Zeolite Microspheres Research Articles

Facile synthesis of rodlike ZSM-5 zeolite microspheres and catalytic performance in methanol to propylene reaction

Facile synthesis of rodlike ZSM-5 zeolite microspheres and catalytic performance in methanol to propylene reaction

Spherical Binderless 4A/5A Zeolite Assemblies: Synthesis, Characterization, and Adsorbent Applications.

Zeolite microspheres have been successfully applied in commercial-scale separators such as oxygen concentrators. However, further enhancement of their applications is hampered by the post-synthetic shaping process that formulates the zeolite powder into packing-sized spherical bodies with various binders leading to active site blockage and suboptimal performance. Herein, binderless zeolite microspheres with a tunable broad size range from 2 µm to 500 µm have been developed with high crystallinity, sphericity over 92%, monodispersity with a coefficient of variation (CV) less than 5%, and hierarchical pore architecture. Combining precursor impregnation and steam-assisted crystallization (SAC), mesoporous silica microspheres with a wide size range could be successfully transformed into zeolite. For preserved size and spherical morphology, a judicious selection of the synthesis conditions is crucial to ensure a pure phase, high crystallinity, and hierarchical architecture. For the sub-2-µm zeolite microsphere, low-temperature prolonged aging was important so as to suppress external zeolization that led to a large, single macroporous crystal. For the large 500 µm sphere, ultrasound pretreatment and vacuum impregnation were crucial and facilitated spatially uniform gel matrix dispersion and homogenous crystallization. The obtained zeolite 5A microspheres exhibited excellent air separation performance, while the 4A microspheres displayed ammonium removal capabilities. This work provides a general strategy to overcome the existing limitations in fabricating binder-free technical bodies of zeolites for various applications.

Protein-assisted synthesis of zeolite-supported pseudo-single-atom cobalt catalyst for nitrobenzene hydrogenation

A novel pseudo-single-atom cobalt catalyst based on a hollow zeolite microsphere (HZM) constructed by MWW nanosheets was prepared with the aid of bovine serum albumin (BSA). BSA was adsorbed on the external surface of nanosheets, forming a protein coating which prevented cobalt ions getting into micropores of HZM and at the same time induced their implantation on the outer surface through specific ion-protein interaction. The cobalt ions on BSA layer were highly dispersive in that one BSA tended to bind no more than one cobalt ion in a specific region, which constituted the basis of single-atom. Cobalt ions were reduced and trapped in the N-doped carbon layer derived from BSA coating during pyrolysis, obtaining the pseudo-single-atom cobalt catalyst (Co@CN@HZM). Co@CN@HZM exhibited high catalytic efficiency and favorable cycle stability in the reaction from nitrobenzene to aniline. The excellent performance of the catalyst mainly benefited from the highly exposed active sites on the outer surface, the hierarchical porous structure facilitating diffusion, and the oscillating effect of substrate in the cavity of microsphere. This work proposed a facile strategy for preparing single-atom or pseudo-single-atom materials with metal atom uniformly dispersed on the outer surface of zeolites or other similar supports.

Synthesis of hierarchical ZSM‐5 microspheres with superior performance for catalytic methanol‐to‐olefin conversion

AbstractMethanol‐to‐olefin (MTO) conversion on zeolites has encountered severe coke deposition and rapid deactivation. Creating different levels of porosity is essential to mitigate such issues. Herein, we demonstrate a facile and green strategy to synthesize uniform and hierarchically macro/mesoporous ZSM‐5 microspheres by combining spray‐freeze drying and steaming‐assisted crystallization (SAC). The structure, crystallinity, and porosity of the zeolite microspheres are controlled by adjusting the water/gel mass ratio and time in the SAC process. The structure evolution during the SAC process is revealed. In the catalytic MTO reaction, the representative hierarchically porous ZSM‐5 catalyst exhibits superior catalytic performance. At a very high weight hourly space velocity of 18 h−1, it shows a dramatically prolonged lifetime (47 h at >99% conversion) and much‐improved selectivity to ethylene and propylene compared with the conventional microporous ZSM‐5 and nano‐sized ZSM‐5. The enhanced performance is originated from the hierarchical structure and suitable acidity of the ZSM‐5 microspheres.

Preparation and conversion mechanism of different geopolymer-based zeolite microspheres and their adsorption properties for Pb2+

In this study, geopolymer zeolite microspheres (GZMs) were prepared from metakaolin by suspension dispersion solidification and in-situ conversion method. Different GZMs were prepared by adjusting n(Na2O)/n(Al2O3), n(H2O)/n(Na2O), curing time and temperature. The data showed that NaA structure was easily formed under low temperature and low alkalinity conditions, which was transformed into sodalite (SOD) with more stable structure under high temperature and high alkalinity conditions. When n(Na2O)/n(Al2O3) = 1.9 and n(H2O)/n(Na2O) = 12, the sphericity of GZMs was the best according to the sphericity and particle size distribution results. Furthermore, different ZMs were prepared by adjusting the curing temperature and time. These ZMs showed maximum adsorption capacities for Pb2+ of 529.67 mg/g (NaA), 345 mg/g (NaA + SOD: the mixture of NaA and sodalite) and 308.30 mg/g (SOD), following pseudo-second-order kinetic model and the Langmuir isotherm model. The fresh and post-adsorption GZMs were analyzed by SEM-EDX, XRD, FTIR and XPS, and the △c (Pb2+): △c (Na+) = 1: 1.92 (≈1:2) in the solition, which confirmed chemisorption phenomenon via ion exchange mechanism. Moreover, the adsorption rate of Pb2+ on NaA ZMs was higher than that of traditional zeolite materials. This study accredited to its simplicity, low cost and remarkable adsorption performance of the NaA ZMs for Pb2+, can be deemed of potential value in practical application of wastewater processing.

Kinetics guided synthesis and performance of monodisperse zeolite LTA microspheres

Monodisperse zeolite microspheres hold great potential for wide industrial applications, but the existing preparation methods could hardly afford a uniform particle size distribution. Herein, the authors, for the first time, achieved the synthesis of monodisperse zeolite microspheres possessing high sphericity and tight particle size distribution with coefficient of variation (CV) less than 5%. Unlike previous methods that produce macroporous zeolites, the current strategy featured as shape-preserving steam assisted crystallization (SAC) successfully transforms aluminum and sodium source impregnated mesoporous silica microspheres into monodisperse zeolite LTA microspheres with tunable particle size between 10 and 30 μm. Spatiotemporal control of crystallization kinetics with balanced silica dissolution and zeolite nucleation is found to be essential for authentically maintaining the monodisperse spherical morphology, with larger-sized silica leading to higher zeolite sphericity. The pore size of the initial silica affects the resulting zeolite crystallinity, viz., larger silica pore size leads to higher zeolite crystallinity. Evolution of the zeolite microspheres involves synchronized silica dissolution and LTA crystallization in trapped domains facilitated by the intermediate, homogenously dispersed gel matrix, allowing to inherit the parent silica morphology. The LTA zeolite microspheres exhibit extremely high crystallinity, mechanical strength, thermal stability, and excellent air separation performance.

Study on the Adsorption of Heavy Metals in Sludge by Calcium Alginate Cross-Linked Zeolite Microspheres

Study on the Adsorption of Heavy Metals in Sludge by Calcium Alginate Cross-Linked Zeolite Microspheres

Using the ash of common water reeds as a silica source for producing high purity ZSM-5 zeolite microspheres

Abstract Utilizing of ash extracted from Iraqi common water reeds as an inexpensive effective silica source in the preparation of ZSM-5 zeolite was investigated for the first time in the present work. This study was conducted using a hydrothermal treatment at autogenous pressure. The molar content of silica (17.84–26.76), sodium oxide (1.71–2.4), water (76.92–304.6), organic template (0.55–2.73), organic solvent (23.46–140.76), and synthesis conditions (crystallization time (24–72 h) and temperature (130–180 °C)) were investigated to obtain high purity ZSM-5 zeolite microspheres. The zeolite samples were characterized using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Analysis by X-Ray (EDAX), N2 adsorption/desorption isotherms, Thermogravimetric Analyzer (TGA), and Fourier transform infrared spectroscopy (FTIR). XRD pattern of all synthesized samples was compared to XRD pattern of the commercial ZSM-5 zeolite. This work allows using locally available solid waste resulted from a dry natural plant as an inexpensive silica source without using an external source of silica. Also, this is the first report of the direct synthesis of a high purity ZSM-5 zeolite microspheres from common water reeds ash containing highly reactive silica. A gel composition of 2Na2O: 26.76SiO2: Al2O3: 2.73TPAOH: 23.46EtOH: 304.6H2O gave an outstanding final product of ZSM-5 zeolite microspheres at 180 °C and 27 h. This high crystallinity ZSM-5 zeolite porous microspheres possess Si/Al ratio of 17, a crystal size of 61.419 nm, BET surface area of 277.482 m2/g, a total pore volume of 0.1659 cm3/g, micropore volume of 0.1131 cm3/g, pore width of 5.28 nm, and hierarchical factor of 0.14.

Facile fabrication of metakaolin/slag-based zeolite microspheres (M/SZMs) geopolymer for the efficient remediation of Cs+ and Sr2+ from aqueous media

Herein we report the fabrication of metakaolin/slag-based geopolymer microspheres by dispersion-suspension-solidification technology, and were then transformed into zeolite microspheres by in-situ thermal curing. The rheological properties and mechanical strength of metakaolin/slag-based zeolite microspheres (M/SZMs) were improved by adding slag. The zeolite microspheres were texturally and morphologically characterized by BET, SEM-EDX and XRD techniques. At 20% slag contents of the total mass of M/SZMs, the specific surface area was significantly increased without changing the structure of the zeolite. Rheological properties analysis of slurry revealed pseudoplastic fluid phase and fitted well to Herschel–Bulkley model. The adsorptive removal data of M/SZMs for Cs+ and Sr2+ from wastewater followed pseudo-second-order kinetics. The maximum adsorption capacity of M/SZMs for Cs+ and Sr2+ was 103.74 mg/g and 54.90 mg/g and were best explained by Freundlich and Langmuir isotherm models, respectively. M/SZMs exhibited excellent dynamic separation effect in column-based experimental set up. In addition, M/SZMs also realized outstanding adsorptive removal performance for Cs+ and Sr2+ from different real wastewater samples. Owing to the simplistic fabrication approach, low cost and highly efficacious nature, M/SZMs can be ranked as alternative candidates for the abatement of Cs+ and Sr2+ from wastewater.

Combination of spray drying encapsulation and steaming transformation toward robust hierarchical zeolite microspheres: Synthesis, formation mechanism and acid catalysis

Binder-free zeolite microspheres with hierarchical porosities are prepared by combining spray-drying encapsulation and steaming transformation. Amorphous aluminosilicate microspheres encapsulating tetrapropylammonium hydroxide (TPAOH) are first synthesized by spray drying. Then, they are successfully transformed into robust zeolite microspheres by using a steam-assisted crystallization (SAC) process. The drying temperature plays a decisive role in encapsulation and preservation of TPAOH guiding zeolite crystallization, as well as the morphology and sizes of the obtained zeolites. The morphology, structure and crystallinity of the resulted zeolites can also be controlled by adjusting the water/gel mass ratio and SAC time. The detailed structure and crystallization evolution over the SAC transformation process is studied and discussed. The typical obtained zeolite microspheres possess surface buckled morphologies, uniform large particle sizes, hierarchical porosities, good mechanic strength and intrinsic strong acid sites. They demonstrate enhanced catalytic activity and stability in acid catalytic aldol condensation.

Solvent-free synthesis of hydroxycancrinite zeolite microspheres during the carbonation process of blast furnace slag

CO2 mineralization is a technological solution to reduce anthropogenic CO2 emissions. It is more cost-effective to use industrial wastes as feedstock than natural minerals and eliminate some of the energy-consuming operations, to recover various value-added byproducts. In this study, hydroxycancrinite zeolite was synthesized by a solvent-free method during the carbonation of blast furnace slag (BFS) as the waste feedstock. The effects of various process factors such as the alkaline dosage, crystallization temperature, and crystallization batch time on the synthesis of hydroxycancrinite were systematically investigated. A well-crystallized spherical hydroxycancrinite was obtained by mixing with NaOH solid and then crystallizing at 100 °C for 4 h. The as-synthesized products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscope, thermogravimetric analysis, and Brunauer-Emmett-Teller analysis. The results revealed that pure microspheres of hydroxycancrinites are obtained with a diameter of ∼1 μm and a surface area of 37.2 m2/g. Based on the material balance and preliminary economic evaluation, 361 kg CO2/t BFS can be stored by calcium and magnesium components, whereas almost all of the silicon and aluminum are recovered as value-added zeolites, which significantly improve the process economy.

Efficient protein delivery systems based on hierarchical zeolite microspheres constructed by MWW-nanosheets

Abstract A hierarchical hollownest-structured zeolite (HSZ) microsphere constructed by MWW-nanosheets and its various functionalized derivatives (HSZ-OH, HSZ-NH2 and HSZ-CHO) were firstly applied in the delivery of bovine serum albumin (BSA). Owing to the unique cup-shaped pores on the nanosheets and the abundant prismatic stacking mesopores and macropores in the shell, HSZ materials exhibited higher BSA loading content than other familiar microporous zeolites. More importantly, HSZ-NH2 and HSZ-CHO could release exceeded 50% of the loaded BSA under simulated physiological ion strength condition of pH 7.4 and 5.0, respectively. The adsorption thermodynamic parameters revealed that the loading of BSA on HSZ-OH was an enthalpy-driven process conducted by hydrogen bonds, but an entropy-driven process predominated by electrostatic forces on HSZ-NH2. The pH-sensitive imine bonds between BSA and hydrophobic HSZ-CHO were sensitive to acidic environment, constituting a pH-responsive intelligent protein delivery system. The synchronous fluorescence spectra corroborated that structural alteration of BSA recovered after desorption. The interaction mechanisms were analyzed by determining the physicochemical property of nanosheet surface. The favorable and controllable loading and release performance of HSZs predicted their huge application potential in delivery, slow-release, separation and purification of proteins and protein drugs.

Controlled synthesis of Zeolite adsorbent from low-grade diatomite: A case study of self-assembled sodalite microspheres

Highly efficient and sustainable conversion technologies to generate uniform sodalite (Na8(AlSiO4)6(OH)2) zeolite microspheres with low-grade waste natural diatomite as raw materials via a solution-mediated crystallization route were developed in the present study. The synthesis process can be considered as an in-situ zeolitization of diatomite precursor without involving any mesoscale template and any post-synthetic modification. The mass ratios of diatomite and AlCl3·6H2O have remarkable effect on the morphology, crystal structure and porosity of sodalite zeolite product. The preferred sodalite microspheres with uniform mesoporous of size 3.5–5.5 nm and large surface area of 162.5 m2/g exhibit well removal performance for heavy metal ions (Pb(II), Cd(II), Zn(II), and Cu(II)), with the highest adsorption abilities for Pb(II) ions of 365 mg/g. In addition, the effect of contact time, initial ion concentration, competitive adsorption and solution pH were evaluated. The removal performance results from synergistic effects of dominating cation-exchange and additional surface chemisorption. The study may broadly help unveil chemical control reactions of the zeolitization processes of diatomite, and thus facilitates the development of promising zeolite materials for the use in natural and engineered aquatic environments by recycling waste diatomite resources.

Hollow zeolite microspheres as a nest for enzymes: a new route to hybrid heterogeneous catalysts.

In the field of heterogeneous catalysis, the successful integration of enzymes and inorganic catalysts could pave the way to multifunctional materials which are able to perform advanced cascade reactions. However, such combination is not straightforward, for example in the case of zeolite catalysts for which enzyme immobilization is restricted to the external surface. Herein, this challenge is overcome by developing a new kind of hybrid catalyst based on hollow zeolite microspheres obtained by the aerosol-assisted assembly of zeolite nanocrystals. The latter spheres possess open entry-ways for enzymes, which are then loaded and cross-linked to form cross-linked enzyme aggregates (CLEAs), securing their entrapment. This controlled design allows the combination of all the decisive features of the zeolite with a high enzyme loading. A chemo-enzymatic reaction is demonstrated, where the structured zeolite material is used both as a nest for the enzyme and as an efficient inorganic catalyst. Glucose oxidase (GOx) ensures the in situ production of H2O2 subsequently utilized by the TS-1 zeolite to catalyze the epoxidation of allylic alcohol toward glycidol. The strategy can also be used to entrap other enzymes or combination of enzymes, as demonstrated here with combi-CLEAs of horseradish peroxidase (HRP) and glucose oxidase. We anticipate that this strategy will open up new perspectives, leveraging on the spray-drying (aerosol) technique to shape microparticles from various nano-building blocks and on the entrapment of biological macromolecules to obtain new multifunctional hybrid microstructures.

Hierarchical micro-/mesoporous zeolite microspheres prepared by colloidal assembly of zeolite nanoparticles.

A novel template-free colloidal assembly method that combines colloidal zeolite (silicalite-1) suspensions in a water-in-oil emulsion with an evaporation-induced assembly process has been developed for preparing hierarchical micro-/mesoporous zeolite microspheres (MZMs). Such particles have an interconnected mesoporosity and large mesopore diameters (25–40 nm) combined with 5.5 Å diameter micropores of the zeolite nanoparticles. The method developed has the advantages of employing mild synthesis conditions, a short preparation time, and not requiring the use of a mesoporogen template or post-treatment methods. The method provides a new range of micro-/mesoporous zeolites with tunable mesoporosity dictated by the size of the zeolite nanoparticles. It also offers the possibility of combining several zeolite particle sizes or optionally adding amorphous silica nanoparticles to tune the mesopore size distribution further. It should be generally applicable to other types of colloidal zeolite suspensions (e.g. ZSM-5, zeolite A, beta) and represents a new route amenable for cost-effective scale-up.

A hierarchical zeolite microsphere prepared by an eco-friendly and practical route for efficient reaction of bulky molecules

The hierarchical zeolite ZSM-5 was synthesized in a CH3CH2OH–H2O hydrothermal system by using hexadecyltrimethyl ammonium bromide (CTAB) as sole template at a low crystallization temperature (130 °C). The effects of ethanol and CTAB on crystallization process and morphologies of ZSM-5 products were investigated. Ethanol molecules in synthesis system were beneficial to speed up crystallization, though crystal growth in NaOH-CTAB-H2O system was more difficult. The existence of CTAB resulted in highly crystalline and pure phase hierarchical ZSM-5 microspheres assembled by nanocrystals. The traces of crystallization evolution by XRD, FT-IR, N2 adsorption/desorption, SEM/TEM, 29Si MAS NMR, 27Al MAS NMR spectra and TGA revealed that the hierarchical ZSM-5 microspheres were formed through the transformation of mesostructured amorphous aluminosilicates, in which the initial surfactant micelles were gradually excluded and thus acted as a molecule structure-directing agent to direct the crystallization of MFI nanozeolite. At the same time, the CTAB may disrupt nanocrystals further growth and aggregate them into hierarchical microsphere through CTA+. Pyridine (Py) and pivalonitrile (Pn) adsorbed FT-IR spectra showed that the hierarchical ZSM-5 microspheres possessed large number of accessible acid sites due to the introduction of mesopores into zeolite. Therefore, it displayed much higher catalytic activities for both large molecules 1,3,5-trimethylbenzene (TMB) transformation and 1,3,5-triisopropylbenzene (TIPB) cracking reactions than conventional MFI zeolite, and the high selectivity to isomerization products (1,2,3- and 1,2,4-TMB) and benzene product from over-cracking.

One-step template-free hydrothermal synthesis of partially Sr-incorporated hierarchical K-CHA zeolite microspheres

Abstract Partially Sr-incorporated hierarchical K-CHA zeolite microsphere of primary truncated bi-pyramidal crystallites was hydrothermally synthesized by one-step template-free hydrothermal process and the formation mechanism was investigated in detail. Its crystallization was accelerated by addition of strontium, and it was formed by three distinct steps: formation and aggregation of amorphous hollow nanospheres, collapse of agglomerated hollow nanospheres to multilayered disc, and rotational intergrowth into thread ball shape microsphere. The hollow nanosphere was formed by thermal expansion of Sr-coated solid silica nanoparticle, and the multilayered disc, by collapse of spherically aggregated hollow nanospheres. The collapse took place to minimize total surface energy by flattening sticky hollow spheres and oriented attachment of crystallites nucleated in the shell of hollow spheres. The multilayered disc grew finally to be thread ball shape microspheres. K-CHA zeolite microspheres displayed hierarchical character and showed excellent 298 K adsorptions for water (316 cm3 g−1), and CO2 (167.0 mg g−1 at 10 bar). The CO2/N2 adsorption selectivity was 10 due to incorporated potassium ions. Evidently, partially Sr-incorporated K-CHA zeolite microsphere was a good adsorbent for solvent dehydration and carbon capture.

One-Pot Preparation of NaA Zeolite Microspheres for Highly Selective and Continuous Removal of Sr(II) from Aqueous Solution

This paper describes a synthesis method and adsorption properties of geopolymer microspheres toward strontium ions; first, it was prepared by a dispersion–pelletizing–solidification (DPS) method followed by transformation into NaA zeolite microspheres (about 100 μm) through an in situ heat curing process. The adsorption experiments were investigated and the experimental data were fitted well by the pseudo-second-order kinetic model and Freundlich isotherm model. Loading experiments were performed by batch and column process techniques. The maximum adsorption capacity in the batch process was assigned to be 106.28 mg/g, the zeolite microspheres’ adsorption of strontium ions reached adsorption equilibrium in approximately 15 min. In the dynamic column, the most suitable flow rate was found to be 4 mL/min; this was higher compared with other sorbents with the same particle size. Moreover, the zeolite microspheres have a good dynamic separation effect, the concentration of the outlet Sr(II) ions from the colu...

Binderless zeolite NaX microspheres with enhanced CO2 adsorption selectivity

Abstract Zeolite NaX@NaA core-shell microspheres were prepared via a post-treatment secondary growth of zeolite NaA films on outer surface of binderless zeolite NaX microspheres. The obtained core-shell microspheres were composed of intergrown octahedral NaX particles inside, with particles size of ca. 500–750 nm, and continuous zeolite NaA films on the outer surface with the thickness of about 2 μm. Higher CO2 separation performance was observed for the core-shell microspheres comparing to the parental binderless zeolite NaX microspheres. The ideal separation factors of zeolite NaX@NaA core-shell microspheres for CO2/CH4 and CO2/N2 were 13 and 47, and the adsorption selectivities for the corresponding binary mixtures were 308 and 923, significantly higher than the binderless zeolite NaX microspheres of 9 and 19 as well as 264 and 735, respectively. After K+ ion exchanging, the core-shell zeolite microspheres have even higher adsorption selectivities of 326 and 1109 for CO2/CH4 and CO2/N2 binary mixtures. The crushing strength of the binderless zeolite NaX microspheres was increased from 0.46 MPa to 3.42 MPa after the secondary growth. In addition, the growth of zeolite A film was resultant from interzeolite conversion and the interzeolite conversion was investigated by the conversion of zeolite NaX to NaA crystals in NaA membrane synthesis gel.

Synthesis of Binderless ZK-4 Zeolite Microspheres at High Temperature.

Binderless zeolite macrostructures in the form of ZK-4 microspheres were prepared using anion-exchange resin beads as shape-directing macrotemplates. The particles were synthesized under hydrothermal conditions at different temperatures and treatment times. The influence of the different synthesis parameters was investigated by X-ray diffraction, scanning electron microscopy, fluorescence X, nitrogen adsorption measurements and 29Si solid-state NMR. Fully crystalline spheres similar in size and shape to the original resin beads were obtained by a hydrothermal treatment at the highest temperatures (150–180 °C) for a short treatment time of 24 h. The synthesized microspheres showed to be promising in the molecular decontamination of volatile organic compounds (VOCs).