Abstract: The microstructure of four kinds of dealuminated Yzeolites (USY,SSY,US-SSY,DAY) were studied by ²⁹Si,²⁷AlMAS NMR,XRD and IR.The cause of the formation of non-framework Si,Al and Si-OH nests and of difference of their amount were discussed according to the methods of dealumination.It is shown that the different methods of dealumination brings about the removing of different Si(nAl) units on the framework of zeolites.The results of XRD indicate that the relative crystallinity of 97% can be obtained when SSY was further treated by the high temperature steam to US-SSY.After dealumination,if the remains of micropore is more and the secondary mesopore is less,the relative crystallinity of sample is higher.Finally,it was also found that the framework aluminium of unit cell (N_Al)_F measured by ²⁹Si MAS NMR is less than that measured by XRD and IR,and the reason was also discussed.

Key words: Dealuminated Y zeolites, Framework Si and Al distribution, Non-framework component, Relative crystallinity