Molecular Interplay of Cations and Nonpolar/Polar Sorbates in Titanosilicate ETS-10

Molecular simulations are performed to investigate the interplay of the nonframework Na + cations and the nonpolar (CH 4 )/polar (H 2 O) sorbates separately in titanosilicate ETS-10. Five types of Na + cations are identified in the ETS-10 framework based on the different geometric positions and site energies. Located in the 12-ring channels and with the lowest site energy, type V cations show substantially greater mobility than type I−IV cations that remain essentially static in the 7-ring channels and the 7- and 12-ring channel intersections. The predicted adsorption isotherms of both CH 4 and H 2 O in Na-ETS-10 agree well with the literature data. Two and three adsorption sites are observed for CH 4 and H 2 O, respectively. Compared to CH 4, H 2 O exhibits a greater extent of adsorption and a much smaller diffusivity. Diffusion of CH 4 drops monotonically as loading increases due to the steric hindrance. The interplay between Na + and CH 4 is not pronounced because of the weak van der Waals interactions, and the number of each type of Na + ion does not change appreciably upon the adsorption of CH 4 . However, the interplay is remarkable between Na + and H 2 O as a consequence of strong electrostatic interactions. Redistribution of Na + ions is observed upon the adsorption of H 2 O, in which the number of type V cations increases while other types slightly decrease. As the loading increases, diffusion of H 2 O initially rises and then drops as largely determined by H 2 O in the 12-ring channels. The mobility of Na + follows H 2 O in the 7- and 12-ring channel intersections due to the formation of Na + −H 2 O complex.