Abstract: Dealuminated Y zeolites after mild steaming and (NH₄)₂SiF₆ treatments were studied by ²⁹Si,²⁷Al MAS NMR, ²⁷Al-¹H cross polarization MAS NMR and 2D nutation NMR. ²⁹Si MAS NMR shows that the Si, Al framework distributions of ultrastable Y zeolites and Y zeolites dealuminated by (NH₄)₂SiF₆ isomorphous substitution are different, even if they have almost the same framework Si/Al ratio. The reason is due to their different dealumination experience. Y zeolites with high Si/Al framework ratio can be obtained by a coorperation of isomorphous substitution and hydrothermal dealumination. Based on ²⁷Al MAS NMR, ²⁷Al-¹H CP/MAS NMR and 2D nutation ²⁷Al NMR observations, four aluminuous species, i.e. framework tetrahedral Al(AlFT),distortcd framework tetrahedral Al(Al^FDT), penta-coordinated non framework Al(AlNFP) and non framework octahedral Al(Al^NFO), in dealununated Y zeolites are supposed Si/Al frame ratios of dealuminated Y zeolites determined by ²⁷Al MAS NMR simulations are in good agreement with whose results of ²⁹Si MAS NMR

Key words: Zeolite, NMR, 2D nutation, Cross polarization, Al coordination