A combination of grand canonical Monte Carlo and microcanonical molecular dynamics simulations was used to study the adsorption and diffusion of argon at 77 and 120K confined in previously generated models of a disordered bituminous coal-based carbon, BPL, and an ordered carbon replica of Faujasite zeolite (C-FAU). Both materials exhibited a maximum in the diffusion coefficient as well as anomalous (sub-diffusive) behavior in the mean-squared displacements at short times at some relative pressures. In BPL, the anomalous diffusion occurred at low relative pressures, due to the trapping of argon atoms in small pores. In C-FAU, the anomalous diffusion occurred at high relative pressures, due to competitive diffusion of atoms traveling through windows and constrictions which interconnected the pores. All diffusion eventually tended toward Fickian at longer times.

Adsorption and Diffusion of Argon Confined in Ordered and Disordered Microporous Carbons. J.D.Moore, J.C.Palmer, Y.C.Liu, T.J.Roussel, J.K.Brennan, K.E.Gubbins: Applied Surface Science, 2010, 256[17], 5131-6