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

Abstract

The diffusion of carbon dioxide in both NaX and NaY Faujasite systems is investigated by combining Quasi-Elastic Neutron Scattering (QENS) and Molecular Dynamics (MD) simulations. The transport diffusivity evaluated experimentally increases with the loading whereas the simulated self diffusivity decreases. This general behaviour is in good agreement with those previously reported in the literature for different gases in similar zeolites systems. It was also shown that the corrected diffusivity exhibits a significant concentration dependence. At low loading, the activation energies for diffusion derived from QENS and MD simulations are in agreement. They increase from NaY to NaX due to a stronger interaction between the CO2 molecules and the extra-framework cations. The extrapolation of the transport and self diffusivities to zero coverage allowed us to emphasize a good agreement between experiment and simulation.