MFI Nanosheets Research Articles

MFI nanosheets: a rising star in zeolite materials

MFI nanosheet zeolites, which integrate dual merits of hierarchical zeolites and nano zeolites, with an optimal diffusion efficiency, are regarded as a highly desired material for catalytic reactions and membrane separation.

Production of propyl 4-hydroxybenzoate via selective hydrogenolysis of lignin catalyzed by Ni/MFI-ns

Selective conversion of lignin macromolecules into aromatic monomers is of great significance but remains a great challenge. Here, we present a metallic Ni supported on hierarchical multilamellar MFI nanosheets (MFI-ns)...

Regulating acid properties of ZSM-5 nanosheets by Fe incorporation towards high-performance alkylation of benzene with methanol

A clear understanding of the acidity-activity relationship is an important prerequisite for designing functional materials in alkylation of benzene with methanol. Herein, a series of b-axis-oriented [Fe/Al]-MFI nanosheets with similar thickness but varied acidities were prepared by tuning Fe incorporation to systematically study the effect of acidity on their alkylation performance. Comprehensive physiochemical studies demonstrate that tetrahedral framework type Fe species are dominated. The incorporation of Fe significantly weakens the strong acid strength of zeolite thus endowing the samples with proper acidity, consequently showing a strong inhibition effect on the by-product ethylbenzene. Moreover, a long-term stable operation (>300 h) is further achieved over the [Fe]-S-1 nanosheets by optimizing the content of framework Fe. This work elucidates the important relationship between acidity and alkylation activity.

Selective Hydrodeoxygenation of Guaiacol to Cyclohexane over Ru-Catalysts Based on MFI Nanosheets

Bio-oils derived from the pyrolysis of lignin-based biomass often contain a variety of oxygenated compounds, which can compromise their usefulness as a fuel. To improve the quality of bio-oil, catalytic hydrodeoxygenation (HDO) is a crucial step that removes oxygen from the oil in the form of water. In this study, we showed that MFI nanosheets are excellent supports for Ru-catalysts. We synthesized highly crystalline MFI nanosheets using a simple hydrothermal seeding procedure; the final material was obtained in 56 h of crystallization. We investigated the activity of Ru supported on different materials. Our findings indicated that Ru supported on hierarchical MFI demonstrated excellent activity in HDO of guaiacol. Our results demonstrated that Ru/ZNS-56 achieved nearly 100% selectivity towards cyclohexane under mild conditions (200 °C, 50 bar H2, 1 h).

Urea-assisted morphological engineering of MFI nanosheets with tunable b-thickness

Urea-assisted morphological engineering of MFI nanosheets with tunable b-thickness

Hybridizing zeolite MFI nanosheets with PTMSP membranes for enhanced butane isomer separations

Hybridizing zeolite nanosheets with a high aspect ratio has the potential to improve the gas separation performance of polymeric materials due to their good mechanical strength, thermal stability, and well-defined microporous structure. However, the use of zeolite-nanosheet-based mixed matrix membranes (MMMs) has been limited, and their effects on polymeric materials have not been studied thoroughly. In this study, zeolite MFI nanosheets were directly synthesized and introduced into PTMSP polymer using the shear-coating method. This resulted in a horizontally aligned structure with preferentially b-oriented zeolite MFI fillers. The straight b-channels of zeolite MFI facilitated fast gas permeation, while the high aspect ratio increased the tortuosity for non-permeable gases. The elastic modulus of the composite increased from 306 MPa to 2069 MPa as the zeolite MFI nanosheet content was increased to 50 wt%. The membrane was thermally stable up to 285 °C due to the protection provided by the zeolite MFI filler, which prevented thermal degradation by oxygen. The gas separation performance was improved, with a butane isomer selectivity of 7.3 and a permeability of 5400 barrer, a 20% increase from the neat PTMSP membrane. The selectivity was well preserved even in the binary mixture of butane isomers gas permeation test at 1 bar, while the neat PTMSP membrane showed a dramatic decrease in selectivity under this condition. The compatibility between the nanosheets and the polymer is expected to be important in achieving high separation performance of the composite membrane, as can be inferred from the large difference between the performance predicted by the modified Cussler model and the actual performance.

Twin suppression effect of dihydroxy-benzene isomers during the secondary growth of b-oriented zeolite MFI nanosheet films

MFI twin crystals on b-axis oriented zeolite MFI nanosheet films were suppressed in the presence of dihydroxybenzene isomers. The resulting films presented an ultra-thin grain thickness of 30–45 nm within hours.

Morphology evolution of zeolite MFI nanosheet fragments during secondary growths

Two-dimensional zeolite materials (nanosheets) offer facile ways to fabricate highly selective separation membranes; however, synthetic methods for non-aggregated zeolite nanosheets are still limited. For MFI-type zeolite materials, their nanosheets can be directly synthesized by the seeded growth with diammonium-cation structure-directing agents (SDA). In this study, we further investigated the secondary growth of zeolite MFI nanosheet fragments using diammonium-cation SDAs, to expand our knowledge on the self-regulated growth of zeolite MFI crystals. Owing to the absence of rotational intergrowth, nanosheet-fragment seeds yield zeolite MFI nanosheets with improved uniformity in thickness and shape, facilitating the investigation of their morphological variation under extensive synthesis conditions. This revealed that two distinct nanosheet morphologies, with strongly coupled shapes and predominant thicknesses, can be acquired depending on the synthesis temperature. Particularly, the growth along the c-axis is facilitated with the increasing synthesis temperature, thereby yielding flat zeolite MFI nanosheets with slight thickening. The isolated ad-layers on these nanosheets confirm that the thickening of nanosheets evolves with 2-nm step growth, which is identical to the nanosheet formation from cylindrical nanocrystal seeds. Finally, fractions of rhombus-shaped and rectangular nanosheets vary with the type of fragment seeds, indicating that the transition between those two nanosheets is kinetically hindered. The growth of zeolite MFI nanosheets using the diammonium-cation SDAs provides valuable insights on zeolite crystal growths, which will promote advanced synthesis techniques for the morphology control of zeolites and, probably, other molecular sieve materials.

Ex-situ catalytic co-pyrolysis of sawdust and municipal solid waste based on multilamellar MFI nanosheets to obtain hydrocarbon-rich bio-oil

In this study, H-type multilamellar MFI nanosheets (HMMN) were used for the catalytic reforming of municipal solid waste (MSW) and sawdust co-pyrolysis products to produce high-value bio-oil. Moreover, the catalytic deoxygenation performance of HMMN was studied. HMMN contains abundant surface area, mesopore volume, and a high ratio of Brønsted acid sites to Lewis acid sites. According to the results of thermogravimetric analysis (TGA), adding MSW improves the pyrolysis behaviors of sawdust by enhancing the escape of volatile matter. Analyzing the pyrolysis products reveals that a synergistic effect between sawdust and MSW promotes the formation of monocyclic aromatic hydrocarbons (MAHs) and reduces the relative yield of oxygen-containing compounds (OCCs), which facilitates further catalytic reforming for high-value bio-oil production. When the mass ratio of HMMN to sample is increased from 0% to 120%, the relative yield of MAHs increases from 15.64% to 53.5% (in 25%MSW), implying that HMMN exhibits high selectivity for MAHs. Furthermore, the content of OCCs is significantly reduced, with a maximum reduction of 58.2%. HMMN has a catalytic effect on the deoxygenation and aromatization of long-chain fatty acids and sugars. Relative to HZSM-5(38), HMMN exhibits higher aromatic hydrocarbon selectivity and a more significant inhibitory effect on the OCCs. Ex-situ catalytic reforming under HMMN is confirmed to be a feasible route to obtain hydrocarbon-rich bio-oil.

Fabrication of b-oriented MFI membranes from MFI nanosheet layers by ammonium sulfate modifier for the separation of butane isomers

Fabrication of thin and oriented zeolite membrane is highly preferable and challenging, providing the advantage of less resistance and high permeation for efficient molecular separation. MFI zeolite nanosheets serve as the desirable building block for fabricating thin and preferably b-oriented MFI membranes. However, the secondary growth of deposited MFI zeolite nanosheet layer is an indispensable aspect that comes with the challenges of sealing the nanoscale/interlayer gaps while preserving the orientation and controlling the thickness of fabricated zeolite membrane for efficient gas separation. Herein, ammonium sulfate assisted hydrothermal secondary growth of MFI nanosheet slip coated on the γ-Al2O3 disc was carried out to seal the nanoscale and interlayer gaps for the separation of butane isomers. The addition of ammonium sulfate helps to preserve the b-orientation of the deposited nanosheet layer and plays a critical role in tuning the thickness of the MFI membrane. Ammonium sulfate assisted thin MFI membrane was obtained with preserved b-orientation having a thickness of about 630 nm while exhibiting a separation factor and n-butane permeance of 41 and 1.10 × 10−7 mol m−2 s−1.Pa−1, respectively for the separation of butane isomers.

Facile synthesis of bifunctional Sn–B-self-pillared MFI zeolite nanosheets as highly selective catalyst for sucrose conversion to fructose

Herein, a bifunctional self-pillared MFI nanosheets zeolite (Sn-B-SPP) is designed to achieve the highly selective conversion of sucrose to fructose, which is significant for utilization of the nature abundant sucrose. This Sn- and B-containing SPP zeolite was prepared through a facile solid-state ion exchange approach based on a B-SPP, which overcomes the difficulty of direct nucleation. Sn-B-SPP possesses the structural advantages of ultra-thin intergrown nanosheets materials such as high external surface area, extremely short diffusion length and highly exposed active sites, which are conducive for the conversion of bulky substrates. Meanwhile, the concerted Lewis acidity and weak Brønsted acidity are essential for the sucrose conversion in alcohol, achieving a 77.0% fructose yield in 4 h after hydrolysis, far surpassing the performance of its microporous analogue and conventional hierarchical Sn–B-MFI.

Molecular Simulations Probing the Adsorption and Diffusion of Ammonia, Nitrogen, Hydrogen, and Their Mixtures in Bulk MFI Zeolite and MFI Nanosheets at High Temperature and Pressure

Molecular Simulations Probing the Adsorption and Diffusion of Ammonia, Nitrogen, Hydrogen, and Their Mixtures in Bulk MFI Zeolite and MFI Nanosheets at High Temperature and Pressure

Tuning the Multi-Scale Structure of Mixed-Matrix Membranes for Upgrading CO2 Separation Performances

With virtue of high aspect ratio, high external surface area and tunable surface functionality, burgeoning two-dimensional (2D) materials have been widely applied in to preparing mixed matrix membranes (MMMs) for CO2 separation. A novel Pebax MH 1657-based MMM was fabricated by introducing post-synthetic processed and (3-aminopropyl)-diethoxymethyl silane (APDEMS) functionalized 2D MFI nanosheets (AP-L-MFI) as inorganic fillers to enhance CO2/CH4 separation process. The size of nanosheets was gradually reduced by post-synthetic processing, which can help lower their sedimentation rate and achieve uniform distribution of fillers in the matrix. APDEMS grafted on the surface of nanosheets increased their CO2 adsorption capacity and improved interfacial compatibility with matrix. The MMM containing 5 wt% of AP-L-MFI (AP-L-MFI-5 MMM) exhibited the optimum performance with CO2 permeability of 174.7 Barrer and CO2/CH4 selectivity of 41.1. The as-prepared MMM showed an improvement of 9.8% in CO2 permeability and 50% in CO2/CH4 selectivity compared to the MMM doped by 5 wt% pristine MFI nanosheets (MFI-5 MMM). Moreover, benefiting from the improved filler dispersion and interfacial interaction, the optimal AP-L-MFI-5 MMM gave rise to a 23% higher tensile Young’s modulus and a 74% higher strain at break over MFI-5 MMM.

Twin-free, directly synthesized MFI nanosheets with improved thickness uniformity and their use in membrane fabrication.

Zeolite nanosheets can be used for the fabrication of low-defect-density, thin, and oriented zeolite separation membranes. However, methods for manipulating their morphology are limited, hindering progress toward improved performance. We report the direct synthesis (i.e., without using exfoliation, etching, or other top-down processing) of thin, flat MFI nanosheets and demonstrate their use as high-performance membranes for xylene isomer separations. Our MFI nanosheets were synthesized using nanosheet fragments as seeds instead of the previously used MFI nanoparticles. The obtained MFI nanosheets exhibit improved thickness uniformity and are free of rotational and MEL intergrowths as shown by transmission electron microscopy (TEM) imaging. The nanosheets can form well-packed nanosheet coatings. Upon gel-free secondary growth, the obtained zeolite MFI membranes show high separation performance for xylene isomers at elevated temperature (e.g., p-xylene flux up to 1.5 × 10−3 mol m−2 s−1 and p-/o-xylene separation factor of ~600 at 250°C).

Synthesis and Characterization of Sn, Ge, and Zr Isomorphous Substituted MFI Nanosheets for Glucose Isomerization to Fructose.

Invited for a cover feature this month is the research group of Asst. Prof. Dr. Chularat Wattanakit from School of Energy Science and Engineering, Vidyasirimedhi Institute of Science and Technology (VISTEC), Thailand. The cover picture shows the facile synthesis of Sn, Ge, and Zr isomorphously substituted MFI with hierarchical structures by a one-pot hydrothermal process. These designed materials illustrate the promising catalytic performance in glucose isomerization to fructose. More information can be found in the Full Paper by Chularat Wattanakit, and co-workers.

Cover Feature: Synthesis and Characterization of Sn, Ge, and Zr Isomorphous Substituted MFI Nanosheets for Glucose Isomerization to Fructose (ChemPlusChem 1/2022)

The cover feature shows the fabrication of isomorphous substituted MFI nanosheets. They were shown to remarkably improve the catalytic activity in glucose conversion to fructose due to the major contribution of tetrahedrally coordinated Sn in the framework together with hierarchical structures, eventually facilitating molecular transportation of bulky molecules to the active sites. More information can be found in the Full Paper by Chularat Wattanakit, and co-workers.

Ethanol and Water Adsorption in Conventional and Hierarchical All-Silica MFI Zeolites.

Hierarchical zeolites containing both micro- (<2 nm) and mesopores (2-50 nm) have gained increasing attention in recent years because they combine the intrinsic properties of conventional zeolites with enhanced mass transport rates due to the presence of mesopores. The structure of the hierarchical self-pillared pentasil (SPP) zeolite is of interest because all-silica SPP consists of orthogonally intergrown single-unit-cell MFI nanosheets and contains hydrophilic surface silanol groups on the mesopore surface while its micropores are nominally hydrophobic. Therefore, the distribution of adsorbed polar molecules, like water and ethanol, in the meso- and micropores is of fundamental interest. Here, molecular simulation and experiment are used to investigate the adsorption of water and ethanol on SPP. Vapor-phase single-component adsorption shows that water occupies preferentially the mesopore corner and surface regions of the SPP material at lower pressures (P/P 0 < 0.5) while loading in the mesopore interior dominates adsorption at higher pressures. In contrast, ethanol does not exhibit a marked preference for micro- or mesopores at low pressures. Liquid-phase adsorption from binary water-ethanol mixtures demonstrates a 2 orders of magnitude lower ethanol/water selectivity for the SPP material compared to bulk MFI. For very dilute aqueous solutions of ethanol, the ethanol molecules are mostly adsorbed inside the SPP micropore region due to stronger dispersion interactions and the competition from water for the surface silanols. At high ethanol concentrations (C EtOH > 700 g L-1), the SPP material becomes selective for water over ethanol.

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.

Synthesis and Characterization of Sn, Ge, and Zr Isomorphous Substituted MFI Nanosheets for Glucose Isomerization to Fructose

Various metals including Sn, Ge, and Zr have been successfully incorporated into the MFI nanosheets via a one-pot synthesis. The as-synthesized zeolites exhibit high external surface area and mesopore volume without large metal oxides aggregated on zeolite surfaces. Interestingly, the successful introduction of heteroatoms in MFI nanosheets can be confirmed by shifted XRD peaks corresponding to the unit cell expansion due to the replacement of metals into the framework. In addition, the UV-Vis absorbance spectra reveal that at the suitable metal loading the incorporated tetrahedral coordination of metal species in the zeolite framework has been obtained. To illustrate the benefits of the prepared catalysts, the glucose isomerization to fructose was carried out in a water/dioxane system. Obviously, the SnMFI-NS samples, containing the high dispersion of metal isomorphous species demonstrate the outstanding catalytic behavior in term of fructose selectivity (>85 %).

Pebax/two-dimensional MFI nanosheets mixed-matrix membranes for enhanced CO2 separation

Zeolite crystals as inorganic fillers were widely applied in fabricating mixed matrix membranes (MMMs) for CO2 separation. The poor filler-matrix interaction and the aggregation of high-loaded fillers in MMMs restrict their advantage of overcoming the trade-off limitation between permeability and selectivity. The novel MMMs with two-dimensional (2D) MFI nanosheets as inorganic fillers and Pebax MH 1657 as the matrix were synthesized and applied to achieve an efficient separation of CO2/CH4 gas mixture for the first time. The large interfacial contact areas between MFI nanosheets and Pebax matrix improve their compatibility to form defect-free MMMs with better mechanical properties. The high-aspect-ratio MFI nanosheets function as solid and selective barriers to make MMMs possess a significant promotion in both CO2 permeability and CO2/CH4 selectivity without the trade-off limitation. The MMM containing 5 wt% of MFI nanosheets exhibited the optimum performance with CO2 permeability of 159.1 Barrer and CO2/CH4 selectivity of 27.4. The as-prepared MMMs showed an improvement of 63.5% in CO2 permeability and 76.4% in CO2/CH4 selectivity, compared to pristine Pebax membranes.