THE ZEOLITE AS SORBENT FOR C0 ₂

Technical field

The present disclosure relates deals with zeolites that can be used as a sorbent for carbon dioxide. The present disclosure further relates to a method for making such zeolites.

Technical background

Zeolites and zeolite-like materials comprise a broad range of porous crystalline solids. The structures of zeolite-type materials are essentially based on tetrahedral networks which encompass channels and cavities. According to the study entitled“Nomenclature of structural and compositional characteristics of ordered microporous and mesoporous material with inorganic hosts" by McCusker L. B et al. ( Pure Appl. Chem., 2001 , 73, (2), 381-394), microporous crystalline materials with an inorganic, three-dimensional host structure composed of fully linked, corner-sharing tetrahedra and the same host topology constitute a zeolite framework type. The number of established framework or structure types has increased progressively in the last four to five decades of highly active research in the field of zeolites. Currently, the number of established structure types is clearly in excess of 239. All zeolite structure types are referenced with three capital letter codes. They have different framework densities, chemical compositions, dimensional channel systems and thus, different properties.

Zeolites are generally characterized by their high specific surface areas, high micropore volume, and capacity to undergo cation exchange. Therefore, they can be used in various applications, for example as catalysts (heterogeneous catalysis), absorbents, ion-exchangers, and membranes, in many chemical and petrochemical processes (e.g. in oil refining, fine- and petrochemistry).

Most of the described zeolites are aluminosilicate zeolites and comprise a three-dimensional framework of SiCU and AICU tetrahedra. The electroneutrality of each tetrahedra containing aluminium is balanced by the inclusion in the crystal of a metallic cation, for example, a sodium cation. The micropore spaces (channels and cavities) are occupied by water molecules before dehydration.

The synthesis of nanosized zeolites in the absence of organic structure-directing agents (OSDA) is an important research area in molecular sieve science since the reduction of the synthetic cost is of primary interest.

Over the past decade, renewed efforts were devoted to preparing zeolites with enhanced accessibility to their micropores, including post-synthesis modification, one-step hydrothermal crystallization in the presence of mesopore modifiers and synthesis of nanosized zeolite crystals with or without organic templates. The interest in the preparation of nanosized zeolites has gradually increased, but only 18 from the 239 structures known to date have so far been synthesized with nanosized dimensions and stabilized in colloidal suspensions. Indeed, the particle size reduction of zeolites to the nanometer scale leads to substantial changes in their properties such as increased external surface area and decreased diffusion path lengths. More particularly, the specific conditions employed to lead to nanosized zeolites change their intrinsic characteristics, impeding the full use of their potential.

In the study entitled“Template-free crystallization of zeolite RHO via hydrothermal synthesis: effects of synthesis time, synthesis temperature, water content and alkalinity’, by Mousavi S. F. et al ( Ceramics International, 2013, 39, 7149-7158), the synthesis of organic template-free RHO zeolite was investigated. It was found that by increasing the alkalinity during the synthesis leads to a decrease in the crystal size, down to 400 nm.

In the patent numbered US 2016/0101415, published in 2016, the synthesis of a zeolite RHO without the use of an organic structure-directing agent has been reported. A gel having the molar composition of 10 S1O2: 1.0 AI2O3: 3.0 Na ₂ 0: 0.4 CS2O: 80 H2O has been prepared and has been heated for 1 to 3 days at 100°C to retrieve a crystallized product which has an 8- membered ring channel. The crystallized product shows a microporous region and a mesoporous region with a micropore volume comprised between 0.03 cm ³ g ^_1 and 0.8 cm ³ g ^_1 of the composition, as determined by analysis of Ar sorption isotherms.

In the study entitled “Sorption of carbon dioxide, methane and nitrogen on zeolite-F: Equilibrium adsorption study’, by Belani M. R. et al. (Environmental Progress & Sustainable Energy, 2017, 36 (3), 850-856), the use of a zeolite from the EDI framework, zeolite-F, with a size of the micrometric range, synthesized from the batch composition 3 S1O2: 1.0 AI2O3: 5.26 K2O: 94.5 H2O and thus without an organic template, revealed, at a temperature of 303 K (29.85°C) and a pressure of 850 mmHg (1.13 bar), high selectivity for carbon dioxide in comparison to methane (CO2/CH4 = 30) and nitrogen gas (CO2/N2 = 38). At those conditions, the CO2 uptake by the zeolite-F was measured to be of 1.869 mmol/g.

Yang Xiaobo et al.“High silica zeolite Phi, a CHA type zeolite with ABC-D6R stacking faults” Microporous and Mesoporous material, 248 (2017) 129-138 elaborates a method to synthesize CHA zeolites with Si/AI ratios in a wide range, through adding some weak bases to modify the crystallization kinetics in favour of the desired CHA framework. Several organic and inorganic bases are feasible for this purpose. Pure crystalline CHA materials with Si/AI = 2-30 have been obtained. Bo Liu et al.“Preparation of CHA zeolite (chabazite) crystals and membranes without organic structural directing agents for CO2 separation” Journal of membrane science, vol. 573, 24 (2018) 333-343. This study discloses the preparation of CHA zeolite (chabazite) crystals and membranes from organic structural directing agents-free (OSDA-free) gels. Chabazite membranes were grown on the tubular alumina supports. The effect of caesium and fluoride salts on the crystallization of chabazite crystals and membranes were investigated. Highly crystalline chabazite and uniform chabazite membranes were only obtained from the gel containing the caesium and fluoride salts.

The study entitled“Nanosized Cs-pollucite zeolite synthesized under mild condition and its catalytic behavior” of Aleid Ghadah Mohammad S et al. (Materials Research Express, 2019, 6, 025026) describes the synthesis of nanoscale caesium-pollucite zeolite without an organic template. The resulting zeolites show an ANA topology with a Cs/AI molar ratio of at least 1.

The study entitled“Synthesis of Cs-ABW nanozeolite in organotemplate-free system” of AN Ghrear Tamara Mahmoud et al. ( Microporous and Mesoporous material, 2019, 277, 78-83) concerns a hydrothermal synthesis of nanosized Cs-ABW zeolite in which a first solution comprising the silicate and caesium precursors is mixed with a second solution comprising the aluminate and caesium precursors.

The objective of the present disclosure is to provide zeolite which allows for selective sorption of carbon dioxide over methane and/or nitrogen. Another objective of the disclosure is to provide a process to produce such a zeolite that is cost-effective

Summary

It is an object of the disclosure to provide a new zeolite and a process for the preparation of such zeolite. Another object is to provide the amorphous precursors of the new zeolite and a process for the preparation of such amorphous precursors. Another object is to deal with the use of such zeolites. A further object of the disclosure is to provide new zeolite as a sorbent of carbon dioxide, that can be used in a method of preparing clathrate hydrate substance and that can be used as a catalyst in a chemical process.

According to a first aspect, the disclosure has for object a zeolite, comprising caesium, the zeolite is selected from the EDI family, PHI family or having at least one cage formed with at least one 8-membered ring and a Si/AI molar ratio comprised between 1 and 15 as determined by ²⁹ Si magic angle spinning nuclear magnetic resonance; the zeolite is remarkable in that it is in the form of one or more nanoparticles, said nanoparticles having an average crystal size comprised between 5 nm and 400 nm as determined by the Schemer equation, in that said zeolite has a specific surface area comprised between 40 m ² g ¹ and 250 m ² g ¹ as determined by N2 adsorption measurements; and in that said zeolite has a Cs/AI molar ratio ranging from 0.01 to 0.75 as determined by Inductively Coupled Plasma Optical Emission Spectrometry and an MVCs molar ratio ranging from 0.10 to 5.00 as determined by Inductively Coupled Plasma Optical Emission Spectrometry wherein M ¹ is selected from Na, Li, Ca and/or Rb.

Surprisingly the inventors have found that it was possible to produce, without the need of an organic template, a zeolite with a low Si/AI molar ratio leading to a high content of cations (such as M ¹⁺ , Cs ⁺ , and optional K ⁺ ). The high content of cations partially blocks the pores and subsequently, because the cations are slightly mobile, the zeolite can adsorb selectively certain molecules, such as carbon dioxide (with a diameter of 3.3 A), over other molecules (such as nitrogen and/or methane, having respectively a diameter of 3.6 A and 3.8 A). In fact, due to the different factors, such as the size, the electronic interactions and/or the electronic repulsions, in combination with the presence of the cations, the molecules of carbon dioxide can enter into the zeolite framework by displacing the cations, while the molecules of methane are not able to achieve the displacement of the cations.

With preference, the zeolite having at least one cage formed with at least one 8-membered ring is selected from the AEI, AFX, CHA, DDR, ERI, KFI, LTA, MER, MWF, PAU, RHO, SFW and TSC families; preferably from the CHA and/or the RHO families.

In an embodiment, the zeolite is selected from the RHO, CHA, AEI, DDR, MER, AFX and ERI families; preferably, the zeolite is selected from the RHO, CHA, DDR and AFX families; more preferably, the zeolite is selected from the CHA family and/or the RHO family.

Wth preference, one or more of the following embodiments can be used to better define the zeolite of the present disclosure:

The zeolite forms nanoparticles with a specific surface area comprised between 75 m ² g ¹ and 175 m ² g ¹ as determined by N2 adsorption measurements, preferably comprised between 100 m ² g ¹ and 150 m ² g ¹ .

The zeolite comprises a pore volume comprised between 0.05 cm ³ g ^_1 and 0.5 cm ³ g ^_1 as determined by N2 sorption measurements, preferably between 0.06 cm ³ g ^_1 and 0.4 cm ³ g ¹ , more preferably between 0.08 cm ³ g ^_1 and 0.35 cm ³ g ^-1 , even more preferably between 0.1 cm ³ g ^-1 and 0.32 cm ³ g ^-1 .

The average crystal size of the nanoparticles is comprised between 10 nm and 245 nm as determined by the Schemer 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 400 nm as determined by the Schemer equation, preferably at most 350 nm, more preferably at most 250 nm, even more preferably at most 200; most preferably at most 195 nm, even most preferably at most 185 nm, or at most 175 nm.

The nanoparticles have an average crystal size of at least 15 nm as determined by Schemer equation; preferably at least 20 nm; more preferably at least 40 nm; even more preferably at least 50 nm, most preferably at least 60 nm and even most preferably at least 80 nm or at least 90 nm.

The nanoparticles form monodispersed nanoparticles, or form aggregates having an average size ranging from 100 nm to 2000 nm as determined by Scanning Electron Microscopy; preferably from 150 nm to 500 nm; or from 500 nm to 1800 nm.

In an embodiment, the aggregates have an average size ranging from 100 nm to 500 nm as determined scanning electron microscopy.

For example, the aggregates have an average size ranging from 120 nm to 500 nm as determined scanning electron microscopy; preferably at least 150 nm, more preferably at least 200 nm; even more preferably at least 250 nm and most preferably at least 275 nm.

For example, the aggregates have an average size ranging from 100 nm to 480 nm as determined scanning electron microscopy; preferably at most 450 nm, more preferably at most 400 nm, even more preferably of at most 350 nm, most preferably of at most 320 nm and even most preferably of at most 300 nm.

In an embodiment, the aggregates have an average size ranging from 500 nm to 2000 nm as determined scanning electron microscopy.

For example, the aggregates have an average size ranging from 600 nm to 2000 nm as determined scanning electron microscopy; preferably at least 700 nm, more preferably at least 800 nm; even more preferably at least 900 nm and most preferably at least 1000 nm.

For example, the aggregates have an average size ranging from 500 nm to 1900 nm as determined scanning electron microscopy; preferably at most 1800 nm.

In an embodiment, the zeolite consists of Al, Si, Cs, O and M ¹ wherein M ¹ is selected from Na, Li, Ca and/or Rb; or the zeolite consists of Al, Si, O, K, Cs and M ¹ wherein M ¹ is selected from Na, Li, Ca and/or Rb. In an embodiment, the zeolite is ion-exchanged and consists of Al, Si, Cs, O, H and optional K.

With preference, one or more of the following embodiments can be used to better define the composition of the zeolite of the present disclosure:

The zeolite has a Si/AI molar ratio of at most 10 as determined by ²⁹ Si magic angle spinning nuclear magnetic resonance; preferably of at most 10, more preferably of at most 8, even more preferably of at most 5, most preferably of at most 3.0 or of at most 2.8.

The zeolite has a Si/AI molar ratio of at least 1.1 as determined by ²⁹ Si magic angle spinning nuclear magnetic resonance; preferably of at least 1.2, more preferably of at least 1.5.

The zeolite has a Si/AI molar ratio determined by ²⁹ Si magic angle spinning nuclear magnetic resonance, said Si/AI molar ratio is comprised between 1.10 and 3.50, preferably between 1.20 and 3.00, more preferably between 1.40 and 2.50, even more preferably between 1.50 and 2.00, most preferably between 1.60 and 1.90.

The zeolite has an MVAI molar ratio ranging from 0.075 to 0.80 as determined by Inductively Coupled Plasma Optical Emission Spectrometry wherein M ¹ is selected from Na, Li, Ca and/or Rb; preferably from 0.65 to 0.80 or from 0.075 to 0.20

The zeolite has a Na/AI molar ratio determined by inductively coupled plasma optical emission spectrometry comprised between 0.075 and 0.80; preferably from 0.65 to 0.80 or from 0.075 to 0.20.

The zeolite has an MVCs molar ratio ranging from 0.10 to 5.00 as determined by Inductively Coupled Plasma Optical Emission Spectrometry wherein M ¹ is selected from Na, Li, Ca and/or Rb; preferably from 2.50 to 4.50 or from 0.14 to 0.40.

The zeolite has a Na/Cs molar ratio determined by inductively coupled plasma optical emission spectrometry ranging from 0.10 and 5.00; preferably from 2.50 to 4.50 or from 0.14 to 0.40.

The zeolite has a Cs/AI molar ratio ranging from 0.10 to 0.60 as determined by Inductively Coupled Plasma Optical Emission Spectrometry; preferably from 0.15 to 0.58, more preferably from 0.18 to 0.57, even more preferably from 0.20 to 0.56 The zeolite has a content of aluminium that is equal to the sum of the cations used as metallic precursors. The zeolite has a content of oxygen that is equal to the double of the sum of the amount of silicon and the amount of aluminium.

For example, the zeolite is CHA and/or the zeolite further comprises potassium with a Cs/K molar ratio ranging from 0.1 to 5.0 as determined by Inductively Coupled Plasma Optical Emission Spectrometry; preferably ranging from 0.3 to 3.0; more preferably ranging from 0.5 to 2.0.

For example, the zeolite is RHO and/or in that it is devoid of potassium.

According to a second aspect, the disclosure provides an amorphous precursor of zeolite for the preparation of a zeolite according to the first aspect, remarkable in that said amorphous precursor of zeolite has a molar composition comprising

a Si0 ₂ : b Al ₂ 0 ₃ : c M ¹ ₂ 0: d K ₂ 0: e Cs ₂ 0: f H ₂ 0,

wherein a, b, c, and d are coefficients

wherein

the coefficient a is ranging from 10.0 to 16.0;

the coefficient b is ranging from 0.5 to 2.5;

the coefficient c is ranging from 5.5 to 10.0;

the coefficient d is ranging from 0.0 to 1.6;

the coefficient e is ranging from 0.05 to 0.60; and

the coefficient f is ranging from 80 to 300

and wherein M ¹ is selected from Na, Li, Ca and/or Rb

and with the provision that the M ¹ ₂ 0/ H ₂ 0 ratio is equal to or greater than 0.03.

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

Surprisingly, the inventors have found that a precursor as defined in the second aspect of the disclosure provides for the development of nanosized zeolite according to the first aspect. It is evidenced that the amorphous precursors do not contain any template except one or more metallic cations, such as Na ⁺ , Li ⁺ , Ca ⁺⁺ , Rb ⁺ , K ⁺ and/or Cs ⁺ .

With preference, one or more of the following embodiments can be used to better define the amorphous precursor of zeolite of the present disclosure:

M ¹ ₂ 0 is selected from Na ₂ 0 and/or Li ₂ 0, preferably M ¹ ₂ 0 is Na ₂ 0.

M ¹ ₂ 0 is or comprises Na ₂ 0.

The coefficient a is equal to 10 or 16. The coefficient b is ranging between 0.6 and 2.4, preferably between 0.7 and 2.3, more preferably between 0.8 and 2.2, even more preferably between 1.0 and 2.0.

The coefficient c is ranging between 6.0 and 9.5, preferably between 6.5 and 9.0, more preferably between 7.0 and 8.5, even more preferably between 7.5 and 8.0.

The coefficient e is ranging between 0.10 and 0.55, preferably between 0.15 and 0.50, more preferably between 0.20 and 0.45, even more preferably between 0.25 and 0.40. The coefficient f is ranging between 90 and 290, preferably between 100 and 280, more preferably between 120 and 260, even more preferably between 150 and 230.

The coefficient f is at most 290, preferably at most 280, more preferably at most 260, even more preferably at most 250, most preferably at most 230 and even most preferably at most 200.

The M ¹ ₂ 0/ H2O ratio is equal to or greater than 0.04.

The Na ₂ 0/ H ₂ 0 ratio is equal to or greater than 0.04.

The M ¹ ₂ 0/ AI ₂ C>3 ratio is equal to or greater than 7.0; preferably is equal to or greater than 7.5.

The Na ₂ 0/ AI ₂ C>3 ratio is equal to or greater than 7.0; preferably is equal to or greater than 7.5.

The Cs ₂ 0 / AI ₂ C>3 ratio is equal to or less than 0.75; preferably is equal to or less than 0.65; more is equal to or less than 0.60.

The (M ¹ ₂ 0+CS ₂ 0+ K ₂ 0)/Si0 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. It is understood that when the coefficient d is 0, the (M ¹ ₂ 0+Cs ₂ 0+ K ₂ 0)/Si0 ₂ is the (M ¹ ₂ 0+Cs ₂ 0)/Si0 _2.

The (Na ₂ 0+Cs ₂ 0+ K ₂ 0)/Si0 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. It is understood that when the coefficient d is 0, the (Na ₂ 0+Cs ₂ 0+ K ₂ 0)/Si0 ₂ is the (Na ₂ 0+Cs ₂ 0)/Si0 _2.

The amorphous precursor of zeolite has a pH ranging between 12 and 14. The average crystal size of the zeolite of the first aspect decreases when the pH of the amorphous precursor of zeolite of the second aspect increases.

In an embodiment, the coefficient d is different from zero, and the amorphous precursor is an amorphous precursor of a chabazite-type zeolite; wherein the coefficient a is ranging from 10.0 to 16.0; the coefficient b is ranging from 0.5 to 2.5; the coefficient c is ranging from 6.0 to 10.0; the coefficient d is ranging from 0.8 to 1.5; the coefficient e is ranging from 0.05 to 0.60; and the coefficient f is ranging from 90 to 250. With preference, the coefficient d is ranging between 0.90 and 1.45, preferably between 1.00 and 1.40. more preferably between 1.10 and 1.30.

In another embodiment, the coefficient d is equal to zero and the amorphous precursor is an amorphous precursor of an RHO-type zeolite; with a equal to 10.0; the coefficient b is ranging from 0.8 to 1.0; the coefficient c is ranging from 5.5 to 8.5; the coefficient d is 0; the coefficient e is ranging from 0.29 to 0.60; and the coefficient f is ranging from 80 to 250.

According to a third aspect, the disclosure provides for a method for the preparation of an amorphous precursor of zeolite as defined in the second aspect of the disclosure, said method comprising the following steps:

a) providing an aluminate precursor aqueous suspension;

b) providing a silicate precursor aqueous suspension;

c) adding at least two metallic precursors in the said aluminate precursor aqueous suspension to form a first aqueous suspension and/or in the said silicate precursor aqueous suspension to form a second aqueous suspension;

d) forming an amorphous precursor of zeolite by adding dropwise the 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 the said first or the said second aqueous suspension into said second or said first aqueous suspension respectively;

wherein said first aqueous suspension and said second aqueous suspension are organic structure-directing agent-free.

Surprisingly, the inventors have found that the preparation of amorphous precursors of zeolite without the use of template (no organic structure-directing agent (OSDA) is present) except one or more one or more metallic cations, such as Na ⁺ , Li ⁺ , Ca ⁺⁺ , Rb ⁺ , K ⁺ and/or Cs ⁺ , can lead to a mixture that is capable of being transformed into the crystalline zeolite. Additionally, the amorphous precursors prepared by this method have the interesting advantage to form crystals that are downsized and/or nanosized, that have large pore volumes and that have a low Si/AI molar ratio leading to a high content of cations (Na ⁺ , Li ⁺ , Ca ⁺⁺ , Rb ⁺ , K ⁺ , and/or Cs ⁺ ) that partially block the accessibility of the pores.

In a first and particularly preferred embodiment, the method comprises a step (c) of adding at least two metallic precursors in the said aluminate precursor aqueous suspension to form a first aqueous suspension; and a step (d) of adding dropwise the silicate precursor aqueous suspension into the first aqueous suspension. In a second preferred embodiment, alternative to the first embodiment, the method comprises a step (c) of adding at least two metallic precursors in the silicate precursor aqueous suspension to form a second aqueous suspension, and a step (d) is the step of adding dropwise the aluminate precursor aqueous suspension into the second aqueous suspension.

In a preferred embodiment, the aluminate precursor aqueous suspension comprises one or more aluminate precursors selected among NaaAhC , AhiSC K hydrated alumina, aluminium powder, AlC , AI(OH) ₃ , kaolin clays and a mixture thereof, preferably the aluminate precursor aqueous suspension comprises NaaAhC (note: another notation for NaaAhC is NaAIC> ₂ ).

In a preferred embodiment, the silicate precursor aqueous suspension comprises one or more silicate precursors 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 aqueous suspension comprises colloidal silica.

The metallic precursors

In a preferred embodiment, said at least two metallic precursors are a mixture comprising: one or more caesium precursors; and

one or more further metallic precursors selected from one or more sodium precursors, one or more lithium precursors, one or more rubidium precursors, one or more calcium precursors and/or one or more potassium precursors.

With preference, the one or more further metallic precursors comprise:

one or more potassium precursors, and

one or more selected from one or more sodium precursors, one or more lithium precursors, and/or one or more rubidium precursors and/or one or more calcium precursors.

To form a chabazite-type zeolite, the at least two metallic precursors are a mixture comprising one or more caesium precursors; and

one or more potassium precursors, and

one or more selected from one or more sodium precursors and/or one or more lithium precursors.

To form an RHO-type zeolite, the at least two metallic precursors are a mixture comprising one or more caesium precursors; and

one or more further metallic precursors selected from one or more sodium precursors, and/or one or more lithium precursors.

In a preferred embodiment:

said one or more caesium precursors are or comprise CsOH; and/or said one or more sodium precursors are or comprise NaOH; and/or

said one or more lithium precursors are or comprise LiOH; and/or

said one or more potassium precursors are or comprise KOH: and/or

said one or more rubidium precursors are or comprise RbOH: and/or

said one or more calcium precursors are or comprise Ca(OH)2.

The first aqueous suspension

In a preferred embodiment, the zeolite is of the chabazite-type and the first aqueous suspension comprises water and:

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 1 1.5 wt.%; even more preferably from 6.5 to 10.0 wt.%.

and from 15 wt.% to 80 wt.% of the at least two metallic precursors, comprising

from 1 to 30 wt.% based on the total weight of the first aqueous suspension of one or more caesium precursors; and

from 14 to 50 wt.% based on the total weight of the first aqueous suspension of one or more additional precursors comprising:

• one or more potassium precursors; and

• 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.

In a preferred embodiment, the zeolite is of the RHO-type and the first aqueous suspension comprises water and:

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 1 1.5 wt.%; even more preferably from 6.5 to 10.0 wt.%.

and from 15 wt.% to 80 wt.% of the at least two metallic precursors, comprising

from 1 to 30 wt.% based on the total weight of the first aqueous suspension of one or more caesium precursors; and

from 14 to 50 wt.% based on the total weight of the first aqueous suspension of one or more additional precursors selected from one or more sodium precursors, one or more lithium precursors, and any mixture thereof; preferably one or more sodium precursors. The formation of the amorphous precursor

In a preferred embodiment; 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 0.2 and 2, and more preferably between 0.4 and 1.2; wherein the aqueous suspension containing one or more aluminate precursors is the aluminate precursor aqueous suspension or the first aqueous suspension, and the aqueous suspension containing one or more silicate precursors is the second aqueous suspension or the silicate precursor aqueous suspension respectively.

More preferably, the weight ratio of the first aqueous suspension over the silicate precursor aqueous suspension is comprised between 0.2 and 2, and more preferably between 0.4 and 1.2.

According to a fourth aspect, the disclosure provides a method for the preparation of a zeolite according to the first aspect, comprising the method for the preparation of an amorphous precursor of zeolite according to the third aspect of the disclosure and further comprising the following steps: e) mixing said amorphous precursor;

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 50°C and 160°C during a time comprised between 0.5 hours and 90 hours, such as to form one or more crystals of zeolite;

h) optionally, recovering said one or more crystals of zeolite.

Surprisingly, the inventors have found a method to prepare zeolites that are downsized and/or nanosized and that exhibits a low Si/AI molar ratio. This low Si/AI molar ratio allows for high content of cations, such as Na ⁺ , Li ⁺ , Ca ⁺⁺ , Rb ⁺ , K ⁺ , and/or Cs ⁺ , in the environment of the RHO- type zeolite. This reduces the accessibility of the nitrogen that is used to determine the pore volume since the high content of cations partly block the pores. This feature is helpful for the capability of such zeolite of behaving as a sorbent for carbon dioxide. It has also properties of being capable of adsorbing carbon dioxide selectively over methane. The method of the present disclosure further affords a high crystalline yield and provide a narrow particle size distribution.

For example, step (g) is conducted for a time of at most 48 hours; preferably at most 24 hours, more preferably at most 20 hours.

For example, step (g) is conducted at a temperature of at least 70°C and/or of at most 120°C.

According to a fifth aspect, the disclosure provides for a use of the zeolite as defined in the first aspect as a sorbent for carbon dioxide; with preference 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 N2, He and/or Ar. Surprisingly, the inventors have found that the zeolite of the disclosure is very efficient in the sorption of carbon dioxide. Without being bound by theory, the elevated amount of the pore volume allows for such interesting properties. It is thus possible to develop a system with the zeolite of the first aspect of the disclosure which is used to separate CO2 from other gases, such as methane and/or nitrogen.

According to a sixth aspect, the disclosure provides for a use of the zeolite as defined in the first aspect as an adsorbent for carbon dioxide, preferably as selective adsorbent towards carbon dioxide over methane and/or nitrogen.

Therefore, the disclosure provides a method comprising sorbing polar molecules (H2O, CO2) over less polar ones (N2, CFU ), and thus separating H2O- and/or CO2 -containing gas mixture, sorbing lower alkanes thus separating alkanes from alkenes (C2 -C4 ), or separating nitrogen from a nitrogen-hydrogen gas mixture, by contacting the respective feedstock with the zeolite composition of the disclosure. A method for those separations could be managed as thin films, hollow fibers or membranes assembled from only or a part of the zeolite composition of the disclosure.

According to a seventh aspect, the disclosure provides for a use of the zeolite as defined per the first aspect of the disclosure in a method of preparing clathrate hydrate substance or clathrate gas substance, wherein said clathrate hydrate or clathrate gas entraps preferentially methane.

According to an eighth aspect, the disclosure provides for the use of the zeolite as defined per the first aspect of the disclosure as a catalyst in a chemical process.

Description of the figures

Figure 1 shows the X-ray diffraction (XRD) of samples 1 , 10 and 12.

Figures 2A to 2I respectively show the Scanning Electron Microscope (SEM) images of samples 1 to 9.

Figure 3 shows the N2 adsorption-desorption isotherm of samples 1 , 4, 9, 10, 11 and 12.

Figure 4 shows the CO2 adsorption isotherm of samples 1 , 9, 10, 11 and 12 recorded at 0°C.

Figure 5 shows the Rietveld refinement of sample 10.

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

Figure 6C and 6D respectively show the Transmission Electron Microscope (TEM) images of sample 12 at a magnification of 100 nm and 20 nm. Figures 6E and 6F show the Transmission Electron Microscope (TEM) images of sample 13 at a magnification of 20 nm.

Figure 7 shows the thermogravimetric analysis of nanosized chabazite zeolite of sample 10 subject to 10 subsequent sorption cycles of CO2.

Figure 8 shows the CO2 capacity of the zeolite of sample 10 in 10 sorption cycles of C0 ₂ .

Figure 9 shows the XRD patterns of the zeolite of sample 10 before and after 10 sorption cycles of CO2.

Figure 10 shows the in situ Fourier Transform Infra-Red (FTIR) spectrum recorded for sample 10 under delivery of a small dose of CO2 (3.1 O ⁴ mmol to 1.10 ¹ mmol).

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

Figure 12 shows the LeBail refinement of ion-exchanged zeolite of sample 10 (proton form).

Figure 13 shows the in situ XRD patterns of sample 10 recorded under delivery of 1 bar of CO2.

Figure 14 shows the evolution of the intensity of the peak at 12.8° 2Q of sample 10 under controlled adsorption of CO2.

Figure 15 shows the change of the cell volume of sample 10 under controlled adsorption of CO2.

Figure 16 shows the unit cell parameter under adsorption and desorption of CO2 of sample 10.

Figure 17 shows the z-potential curve of sample 13.

Figure 18 shows the normalised mass adsorption of CO2 and CFU as pure gas followed by TGA experiments for sample 10.

Figure 19 represents the X-Ray Diffraction (XRD) spectrum of the synthetic zeolite material RHO-1 , RHO-2 and RHO-3. The intensity is shown in arbitrary units (a.u.) as a function of the angle 2Q (in degrees) in the range of 5°-50°.

Figure 20 represents the ²⁷ AI magic angle spinning nuclear magnetic resonance (MAS NMR) spectrum of the synthetic zeolite material RHO-1 , RHO-2 and RHO-3 between 150 ppm and -10 ppm.

Figure 21 represents the ²⁹ Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectrum of the synthetic zeolite material RHO-1 , RHO-2 and RHO-3 between - 50 ppm and -130 ppm.

Figure 22 shows the scanning electron microscope (SEM) images of the synthetic zeolite material RHO-1 , RHO-2 and RHO-3. Figure 23 shows the transmission electron microscope (TEM) images of the synthetic zeolite material RHO-1 , RHO-2 and RHO-3.

Figure 24 shows the thermogravimetric analyses (TGA) of the synthetic zeolite material RHO-1 , RHO-2 and RHO-3.

Figure 25 represents the N2 sorption isotherms of the synthetic zeolite material RHO- 1 , RHO-2 and RHO-3.

Figure 26 represents the CO2 sorption isotherms of the synthetic zeolite material RHO- 1 , RHO-2 and RHO-3.

Figure 27 represents the sorption capacity towards CO2 of the synthetic zeolite material RHO-1 , RHO-2 and RHO-3, obtained by TGA under CO2 flow.

Figure 28 represents the sorption behaviour of RHO-3 monitored by FTIR in ten consecutive cycles of CO2 adsorption and desorption at 350°.

Figure 29 represents the stability of RHO-3 after sorption cycles determined by XRD analysis after FTIR.

Figure 30 represents the sorption behaviour of RHO-3 monitored by TGA in ten consecutive cycles of CO2 adsorption and desorption at 350°.

Figure 31 represents the stability of RHO-3 after sorption cycles determined by XRD analysis after TGA.

Figure 32 represents the absorption capacity of RHO-3 towards carbon dioxide and methane.

Figure 33 shows the XRD patterns of samples 16-18.

Figure 34 shows the SEM image of a CHA zeolite (sample 16).

Figure 35 shows the SEM image of an RHO zeolite (sample 17).

Figure 36 shows the SEM image of an FAU zeolite with EMT as a secondary phase (sample 18).

Detailed description

For the disclosure, the following definitions are given:

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

Zeolite codes (e.g., CHA, RHO...) are defined according to the“Atlas of Zeolite Framework Types", 6 ^th revised edition, 2007, Elsevier, to which the present application also refers.

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. 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.

The yield to particular chemical compounds is determined as the mathematical product between the selectivity to said particular chemical compounds and the conversion rate of the chemical reaction. The mathematical product is expressed as a percentage.

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”.

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.

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 zeolite

The disclosure provides for a method for the preparation of an amorphous precursor of zeolite as defined in the second aspect of the disclosure, said method comprising the following steps: a) providing an aluminate precursor aqueous suspension;

b) providing a silicate precursor aqueous suspension;

c) adding at least two metallic precursors in the said aluminate precursor aqueous suspension to form a first aqueous suspension and/or adding at least two metallic precursors in the said silicate precursor aqueous suspension to form a second aqueous suspension;

d) forming an amorphous precursor of zeolite by adding dropwise the 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 the said first or the said second aqueous suspension into said second or said first aqueous suspension respectively; wherein said first aqueous suspension and said second aqueous suspension are organic structure-directing agent-free.

In a first and particularly preferred embodiment, said step (c) is the step of adding at least two metallic precursors in the aluminate precursor aqueous suspension to form a first aqueous suspension, and said step (d) is the step of adding dropwise the silicate precursor aqueous suspension on the first aqueous suspension. This allows for stabilizing the pH during the addition of the one or more silicate precursors into the first aqueous suspension. There is no drop of pH, upon slow addition of the silicate precursors aqueous suspension. In other words, the basic components and the one or more silicates are not added all together. This allows the increase of the Si/AI ratio of the crystalline zeolite upon crystallization. Moreover, providing a higher Si/AI molar ratio to the crystalline zeolite allows for a better sorption capacity of the zeolite towards carbon dioxide. This is why this embodiment is particularly preferred.

In a second preferred embodiment, alternative to the first embodiment, said step (c) is the step of adding, in the silicate precursor aqueous suspension said at least two metallic precursors to form a second aqueous suspension, and said step (d) is the step of adding dropwise the aluminate precursor aqueous suspension on the second aqueous suspension. The inventors have found that upon crystallization, the amorphous precursors will provide aggregates of nanosized zeolites.

The aluminate precursor aqueous suspension

With preference, one or more of the following embodiments can be used to better define the aluminate precursor aqueous suspension:

The aluminate precursor aqueous suspension comprises one or more aluminate precursors selected among NaaAhC , AhiSC K hydrated alumina, aluminium powder, AlC , AI(OH)3, kaolin clays and a mixture thereof, preferably the aluminate precursor aqueous suspension comprises NaaAhC (note: another notation for NaaAhC is NaAI0 ₂ ).

Na ₂ Al ₂ C> ₄ , when selected, comprised between 48 wt.% and 63 wt.% of AI ₂ O ₃ and between 37 wt.% and 52 wt.% of Na ₂ 0, preferably 53 wt.% of AI ₂ O ₃ and 47 wt.% of Na ₂ 0.

The content of the one or more aluminate precursors in the aluminate precursor aqueous suspension is ranging between 2.5 wt.% and 25 wt.% of the total weight of the aluminate precursor aqueous suspension, preferably between 3 wt.% and 20 wt.%, more preferably between 4 wt.% and 10 wt.%. The aluminate precursor 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 zeolites with different counter-cations.

The silicate precursor aqueous suspension

With preference, one or more of the following embodiments can be used to better define the silicate precursor aqueous suspension:

The silicate precursor aqueous suspension comprises one or more silicate precursors 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 aqueous suspension comprises colloidal silica.

Colloidal silica, when selected, comprises amorphous, nonporous, and spherical silica particles in an aqueous suspension at a content ranging 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.% or 40 wt.%.

The content of the one or more silicate precursors in the silicate precursor aqueous suspension is ranging between 10 wt.% and 50 wt.% of the total weight of the silicate precursor aqueous suspension, preferably between 15 wt.% and 40 wt.%, more preferably between 20 wt.% and 35 wt.%.

The silicate precursor 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 zeolites with different counter-cations.

Advantageously, said at least two metallic precursors are a mixture comprising:

- one or more caesium precursors; and

- one or more further metallic precursors selected from one or more sodium precursors, one or more lithium precursors, one or more rubidium precursors, one or more calcium precursors, one or more potassium precursors and any mixture thereof.

Wth preference, the one or more further metallic precursors comprise:

one or more potassium precursors, and

one or more selected from one or more sodium precursors, one or more lithium precursors, one or more rubidium precursors, one or more calcium precursors, and any mixture thereof. The one or more caesium precursors preferably comprise an anion selected from a group of hydroxide, oxide, nitrate, sulfate, carbonate, dicarbonate, halogen, oxalate, citrate, and acetate anion or a mixture thereof, with preference, said anion is hydroxide anion. In a preferred embodiment, the caesium precursor is CsOH.

The one or more sodium precursors preferably comprise an anion selected from hydroxide, oxide, nitrate, sulfate, carbonate, dicarbonate, halogen, oxalate, citrate, acetate anion or a mixture thereof, with preference said anion is hydroxide anion. In a preferred embodiment, the sodium precursor is NaOH.

The one or more potassium precursors preferably comprise an anion selected from hydroxide, oxide, nitrate, sulfate, carbonate, dicarbonate, halogen, oxalate, citrate, acetate anion or a mixture thereof, with preference said anion is hydroxide anion. In a preferred embodiment, the sodium precursor is KOH.

The one or more lithium precursors preferably comprise an anion selected from hydroxide, oxide, nitrate, sulfate, carbonate, dicarbonate, halogen, oxalate, citrate, acetate anion or a mixture thereof, with preference said anion is hydroxide anion. In a preferred embodiment, the sodium precursor is LiOH.

The one or more rubidium precursors preferably comprise an anion selected from hydroxide, oxide, nitrate, sulfate, carbonate, dicarbonate, halogen, oxalate, citrate, acetate anion or a mixture thereof, with preference said anion is hydroxide anion. In a preferred embodiment, the sodium precursor is RbOH.

The one or more calcium precursors preferably comprise an anion selected from hydroxide, oxide, nitrate, sulfate, carbonate, dicarbonate, halogen, oxalate, citrate, acetate anion or a mixture thereof, with preference said anion is hydroxide anion. In a preferred embodiment, the sodium precursor is Ca(OH)2.

In a preferred embodiment, said at least two metallic precursors are a combination of NaOH and CsOH. In another preferred embodiment, there are at least three metallic precursors, preferably a combination of NaOH, CsOH and KOH.

The first aqueous suspension

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.%.

In a more preferred embodiment, the first aqueous suspension comprises water and: 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 1 1.5 wt.%; even more preferably from 6.5 to 10.0 wt.%.

and from 15 wt.% to 80 wt.% of the at least two metallic precursors, comprising

from 1 to 30 wt.% based on the total weight of the first aqueous suspension of one or more caesium precursors; and

from 14 to 50 wt.% based on the total weight of the first aqueous suspension of one or more additional precursors selected from sodium precursors, potassium precursors lithium precursors, calcium precursors and/or of the rubidium precursors.

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.%.

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.%.

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 selected from sodium precursors, potassium precursors lithium precursors, calcium precursors and/or of the rubidium 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.%.

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 selected from sodium precursors, potassium precursors lithium precursors, calcium precursors and/or of the rubidium 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.%.

Obtention of a zeolite of the chabazite-type

In a preferred embodiment, the zeolite is of the chabazite-type and the first aqueous suspension comprises water and:

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 1 1.5 wt.%; even more preferably from 6.5 to 10.0 wt.%;

and from 15 wt.% to 80 wt.% of the at least two metallic precursors, comprising

from 1 to 30 wt.% based on the total weight of the first aqueous suspension of one or more caesium precursors; and from 14 to 50 wt.% based on the total weight of the first aqueous suspension of one or more additional precursors comprising:

• one or more potassium precursors; and

• 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.

The amorphous precursor obtained with such composition affords upon crystallization a chabazite-type zeolite that has a CO2 uptake of at least 3.50 mmol/g of zeolite material.

With preference, the zeolite is of the chabazite-type and 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:

• from 2 wt. % to 15 wt.% based on the total weight of the first aqueous suspension of one or more potassium precursors; and

• 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.

More preferably, the zeolite is of the chabazite-type and 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:

• from 4 wt. % to 12 wt. % based on the total weight of the first aqueous suspension of one or more potassium precursors; and

• 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.

In one instance, the zeolite is of the chabazite-type and the first aqueous suspension comprises water and:

7.66 wt.% based on the total weight of the first aqueous suspension of one or more aluminate precursors;

4.90 wt.% based on the total weight of the first aqueous suspension of one or more caesium precursors;

5.24 wt.% based on the total weight of the first aqueous suspension of one or more potassium precursors; and

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.

In a second instance, the zeolite is of the chabazite-type and the first aqueous suspension comprises water and: 7.06 wt.% based on the total weight of the first aqueous suspension of one or more aluminate precursors;

4.59 wt.% based on the total weight of the first aqueous suspension of one or more caesium precursors;

10.90 wt.% based on the total weight of the first aqueous suspension of one or more potassium precursors; and

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.

Obtention of a zeolite of the RHO-type

In a preferred embodiment, the zeolite is of the RHO-type and the first aqueous suspension comprises water and:

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 1 1.5 wt.%; even more preferably from 6.5 to 10.0 wt.%;

and from 15 wt.% to 80 wt.% of the at least two metallic precursors, comprising

from 1 to 30 wt.% based on the total weight of the first aqueous suspension of one or more caesium precursors; and

from 14 to 50 wt.% based on the total weight of the first aqueous suspension of one or more additional precursors selected from one or more sodium precursors, one or more lithium precursors, and any mixture thereof; preferably one or more sodium precursors. With preference, the zeolite is of the RHO-type and 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 selected from one or more sodium precursors, one or more lithium precursors, and any mixture thereof; preferably one or more sodium precursors.

In one embodiment, the zeolite is of the RHO-type and the first aqueous suspension comprises water and:

- from 5.00 to 9.00 wt.% based on the total weight of the first aqueous suspension of one or more aluminate precursors;

- from 33.01 wt.% to 80.00 wt.% based on the total weight of the first aqueous suspension of the one or more caesium precursors and one or more additional precursors selected from one or more sodium precursors and/or one or more lithium precursors.

The amorphous precursor obtained with such composition affords upon crystallization a RHO- type zeolite that has a CO2 uptake comprised between 1.30 and 1.99 mmol/g of zeolite material.

In one instance, the zeolite is of the RHO-type and the first aqueous suspension comprises water and: 8.71 wt.% based on the total weight of the first aqueous suspension of one or more aluminate precursors;

4.96 wt.% based on the total weight of the first aqueous suspension of one or more caesium precursors; and

30.72 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.

The amorphous precursor obtained with such composition affords upon crystallization an RHO-type zeolite that has a CO2 uptake of 1.56 mmol/g of zeolite material.

In one embodiment, the zeolite is of the RHO-type and the first aqueous suspension comprises water and:

- from 9.01 to 15.00 wt.% based on the total weight of the first aqueous suspension of one or more aluminate precursors;

- from 15.00 wt.% to 33.00 wt.% based on the total weight of the first aqueous suspension of the one or more caesium precursors and one or more additional precursors selected from one or more sodium precursors and/or one or more lithium precursors.

The amorphous precursor obtained with such composition affords upon crystallization an RHO-type zeolite that has a CO2 uptake of at least 2.00 mmol/g of zeolite material.

In a second instance, the zeolite is of the RHO-type and the first aqueous suspension comprises water and:

9.55 wt.% based on the total weight of the first aqueous suspension of one or more aluminate precursors;

3.11 wt.% based on the total weight of the first aqueous suspension of one or more caesium precursors; and

28.69 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.

The amorphous precursor obtained with such composition affords upon crystallization an RHO-type zeolite that has a CO2 uptake of 2.16 mmol/g of zeolite material.

The second aqueous suspension

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.%.

In a more preferred embodiment, the second aqueous suspension comprises water and: 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

from 10 wt.% to 60 wt.% of at least three metallic precursors, comprising:

• from 1 to 25 wt.% based on the total weight of the second aqueous suspension of one or more caesium precursors; and

• from 9 to 35 wt.% based on the total weight of the second aqueous suspension of one or more additional precursors selected from sodium precursors, potassium precursors lithium precursors, calcium precursors and/or of the rubidium precursors.

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.%.

Wth 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.%.

Wth 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 selected from sodium precursors, potassium precursors lithium precursors, calcium precursors and/or of the rubidium 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.%.

Wth 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 selected from sodium precursors, potassium precursors lithium precursors, calcium precursors and/or of the rubidium precursors; preferably at least 10 wt.%; more preferably at least 11 wt.%; even more preferably at least 13 wt.%; and most preferably at least 14 wt.%.

In a preferred embodiment, the zeolite is of the chabazite-type and the second aqueous suspension comprises water and:

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

from 10 wt.% to 60 wt.% of at least three metallic precursors, comprising

from 1 to 25 wt.% based on the total weight of the second aqueous suspension of one or more caesium precursors; and from 9 to 35 wt.% based on the total weight of the second aqueous suspension of one or more additional precursors comprising:

o one or more potassium precursors; and

o 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.

With preference, the zeolite is of the chabazite-type and 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:

• from 1 wt.% to 13 wt. % based on the total weight of the second aqueous suspension of one or more potassium precursors; and

• 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.

More preferably, the zeolite is of the chabazite-type and 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:

• from 2 wt. % to 12 wt. % based on the total weight of the second aqueous suspension of one or more potassium precursors; and

• 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.

In one instance, the zeolite is of the chabazite-type and the second aqueous suspension comprises water and:

23.26 wt.% based on the total weight of the second aqueous suspension of one or more silicate precursors;

2.18 wt.% based on the total weight of the second aqueous suspension of one or more caesium precursors;

3.99 wt. % based on the total weight of the second aqueous suspension of one or more potassium precursors; and

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.

In a preferred embodiment, the zeolite is of the RHO-type and the second aqueous suspension comprises water and: 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

from 10 wt.% to 60 wt.% of the at least two metallic precursors, comprising

• from 1 to 25 wt.% based on the total weight of the second aqueous suspension of one or more caesium precursors; and

• from 9 to 35 wt.% based on the total weight of the second aqueous suspension of one or more additional precursors selected from one or more sodium precursors, one or more lithium precursors, and any mixture thereof; preferably one or more sodium precursors.

The amorphous precursor obtained with such composition affords upon crystallization an RHO-type zeolite that has a CO2 uptake comprised between 1.20 and 1.29 mmol/g of zeolite material.

With preference, the zeolite is of the RHO-type and the second aqueous suspension comprises from 25 to 45 wt.% based on the total weight of the second aqueous suspension of one or more additional precursors selected from one or more sodium precursors, one or more lithium precursors, and any mixture thereof; preferably one or more sodium precursors.

In one instance, the zeolite is of the RHO-type and the second aqueous suspension comprises water and:

26.99 wt.% based on the total weight of the second aqueous suspension of one or more silicate precursors;

3.97 wt.% based on the total weight of the second aqueous suspension of one or more caesium precursors; and

24.56 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.

The amorphous precursor obtained with such composition affords upon crystallization an RHO-type zeolite that has a CO2 uptake of 1.22 mmol/g of zeolite material.

The formation of the amorphous precursor

It is preferred that the weight ratio of the aqueous suspension containing aluminate precursors over the aqueous suspension containing silicate precursors is comprised between 0.2 and 2, and more preferably between 0.4 and 1.2; 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. More preferably, the weight ratio of the first aqueous suspension over the silicate precursor aqueous suspension is comprised between 0.2 and 2, and more preferably between 0.4 and 1.2. The step d)

It is also preferred that the dropwise addition of the aqueous suspension containing aluminate precursors over the aqueous suspension containing 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. The dropwise addition of the aqueous suspension containing aluminate precursors over the aqueous suspension containing silicate precursors is advantageously performed under stirring, preferably under stirring of at least 500 rpm, more preferably of at least 750 rpm.

It is also preferred that the dropwise addition of the aqueous suspension containing silicate precursors over the aqueous suspension containing aluminate precursors is performed in a temperature comprised between 15°C and 25°C. The dropwise addition of the aqueous suspension containing silicate precursors over the aqueous suspension containing aluminate precursors is advantageously performed under stirring, preferably under stirring of at least 500 rpm, more preferably of at least 750 rpm.

The precursor of the zeolite

The disclosure also provides an amorphous precursor of zeolite, remarkable in that said amorphous precursor of zeolite has a molar composition comprising

a Si0 ₂ : b Al ₂ 0 ₃ : c M ¹ ₂ 0: d K ₂ 0: e Cs ₂ 0: f H ₂ 0,

wherein a, b, c, and d are coefficients

the coefficient a is ranging from 10.0 to 16.0;

the coefficient b is ranging from 0.5 to 2.5;

the coefficient c is ranging from 5.5 to 10.0;

the coefficient d is ranging from 0.0 to 1.6;

the coefficient e is ranging from 0.05 to 0.60; and

the coefficient f is ranging from 80 to 300

and wherein M ¹ is selected from Na, Li, Ca and/or Rb

and with the provision that the M ¹ ₂ 0/ H ₂ 0 ratio is equal to or greater than 0.03.

For example, the precursor is amorphous and has a molar composition comprising

a Si0 ₂ : b Al ₂ 0 ₃ : c M ¹ ₂ 0: d K ₂ 0: e Cs ₂ 0: f H ₂ 0,

wherein a, b, c, and d are coefficients

wherein

10 £ a £ 16

0.5 £ b £ 2.5

5.5 £ c £ 10; 0 £ d £ 1.6;

0.05 £ e £ 0.60; and

80 £ f £ 300

wherein M ¹ is selected from Na, Li, Ca and/or Rb,

and with the provision that the M ¹ ₂ 0/ FhO ratio is equal to or greater than 0.03.

Thus M ¹ ₂ 0 is selected from Na ₂ 0, U2O, Ca2<D and/or Rb2<D.

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

This precursor provides for the development of zeolite. It is evidenced that the amorphous precursors do not contain any template except one or more metallic cations, such as Na ⁺ , Li ⁺ , Ca ⁺⁺ , Rb ⁺ , K ⁺ and/or Cs ⁺ .

It is preferred that M ¹ is or comprises Na.

The M ¹ 2q/H2q ratio is advantageously equal to or greater than 0.04, preferably equal to or greater than 0.05, more preferably equal to greater than 0.06. For example, the Na2<D/ H2O ratio is equal to or greater than 0.04, preferably equal to or greater than 0.05, more preferably equal to greater than 0.06.

The (M ¹ ₂ 0+Cs ₂ 0)/SiC> 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 ¹ ₂ 0+Cs ₂ 0)/SiC> ₂ ratio can be selected as followed. The (M ¹ ₂ 0+Cs ₂ 0+ K ₂ 0)/SiC> ₂ ratio is advantageously 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. It is understood that when the coefficient d is 0, the (M ¹ ₂ 0+Cs ₂ 0+ K ₂ 0)/SiC> ₂ is the (M ¹ ₂ 0+Cs ₂ 0)/SiC> ₂ . For example, the (Na ₂ 0+Cs ₂ 0+ K ₂ 0)/SiC> 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. It is understood that when the coefficient d is 0, the (Na ₂ 0+Cs ₂ 0+ K ₂ 0)/Si0 ₂ is the (Na ₂ 0+Cs ₂ 0)/Si0 ₂ .

The M ¹ 2q/Aΐ2q3 ratio is advantageously equal to or greater than 7.0; preferably is equal to or greater than 7.5. For example, the Na ₂ 0/ AI ₂ O ₃ ratio is equal to or greater than 7.0; preferably is equal to or greater than 7.5. The CS2O/AI2O3 ratio is advantageously equal to or less than 0.75; preferably is equal to or less than 0.65; more is equal to or less than 0.60.

Advantageously, the coefficient a, attributed to the molar amount of silica, is ranging from 10 to 16, preferably is equal to 10 or 16.

It is preferred that the coefficient b, attributed to the molar amount of alumina, is ranging between 0.5 and 2.5, preferably between 0.6 and 2.4, more preferably between 0.7 and 2.3, even more preferably between 0.8 and 2.2, most preferably between 1.0 and 2.0.

With preference, the coefficient c, preferably attributed to the molar amount of sodium oxide, is ranging between 5.5 and 10.0, preferably between 6.0 and 9.5, more preferably between 6.5 and 9.0, even more preferably between 7.0 and 8.5, most preferably between 7.5 and 8.0. Wth preference, the coefficient e, attributed to the molar amount of caesium oxide, is ranging between 0.05 and 0.60, preferably between 0.10 and 0.55, more preferably between 0.15 and 0.50, even more preferably between 0.20 and 0.45, most preferably between 0.25 and 0.40. Wth preference, the coefficient f, attributed to the molar amount of water, is ranging between 90 and 290, preferably between 100 and 280, more preferably between 120 and 260, even more preferably between 150 and 230. For example, the coefficient f is at most 290, preferably at most 280, more preferably at most 260, even more preferably at most 250, most preferably 230, even most preferably at most 200.

For example, in one embodiment, when the coefficient d is different from zero, the amorphous precursor is an amorphous precursor of a chabazite-type zeolite; wherein the coefficient a is ranging from 10.0 to 16.0; the coefficient b is ranging from 0.5 to 2.5; the coefficient c is ranging from 6.0 to 10.0; the coefficient d is ranging from 0.8 to 1.5; the coefficient e is ranging from 0.05 to 0.60; and the coefficient f is ranging from 90 to 250.

For example, in another embodiment, when the coefficient d is equal to zero, the amorphous precursor is an amorphous precursor of an RHO-type zeolite; with a equal to 10.0; the coefficient b is ranging from 0.8 to 1.0; the coefficient c is ranging from 5.5 to 8.5; the coefficient d is 0; the coefficient e is ranging from 0.29 to 0.60; and the coefficient f is ranging from 80 to 250.

It is preferred that the amorphous precursor of zeolite has a pH ranging between 12 and 14. Advantageously, the average crystal size of the zeolite of the first aspect decreases when the pH of the amorphous precursor of zeolite of the second aspect increases.

Wth preference, the amorphous precursor is fluoride-free.

In a first more preferred embodiment, when the coefficient a, attributed to the molar amount of silica, is equal to 10, and when M ¹ 20 is Na20, then 0.6 £ b £ 0.8; with preference b = 0.8;

6.0 £ c £ 8.0; with preference c = 8.0;

1.25 £ d £ 1.35; with preference d = 1.35;

0.20 £ e £ 0.30; with preference e = 0.30; and

120 £ f £ 190; with preference f = 120 or alternatively f = 190.

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 and form a chabazite-type zeolite. After crystallization, the resulting nanocrystals have an average crystal size comprised between 5 nm and 200 nm as determined by the Schemer 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 a second more preferred embodiment, when the coefficient a, attributed to the molar amount of silica, is equal to 16, and when M ¹ ₂ 0 is Na ₂ 0, then

b = 0.8;

9.0 £ c £ 9.5

d = 0.85;

e = 0.35; and

120 £ f £ 140.

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 Schemer equation.

In a third more preferred embodiment, when the coefficient a, attributed to the molar amount of silica, is equal to 16, and when M ¹ ₂ 0 is Na ₂ 0, then

0.4 £ b £ 0.6;

c = 6.0;

d = 1.35;

0.15 £ e £ 0.25; with preference e = 0.15; and

130 £ f £ 150.

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 Schemer equation.

In a fourth and fifth more preferred embodiment, when the coefficient a, attributed to the molar amount of silica, is equal to 10, and when M ¹ ₂ 0 is Na ₂ 0, then 0.8 £ b £ 1.0;

5.5 £ c £ 8.5;

0.29 £ d £ 0.60; and

80 £ e £ 300;

with preference, in the fourth embodiment, b = 0.8, c = 8, d = 0.58 and e = 100; or with preference, in the fifth embodiment, b = 0.8, c = 6.6, d = 0.33 and e = 100.

When a first aqueous suspension is formed in step c) and when the silicate precursor aqueous suspension is added dropwise on the first aqueous suspension in step d), then the amount of the free cations will be contained, favouring thus the formation of discrete RHO-type downsized and/or nanosized RHO-type zeolite upon crystallization.

When a second aqueous suspension is formed in step c) and when the aluminate precursor aqueous suspension is added dropwise on the second aqueous suspension in step d), then the basicity of the second aqueous suspension being elevated (compared for example to the basicity of the first aqueous suspension), this will favour the formation of aggregated RHO- type zeolite upon crystallization.

Method for preparing the zeolite from the precursor

The disclosure provides a method for the preparation of a zeolite, comprising the method for the preparation of an amorphous precursor of zeolite as described above and further comprising the following steps: e) mixing said amorphous precursor, preferably at a temperature comprised between 20°C and 30°C;

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 50°C and 160°C during a time comprised between 0.5 hours and 90 hours, such as to form one or more crystals of zeolite;

h) optionally, recovering said one or more crystals of zeolite.

The step (e)

The step (e) of 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 step (e) of mixing is preferably carried out for a period comprised between 8 hours and 15 days, more preferably for at least 15 hours and/or at most 10 days and is preferably carried out under mechanical stirring, for instance at 700 rpm. With preference, one or more of the following embodiments can be used to further define the step (e) of the method for preparation of the zeolite of the present disclosure:

Said step (e) is carried out in a sealed environment, preferably at a pressure of 0.1 MPa.

Said step (e) is carried out under stirring.

Said amorphous precursor has after step (e) and before step (f) a refractive index ranging between 1.303 and 1.363, preferably between 1.313 and 1.353, more preferably between 1.323 and 1.343, even more preferably is 1.333; said refractive index is determined by refractometry. In other words, said amorphous precursor is after step (e) and before step (f) in the form of a water clear suspension.

In a preferred embodiment wherein an RHO-type zeolite is produced, said stirring is selected from magnetic stirring or mechanical stirring or is a first type of stirring during a first period of at least 2 hours and a second type of stirring after said the first period for a second period of at least 6 hours, more preferably the first type of stirring is magnetic stirring or mechanical stirring, and/or the second type of stirring is orbital stirring or shaking.

The step (f)

As some synthesis need a step (f) of the addition of silica precursor to prevent the formation of big amorphous particles and sedimentation, additional silicate precursors aqueous suspension is added during the mixing step (e).

When step (f) is needed, it is carried out after a period comprised between 4 and 7 days after the start of the mixing step (e).

With preference, one or more of the following embodiments can be used to further define the step (f) of the method for preparation of the zeolite of the present disclosure:

The amount of the additional silicate precursors aqueous suspension added in step (f) corresponds to an amount comprised between 50 wt.% and 70 wt.% of the amount of the silicate precursors aqueous 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 additional silicate precursors 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.% or 40 wt.%.

The additional silicate precursors aqueous suspension comprises water, preferably distilled water, more preferably double distilled water.

The mixing step in step (f) is similar to the mixing step (e), except that said mixing step in step (f) is carried out for a period comprised between 0.5 hours and 2 hours, preferably comprised between 1 hour and 1.5 hours.

The use of non-distilled water could afford a tiny amount of one or more 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.

The step (q)

Once the solution has been mixed, the homogenous solution obtained is crystallized to generate the zeolite, preferably in the absence of seeds. The heating step (g) is thus preferably performed at a temperature comprised between 60°C and 150°C, preferably between 70°C and 140°C, more preferably between 80°C and 130°C, even more preferably between 90°C and 120°C. It is highlighted that if the crystallization temperature is too low (below 50°C) or if the crystallization temperature is too high (above 160°C), the crystallization can provide several types of zeolite in one batch. For instance, to obtain a chabazite-type zeolite, it is necessary to perform the crystallization at a temperature comprised between 90°C and 160°C. To obtain an RHO-type zeolite, it is necessary to perform the crystallization at a temperature comprised between 50°C and 140°C. The crystallization is preferably carried out for at least 8 hours and of at most 15 days, more preferably for at least 13 hours and of at most 32 hours, even more preferably of at least 14 hours. For example, the step (g) is conducted for a time of at most 90 hours, preferably at most 72 hours, more preferably at most 48 hours, even more preferably at most 24 hours, most preferably at most 20 hours. The crystallization is preferably carried out in a sealed environment, preferably under autogenous pressure conditions.

In an embodiment to produce a CHA-type zeolite, the step (g) of heating said amorphous precursor is conducted at a temperature comprised between 90°C and 160°C; with preference, during a time comprised between 1 hour and 12 hours. In an embodiment to produce an RHO-type zeolite, the step (g) of heating said amorphous precursor is conducted at a temperature comprised between 50°C and 140°C.

In an embodiment, the method further comprises the step of cooling down said one or more crystals of the zeolite at a temperature comprised between 20°C and 25°C after said step (g).

The step (h)

In a preferred embodiment, a step (h) of recovering said one or more crystals of zeolite can be 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.

With preference, one or more of the following embodiments can be used to further define the step (h) of the method for preparation of the zeolite of the present disclosure:

The step (h), when present, comprises the sub-steps of adding water and separating the one or more crystals of zeolite.

The sub-step of separating the one or more crystals of zeolite is carried out by filtration and/or by centrifugation and/or by dialysis and/or by adding flocculating agents followed by filtration, preferably by centrifugation.

The sub-step of adding water is repeated until the pH of the decanting water reaches a pH comprised between 6.5 and 8.5, preferably between 7 and 8.

The step (h), when present, optionally comprises the sub-step of drying after the sub step of separating the one or more crystals of zeolite.

Said method, when step (h) is present, further comprises a step (i) of performing an ion- exchange. The ion-exchange of step (i) 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 can also be produced.

The zeolite The disclosure provides a zeolite comprising caesium, the zeolite is selected from the EDI family, PHI family or has at least one cage formed with at least one 8-membered ring and a

Si/AI molar ratio ranging from 1 to 15 as determined by ²⁹ Si magic angle spinning nuclear magnetic resonance, the zeolite is remarkable in that said zeolite

is in the form of one or more nanoparticles, said nanoparticles having

an average crystal size comprised between 5 nm and 400 nm as determined by the Scherrer equation;

said zeolite has

a specific surface area comprised between 40 m ² g ¹ and 250 m ² g ¹ as determined by N2 adsorption measurements; and

a Cs/AI molar ratio ranging from 0.01 to 0.75 as determined by Inductively Coupled Plasma Optical Emission Spectrometry and an MVCs molar ratio ranging from 0.10 to 5.00 as determined by Inductively Coupled Plasma Optical Emission Spectrometry wherein M ¹ is selected from Na, Li, Ca and/or Rb.

It is preferred that the zeolite forms nanoparticles with a specific surface area comprised between 75 m ² g ¹ and 75 m ² g ¹ as determined by N2 adsorption measurements, preferably comprised between 100 m ² g ¹ and 150 m ² g ¹ .

Advantageously, the zeolite comprises a pore volume comprised between 0.05 cm ³ g ^-1 and 0.5 cm ³ g ¹ as determined by N2 sorption measurements, preferably between 0.06 cm ³ g ^-1 and 0.4 cm ³ g ^-1 , more preferably between 0.08 cm ³ g ^-1 and 0.35 cm ³ g ^-1 , even more preferably between 0.1 cm ³ g ^-1 and 0.32 cm ³ g ^-1 .

For example, the zeolite has a Si/AI molar ratio of at most 10 as determined by ²⁹ Si magic angle spinning nuclear magnetic resonance; preferably of at most 10, more preferably of at most 8, even more preferably of at most 5, most preferably of at most 3.0 or of at most 2.8. The zeolite has advantageously a Si/AI molar ratio of at least 1.1 as determined by ²⁹ Si magic angle spinning nuclear magnetic resonance; preferably of at least 1.2, more preferably of at least 1.5. The zeolite has preferably a Si/AI molar ratio determined by ²⁹ Si magic angle spinning nuclear magnetic resonance, said Si/AI molar ratio is comprised between 1.10 and 3.50, preferably between 1.20 and 3.00, more preferably between 1.40 and 2.50, even more preferably between 1.50 and 2.00, most preferably between 1.60 and 1.90.

The nanoparticles have advantageously an average crystal size of at least 15 nm as determined by Scherrer equation; preferably at least 20 nm; more preferably at least 40 nm; even more preferably at least 50 nm, most preferably at least 60 nm and even most preferably at least 80 nm or at least 90 nm.

With preference, the nanoparticles have an average crystal size comprised between 10 nm and 400 nm as determined by the Schemer equation or between 10 nm and 245 nm, 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 advantageously at least 10 nm and at most 400 nm as determined by the Schemer equation, preferably at most 350 nm, more preferably at most 250 nm, even more preferably at most 200 nm, most preferably at most 195 nm, even most preferably at most 185 nm or at most 175 nm, or at most 165 nm.

In one preferred embodiment, the zeolite having at least one cage formed with at least one 8- membered ring is selected from the AEI, AFX, CHA, DDR, ERI, KFI, LTA, MER, MWF, PAU, RHO, SFW and TSC families, preferably the zeolite is one zeolite from the AEI, AFX, CHA, DDR, EDI, ERI, KFI, MER, RHO and SFW families, more preferably the zeolite is one zeolite from the AEI, AFX, CHA, DDR, ERI, MER and RHO families, and even more preferably the zeolite is one zeolite from the CHA family or one zeolite from the RHO family.

The zeolite has advantageously an MVAI molar ratio ranging from 0.075 to 0.80 as determined by Inductively Coupled Plasma Optical Emission Spectrometry wherein M ¹ is selected from Na, Li, Ca and/or Rb; preferably from 0.65 to 0.80, more preferably from 0.67 and 0.78, even more preferably from 0.70 and 0.75; or preferably from 0.075 to 0.20, more preferably from 0.080 to 0.15, even more preferably from 0.085 to 0.10.

Thus, when M ¹ is Na, the zeolite has a Na/AI molar ratio determined by inductively coupled plasma optical emission spectrometry comprised between 0.075 and 0.80; preferably from 0.65 to 0.80, more preferably from 0.67 and 0.78, even more preferably from 0.70 and 0.75; or preferably from 0.075 to 0.20, more preferably from 0.080 to 0.15, even more preferably from 0.085 to 0.10.

The zeolite has an MVCs molar ratio ranging from 0.10 to 5.00 as determined by Inductively Coupled Plasma Optical Emission Spectrometry wherein M ¹ is selected from Na, Li, Ca and/or Rb. In an embodiment, the zeolite has an MVCs molar ratio ranging from 1.50 to 5.00; preferably from 2.00 to 5.00, more preferably from 2.50 to 4.50, and even more preferably from 3.00 to 4.00. In another embodiment zeolite has an MVCs molar ratio ranging from 0.10 to 0.50; preferably from 0.14 to 0.40; more preferably from 0.17 and 0.30. Thus, when M ¹ is Na, the zeolite has a Na/Cs molar ratio determined by inductively coupled plasma optical emission spectrometry comprised between 0.10 and 5.00; preferably from 2.00 to 5.00 or from 0.10 to 0.50. In an embodiment, the zeolite has a Na/Cs molar ratio ranging from 1.50 to 5.0; preferably from 2.00 to 5.0, more preferably from 2.50 to 4.50, and even more preferably from 3.00 to 4.00. In another embodiment zeolite has a Na/Cs molar ratio ranging from 0.10 to 0.50; preferably from 0.14 to 0.40; more preferably from 0.17 and 0.30.

The zeolite has advantageously a Cs/AI molar ratio ranging from 0.10 to 0.60 as determined by Inductively Coupled Plasma Optical Emission Spectrometry; preferably from 0.15 to 0.58, more preferably from 0.18 to 0.57, even more preferably from 0.20 to 0.56.

For example, the zeolite is CHA and/or the zeolite further comprises potassium with a Cs/K molar ratio ranging from 0.1 to 5.0 as determined by Inductively Coupled Plasma Optical Emission Spectrometry; preferably ranging from 0.3 to 3.0; more preferably ranging from 0.5 to 2.0.

For example, the zeolite is RHO and/or in that it is devoid of potassium.

In a first alternative, the zeolite is preferably monodispersed. The monodispersed zeolite forms nanoparticles which are nanocrystals with a hexagonal shape, as determined by transmission electron microscopy.

In a second alternative, the zeolite preferably forms aggregates, more preferably aggregates of nanocrystals. The aggregates have a size ranging between 100 nm and 2000 nm as determined by scanning electron microscopy, preferably between 150 nm and 1800 nm, more preferably between 400 nm and 1600 nm, even more preferably between 450 nm and 1500 nm, more preferably comprised between 500 nm and 1000 nm, more preferably comprised between 600 nm and 750 nm, even more preferably between 650 nm and 700 nm.

Said nanoparticles have an average pore size comprised between 2.0 A *3.1 A to 5.6 A *3.1 A, as determined by Brunauer-Emmet-Teller experiments. The shape of the pore is for example elliptical.

With preference, the zeolite is one zeolite from the CHA family, the average pore size diameter is comprised between 3.72 A and 4.20 A, more preferably is of 3.80 A.

Wth preference, the zeolite is one zeolite from the RHO family, the average pore size diameter is comprised between 3.4 A and 3.8 A, more preferably is of 3.6 A. In an embodiment, the zeolite is one zeolite from the CHA family and shows an average crystal size comprised between 5 nm and 250 nm as determined by the Schemer equation.

With preference, one or more of the following embodiments can be used to better define the CHA- zeolite of the present disclosure

The zeolite has a Na/AI molar ratio determined by inductively coupled plasma optical emission spectrometry comprised between 0.075 and 0.12.

The zeolite has a Na/Cs molar ratio determined by inductively coupled plasma optical emission spectrometry comprised between 0.17 and 0.30.

The zeolite forms aggregates, preferably aggregates of nanocrystals, wherein aggregates have a size ranging between 400 nm and 2000 nm as determined by scanning electron microscopy, preferably between 450 nm and 1500 nm, more preferably comprised between 500 nm and 1000 nm, more preferably comprised between 600 nm and 750 nm, even more preferably between 650 nm and 700 nm. The zeolite of the CHA family can be monodispersed or in the form of aggregates. The monodispersed zeolite forms nanoparticles which are nanocrystals with a hexagonal shape, as determined by transmission electron microscopy.

In an embodiment, the zeolite is one zeolite from the RHO family and has a Si/AI molar ratio comprised between 1.2 and 3.0 as determined by ²⁹ Si magic angle spinning nuclear magnetic resonance.

Wth preference, one or more of the following embodiments can be used to better define the RHO- zeolite of the present disclosure

The zeolite has a Na/AI molar ratio determined by inductively coupled plasma optical emission spectrometry comprised between 0.65 and 0.80, preferably between 0.67 and 0.78, more preferably between 0.70 and 0.75.

The zeolite has a Na/Cs molar ratio determined by inductively coupled plasma optical emission spectrometry comprised between 2 and 5, preferably between 2.5 and 4.5, more preferably between 3 and 4.

The aggregates have a size ranging between 100 nm and 500 nm as determined by scanning electron microscopy, preferably comprised between 200 nm and 400 nm, more preferably comprised between 250 nm and 350 nm, even more preferably between 275 nm and 300 nm.

The use of the zeolite

The disclosure provides for a use of the zeolite as defined in the first aspect as a sorbent for carbon dioxide, preferably as an adsorbent for carbon dioxide, more preferably as selective adsorbent towards carbon dioxide over methane and/or nitrogen. 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 N2, He and/or Ar.

The zeolite of the disclosure is very efficient in the sorption of carbon dioxide. The low Si/AI molar ratio, which allows for high content of cation, reduced the accessibility of nitrogen (having a diameter of 3.6 A) and of methane (having a diameter of 3.8 A) while the carbon dioxide (being smaller, with a diameter of 3.3 A) can be adsorbed and desorbed with the 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.

The disclosure also provides for a use of the zeolite as described above in a method of preparing clathrate hydrate substance, wherein said clathrate hydrate substance entraps preferably methane. The zeolite is contacted with a gaseous water feed and 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.

Further use of the 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

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.

The various RHO-type zeolites obtained in the examples were characterized over the following methods and, except the mention of the contrary, after a step of drying which is preferably performed by lyophilization (i.e. freeze-drying), said lyophilization being more preferably carried out at a temperature ranging between -92°C and -76°C.

type zeolite, was performed using a PANalytical X'Pert Pro diffractometer with CuKa monochromatized radiation (l=1.5418 A, 45 kV, 40 mA). The samples of chabazite-type zeolite were scanned in the range 5-50° 2Q with a step size of 0.02°. The samples or RHO-type zeolite were scanned in the range 3-70° 2Q with a step size of 0.016°.

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. Also, 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.

The Schemer 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.

Scanning electron microscopy (SEM) analysis was used to determine the surface features, morphology, homogeneity and size of RHO zeolite nanocrystals obtained after the step (f), when the said step is carried out, of recovering said one or more crystals of RHO-type zeolites. SEM analysis can also be carried out after the drying step. SEM was carried out by using a 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 before the SEM characterization were covered with a conductive layer (Pt or Au).

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. TEM is used to reveal the shape of the nanocrystals.

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/AI molar ratio, the MVCs molar ratio, the Na/AI molar ratio and the Na/Cs molar ratio of zeolite have thus been determined using this technical method.

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 analyzer 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/AI 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/AI molar ratio, the Cs/K molar ratio, the Cs/AI molar ratio, the M1/Cs molar ratio, the Na/AI molar ratio and the Na/Cs molar ratio of the zeolite can be determined using this technical method.

High-Resolution transmission electron microscopy (HR-TEM) has been used to determine the crystal size, morphology, crystallinity and chemical composition of the crystalline solid of RHO- type zeolite. It was operated by HR-TEM using a JEOL Model 2010 FEG system fitted with an EDX analyzer 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.

Nuclear Magnetic Resonance (NMR) analysis was performed to determine the crystallinity and the Si/AI molar ratio of the zeolite materials obtained after the drying step. The NMR spectrum was determined by ²⁹ Si and solid-state magic angle spinning (MAS) NMR on a Bruker Avance lll-HD 500 (11.7 T) spectrometer operating at 99.3 MHz, using 4-mm outer diameter zirconia rotors spun at 12 kHz. ²⁹ Si chemical shift was referenced to tetramethylsilane (TMS). The molecular geometry of aluminium was determined using ²⁷ Al MAS NMR on a Bruker Avance lll-HD 500 (11.7 T) spectrometer using 4-mm outer diameter zirconia rotors spun at 14 kHz. ²⁷ Al chemical shift was referenced to aluminium ammonium sulphate.

The ²⁹ Si chemical shift sensitivity is an indication of the degree of condensation of the Si-0 tetrahedra, that is, the number and type of tetrahedrally coordinated atoms connected to a given Si0 ₄ unit. Furthermore, ²⁹ Si MAS NMR spectra can be used to calculate the Si/AI molar ratio from the NMR signal intensities (/) according to eq. (1): wherein n indicates the number of Al atoms sharing the oxygen atom of the SiCU tetrahedron under consideration and wherein n = 0, 1 , 2, 3 or 4.

The chemical shift range of the silicon atom is comprised between -80 ppm to -1 15 ppm, with the high-field signal for the silicon atom directly linked to the oxygen atom of the -O-AI 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.

N2 sorption analysis was used to determine the nitrogen adsorption/desorption isotherms using Micrometries ASAP 2020 volumetric adsorption analyzer. The dried samples were degassed at 523 K (249.85°C) under vacuum overnight before the measurement. From these measurements, the pore volume accessible to N2 of the RHO-type zeolite has been determined.

C-botential measurement was carried out to determine the stability of nanozeolites (dispersed particles) in water (dispersion medium) using a Malvern Zetasizer Nano Instrument.

Thermogravimetry analyses (TGA) and Differential Thermal analysis (DTA) were performed on zeolite nanocrystals obtained when the step of recovering said one or more crystals of CHA- type zeolite or RHO-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).

After activation (water and CO2 desorption) at 350°C for 2 hours, the zeolitic material was allowed to return and stay at room temperature under a continuous flow of CO2 (flow rate: 40 mL/min, 1 bar) in 9 hours. The quantity of CO2 absorbed was determined using the mass increase compared to the total mass of the sample.

Cycles of CO2 adsorption/desorption were conducted and monitored by TGA. An alternance between activation at 350°C for 2 hours under N2 flow (flow rate: 40 mL/min) and CO2 adsorption at room temperature (flow rate: 40 mL/min, 1 barg) for 2 hours has been performed 10 consecutive times.

Carbon dioxide adsorption/desorption isotherms were measured using Micrometries ASAP 2020 volumetric adsorption analyzer. Samples of the chabazite-type zeolites, after being dried and freeze-dried, were degassed at 623 K (349.85°C) under vacuum overnight before the measurement. This test was performed to evaluate the adsorption properties of the chabazite type zeolites prepared according to the method of the disclosure. Samples of the RHO-type zeolite materials obtained after drying were degassed at 523 K (249.85°C) under vacuum overnight before the measurement.

Fourier Transformation Infra-Red (FTIR) spectroscopic analysis was conducted to characterize the selective adsorption of CO ₂ and CH ₄ with chabazite-type zeolite or RHO-type zeolite. The transmission IR spectra were recorded with a Nicolet Avatar spectrometer.

The adsorption CO 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 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 ₂ and CH ₄ were collected at room temperature. A room temperature IR-cell equipped with a heating device offered the possibility to activate the samples of the RHO-type zeolite at 350°C before the measurements. The cell was connected to a high vacuum line with a reachable pressure of 10 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 350°C for 3.0 hours. All the above steps were performed under secondary vacuum. Little doses of gas have been incrementally introduced onto the RHO pellet (10 mg cm ^-2 ) 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.

Examples

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

The starting materials used in the examples presented below are listed as follow:

- sodium hydroxide: (pellets, purity >99%): Sigma Aldrich;

- caesium hydroxide (purity >98%, aqueous 50%): Alfa Aesar;

- colloidal silica (Ludox-HS 30, 30 wt.% S1O2, pH = 9.8): Sigma Aldrich;

- colloidal silica (Ludox-AS 40, 40 wt.% S1O2): Sigma Aldrich;

- sodium aluminate (AI ₂ O ₃ 53%, Na ₂ 0 47% by mass): Sigma Aldrich

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

Example 1 : Synthesis of agglomerated CHA zeolite (samples 1-9)

An aluminate precursors aqueous suspension comprising aluminate was prepared by dissolving 0.512 g of NaAIC>2 in 3.34 g of double-distilled H2O. This suspension is clear.

An aqueous suspension comprising silicate precursors and metallic precursors was prepared in 4.97 g of double-distilled H2O 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 1 h.

The aluminate precursors aqueous suspension was added dropwise under vigorously stirring to the aqueous suspension comprising silicate precursors and metallic precursors kept on ice. The weight ratio of the aluminate precursors aqueous suspension over the aqueous suspension comprising silicate precursors and metallic precursors is equal to 0.387. The resulting clear suspension for sample 1 had the following molar compositions:

10 Si0 ₂ : O.8 AI2O3 : 8 Na ₂ 0 : 1.25 K ₂ 0 : 0.3 Cs ₂ 0 : 140 H ₂ 0

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

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.

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.

Figure 1 shows the XRD pattern of the CHA zeolite sample 1. Figure 2 shows the SEM images and figure 3 shows the N ₂ adsorption-desorption isotherms of said CHA zeolite sample 1. Figure 4 shows the corresponding C0 ₂ adsorption isotherm.

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: a Si0 ₂ : b Al ₂ 0 ₃ : c Na ₂ 0 : d K ₂ 0: e Cs ₂ 0: f H ₂ 0,

a = 10.0

0.5 £ b £ 2.5;

6.0 £ c £ 10.0;

1.0 £ d £ 1.6;

0.05 £ e £ 0.60; and

90 £ f £ 150.

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

Figure 3 shows respectively the N ₂ adsorption-desorption isotherm of sample 4.

Sample 9 was prepared using the same conditions as for sample 1 , except that 6.33 g of double-distilled H ₂ 0 was used to dissolve the 0.512 g of NaAI0 ₂ .

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

(9) 10 Si0 ₂ : 0.8 Al ₂ 0 ₃ : 8.0 Na ₂ 0: 1.35 K ₂ 0: 0.30 Cs ₂ 0: 190 H ₂ 0

Sample 9 was obtained in a yield of 60%.

Table 1 summarizes the molar composition of the amorphous precursor mixture obtained for the samples 1-9. Table 1 : Molar composition of the amorphous precursor mixture obtained for the 9 different samples prepared following example 1.

The properties of the CHA zeolite samples (Si/AI molar ratio and size of crystals and agglomerates are summarized in Table 2a. The size of the crystals has been determined in the c direction from Schemer’s equation, namely in one of the directions that grow the fastest.

Table 2a: Properties of the CHA zeolite samples 1-9.

*The average sizes of the crystallites in the (ab) plan were obtained from the X-Ray diffraction data using the Schemer’s equation on the reflection [2, -1 , 0] using the

corresponding peak at 12.82°.

** Aggregates size determined by Scanning Electron Microscopy. Sample 9 reveals a higher Si/AI molar ratio (1.90) and bigger particles when compared to sample 1 (1.77) due to higher dilution.

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 Schemer’s equation using the Bragg peak at 9.35 °2Q). The flake like shape of the crystal is very interesting in membrane application, for instance, sorption experiments.

The chemical composition of the samples 1-9 has been determined by ICP analysis and is present on table 2b.

Table 2b: Chemical composition of samples 1 -9 as well as Si/AI and Cs/K molar ratios.

* determination based on ICP analysis

Figures 3 and 4 show respectively the N2 adsorption-desorption isotherms and the CO2 adsorption isotherm of samples 9.

Example 2: Synthesis of monodispersed discrete CHA zeolite (samples 10-11) An aqueous suspension comprising aluminate precursors and metallic precursors was prepared by dissolving 0.546 g of NaAIC>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 2h.

A silicate precursor aqueous suspension was prepared by adding dropwise under vigorously stirring 7.667 g of colloidal silica (LUDOX® HS30) to the first aqueous suspension kept on ice. The weight ratio of the aqueous suspension comprising aluminate precursors and metallic precursors over the silicate precursor aqueous suspension is equal to 0.9.

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

10 Si0 ₂ : 0.8 AI2O3 : c Na ₂ 0 : 0.85 K ₂ 0 : 0.35 Cs ₂ 0 : f H ₂ 0

9.0 £ c £ 9.5;

110 £ f £ 130;

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

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

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

Chabazite monocrystals 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.

The Rietveld refinement data for sample 10 is shown in figure 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.

The TEM images at a magnification of 200 nm of sample 10 are depicted in figures 6A and 6B.

The isotherms of samples 10 and 11 are shown in figure 3 (N2 isotherms) and figure 4 (CO2 isotherms).

The sample 10 (26.91 g) was dehydrated at 350°C for 1 h (ramp: 5K/min). The CO2 flow (40 ml min ^-1 ) was delivered at 350°C, and the measurements were performed under continuous delivery of CO2 and decrease of temperature to 30°C min ¹ (20K min ¹ ). For the cycling procedure, the sample was re-activated at 350°C for 1 h (ramp: 5K min ¹ ) and then the adsorption procedure for CO2 was repeated 9 times. The full reversibility of CO2 absorption in sample 10 is demonstrated in figures 7, 8 and 9.

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

The results from the FTIR analysis performed under adsorption of CO2 and CFU are respectively shown in figures 10 and 11.

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

Table 3 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 3: Molar composition of the amorphous precursor mixture obtained for the 2 different samples prepared following example 2.

The properties of the zeolite samples 10 and 11 are presented in Table 4.

Table 4: Properties of the CHA zeolite samples 10-11.

* The average sizes of the crystallites in the (ab) plan were obtained from the X-Ray diffraction data using the Schemer’s equation on the reflection [2, -1 , 0] using the

corresponding peak at 12.82°.

** BET experiments (At 0°C, 121 kPa; Static CO2 isotherm adsorption).

Sample 10 has been ion-exchanged with NH ₄ NO ₃ . The material was ion-exchanged with a solution of 0.1 M of NH ₄ NO 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 ₂ O, and calcined {e.g. at 400°C for 2h, ramp of 1 °C min ¹ ) to eliminate of the NH ₃ and NOx and obtaining the acidic form of the chabazite zeolite sample 10.

The chemical composition of the parent sample 10 and the ion-exchanged sample 10 are given in table 5:

Table 5: Chemical composition of sample 10 before and after ion-exchanged, determined based on ICP analysis.

Figure 12 shows the XRD pattern and the N2 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 Angstroms and c = 15.047 Angstroms. From the adsorption isotherm of N2 of the as-prepared sample 10 (filled square on the insert of figure 12) and the sample in a protonic form (empty square on the insert of figure 12), it is possible to determine the micropore volume for the sample in protonic form as being equal to 0.16 cm ³ g ¹ . The micropore volume of the sample which is ion-exchanged (with Na, Cs or K) is 0.06 cm ³ g ¹ .

The structural determination was performed for sample 10. In situ XRD characterization of sample 10 under delivery of CO2 was performed. The change in the intensity, position and width of the Bragg peak at 12.8° 2Q under controlled adsorption and desorption of CO2 is presented in figures 13 to 16.

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)

An aqueous suspension comprising aluminate precursors and metallic precursors was prepared by dissolving 0.384 g of NaAIC>2 in 2.551 g of double-distilled H2O. This suspension is clear. Then 1.41 1 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 2h.

A silicate precursor aqueous suspension was prepared by dissolving 10.667 g of colloidal silica (LUDOX® HS30). This suspension is clear. The silicate precursor aqueous suspension was added dropwise under vigorously stirring to the aqueous suspension comprising aluminate precursors and metallic precursors kept on ice. The weight ratio of the aqueous suspension comprising aluminate precursors and metallic precursors over the silicate precursor aqueous suspension is 0.7.

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

16 Si0 ₂ : b Al ₂ 0 ₃ : 6 Na ₂ 0: 1.35 K ₂ 0: e Cs ₂ 0: f H ₂ 0

0.4 £ b £ 0.6;

0.15 £ e £ 0.25;

130 £ f £ 150;

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

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.

The hydrothermal crystallization for CHA zeolite sample 13, 14 and 15 was conducted at 90°C for 1 1 hours and up to 19 hours to obtain monodisperse nanoparticles of synthetic CHA zeolite and 3% of ANA zeolite as a side-product.

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.

The Si/AI 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 Schemer equation of the 1 ^st 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 ² g ¹ was determined by BET method based on N ₂ adsorption measurements.

Table 6 summarizes the molar composition of the amorphous precursor mixture obtained for the samples 12-15.

Table 6: Molar composition of the amorphous precursor mixture obtained for the 4 different samples prepared following example 3.

The chemical compositions and the properties of the zeolite samples 12-15 are presented in Table 7.

Table 7: Properties of the CHA zeolite samples 12-15.

* Determined based on ICP analysis

** The average sizes of the crystallites in the (ab) plan were obtained from the X-Ray diffraction data using the Schemer’s equation on the reflection [2, -1 , 0] using the corresponding peak at 12.82°.

** BET experiments (At 0°C, 121 kPa; Static CO ₂ isotherm adsorption).

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

The TEM images of sample 12 are shown in figures 6C and 6D. Figures 3 and 4 show respectively the N ₂ adsorption-desorption isotherms and the CO ₂ adsorption isotherm of sample 12.

The TEM images of sample 13 are shown in figures 4E and 4F.

Figure 17 shows the z-potential curve of sample 13 at a pH of 8 in an aqueous solution comprising 0.5 wt.% of sample 13. The z-potential is a key indicator of the stability of colloidal dispersion. The relatively high z-potential of sample 13 shows sample 13 is highly stable in the aqueous phase. The as-prepared sample 13 was stable up to 800°C. The ion-exchanged sample 13 with NH ₄ NO ₃ (following the same ion-exchange protocol as for sample 10), did not collapse after calcination (450°C, 2 h).

The normalized mass adsorption of CO2 and ChU as pure gas followed by TGA experiments is shown in figure 18 for sample 10. After activation at 350°C and stabilization at room temperature, the CHA-type zeolite was subjected to either pure CO2 or pure ChU gas. It is observed that CHA-type zeolite has a higher capacity towards CO2 compared to CH4 gas. In numbers, 0.64 mmol and 2.31 mmol were absorbed per gram of CHA-type zeolite for CH4 and CO2 gas, respectively. Also, the rate of absorption is faster for CO2 adsorption compared to CH4 adsorption.

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

Example 4: Preparation of aggregated RHO-type zeolite (RHO-1)

An aluminate precursor aqueous suspension was prepared by mixing 516 mg of sodium aluminate in 3 g of double-distilled H2O. This suspension is clear.

An aqueous suspension comprising silicate precursors and metallic precursors was prepared by mixing 5.0 g of LUDOX AS40 with 1.82 g of sodium hydroxide and 0.588 g of caesium hydroxide. The reaction is a gel. After vigorous shaking by hand, the reaction turns into a clear suspension thanks to its exothermic character. This aqueous suspension comprising silicate precursors and metallic precursors was stirred at room temperature (/.e., 25°C).

The aluminate precursor aqueous suspension was added dropwise to the aqueous suspension comprising silicate precursors and metallic precursors. During the addition, the aqueous suspension comprising silicate precursors and metallic precursors was maintained at room temperature while being vigorously stirred. A clear aqueous suspension was obtained.

The resulting amorphous precursor in the clear aqueous suspension has the following molar composition:

10 Si0 ₂ : 0.8 AI2O3 : 8 Na ₂ 0 : 0.58 Cs ₂ 0 : 100 H ₂ 0

The pH of said clear aqueous suspension is 12, and water clear suspension is obtained.

The resulting clear aqueous suspension was then aged by magnetic stirring for 14h at room temperature. Then, the hydrothermal crystallization was conducted during 1 hour at 100°C to obtain a solid comprising nanocrystals of synthetic zeolite material RHO-1 , said solid being dispersed in the mother liquor.

The solid was then 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) were performed until the pH of the remaining water was 7.5.

Nanocrystals of zeolite material RHO-1 were thus obtained. The Si/AI molar ratio has been determined to be 1.46. Also, the Na/AI molar ratio has been determined to be 0.80 and the Na/Cs molar ratio has been determined to be 4.

The nanocrystals have a size of 30 nm and form aggregates with a size ranging between 300 nm and 400 nm.

The yield in nanocrystal of RHO-1 was measured to be of 65% by mass.

The chemical composition of RHO-1 has been determined by ICP analysis and is as follows: Na15.6Cs3.9Si28.5AI19.5O96

This example provides aggregates of RHO-type nanosized zeolites having a low Si/AI molar ratio and high content of Na and Cs cations.

Example 5: Preparation of discrete RHO-type zeolite (RHO-2)

An aluminate precursor aqueous suspension was prepared by mixing 516 mg of sodium aluminate in 3 g of double-distilled H2O. This suspension is clear.

1.82 g of sodium hydroxide and 588 mg of caesium hydroxide were added to the aluminate precursor aqueous suspension. During the addition, the aluminate precursor aqueous suspension was maintained at room temperature (i.e. 25 °C) while being vigorously stirred. The stirring at room temperature was continued for at least 2 hours and afforded a clear aqueous suspension.

A silicate precursor aqueous suspension, namely 5 g of LUDOX AS40, was added dropwise. During the addition, it was maintained at room temperature while being vigorously stirred.

The resulting amorphous precursor in the clear aqueous suspension has the following molar composition:

10 Si0 ₂ : 0.8 AI2O3 : 8 Na ₂ 0 : 0.58 Cs ₂ 0 : 100 H ₂ 0

The pH of said clear aqueous suspension is 12. The clear aqueous suspension was then aged by magnetic stirring for 14 hours at room temperature.

Then, the hydrothermal crystallization was conducted at 90°C for 1 hour to obtain a solid comprising nanocrystals of synthetic zeolite material RHO-2, said solid being dispersed in the mother liquor.

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.

Nanocrystals of synthetic zeolite material RHO-2 with a Si/AI molar ratio of 1.56, a Na/AI molar ratio of 0.73 and a Na/Cs molar ratio of 2.6 were obtained.

The nanocrystals had a size of 80 nm with a hexagonal shape.

The yield in nanocrystal of RHO-2 was 65% by mass.

The chemical composition of RHO-2 has been determined by ICP analysis and is as follows: Na13.7Cs5.2Si29.3Ali 8.8O96

This example provides discrete RHO-type nanosized zeolites having a low Si/AI molar ratio and high content of Na and Cs cations.

Example 6: Preparation of higher silica containing-RHO-type zeolite (RHO-3) in discrete form

An aluminate precursor aqueous suspension was prepared by mixing 516 mg of sodium aluminate in 3 g of dd H2O. This suspension is clear.

1.55 g of sodium hydroxide and 336 mg of caesium hydroxide were added to the clear suspension. During the addition, the aluminate precursor aqueous suspension was maintained at room temperature (i.e. 25 °C) while being vigorously stirred. The stirring at room temperature was continued for at least 2 hours and afforded a clear aqueous suspension.

A silicate precursor aqueous suspension comprising a silicate, namely 5 g of LUDOX AS40, was added dropwise. During the addition, it was maintained at room temperature while being vigorously stirred.

The resulting amorphous precursor in the clear aqueous suspension has the following molar composition:

10 Si0 ₂ : 0.8 AI2O3 : 6.6 Na ₂ 0 : 0.33 Cs ₂ 0 : 100 H ₂ 0 (III)

The pH of said clear aqueous suspension is 12. The resulting clear aqueous suspension was then aged by magnetic stirring for 14 hours at room temperature.

Then, the hydrothermal crystallization was conducted at 90°C for 5 hours to obtain a solid comprising nanocrystals of synthetic zeolite material RHO-3, said solid being dispersed in the mother liquor.

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.

Nanocrystals of synthetic zeolite material RHO-3 with a Si/AI molar ratio of 1.76, a Na/AI molar ratio of 0.66 and a Na/Cs molar ratio of 2 were obtained.

The nanocrystals had a size of 150 nm.

The yield in nanocrystal of RHO-3 was 65% by mass.

The chemical composition of RHO-3 has been determined by ICP analysis and is as follows: Nai 1 .5Cs5.8Si30.6AI17.4O96

This example provides discrete RHO-type nanosized zeolites having a higher Si/AI molar ratio and lower content of Na and Cs cations.

The samples RHO-1 , RHO-2 and RHO-3 were characterized by using XRD, NMR, SEM, HR- TEM, TGA and N2 sorption methods.

The XRD analysis, displayed in figure 19, shows only Bragg peaks corresponding to RHO-type zeolite. Also, the XRD patterns display distinct broad diffraction peaks, typical for nanosized RHO-type zeolite nanocrystals.

Figure 20 displays the ²⁷ Al MAS NMR spectrum of the RHO-type zeolites of the examples. A single peak can be observed at around 60 ppm. This corresponds to aluminium in a tetrahedral position. No peaks at 0 ppm are observed, which means that aluminium is not octahedral aluminium.

Figure 21 displays the ²⁹ Si MAS NMR spectrum of the RHO-type zeolites of the examples. Peaks corresponding to Q° (4AI), Q ¹ (3AI), Q ² (2AI), Q ³ (1AI) and Q ⁴ (0AI) types of silicon tetrahedrons can be observed at around -84 ppm, -88 ppm, -92 ppm, -98 ppm and -102 ppm respectively. After being normalized with the mass of material samples, those peaks have been deconvoluted and their respective areas allowed the calculation of following Si/AI molar ratio of RHO-1 , RHO-2 and RHO-3 zeolite materials: 1.35; 1.55 and 1.77, respectively. The ICP analyses confirmed the range of those Si/AI molar ratios: 1.46, 1.50 and 1.83 obtained for RHO-1 , RHO-2 and RHO-3 zeolite materials, respectively.

Figure 22 shows the SEM images which reveal the presence of aggregates of nanocrystals with a size between 300 to 500 nm (Figure 22a), nanocrystals having a size below 100 nm (Figure 22b) and aggregates of nanocrystals with a size of 150 nm (Figure 22c) corresponding to RHO-1 , RHO-2 and RHO-3 respectively.

Figure 23 shows the TEM images which reveal the shape of the nanocrystal of the RHO-type zeolite. TEM images confirmed the size and degree of aggregation of zeolite crystals observed in SEM images. Also, it reveals that nanocrystals of RHO-1 , obtained when the addition of the one or more sodium precursors and the one or more caesium precursor is carried out in the second aqueous suspension comprising the one or more silicate precursors, are poorly defined (Figure 23a), while the nanocrystals of RHO-2 and RHO-3, obtained when the addition of the one or more sodium precursors and the one or more caesium precursor is carried out in the first aqueous suspension comprising the one or more aluminate precursors, have a clear hexagonal shape (Figure 23b), even aggregated (Figure 23c).

Figure 24 displays the thermogravimetric analysis (TGA) to reveal the quantity of water absorbed by the RHO-type zeolite. It is visible that a similar amount of water has been absorbed by the three zeolitic materials with a slight, but expected, increase for the RHO-1 having a lower Si/AI molar ratio. The mass of water reported to the total mass of the zeolite materials is 15.7 %, 13.9% and 13.3% for RHO-1 , RHO-2 and RHO-3 zeolite materials, respectively.

Figure 25 displays the N2 sorption isotherms of the RHO-type zeolite of the present disclosure. Very low microporosity is observed as a polar molecule such as N2 is not able to enter the micropores being blocked by cations (Na ⁺ , Cs ⁺ ) contained in the zeolite structures. Nevertheless, the substantially high total pore volume is explained by the high external surface area due to the nanometer size of the crystals.

Example 7: Use of the RHO-type zeolite of the present disclosure as adsorbents for CO2.

The detection of CO2 gases with RHO-1 , RHO-2 and RHO-3 zeolite materials prepared in examples 4, 5 and 6 respectively were studied using CO2 sorption isotherms, FTIR and TGA.

Figure 26 represents the CO2 sorption isotherms. The CO2 isotherms have been recorded up to 900 mmHg which corresponds to a relative pressure of 0.35 due to instrument limitations. All isotherms described a similar trend of adsorption of CO2, specifically a Langmuir shape until P/P° = 0.01 followed by a nearly linear trend up to P/P° = 0.03. It has been calculated that at the highest pressure reached (P = 1.2 bar) and at room temperature, the RHO-1 , RHO-2 and RHO-3 zeolite materials absorbed 1.22, 1.56 and 2.16 mmol of CO2 per gram of zeolite material, respectively.

Figure 27 represents the sorption capacity towards CO2. The analysis of the thermogravimetry showed that 8.70% of CO2 has been absorbed by the RHO-3 zeolite material under 1 bar of CO2 at room temperature, which corresponds to 2.01 mmol of CO2 per gram of zeolite material. Similarly, RHO-1 and RHO-2 were found to absorb 0.87 and 1.37 mmol.g ¹ , respectively.

Moreover, under 1 bar, the very similar values were obtained using BET (see table 8)

Table 8: Sorption capacity of the RHO-type zeolite determined either by BET or TGA.

Example 8:

Use of the RHO-type zeolite of the present disclosure as sorbents for CO2 during several cycles of adsorption and desorption.

The detection of carbon dioxide gas with RHO-3 zeolite was studied using FTIR and TG.

In figure 28, ten consecutive cycles of CO2 adsorption at 1 atm, followed by desorption at 350°C, have been performed and monitored by the integration of the FTIR bands attributed to physisorbed and chemisorbed CO2 within RHO-3 zeolite material. The adsorption capacity is not perturbed even after 10 cycles as the band areas (materialized by the rounds on figure 28) reached the same level (around 6) in all cycles. Also, this adsorption appeared fully reversible as the band area after 350°C desorption (materialized by the square on figure 28) always reached back the initial reference point (triangle mark). Moreover, no crystalline loss could be observed by XRD after the consecutive cycles monitored by FTIR (Figure 29).

Figure 30 confirms by TGA that the adsorption capacity of RHO-3 zeolite material is preserved during the ten cycles at 1 bar followed by desorption at 35°C. Figure 31 also demonstrates that no crystalline loss is observed with XRD after ten consecutive cycles.

These experiments show that the RHO-3 zeolite material is stable under CO2 sorption cycles.

Example 9:

Use of the RHO-type zeolite of the present disclosure as selective adsorbents towards carbon dioxide over methane. The detection of a mixture of CO2 and CFU (1/1 in volume) gases up to 1 bar with RHO-3 zeolite material prepared in Example 6 was studied. The zeolite materials were used as self- supported pellets and the detection was followed using in situ FTIR spectroscopy.

The CO2 absorption phenomenon is due to physisorption (band at around 2650 cm ^-1 ) as well as chemisorption by the formation of carbonates (bands at around 1650 cm ^-1 and below), as shown by figure 32. This phenomenon is fully reversible desorbed at 150°C under vacuum. At the same time, no CFU adsorption could be observed. Indeed, only free CFU molecules afford the very small rotational bands observed at 3050 cm ^-1 on figure 32.

Example 10 Advantage of potassium and caesium

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

10 Si0 ₂ : 0.8 Al ₂ 0 ₃ : 8 Na ₂ 0: 0.6 Cs ₂ 0: 1.25 K ₂ 0: 110 H ₂ 0

The template-free of nanosized zeolite without KOFI was prepared from the precursor suspension having the following molar composition:

10 Si0 ₂ : 0.8 Al ₂ 0 ₃ : 8 Na ₂ 0: 0.6 Cs ₂ 0: 110 H ₂ 0

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.

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

10 Si0 ₂ : 0.8 Al ₂ 0 ₃ : 8 Na ₂ 0: 1.25 K ₂ 0: 110 H ₂ 0

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 ai. ( Cryst . Growth Des., 2010, 10, 3471-3479). Sample 18 is thus obtained.

Figure 33 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.

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

Figure 34 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. Figures 35 and 36 respectively show the SEM images of samples 17 and 18, which are respectively a sample of RHO zeolite and FAU zeolite. Figures 35 and 36 show that individual crystallites have a size ranging between 50 nm and 200 nm.

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

Table 9: Conditions and results of the zeolite preparation