Adsorption of Nitrogen and Oxygen in the Zeolites LiA and LiX Investigated by 6Li and 7Li MAS NMR Spectroscopy

Abstract

The dehydrated zeolites LiX-1.0 [(SiAlO4)96Li96], LiX-1.25 [(Si106Al86O384)Li86], LiA [(SiAlO4)96Li96], and LiA-1.15 [(Si102.7Al89.3O384)Li89.3] have been studied in a vacuum and in the presence of oxygen and nitrogen gases by 7Li and 6Li MAS NMR spectroscopy. The adsorption of N2 molecules causes a small shift (Δδ = 0.2 ppm) to higher frequencies for the component belonging to cations interacting with N2 molecules. In contrast, the adsorption of oxygen causes a strong downfield (paramagnetic) shift depending on the accessibility of the Li cations. Observations made in the 7Li MAS NMR spectra recorded at the different conditions were used to propose a model for the location of the Li cations in zeolite LiA. As determined from the NMR spectra, the difference in nitrogen adsorption capacity of LiX and LiA is directly related to the accessibility of Li cations in each material.