Crystal structure of zeolite omega, the synthetic counterpart of the natural zeolite mazzite

Abstract

Rietveld refinement of the structure of synthetic zeolite omega |Na6.6TMA1.8(H2O)22.2 |[Al8.4Si27.6O72]-MAZ, using high-resolution X-ray powder diffraction data, by Rietveld method, provided the missing evidence that this material has the same framework type (MAZ) as the natural mazzite. Its real symmetry is P63/mmc, the same as the topological one, where a=18.215 Å, c=7.634 Å. TMA molecules are located inside the gmelinite cage, with two possible orientations, which are symmetric with respect to the plane passing through the center and orthogonal to the threefold axis of the cage. Sodium cations are distributed over two sites: one, at the center of the 8-ring channel, hosts most of Na and is 8-fold coordinated to six framework oxygens and two water molecules, while the other, located along the axis of the 12-ring channel, coordinates nine H2O. © 2003 Elsevier Inc. All rights reserved.