Transport Diffusivity of N₂ and CO₂ in Silicalite:  Coherent Quasielastic Neutron Scattering Measurements and Molecular Dynamics Simulations

Abstract

A direct comparison of experimental measurements (coherent quasielastic neutron scattering) and simulation (molecular dynamics) is carried out for the first time to investigate the concentration dependence of transport diffusivity of nitrogen and carbon dioxide in silicalite-1. Theoretical elaboration of the simulation results on the basis of the quasichemical mean field approximation and a model of surface diffusion due to D. A. Reed and G. Ehrlich (Surf. Sci. 1981, 102, 588) leads to the conclusion that the corrected (Darken) diffusivity D 0 can exhibit significant dependence on the loading θ of the sorbed phase, varying with the strength of interactions between the sorbate molecules. As a consequence of sorbate−sorbate interactions being considerably more attractive in CO2/silicalite-1 than in N2/silicalite-1, D 0(θ) is a decreasing function in CO2/silicalite-1 but displays a weak maximum in N2/silicalite-1.

Loading Dependence of the Diffusion Coefficient of Methane in Nanoporous Materials

“…9,[38][39][40] The model works well for materials in which all adsorption sites are equal (in other words, diffusional barriers do not change as a function of loading or f ) 1 in the Reed-Ehrlich formulation) and for which the adsorption can thus be described by a single Langmuir isotherm.…”

DL_MONTE: a general purpose program for parallel Monte Carlo simulation

“…The adsorption and separation of CO 2 from gas streams is an important area of research, and there are many published works, both experimental and computational, on adsorption and diffusion in bulk zeolite structures [28][29][30][31][32][33][34][35][36][37][38][39][40] using a variety of potential models. [41][42][43][44] Surface effects are very important for adsorption and much less work has been carried out on the adsorption and transport of CO 2 at zeolite surfaces, so this is where we chose to focus our work.…”

Intracrystalline Diffusion in Zeolites Studied by Neutron Scattering Techniques

“…However, it has recently been shown that transport diffusivities can be measured by coherent QENS, at equilibrium [1,2]. It may seem surprising to derive a non-equilibrium quantity from QENS experiments performed at equilibrium.…”