Pour voir les autres types de publications sur ce sujet consultez le lien suivant : Organic zeolites.
Articles de revues sur le sujet « Organic zeolites »
Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres
Consultez les 50 meilleurs articles de revues pour votre recherche sur le sujet « Organic zeolites ».
À côté de chaque source dans la liste de références il y a un bouton « Ajouter à la bibliographie ». Cliquez sur ce bouton, et nous générerons automatiquement la référence bibliographique pour la source choisie selon votre style de citation préféré : APA, MLA, Harvard, Vancouver, Chicago, etc.
Vous pouvez aussi télécharger le texte intégral de la publication scolaire au format pdf et consulter son résumé en ligne lorsque ces informations sont inclues dans les métadonnées.
Parcourez les articles de revues sur diverses disciplines et organisez correctement votre bibliographie.
1
Nursanti, Ida, et Nida Kemala. « Peranan Zeolit dalam Peningkatan Kesuburan Tanah Pasca Penambangan ». Jurnal Media Pertanian 4, no 2 (11 novembre 2019) : 88. http://dx.doi.org/10.33087/jagro.v4i2.84.
Texte intégralRésumé :
ABSTRACTPost-mining soils have poor chemical and physical properties and have very low fertility rates. The study aims to determine the best dose of zeolite in order to improve soil fertility after mining as a planting medium. The experiment was carried out experimentally by giving zeolites (Z) and 3 treatment levels, namely: Z0 = without zeolites, Z1 = zeolites 100 g, Z2 = zeolites 200 g. There were 3 replications, so 9 unit experiments were obtained. The final analysis of research on soil chemistry consists of; Available P, total N, K-exs, C-organic and CEC, pH. Data analysis of the diversity of characteristics of post-mining soil types is presented in tabular form and discussed descriptively. Provision of 200 grams zeolite of 10 kg post-mining land (equivalent to 20 tons Ha-1 of zeolite ) and incubated for eight weeks can increase soil pH, total N, K-dd, available P andCECsoil. Keywords: Zeolites and post-mining soils ABSTRAKTanah pasca penambangan memiliki sifat kimia dan fisik yang kurang baik serta memiliki tingkat kesuburan yang sangat rendah. Penelitian bertujuan mengetahui menentukan dosis zeolit terbaik agar dapat memperbaiki kesuburan tanah pasca penambangan terkait sebagai media tanam. Percobaan dilakukan secara eksperimen dengan pemberian zeolit (Z) dan 3 taraf perlakuan yaitu :Z0= tanpa zeolit, Z1 = zeolit 100 g, Z2 = zeolit 200 g. Terdapat 3 ulangan, sehingga diperoleh 9 unit percobaan. Analisis akhir penelitian terhadap kimia tanah terdiri dari; P tersedia, N total, K-dd, C-organik dan KTK, pH. Analisis data keragaman karakteristik jenis tanah pasca penambangan disajikan dalam bentuk tabel dan dibahas secara deskriptif. Pemberian zeolit 200 gram per 10 kg tanah pasca tambang (setara 20 ton zeolit per Ha) dan diinkubasi selama delapan minggu dapat meningkatkan pH tanah, N-total, K-dd, P tersedia dan KTK tanah. Kata kunci : Zeolit dan tanah pasca penambangan.
2
Asgar Pour, Zahra, et Khaled O. Sebakhy. « A Review on the Effects of Organic Structure-Directing Agents on the Hydrothermal Synthesis and Physicochemical Properties of Zeolites ». Chemistry 4, no 2 (13 mai 2022) : 431–46. http://dx.doi.org/10.3390/chemistry4020032.
Texte intégralRésumé :
The study on the synthesis of zeolites, including both the development of novel techniques of synthesis and the discovery of new zeolitic frameworks, has a background of several decades. In this context, the application of organic structure-directing agents (SDAs) is one of the key factors having an important role in the formation of porous zeolitic networks as well as the crystallization process of zeolites. There are various elements that are needed to be explored for elucidating the effects of organic SDAs on the final physicochemical properties of zeolites. Although SDAs were firstly used as pore generators in the synthesis of high-silica zeolites, further studies proved their multiple roles during the synthesis of zeolites, such as their influences on the crystallization evolution of zeolite, the size of the crystal and the chemical composition, which is beyond their porogen properties. The aim of this mini review is to present and briefly summarize these features as well as the advances in the synthesis of new SDAs during the last decades.
3
Qiu, Liyan, Patricia A. Laws, Bi-Zeng Zhan et Mary Anne White. « Thermodynamic investigations of zeolites NaX and NaY ». Canadian Journal of Chemistry 84, no 2 (1 février 2006) : 134–39. http://dx.doi.org/10.1139/v05-244.
Texte intégralRésumé :
Understanding of the thermodynamic stability of zeolites is important in the prediction of thermodynamic equilibrium. Therefore, we have undertaken an investigation of the thermodynamic stability of the zeolites NaX and NaY through heat capacity measurements from ca. 30 to 300 K. No phase transitions were observed, and zeolite NaX does not show a significant particle size effect when the particle size is reduced to ca. 30 nm. The results show that the specific heat capacity increases with the Al content in the zeolite. Both NaX and NaY are found to be thermodynamically stable with respect to their elements because of enthalpic stabilization and with slight entropic destabilization. These data are used along with literature data for many other zeolitic materials to show that the thermodynamic stability of zeolites is enhanced with increasing aluminum content. Key words: zeolite, heat capacity, thermodynamic stability, nano effects.
4
Gackowski, Mariusz, Jerzy Podobiński, Ewa Broclawik et Jerzy Datka. « IR and NMR Studies of the Status of Al and Acid Sites in Desilicated Zeolite Y ». Molecules 25, no 1 (20 décembre 2019) : 31. http://dx.doi.org/10.3390/molecules25010031.
Texte intégralRésumé :
The desilication of zeolite Y (of Si/Al = 31) that was previously dealuminated by steaming and acid treatment was studied. Desilication of zeolites of high Si/Al module in alkali solutions extracts both Si and Al from zeolite crystals, but while Si remains in solution, Al is reinserted into the zeolite grain. The main goal of our study was to follow the status of Al reinserted into zeolite during the desilication procedure, and its role in the formation of acid sites of the Brønsted and Lewis types. The properties of Al were followed by 27Al MAS NMR spectroscopy (for parent samples and zeolites treated either with NaOH or NaOH/tetrabutylammonium hydroxide), whereas the acid sites generated in the final stages were studied by IR spectroscopy with NH3 and CO as probe molecules. In non-desilicated zeolite, most of the Al was in a typically zeolitic tetrahedral coordination, while both NMR and quantitative IR studies of NH3 sorption evidenced that Al that was extracted by desilication and was subsequently reinserted had a tetrahedral coordination similar to amorphous aluminosilicates and showed an ion exchange ability. After the exchange of Na+ to NH4+ and decomposition of NH4+ ions, reinserted Al forms generated protonic sites from which some condensed at higher temperatures producing Lewis acid sites (with stoichiometry typical for zeolites i.e., the condensation of two protonic sites produces one Lewis site) but some other kept their character.
5
Erofeev, Vladimir I., Sofiya N. Dzhalilova, Mikhail V. Erofeev, Vasilii S. Ripenko et Vladimir P. Reschetilowski. « Conversion of the Propane–Butane Fraction into Arenes on MFI Zeolites Modified by Zinc Oxide and Activated by Low-Temperature Plasma ». Molecules 25, no 11 (11 juin 2020) : 2704. http://dx.doi.org/10.3390/molecules25112704.
Texte intégralRésumé :
The effect of modification of MFI zeolite 1–5 wt.% ZnO activated by plasma on acid and catalytic properties in the conversion of the propane–butane fraction into arenes was investigated. The high-silica zeolites with silicate module 45 were synthesized from alkaline alumina–silica gels in the presence of an ‘X-oil’ organic structure-forming additive. The modification of the zeolite with zinc was carried out by impregnating the zeolite granules in the H-form with an aqueous solution of Zn(NO3)2. The obtained zeolites were characterized by X-ray phase analysis and IR spectroscopy. It is shown that the synthesized zeolites belong to the high-silica MFI zeolites. The study of microporous zeolite-containing catalysts during the conversion of C3-C4 alkanes to aromatic hydrocarbons made it possible to establish that the highest yield of aromatic hydrocarbons is observed on zeolite catalysts modified with 1 and 3% ZnO and amount to 63.7 and 64.4% at 600 °C, respectively, which is 7.7–8.4% more than on the original zeolite. The preliminary activation of microporous zeolites modified with 1–5% ZnO and plasma leads to an increase in the yield of aromatic hydrocarbons from the propane–butane fraction; the maximum yield of arenes is observed in zeolite catalysts modified with 1 and 3% ZnO and activated by plasma, amounting to 64.9 and 65.5% at 600 °C, respectively, which is 8.9–9.5% more than on the initial zeolite. The activity of the zeolite catalysts modified by ZnO and activated by plasma show good agreement with their acid properties. Activation of the zeolites modified by 1 and 3% ZnO and plasma leads to an increase in the concentration of the weak acid sites of the catalyst to 707 and 764 mmol/g in comparison with plasma-inactivated 1 and 3% ZnO/ZKE-XM catalysts at 626 and 572 mmol/g, respectively.
6
Asefa, Misikir Tamiru, et Gebisa Bekele Feyisa. « Comparative Investigation on Two Synthesizing Methods of Zeolites for Removal of Methylene Blue from Aqueous Solution ». International Journal of Chemical Engineering 2022 (12 février 2022) : 1–12. http://dx.doi.org/10.1155/2022/9378712.
Texte intégralRésumé :
Organic dyes discharged from industries have significant effect on ecosystem and health of human being because of their toxicity and appearing colour in the wastewater. Absorption method is a more preferable method than other wastewater treatment methods due to its characteristics of being eco-friendly, simple, and efficient. Zeolites are among the porous materials often used as absorbent of organic dye from wastewater. However, wide use of zeolite has been limited due to its expensive precursors and synthesized methods (i.e., hydrothermal method which needs expensive autoclave). In this work, cheap and widely available precursors aluminum from waste food packaging aluminum foil and low cost silica from sugar cane bagasse ash were used to synthesized zeolite without hydrothermal method (Z-B), where hydrothermally synthesized zeolite (Z-A) was used as a reference. The XRD patterns revealed that Z-B was sodalite octahydrate zeolite and Z-A was zeolite Linde Type A (LTA). The morphology and type of bond in both zeolites were investigated by SEM and FTIR. The synthesized zeolites were used as absorbents for absorbing methylene blue (MB) from aqueous solutions. The MB removal efficiency of the synthesized zeolites was evaluated by using UV-Visible spectroscopy. The results indicate that the absorption capacities of Z-B and Z-A were 3.5 mg/g and 3.9 mg/g at 40 mg/L, respectively. Optimum removal efficiencies of both zeolites were observed at PH of 7 and adsorbent dosage of 0.005 mg/L. The stabilities of both zeolites were tested three times. The absorption isotherms of sodalite octahydrate zeolite and zeolite LTA were effectively fitted with the Freundlich and Langmuir modes. Moreover, the absorption kinetics of both zeolites follow pseudo-second-order kinetics. Therefore, nonhydrothermally synthesized zeolite is alternative absorbent for dye removal due to its safety, cheap cost, using low cost and widely available precursors, and using easy and safe synthesizing method.
7
Behin, Jamshid, Elmira Ghadamnan et Hossein Kazemian. « Recent advances in the science and technology of natural zeolites in Iran ». Clay Minerals 54, no 2 (24 mai 2019) : 131–44. http://dx.doi.org/10.1180/clm.2019.19.
Texte intégralRésumé :
AbstractIran has significant deposits of high-purity natural zeolites. Many Iranian scholars conduct scientific research on porous materials, from natural and synthetic zeolites to metal organic framework materials. Iranian zeolite deposits and associated research are reviewed here. Various industrial applications of natural zeolites, from agriculture to animal husbandry to the construction industry and beyond are discussed here.
8
Cadar, Oana, Marin Senila, Maria-Alexandra Hoaghia, Daniela Scurtu, Ion Miu et Erika Andrea Levei. « Effects of Thermal Treatment on Natural Clinoptilolite-Rich Zeolite Behavior in Simulated Biological Fluids ». Molecules 25, no 11 (31 mai 2020) : 2570. http://dx.doi.org/10.3390/molecules25112570.
Texte intégralRésumé :
This study presents the effect of thermal treatment (450, 500, 600, 750, and 800 °C) on a Romanian clinoptilolite-rich natural zeolite, along with the interaction of raw and thermally treated zeolites with simulated gastric fluid (SGF, pH = 1.20) at different zeolite to SGF ratios and exposure times. The zeolites were characterized using gravimetric analysis, X-ray fluorescence, powder X-ray diffraction (pXRD), and Fourier transform infrared (FT-IR) spectroscopy. The chemical composition of the zeolite subjected to thermal treatment did not change significantly with the increase of temperature. Structural changes were not detectable by pXRD and FT-IR analyses in the zeolites thermally treated up to 500 °C, while above 600 °C a gradual structural breakdown of zeolite was noticed. At high temperatures, the broad, low-intensity peaks in pXRD patterns indicated the partial amorphization of the crystalline structure. The pXRD and FT-IR analyses showed that the crystalline structure of zeolites remains unaffected after their exposure to SGF. The results revealed that the amounts of Fe, Na, Mg, K, Ca, Al, and Si released depends mainly on the zeolite to SGF ratio, and to a lower extent on the thermal treatment temperature, while the exposure time of 1 to 7 days does not have a significant impact on the elements released in SGF.
9
Gackowski, Mariusz, et Jerzy Datka. « Acid Properties of Hierarchical Zeolites Y ». Molecules 25, no 5 (26 février 2020) : 1044. http://dx.doi.org/10.3390/molecules25051044.
Texte intégralRésumé :
The article reviews different strategies towards obtaining mesoporous zeolites Y: desilication; surfactant templating and assembly of zeolite crystals. The impact of those methods on physicochemical properties is covered, with a special focus on the acidity of the samples measured with infrared (IR) spectroscopy. The methods of characterization of acidity are presented. Quaternary ammonium cations used for desilication lead to obtaining crystalline; mesoporous and highly acidic zeolites. Si-OH-Al groups of extremely high acidity can be produced by calcination in a humid atmosphere. When the conditions are optimized, post-synthetic surfactant templating allows crystalline mesoporous zeolite to be obtained with no loss of material. All mesoporous zeolites Y proved to be active catalysts in liquid phase isomerization, catalytic cracking, and other reactions.
10
Azizi, Seyed Naser, Akram Alavi Daghigh et Maryam Abrishamkar. « Phase Transformation of Zeolite P to Y and Analcime Zeolites due to Changing the Time and Temperature ». Journal of Spectroscopy 2013 (2013) : 1–5. http://dx.doi.org/10.1155/2013/428216.
Texte intégralRésumé :
In the present study, the synthesis of template free zeolite P under hydrothermal condition was investigated. The effects of parameters such as Si/Al ratios (3–45), crystallization temperatures (80–160°C), and cry (40–60 h) on the synthesis of zeolite P were studied. The phase transformation of zeolite P to two types of high crystallinity Y and analcime zeolites due to change of temperature was observed. The effect of temperature on the achievement of two different zeolite types (Y and analcime) with a constant initial synthetic composition under organic free synthesis of zeolite P was studied. The zeolitic products were characterized by X-ray diffraction, scanning electron microscopy, and IR spectroscopy techniques.
11
Li, Jian, Zihao Rei Gao, Qing-Fang Lin, Chenxu Liu, Fangxin Gao, Cong Lin, Siyao Zhang et al. « A 3D extra-large-pore zeolite enabled by 1D-to-3D topotactic condensation of a chain silicate ». Science 379, no 6629 (20 janvier 2023) : 283–87. http://dx.doi.org/10.1126/science.ade1771.
Texte intégralRésumé :
Zeolites are microporous silicates with a large variety of applications as catalysts, adsorbents, and cation exchangers. Stable silica-based zeolites with increased porosity are in demand to allow adsorption and processing of large molecules but challenge our synthetic ability. We report a new, highly stable pure silica zeolite called ZEO-3, which has a multidimensional, interconnected system of extra-large pores open through windows made by 16 and 14 silicate tetrahedra, the least dense polymorph of silica known so far. This zeolite was formed by an unprecedented one-dimensional to three-dimensional (1D-to-3D) topotactic condensation of a chain silicate. With a specific surface area of more than 1000 square meters per gram, ZEO-3 showed a high performance for volatile organic compound abatement and recovery compared with other zeolites and metal-organic frameworks.
12
Król, Magdalena, Andrzej Koleżyński et Włodzimierz Mozgawa. « Vibrational Spectra of Zeolite Y as a Function of Ion Exchange ». Molecules 26, no 2 (11 janvier 2021) : 342. http://dx.doi.org/10.3390/molecules26020342.
Texte intégralRésumé :
Zeolite Y is one of the earliest known and most widely used synthetic zeolites. Many experimental investigations verify the valuable ion exchange capability of this zeolite. In this study, we assessed the effects of ion exchange on its vibrational spectra. We applied classical lattice dynamics methods for IR and Raman intensity calculations. Computed spectra of optimized zeolite Y structures with different cations were compared with experimental data. The spectra obtained in this study are in agreement with previous experimental and computational studies on zeolites from the faujasite group.
13
Zhu, Longfeng, Jian Zhang, Liang Wang, Qinming Wu, Chaoqun Bian, Shuxiang Pan, Xiangju Meng et Feng-Shou Xiao. « Solvent-free synthesis of titanosilicate zeolites ». Journal of Materials Chemistry A 3, no 27 (2015) : 14093–95. http://dx.doi.org/10.1039/c5ta02680f.
Texte intégralRésumé :
Titanosilicate zeolites with MFI and *BEA structures are successfully synthesized using raw materials of fumed silica, titanium sulfate, organic templates, and zeolite seeds in the absence of solvents.
14
Tung, Chen-Ho, Li-Zhu Wu, Li-Ping Zhang, Hong-Ru Li, Xiu-Yu Yi, Kai Song, Ming Xu et al. « Microreactor-controlled selectivity in organic photochemical reactions ». Pure and Applied Chemistry 72, no 12 (1 janvier 2000) : 2289–98. http://dx.doi.org/10.1351/pac200072122289.
Texte intégralRésumé :
Molecular-sieve zeolites, Nafion membranes, low-density polyethylene films, and mixed surfactant vesicles have been used as microreactors to carry out organic photochemical reactions. The photo-cycloadditions of diaryl compounds with long flexible chains included in NaY zeolite or low-density polyethylene films yield intramolecular photocyclomers to the exclusion of intermolecular products. The photosensitized oxidation of alkenes included in pentasil zeolites or Nafion membranes or vesicles can be directed selectively toward either the singlet oxygen-mediated or the superoxide radical anion-mediated products by controlling the status and location of the substrate and sensitizer molecules in the reaction media. The photo-Fries rearrangement of phenyl phenylacetates included within NaY and pentasil zeolites or Nafion membranes gives either ortho-hydroxyphenones or decarbonylation products depending on the size/shape of the microreactors and the substrate molecules. All these results demonstrate the utility of microreactors to control the product selectivity in organic photochemical reactions.
15
Dai, Shujie, Yichang Yang, Jinghuai Yang, Shichang Chen et Longfeng Zhu. « Recent Advances in the Seed-Directed Synthesis of Zeolites without Addition of Organic Templates ». Nanomaterials 12, no 16 (21 août 2022) : 2873. http://dx.doi.org/10.3390/nano12162873.
Texte intégralRésumé :
Zeolites have been widely employed in fields of petroleum refining, fine chemicals and environmental protection, but their syntheses are always performed in the presence of organic templates, which have many drawbacks such as high cost and polluted wastes. In recent years, the seed-directed synthesis of zeolites has been paid much attention due to its low-cost and environmentally friendly features. In this review, the seed-directed synthesis of Al-rich zeolites with homonuclear and heteronuclear features, the seed-directed synthesis of Si-rich zeolites assisted with ethanol and the utility of seed-directed synthesis have been summarized. This review could help zeolite researchers understand the recent progress of seed-directed synthesis.
16
Jovanović, V., V. Dondur, Lj Damjanović, J. Zakrzewska et M. Tomašević-Čanović. « Improved Materials for Environmental Application : Surfactant-Modified Zeolites ». Materials Science Forum 518 (juillet 2006) : 223–28. http://dx.doi.org/10.4028/www.scientific.net/msf.518.223.
Texte intégralRésumé :
The surface properties of zeolites A, X, Y and natural zeolite clinoptilolite (CLI) functionalized by cationic surfactants were investigated. The quaternary ammonium type surfactants, such as hexadecyltrimethylammonium (HDTMA) chloride, stearildimethylbenzylammonium (SDMBA) chloride and distearildimethylammonium (DSDMA) chloride, replaced inorganic cations like Na+ and Ca2+ on the external surface of zeolites. The adsorption capacities of all organic cations followed the order of CLI>CaY>CaX>CaA>NaY>NaX>NaA and increased with the increase of Si/Al molar ratio in zeolite structure. This modification resulted in an alteration in the surface property of zeolites - it changed from hydrophilic to hydrophobic. The adsorption of selected pesticides with different hydrophobicity on surfactant-modified zeolites was studied. It is shown that surfactant-modified zeolites can be used for removal of pesticides from the environment. The increase in hydrophobicity of pesticides resulted in an increase in pesticide adsorption on SDMBA and DSDMA modified zeolites.
17
Dang, Long Van, Thu Thi Minh Nguyen, Dang Van Do, Son Thanh Le, Trong Dinh Pham et Anh Thi Mai Le. « Study on the Synthesis of Chabazite Zeolites via Interzeolite Conversion of Faujasites ». Journal of Analytical Methods in Chemistry 2021 (29 mars 2021) : 1–10. http://dx.doi.org/10.1155/2021/5554568.
Texte intégralRésumé :
The interzeolite conversion of faujasite (FAU-type) zeolites to chabazite (CHA-type) zeolite in the presence of N,N,N-trimethyladamantammonium and N,N,N-dimethylethylcyclohexylammonium cations was investigated over a large compositional range by carefully controlling the reaction mixture compositions. Highly crystalline CHA zeolites were also obtained by the transformation of several zeolite types including EMT, LTL, LEV, RTH, and MFI frameworks. The formation of CHA zeolite from FAU zeolite precursors was substantially faster than that from zeolite L with a similar composition. High-silica CHA zeolites were also produced successfully using a mixture of TMAda with a number of less expensive organic structure-directing agents. The CHA zeolite materials have been synthesized with high crystallinity and with a Si/Al ratio ranging from 5 to 140. Our data support the importance of structural similarity between the zeolite precursors, nucleation/crystallization processes, and the zeolite product in the interzeolite conversion compared to conventional amorphous aluminosilicate gels. Our synthetic methods could be used to prepare other 8-membered ring zeolites such as AEI and AFX frameworks, potential candidates for selective catalytic reduction of NOx, light olefin production, and CO2 abatement.
18
Mu, Y., H. Shi, Y. Wang, H. Ding et J. Li. « CNDs@zeolite : new room-temperature phosphorescent materials derived by pyrolysis of organo-templated zeolites ». J. Mater. Chem. C 5, no 41 (2017) : 10894–99. http://dx.doi.org/10.1039/c7tc03487c.
Texte intégral
19
Mio, Matthew J., et Jeffrey S. Moore. « Supramolecular Aufbau : Folded Polymers as Building Blocks for Adaptive Organic Materials ». MRS Bulletin 25, no 4 (avril 2000) : 36–41. http://dx.doi.org/10.1557/mrs2000.27.
Texte intégralRésumé :
The design of inorganic and organic solids with novel structures and properties has long been the object of materials research. The classical examples of porous materials (i.e., involving reversible guest passage) are zeolites. First discovered in the mid-1700s, zeolites are hydrated, crystalline aluminosilicates that organize into stable, discrete frameworks. Basic structures employ tetrahedral atoms (silicon or aluminum) bridged by oxygen atoms, where each oxygen is shared between two metalloid tetrahedra. Resulting covalent lattices can be neutral or negatively charged (as a result of bridging oxides) and often employ alkali metal or alkalineearth counterions. As a consequence of this ordered structure, zeolites both benefit from and are limited by their highly geometrical nature: their rigid structures are inherently robust, yet they are difficult to process. In addition, while natural and unnatural zeolites have been characterized, harsh synthetic conditions are common to both and lead to limitations in design and processability. Even so, these impediments have not prevented constructing a myriad of architectures on zeolite host lattices. Strengths and weaknesses aside, zeolites demonstrate a major objective of materials chemistry: the ability to manifest macroscopic physical properties based on embedded microscopic structure.
20
Ramamurthy. « Achiral Zeolites as Reaction Media for Chiral Photochemistry ». Molecules 24, no 19 (2 octobre 2019) : 3570. http://dx.doi.org/10.3390/molecules24193570.
Texte intégralRésumé :
Obtaining enantiomerically-enriched photoproducts from achiral reactants has been a long-sought goal. The various methods developed to achieve chiral induction in photoproducts during the last fifty years still suffer from a lack of predictability, generality, and simplicity. With the current emphasis on green chemistry, obtaining enantiomerically enriched products via photochemistry is a likely viable alternative for the future. Of the various approaches developed during the last three decades, the one pioneered in the author’s laboratory involved the use of commercially-available and inexpensive achiral zeolites as the media. This approach does not use any solvent for the reaction. Examples from these studies are highlighted in this article. Since no chiral zeolites were available, when the work was initiated in the author’s laboratory, commercially-available zeolites X and Y were modified with chiral inductors so that the reaction space becomes chiral. The results obtained established the value of chirally-modified, commercial zeolites as media for achieving chiral induction in photochemical reactions. A recent report of the synthesis of a chiral zeolite is likely to stimulate zeolite-based chiral photochemistry in synthesizing enantiomerically-pure organic molecules. The availability of chiral zeolites in future is likely to energize research in this area. Our earlier observations on this topic, we believe, would be valuable for progress of the field. Keeping this in mind, I have summarized the work carried out in our laboratory on chiral photochemistry on chirally-modified zeolites. This review does not include examples where high chiral induction has been obtained via a strategy that examines molecules appended with chiral auxiliary within achiral and chirally-modified zeolites. The latter approach yields products with diastereomeric excess >80%.
21
Lim, Hyung Mi, Ji Sook Jung, Bong Young Kim et Seung Ho Lee. « Application of Zeolites on Cellulose Fiber ». Key Engineering Materials 317-318 (août 2006) : 777–80. http://dx.doi.org/10.4028/www.scientific.net/kem.317-318.777.
Texte intégralRésumé :
Zeolites with different sizes and structures were applied on the surface of cellulose fibers with organic and inorganic binders. The effects of zeolite structure and size and choice of binder on the deodorization rate have been studied. The smaller the particle size, the more effective the deodorization rate of both the zeolite coated cellulose fibers and the powder itself. The deodorization rate depends on both the type and amount of inorganic binder. A silica based inorganic binder revealed higher efficiency on deodorization than silicate based inorganic binder and also higher than organic binders.
22
Turan, Abdullah Zahid, et Mustafa Turan. « A review on the application of nanoporous zeolite for sanitary landfill leachate treatment ». Water Science and Technology 84, no 12 (27 octobre 2021) : 3425–41. http://dx.doi.org/10.2166/wst.2021.468.
Texte intégralRésumé :
Abstract This review deals with low-cost nanoporous zeolites for the treatment of sanitary landfill leachate. Organic contaminants and ammoniacal nitrogen are significant parameters in landfill leachate treatment. Adsorption processes are regarded as promising alternative treatment options in this respect. Zeolites are aluminosilicate materials that are widely used in separation, filtration, adsorption and catalysis. Natural zeolite is a low-cost and readily available form of zeolite and is a promising candidate to be used as an ion-exchange material for ammonia and other inorganic pollutant removal from landfill leachate. In this review, adsorption isotherms and kinetic models in batch systems are evaluated and adsorption design parameters of the fixed-bed system are presented. Studies on ammonia removal from landfill leachate via zeolites have been thoroughly investigated. Leachate treatment systems combined with zeolites are presented. Cost of zeolites are also reported in comparison with other adsorbents. The investigated studies demonstrate that activated zeolite can improve the removal of chemical oxygen demand, NH3-N and colour significantly compared to the case where raw zeolite is used. Moreover, the composite of activated carbon and zeolite is also favorable for ammonia removal according to reported findings, where best adsorptive removal is attained on the composite media (24.39 mg/g).
23
Barros, Thiago Rodrigo Barbosa, Thianne Silva Batista Barbosa et Meiry Gláucia Freire Rodrigues. « Adsorption of reactive yellow BF-3R dye by CTABr modified zeolite NaY ». Research, Society and Development 10, no 14 (3 novembre 2021) : e323101422147. http://dx.doi.org/10.33448/rsd-v10i14.22147.
Texte intégralRésumé :
Textile industries generate effluents composed of organic salts and complexes from dyes not fixed on fabrics, or not degraded by the inefficiency of conventional treatment processes, which represents a high potential for environmental impact due to inadequate disposal of the generated effluent. Zeolites are porous materials that have a three-dimensional structure containing tetrahedrals of AlO4 e SiO4 which can be modified to improve its properties. The adsorption process using zeolites as adsorbents can be considered an excellent economic physical treatment to solve or minimize such a problem. This work presents an experimental study focusing on the preparation and characterization of zeolite NaY and modified with organic surfactant cetyltrimethylammonium bromide (CTABr) intended to be used as adsorbent in the process of removing yellow dye BF-3R in dye-water system batch system. The samples were characterized by X-ray diffraction (XRD), Infrared spectroscopy (IR) and thermogravimetry (TG). The effect of process parameter such as pH was studied. Results revealed that even though the modified cetyltrimethylammonium bromide organic surfactant (CTABr) did not cause alterations on the zeolite NaY structure. The IR results revealed that CTABr was successfully incorporated to zeolite NaY structure. The best conditions were established with respect to pH to saturate the available sites located on the zeolite NaY and NaY_CTABr surface. The maximum adsorption capacities were 3.35 and mg/g for dye 5.35 using as-synthesized zeolite NaY and CTABr modified zeolite NaY. Modified zeolites are excellent adsorbents for removing reactive dyes from industrial wastewater.
24
Martinez-Ortigosa, Joaquin, Jorge Simancas, Jose A. Vidal-Moya, Fernando Rey, Susana Valencia et Teresa Blasco. « A Multi-Nuclear MAS-NMR Study on the Structural Properties of Silicalite-1 Zeolite Synthesized Using N- and P-Based Organic Structure Directing Agents ». Applied Sciences 11, no 15 (26 juillet 2021) : 6850. http://dx.doi.org/10.3390/app11156850.
Texte intégralRésumé :
The nature of organic structure directing agents (OSDAs) is of paramount importance in the final properties of zeolites, particularly the framework and porosity. Recently, the use of P-containing OSDAs has been employed for new zeolites, but there is little discussion compared to their analogues N-OSDAs. The main objective of this work is the characterization of pure silica MFI zeolite (silicalite-1) prepared by the dual-template route with tetrapropylammonium (TPA), tetrapropylphosphonium (TPP) cations, and mixtures thereof aiming to understand by advanced NMR methods how the nature of the organic influences the physico-chemical properties of the zeolite. Silicalite-1 has been successfully synthesized using the dual-template procedure with TPA and TPP molecules. Both OSDAs are incorporated into the zeolite without any specific preference, differently to that observed before for the TEA/TEP system, and homogenously mixed inside of the zeolite voids. The presence of TPP leads to the incorporation of less F, raising the concentration of Q3-defective sites in the silicalite-1 zeolites. Detailed NMR results indicate that those structural defects are close to the –CH3 group of the entrapped OSDAs in the zeolite and these defects consist of at least two silanol groups stabilizing the Si-O- species, which is responsible for the charge balancing.
25
Kuterasiński, Łukasz, Jerzy Podobiński, Dorota Rutkowska-Zbik et Jerzy Datka. « IR Studies of the Cu Ions in Cu-Faujasites ». Molecules 24, no 23 (22 novembre 2019) : 4250. http://dx.doi.org/10.3390/molecules24234250.
Texte intégralRésumé :
The properties of Cu ions in dealuminated faujasite-type zeolites (Si/Al = 31) containing 1, 2, and 5 wt.% of Cu were investigated by IR spectroscopy with CO and NO as probe molecules. Cu was introduced by impregnation into zeolites in both protonic (HFAU) and sodium (NaFAU) forms of zeolite. Four kinds of Cu species were found: Cu+exch., Cu+oxide, Cu2+exch. (square, planar, and square pyramidal), and Cu2+oxide (CuO). The proportions between these four kinds of Cu depended on the amount of Cu and on the form of zeolite to which Cu was introduced (HFAU or NaFAU). Zeolites with 1 wt.% of Cu introduced to HFAU (denoted as Cu(1)HFAU) contained only Cu+exch., whereas other forms of Cu were present in zeolites of higher Cu contents. The concentration of Cu+exch. was determined by quantitative IR studies of CO adsorption. According to the IR results, some Cu ions were situated inside hexagonal prisms and/or cuboctahedra, and were inaccessible to adsorbed molecules. IR studies also evidenced that Cu ions in oxide forms—Cu+oxide and Cu2+oxide (CuO)—were better electron donors than Cu in exchange positions (Cu+exch. and Cu2+exch).
26
Yang, Hu, Zhenghua Ping, Yingcai Long et Quang Trong Nguyen. « Article ». Canadian Journal of Chemistry 77, no 10 (1 octobre 1999) : 1671–77. http://dx.doi.org/10.1139/v99-197.
Texte intégralRésumé :
Two types of hydrophobic zeolites Y were prepared by treating the NaY-type zeolite with SiCl4, with or without subsequent hydrothermal treatment. X-ray diffraction analysis showed that the framework of the two modified zeolites Y are more perfect than that of the NaY one, and the Si/Al ratio is greatly enhanced by hydrothermal treatment. The determined sorption isotherms indicate an improvement of the ester-to-water sorption ratio with the increase in Si/Al ratio. When the zeolite-filled silicone membranes are used in separation of ethyl acetate - water mixture by pervaporation, both the total permeation flux and the selectivity to the ester are improved by the use of the hydrophobic zeolite Y as the filler in the membrane. The stronger the hydrophobicity of the zeolite Y, the higher the filled membrane selectivity.Key words: hydrophobic zeolites Y, silicone-filled membranes, ethyl acetate - water mixture, sorption, pervaporation.
27
Khivantsev, Konstantin, Nicholas R. Jaegers, Libor Kovarik, Miroslaw A. Derewinski, Ja-Hun Kwak et Janos Szanyi. « On the Nature of Extra-Framework Aluminum Species and Improved Catalytic Properties in Steamed Zeolites ». Molecules 27, no 7 (6 avril 2022) : 2352. http://dx.doi.org/10.3390/molecules27072352.
Texte intégralRésumé :
Steamed zeolites exhibit improved catalytic properties for hydrocarbon activation (alkane cracking and dehydrogenation). The nature of this practically important phenomenon has remained a mystery for the last six decades and was suggested to be related to the increased strength of zeolitic Bronsted acid sites after dealumination. We now utilize state-of-the-art infrared spectroscopy measurements and prove that during steaming, aluminum oxide clusters evolve (due to hydrolysis of Al out of framework positions with the following clustering) in the zeolitic micropores with properties very similar to (nano) facets of hydroxylated transition alumina surfaces. The Bronsted acidity of the zeolite does not increase and the total number of Bronsted acid sites decreases during steaming. O5Al(VI)-OH surface sites of alumina clusters dehydroxylate at elevated temperatures to form penta-coordinate Al1O5 sites that are capable of initiating alkane cracking by breaking the first C-H bond very effectively with much lower barriers (at lower temperatures) than for protolytic C-H bond activation, with the following reaction steps catalyzed by nearby zeolitic Bronsted acid sites. This explains the underlying mechanism behind the improved alkane cracking and alkane dehydrogenation activity of steamed zeolites: heterolytic C-H bond breaking occurs on Al-O sites of aluminum oxide clusters confined in zeolitic pores. Our findings explain the origin of enhanced activity of steamed zeolites at the molecular level and provide the missing understanding of the nature of extra-framework Al species formed in steamed/dealuminated zeolites.
28
Nearchou, Antony, Catherine Dejoie, Paul R. Raithby et Asel Sartbaeva. « The Structure and Location of 18-Crown-6 Ether in Zeolites RHO and ZK-5 ». Chemistry 4, no 1 (13 mars 2022) : 168–84. http://dx.doi.org/10.3390/chemistry4010015.
Texte intégralRésumé :
The use of organic additives presents the greatest versatility and control of zeolite synthesis in order to prepare novel architectures for desired applications. Despite this prospect, there is little clarity of how organic additives are involved in framework assembly and the range of behaviours that are available. To address this issue, we have considered zeolites RHO and ZK-5 which can both be prepared using 18-crown-6 ether as an additive. Previously, this additive has shown to employ different structure directing behaviours to assemble a variety of zeolites. We have used high resolution powder X-ray diffraction and Rietveld refinement to determine structural models for zeolites RHO and ZK-5 with 18-crown-6 ether occluded in the framework. In doing so, we can observe the identity, location and orientation of the occluded additive and reason the structure directing behaviour in synthesis. We report that the isolated 18-crown-6 ether molecule is involved in the assembly of zeolite RHO, and for zeolite ZK-5 it is the K+ coordinated macrocation. In both cases the relevant additive is disordered in the framework, suggesting that they behave as space-filling species that stabilise the formation of the α-cage.
29
O'Neill, Melanie A., et Frances L. Cozens. « Influence of alkali metal cations on the photoheterolysis of 9-cyclopropyl-9-fluorenol and the reactivity of the 9-cyclopropyl-9-fluorenyl cation in non-acidic zeolites ». Canadian Journal of Chemistry 81, no 6 (1 juin 2003) : 647–59. http://dx.doi.org/10.1139/v03-071.
Texte intégralRésumé :
Alkali metal cation regulation of carbocation formation and reactivity in non-acidic zeolites is probed using the photoheterolysis reaction of 9-cyclopropyl-9-fluorenol. Nanosecond time-resolved diffuse reflectance is employed to directly observe the 9-cyclopropyl-9-fluorenyl cation as a transient species within the non-acidic zeolites. The efficiency of carbocation formation via photoheterolysis and the dynamics of other reaction pathways available to photoexcited 9-cyclopropyl-9-fluorenol are found to be strongly dependent on the zeolite alkali metal counterion. In particular, the yield of carbocation decreases with increasing counterion size in a manner consistent with the zeolite assisting the excited state CO bond cleavage via Lewis acid catalysis involving the metal cation. Zeolite encapsulation is also found to modulate the ability of water and methanol to assist photoheterolysis. For instance, the influence of coadsorbed water on the photoheterolysis reaction within zeolites is found to be highly sensitive to the alkali metal cation. The rate constant for intrazeolite decay of the 9-cyclopropyl-9-fluorenyl cation increases significantly as the alkali metal cation size increases and as the SiAl ratio decreases. These reactivity trends suggest that the intrazeolite decay of the 9-cyclopropyl-9-fluorenyl cation involves nucleophilic addition at the active site [Si-O-Al] bridges of the zeolite framework. In addition, the reactivity of the 9-cyclopropyl-9-fluorenyl cation within alkali metal zeolites can be regulated by the co-inclusion of reagents such as methanol, water, and 1,1,1,3,3,3-hexafluoro-2-propanol.Key words: cation-exchanged zeolites, 9-cyclopropyl-9-fluorenyl cation, laser photolysis, reactivity.
30
Xu, Hao, Jie Zhu, Longfeng Zhu, Enmu Zhou et Chao Shen. « Advances in the Synthesis of Ferrierite Zeolite ». Molecules 25, no 16 (14 août 2020) : 3722. http://dx.doi.org/10.3390/molecules25163722.
Texte intégralRésumé :
As one of the most important porous materials, zeolites with intricate micropores have been widely employed as catalysts for decades due to their large pore volume, high surface area, and good thermal and hydrothermal stabilities. Among them, ferrierite (FER) zeolite with a two-dimensional micropore structure is an excellent heterogeneous catalyst for isomerization, carbonylation, cracking, and so on. In the past years, considering the important industrial application of FER zeolite, great efforts have been made to improve the synthesis of FER zeolite and thus decrease the synthesis cost and enhance catalytic performance. In this review, we briefly summarize the advances in the synthesis of FER zeolite including the development of synthesis routes, the use of organic templates, organotemplate-free synthesis, the strategies of morphology control, and the creation of intra-crystalline mesopores. Furthermore, the synthesis of hetero-atomic FER zeolites such as Fe-FER and Ti-FER has been discussed.
31
Cataldo, Eleonora, Linda Salvi, Sofia Sbraci, Davide Manzi, Grazia Masciandaro, Cosimo Maria Masini et Giovan Battista Mattii. « Zeowine : The synergy of zeolite and compost. Effects on the physiology of the vine and on the quality of the grapes ». BIO Web of Conferences 44 (2022) : 02002. http://dx.doi.org/10.1051/bioconf/20224402002.
Texte intégralRésumé :
The trial aims to improve the protection and management of the soil, the well-being of the plant and the quality of production in the wine supply chain organic and biodynamic, using an innovative product “ZEOWINE” resulting from the composting of waste of the wine and zeolite supply chain. At present, the use of zeolites in agriculture is a fast-spreading practice; their application to soils (both as natural zeolites and in combination with organic and mineral fertilizers) not only increases production but also leads to the exaltation of quality indices. The research was conducted in the 2019 season in San Miniato (Tuscany) on the vineyard of Sangiovese in production, performing the following inter-row treatments at the beginning of January: commercial organic fertilizer, zeolite (clinopthylolite) and zeowine (combination zeolite and compost obtained through grape processing waste) in the respective doses of 20 t/ha, 10 t/ha and 30 t/ha. Following the treatment, we measured gas exchanges and water potential, berry weight, °Brix, pH, acidity, total and extractable anthocyanins and polyphenols. Treatments with Zeowine and zeolites reduced water stress. In Zeowine treatment, soluble solids were lower, while acidity, pH and berry weight do not vary from control. Statistical differences are also noted in the concentrations of anthocyanins and polyphenols. Results suggest a positive impact of Zeowine treatment on physiology and quality characteristics in V. vinifera.
32
Mastinu, Kumar, Maccarinelli, Bonini, Premoli, Aria, Gianoncelli et Memo. « Zeolite Clinoptilolite : Therapeutic Virtues of an Ancient Mineral ». Molecules 24, no 8 (17 avril 2019) : 1517. http://dx.doi.org/10.3390/molecules24081517.
Texte intégralRésumé :
Zeolites are porous minerals with high absorbency and ion-exchange capacity. Their molecular structure is a dense network of AlO4 and SiO4 that generates cavities where water and other polar molecules or ions are inserted/exchanged. Even though there are several synthetic or natural occurring species of zeolites, the most widespread and studied is the naturally occurring zeolite clinoptilolite (ZC). ZC is an excellent detoxifying, antioxidant and anti-inflammatory agent. As a result, it is been used in many industrial applications ranging from environmental remediation to oral applications/supplementation in vivo in humans as food supplements or medical devices. Moreover, the modification as micronization of ZC (M-ZC) or tribomechanically activated zeolite clinoptilolite (TMAZ) or furthermore as double tribomechanically activated zeolite clinoptilolite (PMA-ZC) allows improving its benefits in preclinical and clinical models. Despite its extensive use, many underlying action mechanisms of ZC in its natural or modified forms are still unclear, especially in humans. The main aim of this review is to shed light on the geochemical aspects and therapeutic potentials of ZC with a vision of endorsing further preclinical and clinical research on zeolites, in specific on the ZC and its modified forms as a potential agent for promoting human brain health and overall well-being.
33
Mlekodaj, Kinga, Joanna E. Olszowka, Venceslava Tokarova, Edyta Tabor, Ales Kasparek, Jana Novakova, Gabriela Stavova et al. « Effect of Alkali-Free Synthesis and Post-Synthetic Treatment on Acid Sites in Beta Zeolites ». Molecules 25, no 15 (28 juillet 2020) : 3434. http://dx.doi.org/10.3390/molecules25153434.
Texte intégralRésumé :
Beta zeolites with Si/Al around 14 were prepared using three new alkali-free synthesis methods based on the application of amorphous aluminosilicate precursor and calcined in ammonia or air. All samples exhibit structural and textural properties of standard beta zeolite. Comprehensive study by 27Al and 29Si MAS NMR, together with FTIR adsorption of d3-acetonitrile and pyridine were used to characterize the influence of both the synthesis and calcination procedure on the framework Al atoms and related Brønsted and Lewis acid sites. While calcination in ammonia preserves all framework Al atoms, calcination in air results in 15% release of framework Al, but without restrictions of the accessibility of the beta zeolite channel system for bulky pyridine molecules. Terminal (SiO)3AlOH groups present in the hydrated zeolites were suggested as a precursor of framework Al-Lewis sites. Surprisingly, the mild dealumination of the air-calcined zeolites result in an increase of the concentration of Brønsted acid sites and a decrease of the total concentration of Lewis sites with the formation of the extra-framework ones.
34
Moliner, Manuel. « Direct Synthesis of Functional Zeolitic Materials ». ISRN Materials Science 2012 (29 novembre 2012) : 1–24. http://dx.doi.org/10.5402/2012/789525.
Texte intégralRésumé :
Recently, the direct synthesis of zeolitic materials has received much attention because several well-defined functionalities have been introduced in those materials by “one-pot” methodologies. The rationalization of the physics and chemistry of the processes involved in the zeolite growth has allowed the direct preparation of different functional molecular sieves with unique properties and potential applicability in industry. In the present paper, the “one-pot” preparations of metal-containing zeolites (both in framework and extra-framework positions), hybrid organic-inorganic molecular sieves, hierarchical microporous mesoporous zeotypes, nanosheets, nanozeolites, or template-free molecular sieves are intensively evaluated.
35
Cintoli, R., B. Di Sabatino, L. Galeotti et G. Bruno. « Ammonium uptake by zeolite and treatment in UASB reactor of piggery wastewater ». Water Science and Technology 32, no 12 (1 décembre 1995) : 73–81. http://dx.doi.org/10.2166/wst.1995.0461.
Texte intégralRésumé :
A treatment plant of pre-screened piggery wastewater is tested at lab-scale using Italian zeolites (of very low cost) to strongly reduce the NH4+ from 1500 mg/l to 300–400 mg/l and anaerobic digestion in UASB and UASB-AF reactors to remove organics. The ion-exchange pre-treatment by zeolite leads to a reduction of toxicity of wastewater towards anaerobic microbial population and improves the UASB and UASB-AF reactors yields in organics reduction and gas production. The laboratory plant in this configuration reaches a COD removal range of 60–80% and a good reduction of effluent nutrients concentration whereas the use of a anaerobic second stage gave modest results in organics removal because of low applied organic load. A treatment cycle composed of a pre-treatment with zeolites, anaerobic digestion in UASB-AF reactor and a final treatment in an aerobic activated sludge plant is giving very good preliminary results.
36
Tahraoui, Zakaria, Habiba Nouali, Claire Marichal, Patrice Forler, Julien Klein et T. Jean Daou. « Influence of the Compensating Cation Nature on the Water Adsorption Properties of Zeolites ». Molecules 25, no 4 (20 février 2020) : 944. http://dx.doi.org/10.3390/molecules25040944.
Texte intégralRésumé :
The influence of the compensating cation (Na+, Li+, Mg2+) nature on the water adsorption properties of LTA and FAU-type zeolites was investigated. Cation exchanges were performed at 80 °C for 2 h using 1 M aqueous solutions of lithium chloride (LiCl) or magnesium chloride (MgCl2). XRF and ICP-OES analyses indicate that the cation exchange yields reach values between 59 to 89% depending on the number of exchange cycles and the nature of the zeolite and cation, while both zeolites structures are preserved during the process, as shown by XRD and solid state NMR analyses. Nitrogen adsorption-desorption experiments indicate a higher available microporous volume when sodium cations are replaced by smaller monovalent lithium cations or by divalent magnesium cations because twice less cations are needed compared to monovalent cations. Up to 15% of gain in the available microporous volume is obtained for FAU-type zeolites exchanged with magnesium cation. This improvement facilitates the adsorption of water with an increase in the water uptake up to 30% for the LTA and FAU type zeolites exchanged with magnesium. These exchanged zeolites are promising for uses in water decontamination because a smaller amount is needed to trap the same amount of water compared to their sodium counterparts.
37
Fawaz, Elyssa G., Darine A. Salam, Severinne S. Rigolet et T. Jean Daou. « Hierarchical Zeolites as Catalysts for Biodiesel Production from Waste Frying Oils to Overcome Mass Transfer Limitations ». Molecules 26, no 16 (12 août 2021) : 4879. http://dx.doi.org/10.3390/molecules26164879.
Texte intégralRésumé :
Hierarchical crystals with short diffusion path, conventional microcrystals and nanocrystals of ZSM-5 zeolites were used for biodiesel production from waste frying oils and were assessed for their catalytic activity in regard to their pore structure and acidic properties. Produced zeolites were characterized using XRD, nitrogen adsorption–desorption, SEM, TEM, X-ray fluorescence, and FTIR. Pore size effect on molecular diffusion limitation was assessed by Thiele modulus calculations and turnover frequencies (TOF) were used to discuss the correlation between acidic character and catalytic performance of the zeolites. Owing to the enhanced accessibility and mass transfer of triglycerides and free fatty acids to the elemental active zeolitic structure, the catalytic performance of nanosponge and nanosheet hierarchical zeolites was the highest. A maximum yield of 48.29% was reached for the transesterification of waste frying oils (WFOs) using HZSM-5 nanosheets at 12:1 methanol to WFOs molar ratio, 180 °C, 10 wt % catalyst loading, and 4 h reaction time. Although HZSM-5 nanosponges achieved high conversions, these more hydrophilic zeolites did not function according to their entire acidic strength in comparison to HZSM-5 nanosheets. NSh-HZSM5 catalytic performance was still high after 4 consecutive cycles as a result of the zeolite regeneration.
38
Nearchou, Antony, Mero-Lee U. Cornelius, Zöe L. Jones, I. E. Collings, Stephen A. Wells, Paul R. Raithby et Asel Sartbaeva. « Pressure-induced symmetry changes in body-centred cubic zeolites ». Royal Society Open Science 6, no 7 (juillet 2019) : 182158. http://dx.doi.org/10.1098/rsos.182158.
Texte intégralRésumé :
Previous work has shown a strong correlation between zeolite framework flexibility and the nature of structural symmetry and phase transitions. However, there is little experimental data regarding this relationship, in addition to how flexibility can be connected to the synthesis of these open-framework materials. This is of interest for the synthesis of novel zeolites, which require organic additives to permutate the resulting geometry and symmetry of the framework. Here, we have used high-pressure powder X-ray diffraction to study the three zeolites: Na-X, RHO and ZK-5, which can all be prepared using 18-crown-6 ether as an organic additive. We observe significant differences in how the occluded 18-crown-6 ether influences the framework flexibility—this being dependent on the geometry of the framework. We use these differences as an indicator to define the role of 18-crown-6 ether during zeolite crystallization. Furthermore, in conjunction with previous work, we predict that pressure-induced symmetry transitions are intrinsic to body-centred cubic zeolites. The high symmetry yields fewer degrees of freedom, meaning it is energetically favourable to lower the symmetry to facilitate further compression.
39
Pyra, Kamila, Karolina A. Tarach, Ewa Janiszewska, Dorota Majda et Kinga Góra-Marek. « Evaluation of the Textural Parameters of Zeolite Beta in LDPE Catalytic Degradation : Thermogravimetric Analysis Coupled with FTIR Operando Studies ». Molecules 25, no 4 (19 février 2020) : 926. http://dx.doi.org/10.3390/molecules25040926.
Texte intégralRésumé :
Zeolite-based catalysts are globally employed in many industrial processes, such as crude-oil refining and bulk chemical production. In this work, the cracking of low-density polyethylene (LDPE) was thoroughly followed in a FTIR operando study to examine the catalytic efficiency of purely microporous zeolites of various textural characteristics. To provide complementary and valuable information on the catalytic activity of the zeolite studied, the thermogravimetric analysis results were compared with yields of the products generated under operating conditions. The reaction products were analyzed via GC–MS to determine the hydrocarbon chain distribution in terms of paraffin, olefins, and aromatics. The individual impact of textural and acidic parameters on catalytic parameters was assessed. The accumulation of bridging hydroxyls of high strength in the zeolite benefited the decrease in polymer decomposition temperature. Through a strategic comparison of purely microporous zeolites, we showed that the catalytic cracking of LDPE is dominated by the acidic feature inherent to the microporous environment.
40
Díaz, Urbano. « Layered Materials with Catalytic Applications : Pillared and Delaminated Zeolites from MWW Precursors ». ISRN Chemical Engineering 2012 (14 novembre 2012) : 1–35. http://dx.doi.org/10.5402/2012/537164.
Texte intégralRésumé :
Delaminated and pillared zeolites are an innovative family of molecular sieves which introduced a different concept inside the synthesis of active catalysts or inorganic supports. These types of materials exhibit an elevated accessibility due to their open structure, characterized by the high external surface area without imposed restrictions controlled by the pore sizes. These open zeolites are conformed by crystalline ordered (pillared zeolites) or disordered (delaminated zeolites) individual layers, exhibiting textural properties which are favorable to carry out catalytic processes in which it is necessary to employ catalysts with completely accessible active sites. The elevated external surface area of these zeolites is profitable to generate more specific organic-inorganic materials, acting in this case as stable inorganic matrixes. The preparation of this open type-zeolites family is based on the modification of, previously synthesized, zeolitic precursors which are preexpanded to obtain the final delaminated or pillared zeolites which exhibit very different physicochemical properties compared with the starting precursors. Along this paper, the most relevant MWW-type high accessible zeolitic materials will be considered. Their nature, characteristics, and reactivity will be shown in the function of the employed synthesis method for their preparation and the postsynthesis treatments carried out, tuning their properties.
41
Araújo, Ana Paula, Aline Cadigena Lima Patrício, Anna Karoline Freires de Sousa, Mariaugusta Ferreira Mota et Meiry Glaúcia Freire Rodrigues. « Adsorption Capacity of Y Zeolite Using Organic Solvents such as Adsorbates ». Materials Science Forum 805 (septembre 2014) : 641–45. http://dx.doi.org/10.4028/www.scientific.net/msf.805.641.
Texte intégralRésumé :
The zeolites differ from traditional adsorbents for selective adsorption of small molecules, the high adsorption capacity at low concentrations and affinity for organic compounds and unsaturated polar molecules. In this work a Y-type zeolite was synthesized, characterized by x-ray diffraction, scanning electron microscopy and adsorption of nitrogen and subjected to test adsorption capacity where it was found that the Y zeolite has the potential adsorption capacity compared to other materials being studied and marketed.
42
Shea, Suzanne, Norman P. Schepp, Amy E. Keirstead et Frances L. Cozens. « Dynamics of the transient species generated upon photolysis of diarylmethanes within zeolites Deprotonation and oxidation reactions ». Canadian Journal of Chemistry 83, no 9 (1 septembre 2005) : 1637–48. http://dx.doi.org/10.1139/v05-208.
Texte intégralRésumé :
The oxidation of diarylmethanes is a multistep process involving initial formation of a radical cation, deprotonation of the radical cation to the radical, and oxidation of the radical to the carbocation. The dynamics and efficiency of the last two steps in this process, namely deprotonation and oxidation, in acidic zeolites and non-acid zeolites are examined in the present work as a function of the acidity of the diarylmethane radical cations and the oxidation potential of the diarylmethyl radicals. Our results indicate that rate constants for deprotonation strongly depend on the acidity of the radical cations, but not on the composition of the zeolites. In addition, oxidation of the radicals to the diarylmethyl cations is strongly dependent on both the oxidation potential of the radicals and the oxidizing ability of the zeolite. This dependence allows oxidation potentials of the zeolites to be estimated.Key words: radical cations, carbocations, zeolites, laser flash photolysis.
43
Mancinelli, Maura, Antonella Arfè, Annalisa Martucci, Luisa Pasti, Tatiana Chenet, Elena Sarti, Giulia Vergine et Claudia Belviso. « Evaluation for the Removal Efficiency of VOCs and Heavy Metals by Zeolites-Based Materials in the Wastewater : A Case Study in the Tito Scalo Industrial Area ». Processes 8, no 11 (22 novembre 2020) : 1519. http://dx.doi.org/10.3390/pr8111519.
Texte intégralRésumé :
The current study was designed to demonstrate the efficiency of selected zeolites in the immobilization of heavy metals and volatile organic compounds from water in the industrial area of Tito Scalo (Basilicata Region in Southern Italy). The efficiency of zeolite materials has been evaluated by analyzing real water samples, by a multi-technique approach. Gas chromatography (GC) and inductively coupled plasma optical emission spectrometry (ICP-OES) were selected for the detection of volatile organic compounds (VOCs) and heavy metals respectively, and then by thermal analysis (TG, DTA) and X-ray powder diffraction (XRD) to verify the presence of contaminants in the structural channels of the adsorbents. ZSM-5 zeolite (MFI topology) was suitable for volatile organic compounds, showing removal efficiencies 87%. 13X (FAU topology) was more selective for in situ abatements of heavy metals, with efficiencies up to 100%. After VOCs and heavy metals removal, structure refinements of loaded zeolites highlighted variations of both lattice parameters and extraframework content confirming the pollutants immobilization in the framework microporosities. The occurrence of these species was also confirmed by DTA curves showing different phenomena explained on the basis of the nature and number of extraframework species hosted in the zeolite micropores.
44
Cakicioglu-Ozkan, Fehime. « Adsorption of carbon dioxide on MIL53(Al), CuBTC and K- NaX zeolite ». ICONTECH INTERNATIONAL JOURNAL 4, no 3 (17 décembre 2020) : 30–42. http://dx.doi.org/10.46291/icontechvol4iss3pp30-42.
Texte intégralRésumé :
CO2 adsorption on K exchanged NaX zeolites, and metal organic frameworks (MOFs), namely Cu-BTC and MIL53 (Al) was studied at 5 °C and 25 °C. Exchange via ultrasonic and traditional methods, was conducted at 50 °C and 70 °C. The maximum replacement of Na+ ion with K+ ion in the extra framework of zeolite was increased from 76% to 83% with increasing temperature from 50 °C to 70 °C in the ultrasonic method which is more effective than traditional one. Compared with the zeolites, the MOF adsorbents used in this work have higher Langmuir specific surface area values namely 1278, 1473 and about 1000 m2/g for MIL 53, Cu-BTC and zeolite adsorbents respectively. The resulting CO2 isotherms can be well represented by the Toth equation. Comparison of the isosteric heat of adsorption at zero loading shows that CO2 was adsorbed more weakly on MOFs than zeolites.
45
Qazi, Umair Yaqub, Rahat Javaid, Amir Ikhlaq, Asif Hussain Khoja et Faisal Saleem. « A Comprehensive Review on Zeolite Chemistry for Catalytic Conversion of Biomass/Waste into Green Fuels ». Molecules 27, no 23 (5 décembre 2022) : 8578. http://dx.doi.org/10.3390/molecules27238578.
Texte intégralRésumé :
Numerous attempts have been made to produce new materials and technology for renewable energy and environmental improvements in response to global sustainable solutions stemming from fast industrial expansion and population growth. Zeolites are a group of crystalline materials having molecularly ordered micropore arrangements. Over the past few years, progress in zeolites has been observed in transforming biomass and waste into fuels. To ensure effective transition of fossil energy carriers into chemicals and fuels, zeolite catalysts play a key role; however, their function in biomass usage is more obscure. Herein, the effectiveness of zeolites has been discussed in the context of biomass transformation into valuable products. Established zeolites emphasise conversion of lignocellulosic materials into green fuels. Lewis acidic zeolites employ transition of carbohydrates into significant chemical production. Zeolites utilise several procedures, such as catalytic pyrolysis, hydrothermal liquefaction, and hydro-pyrolysis, to convert biomass and lignocelluloses. Zeolites exhibit distinctive features and encounter significant obstacles, such as mesoporosity, pore interconnectivity, and stability of zeolites in the liquid phase. In order to complete these transformations successfully, it is necessary to have a thorough understanding of the chemistry of zeolites. Hence, further examination of the technical difficulties associated with catalytic transformation in zeolites will be required. This review article highlights the reaction pathways for biomass conversion using zeolites, their challenges, and their potential utilisation. Future recommendations for zeolite-based biomass conversion are also presented.
46
Coughlan, Brendan, et Mark A. Keane. « A characterization and catalytic study of Y zeolite supported Ni/Cu bimetallics ». Canadian Journal of Chemistry 68, no 9 (1 septembre 1990) : 1471–76. http://dx.doi.org/10.1139/v90-225.
Texte intégralRésumé :
A wide range of CuNiNaY andCuNiKY zeolites were prepared by ion exchange. The location of both Ni2+ and Cu2+ cations within the zeolite framework was monitored after various stages of thermal treatment and the reduction process of the transition metal ions in a flowing hydrogen atmosphere was investigated and correlated with reduction time and temperature. The metallic phase generated on reduction was characterized by X-ray diffraction line broadening. The catalytic activity of the reduced zeolites in the hydrogenation of benzene is discussed in the light of these physical characterizations.Keywords: zeolites, supported Ni/Cu bimetals, cation location, crystallite size, catalysis.
47
Cadar, Oana, Irina Vagner, Ion Miu, Daniela Scurtu et Marin Senila. « Preparation, Characterization, and Performance of Natural Zeolites as Alternative Materials for Beer Filtration ». Materials 16, no 5 (25 février 2023) : 1914. http://dx.doi.org/10.3390/ma16051914.
Texte intégralRésumé :
The clarity of the beer is essential to its marketability and good consumer approval. Moreover, the beer filtration aims to remove the unwanted constituents that cause beer haze formation. Natural zeolite, an inexpensive and widespread material, was tested as a substitute filter media for diatomaceous earth in removing the haze constituents in beer. The zeolitic tuff samples were collected from two quarries in Northern Romania: Chilioara, in which the zeolitic tuff has a clinoptilolite content of about 65%, and the Valea Pomilor quarry, containing zeolitic tuff with a clinoptilolite content of about 40%. Two-grain sizes, <40 and <100 µm, from each quarry were prepared and thermally treated at 450 °C in order to improve their adsorption properties and remove organic compounds and for physico-chemical characterization. The prepared zeolites were used for beer filtration in different mixtures with commercial filter aids (DIF BO and CBL3) in laboratory-scale experiments, and the filtered beer was characterized in terms of pH, turbidity, color, taste, flavor, and concentrations of the major and trace elements. The results showed that the taste, flavor, and pH of the filtered beer were generally not affected by filtration, while turbidity and color decreased with an increase in the zeolite content used in the filtration. The concentrations of Na and Mg in the beer were not significantly altered by filtration; Ca and K slowly increased, while Cd and Co were below the limits of quantification. Our results show that natural zeolites are promising aids for beer filtration and can be readily substituted for diatomaceous earth without significant changes in brewery industry process equipment and protocols for preparation.
48
Jendrlin, Martin, Julien Grand, Louwanda Lakiss, Florent Dubray, Philippe Bazin, Jaafar El Fallah, Svetlana Mintova et Vladimir Zholobenko. « Environmental Applications of Zeolites : Hydrophobic Sn-BEA as a Selective Gas Sensor for Exhaust Fumes ». Chemistry 5, no 1 (21 février 2023) : 334–47. http://dx.doi.org/10.3390/chemistry5010025.
Texte intégralRésumé :
Environmental monitoring of pollutants, such as NOx and COx, which can be facilitated by a range of gas sensors, is of considerable fundamental and practical importance. This work has been focused on the synthesis and evaluation of zeolite β with tin (Sn-BEA) and dealuminated β (DeAl-BEA) zeolites. The zeolite samples have been extensively investigated by IR, UV-VIS and NMR spectroscopy, XRD, TGA, and N2 adsorption-desorption. The prepared Sn-BEA sample is characterised by the submicron particle size, an almost defect-free structure, and high hydrophobicity. Sensors containing selective microporous layers based on Sn-BEA and DeAl-BEA zeolites have been prepared and extensively tested. Both the Sn-BEA and DeAl-BEA zeolites have been deposited in thin films and evaluated as gas sensors for CO, CO2, NO, and NO2 in the presence of water vapour at room temperature. The Sn-BEA zeolite-based sensor showed high selectivity towards NO2, while the DeAl-BEA is selective towards CO2 and NO2.
49
Climent, María José, Avelino Corma, Hermenegildo García et Jaime Primo. « Zeolites in organic reactions ». Applied Catalysis 51, no 1 (juin 1989) : 113–25. http://dx.doi.org/10.1016/s0166-9834(00)80199-2.
Texte intégral
50
LEE, S., et D. VENKATARAMAN. « ChemInform Abstract : Organic Zeolites ? » ChemInform 28, no 10 (4 août 2010) : no. http://dx.doi.org/10.1002/chin.199710228.
Texte intégral