METHOD FOR THE PREPARATION OF DEFECT-FREE NANOSIZED SYNTHETIC ZEOLITE MATERIALS

Abstract

Some embodiments are directed to a method for the preparation of defect-free nanosized synthetic zeolite materials, to the defect-free nanosized synthetic zeolite materials, to stable colloidal suspensions of the defect-free synthetic zeolite materials, and to the use of the defect-free nanosized synthetic zeolite materials and the stable colloidal suspensions in various applications.

Claims

1. A method for the preparation of a defect-free synthetic zeolite material in the form of monodisperse single nanocrystals having a size ranging from 10 to 400 nm, the defect-free synthetic zeolite material having a MFI-, BEA- or MEL-framework type and a silicon to metal M molar ratio Si/M ranging from 179 to 65440, the metal M being selected from W, V, Mo, Sn and Zr, the method comprising: 1) contacting at least one source of silicon, at least one source of alkali metal M selected from Na and K, at least one source of metal M selected from W, V, Mo, Sn and Zr, at least one tetraalkylammonium hydroxide structure-directing agent and water, so as to obtain a clear aqueous suspension having the following molar composition:
xM.sub.nO.sub.m:25SiO.sub.2:yTAA.sub.2O:zM.sub.2O:uH.sub.2O(I) in which: 0.01x1.5, 2y9, 0.01z4, 300u3000, n is an integer equal to 1 or 2, and m is an integer and 2m5; 2) aging the resulting clear suspension of step 1) at a temperature ranging from 20 C. to 30 C.; 3) heating the resulting clear suspension at a temperature ranging from 40 C. to 180 C. so as to form a dispersion of a solid comprising monodisperse single nanocrystals of the synthetic zeolite material in a liquid; 4) separating and recovering the solid from the liquid; and 5) calcining the solid so as to obtain the synthetic zeolite material in the form of monodisperse single nanocrystals.

2. The method according to claim 1, wherein the source of silicon is selected from silica hydrogel, silicic acid, colloidal silica, fumed silica, tetraalkyl orthosilicates, silica hydroxides, precipitated silica and sodium silicates.

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

4. The method according to claim 1, wherein the source of M and M is a sodium or a potassium salt of the metal M.

5. The method according to claim 4, wherein the source of M and M is Na.sub.2WO.sub.4.2H.sub.2O, K.sub.2WO.sub.4, NaVO.sub.3, KVO.sub.3, Na.sub.2MoO.sub.4.2H.sub.2O, K.sub.2MoO.sub.4, Na.sub.2SnO.sub.3.3H.sub.2O, K.sub.2SnO.sub.3.3H.sub.2O, Na.sub.2ZrO.sub.3 or K.sub.2ZrO.sub.3.

6. The method according to claim 1, wherein the tetraalkylammonium hydroxide structure-directing agent is tetraethylammonium hydroxide, tetrabutylammonium hydroxide or tetrapropylammonium hydroxide.

7. The method according to claim 1, wherein step 1) is performed at a temperature ranging from 0 C. to 30 C.

8. The method according to claim 1, wherein the clear aqueous suspension of molar composition (I) has a pH ranging from 12 to 14.

9. The method according to claim 1, wherein step 1) is performed according to the following sub-steps: 1-a) separately preparing a clear aqueous silicate suspension A including at least one source of silicon, at least one tetraalkylammonium hydroxide structure-directing agent and water, and a clear aqueous suspension B including at least one source of alkali metal M selected from Na and K, at least one source of metal M selected from W, V, Mo, Sn and Zr, and water, and 1-b) admixing the clear aqueous silicate suspension A and the clear aqueous suspension B until a clear aqueous suspension having the molar composition (I) is obtained.

10. The method according to claim 9, wherein in the admixing sub-step 1-b), the clear aqueous suspension B is added drop wise to the clear aqueous silicate suspension A.

11. The method according to claim 1, wherein the aging step 2) is carried out by stirring the clear aqueous suspension of step 1).

12. The method according to claim 1, wherein the separation and recovering step 4) is performed by filtration, by centrifugation, by dialysis or by using flocculating agents followed by filtration.

13. The method according to claim 1, wherein step 5) is carried out at a temperature ranging from 400 C. to 800 C. under an air, oxygen or inert atmosphere.

14. The method according to claim 1, further comprising, between steps 4) and 5), a step i) of storing the solid obtained in step 4).

15. A defect-free synthetic zeolite material prepared according the method as defined in claim 1, wherein: the material is in the form of monodisperse single nanocrystals having a size ranging from 10 to 400 nm, the material has a MFI-, BEA- or MEL-framework type, and the material a silicon to metal M molar ratio Si/M ranging from 179 to 65440, the metal M being selected from W, V, Mo, Sn and Zr.

16. The defect-free synthetic zeolite material according to claim 15, further comprising at most 1% by mass of metal M, with respect to the total mass of the defect-free synthetic zeolite material.

17. A stable colloidal suspension of a defect-free synthetic zeolite material in the form of monodisperse single nanocrystals having a size ranging from 10 to 400 nm, the defect-free synthetic zeolite material having a MFI-, BEA- or MEL-framework type and a silicon to metal M molar ratio Si/M ranging from 179 to 65440, the metal M being selected from W, V, Mo, Sn and Zr, the material comprising: at least one solvent, and the defect-free synthetic zeolite material as defined in claim 15.

18. The stable colloidal suspension according to claim 17, wherein the mass concentration of the defect-free synthetic zeolite material in the colloidal suspension ranges from 0.1 to 10% by mass, with respect to the total mass of the colloidal suspension.

19. The stable colloidal suspension according to claim 17, wherein the solvent is selected from water, acetone and alcohols.

20. Use of a defect-free synthetic zeolite material in the form of monodisperse single nanocrystals as prepared according to the method as defined in claim 1, as a catalyst or adsorbent in gas-solid and liquid-solid reactions, as seed crystals for zeolite synthesis, and for the preparation of membranes or layers.

21. Use of a stable colloidal suspension of a defect-free synthetic zeolite material in the form of monodisperse single nanocrystals as defined in claim 18, as a catalyst or adsorbent in gas-solid and liquid-solid reactions, as seed crystals for zeolite synthesis, and for the preparation of membranes or layers.

Description

EXAMPLES

[0161] The starting materials used in the examples which follow, are listed below:

[0162] tetra-n-propylammonium hydroxide (TPAOH solution): 20% by mass in water solution, Alfa aesar;

[0163] tetraethyl orthosilicate (TEOS): 98%, Aldrich;

[0164] sodium tungstate dihydrate: 99%, Aldrich;

[0165] sodium metavanadate: 98%, Aldrich;

[0166] sodium zirconium oxide: 98%, Alfa Aesar;

[0167] sodium stannate trihydrate: 95%, Aldrich; and

[0168] sodium molybdate dihydrate: 98%, Alfa Aesar.

[0169] These starting materials were used as received from the manufacturers, without additional purification.

[0170] The various zeolites obtained in the examples were characterized over various scales of sizes.

[0171] Powder X-Ray Diffraction (XRD) Analysis:

[0172] Powder samples of the zeolite materials obtained after step 4) or step 5) were measured using a PANalytical X'Pert Pro diffractometer with CuK monochromatized radiation (=1.5418 , 45 kV, 40 mA). The samples were scanned in the range 3-70 2 with a step size of 0.016.

[0173] Nuclear Magnetic Resonance (NMR) Analysis:

[0174] The crystallinity and defects of the zeolite materials obtained after step 4) or step 5) were determined by .sup.29Si and {.sup.1H}.sup.29Si cross-polarization (CP) solid state MAS NMR on a Bruker Avance III-HD 500 (11.7 T) spectrometer operating at 99.3 MHz, using 4-mm outer diameter zirconia rotors spun at 12 kHz.

[0175] For .sup.29Si MAS NMR, a single pulse excitation (30 flip angle) was used with a recycle delay of 30 s.

[0176] For {.sup.1H}.sup.29Si CP-MAS NMR, a contact time of 5 ms and a recycle delay of 2 s were used.

[0177] .sup.29Si chemical shift were referenced to tetramethylsilane (TMS).

[0178] The location of the structure-directing agent in the zeolite materials was determined by .sup.13C (.sup.1H decoupled, 75 kHz) NMR on a Bruker Avance III-HD 500 (11.7 T) spectrometer operating at 125.7 MHz, using 4-mm outer diameter zirconia rotors with a spinning frequency of 12 kHz.

[0179] Transmission IR Spectroscopy (FTIR) Analysis:

[0180] The presence of surface and bulk defects in the zeolite materials obtained after step 5) was evaluated on self-supporting pellets by transmission IR spectroscopy (Nicolet Magna 550-FT-IR spectrometer at 2 cm.sup.1 optical resolution).

[0181] Raman Spectroscopy Analysis:

[0182] In order to confirm the absence of metal oxides in the zeolite nanocrystals, the zeolite materials obtained after step 5) were analyzed with a Jobin Yvon Labram 300 spectrometer with a confocal microscope (laser: 532 nm, acquisition time: 240 s).

[0183] High-Resolution Transmission Electron Microscopy (HR-TEM):

[0184] Diluted colloidal suspensions of zeolite materials obtained after step 4) or 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, crystallinity and chemical composition of solids were determined by high-resolution transmission electron microscopy (TEM) using a JEOL Model 2010 FEG system fitted with an EDX analyzer operating at 200 kV.

[0185] Scanning Electron Microscopy (SEM):

[0186] The surface features, morphology, homogeneity and size of zeolite nanocrystals obtained after step 5) were determined by field-emission scanning electron microscope using a MIRA-LMH (TESCAN) fitted with a field emission gun using an accelerating voltage of 30.0 kV. All samples prior the SEM characterization were covered with a conductive layer (Pt or Au).

[0187] Dynamic Light Scattering (DLS) Analysis:

[0188] The hydrodynamic diameters of the zeolite materials in the various suspensions were determined with a Malvern Zetasizer Nano dynamic light scattering (DLS). The analyses were performed on samples obtained after step 4) with a solid mass concentration of 1% 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.

[0189] N.sub.2 Sorption Analysis:

[0190] Nitrogen adsorption/desorption isotherms were measured using Micrometrics ASAP 2020 volumetric adsorption analyzer. Samples of the zeolite materials obtained after step 5) 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.

[0191] Chemical Analysis:

[0192] The chemical compositions of the zeolite materials obtained after step 5) were determined by inductively coupled plasma (ICP) optical emission spectroscopy using a Varian ICP-OES 720-ES and EDX-TEM.

Example 1

1.1 Preparation of a Defect-Free MFI-Type Synthetic Zeolite Material W-MFI-1 According to the Method of Some Embodiments

[0193] Step 1):

[0194] A clear aqueous silicate suspension A was prepared by mixing 5.0 g of TEOS with 5.85 g of TPAOH solution. The clear aqueous silicate suspension A was stirring at room temperature (i.e. 25 C.).

[0195] A clear aqueous suspension B was prepared by mixing 0.45 g of sodium tungstate dihydrate in 3.95 g of dd H.sub.2O.

[0196] Suspension B was added drop wise to the suspension A. During the addition, suspension A was maintained at room temperature while being vigorously stirred. The pH of the resulting clear aqueous suspension was about 12.

[0197] The resulting clear aqueous suspension had the following molar composition:

WO.sub.3:25SiO.sub.2:3TPA.sub.2O:1Na.sub.2O:500H.sub.2O(I).

[0198] Step 2):

[0199] The resulting clear aqueous suspension was then aged by magnetic stirring for 3 hours at room temperature and by orbital stirring for 14 hours at room temperature.

[0200] Step 3):

[0201] Then, the hydrothermal crystallization was conducted at 100 C. for 15 hours so as to obtain a solid including monodisperse single nanocrystals of defect-free synthetic zeolite material W-MFI-1, the solid being dispersed in mother liquor.

[0202] Step 4):

[0203] The solid was separated and recovered by high-speed centrifugation (20000 rpm, 10 min) and several washes with hot double distilled water (heated at 100 C. for 30 min) until the pH of the remaining water was about 7.5.

[0204] Step 5):

[0205] The solid was subjected to freeze-drying and calcined at 550 C. in air for 6 hours.

[0206] Monodisperse single nanocrystals of synthetic zeolite material W-MFI-1 with a Si/W molar ratio=647 and a Si/Na molar ratio=40 were obtained with a yield of about 25% by mass.

[0207] The monodisperse single nanocrystals had a size of about 70 nm.

1.2 Preparation of a MFI-Type Synthetic Zeolite Material Si-MFI-A According to a Method which is not Part of Some Embodiments for Comparison

[0208] A clear aqueous suspension was prepared by mixing 5.0 g of TEOS, 5.85 g of TPAOH solution and 3.95 g of dd H.sub.2O. The clear aqueous suspension was stirring at room temperature (i.e. 25 C.).

[0209] The pH of the resulting clear suspension was about 12.

[0210] The resulting clear suspension had the following molar composition:

25SiO.sub.2:3TPA.sub.2O:500H.sub.2O.

[0211] The resulting clear aqueous suspension was then aged by magnetic stirring for 3 hours at room temperature and by orbital stirring for 14 hours at room temperature.

[0212] Then, the hydrothermal crystallization was conducted at 100 C. for 15 hours to obtain a solid including monodisperse single nanocrystals of synthetic zeolite material Si-MFI-A, the solid being dispersed in mother liquor.

[0213] The solid was separated and recovered by high-speed centrifugation (20000 rpm, 10 min) and several washes with hot double distilled water (heated at 100 C. for 30 min) until the pH of the remaining water was about 7.5.

[0214] The solid was subjected to freeze-drying and calcined at 550 C. in air for 6 hours.

[0215] Monodisperse single nanocrystals of synthetic zeolite material Si-MFI-A were obtained with a yield of about 25% by mass.

[0216] Si-MFI-A zeolite material is not part of some embodiments since it does not include a metal M as defined in some embodiments.

[0217] The monodisperse single nanocrystals had a size of about 100 nm.

1.3 Preparation of a Defect-Free MFI-Type Synthetic Zeolite Material F-MFI-B According to a Method which is not Part of Some Embodiments for Comparison

[0218] A defect-free synthetic zeolite material F-MFI-B was prepared according to the method described in Guth et al. [Stud. Surf. Sci. Catal., 1986, 28, 121].

[0219] The defect-free F-MFI-B synthetic zeolite material was obtained by hydrothermal crystallization at 60-200 C. in the presence of a structure-directing agent and in fluoride medium (instead of an alkaline medium).

[0220] A defect-free synthetic zeolite material F-MFI-B in the form of monodisperse single nanocrystals having a size of about 50 m was obtained.

[0221] F-MFI-B zeolite material is not part of some embodiments since it does not include a metal M as defined in some embodiments.

1.4 Characterizations of W-MFI-1 and Si-MFI-A

1.4.1 Powder X-Ray Diffraction (XRD), Raman and IR Analyses

[0222] FIG. 1 represents the XRD diffraction spectrum of the defect-free synthetic zeolite material W-MFI-1 prepared according to example 1.1 [FIG. 1grey line (b)] and for comparison of the synthetic zeolite material Si-MFI-A prepared according to example 1.2 [FIG. 1black line (a)]. FIG. 1 shows the intensity (in arbitrary units: a.u.) as a function of the angle 2 (in degree) in the range of 15-50 degrees [FIG. 1(A)], of 7.5-9.5 degrees [FIG. 1(B)] and in the range of 22.5-25 degrees [FIG. 1(C)].

[0223] Only Bragg peaks corresponding to MFI are present in both zeolite materials [cf. FIG. 1(A)]. In addition, the XRD patterns display distinct broad diffraction peaks, typical for nanosized MFI zeolite crystals. The peak positions vary significantly when W is introduced in the MFI type framework (W-MFI-1 zeolite material), i.e. they shift gradually to lower 2 values [see FIGS. 1(B) and 1(C)].

[0224] FIG. 2 represents a Raman spectrum of the defect-free synthetic zeolite material W-MFI-1 prepared according to example 1.1 [FIG. 2grey line (b)] and for comparison of the synthetic zeolite material Si-MFI-A prepared according to example 1.2 [FIG. 2black line (a)]. FIG. 2 shows the absorbance (in arbitrary units: a.u.) as a function of the wavenumber (in cm.sup.1) in the range of 200-1500 cm.sup.1 [FIG. 2(A)] and in the range of 900-1400 cm.sup.1 [FIG. 2(B)].

[0225] FIG. 2 clearly indicates that no Raman signal corresponding to crystalline WO.sub.3 (713 cm.sup.1 and 808 cm.sup.1) is detected, thus excluding the occurrence of a segregated WO.sub.3 phase. W-MFI-1 zeolite material exhibits two new Raman bands (1036 cm.sup.1 and 1062 cm.sup.1) assigned to bending and symmetric stretching vibrations of framework OWOSi, analogous to the M-OSi vibration in the Ti-Silicate-1, Fe-Silicate-1, and Nb-Silicate-1 zeolites. The strong Raman band at 981 cm.sup.1 observed on Si-MFI-A zeolite material, does not appear on W-MFI-1 zeolite material [FIG. 2(B)]; the band is commonly assigned to the SiOH stretching mode of O.sub.3SiOH groups, and thus related to the presence of defects in the MFI-type structure of Si-MFI-A zeolite material. The absence of this band in the W-MFI-1 zeolite material obviously implies the absence of framework defects.

[0226] FIG. 3 represents a FTIR spectrum of the defect-free synthetic zeolite material W-MFI-1 prepared according to example 1.1 [FIG. 3-(b)] and for comparison of the synthetic zeolite material Si-MFI-A prepared according to example 1.2 [FIG. 3-(a)].

[0227] The absence of the defective silanol groups in the W-MFI-1 zeolite material is confirmed by FIG. 3. Indeed, two intense bands at 3500 cm.sup.1 and 3734 cm.sup.1 are present on the Si-MFI-A zeolite material's spectra: the band at 3500 cm.sup.1 corresponds to silanol nests in the porous matrix, and the band at 3734 cm.sup.1 is attributed to both isolated external and internal silanol groups. They are absent on the IR spectrum of the W-MFI-1 zeolite material, suggesting that it is free from defects.

[0228] Hence, from the Raman and IR spectroscopic results, there is strong evidence that the W-MFI-1 nanosized zeolite material is defect-free.

1.4.2 NMR Analyses

[0229] The .sup.29Si NMR spectrum of the F-MFI-B zeolite material prepared according to example 1.3 [FIG. 4(A)-(c)] displays well resolved peaks between 108 ppm and 120 ppm, corresponding to the twelve nonequivalent framework silicon atoms [Si(OSi).sub.4, denoted as Q.sub.4], in the orthorhombic structure; their chemical shifts are related to the average SiOSi bond angles. The .sup.29Si NMR spectrum of the Si-MFI-A zeolite material [FIG. 4(A)-(a)] consists of the Q.sub.4 considerably less resolved than on the F-MFI-B zeolite material. An addition, a weak signal centered at 103 ppm is observed on Si-MFI-A zeolite material (6-7% of the total .sup.29Si signal), indicating the presence of many defective Q.sub.3 sites such as terminal silanols, [(HO)Si(OSi).sub.3], on the crystals surface or in silanol nests. On the contrary, W-MFI-1 zeolite material [FIG. 4(A)-(b)] exhibits only well-resolved Q.sub.4 signals, similar to F-MFI-B zeolite material, albeit slightly broader. This implies lower local distortions in the immediate vicinity of the Q.sub.4 silicon sites than on Si-MFI-A zeolite material. Furthermore, only a broad signal at 100 ppm is observed for W-MFI-1 zeolite material [FIG. 4(A)-(b)], accounting for about 1-2% of the total intensity and disappearing in the cross-polarization spectrum. More importantly, it is known that when silicon atoms linked to the Q.sub.4 site are substituted by heteroatoms, a downfield shift is observed; for instance, in the case of Q.sub.4(OZn), it is known that a signal appears around 95 ppm. Thus, a possible assignment for the 100 ppm peak in W-MFI-1 zeolite material is a Q.sub.4(OW) site. The slight distortion introduced by the incorporation of W in the MFI framework can explain the broadening of the .sup.29Si RMN line in the W-MFI-1 zeolite material compared to the F-MFI-B zeolite material [FIGS. 4(A)-(b) and 4(A)-(c)]. Such an assignment is further supported by cross-polarization {.sup.1H}.sup.29SiCP MAS NMR spectra of nanosized zeolites W-MFI-1 and Si-MFI-A [FIGS. 4(B)-(b) and 4(B)-(a)]: while no signal is detected in the F-MFI-B zeolite material spectrum [FIG. 4(B)-(c)], the Si-MFI-A zeolite material exhibits strong Q and even Q.sub.2 units [(HO).sub.2Si(OSi).sub.2] [FIG. 4(B)-(a)]. The formation of defect-free W-MFI-1 zeolite material is confirmed by the absence of any Q.sub.3 and Q.sub.2 signals in the {.sup.1H}.sup.29SiCP MAS NMR spectrum [FIG. 4(B)-(b)], indicating no short-range defects, as in the F-MFI-B zeolite material [FIG. 4(B)-(c)].

[0230] Moreover, .sup.29Si NMR spectra were recorded on as-synthesized (i.e. after step 4)) and calcined samples (i.e. after step 5)) to verify whether existing defects in W-MFI-1 zeolite material are healed during calcination or are already absent at the synthesis stage. As shown in FIG. 5, the spectra of the as-synthesized (FIG. 5-b.sub.1) and calcined (FIG. 5-b.sub.2) W-MFI-1 zeolite material contain well-resolved resonances, highlighting that no defects are present after the synthesis. By comparison, the spectra of the as-synthesized (FIG. 5-a.sub.1) and calcined (FIG. 5-a.sub.2) Si-MFI-A zeolite material show strong Q.sub.3 and even Q.sub.2 units [(HO).sub.2Si(OSi).sub.2] like in FIG. 4(B)-(a).

1.4.3 HR-TEM Analyses

[0231] High-resolution transmission electron microscopy (HR-TEM) of W-MFI-1 zeolite material [FIGS. 6-(a) and 6-(b)] revealed the presence of nanocrystals with a size around 60-70 nm.

[0232] High-resolution transmission electron microscopy (HR-TEM) of Si-MFI-A zeolite material [FIGS. 6-(c) and 6-(d)] revealed the presence of nanocrystals with a size around 100 nm.

[0233] These results are consistent with the data obtained from SEM and Dynamic light scattering (DLS) (FIG. 7). FIG. 7(A) represents a FE-SEM image of Si-MFI-A zeolite material and FIG. 7(B) represents a FE-SEM image of W-MFI-1 zeolite material. FIG. 7(C) represents DLS curves of Si-MFI-A zeolite material (FIG. 7(C)-(a)) and W-MFI-1 zeolite material (FIG. 7(C)-(b)).

[0234] Indeed, the introduction of WI in the W-MFI zeolite crystals cures structural framework defects and removes silanol groups from the surface by forming double bonds with oxygen, thus eliminating the need to terminate the crystals with silanols.

[0235] EDX-HR-TEM analyses of W-MFI-1 zeolite material and Si-MFI-A zeolite material indicated the presence of W in the former sample (FIG. 8). A peak at 8.4 keV corresponding to tungsten (1% by mass approximately) was clearly seen in the EDX spectrum, in agreement with ICP analyses.

[0236] In conclusion, nanosized defect-free tungsten containing MFI zeolite single nanocrystals were obtained with the method of some embodiments. Indeed, Tungsten acts as a defect-suppressing element due to its flexible coordination state; the defect sites (internal and external silanols) in the MFI zeolite nanocrystals can be saturated with W.sup.VI coordinated with 4 or 2 Si (T-atoms) via oxygen bridges, thus preventing the formation of silanols.

Example 2

Preparation of a Defect-Free MFI-Type Synthetic Zeolite Material V-MFI-2 According to the Method of Some Embodiments

[0237] A defect-free MFI-type synthetic zeolite material V-MFI-2 was prepared according to the same procedure described in example 1.1, except that 0.15 g of NaVO.sub.3 was used instead of 0.45 g of sodium tungstate dihydrate.

[0238] The resulting clear aqueous suspension obtained after step 1) had the following molar composition:

VO.sub.3:25SiO.sub.2:3TPA.sub.2O:0.5Na.sub.2O:500H.sub.2O(I).

[0239] After step 5), monodisperse single nanocrystals of synthetic zeolite material V-MFI-2 were obtained. They had a size of about 60 nm.

Example 3

Preparation of a Defect-Free MFI-Type Synthetic Zeolite Material Mo-MFI-3 According to the Method of Some Embodiments

[0240] A defect-free MFI-type synthetic zeolite material Mo-MFI-3 was prepared according to the same procedure described in example 1.1, except that 0.39 g of Na.sub.2MoO.sub.4.2H.sub.2O was used instead of 0.45 g of sodium tungstate dihydrate.

[0241] The resulting clear aqueous suspension obtained after step 1) had the following molar composition:

MoO.sub.3:25SiO.sub.2:3TPA.sub.2O:1Na.sub.2O:500H.sub.2O(I).

[0242] After step 5), monodisperse single nanocrystals of synthetic zeolite material Mo-MFI-3 were obtained. They had a size of about 70 nm.

Example 4

Preparation of a Defect-Free MFI-Type Synthetic Zeolite Material Zr-MFI-4 According to the Method of Some Embodiments

[0243] A defect-free MFI-type synthetic zeolite material Zr-MFI-4 was prepared according to the same procedure described in example 1.1, except that 0.27 g of Na.sub.2ZrO.sub.3 was used instead of 0.45 g of sodium tungstate dihydrate.

[0244] The resulting clear aqueous suspension obtained after step 1) had the following molar composition:

ZrO.sub.2:25SiO.sub.2:3TPA.sub.2O:1Na.sub.2O:500H.sub.2O(I).

[0245] After step 5), monodisperse single nanocrystals of synthetic zeolite material Zr-MFI-4 were obtained. They had a size of about 90 nm.

Example 5

Preparation of a Defect-Free MFI-Type Synthetic Zeolite Material Sn-MFI-5 According to the Method of Some Embodiments

[0246] A defect-free MFI-type synthetic zeolite material Sn-MFI-5 was prepared according to the same procedure described in example 1.1, except that 0.48 g of Na.sub.2Sn.sub.3.3H.sub.2O was used instead of 0.45 g of sodium tungstate dihydrate.

[0247] The resulting clear aqueous suspension obtained after step 1) had the following molar composition:

SnO.sub.2:25SiO.sub.2:3TPA.sub.2O:1Na.sub.2O:500H.sub.2O(I).

[0248] After step 5), monodisperse single nanocrystals of synthetic zeolite material Sn-MFI-5 were obtained. They had a size of about 50 nm.

Example 6

Characterization of Defect-Free MFI-Type Synthetic Zeolite Materials Prepared in Examples 1 to 5

[0249] The table 1 below represents the porosity properties of the defect-free synthetic zeolite materials W-MFI-1, V-MFI-2, Mo-MFI-3 and Zr-MFI-4 which are part of some embodiments, and by comparison the ones of Si-MFI-A which is not part of the presently disclosed subject matter. There data were obtained by N.sub.2 sorption analysis.

TABLE-US-00001 TABLE 1 Zeolite S.sub.BET S.sub.ext V.sub.micro V.sub.total material (m.sup.2 .Math. g.sup.1) (m.sup.2 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) W-MFI-1 345 106 0.17 0.70 V-MFI-2 368 106 0.14 0.48 Mo-MFI-3 323 110 0.11 0.38 Zr-MFI-4 308 55 0.12 0.21 Sl-MFI-A (*) 517 128 0.19 0.65 (*) not part of the presently disclosed subject matter

[0250] FIG. 9 represents the XRD diffraction spectrum of the defect-free synthetic zeolite materials V-MFI-2, Zr-MFI-4, Mo-MFI-3 and Sn-MFI-5 respectively prepared in example 2 [FIG. 8-(a)], example 4 [FIG. 8-(b)], example 3 [FIG. 8-(c)] and example 5 [FIG. 8-(d)].

[0251] FIG. 9(A) shows the intensity (in arbitrary units: a.u.) as a function of the angle 2 (in degree) in the range of 3-50 degrees and FIG. 9(B) in the range of 20-28 degrees.

[0252] FIG. 10 represents SEM and TEM images of defect-free synthetic zeolite materials prepared in examples 2 to 4.

[0253] More particularly, FIGS. 10-(a) and FIG. 10-(d) respectively represent SEM and TEM images of defect-free V-MFI-2 zeolite material, FIG. 10-(b) and FIG. 10-(e) respectively represent SEM and TEM images of defect-free Mo-MFI-3 zeolite material, and FIG. 10-(c) and FIG. 10-(f) respectively represent SEM and TEM images of defect-free Zr-MFI-4 zeolite material.

Example 7

Use of the Defect-Free MFI-Type Synthetic Zeolite Material W-MFI-1 as an Adsorbent

[0254] The detection of gases such as CO, CO.sub.2, NO or NO.sub.2 gases with defect-free W-MFI-1 zeolite material prepared in example 1.1 and for comparison with Si-MFI-A zeolite material prepared in example 1.2 was studied.

[0255] The zeolite materials were used as self-supported pellets and as thin films and the detection was followed using in situ FTIR spectroscopy.

[0256] For characterization of self-supported pellets (10 mg.Math.cm.sup.2), the transmission IR spectra were recorded with a Nicolet Avatar spectrometer. A room temperature IR-cell equipped with a heating device offered the possibility to activate the samples at 525 C. prior to the measurements. The cell was connected to a high vacuum line with a reachable pressure of 10.sup.5 Pa. Three-step activation was applied to the samples: a first step at 100 C. for 0.5 h to desorb most the adsorbed water, second and third steps at 200 C. and 525 C. for 0.5 h and 1.0 h, respectively to remove the residue (i.e. hydrocarbons) coming from the structure-directing agent. All above steps were performed under secondary vacuum. Little doses of gas have been incrementally introduced onto the MFI pellet present in FTIR cell at room temperature. All IR spectra were recorded at room temperature, and as a background the IR spectrum recorded in empty transmission cell under secondary vacuum at room temperature was used.

[0257] For characterization of films, a reactor-cell working in the temperature range 25-300 C. connected to operando IR system was used. The entire process, including activation of samples (removal of adsorbed water and contaminants at 300 C.) and controlled adsorption and desorption of pure CO.sub.2, CO, NO.sub.2 and NO as pure compounds in argon (Ar), were performed in the operando IR cell at room temperature. All experiments were performed in the presence of water with a concentration of 100 ppm coming from the Ar used as a carrier gas. The spectra were collected in a continuous mode (32 scans/spectrum) using a Bruker Tensor 27 spectrometer equipped with a DTGS detector.

[0258] Films Preparation:

[0259] Zeolite films were prepared by deposition of a coating suspension of the W-MFI-1 or Si-MFI-A zeolite material on a silicon wafer (spin coating method). The silicon wafers having a dimension of 1010 mm.sup.2 was first pre-cleaned with ethanol, and then placed in a WS-400B-6NPP-LITE spin coater system. The samples were vacuum-locked under nitrogen atmosphere during spinning process. In order to ensure the preparation of smooth and homogenous films, the coating suspensions of W-MFI-1 and Si-MFI-A zeolite nanocrystals were filtered (filters diameter of 200 nm) prior to deposition. In order to prepare films with good mechanical stability, firstly a solution of 5% by mass of polyvinylpyrrolidone (PVP) in ethanol was deposited on the wafer to form a smooth layer of polyvinylpyrrolidone (PVP)-based binder (spinning rate of 3000 rpm for 60 s). Then, after complete drying under air atmosphere, a zeolite coating suspension containing 1% by mass of W-MFI-1 zeolite nanocrystals or Si-MFI-A zeolite nanocrystals in ethanol solvent was deposited (500 rpm for 600 s). Finally, the obtained zeolite films were annealed at 550 C. for 6 h (heating rate of 3 C./min).

[0260] It is noted that the zeolite films can also be prepared by seed approach, dip coating, ink jet printing, drop casting or direct crystallization. Others organic or inorganic binders different from PVP can also be used and are described in Lakiss et al. [Thin Solid Films, 2010, 518, 2241-2246] and Mintova et al. [Nanoscale, 2013, 5, 6693-6703].

[0261] FIG. 11 represents the absorption capacity of W-MFI-1 zeolite material (curve with circles) and Si-MFI-A zeolite material (curve with squares) towards NO.sub.2.

[0262] More particularly, FIG. 11(A) shows the FTIR band area (in arbitrary units, a.u.) of W-MFI-1 zeolite material (curve with circles) and Si-MFI-A zeolite material (curve with squares) assembled as self-supported pellets, as a function of the concentration of NO.sub.2 (in g/mol, n.sub.NO2) and FIG. 11(B) shows the FTIR band area (in arbitrary units, a.u.) of W-MFI-1 zeolite material (curve with circles) and Si-MFI-A zeolite material (curve with squares) assembled as thin films, as a function of the concentration of NO.sub.2 (in ppm, n.sub.NO2).

[0263] FIG. 12 represents the absorption capacity of the W-MFI-1 zeolite films towards NO.sub.2 (curve with squares), NO (curve with circles), CO (curve with triangles) and CO.sub.2 (curve with inversed triangles).