Assignment of ²³Na MAS NMR signals of ammonium- and lanthanum-exchanged sodium Y zeolites

Two distinct 23Na MAS NMR lines in spectra of hydrated Na,NH4-Y zeolites at about -9 and -13 ppm (referenced to crystalline NaCl) were assigned to sodium lattice cations located in the large cavities (SIII) and inside the truncated octahedra (SI′ or SII′). This assignment was supported by the appearance of these two signals in spectra of air-dried and heat-treated La,Na-Y zeolites (obtained by conventional or contact-induced solid-state ion exchange), the more so as the intensity ratios corresponded to the cation distribution known to arise after the distinctly different pretreatments. It is concluded that slowly tumbling sodium cations are located in SIII whereas Na cations in truncated octahedra show stronger quadrupole interactions. A 23Na signal at -5.5 ppm sometimes observed in spectra of La,Na-Y zeolites was tentatively assigned to sodium cations located in the hexagonal prisms (SI)

Solid-State Ion Exchange - Phenomenon and Mechanism

Highly exchanged MeI-Y (MeI = Li, Na, K, Rb, Cs) as well as La-Y zeolites were prepared through solid-state ion exchange between NH4-Y (98%) and the respective chlorides. It was shown that, except for the case of Li-Y, both low- temperature and high-temperature exchange processes occurred. With the system MeICl/NH4-Y the high-temperature reaction seemed to proceed more easily the lower the lattice energy of the alkaline chloride. In La-Y, the bare La3+ ions introduced via solid-state ion exchange were catalytically inactive. However, La-Y obtained via solid-state ion exchange was rendered an active catalyst for both ethylbenzene disproportionation and n-decane cracking after a brief contact with traces of water vapor. For the solid-state reaction itself, the presence of water is not a prerequisite