Characterization of Li Cations in Zeolite LiX by Solid-State NMR Spectroscopy and Neutron Diffraction

Lithium cations in the dehydrated zeolites LiX-1.0 [(SiAlO4)96Li96] and LiX-1.25 [(Si106Al86O384)Li86] are characterized by a combination of neutron diffraction and magic-angle spinning (MAS) NMR spectroscopy. Both samples show in the 6Li and the 7Li MAS NMR spectra three lines assigned to Li cations in three different crystallographic sites (SI‘, SII, and SIII‘). The low-field component in 6Li and 7Li MAS NMR spectra recorded at a temperature of 295 K belongs to mobile Li cations, as proven by variable-temperature 7Li MAS NMR spectra. Variable-temperature neutron diffraction experiments show a phase transition in the temperature range T = 220−230 K in case of LiX-1.0. Neutron diffraction data recorded at 296 K were refined in the cubic space group Fd and data obtained at 20 K were refined in the orthorhombic space group Fddd. No phase transitions were observed in the refinement of the neutron diffraction data of zeolite LiX-1.25 (Fd ) recorded at 10 K.