The crystal structure of a low-silica zeolite with the faujasite structure, Ca LSX (Si/Al = 1), was determined from powder X-ray and neutron diffraction data. The crystal structure was refined by the Rietveld least-squares method in the cubic space group Fd3 [a = 25.1080A]. The final Rwp-factor and the X2 for the combined refinement were 10.1% and 1.81, respectively. The calcium ions were located preferentially in site I and site II, and distortions of the zeolite framework were ascribed to the interaction between these calcium ions and framework oxygen atoms. 2H NMR studies of C6D6 adsorbed in Ca LSX (1 molecule per super-cage) confirmed that deuterated benzene was bound strongly at site II and interacted facially with calcium so that rapid rotation about the six-fold axis of the sorbate was observed at 260 to 330K. The activation energy for this rotation was only 4.9kJ/mol. By contrast, deuterated benzene in Na LSX exhibited rapid isotropic motion down to 260K; the diffusion coefficient (298K) and activation energy for this system were calculated to be 1.9 x 10-11m2/s and 10.6kJ/mol, respectively, from 2H NMR spin-lattice relaxation measurements.

Combined Neutron and X-Ray Powder Diffraction Study of Zeolite Ca LSX and a 2H NMR Study of its Complex with Benzene. G.Vitale, L.M.Bull, R.E.Morris, A.K.Cheetham, B.H.Toby, C.G.Coe, J.E.MacDougall: Journal of physical chemistry, 1995, 99[43], 16087-92