Probing the Location and Distribution of Paramagnetic Centres in Alkali Metal Loaded Zeolites through ⁷Li MAS NMR

The nature and surroundings of lithium cations in lithium-exchanged X and A zeolites following loading with the alkali metals Na, K, Rb, and Cs have been studied through Li-7 solid-state NMR spectroscopy. It is demonstrated that the lithium in these zeolites is stable with respect to reduction by the other alkali metals. Even though the lithium cations are not directly involved in chemical interactions with the excess electrons introduced in the doping process, the corresponding Li-7 NMR spectra are extremely sensitive to paramagnetic species that are located inside the zeolite cavities. This sensitivity makes Li-7 NMR a useful probe to study the formation, distribution, and transformation of such species.