Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B37/00—Compounds having molecular sieve properties but not having base-exchange properties
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]

Definitions

• the present invention relates to a new ordered, partially crystalline, mesostructured or mesoporous material, consisting of cerium oxide, zirconium or titanium.
• mesoporous compounds are solids having, within their structure, pores having a size intermediate between that of the micropores of materials of the zeolite type and that of the macroscopic pores. More precisely, the expression “mesoporous compounds” originally denotes a compound which specifically comprises pores with an average diameter of between 2 and 50 nm, designated by the term “mesopores”. Typically, these compounds are amorphous or paracristalline silica type compounds in which the pores are generally distributed randomly, with a very wide distribution of the pore size.
• the so-called “structured” compounds are, for their part, compounds having an organized structure, and characterized more precisely by the fact that they exhibit at least one scattering peak in a radiation scattering diagram of the type scattering by X-rays or neutrons.
• Such diffusion diagrams as well as their method of obtaining are notably described in Small Angle X-Rays Scattering (Glatter and Kratky - Académie Press London - 1982).
• the diffusion peak observed in this type of diagram can be associated with a repetition distance characteristic of the compound considered, which will be designated in the remainder of this description by the term "spatial repetition period" of the structured system.
• the term “mesostructured compound” means a structured compound having a spatial repetition period included between 2 and 50 nm.
• the organized structure present in such a material will be designated here by the term “mesostructure”.
• the ordered mesoporous compounds constitute a special case of mesostructured compounds. These are in fact mesoporous compounds which exhibit an organized spatial arrangement of the mesopores present in their structure, and which therefore effectively have a repeating spatial period associated with the appearance of a peak in a diffusion diagram.
• the ordered mesostructured or mesoporous compounds comprising a mineral phase are well known and are of great interest, in particular in the field of catalysis, absorption chemistry or membrane separation.
• doped that is to say comprising a metallic element, other than the metallic element forming the oxide, in solid solution within the crystal lattice of said oxide.
• the object of the present invention is to obtain materials which meet these needs.
• the material of the invention is a partially crystalline mesostructured material, which essentially consists of a compound chosen from cerium oxide, zirconium oxide, titanium oxide or a mixture of these compounds. and it is characterized in that it comprises at least one element M in solid solution in said oxide.
• the invention relates to a process for the preparation of such a material which is characterized in that it comprises the following stages:
• a partially crystalline mesostructured material is brought into contact, consisting essentially of a compound chosen from cerium oxide, zirconium oxide, titanium oxide or a mixture of these compounds with a solution of 1 element M which has a concentration of this element of at most 2 mol / l;
• Mesostructured should be understood as applying to both mesostructured and ordered mesoporous materials.
• rare earth is meant an element chosen from yttrium or the lanthanides, the lanthanides designating all of the elements whose atomic number is inclusive, between 57 (lanthanum) and 71 (lutetium).
• transition metals is meant the elements included in groups IIIA to IIB inclusive of the periodic table. The periodic classification of the elements to which reference is made is that published in the Supplement to the Bulletin of the French Chemical Society n ° 1 (January 1966).
• specific surface is meant the BET specific surface determined by nitrogen adsorption in accordance with standard ASTM D 3663-78 established on the basis of the BRUNAUER - EMMETT-TELLER method described in the periodical "The Journal of the American Chemical Society , 60, 309 (1938) ".
• the material of the invention consists essentially of a compound chosen from cerium oxide Ce0 2 , zirconium oxide Zr0 2 , titanium oxide Ti0 2 or a mixture of these compounds in any proportions. As mixtures of these compounds, mention may very particularly be made of Ce ⁇ 2 / Zr0 2 mixtures in which cerium is predominant and Zr0 2 / Ce0 2 mixtures in which zirconium is predominant.
• the abovementioned oxides are in the form of particles of nanometric size.
• nanometric particles is meant, within the meaning of the present invention, particles preferably of spherical or isotropic morphology of which at least 50% of the population has an average diameter between 1 and 10 nm, advantageously less than 6 nm , with a particle size distribution of these particles, preferably monodisperse.
• particles of nanometric size can also designate according to the invention anisotropic particles, of rod type, on the condition that, for at least 50% of the population of these particles, the mean transverse diameter is understood between 1 and 10 nm and the length does not exceed 100 nm, with a particle size distribution of these preferably monodisperse particles.
• the material of the invention is partially crystalline or, in other words, the particles of nanometric dimension which constitute it are particles at least partially crystalline, that is to say that they have a degree of crystallinity greater than 20%. , preferably at least 30%, this rate being able to go up to 100% by volume.
• This degree of crystallinity can be calculated by the ratio of the area of a diffraction peak measured by X-ray diffraction for a sample of the material according to the invention to the area of the same diffraction peak measured for a control sample in which l he constituent element of the particle is in a fully crystallized state and corrected for the absorption coefficients of the corresponding oxides.
• the “crystallinity” of the material corresponds to a microscopic organization detectable in particular by diffraction (for example by X-ray diffraction at wide angles), which is to be distinguished in particular from the "order" presented, at a more macroscopic level, by the mesostructure of the material.
• material composed essentially of a cerium, zirconium and / or titanium oxide is meant a compound which does not specifically contain any additional element introduced so as to ensure cohesion of the material.
• the materials composed essentially of a cerium, zirconium and / or titanium oxide within the meaning of the present invention are not materials comprising a mineral phase of silica or alumina type playing the role of binder between particles of cerium oxide, zirconium oxide and / or titanium oxide.
• the essential characteristic of the material of the invention is that it contains an element M in solid solution in the oxide constituting the material, that is to say in the oxide of cerium, zirconium and / or titanium.
• This element M is in the cationic state, generally in solid solution of insertion and / or substitution, within the crystal structure of the oxide.
• element in solid solution within an oxide is understood to mean the presence of this element as a cation, by way of an insertion and / or substitution cation, within a crystalline oxide typically playing the role of a host crystal lattice, said cation of the element M generally representing strictly less than 50% by mole of the total quantity of metal cations present in the oxide (cations of the metal of the oxide + cations of the metal M), c ' that is to say that the cation integrated in solid solution is preferably a minority cation compared to the constituent cations of the metal oxide where it is integrated in solid solution, the content of this cation of the element M however being able to reach 50% in some cases.
• a crystalline oxide integrating cations in solid solution consents 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 more or less significant shift of the peaks.
• element M is chosen from rare earths and transition metals capable of being able to be integrated in cationic form in solid solution within a cerium oxide, a zirconium oxide and / or an oxide. titanium.
• the metal M can be chosen more specifically according to the nature of the metal oxide within which it is integrated in solid solution. Note that the quantity of metal M that we can introducing into a solid solution within the oxide depends on the nature of said metal M and on the nature of the constituent element of said oxide.
• the element M present in solid solution can, in general, be chosen from rare earths other than cerium.
• the metal M can be more particularly lanthanum, Pyttrium, neodymium, praseodymium, dysprosium or europium.
• Element M can also be chosen from transition metals capable of being able to be integrated in cationic form in solid solution within a cerium oxide, in particular zirconium, manganese and titanium.
• the quantity of cations of the metal M which can be integrated in solid solution can represent a value such that the molar ratio M / Ce is at most 1
• the quantity of titanium which can be integrated in solid solution can represent a value such that the molar ratio Ti / Ce is at most 0.5.
• the metal M present in solid solution can be chosen from cerium and rare earths other than cerium.
• M can advantageously be cerium, lanthanum, yttrium, neodymium, praseodymium, dysprosium or europium.
• M can also be chosen from transition metals capable of being able to be integrated in cationic form in solid solution within a zirconium oxide.
• the doping metal M represents cerium or another rare earth
• the quantity of cations of the metal M which can be integrated in solid solution can represent a value such that the molar ratio M / Zr is at most 1.
• the metal M present in the cationic state in solid solution can also be chosen from rare earths, the transition metals capable of being able to be integrated in solid solution within an oxide. titanium.
• the metal M can be more particularly manganese, tin, vanadium, niobium, molybdenum or antimony.
• the element M is chosen from titanium, cerium, zirconium, manganese, lanthanum, praseodymium and neodymium, said element M being different from the element constituting the material oxide (cerium, zirconium or titanium oxide).
• the material may also comprise metal cations of the metal M or of an alkali or alkaline earth metal and / or clusters based on the metal M or of an alkali or alkaline earth metal and / or crystallites of these same elements. These cations, these clusters or these crystallites are dispersed, preferably homogeneously, on the surface of the oxide constituting the material.
• the crystallites can be, for example, Ti0 2 crystallites in anatase form, Zr0 2 crystallites and, for the alkalis or alkaline earths, hydroxides, carbonates, hydroxycarbonates or other salts.
• cluster based on the metal M, is meant a polyatomic entity of dimension less than 2 nm, preferably less than 1 nm, comprising at least atoms of the metal M, 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 bridges -O- or -OH-, each of the atoms of the metal M being able to be linked to one or more groups -OH).
• This variant can be applied in particular to the case where the metal M is zirconium, manganese, or even a rare earth (in particular lanthanum, yttrium, neodymium, praseodymium, dysprosium or europium).
• a rare earth in particular lanthanum, yttrium, neodymium, praseodymium, dysprosium or europium.
• the amount of this alkali or alkaline earth metal under this form is generally between 2% and 30%.
• the ratio expressed in moles of M relative to the moles of the constituent oxide or oxides and of metal M can vary between 2% and 80%.
• the mesostructured materials of the present invention are solids having, at least at a local level, one or more mesostructure (s) chosen from: mesoporous mesostructures of three-dimensional hexagonal symmetry P63 / mmc, of two-dimensional hexagonal symmetry P6mm , with three-dimensional cubic symmetry Ia3d, Im3m or Pn3m; mesostructures of the vesicular, lamellar or vermicular type or mesostructures of L3 symmetry known as the sponge phase.
• mesostructure chosen from: mesoporous mesostructures of three-dimensional hexagonal symmetry P63 / mmc, of two-dimensional hexagonal symmetry P6mm , with three-dimensional cubic symmetry Ia3d, Im3m or Pn3m; mesostructures of the vesicular, lamellar or vermicular type or mesostructures of L3 symmetry known as the sponge phase.
• the pores observed within the mesostructure of the material of the invention are generally such that at least 50% of the population of pores present within the structure has an average diameter of between 2 and 10 nm.
• the average thickness of the walls of the structure of said material is between 4 and 10 nm.
• the materials of the invention generally have, after their preparation, a high BET specific surface area, of at least 600 m 2 / cm 3 , more particularly of at least 800 m 2 / cm 3 and even more particularly of at least 1000m 2 / cm 3 .
• this surface can be at least 100m 2 / g, more particularly at least 120m 2 / g and even more particularly d '' at least 140m 2 / g.
• this surface can be at least
• the pore volume of the materials of the invention is generally at least 0.10 cm 3 / g, more particularly at least 0.15 cm 3 / g and even more particularly at least 0.20 cm 3 / g.
• a 100 mg sample of the solid to be tested is placed at room temperature (generally between 15 ° C and 25 ° C) under a gas flow of a hydrogen / argon mixture containing 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.
• 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.
• a conversion rate of the cerium IV species initially present is generally measured which is at least 30%, this conversion rate advantageously being at least 40%, more preferably at least equal to 50%.
• the cerium reduction peak determined by the above protocol is centered on temperatures of at most 450 ° C, preferably of at most 400 ° C and even more preferably of at most 375 ° C.
• the first step of this process consists in bringing a starting material into contact with a solution of element M.
• the starting material is a partially crystalline mesostructured material, essentially consisting of a compound chosen from cerium oxide, zirconium oxide, titanium oxide or a mixture of these compounds and which can be prepared by any known means.
• a process for preparing such a starting material mention may be made more particularly of that described in patent application WO 01/49606, to the teaching of which it will be possible to refer and whose main characteristics are recalled below.
• This preparation process comprises the stages consisting in forming an initial dispersion comprising colloidal particles of nanometric size at least partially crystalline and a texturing agent; then concentrating the dispersion obtained so as to obtain a solid by texturing and progressive consolidation of the colloidal particles; and finally removing the texturing agent from the solid obtained.
• Said colloidal particles of nanometric size are particles based on at least one compound of a metal chosen from cerium, zirconium or titanium, preferably chosen from particles of cerium oxide Ce0 2 , of oxide of zirconium Zr0 2 and titanium oxide Ti0 2 .
• the colloidal particles of the compound of cerium, titanium or zirconium are functionalized with a surfactant of formula X-A-Y.
• the surfactant can also be in free form within the dispersion comprising the particles.
• This surfactant is an organic compound in which A is an optionally substituted linear or branched alkyl group, which can for example comprise from 1 to 12 carbon atoms, preferably between 2 and 8 carbon atoms.
• Function X is a complexing function of the metal cation of the colloid of the colloidal dispersion of the compound of cerium, titanium or zirconium.
• complexing function is meant a function which allows the formation of a complexing bond between the colloid cation, for example the cerium cation, and the surfactant.
• This function can be a function of the phosphonate -PO 3 2 "type , or phosphate -PO 2" , carboxylate -CO 2 " , or sulphate - SO 2" , sulphonate -SO 3 2 for example.
• the Y function is an amino or hydroxy function. It can be an amino function of the type - NH 2 , - NHR 1 , or - NR 2 R 1 , or - NH 4 + , Ri and R 2 , identical or different, denoting a hydrogen or an alkyl group comprising from 1 to 8 carbon atoms. It can also be an OH function. Among the agents with OH functions, there may be mentioned for example glycolic acid, gluconic acid, lactic acid, hydroxybenzoic acid, glycerol disodium phosphate.
• surfactants which are particularly suitable, mention may be made of amino acids, and in particular aliphatic amino acids.
• amino acids constituting proteins of structure R— CH (NH 2 ) - COOH where R is an aliphatic radical.
• R is an aliphatic radical.
• the preferred surfactant is aminohexanoic acid.
• the amount of surfactant used to functionalize the compound of the dispersion is expressed by the ratio Rb, determined by the following formula:
• the ratio Rb is advantageously between 0.1 and 0.5.
• the functionalization of the cerium, titanium or zirconium compound is carried out by bringing a dispersion of said compound into contact with the surfactant.
• the texturing agent used is a nonionic surfactant of the block copolymer type, preferably chosen from polyblock (ethylene oxide) copolymers ) -poly (propylene oxide) - poly (ethylene oxide) or the grafted poly (ethylene oxide).
• the texturing agent used is then a surfactant of primary alkylamine type.
• the solution of element M used in the case of the process according to the invention is usually an aqueous solution based on salts of this element. You can choose the salts of inorganic acids such as nitrates, sulfates or chlorides.
• salts of organic acids and in particular the salts of saturated aliphatic carboxylic acids or the salts of hydroxycarboxylic acids.
• an aqueous or hydro-alcoholic solution comprising cations of the metal M in the complexed state, or alternatively a solution, generally in an anhydrous organic solvent medium, comprising an alkoxide of the metal M.
• titanium it is possible to use more particularly a titanium alkoxide in an acidified hydroalcoholic medium.
• the solution which is brought into contact with the starting material has a concentration of this element M which is at most 2M, preferably at most 1, 2M. A higher concentration may prevent the formation of a solid solution of element M in the oxide constituting the material.
• the contacting can be done by immersing the starting mesostructured material in a solution comprising the element M and then subjecting the medium obtained to centrifugation.
• the centrifugation is carried out, at a rate of 2000 to 5000 revolutions per minute, for a duration generally not exceeding 30 minutes.
• the contacting is done by dry impregnation.
• Dry impregnation consists in adding to the product to be impregnated a volume of an aqueous solution of element M which is equal to the pore volume of the material to be impregnated.
• This calcination step is essentially intended to achieve at least partial integration of cations of the element M in solid solution within the oxide constituting the mesostructured material.
• this calcination is carried out at a temperature at least equal to 300 ° C., this temperature preferably being at least equal to 350 ° C. but it is at most 500 ° C. Higher temperatures are not required with respect to the integration of the cations of the element M within the oxide.
• the process of the present invention makes it possible, surprisingly, to integrate metal cations in solid solution for insertion and or substitution within the metal oxide of the material at low temperatures.
• the calcination step 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 500 ° C, advantageously with a temperature rise of between 0.5 ° C per minute and 2 ° C per minute, and with one or more successive stages of maintaining at intermediate temperatures, preferably between 350 and 500 ° C, for variable durations, generally between 1 hour and 24 hours.
• the preparation process of the invention may include a drying step, prior to calcination.
• this preliminary drying is generally carried out in the slowest possible way, in particular so as to favor the ionic exchanges.
• the drying is most often carried out at a temperature between 15 and 80 ° C, preferably at a temperature below 50 ° C, or even 40 ° C, 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.
• the drying is advantageously carried out in a water-free atmosphere.
• the method of the invention may comprise, following steps (a) and (b), one or more subsequent contacting / calcination cycles implementing steps of type (a) and (b), conducted on the solid obtained at the end of the previous cycle.
• steps (a) and (b) By implementing this type of process with several successive contacting / calcining cycles, it is possible to achieve very good incorporation of the element M in solid solution within the oxide particles. These cycles are repeated until a material with the desired content of element M is obtained. It is also possible to envisage the implementation of several contacting / calcination cycles using doping elements of the type M separate, whereby one can obtain materials consisting of oxides doped with several metallic elements in solid solution.
• solutions of salts of inorganic acids such as nitrates, sulfates or chlorides are generally used. It is also possible to use the salts of organic acids and in particular the salts of saturated aliphatic carboxylic acids or the salts of hydroxycarboxylic acids. By way of examples, mention may be made of formates, acetates, propionates, oxalates or citrates.
• the materials of the present invention may prove to be particularly useful as heterogeneous catalysts, in particular as acidic heterogeneous catalysts. , basic or redox.
• the materials of the invention based on cerium oxide particles integrating in solid solution zirconium or a rare earth and more particularly praseodymium, or conversely the materials to based on zirconium oxide particles integrating cerium in solid solution prove to be particularly advantageous insofar as they have significant oxygen storage capacities.
• the materials of the invention based on cerium oxide particles integrating zirconium in solid solution also exhibit, in general, significant thermal stability.
• the materials of the invention in particular materials based on cerium oxide particles integrating cations of zirconium or of a rare earth (other than cerium) in solid solution, can prove to be particularly useful for title of supports for catalytic species, in particular metallic species of noble metals type (platinum for example).
• the invention therefore also relates to catalysts which contain catalytic species on a support which is a material of the type of that described above or a material capable of being obtained by a process of the type of that also described above.
• catalytic species can be precious metals such as platinum, palladium, rhodium for example. Examples will now be given.
• This example relates to a mesostructured material consisting of cerium oxide and further comprising zirconium.
• the mesostructured material consisting of cerium oxide was firstly prepared according to the method described in Example 1 of WO-A-01/49606.
• 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 in air at the rate of a temperature rise of 1 ° C / min.
• the solid was then left at 400 ° C for 6 hours, then the temperature was allowed to gradually decrease to 25 ° C.
• the specific surface of the product obtained is measured equal to 105 m 2 / g and the pore distribution observed is centered on 4 nm with a pore volume of 0.145 cm 3 / g.
• This example relates to a mesostructured material consisting of cerium oxide and further comprising praseodymium.
• a solution of Pr (NO 3 ) 3 at 1.21 M in Pr is prepared by addition to 51.9 ml of solution of Pr (NO 3 ) 3 at 2.91 M in Pr, with a density of 1.73 and 28, 6% of praseodymium oxide contained in demineralized water until a final volume of 125 cm 3 is obtained.
• the mesostructured material of example 1 is also used. 8 g of this material (i.e. 46.51 millimoles of Ce) are impregnated with 5.76 cm 3 of solution of the praseodymium nitrate solution previously prepared at 1.21 M in Pr (i.e. 6.97 millimoles of Pr). The molar ratio (Pr / Ce) is then equal to 0.15. The product is dried at room temperature for 16 hours, then at 80 ° C for 8 hours. The product is then calcined in air at 400 ° C with a temperature rise of 1 ° C / min and a plateau of 6 hours.
• the BET specific surface is determined equal to 123m 2 / g. A porous distribution is observed centered on a pore diameter of
• the pore volume is determined equal to 0.21 cm 3 / g.
• This example relates to a mesostructured material consisting of cerium oxide and further comprising titanium.
• An acidified butyl titanate solution is prepared by dissolving 20.65 g of Ti (OBu) 4 at 23.45% in Ti0 2 in 15 cm 3 of ethanol, and 8 cm 3 of 15 M HN03 which is completed to 50 cm 3 with ethanol.
• the impregnation of 4 g of mesoporous product of Example 1 is carried out, ie 23.25 millimoles of Ce, calcined at 400 ° C. for 6 hours with 2.91 cm 3 of solution of the previously prepared titanium solution (ie 3.49 millimoles of Ti).
• the molar ratio (Ti / Ce) is then equal to 0.15.
• the product is dried at room temperature for 16 hours, then at 80 ° C for 6 hours.
• the product is then calcined in an air atmosphere at 400 ° C with a temperature rise of 1 ° C / min and a plateau of 6 hours.
• the impregnation and heat treatment operation is then repeated.
• the final molar ratio (Ti / Ce) is then equal to 0.3.
• the BET specific surface is determined to be 130 m 2 / g. A porous distribution is observed centered on a pore diameter of
• the pore volume is determined equal to 0.20 cm 3 / g.

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