FR3066706B1

FR3066706B1 - PROCESS FOR THE PREPARATION OF A NANOMETRIC Y ZEOLITE IN PROTONED FORM

Info

Publication number: FR3066706B1
Application number: FR1754631A
Authority: FR
Inventors: Mathias Dodin; Nicolas Bats; Joel Patarin; Jean Daou; Maeva Borel
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 2017-05-24
Filing date: 2017-05-24
Publication date: 2019-06-21
Anticipated expiration: 2037-05-24
Also published as: FR3066706A1; WO2018215313A1

Abstract

L'invention concerne un procédé de préparation de la forme protonée d'une zéolithe Y nanométrique synthétisée en l'absence d'agent organique structurant ledit procédé comprenant au moins une étape d'échange d'ions de ladite zéolithe Y sous la forme sodium par mise en suspension de ladite zéolithe dans une solution aqueuse contenant au moins un composé pouvant libérer un cation ammonium choisi parmi le nitrate d'ammonium, le chlorure d'ammonium, le sulfate d'ammonium, le phosphate d'ammonium, l'acétate d'ammonium et l'oxalate d'ammonium seul ou en mélange, ladite solution aqueuse ayant une concentration comprise entre 0,01 et 5 mol/L, pour obtenir une zéolithe sous forme ammonium, une étape de traitement thermique de la zéolithe sous forme ammonium réalisée sous air ou sous atmosphère inerte, avec une montée en température comprise entre 0,01 et 10 °C/minute, jusqu'à des températures comprises entre 180 et 350 °C, suivie d'un palier d'une durée comprise entre 30 minutes et 10 heures, de manière préférée entre 1 heure et 5 heures.The invention relates to a process for preparing the protonated form of a nanoscale Y zeolite synthesized in the absence of an organic agent structuring said process comprising at least one step of ion exchange of said zeolite Y in the sodium form by suspending said zeolite in an aqueous solution containing at least one compound capable of releasing an ammonium cation chosen from ammonium nitrate, ammonium chloride, ammonium sulfate, ammonium phosphate, sodium acetate, ammonium and ammonium oxalate alone or as a mixture, said aqueous solution having a concentration of between 0.01 and 5 mol / L, to obtain a zeolite in ammonium form, a step of thermal treatment of the zeolite in ammonium form carried out under air or in an inert atmosphere, with a temperature rise of between 0.01 and 10 ° C / min, up to temperatures between 180 and 350 ° C, followed by a step of a duration comprised between 30 minutes and 10 hours, preferably between 1 hour and 5 hours.

Description

Zeolites, or molecular sieves, are crystalline materials consisting of a three-dimensional arrangement of interconnected TO4 tetrahedra (T may be Si, Al, B, P, Ge, Ti, Ga, Fe, for example). The organization of elements TO4 generates an ordered network of micropores consisting of channels and cavities whose dimensions are compatible with small organic molecules. Depending on how the framework atoms are arranged, different zeolitic structures can be distinguished (there are currently more than 230 [http://www.iza-structure.org/databases]). Each structure therefore has a clean crystal lattice that can be identified by its X-ray diffraction pattern.

The applications of zeolites are numerous and relate to fields such as catalysis, adsorption, ion exchange or purification. The use of a zeolite is conditioned by the characteristics of its porous network (dimensions, etc.) and its chemical composition. An aluminosilicic zeolite has a negatively charged framework, because of the charge deficit provided by each aluminum atom relative to silicon, and which therefore requires the presence of easily exchangeable compensation cations (Na +, K +, etc.). When these are replaced, partially or completely, with NH 4 + ammonium cations, it is then possible to calcine the zeolite to obtain the acid form (the NH 4 + are converted to H + by removal of NH 3). Such materials then find applications in acid catalysis, where their activity and their selectivity will depend on the strength of the acid sites, their density and their location, as well as their accessibility.

Among the main zeolites used today are zeolites of structural type FAU, which are used in many industrial processes such as catalytic cracking of heavy oil cuts. These zeolites exist in their natural state: faujasite was first described in 1842 following its discovery in Germany [A. Damour, Annales des Mines 4 (1842) 395], but it was not until more than a century later that it was first obtained in the laboratory. In the synthetic state, there are three forms: zeolite X having a Si / Al ratio of structure between 1 and 1.5 [Milton RM, US Pat. No. 2,882,244, 1959], zeolite Y for which the Si ratio / AI is greater than 1.5 [DW Breck, US Pat. No. 3,130,007, 1964] and the EMC-1 zeolite (Elf Mulhouse Chemistry One) having a framework Si / Al ratio of between 3 and 4 [F. Delprato, L. Delmote, JL Guth, L. Huve, Zeolites, 10 (1990) 546].

The face-centered cubic structure with 192 T04 tetrahedra (Fd-3m space group) of faujasite was solved as early as 1958 [G. Bergerhoff, WH Baur, W. Nowaki, Neues Jahrbuch für Mineralogie - Monatshefte 9 (1958) 193] and can be described as an assembly of sodalite cages, consisting of 24 tetrahedra, interconnected by 6-6 building units (" double cycles at 6 "or" d6r ") in inversion center symmetry. The mesh parameter a0 of faujasite can vary between 24.2 and 24.8 Å according to the Si / Al framework ratio [DW Breck, EM Flanigen, Molecular Sieves, Society of Chemical Industry, London (1968) 47; JR Sohn, SJ DeCanio, JH Lunsford, DJ O'Donnell, Zeolites 6 (1986) 225; H. Fichtner-Schmittler, U. Lohse, G. Engelhardt, V. Patzelova, Crystal Research and Technology 19 (1984)]. Within the structure, the arrangement of the tetrahedra gives rise to supercages with a maximum diameter of 11.6 Å and acting as nanoreactors suitable for hydrocarbon cracking and gas adsorption; moreover, the pore of faujasite, with a diameter of 7.4 Å for 12 TO4 tetrahedra, allows a good diffusion of the molecules within the porous lattice [C. Baerlocher, LB McCusker, DH Oison, Atlas of the Zeolite Framework Type, 6th revised edition, Elsevier (2007)].

There is now a great interest for zeolites of nanometric dimensions [S. Mintova, J. Grand, V. Valtchev, Comptes Rendus Chimie 19 (2016) 183] because of their improved diffusion properties: unlike zeolites of micrometric dimensions in which the length of the intracrystalline diffusion paths leads to a restriction of the catalytic performances [Y . Tao, H. Kanoh, L. Abrams, K. Kaneko, Chemical Reviews 106 (2006) 896] and progressive deactivation of the catalyst [K. Na, M. Choi, Ryoo R., Microporous and Mesoporous Materials 166 (2013) 3], nanoscale zeolites show gains in activity and selectivity [D. Karami, S. Rohani, Petroleum Science and Technology 31 (2013) 1625; Q. Cui, Y. Zhou, Q. Wei, X. Tao, Yu G., Y. Wang, J. Yang, Energy & Fuels 26 (2012) 4664], However, nanoscale zeolites also have disadvantages due to their reduced dimensions. For the targeted catalytic applications, it is necessary to convert the zeolites into their acid form (ie protonated) by ion exchange with an ammonium salt followed by calcination [H. Toulhoat, P. Raybaud, Catalysis by metal transition sulphides, Ed Technip, 2013]. But this calcination can affect the zeolite structure, especially that of nanoscale zeolites which are more fragile. However, the physicochemical characteristics (including stability) of a zeolite depend on its method of preparation, in particular the nature of the reagents used and in particular the structuring agent. For example, the nanoscale Y zeolite can be obtained in the presence of the tetramethylammonium cation (TMA +), the latter having a structuring and stabilizing role of the sodalite cage [RB Benarmas, A. Bengueddach, F. Di Renzo, Catalysis Today 227 (2014) 33]. Its removal by heat treatment requires heating the zeolite to a temperature greater than 487 ° C. [S. Mintova, NH Oison, T. Bein, Angewandte Chemie: International Edition 38 (1999) 3201]. Thus, the calcination of such a nanoscale Y zeolite at a temperature of 450 ° C. after ion exchange does not cause an amorphization of the zeolite structure [MS Katsiotis, M. Fardis, Y. Al Wahedi, S. Stephen, V Tzitzios, N. Boukos, HJ Kim, SM Alhassan, G. Papavassiliou, Journal of Physical Chemistry C 119 (2015) 3428]. It may be thought that the presence of TMA cations after exchange stabilizes the zeolite structure. In addition, ion exchange prior to calcination also plays a role in the stability of the zeolite. This is the conclusion that can be drawn from the exchange conditions used by P. Morales et al. who obtained a protonated nanometric Y zeolite. However, their nanoscale Y zeolite was synthesized in the presence of TMA + cations and the authors clearly indicate that after exchange and calcination at 550 ° C., the crystallinity of the protonated nanometric zeolite Y is greatly diminished [P. Morales-Pacheco, F. Alvarez, L. Bucio, JM Dominguez, Journal of Physical Chemistry C 113 (2009) 2247], A fortiori, obtaining the protonated form of nanometer zeolites having undergone a high ion exchange is therefore particularly delicate.

The present invention makes it possible to obtain the protonated form of an FAU type Y zeolite whose crystals have dimensions of less than 100 nanometers and which is synthesized in the absence of a structuring organic agent. An advantage of the preparation process according to the invention is that it makes it possible to obtain such a nanometric Y zeolite of structural type FAU in the protonated form with a very good crystallinity with respect to the nanoscale zeolites synthesized according to the prior art. Summary of the invention

The present invention relates to a method for preparing the protonated form of a nanoscale Y zeolite synthesized in the absence of organic structuring agent and having an average crystal size of less than 100 nm, said method comprising at least the following steps i) at least one ion exchange step of a nanoscale Y zeolite synthesized in the absence of a structuring organic agent in the sodium form by suspending said zeolite in an aqueous solution containing at least one compound which can be releasing an ammonium cation selected from ammonium nitrate, ammonium chloride, ammonium sulfate, ammonium phosphate, ammonium acetate and ammonium oxalate alone or as a mixture, said solution aqueous composition having a concentration of between 0.01 and 5 mol / L, preferably between 0.05 and 3 mol / L, very preferably between 0.3 and 2 mol / L, and more preferably between 0.5 and 1 mol / L, to obtain a zeolite in ammonium form, ii) a thermal treatment step of the zeolite in ammonium form obtained at the end of step (i), said step being carried out under air or in an inert atmosphere, with a temperature rise between 0.01 and 10 ° C / minute, preferably between 0.02 and 5 ° C / minute, preferably between 0.03 and 3 ° C / minute and very preferably between 0.5 and 1 ° C / minute to temperatures between 180 and 350 ° C, preferably between 200 and 300 ° C, very preferably between 200 and 250 ° C and more preferably between 230 and 250 ° C, followed by a bearing of a duration between 30 minutes and 10 hours, preferably between 1 hour and 5 hours and very preferably between 1 hour 30 minutes and 2 hours, to obtain said protonated form of the nanoscale Y zeolite synthesized in 1 absence of organic structuring agent.

An advantage of the present invention is therefore to provide a method for obtaining the protonated form of a nanoscale Y zeolite synthesized in the absence of structuring organic agent having a very good crystallinity and having an average crystal size of less than 100 nm, thanks to the implementation of a moderate heat treatment.

It should be noted that when the heat treatment of the material in ammonium form obtained at the end of step (i) is carried out at temperatures higher than 350 ° C., a significant drop in the crystallinity is observed.

Description of the invention

The nanoscale zeolite Y starting in sodium form can be any zeolite Y of nanometric dimensions synthesized in the absence of organic structuring agent.

For example, the nanoscale Y zeolite in its starting sodium form may be synthesized according to a preparation method comprising the following steps: a) the mixing, in an aqueous medium, of at least one AO2 source of at least one tetravalent element A selected from silicon, germanium, titanium alone or as a mixture of at least one source BOb of at least one trivalent element B selected from aluminum, boron, iron, indium, gallium, alone or in admixture, at least one C2 / mO source of an alkali or alkaline earth metal C selected from lithium, sodium, potassium, calcium, magnesium alone or as a mixture, said C2 / mO source of alkali or alkaline earth metal C also comprising at least one source of hydroxide ions to obtain a gel, the reaction mixture of step a) being carried out in the absence of organic structurant and having the following molar composition:

## STR2 ## where A is preferably silicon, B being preferably aluminum, C being preferably sodium, V being between 1 and 40, preferably between 1 and 40, preferably between 1 and 40, preferably between 1 and 40, preferably between 1 and 40, preferably between 1 and 40; And most preferably between 15 and 20, w being between 0.1 and 5, preferably between 0.2 and 1.5 - x being between 1 and 40, preferably between 1 and 20 - y being between 30 and 1000, preferably between 100 and 400 - b being between 1 and 3, b being an integer or rational number - m being equal to 1 or 2, b) the maturation of the gel obtained at the end of step (i) at a temperature between -15 and 60 ° C, preferably between 0 and 50 ° C, and very preferably between 20 and 40 ° C, with or without agitation, for a period of time between hours and 60 days, preferably between 10 hours and 30 days, very preferably between 1 day and 30 days, and even more preferably between 1 day and 20 days, c) after at least 10 hours and less than 15 days of maturing and preferably after at least 12 hours and less than 7 days, preferably after at least 12 hours and less than 3 days, very preferably after at least 12 hours and less than 48 hours and even more preferably after at least 24 hours and less than 48 hours, the single or repeated addition of at least one AO2 source of at least one tetravalent element A selected from silicon, germanium, titanium, alone or as a mixture in said gel, A being preferably silicon, the molar composition of the gel after the addition being the following:

v AO2: w BOb: x C2 / mO: y H2O - v being between 5 and 50, preferably between 10 and 35 and very preferably between 20 and 30, w being between 0.1 and 5, preferably between 0.2 and 1.5 - x being between 1 and 40, preferably between 1 and 20 - y being between 200 and 1000, preferably between 200 and 500 - b being between 1 and 3, b being an integer or rational number - m being equal to 1 or 2, d) the hydrothermal treatment of the gel obtained at the end of step c) at a temperature of between 20 and 200 ° C., preferably between 40 and 140 ° C. C, preferably between 50 and 100 ° C, and very preferably between 60 and 80 ° C, under autogenous reaction pressure, for a period of between 1 hour and 14 days, preferably between 6 hours and 7 days, preferably between 10 hours and 3 days and very preferably between 16 hours and 24 hours, to obtain the crystallization of said zeo Nanoscale lithe Y having a crystal size of less than 100 nm, preferably less than 60 nm and preferably less than 50 nm and an A / B ratio and preferably Si / Al greater than 2, preferably greater than 2.3 preferably more than 2.5 and most preferably greater than 2.6. The size of the crystals of the zeolite obtained is measured on one or more transmission electron micrographs; this is the maximum size observed on the snapshots.

The structure of said starting Y zeolite in sodium form is identified by X-ray diffractometry, in the diffraction angle range 2Θ = 5 ° at 40 ° ± 0.02 °, in reflection geometry. The X-ray source is a copper anticathode energized at 40 kV and 40 mA, providing a Cu-Ka1 monochromatic radiation (λ = 1.5406 Å). Said zeolite Y of structural type FAU obtained by the process according to the invention advantageously has an X-ray diffraction pattern including at least the lines listed in the table corresponding to the X-ray diffraction pattern of the zeolite below:

Inter-Responsive Distance (A) Intensity (%) ______________ 14,11__E _______________ 8,68__f __________ _______________ 7,40__f __________ _______________ 5.63__m _______________________ 4.72__f __________ _____________ 4.35__mf ________ _______________ 3.87__f __________ ______________ 3.75__FF ______________ 3.44__ff __________ _____________ 3.29__F ________ _____________ 3.01__mf ________ ____________ 2.89__m _______________________ 2.85__FF _______ _____________2, 75 _______________________________________ 2.62__f __________ _______________ 2.37__f __________ _______________ 2.18__f __________ ________________ 2.09 ________________ ff__________ FF = very strong; F = strong; m = average; mf = weak medium; f = weak; ff = very weak The relative intensity I / IO is given in relation to a relative intensity scale where it is assigned a value of 100 to the most intense line of the X-ray diffraction pattern: ff <15; 15 <f <30; 30 <mf <50; 50 <m <65; 65 <F <85;FF> 85.

According to the invention, the sodium form of a nanoscale Y zeolite synthesized in the absence of organic structuring agent is subjected to at least one ion exchange step by suspension in step (i) of said zeolite in an aqueous solution containing at least one compound capable of releasing an ammonium cation selected from ammonium nitrate, ammonium chloride, ammonium sulfate, ammonium phosphate, ammonium acetate and oxalate ammonium alone or as a mixture, said aqueous solution having a concentration of between 0.01 and 5 mol / L, preferably between 0.05 and 3 mol / L, very preferably between 0.3 and 2 mol / L , and more preferably between 0.5 and 1mol / L, to obtain a zeolite in ammonium form.

In a preferred embodiment, the compound capable of releasing an ammonium cation is ammonium nitrate. In another preferred embodiment, the compound capable of releasing an ammonium cation is ammonium chloride.

Preferably, said ion exchange step i) is carried out at a temperature between -15 and 150 ° C, preferably between 0 and 100 ° C and very preferably between 50 and 80 ° C, with or without agitation for a period of between 1 minute and 24 hours, preferably between 5 minutes and 15 hours, very preferably between 10 minutes and 8 hours, and even more preferably between 30 minutes and 2 hours.

Preferably, the exchange number is between 1 and 10, preferably between 2 and 10, very preferably between 2 and 8, and more preferably between 3 and 6.

After each ion exchange reaction necessary for the formation of the ammonium form of the nanometric zeolite Y, said zeolite is advantageously centrifuged and washed. After the last exchange reaction, the ammonium form of zeolite Y is centrifuged, washed and dried. The drying is preferably carried out at a temperature between 20 and 150 ° C, preferably between 70 and 120 ° C for a period of between 5 and 20 hours.

According to step (ii) of the process according to the invention, the zeolite in ammonium form obtained at the end of step (i), optionally centrifuged, washed and dried, is subjected to a heat treatment, carried out under air or under an inert atmosphere, with a temperature rise of between 0.01 and 10 ° C / minute, preferably between 0.02 and 5 ° C / minute, preferably between 0.03 and 3 ° C / minute, and very preferably between 0.5 and 1 ° C / minute up to temperatures between 180 and 350 ° C, preferably between 200 and 300 ° C, very preferably between 200 and 250 ° C and more preferably preferably between 230 and 250 ° C, followed by a step of between 30 minutes and 10 hours, preferably between 1 hour and 5 hours and very preferably between 1 hour 30 minutes and 2 hours, to obtain said protonated form of the nanoscale Y zeolite synthesized in the absence of agent o structuring organism.

The protonated form of the nanoscale Y zeolite is generally analyzed by X-ray diffraction, this technique also making it possible to determine the purity and crystallinity of said zeolite obtained by the process of the invention. Very advantageously, the process of the invention leads to the formation of the protonated form of a nanometric Y zeolite of pure FAU structural type, in the absence of amorphous phase. Said nanometric zeolite of structural type FAU in protonated form obtained by the process according to the invention advantageously has an X-ray diffraction pattern including at least the lines listed in the table corresponding to the X-ray diffraction pattern of the zeolite below. below:

FF = very strong; F = strong; m = average; mf = weak medium; f = weak; ff = very weak

On the other hand, the acidity of said protonated form of the nanoscale Y zeolite is commonly measured by NH3-TPD or by adsorption of pyridine.

The zeolite obtained by the process of the invention can be used as an acid solid for catalysis, that is to say as a catalyst in the fields of refining and petrochemistry. It can be associated with an inorganic matrix, which can be inert or catalytically active, and with a metallic phase. The inorganic matrix may be present merely as a binder to hold together the small zeolite particles in the various known forms of the catalysts (extrudates, pellets, beads, powders), or may be added as a diluent to dictate the degree of conversion in a process which would progress if not at a rate too fast leading to fouling of the catalyst as a result of a significant formation of coke. Typical inorganic matrices are in particular support materials for catalysts such as silica, the various forms of alumina, magnesia, zirconia, oxides of titanium, boron, zirconium, aluminum phosphates, titanium, kaolinic clays, bentonites, montmorillonites, sepiolite, attapulgite, fuller's earth, synthetic porous materials such as SiO2-Al2O3, SiO2-ZrO2, SiO2-ThO2, SiO2-BeO, SiO2-TiO2 or any combination of these compounds. The inorganic matrix may be a mixture of different compounds, in particular an inert phase and an active phase.

The metal phase is introduced on the zeolite alone, the inorganic matrix alone or the inorganic-zeolite matrix assembly by ion exchange or impregnation with cations or oxides chosen from the following elements; Cu, Ag, Ga, Mg, Ca, Sr, Zn, Cd, B, Al, Sn, Pb, V, P, Sb, Cr, Mo, W, Mn, Re, Fe, Co, Ni, Pt, Pd, Ru, Rh, Os, Ir and any other element of the periodic table of elements.

The metals can be introduced either all in the same way, or by different techniques, at any time of the preparation, before or after shaping and in any order. In addition, intermediate treatments such as for example calcination and / or reduction can be applied between the deposits of different metals.

The catalytic compositions comprising the protonated form of the nanoscale Y zeolite prepared according to the method of the invention are generally suitable for carrying out the main processes of organic compounds such as ethers.

Any shaping method known to those skilled in the art is suitable for the catalyst comprising the protonated form of nanoscale Y zeolite. It is possible to use, for example, pelletizing or extruding or forming beads. The shaping of the catalyst containing the zeolite prepared by the process of the invention and at least partly in acid form is generally such that the catalyst is preferably in the form of extrudates or beads for use.

Description of figures

FIGS. 1, 3 and 5 compare the X-ray diffractograms of nanometric Y zeolites in sodium form (bottom in the figure) and in protonated form (top in the figure) respectively obtained in Examples 2, 3 and 4 in FIG. diffraction angle range 2Θ = 5 ° to 50 °.

Figures 2, 4 and 6 show the isosphere adsorption-desorption of zeolite Y zeolites in protonated form respectively obtained in Examples 2, 3 and 4.

FIG. 7 represents the X-ray diffractogram of the protonated form of a nanometric Y zeolite obtained in Example 5, in the diffraction angle range 2Θ = 5 ° at 50 °.

Examples:

EXAMPLE 1 Preparation of the Nanoscale Y-zeolite in sodium form and with an Si / Al ratio of 2.3.

A nanometric Y zeolite of structural type FAU containing the elements Si and Al, with an Si / Al molar ratio equal to 2.3, is synthesized in the absence of an organic structuring agent according to a mode of preparation in which a source of aluminum ( sodium aluminate, Sigma Aldrich, 53% Al2O3, 43% Na2O, 4% H2O) and a mineralizing agent (sodium hydroxide, Carlo Erba, 99%) are dissolved in deionized water, with stirring. A source of silicon (Ludox AS-40, 40%, Sigma Aldrich) is then added dropwise, in order to obtain a reaction mixture whose molar composition is SiO 2: 1 Al 2 O 3: 17 Na 2 O: 360H 2 O. The gel thus formed is stirred at room temperature. After 1 day of maturation, a new silicon source (Aerosil 130V, Evonik,> 99.8%) is added. After this silicon source addition, the gel thus formed has the following composition: SiO 2: Al 2 O 3: Na 2 O: 360H 2 O. The reaction mixture is stirred for a further 6 days at room temperature and is transferred to a polypropylene bottle. This vial is placed in an oven at 70 ° C for 16 hours under autogenous pressure and without addition of gas. After cooling the flask to room temperature, the product is washed by centrifugation, before being dried in an oven overnight at 100 ° C.

Example 2 Preparation of zeolite Y nanocrystals in the protonated form of Si / Al ratio equal to 2.3 according to a process according to the invention.

A mass of 0.5 g of nanometric zeolite Y in the sodium form prepared according to Example 1 is incorporated in 12.5 ml of a 1 mol / l solution of ammonium chloride. The ammonium form of this nanoscale Y zeolite of dehydrated idealized formula (NH4) 44Na14 [Al58Si134O384] was obtained by carrying out three exchanges at 50 ° C. for 2 hours with slow stirring (200 rpm). After each exchange, the product is washed with deionized water four times by centrifugation at a speed of 10,000 rpm for 5 minutes. This is then dried overnight in an oven at 100 ° C. Calcination in air in a muffle furnace, with a rise in temperature of 0.5 ° C. per minute up to 240 ° C., followed by a step of 1 hour 30 minutes, makes it possible to obtain a nanometric zeolite Y in crystallized protonated form, the dehydrated mesh formula determined by elemental analysis is H44Nai4 [AI58Sii34O384].

In FIG. 1, the X-ray diffractograms correspond to zeolite Y in sodium form (bottom) and in protonated form (top), they are indexable in the cubic system of the zeolite of structural type FAU. Moreover, the microporous volume of 0.23 cm 3 / g deduced from the isotherm of adsorption-desorption of nitrogen represented in FIG. 2, makes it possible to confirm the maintenance of the structure and the porosity of the nanoscale Y zeolite under protonated form.

Example 3 Preparation of zeolite Y nanocrystals in the protonated form of Si / Al ratio equal to 2.3 according to a process according to the invention under exchange conditions different from Example 2.

A mass of 0.5 g of nanometric zeolite Y in sodium form prepared according to Example 1 is incorporated in 12.5 ml of a 1 mol / l solution of ammonium chloride. The ammonium form of this nanoscale Y zeolite of dehydrated idealized formula (NH4) 48Na10 [Al58Si134O384] was obtained by carrying out six exchanges at 80 ° C. for 30 minutes with slow stirring (200 rpm). After each exchange, the product is washed with deionized water four times by centrifugation at a speed of 10,000 rpm for 5 minutes. This is then dried overnight in an oven at 100 ° C. Calcination in air in a muffle furnace, with a rise in temperature of 0.5 ° C. per minute up to 240 ° C., followed by a step of 1 hour 30 minutes, makes it possible to obtain a nanometric zeolite Y in crystallized protonated form, the dehydrated mesh formula determined by elemental analysis is H48Na10 [AI58Si134O384].

In FIG. 3, the X-ray diffractograms correspond to zeolite Y in sodium form (low) and in protonated form (high), they are indexable in the cubic system of the zeolite of structural type FAU. Moreover, the microporous volume of 0.22 cm 3 / g deduced from the nitrogen adsorption-desorption isotherm shown in FIG. 4 confirms the maintenance of the structure and the porosity of the nanoscale Y zeolite under protonated form.

EXAMPLE 4 Preparation of nanocrystals of zeolite Y in protonated form not in accordance with the invention

The nanometric Y zeolite in ammonium form was prepared according to the protocol described in Example 2, except that the calcination was carried out in air, in a muffle furnace, with a temperature rise of 1 ° C. per minute up to 450 ° C followed by a stop of 10 hours.

In FIG. 5, the X-ray diffractograms correspond to zeolite Y in sodium form (bottom) and in protonated form (top), they are indexable in the cubic system of the zeolite of structural type FAU. According to these diffractograms, the structure of zeolite Y in protonated form is slightly affected by the heat treatment. However, the microporous volume of 0.17 cm 3 / g deduced from the isotherm of adsorption-desorption of nitrous represented in FIG. 6, makes it possible to confirm that this heat treatment generates an amorphization of the material and a strong decrease of the porosity nanoscale Y zeolite in protonated form.

Example 5: Not in accordance with the invention

The nanometric Y zeolite in ammonium form was prepared according to the protocol described in Example 3 except that the calcination was carried out under air, in a muffle furnace, with a temperature rise of 1 ° C. per minute up to 560 ° C, followed by a step of 1 hour 30 minutes.

The X-ray diffractogram of the material shown in Figure 7 shows that no crystallized product remains after the heat treatment detailed above. The calcination process described in this example therefore does not make it possible to obtain a nanometric Y zeolite in protonated form with an accessible porosity.

Claims

A process for preparing the protonated form of a nanoscale Y zeolite synthesized in the absence of organic structuring agent and having an average crystal size of less than 100 nm, said method comprising at least the following steps: i. at least one ion exchange step of said nanoscale Y zeolite synthesized in the absence of structuring organic agent, in the sodium form, by suspending said zeolite in an aqueous solution containing at least one compound capable of releasing a ammonium cation selected from ammonium nitrate, ammonium chloride, ammonium sulfate, ammonium phosphate, ammonium acetate and ammonium oxalate alone or as a mixture, said aqueous solution having a concentration of between 0.01 and 5 mol / L, to obtain a zeolite in ammonium form, ii. a step of thermal treatment of the zeolite in ammonium form obtained at the end of step (i), said step being carried out under air or under an inert atmosphere, with a temperature rise of between 0.01 and 10 ° C / minute, up to temperatures between 180 and 350 ° C, followed by a step of a duration between 30 minutes and 10 hours to obtain said protonated form of nanoscale Y zeolite.

2. Process according to claim 1, in which the nanometric zeolite Y in its sodium form used in stage i) is synthesized according to a method of preparation comprising the following steps: a) the mixing, in an aqueous medium, of at least one source AO2 of at least one tetravalent element A chosen from silicon, germanium, titanium alone or as a mixture, of at least one source BOb of at least one trivalent element B chosen from aluminum, boron, iron, indium, gallium, alone or as a mixture, of at least one C2 / mO source of an alkaline or alkaline-earth metal C selected from lithium, sodium, potassium, calcium, magnesium alone or in a mixture, said C2 / mO source of alkali metal or alkaline earth metal C also comprising at least one source of hydroxide ions to obtain a gel, the reaction mixture being produced in the absence of organic structuring agent and having the following molar composition : v A02: w BOb: x C2 / mO: y H2O - v being between 1 and 40, w being between 0.1 and 5, x being between 1 and 40, y being between 30 and 1000, b being between 1 and 3, b being an integer or rational number - m being equal to 1 or 2, b) the maturation of the gel obtained at the end of step (a) at a temperature of between -15 and 60 ° C., with or without stirring, during a duration of between 10 hours and 60 days, c) after at least 10 hours and less than 15 days of maturation, the single or repeated addition of at least one AO2 source of at least one tetravalent element A chosen from silicon , germanium, titanium, alone or as a mixture in said gel, A being preferably silicon, the molar composition of the gel after the addition being the following: v AO2: w BOb: x C2 / mO: y H2O - v being between 5 and 50, w being between 0.1 and 5, x being between 1 and 40, y being between 200 and 1000, b being between 1 and 5; 3, b being an integer or rational number - m being equal to 1 or 2, d) the hydrothermal treatment of the gel obtained at the end of stage c) at a temperature of between 20 and 200 ° C., under a pressure of autogenous reaction, for a period of between 1 hour and 14 days, to obtain the crystallization of said nanoscale Y zeolite.

3. Method according to one of claims 1 or 2 wherein the compound capable of releasing an ammonium cation used in step i) is ammonium nitrate.

4. Method according to one of claims 1 or 2 wherein the compound capable of releasing an ammonium cation used in step i) is ammonium chloride.

5. Method according to one of claims 1 to 4 wherein the aqueous solution containing at least one compound capable of releasing an ammonium cation used in step i) has a concentration of between 0.3 and 2 mol / l.

6. Method according to one of claims 1 to 5 wherein said ion exchange step i) is carried out at a temperature between -15 and 150 ° C, with or without stirring for a period of between 1 minute and 24 hours. .

7. Method according to one of claims 1 to 5 wherein the exchange number of said step i) is between 1 and 10.

8. The method of claim 7 wherein the exchange number of said step i) is between 2 and 8.

9. Method according to one of claims 1 to 8 wherein after the last exchange reaction, the ammonium form of zeolite Y obtained at the end of step i) is centrifuged, washed and then dried at a temperature of between 20 and 150 ° C for a period of between 5 and 20 hours.

10. Method according to one of claims 1 to 8 wherein the heat treatment of step ii) is carried out with a temperature rise of between 0.02 and 5 ° C / minute, up to temperatures between 200 and 300 ° C followed by a step of between 1 hour and 5 hours.

11. The method of claim 10 wherein the heat treatment of step ii) is carried out with a temperature rise of between 0.5 and 1 ° C / minute to temperatures between 200 and 250 ° C followed by a stage lasting between 1 hour 30 minutes and 2 hours.