Zeolite Nanosheets Research Articles

Design of a Small Organic Template for the Synthesis of Self-Pillared Pentasil Zeolite Nanosheets.

Zeolite nanosheets with excellent mass transfer are attractive, but their successful syntheses are normally resulted from a huge number of experiments. Here, we show the design of a small organic template for the synthesis of self-pillared pentasil (SPP) zeolite nanosheets from theoretical calculations in interaction energies between organic templates and pentasil zeolite skeletons. As expected, the SPP zeolite nanosheets with the thickness at 10-20 nm have been synthesized successfully. Characterizations show that the SPP zeolite nanosheets with about 90% MFI and 10% MEL structures have good crystallinity, the house-of-card morphology, large surface area, and fully four-coordinated aluminum species. More importantly, methanol-to-propylene tests show that the SPP zeolite nanosheets exhibit much higher propylene selectivity and longer reaction lifetime than conventional ZSM-5 zeolite. These results offer a good opportunity to develop highly efficient zeolite catalysts in the future.

Enhanced Dehydrogenative H2 Release from N-Containing Amphicyclic LOHC Boosted by Pd-Supported Nanosheet MFI Zeolites Having Strong Acidity and Large Mesoporosity

The amount and rate of H2 discharge from 2-[(n-methylcyclohexyl)methyl]piperidine (H12-MBP), an amphicyclic liquid organic hydrogen carrier (LOHC) having two cycle moieties (cyclohexane and piperidine) with different reactivities, are determined by dehydrogenation of a cyclohexane ring with less reactivity. To realize high H2 yields with rapid kinetics, the cyclohexane ring in the partially dehydrogenated 2-[n-methylcyclohexyl]methyl)pyridine (H6-MBP) that is generated as the intermediate species should be fully dehydrogenated to 2-(n-methylbenzyl)pyridine (H0-MBP). This is approached using Pd-supported nanosheet zeolites having mesoporous structures bearing high concentrations of strongly acidic sites on external surfaces, which can not only enhance the diffusion of bulky H12-MBP but also strongly bind the basic piperidine ring in H12-MBP and H6-MBP. The H2 yields and rate constants are correlated with the acidity, mesoporosity, and adsorption behaviors of the LOHCs. As these factors are strengthened, H2 yield and rate constants increased dramatically within the ranges of 16.0–64.7% and 0.0001–0.0013 min–1, respectively. The results prove that mesoporous zeolites can be used for constructing supported Pd catalysts achieving high H2 yields with rapid kinetics from N-containing amphicyclic LOHCs.

Wet-oxidization and exfoliation of non-swollen MCM-22P to dispersible two-dimensional MWW zeolite nanosheets

Two-dimensional (2D) zeolite nanosheets open exciting opportunities for the application in catalysis and separations. Exfoliation of layered zeolite shows a promising way for the preparation of 2D zeolite nanosheets. Herein, non-swollen MCM-22P with ordered layer spacing was successfully exfoliated to dispersible MWW nanosheets. Firstly, a wet-oxidization method, i.e., heating in a mixture of H 2 SO 4 and H 2 O 2 (called piranha solution) was adopted to remove the template of pyridine (PI) from as-synthesized MCM-22P zeolite. IR, TG, XRD, N 2 adsorption confirmed that the wet-oxidization could efficiently remove PI from MCM-22P zeolite while preserving the MWW crystal structure. Exfoliation of the detemplated MCM-22P zeolite was successfully achieved by an ultrasonic treatment in water. After purification by sedimentation, 2D MWW zeolite nanosheets dispersed in aqueous solution were obtained. The monolayer MWW nanosheets with high purity are confirmed by SEM and TEM observations. The wet oxidation followed by the sonication method provides an alternative way for the exfoliation of layered zeolite to dispersed nanosheets. • Non-swollen MCM-22P was successfully exfoliated to dispersible MWW nanosheets. • Piranha solution was used to eliminate template from MCM-22P. • The template-free MCM-22P was exfoliated by sonication treatment. • Two-dimensional template-free MWW zeolite nanosheets dispersed in solvent were prepared.

Stacking-faulted CDO zeolite nanosheets efficient for bulky molecular reactions.

The synthesis of thin zeolite nanosheets beneficial for catalytic reactions, adsorption and diffusion involving bulky molecules remains a great challenge. Herein, we report a unique layered zeolitic nanosheet ECNU-57 with a CDO-type structure that was synthesized by employing small-molecular 1,4-bis(N-methylpyrrolidinium) cations as the organic structure-directing agent (OSDA). The ECNU-57 nanosheets are 50 nm thick along the b-axis and have an open hierarchical porosity with 486 m2 g-1 surface area. HRTEM investigation indicates that the nanosheets exhibit a stacking fault structure along the b-axis with the inclusion of the FER structure since the CDO and FER topologies possess very similar building layers. As a solid-acid catalyst, ECNU-57 exhibits promising performances in the reactions of 1,3,5-triisopropylbenzene cracking and Friedel-Crafts acylation, due to its enhanced mass transfer and more accessible active sites to bulky organic molecules.

Zeolite nanosheets for catalysis.

Zeolites with well-defined micropores have been widely used as heterogeneous catalysts in the fields of petroleum refining, fine chemicals, and environment protection. However, the sole micropores in the zeolite structures usually impose diffusion constraints, which would greatly influence their catalytic performances. Therefore, it is highly desirable to shorten the diffusion pathway of zeolites and thus eliminate the diffusion constraints. One of the efficient methods is to synthesize zeolite nanosheets, which has become a hot topic in the past decades. In this tutorial review, the recent progresses in the synthesis of zeolite nanosheets and their relevant catalysis are briefly discussed. Various strategies for the synthesis of zeolite nanosheets are summarized including delamination, templated crystallization, additive-assisted synthesis, seed-directed synthesis, and gaseous expansion synthesis. In addition, the catalytic reactions of zeolite nanosheets with acidic and metal sites are also outlined. This tutorial review should be significant for the design and preparation of highly efficient zeolite catalysts.

Direct synthesis of ultrathin FER zeolite nanosheets via a dual-template approach.

The synthesis of zeolites with nanosheet morphology has been attracting extensive attention. Despite the steady progress, the direct synthesis of ultrathin nanosheets of FER zeolite with thickness of less than 10 nm is still a great challenge. Herein we report a facile synthesis of FER zeolite nanosheets (named SCM-37) by using octyltrimethylammonium chloride (OTMAC) and 4-dimethylaminopyridine (4-DMAP) as dual organic templates. The effects of synthesis parameters, including initial molar ratio of SiO2/Al2O3, crystallization temperature and time were investigated. It turned out that the crystallization field of SCM-37 was narrow. A two-step crystallization method was utilized to obtain pure and completely crystallized SCM-37 zeolite. SCM-37 was characterized by multiple techniques, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen physisorption, Fourier transform infrared (FTIR), ammonia-temperature programmed desorption (NH3-TPD) and nuclear magnetic resonance (NMR), and compared with the conventional FER zeolite (C-FER). The two most significant features of SCM-37 are the ultrathin crystal nanosheet and extremely high external surface area. The thickness of SCM-37 along the a-axis is 4∼7 nm, while that of C-FER is over 20 nm. The external surface area reaches 198 m2 g−1, which is over ten times larger than that of C-FER. The catalytic performances of the FER zeolites were evaluated by the cracking of 1,3,5-triisopropylbenzene (TiPB). Although possessing a lower amount of total acid sites, SCM-37 showed higher conversion of TiPB, as well as selectivity to the deep cracking products. The superior performance of SCM-37 was attributed to the higher external surface area arising from the ultrathin nanosheets.

C-Axis-penetrated mesoporous MWW zeolite nanosheets: preparation by H2O2-induced micro-explosion and their enhanced properties

A series of highly dispersed and c-axis-penetrated mesoporous MWW oligolayers with enhanced properties was prepared via an efficient, green, and controllable method through H2O2-induced micro-explosion.

Porous liquids unlock a new class of spatially orthogonal catalyst

Catalytic cascades epitomize green chemistry principles, enabling ultra-efficient transformations while minimizing unit operations. In the last Chem issue, Chen et al. demonstrate a new strategy to combine antagonistic catalytic functions by incorporating an acidic zeolite in the pores of a sterically hindered, basic ionic liquid to drive a deacetalization-Knoevenagel condensation cascade. Catalytic cascades epitomize green chemistry principles, enabling ultra-efficient transformations while minimizing unit operations. In the last Chem issue, Chen et al. demonstrate a new strategy to combine antagonistic catalytic functions by incorporating an acidic zeolite in the pores of a sterically hindered, basic ionic liquid to drive a deacetalization-Knoevenagel condensation cascade. A bifunctional zeolitic porous liquid with incompatible Lewis pairs for antagonistic cascade catalysisChen et al.ChemSeptember 22, 2021In BriefUnique bifunctional type III porous-liquid (PL)-based systems were facilely fabricated via assembly of zeolite nanosheets with ionic liquids. Rational structural design afforded PLs featured by high zeolite concentration, stable dispersion after 2 years, abundant cavity distribution, and involvement of antagonistic groups (acid and base sites) in separated and active form via steric hindrance control and electronic repulsion regulation. These unique properties worked cooperatively to fulfill the cascade deacetalization-Knoevenagel/Aldol condensation in one pot with catalytic efficiency outperforming the traditional systems. Full-Text PDF

Rapid and Low-Cost Synthesis of Zsm-5 Zeolite Nanosheet Assemblies for Conversion of Methanol to Gasoline

Rapid and Low-Cost Synthesis of Zsm-5 Zeolite Nanosheet Assemblies for Conversion of Methanol to Gasoline

Nonuniformity of Transport Coefficients in Ultrathin Nanoscale Membranes and Nanomaterials.

The quest to reduce transport resistance in separations using nanomaterials has led to considerable interest in nanoscale adsorbents and ultrathin membranes. It is now established that interfacial resistance limits the performance of such nanosized materials; however, the origin of this resistance is uncertain. While it is associated with surface pore blockages and distortions in some materials, its existence even in ideal materials is largely putative. Here, we report equilibrium molecular dynamics (EMD) simulations with ideal zeolite-based nanosheets, indicating the transport resistance to be entirely distributed within the solid, without contribution from an interfacial effect. We demonstrate the presence of an internal entry region over which fluid decorrelation occurs, and in which the local transport coefficient inside the crystal is nonuniform and position-dependent, increasing to the uniform value in the bulk material at larger distances. Our EMD-based diffusivity profiles within the nanomaterial enable us to unequivocally determine the entry length, and reveal an internal excess resistance, frequently assumed to be an interfacial resistance, due to significant reduction of the internal transport coefficient in the entrance and exit regions. A decrease in the entry length with loading in PON zeolite nanosheets is seen. We demonstrate a reduction in external resistance in the external bulk chambers used in simulations, triggered by the interplay of incomplete decorrelation in the nanosheet and periodic boundary conditions imposed on the system comprising the nanosheet and surrounding bulk reservoirs when the nanosheet thickness is less than the entry length. Our analysis of the transport dynamics within the nanosheet demonstrates that, at least for ideal systems, decomposition of the inhomogeneous diffusivity-based internal resistance into an interfacial and a uniform transport coefficient-based internal contribution is not appropriate for finite-sized systems. Our results will enable the improved design of nanoscale membranes and materials for applications in separation and other processes.

Assembly of Silicalite-1 Crystals Like Toy Lego Bricks into One-, Two-, and Three-Dimensional Architectures for Enhancing Its Adsorptive Separation and Catalytic Performances.

Many researchers have contributed to the assembly of zeolitic nanosheets and nanocrystallites into three-dimensional (3D) networks as it can remarkably improve the catalytic and/or adsorptive performances of zeolites. However, the applications of these synthesized materials are seriously limited because of low hydrothermal stability. A highly interesting strategy, but a great challenge, is the alignment of well-crystallized zeolite crystals into desirable architectures. Here, well-crystallized silicalite-1 crystals are assembled like toy Lego bricks into one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) architectures, and the assembly mechanism is investigated by combining elaborate experiments, in situ spectroscopy, and theoretical calculations. A 1D architecture was formed by stacking crystals along the b axis with the assistance of ethanol that is selectively adsorbed on (100) and (001) crystal facets. Such adsorption increases the condensation energy barriers along a and c axes, but facilitates the condensation between (010) facets. The assembly of the crystals into well-arrayed 2D architectures is achieved using both ethanol and benzaldehyde because of their preferable adsorption on the (001) facet. When an amphiphilic copolymer (P123) was further added in the gel along with the substitution of ethanol by 1-propanol, a 3D network was fabricated by the agglomeration and self-pillaring of the 2D Lego bricks possibly with P123 aggregates as the substrate matrix. Excitingly, upon alignment of crystals into 2D architectures, the adsorptive selectivity of 1-butanol (2 wt %) to water of silicalite-1 increases by 45.3 times, while into 3D networks, the catalytic activity for the Beckmann rearrangement of cyclohexanone oxime elevates by 79% along with a great enhancement of catalytic stability.

A mixed matrix membrane for enhanced CO2/N2 separation via aligning hierarchical porous zeolite with a polyethersulfone based comb-like polymer

BackgroundMixed matrix membranes (MMM)s for CO2/N2 separation still suffer from interfacial defects. MethodTo address this, a series of MMMs were prepared using polyethersulfone-g-poly (ethylene glycol) (PES-g-PEG) comb-like copolymer to tune the interfacial interaction with a pillared MFI (PMFI) zeolite nanosheets, which has a hierarchical porous structure to improve permeance. The composite membranes were examined by SEM, EDX and XRD. The dependence of gas permeabilities, diffusion and solubility coefficients of CO2 and N2 were determined by the time-lag method. ResultsThe increase in PMFI zeolite loading led to an increase in the permeability coefficient of CO2, which is mainly caused by the increase in CO2 diffusion coefficient. The CO2/N2 gas separation was optimized at a loading of 20wt% PMFI zeolite, which produces a composite membrane with a CO2 permeability of 66.9 Barrer and an ideal permeability selectivity coefficient of 9.6.

Preparation of MFI Nanosheets with Distinctive Microstructures via Facile Alkaline Etching

Although zeolite nanosheets (NSs) exhibit great prospects for a wide range of applications due to microstructural superiority, their facile preparation and microstructural tailoring remain a great challenge. In this study, uniform coffin-shaped MFI microcrystals were subjected to hydrothermal treatment in the presence of different types of alkaline etching agents, i.e., TMAOH, TEAOH, and TPAOH, for preparing MFI NSs with distinctive microstructures. It was found that the morphological and textural properties of MFI NSs could be readily tuned by varying etching agent types, etching agent contents, and hydrothermal treatment parameters, thereby leading to the formation of 10 nm thick leaf-shaped MFI NSs, ellipse-shaped MFI NSs, and single-crystal-like MFI NS aggregates through an in-plane oriented attachment. Simultaneously, the possible mechanisms involved in the formation of MFI NSs with distinctive microstructures were proposed. Among the prepared MFI NSs, 10 nm thick (ca. 5 unit cell) leaf-shaped MFI NSs represented one of the thinnest MFI NSs ever reported by the top-down method, while single-crystal-like MFI NS aggregates were prepared for the first time, which may endow them with superior performances in relevant application areas.

One-Pot Exfoliation and Functionalization of Zeolite Nanosheets for Protection of Paper-Based Relics

One-Pot Exfoliation and Functionalization of Zeolite Nanosheets for Protection of Paper-Based Relics

A bifunctional zeolitic porous liquid with incompatible Lewis pairs for antagonistic cascade catalysis

•Synthesize type III porous liquids via assembly of zeolite and ionic liquids •Achieve high zeolite content, stable dispersion, and abundant cavity distribution •Involvement of separated antagonistic groups via steric hindrance regulation •Exhibiting superior catalytic performance in cascade reaction in one pot The emergence of porous liquids (PLs) opened opportunities to form unique antagonistic systems capable of fulfilling cascade reactions promoted by incompatible active sites in one pot, which is a long-term challenging subject in catalysis. Herein, unique bifunctional type III PL-based systems were facilely fabricated via assembly of zeolite nanosheets with ionic liquids. Rational structural design afforded PLs that feature high zeolite concentration, stable dispersion after 2 years, abundant cavity distribution, and involvement of antagonistic groups (acid and base sites) in separated and active form via steric hindrance control and electronic repulsion regulation. These unique properties worked cooperatively to fulfill the cascade deacetalization-Knoevenagel/Aldol condensation in one pot with superior catalytic efficiency outperforming the traditional systems. The key to success lies in the formation of bifunctional composites, transformation of zeolite from heterogeneous to homogeneous via surface modification, and rapid mass transfer ensured by the rigid porous architecture. The emergence of porous liquids (PLs) opened opportunities to form unique antagonistic systems capable of fulfilling cascade reactions promoted by incompatible active sites in one pot, which is a long-term challenging subject in catalysis. Herein, unique bifunctional type III PL-based systems were facilely fabricated via assembly of zeolite nanosheets with ionic liquids. Rational structural design afforded PLs that feature high zeolite concentration, stable dispersion after 2 years, abundant cavity distribution, and involvement of antagonistic groups (acid and base sites) in separated and active form via steric hindrance control and electronic repulsion regulation. These unique properties worked cooperatively to fulfill the cascade deacetalization-Knoevenagel/Aldol condensation in one pot with superior catalytic efficiency outperforming the traditional systems. The key to success lies in the formation of bifunctional composites, transformation of zeolite from heterogeneous to homogeneous via surface modification, and rapid mass transfer ensured by the rigid porous architecture.

Two-Dimensional MFI Zeolite Nanosheets Exfoliated by Surfactant Assisted Solution Process

Two-dimensional (2D) zeolite nanosheets are important for the synthesis of high flux zeolite membranes due to their lateral size in a preferred orientation. A way to obtain 2D zeolite nanosheets is to exfoliate interlocked structures generated during the hydrothermal synthesis. The mechanical and polymer assisted exfoliation process leads to mechanical damage in nanosheets and short lateral size. In the present study, polyvinylpyrrolidone (PVP) was introduced as an exfoliation agent and dispersant, so that multilamellar interlocked silicalite-1 zeolite nanosheets successfully exfoliated into a large lateral size (individual nanosheets 500~1200 nm). The good exfoliation behavior was due to the strong penetration of PVP into multilamellar nanosheets. Sonication assisted by mild milling helps PVP molecules to penetrate through the lamellar structure, contributing to the expansion of the distance between adjacent layers and thus decreasing the interactions between each layer. In addition, the stability of exfoliated nanosheets was evaluated with a series of organic solvents. The exfoliated nanosheets were well dispersed in n-butanol and stable for 30 days. Therefore, the PVP-assisted solution-based exfoliation process provides high aspect ratio MFI zeolite nanosheets in organic solvents for a long period.

Two Coexisting Forms of Simple Molecules for Directing Sesqui-Unit-Cell Zeolite Nanosheets

Feasible strategies are desirable for preparing zeolitic nanosheets with opener porosities and more accessible active sites. Highly delaminated FER nanosheets (ECNU-17) with unit-cell scale thickness were hydrothermally synthesized using a simple, small, and low-cost imidazole molecule as the sole organic structure-directing agent (OSDA). The single OSDA directed the formation of the FER framework, while the π–π stacked OSDAs terminated the growth perpendicular to the zeolite sheets. The ECNU-17 nanosheet is only 2.9 nm in thickness, corresponding to one and a half FER unit cells along a-axis. With open hierarchical porosity and an enhanced external surface area of 253 m2 g–1, ECNU-17 is endowed with improved mass transport and a significantly increased number of active acid sites accessible to bulky organic molecules. The ultrathin sheets of ECNU-17 aluminosilicate display excellent activity and selectivity for the protection reaction of benzaldehyde with pentaerythritol as well as the cracking of 1,3,5-triisopropylbenzene.

Fabrication of size-controlled hierarchical ZnS@ZnIn2S4 heterostructured cages for enhanced gas-phase CO2 photoreduction

Designing and constructing advanced heterojunction architectures are desirable for boosting CO2 photoreduction performance of semiconductor photocatalysts. Herein, we have prepared hierarchical ZnS@ZnIn2S4 core-shell cages with controlled particle sizes using sequential synthesis of Zeolitic imidazolate (ZIF-8) polyhedrons, ZnS cages, and ZnIn2S4 nanosheets on the ZnS polyhedron cages. ZIF-8 polyhedrons are firstly synthesized by a liquid-phase approach. The subsequent sulfidation of the ZIF-8 polyhedrons results in the formation of ZnS polyhedron cages, which act as substrates for fabricating ZnS@ZnIn2S4 core-shell cages by growing ZnIn2S4 nanosheets. The size of ZnS cages can be tuned to optimize CO2 photoreduction performance of hierarchical ZnS@ZnIn2S4 core-shell cages. The synergy of the unique hierarchical core-shell cage-like structure and heterojunction composition endows the hybrid catalyst high incident light utilization, abundant active sites, and effective separation of photoexcited charge carriers. Benefiting from these advantages, the optimized hierarchical ZnS@ZnIn2S4 core-shell cages exhibit enhanced performance for CO2 photoreduction with the CO yield of 87.43 μmol h−1g−1 and 84.3% selectivity, which are much superior to those of single ZnIn2S4 or ZnS. Upon Au decoration, the CO2 photoreduction performance of ZnS@ZnIn2S4 core-shell cages is further enhanced because of the Schottky junctions and surface plasmon resonance effect.

MEL zeolite nanosheet membranes for water purification: insights from molecular dynamics simulations

MEL zeolite nanosheet membranes for water purification: insights from molecular dynamics simulations

Direct Synthesis of Nanosheet-Stacked Hierarchical "Honey Stick-like" MFI Zeolites by an Aromatic Heterocyclic Dual-Functional Organic Structure-Directing Agent.

Soft template designing is the most promising strategy for the synthesis of zeolite nanosheets. MFI nanosheets directed by soft templates (containing long-chain alkyl groups or aromatic groups as hydrophobic component) can be found frequently; however, so far, MFI nanosheets synthesized by soft templates with aromatic heterocycle groups (e. g., s-triazine groups) are rare. Herein, a nanosheet-stacked hierarchical MFI zeolite (NSHM) has been synthesized by using a triply branched s-triazine-based surfactant as a bifunctional organic structure-directing agent. On the basis of a geometrical match relationship, a formation model has been proposed. Synthesized NSHM had abundant mesopores stacked by nanosheets and exhibited a high surface area (430 m2 ⋅ g-1 ). The 1 wt% Pd/NSHM attained a significant increase in yield of cyclohexanol/cyclohexanone mixture (from 66 to 85 %) in the oxidation of cyclohexane compared with Silicalite-1 and SBA-15 as supports.