Polycrystalline Zeolite Research Articles

Implanting Colloidal Nanoparticles into Single-Crystalline Zeolites for Catalytic Dehydration.

The encapsulation of functional colloidal nanoparticles (100 nm) into single-crystalline ZSM-5 zeolites, aiming to create uniform core-shell structures, is a highly sought-after yet formidable objective due to significant lattice mismatch and distinct crystallization properties. In this study, we demonstrate the fabrication of a core-shell structured single-crystal zeolite encompassing an Fe3O4 colloidal core via a novel confinement stepwise crystallization methodology. By engineering a confined nanocavity, anchoring nucleation sites, and executing stepwise crystallization, we have successfully encapsulated colloidal nanoparticles (CN) within single-crystal zeolites. These grafted sites, alongside the controlled crystallization process, compel the zeolite seed to nucleate and expand along the Fe3O4 colloidal nanoparticle surface, within a meticulously defined volume (1.5×107≤V≤1.3×108 nm3). Our strategy exhibits versatility and adaptability to an array of zeolites, including but not restricted to ZSM-5, NaA, ZSM-11, and TS-1 with polycrystalline zeolite shell. We highlight the uniformly structured magnetic-nucleus single-crystalline zeolite, which displays pronounced superparamagnetism (14 emu/g) and robust acidity (~0.83 mmol/g). This innovative material has been effectively utilized in a magnetically stabilized bed (MSB) reactor for the dehydration of ethanol, delivering an exceptional conversion rate (98 %), supreme ethylene selectivity (98 %), and superior catalytic endurance (in excess of 100 hours).

Implanting Colloidal Nanoparticles into Single‐Crystalline Zeolites for Catalytic Dehydration

AbstractThe encapsulation of functional colloidal nanoparticles (100 nm) into single‐crystalline ZSM‐5 zeolites, aiming to create uniform core–shell structures, is a highly sought‐after yet formidable objective due to significant lattice mismatch and distinct crystallization properties. In this study, we demonstrate the fabrication of a core–shell structured single‐crystal zeolite encompassing an Fe3O4 colloidal core via a novel confinement stepwise crystallization methodology. By engineering a confined nanocavity, anchoring nucleation sites, and executing stepwise crystallization, we have successfully encapsulated colloidal nanoparticles (CN) within single‐crystal zeolites. These grafted sites, alongside the controlled crystallization process, compel the zeolite seed to nucleate and expand along the Fe3O4 colloidal nanoparticle surface, within a meticulously defined volume (1.5×107≤V≤1.3×108 nm3). Our strategy exhibits versatility and adaptability to an array of zeolites, including but not restricted to ZSM‐5, NaA, ZSM‐11, and TS‐1 with polycrystalline zeolite shell. We highlight the uniformly structured magnetic‐nucleus single‐crystalline zeolite, which displays pronounced superparamagnetism (14 emu/g) and robust acidity (~0.83 mmol/g). This innovative material has been effectively utilized in a magnetically stabilized bed (MSB) reactor for the dehydration of ethanol, delivering an exceptional conversion rate (98 %), supreme ethylene selectivity (98 %), and superior catalytic endurance (in excess of 100 hours).

High-throughput phase elucidation of polycrystalline materials using serial rotation electron diffraction

Rapid phase elucidation of polycrystalline materials is essential for developing new materials of chemical, pharmaceutical and industrial interest. Yet, the size and quantity of many crystalline phases are too small for routine X-ray diffraction analysis. This has become a workflow bottleneck in materials development, especially in high-throughput synthesis screening. Here we demonstrate the application of serial rotation electron diffraction (SerialRED) for high-throughput phase identification of complex polycrystalline zeolite products. The products were prepared from a combination of multiple framework T atoms ([Si,Ge,Al] or [Si,Ge,B]) and a simple organic structure-directing agent. We show that using SerialRED, five zeolite phases can be identified from a highly complex mixture. This includes phases with ultra-low contents undetectable using X-ray diffraction and phases with identical crystal morphology and similar unit cell parameters. By automatically and rapidly examining hundreds of crystals, SerialRED enables high-throughput phase analysis and allows the exploration of complex synthesis systems. It provides new opportunities for rapid development of polycrystalline materials.

Optimal zeolite structure design for VOC emission reduction in asphalt materials

Asphalt releases a large amount of VOC when it is being heated, which is harmful to both workers and environment. Literatures indicates that porous materials might reduce asphalt VOC through physical adsorption and chemical adsorption, so that zeolite material is promoted to reduce the asphalt VOC due to its adsorption and catalytic properties. In this study, the VOC from zeolite-modified asphalt with different Si/Al ratio, particle size and crystal form were compared to explore the influence law of three zeolite structural characteristics on VOC reduction effect. Results show that Si/Al ratio influence the released VOC types. Small Si/Al ratio leads to inhibit branched alkanes, while large Si/Al ratios leads to inhibit alkenes and cyclic substances. Zeolite particle size has a greater impact on VOC emission amount than that of Si/Al ratio. Larger particle size has a better VOC reduction effect. Nano polycrystalline zeolite has stronger VOC reduction effect than single crystal zeolite. Above all, nano-polycrystalline zeolite with large particle size is a better choice to reduce benzene series.

Low-temperature ozone treatment for p-xylene perm-selective MFI type zeolite membranes: Unprecedented revelation of performance-negating cracks larger than 10 nm in polycrystalline membrane structures

We report that low-temperature ozone calcination allowed MFI type polycrystalline zeolite membranes to maximize their p-/o-xylene separation factor (as high as ca. 2000) by suppressing defect formation. Conventional high-temperature calcination and rapid thermal processing, which provide poor and marked p-/o-xylene separation abilities, respectively, were used for comparison. The corresponding defect structures were quantitatively analyzed by image processing of fluorescence confocal optical microscopy images combined with membrane permeation modeling, revealing the main defects (grain boundary defects and cracks) and their tortuosity, porosity, and size. To the best of our knowledge, we, for the first time, demonstrated that in contrast to common belief, the minor portion of wider cracks instead of the major portion of narrower grain boundary defects determined the final permeation rates. Specifically, the MFI membrane prepared by high-temperature calcination contained many grain boundary defects (narrow; ca. 1 nm) and few cracks (wide; ca. 20 nm) that accounted for ca. 0.1% and 99.8%, respectively, of the slowly permeating o-xylene molar flux. In contrast, the ozone-treated MFI membranes, which only possessed grain boundary defects, achieved the high p-/o-xylene separation performance, underlining the need for the selective reduction in the number of wider cracks rather than ubiquitous, narrow grain boundary defects.

Cr(VI) adsorption by the polyanyline and zeolite/polyaniline–sulphuric acid composite

The adsorption properties of the samples of polyaniline (PAn) and zeolite/polyaniline (Zt/PAn) composite regard to Cr(VI) have been studied. The samples of the PAn and Zt/PAn composite were prepared in the 0.5 M sulfuric acid aqueous solution by oxidative polycondensation of aniline by ammonium peroxydisulfate respectively under the presence and absence of the zeolite powder in the reaction mixture. The molar ratio of aniline to ammonium peroxydisulfate during synthesis was 1 : 1.1, while the weight ratio of aniline to zeolite was equal to 1 : 1. The formation of PAn and Zt/PAn composite was confirmed by X-ray phase analysis, FT-IR spectroscopy, thermogravimetric studies and results of electrical conductivity measurements. Analysis of the spectral, thermal and electrical properties of the synthesized samples of Zt/PAn composites showed their essential differences in relation to individual samples of the zeolite and polyaniline. It was determined that the structure of polyaniline in the synthesized samples of PAn and Zt/PAn is amorphous with insignificant inclusions of polyaniline crystallites (in the form of emeraldine salt of sulfuric acid) deposited on polycrystalline zeolite particles as carrier-matrices. Thermogravimetric studies of PAn samples and Zt/PAn composites confirmed the composition of composites and the dependence of their thermal stability on the content of natural mineral. The defined values of the specific conductivity for the synthesized samples of zeolite/polyaniline composites confirmed the presence of sulfuric acid in the composites. It is determined the availability and high efficiency of the use of PAn and Zt/PAn composites, in which polyaniline is doped by sulfuric acid during synthesis, for Cr(VI) sorption from aqueous solutions. It was demonstrated that Cr(VI) adsorption by produced samples can be described sufficiently good by Langmuir or Freundlich adsorption isotherms, while the kinetics of process is in good agreement with the model of pseudo second order. Keywords : polyaniline, zeolite/polyaniline, properties, adsorption of Cr(VI).

Simultaneous Electrochemical Sensing of Ceftriaxone and Piroxicam Using Zeolite Modified Electrode for Medical Applications

AbstractThe simultaneous sensing of Ceftriaxone (Cef) and Piroxicam (Pir) was presented in detail through the electrochemical method in which carbon paste electrode (CPE) was modified by meso‐structured Zeolite for medical application. The results indicated a polycrystalline Zeolite phase with a relatively high surface contact for charge transportation in the sensing process. Electrochemical impedance spectroscopy (EIS) plots also showed better charge transportation parameters for the modified electrode. The effect of analytes concentration, in both individual and simultaneous states, on the electrochemical sensor quality parameters was investigated by different methods and the obtained results were thoroughly discussed.

Sustainable synthesis of highly water-selective ZSM-5 membrane by wet gel conversion

High-performance zeolite socony mobil five (ZSM-5) membranes were successfully prepared on a cheap, tubular α-Al2O3 support via a proposed wet gel conversion (WGC), aiming at avoiding the competitive zeolite crystals growth in the solution and ensuring the formation of polycrystalline zeolite layer onto the support surface. A small amount of gel was loaded on seeded tubes via dip-coating and then converted to ZSM-5 membranes via direct crystallization without using any additional synthesis solution for membrane growth. By using this method, the amount of synthetic gel was largely reduced as compared with the traditional hydrothermal synthesis. The effects of crystallization temperature, crystallization duration, and synthetic gel silica source dissolution duration on the morphologies, microstructures, and pervaporation performances of ZSM-5 membranes were investigated. Under optimized synthesis conditions, the as-synthesized ZSM-5 membrane showed high separation performance and stability in isopropanol dehydration. During the 104-h pervaporation test, the permeation flux was stable at 2.96 kg m−2 h−1 with a separation coefficient exceeding 10,000. The synthetic route exhibited excellent reproducibility for the fabrication of highly water-selective ZSM-5 membrane. This work provides a novel, feasible method for the preparation of zeolite membranes with high performance, high atom economy, low cost, and reduced waste solution.

CoFe2O4 Nanocrystals Mediated Crystallization Strategy for Magnetic Functioned ZSM‐5 Catalysts

AbstractZeolites have many applications in the petrochemical and fine chemical industry and their functionalization does expand the spectrum of potentials. However, the integration of functional nanocrystals into zeolite frameworks with controlled size, dispersion, and crystallization behavior still remains a significant challenge. Here, a new synthesis of magnetic functioned ZSM‐5 zeolite catalysts via a CoFe2O4 nanocrystal mediated crystallization strategy is reported. It is found that high crystallinity of CoFe2O4 nanocrystals results in a well‐dispersed encapsulation of them into a single‐crystal of ZSM‐5 due to non‐further‐grown nanocrystals during the fast ZSM‐5 growth. On the contrary, low crystallinity of CoFe2O4 nanocrystals leads to the polycrystalline zeolite growth due to the secondary growth of nanocrystals accompanied by the zeolite crystallization and large lattice mismatch between them. The successful encapsulation of small CoFe2O4 nanocrystals (≈4 nm) into single crystals lies on the preattachment of them into solid silica gel. During the growth of ZSM‐5 crystals, no secondary growth of nanocrystals happens and its motion is restricted. The encapsulation of magnetic CoFe2O4 nanocrystals not only endows magnetic function into zeolites for the first time, but also does not impact catalytic performance of ZSM‐5 in acetalization of cyclohexanone with methanol, which is highly promising in catalytic industries.

Micro-structure change of polycrystalline FAU zeolite membranes during a hydrothermal synthesis in a dilute solution

Faujasite (FAU) zeolite membranes were prepared by seed growth method. The polycrystalline zeolite membrane became less porous with the growth of zeolite crystals. The microstructure of the membrane was characterized by SEM and TEM after several rates of crystal growth. In addition, Si/Al ratio was analysed by TEM-EDS. Meso-voids existed in the zeolite membrane after 1-h synthesis, and hexagonal shaped FAU crystals were easily distinguished. Twin relations were quite often observed for the connection between FAU crystals, while they were seldom found in the seed crystals. On the other hand, crystals lost hexagonal shape with further synthesis time. Moreover, the density of twin relations became less. While voids could hardly being observed by SEM in the zeolite membrane, there existed intercrystalline boundaries formed by two crystals of different orientation. Microstructures of these boundaries were directly observed by HREM. Si/Al ratio of the zeolite membrane was close to 1, which is smaller than that of seed crystals (Si/Al = 2.5). Step growth at the twin boundary was firstly observed. This growth process is assumed to be the key growth mechanism in densification of the polycrystalline zeolite membrane. Finally, densification process of zeolite membrane is proposed based on the microscopic analysis.

Fabrication of zeolite/polymer multilayer composite membranes for carbon dioxide capture: Deposition of zeolite particles on polymer supports

Membranes, due to their smaller footprint and potentially lower energy consumption than the amine process, offer a promising route for post-combustion CO2 capture. Zeolite Y based inorganic selective layers offer a favorable combination of CO2 permeance and CO2/N2 selectivity, membrane properties crucial to the economics. For economic viability on large scale, we propose to use flexible and scalable polymer supports for inorganic selective layers. The work described in this paper developed a detailed protocol for depositing thin zeolite Y seed layers on polymer supports, the first step in the synthesis of a polycrystalline zeolite Y membrane. We also studied the effects of support surface morphology (pore size and surface porosity) on the quality of deposition and identified favorable supports for the deposition. Two different zeolite Y particles with nominal sizes of 200nm and 40nm were investigated. To obtain a complete coverage of zeolite particles on the support surface with minimum defects and in a reproducible manner, a vacuum-assisted dip-coating technique was developed. Images obtained using both digital camera and optical microscope showed the presence of color patterns on the deposited surface which suggested that the coverage was complete. Electron microscopy revealed that the particle packing was dense with some drying cracks. Layer thickness with the larger zeolite Y particles was close to 1μm while that with the smaller particles was reduced to less than 0.5μm. In order to reduce drying cracks for layers with smaller zeolite Y particles, thickness was reduced by lowering the dispersion concentration. Transport measurement was used as an additional technique to characterize these layers.

Pore structure characterization of supported polycrystalline zeolite membranes by positron annihilation spectroscopy

It is important to characterize the pore structure of supported polycrystalline zeolite membranes but it has remained a major challenge in studying microporous inorganic membranes. This paper reports the use of positron annihilation spectroscopy including positron annihilation lifetime spectroscopy and Doppler broadening energy spectroscopy to non-destructively characterize the pore structure of four MFI zeolite membranes of different microstructures on alumina supports. Positron annihilation lifetime spectroscopy analysis reveals a bimodal pore structure consisting of intracrystalline zeolitic micropores of around 0.6nm in diameter and irregular intercrystalline micropores of 1.4−1.8nm in size for the four MFI zeolite membranes studied. Distributions of the micropores along the membrane thickness direction can be inferred from Doppler broadening energy spectroscopy results, illustrating development of intercrystalline gaps during the growth of the zeolite layer. The amount and size of the intercrystalline micropores of the zeolite membranes vary with the synthesis method, and are the smallest for the randomly oriented MFI zeolite membrane synthesized without template and the largest for the c-oriented MFI zeolite membrane synthesized with the template. The c-oriented membrane has an asymmetrical distribution of intercrystalline pores along the film growth direction as compared to the uniform distribution of the bimodal structure for the other three membranes. The pore structure data obtained by positron annihilation spectroscopy are consistent with the xylene isomer separation performance of these membranes.

Preparation of Na‐P1‐Type Zeolite and its Composite Material with Nanosized Magnetite

The Na‐P1‐type zeolite having a high cation‐exchange capacity (CEC) was obtained using the waste coal fly ash from thermal power stations and a 2M NaOH solution at 100°C. The Na‐P1‐type zeolite was formed with the reaction time of 6 h at 100°C, and its CEC value increased with an increase in the reaction time. The addition of a suitable amount of NaAlO2 to the fly ash was also effective for improving the CEC value. A new composite material consisting of the Na‐P1‐type zeolite and magnetite was synthesized from the fly ash and iron chlorides because the magnetic collection was possible using this composite material after radioactive Cs+ ion adsorption. The existence of nanosized magnetites in the polycrystalline zeolite (several micrometers) was confirmed by TEM observations. The CEC and magnetic property of these composite materials were characterized.

Effect of MFI zeolite intermediate layers on gas separation performance of carbon molecular sieve (CMS) membranes

To strengthen interfacial adhesion between selective carbon molecular sieve (CMS) layers and α-Al2O3 substrates, mordenite framework inverted (MFI)-type intermediate layers were synthesized to reduce pore sizes and improve chemical characteristics of underlying substrates and consequently facilitate formation of CMS layers. MFI-type zeolite intermediate layers were prepared on α-Al2O3 substrates via secondary growth of seeds to form polycrystalline zeolite layers with a-oriented crystallites. These crystallites increased cross-link strength between separation layers as well as gas pair separation performance. When a porous substrate was treated with silica seeds and covered with an MFI intermediate layer, CMS selectivity for H2/CH4 increased to 260.9 with permeability towards H2 of 2224Barrer. These modifications improved the mechanical stability of CMS layers and will assist in their commercialization.

Preparation of Composite Material of Na-P1-Type Zeolite and Magnetite for Cs Decontamination

Abstract For the decontamination of radioactive 134Cs and 137Cs using magnetic collection, a new composite material consisting of a Na-P1-type zeolite and magnetite was synthesized from the waste fly-ash from thermal power stations and iron chlorides. The presence of nanosized magnetites in the polycrystalline zeolite (several micrometers) was confirmed by TEM observations. The cation-exchange capacity (CEC) and magnetic properties of these composite materials were characterized.

Patterson selectivity by modulation-enhanced diffraction

Modulation excitation spectroscopy is a powerful and well established technique for investigating the dynamic behaviour of chemical and physical systems. Recently, an expansion of this technique for diffraction was proposed and the theory deriving the diffraction response of a crystal subjected to a periodically varying external perturbation was developed [Chernyshov, van Beek, Emerich, Milanesio, Urakawa, Viterbo, Palin & Caliandro (2011).Acta Cryst.A67, 327–335]. The result of this is that a substructure composed of atoms actively responding to the stimulus may be separated out by analysing the diffraction signal at a frequency twice that of the stimulus. This technique is called modulation-enhanced diffraction. Here, a version of the theory dealing with the modulation of the site occupancies of a selected subset of atoms is formulated, and this is supported by experiments carried out at the Swiss–Norwegian Beam Lines at the ESRF, involving periodic variation of the xenon content of a polycrystalline zeolite as a function of temperature. The data analysis involves three steps: (i) data selection is carried out to mimic a linear response; (ii) phase-sensitive detection is applied to obtain contributions both from the responding part of the electron density associated with the Xe atoms and from the interference term; (iii) a phasing procedure is applied to both. A Patterson deconvolution technique has been successfully used to phase the demodulated diffraction patterns and obtain the active substructure.

Synthesis of zeolite composite from alkali processing of cordierite powder

Zeolite phases of Z-21, zeolite P, and basic sodalite were successfully synthesized via a reaction between the commercial cordierite powder and boiling NaOH solution under atmospheric pressure. The phase change of as-prepared products was investigated using XRD analyses. The most well crystallized zeolite composite was isolated from these products. Such a composite consists of cubical Z-21 and polycrystalline zeolite P crystals with homogeneous particle size of about 5 μm. The composite is thermally stable below 250 °C. A remarkable cation exchange capacity of 377.06 cmol/kg is determined using the modified ammonium acetate saturation method, which makes it desirable candidate as ion-exchange media.

Zeolite Membranes: Microstructure Characterization and Permeation Mechanisms

Since their first synthesis in the 1940s, zeolites have found wide applications in catalysis, ion-exchange, and adsorption. Although the uniform, molecular-size pores of zeolites and their excellent thermal and chemical stability suggest that zeolites could be an ideal membrane material, continuous polycrystalline zeolite layers for separations were first prepared in the 1990s. Initial attempts to grow continuous zeolite layers on porous supports by in situ hydrothermal synthesis have resulted in membranes with the potential to separate molecules based on differences in molecular size and adsorption strength. Since then, further synthesis efforts have led to the preparation of many types of zeolite membranes and better quality membranes. However, the microstructure features of these membranes, such as defect size, number, and distribution as well as structure flexibility were poorly understood, and the fundamental mechanisms of permeation (adsorption and diffusion), especially for mixtures, were not clear. These gaps in understanding have hindered the design and control of separation processes using zeolite membranes. In this Account, we describe our efforts to characterize microstructures of zeolite membranes and to understand the fundamental adsorption and diffusion behavior of permeating solutes. This Account will focus on the MFI membranes which have been the most widely used but will also present results on other types of zeolite membranes. Using permeation, x-ray diffraction, and optical measurements, we found that the zeolite membrane structures are flexible. The size of defects changed due to adsorption and with variations in temperature. These changes in defect sizes can significantly affect the permeation properties of the membranes. We designed methods to measure mixture adsorption in zeolite crystals from the liquid phase, pure component adsorption in zeolite membranes, and diffusion through zeolite membranes. We hope that better understanding can lead to improved zeolite membranes and eventually facilitate the large-scale application of zeolite membranes to industrial separations.

Investigation on the pore structure of binderless zeolite 13× shapes

In the last few years novel binderless molecular sieves as high-performance materials were introduced into technical adsorption processes. Besides of the 100% active adsorption matter such material exhibits an advantageous secondary pore system. In this paper a more detailed investigation of the structure and the generation thereof is presented. To characterize the pore structure of the system SEM, EDX, Hg-porosimetry, as well as adsorption measurements (N2 and CO2) were used. For additional investigations XRD and XRF were applied.As a result of the special manufacturing process – granulation of zeolite NaMSX powder with metakaolin/caustic under high energy input followed by an alkaline treatment – two different types of zeolite morphologies were obtained: On the outer surface of the beads typical octahedral zeolite X crystals are monitored as a result of conventional and epitaxial crystal growth. In contrast the interior of the beads exhibits polycrystalline structures consisting of zeolite X in untypical shape, which is most probably the result of zeolite formation in dense matter. Due to the confined space conventional and epitaxial growth is inhibited. Obviously the original zeolite crystals are intergrown by polycrystalline zeolite NaMSX matter originated from converted metakaolin, and by the way forming macro pores. Said structure formation is the cause for the surprisingly high mechanical stability of the binderless shaped bodies.The existence of the superior secondary pore system and the high mechanical stability of binderless type NaMSX shapes can be explained as result of different pathways of the conversion of metakaolin into zeolite matter due to the existence of areas of different densities after the granulation process.

Preparation of zeolite MFI membranes on alumina hollow fibers with high flux for pervaporation

Polycrystalline zeolite MFI (silicalite-1) membranes are successfully prepared by the secondary growth method on the α-Al 2O 3 hollow fibers with a high surface/volume ratio. Influences of the seed suspension concentration, the crystallization time and the content of the structure-directing agent (SDA, e.g., TPAOH) in the synthesis solution are investigated. As-synthesized zeolite seeds and membranes are characterized by X-ray diffraction (XRD), dynamic light scattering (DLS) and scanning electron microscopy (SEM) with energy dispersive X-ray (EDX). The membrane formation and integrity are found to be sensitively depending on the SDA contents in the synthesis solution and the seed amount of the seeded layer. High TPAOH content may cause aluminum leaching from the alumina support seriously and low TPAOH content may lead to non-continuous zeolite layer, leading to poor separation performance. A continuous and dense zeolite seed layer is necessary to obtain the silicalite-1 membrane with good quality. However, too thick seed layer may cause peeling and cracking of the membrane and thus decrease the separation performance. Appropriate TPAOH and seed amount may prevent the α-Al 2O 3 support leaching effectively. The silicalite-1 membranes prepared in this paper show the highest flux and relatively high separation factor of ethanol/water mixtures compared with the literature data.