Method for making CHA zeolites and zeotypes

Abstract

Nanosheet CHA structures and methods for making same. The nanosheet CHA structures have an average size of less than 200 nm and average pore openings having a diameter of less than 2 nm. The nanosheet CHA structures are particularly useful in methane to olefins (MTO) and dehydroaromatization (DHA) processes due to high thermal stability. It has been surprisingly and unexpectedly discovered that plate-shape or nanosheet-shape CHA zeolites ("nanosheet-CHA") can be synthesized using amorphous precursors and dimethyloctadecyl[3-(trimethoxysilyl) propyl]ammonium chloride ("TPOAC") during hydrothermal synthesis, in a simple "one-pot" reaction.

Description

METHOD FOR MAKING CHA ZEOLITES AND ZEOTYPESGOVERNMENT LICENSE RIGHTS

[0001] This invention was made with government support under Cooperative Agreement No. EEC-1647722 awarded by the National Science Foundation. The government has certain rights in the invention.BACKGROUNDField of the Invention

[0002] Embodiments provided herein related to Chabazite (CHA) zeolites, CHA zeotypes and methods for making same.Description of the Related Art

[0003] Zeolites are used for catalysis, separations, and various purification processes. Specific applications vary depending on the zeolite framework. Zeolites are microporous aluminosilicate materials that contain tetrahedral silicon atoms linked by oxygen, forming charge-neutral crystalline structures. The isomorphous substitution of trivalent aluminum atoms for tetravalent silicon introduces a negative charge imbalance that can be compensated by protons or metal cation or complexes, all of which can serve as active sites for catalytic reactions. The network of tetrahedral silicon atoms can be synthetically modified into different structures forming various and distinct zeolite frameworks or topologies. Various synthetic methods have been used to influence material properties such as crystallite size, bulk aluminum content, and aluminum distribution. Zeotypes are a related class of microporous materials, but zeotypes can include elements in addition to just Si, Al, O and H.

[0004] Chabazite (CHA) zeolites and zeotypes have been used as catalysts for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) in diesel aftertreatment and in the conversion of methanol-to-olefins (MTO), among other applications. CHA is a high symmetry (only one distinct tetrahedral-site), three-dimensional pore connectivity framework consisting of double six-membered (6-MR) ring building units that interconnect to form 8-MR windows (-0.38 nm in diameter) and larger CHA cages. CHA is known for its improved hydrothermal stability compared to other zeolite topologies. CHA is also known for its small pores that present diffusion constraints for molecules to travel into and out of individual crystallites.

[0005] Achieving control of CHA crystallite size has been done through the addition of a growth modifier (commonly a surfactant molecule) to the typical synthesis gels used tocrystallize CHA zeolites. For example, Kumar, M., et al. J. Am. Chem. Soc. 137 (2015) 13007- 13017 discloses the use of polyethylenimine (PEIM) and cetryltrimethylammonium (CTAB) surfactants, during hydrothermal synthesis to obtain crystallites of 0.1 and 20 pm in size, respectively. Li, Z., et al. Catal. Sci. Technol. 6 (2016) 5856-5863 also discloses the uses of a CTAB growth modifier, added after 24 h of crystallization time, to obtain crystallites with sizes ranging between 50-200 nm. These materials were reported to have bulk Si / Al ratios of 15-17 and had slightly lower micropore volumes compared to the theoretical micropore volume of the CHA framework. US 20190262779A1 discloses a procedure that uses dry gel conversion to grow zeolite monolayers in solvents, followed by contact with gaseous water to form nanosheet CHA zeolites without agglomeration of particles that were reported to have sizes between 1-100 nm. US 20220332594A1 discloses another method to prepare hierarchical CHA zeolite sheet-like membranes by using a dimethyloctadecyl[3- (trimethoxysilyl)propyl]ammonium chloride (TPOAC) surfactant in a multi-step procedure, where seed crystals are first prepared, and then a crystal layer is coated on a porous support using a dip-coating method. Afterward, amorphous precursors along with TPOAC and the coated seed crystals are mixed, and the final CHA materials are obtained through scroll synthesis.

[0006] There is still a need for new methods to minimize CHA crystallite size to maximize the external surface area of individual crystallites and alleviate diffusion constraints within the micropores. Increasing the external surface area will also increase the number of accessible active sites for reactions of molecules that are too large to diffuse into or out of the CHA micropores, which can influence various aspects of catalytic performance including conversion, rates, selectivity and lifetime.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are, therefore, not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. It is emphasized that the figures are not necessarily to scale and certain features and certain views of the figures can be shown exaggerated in scale or in schematic for clarity and / or conciseness.

[0008] FIG. 1 depicts the XRD patterns for the synthesized: a) Al-CHA; b) nano-CHA; and c) nanosheet-CHA.

[0009] FIG. 1 shows the micropore volume measurement with argon (87 K) of the synthesized (a) nano-CHA and (b) nanosheet-CHA. Isotherms are offset for clarity.

[0010] FIG. 2A depicts a SEM image of the nano-CHA (comparative example) at one magnification level, with scale bars corresponding to 2 pm.

[0011] FIG. 3B depicts another SEM image of the nano-CHA (comparative example) at a different magnification level, with scale bars corresponding to 500 nm.

[0012] FIG. 4A depicts a SEM image of the nanosheet-CHA using TPOAC as a growth inhibitor, at one magnification level, with scale bars corresponding to 5 pm.

[0013] FIG. 4B depicts another SEM image of the nanosheet-CHA using TPOAC as a growth inhibitor, at a different magnification level, with scale bars corresponding to 1 pm.SUMMARY OF THE INVENTION

[0014] Nanosheet CHA zeolites and / or zeotypes and methods for making same are provided herein. The nanosheet CHA structures have an average size of <200 nm and average pore openings having a diameter of less than 2 nm. The nanosheet CHA structures are particularly useful in methane (or methanol) to olefins (MTO) or to hydrocarbons (MTH) and in methane dehydroaromatization (DHA) processes due to high thermal stability. It has been surprisingly and unexpectedly discovered that plate-shape or nanosheet-shape CHA zeolites (“nanosheet-CHA”) can be synthesized using amorphous precursors and dimethyloctadecyl[3- (trimethoxysilyl) propyl] ammonium chloride (“TPOAC”) during hydrothermal synthesis, in a simple “one-pot” reaction.

[0015] In at least one embodiment, the nanosheet CHA structures are made by preparing an aqueous solution comprising one or more structure directing agents, mixing the aqueous solution with dimethyloctadecyl [3-(trimethoxysilyl)propyl] ammonium chloride (“TPOAC”), at least one silicon precursor, and at least one aluminum precursor to provide a synthesis gel; and recovering crystalline solids from the synthesis gel, wherein the crystalline solids consist of CHA zeolite crystallites having an average size of <200 nm and average pore openings having a diameter of less than 2 nm. The TPOAC, at least one silicon precursor, and at least one aluminum precursor are combined in a single vessel to provide the synthesis gel.

[0016] In at least one other embodiment, a method for dehydroaromatization (“DHA”) is provided. The DHA method can include providing a nanosheet CHA crystallite catalyst bypreparing an aqueous solution comprising one or more structure directing agents; mixing the aqueous solution with dimethyloctadecyl [3 -(trimethoxy silyl)propyl] ammonium chloride (“TPOAC”), at least one silicon precursor, and at least one aluminum precursor to provide a synthesis gel; and recovering crystalline solids from the synthesis gel, wherein the crystalline solids consist of CHA zeolite crystallites having an average size of <200 nm and average pore openings having a diameter of less than 2 nm. Methane can then be contacted with the nanosheet CHA crystallite catalyst at conditions sufficient to convert the methane to a product comprising one or more aromatics selected from the group consisting of benzene, toluene, xylene and naphthalene. The methane can be a shale gas or derived from a shale gas.DETAILED DESCRIPTION

[0017] Embodiments provided herein include a hydrothermal synthesis route for nanosheet-CHA zeolites having crystallite sizes of less than 200 nm using TPOAC as a growth modifier combined with amorphous oxide precursors. Embodiments provided herein further include synthesized CHA materials that are microporous (with minimal amounts of mesopores, or in other words, not hierarchical) and have aluminum incorporation in the framework. The resulting CHA zeolites and zeotypes are particularly useful in MTO and DHA processes due to high thermal stability.

[0018] It has been surprisingly and unexpectedly discovered that plate-shape or nanosheetshape CHA zeolites (“nanosheet-CHA”) can he synthesized using amorphous precursors and dimethyloctadecyl[3-(trimethoxysilyl) propyl]ammonium chloride (“TPOAC”) during hydrothermal synthesis, in a simple “one-pot” reaction. The nanosheet-CHA crystallites are microporous, meaning the crystallites have average pore openings less than 2 nanometers in diameter, and more specifically average pore openings that are about 0.4 nanometers in diameter as determined by the CHA crystal framework. The nanosheet-CHA crystallites also have minimal mesoporosity, meaning they have a minimum percentage (such as less than 1%) of pores that are larger than 2 nanometers in diameter; therefore, they are morphologically distinct from hierarchical CHA zeolites prepared using other multi-step methods. According to one or more embodiments, the nanosheet-CHA crystallite is less <200 nm. The size of the nanosheet-CHA crystallites can range from 1 nm to 200 nm; 2 nm to 200 nm; or 3 to 190 nm. The crystallites can also range from a low of about 1, 2, 3, or 5 nm to a high of about 50, 100, 150 or 199 nm.

[0019] The nanosheet-CHA crystallites provided herein have significantly more catalytic active sites at or near the exterior surfaces, and therefore provides shorter diffusion paths formolecules in various chemical reactions. Stated another way, the local pore environments at the external surfaces provide shorter diffusion paths to the active sites located at (or near to) the external surfaces, compared to the much longer diffusion paths to active sites located within the microporous region. This can be advantageous for several chemical reactions including, but not limited to, conversions of methane (and methanol) to olefins (MTO), to hydrocarbons (MTH) and to aromatics. Methane to aromatics, or methane dehydroaromatization (DHA), is a promising pathway to convert methane into higher liquid density chemicals such as aromatics (e.g., benzene) while co-producing H2. The reaction is endothermic and constrained by thermodynamics, so it requires high temperatures (>873 K) to obtain methane conversions of >5%.

[0020] It is to be understood that the following disclosure describes several exemplary embodiments for implementing different features, structures, or functions of the invention. Exemplary embodiments of components, arrangements, and configurations are described below to simplify the present disclosure; however, these exemplary embodiments are provided merely as examples and are not intended to limit the scope of the invention. Additionally, the present disclosure can repeat reference numerals and / or letters in the various embodiments and across the figures provided herein. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and / or configurations. Moreover, the exemplary embodiments presented below can be combined in any combination of ways, i.e., any element from one exemplary embodiment can be used in any other exemplary embodiment, without departing from the scope of the disclosure.

[0021] Additionally, certain terms are used throughout the following description and claims to refer to particular components. As one skilled in the art will appreciate, various entities can refer to the same component by different names, and as such, the naming convention for the elements described herein is not intended to limit the scope of the invention, unless otherwise specifically defined herein. Further, the naming convention used herein is not intended to distinguish between components that differ in name but not function.

[0022] Furthermore, in the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to.” The phrase “consisting essentially of’ means that the described / claimed composition does not include any other components that will materially alter its properties by any more than 5% of that property, and in any case does not include any other component to a level greater than 3 mass%.

[0023] Unless otherwise indicated, all numerical values are "about" or "approximately" the indicated value, meaning the values take into account experimental error, machine tolerances and other variations that would be expected by a person having ordinary skill in the art. It should also be understood that the precise numerical values used in the specification and claims constitute specific embodiments. Efforts have been made to ensure the accuracy of the data in the examples. However, it should be understood that any measured data inherently contains a certain level of error due to the limitation of the technique and / or equipment used for making the measurement.

[0024] The term “or” is intended to encompass both exclusive and inclusive cases, i.e., “A or B” is intended to be synonymous with “at least one of A and B,” unless otherwise expressly specified herein.

[0025] The indefinite articles “a” and “an” refer to both singular forms (i.e., “one”) and plural referents (i.e., one or more) unless the context clearly dictates otherwise. For example, embodiments using “an olefin” include embodiments where one, two, or more olefins are used, unless specified to the contrary or the context clearly indicates that only one olefin is used.

[0026] The term “wt%” means percentage by weight, “vol%” means percentage by volume, “mol%” means percentage by mole, “ppm” means parts per million, and “ppm wt” and “ppmw” are used interchangeably and mean parts per million on a weight basis. All concentrations herein, unless otherwise stated, are expressed on the basis of the total amount of the composition in question.

[0027] As used herein, the term “nano-CHA” refers to CHA type zeolite and / or zeotype samples made with a polyethylenimine (“PEIM”) growth modifier and have a crystallite size of 180 nm.

[0028] As used herein, the term “nanosheet-CHA” refers to CHA type zeolite and / or zeotype samples made with a dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (“TPOAC”) growth modifier and have crystallite sizes of less than 200 nm, such as 2- 100 nm; 5 to 85 nm; 10-70 nm; 15-60 nm and / or 20-50 nm.

[0029] As used herein, the terms “crystallite” and “crystal” are used interchangeably and meant to refer to the same.

[0030] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references to the “invention” may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that referencesto the “invention” will refer to subject matter recited in one or more, but not necessarily all, of the claims. Each of the inventions will now be described in greater detail below, including specific embodiments, versions and examples, but the inventions are not limited to these embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the inventions, when the information in this disclosure is combined with publicly available information and technology.

[0031] In one embodiment, the nanosheet-CHA zeolite and / or zeotype provided herein can be synthesized by modifying a typical hydrothermal synthesis procedure, such as that described in Di Iorio, J. and Gounder, R. et al. Chem. Mater. 28 (2016) 2236-2247. For example, an aqueous solution containing organic and / or inorganic structure directing agents (SDAs) is first prepared to provide a “precursor solution”. Any suitable SDA can be used. Suitable SDAs can include molecules providing N,N,N-trimethyl- 1 -adamantylammonium (TMAda+) and / or sodium (Na+) cations. Dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (TPOAC), at least one aluminum precursor and at least one silicon precursor are added simultaneously, near simultaneously or sequentially in any order, to the precursor solution, to prepare a final synthesis gel. The final synthesis gel is then subjected to a crystallization procedure where crystalline solids are recovered, then treated in air at high temperatures to remove any unreacted organic SDAs, and then subjected to an ion-exchange (commonly with NH4+) to remove any unreacted inorganic SDAs.

[0032] The source of aluminum can be aluminum hydroxide, aluminum nitrate, aluminosilicate, and any combinations or derivatives thereof. The source of silicon can be colloidal silica, a silicon alkoxide compound, fumed silica, amorphous silica, aluminosilicate, and any combinations or derivatives thereof. The Si: Al ratio can range from a low of about 10, 20, 30 or 40 to high of about 50, 80, 100, or 200.

[0033] The crystallization process preferably occurs at about 130°C to about 150°C, but can range from as low of about 60°C, 70°C, 80°C or 90°C to a high of about 150°C, 180°C, 200°C or 240°C. The crystallization process can also take place at about 100°C, 130°C, 140°C, 150°C, 160°C, 170°C, or 180°C.

[0034] The high temperature air calcination treatment can occur at about 450°C to about 550°C. The air calcination treatment can also range from as low of about 400°C, 410°C, or 420°C to a high of about 500°C, 550°C or 600°C.

[0035] The resulting CHA zeolites and zeotypes are particularly useful in MTO, MTH, and DHA processes due to high thermal stability. In certain embodiments, thedehydroaromatization can be performed in any suitable reactor, such as a fixed bed gas-phase reactor. A dual bed circulating fluidized bed reactor system can be used to allow for continuous regeneration of deactivated catalyst using hot air or H2. The feed for the dehydroaromatization reactor can include argon gas (generally ranging between 0-99 vol%, but typically ranging between 5-60 vol%, when used) in addition to methane. The dehydroaromatization reaction can be performed at 600 to 900°C in the presence of the nanosheet CHA catalyst described herein. The dehydroaromatization reaction typically includes a mixture of methane and argon in a 2:1 volume ratio at a GHSV of from 100-100,000 ml / hr g-cat, a total pressure of 1 atm (but generally ranging between 0.1-100 atm) and a reaction temperature of 750°C (but ranging between 600-900°C, more preferably between 700-800 °C) in the presence of the catalyst for about 1 hour. The GHSV also can range from a low of about of about 100, 1,500, or 3,500 ml / hr g-cat to a high of about 7,000, 20,000, or 90,000 ml / hr g-cat. The GHSV also can be about 4,000 ml / hr g-cat, 4,500 ml / hr g-cat, 5,000 ml / hr g-cat, or 5,200 ml / hr g-cat.

[0036] The methane can be derived from any hydrocarbon stream, such as natural gas or shale gas. The methane also can be any hydrocarbon stream. The term “hydrocarbon stream” refers to any stream that naturally contains methane and one or more other hydrocarbons. Illustrative hydrocarbon streams can be or can include a raw shale gas stream or raw natural gas stream or other raw hydrocarbon gaseous stream that is obtained directly (z'.e. without processing to remove water and / or acid gas) from a reservoir, wellhead, or pipeline. Suitable hydrocarbon streams can also originate from a refinery, such as from a FCC, coker, steam cracker, and pyrolysis gasoline (pygas). Suitable hydrocarbon streams can also be or can include coal gas. Illustrative hydrocarbon streams can also be or can also include a gas stream that has been treated for acid gas and water removal.

[0037] The term “liquid hydrocarbon” refers to a hydrocarbon that is liquid at room temperature and ambient pressure, and primarily includes C5+ hydrocarbons. Moreover, this term can also refer to hydrocarbons that are liquid at room temperature but require high pressure such C4 alkane and alkenes.

[0038] The term “shale gas” refers to natural gas that is produced from a shale or other tight formation, is a gaseous phase mixture containing natural gas liquids, acid gases, water, nitrogen (N2), and possibly trace amounts of contaminants. A suitable shale gas (or natural gas) contains at least 50 mol% CH4 and up to 50 mol% of C2H6, C3H8, C4H10, and / or C5+ hydrocarbons. For example, a suitable shale gas (or natural gas) contains about 60 mol% to about 95 mol% CH4 and about 5 mol% to about 45 mol% of C2H6, C3H8, C4H10, and / or C5+hydrocarbons (or collectively referred to as “C2+ hydrocarbons” or “C2+ alkanes”). Among the C2+ hydrocarbons, C2H6 IS generally the highest concentration followed by CrHs then C4H10. Nitrogen gas (N2) can also be present in the shale gas.

[0039] The resulting aromatic products can be selected from the group consisting of benzene, toluene, xylene, naphthalene, and coke. An illustrative aromatic product slate can include benzene (50-60 mol%), toluene (0-5 mol%), xylene (0-1 mol%), naphthalene (10-20 mol%), and coke (10-50 mol%), for example. The aromatic product also can contain benzene in amounts that range from about 50-60 mol%; about 55-65 mor%, or about 50-70 mol%.EXAMPLES

[0040] Embodiments discussed and described herein can be further described with the following examples. Although the following examples are directed to specific embodiments, they are not to be viewed as limiting in any specific respect.

[0041] For all CHA syntheses, an aqueous solution containing N,N,N-trimethyl-l- adamantylammonium hydroxide (TMAdaOH) and sodium hydroxide (NaOH) (10 wt.% made from NaOH (98 wt.%, Alfa Aesar) pellets) were first mixed with deionized water (18.2 MQ) for 0.25 hr in a PFA container with a Teflon stir bar at ambient temperature, to prepare a precursor solution.

[0042] Inventive Example 1 (Ex. 1) was a nanosheet-CHA that was synthesized by taking the precursor solution, and then adding dimethyloctadecyl[3- ( trimethoxy silyl)propyl] ammonium chloride (TPOAC, 42 wt.% in methanol, Sigma- Aldrich). Next, aluminum hydroxide (A1(OH)3, 98 wt.%, SPI Pharma) was added to the solution and mixed for 0.25-0.5 hr until solids were completely dissolved. Next, a silica source (Ludox HS- 40, 40 wt.%, Sigma-Aldrich) was added to the solution and homogenized for 2-4 hr to provide a synthesis gel. The molar composition of the final synthesis gel for the nanosheet-CHA was 0.033 AI2O3 / O.96 SiO2 / 0.04 TPOAC / O.25 NaOH / O.25 TMAdaOH / 44 H2O.

[0043] Comp.Ex.l was a reference Al-CHA that was synthesized according to the disclosure of Di Iorio, J. and Gounder, R. et al. Chem. Mater. 28 (2016) 2236-2247. Starting with the precursor solution, aluminum isopropoxide (Al(i-pro)3, 98 wt.%, Sigma-Aldrich) was added and mixed for 0.25-0.5 hr until solids were completely dissolved. Next, the silica source (Ludox HS-40, 40 wt .%, Sigma-Aldrich) was added to the solution and homogenized for 2-4 hr. The molar composition of the final synthesis gel for the reference Al-CHA was 0.033 AI2O3 / I SiO2 / 0.25 NaOH / O.25 TMAdaOH / 44 H2O.

[0044] Comp.Ex.2 was a nano-CHA that was synthesized according to the disclosure of Kumar, M., et al. J. Am. Chem. Soc. 137 (2015) 13007-13017. Starting with the precursor solution, polyethylenime (PEIM, 50 wt.% in water, Sigma- Aldrich) was added to form 1.6 wt.% PEIM solution gel. Next, aluminum hydroxide (A1(OH)3, 98 wt.%, SPI Pharma) was added to the solution and mixed for 0.25-0.5 hr until solids were completely dissolved. Next, the silica source (Ludox HS-40, 40 wt.%, Sigma-Aldrich) was added to the solution and homogenized for 2-4 hr. The molar composition of the final synthesis gel for nano-CHA was 1 SiO2 / 0.033 AI2O3 / O.3 TMAdaOH / 0.2 NaOH / 44 H2O.

[0045] For all CHA syntheses, the final synthesis gels were loaded into separate Parr reactors and sealed under autogenous pressure (around 6 bar), and then placed in a rotation oven at 433 K for 144 hr.

[0046] Solids were recovered using crystallization and washed with deionized water until a neutral pH was obtained. Solids were dried in a static oven at 373 K overnight and then treated in dry flowing air (1.67 cm3s’1g1, Air Zero, Indiana Oxygen) at 853 K (0.0167 K s’1) to remove occluded organic structure directing agents.

[0047] NHC-exchanged forms of all CHA samples were prepared by contacting ALCHA samples (after treatment in dry flowing air at 853 K) with a 1.0 M NH4NO3 solution (150 g solution (g solid)’1) in PFA containers with Teflon magnetic bars for 24 hr at ambient temperature. Solids were recovered via centrifugation using 4-5 cycles of deionized water (18.2 MQ) until the supernatant had a neutral pH and dried overnight in a static oven at 373 K.

[0048] Zeolite frameworks were determined by powder X-ray diffraction (XRD) using a Rigaku SmartLab X-ray diffractometer with Cu Ka radiation source. XRD patterns were collected over a range of 4-40° 20 with a scan rate of 0.04° s-1using a low-dead volume sample holder (Rigaku). Diffractograms were compared to known reference materials.

[0049] Ar adsorption isotherms (87 K) were used for micropore volume measurements obtained with a Micromeritics 3Flex Adsorption Analyzer. Samples (0.04-0.05 g) were degassed by heating under vacuum to 393 K for 2 h followed by heating to 623 K for 9 hr.

[0050] Elemental analysis was performed by inductively coupled plasma optical emission spectrometry (ICP-OES) using a Thermo Scientific iCAP 7000 Plus Series ICP-OES. Around 0.02-0.04 g of sample was digested in 2.5 g of hydrofluoric (HF) acid (48 wt %, Alfa Aesar) for 48 hr and then diluted in 50 g of deionized water (18.2 MQ). For ICP analysis, 10 g of the digested sample was mixed with 0.3 g of HNO3 (70 wt.%, Sigma- Aldrich) before analysis.

[0051] Scanning electron microscopy (SEM) images were collected with a FEI Quanta 3D FEG Dual-beam SEM instrument with an Everhart-Thornley detector operating at 2 keV. Samples were coated with platinum and the spot was chosen to be between 0.5-2 pm.

[0052] Ammonia temperature program desorption (NH3 TPD) were used for quantification of Brpnsted acid sites (BAS) using a Micromeritics Autochem II 2920 connected to a residual gas analyzer (MKS Cirrus). An NH3 response factor was generated by diluting a stream of gaseous NH3 (Certified Mixture 500 ppm NH3 in He, Indiana Oxygen) with He (UHP, 99.999%, Indiana Oxygen). NH4+-CHA (0.03-0.05 g) were placed between two quartz wool plugs in a U-tube quartz reactor and a clam-shell furnace controlled the temperature measured by a thermocouple above the sample bed. Temperature was ramped in dry He (0.833 cm3s ') to 873 K (0.167 K s’1) hold for 0.5 h.

[0053] The resulting CHA zeolites in Comp.Ex.2 had an average particle size of 180 nm and were compared to the nanosheet-CHA synthesized in Ex. 1 with TPOAC, which is a surfactant that contains a chain alkylammonium moiety and a hydrolysable methoxysilyl group, linked together by a Si-C bond.

[0054] FIG. 1 shows the XRD patterns for the synthesized materials (a) Al-CHA; b) nano- CHA; and c) nanosheet-CHA ). All materials showed the patterns consistent with the CHA topology. In addition, the micropore volume (Ar, 87 K) were measured for both the nano-CHA and nanosheet-CHA zeolites.

[0055] FIG. 2 shows the micropore volume measurement with Argon (87 K) of the synthesized (a) nano-CHA and (b) nanosheet-CHA. The micropore volume (Ar, 87 K) were measured for both the nano-CHA and nanosheet-CHA zeolites. Isotherms are offset for clarity. The nanosheet-CHA synthesized with TPOAC showed a hysteresis in the adsorptiondesorption isotherm around P / Po 0.8-1, which was not observed in the nano-CHA. According to Sing, K., Williams, R., Adsorption Science and Technology. 22 (2004) 773-782, the Ar uptake at high P / Po and the absence of a plateau indicates the aggregation of plate-shaped (or nanosheet-like) particles, and should not be interpreted as mesopores in the crystal.

[0056] Table 1 below shows the elemental composition and quantification of the number of Brpnsted acid sites (H+) in the synthesized materials.

[0057] Table 1. Physical properties of CHA zeolites.* the Si and Al content were measured with ICP-OES.** the H+density was measured with NH3 TPD and Al content with ICP-OES.

[0058] FIG. 3A depicts a SEM image of the nano-CHA (comparative example) at one magnification level, with scale bars corresponding to 2 pm. FIG. 3B depicts another SEM image of the nano-CHA (comparative example) at a different magnification level, with scale bars corresponding to 500 nm.

[0059] FIGs. 4A and 4B depict the SEM images of the nanosheet-CHA using TPOAC as a growth inhibitor. More particularly, FIG. 4A depicts a SEM image of the nanosheet-CHA using TPOAC as a growth inhibitor, at one magnification level, with scale bars corresponding to 5 pm. FIG. 4B depicts another SEM image of the nanosheet-CHA using TPOAC as a growth inhibitor, at a different magnification level, with scale bars corresponding to 1 pm.

[0060] FIGs. 4A and 4B confirm the presence of particles with a plate-like (or nanosheet) morphology. FIGs. 4 A and 4B further confirm the presence of crystals that were larger and cube shaped. These crystals were estimated to have crystal sizes less than 200 nm, with sheetlike crystals <50 nm in size. Conversely, the nano-CHA showed a homogenous distribution of crystal sizes with an average crystallite size (>40 crystallite images) estimated to be 180 nm.

[0061] The above results show that nanosheet-CHA can be synthesized with crystallite sizes less than 200 nm and without significant mesoporosity, evidenced by the absence of a plateau in the Ar adsorption-desorption isotherm at high P / Po values (>0.7) corresponding to mesopore filling, as discussed in Sing, K., Colloids (and Surfaces, 38 (1989) 113-124 and Schlumberger, C., and Thommes, M., Adv. Mater. Interfaces, 8 (2021 ) 2002181, using a “one- pot” hydrothermal synthesis method with the amorphous precursors and TPOAC as a growth inhibitor. The resulting nanosheet-CHA material can be advantageous for a variety of chemistries where diffusion of molecules through the CHA micropore structure is limited dues to its particle size, and the amount of active sites at or near the external crystallite surface is maximized, which is beneficial for catalytic performance.

[0062] Other specific embodiments provided herein can further include any one or more of the following numbered paragraphs 1-15:

[0063] Embodiment 1: A method for making nanosheet CHA structures, comprising preparing an aqueous solution comprising one or more structure directing agents, mixing the aqueous solution with dimethyloctadecyl [3 -(trimethoxy silyl)propyl] ammonium chloride (“TPOAC”), at least one silicon precursor, and at least one aluminum precursor to provide a synthesis gel; and recovering crystalline solids from the synthesis gel, wherein the crystallinesolids consist of CHA zeolite crystallites having an average size of less than 200 nm and average pore openings having a diameter of less than 2 nm.

[0064] Embodiment 2: The method according to embodiment 1, wherein the TPOAC, at least one silicon precursor, and at least one aluminum precursor are combined in a single vessel to provide the synthesis gel.

[0065] Embodiment 3 : The method according to embodiment 1 or 2, wherein the average pore openings have a diameter of less than 0.4 nm.

[0066] Embodiment 4: The method according to any embodiment 1 to 3, wherein the CHA zeolite crystallites having an average size of 2 nm to 50 nm.

[0067] Embodiment 5 : The method according to any embodiment 1 to 4, wherein the one or more structure directing agents comprises N,N,N-trimethyl-l-adamantylammonium (TMAda+) cations, sodium (Na+) cations, or a combination thereof.

[0068] Embodiment 6: The method according to and embodiment 1 to 5 wherein recovering crystalline solids from the synthesis gel comprises treating the synthesis gel in air at a temperature of about 60°C to 240°C and then contacting the heated gel with an ionexchange cation.

[0069] Embodiment 7 : The method according to embodiment 6, wherein the ion-exchange cation comprises NH4+.

[0070] Embodiment 8: The method according to embodiment 1, wherein a Si: Al weight ratio of the at least one silicon precursor and at least one aluminum precursor ranges from 20- 100.

[0071] Embodiment 9: The method according to embodiment 1, wherein the aluminum precursor is selected from the group consisting of aluminum hydroxide, aluminum nitrate, aluminosilicate, combinations thereof and derivatives thereof.

[0072] Embodiment 10: The method according to embodiment 1, wherein the silicon precursor is selected from the group consisting of colloidal silica, a silicon alkoxide compound, fumed silica, amorphous silica, aluminosilicate, combinations thereof and derivatives thereof.

[0073] Embodiment 11: A method for dehydroaromatization, comprising providing a nanosheet CHA crystallite catalyst by preparing an aqueous solution comprising one or more structure directing agents, mixing the aqueous solution with dimethyloctadecyl [3- (trimethoxysilyl)propyl] ammonium chloride (“TPOAC”), at least one silicon precursor, and at least one aluminum precursor to provide a synthesis gel; and recovering crystalline solids from the synthesis gel, wherein the crystalline solids consist of CHA zeolite crystallites having anaverage size of less than 200 nm and average pore openings having a diameter of less than 2 nm; and contacting methane with the nanosheet CHA crystallite catalyst at conditions sufficient to convert the methane to a product comprising one or more aromatics selected from the group consisting of benzene, toluene, xylene and naphthalene.

[0074] Embodiment 12: The method according to embodiment 11, wherein the product comprises 50-60 mol% benzene, 0-5 mol% toluene, 0-1 mol% xylene, 10-20 mol% naphthalene, and 10-50 mol% and coke.

[0075] Embodiment 13: The method according to embodiment 11, wherein the product comprises at least 50 mol% benzene.

[0076] Embodiment 14: The method according to embodiment 11, wherein the product comprises at least 50 mol% benzene and at least 10 mol% naphthalene.

[0077] Embodiment 15: The method according to any embodiment 11 to 14, wherein the methane is a shale gas or derived from a shale gas.

[0078] All patents and patent applications, test procedures (such as ASTM methods, UL methods, and the like), and other documents cited herein are fully incorporated by reference to the extent such disclosure is not inconsistent with this disclosure and for all jurisdictions in which such incorporation is permitted.

[0079] Certain embodiments and features have been described using a set of numerical upper limits and a set of numerical lower limits. It should be appreciated that ranges including the combination of any two values, e.g., the combination of any lower value with any upper value, the combination of any two lower values, and / or the combination of any two upper values are contemplated unless otherwise indicated. Certain lower limits, upper limits and ranges appear in one or more claims below. All numerical values are “about” or “approximately” the indicated value, meaning the values take into account experimental error, machine tolerances and other variations that would be expected by a person having ordinary skill in the art.

[0080] The foregoing has also outlined features of several embodiments so that those skilled in the art can better understand the present disclosure. Those skilled in the art should appreciate that they can readily use the present disclosure as a basis for designing or modifying other methods or devices for carrying out the same purposes and / or achieving the same advantages of the embodiments disclosed herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they can make various changes, substitutions, and alterations hereinwithout departing from the spirit and scope of the present disclosure, and the scope thereof is determined by the claims that follow.

[0081] Various terms have been defined above. To the extent a term used in a claim is not defined above, it should be given the broadest definition persons in the pertinent art have given that term as reflected in at least one printed publication or issued patent. Furthermore, all patents, test procedures, and other documents cited in this application are fully incorporated by reference to the extent such disclosure is not inconsistent with this application and for all jurisdictions in which such incorporation is permitted.

[0082] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

CLAIMSWHAT IS CLAIMED IS:

1. A method for making nanosheet CHA structures, comprising: preparing an aqueous solution comprising one or more structure directing agents; mixing the aqueous solution with dimethyloctadecyl [3-(trimethoxysilyl)propyl] ammonium chloride (“TPOAC”), at least one silicon precursor, and at least one aluminum precursor to provide a synthesis gel; and recovering crystalline solids from the synthesis gel, wherein the crystalline solids consist of CHA zeolite crystallites having an average size of less than 200 nm and average pore openings having a diameter of less than 2 nm.

2. The method of claim 1 , wherein the TPOAC, at least one silicon precursor, and at least one aluminum precursor are combined in a single vessel to provide the synthesis gel.

3. The method of claims 1 or 2, wherein the average pore openings have a diameter of less than 0.4 nm.

4. The method of claim 1, wherein the CHA zeolite crystallites having an average size of 2 nm to 50 nm.

5. The method of claims 1, 2 or 4, wherein the one or more structure directing agents comprises N,N,N-trimethyl-l-adamantylammonium (TMAda+) cations, sodium (Na+) cations, or a combination thereof.

6. The method of claim 1, wherein recovering crystalline solids from the synthesis gel comprises treating the synthesis gel in air at a temperature of about 60°C to 240°C and then contacting the heated gel with an ion-exchange cation.

7. The method of claim 6, wherein the ion-exchange cation comprises NH4+.

8. The method of claim 1 , wherein a Si: Al weight ratio of the at least one silicon precursor and at least one aluminum precursor ranges from 20-100.

9. The method of claim 1, wherein the aluminum precursor is selected from the group consisting of aluminum hydroxide, aluminum nitrate, aluminosilicate, combinations thereof and derivatives thereof.

10. The method of claim 1, wherein the silicon precursor is selected from the group consisting of colloidal silica, a silicon alkoxide compound, fumed silica, amorphous silica, aluminosilicate, combinations thereof and derivatives thereof.

11. A method for dehydroaromatization, comprising: providing a nanosheet CHA crystallite catalyst by preparing an aqueous solution comprising one or more structure directing agents, mixing the aqueous solution with dimethyloctadecyl [3-(trimethoxysilyl)propyl] ammonium chloride (“TPOAC”), at least one silicon precursor, and at least one aluminum precursor to provide a synthesis gel; and recovering crystalline solids from the synthesis gel, wherein the crystalline solids consist of CHA zeolite crystallites having an average size of less than 200 nm and average pore openings having a diameter of less than 2 nm; and contacting methane with the nanosheet CHA crystallite catalyst at conditions sufficient to convert the methane to a product comprising one or more aromatics selected from the group consisting of benzene, toluene, xylene and naphthalene.

12. The method of claim 11, wherein the product comprises 50-60 mol% benzene, 0-5 mol% toluene, 0-1 mol% xylene, 10-20 mol% naphthalene, and 10-50 mol% and coke.

13. The method of claim 11 , wherein the product comprises at least 50 mol% benzene.

14. The method of claim 11, wherein the product comprises at least 50 mol% benzene and at least 10 mol% naphthalene.

15. The method of any claim 11 to 14, wherein the methane is a shale gas or derived from a shale gas.

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