Static Hydrothermal Conditions Research Articles

Friedel-Crafts alkylation of benzene with benzyl alcohol over H-MCM-22

Abstract MCM-22 was synthesized by using silicic acid powder as a silica source under the static hydrothermal condition and characterized by X-ray diffraction, nitrogen adsorption-desorption isotherms, scanning electron microscopy, inductively coupled plasma optical emission spectrometry, and temperature-programmed desorption of ammonia. The liquid phase benzylation of benzene with benzyl alcohol to diphenylmethane was investigated over H-MCM-22. The effects of reaction parameters on the conversion of benzyl alcohol and product distribution were determined. Under optimal reaction conditions, diphenylmethane yield of 92.1% was achieved for 99.3% conversion of benzyl alcohol in 3 h of reaction period. The reusability of the catalyst was also investigated after calcination of the catalyst in stagnant air at 500 °C for 4 h. The results show that the organic species produced during the reaction deposited in the catalyst lead to the deactivation of the catalyst and the calcination of the deactivated catalyst causes catalyst dealumination.

One-step self-assembly of lamellar MWW crystals through intergrowth driven by centrifugal force to form hollownest structure Zeolite

From the considering of simple synthesis step, low cost, and energy saving, one-step synthesis of hierarchical zeolite without involving additional template has obvious advantages compared with post-synthetic modification or one-step templating methods, by which Ti-containing hollownest structure zeolite (Ti-HSZ) has been successfully synthesized. Herein, the origin of Ti-HSZʼs hollownest structure has been investigated by systematical comparison study between the rotating hydrothermal (RH) and static hydrothermal (SH) synthesis routes. It is found that different synthesis routes not only influence the crystallization but also determine the chemical and physical properties of zeolites. Compared with the catalyst prepared by flower-like precursor with larger size obtained by SH route in 12 days, Ti-HSZ catalyst with smaller size formed by RH route in 3.5 days shows higher catalytic activity for the epoxidation of bulky alkenes with H2O2. On one hand, the rapid and efficient transports of various reaction species in RH environment has accelerated the crystallization rate greatly; on the other hand, the one-step self-assembly of lamellar MWW crystals has happened to facilitate the formation of hollownest structure with hierarchical pores through intergrowth driven by centrifugal force. The different evolution processes of the Si chemical environments during the early stages of crystallization reflected by the percentage of intrinsic defects origin from the different hydrothermal environments. Highly mixed and dispersed reaction species under RH condition accelerate the uniform of gel concentration, and the condensation of smaller clusters with different orientation direction through frequent contacting under dynamic condition is easy to happen to form bigger clusters, which is the basis for the further crystal intergrowth. In contrast, the relatively inhomogeneous gel environments under SH condition has led to the increase of intrinsic defects in the solid phases, and bigger clusters tend to be formed by the condensation of smaller ones with the same orientation direction. This work will be instructive not only for the understanding of zeolites’ crystallization mechanism, but also for the design and synthesis of zeolite materials with unique morphology characteristics.

Influence of Alkalinity on the Synthesis of Zeolite A and Hydroxysodalite from Metakaolin

Kaolin is a cheap and abundant source of silica and alumina, which may be used as precursors for the production of zeolites, molecular sieves with pores in the nanometer scale. Brazil, one the largest producers of kaolin, generates tons of kaolin waste in the paper coating process. That waste may be used to synthesize zeolite A and hydroxysodalite, greater added value materials with a wide range of applications. In this work, Zeolite A and hydroxysodalite were synthesized from kaolin waste of processing industries for paper coating. Kaolin was calcined to dehydroxylate kaolinite and obtain metakaolin, an amorphous material with Si/Al ratio equal to 1, being suitable for production of zeolite A and hydroxysodalite. Zeolites were synthesized under static hydrothermal conditions by reacting metakaolin with NaOH solutions of different concentrations. The zeolitic products were characterized by means of X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). The results showed that the higher the NaOH concentration in the reaction medium, the higher the proportion of hydroxysodalite in the zeolitic samples.

Synthesis of Nano‐Hierarchical Ferrierite with Sole Template and Its Catalytic Application in n‐Butene Skeletal Isomerization

AbstractNano‐hierarchical ferrierite(FER) was successfully synthesized by using pyrrolidine as sole organic structure directing(OSDA) agent under static hydrothermal conditions.SEM images showed that the morphology of the product was a loose three‐stage accumulation structure by nano‐rod crystal grains .The influence of crystallization temperature, gel alkalinity, crystallization time and the amount of OSDA on synthesis of FER was investigated in detail.Moreover,FER catalytic performance in n‐butene skeletal isomerizatio was investigated.The results showed that, compared with the commercial FER, the nano‐hierarchical FER showed better catalytic activity.

Facile Synthesis of Perovskite-Structured Powders Using Barite–Celestite Ore under Hydrothermal Alkaline Conditions

Barite–celestite (BC) crystals were treated in highly concentrated alkaline hydrothermal fluid (5 M KOH) coexisting with a Ti(OH)4·4.5H2O gel to produce SrTiO3 particles between 150 and 250 °C for several intervals between 6 h and 96 h. The BC transformation was initiated at a lower temperature (150 °C) and the total precursors consumption was completed at 250 °C for 96 h, resulting only in the crystallization of SrTiO3 particles. Different temperatures of reaction (≤200 °C) lead to variations in morphology and particle size of the SrTiO3. The crystal growth of faceted cubic agglomerates was achieved at 250 °C, and it is provoked by the Oswald ripening mechanism. The release of barium to the hydrothermal fluid from the precursor occurred simultaneously with the transformation process. A low value of activation energy required for the single-step transformation of the BC plates into SrTiO3 particles was observed (26.33 kJ mol–1), under static hydrothermal conditions.

Nanocrystalline TON-type zeolites synthesized under static conditions

Pure-phase zeolites of the TON-type were synthesized under static hydrothermal conditions, which previously have, typically, required stirring during synthesis. Heterocyclic structure directing agents (SDAs) were observed to play important roles in both the selection of the polymorphs as well as in affecting the morphology of the particles formed. When an imidazole-based SDA was used snowflake-shaped particles formed, which indicated a dendritic growth pattern of the zeolite. These zeolite particles possessed intercrystalline mesopores. To the best of our knowledge, it is for the first time that snowflake-shaped particles have been observed for TON-type zeolites. Other synthesis parameters were optimized to obtain crystals with short c-axes. The c-axis shortened with an increased solid concentration used during synthesis. This shortening was attributed to both the degree of supersaturation, and a change of the crystal growth mechanism. Short c-axes could increase the concentration of pore mouths in TON-type zeolites. Altogether, synthesis of nanocrystalline zeolites of the TON type under static condition could, potentially, be advantageous to large-scale production.

Feather-like hornblende aggregates in the phyllites from the southern Sanandaj–Sirjan zone, Iran; their origin and mode of formation

Several outcrops of spectacular feather-like hornblende aggregates occur in the phyllites of the Gol-e-Gohar complex (southeast of Iran) and form special Garbenschiefer rock types. The Gol-e-Gohar complex, as a part of the southern Sanandaj-Sirjan metamorphic zone, contains a succession of metabasites, phyllites, and slates intruded by dioritic intrusions. There are two types of hornblendes in the phyllites; the first one is concentrated around the fractures and the second one is randomly distributed in the rocks and forms radial feather-like hornblende aggregates. Petrographical and chemical characteristics of these two shapes of hornblendes are the same, except the latter is developed parallel to the foliation planes. The hornblendes occur as unstrained needle-shaped porphyroblasts with oriented quartz and feldspar inclusions as well as polygonal grains in the matrix with mosaic texture, which implies the matrix has been recrystallized. On the basis of field observations, petrography, and chemical compositions of the hornblendes, we inferred that the Garbenschiefer phyllites formed during hydrothermal metamorphism in association with penetration of hot fluids. The compositions of hornblende aggregates are similar to those formed in hydrothermal systems and differ from regional and thermal metamorphic amphiboles. All evidence shows that, in the studied area, ascending of dioritic intrusions increases fluid temperature, the hot fluids leach some elements from the metabasites, and finally the enriched fluids flow upward via the fractures. In the upper levels, the fluids penetrate into the phyllites along their foliation planes and, with a decrease in temperature and pressure, they crystallize hornblende aggregates under static hydrothermal conditions.

On The Synthesis of Zeolite Y/ZSM-5 Composite via Novel Technique

This work focused on the development of Zeolite Y/ZMS-5 Composite via a novel synthesis strategy and thereafter determine its structure, chemical composition, morphology, surface area and pore size. Zeolite Y/ZSM-5 was developed via a novel two step crystallization process, under static hydrothermal conditions. Micro-porous precursor gel containing the nucleus of zeolite Y was first developed and used in the development of zeolite Y/ZSM-5 composite in the second step. The XRD analysis of the synthesized composite showed high crystallinity of approximately 71 %. It also possessed a DR pore diameter of 3.2 x 10-2 µm, Lewis to Bronsted acid site ratio of 0.287, particle size of 0.816 µm, Si to Al ratio of 42, pore volume of 0.089cc/g and BET surface area of 277.3 m2/g. The characterization result for the composite showed that both zeolite Y and ZSM-5 were present in the composite. Hence, the synthesized zeolite Y/ZSM-5 possesses good acid site, surface area, pore volume, particle size, high silica to alumina ratio and crystallinity, and it is potentially suitable for use as a fluid catalytic cracking catalyst.

Factors influencing formation of highly dispersed BaTiO3 nanospheres with uniform sizes in static hydrothermal synthesis

Highly dispersed BaTiO3 nanospheres with uniform sizes have important applications in micro/nanoscale functional devices. To achieve well-dispersed spherical BaTiO3 nanocrystals, we carried out as reported in this paper the systematic investigation on the factors that influence the formation of BaTiO3 nanospheres by the static hydrothermal process, including the NaOH concentrations [NaOH], molar Ba/Ti ratios (RBa/Ti), hydrothermal temperatures, and durations, with an emphasis on understanding the related mechanisms. Barium nitrate and TiO2 sols derived from tetrabutyl titanate were used as the starting materials. The as-synthesized BaTiO3 samples were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, thermogravimetry, differential thermal analysis, and FT-IR spectra. The highly dispersed BaTiO3 nanospheres (76 ± 13 nm) were achieved under the optimum hydrothermal conditions at 200 °C for 10 h: [NaOH] = 2.0 mol L−1 and RBa/Ti = 1.5. Higher NaOH concentrations, higher Ba/Ti ratios, higher hydrothermal temperatures, and longer hydrothermal durations are favorable in forming BaTiO3 nanospheres with larger fractions of tetragonal phase and higher yields; but too long hydrothermal durations resulted in abnormal growth and reduced the uniformity in particle sizes. The possible formation mechanisms for BaTiO3 nanocrystals under the static hydrothermal conditions were investigated.

Effects of Hydrothermal Duration on Synthesized Zeolite Rice Husk Particles

Zeolite particles were synthesized through in-situ extraction of silica from rice husk ash without seeding method in the absence of organic template by a static hydrothermal condition at various duration for 8, 12, and 24h. The effect amorphous silica content on hydrothermal duration of synthesis products was evaluated with X-ray diffraction (XRD), and field emission microscopy (FESEM). The present of zeolite Y without seeding method via XRD analysis show a mixture of zeolite A, Y and P. The transformation of amorphous rice husk particle was increased gradually with the increased of hydrothermal reaction. The FESEM images showed agglomerated cubic-shaped morphology of the powders with increase in crystallization reaction. .

The Characteristic of Synthesized Zeolite Rice Husk Particles via Different Routes

Zeolite particles were synthesized through in-situ extraction of silica from rice husk ash without seeding method in the absence of organic template by a static hydrothermal condition at 100oC/24h at varied ageing 8-24h. The effect of amorphous silica content on ageing time of synthesis products was evaluated with X-ray diffraction (XRD), Fourier transform infrared (FTIR) and field emission microscopy (FESEM). The present of zeolite Y without seeding method by XRD analysis show a mixture of zeolite A, Y and P. The transformation of amorphous rice husk particle gradually increased as early at 8 hours in ageing and increased with increase in ageing reaction. The vibration bands at around 974 cm-1 indicated Si-OH vibrations of the surface silanols, which is the characteristic of mesoporous silica. The FESEM images showed cubic-shaped morphology of the powders increased with increase in ageing reaction.

Hydrothermal controlled synthesis of Fe3O4 nanorods/graphene nanocomposite for high-performance lithium ion batteries

Controllably synthesized Fe3O4 nanorods/graphene nanocomposites (FNGC) with hydrothermal method were characterized by X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), N2 adsorption/desorption isotherms and Raman Spectra. The results illustrated that multicrystal Fe3O4 nanorods with a diameter of about 11nm and a length of more than 100nm were uniformly anchored on the surface of graphene sheets. N2 adsorption/desorption isotherms indicated that FNGC with mesoporous structure of 3–4nm possessed the specific surface area of 180m2/g. The influences of experiment conditions such as amount of graphite oxide, pH value, hydrothermal condition etc. on the morphologies of Fe3O4 in nanocomposites were investigated. The results indicated that the amount of graphite oxide, pH and static hydrothermal condition played crucial roles in the formation of FNGC. Besides, the relationship between the structure of Fe3O4/graphene nanocomposites and electrochemical properties has been investigated in this work..

THE EFFECT OF ULTRASONIC AND MICROWAVE-ASSISTED AGING ON THE SYNTHESIS OF ZEOLITE P FROM IRANIAN PERLITE USING BOX-BEHNKEN EXPERIMENTAL DESIGN

The synthesis of zeolite P under static hydrothermal conditions was performed with the synthesis mixture being treated by ultrasonic and microwave-assisted aging process prior to the onset of crystallization using perlite as silica and alumina sources. A statistical Box-Behnken design of experiments was employed to evaluate the effects of the synthetic process variables. The optimum condition for maximum zeolite crystallinity (97%) was obtained as microwave-assisted aging, 55 min aging time, and 4 h hydrothermal crystallization time from the statistical analysis of the experimental results. Also, the results showed that the synthesized zeolite formation time was drastically reduced in the case of the synthesis of zeolite P by microwave-assisted aging. The average pore diameter of synthesized zeolite P was increased 3 nm using ultrasonic-assisted aging, and the surface area of the product was three and one-half times that obtained using both ultrasonic and microwave-assisted aging.

Synthesis of ZSM‐5 Zeolite Particles Using Triethanol Amine as Structure‐Directing Agent

The ZSM‐5 zeolite particles have been prepared using triethanol amine as structure‐directing agent under static hydrothermal condition at 170°C for 7 days. The particles were characterized by X‐ray diffraction (XRD), thermogravimetry analysis (TGA), differential thermal analysis (DTA), Fourier transform infrared (FTIR) spectroscopy, N2 physisorption measurements, and field emission scanning electron microscopy (FESEM). The crystalline ZSM‐5 was found at 170°C/7 days as shown by XRD. The vibration bands at around 549 and 1226 cm−1 in the FTIR spectra indicated the presence of double 5‐ring in ZSM‐5. The exothermic peak at 395°C in DTA curve indicated the removal of structure‐directing agent. The BET surface area of the particles was 100 m2/g. The FESEM images showed coffin‐shaped and broom‐like crystals of ZSM‐5.

Hydrothermal synthesis of nanocrystalline zeolite Beta by acid-catalyzed hydrolysis of teraethylorthosilicate

Nanocrystalline zeolite Beta was synthesized via the acid-catalyzed hydrolysis of teraethylorthosilicate (TEOS) under static hydrothermal conditions. Various parameters, such as pH value for hydrolyzing TEOS, SiO 2/Al 2O 3 ratio, template content, crystallization temperature and time, were investigated to obtain the suitable synthesis conditions. The produced samples were characterized by XRD, SEM, TEM, IR, ICP, surface areas, pore volumes and pore distributions. Compared with the traditional base-catalyzed hydrolysis of TEOS, the silicate precursors created by the acid-catalyzed hydrolysis of TEOS are proved to be favorable to the formation of nanocrystalline zeolite Beta.

Organotemplate-free route for synthesizing SUZ-4 zeolite under static hydrothermal condition

SUZ-4 zeolite was prepared by the seeded static hydrothermal synthesis without the use of any organic templates. Non-seeded synthesis and dynamic hydrothermal procedure were also conducted for comparison. The produced samples were characterized by XRD, SEM, TEM, N 2-adsorption and TG techniques. It is found that the well crystallized SUZ-4 zeolite can be successfully achieved in the presence of a small amount of calcined seeds. The as-synthesized SUZ-4 structure already has open microporous channels, needless to be subjected to a further high-temperature calcination. It is suggested that the addition of the seed crystal causes the deposition of amorphous gel particles on its surface and induces the crystallization therein, through which the use of organic templates is avoided. This new route for the synthesis of SUZ-4 zeolite is simple and efficient to handle, more environmentally benign, and energy saving.

Ultrasonic‐Assistance and Aging Time Effects on the Zeolitation Process of BZSM‐5 Zeolite

AbstractThe isomorphic substitution of boron into ZSM‐5 zeolite under static hydrothermal condition was investigated. Evaluation of hydrothermal synthesis of BZSM‐5 was performed by treating the synthesis mixture by different aging processes, namely, ultrasonic, static, stirring, and microwave‐assisted aging prior to the conventional hydrothermal treatment. The synthetic processes with different techniques of aging prior to the onset of conventional hydrothermal crystallization were compared with a process without any prior aging. The obtained results showed that the ultrasonic and microwave assisted aging shortened the crystallization time and altered the crystal size and the morphology of the obtained products. The characteristics of the synthesized products were obtained by FT‐IR spectroscopic, XRD and SEM techniques.

Static and Ultrasonic‐assisted Aging Effects on the Synthesis of Analcime Zeolite

AbstractThe synthesis of zeolite ANA under static hydrothermal conditions was performed accompanied by an additional static and ultrasonic‐assisted aging of the reaction mixture prior to crystallization. The aging process was compared with stirring‐assisted aging, microwave‐assisted aging and syntheses without any aging. The influence of aging time on the crystallization time of zeolite ANA was investigated. The static and ultrasonic‐assisted aging can shorten the crystallization time of the ANA phase. Moreover, ultrasonic‐assisted aging leads to altered morphologies of the particles. The products were characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM).

A model for wet silicon carbide tribo-corrosion

Silicon carbide sustains chemical and mechanical deterioration during tribological exposure under water lubrication. In particular, tribochemical wear leads to the formation of a thin (tens to hundreds of nanometre) layer composed of nanoscale SiC wear debris embedded in a silica-like matrix (SiO x H y ) with possibly some minor oxycarbidic content. The SiC wear particles are plastically deformed and rounded as a result of mechanical tribolapping. Below that layer, subsurface damage builds up in the form of dislocations, ruptures and shear cracks. As a result of plastic deformation (similar to indentation plasticity) SiC single crystals within that transition zone are transformed into mosaic crystals with smaller domains due to slip plane gliding. Comparing results for static hydrothermal conditions (using a hydrothermal diamond anvil cell) and tribotest for the mild and severe wear regime (i.e., with and without external cooling) we derived a qualitative wear-model of wet silicon carbide tribo-corrosion. While mechanical contact yields pathways for water inflow and generally disrupts the structural integrity of SiC grains, hydrothermal reactions of trapped water and subsequent pressure relief leads to a mechanism of dissolution and reprecipitation. The latter produces the observed amount of SiO x H y which acts as an adhesive for the SiC wear debris.

Facile synthesis and morphology control of zeolite MCM-22 via a two-step sol–gel route with tetraethyl orthosilicate as silica source

MCM-22 zeolite was synthesized via a two-step sol–gel route (low pH sol–gel reaction followed by high pH crystallization) under static hydrothermal conditions using tetraethyl orthosilicate (TEOS) as silica source. Various parameters that significantly influence the synthesis results during both the hydrolysis reaction of TEOS in acid media and the hydrothermal reaction in base media were investigated in detail. The produced samples were characterized by XRD, ICP, and SEM techniques. It is found that pure MCM-22 with high crystallinity can be obtained via the novel two-step sol–gel route in a broad window of reaction conditions. The increase of temperature and pH value for the hydrolysis of TEOS favors the shortening of crystallization time and decreasing of MCM-22 particle size. Moreover, by adjusting the hydrothermal reaction parameters, such as increasing the crystallization temperature, increasing the alkalinity of the synthesis gel mixture, and decreasing the SiO 2/Al 2O 3 ratio, the crystallization is accelerated substantially. Also, rose-like or lamellar-like morphologies of MCM-22 particles with different sizes can be achieved by changing these reaction parameters. Using this two-step sol–gel route, MCM-22 is able to be well produced in a wide range of the SiO 2/Al 2O 3 ratio from 20 to 100.