For four REUSY zeolites, the framework (Si/Al)F ratio were measured by 29Si MAS, NMR, XRD, techniques, and obtained good results. The change of distribution of Si and Al of framework during dealumination and the mechanism of stabilizing the framework aluminum by rare-earth ions were also investigated by 29Si MAS-NMR. When the range of (Si/Al) is from 2.6 to 4.0, the aluminums in Si(2Al) and Si(3Al) are mainly removed, if the (Si/Al)F is from 4.0 to 6.0, the aluminums removed are mainly that of Si (1Al) and a little of Si (2Al). Comparing the relative populations of Si(OSi)4-n(0Al)n in framework structure of REUSY zeolites with that of in framework of HY zeolite, the distribution of framework Si and Al for both Y zeolites are very different, particularly for Si (3Al) in REUSY zeolites, its relative population are changed slightly at the whole range of dealumination.

Key words: ZEOLITE, X-RAY DIFFRACTION ANALYSIS, NMR SPECTROMETRY, SILICONE ISOTOPES, RARE EARTH, ALUMINIUM ISOTOPES