New options for measuring molecular diffusion in zeolites by MAS PFG NMR

Combination of pulsed field gradient (PFG) NMR with magic-angle spinning (MAS) NMR is demonstrated to have remarkable advantages in comparison with conventional PFG NMR, if applied to diffusion measurements in beds of nanoporous particles, notably zeolites. These advantages are based on the effect of line narrowing and concern: (i) a prolongation of the intervals during which the magnetic field gradients may be applied and a corresponding enhancement in the sensitivity towards small molecular displacements, and (ii) an enhanced resolution in the chemical shift scale. Both options are illustrated by measuring the diffusion coefficient of n-butane adsorbed in silicalite-1.