Intrinsic Flexibility of the EMT Zeolite Framework under Pressure

Nearchou, Antony; Cornelius, Mero Lee U.; Skelton, Jonathan M.; Jones, Zöe L.; Cairns, Andrew B.; Collings, Ines E.; Raithby, Paul R.; Wells, Stephen A.; Sartbaeva, Asel

doi:10.3390/molecules24030641

Cited by 9 publications

(8 citation statements)

References 56 publications

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“…Alternatively, the size of the cubic flexibility window is identical between the filled and empty KFI frameworks. This behaviour mirrors what has been observed previously with the EMT framework [ 33 , 34 ] and is similar to the C-form of zeolite RHO herein.…”

Section: Resultssupporting

confidence: 90%

“…This mirrors the predictions of Fletcher et al . [ 33 ] from geometric simulations and our previous high-pressure study of the EMT framework containing the 18C6 molecule [ 34 ]. However, there is a discrepancy as the flexibility of the filled and empty EMT frameworks is identical, unlike that seen herein for the FAU framework.…”

Section: Resultsmentioning

confidence: 99%

“…Consequently, this leads to a decrease in compressibility as a function of pressure. However, other work has shown how the intrinsic flexibility window and compression of the EMT framework is unperturbed by the occlusion of 18-crown-6 ether (18C6) [ 33 , 34 ]. This is of particular interest, as 18C6 is used as an organic additive in the preparation of EMT-type zeolites like EMC-2 [ 35 , 36 ], where synthesis without 18C6 has not been achieved [ 37 ].…”

Section: Introductionmentioning

confidence: 99%

“…This is of particular interest, as 18C6 is used as an organic additive in the preparation of EMT-type zeolites like EMC-2 [ 35 , 36 ], where synthesis without 18C6 has not been achieved [ 37 ]. Our earlier high-pressure and computational studies suggest that 18C6 may not necessarily behave as a true geometric template but rather influences the free-energy landscape of crystallization [ 34 ]. This highlights how the study of framework flexibility can provide valuable insights into the nature of zeolite synthesis.…”

Section: Introductionmentioning

confidence: 99%

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Pressure-induced symmetry changes in body-centred cubic zeolites

et al. 2019

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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.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Pressure-induced symmetry changes in body-centred cubic zeolites

et al. 2019

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“…All data created during this study is available free of charge from the University of Bath data archive [61].…”

Section: Data Availabilitymentioning

confidence: 99%

Intrinsic Flexibility of the EMT Zeolite Framework Under Pressure

Nearchou¹,

Cornelius²,

Skelton³

et al. 2019

Preprint

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<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>

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