Localization of benzene in sodium-Y-zeolite by powder neutron diffraction

Abstract

The structure of sodium-Y zeolite, Na/sub 56/Si/sub 136/O/sub 384/Al/sub 56/, containing chemisorbed deuterated benzene has been studied for two different benzene coverages at 4 K and room temperature by powder neutron diffraction. The space group is Fd3m. The sodium ions are distributed over three sites. At 4 K, the benzene molecules are localized on two distinct sites within the cavities of the zeolite. Benzene(1) is in the supercage with the center of the molecule on the cube diagonal at 32e (x,x,x). Benzene(2) is centered at 16d (1/2, 1/2, 1/2) in the window between adjacent supercages. At 4 K the average separation between adjacent benzene(1) sites decreases on increasing the benzene coverage, and Na(1) appears to migrate toward the center of the supercage. At room temperature, the benzene molecules are largely delocalized but are still confined to the supercages in the region of their positions at 4 K. 30 references, 7 figures, 5 tables.