CHABAZITE-TYPE ZEOLITE, PRECURSORS THEREOF, METHODS FOR MAKING THE SAME AND USE OF THE ZEOLITE AS SORBENT FOR CO2

Abstract

The present disclosure relates to a chabazite-type zeolite, comprising at least two cages composed of 4- and 8-membered rings connected by one 6-membered double ring, remarkable in that it has a Si/Al molar ratio comprised between 1 and 15, in that it comprises caesium and potassium with a Cs/K molar ratio of at most 5.0 and in that it forms nanoparticles with an average crystal size comprised between 5 nm and 250 nm and with a specific surface area comprised between 50 m.sup.2g.sup.−1 and 200 m.sup.2g.sup.−1. Amorphous precursors, devoid of an organic structure-directing agent, as well as a method for preparation of these amorphous precursors in the absence of such organic structure-directing agent and method for preparation of the chabazite-type zeolite, are also described. Finally, the use of the chabazite-type zeolite as a sorbent for carbon dioxide is also demonstrated.

Claims

1. A chabazite-type zeolite, comprising at least two cages composed of 4- and 8-membered rings connected by one 6-membered double ring, characterized by having a Si/Al molar ratio comprised between 1 and 15 as determined by .sup.29Si magic angle spinning nuclear magnetic resonance, said chabazite-type zeolite comprises caesium and potassium with a Cs/K molar ratio of at most 5.0 as determined by Inductively Coupled Plasma Optical Emission Spectrometry; and said chabazite-type zeolite forming nanoparticles with an average crystal size comprised between 5 nm and 250 nm as determined by the Scherrer equation and with a specific surface area comprised between 50 m.sup.2 g.sup.−1 and 200 m.sup.2 g.sup.−1, as determined by N.sub.2 sorption measurements.

2. The chabazite-type zeolite according to claim 1, characterized in that said nanoparticles have a pore volume comprised between 0.10 cm.sup.3 g.sup.−1 and 0.50 cm.sup.3 g.sup.−1, as determined by N.sub.2 sorption measurements.

3. (canceled)

4. The chabazite-type zeolite according to claim 1, characterized in that said chabazite-type zeolite has an M.sup.1/Al molar ratio ranging from 0.02 to 0.20, as determined by Inductively Coupled Plasma Optical Emission Spectrometry wherein M.sup.1 is selected from Na and/or Li; preferably from 0.05 to 0.15; more preferably from 0.075 and 0.12.

5. The chabazite-type zeolite according to claim 1, characterized in that said chabazite-type zeolite has an M.sup.1/Cs molar ratio ranging from 0.10 to 0.50, as determined by Inductively Coupled Plasma Optical Emission Spectrometry wherein M.sup.1 is selected from Na and/or Li; preferably from 0.14 to 0.40; more preferably from 0.17 and 0.30.

6. The chabazite-type zeolite according to claim 1, characterized in that the Si/Al molar ratio as determined by .sup.29Si magic angle spinning nuclear magnetic resonance is at least 1.5; preferably at least 2.1.

7. The chabazite-type zeolite according to claim 1, characterized in that the Si/Al molar ratio as determined by .sup.29Si magic angle spinning nuclear magnetic resonance is at most 5, preferably at most 3.0.

8. (canceled)

9. The chabazite-type zeolite according to claim 1, characterized in that the Cs/K molar ratio is at least 0.1 as determined by Inductively Coupled Plasma Optical Emission Spectrometry; preferably at least 0.3; more preferably at least 0.5.

10. The chabazite-type zeolite according to claim 1, characterized in that said chabazite-type zeolite has a Cs/Al molar ratio comprised between 0.15 and 0.45 as determined by Inductively Coupled Plasma Optical Emission Spectrometry, preferably between 0.20 and 0.40, more preferably between 0.22 and 0.38.

11. (canceled)

12. An amorphous precursor of chabazite-type zeolite for the preparation of a chabazite-type zeolite according to claim 1, characterized in that said amorphous precursor of chabazite-type zeolite has a molar composition comprising a SiO.sub.2:b Al.sub.2O.sub.3:c M.sup.1.sub.2O:d K.sub.2O:e Cs.sub.2O:f H.sub.2O, wherein a, b, c, d, e, and f are coefficients, wherein the coefficient a is ranging from at least 10.0 and at most 20.0; the coefficient b is ranging from at least 0.3 and at most 2.5; the coefficient c is ranging from at least 5.0 and at most 11.0; the coefficient d is ranging from at least 0.7 and at most 1.6; the coefficient e is ranging from at least 0.05 and at most 0.60; and the coefficient f is ranging from at least 60 and at most 200 wherein M.sup.1.sub.2O is selected from Na.sub.2O and/or Li.sub.2O.

13. The amorphous precursor of claim 12, characterized in that the coefficient a is ranging from at least 10.0 and at most 16.0; and/or the coefficient b is ranging from at least 0.5 and at most 1.5.

14. The amorphous precursor of claim 12, characterized in that the coefficient c is ranging from at least 6.0 and at most 10.0; and/or the coefficient d is ranging from at least 0.8 and at most 1.6.

15. The amorphous precursor of claim 12, characterized in that the coefficient e is ranging from at least 0.15 and at most 0.45 and/or the coefficient f is at least 80 and at most 190; preferably at least 90 and at most 160.

16. The amorphous precursor of claim 12, characterized in that the (M.sup.1.sub.2O+Cs.sub.2O+K.sub.2O)/SiO.sub.2 ratio is at least 0.55 wherein M.sup.1 is selected from Na and/or Li, preferably is ranging from 0.55 to 1.00; more preferably from 0.58 to 0.95 and even more preferably from 0.60 to 0.90.

17. The amorphous precursor of claim 12, characterized in that the ratio M.sup.1.sub.2O/H.sub.2O is superior or equal to 0.03, preferably superior or equal to 0.04, more preferably superior or equal to 0.05.

18. The amorphous precursor of claim 12, characterized in that the ratio M.sup.1.sub.2O/Al.sub.2O.sub.3 is superior or equal to 7.0, preferably superior or equal to 7.5.

19. The amorphous precursor of claim 12, characterized in that the ratio Cs.sub.2O /Al.sub.2O.sub.3 is inferior or equal to 0.80, preferably inferior or equal to 0.60.

20. Method for the preparation of an amorphous precursor of a chabazite-type zeolite as defined in claim 12, comprising the following steps: a) providing an aluminate precursors aqueous suspension; b) providing a silicate precursors aqueous suspension; c) adding at least three metallic precursors in the said aluminate precursors aqueous suspension to form a first aqueous suspension, wherein the at least three metallic precursors comprises caesium hydroxide, potassium hydroxide and at least one selected from sodium hydroxide and/or lithium hydroxide; d) forming an amorphous precursor of zeolite by adding dropwise the silicate precursors aqueous suspension into said first aqueous suspension; with preference, the at least three metallic precursors comprise caesium hydroxide, potassium hydroxide and sodium hydroxide.

21. (canceled)

22. Method for the preparation of an amorphous precursor of a chabazite-type zeolite as defined in claim 12, comprising the following steps: a) providing an aluminate precursors aqueous suspension; b) providing a silicate precursors aqueous suspension; c) adding at least three metallic precursors in the said silicate precursors aqueous suspension to form a second aqueous suspension, wherein the at least three metallic precursors comprise caesium hydroxide, potassium hydroxide and at least one selected from sodium hydroxide and/or lithium hydroxide; d) forming an amorphous precursor of zeolite by adding dropwise the aluminate precursors aqueous suspension into said second aqueous suspension; with preference, the at least three metallic precursors comprise caesium hydroxide, potassium hydroxide and sodium hydroxide.

23. (canceled)

24. Method for the preparation of an amorphous precursor of a chabazite-type zeolite as defined in claim 12, comprising the following steps, a) providing an aluminate precursors aqueous suspension; b) providing a silicate precursors aqueous suspension; c) adding at least three metallic precursors in the said aluminate precursors aqueous suspension to form a first aqueous suspension and in the said silicate precursors aqueous suspension to form a second aqueous suspension, wherein the at least three metallic precursors comprise caesium hydroxide, potassium hydroxide and at least one selected from sodium hydroxide and/or lithium hydroxide; d) forming an amorphous precursor of zeolite by adding dropwise the said first aqueous suspension into said second aqueous suspension or by adding dropwise the said second aqueous suspension into said first aqueous suspension; with preference, the at least three metallic precursors comprise caesium hydroxide, potassium hydroxide and sodium hydroxide.

25. (canceled)

26. (canceled)

27. Method for the preparation of a chabazite-type zeolite as defined in claim 1, comprising the method for the preparation of an amorphous precursor of a chabazite-type zeolite according to claim 20 and further comprising the following steps: e) mixing the amorphous precursor according to claim 12 under stirring and/or orbital shaking; f) optionally, adding an additional silicate precursors aqueous suspension and mixing said amorphous precursor under stirring and/or orbital shaking; g) heating said amorphous precursor at a temperature comprised between 90° C. and 160° C. such as to form one or more crystals of chabazite-type zeolite; h) cooling down said one or more crystals of chabazite-type zeolite at a temperature comprised between 20° C. and 25° C., i) dispersing said one or more crystals of chabazite-type zeolite in water, j) optionally, recovering said one or more crystals of chabazite-type zeolite.

28.-30. (canceled)

Description

DESCRIPTION OF THE FIGURES

[0257] FIG. 1 shows the X-ray diffraction (XRD) of samples 1, 10 and 12.

[0258] FIGS. 2A to 2I respectively show the Scanning Electron Microscope (SEM) images of samples 1 to 9.

[0259] FIG. 3 shows the N.sub.2 adsorption-desorption isotherm of samples 1, 4, 9, 10, 11 and 12.

[0260] FIG. 4 shows the CO.sub.2 adsorption isotherm of samples 1, 9, 10, 11 and 12 recorded at 0° C.

[0261] FIG. 5 shows the Rietveld refinement of sample 10.

[0262] FIGS. 6A and 6B show the Transmission Electron Microscope (TEM) images of sample 10 at a magnification of 200 nm.

[0263] FIG. 6C and 6D respectively show the Transmission Electron Microscope (TEM) images of sample 12 at a magnification of 100 nm and 20 nm.

[0264] FIGS. 6E and 6F show the Transmission Electron Microscope (TEM) images of sample 13 at a magnification of 20 nm.

[0265] FIG. 7 shows the thermogravimetric analysis of nanosized chabazite zeolite of sample 10 subject to 10 subsequent sorption cycles of CO.sub.2.

[0266] FIG. 8 shows the CO.sub.2 capacity of the zeolite of sample 10 in 10 sorption cycles of CO.sub.2.

[0267] FIG. 9 shows the XRD patterns of the zeolite of sample 10 before and after 10 sorption cycles of CO.sub.2.

[0268] FIG. 10 shows the in situ Fourier Transform Infra-Red (FTIR) spectrum recorded for sample 10 under delivery of a small dose of CO.sub.2 (3.10.sup.−4 mmol to 1.10.sup.−1 mmol).

[0269] FIG. 11 shows the in situ Fourier Transform Infra-Red (FTIR) spectrum recorded for sample 10 under delivery of a small dose of CH.sub.4 at a partial pressure of 0.1 mbar, 20 mbar, 28 mbar and 33 mbar at room temperature.

[0270] FIG. 12 shows the LeBail refinement of ion-exchanged zeolite of sample 10 (proton form).

[0271] FIG. 13 shows the in situ XRD patterns of sample 10 recorded under delivery of 1 bar of CO.sub.2.

[0272] FIG. 14 shows the evolution of the intensity of the peak at 12.8° 2θ of sample 10 under controlled adsorption of CO.sub.2.

[0273] FIG. 15 shows the change of the cell volume of sample 10 under controlled adsorption of CO.sub.2.

[0274] FIG. 16 shows the unit cell parameter under adsorption and desorption of CO.sub.2 of sample 10.

[0275] FIG. 17 shows the c-potential curve of sample 13.

[0276] FIG. 18 shows the normalised mass adsorption of CO.sub.2 and CH.sub.4 as pure gas followed by TGA experiments for sample 10.

[0277] FIG. 19 shows the XRD patterns of samples 16-18.

[0278] FIG. 20 shows the SEM image of a CHA zeolite (sample 16).

[0279] FIG. 21 shows the SEM image of an RHO zeolite (sample 17).

[0280] FIG. 22 shows the SEM image of an FAU zeolite with EMT as the secondary phase (sample 18).

DETAILED DESCRIPTION

[0281] For the disclosure, the following definitions are given:

[0282] The terms “nanosized” and “nanozeolites” refers to crystals of zeolite having a size lower than 200 nm.

[0283] Zeolite codes (e.g., CHA . . . ) are defined according to the “Atlas of Zeolite Framework Types”, 6.sup.th revised edition, 2007, Elsevier, to which the present application also refers.

[0284] The term “alkali metal” refers to an element classified as an element from group 1 of the periodic table of elements, excluding hydrogen. According to this definition, the alkali metals are Li, Na, K, Rb, Cs, and Fr.

[0285] The term “alkaline earth metal” refers to an element classified as an element from group 2 of the periodic table of elements. According to this definition, the alkaline earth metals are Be, Mg, Ca, Sr, Ba, and Ra.

[0286] The terms “comprising”, “comprises” and “comprised of” as used herein are synonymous with “including”, “includes” or “containing”, “contains”, and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. The terms “comprising”, “comprises” and “comprised of” also include the term “consisting of”.

[0287] The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g. 1 to 5 can include 1, 2, 3, 4 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of endpoints also includes the recited endpoint values themselves (e.g. from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein.

[0288] The particular features, structures, characteristics or embodiments may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments.

Method for Preparing the Precursor of the Chabazite-Type

[0289] The disclosure provides a method for the preparation of an aqueous amorphous precursor of chabazite-type zeolite, comprising the following steps:

[0290] a) providing an aluminate precursors aqueous suspension;

[0291] b) providing a silicate precursors aqueous suspension;

[0292] c) adding at least three metallic precursors in the said aluminate precursors aqueous suspension to form a first aqueous suspension and/or in the said silicate precursors aqueous suspension to form a second aqueous suspension;

[0293] d) forming an amorphous precursor of chabazite-type zeolite by adding dropwise said aluminate precursors aqueous suspension into said second aqueous suspension or by adding dropwise the silicate precursors aqueous suspension into said first aqueous suspension; or by adding dropwise that said first or the said second aqueous suspension into said second or said first aqueous suspension respectively;

[0294] wherein the at least three metallic precursors comprises caesium hydroxide, potassium hydroxide and at least one selected from sodium hydroxide and/or lithium hydroxide. With preference, the at least three metallic precursors comprise caesium hydroxide, potassium hydroxide and sodium hydroxide.

[0295] In a preferred embodiment, said aluminate precursors aqueous suspension and said silicate precursors aqueous suspension are organic structure-directing agent-free.

[0296] The one or more aluminate precursors in the aluminate precursors aqueous suspension provided in step (a) are preferably selected among Na.sub.2l.sub.2O.sub.4, Al.sub.2(SO.sub.4).sub.3, hydrated alumina, aluminium powder, AlCl.sub.3, Al(OH).sub.3, kaolin clays and a mixture thereof, preferably Na.sub.2Al.sub.2O.sub.4 (note: another notation for Na.sub.2Al.sub.2O.sub.4 is NaAlO.sub.2). Na.sub.2Al.sub.2O.sub.4, when selected, comprised between 48 wt. % and 63 wt. % of Al.sub.2O.sub.3 and between 37 wt. % and 52 wt. % of Na.sub.2O, preferably 53 wt. % of Al.sub.2O.sub.3 and between 47 wt. % of Na.sub.2O.

[0297] The one or more aluminate precursors in the aluminate precursors aqueous suspension provided in step (a) are preferably present in an amount comprised between 3 wt. % and 25 wt. % of the total weight of the aluminate precursors aqueous suspension, more preferably between 5 wt. % and 20 wt. %, even more preferably between 6 wt. % and 10 wt. %. The aluminate precursors aqueous suspension comprises water, preferably distilled water, more preferably double distilled water.

[0298] The one or more silicate precursors in the silicate precursors aqueous suspension provided in step (b) are selected among colloidal silica, silica oxyhydroxide species, silica hydrogel, silicic acid, fumed silica, tetraalkyl orthosilicates, silica hydroxides, precipitated silica, clays and a mixture thereof, preferably colloidal silica. Colloidal silica, when selected, comprises amorphous, nonporous, and spherical silica particles in an aqueous suspension in an amount comprised between 20 wt. % and 50 wt. % of the total weight of said aqueous suspension, preferably between 25 wt. % and 45 wt. %, more preferably of 30 wt. % (e.g. Ludox®HS30) or 40 wt. % (e.g. Ludox®HS40).

[0299] The one or more silicate precursors in the silicate precursors aqueous suspension provided in step (b) are preferably present in an amount comprised between 10 wt. % and 50 wt. % of the total weight of the silicate precursors aqueous suspension, more preferably between 15 wt. % and 45 wt. %, even more preferably between 20 wt. % and 40 wt. %, even more preferably is 15 wt. % or 35 wt. %. The silicate precursors aqueous suspension comprises water, preferably distilled water, more preferably double distilled water.

[0300] Said step (c) comprises the step of adding in both of said aluminate precursors and silicate precursors aqueous suspensions at least three metallic precursors.

[0301] In a preferred embodiment, said at least three metallic precursors are a combination of NaOH, KOH, and CsOH.

[0302] In a preferred embodiment, the content of the at least two metallic precursors in the first aqueous suspension is ranging from 1 wt. % to 97.5 wt. % of the total weight of the first aqueous suspension, preferably from 20 wt. % to 80 wt. %, more preferably from 25 wt. % and 55 wt. %, and most preferably from 30 to 50 wt. %.

[0303] In a more preferred embodiment, the first aqueous suspension comprises water and: [0304] from 5.0 to 15.0 wt. % based on the total weight of the first aqueous suspension of one or more aluminate precursors; preferably from 5.5 to 12.5 wt. %; more preferably from 6.0 to 11.5 wt. %; even more preferably from 6.5 to 10.0 wt. %. and from 15 wt. % to 80 wt. % of the at least three metallic precursors, comprising [0305] from 1 to 30 wt. % based on the total weight of the first aqueous suspension of one or more caesium precursors; and [0306] from 14 to 50 wt. % based on the total weight of the first aqueous suspension of one or more additional precursors comprising: [0307] one or more potassium precursors; and [0308] one or more selected from one or more sodium precursors, one or more lithium precursors, and any mixture thereof; preferably one or more sodium precursors.

[0309] The amorphous precursor obtained with such composition affords upon crystallization a chabazite-type zeolite that has a CO.sub.2 uptake of at least 3.50 mmol/g of zeolite material

[0310] With preference, the first aqueous suspension comprises at most 30 wt. % based on the total weight of the first aqueous suspension of one or more caesium precursors; preferably at most 25 wt. %; more preferably at most 20 wt. %; even more preferably at most 15 wt. %; and most preferably at most 10 wt. %.

[0311] With preference, the first aqueous suspension comprises at least 1 wt. % based on the total weight of the first aqueous suspension of one or more caesium precursors; preferably at least 1.5 wt. %; more preferably at least 2 wt. %; even more preferably at least 2.5 wt. %; and most preferably at least 3 wt. %.

[0312] With preference, the first aqueous suspension comprises at most 50 wt. % based on the total weight of the first aqueous suspension of one or more additional precursors comprising one or more potassium precursors; one or more selected from sodium precursors, and/or lithium precursors; preferably at most 48 wt. %; more preferably at most 45 wt. %; even more preferably at most 40 wt. %; and most preferably at most 38 wt. %.

[0313] With preference, the first aqueous suspension comprises at least 14 wt. % based on the total weight of the first aqueous suspension of one or more additional precursors comprising one or more potassium precursors; one or more selected from sodium precursors, and/or lithium precursors; preferably at least 15 wt. %; more preferably at least 20 wt. %; even more preferably at least 22 wt. %; and most preferably at least 25 wt. %.

[0314] With preference, the first aqueous suspension comprises from 14 to 50 wt. % based on the total weight of the first aqueous suspension of one or more additional precursors comprising: [0315] from 2 wt. % to 15 wt. % based on the total weight of the first aqueous suspension of one or more potassium precursors; and [0316] from 12 wt. % to 35 wt. % based on the total weight of the first aqueous suspension of one or more selected from one or more sodium precursors, one or more lithium precursors, and any mixture thereof; preferably one or more sodium precursors.

[0317] More preferably, the first aqueous suspension comprises from 25 to 45 wt. % based on the total weight of the first aqueous suspension of one or more additional precursors comprising: [0318] from 4 wt. % to 12 wt. % based on the total weight of the first aqueous suspension of one or more potassium precursors; and [0319] from 21 wt. % to 33 wt. % based on the total weight of the first aqueous suspension of one or more selected from one or more sodium precursors, one or more lithium precursors, and any mixture thereof; preferably one or more sodium precursors.

[0320] In one instance, the first aqueous suspension comprises water and: [0321] 7.66 wt. % based on the total weight of the first aqueous suspension of one or more aluminate precursors; [0322] 4.90 wt. % based on the total weight of the first aqueous suspension of one or more caesium precursors; [0323] 5.24 wt. % based on the total weight of the first aqueous suspension of one or more potassium precursors; and [0324] 31.77 wt. % based on the total weight of the first aqueous suspension of one or more selected from one or more sodium precursors, one or more lithium precursors, and any mixture thereof; preferably one or more sodium precursors.

[0325] In a second instance, the first aqueous suspension comprises water and: [0326] 7.06 wt. % based on the total weight of the first aqueous suspension of one or more aluminate precursors; [0327] 4.59 wt. % based on the total weight of the first aqueous suspension of one or more caesium precursors; [0328] 10.90 wt. % based on the total weight of the first aqueous suspension of one or more potassium precursors; and [0329] 25.95 wt. % based on the total weight of the first aqueous suspension of one or more selected from one or more sodium precursors, one or more lithium precursors, and any mixture thereof; preferably one or more sodium precursors.

[0330] In another embodiment, the content of the at least two metallic precursors in the second aqueous suspension is ranging from 1 wt. % to 97.5 wt. % of the total weight of the second aqueous suspension, preferably from 20 wt. % to 80 wt. %, more preferably from 25 wt. % and 55 wt. %, and most preferably from 30 to 50 wt. %.

[0331] In a more preferred embodiment, the second aqueous suspension comprises water and: [0332] from 10 to 35 wt. % based on the total weight of the second aqueous suspension of one or more silicate precursors; preferably from 15 to 30 wt. %; more preferably from 18 to 27 wt. %; and [0333] from 10 wt. % to 60 wt. % of the at least three metallic precursors, comprising: [0334] from 1 to 25 wt. % based on the total weight of the second aqueous suspension of one or more caesium precursors; and [0335] from 9 to 35 wt. % based on the total weight of the second aqueous suspension of one or more additional precursors comprising: [0336] one or more potassium precursors; and [0337] one or more selected from one or more sodium precursors, one or more lithium precursors, and any mixture thereof; preferably one or more sodium precursors.

[0338] With preference, the second aqueous suspension comprises at most 25 wt. % based on the total weight of the second aqueous suspension of one or more caesium precursors; preferably at most 20 wt. %; more preferably at most 15 wt. %; even more preferably at most 10 wt. %; and most preferably at most 5 wt. %.

[0339] With preference, the second aqueous suspension comprises at least 1 wt. % based on the total weight of the second aqueous suspension of one or more caesium precursors; preferably at least 1.5 wt. %; more preferably at least 2 wt. %; even more preferably at least 2.5 wt. %; and most preferably at least 3 wt. %.

[0340] With preference, the second aqueous suspension comprises at most 35 wt. % based on the total weight of the second aqueous suspension of one or more additional precursors comprising one or more potassium precursors and one or more selected from sodium precursors, and/or lithium precursors; preferably at most 30 wt. %; more preferably at most 25 wt. %; even more preferably at most 20 wt. %; and most preferably at most 15 wt. %.

[0341] With preference, the second aqueous suspension comprises at least 9 wt. % based on the total weight of the second aqueous suspension of one or more additional precursors comprising one or more potassium precursors and one or more selected from sodium precursors, and/or lithium precursors; preferably at least 10 wt. %; more preferably at least 11 wt. %; even more preferably at least 12 wt. %; and most preferably at least 13 wt. %.

[0342] With preference, the second aqueous suspension comprises from 9 to 35 wt. % based on the total weight of the second aqueous suspension of one or more additional precursors comprising: [0343] from 1 wt. % to 13 wt. % based on the total weight of the second aqueous suspension of one or more potassium precursors; and [0344] from 8 wt. % to 22 wt. % based on the total weight of the second aqueous suspension of one or more selected from one or more sodium precursors, one or more lithium precursors, and any mixture thereof; preferably one or more sodium precursors.

[0345] More preferably, the second aqueous suspension comprises from 12 to 32 wt. % based on the total weight of the second aqueous suspension of one or more additional precursors comprising: [0346] from 2 wt. % to 12 wt. % based on the total weight of the second aqueous suspension of one or more potassium precursors; and [0347] from 10 wt. % to 20 wt. % based on the total weight of the second aqueous suspension of one or more selected from one or more sodium precursors, one or more lithium precursors, and any mixture thereof; preferably one or more sodium precursors.

[0348] In one instance, the second aqueous suspension comprises water and: [0349] 23.26 wt. % based on the total weight of the second aqueous suspension of one or more silicate precursors; [0350] 2.18 wt. % based on the total weight of the second aqueous suspension of one or more caesium precursors; [0351] 3.99 wt. % based on the total weight of the second aqueous suspension of one or more potassium precursors; and [0352] 14.10 wt. % based on the total weight of the second aqueous suspension of one or more selected from one or more sodium precursors, one or more lithium precursors, and any mixture thereof; preferably one or more sodium precursors.

[0353] It is preferred that the weight ratio of the aqueous suspension containing one or more aluminate precursors over the aqueous suspension containing one or more silicate precursors is comprised between 0.25 and 1.5, preferably between 0.30 and 1.45, more preferably between 0.35 and 1.40, even more preferably between 0.40 and 1.35, most preferably between 0.50 and 1.25; wherein the aqueous suspension containing aluminate precursors is the aluminate precursor aqueous suspension or the first aqueous suspension; and the aqueous suspension containing silicate precursors is second aqueous suspension or the silicate precursor aqueous suspension respectively.

[0354] In another preferred embodiment, the dropwise addition of the aqueous suspension containing one or more aluminate precursors over the aqueous suspension containing one or more silicate precursors is performed in a temperature comprised between −5° C. and 25° C., preferably in a temperature comprised between 20° C. and 25° C. Advantageously, the dropwise addition of the aqueous suspension containing one or more aluminate precursors over the aqueous suspension containing one or more silicate precursors is performed under stirring, preferably under stirring of at least 500 rpm, more preferably of at least 750 rpm.

[0355] In yet another preferred embodiment, the dropwise addition of the aqueous suspension containing one or more silicate precursors onto the aqueous suspension containing one or more aluminate precursors is performed in a temperature comprised between 15° C. and 25° C. Advantageously, the dropwise addition of the aqueous suspension containing one or more silicate precursors onto the aqueous suspension containing one or more aluminate precursors is performed under stirring, preferably under stirring of at least 500 rpm, more preferably of at least 750 rpm.

The Precursor of the Chabazite-Type Zeolite

[0356] The disclosure also provides the precursor of the chabazite-type zeolite. The precursors of the chabazite-type zeolite are obtainable by the method for the preparation of amorphous precursors of chabazite-type zeolite described above. The precursor is amorphous and has a molar composition comprising [0357] a SiO.sub.2:b Al.sub.2O.sub.3:c M.sup.1.sub.2O:d K.sub.2O:e Cs.sub.2O:f H.sub.2O,

[0358] wherein a, b, c, d, e, and f are coefficient; and wherein

[0359] the coefficient a is ranging from at least 10.0 and at most 20.0;

[0360] the coefficient b is ranging from at least 0.3 and at most 2.5;

[0361] the coefficient c is ranging from at least 5.0 and at most 11.0;

[0362] the coefficient d is ranging from at least 0.7 and at most 1.6;

[0363] the coefficient e is ranging from at least 0.05 and at most 0.60; and

[0364] the coefficient f is ranging from at least 60 and at most 200

[0365] wherein M.sup.1 is selected from Na and/or Li.

[0366] For example, the precursor is amorphous and has a molar composition comprising [0367] a SiO.sub.2:b Al.sub.2O.sub.3:c M.sup.1.sub.2O:d K.sub.2O:e Cs.sub.2O:f H.sub.2O,

[0368] wherein a, b, c, d, e, and f are coefficient; and wherein

[0369] 10.0≤a≤16.0;

[0370] 0.5≤b≤2.5;

[0371] 6.0≤c≤10.0;

[0372] 0.8≤d≤1.6;

[0373] 0.05≤e≤0.60; and

[0374] 90≤f≤190;

[0375] wherein M.sup.1 is selected from Na and/or Li.

[0376] According to the disclosure, the said molar composition is devoid of an organic structure-directing agent.

[0377] The amorphous precursors do not contain any seeds of a previously formed crystal of chabazite zeolite. No organic structure-directing agent is present either. The amorphous precursor of chabazite zeolite is fluoride-free. The chemical composition of the precursor suspension has been controlled to avoid the formation of side crystalline phases, such as ANA (pollucite), EDI, RHO, FAU and/or BPH. Additional control of the crystallization temperature will prevent the generation of these side crystalline phases.

[0378] The (M.sup.1O+Cs.sub.2O+K.sub.2O)/SiO.sub.2 ratio and the (M.sup.1.sub.2O+Cs.sub.2O)/SiO.sub.2 ratio provide guidance to select the content of cations in the precursor which influence the size of the nanocrystals. Per the disclosure, the .M.sup.1.sub.2O+Cs.sub.2O+K.sub.2O)/SiO.sub.2 ratio and the (M.sup.1.sub.2O+Cs.sub.2O)/SiO.sub.2 ratio can be selected as followed.

[0379] For example, the (M.sup.1.sub.2O+Cs.sub.2O)/SiO.sub.2 ratio is at least 0.25 wherein M.sup.1 is selected from Na and/or Li; preferably at least 0.30, more preferably at least 0.35, even more preferably at least 0.40, most preferably at least 0.50, even most preferably at least 0.55. Thus, in a preferred embodiment, M.sup.1.sub.2O is Na2O; the (Na.sub.2O+Cs.sub.2O)/SiO.sub.2 ratio is at least 0.25, preferably at least 0.30, more preferably at least 0.35, even more preferably at least 0.40, most preferably at least 0.50, even most preferably at least 0.55.

[0380] For example, the (M.sup.1.sub.2O+Cs.sub.2O)/SiO.sub.2 ratio is ranging from 0.25 to 1.25, preferably from 0.30 to 1.20, more preferably from 0.35 to 1.15, even more preferably from 0.40 to 1.10, most preferably from 0.45 to 1.05. Thus, in a preferred embodiment, M.sup.1.sub.2O is Na.sub.2O; the (Na.sub.2O+Cs.sub.2O)/SiO.sub.2 ratio is ranging from 0.25 to 1.25, preferably from 0.30 to 1.20, more preferably from 0.35 to 1.15, even more preferably from 0.40 to 1.10, most preferably from 0.45 to 1.05.

[0381] For example, the (M.sup.1.sub.2O+Cs.sub.2O+K.sub.2O)/SiO.sub.2 ratio is at least 0.55 wherein M.sup.1 is selected from Na and/or Li, preferably is ranging from 0.55 to 1.00; more preferably from 0.58 to 0.95 and even more preferably from 0.60 to 0.90. Thus, in a preferred embodiment, M.sup.1.sub.2O is Na.sub.2O; the (Na.sub.2O+Cs.sub.2O+K.sub.2O)/SiO.sub.2 ratio is at least 0.55, preferably is ranging from 0.55 to 1.00; more preferably from 0.58 to 0.95 and even more preferably from 0.60 to 0.90.

[0382] The ratio M.sup.1.sub.2O/H.sub.2O provides guidance to select the content of water in the precursor which influence the size of the nanocrystals.

[0383] For example, the ratio M.sup.1.sub.2O/H.sub.2O is superior or equal to 0.025, preferably superior or equal to 0.03, more preferably superior or equal to 0.04, even more preferably superior or equal to 0.05. The ratio M.sup.1.sub.2O/H.sub.2O is the ratio c/f. Thus, in a preferred embodiment, M.sup.1.sub.2O is Na.sub.2O; the ratio Na.sub.2O/H.sub.2O is superior or equal to 0.025, preferably superior or equal to 0.03, more preferably superior or equal to 0.04, even more preferably superior or equal to 0.05.

[0384] For example, the ratio M.sup.1.sub.2O/Al.sub.2O.sub.3 is superior or equal to 4.0, preferably superior or equal to 7.0, more preferably superior or equal to 7.5. The ratio M.sup.1.sub.2O/Al.sub.2O.sub.3 is the ratio c/b. Thus, in a preferred embodiment, M.sup.1.sub.2O is Na.sub.2O; the ratio Na.sub.2O/Al.sub.2O.sub.3 is superior or equal to 4.0, preferably superior or equal to 7.0, more preferably superior or equal to 7.5.

[0385] For example, the ratio Cs.sub.2O/Al.sub.2O.sub.3 is inferior or equal to 0.90, preferably inferior or equal to 0.80, more preferably inferior or equal to 0.75, even more preferably inferior or equal to 0.60. The ratio Cs.sub.2O/Al.sub.2O.sub.3 is the ratio e/b.

[0386] In a preferred embodiment, M.sup.1.sub.2O is or comprises Na.sub.2O.

[0387] Advantageously, the coefficient a, attributed to the molar amount of silica, is equal to 10 or 16. It is preferred that the coefficient b, attributed to the molar amount of alumina is ranging between 0.70 and 2.30, more preferably is ranging between 0.80 and 2.20, even more preferably is equal to 0.70 or 0.80, most preferably is equal to 0.8.

[0388] With preference, the Si/Al molar ratio of the amorphous precursor of chabazite-type zeolite is comprised between 2 and 16.

[0389] With preference, the coefficient c, preferably attributed to the molar amount of sodium oxide, is ranging between 6.5 and 9.5, more preferably between 7.5 and 8.5, even more preferably is equal to 9.5.

[0390] With preference, the coefficient d, preferably attributed to the molar amount of potassium oxide, is ranging between 1.00 and 1.50, more preferably between 1.10 and 1.40, even more preferably between 1.20 and 1.30, most preferably is equal to 1.25.

[0391] With preference, the coefficient e, preferably attributed to the molar amount of caesium oxide, is ranging between 0.15 and 0.50, more preferably between 0.25 and 0.40, even more preferably between 0.30 and 0.35, preferably is equal to 0.15.

[0392] With preference, the coefficient f, attributed to the molar amount of water, is ranging between 100 and 180, more preferably between 120 and 160, even more preferably between 130 and 140, most preferably is equal to 140.

[0393] In a more preferred embodiment, when the coefficient a, attributed to the molar amount of silica, is equal to 10, then [0394] 0.6≤b≤0.8; with preference b=0.8; [0395] 6.0≤c≤8.0; with preference c=8.0; [0396] 1.25≤d≤1.35; with preference d=1.35; [0397] 0.20≤e≤0.30; with preference e=0.30; and [0398] 120≤f≤190; with preference f=120 or alternatively f=190.

[0399] The amorphous precursors with this molar composition are, after stirring, in a clear aqueous suspension and have a trend, when crystallized, to lead to nanocrystals which are going to agglomerate together. After crystallization, the resulting nanocrystals have an average crystal size comprised between 5 nm and 200 nm as determined by the Scherrer equation and they aggregate into aggregates having a size comprised between 400 nm and 2000 nm, as determined by Scanning Electron Microscopy. The agglomerates can be flake-like, which is very interesting when the chabazite-type zeolite is to be used in membrane application. In another more preferred embodiment, when the coefficient a, attributed to the molar amount of silica, is equal to 16, then [0400] b=0.8; [0401] 9.0≤c≤9.5 [0402] d=0.85; [0403] e=0.35; and [0404] 120≤f≤140.

[0405] The amorphous precursors with this molar composition are milky and have a trend to lead to nanocrystals, in particular to monodispersed discrete chabazite-type zeolite. After crystallization, the resulting nanocrystals have an average crystal size comprised between 130 nm and 200 nm as determined by the Scherrer equation.

[0406] In another more preferred embodiment, when the coefficient a, attributed to the molar amount of silica, is equal to 16, then [0407] 0.4≤b≤0.6; [0408] c=6.0; [0409] d=1.35; [0410] 0.15≤e≤0.25; with preference e=0.15; and [0411] 130≤f≤150.

[0412] The amorphous precursors with this molar composition are milky and have a trend to lead to smaller nanocrystals, in particular to a monodispersed discrete chabazite-type zeolite having an average crystal size comprised between 5 nm and 130 nm, as determined by the Scherrer equation.

Method for Preparing the Chabazite-Type Zeolite From the Precursor

[0413] The disclosure provides a method for the preparation of chabazite-type zeolite, comprising the method for the preparation of an aqueous amorphous precursor of chabazite-type zeolite as described above and further comprising the following steps: [0414] e) mixing said amorphous precursor under stirring and/or orbital shaking; [0415] f) optionally, adding an additional silicate precursors aqueous suspension and mixing said amorphous precursor under stirring and/or orbital shaking; [0416] g) heating said amorphous precursor at a temperature comprised between 90° C. and 160° C. such as to form one or more crystals of chabazite-type zeolite; [0417] h) cooling down said one or more crystals of chabazite-type zeolite at a temperature comprised between 20° C. and 25° C., [0418] i) dispersing said one or more crystals of chabazite-type zeolite in water.

[0419] The mixing is performed by maintaining the suspension at room temperature (e.g., between 20° C. and 25° C.) in a closed space to avoid the water vapour. This temperature should be maintained for a time sufficient to favour the nucleation and to reduce the agglomeration of the amorphous nanoparticles of precursors in the crystalline phase. The pressure of the mixing step is preferably 0.1 MPa. The mixing is preferably carried out for a period comprised between 15 hours and 15 days, more preferably for at least 20 hours and/or at most 15 days and is preferably carried out under mechanical stirring, for instance at 700 rpm.

[0420] As some synthesis need an addition of silica precursor to prevent the formation of big amorphous particles and sedimentation, an additional silicate precursors aqueous suspension is added during the mixing step (e). When this is done, this is carried out after a period comprised between 4 and 7 days after the start of the mixing step (e). The amount of the additional silicate precursors aqueous suspension added in step (f) when said step (f) is carried out corresponds to an amount comprised between 50 wt. % and 70 wt. % of the amount of the silicate precursors suspension, preferably between 55 wt. % and 65 wt. %, more preferably is 60 wt. %. The one or more silicate precursors of the additional silicate precursors aqueous suspension are different or the same as the one or more silicate precursors of the silicate precursors aqueous suspension. The one or more silicate precursors of the additional silicate precursors aqueous suspension are selected among colloidal silica, silica oxyhydroxide species, silica hydrogel, silicic acid, fumed silica, tetraalkyl orthosilicates, silica hydroxides, precipitated silica, clays and a mixture thereof, preferably the silicate precursor of the third aqueous suspension is colloidal silica. The one or more silica precursors of the additional silicate precursors aqueous suspension are present in an amount comprised between 20 wt. % and 70 wt. % of the total weight of the additional silicate precursors aqueous suspension, preferably between 25 wt. % and 60 wt. %, more preferably between 28 wt. % and 50 wt. %, even more preferably is 30 wt. %. The additional silicate precursors aqueous suspension comprises water, preferably distilled water, more preferably double distilled water. The use of non-distilled water could afford a tiny amount of one or more chabazite-type zeolites with different counter-cations. The mixing step in step (f) is similar to the mixing step (e) and is required to obtain a homogeneous solution. However, the mixing step in step (f) is carried out during a shorter period that the mixing step (e), for example, the mixing step in step (f) is carried out for 1 hour. Once the solution has been mixed, the homogeneous solution obtained is crystallized to generate the chabazite-type zeolite. The heating step (g) is thus preferably performed at a temperature comprised between 100° C. and 150° C., preferably between 110° C. and 140° C., more preferably between 120° C. and 130° C. It is highlighted that if crystallization temperature is too low (below 90° C.) or if the crystallization temperature is too high (above 160° C.), the crystallization can provide other crystalline zeolite phases, such as ANA (pollucite), EDI, RHO, FAU and/or BPH. The crystallization is also performed in the absence of seed crystals. The crystallization is preferably carried out for a period comprised between 0.5 hour and 15 hours, more preferably between 2 hours and 12 hours, even more preferably between 7 hours and 11 hours, most preferably between 8 hours and 10 hours. The crystallization is preferably carried out in a sealed environment. After the crystallization has been carried, the nanocrystals must be cooled down at room temperature to control the size of the nanocrystals.

[0421] In a preferred embodiment, a step of recovering said one or more crystals of chabazite zeolite is performed once the nanocrystals have been cooled down and dispersed in water, preferably in distilled water, more preferably in double-distilled water. This performed by performing a washing step with the addition of water until the decanting water reaches a slightly basic pH, namely at least 7.5, followed by separation (either by filtration or by centrifugation or both). The nanocrystals are then dried, for instance in a conventional oven at a temperature of at least 50° C., preferably of at 80° C. A freeze-drying step is optionally carried out to remove the traces of water. The freeze-drying step is performed at a temperature comprised between −100° C. and −70° C., preferably between −92° C. and −76° C.

[0422] In a yet another preferred embodiment, the nanocrystals of chabazite can be ion-exchanged. This is carried out in presence of one salt, the cation of said salt being selected from the alkali metals, the alkaline earth metal, or ammonium; and the anion of said salt is selected from halogens or nitrate, preferably from chloride or nitrate. The protonic form of the nanocrystals of chabazite can also be produced.

The Chabazite-Type Zeolite

[0423] The disclosure provides a chabazite-type zeolite, comprising at least two cages composed of 4- and 8-membered rings connected by one 6-membered double ring, remarkable in that it has a Si/Al molar ratio comprised between 1 and 15 as determined by .sup.29Si magic angle spinning nuclear magnetic resonance, said chabazite-type zeolite comprises caesium and potassium with a Cs/K molar ratio of at most 5.0 as determined by Inductively Coupled Plasma Optical Emission Spectrometry; and said chabazite-type zeolite forms nanoparticles with an average crystal size comprised between 5 nm and 250 nm as determined by the Scherrer equation and with a specific surface area comprised between 50 m.sup.2 g.sup.−1 and 200 m.sup.2 g.sup.−1, as determined by N.sub.2 sorption measurements.

[0424] The nanoparticle has a specific surface area preferably comprised between 60 m.sup.2 g.sup.−1 and 190 m.sup.2 g.sup.−1 as determined by N.sub.2 adsorption measurements; preferably 75 m.sup.2 g.sup.−1 and 175 m.sup.2 g.sup.−1; more preferably comprised between 100 m.sup.2 g.sup.−1 and 150 m.sup.2 g.sup.−1

[0425] For example, the Si/Al molar ratio as determined by .sup.29Si magic angle spinning nuclear magnetic resonance is at least 1.0 or at least 1.1, preferably at least 1.2 or at least 1.25, more preferably at least 1.4 or at least 1.5; more preferably at least 1.9; even more preferably at least 2.1 and most preferably at least 2.4.

[0426] For example, the Si/Al molar ratio as determined by .sup.29Si magic angle spinning nuclear magnetic resonance is at most 10, preferably at most 8, more preferably at most 5; even more preferably at most 4, most preferably at most 3.0 and even most preferably at most 2.9, or at most 2.8 or at most 2.7, or at most 2.6.

[0427] It is preferred that the chabazite-type zeolite has a Si/Al molar ratio comprised between 1.10 and 3.00, more preferably comprised between 1.25 and 2.60, even more preferably between 1.40 and 2.40, most preferably between 1.50 and 2.10.

[0428] For example, the Cs/K molar ratio is at most 4.0 as determined by Inductively Coupled Plasma Optical Emission Spectrometry, preferably at most 3.0; more preferably at most 2.5; even more preferably at most 2.0, and more preferably at most 1.9 and at most 1.8

[0429] For example, the Cs/K molar ratio is at least 0.1 as determined by Inductively Coupled Plasma Optical Emission Spectrometry; preferably at least 0.2, more preferably at least 0.3; even more preferably at least 0.4 and most preferably at least 0.5.

[0430] For example, the chabazite-type zeolite has an M.sup.1/Al molar ratio ranging from 0.02 to 0.20 wherein M.sup.1 is selected from Na and/or Li; as determined by Inductively Coupled Plasma Optical Emission Spectrometry; preferably from 0.05 to 0.15; more preferably from 0.075 and 0.12.

[0431] For example, the chabazite-type zeolite has a Na/Al molar ratio ranging from 0.02 to 0.20 as determined by Inductively Coupled Plasma Optical Emission Spectrometry; preferably from 0.05 to 0.15; more preferably from 0.075 and 0.12.

[0432] For example, the chabazite-type zeolite has an M.sup.1/Cs molar ratio ranging from 0.10 to 0.50 wherein M.sup.1 is selected from Na and/or Li, as determined by Inductively Coupled Plasma Optical Emission Spectrometry preferably from 0.14 to 0.40; more preferably from 0.17 and 0.30.

[0433] For example, the chabazite-type zeolite has a Na/Cs molar ratio ranging from 0.10 to 0.50 wherein M.sup.1 is selected from Na and/or Li, as determined by Inductively Coupled Plasma Optical Emission Spectrometry preferably from 0.14 to 0.40; more preferably from 0.17 and 0.30.

[0434] For example, the chabazite-type zeolite has a Cs/Al molar ratio comprised between 0.15 and 0.45, preferably between 0.20 and 0.40, more preferably between 0.21 and 0.39, even more preferably between 0.22 and 0.38.

[0435] In an embodiment, the zeolite consists of Al, Si, O, K, Cs and M.sup.1 wherein M.sup.1 is selected from Na and/or Li.

[0436] In an embodiment, the zeolite is ion-exchanged and consists of Al, Si, Cs, O, H and K.

[0437] Advantageously, the average crystal size of the nanoparticles is comprised between 10 nm and 245 nm as determined by the Scherrer equation, preferably between 15 nm and 235 nm, more preferably between 20 nm and 225 nm, even more preferably between 50 nm and 220 nm, most preferably between 80 nm and 200 nm, even most preferably between 90 nm and 145 nm. The average crystal size of the nanoparticles is at least 10 nm and at most 250 nm as determined by the Scherrer equation, preferably at most 200 nm, more preferably at most 195 nm, even more preferably at most 185 nm, most preferably at most 175 nm, even most preferably at most 165 nm.

[0438] The chabazite-type zeolites of the present disclosure are therefore downsized and/or nanosized. They thus provide high accessibility when used as catalysts and provide fast diffusion of the interacting components. Moreover, their size is advantageous for being highly stable into suspensions.

[0439] The pore volume of the chabazite-type zeolite has been determined by N.sub.2 sorption measurements and is comprised between 0.10 cm.sup.3 g.sup.−1 and 0.50 cm.sup.3 g.sup.−1, preferably between 0.20 cm.sup.3 g.sup.−1 and 0.40 cm.sup.3 g.sup.−1, more preferably between 0.25 cm.sup.3 g.sup.−1 and 0.35 cm.sup.3 g.sup.−1. The pore volume is thus accessible to nitrogen.

[0440] Said nanoparticles have an average pore size diameter comprised between 3.72 Å and 4.20 Å, as determined by Brunauer-Emmet-Teller experiments, preferably of 3.80 Å.

[0441] The pore volume of the chabazite-type zeolite has been determined by N.sub.2 sorption measurements and is comprised between 0.10 cm.sup.3 g.sup.−1 and 0.50 cm.sup.3 g.sup.−1, preferably between 0.20 cm.sup.3 g.sup.−1 and 0.40 cm.sup.3 g.sup.−1, more preferably between 0.25 cm.sup.3 g.sup.−1 and 0.35 cm.sup.3 g.sup.−1. The pore volume is N.sub.2 accessible.

[0442] Preferably, the chabazite-type zeolite comprises at least one 8-membered ring channel.

[0443] In a first preferred embodiment, the chabazite-type zeolite forms monodispersed nanoparticles preferably monodispersed nanoparticles comprising single nanocrystals.

[0444] In a second preferred embodiment, alternative to the first preferred embodiment, the chabazite-type zeolite forms aggregates, preferably aggregates of nanocrystals. The aggregates have a size preferably ranging between 400 nm and 2000 nm as determined by Scanning Electron Microscopy, more preferably between 450 nm and 1800 nm, even more preferably between 500 nm and 1700 nm, most preferably between 550 nm and 1600 nm, even most preferably between 600 nm and 1500 nm. The aggregates have preferably a size of at least 400 nm and/or of at most 2000 nm as determined by Scanning Electron Microscopy, more preferably of at least 600 nm, even more preferably of at least 650 nm, most preferably of at least 1000 nm, even most preferably of at least 1600 nm, and/or preferably of at most 1800 nm, more preferably of at most 1600 nm, even more preferably of at most 1000 nm, most preferably of at most 650 nm, even most preferably of at most 600 nm.

[0445] In yet another preferred embodiment, the chabazite-type zeolite forms aggregated nanocrystals forming spheroidal particles and/or flake-shape particles.

The Use of the Chabazite-Type Zeolite

[0446] The disclosure provides for a use of the chabazite zeolite as defined in accordance with the first aspect of the disclosure as a sorbent for carbon dioxide. Selective separation of carbon dioxide from methane has been achieved in a multi-cycle adsorption/desorption steps. With preference, the use is made in a process for separation of carbon dioxide from methane or in a process for separation of carbon dioxide from an inert gas such as N.sub.2, He and/or Ar.

[0447] The disclosure provides for a use of the chabazite-type zeolite as described above as a sorbent of carbon dioxide. The low Si/Al molar ratio, which allows for high content of cation, reduces the accessibility of nitrogen (having a diameter of 3.6 Å) and of methane (having a diameter of 3.8 Å) while the carbon dioxide (being smaller, with a diameter of 3.3 Å) can be adsorbed and desorbed with the chabazite-type zeolite of the present disclosure In addition to the size of the molecules, the electronic interactions and/or the electronic repulsion play an essential role in the possibility of the molecule to displace the cations to enter the zeolite.

[0448] The disclosure also provides for a use of the chabazite-type zeolite as described above in a method of preparing clathrate hydrate substance, wherein said clathrate hydrate substance entraps preferably methane. The chabazite-type zeolite is contacted with a gaseous water feed and a gaseous material, for instance methane, under determined conditions of temperature and pressure. In this instance, methane can thus be entrapped into a lattice of water and forming thus a clathrate hydrate entrapping methane.

[0449] Further use of the chabazite-type zeolite as described above is its use as a catalyst in a chemical process. For instance, said chemical process can be the conversion of methyl halides to olefins, the conversion of sulfurized hydrocarbons to olefins, the partial oxidation of methane, the oligomerizing of alkenes, the carbonylation of dimethyl ether with carbon monoxide, the methylation of amines, a cracking process, a dehydrogenating process, the isomerization of olefins, or a reforming process.

Test and Determination Methods

[0450] The various chabazite-type zeolites obtained in the examples were characterized over the following methods and after a step of drying which is performed at a temperature of at least 50° C., preferably at 80° C. in a conventional oven.

[0451] Powder X-ray diffraction (XRD) analysis, carried out on powder samples of the synthetic chabazite, was performed using a PANalytical X'Pert Pro diffractometer with CuKα monochromatized radiation (λ=1.5418 Å, 45 kV, 40 mA). The samples were scanned in the range 5-50° 2θ with a step size of 0.02°.

[0452] Unit cell parameters of chabazite particles were determined from the powder X-Ray diffraction data by calculation based on a Le Bail profile refinement and pseudo-Voigt profile function using the JANA2006 software. In addition, a progressive Rietveld refinement to minimize the differences between the pattern observed and the calculated one with structural models was carried out to solve and quantify the framework and extra-framework structure (structural type and atomic positions) using JANA2006 software.

[0453] In situ Powder X-ray diffraction (XRD) analysis was carried out to follow CO.sub.2 sorption in chabazite samples, using a PANalytical X'Pert Pro diffractometer with CuKα monochromatized radiation (λ=1.5418 Å). The samples were scanned in the range 5-110° 2θ with a step size of 0.02°. The samples were in situ activated at 350° C. for 2 h to remove the adsorbed water. The activation and measurements were carried out at identical conditions to those applied in the TG experiments. The CO.sub.2 flow (1bar) was delivered at 350° C., and the measurements were performed under continuous delivery of CO.sub.2 and decrease of temperature to 30° C. (20 K min.sup.−1). For the cycling procedure, the sample was re-activated at 350° C. for 1 h (ramp: 5K min.sup.−1) and then the adsorption procedure for CO.sub.2 was repeated one more time.

[0454] The Scherrer equation links the broadening of the XRD peaks to the size of the crystallites. It has been used to quantify the size of crystals in powder form using powder XRD pattern and X-Pert software. The first Bragg peak of the XRD pattern is usually taken into consideration.

[0455] Transmission electron microscopy (TEM) was carried out determine the crystal size, morphology and crystallinity of solids using a JEOL 2010 FEG or TECHNAI operating at 200 kV.

[0456] Scanning electron microscopy (SEM) analysis was used to determine the surface state, morphology and particle size, using a field-emission scanning electron microscope (SEM, Philips XL30 FEG) with an accelerating voltage 10-30 kV.

[0457] Inductively coupled plasma (ICP) optical emission spectrometry was used to determine the chemical compositions using a Varian ICP-OES 720-ES. The Cs/K molar ratio, the Cs/Al molar ratio, the M.sup.1/Cs molar ratio, the Na/Al molar ratio and the Na/Cs molar ratio of the chabazite-type zeolite have thus been determined using this technical method.

[0458] Energy-dispersive X-ray Transmission Electron Microscopy (EDX-TEM) was used to determine the chemical compositions using a JEOL Model 2010 FEG system fitted with an EDX analyser operating at 200 kV on diluted colloidal suspensions of zeolite materials obtained either after step (f) or after the drying step, that was sonicated for 15 min. Then 2-3 drops of fine particle suspensions were dried on carbon-film-covered 300-mesh copper electron microscope grids. EDX-TEM is an alternative method to determine the composition of the zeolite such as the Cs content or the molar ratios such as the Cs/Al molar ratio. In such a case, at least ten analysis of the same zeolite material at different TEM spots are averaged to obtain the chemical composition of the zeolite materials. The Si/Al molar ratio, the Cs/K molar ratio, the Cs/Al molar ratio, the M1/Cs molar ratio, the Na/Al molar ratio and the Na/Cs molar ratio of the chabazite-type zeolite can be determined using this technical method.

[0459] Nuclear Magnetic Resonance (NMR) analysis was performed to determine the crystallinity and the Si/Al molar ratio of the zeolite materials obtained after the drying step. NMR spectrum was determined by .sup.29Si and solid-state magic angle spinning (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. .sup.29Si chemical shift was referenced to tetramethylsilane (TMS). The molecular geometry of aluminium was determined using .sup.27Al MAS NMR on a Bruker Avance III-HD 500 (11.7 T) spectrometer using 4-mm outer diameter zirconia rotors spun at 14 kHz. .sup.27Al chemical shift was referenced to aluminium ammonium sulphate.

[0460] The .sup.29Si chemical shift sensitivity is an indication of the degree of condensation of the Si—O tetrahedra, that is, the number and type of tetrahedrally coordinated atoms connected to a given SiO.sub.4 unit. Furthermore, .sup.29Si MAS NMR spectra can be used to calculate the Si/Al molar ratio from the NMR signal intensities (I) according to eq. (1):

[00001]$\begin{array}{cc}\frac{\mathrm{Si}}{\mathrm{Al}}=\frac{\underset{n=0}{\overset{4}{.Math.}}{I}_{\mathrm{Si}\left(\mathrm{nAl}\right)}}{\underset{n=0}{\overset{4}{.Math.}}0.25{\mathrm{nI}}_{\mathrm{Si}\left(\mathrm{nAL}\right)}}& \left(1\right)\end{array}$

[0461] wherein n indicates the number of Al atoms sharing the oxygen atom of the SiO.sub.4 tetrahedron under consideration and wherein n=0, 1, 2, 3 or 4.

[0462] The chemical shift range of the silicon atom is comprised between −80 ppm to −115 ppm, with the high-field signal for the silicon atom directly linked to the oxygen atom of the —O—Al moiety. The differences in chemical shifts between Si (n Al) and Si (n+1 Al) are about 5-6 ppm in the low-field signal.

[0463] N.sub.2 sorption analysis was used to determine the nitrogen adsorption/desorption isotherms using Micrometrics ASAP 2020 volumetric adsorption analyser. The samples were degassed at 350° C. under vacuum overnight before the measurement. From these measurements, the pore volume of the chabazite-type zeolite has been determined.

[0464] ζ-potential curve is was carried out to determine the stability of nanozeolites (dispersed particles) in water (dispersion medium) using a Malvern Zetasizer Nano Instrument.

[0465] Thermogravimetry analyses (TGA) and Differential Thermal analysis (DTA) were performed on zeolite nanocrystals obtained when the step (f) of recovering said one or more crystals of CHA-type zeolite is performed (before drying). TGA and DTA were carried out on a SETSYS 1750 CS evolution instrument (SETARAM). The sample was heated from 25° C. to 800° C. with a heating ramp of 5° C./min under carbon dioxide or nitrogen (flow rate: 40 mL/min).

[0466] After activation (water desorption) at 350° C. for 2 hours, the zeolitic material was allowed to return and stay at room temperature under a continuous flow of CO.sub.2 (flow rate: 40 mL/min, 1 bar) in 9 hours. The quantity of CO.sub.2 absorbed was determined using the mass increase compared to the total mass of the sample.

[0467] Cycles of CO.sub.2 adsorption/desorption were conducted and monitored by TGA. An alternance between activation at 350° C. for 2 hours under N.sub.2 flow (flow rate: 40 mL/min) and CO.sub.2 adsorption at room temperature (flow rate: 40 mL/min, 1 barg) for 2 hours has been performed 10 consecutive times.

[0468] Carbon dioxide adsorption isotherms were measured using Micrometrics ASAP 2020 volumetric adsorption analyser. Samples after being dried and freeze-dried were degassed at 623 K under vacuum overnight before the measurement. This test was performed to evaluate the adsorption properties of the zeolites prepared according to the method of the disclosure.

[0469] Fourier Transformation Infra-Red (FTI R) spectroscopic analysis was conducted to characterize the selective adsorption of CO.sub.2 and CH.sub.4 with nanosized chabazite-type zeolite. The adsorption CO.sub.2 on 23.18 g of self-supported pellets of as-prepared CHA zeolite was followed using in-situ FTIR spectroscopy. The infra-red cell was kept under high-vacuum (10.sup.−5 Pa). The sample was activated at 350° C. for 2 h to desorb the water before the measurements. The infra-red spectra from the chabazite samples under adsorption of CO.sub.2 and CH.sub.4 were collected at room temperature.

EXAMPLES

[0470] The embodiments of the present disclosure will be better understood by looking at the different examples below.

[0471] The starting materials used in the examples presented below are listed as follow: [0472] sodium hydroxide: (pellets, purity >99%): Sigma Aldrich; [0473] potassium hydroxide (pellets, purity >85%): Sigma Aldrich; [0474] caesium hydroxide (purity >98%, aqueous 50%): Alfa Aesar; [0475] colloidal silica (Ludox-HS 30, 30 wt. % SiO.sub.2, pH=9.8): Sigma Aldrich; [0476] colloidal silica (Ludox-AS 40, 40 wt. % SiO2): Sigma Aldrich; [0477] sodium aluminate (Al.sub.2O.sub.3 53%, Na.sub.2O 47% by mass): Sigma Aldrich

[0478] These starting materials were used as received from the manufacturers, without additional purification.

Example 1: Synthesis of Agglomerated CHA Zeolite (Samples 1-9)

[0479] An aluminate precursors aqueous suspension was prepared by dissolving 0.512 g of NaAlO.sub.2 in 3.34 g of double-distilled H2O. This suspension is clear.

[0480] A silicate precursors aqueous suspension was prepared in 4.97 g of double-distilled H.sub.2O by mixing 6.667 g of colloidal silica (LUDOX® HS30) with 1.94 g of NaOH, 0.550 g of KOH, 0.599 g of CsOH (aq. 50%). As a result, a warm turbid suspension was obtained due to the exothermic reaction. The turbid turns into clear suspension after 10 minutes and it is stirred for additional 1h.

[0481] The aluminate precursors aqueous suspension was added dropwise under vigorously stirring to the silicate precursors aqueous suspension kept in ice. The weight ratio of the aluminate precursors aqueous suspension over the silicate precursors aqueous suspension is equal to 0.387.

[0482] The resulting clear suspension for sample 1 had the following molar compositions:

[0483] 10 SiO.sub.2:0.8 Al.sub.2O.sub.3:8 Na.sub.2O :1.25 K.sub.2O:0.3 Cs.sub.2O :140 H.sub.2O

[0484] This resulting clear suspension was then mixed during 20h at room temperature (e.g. 25° C.) under vigorous stirring (e.g. 800 rpm).

[0485] Then, the hydrothermal crystallization was conducted at 90° C. for 8 hours to obtain a different type of particles in term of size, morphology, chemical composition. The time of hydrothermal treatment depends on the temperature and the chemical composition.

[0486] The CHA zeolite samples were purified by repeating steps of centrifugation (20000 rpm for 20 min) and dispersed in distilled water until reaching pH=8, and then freeze-dried.

[0487] FIG. 1 shows the XRD pattern of the CHA zeolite sample 1. FIG. 2 shows the SEM images and FIG. 3 shows the N.sub.2 adsorption-desorption isotherms of said CHA zeolite sample 1. FIG. 4 shows the corresponding CO.sub.2 adsorption isotherm.

[0488] The molar composition for samples 1-8 of the clear suspension after addition of the first aqueous suspension to the second aqueous suspension has the following composition:

[0489] a SiO.sub.2:b Al.sub.2O.sub.3:c Na.sub.2O :d K.sub.2O:e Cs.sub.2O:f H.sub.2O,

[0490] a=10.0

[0491] 0.5≤b≤2.5;

[0492] 6.0≤c≤10.0;

[0493] 1.0≤d≤1.6;

[0494] 0.05≤e≤0.60; and

[0495] 90≤f≤150.

[0496] Samples 1-8 were obtained in a yield varying between 60% and 65%.

[0497] FIG. 3 shows respectively the N.sub.2 adsorption-desorption isotherm of sample 4.

[0498] Sample 9 was prepared using the same conditions as for sample 1, except that 6.33 g of double-distilled H.sub.2O was used to dissolve the 0.512 g of NaAlO.sub.2.

[0499] The molar composition of the precursor mixture for sample 9 is:

[0500] (9) 10 SiO.sub.2:0.8 Al.sub.2O.sub.3:8.0 Na.sub.2O:1.35 K.sub.2O:0.30 Cs.sub.2O:190 H.sub.2O

[0501] Sample 9 was obtained in a yield of 60%.

[0502] Table 1 summarizes the molar composition of the amorphous precursor mixture obtained for the samples 1-9.

TABLE-US-00001 TABLE 1 Molar composition of the amorphous precursor mixture obtained for the 9 different samples prepared in accordance with example 1. Mixing time Synthesis Synthesis SiO.sub.2 Na.sub.2O K.sub.2O Cs.sub.2O Al.sub.2O.sub.3 H.sub.2O (day) temperature time 1 10 8 1.25 0.3 0.8 140 1 90° C. 8 h 2 10 6 1.25 0.3 0.6 140 4 100° C. 2 h 45 3 10 6 1.35 0.2 0.8 140 1 100° C. 5 h 4 10 8 1.35 0.2 0.6 140 4 90° C. 8 h 5 10 6 1.35 0.2 0.8 120 4 90° C. 8 h 6 10 8 1.35 0.2 0.6 120 1 100° C. 5 h 7 10 8 1.25 0.3 0.8 120 4 100° C. 5 h 8 10 6 1.25 0.3 0.6 120 1 90° C. 6 h 9 10 8 1.25 0.3 0.8 190 1 90° C. 8 h

[0503] The properties of the CHA zeolite samples (Si/Al molar ratio and the average size of crystals and agglomerates are summarized in table 2. The size of the crystals has been determined in the c direction from Scherrer's equation, namely in one of the directions that grow the fastest.

TABLE-US-00002 TABLE 2 Properties of the CHA zeolite samples 1-9. Size of Size of crystals* aggregates** Sample nm Nm Si/Al 1 136 1600 1.77 2 109  650 1.90 3 105 1800 1.75 4 233 1600 1.65 5  90  600 1.68 6 156 1800 1.58 7 222  450 1.71 8 107 1000 1.88 9 195 1800 1.90 *The average sizes of the crystallites in the (ab) plan were obtained from the X-Ray diffraction data using the Scherrer’s equation on the reflection [2, −1, 0] using the corresponding peak at 12.82°. **Aggregates size determined by Scanning Electron Microscopy (direction ab)

[0504] Sample 9 reveals a higher Si/Al molar ratio (1.90) and bigger particles when compared to sample 1 (1.77) due to higher dilution.

[0505] The crystal shape is flake-like and the size is from 80 to 200 nm in the c direction and thickness of 50 nm (obtained from the Scherrer's equation using the Bragg peak at 9.35° 2θ). The flake-like shape of the crystal is very interesting in membrane application, for instance, sorption experiments.

[0506] FIGS. 3 and 4 show respectively the N.sub.2 adsorption-desorption isotherms and the CO.sub.2 adsorption isotherm of samples 9.

[0507] The chemical composition of the samples 1-9 has been determined by ICP analysis and is present in table 3.

TABLE-US-00003 TABLE 3 Chemical composition of samples 1-9 as well as Si/Al and Cs/K molar ratios. Sample Formula* Si/Al Cs/K 1 (Cs.sub.4.8K.sub.4.9Na.sub.3.6)Si.sub.22.7Al.sub.13.3O.sub.72 1.77 0.98 2 (Cs.sub.4.6K.sub.3.9Na.sub.5.3)Si.sub.22.2Al.sub.13.8O.sub.72 1.67 1.18 3 (Cs.sub.3.6K.sub.6.0Na.sub.3.8)Si.sub.22.6Al.sub.13.4O.sub.72 1.75 0.60 4 (Cs.sub.5.2K.sub.5.1Na.sub.3.7)Si.sub.22.0Al.sub.14.0O.sub.72 1.63 1.02 5 (Cs.sub.3.9K.sub.6.0Na.sub.3.9)Si.sub.22.2Al.sub.13.8O.sub.72 1.68 0.65 6 (Cs.sub.4.3K.sub.5.0Na.sub.5.1)Si.sub.21.6Al.sub.14.4O.sub.72 1.56 0.86 7 (Cs.sub.5.8K.sub.4.8Na.sub.2.4)Si.sub.23.0Al.sub.13.0O.sub.72 1.84 1.21 8 (Cs.sub.5.8K.sub.4.3Na.sub.2.7)Si.sub.23.2Al.sub.12.8O.sub.72 1.88 1.35 9 (Cs.sub.4.4K.sub.4.9Na.sub.3.4)Si.sub.23.3Al.sub.12.7O.sub.72 1.90 0.90 *determination based on lop analysis

Example 2: Synthesis of Monodispersed Discrete CHA Zeolite (Samples 10-11)

[0508] An aluminate precursors aqueous suspension was prepared by dissolving 0.546 g of NaAlO.sub.2 in 3.242 g of double-distilled H2O. This suspension is clear. Then 2.264 g of NaOH, 0.374 g of KOH, 0.699 g of CsOH (aq. 50%) was added. As a result, a worm turbid suspension was obtained due to the exothermic process. The turbid suspension turns into clear suspension after 10 minutes, and it is stirred for 2 h.

[0509] A silicate precursors aqueous suspension was prepared by adding dropwise under vigorously stirring 7.667 g of colloidal silica (LUDOX® HS30) to the first aqueous suspension kept in ice. The weight ratio of the aluminate precursors aqueous solution over the silicate precursors aqueous solution is equal to 0.9.

[0510] The resulting milky suspension for samples 10 and 11 had the following molar compositions:

[0511] 10 SiO.sub.2:0.8 Al.sub.2O.sub.3:c Na.sub.2O:0.85 K.sub.2O:0.35 Cs.sub.2O:f H.sub.2O

[0512] 9.0≤c≤9.5;

[0513] 110≤f≤130;

[0514] This resulting milky suspension was then mixed during 7 days at room temperature (e.g. 25° C.) under vigorous stirring (e.g. 800 rpm).

[0515] Then 3 g of aqueous silicate (colloidal silica (LUDOX® HS30)) was added dropwise to increase de Si/Al molar ratio in the precursor suspension. Then the suspension is stirred for 1 hour at 650 rpm.

[0516] Then, the hydrothermal crystallization was conducted at 90° C. for 8 hours to obtain monodisperse nanoparticles of synthetic CHA zeolite.

[0517] Chabazite monocrystals were purified by three steps centrifugation (25,000 rpm for 4 h) followed by redispersion in water until the decanting water reached a pH of 7, and then freeze-dried before further characterization.

[0518] The Rietveld refinement data for sample 10 is shown in FIG. 5. The Rietveld method allows to “refine” the structural model taking into account the shape, the position and the intensity of the diffraction peaks. The good agreement between the experimental pattern and the calculated profile has confirmed the good quality of the proposed model.

[0519] The TEM images at a magnification of 200 nm of sample 10 are depicted in FIGS. 6A and 6B.

[0520] The isotherms of samples 10 and 11 are shown in FIG. 3 (N.sub.2 isotherms) and in FIG. 4 (CO.sub.2 isotherms).

[0521] The sample 10 (26.91 g) was dehydrated at 350° C. for 1 h (ramp: 5K/min). The CO.sub.2 flow (40 ml min.sup.−1) was delivered at 350° C., and the measurements were performed under continuous delivery of CO.sub.2 and decrease of temperature to 30° C. min.sup.−1 (20K min.sup.−1). For the cycling procedure, the sample was re-activated at 350° C. for 1 h (ramp: 5K min.sup.−1) and then the adsorption procedure for CO.sub.2 was repeated 9 times. The full reversibility of CO.sub.2 absorption in sample 10 is demonstrated in FIGS. 7, 8 and 9.

[0522] The adsorption capacity is not perturbed even after ten consecutive cycles as the band areas on FIG. 9 reach the same level in all cycles.

[0523] The results from the FTIR analysis performed under adsorption of CO.sub.2 and CH.sub.4 are respectively shown in FIGS. 10 and 11.

[0524] The multi-cycle adsorption-desorption step can be carried out ten consecutive times, each step lasting of 3 h20.

[0525] Table 4 reports the molar composition of the amorphous precursor mixture obtained for the samples 10 and 11, after that the extra amount silicate has been added.

TABLE-US-00004 TABLE 4 Molar composition of the amorphous precursor mixture obtained for the 2 different samples prepared in accordance with example 2. Mixing time Synthesis Synthesis SiO.sub.2 Na.sub.2O K.sub.2O Cs.sub.2O Al.sub.2O.sub.3 H.sub.2O (days) temperature time 10 16 9.5 0.85 0.35 0.8 140 7 + 10 90° C. 7 h 11 16 9 0.85 0.35 0.8 120 7 + 10 90° C. 7 h

[0526] The properties of the zeolite samples 10 and 11 are presented in Table 5.

TABLE-US-00005 TABLE 5 Properties of the CHA zeolite samples 10-11. Si/Al molar Crystals CO.sub.2 uptake Sample ratio size (nm)* (mmol g.sup.−1)** 10 2.13 170 3.82 11 2.03 153 3.91 *The average sizes of the crystallites in the (ab) plan were obtained from the X-Ray diffraction data using the Scherrer’s equation on the reflection [2, −1, 0] using the corresponding peak at 12.82°. **BET experiments (At 0° C., 121 kPa; Static CO.sub.2 isotherm adsorption).

[0527] Sample 10 has been ion-exchanged with NH.sub.4NO.sub.3. The material was ion-exchanged with a solution of 0.1 M of NH.sub.4NO.sub.3 for 20 h at room temperature (e.g. 25° C.). The resulting powder was washed twice by centrifugation (20,000 rpm). The procedure was repeated until a pH of 8 is obtained for the decanting water. Then the zeolite was washed with double-distilled H.sub.2O, and calcined (e.g. at 400° C. for 2 h, ramp of 1° C. min.sup.−1) to eliminate of the NH.sub.3 and NOx and obtaining the acidic form of the chabazite zeolite sample 10.

[0528] The chemical composition of the parent sample 10 and the ion-exchanged sample 10 are given in table 6:

TABLE-US-00006 TABLE 6 Chemical composition of sample 10 before and after ion-exchanged, determined based on ICP analysis. Sample 10 Formula Parent (Cs.sub.6.3K.sub.4.2Na.sub.1.3)Si.sub.24.2Al.sub.11.8O.sub.72 Exchanged (Cs.sub.0.6K.sub.0.4H.sub.10.6)Si.sub.24.2Al.sub.11.8O.sub.72

[0529] FIG. 12 shows the XRD pattern and the N.sub.2 sorption isotherms of ion-exchanged sample 10. The Le Bail refinement of ion-exchanged zeolite reveals a space group R-3m and a unit cell parameter of a=b=13.823 Ångströms and c=15.047 Ångströms. From the adsorption isotherm of N.sub.2 of the as-prepared sample 10 (filled square on the insert of FIG. 12) and the sample in protonic form (empty square on the insert of FIG. 12), it is possible to determine the micropore volume for the sample in protonic form as being equal to 0.16 cm.sup.3 g.sup.−1. The micropore volume of the sample which is ion-exchanged (with Na, Cs or K) is 0.06 cm.sup.3 g.sup.−1.

[0530] The structural determination was performed for sample 10. In situ XRD characterization of sample 10 under delivery of CO.sub.2 was performed. The change in the intensity, position and width of the Bragg peak at 12.8° 2θ under controlled adsorption and desorption of CO.sub.2 is presented in FIGS. 13 to 16.

[0531] The crystalline yield of samples 10 and 11 was respectively 71.2% and 70%.

Example 3: Synthesis of Monodispersed Discrete CHA Zeolite (Samples 12-15)

[0532] An aluminate precursors aqueous suspension was prepared by dissolving 0.384 g of NaAlO.sub.2 in 2.551 g of double-distilled H.sub.2O. This suspension is clear. Then 1.411 g of NaOH, 0.593 g of KOH, 0.499 g of CsOH (aq. 50%) was added. As a result, a worm turbid suspension was obtained. The turbid turns into clear suspension after 10 minutes and then stirred for 2 h.

[0533] A silicate precursors aqueous suspension was prepared by dissolving 10.667 g of colloidal silica (LUDOX® HS30). This suspension is clear.

[0534] The silicate precursors aqueous suspension was added dropwise under vigorously stirring to the aluminate precursors aqueous suspension kept in ice. The weight ratio of the aluminate precursors aqueous suspension over the silicate precursors aqueous suspension is 0.7.

[0535] The resulting turbid suspension for samples 12 to 15 had the following molar compositions:

[0536] 16 SiO.sub.2:b Al.sub.2O.sub.3:6 Na.sub.2O:1.35 K.sub.2O:e Cs.sub.2O:f H.sub.2O

[0537] 0.4≤b≤0.6;

[0538] 0.15≤e≤0.25;

[0539] 130≤f≤150;

[0540] This resulting turbid suspension was then mixed during 12 days at room temperature (e.g. 25° C.) under vigorous stirring (e.g. 800 rpm).

[0541] Then, the hydrothermal crystallization for CHA zeolite sample 12 was conducted at 90° C. for 2.5 hours to obtain monodisperse nanoparticles of synthetic CHA zeolite.

[0542] The hydrothermal crystallization for CHA zeolite sample 13, 14 and 15 was conducted at 90° C. for 11 hours and up to 19 hours to obtain monodisperse nanoparticles of synthetic CHA zeolite and 3% of ANA zeolite as a side-product.

[0543] Chabazite crystals were purified by three steps centrifugation (25,000 rpm for 4h) followed by redispersion in water until the decanting water reached a pH of 7, and then freeze-dried before further characterization.

[0544] The Si/Al molar ratio of the synthetic chabazite is in the range of 2.4-2.6. The prism-like crystals with the longest size between 80 nm and 120 nm in the c direction and a thickness comprised between 15 nm and 25 nm (according to the Scherrer equation of the 1s.sup.t Bragg's peak) are measured. The TEM images show crystals with a size between 30 nm and 70 nm. The surface area of 121 m.sup.2 g.sup.−1 was determined by BET method based on N.sub.2 adsorption measurements.

[0545] Table 7 summarizes the molar composition of the amorphous precursor mixture obtained for the samples 12-15.

TABLE-US-00007 TABLE 7 Molar composition of the amorphous precursor mixture obtained for the 4 different samples prepared in accordance with example 3. Mixing time Synthesis Synthesis SiO.sub.2 Na.sub.2O K.sub.2O Cs.sub.2O Al.sub.2O.sub.3 H.sub.2O (days) temperature time 12 16 6.0 1.35 0.25 0.6 130 12 90° C. 2.5 h 13 16 6.0 1.35 0.15 0.6 130 12 90° C. 11 h 14 16 6.0 1.35 0.15 0.4 130 12 90° C. 11 h 15 16 6.0 1.35 0.15 0.6 150 12 90° C. 11 h

[0546] The chemical compositions and the properties of the zeolite samples 12-15 are presented in Table 8.

TABLE-US-00008 TABLE 8 Properties of the CHA zeolite samples 12-15. Crystal Specific size surface CO.sub.2 uptake Formula* Si/Al (nm)** area (m.sup.2/g) (mmol g.sup.−1)*** 12 (Cs.sub.4.2K.sub.5.3Na.sub.1.1)Si.sub.25.4Al.sub.10.6O.sub.72 2.5  87 12 4.70 13 (Cs.sub.5.2K.sub.4.7Na.sub.0.9)Si.sub.25.2Al.sub.10.8O.sub.72 2.4  99 83 3.80 14 (Cs.sub.4.5K.sub.4.9Na.sub.0.8)Si.sub.25.8Al.sub.10.2O.sub.72 2.6 119 — — 15 (Cs.sub.3.7K.sub.5.4Na.sub.1.1)Si.sub.25.8Al.sub.10.2O.sub.72 2.6  90 — — *determination based on ICP analysis **The average sizes of the crystallites in the (ab) plan were obtained from the X-Ray diffraction data using Scherrer’s equation on the reflection [2, −1, 0] using the corresponding peak at 12.82°. ***BET experiments (At 0° C., 121 kPa; Static CO.sub.2 isotherm adsorption).

[0547] The crystalline yield of samples 12, 13, 14 and 15 was respectively 55%, 54%, 47%, and 54%.

[0548] The TEM images of sample 12 are shown in FIGS. 6C and 6D. FIGS. 3 and 4 show respectively the N.sub.2 adsorption-desorption isotherms and the CO.sub.2 adsorption isotherm of sample 12.

[0549] The TEM images of sample 13 are shown in FIGS. 4E and 4F.

[0550] FIG. 17 shows the ζ-potential curve of sample 13 at a pH of 8 in an aqueous solution comprising 0.5 wt. % of sample 13. The ζ-potential is a key indicator of the stability of colloidal dispersion. The relatively high c-potential of sample 13 shows sample 13 is highly stable in the aqueous phase.

[0551] The as-prepared sample 13 was stable up to 800° C. The ion-exchanged sample 13 with NH.sub.4NO.sub.3 (following the same ion-exchange protocol as for sample 10), did not collapse after calcination (450° C., 2 h).

[0552] The normalized mass adsorption of CO.sub.2 and CH.sub.4 as pure gas followed by TGA experiments is shown in FIG. 18 for sample 10. After activation at 350° C. and stabilization at room temperature, the CHA-type zeolite was subjected to either pure CO.sub.2 or pure CH.sub.4 gas. It is observed that CHA-type zeolite has a higher capacity towards CO.sub.2 compared to CH.sub.4 gas. In numbers, 0.64 mmol and 2.31 mmol were absorbed per gram of CHA-type zeolite for CH.sub.4 and CO.sub.2 gas, respectively. Also, the rate of absorption is faster for CO.sub.2 adsorption compared to CH.sub.4 adsorption.

[0553] The TGA values are lower than the capacity obtained using BET isotherms (3.6 mmol/g) because TGA experiments were performed underflow and at 25° C. while BET experiments were performed at 0° C. under static conditions.

Example 4: Advantage of Potassium and Caesium

[0554] A zeolite comprising caesium and potassium (sample 16) was prepared from the following molar composition:

[0555] 10 SiO.sub.2:0.8 Al.sub.2O.sub.3:8 Na.sub.2O:0.6 Cs.sub.2O:1.25 K.sub.2O:110 H.sub.2O

[0556] The template-free of nanosized zeolite without KOH was prepared from the precursor suspension having the following molar composition:

[0557] 10 SiO.sub.2:0.8 Al.sub.2O.sub.3:8 Na.sub.2O:0.6 Cs.sub.2O:110 H.sub.2O

[0558] The suspension was aged at room temperature for 20 h under stirring. The hydrothermal treatment was performed at 90° C. for 7 hours to afford sample 17.

[0559] The template-free of nanosized zeolite without CsOH was prepared from a precursor solution having the following molar composition:

[0560] 10 SiO.sub.2:0.8 Al.sub.2O.sub.3:8 Na.sub.2O:1.25 K.sub.2O:110 H.sub.2O

[0561] The suspension was aged at room temperature for 20 h under stirring. The hydrothermal treatment was performed at 90° C. for 7 hours, according to the study entitled “Location of alkali ions and their relevance to the crystallization of low silica X zeolite” of Iwama M. et al. (Cryst. Growth Des., 2010, 10, 3471-3479). Sample 18 is thus obtained.

[0562] FIG. 19 shows the XRD pattern of the as-prepared material. While sample 16 is the pattern of a chabazite-type zeolite, sample 17 is the pattern that corresponds to pure RHO zeolite and sample 18 is a pattern that corresponds to an FAU zeolite with EMT as a secondary phase.

[0563] Using ICP analysis, the Si/Al ratio of samples 17 and 18 has been determined to be of 1.4.

[0564] FIG. 20 shows the SEM image of sample 16, corresponding to a CHA zeolite. It shows aggregates of the size of 800 nm with individual crystallites with a size ranging between 30 nm and 100 nm. FIGS. 21 and 22 respectively show the SEM images of samples 17 and 18, which are respectively a sample of RHO zeolite and FAU zeolite. FIGS. 21 and 22 show that individual crystallites have a size ranging between 50 nm and 200 nm.

[0565] Table 9 summarizes the synthesis conditions and the phases that were obtained.

TABLE-US-00009 TABLE 9 Conditions and results of the zeolite preparation Synthesis Synthesis Phase SiO.sub.2 Na.sub.2O K.sub.2O Cs.sub.2O Al.sub.2O.sub.3 H.sub.2O temperature time obtained 16 10 8.0 1.25 0.60 0.80 110 90° C. 7 h CHA 17 10 8.0 0 0.60 0.80 110 90° C. 7 h RHO 18 10 8.0 1.25 0 0.80 110 90° C. 7 h FAU + (EMT)