Synthesis of zeolites containing interconnected nanosheets

Abstract

Interconnected zeolite nanosheets with structural motifs similar to those of self-pillared pentasil zeolites were synthesized using MEL or MFI zeolites as crystal seeds. The use of MEL or MFI zeolites as crystal seeds induced the spontaneous formation of pillared zeolites, thus, for the first time, avoiding the use of any organic or branching templates in the crystallization of these hierarchical structures.

Description

[Technical Field]

[0001] This application claims priority to U.S. Provisional Application No. 63 / 150,376, “Synthesis of Zeolites Having Interconnected Nanosheets,” filed on 17 February 2021, which is incorporated herein by reference in its entirety.

[0002] This invention was developed with government support under grant DE-SC0014468 from the Department of Basic Energy Sciences, Ministry of Energy. The government has certain rights to this invention.

[0003] This disclosure relates to the synthesis of zeolites. [Background technology]

[0004] The micropore network in zeolite catalysts imposes diffusion-limiting properties that can degrade their performance in numerous applications. Various approaches exist to improve mass transfer in these porous aluminosilicates, including the introduction of secondary pore structures (meso / macro) through post-siliconization / dealuminization or surfactant treatment (resulting in hierarchical materials with pore distributions). Hierarchical zeolites have been shown to exhibit superior catalytic performance compared to conventional materials (counterparts) in various industrially important chemical reactions (e.g., alkylation, Fischer-Tropsch synthesis, methanol / methane upgrading, cracking, and biomass conversion). Another approach to reduce internal diffusion constraints involves the synthesis of nanoscale zeolites. Methods have been introduced to fabricate two-dimensional (2D) MFI-type zeolites (unilamellae and multilamellae) that are the size of several unit cells in the crystal structure. Furthermore, a direct method for fabricating columnar nanosheets has been introduced, called self-columnarizing pentasil-type (SPP) zeolites, which improve mass transfer rates by introducing meso / macropores that enhance access to acid sites. While these hierarchical zeolites significantly improve catalytic performance, their synthesis has several drawbacks, including, for example, a limited range of acid concentrations (i.e., a high Si / Al ratio), low product yield, complex synthesis steps, or the need to use organic structure-controlling agents (OSDAs). All of these drawbacks impose constraints on commercialization.

[0005] Conventional methods for producing hierarchical zeolites rely on the use of organic structure-controlling agents, involve complex synthesis steps with limited yields, and often require high concentrations of Brønsted acid. [Overview of the project] [Problems that the invention aims to solve]

[0006] This disclosure relates in general to the synthesis of zeolites.

[0007] In particular, this disclosure relates to the synthesis of interbonded zeolite nanosheets having structural motifs similar to self-columnar pentasylzeolites by using MEL or MFI-type zeolites as crystalline seeds. The use of MEL or MFI-type zeolites as crystalline seeds induces the spontaneous generation of columnar pentasylzeolites, thus avoiding the use of any organic or branching templates for the crystallization of these hierarchical structures. The mechanism of the above generation was evaluated by time-resolved electron microscopy in heterogeneous nucleation and growth in continuous branching nanosheets derived from amorphous precursors, yielding unprecedented evidence. The resulting hierarchical zeolites have a large external surface area and an unusually high percentage of external acid sites, which significantly improves the catalytic performance of the zeolite in Friedel-Crafts alkylation and methanol-to-hydrocarbon reactions. These findings highlight an easy and commercially viable synthetic method for easing the limitations of mass transfer and improving the performance of zeolite catalysts. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1(A) shows the time-resolved PXRD pattern of the solid extracted during the synthesis of S1 using SilicaLite-2 (MEL) seeds (Table 1), Figure 1(B) shows a scanning electron microscope image of the SilicaLite-2 seeds, Figure 1(C) shows a scanning electron microscope image of the S1 product 3 days after seed growth, and Figure 1(D) shows a high-magnification SEM image of a typical hierarchical S1 crystal with pentasil nanosheets. [Figure 2] Figures 2(A) to (C) show SEM images of solid (A) extracted one day after S1 synthesis (Table 1), and solids (B and C) extracted two days later. Figure 2(D) shows an idealized schematic of heterogeneous nucleation and growth of zeolite interconnected nanosheets on amorphous interfaces in the absence of organic matter. [Figure 3]Figure 3(A) shows the crystallinity percentage as a function of synthesis time, measured from the PXRD pattern, and Figure 3(B) shows the zeolite phase percentage as a function of synthesis time. [Figure 4] Figure 4(A) shows an SEM image of the S2 product after 3 days of heating, Figure 4(B) shows an SEM image of the S3 product after 3 days of heating, and Figure 4(C) shows an SEM image of the S4 product after 5 days of heating. [Figure 5] Figure 5(A) shows the Friedel-Crafts alkylation reaction between mesitylene (M) and benzyl alcohol (BA), used as a liquid-phase reaction model for testing the self-columnar pentasyl catalyst for ZSM-5; Figure 5(B) shows the conversion rate of benzyl alcohol during the Friedel-Crafts alkylation reaction at 120°C for zeolite interconnected nanosheets and conventional ZSM-5; and Figure 5(C) shows the alkylation product (T) in isoconversion (approximately 75%). Figure 5(D) shows the selectivity of MBB) and the sub-complete methanol conversion rate in the reaction from methanol to hydrocarbons (MTH) at 350°C, as well as the gravitational space velocities of 28, 28, 28, 21, and 33h-1 for S1, S2, S3, S4, and ZSM-5, respectively. Figure 5(E) shows the estimated turnover number (histogram, left axis) at conversion rates of 50-30%, and the ratio of ethane to 2MBu of total catalyst at a conversion rate of approximately 40% (symbol, right axis). [Figure 6] Figure 6 shows SEM images of typical interconnected zeolite nanosheets extracted from synthesis using SilicaLite-2 seeds and an organic matter-free growth medium. The molar composition of the organic matter-free growth medium is expressed as 3.42Na2O:18SiO2:1Al2O3:XH2O(A~C) and 3.42Na2O:24.62SiO2:1.37Al2O3:XH2O(D~F) [where (A)X=224, (B)X=424, (C)X=600, (D)X=224, (E)X=324, (F)X=443]. [Figure 7]Figure 7 shows the powder XRD patterns of typical interconnected zeolite nanosheets extracted from synthesis using silicalite-2 seeds and an organic-free growth medium, and the molar composition of the organic-free growth medium is 3.42 Na2O:18 SiO2:1 Al2O3:XH2O (i - iii), and 3.42 Na2O:24.62 SiO2:1.37 Al2O3:XH2O (iv - vi) [where (i) X = 224, (ii) X = 424, (iii) X = 600, (iv) X = 224, (v) X = 324, (vi) X = 443].

Mode for Carrying Out the Invention

[0009] The present disclosure relates to the synthesis of zeolites, particularly to the synthesis of zeolites having interconnected nanosheets.

[0010] The preferred embodiments described herein relate to a seed-assisted method for fabricating interconnected nanosheets of pentasil zeolites without an organic structure-directing agent (OSDA). This appears to be the first direct synthesis of mainly MFI-type columnar zeolite nanosheets without using an organic substance. The seed-assisted synthesis of interconnected nanosheet zeolites provides higher product yields compared to conventional ZSM-5 catalysts, and further advantages of providing a high acid site concentration that enhances catalytic performance in the reaction of methanol to hydrocarbons (MTH) and the Friedel-Crafts alkylation (FCA) reaction.

[0011] In a preferred embodiment, an organic free medium (Si / Al=9) is used for crystallization having compositions located near the boundaries of three zeolites: mordenite (MOR type), ZSM-11 (MEL type), and ZSM-5 (MFI type). Seed-assisted synthesis is carried out by adding calcined crystals (preferably 10% by mass) to this growth mixture. Two days after synthesis, a Bragg peak corresponding to the pentasyl zeolite (MEL or MFI type) can be detected in the PXRD pattern; and crystallization is completed within three days. Analysis revealed that the final product is mainly of the MFI type structure, although given the striking similarity of the PXRD patterns of the two zeolites (MEL type and MFI type), the presence of MEL type zeolite is possible. A preferred embodiment of the pentasyl zeolite has a high Al content (i.e., Si / Al=8, approximately equivalent to the starting gel) and about 28% of all Brønsted acid sites are located on the outer surface. Interestingly, scanning electron microscope images revealed a hierarchical morphology similar to that of self-columnar pentasylzeolite. High-magnification images of preferred embodiments of the zeolite crystal show that the columnar nanosheets are arranged in a "house of cards" pattern, having a thickness of approximately 30 nm and exhibiting both mesopore and macropore distributions.

[0012] Conventional synthesis of self-columnar pentasils and related two-dimensional zeolites (e.g., multi-lamellar nanosheets) all required the use of OSDAs. The synthesis of zeolite crystals described herein is the first OSDA-free bottom-up route for realizing hierarchical zeolites. The use of crystal seeds is crucial for realizing the columnar structure. It has been shown that while the interconnected nanosheets are mostly MFI-type zeolites, the intersections (or junctions) between the nanosheets can be MEL-type zeolites, acting as a four-fold symmetric connector.

[0013] A preferred embodiment of the present invention relates to a method for synthesizing zeolites having interconnected nanosheets. The method comprises placing calcined zeolite seed crystals in an organic matter-free growth medium and preparing a growth solution, wherein the organic matter-free growth medium essentially consists of silica and alumina in sodium hydroxide. The organic matter-free growth medium does not contain any organic structure-determining agents and / or branching templates. A preferred embodiment of the organic matter-free growth medium has a molar composition where A is 3.4 to 3.5, B is 18 to 25, C is 1 to 1.4, and X is 220 to 600, where A:B:C:X is the ratio of Na2O:SiO2:Al2O3:H2O. In a further preferred embodiment, the organic matter-free growth medium has a molar composition where A is 3.42, B is 18, C is 1, and X is 224, 324, 424, or 600. In a further preferred embodiment, the organic matter-free growth medium has a molar composition of A = 3.42, B = 24.62, C = 1.37, and X = 224, 324, or 443.

[0014] In a preferred embodiment, the calcined zeolite seed crystal is a MEL or MFI type zeolite seed crystal. In a further preferred embodiment, the calcined zeolite seed crystal is a Silicalite-2, ZSM-11, Silicalite-1, or ZSM-5 crystal. The method further comprises forming the calcined zeolite seed crystal into zeolite interconnected nanosheets in a growth solution. The growth solution may be heated and pressurized during the formation of the zeolite interconnected nanosheets. The method further comprises separating the zeolite interconnected nanosheets from the growth solution. Hierarchical zeolites include interconnected nanosheets. A preferred embodiment of the zeolite interconnected nanosheet has a hierarchical columnar morphology and a thickness of 30 nm.

[0015] Further preferred embodiments include zeolite interconnected nanosheets prepared by the method described herein. Further preferred embodiments include catalysts containing zeolite interconnected nanosheets prepared by the method described herein. Further preferred embodiments include methods for preparing or converting organic compounds, the method comprising contacting the organic compound with a catalyst containing zeolite interconnected nanosheets prepared by the method described herein. In further preferred embodiments, the preparation or conversion of the organic compound may further include alkylation, Fischer-Tropsch synthesis, methanol or methane upgrading, cracking, or biomass conversion, in combination with the use of a catalyst containing zeolite interconnected nanosheets prepared by the method described herein. Further preferred embodiments include organic matter-free growth media described herein.

[0016] Further aspects of the present invention will become clearer from the following description, which is provided only as examples.

[0017] Example 1 material The following chemicals for zeolite synthesis were purchased from Sigma Aldrich: monodisperse colloidal silica (LUDOX AS-40) (40% by mass suspension in water), tetraethyl orthosilicate (TEOS, ≥99.5%), sodium aluminate (57.1% Al2O3 and 37.2% Na2O), 1,8-diaminooctane (DAO, 98%), and tetrapropylammonium bromide (TPABr, 98%). Further chemicals, including sodium hydroxide (98% pellet) and tetrabutylammonium hydroxide (TBAOH, 40%), were purchased from Alfa Aesar. All reagents were used as purchased without further purification. In all experiments, the deionized water (DI) used was purified using an Aqua Solutions RODI-C-12A purification system (18.2 MΩ).

[0018] method: Synthesis of seed crystals MEL-type zeolite seeds with Si / Al ratios of ∞ (Silicalite-2) and 33 (ZSM-11), and MFI-type seeds with a Si / Al ratio of ∞ (Silicalite-1) were synthesized according to the previously reported procedure (R. Jain, JD Rimer, Seed-Assisted zeolite synthesis: The impact of seeding conditions and interzeolite transformations on crystal structure and morphology. Microporous and Mesoporous Materials, 110174 (2020)). ZSM-5 seeds with a Si / Al ratio of 40 were purchased from Zeolyst (CBV 8014). All seeds were synthesized in a Thermo Fisher Lindberg Blue furnace under a constant flow rate of compressed air (Matheson, 100 cm³) before application. 3 min -1 ), 550℃ (heating rate 1℃ min) -1 It was baked for 10 hours.

[0019] Synthesis of zeolite interconnected nanosheets Seed-assisted synthesis was performed by first adding sodium aluminate to an aqueous NaOH solution, followed by the addition of LUDOX AS-40 to obtain a growth solution with a molar ratio of 3.42Na2O:18SiO2:1Al2O3:324H2O. The small amount of calcined seed used in the experiment was 10% by mass. The growth solution was allowed to stand at room temperature for approximately 24 hours, and then transferred to a 23 mL acid digestion bomb (Parr Instruments). Hot water treatment was performed at 150°C in an oven under autogenous pressure. Two cycles of centrifugation and washing with deionized water were performed, and the extracted solid was separated from the mother liquor after a selection time interval. These were then dried in an oven at 60°C. These samples were washed with 0.1 M hydrochloric acid in a 3% by mass suspension at room temperature for 5 hours to remove any amorphous material residue. The calcined zeolite was mixed with a 1.0 M NH4NO3 solution to obtain a 2% by mass suspension. The sample immediately after synthesis was converted to proton form by ion exchange. This mixture was heated at 80°C for 2 hours, and centrifugation / washing was repeated three times between each ion exchange cycle. The final NH4 zeolite sample was calcined once more under the same conditions as above to obtain H-form zeolite.

[0020] Synthesis of conventional ZSM-5 catalyst Conventional ZSM-5 catalysts were prepared according to a previously reported procedure (Y. Shen et al., Deconvoluting the competing effects of zeolite framework topology and diffusion path length on methanol to hydrocarbons reaction. ACS Catalysis 8, 11042-11053 (2018)). After converting the sample immediately after synthesis to proton form by ion exchange, calcination was performed using the same procedure as described above.

[0021] Four different zeolite seeds: silicalite-2 (silica equivalent structure of ZSM-11), ZSM-11 (Si / Al = 33), silicalite-1 (silica equivalent structure of ZSM-5), and ZSM-5 (Si / Al = 40) (shown in Table 1 below) were synthesized according to the reported procedure.

[0022]

Table 1

[0023] Characterization Powder X-ray diffraction (PXRD) patterns of the dried solid were collected on a Rigaku SmartLab diffractometer equipped with a Cu Kα source (40 kV, 30 mA). Scanning electron microscope (SEM) images were obtained at 10 kV using a Zeiss Leo 1525 instrument equipped with a FEG. All samples were carbon coated (film thickness approximately 30 nm) to reduce charging prior to imaging. Crystal size and morphology were measured from multiple SEM images of a single batch. Elemental analysis was performed by energy-dispersive X-ray (EDX) analysis. EDX spectra were collected using a JEOL SM-31010 / METEK EDAX system at 15 kV and an operating distance of 15 mm.

[0024] N2 was used as the probe gas for physical adsorption, and texture analysis was performed using a Micromeritics 3flex instrument. Surface area was calculated from BET isotherms, and micropore volume was estimated using the t-plot method. Pore size distribution was obtained from adsorption isotherms using the BJH method. A JEOL ECA-500 spectrometer equipped with a 3.2 mm magnetic field gradient magic rotation probe was used to analyze the solid at 11.7 T. 27 Al NMR experiments were performed with a rotation frequency of 12.5 kHz, a pulse width of π / 12 of 1.25 μs, and a recycle delay of 0.8 s. 27 Al MAS NMR data were obtained. The total number of precipitation cycles was 4096 for all measurements. The total amount of acid sites was determined by temperature-programmed desorption of ammonia (NH3-TPD). Approximately 50 mg of catalyst was added before TPD, first using Ar (Matheson, 30 cm³). 3 min -1 The solution was degassed at 550°C for 4 hours at a heating rate of 2°C / min. Ammonia was adsorbed at 150°C until saturated, followed by flushing with Ar at 150°C for 120 minutes. Ammonia desorption was monitored up to 700°C at a heating rate of 5°C / min using a quadrupole mass spectrometer (Cirrus 3-XRd, MKS Instruments). The type of acid site fraction (Brønsted vs. Lewis) and the acid site fraction present on the outer surface were estimated by FTIR using pyridine (Py) and 2,6-di-tert-butylpyridine (diTPy) as probe molecules, respectively. Infrared spectra were taken at 2 cm. -1 The optical resolution was recorded using a Thermo Scientific Nicolet 6700 FTIR spectrophotometer. Before the FTIR measurement, the catalyst was pressed into self-supporting discs and then subjected to N2 (Matheson, 50 cm³) in a sample cell. 3 min -1The sample was pretreated at 450°C for 2 hours. Excess probe molecules were introduced by injecting multiple 1.0 μl pulses into the FTIR sample cell. Subsequently, the physicoadsorbed molecules were removed by evaporation at the adsorption temperature. A difference spectrum was obtained by subtracting the spectrum of the zeolite before probe molecule adsorption using Thermo Scientific OMNIC series software. The amount of adsorbed probe molecules was determined using the integrated area of ​​the given band and the molar extinction coefficient described in prior literature.

[0025] Catalyst measurement The reaction from methanol to hydrocarbons (MTH) was carried out in a 1 / 4-inch stainless steel tube introduced into a resistance heating furnace (Model 3210, Applied Test System). The catalyst bed was supported between two plugs of quartz wool. A K-type thermocouple (Omega Engineering) was inserted into the stainless steel tube to measure the temperature of the catalyst bed. Before the reaction, a dry air flow (6 cm) was used. 3 min -1 Oxygen, 24cm 3 min -1 The catalyst bed was pretreated in situ at 550°C for 3 hours under N2 conditions. Subsequently, the catalyst bed was cooled to the reaction temperature (350°C). 7 μL min -1 Using a syringe pump (Harvard Apparatus), methanol was injected into an Ar gas stream (Matheson, 30 cm). 3 min -1 The reaction effluent was evaluated using an on-stream gas chromatograph (Agilent 7890B) equipped with a flame ionization detector. To compare the catalyst deactivation rates, the reaction was carried out at a near-perfect methanol conversion rate X, and the initial conversion rate was adjusted by adjusting the catalyst mass. The methanol conversion rate is given by the following formula:

number

number

[0026] To compare the deactivation rates between different catalyst samples, the turnover number (TON) is expressed using the following modified formula, which is a previously reported formula:

number

[0027] The Friedel-Crafts alkylation reaction of mesitylene and benzyl alcohol was carried out in a septum-sealed round-bottom flask (100 ml) using a magnetic stirrer. A predetermined amount of catalyst (100 mg) was added to 190 mmol of mesitylene, and the mixture was heated in an oil bath at 120°C for 15 minutes. Subsequently, 2 mmol of benzyl alcohol (BA) was injected into the mixture using a long, thin steel needle, and this was defined as the reaction start time. Samples were collected at different time intervals and filtered through a 0.2 μm filter. The filtered liquid samples were analyzed using a gas chromatograph (Agilent 7890B) equipped with a flame ionization detector. Since mesitylene was present in excess, benzyl alcohol was considered the main reactant, and the conversion rate (X) was calculated. BA ) and selectivity of alkylation products (S TMBB ) can be expressed as follows:

number

number

[0028] result Figure 1(A) shows the time-resolved PXRD pattern of the solid extracted during the synthesis of S1 using SilicaLite-2 (MEL) seeds (Table 1), Figure 1(B) shows a scanning electron microscope image of the SilicaLite-2 seeds, Figure 1(C) shows a scanning electron microscope image of the S1 product 3 days after seed growth, and Figure 1(D) shows a high-magnification SEM image of a typical hierarchical S1 crystal having pentasil nanosheets with a thickness of 30-50 nm and mesopores with voids between the intersecting nanosheets.

[0029] First, focusing on seed-assisted synthesis using SilicaLite-2, the powder X-ray diffraction (PXRD) patterns of solids extracted from synthesis at regular intervals (Figure 1(A)) revealed that the MEL-type seeds dissolved within one day after hot water treatment. Considering that the above sample mainly consists of amorphous aluminosilicate precursors, it was difficult to confirm whether the SilicaLite-2 seed crystals (Figure 1(B)) were completely or partially dissolved.

[0030] Zeolite synthesis typically involves a long induction period followed by rapid crystallization, which makes it difficult to visualize the early stages of nucleation. For a long time, many zeolites, including ZSM-5, were assumed to be formed by heterogeneous nucleation on (or within) amorphous precursors, despite a generally lack of direct evidence.

[0031] Figures 2(A)-(C) show SEM images of solids extracted after the following time intervals from S1 synthesis (Table 1): (A) 1 day, (B) 2 days, and (C) 3 days, representing typical zeolite interconnected nanosheets with spherical protrusions characteristic of non-classical crystallization. Figures 2(D) and (E) show high-resolution images of solids extracted 2 days after heating, capturing heterogeneous nucleation and columnarization of hierarchical pentasylzeolite crystals generated from the surface of the amorphous precursor. Figure 2(F) shows an idealized conceptual diagram of heterogeneous nucleation and growth of interconnected nanosheet zeolites on an amorphous surface in the absence of organic matter. Previous studies have suggested that columnarization may be promoted by the presence of MEL-type nanosheet intersections connected to four MFI-type nanosheets.

[0032] A unique aspect of the inventors' S1 synthesis is the relatively slow growth rate following nucleation, which allows for direct visualization of crystallization at various stages. Solids extracted from the growth mixture at an early stage contain mostly amorphous particles, but the occurrence of crystallization on the surface of the amorphous precursor is observed after 1 day of heating (Figure 2(A)). Solids extracted at longer times (Figures 2(B) and 2(C)) contain a population of interconnected nanosheet crystals on the precursor surface. SEM images reveal spherical protrusions on the surface of the nanosheets, which are a signature of the non-classical growth pathway. Previous studies have shown that MFI-type zeolites grow via a combination of monomer addition (classical pathway) and attachment of amorphous particles, followed by a disorder-order transition that initiates three-dimensional nucleation of a new layer on the zeolite surface. Here, heterogeneous nucleation of interconnected nanosheet crystals, in which pillars originate from amorphous particles (Figures 2(A) and 2(C)) and branch into a larger hierarchical network of intersecting nanosheets (Figure 2(D)), is directly visualized with unprecedented resolution. These observations contradict the conventional belief that organic matter is necessary for nanosheet formation and / or to promote columnarization in zeolite crystallization.

[0033] The precise mechanism of columnarization in the absence of organic structure-determining agents (OSDAs) is unknown, but it is hypothesized that the growth mixture before the initiation of nucleation contains some "memory" of dissolved silicalite-2 seeds. In the absence of seeds, the growth mixture selected for this study produced mordenite crystals lacking hierarchical structure.

[0034] Figure 3(A) shows the crystallinity percentage as a function of synthesis time, measured from the PXRD pattern. The addition of MEL (ring-opening) or MFI (closed square) seeds during the synthesis of S1 and S4 reduces the crystallization time compared to unseeded controlled synthesis (closed diamond), respectively. Figure 3(B) shows that the extension of the synthesis time for S1 (more than 3 days) leads to the nucleation and growth of MOR through the conversion of pentasyl to mordenite (MOR) between zeolites.

[0035] Figure 4(A) shows an SEM image of a solid extracted from S2 synthesis using ZSM-11 seeds three days after heating, Figure 4(B) shows an SEM image of a solid extracted from S3 synthesis using SilicaLite-1 seeds three days after heating, and Figure 4(C) shows an SEM image of a solid extracted from S4 synthesis using ZSM-5 seeds five days after heating.

[0036] Interestingly, time-resolved studies of seed growth show that S1 is fully crystalline after 3 days of heating (Figure 3(A)). This is about a quarter of the time required in the non-seeded growth mixture. Further synthesis time results in inter-zeolite conversion from S1 to mordenite (Figure 3(B)). Mordenite acts as a nucleus within the S1 cluster, gradually consuming the hierarchical zeolite with prolonged heating. Columnar structures may originate from seed residues with MEL-type structures that promote branching (i.e., nanosheet junctions, Figure 2(D)). To test this, similar synthesis was performed using three different seeds: ZSM-11(MEL), Silicalite-1(MFI), and ZSM-5(MFI). All synthesis yielded zeolite interconnected nanosheets (Table 1), designated S2, S3, and S4, respectively. The reaction rates (kinetics) of S2 and S3 crystallization were similar to those in Figure 1 (Figure 3(A)), but S4 deviated from the others in that it reached a maximum crystallinity of 80%, accompanied by approximately 20% amorphous material residue before the initiation of interzeolite conversion. Time-resolved SEM images of S2, S3, and S4 samples at various stages of growth (Figures 3(A), 3(B), and 3(C), respectively) revealed that the mechanism of heterogeneous nucleation from amorphous precursors is similar. All zeolite interconnected nanosheet materials have similar hierarchical structures and varying degrees of branching, while the morphology of S3 derived from the silicalite-1 seed (Figure 3(B)) shows a higher degree of aggregation. This suggests that branching occurs regardless of the seed crystal structure. The use of MEL-type seeds results in a higher surface area (Table 1), but its average nanosheet thickness (approximately 40 nm) is comparable to other zeolite interconnected nanosheet materials (with the exception of S3, which is approximately 60 nm). All materials fabricated by seed growth (with the exception of S3) showed an unusually high proportion of Brønsted acid sites on their outer surface, seven times that of conventional ZSM-5.

[0037] The catalytic performance of all zeolite interconnected nanosheet samples with an overall particle size of 1.1–2.3 μm was tested and compared with that of a conventional ZSM-5 catalyst with an overall crystal size of 300 nm. All zeolite interconnected nanosheet samples were pre-treated with a mild acid to remove any residual amorphous material, followed by NH3 4+ Ion exchange and calcination were performed to produce H-type catalysts. Elemental analysis of zeolite interconnected nanosheets and ZSM-5 samples revealed similar acid concentrations and distributions of Brønsted and Lewis acids (Table 1).

[0038] Figure 5(A) shows the Friedel-Crafts alkylation reaction of mesitylene (M) and benzyl alcohol (BA), used as a model of the liquid-phase reaction for testing the self-columnar pentasyl catalyst for ZSM-5. Figure 5(B) shows the conversion rate of benzyl alcohol during the Friedel-Crafts alkylation reaction at 120°C in zeolite interconnected nanosheets and conventional ZSM-5, with the lines in the figure being interpolations to guide the line of sight. Figure 5(C) shows the selectivity of the alkylation product (TMBB) in equiconversion (approximately 75%). Figure 5(D) shows the reaction at 350°C and with gravimetric space velocities of S1, S2, S3, S4, and ZSM-5 of 28, 28, 28, 21, and 33 h, respectively. -1 The near-complete methanol conversion rate in the MTH reaction is shown. Here, the zeolite interconnected nanosheet catalyst exhibits higher stability compared to the conventional ZSM-5. The line in the figure represents linear regression. Figure 5(E) shows the estimated turnover number (histogram, left axis) for conversion rates between 50% and 30%, and the ratio of ethene to 2MBu for all catalysts (symbol, right axis) at a conversion rate of approximately 40%.

[0039] The effects of two key features of zeolite interconnected nanosheet catalysts, namely a high external acid site concentration and a high surface area, were first tested using the Friedel-Crafts alkylation reaction of mesitylene and benzyl alcohol (Figure 5(A)). This liquid-phase reaction occurs mainly on the external surface of the zeolite due to the bulky size of mesitylene, which does not readily access the internal channels of the medium-porous zeolite (i.e., MFI and MEL types). A comparison of all five catalysts revealed the significantly higher activity of the zeolite interconnected nanosheet material compared to ZSM-5, along with the fact that S2 showed the most rapid increase in benzyl alcohol conversion rate (Figure 5(B)). Interestingly, the selectivity of the zeolite interconnected nanosheet catalyst for the desired product, namely 2-benzyl-1,3,5-trimethylbenzene (TMBB), was approximately twice that of ZSM-5 (Figure 5(C)). This superior performance is due to the unique physicochemical characteristics of the hierarchical zeolite, but a distinguishing feature of the zeolite interconnected nanosheets fabricated by seed-assisted synthesis is their unusually high Al content (Si / Al < 15, Table 1). Self-columnar pentasil and other hierarchical MFI-type zeolites reported in previous literature were not directly synthesized with a Si / Al ratio of less than 30. This is outside the range of most commercially available ZSM-5 zeolites (i.e., Si / Al < 20).

[0040] To evaluate the performance of hierarchical and conventional catalysts, methanol-to-hydrocarbon conversion (MTH) was used as the second reaction. Gas-phase reactions at near-complete conversion rates (50-60%) revealed that the lifetime of all zeolite interconnected nanosheet catalysts was improved compared to conventional ZSM-5 (Figure 5(D)). The performance of the zeolite interconnected nanosheet catalysts can be classified into two general categories: deactivation rates of approximately half (S2 and S3) and approximately one-quarter (S1 and S4) compared to ZSM-5. These groupings were also applied to the measured turnover number (TON), or the number of moles of methanol converted per mole of Brønsted acid (Figure 5(E)). The two groupings of zeolite interconnected nanosheet catalysts correspond to TON numbers of approximately 900 and approximately 450 mol MeOH / H, respectively.+ These values ​​were the same as those for the conventional ZSM-5 (240 mol MeOH / H + This is significantly larger compared to [another example]. Product selectivity, evaluated using the ratio of ethene to 2MBu, was similar for all five catalysts (where 2MBu represents both 2-methylbutane and 2-methyl-2-butene). This ratio is characteristic of the dominant MTH cycle (olefin vs. aromatic), with lower values ​​indicating accelerated propagation of the olefin cycle. The slightly lower ethene / 2MBu ratio in the zeolite interconnected nanosheet catalyst is qualitatively consistent with previous studies showing that ZSM-5, with relaxed internal mass transport constraints (e.g., smaller crystal dimensions), promotes the olefin cycle. Overall, this study demonstrates that zeolite interconnected nanosheet zeolites produced by seed-assisted synthesis exhibit superior catalytic performance. Furthermore, a qualitative comparison between the zeolite interconnected nanosheet catalyst and the previously reported hierarchical ZSM-5 with low aluminum content and thin nanosheets (approximately 3 nm) suggests that their performance is equivalent. However, previous studies reported the MTH reaction at 100% methanol conversion, which overestimates the catalyst lifetime.

[0041] In summary, zeolite interconnected nanosheets were fabricated using either MEL or MFI type zeolite seeds without the aid of any organic structure-determining or branching agents. Time-resolved electron microscopy visualized heterogeneous nucleation, followed by the generation of these hierarchical zeolites from the surface of the amorphous precursor. After crystallization began, the zeolite interconnected nanosheets exhibited a distinct columnar structure, undergoing coordinated growth and branching over reaction time. While the exact mechanism of columnarization is unknown, it is likely that residues from the dissolved seed imprinted several "memories" in the growth mixture, promoting branching. This phenomenon occurred with both MEL and MFI type seeds, resulting in similar hierarchical structures with varying degrees of branching. These zeolite interconnected nanosheet materials exhibit a large external surface area (almost three times that of conventional ZSM-5) and a very high proportion of external acid sites (up to seven times that of conventional ZSM-5). These two important features significantly improve catalytic performance. The evolution of zeolite interconnected nanosheets in the Friedel-Crafts alkylation reaction of mesitylene and benzyl alcohol results in higher conversion rates and approximately twofold improved selectivity to the desired product. Similarly, the MTH reaction demonstrates that zeolite interconnected nanosheets extend catalyst lifetime and significantly improve turnover (four times compared to conventional ZSM-5). These findings highlight the potential of seed-assisted synthesis as a simple and efficient method toward the realization of commercially viable hierarchical zeolite catalysts.

[0042] Example 2 Synthesis of interconnected nanosheets First, sodium aluminate is added to an aqueous sodium hydroxide solution, followed by the addition of the silicon source LUDOX AS-40, resulting in the following molar composition: 3.42Na2O:18SiO2:1Al2O3:XH2O(X=224, 324, 424, 600) 3.42Na2O:24.62SiO2:1.37Al2O3:XH2O(X=324, 224, 443) Seed-assisted synthesis was performed by obtaining a growth solution containing [the specified substance]. Silicalite-2 seeds prepared as described above were added to each solution. In all experiments, the small amount of calcined seeds used was 10% by mass. The growth solution was allowed to stand at room temperature for approximately 24 hours, and then transferred to an acid digestion bomb (Parr Instruments). Under self-growing pressure, it was treated with hot water at 150°C in an oven. Two cycles of centrifugation and washing with deionized water were performed, and after a selection time interval, the extracted solids were separated from the parent material and dried in an oven at 60°C.

[0043] Figure 6 shows SEM images of interconnected zeolite nanosheets extracted from the various synthesis methods described above using SilicaLite-2 seeds. The molar compositions are (A-C) 3.42Na2O:18SiO2:1Al2O3:XH2O and (D-F) 3.42Na2O:24.62SiO2:1.37Al2O3:XH2O, with the water content being (A)X=224, (B)X=424, (C)X=600, (D)X=224, (E)X=324, and (F)X=443.

[0044] Figure 7 shows the powder XRD patterns of interconnected zeolite nanosheets extracted from the various synthesis methods described above using SilicaLite-2 seeds. The molar compositions are (i-iii) 3.42Na2O:18SiO2:1Al2O3:XH2O and 3.42Na2O:24.62SiO2:1.37Al2O3:XH2O (iv-vi), with the water content of each being (i) X=224, (ii) X=424, (iii) X=600, (iv) X=224, (v) X=324, and (vi) X=443.

[0045] Optional post-composition processing The performance of the interconnected nanosheet products was observed to improve with simple post-synthesis treatment. The sample immediately after synthesis was washed with 0.1 M HCl (3% by mass suspension) at room temperature for 5 hours. This mild acid treatment was performed to remove any amorphous material residue. The sample immediately after synthesis was converted to proton form by ion exchange by mixing calcined zeolite with a 1.0 M NH4NO3 solution to obtain a 2% by mass suspension. This mixture was heated to 80°C for 2 hours, and the above process was repeated three times, with centrifugation / washing between each ion exchange cycle. The final NH4-zeolite sample was calcined again under the same conditions as above to obtain H-form zeolite.

[0046] References The following references are cited herein by reference. M. Milina, S. Mitchell, P. Crivelli, D. Cooke, J. Perez-Ramirez, Mesopore quality determines the lifetime of hierarchically structured zeolite catalysts. Nature Communications 5, 1-10 (2014). AH Janssen, AJ Koster, KP de Jong, Three-dimensional transmission electron microscopic observations of mesopores in dealuminated zeolite Y. Angewandte Chemie International Edition 40, 1102-1104 (2001). J. C. Groen, J. C. Jansen, J. A. Moulijn, J. Perez-Ramirez, Optimal aluminum-assisted mesoporosity development in MFI zeolites by desilication. The Journal of Physical Chemistry B 108, 13062-13065 (2004). J. Garcia-Martinez, M. Johnson, J. Valla, K. Li, J. Y. Ying, Mesostructured zeolite Y-high hydrothermal stability and superior FCC catalytic performance. Catalysis Science & Technology 2, 987-994 (2012). A. Sachse, J. Garcia-Martinez, Surfactant-templating of zeolites: from design to application. Chemistry of Materials 29, 3827-3853 (2017). D. Xu et al., π-π interaction of aromatic groups in amphiphilic molecules directing for single-crystalline mesostructured zeolite nanosheets. Nature Communications 5, 4262 (2014). L.-H. Chen et al., Hierarchically Structured Zeolites: From Design to Application. Chemical Reviews, (2020). K. Li, J. Valla, J. Garcia-Martinez, Realizing the commercial potential of hierarchical zeolites: new opportunities in catalytic cracking. ChemCatChem 6, 46-66 (2014). M. E. Davis, Ordered porous materials for emerging applications. Nature 417, 813-821 (2002). H. Awala et al., Template-free nanosized faujasite-type zeolites. Nature Materials 14, 447-451 (2015). S. Mintova, N. H. Olson, V. Valtchev, T. Bein, Mechanism of zeolite A nanocrystal growth from colloids at room temperature. Science 283, 958-960 (1999). E.-P. Ng, D. Chateigner, T. Bein, V. Valtchev, S. Mintova, Capturing ultrasmall EMT zeolite from template-free systems. Science 335, 70-73 (2012). M. Kumar et al., Crystallization of Mordenite Platelets using Cooperative Organic Structure-Directing Agents. Journal of the American Chemical Society 141, 20155-20165 (2019). M. Choi et al., Stable single-unit-cell nanosheets of zeolite MFI as active and long-lived catalysts. Nature 461, 246-249 (2009). K. Na et al., Directing zeolite structures into hierarchically nanoporous architectures. Science 333, 328-332 (2011). K. Na et al., Pillared MFI zeolite nanosheets of a single-unit-cell thickness. Journal of the American Chemical Society 132, 4169-4177 (2010). X. Zhang et al., Synthesis of self-pillared zeolite nanosheets by repetitive branching. Science 336, 1684-1687 (2012). D. Xu et al., On the synthesis and adsorption properties of single‐unit‐cell hierarchical zeolites made by rotational intergrowths. Advanced Functional Materials 24, 201-208 (2014). P. Kumar et al., One-dimensional intergrowths in two-dimensional zeolite nanosheets and their effect on ultra-selective transport. Nature Materials 19, 443-449 (2020). W. Chaikittisilp et al., Formation of hierarchically organized zeolites by sequential intergrowth. Angewandte Chemie International Edition 125, 3439-3443 (2013). Y. Shen et al., Deconvoluting the competing effects of zeolite framework topology and diffusion path length on methanol to hydrocarbons reaction. ACS Catalysis 8, 11042-11053 (2018). S. Kumar, Z. Wang, R. L. Penn, M. Tsapatsis, A structural resolution cryo-TEM study of the early stages of MFI growth. Journal of the American Chemical Society 130, 17284-17286 (2008). J. J. De Yoreo et al., Crystallization by particle attachment in synthetic, biogenic, and geologic environments. Science 349, (2015). M. Kumar, M. K. Choudhary, J. D. Rimer, Transient modes of zeolite surface growth from 3D gel-like islands to 2D single layers. Nature Communications 9, 1-9 (2018). A. I. Lupulescu, J. D. Rimer, In situ imaging of silicalite-1 surface growth reveals the mechanism of crystallization. Science 344, 729-732 (2014). M. Shete et al., Nanoscale Control of Homoepitaxial Growth on a Two‐Dimensional Zeolite. Angewandte Chemie International Edition 56, 535-539 (2017). T. M. Davis et al., Mechanistic principles of nanoparticle evolution to zeolite crystals. Nature Materials 5, 400-408 (2006). S. Ilias, R. Khare, A. Malek, A. Bhan, A descriptor for the relative propagation of the aromatic-and olefin-based cycles in methanol-to-hydrocarbons conversion on H-ZSM-5. Journal of Catalysis 303, 135-140 (2013). R. Khare, D. Millar, A. Bhan, A mechanistic basis for the effects of crystallite size on light olefin selectivity in methanol-to-hydrocarbons conversion on MFI. Journal of Catalysis 321, 23-31 (2015). S. L. Scott, A Matter of Life(time) and Death. ACS Catalysis 8, 8597-8599 (2018).

Claims

1. A method for synthesizing zeolite interconnected nanosheets, the following: A calcined zeolite seed crystal is placed in an organic matter-free growth medium to prepare a growth solution, wherein the organic matter-free growth medium is Na ２ O: SiO ２ : Al ２ O ３ : H ２ An aqueous solution having a molar composition ratio of A:B:C:X, where A is 3.4 to 3.5, B is 18 to 25, C is 1 to 1.4, and X is 220 to 600; To enable the calcined zeolite seed crystals to form zeolite interconnected nanosheets in the growth solution; and Separating the zeolite interconnected nanosheets from the growth solution, A synthesis method that includes this.

2. The synthesis method according to claim 1, wherein the calcined zeolite seed crystal is a MEL or MFI type zeolite seed crystal.

3. The synthesis method according to claim 1, wherein the calcined zeolite seed crystal is a Silicalite-2, ZSM-11, Silicalite-1, or ZSM-5 crystal.

4. The synthesis method according to claim 1, wherein the organic matter-free growth medium does not contain an organic structure-determining agent.

5. The synthesis method according to claim 1, wherein the organic matter-free growth medium does not include a branching template.

6. The synthesis method according to claim 1, wherein A is 3.42, B is 18, C is 1, and X is 224, 324, 424, or 600.

7. The synthesis method according to claim 1, wherein A is 3.42, B is 24.62, C is 1.37, and X is 224, 324, or 443.

8. The synthesis method according to claim 1, wherein the zeolite interconnected nanosheet has a hierarchical columnar morphology and a thickness of 30 nm.

9. A zeolite interconnected nanosheet prepared by the method described in claim 1.

10. A catalyst comprising zeolite interconnected nanosheets prepared by the method described in claim 1.

11. The catalyst according to claim 10, wherein the zeolite interconnected nanosheet has a hierarchical columnar morphology and a thickness of 30 nm.

12. A method for producing or transforming an organic compound, comprising contacting the organic compound with the catalyst described in claim 10.

13. The method according to claim 12, wherein the method for producing or converting an organic compound further comprises alkylation, Fischer-Tropsch synthesis, upgrading of methanol or methane, cracking, or biomass conversion.

14. An organic-free growth medium for the synthesis of zeolite interconnected nanosheets, which is essentially as follows: silica; Aluminum; and Sodium hydroxide, composed of Na ２ O:SiO ２ :Al ２ O ３ :H ２ When the molar ratios of O:SiO:AlO:H are A:B:C:X, the organic - free growth medium has a molar composition ratio where A is 3.4 - 3.5, B is 18 - 25, C is 1 - 1.4, and X is 220 - 600.

15. An organic matter-free growth medium according to claim 14, which does not contain an organic structure-determining agent.

16. An organic matter-free growth medium according to claim 14, which does not include a branching template.

17. The organic matter-free growth medium according to claim 14, wherein A is 3.42, B is 18, C is 1, and X is 224, 324, 424, or 600.

18. The organic matter-free growth medium according to claim 14, wherein A is 3.42, B is 24.62, C is 1.37, and X is 224, 324, or 443.

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