Effects of ultrasonic treatment on zeolite NaA synthesized from by-product silica

The synthesis of zeolite NaA from silica by-product was carried out in the presence of 20 kHz ultrasound at room temperature. Zeolites obtained in this type of synthesis were compared to zeolites obtained by performing conventional static syntheses under similar conditions. The sonication effects on zeolite NaA synthesis were characterized by phase identification, crystallinity etc. The effects of different parameters such as crystallization time and initial materials preparation methods on the crystallinity and morphology of the synthesized zeolites were investigated. The final products were characterized by XRD and FT-IR. It was possible to obtain crystalline zeolite NaA from by-product silica in the presence of ultrasound.     

Synthesis of NaP zeolite at room temperature and short crystallization time by sonochemical method

NaP zeolite nano crystals were synthesized by sonochemical method at room temperature with crystallization time of 3 h. For comparison, to insure the effect of sonochemical method, the hydrothermal method at conventional synthesis condition, with same initial sol composition was studied. NaP zeolites are directly formed by ultrasonic treatment without the application of autogenous pressure and also hydrothermal treatment. The effect of ultrasonic energy and irradiation time showed that with increasing sonication energy, the crystallinity of the powders decreased but phase purity remain unchanged. The synthesized powders were characterized by XRD, IR, DTA TGA, FESEM, and TEM analysis. FESEM images revealed that 50 nm zeolite crystals were formed at room temperature by using sonochemical method. However, agglomerated particles having cactus/cabbage like structure was obtained by sonochemical method followed by hydrothermal treatment. In sonochemical process, formation of cavitation and the collapsing of bubbles produced huge energy which is sufficient for crystallization of zeolite compared to that supplied by hydrothermal process for conventional synthesis. With increasing irradiation energy and time, the crystallinity of the synthesized zeolite samples increased slightly.     

Ultrasonic assisted synthesis of Bikitaite zeolite: A potential material for hydrogen storage application

Li containing Bikitaite zeolite has been synthesized by an ultrasound-assisted method and used as a potential material for hydrogen storage application. The Sonication energy was varied from 150 W to 250 W and irradiation time from 3 h to 6 h. The Bikitaite nanoparticles were characterized by X-ray diffraction (XRD), infrared (IR) spectral analysis, and field-emission scanning electron microscopy (FESEM) thermo-gravimetrical analysis and differential thermal analysis (TGA, DTA). XRD and IR results showed that phase pure, nano crystalline Bikitaite zeolites were started forming after 3 h irradiation and 72 h of aging with a sonication energy of 150 W and nano crystalline Bikitaite zeolite with prominent peaks were obtained after 6 h irradiation of 250 W sonic energy. The Brunauer–Emmett–Teller (BET) surface area of the powder by N₂ adsorption–desorption measurements was found to be 209 m²/g. The TEM micrograph and elemental analysis showed that desired atomic ratio of the zeolite was obtained after 6 h irradiation. For comparison, sonochemical method, followed by the hydrothermal method, with same initial sol composition was studied. The effect of ultrasonic energy and irradiation time showed that with increasing sonication energy, and sonication time phase formation was almost completed. The FESEM images revealed that 50 nm zeolite crystals were formed at room temperature. However, agglomerated particles having woollen ball like structure was obtained by sonochemical method followed by hydrothermal treatment at 100 °C for 24 h. The hydrogen adsorption capacity of Bikitaite zeolite with different Li content, has been investigated. Experimental results indicated that the hydrogen adsorption capacities were dominantly related to their surface areas as well as total pore volume of the zeolite. The hydrogen adsorption capacity of 143.2 c.c/g was obtained at 77 K and ambient pressure of (0.11 MPa) for the Bikitaite zeolite with 100% Li, which was higher than the reported values for other zeolites. To the best of our knowledge, there is no report on the synthesis of a Bikitaite zeolite by sonochemical method for H₂ storage.     

Facile synthesis of mesoporous ZSM-5 aided by sonication and its application for VOCs capture

Application of ultrasound power to the mother liquor is popular pretreatment for zeolite synthesis which offers a simple way of accelerating crystallization process and finetuning the properties of nanocrystalline zeolites. In this work, sonication-aided synthesis of mesoporous ZSM-5 at low temperature and ambient pressure was systematically studied, in an attempt to reach efficient and benign synthesis of zeolites with hierarchical pore structure, which has wide applications as catalysts and sorbents. The effects of sonication duration, power density, sonication temperature and seeding on the crystallization of ZSM-5 were investigated. The obtained samples were characterized by XRD, SEM, BET and VOCs capture. High quality mesoporous ZSM-5 can be obtained by a facile 5 d synthesis at 363 K, much faster than conventional hydrothermal synthesis. The reduced synthesis time was mainly attributed to the enhanced crystallization kinetics caused by the fragmentation of seeds and nuclei, while sonication radiation had little impact on the nucleation process. Compared with control sample, mesoporous ZSM-5 prepared by sonochemical method had higher surface area and mesoporosity which demonstrated improved adsorption performance for the capture of isopropanol.     

Experimental and numerical investigation of the effect of ultrasound on the growth kinetics of zeolite A

Ultrasound is a promising technology for the improvement of zeolite production, due to its beneficial effects on mass transfer and nucleation. However, a broad understanding of the sonication parameters that influence the growth of zeolites most is still lacking. In the present work, zeolite A was synthesized and the kinetic model of Gualtieri was used to obtain information about the crystallization parameters. The effect of the sonication power and duration on the relative crystallinity and particle size distribution were investigated using a Langevin-type transducer operating at 40 kHz. The experimental data shows that ultrasound has a significant effect on the nucleation and growth. With that, a reduction of up to 40 % of the initial synthesis time can be achieved. Additionally, a narrower particle size distribution is achieved when ultrasound is used during the zeolite A synthesis.     

Nanocrystalline zeolite beta and zeolite Y as catalysts in used palm oil cracking for the production of biofuel

Nanocrystalline zeolites with crystal size smaller than 100 nm are potential replacement for conventional zeolite catalysts due to their unique characteristics and advantages. In this study, the synthesis of nanocrystalline zeolite Y (FAU) and nanocrystalline zeolite beta (BEA) under hydrothermal conditions is reported. The effect of crystal size on the physico-chemical characteristics of the zeolite, Y (FAU), and beta (BEA) is reported. The properties of nanocrystalline zeolites Y and Beta with crystal size around 50 nm are compared with the microcrystalline zeolite Y and microcrystalline zeolite beta, respectively. The performance of the nanocrystalline zeolite as a catalyst was investigated in the cracking of used palm oil for the production of biofuel. The nanocrystalline zeolite catalytic activity was compared with the activity of microcrystalline zeolite in order to study the effect of crystal size on the catalytic activity. Both nanocrystalline zeolites gave better performance in terms of conversion of used palm oil as well as selectivity for the formation of gasoline fraction. The increase in surface area and improved accessibility of the reactant in nanocrystalline zeolites enhanced the cracking activity as well as the desired product selectivity.     

Sonochemically prepared hierarchical MFI-type zeolites as active catalysts for catalytic ethanol dehydration

In this paper, the ultrasonic-assisted desilication technique was reported as an attractive and efficient way for the preparation of hierarchical zeolites with MFI structure type. The prepared materials were used as active catalysts for the dehydration of ethanol into diethyl ether and ethylene. For all catalysts, the selectivity to diethyl ether was ca 95% or higher up to 210 °C, with catalytic activity in the range of 40–68%. In case of desilicated zeolites, at 270–290 °C, the conversion of ethanol was full with selectivity to ethylene ca 80%. MFI-type commercial zeolite was treated with a sodium and/or tetrabutylammonium hydroxide aqueous solutions (NaOH or NaOH/TBAOH) for 30 min. In the case of the application of ultrasounds, a QSonica Q700 sonicator (60 W and 20 kHz) equipped with a “1” diameter horn was used. In all cases, desilication was performed in an ice bath in order to keep the procedure conditions at low temperature.It was indicated that the use of ultrasounds during desilication procedure caused higher extraction of silicon and aluminum, which was connected with an elevated mesoporosity in relation to the samples modified in the absence of ultrasounds. Ultrasonic-assisted treatment of MFI-type zeolite caused also an apparent formation of numerous holes inside zeolite grains, resembling the look of “swiss cheese”. Furthermore, it was indicated that the samples prepared using ultrasonic irradiation exhibited enhanced catalytic properties in the dehydration of ethanol. For instance, MFI-type zeolite treated with NaOH/TBAOH alkaline mixture containing 10 mol% of TBAOH in the presence of ultrasounds (M−10 s) demonstrated higher both conversion of ethanol (59% vs. 47%) and selectivity to diethyl ether (95% vs. 93%) in comparison with zeolite modified conventionally (M−10c).The best catalyst was zeolite ultrasonically desilicated with NaOH/TBAOH solution of 70 mol% of TBAOH (M-70s). Generally, this catalyst indicated the highest conversion of ethanol, very high selectivity to diethyl ether (94-100%) at 150-210  °C and the highest selectivity to ethylene among investigated catalysts (21%, 66% and 84%) at 230  °C, 250 ^oC and 270  °C.     

Ultrasound-assisted rapid hydrothermal design of efficient nanostructured MFI-Type aluminosilicate catalyst for methanol to propylene reaction

The influence of ultrasound-assisted rapid hydrothermal synthesis of aluminosilicate ZSM-5 catalysts was examined in this work. A series of MFI-type nanostructured materials with sonochemical approach and conventional heating were synthesized and evaluated for conversion of methanol to propylene reaction. The prepared samples were tested by characterization analyses such as XRD, FESEM, BET-BJH, FTIR, TPD-NH₃ and TG/DTG. The obtained results confirmed that ultrasound treatment enhanced the nucleation process and crystal growth for ZSM-5 sample synthesized at moderate temperature of 250 °C. Therefore, it was found the formation of pure MFI zeolite with high crystallinity and improved textural, structural and acidic properties for ZSM-5(UH-250) sample compared with the other zeolites. This observation was attributed to the relationship between the perfect crystallization mechanism and catalytic properties, which led to producing an efficient MFI zeolite toward the optimal catalytic performance. In this manner, the methanol conversion and products selectivity of prepared materials were carried out in MTP reaction at 460 °C and atmospheric pressure. The ZSM-5(UH-250) zeolite with slower deactivation regime exhibited the constant level of methanol conversion (84%) and high propylene selectivity (78%) after 2100 min time on stream. Moreover, the synthesis pathway for MFI zeolite at moderate temperature and also deactivation mechanism of improved sample were proposed.     

Rapid-synthesis of zeolite T via sonochemical-assisted hydrothermal growth method

Sonochemical-assisted method has been identified as one of the potential pre-treatment methods which could reduce the formation duration of zeolite as well as other microporous and mesoporous materials. In the present work, zeolite T was synthesized via sonochemical-assisted pre-treatment prior to hydrothermal growth. The durations for sonochemical-assisted pre-treatment were varied from 30 min to 90 min. Meanwhile, the hydrothermal growth durations were ranged from 0.5 to 3 days. The physicochemical properties of the resulting samples were characterized using XRD, FESEM, FTIR and BET. As verified by XRD, the samples synthesized via hydrothermal growth durations of 1, 2 and 3 days and sonochemical-assisted pre-treatment durations of 60 min and 90 min demonstrated zeolite T structure. The samples which underwent sonochemical-assisted pre-treatment duration of 60 min yielded higher crystallinity with negligible change of zeolite T morphology. Overall, the lengthy synthesis duration of zeolite T has been successfully reduced from 7 days to 1 day by applying sonochemical-assisted pre-treatment of 60 min, while synthesis duration of 0.5 days via sonochemical-assisted pre-treatment of 60 min was not sufficient to produce zeolite T structure.     

Synthesis of zeolite A from coal fly ash using ultrasonic treatment – A replacement for fusion step

The synthesis of zeolites from fly ash has become an increasingly promising remedy to the crisis of coal fly ash production and disposal in South Africa. In recent studies, South African fly ash was proven to be a suitable feedstock for the synthesis of essential industrially used zeolite A. However, the process involves a costly energy intensive step whereby fly ash is fused at high temperatures, which may make the process economically unattractive on a large scale. The aim of this study is to investigate the possibility of replacing high temperature fusion with less energy intensive sonochemical treatment for the synthesis of zeolite A. Sonochemical treatment was first thought possible due to the violent cavitation caused by high intensity sonication. The results of the study showed that fusion can be replaced by 10 min of high intensity sonication. The incorporation of sonication also consequently reduced the crystallization temperature of the process making it possible to synthesize a pure phase zeolite A at lower temperatures and reduced times. This study effectively developed a novel process to replace the energy intensive fusion step with a short, easy and inexpensive treatment. Scale up of this synthesis approach may proffer a promising alternative option to the anticipated energy demand of the synthesis of fly ash-based zeolite with fusion method.     

The use of the high pressure hydrothermal method for tailored synthesis of zeolites without structure directing agents. Instance: Synthesis of natural zeolites with 5-1 building units

Abstract

The synthetic counterparts of natural alumosilicate zeolites containing 5-1 structural building units have been synthesized by simulating the natural hydrothermal formation conditions. Synthetic glasses of the respective zeolite composition were used as starting materials, while distilled water under hydrothermal conditions was used as pressure and reaction medium. No structure directing agents, additional solutions or sol-gel material has been employed.

The experience of former investigations on the tailored synthesis of alumosilicate zeolites showed, that 220°C is the expected temperature of maximum gain. Synthesis time was always 60 d. Synthesis pressure for mazzite (MAZ), mordenite (MOR), fer-rierite (FER), epistilbite (EPI) and dachiardite PAC) was 1 kbar while bikitaite (BIK) could only be synthesized at 2 kbar pressure.

The results of the investigations on hand show, that this process can be applied for the tailored synthesis of zeolites with completely new properties (e.g., semiconducting frameworks).     

Key factor affecting the structural and textural properties of ZSM-5/MCM-41 composite

ZSM-5/MCM-41 micro/mesoporous composite materials were synthesized by the hydrothermal technique with alkali-treated ZSM-5 zeolite as source of silica and aluminum and characterized by various physico-chemical techniques such as X-ray diffraction (XRD), nitrogen sorption at 77 K, transmission electronic microscopy (TEM), FTIR spectroscopy and NH₃ temperature programmed desorption (TPD) techniques. The effect of concentration of CTAB in the synthesis of these solids has been investigated, the mesopore volume, surface area and surface acidity decrease with increasing the concentration of CTAB. Increasing the CTAB concentration causes the recrystallization of zeolite ZSM-5 and it disadvantage the formation of mesoporous materials MCM-41. The catalytic activity of ZSM-5/MCM-41 materials has been evaluated in the Friedel–Crafts acylation of anisole with benzoyl chloride as alkylating agent. The results revealed the reaction to be influenced by surface area, pore volume and surface acidity.     

Synthesis of MCM-22 zeolite by an ultrasonic-assisted aging procedure

The synthesis of MCM-22 zeolite under hydrothermal crystallization conditions has been performed by an ultrasonic-assisted aging procedure. The ultrasonic-assisted aging of the initial aluminosilicate gel can shorten the crystallization time of MCM-22, decrease the amount of hexamethyleneimine (HMI) used, and broaden the range of SiO(2)/Al(2)O(3) ratios. By using the ultrasonic aging, pure phase of high-silica MCM-22 products with SiO(2)/Al(2)O(3)>100 can be obtained. When SiO(2)/Al(2)O(3) 相似文献   

Sonochemical synthesis of zeolite NaP from clinoptilolite

In the present work, natural clinoptilolite was converted to zeolite NaP using ultrasonic energy, in which the transformation time shortened remarkably. The effect of post-synthesis treatment using conventional hydrothermal was also investigated. The synthesized powders were characterized by XRD, TGA/DTA, SEM, and PSD analysis. The results showed that, increasing the sonication time (energy) has no significant effect on the product’s morphology. The crystallinity of the synthesized samples increased slightly with increasing sonication time, but their yield remained relatively unchanged. Furthermore, post-synthesis hydrothermal treatment showed very little influence on properties of the final product. Because the ultrasonic irradiation creates acoustic cavitation cracks on the surface structure of clinoptilolite particulates and increases the concentration of soluble alumino-silicate species, which favors the prevailing super-saturation, crystallization and crystal growth of zeolite NaP happen faster. The particles of zeolite NaP synthesized by ultrasonic irradiation consist of small crystallites of uniform size.     

Effects of ultrasonic irradiation on crystallization kinetics,morphological and structural properties of zeolite FAU

In this work, NaX zeolite was synthesized and the effect of ultrasound irradiation on reaction kinetics, morphological and structural properties was investigated. Ultrasound was applied, by using a plate transducer (91.8 kHz), for the first time during the crystallization of zeolite NaX, at high temperature, varying the irradiation moment and its duration. Furthermore, ultrasound was applied after the crystallization by a horn-type transducer (20–24 kHz) at low temperature. The effects of irradiated volume (100–300 mL), sonication time (2–10 min) and ultrasound power (10–200 W) were studied with a power intensity up to 100 W/cm². It was found that the application of ultrasound during the first hour of crystallization resulted in 20% reduction of reaction time compared to a standard crystallization. Ultrasound can also reduce the agglomeration degree of the final powder by combining high power and long sonication time. After 5 min sonication time at 0.3 W/mL, the tapped density of the powder was increased by 10%, from 0.37 to 0.41 g/mL. Finally, by scanning electron microscopy (SEM) it was demonstrated that ultrasound can disrupt the agglomerates without affecting the morphology of individual crystals.     

Synthesis, characterization, and ion-exchange properties of colloidal zeolite nanocrystals

Here, we present physical–chemical properties of Linde type A (LTA) zeolite crystals synthesized via conventional hydrothermal and microwave heating methods. Both heating methods produced LTA crystals that were sub-micron in size, highly negatively charged, super-hydrophilic, and stable when dispersed in water. However, microwave heating produced relatively narrow crystal size distributions, required much shorter heating times, and did not significantly change composition, crystallinity, or surface chemistry. Moreover, microwave heating allowed systematic variation of crystal size by varying heating temperature and time during the crystallization reaction, thus producing a continuous gradient of crystal sizes ranging from about 90 to 300 nm. In ion-exchange studies, colloidal zeolites exhibited excellent sorption kinetics and capacity for divalent metal ions, suggesting their potential for use in water softening, scale inhibition, and scavenging of toxic metal ions from water.     

Effect of ultrasound on the synthesis of low-modulus zeolites from a metakaolin

It was studied the effect of ultrasonic processing (22 kHz) of the aqueous suspension of metakaolin, sodium hydroxide and alumina with a molar ratio 2Al₂Si₂O₇:12NaOH:2Al₂O₃ on the low-modulus zeolite synthesis processes. To investigate the XRD, SEM, IR, EDS had been used. It was shown that after ultrasonic processing, sodium aluminates are formed, what leads to a change in process of further synthesis. It was found that without ultrasonic processing on the stage of thermal treatment at 650 °C, SOD zeolite (|Na₆|[Al₆Si₆O₂₄]) and sodium aluminosilicate (Na₆Al₄Si₄O₁₇) are synthesized. In the sample after ultrasound during thermal treatment, only sodium aluminosilicates of cubic syngony (Na₆Al₄Si₄O₁₇ and Na₈Al₄Si₄O₁₈) are formed. It was demonstrated that sodium aluminosilicates are precursors for the formation of LTA zeolite (|Na₁₂|[Al₁₂Si₁₂O₄₈]). As a result zeolitization of sodium aluminosilicates after the hydrothermal crystallization in alkaline solution, the sonicated sample contained 97 wt% LTA. Without ultrasonic processing, the product of synthesis contained 50 wt% SOD and 40 wt% LTA.     

Novel two-layered zeolite NaA-silicalite-1 membranes

A two-layered zeolite NaA-silicalite-1 membrane has been successfully prepared on a porous α-alumina tube by using seeded hydrothermal synthesis. The procedure involves pre-seeding with nanosized seed and subsequent regrowth by hydrothermal treatment. Single-layered NaA and silicalite-1 membranes were also synthesized for comparison. The membrane was composed of a silicalite-1 layer on top and a NaA layer on the porous support. SEM results of the membrane indicate that both the silicalite-1 layer and the NaA layer are uniform and well-intergrown. The silicalite-1 and NaA layers in the ‘sandwich’ mode have similar thickness of 3-4 μm, whereas the thickness of their respective seed layer is different. The NaA seed layer is much thicker than the silicalite-1seed layer. This may be attributed to the different capillary action on the support and NaA layer during using a slip-casting seeding method. XRD analysis has also proved both zeolite NaA and zeolite silicalite-1 layers coexist in the dual-layered membrane. This method is also suitable for preparing other multi-layer zeolite membranes.     

Ultrasonic waves induce rapid zeolite synthesis in a seawater solution

The synthesis of zeolites from fly ash was performed through a low-temperature hydrothermal process with seawater. Compared with the results obtained using the same hydrothermal method but in the absence of sonication, the application of an ultrasonic pre-treatment to the conventional hydrothermal process with seawater reduces the crystallization temperature below that observed when hydrothermal synthesis is performed using distilled water.     

Hydrothermal stability of zeolites: Determination of extra-framework species of H-Y faujasite-type steamed zeolite

Zeolite H-Y of faujasite type (Si/Al=2.70) was hydrothermally treated at different temperatures in the range between 403 and 473 K for 72 h in liquid water (=saturated steam), by use of a water/H-Y zeolite ratio of 100. The batch was treated in Teflon-coated autoclaves at different temperatures and thus different steam pressures. Treated samples show growth of decomposition with increasing temperature. The parent H-Y zeolite and the hydrothermally treated H-Y zeolite samples, as well as obtained transformation products, were characterized by IR spectroscopy, water sorption uptake and XRD methods. The hydrothermal destruction process of H-Y zeolite into extra framework aluminum and silicon species is visible at 423 K and is followed by growth of kaolinite and amorphous substances such as silica and probably metakaolinite. These processes are slow at 423 K and accelerate between 443 and 473 K. The appearance of kaolinite as transformation product is experimentally identified for the first time. The structural transformation mechanism of H-Y zeolite to kaolinite, silica gel and metakaolinite was suggested and discussed.