Hydrothermal Synthesis Of Zeolites Research Articles

Application of Multinuclear MAS NMR for the in situ Monitoring of Hydrothermal Synthesis of Zeolites.

In situ MAS NMR studies on the monitoring of hydrothermal synthesis of zeolites are reviewed. The first part of the review contains information on the experimental techniques used for the in situ NMR studies in static and MAS conditions. In the second part, the main capabilities of the in situ 1 H, 11 B, 13 C, 14 N, 19 F, 23 Na, 27 Al, 29 Si and 31 P MAS NMR for the elucidation of the mechanism of hydrothermal synthesis of zeolites are examined and the data on NMR lines identification are summarized. In the last part the main application areas of the techniques are considered and illustrated with examples taken from the mechanistic studies of zeolites A, X, MFI and BEA synthesis. A cross-reference index between the materials studied, the experimental approaches used, the mechanistic information obtained, and the corresponding literature sources is established.

Direct hydrothermal synthesis of Mo-containing MFI zeolites using Mo-EDTA complex and their catalytic application in cyclohexene epoxidation

A series of Mo-containing MFI zeolites with different Mo loadings (Mo-MFI-n, n represent the initial Si/Mo molar ratio) was hydrothermally synthesized by using tetrapropylammonium hydroxide as the template and Mo-EDTA complex as the Mo source. Various characterization results demonstrated that the use of the Mo-EDTA complex is beneficial for the incorporation of more Mo species into the MFI-type zeolites. The special complexing capability of EDTA2– plays a critical role in adjusting the release rate of the Mo species to combine with the Si tetrahedron species during the zeolite growth process, thus leading to a uniform distribution of Mo in the MFI framework. In addition, a small portion of extra-framework Mo clusters may be distributed inside the channels or near the pore window of the zeolites. The catalytic properties of these Mo-containing MFI zeolites were evaluated for the epoxidation of cyclohexene with H2O2 as the oxidant. The composition-optimized catalyst, Mo-MFI-50, efficiently converted cyclohexene to the corresponding epoxide with a relatively high conversion (93%) and epoxide selectivity (82%) at 75 °C after 9 h of reaction. Moreover, the resultant Mo-containing MFI catalyst exhibited excellent structural stability and recoverability and was easily recycled by simple filtration without the need for calcination treatment.

Hydrothermal Synthesis and Characterization of Zeolite A from Corn (Zea Mays) Stover Ash.

This study deals with the impact of calcination, alkalinity, and curing time parameters on the hydrothermal synthesis of zeolite A. The zeolite A sample, produced from corncob-stalk-and-leaves (corn stover) ash was characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermo-gravimetric analysis (TGA), and scanning electron microscopy (SEM). The results showed that calcination, alkalinity, and curing time have significant effects on the crystallization and the morphology of zeolite A. In addition, these parameters also impacted the cation exchange capacity. Furthermore, the synthesized zeolite A was obtained using a calcination temperature of 500 °C within two hours of airflow, which is much lower than the temperatures previously reported in the literature for an agricultural waste and other waste materials. A fusion ratio of corn stover ash:NaOH of 1.0:1.5 and a curing time of nine hours were achieved. This is a major result as this curing time is much lower than those featured in other studies, which can reach up to twenty-four hours. In this paper, cubic crystal with rounded edge of zeolite A, having a cation exchange capacity of 2.439 meq Na+/g of synthesized anhydrous zeolite A, was obtained, which can be a good candidate for ion-exchange separation.

The Promoter Role of Amines in the Condensation of Silicic Acid: A First-Principles Investigation.

Though well-recognized, the molecular-level understanding of the multifunctional roles of amines in the condensation of polysilicic acids, which is one of the key processes in hydrothermal synthesis of zeolites, is still limited. Taking ethylamine as a prototype, we investigated the mechanism of polysilicic acid condensation in the existence of organic amines in aqueous solution with extensive first-principles-based calculations. Because of the high proton affinity, ethylamine exists as amine silicates and alters the subsequent condensation mechanisms from a 1-step lateral attack mechanism accompanied with simultaneous intermolecular proton transfer in neutral aqueous solution to a 2-step SN2-like mechanism. Specifically, the 5-coordinated Si species that were not observed on pathways of condensation in neutral solution are effectively stabilized by the ethylamine cations as intermediates, and the barriers for condensation of ortho-silicic acid are significantly reduced from 133 kJ/mol in neutral solution to 58 and 63 kJ/mol for formation of the 5-coordinated Si intermediate and proton transfer for water release, respectively. Similar variations of mechanisms and barriers for condensation were also observed in the formation of cyclic trimers as well as linear and cyclic tetramers of ortho-silicic acids. Based on these, it was proposed that apart from acting as structure-directing agents, pore fillers, and pH adjusters, organic amines can also function as promoters in the condensation of polysilicic acids.

Synthesizing of Zeolite Particle Using Alkaline Plant Extract

The study explored the hydrothermal synthesis of zeolite using kaolin clay precursor in the presence of three different solvents namely, garlic extract, watermelon extract and 2M NaOH solution, with the view of testing their efficacy and potency for green synthesis. Before the zeolitization, the kaolin precursor was activated at a temperature of 850°C to produce metakaolin. The crystallization was achieved in an oven at a temperature of 90°C for 12 hours. The final product is grounded to a fine powder and subsequently undergo testing and characterization via X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscopes (FESEM) methods. The purity and grade of the synthesized products vary accordingly with the suitability of the reaction solvent. The synthesized product using a solvent of watermelon plant extract was able to produce zeolite LTA of a good grade. However, the presence of secondary phases informed the effect of the accompanied impurities that might originate from the kaolin precursor or the solvent. The result also portrays the possibility of obtaining a well crystalline zeolite from the Malaysian kaolin without using any structural directing agent or chemical solvents.

Investigation of Various Influencing Factors of Hydrothermal Synthesis of Analcime Zeolite

This study presents an investigation of the use of the natural mineral of Nakhchivan Autonomous Republic to produce analcime zeolite of potential practical importance. The influence of temperature and crystallization time, the concentration of alkaline solution and mineralizer on the process of synthesis of analcime has been evaluated. The optimal conditions established for the synthesis of pure analcime with a 100% degree of crystallinity are as follows: temperature of 180°C, alkaline and mineralizer solution of 10-15% KOH and 5-10% KCl and processing time of 50 hours. It has been shown that the presence of the KCl mineralizer promotes the production of pure analcime with a 100% crystallinity, and the natural mineral of Nakhchivan represents a good source for the synthesis process.

Aerosol-assisted hydrothermal synthesis of hierarchical Sn-Beta nanoaggregates in fluoride media

The hydrothermal synthesis of nanosized zeolite in fluoride media is a great challenge. In this study, Sn-Beta zeolites with tunable morphologies from typical truncated bipyramid to hierarchical nanoaggregates were successfully synthesized by a facile aerosol-assisted hydrothermal method. Firstly, organosilane trimethoxy [3-(phenyl) propyl] silane (PHAPTMS) was introduced into the Sn-Si oxide by a simple aerosol process, which can act as the synthesis precursor. Then the Sn-Si precursor was hydrothermally crystallized in the presence of fluoride and seeds. A comprehensive characterization of XRD, N2 physisorption, SEM, TEM, UV–vis and FTIR spectroscopy with pyridine and deuterated acetonitrile adsorption were used to confirm its physicochemical properties. It was found that the amount of the added PHAPTMS has a great influence on the morphologies, compositions, pore structure and acid properties of the resultant hierarchical Sn-Beta nanoaggregates. The investigation of the crystallization process demonstrated that the addition of PHAPTMS has a crucial role for the formation of hierarchical Sn-Beta nanoaggregates. The obtained Sn-Beta nanoaggregates exhibited enhanced catalytic performance in the Baeyer–Villiger oxidation of ketones to lactones due to the improved diffusion property. This strategy provides a new route for the hydrothermal synthesis of hierarchical nano zeolites in the fluoride media.

Synthesis and characterization of Na-P1 (GIS) zeolite using a kaolinitic rock

This work focuses on the hydrothermal synthesis of Na-P1 zeolite by using a kaolinite rock coming from Romana (Sassari, Italy). The kaolin is calcined at a temperature of 650 °C and then mixed with calculated quantities of NaOH. The synthesis runs are carried out at ambient pressure and at variable temperatures of 65 and 100 °C. For the first time compared to the past, the Na-P1 zeolite is synthesized without the use of additives and through a protocol that reduces both temperatures and synthesis times. The synthesis products are analysed by X-ray diffraction, high temperature X-ray diffraction, infrared spectroscopy, scanning electron microscopy and inductively coupled plasma optical emission spectrometry. The cell parameters are calculated using the Rietveld method. Density and specific surface area are also calculated. The absence of amorphous phases and impurities in synthetic powders is verified through quantitative phase analysis using the combined Rietveld and reference intensity ratio methods. The results make the experimental protocol very promising for an industrial transfer.

Hydrothermal synthesis of zeolite Y from green materials

AbstractSeveral probes have been conducted by the scientific community to reduce emissions of greenhouse gases such as carbon dioxide (CO2). A zeolitic material is capable of CO2 adsorption with the aid of such technologies. Our present work is to efficiently synthesize zeolite Y with four Si/Al ratios (2.0, 2.5, 3.0, and 3.5) from green materials such as rice husk ash (source of Si) and metakaolin (source of Al). The method for preparing zeolite Y involves hydrothermal synthesis in a hydrodynamic reactor at 120°C temperature, for a reaction time of 24 hours. These synthetic zeolites represent high values for surface area as well as pore volume in micropore range and are compatible with the size of CO2 molecules. The zeolite Y (with Si/Al ratio 3.5) has an absorption capacity of 3.35 mmol CO2/g at (900 kPa) pressure, thereby demonstrating high efficiency for CO2 adsorption. The spectra of FTIR indicate Si‐OH‐Al groups, while the vibrations corresponding to Si‐O‐Si or Si‐O‐Al compounds display the characteristic structure of zeolite Y. Several tests have been conducted with the synthesized zeolites Y, which portrayed strong evidence of CO2 absorption abilities. Henceforth, it can be concluded that zeolites Y have significant potential for application in adsorption/desorption cycles of carbon dioxide.

Effects of Synthesis Parameters on Organic Template-Free Preparation of Zeolite Y

In this work, the effects of reaction conditions on the conventional hydrothermal synthesis and crystal growth kinetics of zeolites Y in aqueous sodium alkaline solutions without the use of organic templates were studied. For this purpose, a series of Y-type zeolites were synthesized at different reaction conditions such as various aging temperatures, crystallization temperatures, Na2O contents of the initial gel and crystallization times using hydrothermal process. The prepared samples were well characterized by the X-ray diffraction (XRD) and N2 adsorption–desorption techniques. The results prove that the Na2O contents of the initial gel and synthesis temperature increase the rate of the Y and P zeolite crystallization. The effect of Na2O and temperature on the synthesis of two different zeolite types (Y and P) with a constant initial synthetic composition under the organic template-free synthesis of zeolite Y was studied. In inappropriate conditions, the P-type zeolite was the major impurity obtained along with the Y-type zeolite. Also from the experimental results, the kinetic parameters for both zeolite Y and zeolite P were calculated. The kinetic study show that the activation energy for crystallization of both zeolites was enhanced by increasing the Na2O content of the initial gel due to the structure-directing role of Na+ cation in the induction period and crystal growth step.

Synthesis of geopolymers derived from fly ash with an addition of perlite

The study summarizes the results of fly ash-based geopolymer testing. Geopolymer samples were synthesized in a process involving two cycles. In the first cycle the activating agent was sodium hydroxide. The second method used the liquid residue from the synthesis of zeolites with the hydrothermal method. These processes were investigated to find out how the addition of perlite affects the mechanical properties of geopolymers (compressive strength, Young’s modulus, shear modulus, Poisson’s ratio) and their thermal expansion behaviour. It was shown that the addition of perlite enables the control of geopolymer elasticity, whilst only affecting the compressive strength to a minor degree. The conducted analysis showed that the 10% addition of perlite during the synthesis of geopolymers from fly ash causes an increase in the material elasticity, whilst reducing its compressive strength by 40%. It was also established that the application of the residual solution from the hydrothermal synthesis of zeolites produces geopolymer materials with improved heat-insulating properties, though with lower compressive strength than specimens obtained using NaOH. The proposed experiment confirms the possibility that fly ash can be effectively utilized to produce two useful materials (zeolites and geopolymers) without generating waste. This approach is fully in line with the principles of circular economy.

Phase transition pathway of hydrothermal zeolite synthesis

Zeolites are aluminosilicate minerals with multiple channels and cages. They are widely used in industry; further, owing to its increasing demand, the hydrothermal synthesis of zeolites from natural minerals/rocks has attracted great attention. This study aims to discuss the crystal growth mechanisms of zeolites from pumice. Pumice is a widely available porous volcanic glass (mainly consisting of 65–75% SiO2 and 9–20% Al2O3) that can be used in the fabrication of zeolites. In this study, zeolite was formed from pumice via a hydrothermal method with varying alkaline concentrations, reaction times and temperatures, and addition of NaCl. Zeolite Na-P1 was synthesized under conditions of 0.1 or 0.5 M at 150 °C. The feldspar phase (albite) initially occurred, followed by the zeolite phase (zeolite Na-P1). Phillipsite was an unstable intermediate product during this synthesis process. Based on these results, we suggest that the phase transformation sequence follows the order of albite, phillipsite, and zeolite Na-P1. Moreover, it can be speculated that an increase in cation concentration can induce a rapid occurrence of the zeolite phase (zeolite Na-P1). Raman spectrometry analyses provided insights into the formation mechanism of zeolite structures, indicating differences related to the number of sodium ions. Both zeolite Na-P1 and phillipsite are composed of four- and eight-membered rings, and the former is mainly grown with four-membered rings as the main structure. This study provides a low-cost and simple synthetic method for producing zeolite Na-P1 and phillipsite, which can be used as indicator minerals for marine/lake facies and in environmental treatment.

Study on One-Step Hydrothermal Synthesis of REY Zeolite from Kaolin Activated by Microwave Heating

Study on One-Step Hydrothermal Synthesis of REY Zeolite from Kaolin Activated by Microwave Heating

Hydrothermal synthesis of zeolites from green container glass

Landfilling and stockpiling unrecycled colored container glass represents a considerable failure in sustainability with respect to the conservation of energy and mineral resources. In this study, the single-step hydrothermal synthesis of low-silica zeolites from a mixture of waste green container glass and aluminum foil (Al:Si = 1) in 4 M NaOH(aq) at 125 °C was followed at 1, 3, 7 and 14 days. The principal phases, sodalite and cancrinite, appeared within 1 day accompanied by minor quantities of hydrogarnet and tobermorite arising from a stoichiometric excess of calcium ions in the parent glass. Products of 63, 67, 71 and 72% crystallinity were obtained at 1, 3, 7 and 14 days, respectively, with partial successive conversion of sodalite to cancrinite over time. Ion-exchange and catalytic applications of sodalite and cancrinite arise from the high anionic charge of the 1:1 ratio of alternating SiO44- and AlO45- units within their aluminosilicate frameworks. In this respect, the uptake capacity of the 14-day zeolitic product for Cu2+ and Cd2+ ions (1.58 meq g-1 and 1.66 meq g-1, respectively) was within the expected range for zeolites and compared favorably with those reported for other inorganic sorbents derived from industrial and municipal wastes. The 14-day product was also found to be an effective basic heterogeneous catalyst for the Knoevenagel condensation reaction.

Celgard-supported LiX zeolite membrane as ion-permselective separator in lithium sulfur battery

A novel ion-permselective separator comprised the top layer of LiX zeolite membrane and the support layer of commercial Celgard membrane, namely LiX@Celgard, was prepared and employed for the first time in Li–S battery. The LiX zeolite membrane was obtained via the in situ hydrothermal synthesis of NaX zeolite over the X-type zeolite-seeded Celgard membrane and the subsequent Li+ ion-exchange. The characterizations of LiX/Celgard separator by means of XRD, SEM, EDS and XPS showed that a continuous and compact layer of LiX zeolite crystals, with a thickness of ca. 6 μm, has been tightly grafted over the surface of Celgard support. The LiX@Celgard separator was proved to possess an improved electrolyte wettability and high efficiency for inhibiting the penetration of polysulfide (PSs). The electrochemical performance determination indicated that the Li-ion conductivity, diffusion coefficient and transference number were all larger for the battery basing on the LiX/Celgard separator than for that basing on the pristine Celgard separator. The above superior properties of LiX/Celgard separator restrained significantly the shuttle of PSs and improved obviously the efficiency in the utilization of sulfur. At a C-rate of 0.2 C, a specific capacity of ca. 1083 mAh/g, with a capacity retention of 70% after 400 cycles, had been achieved for the Li–S battery employing the LiX/Celgard separator. The strategy adopted in this work can be an enlightenment for the development of ion-selective membranes used in rechargeable battery and other energy storage field.

Evaluation of TiO2/ LTA Zeolite Incorporated Composite for Mutual Removal of Organic and Inorganic Pollutants: Simulation Study for Prediction of Removal Beyond Equilibrium

In this paper, incorporation of titanium nanoparticles into LTA zeolite (Linde Type A Zeolite) was synthesized by in-situ incorporation of titanium precursors within hydrothermal synthesis of LTA zeolite from local kaolin. More than one evidence for the presence of nano TiO2 including XRD, IR, DR, and SEM techniques. Mutual removal /photodecomposition of heavy metal/organic dye including methylene blue combined with as set of Co2+, Cu2+, Ni2+and Pb2+ ions was the main aim of this study. A four dimensional simulation program were written to predict for the first time both dye and ions with the fourth dimension of time. This program for the first time , is capable of prediction of the removal beyond the equilibrium state. The program was verified and percentage of error did not exceeds 3% with high accuracy. This study will open a new sight the use the modified zeolite as an effective photocatalyst in addition to its high performance of removal of heavy metals. New definitions of some new terminologies was impeded in the literature for the first time such as; Amount selectivity, Partial capacity, Time selectivity, Normalized selectivity, Remained capacity and Loop selectivity

Hydrothermal synthesis of tungsten-tin bimetallic MFI type zeolites and their catalytic properties for cyclohexene epoxidation

Abstract A series of tungsten-tin bimetallic MFI type zeolites (WSn-MFI) with different Sn and W contents were hydrothermally synthesized using tetrapropyl ammonium hydroxide (TPAOH) as a template and polypyrrolidone as a co-surfactant. Tetraethylorthosilicate (TEOS), ammonium tungstate hydrate and tin (IV) chloride pentahydrate were used as the Si, W and Sn sources, respectively. The resultant samples were characterized by various techniques, and were evaluated as catalysts for the epoxidation of cyclohexene with hydrogen peroxide. The results reveal that all the W–Sn bimetallic zeolites have the typical MFI structure, and their relative crystallinities and morphologies change somewhat with the variety of W and Sn contents. Both the isolated framework SnO4 species and the extra-framework SnO2 species could be detected in all WSn-MFI samples, while only trace amount of extra-framework W species are present inside the channels/cages of the bimetallic zeolites. Compared with the monometallic zeolites of W-MFI and Sn-MFI, the bimetallic WSn-MFI zeolites exhibit much higher catalytic activity for the epoxidation of cyclohexene. Of these, the sample named WSn-MFI-a could efficiently convert cyclohexene to the corresponding epoxide with a high yield of 79% under an optimized reaction condition. A synergistic effect between the W and Sn species should play critical role in improving the catalytic activity and the epoxide selectivity of the bimetallic zeolite catalysts.

Cost-effective and facile one step synthesis of ZSM-5 from silica fume waste with the aid of metakaolin and its NOx removal performance

The disposal of powdery silica fume waste has become an urgent environmental problem, the synthesis of zeolitic materials using silica fume is a commendable remedy to this crisis. In this study, a cost-effective and facile one-step strategy was proposed for the first time for hydrothermal synthesis of ZSM-5 zeolite using silica fume waste with the aid of inexpensive metakaolin in the absence of organic templates. This method allowed the total transformation of silica fume into ZSM-5 which exhibited similar characteristics to those obtained from conventional chemical reagents. The as-synthesized ZSM-5 under the optimized condition was used to prepare Ni, Cu and Zn/ZSM-5 catalysts by means of ion exchange and calcination treatments for NOx removal by NH3-SCR, and they exhibited high NO conversion of 92, 100, and 95%, respectively. This study would be a promising candidate for cost-effective and environment friendly synthesis of zeolite using silica fume waste in large scale.

Gas diffusion and adsorption capacity enhancement via ultrasonic pretreatment for hydrothermal synthesis of K-KFI zeolite with nano/micro-scale crystals

Abstract Small-pore zeolites have been a research hotspot in the field of gas adsorption and separation. Despite the high adsorption levels of these zeolites, the slow adsorption and desorption rate as well as desorption hysteresis are detrimental to the industrial applications. In this work, nano/micro-scale (~500 nm) K-KFI zeolite crystals were synthesized via hydrothermal and ultrasound-assisted (US) methods. The US-K-KFI zeolites obtained were characterized by means of X-ray diffraction, scanning electron microscopy, and nitrogen adsorption-desorption isotherms at 77 K. The effect of the ultrasonic treatment time on zeolite formation was investigated. The results revealed that the ultrasonic time had a significant effect on the morphology of the K-KFI zeolite, and the particle size was reduced from 1.5 μm to 500 nm. Furthermore, the sample ultrasonically treated for 3 h and crystallized for 1 day (US-K-KFI-3h/1d) exhibited the same high level of crystallinity as the sample hydrothermally crystallized for 3 days without ultrasonic treatment (HT-K-KFI-0h/3d). Compared with large-crystal (3 μm) zeolite (HT-K-KFI-0h/3d) at a given pressure, nano/micro-scale (500 nm) zeolite (US-K-KFI-10h/1d) was characterized by a shorter adsorption equilibrium time and exhibited enhanced mass transfer due to its shorter diffusion path. Moreover, compared with that of HT-K-KFI-0h/3d, the adsorption capacity of US-K-KFI-10h/1d for CO2, CH4, N2, and O2 was 31%, 24%, 18%, and 26% higher, respectively, at room temperature (298 K) and 1 bar. The results of this work showed that the ultrasound-assisted method represents a rapid and controllable means of synthesizing nano/micro-scale zeolites.

Spectroscopic studies of MFI and USY zeolite layers over stainless steel 316L wire gauze meshes.

The objective of our study was to develop and optimize the in situ synthesis of zeolitic thin coatings with USY (ultrastabilised form of faujasite) and MFI (Model Five) type structure on metallic structured catalysts supports using the hydrothermal method. Thus, obtained zeolitic materials were studied in terms of their prospective activity in selective catalytic reduction of nitrogen oxides (SCR of NOx) with ammonia. Optimization of the preparation method consisted of several steps including: the pretreatment of steel carrier to obtain an adhesive surface, hydrothermal synthesis of zeolites at different conditions and adjustment of the zeolite structure type (MFI vs. USY). As a result, uniform zeolitic layers were deposited on steel supports. Prepared structured supports were ion-exchanged with copper or cobalt precursors to obtain active catalysts and then characterised by various physicochemical methods with a particular reference to the in situ Fourier-Transform Infrared Spectroscopy (FTIR), Ultraviolet-Visible Diffusion Reflectance Spectroscopy (DRS-UV/VIS) and Raman spectroscopy. For CuUSY sample, slightly better catalytic properties are related to higher copper content. In the case of Co-samples, worse catalytic properties in comparison with Cu counterparts might imply from higher concentration of Brønsted acid sites, lower cobalt loading (thus concentration of Lewis acid sites) and the presence of cobalt cation significantly in oxide form (evidenced by Raman, DRS-UV/VIS spectroscopy and by in situ FT-IR sorption studies).