Hydrothermal Synthesis Of Zeolites Research Articles

Hydrothermal Synthesis and Characterization of Zeolite A Using Amorphous Gel from Industrial Reagents

Zeolites are crystalline microporous aluminosilicate of alkali metals and alkaline-earth metals. These materials have large commercial application due to their physical and chemical properties. The synthesis of zeolite A was carried out based on procedures described by International Zeolite Association (IZA), the sodium silicate was used as a source of silicon and the sodium aluminate as a source of aluminum for the produced zeolite. The synthesis occurred at hydrothermal conditions through static autoclaving. The material formed was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The results obtained from the characterization analysis were satisfactory and the method of synthesis showed to have high reproducibility in the production of zeolite A with good crystallinity as predominant phase. This result is very interesting because this method is simple and did not use toxic organic compounds as templates.

Perspectives on the multi-functions of aniline: Cases from the temperature-controlled phase transfer hydrothermal synthesis of MWW zeolites

The relationship between properties of aniline and its function was summarized concerning the hydrothermal synthesis of MWW zeolites with hexamethyleneimine as the structure-directing agent. Positive temperature-dependent solubility of aniline makes organics completely dissolved during crystallization and easily separated and recovered by liquid separation, which is defined as temperature-controlled phase transfer hydrothermal synthesis. For aniline, p-π conjunction significantly decreased basicity (determined by electronegativity) of amino groups, which accounted for poor charge-balancing and structure-directing capability. With hexamethyleneimine as the structure-directing agent, Aniline could promote crystallization as space-filling agent at much lower HMI/SiO2 ratio without being trapped within as-made MWW zeolites. Furthermore, the utilization of aniline as the structure-promoting agent could modify morphology into disorder packing of MWW platelets via directing gel method. HMI/SiO2 is the key to the distribution and stability of Al within final MWW zeolites. All referred advantages were originated from structure and properties of aniline. In future studies, efforts could be focused on property-oriented function design of hydrothermal synthesis.

Influence of the nature of amino acids on the formation of mesoporous LTA-type zeolite

Hydrothermal crystallization of LTA zeolite has been conducted in the presence of amino acid in order to introduce mesoporosity. Eight different types of proteinogenic amino acids have been employed. The influence of their structure and physicochemical properties on the formation of hierarchically mesoporous LTA (MLTA) zeolite have been investigated. All eight amino acids bearing either basic, or acidic, or polar non-ionizable, or non-polar non-ionizable side chains were able to generate mesopores within LTA crystals. The isoelectric points of amino acids influenced the resulting MLTA's morphology, crystallization kinetics, and impurity content. Pure phase MLTA with controllable shape was obtained. Amino acid with a higher isoelectric point generated smaller and more spherical MLTA in less crystallization time, but induced slightly more impurity FAU phase. The mesopore size generally decreased with hydropathy index so that amino acids with non-polar, non-ionizable side groups generated 14–15 nm mesopores, 5–10 nm smaller than those generated by amino acids in other categories. The hydrophobic moieties in amino acids tended to shrink the mesopores, in contrast with their pore expansion effect in surfactant-mediated mesopore generation route, suggesting a different mesopore formation mechanism. Stability of amino acid during the hydrothermal zeolite synthesis and easy amino acid removal by washing with water was further confirmed. The findings discovered in this study paves a new way for tailoring hierarchical zeolite materials with controlled texture properties.

Effect of ultrasound pretreatment on the hydrothermal synthesis of SSZ-13 zeolite

SSZ-13 zeolite has been identified as effective material for catalysts and membranes for years because of its structure, but the long crystallization time is the main obstacle for the industry application. The sonochemical-assisted method was identified as one of the potential pre-treatment methods which could reduce the formation duration of zeolites as well as other microporous and mesoporous materials. In this work, zeolite SSZ-13 was prepared by ultrasound pretreatment prior to hydrothermal crystallization. For comparison, samples by the conventional pretreatment and hydrothermal method were also prepared. The synthesized powders were characterized by XRD, SEM, BET, FTIR, NMR and TGA. The results showed that the complete crystallization of SSZ-13 synthesized by the ultrasound-assisted hydrothermal method was achieved within 72h, and much faster than conventional hydrothermal synthesis (120h). Furthermore, the ultrasound pretreatment showed very little effect on the structure properties of the final product compared with the conventional aging method.

Novel Ce-incorporated zeolite modified-carbon paste electrode for simultaneous trace electroanalysis of lead and cadmium

Cerium incorporated zeolite-modified carbon paste electrode (Ce-ZCPME) was studied for the anodic stripping voltammetric detection of lead and cadmium ions. The modified electrode which was fabricated in-house by a prior hydrothermal synthesis of Ce-impregnated zeolite displayed satisfactory results compared to other reported electrodes. Deposition of the metal was achieved at a potential of −1.2 V (vs. Ag/AgCl) for 120 s followed by a square wave stripping scan from −1.6–0.0 V. Various experimental conditions which include nature of supporting electrolyte, pH, amplitude, frequency, deposition potential and deposition time were optimized prior to the analyses. The fabricated electrode revealed a linear behavior over the metal ion concentrations with a LOD (S/N = 3) of 0.07 ppb and 0.46 ppb for lead and cadmium detection, as well as a good reproducibility (RSD 2.23%) respectively. The fabricated electrode has the potential to be used in the analysis of environmental samples due to its lack of toxicity, ease of fabrication and relative inexpensiveness.

Synthesis of ZSM-5 aggregates made of zeolite nanocrystals through a simple solvent-free method

In the traditional hydrothermal synthesis of zeolites, the solvent of water is necessary for crystallization, so large amount of wastewater containing NaOH and organic pollutants could be inevitably produced. The solvent-free route is considered to remarkably enhance the synthesis efficiency and reduce the energy and pollutants in large scale production of zeolites, but the zeolites obtained usually consist of micrometer sized single crystals which only possess micropores and long diffusion pathway for molecules. In this study, a novel solvent-free synthesis system made of solid raw materials of anhydrous silica and aluminum sources, organic template and Na2CO3·10H2O, was demonstrated to synthesize ZSM-5 zeolite particles composed of nanocrystals of about 10–40 nm in size. The obtained ZSM-5 particles possess high crystallinity and surface area, and well-developed mesoporosity (5.2 nm) and excellent catalytic activity in polymer cracking, such as low-density polyethylene (LDPE), which is the main source of white pollution. The ZSM-5 aggregate particles with the micro-/meso- porous structure have the potential used as catalysts and adsorbents in industry.

Hydrothermal assisted synthesis of zeolite based nickel deposited poly(pyrrole-co-fluoro aniline)/CuS catalyst for methanol and sulphur fuel cell applications

With the ultimate aim of improving overall performance of direct alkaline methanol fuel cell and direct alkaline sulphur fuel cell (DSFC), an innovative attempt is made for the development of cost effective electrocatalyst with fascinating morphology as an anode material. In this study, copper sulphide doped Poly(Py-co-FA) coated coal fly ash (CFA) based zeolite (CFA-Ze) as a supporting material was synthesized through the hydrothermal process. The obtained nickel deposited Poly(Py-co-FA)/CuS/CFA-Ze composite was characterized by infrared spectroscopy, X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy and cyclic voltammetry studies. The SEM and TEM pictures confirm the graphene sheet like structure formation through the interconnected bucky cage like shaped constitutions. Electrode modified with the synthesized catalyst exhibits improved catalytic activity for both oxidation of methanol and sulphide ion in alkaline medium. The novel catalyst used here is not only employed for the power generation, but also for the removal of sulphide waste, which is serving as a unique promoter of energy, waste management and green energy applications. Further, Ni/Poly(Py-co-FA)/CuS/CFA-Ze shows enhanced catalytic activity and stability when compared to that of Ni/Poly(Py-co-FA), Ni/CuS/CFA-Zeand Ni/CFA-Ze catalysts. The single stack alkaline fuel cell shows the maximum power density of 88.64 and 34.78·mWcm−2 for methanol and Na2S, respectively. From the overall studies, it was concluded that the prepared Ni/Poly(Py-co-FA)/CuS/CFA-Ze catalyst is a potent, low cost and non-precious metal loaded electrode material with enhanced catalytic activity for direct alkaline fuel cells.

Continuous flow synthesis of ZSM-5 zeolite on the order of seconds

The hydrothermal synthesis of zeolites carried out in batch reactors takes a time so long (typically, on the order of days) that the crystallization of zeolites has long been believed to be very slow in nature. We herein present a synthetic process for ZSM-5, an industrially important zeolite, on the order of seconds in a continuous flow reactor using pressurized hot water as a heating medium. Direct mixing of a well-tuned precursor (90 °C) with the pressurized water preheated to extremely high temperature (370 °C) in the millimeter-sized continuous flow reactor resulted in immediate heating to high temperatures (240-300 °C); consequently, the crystallization of ZSM-5 in a seed-free system proceeded to completion within tens of or even several seconds. These results indicate that the crystallization of zeolites can complete in a period on the order of seconds. The subtle design combining a continuous flow reactor with pressurized hot water can greatly facilitate the mass production of zeolites in the future.

Direct Hydrothermal Synthesis of High-silica SSZ-39 Zeolite with Small Particle Size

A high-silica SSZ-39 zeolite with an Si/Al molar ratio as high as 16 and with a particle size as low as 300 nm has been directly synthesized by tuning both alkali and water contents in the synthesis mixture, followed by adding relatively high-silica FAU crystals.

In situ ultrasonic measurements: a powerful tool to control the synthesis of zeolites from coal fly ash

An in situ ultrasonic diagnostic technique was applied to monitoring the hydrothermal synthesis of zeolite A and X of clear solution extracted from alkaline fused class F coal fly ash. In this context, kinetic evaluations based on in situ ultrasonic diagnostic data displayed an important approach to study the synthesis process. The impact on nucleation and crystal growth was demonstrated by variation of a few relevant parameters such as reaction temperature, amount of water, Na2O and ageing time, including templated colloidal synthesis mixtures as model solution. To complement the kinetic analysis, ex situ techniques such as ICP, X-ray diffraction, scanning electron microscopy and dynamic light scattering were used to investigate liquid phase and reaction products extracted from the reaction mixture during the synthesis.

Synergy between structure direction and alkalinity toward fast crystallization, controlled morphology and high phase purity of ZSM-12 zeolite

Aiming for a control of the morphology and phase purity of the final product, two commercially available organic templates, supplying tetraethylammonium (TEA+) and methyltriethylammonium (MTEA+) cations in the synthesis mixture, were used for the hydrothermal synthesis of ZSM-12 zeolite. As key factors, alkalinity and water content of the synthesis mixture and silicon and aluminum source types were comprehensively studied using these two organic templates. All the products obtained were characterized by powder XRD, SEM, N2 physisorption, 29Si and 27Al-MAS solid state NMR and TGA techniques. Using TEAOH organic template and organic Si and Al sources along with the proper adjustment of water and sodium hydroxide contents in synthesis mixture, mono-sized polycrystalline particles of ZSM-12 with high crystallinity and purity were synthesized. Alleviating TEAOH drawbacks, MTEA+ organocation in the hydroxide form was used which led to the formation of mono-sized ZSM-12 single crystals. When using MTEAOH organic template, hydroxide ion and Na+ contents and the type of Al source were found to be playing major roles toward nucleation and growth of ZSM-12 crystals. Owing to increased alkalinity of the synthesis mixture, MTEAOH also promoted faster crystallization over a wide-range of Si/Al ratio (30 to ∼infinity). The discrete mono-dispersed synthesized crystals possessed a well-defined cubic morphology with no impurities.

Facile control of nanosized ZSM-22 crystals using dynamic crystallization technique

Hydrothermal synthesis of ZSM-22 zeolite was investigated under rotating and static crystallization conditions. The effect of crystallization temperature, speed of horizontal rotation, Si/Al ratio and water content were studied on the properties of the produced ZSM-22 zeolites. The static crystallization resulted in microscale ZSM-22 particles combined with the impurities of ZSM-5 and cristobalite, whereas crystallization at suitable rotational speed resulted in smaller and pure ZSM-22 crystals. Depending on the rotational speed, ZSM-22 zeolite with different crystal sizes, morphologies and crystallinities were produced. The crystallinity and morphology of the resulted ZSM-22 zeolite were examined using XRD patterns and FE-SEM images.

Oxidative desulfurization of thiophene on TiO2/ZSM-12 zeolite

In this work the hydrothermal synthesis of ZSM-12 zeolite was performed, varying the MTEACl/SiO2 ratio, where the synthesis temperature was 140 oC and the crystallization time was 144 hours. The catalysts were characterized by XRD, FTIR and TG. TiO2/ZSM-12 catalysts were used with titanium ions concentrations of 5, 10 and 15%. The oxidative desulfurization (ODS) reactions were performed using a model mixture containing n-heptane as solvent and thiophene as sulfur compound, H2O2 as an oxidizing agent, and acetonitrile as an extractor solvent at reaction temperatures of 30, 50 and 70 oC. The obtained results shows that TiO2/ZSM-12 with 15% of Ti catalyst has a better performance in the ODS reaction converting thiophene at about 60%.

Synthesis of mesoporous zeolite Y nanocrystals in octahedral motifs mediated by amphiphilic organosilane surfactant

Hydrothermal synthesis of octahedron-shaped nanocrystalline zeolite Y in the presence of amphiphilic organosilane surfactant is described. The influence of parameters, such as the surfactant concentration, temperature and reaction time on the structure, size, surface area and porosity of the zeolite Y nanocrystals was systematically investigated. The role of surfactant was bifunctional, contributing towards the preferential crystal growth as well as the mesoporosity in the material. The morphology, structure and composition of the zeolite Y particles were thoroughly characterized by various techniques. Precise tailoring of size of the particles and pores was found to be an artifact of synthesis and processing parameters. A plausible mechanism for the formation and directional growth of octahedron-shaped nanocrystalline zeolite Y is proposed.

The process of fly ash magnetic separation impact on hydrothermal synthesis of zeolites

The aim of the experiment was modifying raw fly ash through the demagnetisation process and determining its influence on the efficiency of the synthesis of zeolite materials out of fly ash. A series of experiments have been performed on modified samples and, for the purpose of verification, on non-modified fly ash. No direct correlation has been confirmed in relation to synthesis efficiency as well as the type of obtained zeolite material. The research results indicate that the composition of fly ash determines the type of the zeolitic phases obtained. Based on the analysis of experimental data, it was found that the demagnetisation process allows to obtain additional zeolite phases, while there is no direct impact of the process used on the increase of synthesis reaction efficiency.

Temperature-controlled phase-transfer hydrothermal synthesis of MWW zeolites and their alkylation performances

MWW zeolites have been synthesized with hexamethyleneimine/aniline as the structure-directing/promoting agent. High conversion is achieved in the liquid-phase alkylation of benzene with ethylene above 210 °C for MCM-56.

Hydrothermal synthesis of high silica zeolite Y using tetraethylammonium hydroxide as a structure-directing agent.

High silica zeolite Y with a SiO2/Al2O3 ratio of 7.76 is successfully synthesized with tetraethylammonium hydroxide (TEAOH) as a structure-directing agent. The high silica zeolite Y shows outstanding high temperature thermal stability and hydrothermal stability.

Fluoride-assisted synthesis of bimodal microporous SSZ-13 zeolite.

The presence of small amount of fluoride in alkaline hydrothermal synthesis of SSZ-13 zeolite yields bimodal microporous particles with substantially improved performance in the methanol-to-olefins (MTO) reaction. Hydrocarbon uptake measurements and fluorescence microspectroscopy of spent catalysts demonstrate enhanced diffusion through micropores at the grain boundaries of nanocrystals running through the zeolite particles. Fluoride-assisted SSZ-13 synthesis is a cheap and scalable approach to optimize the performance of MTO zeolite catalysts.

Lanthanum-impregnated zeolite modified carbon paste electrode for determination of Cadmium (II)

We report the hydrothermal synthesis of mordenite zeolite in the absence of organic structuring directing agent (OSDA). The mordenite (MOR) zeolite with molar composition 6Na2O:Al2O3:30SiO2:780H2O was characterized by XRD, SEM, EDX, and NMR. It was further impregnated with lanthanum and was used in the construction of zeolite modified carbon paste electrode by mixing with different amounts of graphite and paraffin oil to form a paste. The paste composite with the ratio 65:5:30 (graphite:zeolite:paraffin) displayed the best electrochemical behavior in the cyclic voltammetry of K4Fe(CN)6 and was hence used for the detection of Cd (II) ions.

Hydrothermal synthesis of zeolite A from K-feldspar and its crystallization mechanism

Zeolite A was indirectly synthesized from K-feldspar using hydrothermal conversion method. In order to gain active SiO2 and Al2O3, the K-feldspar powders were pretreated with KOH solution followed by H2SO4 solution to form X-ray amorphous materials (AS). The effects of reaction time on the conversion of the obtained AS to zeolite A were investigated. X-ray diffraction (XRD), wet chemistry analysis, scanning electron microscope (SEM), Fourier Transform Infrared spectroscopy (FTIR), and 29Si and 27Al magic-angle-spinning nuclear magnetic resonance (29Si MAS-NMR and 27Al MAS-NMR) were used to characterize the nucleation and crystal growth processes. The results indicated that the AS was dissolved completely and abundant nuclei were formed during the first hour of the crystallization stage. With the crystallization time increasing, the nuclei were rapidly grown into zeolite A crystals and relative crystallinity of pure zeolite A reached its maximum when crystallization time reached to 3h. An excess time resulted in further dissolution of zeolite A and replacement by hydroxyl sodalite. The mechanism of synthesis of zeolite A from pretreated K-feldspar can be described by three main stages: (1) the dissolution of amorphous aluminosilicate releasing [SiO2(OH)2]2− and Al(OH)4−; (2) the formation sodium aluminosilicate gel as zeolite precursor; (3) the crystallization of zeolite A.