scholarly journals Local Distortions in a Prototypical Zeolite Framework Containing Double Four‐Ring Cages: The Role of Framework Composition and Organic Guests**

ChemPhysChem ◽  
2020 ◽  
Author(s):  
Michael Fischer ◽  
Linus Freymann
Keyword(s):  
Zeolite Framework ◽  
Organic Guests ◽  
Local Distortions ◽  
Framework Composition

scholarly journals Local Distortions in a Prototypical Zeolite Framework Containing Double Four-Ring Cages: The Role of Framework Composition and Organic Guests

2020 ◽  
Author(s):  
Michael Fischer ◽  
Linus Freymann
Keyword(s):  
Density Functional ◽  
Zeolite Framework ◽  
Functional Theory ◽  
Organic Structure ◽  
Judicious Choice ◽  
Dynamics Simulations ◽  
The Impact ◽  
Local Distortions ◽  
Framework Composition

<p>Cube-like double four-ring (<i>d4r</i>) cages are among the most frequent building units of zeolites and zeotypes. In materials synthesised in fluoride-containing media, the fluoride anions are preferentially incorporated in these cages. In order to study the impact of framework composition and organic structure-directing agents (OSDAs) on the possible occurrence of local distortions of fluoride-containing <i>d4r</i> cages, density functional theory (DFT) calculations and DFT-based molecular dynamics simulations were performed for AST-type zeotypes, considering four different compositions (SiO<sub>2</sub>, GeO<sub>2</sub>, AlPO<sub>4</sub>, GaPO<sub>4</sub>) and two different OSDA cations (tetramethylammonium [TMA] and quinuclidinium [QNU]). All systems except SiO<sub>2</sub>-AST show significant deformations, with a pyritohedron-like distortion of the <i>d4r</i> cages occurring in GeO<sub>2</sub>- and GaPO<sub>4</sub>-AST, and a displacement of the fluoride anions towards one of the corners of the cage in AlPO<sub>4</sub>- and GaPO<sub>4</sub>-AST. While the distortions occur at random in TMA-containing zeotypes, they exhibit a preferential orientation in systems that incorporate QNU cations. </p><p>In addition to providing detailed understanding of the local structure of a complex host-guest system on the picosecond timescale, this work indicates the possibility to stabilise ordered distortions through a judicious choice of the OSDA, which might enable a tuning of the material’s properties.</p>

scholarly journals Local Distortions in a Prototypical Zeolite Framework Containing Double Four-Ring Cages: The Role of Framework Composition and Organic Guests

2020 ◽  
Author(s):  
Michael Fischer ◽  
Linus Freymann
Keyword(s):  
Density Functional ◽  
Zeolite Framework ◽  
Functional Theory ◽  
Organic Structure ◽  
Judicious Choice ◽  
Dynamics Simulations ◽  
The Impact ◽  
Local Distortions ◽  
Framework Composition

<p>Cube-like double four-ring (<i>d4r</i>) cages are among the most frequent building units of zeolites and zeotypes. In materials synthesised in fluoride-containing media, the fluoride anions are preferentially incorporated in these cages. In order to study the impact of framework composition and organic structure-directing agents (OSDAs) on the possible occurrence of local distortions of fluoride-containing <i>d4r</i> cages, density functional theory (DFT) calculations and DFT-based molecular dynamics simulations were performed for AST-type zeotypes, considering four different compositions (SiO<sub>2</sub>, GeO<sub>2</sub>, AlPO<sub>4</sub>, GaPO<sub>4</sub>) and two different OSDA cations (tetramethylammonium [TMA] and quinuclidinium [QNU]). All systems except SiO<sub>2</sub>-AST show significant deformations, with a pyritohedron-like distortion of the <i>d4r</i> cages occurring in GeO<sub>2</sub>- and GaPO<sub>4</sub>-AST, and a displacement of the fluoride anions towards one of the corners of the cage in AlPO<sub>4</sub>- and GaPO<sub>4</sub>-AST. While the distortions occur at random in TMA-containing zeotypes, they exhibit a preferential orientation in systems that incorporate QNU cations. </p><p>In addition to providing detailed understanding of the local structure of a complex host-guest system on the picosecond timescale, this work indicates the possibility to stabilise ordered distortions through a judicious choice of the OSDA, which might enable a tuning of the material’s properties.</p>

scholarly journals Local Distortions in a Prototypical Zeolite Framework Containing Double Four-Ring Cages: The Role of Framework Composition and Organic Guests

2020 ◽  
Author(s):  
Michael Fischer ◽  
Linus Freymann
Keyword(s):  
Density Functional ◽  
Zeolite Framework ◽  
Functional Theory ◽  
Organic Structure ◽  
Judicious Choice ◽  
Dynamics Simulations ◽  
The Impact ◽  
Local Distortions ◽  
Framework Composition

<p>Cube-like double four-ring (<i>d4r</i>) cages are among the most frequent building units of zeolites and zeotypes. In materials synthesised in fluoride-containing media, the fluoride anions are preferentially incorporated in these cages. In order to study the impact of framework composition and organic structure-directing agents (OSDAs) on the possible occurrence of local distortions of fluoride-containing <i>d4r</i> cages, density functional theory (DFT) calculations and DFT-based molecular dynamics simulations were performed for AST-type zeotypes, considering four different compositions (SiO<sub>2</sub>, GeO<sub>2</sub>, AlPO<sub>4</sub>, GaPO<sub>4</sub>) and two different OSDA cations (tetramethylammonium [TMA] and quinuclidinium [QNU]). All systems except SiO<sub>2</sub>-AST show significant deformations, with a pyritohedron-like distortion of the <i>d4r</i> cages occurring in GeO<sub>2</sub>- and GaPO<sub>4</sub>-AST, and a displacement of the fluoride anions towards one of the corners of the cage in AlPO<sub>4</sub>- and GaPO<sub>4</sub>-AST. While the distortions occur at random in TMA-containing zeotypes, they exhibit a preferential orientation in systems that incorporate QNU cations. </p><p>In addition to providing detailed understanding of the local structure of a complex host-guest system on the picosecond timescale, this work indicates the possibility to stabilise ordered distortions through a judicious choice of the OSDA, which might enable a tuning of the material’s properties.</p>

scholarly journals Intrinsic Flexibility of the EMT Zeolite Framework Under Pressure

2019 ◽  
Author(s):  
Antony Nearchou ◽  
Mero-Lee U. Cornelius ◽  
Jonathan M. Skelton ◽  
Zoe Jones ◽  
Andrew Cairns ◽  
...  
Keyword(s):  
Free Energy ◽  
Computational Modelling ◽  
Lattice Energy ◽  
Vibrational Entropy ◽  
Organic Additives ◽  
X Ray Diffraction ◽  
Zeolite Framework ◽  
Guest Molecules ◽  
Fau Zeolite

<p>The roles of organic additives in the assembly and crystallisation of zeolites is still not fully understood. This is important when attempting to prepare novel frameworks to produce new zeolites. We consider 18-crown-6 ether as an additive, which has previously been shown to differentiate between the EMT and FAU zeolite frameworks. However, it is unclear whether this distinction is dictated by influences on the metastable free-energy landscape or geometric templating. Using high pressure synchrotron X-ray diffraction, we have observed that the presence of 18C6 does not impact the EMT framework flexibility – agreeing with our previous geometric simulations and suggesting that 18C6 does not behave as a true geometric template. This was further studied with computational modelling, using first-principles comparative periodic DFT and lattice-dynamics calculations. It is shown that the lattice energy of FAU is more stable than EMT, however this is strongly impacted by the presence of solvent/guest molecules in the framework. Furthermore, the EMT topology possesses a greater vibrational entropy, being stabilised by free energy at finite temperature. Overall, these findings demonstrate that the role of the 18C6 additive is to influence the free-energy of crystallisation to assemble the EMT framework as opposed to FAU. </p>

scholarly journals Intrinsic flexibility of porous materials; theory, modelling and the flexibility window of the EMT zeolite framework

2015 ◽  
Vol 71 (6) ◽  
pp. 641-647 ◽  
Author(s):  
Rachel E. Fletcher ◽  
Stephen A. Wells ◽  
Ka Ming Leung ◽  
Peter P. Edwards ◽  
Asel Sartbaeva
Keyword(s):  
Real Space ◽  
Ionic Conductors ◽  
Static Properties ◽  
Zeolite Framework ◽  
Framework Materials ◽  
Collective Motions ◽  
The Cost ◽  
Insight Into ◽  
Shed Light

Framework materials have structures containing strongly bonded polyhedral groups of atoms connected through their vertices. Typically the energy cost for variations of the inter-polyhedral geometry is much less than the cost of distortions of the polyhedra themselves – as in the case of silicates, where the geometry of the SiO4 tetrahedral group is much more strongly constrained than the Si—O—Si bridging angle. As a result, framework materials frequently display intrinsic flexibility, and their dynamic and static properties are strongly influenced by low-energy collective motions of the polyhedra. Insight into these motions can be obtained in reciprocal space through the `rigid unit mode' (RUM) model, and in real-space through template-based geometric simulations. We briefly review the framework flexibility phenomena in energy-relevant materials, including ionic conductors, perovskites and zeolites. In particular we examine the `flexibility window' phenomenon in zeolites and present novel results on the flexibility window of the EMT framework, which shed light on the role of structure-directing agents. Our key finding is that the crown ether, despite its steric bulk, does not limit the geometric flexibility of the framework.

scholarly journals Impact of Zeolite Framework Composition and Flexibility on Methanol‐To‐Olefins Selectivity: Confinement or Diffusion?

2020 ◽  
Vol 59 (44) ◽  
pp. 19708-19715 ◽  
Author(s):  
Pau Ferri ◽  
Chengeng Li ◽  
Reisel Millán ◽  
Joaquín Martínez‐Triguero ◽  
Manuel Moliner ◽  
...  
Keyword(s):  
Zeolite Framework ◽  
Framework Composition
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