Method for the preparation of a synthetic faujasite material comprising monodisperse nanoparticles composed of single nanocrystals

Abstract

The present invention relates to a method for the preparation of faujasite nanocrystals, to faujasite nanocrystals, to a method for the preparation of a stable colloidal suspension of faujasite nanocrystals, to a stable colloidal suspension of faujasite nanocrystals, and to the use of said faujasite nanocrystals and said stable colloidal suspension of faujasite nanocrystals in various applications.

Claims

1. A method for the preparation of a synthetic faujasite material having monodisperse nanoparticles composed of single nanocrystals, said nanoparticles having a size going from 5 to 400 nm and a silicon to aluminum molar ratio Si/Al going from 1 to 2.5, wherein said method comprises the following steps: A) separately preparing a clear aqueous aluminate suspension A comprising at least one source of aluminum and at least one source of an alkali metal M1, and a clear aqueous silicate suspension B comprising at least one source of silicon and at least one source of an alkali metal M1, said separate preparations being prepared at 20-25 C.; B) admixing the clear aqueous aluminate suspension A and the clear aqueous silicate suspension B until a resulting aqueous suspension is obtained, said resulting aqueous suspension being free of organic-templating agents and having the following molar composition:
x.sub.1M1.sub.2O:yAl.sub.2O.sub.3:10SiO.sub.2:zH.sub.2O(I) in which: 0.1y5, 20z400, and preferably 20z320, 5x.sub.113; wherein in step B), the clear aqueous silicate suspension B only is cooled to a temperature of 0 to 5 C., then the clear aqueous aluminate suspension A is added drop wise to the cooled clear aqueous silicate suspension B, while said clear aqueous silicate suspension B is kept at a temperature going from 0 to 5 C. for the duration of the dropwise addition, C) aging the resulting suspension of step 2) at a temperature going from about 20 C. to about 30 C. to form nuclei; D) heating the resulting suspension of step 3) at a temperature going from about 40 C. to about 150 C., for a period of time sufficient to produce the desired synthetic faujasite material comprising monodisperse nanoparticles composed of single nanocrystals; and E) recovering said synthetic faujasite material comprising monodisperse nanoparticles composed of single nanocrystals.

2. The method according to claim 1, wherein the source of aluminum is aluminum powder.

3. The method according to claim 1, wherein the source of silicon is colloidal silica.

4. The method according to claim 1, wherein the source of alkali metal M1 is selected from a source of Na, a source of K and a source of Li.

5. The method according to claim 1, wherein in step B), the clear aqueous aluminate suspension A and the clear aqueous silicate suspension B are mixed under vigorous mechanical stirring or sonication.

6. The method according to claim 1, wherein the temperature of step C) is maintained for at least 12 hours.

7. The method according to claim 1, wherein step E) is performed by filtration, centrifugation or dialysis.

8. The method according to claim 1, wherein it further comprises the following step: F) drying the single nanocrystals of synthetic faujasite material obtained in step E).

9. A method for the preparation of a stable colloidal suspension of a synthetic faujasite material having monodisperse nanoparticles composed of single nanocrystals, said method comprising the following steps: A) preparing a synthetic faujasite material comprising monodisperse nanoparticles composed of single nanocrystals according to the method as defined in claim 1; and B) dispersing in a solvent the synthetic faujasite material comprising monodisperse nanoparticles composed of single nanocrystals of step A).

10. The method according to claim 9, wherein the solvent is selected from water, acetone and alcohols.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 represents the XRD diffraction spectrum of the synthetic faujasite material FAU-Y-10a prepared according to example 1:

(2) FIG. 2 represents the XRD diffraction spectrum of the synthetic faujasite material FAU-X-10a prepared according to example 5;

(3) FIGS. 3a and 3b represent the DLS curves of the suspension prior to and after the crystallization step 4), for the synthetic faujasite materials FAU-Y-10a (FIG. 3a) and FAU-Y-70a (FIG. 3b):

(4) FIGS. 4a and 4b represents high resolution transmission electron microscopy (HR-TEM) images of FAU-Y-10a (FIG. 4a) and FAU-Y-70a (FIG. 4b);

(5) FIG. 5 represents high-resolution TEM images of FAU-X-10a:

(6) FIGS. 6a and 6b represents scanning electron microscopy (SEM) images of FAU-Y-10a (FIG. 6a: 500 nm scale and FIG. 6b: 1 m scale);

(7) FIGS. 7a, 7b and 8 represent nitrogen adsorption/desorption isotherms of FAU-Y-10a (FIG. 7a), FAU-Y-70a (FIG. 7b) and FAU-X-10a (FIG. 8); and

(8) FIG. 9 represents TG/DTG data of FAU-Y-10a (curves with dotted lines) and FAU-Y-70 (curves with plain lines) obtained after step 6) and a calcination step at 550 C. under air (FIG. 9a), and obtained after ion exchange with ammonia (step 7) and a calcination step at 400 C. under air (step 8) (FIG. 9b).

(9) FIG. 10 is a graph of the TiPBz conversion in % as a function of the catalyst used, in accordance with one embodiment; and

(10) Figures 11a and 11b are graphs of the associated selectivities at 200 C. (FIG. 11a) and at 225 C. (FIG. 11b) showing the proportions in % of the various products obtained during the TiPBz conversion as a function of the catalyst used in accordance with one embodiment

DETAILED DESCRIPTION

Examples

(11) The starting materials used in the examples which follow, are listed below: sodium hydroxide: Sigma Aldrich; colloidal silica (Ludox-HS 30, 30 wt % SiO.sub.2, pH=9.8): Aldrich; aluminum powder (325 mesh, 99.5% purity): Alfa Aesar; Commercial zeolite Y UOP (LZY-62) with a size of crystals of 0.5 to 3 m, and a Si/Al molar ratio of 2.5 was used as a reference sample.

(12) These starting materials were used as received from the manufacturers, without additional purification.

(13) The various zeolites obtained in the examples were characterized over various scales of sizes.

(14) Ammonia Exchange and Thermal Treatment:

(15) The synthetic faujasite material obtained after step 6) was ion-exchanged with a solution of 0.2M of NH.sub.4Cl (1 h, 25 C.). The ion-exchange procedure was repeated 2 times. After the third ion exchange step, the zeolite was washed with dd H.sub.2O, and calcined (e.g. at 400 C.) for elimination of the NH.sub.3 and obtaining the synthetic faujasite material in acidic form.

(16) Powder X-Ray Diffraction (XRD) Analysis:

(17) Powder samples of the synthetic faujasite material obtained after step 6) were measured using a PANalytical X'Pert Pro diffractometer with CuK monochromatized radiation (=1.5418 ). The samples were scanned in the range 4-50 2 with a step size of 0.020.

(18) Dynamic Light Scattering (DLS) Analysis:

(19) The hydrodynamic diameters of the synthetic faujasite material in the various suspensions were determined with a Malvern Zetasizer Nano. The analyses were performed on samples after purification with a solid concentration of 10 wt % and pH=8. The back scattering geometry (scattering angle 173, HeNe laser with 3 mW output power at 632.8 nm wavelength) allows measurements at high sample concentration, since a complete penetration of the incident light through the sample is not required.

(20) Transmission Electron Microscopy (TEM):

(21) Diluted colloidal suspensions of synthetic faujasite material obtained after step 5) were sonicated for 15 min and then 2-3 drops of fine particle suspensions were dried on carbon-film-covered 300-mesh copper electron microscope grids. The crystal size, morphology and crystallinity of solids were determined by a transmission electron microscopy (TEM) using a JEOL 2010 FEG operating at 200 kV.

(22) Scanning Electron Microscopy (SEM):

(23) The surface features, morphology and size of zeolite nanocrystals were determined by field-emission scanning electron microscope (SEM, Philips XL30 FEG) with an accelerating voltage 10-30 kV. All samples prior the SEM characterization were covered with a conductive layer (Pt or Au).

(24) N.sub.2 Sorption Analysis:

(25) Nitrogen adsorption/desorption isotherms were measured using Micrometrics ASAP 2020 volumetric adsorption analyzer. Samples of the synthetic faujasite material obtained after step 6) were degassed at 523 K under vacuum overnight prior to the measurement. The external surface area and micropore volume were estimated by alpha-plot method using Silica-1000 (22.1 m.sup.2.Math.g.sup.1 assumed) as a reference. The micropore and mesopore size distributions of solids were estimated by Nonlocal Density Functional Theory (NLDFT) and Barret-Joyner-Halenda (BJH) methods, respectively.

(26) Thermal (TG/DTG) Analyses:

(27) The analyses were performed on samples of the synthetic faujasite material obtained after step 6 using a Setaram TGDSC 111 analyzer (heating rate of 5 C..Math.min.sup.1) under an air flow of 40 ml.Math.min.sup.1.

(28) Chemical Analysis:

(29) The chemical compositions of the synthetic faujasite materials obtained after step 6) were determined by inductively coupled plasma (ICP) optical emission spectroscopy using a Varian ICP-OES 720-ES.

Example 1

Preparation of a Synthetic Faujasite Material FAU-Y-10a According to the Method of the Invention

(30) Step 1):

(31) A clear aqueous aluminate suspension A was prepared by dissolving 2.5 g of NaOH in 4.4 g of dd H.sub.2O, followed by slow addition of 0.243 g of aluminum powder.

(32) A clear aqueous silicate suspension B was prepared by mixing 10 g of colloidal silica with 1.1 g of NaOH, and 3 g of dd H.sub.2O. As a result, a turbid suspension was obtained. In order to transform the turbid into clear suspension, the turbid suspension was placed in an oven at 100 C. for 6 minutes.

(33) Step 2):

(34) Solution A was added drop wise under vigorously stirring to the solution B; during the mixing, solution B was kept in ice.

(35) The resulting clear suspension had the following molar composition: 9Na.sub.2O:0.9Al.sub.2O.sub.3:10SiO.sub.2:160H.sub.2O.

(36) Step 3):

(37) The resulting clear suspension was then aged 24 h at room temperature (i.e. 25 C.).

(38) Step 4):

(39) Then, the hydrothermal crystallization was conducted at 50 C. for 2 days to obtain monodisperse nanoparticles of synthetic faujasite material FAU-Y-10a dispersed in mother liquor, said nanoparticles having a size of 10 nm.

(40) Steps 5) and 6):

(41) Single nanocrystals of synthetic faujasite material FAU-Y-10a with a Si/Al molar ratio=1.6 were purified by repeating steps of centrifugation (25.000 rpm for 4 h) and redispersion in distilled water until reaching pH=7, and then freeze-dried prior further characterization.

(42) The yield was 80%.

(43) The Si concentration was 99.27 mg/l, the Al concentration was 61.43 mg/l, and the Na concentration was 48.44 mg/l.

Example 2

Preparation of Synthetic Faujasite Materials FAU-Y-10b. FAU-Y-10c and FAU-Y-10d with Different Si/Al Molar Ratios According to the Method of the Invention

(44) 3 synthetic faujasite materials FAU-Y-10 with different Si/Al molar ratios, were prepared according to the method described in example 1, except that step 2) the resulting clear aqueous suspensions had the following molar compositions:
8Na.sub.2O:0.8Al.sub.2O.sub.3:10SiO.sub.2:160H.sub.2O(FAU-Y-10b),
8Na.sub.2O:0.7Al.sub.2O.sub.3:10SiO.sub.2:160H.sub.2O(FAU-Y-10c,d), and

(45) step 4) was performed in other conditions.

(46) The conditions used in step 4) for each of the synthetic faujasite materials FAU-Y-10, their respective Si/Al molar ratio, and their respective Si, Al and Na concentrations (conc.) are given in Table 1 below:

(47) TABLE-US-00001 TABLE 1 synthetic Si/Al Conc. Conc. Conc. faujasite Conditions molar of Si of Al of Na material of step 4) ratio (mg/l) (mg/l) (mg/l) FAU-Y-10b 80 C., 8 h.sup. 1.62 99.27 61.43 48.44 FAU-Y-10c 100 C., 2 h 1.73 98.49 57.12 60.39 FAU-Y-10d 120 C., 1 h 10 1.84 112.33 61.05 57.23

(48) The yield was 80% for FAU-Y-10b, 78% for FAU-Y-10c, and 75% for FAU-Y-10d.

Example 3

Preparation of a Synthetic Faujasite Material FAU-Y-70a According to the Method of the Invention

(49) Step 1):

(50) A clear aqueous aluminate suspension A was prepared by dissolving 2.4 g of NaOH in 6 g of dd H.sub.2O, followed by slow addition of 0.189 g of aluminum powder.

(51) A clear aqueous silicate suspension B was prepared by mixing 10 g of colloidal silica with 1.2 g of NaOH, and 5 g of dd H.sub.2O. As a result, a turbid suspension was obtained. In order to transform the turbid into clear suspension, the turbid suspension was placed in an oven at 100 C. for 6 minutes.

(52) Step 2):

(53) Solution A was added drop wise under vigorously stirring to the solution B; during the mixing, solution B was kept in ice.

(54) The resulting turbid suspension had the following molar composition: 9Na.sub.2O:0.7Al.sub.2O.sub.3:10SiO.sub.2:200H.sub.2O.

(55) Step 3):

(56) The resulting turbid suspension was then aged 24 h at room temperature (i.e. 25 C.).

(57) Step 4):

(58) Then, the hydrothermal crystallization was conducted at 150 C. for 45 minutes to obtain monodisperse nanoparticles of a synthetic faujasite material FAU-Y-70a dispersed in mother liquor, said nanoparticles having a particle size of 70 nm.

(59) Steps 5) and 6):

(60) Single nanocrystals of a synthetic faujasite material FAU-Y-70a with a Si/Al molar ratio=1.65 were purified by three steps centrifugation (25.000 rpm for 4 h) followed by redispersion in water until reached pH=7, and then freeze-dried prior further characterization.

(61) The yield was 80%.

(62) The Si concentration was 107.45 mg/l, the Al concentration was 65.12 mg/ml, and the Na concentration was 55.94 mg/l.

Example 4

Preparation of Synthetic Faujasite Materials FAU-Y-70b and FAU-Y-70c with Different Si/Al Molar Ratios According to the Method of the Invention

(63) 2 synthetic faujasite materials FAU-Y-70 with different Si/Al molar ratio, were prepared according to the method described in example 3, except that step 4) was performed in other conditions.

(64) The conditions used in step 4) for each of the synthetic faujasite materials FAU-Y-70, their respective Si/Al molar ratio and their respective Si, Al and Na concentrations (conc.) are given in Table 2 below:

(65) TABLE-US-00002 TABLE 2 synthetic Si/Al Conc. Conc. Conc. faujasite Conditions molar of Si of Al of Na material of step 4) ratio (mg/l) (mg/l) (mg/l) FAU-Y-70b 100 C., 4 h 30 1.75 110.95 63.40 50.94 FAU-Y-70c 120 C., 1 h 10 1.9 123.52 65.01 59.40

(66) The yield was 85% for FAU-Y-70b and 82% for FAU-Y-70c.

Example 5

Preparation of a Synthetic Faujasite Material FAU-X-10a According to the Method of the Invention

(67) Step 1):

(68) A clear aqueous aluminate suspension A was prepared by dissolving 2.5 g of NaOH in 3 g of dd H.sub.2O, followed by slow addition of 0.297 g of aluminum powder.

(69) A clear aqueous silicate suspension B was prepared by mixing 10 g of colloidal silica with 1.1 g of NaOH, and 1 g of dd H.sub.2O. As a result, a turbid suspension was obtained. In order to transform the turbid into clear suspension, the turbid suspension was placed in an oven at 100 C. for 6 minutes.

(70) Step 2):

(71) Solution A was added drop wise under vigorously stirring to the solution B; during the mixing, solution B was kept in ice.

(72) The resulting clear suspension had the following molar composition: 9Na.sub.2O:1.1Al.sub.2O.sub.3:10SiO.sub.2:25H.sub.2O.

(73) Step 3):

(74) The resulting clear suspension was then aged 24 h at room temperature (i.e. 25 C.), freeze dried, and the water content was adjusted.

(75) Step 4):

(76) Then, the hydrothermal crystallization was conducted at 50 C. for 2 days to obtain monodisperse nanoparticles of a synthetic faujasite material FAU-X-10a dispersed in mother liquor, said nanoparticles having a particle size of 10 nm.

(77) Steps 5) and 6):

(78) Single nanocrystals of the synthetic faujasite material FAU-X-10a were purified by three steps centrifugation (25.000 rpm for 4 h) followed by redispersion in water until reached pH=7, and then freeze-dried prior further characterization.

(79) The yield was 78%.

(80) The Si/Al molar ratio of the obtained synthetic faujasite material FAU-X-10 was 1.14, with a Si concentration of 78.84 mg/l, an Al concentration of 69.13 mg/ml, and a Na concentration of 62.23 mg/l.

Example 6

Preparation of Synthetic Faujasite Materials FAU-X-10b, FAU-X-10c and FAU-X-10d with Different Si/Al Molar Ratios According to the Method of the Invention

(81) 3 synthetic faujasite materials FAU-X-10 with different Si/Al molar ratios, were prepared according to the method described in example 5, except that step 4) was performed in other conditions.

(82) The conditions used in step 4) for each of the synthetic faujasite materials FAU-X-10, their respective Si/Al molar ratio and their respective Si, Al and Na concentrations (conc.) are given in Table 3 below:

(83) TABLE-US-00003 TABLE 3 synthetic Si/Al Conc. Conc. Conc. faujasite Conditions molar of Si of Al of Na material of step 4) ratio (mg/l) (mg/l) (mg/l) FAU-X-10b 80 C., 10 h 1.10 75.64 68.76 63.87 FAU-X-10c 100 C., 3 h 1.17 81.33 69.12 58.75 FAU-X-10d 120 C., 1 h 30 1.22 85.83 70.35 59.32

(84) The yield was 80% for FAU-X-10b, 78% for FAU-X-10c, and 85% for FAU-X-10d.

(85) Thus, the crystal engineering strategy developed in this invention leads to extremely small FAU-type nanocrystals with exceptional crystalline yield.

Example 7

Characterization of the Synthetic Faujasite Materials Prepared According to the Method of the Invention

(86) 7.1 Powder X-Ray Diffraction (XRD) Analysis

(87) FIG. 1 represents the XRD diffraction spectrum of the synthetic faujasite material FAU-Y-10a prepared according to example 1 (FIG. 1a) and the synthetic faujasite material FAU-Y-70a prepared according to example 3 (FIG. 1b). FIG. 1 shows the intensity (in arbitrary units: a.u.) as a function of the angle 2 (in degree). Crystallites with sizes of 10 nm exhibit broadened but intensive Bragg peaks. Sharper Bragg peaks are present on the FAU-Y-70 sample (FIG. 1b).

(88) FIG. 2 represents the XRD diffraction spectrum of the synthetic faujasite material FAU-X-10a prepared according to example 5. FIG. 2 shows the intensity (in arbitrary units: a.u.) as a function of the angle 2 (in degree). Crystallites with sizes of 10 nm exhibit broadened Bragg peaks.

(89) 7.2 Dynamic Light Scattering (DLS) Analysis

(90) FIG. 3 represents the DLS curves of the suspension prior to the crystallization step 4) (FIGS. 3a and 3b, curves with plain lines) and after the crystallization step 4) (FIGS. 3a and 3b, curves with dotted lines) for the synthetic faujasite materials FAU-Y-10a (FIG. 3a) and FAU-Y-70a (FIG. 3b). FIG. 3 shows the scattering intensity (in arbitrary units: a.u.) as a function of the diameter of the obtained nanoparticles (in nm).

(91) For the synthetic faujasite material FAU-Y-10a, the resulting suspension obtained in step 2) or step 3) is clear (FIG. 3a, left picture) and evolves to a milky suspension after a 40 h hydrothermal crystallization 4) at 50 C. (FIG. 3a, right picture). The average hydrodynamic diameter of the amorphous and crystalline particles changes from 12 nm to 20 nm, which corresponds to the transformation from clear suspension to a crystalline milky suspension (polydispersity index of 0.01). This is consistent with the particle size distribution measurements indicating that both amorphous and crystalline suspensions contain narrowly distributed particles.

(92) The DLS curves of the synthetic faujasite material FAU-Y-70a show a substantial difference between the size of the particles in the resulting suspension obtained in step 2) or step 3) (20 nm) (FIG. 3b, left picture) and the size of the particles in the milky suspension after the hydrothermal crystallization 4) (70 nm) (FIG. 3b, right picture).

(93) The growth of the synthetic faujasite material FAU-Y-10a is very limited by the low temperature and crystallization is done mainly by propagation through the gel network. With the synthetic faujasite material FAU-Y-70a, the higher temperature (150 C.) during crystal growth favors the Ostwald ripening and thus larger particles grow at the expense of smaller ones.

(94) The crystalline suspensions after step 4) of the synthetic faujasite materials FAU-Y-10a and FAU-Y-70a are stable, as such, for 6 months without any noticeable change.

(95) 7.3 Transmission Electron Microscopy (TEM)

(96) FIG. 4 represents high resolution transmission electron microscopy (HR-TEM) images of FAU-Y-10a (FIG. 4a) and FAU-Y-70a (FIG. 4b). The HR-TEM indicates that the zeolite particles are single crystals of about 10 nm (FAU-Y-10a) and 70 nm (FAU-Y-70a) and the reticular distances between lattice fringes are those expected for FAU-type zeolites. No intergrowths with different lattice orientations are observed, which is a strong indication that each crystal originates from a single nucleus in one isolated amorphous particle. The process of crystal growth is completed since even the smallest crystals (FAU-Y-10a) are well shaped with the typical octahedral morphology observed in natural faujasite.

(97) FIG. 5 represents high-resolution TEM images of FAU-X-10a. The HR-TEM indicates that the nanoparticles are composed of single nanocrystals with size of about 10 nm (FAU-X-10a).

(98) The crystal sizes calculated using the Scherrer equation (XRD analysis) are in good agreement with dynamic light scattering (DLS) measurements as well as with HRTEM results.

(99) 7.4 Scanning Electron Microscopy (SEM)

(100) FIG. 6 represents scanning electron microscopy (SEM) images of FAU-Y-10a (FIG. 6a: 500 nm scale and FIG. 6b: 1 m scale). FIG. 6 shows no aggregates of nanocrystals or no polycrystalline agglomerates.

(101) 7.5 Nitrogen Adsorotion/Desorotion Measurements

(102) 7.5.1 Nitrogen Sorption Data

(103) The results of the N.sub.2 sorption measurements carried out on each of the zeolites synthesized examples 1, 3 and 5 are collated in table 4 below. Thus, the total volume (V.sub.total), the mesopore diameter (d.sub.meso), the mesopore volume (V.sub.meso), the external surface area (S.sub.ext), the micropore volume (V.sub.micro), and the specific surface area (S.sub.BET) for each zeolite prepared according to the invention and for a commercial reference are reported below in Table 4.

(104) TABLE-US-00004 TABLE 4 V.sub.total d.sub.meso.sup.a V.sub.meso S.sub.ext V.sub.micro S.sub.BET Zeolite (cm.sup.3 .Math. g.sup.1) (nm) (cm.sup.3 .Math. g.sup.1) (m.sup.2 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) (m.sup.2 .Math. g.sup.1) FAU-Y-10a 1.27 30 0.97 223 0.30 842 FAU-Y-70a 0.64 80 0.32 59 0.32 856 FAU-X-10a 1.26 25 0.98 175 0.28 820 UOP 0.37 No 0.06 26 0.31 810 LZY-62 .sup.aDetermined by BJH method
7.5.2 Nitrogen Adsorption/Desorption Isotherms

(105) FIGS. 7 and 8 represent nitrogen adsorption/desorption isotherms of FAU-Y-10a (FIG. 7a), FAU-Y-70a (FIG. 7b) and FAU-X-10a (FIG. 8). FIGS. 7 and 8 show the volume adsorbed in cm.sup.3.Math.g.sup.1 as a function of the relative pressure P/P.sub.0.

(106) Nitrogen adsorption characterizes the porosity and specific surface area of the two zeolites. According to FIGS. 7 and 8, it can be concluded that all zeolites exhibit type I sorption isotherms. As can be seen, the intense uptake at low relative pressure is combined with a large hysteresis loop at high relative pressure. Such a feature is clearly related with textural pores formed by the closed packing of monodispersed and well-shaped nanocrystals. The unusually high mesoporosity is attributed to the packing of FAU-Y-10a and FAU-Y-70a crystals delineating regular mesopores with a diameter of 40 nm and 80 nm, respectively.

(107) Their Brunauer-Emmett-Teller (BET) surface area is 842, 856 and 820 m.sup.2.Math.g.sup.1 while their total pore volume is 1.27, 0.64 and 1.26 cm.sup.3.Math.g.sup.1, respectively (Table 4). The extremely high micropore volume of 0.30 m.sup.3.Math.g.sup.1 is noteworthy for the extremely small (10 nm) nanocrystals, as it corresponds to the theoretical value for highly crystalline FAU-type zeolite. These results underline the high crystallinity of the materials. In particular, this is not observed for ultrasmall FAU crystals synthesized in the prior art in the presence of an organic structure-directing agent. Another important feature of FAU-Y-10a is its high external surface area of 223 m.sup.2.Math.g.sup.1, opening opportunities for processes taking place on the crystal surface. The corresponding values for FAU-Y-70a and FAU-X-10a are 59 and 175 m.sup.2.Math.g.sup.1.

(108) 7.6 Stability of the Synthetic Faujasite Materials Prepared According to the Method of the Invention

(109) 7.6.1 Powder X-Ray Diffraction (XRD) Analysis

(110) The stability of FAU-Y-10a and FAU-Y-70a samples after a thermal treatment at 550 C. for 4 h with or without a preliminary ion exchange with ammonia was studied by XRD. The XRD patterns of FAU-Y-10a and FAU-Y-70a did not change under these treatments; in particular, both positions and intensities of all Bragg peaks were preserved (data not shown).

(111) 7.6.2 Thermal (TG/DTG) Analyses

(112) FIG. 9 represents TG/DTG data of FAU-Y-10a (curves with dotted lines) and FAU-Y-70 (curves with plain lines) obtained after step 6) and a calcination step at 550 C. under air (FIG. 9a), and obtained after ion exchange with ammonia (step 7) and a calcination step at 400 C. under air (step 8) (FIG. 9b). More particularly, FIG. 8 shows on the left the m in % as a function of temperature in C., and on the right the differential thermogravimetric (DTG) in mg/min as a function of temperature in C.

(113) Thus, TG/DTG data on thermally treated samples confirmed the high stability of the zeolites prepared by the method of the invention. In addition, thermogravimetry indicated that all synthetic faujasite materials retain their water capacity after such a thermal treatment. The water desorbed from FAU-Y-10a and FAU-Y-70a amount to approximately 23 wt %.

(114) The Zeta potential for both suspensions of FAU-Y-10a and FAU-Y-70a was found to be of 55 mV, explaining their colloidal stability (data not shown).

Example 8

Catalytic Activity of the Synthetic Faujasite Material Prepared According to the Method of the Invention

(115) A catalytic test was performed to evaluate the external surface properties of the zeolites prepared according to the method of the invention.

(116) The synthetic faujasite materials prepared in examples 1 and 3 were ion-exchanged with ammonia (step 7) and heat treated at 400 C. to eliminate NH.sub.3 (step 8) and obtain the synthetic faujasite materials in acidic form.

(117) Thus, the conversion of a bulky molecule such as 1,3,5-triisopropylbenzene (TiPBz, kinetic diameter of 0.95 nm, well above the 0.73 nm pore opening of the FAU structure) in the presence of the corresponding catalysts FAU-Y-10a or FAU-Y-70a or a commercial zeolite LZY-62 (UOP) was studied. TiPBz is commonly used to study the external surface properties of large pore zeolites. The tests were performed under identical conditions (P.sub.Tot=1.01.Math.10.sup.5 Pa, P.sub.TiPBz=180 Pa, W/F.sup.o.sub.TiPBz=82 kg.Math.s.Math.mol.sup.1) in a downflow fixed bed gas phase reactor at two temperatures: 200 C. and 225 C. FIG. 10 shows the TiPBz conversion in % as a function of the catalyst used. FIG. 11 reports the associated selectivities at 200 C. (FIG. 11a) and at 225 C. (FIG. 11b) by showing the proportions in % of the various products obtained during the TiPBz conversion as a function of the catalyst used. Said products can be cumene, 1,3-diisopropylbenzol (1,3-DiPBz) and 1,4-diisopropylbenzol (1,4-DiPBz).

(118) They show that nanosized catalysts FAU-Y-70a and FAU-Y-10a are more active than a good quality commercial zeolite such as LZY-62 (UOP). In addition, there is a clear trend between particle size and activity at both temperatures. The FAU-Y-10a and the FAU-Y-70a catalysts display similar performances although their external surface areas are quite different and their bulk Si/Al ratios are very close.

(119) The selectivity data (FIG. 11) provide further insight, especially at 200 C. While conversion steadily increases from the LZY-62 to the FAU-Y-70a/FAU-Y-10a catalysts, the latter remain very selective towards the mono-dealkylated products, further indicating that the external surface is the main locus of the reaction.

(120) The above results highlight that the synthetic faujasite materials prepared according to the method of the invention display the qualities required to have a strong impact in potential applications. In particular, they display desirable physico-chemical properties while their large scale production could meet strict health, safety and environmental requirements at an affordable cost.

(121) These FAU nanocrystals reach the theoretical maximum porosity and stay stable as colloidal suspension and as powders. The properties of the nanocrystalline FAU zeolite for adsorption and intracrystalline diffusion afford many potential opportunities for applications in environmental catalysis, environmental remediation, decontamination, and drug delivery. The possible green mass production of nanosized FAU-type zeolite provides excellent opportunities for applications in catalysis, adsorption and separations involving larger molecules. Besides, design of nanoscale devices including optical layers, de-humidifiers, thin films, membranes will be possible by using ultra small nanocrystals with a size smaller than 10 nm via pattering techniques.