A new framework topology in the dehydrated form of zeolite levyne

Arletti, Rossella; Vezzalini, Giovanna; Quartieri, Simona; Cámara, Fernando; Alvaro, Matteo

doi:10.2138/am.2013.4583

Cited by 15 publications

(20 citation statements)

References 52 publications

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“…Nevertheless, an attempt to insert it in the structural refinement did not lead to satisfactory results; the refined value was as big as the computed error. Interestingly, the occurrence of a cation at this position, i.e., (0,0,0), was found in the dehydrated form of levyne-Ca (Arletti et al 2013;Cametti 2018).…”

Section: Discussionmentioning

confidence: 97%

Crystal structure of Ag-exchanged levyne intergrown with erionite: Single-crystal X-ray diffraction and Molecular Dynamics simulations

Cametti

Churakov

2020

American Mineralogist

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The modification of natural zeolites via ion exchange is an efficient technique used to improve their performances and tune their properties for specific applications. In this study, a natural levyne-Ca intergrown with erionite was fully exchanged by Ag+ and its structure [with idealized chemical composition Ag6(Si,Al)18O36·18H2O] was investigated by combining a theoretical and experimental approach. Single-crystal X-ray diffraction data demonstrated that Ag-levyne maintained the R3m space group, characteristic of the natural levyne. Ag ions distribute over partially occupied sites along the threefold axis and, differently from the pristine material, at the wall of the 8-membered ring window of the lev cavity. The lack of ~30% of Ag ions that could not be located by the structural refinement is ascribed to the strong disorder of the extraframework occupants. The structural results obtained by Molecular Dynamics simulations are in overall agreement with the experimental data and showed that, on average, Ag+ is surrounded by ~2 H2O and 1 framework oxygen at distances between 2.43 and 2.6 Å. Molecular Dynamics trajectories indicate that the occurrence of silver inside the D6R cage depends on the water content: silver occupancy of D6R cages is estimated to be 83, 30, and 0% when the structure contains 3, 2.5, and 2 H2O per Ag ion, respectively. The cation-exchange process, as demonstrated by scanning electron microscopy and energy-dispersive spectroscopy (SEM-EDS) spectrometry, affects the intergrown erionite as well. A structural characterization of the Ag-erionite phase (with dimension <100 μm) was possible by means of a CuKα micro-focus source: structure solution pointed to P63/mmc space group, indicating no change with respect to natural erionite. In agreement with previous studies, K ions in the cancrinite cage could not be exchanged, whereas Ag+ is found in the eri cavity.

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Section: Discussionmentioning

confidence: 97%

Crystal structure of Ag-exchanged levyne intergrown with erionite: Single-crystal X-ray diffraction and Molecular Dynamics simulations

Cametti

Churakov

2020

American Mineralogist

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“…They differentiated their response to temperature increase mainly on the basis of (1) zeolites that undergo dehydration accompanied by rearrangement of the cations, but without significant changes in the framework structure and unit-cell volume; (2) zeolites that undergo significant framework distortion and reduction of unitcell volume, but do not change their topology up to the collapse or breakdown, and (3) zeolites that undergo topological changes in the framework, due to the breaking of T-O-T bridges and the migration of the tetrahedral cations to new tetrahedral sites. In particular, the thermal behavior of this last zeolite group has been studied in detail by many authors and was recently reviewed in Arletti et al (2013).…”

Section: Introductionmentioning

confidence: 99%

High-temperature behavior of natural ferrierite: In-situ synchrotron X-ray powder diffraction study

Arletti

Fantini

Giacobbe

et al. 2018

American Mineralogist

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In this paper, we report the results of the first study focused on the thermal stability and dehydration dynamics of the natural zeolite mineral ferrierite. A sample from Monastir, Sardinia [(Na0.56K1.19Mg2.02Ca0.52Sr0.14) (Al6.89Si29.04)O72·17.86H2O; a = 19.2241(3) Å; b = 14.1563(2) Å; c = 7.5106(1) Å, V = 2043.95(7) Å3] was investigated by thermogravimetric analysis and in-situ synchrotron X-ray powder diffraction. Thermogravimetric data show that H2O release begins already in the range 50–100 °C and is complete at ~600 °C. The results of the structure refinements performed in Immm space group by Rietveld analysis with data collected up to 670 °C show that ferrierite belongs to the group of zeolites that do not undergo phase transitions. Upon heating to 670 °C, ferrierite behaves as a non-collapsible structure displaying only a slight contraction of the unit-cell volume (ΔV = −3%). The unit-cell parameter reductions are anisotropic, more pronounced for a than for b and c (Δa = −1.6%; Δb = −0.76%; Δc = −0.70%). This anisotropic response to a temperature increase is interpreted as due to the presence in the ferrierite framework of five-membered ring chains of SiO4 tetrahedra, which impart a higher structural rigidity along b and c. Upon dehydration we observe: (1) the gradual H2O loss, beginning with the molecules hosted in the 10MR channel, is almost complete at 670 °C, in good agreement with the TG data; (2) as a consequence of the decreased H2O content, Mg and K migrate from their original positions, moving from the center of the 10MR channel toward the walls to coordinate the framework oxygen atoms. The observation of transmission electron microscopy selected-area electron diffraction patterns revealed defective crystals with an occasional and moderate structural disorder. Beyond providing information on the thermal stability and behavior of natural ferrierite, the results of this work have significant implications for possible technological applications. These data allow for comparison with the dehydration kinetics/mechanisms of the corresponding synthetic phases, clarifying the role played by framework and extra-framework species on the high-temperature behavior of porous materials with ferrierite topology. Moreover, the information on the thermal behavior of natural ferrierite can be used to predict the energetic performances of analogous synthetic Si-pure counterparts, namely “zeosil-electrolyte” systems, under non-ambient conditions. Specifically, the very high thermal stability of ferrierite determined in this study, coupled with the baric behavior determined in other investigations, suggests that the “Si-FER–electrolyte” system may be an excellent candidate for use as an energy reservoir. Indeed, ferrierite exhibits the so-called “spring behavior,” i.e., upon compression in water or in an electrolyte solution, it converts the mechanical energy into interfacial energy, and—when pressure is released—it can completely restore the supplied mechanical energy accumulated during the compression step.

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“…Two 8-memebered ring channels run perpendicular to this direction. The dominant extraframework (EF) cations are Ca and Na (Coombs et al 1997), distributed along the threefold axis at different crystallographic positions that can vary depending on the sample composition (Sacerdoti 1996;Gatta et al 2005;Arletti et al 2013;Ballirano and Cametti 2013).…”

Section: Introductionmentioning

confidence: 99%

Stepwise dehydration of Cd-exchanged levyne: thermal stability and structural modifications

Cametti¹

2021

Phys Chem Minerals

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Zeolites show remarkable properties that can be tuned through cation exchange of their original extraframework content. In this respect, the response of the modified zeolite to the heating stimuli, in terms of structural modifications and thermal stability, can drastically change and is, therefore, an important factor to consider. In this study, the dehydration mechanism of a natural levyne previously exchanged with Cd2+ has been monitored in situ by single crystal X-ray diffraction. The initial dehydration trend between 50 and 175 °C is similar to that observed for the pristine material, levyne-Ca. The water loss is accompanied by extraframework cation migration within the zeolitic cavities and the unit-cell volume slightly contracts from 3503.8(1) to 3467.8(6) Å3. From 200 to 250 °C, a pronounced drop of the unit-cell volume (− 7%) is observed. The dehydrated structure at 250 °C corresponds to levyne B topology of natural levyne, characterized by the statistical rupture of the T–O–T bonds of the double six-ring membered cage. However, in contrast to levyne-Ca, the fraction of broken connections reached 50% instead of 37%, and no additional structural modifications were detected up to 350 °C. At 400 °C, diffraction data pointed to the onset of the structural collapse. At this temperature, the measured unit-cell volume was 8% smaller compared to that of the RT structure. The corresponding contracted structure did not rehydrate after exposure to humid conditions for 21 days.

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A new framework topology in the dehydrated form of zeolite levyne

Cited by 15 publications

References 52 publications

Crystal structure of Ag-exchanged levyne intergrown with erionite: Single-crystal X-ray diffraction and Molecular Dynamics simulations

Crystal structure of Ag-exchanged levyne intergrown with erionite: Single-crystal X-ray diffraction and Molecular Dynamics simulations

High-temperature behavior of natural ferrierite: In-situ synchrotron X-ray powder diffraction study

Stepwise dehydration of Cd-exchanged levyne: thermal stability and structural modifications

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