THE CRYSTAL STRUCTURE OF A LOW-SILICA DEHYDRATED NAX ZEOLITE

Abstract

The crystal structure of a low-silica and fully dehydrated NaX zeolite, the synthetic analogue of natural faujasite, with approximate chemical composition Na93Al93Si99O384 (Si/Al = 1.06) as determined by microprobe and NMR analysis, has been determined using single-crystal Cu(Kα) X-ray diffraction (a = 25.104(3) A). X-ray data reduction clearly shows that this crystal has Fd3 symmetry, as confirmed by the large difference between the Si-O and Al-O distances which indicates a substantial ordering of the Si and Al atoms in tetrahedral sites. All Na+ cations have been located, with refined occupancies of 97% (site I'), 93% (site II), 16% (site III'a) and 18% (site III'b); these sites are also those found in a fully dehydrated T1X zeolite.