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Abstract: The control of the inter-particle porosity in polycrystalline zeolite bodies remains a challenge. The present study reports on the preparation of centimeter-sized zeolite bodies (32×2mm pellets) with reduced inter-particle porosity. The bodies were prepared by assembling zeolite colloidal nanocrystals with monomodal particle size distribution and sub-colloidal aluminum hydroxide binder. A secondary growth treatment under hydrothermal conditions was performed in order to fill up the inter-particle voids and obtain polycrystalline zeolite materials with textural characteristics close to those of single zeolite crystals. Initial material, intermediates and ultimate product were studied with a combination of complementary methods revealing a substantial reduction even an elimination of the inter-particle porosity. Particular attention was paid to the chemical evolution of the binder and the migration of aluminum species, employing X-ray powder diffraction, 27Al-MAS, 27Al-3QMAS NMR and X-ray fluorescence spectroscopy analyses. Evidences for insertion of aluminum from the binder into the zeolite framework during secondary growth step were found. Consequently the ultimate pellets comprised aluminum-rich zeolite beta crystals and very low binder content. [ABSTRACT FROM AUTHOR]

Abstract: The nanoscale events in an organic-template-free gel leading to the formation of a FAU-type zeolite at 90°C were investigated by transmission electron microscopy (TEM). The study was complemented by ex situ X-ray diffraction (XRD), infrared (IR), 23Na 3Q-MAS NMR, N2 adsorption measurements and chemical analyses. It was found that the critical factor that triggers the growth process and mass transformation from amorphous into crystalline zeolite material is the attainment of a specific level of chemical evolution of the system, expressed in homogenization of the starting gel approaching stoichiometric FAU-type zeolite composition. This period was also marked by the formation and development of voids in the gel particles, containing highly hydrated material transformed later on into negative crystals. The evolution of these areas has been found to be an integral and noteworthy part of the chemical transformation of the gel that preceded the nucleation in the system. The observed transformations in the solid part of the system were induced by sodium, which progressively penetrated in the aluminosilicate matrix, breaking its structure and reorganizing the aluminosilicate species. The sodium behaviour was tracked down by a combination of local and bulk chemical analyses complemented by 23Na 3Q-MAS NMR study. During the initial stage of reaction a growth via propagation through the amorphous network co-existed with the typical solution-assisted hydrothermal crystallization. The later stages of development of the system followed the classical for zeolite-yielding systems crystallization that could be described by the autocatalytic nucleation. [Copyright &y& Elsevier]

Abstract: Previous investigations have shown that an all-silica BEA-type (Si-BEA) material is difficult to be nucleated in basic media and that the fluorosilicic precursors formed in near neutral media play an important role in its formation. The present study reports on the synthesis of this microporous material under basic conditions by using TEA2SiF6 as an additional silica source that provides preformed fluorosilicate species. The effect of the amount of TEA2SiF6 on the purity of the final product, crystallization kinetics and morphological features of Si-BEA were systematically studied. The investigation showed that above a certain concentration corresponding to TEA2SiF6/SiO2 =0.07 pure Si-BEA was obtained and further increase in the concentration improved substantially the crystallization kinetics. The increase in TEA2SiF6 content led also to a gradual increase of the size of the pyramidal (h 0l) face coupled with the decrease of pinacoidal (001) one. Thus, the morphology of the zeolite crystals can be varied from well developed truncated bipyramids to plate-like crystals with dominating pinacoidal faces. A consequence of this morphological changes is the number the pore openings of the channel systems running along the a- and c-axes per total external surface. The framework defectness and water content in the synthesized materials were studied by 29Si NMR spectroscopy and TG analysis, respectively. This combined study revealed that materials with a high level of hydrophobicity, due to the specific effect of fluorine anions, have been synthesized under basic conditions. [Copyright &y& Elsevier]

Abstract: Silicalite-1 was in situ crystallized from clear synthesis solutions onto commercial millipore glass fiber filters. The filters with diameter 2.5cm were soaked in the precursor mixtures and hydrothermally treated at 80°C or 150°C for time up to 150h. After the synthesis, the filters were treated in an ultrasonic bath for 15min with a 0.1M ammonia solution. The disc composites prepared at 80°C swelled during synthesis, were easy to disintegrate upon subsequent manipulations and wrinkled when dried. The calcined materials were brittle with a porcelain-like appearance. The filters synthesized at 150°C, both as synthesized and calcined, seemed identical in shape and mechanical characteristics to the initial glass fiber filters. Prolongation of the treatment at 150°C up to 100h led to densified fiber discs according to the SEM study but without visual changes in their mechanical strength. The difference in crystallization at the two different temperatures was attributed to the slower nucleation process at 80°C, which resulted in greater dissolution of the fiber units and a certain inhibition of the crystallization process caused by the changed chemical environment at the fiber–synthesis solution interface. The silicalite-1/filter composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering (DLS), chemical analysis and N2 adsorption measurements. [Copyright &y& Elsevier]

The effect of room temperature aging on the crystallization rate and size of MFI-type crystals synthesized under high temperature was investigated. First, synthesis mixtures yielding MFI-type zeolite were aged at room temperature for periods of time between 1 and 60 days. This was followed by a rapid synthesis in a pre-heated at 230 °C conventional oven. The utilization of a pre-aged initial systems and high heating rates allowed very rapid synthesis of zeolite. The effect of aging time, crystallization temperature, duration of synthesis and aluminum content on the crystal size and yield was systematically studied. Zeolite nanoparticles with sizes ranging from 130 to 260 nm and relatively narrow particle size distributions were synthesized employing the pure-silica system. The obtained nanocrystals were characterized by X-ray diffraction, scanning electron microscopy, dynamic light scattering and N2 adsorption measurements. [Copyright &y& Elsevier]

Water extraction from air is a promising strategy for alleviating the current water crisis since it provides inexhaustible water resources to the places where surface and groundwater are scarce. This study systematically assesses 12 selected microporous materials out of zeolites, aluminophosphate zeotypes (AlPOs), and metal-organic frameworks (MOFs), the most promising adsorbents to meet the stringy criteria for economic water harvesting. Through a comparative study of water adsorption isotherms, desorption enthalpies, regeneration temperatures, water capacity, and kinetics at the same condition, the zeotype aluminophosphate with AEI framework topology (AlPO-18) stands out. Using AlPO-18, 0.29 g/g water uptake is achieved in a narrow relative humidity range before 13%. The adsorbent regeneration is almost completed below 70 °C. Moreover, AlPO-18 is non-toxic and the synthesis is low-cost. Therefore, AlPO-18 is a good candidate for adsorbent in developing energy-saving atmospheric water harvest (AWH) technology to extract water from "dry" air. [Display omitted] • Nanoporous materials were studied as atmospheric water harvesting (AWH) sorbents. • Micropoous AlPOs demonstrate high capacity and low-temperature water desorption. • AlPO-18 is potential candidate for developing an energy-saving AWH system. [ABSTRACT FROM AUTHOR]

Abstract: The present work deals with the removal of organic template, tetraethylammonium (TEA) and activation of Beta zeolite nanocrystals using cold plasma (nonthermal) treatment as efficient and environmentally benign approach. The entire process of nonthermal plasma activation of the nanosized zeolite is monitored in a reactor using real time in situ FTIR. The influence of the environmentally friendly cold plasma treatment in comparison to conventional activation (heating at high temperature in the presence of reducing gases) on the physicochemical properties of Beta zeolite nanocrystals is investigated. It is shown that the cold plasma treatment removes the organic template from the nanosized Beta crystals within several minutes, without carbon deposition and thus eliminating the high temperature treatment and the use of hazardous chemicals. The acidic properties of the nanosized Beta zeolite after calcination and cold plasma treatment using pyridine adsorption and temperature programmed desorption are studied by in situ IR spectroscopy. In addition, the Beta nanocrystals treated by the two methods are characterized by X-ray diffraction, 29Si NMR spectroscopy and nitrogen sorption. It is shown that the cold plasma treatment is an environmental solution for removal of unwanted products (organic templates) in very short time resulting in energy saving and reduction of hazardous solvents and gases. [Copyright &y& Elsevier]

Abstract: Core–shell zeolite composites possessing a mordenite core and a shell of intergrown silicalite-1 crystals were synthesized. A classical hydrothermal treatment of mordenite crystals with a silicalite-1 precursor mixture did not result in the formation of an extended silicalite-1 layer on the mordenite surface. The incompatibility between the core crystals and the shell precursor was circumvented by adsorption of nanoseeds on the core surface, which upon a subsequent hydrothermal treatment induced the formation of a well intergrown shell. The kinetics of shell growth was studied at 150 and 200°C and the optimum conditions further used for the preparation of composites subjected to XRD, SEM, TG/DTA, EDS and X-ray fluorescence analyses. The integrity of the shell layer was tested by N2 adsorption measurements on materials comprising Na- and Na,H-mordenite and a non-calcined tetrapropylammonium (TPA)-containing shell, the latter being non-permeable for the N2 molecules. These measurements showed that 96–98% of the mordenite crystals were covered with a defect-free TPA-silicalite-1 shell after a single hydrothermal treatment. A characteristic feature of the obtained composites is the relatively large single crystal core and the very thin polycrystalline shell. Thus, the relatively large active part of the composite is covered by a tiny shell that ensures fast kinetics. [Copyright &y& Elsevier]

The synthesis of zeolites in a strongly acidic medium is a new and nearly unexplored chemistry field. In addition to the previously reported silicalite-1 and the several clathrasils, this paper elaborates that one more material of unique properties could be successfully crystallized in the strongly acidic fluoride medium. A pure-silica zeolite ZSM-8 has been obtained using tetraethylammonium ion as a structure-directing agent. Rietveld refinement proves that ZSM-8 is of the MFI topology, i.e., it is another silicalite-1 but different in framework distortions. Moreover, the discrete and uniform crystals of the acidic-medium synthesized pure-silica ZSM-8 possess a substantially perfect framework structure and thus hydrophobic surfaces. This remarkable character renders the material an ideal adsorbent for discriminating molecules on the polarity basis, which is desired in developing green separation processes. C 3 H 8 , CH 4, and CO 2 are chosen as examples respecting their different polarities and tested for the adsorptive parameters. Acidic-medium synthesized pure-silica ZSM-8 zeolite has perfect framework connectivity, thus extremly hydrophobic surface, which makes it an ideal adsorbent for separations of polar and apolar molecules. [Display omitted] • Pure-silica ZSM-8 crystallizes at pH = 2.9∼4.8 using TEABr as the SDA. • Pure-silica ZSM-8 has MFI framework. Other than TPA+, TEA+ interacts stronger with the framework, leading to distortions. • Acidic-medium synthesized ZSM-8 possesses unprecedently perfect framework, thus extremely hydrophobic surface. • The adsorption energies of CH 4 , C 3 H 8 are obviously different from that of CO 2. [ABSTRACT FROM AUTHOR]

Chemical interactions occurring between zeolites and alumina binders during the critical steps of catalyst forming are the focus of this study. Three widely used and commercially significant variants of FAU zeolite, covering a wide range of Si/Al ratios, micro- and meso-porosity and acidic properties (Y [LZY-64, Si/Al = 2.3] and USY [CBV 720 and CBV 760 with Si/Al = 16 and Si/Al = 28, respectively]) were shaped by extrusion with pseudoboehmite to produce bound extrudates. These extrudates were characterized by conventional techniques (XRD, 27Al NMR and IR spectroscopy, N 2 physisorption ...) and compared to their parent powders activated under the same conditions. The catalytic performances of the zeolite powders, their derived alumina extrudates and physical zeolite/γ-Al 2 O 3 mixtures were also evaluated employing two different reactions: i) n-octane hydroisomerization, to probe all catalytic sites and ii) 1,3,5 tri-isopropyl benzene dealkylation to probe only the external/mesoporous surfaces. The bound zeolites systematically displayed catalytic performance superior to their parent powders or physical mixtures, especially in the dealkylation of 1,3,5 tri-isopropyl benzene. Infrared spectroscopy measurements of the number, nature and strength of the acid sites were consistent with these catalytic results demonstrating that new catalytic sites are created and located on the external or mesoporous surface of the zeolites, i.e. at the zeolite-binder interface. The work reported here clearly illustrates that binding and subsequent thermal treatment of zeolite powders to produce commercially representative forms can significantly alter the quality and quantity of active sites creating active centers not usually present in pure powders which are typically studied and reported in much of the open literature. Such a study is also a blueprint for other catalytic phases, other forming processes (spray-drying, oil-dropping, pelletizing ...) and could also be applied to the shaping of adsorbents. Image 1 • Zeolite Y were shaped by extrusion using pseudoboehmite as binder. • Acidic properties of zeolite extrudates were probed using basic probe molecule and monitored by infrared. • Zeolite shaping alter qualitatively and quantitatively the acidic properties of the final compounds. • Zeolite Y extrudates systematically displayed catalytic performance superior to their parent powders or physical mixtures, especially in the dealkylation of 1,3,5 tri-isopropyl benzene. • New acid sites are formed during shaping, reminiscent of amorphous silica-alumina. [ABSTRACT FROM AUTHOR]

The zeolite community spent 50 years in pursuing the synthesis of high-silica LTA -type zeolites, and ultimately succeeded with the pure-silica polymorph by applying specific structure-directing agents (SDA). The high-silica zeolite A has exhibited unique properties and strong potential to be applied as an adsorbent and catalyst in several novel processes. In the present study, the high-silica polymorphs of Si/Al ratios from 15 to ∞ were synthesized and subjected to thorough characterizations using multiple physicochemical methods. It has been revealed that there exists strong interactions between the organic SDAs and the framework. Therefore, removing the SDAs by calcination in air is difficult, and can only be done above 700 °C with a certain degree of framework dealumination. The retained framework structure shows connectivity defects and a unique combination of Brønsted and Lewis acidity. Using methanol-to-olefins (MTO) as a probe reaction, the catalytic performance of high-silica LTA -type zeolites has been evaluated. Compared to the well-studied CHA and MFI -type catalysts, high-silica zeolite A exhibited a shorter life-time and higher selectivity towards C 4 olefins, while methane selectivity increased with the deactivation. [Display omitted] • The crystallization of high-silica LTA -type zeolites requires specific structure-directing agents (SDAs). • Strong SDA/framework interactions are evidenced by XRD, NMR and TG. • Complete removal of SDA by calcination accompanied by framework dealumination, while the framework structure retained. • High-silica LTA-type material possesses unique acidity that renders different catalytic performances in MTO reactions. [ABSTRACT FROM AUTHOR]

Abstract Highly crystalline and pure SSZ-13 zeolite is obtained by interzeolite conversion of zeolite Beta and zeolite L. Zeolite Beta is used without preliminary treatment, while zeolite L is subjected to dealumination in order to reach the Si/Al ratio appropriate for the synthesis of SSZ-13. The formation of SSZ-13 from conventional chemicals is also studied. The crystallization from zeolite precursors is much faster and provides pure and highly crystalline SSZ-13. The improved crystal growth kinetics is attributed to the directing effect of the dissolved Si-O-Al fragments from zeolite Beta and zeolite L frameworks. CHA-type zeolites obtained from dealuminated zeolite L crystallized faster, showed higher crystallinity and more defined crystals morphology in respect to those obtained from zeolite Beta. The dealuminated zeolite L was found to be an outstanding starting material for the crystallization of SSZ-13. Graphical abstract Image 1 Highlights • Zeolite Beta and Zeolite L are used as silica-alumina sources for the synthesis of zeolite SSZ-13 (CHA-type). • Factors controlling the interzeolite conversion of zeolite Beta and zeolite L in SSZ-13 are studied. • SSZ-13 shows higher crystallinity and crystallizes faster from zeolite precursors rather than the conventional gels. • Dealuminated zeolite L is a more efficient initial source for the SSZ-13 synthesis in respect to zeolite Beta. [ABSTRACT FROM AUTHOR]

Abstract The NH 4 F etching is a chemical approach for the preparation of hierarchical zeolites without substantial modification of their framework composition and acidic properties. We employed this approach to modify the 2-dimensional form of ZSM-5 and obtain a catalyst for bulky molecules conversion. The etching conditions were varied in order to obtain hierarchical ZSM-5 with different level of dissolution. Thus, obtained derivatives of 2-dimensional ZSM-5 were thoroughly studied in order to get deep insights into the effect of fluoride treatment. The 2-dimensional ZSM-5 was found unexpectedly stable under etching conditions, which is a consequence of the high quality of zeolite crystals containing a limited number of defect zones and misoriented crystalline domains, in contrast to conventional ZSM-5. Fluoride etching was also used to de-pillar 2-dimensional ZSM-5. The morphology and textural properties of the de-pillared ZSM-5 were very similar to those of the parent layered ZSM-5. Accordingly, amorphous and extra-framework species were dissolved first, resulting in the complete removal of extra-framework Al, thereby strengthening the active sites. In summary, the fluoride etching opens the structure of layered ZSM-5 and strengthens its acid sites when combined with dealumination during calcination. Graphical abstract Image 1 Highlights • Layered ZSM-5 was etched using concentrated NH 4 F solutions. • Layered ZSM-5 is unexpectedly stable under etching conditions. • Fluoride etching opens the structure of layered ZSM-5 increasing the external surface. • Pillared ZSM-5 was de-pillared by removing the amorphous silica pillars. • Removal of extra-framework Al strengthens the active sites. [ABSTRACT FROM AUTHOR]

Abstract A growing interest is currently directed to find an efficient NO and CO 2 gas carriers for biomedical applications. The gas adsorption properties of sodium- (Na-X) and copper- (Cu-X) containing FAU nanozeolites toward nitric oxide and carbon dioxide were studied. The materials were fully characterised by XRD, TEM, ICP, DLS and in-situ FTIR. The as-prepared Na-X showed higher gas adsorption ability towards carbon dioxide, whereas the ion-exchanged Cu-X was more efficient adsorbent with regards to nitric oxide. In addition, the cytotoxicity tests disclosed that both nanozeolites have no toxicity making them suitable for further tests in biomedical field as gas transporters. Graphical abstract Image 1 Highlights • Preparation of colloidally stable Na- and Cu-containing FAU nanozeolite. • Evaluation of CO 2 and NO adsorption properties on metal exchanged FAU. • Cytotoxicity assessment of nanozeolite towards three types of cells. • Verified biocompability of FAU for biomedical (gas delivery) applications. [ABSTRACT FROM AUTHOR]

The fluoride medium synthesis of zeolites, especially in the strongly acidic regions, yields products with unique characteristics such as ultra-hydrophobic surfaces and defect-free lattices. However, it is often difficult to incorporate aluminum into the framework of zeolites in this medium, limiting the acquisition and development of catalytic materials. The present paper shows that inter-zeolite transformation is efficient for obtaining ZSM-5 zeolites with lower Si/Al ratios in a strongly acidic fluoride medium. The critical point is that the parent zeolites can retain some locally ordered fragments during their dissolution, including framework Al atoms, and incorporate them into the ZSM-5 product. The acidic properties of the trans -crystallization products obtained in an acidic medium display significant differences from the traditional ZSM-5 with a similar Si/Al ratio in the amounts, strength, and types of the acid sites; thus, they behave differently in typical acid-catalysed reactions, such as dehydration of alcohols. In strongly acidic fluoride medium * BEA , FER and MOR -type zeolites transform readily into nanometer plates of MFI zeolite because they possess common mor CBU, while FAU zeolite transforms slowly to micrometer MFI crystals. These Al-rich ZSM-5 zeolites have unique acidity and perform differently in catalytic dehydration of light alcohols from the conventional ZSM-5. [Display omitted] • Al-rich ZSM-5 of Si/Al ∼ 20 obtained in acidic fluoride medium via inter-zeolite transformation. • In acidic medium * BEA , FER and MOR zeolites transforms readily into nanometersized plates of MFI because of common mor CBU. • FAU zeolite transforms slowly to micrometer MFI crystals. • These Al-rich ZSM-5 zeolites have unique acidity and perform differently in catalytic dehydration of light alcohols. [ABSTRACT FROM AUTHOR]

A facile and effective fluoride post-treated route has been systematically applied for the preparation of hierarchical zeolite catalysts in three different SAPO-34 systems using morpholine, triethylamine and tetraethylammonium hydroxide as template, respectively. Secondary pores in SAPO-34 zeolite crystals are formed by etching with HF-NH 4 F containing solutions under ultrasonic condition. The samples were characterized by XRD, SEM, N 2 adsorption-desorption, XRF, TG, 29 Si MAS NMR and NH 3 -TPD techniques. The set of experimental data demonstrate that the organic templates impact the etching process by fluoride route, most probably the distribution of active sites, thus influence the catalytic properties. It is worth underline that the selectivity to C 2 H 4 and C 3 H 6 over the obtained hierarchical SAPO-34 catalysts in the methanol-to-olefin (MTO) reaction is improved as compared to the parent SAPO-34 catalysts, while an undesired diminished catalyst lifetime is observed for hierarchical SAPO-34 templated by morpholine and tetraethylammonium hydroxide. [ABSTRACT FROM AUTHOR]

The preparation of iron-loaded nanosized zeolite with EMT-type structure (Fe-EMT) is reported. The sorption capacity of the Fe-EMT zeolite crystals for NO and CO 2 is evaluated. The application of Fe-EMT zeolite as a gas delivery system with high capacity for CO 2 and NO in biomedicine is considered. Therefore the toxicity of the pure EMT and Fe-EMT zeolite nanocrystals is studied. Primary culture of astrocytes was exposed to zeolite nanocrystals. In addition, two human cell lines, U87-MG glioblastoma and HEK-293T were used. Cells were exposed to zeolites nanocrystals with concentrations of 50, 100 and 400 μg/ml for 24 h and 48 h. Cytotoxicity was assessed by a cell viability assay and no alteration of cell viability exposed to zeolite nanoparticles was observed. [ABSTRACT FROM AUTHOR]

FER-type zeolites were synthesized in the presence of Na-Ethylendiamine (Na–En), Na–Pyrrolidine (Na–Py) and Na–K. The crystallization times varied between 96 and 240 h. Ferrierite harvested from the Na–En synthesis was also used as seeds and reduced crystallization time from 240 to 30 h. The product of seeded synthesis was not uniform: nanosized with micronsized crystals as well as complex aggregates of different sizes were obtained. Hierarchical FER-type zeolites were prepared using seeded Na–En synthesized FER as a parent. Secondary pores in zeolite crystals were formed by etching at room temperature with HF-NH 4 F containing solutions, using the HF concentration and treatment time as variables. Crystal morphology and physicochemical characteristics of micron-, nano-sized and hierarchical FER-type crystals were studied by complementary methods including: X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG/dTG), 27 Al and 29 Si MAS NMR, IR spectroscopy of adsorbed probe molecules (Pyridine, Acetonitrile and Lutidine), nitrogen adsorption and chemical analysis. We demonstrate that FER-type zeolites with pre-determined properties can be easily prepared. [ABSTRACT FROM AUTHOR]

A new procedure for zeolite synthesis based on a silicate ionic liquid is reported. The method consists of a two-step precursor preparation. In the first step, a liquid silicate is prepared by hydrolyzing tetraethylorthosilicate (TEOS) with KOH–H 2 O mixture, which induces coacervation resolved into full phase demixing and subsequent separation from a water–ethanol phase by simple decantation. In the second step, an appropriate amount of an alkaline aluminate is mixed with the first liquid silicate, avoiding therefore precipitation. To the best of our knowledge, this represents the first example of homogeneous liquid synthesis, and not a clear sol or a gel, of an Al-rich zeolite, free of organic template. The approach is exemplified by the synthesis of merlinoite with potassium hydroxide as mineral base and could be extended to other zeolitic systems by varying the chemical composition and the nature of the alkali cation. The synthesis yield depends on the Al content and the crystalline products showed a very large range of particle sizes varying from nanometer scale to about a hundred microns when increasing the Al concentration. Crystallization proceeds most likely through nucleation from a liquid where nucleation and growth directly affects the ultimate crystal size and morphology. [ABSTRACT FROM AUTHOR]

Highlights: [•] Mechanochemical treatment, a versatile tool for zeolite synthesis and modification. [•] Scalable, efficient, and mechanistically-distinct to solvent-intensive routes. [•] Structural transformations classified according to the energy required. [•] Catalytic properties enhanced by mechanochemical activation. [•] Rationalization will facilitate the scale up of future zeolite technologies. [ABSTRACT FROM AUTHOR]

Highlights: [•] We introduce the rotation electron diffraction (RED) method. [•] We discuss the advantages of RED over powder XRD and single crystal XRD. [•] We demonstrate the power and limitations of the RED method. [•] We determined the structures of silicalite-1, the EUO-, FER- and AST-type zeolites by RED. [•] We study how different parameters affect unit cell, structure solution and refinement. [ABSTRACT FROM AUTHOR]

YNU-5 zeolite has the YFI -type framework with a 12-12-8-ring system (2-dimensional 12-oxygen membered ring pores 3-dimensionally connected by twin 8-ring channels), and isolated 8-ring channels separated from the system by a thin (mono-atomic silicate) wall. In this study, the acidic property of YNU-5 zeolite was analyzed mainly by means of the ammonia IRMS-TPD (infrared/mass spectroscopy temperature-programmed desorption) method. In addition, the accessibility of acid sites was evaluated through adsorption of pyridine. The number of Brønsted acid sites approximately agreed with the number of Al atoms, and the amount of Lewis acid sites was negligible, indicating that most acid sites have the nature of bridging Si(OH)Al group in the YFI framework. Most of the Brønsted acidic OH groups on the YNU-5 zeolites (including the dealuminated samples) reacted with pyridine vapor at 343 K to form pyridinium cations, indicating that the Brønsted acid sites are highly accessible through the 12-12-8-ring system. Enthalpy of ammonia desorption from the Brønsted acid site, which can be an index of acid strength or reactivity of the acid site with a basic reactant, was in the following order: FAU < MOR (12-ring) ≈ *BEA < MFI < MWW ≈ YFI < MOR (8-ring), indicating the markedly large ammonia desorption enthalpy on the YNU-5 zeolite compared to the other 12-ring zeolites. The DFT calculations suggest that the Brønsted acidic protons with especially high ammonia desorption enthalpy are located in the isolated 8-ring but accessible from the 12-12-8-ring system side. In addition, dealumination at a high temperature under the reflux conditions with nitric acid resulted in the preferential removal of Brønsted acid sites with low ammonia desorption enthalpy, probably in the 12-12-8-ring system. The presence of reactive Brønsted acid sites in the isolated 8-ring, accessibility to them from the 12-12-8-ring system, and preferential removal of the Brønsted acid sites from the 12-12-8-ring system are reasonably consistent with the previously reported catalytic properties for dimethyl ether-to-olefin reaction. [Display omitted] • Enthalpy of ammonia desorption (Δ H) from the Brønsted acid site on the YNU-5 zeolite was high. • The Brønsted acidic protons with high Δ H were located in the isolated 8-ring but accessible from the 12-12-8-ring system. • Dealumination in the reflux conditions of nitric acid preferential proceeded in the 12-12-8-ring system. [ABSTRACT FROM AUTHOR]

Zeolites are the catalytic materials that are widly applied in the processing of conventional and renewable fuels and chemicals. The present study provides a comprehensive analysis of the factors controlling the acidic medium synthesis of high silica silicalite-1 zeolite. The effect of various silica sources (TEOS, fumed and colloidal silica) and alkali metal cations (Na and K) on the silicalite-1 formation is studied. The efficiency of different types of seeds (micron-sized, nanosized, and silicalite-1 amorphous colloidal precursor) on the silicalite-1 crystal growth kinetics and crystal size formed under acidic conditions is also investigated. Further, the zeolite crystallization kinetics under acidic, neutral, and basic conditions is compared. The obtained highly crystalline samples are used to compare the physicochemical properties of zeolites synthesized in acidic, neutral, and basic medium. Thus, the crystallinity, thermal stability, and local order in silicalite-1 samples synthesized in the (2–12) pH range are evaluated. [Display omitted] • Silicalite-1 crystallization in an acidic medium is slow and results in giant crystals no matter of the silica source. • Silicalite-1 crystals synthesized in acidic medium exhibit unprecedented defect-free structure. • The use of nanosized seeds yeilds silicalite-1 crystals with a size of a few hundred nanometers. • Seeding with amorphous zeolite embryos results in crystals of around 20 μm. [ABSTRACT FROM AUTHOR]

Commercial zeolites with CHA, MFI, and LTL framework topology are subjected to acid treatment with chromic acid (H 2 CrO 4) solutions with concentrations ranging between 0.1 and 10 w /%. As chromic acid forms polymeric species as a function of concentration, specific effects are obtained with these three zeolites, differing by their framework topology, pore size, Si/Al ratios and crystal size. The etched zeolites are characterized by X-ray diffraction, SEM, TEM, N 2 physisorption, ICP-AES, 27Al and 29Si MAS NMR, 29Si{1H} cross-polarization spectra, EDX. Their acidic properties are probed with pyridine and d 3 -acetonitrile by in situ FTIR. Results indicate that the 8 MR (CHA) and 10 MR (MFI) zeolites are more resistant to acid treatment with chromic acid than the 12 MR (LTL) zeolite. This paves the way for rational control of zeolite dealumination since adjusting chromic acid concentration will generate anions appropriate for treating a particular zeolite. [Display omitted] • CHA, MFI, and LTL zeolites are subjected to treatment with chromic acid (H 2 CrO 4). • Chromic acid forms polymeric species as a function of concentration. • CHA and MFI zeolites resist more to the chromic acid treatment than the LTL zeolite. • Tuning the acid concentration yields anions apt for treating a particular zeolite. [ABSTRACT FROM AUTHOR]

Abstract: A zeolite beta–silicalite-1 composite was prepared by growing polycrystalline silicalite-1 shells on single micron-sized zeolite beta crystals. The obtained core–shell material was employed for the separation of hexane isomers. Gravimetric uptake measurements revealed that the silicalite-1 shell acted as a membrane that controlled the transport to zeolite beta core. The positive impact of the silicalite-1 membrane on the separation of mono- and di-branched hexane isomers was confirmed by breakthrough experiments. The core–shell composite material allowed more selective separation of mono- and di-branched isomers than either of its components alone and had a significantly higher adsorption capacity than silicalite-1. [Copyright &y& Elsevier]

Abstract: This study reports the preparation of a FAU-type membrane for the separation of CO2/N2. The membrane is prepared by in situ seeding followed by a two-step secondary growth to plug the 0.2μm macropores of a multilayer α-Al2O3 tube. The key factor for successful in situ seeding is the infiltration of the synthesis mixture in the pores of the α-Al2O3 tube. Infiltration is achieved by cooling down of the initial mixture in order to slow down its gelation. The infiltrated support is hydrothermally treated to provide a uniform layer of zeolite crystals in pores of the α-Al2O3 support. The hydrothermal treatment is repeated with a gel mixture of low viscosity. SEM analysis shows that the FAU crystals close the interparticle porosity after two such hydrothermal treatments. However, there is also some zeolite formation in the larger pores (1.5 and 12μm) of the multilayer α-Al2O3 tube, which can negatively affect the membrane performance. Nevertheless, the membrane exhibits a CO2 permeance of 3.5×10−7 mols−1 m−2 Pa−1 and a separation selectivity of 12 in the separation of equimolar CO2 and N2 gas mixtures at 323K. [Copyright &y& Elsevier]

Abstract: Smooth and homogeneous monolayer Silicalite-1 seeds were deposited on silicon substrate surfaces via the Langmuir–Blodgett (LB) technique. The LB films were prepared by vertical dipping leaving part of the substrate uncoated. Neither substrate modification nor additives were required to produce densely packed monolayer seeds. The degree of coverage and packing of the seed layers were dependent on the target pressure used for film deposition. Dense Silicalite-1 films with controlled thickness in the range 100–650nm were synthesized after secondary synthesis. The (0 k 0) reflections dominated in all the XRD patterns, suggesting that the prepared polycrystalline films were preferentially b-oriented perpendicular to the substrate surface. The degree of in-plane orientation was preserved with increasing film thickness. All secondary growth films were very smooth with a clear boundary between the seeded and non seeded substrate sections. The Silicalite-1 films were highly stable upon both ultrasonic treatment and calcination. [Copyright &y& Elsevier]

Embryonic X-ray amorphous semi-formed MFI-type zeolite units mixed with the Cu–Zn–Al catalyst have been used for the direct synthesis of dimethyl ether (DME) from syngas. The hybrid catalyst with embryonic zeolite (EZ) with the particle size of 5 nm has demonstrated superior performance in terms of activity, selectivity, and stability compared to the crystalline ZSM-5 zeolite counterpart and the amorphous aluminosilicate material. The FTIR pyridine adsorption uncovered several types of active sites in EZ, including Brønsted acid sites of medium strength. The DFT modeling pointed out the key role of defect sites leading to lower strength of the acid sites in the embryonic MFI zeolite in comparison with the fully crystalline material. The effect of embryonic zeolite on the DME synthesis has been assigned to enhanced transport of methanol from Cu to ultra-small zeolite precursor units with moderate acidity, hence promoting the efficient dehydration to DME with high selectivity and stability. [Display omitted] • Embryonic zeolite with X-ray amorphous semi-formed MFI units have been synthesized. • It has been mixed with Cu–Zn–Al catalyst for direct DME synthesis from syngas. • Material demonstrated superior performance in activity, selectivity and stability. • Ultra-small zeolite precursor units with medium acidity provide efficient dehydration to DME. [ABSTRACT FROM AUTHOR]

NH 4 -SSZ-13 is etched with an aqueous solution of 40 w /% NH 4 F under different time/temperature conditions to obtain hierarchical derivatives. The etched zeolites are characterized by XRD, SEM, N 2 physisorption, 29Si/27Al/19F MAS NMR, ICP-AES, and their acidity monitored by in situ FTIR spectroscopy using acetonitrile as a probe molecule. The results highlight that the zeolite is very sensitive to high temperature and high liquid-solid ratio treatments leading to substantial crystallinity losses. These two parameters need careful tuning to obtain hierarchical derivatives retaining important characteristics as micropore volume and framework Si/Al ratio. The catalytic activity of the modified SSZ-13 is evaluated in the n-propanol conversion. Image 1 • Zeolite SSZ-13 (CHA-type) is subjected to chemical etching in an aqueous NH 4 F solution to introduce mesopores. • The hierarchical zeolite preserved the parent zeolite properties in terms of framework composition and Brønsted acidity. • The obtained SSZ-13 derivatives show higher coke contents but slower deactivation in the dehydration of n-propanol. [ABSTRACT FROM AUTHOR]

The development of covalent organic frameworks (COFs) with new building units is of critical importance for enriching the structural diversity and expanding their functions. However, the construction of COFs has been thus far limited primarily to traditional organic linkers. Herein, we report three-dimensional porous crystalline covalent polyoxometalate-organic frameworks (CPOFs) constructed from both inorganic and organic building blocks with reversible covalent bonds. These highly crystalline CPOFs exhibited 3-fold interpenetrated diamondoid topology, permanent porosity and high stability. Furthermore, these CPOFs could be directly applied as anode materials for lithium-ion batteries (LIBs) and displayed high reversible capacity (as high as 550 mA h g−1), rate performance, and cycling stability (up to 500 cycles). Image 1 • Three-dimensional porous crystalline covalent polyoxometalate-organic frameworks. • Constructed from both inorganic and organic building blocks with reversible covalent bonds. • Interpenetrated diamondoid topology, permanent porosity and high stability. • High reversible capacity, rate performance, and cycling stability. [ABSTRACT FROM AUTHOR]

Zeolites are materials widely used in many fields of human activities. Furthermore, new potential applications constantly emerge, so understanding their possible impact on the environment is necessary. Within this study, the potential toxicity of nanosized particles (140 and 600 nm) of a widely used zeolite beta was evaluated using zebrafish Danio rerio embryos. Embryotoxicity test, with an emphasis on sublethal changes, was performed on three concentrations of each nanosized zeolite sample (calcined and non-calcined). Toxicity of tetraethylammonium species (TEA) present in non-calcined zeolite samples was also investigated using experimental and computational approaches. The data suggest that non-calcined zeolites and tetraethylammonium hydroxide (TEAOH) itself caused hatching failure, but also initiated oxidative stress and apoptosis. Such observation confirmed certain TEA leaching from the zeolite framework, thus impacting embryonic development. Since molecular docking and molecular dynamics simulations did not show TEA inhibition of the hatching enzyme ZHE1 and the ROS formation was detected using fluorescence microscopy, it was concluded that oxidative stress is the major mechanism underlying the toxicity of non-calcined samples and TEAOH. Contrary to that, calcined zeolite nanoparticles, although having a strong interaction with the chorion and subsequently with the embryos, did not show a negative impact on zebrafish survival/development. Such a comprehensive study pinpointed zeolite nanoparticles as safe materials and opened the door for their application. Image 1 • Zeolite nanoparticles showed no impact on zebrafish embryonic development. • Tetraethylammonium cations tend to leach from the zeolite *BEA framework. • Oxidative stress leads to hatching delay in zebrafish exposed to non-calcined zeolite samples and TEAOH. [ABSTRACT FROM AUTHOR]

Tailoring of physicochemical properties of synthetic zeolites is of paramount importance when these materials are applied as heterogenous catalysts. In this work, the effect of the synthesis system and in particular of the organic structure directing agent (OSDA) on acidity, crystal morphology, and catalytic behaviour of FER-type materials is studied. FER-type zeolites with similar Si/Al ratio and crystal size range 0.3–15 μm are synthesised by changing OSDA type or by adding surfactant. A crystallization kinetic analysis shows that the stability of the zeolitic phase strongly depends on the OSDA type. In particular, the crystallization time strongly affects the purity of the FER phase when tetrahydrofuran is used as a template. Furthermore, it is found that long amines as 1,8-diaminooctane can play a role of OSDA obtaining highly crystalline FER-type crystals and with a high Lewis acid sites concentration. FT-IR and 27Al-NMR analyses show that all of the synthesised samples possess different Lewis acid sites concentration associated with extra-framework Al–OH species that are not detected by NMR analysis. Catalytic tests in methanol-to-dimethyl ether reaction reveal that synthesised samples exhibit different catalytic behaviour. In particular, large (10–15 μm) FER-type catalyst synthesised with tetrahydrofuran suffer deactivation caused by a higher carbon deposit level. On the contrary, nano-sized FER-type crystals, prepared by using pyrrolidine as OSDA and a surfactant, exhibits high selectivity and considerable resistance to coke deposition. Image 1 • FER-Type zeolite synthesis was performed with four different OSDA. • OSDA characteristics affected the crystal growth. • The crystal size (from micro-down to nano-sized) was varied by using a surfactant. • Catalytic properties, in MetOH-to-DME, are affected by crystal size. • Coke formation could be reduced with nano-sized FER. [ABSTRACT FROM AUTHOR]

Ferrierite zeolite crystals were successfully prepared by a long amine as 1,8-diaminoctane (DAO) as organic structure directing agent. By comparison, shorter amine, i.e. ethylenediamine (EN), was also used as OSDA. Results shows that the presence of DAO reduces the crystallization time and allows to obtain single FER-type crystals with smaller size and higher acidity, being these significant parameters to take into account when zeolites are applied in catalysis. The obtained samples were characterised with XRD, TG/DTA, SEM, N 2 adsorption/desorption, FTIR and 27Al-NMR. In particular, TGA clearly shows that DAO may be accommodate in zeolite framework and theoretical modeling suggests a preferential location in the 10-MR ring channels. Image 1 • FER-Type zeolite synthesis was performed with 1,8-diaminoctane (DAO). • Both experimental and theoretical study confirmed 1,8-diammioctane as OSDA for FER-type structure. • 1,8-diaminoctane is preferably located along 10-membered ring channels. • Respect to ethylenediamine, 1,8-diaminoctane leads to generation of stronger Lewis acid sites. [ABSTRACT FROM AUTHOR]