Aluminosilicate Zeolites Research Articles

Rejection of heavy metal ions in water by zeolite forward osmosis membrane

Water treatment of heavy metals using zeolite membranes in forward osmosis was demonstrated. A continuous Na-ZSM-5, aluminosilicate zeolite, crystal layer was synthesized on the outer surface of a porous tubular α-alumina support and used as the forward osmosis membrane. The rejection performances and fouling resistances of Na-ZSM-5 membrane were studied. Na-ZSM-5 membrane exhibited a high rejection performance of 99 % for various metal species (As(III), As(V), Se(IV), Se(VI), Cr(VI)). This superior rejection performance was achieved by combining the molecular sieving effect and electrostatic repulsion between the anions and the anionic framework of the zeolite. Na-ZSM-5 membrane exhibited a stable water flux in the presence of model foulants such as sodium alginate, humic acid, bovine serum albumin, and silica particles, suggesting that the membrane had excellent antifouling properties against both organic and inorganic foulants.

Rapid Synthesis of Nine-Membered-Ring STT Aluminosilicate Zeolite from Chain Rearrangement of Lamella MWW Zeolite and Its Catalytic Performance in the Methanol-to-Olefin Reaction

Rapid Synthesis of Nine-Membered-Ring STT Aluminosilicate Zeolite from Chain Rearrangement of Lamella MWW Zeolite and Its Catalytic Performance in the Methanol-to-Olefin Reaction

Preparation of MAZ-Type Zeolite with High Silica.

The Si/Al molar ratio of MAZ aluminosilicate zeolite prepared by the direct hydrothermal method is generally less than five, thus giving rise to poor thermal and hydrothermal stability for this low-silica zeolite. With the purpose of enhancing the Si/Al molar ratio of MAZ zeolite, post-synthesized methods including acetic acid treatment and steaming treatment, as well as interzeolite transformation from FAU zeolite, were employed to prepare MAZ zeolite with high silica. It was found that steaming treatment was more effective in increasing the Si/Al molar ratio in comparison with acetic acid treatment, affording a maximum Si/Al molar ratio of 16.9 along with a preserved crystallinity of approximately 75%. Additionally, high-silica MAZ zeolite with a Si/Al molar ratio of up to 7.3 was also capable of being directly hydrothermally synthesized using interzeolite transformation from FAU zeolite.

Zeolites and their composites as novel remediation agent for antibiotics: A review

Antibiotic residues in aquatic environments pose significant challenges when exceeding permissible limits. Zeolites, particularly aluminosilicate zeolites, have emerged as effective adsorption materials and solid substrates for semiconductor photocatalysts, facilitating the removal of antibiotics from wastewater. This review highlights the versatility of zeolites and their composites in antibiotic remediation, showcasing recent advancements in adsorption and photocatalytic degradation. Noteworthy examples include Fe (III)-modified synthetic zeolite 13X, exhibiting a maximum tetracycline adsorption capacity of approximately 200 mg/g, and MoS2@Zeolite achieving a remarkable efficiency of 396.70 mg/g for tetracycline removal. Additionally, zeolite-based photocatalysts like Fe-TiO2/BEA zeolite and exceptional CdS/CaFe2O4-clinoptilolite demonstrate high removal percentages, reaching 100% for tetracycline and 86% for cefazolin, respectively. The discussion encompasses an introduction to zeolites, including synthetic and natural zeolites, as well as techniques for modifying natural zeolites. It further delves into the production of synthetic zeolites as well as the fabrication of zeolite-based composite materials. These findings underscore the potential of zeolites and their composites as novel remediation agents for tackling antibiotic contamination in aquatic ecosystems, paving the way for sustainable wastewater treatment strategies. It highlights key elements, distinct qualities, and areas needing further research, paving the way for future studies.

A reactive neural network framework for water-loaded acidic zeolites

Under operating conditions, the dynamics of water and ions confined within protonic aluminosilicate zeolite micropores are responsible for many of their properties, including hydrothermal stability, acidity and catalytic activity. However, due to high computational cost, operando studies of acidic zeolites are currently rare and limited to specific cases and simplified models. In this work, we have developed a reactive neural network potential (NNP) attempting to cover the entire class of acidic zeolites, including the full range of experimentally relevant water concentrations and Si/Al ratios. This NNP has the potential to dramatically improve sampling, retaining the (meta)GGA DFT level accuracy, with the capacity for discovery of new chemistry, such as collective defect formation mechanisms at the zeolite surface. Furthermore, we exemplify how the NNP can be used as a basis for further extensions/improvements which include data-efficient adoption of higher-level (hybrid) references via Δ-learning and the acceleration of rare event sampling via automatic construction of collective variables. These developments represent a significant step towards accurate simulations of realistic catalysts under operando conditions.

Synthesis‐structure‐catalysis relations in CHA zeolites applied for selective catalytic reduction of NOx with ammonia

Microporous aluminosilicate zeolites are useful industrial catalysts. However, their hydrothermal synthesis is a multistep process with complicated and unclear reactions, limiting their rational functional design. Herein, we compare the formation pathway and the structural and catalytic properties of several CHA zeolites to obtain fundamental knowledge for intentionally controlling the catalytic function of zeolites. Three CHA zeolites were synthesized using different starting silica/alumina sources in the presence of tetraethylammonium hydroxide as an inexpensive organic structure‐directing agent. FAU zeolite and an amorphous synthesis gel prepared using two different methods were used as starting materials. The obtained CHA zeolites were applied for exhaust gas purification (selective catalytic reduction of NOx with ammonia, NH3‐SCR), and their structural characteristics and formation pathways were investigated using a combination of analytical methods. Stepwise gel preparation (SGP), which divides the compositional control of the amorphous synthesis gel, promotes the decomposition of the initial additive (zeolite seed), resulting in the formation of CHA zeolites with abundant micropores and paired Al sites. This structural feature obtained using the SGP method improves the catalytic durability of the NH3‐SCR reaction. The present relationship, including different crystallization phenomena, structures, and catalytic abilities, provides useful insights into rational zeolite synthesis and its application.

Hydrophobic nanosheet silicalite-1 zeolite for iodine and methyl iodide capture

Effective capture of radioactive iodine from nuclear fuel reprocessing is of great importance for public safety as well as the secure utility of nuclear energy. In this work, a hydrophobic nanosheet silicalite-1 (NSL-1) zeolite with an adjustable size was developed for efficient iodine (I2) and methyl iodide (CH3I) adsorption. The optimized all-silica zeolite NSL-1 exhibits an excellent I2 uptake capacity of 553 mg/g within 45 min and a CH3I uptake capacity of 262 mg/g within 1 h. Benefiting from the reduced thickness and enhanced porosity, microporous NSL-1 possesses enhanced iodine adsorption capacity and fast adsorption kinetics, which is a considerable high value among inorganic materials. Unexpectedly, the remarkable characters of high hydrophobicity, acid-resistance and anti-oxidation endow it a higher iodine uptake capacity than traditional aluminosilicate zeolites. More importantly, the high uptake selectivity toward I2 possessed by NSL-1 owing to its hydrophobic skeleton under simulated dynamic conditions. The low cost, facile and scalable synthesis of NSL-1 further highlights great prospects for applications in the nuclear industry. This work provides useful insights for designing efficient adsorbents for iodine capture.

Probing the Role of Acid Site Distribution on the Water Structure in Aluminosilicate Zeolites: Insights from Molecular Dynamics

Probing the Role of Acid Site Distribution on the Water Structure in Aluminosilicate Zeolites: Insights from Molecular Dynamics

Understanding the effect of spatially separated Cu and acid sites in zeolite catalysts on oxidation of methane

Unraveling the effect of spatially separated bifunctional sites on catalytic reactions is significant yet challenging. In this report, we investigate the role of spatial separation on the oxidation of methane in a series of Cu-exchanged aluminosilicate zeolites. Regulation of the bifunctional sites is done either through studying a physical mixture of Cu-exchanged zeolites and acidic zeolites or by systematically varying the Cu and acid density within a family of zeolite materials. We show that separated Cu and acid sites are beneficial for the formation of hydrocarbons while high-density Cu sites, which are closer together, facilitate the production of CO2. By contrast, a balance of the spatial separation of Cu and acid sites shows more favorable formation of methanol. This work will further guide approaches to methane oxidation to methanol and open an avenue for promoting hydrocarbon synthesis using methanol as an intermediate.

Interchain-expanded extra-large-pore zeolites.

Stable aluminosilicate zeolites with extra-large pores that areopen through rings of more than 12 tetrahedra could be used to process molecules larger than those currently manageable in zeolite materials. However, until very recently1-3, they proved elusive. In analogy to the interlayer expansion of layered zeolite precursors4,5, we report a strategy that yields thermally and hydrothermally stable silicates by expansion of a one-dimensional silicate chain with an intercalated silylating agent that separates and connects the chains. As a result, zeolites with extra-large pores delimited by 20, 16 and 16 Si tetrahedra along the three crystallographic directions are obtained. The as-made interchain-expanded zeolite contains dangling Si-CH3 groups that, by calcination, connect to each other, resulting in a true, fully connected (except possible defects) three-dimensional zeolite framework with a very low density. Additionally, it features triple four-ring units not seen before in any type of zeolite. The silicate expansion-condensation approach we report may be amenable to further extra-large-pore zeolite formation. Ti can be introduced in this zeolite, leading to a catalyst that isactive in liquid-phase alkene oxidations involving bulky molecules, which shows promise in the industrially relevant clean production of propylene oxide using cumene hydroperoxide as an oxidant.

Improving mechanical stability of ZSM-5 zeolite by defect-healing treatment

Aluminosilicate zeolites are a group of microporous materials widely used in numerous technical applications as catalysts, adsorbents and ion exchangers. Zeolites are subjected to mechanical stress throughout their lifecycle, resulting in the loss of their crystallinity and micropore volume. Therefore, developing zeolites with excellent mechanical properties is important. Recently, our group has reported a liquid-mediated, defect-healing treatment to eliminate the silanol defects in aluminosilicate zeolites with high Si/Al ratios, resulting in imparting extreme chemical stability against water vapor, one of the major chemical damages to destroy zeolite structures. Herein, we investigate an influence of a liquid-mediated, defect-healing treatment on the intrinsic mechanical features of zeolites. ZSM-5 is selected as the target zeolite in this study. Silanol defects in the parent ZSM-5 (HSZ-890HOA, Tosoh) are eliminated by a liquid-mediated, defect-healing treatment. The parent and healed zeolites are subjected to planetary ball milling to compare their mechanical stabilities. Planetary ball-milling treatments, such as rotation at 600 rpm, degrade the crystalline structures of both the parent and healed ZSM-5 with an increase in duration. The diffraction peaks corresponding to the MFI-type structure in parent ZSM-5 completely diminish after planetary ball milling for 60 min. Conversely, diffraction peaks in healed ZSM-5 were retained after such operations, confirming that the mechanical stability of zeolites was enhanced by the liquid-mediated, defect-healing treatment.

Unravelling Irreversible Adsorbate Thermodynamics through Adsorption-Assisted Desorption.

Strongly bound surface species like alkylamines adsorbed on the Brønsted acid site of aluminosilicate zeolites exhibit negligible rates of molecular desorption, preventing them from achieving an equilibrated state on experimentally relevant time scales that limit the measurement of their adsorption thermodynamics. Through adsorption-assisted desorption, whereby distinct alkylamines facilitate desorption from Brønsted acid sites, we demonstrate that equilibrated states are achieved. Breakthrough adsorption measurements reveal that while 2-butylammonium on a Brønsted acid site is irreversibly adsorbed, it readily undergoes molecular desorption when exposed to a distinct alkylamine like 2-propanamine. As a result, two-adsorbate equilibrium was achieved when the Brønsted acid sites of aluminosilicate zeolites were exposed to a binary vapor-phase alkylamine mixture. By varying relative vapor-phase partial pressures and temperatures, we demonstrate the ability to experimentally measure the adsorption enthalpy and entropy of alkylammonium adsorbates on mostly isolated Brønsted acid sites in H-ZSM-5 (Si/Al = 140). A multiadsorbate Langmuir isotherm was found to quantitatively describe the coadsorption of alkylamines varying in size and basicity over a wide range of conditions through which the relative adsorption enthalpy and entropy of alkylamines were measured. Across a homologous family of sec-alkylamines (C3-C5) adsorbed on isolated Brønsted acid sites, a fixed contribution to the enthalpy (19 ± 4 kJ mol CH2-1) and entropy (25 ± 4 J mol CH2-1 K-1) of adsorption per methylene unit was found to exist, likely resulting from electrostatic interactions between the alkyl chain and the surrounding pore environment.

A Hydrothermal Synthesis Process of ZSM-5 Zeolite for VOCs Adsorption Using Desilication Solution

ZSM-5 zeolite is a kind of high-value-added porous aluminosilicate zeolite. The use of the coal gasification slag utilization process by-product desilication liquid as a silicon raw material to replace the current raw materials such as water glass will help reduce production costs and achieve high-value utilization of solid waste. ZSM-5 zeolites for volatile organic compounds (VOCs) adsorption were prepared by a one-step hydrothermal method using the desilication solution prepared from coal gasification slag as the main silicon source and sodium source. The effects of crystallization reaction time, the crystallization temperature, the Na2O/SiO2 molar ratio, and the SiO2/Al2O3 molar ratio on the relative crystallinity and the specific surface area of the ZSM-5 zeolite were investigated and optimized. The optical reaction conditions were as follows: a crystallization time of 12 h, a crystallization temperature of 170 °C, a Na2O/SiO2 molar ratio of 0.2, and a SiO2/Al2O3 molar ratio of 200. The optimal ZSM-5 zeolite synthesized is hexagonal, with regular grains, a relative crystallinity of 101.48%, a specific surface area of 337.48 m2·g−1, and a pore volume of 0.190 cm3·g−1. And the optimal ZSM-5 zeolite was composed of SiO2 content of 97.52 wt%, Al2O3 content of 1.58 wt%, Na2O content of 0.33 wt%, and SiO2/Al2O3 molar ratio of 104.93. Na2O/SiO2 molar ratio is 0.0033. The results of static adsorption experiments show that the static adsorption capacities of ZSM-5 zeolite for p-xylene, benzene, toluene, and butyl acetate were 118.85, 69.98, 68.74, and 95.85 mg·g−1, respectively, which can effectively adsorb VOCs. The synthetic process of the ZSM-5 zeolite is a simple preparation process and short in synthesis time. The results of this study not only help to realize the high-value utilization of silicon components in solid waste, but also provide an economical and effective way to synthesize VOCs adsorption materials.

A fast crystallization of TUN zeolite via the interzeolite conversion method

Abstract A TUN-type aluminosilicate zeolite was rapidly synthesized via the interzeolite conversion method (IZC) using a MWW-type one as a starting material. It was found that the co-addition of the organic structure direct agent (OSDA) and the seed played a crucial role in accelerating the crystallization of the TUN phase. The TUN zeolite synthesized via the IZC method exhibited comparable physicochemical properties to those of the conventional one crystallized from amorphous silica and alumina materials.

Hollow Zeolite Nanoreactor with Double Shells for Methanol Aromatization: Explicit Recognition on Catalytic Function of Inverse Elemental Zone and Shell-Cavity.

Core@shell catalyst composited of dual aluminosilicate zeolite can effectively regulate the distribution of acid sites to control hydrocarbon conversion process for the stable formation of target product. However, the diffusion restriction reduces the accessibility of inner active sites and affects synergy between core and shell. Herein, hollow ZSM-5 zeolite nanoreactor with inverse aluminum distribution and double shells are prepared and employed for methanol aromatization. It is demonstrated that the intershell cavity alleviated the steric hindrance from zeolites channel and provided more paths and pore entrance for guest molecule. Correspondingly, olefin intermediates generated from methanol over the external shell are easier to adsorb at internal acid sites for further reactions. Importantly, the diffusion of generated aromatic macromolecules to the external surface is also promoted, which slows down the formation of internal coke, and ensures the use of internal acid sites for aromatization. The aromatics selectivity of the nanoreactor remained at 8% after 154h, while that of solid core@shell catalyst decreased to 2% after 75h. This finding promises broader insight to improve internal active site utilization of core@shell catalyst at the diffusion level and can be great aid in the flexible design of multifunctional nanoreactors to enhance the relay efficiency.

STEM SerialED: achieving high-resolution data for ab initio structure determination of beam-sensitive nanocrystalline materials.

Serial electron diffraction (SerialED), which applies a snapshot data acquisition strategy for each crystal, was introduced to tackle the problem of radiation damage in the structure determination of beam-sensitive materials by three-dimensional electron diffraction (3DED). The snapshot data acquisition in SerialED can be realized using both transmission and scanning transmission electron microscopes (TEM/STEM). However, the current SerialED workflow based on STEM setups requires special external devices and software, which limits broader adoption. Here, we present a simplified experimental implementation of STEM-based SerialED on Thermo Fisher Scientific STEMs using common proprietary software interfaced through Python scripts to automate data collection. Specifically, we utilize TEM Imaging and Analysis (TIA) scripting and TEM scripting to access the STEM functionalities of the microscope, and DigitalMicrograph scripting to control the camera for snapshot data acquisition. Data analysis adapts the existing workflow using the software CrystFEL, which was developed for serial X-ray crystallography. Our workflow for STEM SerialED can be used on any Gatan or Thermo Fisher Scientific camera. We apply this workflow to collect high-resolution STEM SerialED data from two aluminosilicate zeolites, zeolite Y and ZSM-25. We demonstrate, for the first time, ab initio structure determination through direct methods using STEM SerialED data. Zeolite Y is relatively stable under the electron beam, and STEM SerialED data extend to 0.60 Å. We show that the structural model obtained using STEM SerialED data merged from 358 crystals is nearly identical to that using continuous rotation electron diffraction data from one crystal. This demonstrates that accurate structures can be obtained from STEM SerialED. Zeolite ZSM-25 is very beam-sensitive and has a complex structure. We show that STEM SerialED greatly improves the data resolution of ZSM-25, compared with serial rotation electron diffraction (SerialRED), from 1.50 to 0.90 Å. This allows, for the first time, the use of standard phasing methods, such as direct methods, for the ab initio structure determination of ZSM-25.

HYDROGEN ABSORBERS BASED ON POROUS CERAMICS SYNTHESIZED IN A SOLAR FURNACE

In this study, we investigated the processes of hydrogen absorption in porous ceramic materials sythesized in a solar furnace. We used burning additives inserted into ceramic materials and melted in a solar furnace in a high-density stream of concentrated solar radiation (200 W/cm<sup>2</sup>). The melt was cooled by pouring it into water at a cooling rate of 10<sup>3</sup>-10<sup>4</sup> degree/s. The castings were characterized by a fine-grained microstructure (in which the grain size did not exceed 10 µm). The crushed and molded samples were fired at a temperature of 1150°C for 2 hours. Thr results obtained showed that the sodium aluminosilicate zeolite ceramic porous material based on a mixture of aluminum powder, quartz sand, and polyvinyl alcohol exhibited high hydrogen absorption-up to 13% (at temperature = 250°C and pressure = 13 atm).

A machine learning approach for dynamical modelling of Al distributions in zeolites via23Na/27Al solid-state NMR.

One of the main limitations in supporting experimental characterization of Al siting/pairing via modelling is the high computational cost of ab initio calculations. For this reason, most works rely on static or very short dynamical simulations, considering limited Al pairing/siting combinations. As a result, comparison with experiment suffers from a large degree of uncertainty. To alleviate this limitation we have developed neural network potentials (NNPs) which can dynamically sample across broad configurational and chemical spaces of sodium-form aluminosilicate zeolites, preserving the level of accuracy of the ab initio (dispersion-corrected metaGGA) training set. By exploring a wide range of Al/Na arrangements and a combination of experimentally relevant Si/Al ratios, we found that the 23Na NMR spectra of dehydrated high-silica CHA zeolite offer an opportunity to assess the distribution and pairing of Al atoms. We observed that the 23Na chemical shift is sensitive not only to the location of sodium in 6- and 8MRs, but also to the Al-Sin-Al sequence length. Furthermore, neglect of thermal and dynamical contributions was found to lead to errors of several ppm, and has a profound influence on the shape of the spectra and the dipolar coupling constants, thus necessitating the long-term dynamical simulations made feasible by NNPs. Finally, we obtained a predictive regression model for the 23Na chemical shift in CHA (Si/Al = 35, 17, 11) that circumvents the need for expensive NMR density functional calculations and can be easily extended to other zeolite frameworks. By combining NNPs and regression methods, we can expedite the simulations of NMR properties and capture the effect of dynamics on the spectra, which is often overlooked in computational studies despite its clear manifestation in experimental setups.

Conversion of NOx over Aluminosilicate Cu-CHA Zeolite Catalysts Synthesized Free of Organic Structure-Directing Agents

Cu-CHA zeolites have proven to be effective for NOx reduction, but a drawback in using CHA zeolites is the cost associated with using expensive organic structure-directing agents. To overcome this drawback, we are reporting here the synthesis of Cu-CHA zeolite catalysts in both their NH4-form as well as K-form that do not require the use of organic structure-directing agents. After comprehensive characterization by XRF, XRD, 27Al NMR spectroscopy, FE-SEM, SEM/EDS, N2-adsorption/desorption, NH3-TPD, H2-TPR, and XPS, the zeolite catalysts were tested for NOx conversion by NH3-selective catalytic reduction (NH3-SCR). Cu-NH4-CHA zeolite catalysts exhibited remarkable activity and thermal stability over a wide temperature window, outperforming their counterpart K-forms. Among the NH4-forms of CHA zeolite catalysts, the 0.1 M Cu-NH4-CHA showed the best catalytic performance, achieving 50% NOx conversion at a temperature as low as 192 °C, and reaching full conversion of NOx at 261 °C. These Cu-based CHA zeolite catalysts are promising thanks to their environmentally friendly synthesis and offer the opportunity of maximizing DeNOx strategies in applications for NOx pollution abatement.

Paired Site Characterization in Aluminosilicate Zeolites through Limited Alkylammonium Stability

Paired Site Characterization in Aluminosilicate Zeolites through Limited Alkylammonium Stability