Rietveld refinement and solid state NMR study of Nd-, Sm-, Gd-, and Dy-containing Y zeolites

Na-Y zeolites ion exchanged with rare earth cations (Nd3+, Sm3+, Gd3+, Dy3+) were studied by X-ray diffraction in order to locate the rare earth cations in the zeolite framework and the resulting changes in its structural properties. The results indicate that the rare earth cations dealuminate the framework differently. This is observed as a decrease in the values of the unit cell parameters, ao. This systematic decrease in ao is related to the rare earth ionic radius and its coordination to the oxygen framework. The correlation between the Si/Al ratio obtained from the Fichtner-Schmittler equation and the ionic radius of the rare earth cations reveals that smaller ionic radii gives higher dealumination and smaller ao. This is related to hydrolysis constant cation. Samples treated with Dy3+ cations show a higher level of dealumination than those treated with the other cations (Sm3+, Gd3+, Nd3+). In order to characterize the dealumination process Si-29 and Al-27 magic angle spinning NMR measurements were attempted. Except for the Sm3+ treated sample, the Nd3+, Gd3+, Dy3+ samples could not have their tetrahedral and octahedral aluminum signal detected due to the high concentration of the paramagnetic ions with large effective number of Bohr magnetons. (C) 2000 Elsevier Science B.V. All rights reserved.