metal M present in the state of cations in a tetrahedral position within silica represents at least 10% by mole of the total quantity of metallic element M present in the material, with a total amount of metallic element M present in the material being such that the overall molar ratio M / Si of the material is greater than or equal to 5%; (ii) the metal cations M present in the silica are distributed in the mineral phase (m) with a decreasing concentration gradient from the surface to the core; and (iii) the particles (p) present within the material have a partially accessible surface.  2. Material according to claim 1, characterized in that the total quantity of metallic element M present in the material is such that the overall molar ratio M / Si of the material is greater than or equal to 10%.  3. Material according to claim 1 or according to claim 2, characterized in that the metal cations of the metal M integrated in tetrahedral position within the silica of the mineral matrix (m) represent at least 15% of the total amount of metallic element M present in the material. <Desc / Clms Page number 52>  4. Material according to any one of claims 1 to 3, characterized in that it specifically comprises aluminum cations in tetrahedral position within the silica of its mineral matrix (m).  5. Material according to claim 4, characterized in that the molar ratio of the amount of aluminum cations in tetrahedral position relative to the total amount of aluminum cations present in said material is at least 20% by mole.  6. Material according to claim 4 or according to claim 5, characterized in that the AI / Si molar ratio of the total amount of aluminum present relative to the total amount of silicon present is between 5% and 50%.  7. Material according to any one of claims 1 to 3, characterized in that it specifically comprises titanium cations in a tetrahedral position within the silica of its mineral matrix (m).  8. Material according to claim 7, characterized in that the molar ratio of the amount of titanium cations in the tetrahedral position relative to the total amount of titanium cations present in said material is at least equal to 10% by mole.  9. Material according to claim 7 or according to claim 8, characterized in that the Ti / Si molar ratio of the total amount of titanium present relative to the total amount of silicon present is between 5% and 80%.  10. Material according to any one of claims 1 to 9 characterized in that it comprises, in the tetrahedral position within the silica of its mineral matrix (m), both aluminum cations and titanium cations.  11. Material according to any one of claims 1 to 10, characterized in that it is thermally stable. <Desc / Clms Page number 53>  12. Material according to any one of claims 1 to 11, characterized in that it has, at least at a local level, one or more mesostructure (s) chosen (s) from mesoporous mesostructures of three-dimensional hexagonal symmetry P63 / mmc, two-dimensional hexagonal symmetry, three-dimensional cubic symmetry la3d, Im3m or Pn3m; among mesostructures of the vesicular or lamellar type, or among mesostructures of the vermicular type.  13. Material according to any one of claims 1 to 3, characterized in that the particles (p) are particles of spherical or isotropic morphology in which at least 50% of the population has an average diameter between 1 and 10 nm.  14. Material according to any one of claims 1 to 13, characterized in that the molar ratio Si02 / (Ce02 + Zr02 + Ti02) within said material is between 20: 80 and 99.5: 0.5.  15. Material according to any one of claims 1 to 14, characterized in that the particles (p) are at least partially crystalline particles, within which the cerium oxide, zirconium oxide or the oxide of titanium has a degree of crystallinity ranging from 30 to 100% by volume.  16. Material according to claim 15, characterized in that the cerium oxide, zirconium oxide, or at least partially crystalline titanium oxide comprises at least one metallic element M1, in cationic form, in solid solution at within its crystal lattice.  17. Material according to claim 16, characterized in that the particles (p) are particles based on a cerium oxide at least partially crystalline, and in that the element M1 is chosen from rare earths other than the cerium, the transition metals capable of being able to be integrated in cationic form in solid solution within a cerium oxide, or else among the alkaline-earth metals. <Desc / Clms Page number 54>  18. Material according to claim 16, characterized in that the particles (p) are particles based on an zirconium oxide at least partially crystalline, and in that the metal M1 is chosen from cerium, rare earths other as cerium, the transition metals capable of being able to be integrated in cationic form in solid solution within a zirconium oxide, or else among the alkaline-earth metals.  19. Material according to claim 16, characterized in that the particles (p) are particles based on an at least partially crystalline titanium oxide, and in that the metal M1 is chosen from rare earths, the metals of transition capable of being able to be incorporated in cationic form in solid solution within a titanium oxide, or else among the alkaline earth metals.  20. Material according to any one of claims 1 to 19, characterized in that it further comprises crystallites based on hydroxide or oxy-hydroxide of the metal M.  21. Material according to any one of claims 1 to 20, characterized in that it further comprises cations of at least one metal M2 or clusters based on said metal M2, this metal M2 being chosen from alkali metals or alkaline earth, rare earths, or manganese.  22. Material according to any one of claims 1 to 21, characterized in that it further comprises crystallites based on oxide, hydroxide, oxy-hydroxide, carbonate or hydroxy-carbonate d a metal M1 as defined in claims 16 to 19, or a metal M2 as defined in claim 21.  23. Material according to any one of claims 1 to 22, characterized in that it further comprises lanthanum compounds, at least in the form of lanthanum cations and / or lanthanum-based clusters within its matrix ( m) and / or at the surface of this matrix (m). <Desc / Clms Page number 55>  24. Material according to any one of claims 1 to 23, characterized in that it comprises: - particles (p) of cerium or zirconium oxide, doped with a metallic element M1 as defined in claims 16 at 19; and - a matrix (m) comprising cations and / or lanthanum-based clusters.  25. Material according to claim 24, characterized in that it further comprises an alkaline or alkaline-earth element and / or manganese.  26. A method of preparing a material according to any one of claims 1 to 25, characterized in that it comprises the steps consisting in: (a) producing a mineral mesostructure integrating, within its walls, particles of nanometric dimensions based on a cerium oxide, a zirconium oxide, or a titanium oxide, linked together by an inorganic matrix based on silica, said matrix not completely covering said particles; (b) introducing into the mesoporous structure thus obtained a compound of element M, the total content of element M introduced into the structure, relative to the total surface developed by the mesostructure, being less than 5 micromoles of cation per m2 of surface; and (c) subjecting the mesostructure thus produced to a temperature at least equal to 300 C and not higher than 1000 C.  27. Preparation process according to claim 26, characterized in that step (a) is carried out by implementing the steps consisting in: <Desc / Clms Page number 56>  (a1) forming an initial medium comprising a texturing agent, namely an amphiphilic compound of surfactant type capable of forming micelles in the reaction medium; (a2) adding in the middle of step (a1) a colloidal dispersion of particles of nanometric dimensions; (a3) forming, by adding a mineral precursor of the alkali silicate or silicon alkoxide type to the medium, a mesostructured mineral phase, at least partially made of silica, said mineral phase then integrating, within its mesostructured walls, at least part of the particles of nanometric dimensions introduced during step (a2); and (a4) removing the texturing agent by heat treatment or entrainment with a solvent.  28. Preparation process according to claim 26 or according to claim 27, characterized in that the mesostructure produced during step (a) has a BET specific surface at least equal to 1500 m2 per cm3 of material.  29. Preparation process according to any one of claims 26 to 28, characterized in that step (b) is carried out: - by immersing the mesostructured material obtained at the end of step (a) within d 'A solution comprising the element M at a concentration between 0.1 and 1.5 mol / L, then by filtering the medium obtained; or - by immersing the mesostructured material obtained at the end of step (a) in a solution comprising the element M at a concentration of between 0.2 and 1.5 mol / L, then subjecting the medium obtained by centrifugation, at the rate of 2000 to 5000 revolutions per minute, for a duration not exceeding 30 minutes; or - by adding to the mesostructured material obtained at the end of step (a) a volume V, representing between 0.2 and 3 times the volume of the material, of a solution <Desc / Clms Page number 57>  comprising the element M at a concentration between 0.1 and 2 mol / L, then evaporating the solvent in the mixture obtained.  30. Preparation process according to any one of claims 26 to 29, characterized in that it comprises, following the impregnation / heat treatment process of steps (b) and (c), one or more subsequent cycles of impregnation / heat treatment using steps of type (b) and (c), carried out on the solid obtained at the end of the previous cycle.  31. Preparation process according to any one of claims 26 to 30, characterized in that it further comprises steps consisting in: (b ') introducing, into at least part of the porous zones of the material, a compound of a metal M 'different from the metal M (the content of said element M' introduced into the structure, relative to the total surface developed by the mesostructure, being less than 5 micromole of cation per m2 of surface; and (c ') subjecting the material thus impregnated to a temperature at least equal to 300 C, and not higher than 1000 C.  32. Preparation process according to claim 31, characterized in that the said process comprises several successive cycles implementing steps of the type of the steps (b ') and (c'), the nature of the metal M 'used being or not the same during each of these cycles.  33. Use of a material according to any one of claims 1 to 25 or of a material capable of being obtained according to any one of claims 26 to 32, as heterogeneous acid-base or redox catalyst.  34. Use of a material according to claim 23, for the heterogeneous catalysis of a hydrocarbon oxidation reaction. <Desc / Clms Page number 58>  35. Use of a material according to claim 25, as catalysts for the absorption of nitrogen oxides.  36. Use of a material according to one of claims 16 to 19, as supports for catalytic species.  37. Catalyst capable of being obtained by supporting catalytic species on a material according to one of claims 16 to 19.