Temperature-induced monoclinic/orthorhombic transition in germanium MFI-type zeolites

López, Ana Cristina; Soulard, Michel; Guth, J.L.

doi:10.1016/0144-2449(90)90032-m

Cited by 26 publications

(22 citation statements)

References 10 publications

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“…For example, MFI is known to undergo a phase transition with increasing T, from orthorhomic to monoclinic. 33 However, we use the "zero Kelvin" structure also for rigid-lattice simulations.…”

Section: Methodsmentioning

confidence: 99%

In-Depth Study of the Influence of Host−Framework Flexibility on the Diffusion of Small Gas Molecules in One-Dimensional Zeolitic Pore Systems

et al. 2007

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Molecular-dynamics simulations are performed to understand the role of host-framework flexibility on the diffusion of methane molecules in the one-dimensional pores of AFI-, LTL-, and MTW-type zeolites. In particular, the impact of the choice of the host model is studied. Dynamically corrected Transition State Theory is used to provide insights into the diffusion mechanism on a molecular level. Free-energy barriers and dynamical correction factors can change significantly by introducing lattice flexibility. In order to understand the phenomenon of free-energy barriers reduction, we investigate the motion of the window atoms. The influence that host-framework flexibility exerts on gas diffusion in zeolites is, generally, a complex function of material, host model, and loading such that transferability of conclusions from one zeolite to the other is not guaranteed.

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Section: Methodsmentioning

confidence: 99%

In-Depth Study of the Influence of Host−Framework Flexibility on the Diffusion of Small Gas Molecules in One-Dimensional Zeolitic Pore Systems

et al. 2007

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“…The analysis of the patterns collected using in situ synchrotron XRPD on both Y-SMX and ZSM-5-SMX and the pattern collected ex situ on the regenerated Y zeolite (Yrev AC ) showed no heat-induced symmetry change. On the contrary, in the case of ZSM-5rev AC , peak splitting at 2y = 10.27º ((133) orthorhombic reflection) into a doublet at 2y = 10.25º and 10.34º is clear evidence of an orthorhombic to monoclinic phase transition (Hay and Jaeger, 1984;Lopez et al, 1990;Marra et al, 2000;Bhange and Ramaswamy, 2006). As a consequence, the structure refinement of this sample was performed in the monoclinic P2 1 /n space group, using the site positions reported by Pasti et al (2012).…”

Section: In Situ Synchrotron X-ray Powder Diffraction and Rietveld Rementioning

confidence: 99%

Regeneration of high-silica zeolites after sulfamethoxazole antibiotic adsorption: a combined in situ high-temperature synchrotron X-ray powder diffraction and thermal degradation study

et al. 2014

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The thermal regeneration of sulfamethoxazole (SMX)-loaded Y and ZSM-5 zeolites was studied using a combined in situ high-temperature synchrotron X-ray powder diffraction and thermal degradation study. The evolution of the structural features was monitored in real time in the 30À575ºC temperature range by full-profile Rietveld analysis. SMX thermal degradation pathways into high-silica zeolite antibiotic adducts, as well as the release of evolved species are similar to those for pure SMX. The adsorption/desorption process occurs without any significant loss of zeolite crystallinity, though slight deformations to the channel apertures are observed. Regenerated zeolites regain almost perfectly 'bare' (i.e. unloaded) material unit-cell parameters and only a slight memory effect, in terms of structural deformations induced by the process, is registered in the channel geometry. Interestingly, these changes do not affect the adsorption properties of the regenerated samples, which are able to re-adsorb comparable amounts of antibiotic molecules as in the first adsorption cycle.

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“…Cations reside within the zeolite framework ensuring electroneutrality by compensating for the excess negative charge caused by the substitution of silicon (Si 4+ ) atoms by aluminum (Al 3+ ) atoms. Other elements, such as zirconium, titanium, zinc, and germanium can also be found in the framework, attributing different properties and functionalities to the zeolite. Zeolites have been attracting the interest of the scientific and industrial community since their discovery in 1756 .…”

Section: Introductionmentioning

confidence: 99%

Pressure- and Temperature-Induced Monoclinic-to-Orthorhombic Phase Transition in Silicalite-1

et al. 2018

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The thermal, mechanical, and volumetric behavior of silicalite-1, an all-silica Mobil Five (MFI) zeolite, is elucidated by atomistic simulations. A flexible force field was selected and validated from a set of force fields to capture the intramolecular interactions of the crystal lattice. This force field accounts for realistic bond, angle, and torsional interactions among atoms of the framework alongside with conventional Lennard-Jones and Coulomb interactions. By monitoring the behavior of silicalite-1 as a function of pressure and temperature, a fully reversible monoclinic-to-orthorhombic phase transition (polymorphism) was revealed in accordance with experimental data. Thermodynamic considerations dictate that this is a second-order phase transition in the Ehrenfest classification. Additionally, reversible pressure-induced amorphization was captured by our model and was associated with the formation of linear zones of increased distortion running parallel to the straight and sinusoidal channels of this zeolite. Remarkably high isothermal compressibility (small bulk modulus) was calculated for orthorhombic silicalite-1, in excellent agreement with experimental data, rendering silicalite-1 as the most compressible zeolite known to date. The rigid unit mode model was identified as the dominant structural mechanism for negative thermal expansion (NTE), typically observed over a wide temperature range in MFI zeolites. Better understanding of the monoclinic-to-orthorhombic phase transition and molecular mechanisms associated with energy dissipation and NTE in zeolites provides control over the framework microstructure, allowing for enhanced molecular sieving, tunable selectivity in separation processes, mechanical stability, and substantially amplified catalytic efficiency in petrochemical applications.

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Temperature-induced monoclinic/orthorhombic transition in germanium MFI-type zeolites

Cited by 26 publications

References 10 publications

In-Depth Study of the Influence of Host−Framework Flexibility on the Diffusion of Small Gas Molecules in One-Dimensional Zeolitic Pore Systems

In-Depth Study of the Influence of Host−Framework Flexibility on the Diffusion of Small Gas Molecules in One-Dimensional Zeolitic Pore Systems

Regeneration of high-silica zeolites after sulfamethoxazole antibiotic adsorption: a combined in situ high-temperature synchrotron X-ray powder diffraction and thermal degradation study

Pressure- and Temperature-Induced Monoclinic-to-Orthorhombic Phase Transition in Silicalite-1

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