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Item type:Publication, Access status: with files , Predicting local transport coefficients at solid-gas interfacesThe regular nanoporous structure make zeolite membranes attractive candidates for separating molecules on the basis of differences in transport rates (diffusion). Since improvements in synthesis have led to membranes as thin as several hundred nanometers by now, the slow transport in the boundary layer separating bulk gas and core of the nanoporous membrane is becoming increasingly important. Therefore, we investigate the predictability of the coefficient quantifying this local process – the surface permeability α – by means of a two-scale simulation approach. Methane tracer-release from the one-dimensional nanopores of an AFI-type zeolite is employed. Besides a pitfall in determining α on the basis of tracer exchange, we, importantly, present an accurate prediction of the surface permeability using readily available information from molecular simulations. Moreover, we show that the prediction is strongly influenced by the degree of detail with which the boundary region is modeled. It turns out that not accounting for the fact that molecules aiming to escape the host structure must indeed overcome two boundary regions yields too large a permeability by a factor of 1.7 to 3.3, depending on the temperature. Finally, our results have far-reaching implications for the design of future membrane applications.Publicationtype: Journal ArticleScopus© Citations 36 261 496 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Adsorption and diffusion in zeolites : the pitfall of isotypic crystal structures(Taylor & Francis, 2011-06-27); ; ; ; The influence of isotypic crystal structures on adsorption and diffusion of methane in all-silica LTA, SAS and ITE zeolites is studied. Results obtained with the experimental structures are compared with structure predictions and approximations that are commonly employed. The results indicate that diffusion coefficients are much more affected than Henry coefficients. In fact, orders of magnitude deviations in the diffusivity can be observed and a systematic parameter study finally gives rise to the correlation between structure sensitivity and diffusion-window size.Publicationtype: Journal ArticleScopus© Citations 13 330 473 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , 190 233 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , In-depth study of the influence of host-framework flexibility on the diffusion of small gas molecules in one-dimensional zeolitic pore systemsMolecular-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.Publicationtype: Journal ArticleScopus© Citations 61 266 391