Diffusion of CO2 in NaY and NaX Faujasite systems: Quasi-elastic neutron scattering experiments and molecular dynamics simulations

Probing the Dynamics of CO2 and CH4 within the Porous Zirconium Terephthalate UiO‐66(Zr): A Synergic Combination of Neutron Scattering Measurements and Molecular Simulations

“…This nonmonotonic variation of D s of CO 2 presented in Figure 5 is similar to those previously predicted in ZIF‐68 and ZIF‐70 with cagelike structures,11a but is different from those in MIL‐47(V),12b DDR,15b and NaX,8b which show a decreasing trend with increasing CO 2 loading. In addition, as can be seen from Table 1, the predicted D s of CO 2 of (2.4–6.7)×10 −10 m 2 s −1 in UiO‐66(Zr) at 230 K is comparable to those simulated in ZIF‐6812b and NaX8b at 300 K, but almost one order of magnitude smaller than those in ZIF‐7011a at 300 K and MIL‐47(V)12b at 230 K and similar loadings as well as in DDR at 300 K 15b.…”

“…Indeed, CO 2 also combines both intra‐ and intercage motions, whereby the tetrahedral–octahedral–tetrahedral cage‐jump sequence is affected by the loading in the same way as for CH 4 . This microscopic mechanism, which was also previously proposed to explain the same monotonic D s profile for CO 2 in ZIF‐68 and ZIF‐70,11a differs from those invoked for DDR,21 MIL‐47(V),12b and NaX,8b wherein the steric effect causes a decreasing evolution of D s as a function of loading.…”

Transport Diffusivity of CO2 in the Highly Flexible Metal–Organic Framework MIL‐53(Cr)

“…no broadening could be measured, that is, diffusivity is lower than 5 The activation energy for transport diffusion was obtained for a CO 2 concentration of 5.2 molecules/u.c., by measuring spectra at three different temperatures. The thus-obtained value of 9.7 kJ mol À1 is higher than those previously reported in zeolites (5.1 and 6.3 kJ mol À1 in silicalite and NaY, respectively), [24,25] which means that the interactions between CO 2 and the m 2 -OH groups at the MIL-53(Cr) surface are rather strong, as previously shown by microcalorimetry and Monte Carlo calculations. [26] The corrected diffusivities D 0 can further be determined by correcting the transport diffusivities by the thermodynamic correction factors, calculated from the experimental adsorption isotherm measured at 230 K ( Figures S3 and S5, Supporting Information) by means of Equation (1) where the partial derivative involving the…”

“…These D t values are similar to those previously predicted for other MOFs [12,13] and about one order of magnitude larger than those previously measured in various zeolites by QENS experiments. [24,25] For the first investigated loading (1 molecule/u.c.) no broadening could be measured, that is, diffusivity is lower than 5 The activation energy for transport diffusion was obtained for a CO 2 concentration of 5.2 molecules/u.c., by measuring spectra at three different temperatures.…”

CO2 diffusivity in LiY and NaY faujasite systems: a combination of molecular dynamics simulations and quasi-elastic neutron scattering experiments

“…The main theoretical studies were based on Molecular Dynamics simulations and reliable interatomic potentials (Demontis and Suffriti 1997), some others dealing with Monte Carlo procedures coupled with transition state theory (Maginn et al 1996). In a previous study, we have shown that combining QENS and Molecular Dynamics simulations is a powerful tool to investigate the diffusion of CO 2 , a typical coherent scattered, in Faujasite systems as a function of the density of the cations (Plant et al 2007a). Here, the diffusion of this adsorbate, is investigated in both LiY and NaY using the same approach, in order to emphasize the influence of the nature of the extraframework cations on the dynamics of CO 2 .…”