Dynamics of propene and propane in ZIF-8 probed by solid-state 2H NMR

We present a detailed H-2 NMR characterization of molecular mobility of propene and propane propagating though the microporous ZIF-8, a zeolitic imidazolate framework renowned for its outstandingly high separation selectivity for industrially relevant propene/propane mixtures. Experimental characterization of both propene and propane diffusivity in ZIF-8 has been provided. Using H-2 NMR spin relaxation analysis, the motional mechanisms for propene and propane guests trapped within the ZIF-8 framework have been elucidated. Kinetic parameters for each type of motion were derived. The characteristic times for microscopic translational diffusion and activation barriers (E-C3H8 = 38 kJ mol(-1), E-C3H6 = 13.5 kJ mol(-1)) for propane and propene diffusivities have been estimated. A notable difference in the observed activation barriers emphasizes that the ZIF-8 window crossing is associated with the gate-opening and represents an extremely shape selective process. Finally, we show that the H-2 NMR technique is capable of providing reliable information on microscopic diffusivity in the ZIF-8 MOF even for molecules with slow diffusivity (<10(-14) m(2) s(-1)).