Zeolites are natural or synthetic crystalline, microporous, aluminosilicate materials with well-defined structures and unique characteristics. Faujasite-type zeolites have been widely used in range of applications as ion exchangers, catalysts, and adsorbents due to their industrial importance. 1,2 Zeolite Y is more stable than zeolite X at high temperatures due to the higher Si/Al ratio. The framework structure of zeolite Y is characterized by the double 6-ring (D6R, hexagonal prism), the

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... te cavity (a cubooctahedron), and the supercage (see Figure 1 ). 3 Each unit cell has 8 supercages, 8 sodalite cavities, 16 D6Rs (32 S6Rs), 16 12-rings, and 32 single 6-rings (S6Rs). The exchangeable cations, which balance the negative charge of the zeolite Y framework, usually occupy some or all of the sites shown with Roman numerals in Figure 1 . The maximum occupancies at the cation sites I, I', II, II', and III in zeolite Y are 16, 32, 32, 32, and 48, respectively. Site III' in zeolite Y studied using space group Fd3m is a 192-fold position. Further description is available. 5 The positions of the extraframework cations in zeolites directly affect the physical and chemical properties of zeolite. The cation sites depend on the distribution of surrounding Al atoms and the distortion of the zeolite framework. 6 Position and fractional occupation of cationic sites change with the Si/Al ratio in zeolite. This work was done to investigate the distribution of Na + ions in fully dehydrated zeolite Y (Si/Al = 1.56) by singlecrystal synchrotron X-ray diffraction technique. Single-crystal synchrotron X-ray diffraction data were collected at 100(1) K using an Mar Research Gmbh mar345 image plate detector at Beamline 1W2B in Beijing Synchrotron Radiation Laboratory. The crystal evaluation and data collection were done using λ = 0.75000 Å radiation with a detector-to-crystal distance of 50 mm. Preliminary cell constants and an orientation matrix were determined from 72 sets of frames collected at scan intervals of 5 o with an exposure time of 1 second per frame. The basic scale file was prepared using the program HKL2000. 7 The reflections were successfully indexed by the automated indexing routine of the DENZO program. 7 The total reflections were harvested by collecting 72 sets of frames with 5 o scans and an exposure time of 1 second per frame. These highly redundant data sets were corrected for Lorentz and polarization effects, and (negligible) corrections for crystal decay were also applied. The cubic space group Fd3m was determined by the program XPREP. 8