QUASI-ELASTIC NEUTRON-SCATTERING STUDY OF THE DYNAMICS OF METHANE ADSORBED IN NA-MORDENITE

The dynamics of methane adsorbed at different loadings and temperatures in Na-mordenite have been studied by quasi-elastic neutron scattering. Two methane species have been characterized: molecules diffusing in the straight channels, and molecules trapped in the side pockets. For an average loading of 0.8 molecule per unit cell, the proportion of mobile molecules in the channels is approximate to 35%. There is an equilibrium between the two species depending on the loading and temperature. The self-diffusion coefficient is of the order of 10(-9) m(2) s(-1). This value is smaller than in the MFI or FAU structures because of the trapping in the side pockets.