H NMR Signal Broadening in Spectra of MFI Type Zeolites

1. Introduction Isotropic mobility of molecules adsorbed in zeolites should completely average out spin interactions which cause line broadening in nuclear magnetic resonance (NMR) spectroscopy. But it is well-known that additional application of magic-angle spinning (MAS), Hahn-Echo (HE) or Carr-Purcell (CPMG) pulse sequences reduces the effective line broadening in such systems. This is essential for pulsed field gradient (PFG) NMR experiments, since the cutback of line broadening corresponds to a prolongation of the effective transverse relaxation time T 2 , which increases the sensitivity of NMR diffuso-metry. Short relaxation times limit the duration of the gradient pulses in PFG NMR.