Crystal structure of novel layered silicate PLS-3 as a FER-zeolite precursor determined by X-ray powder diffraction

Research Center for Compact Chemical Process, National Institute of Advanced Industrial Science and Technology
â—‹Ikeda Takuji Syunsuke Kayamori Takaaki Hanaoka Fujio Mizukami

Recently, a new zeolite synthetic method by the topotactic conversion using zeolitic layered silicates is interested and produced novel framework zeolites, e.g., Nu-6(2)(NSI), RUB-41(RRO), RUB-24(RWR) and CDS-1(CDO). On the other hand, layered silicate PREFER, which have been known as the first example by the above method, can be converted to FER zeolite. In this work, we report that a novel layered silicate PLS-3, which has a similar framework topology to PREFER[1], was synthesized from H-formed layered silicate kanemite by steam assisted solid-state reaction. Crystal structure of PLS-3 was determined by the ab-initio analysis using X-ray powder diffraction data. PLS-3 was successfully converted to seliceous zeolite CDS-3 with FER-topology by carefully calcination.
X-ray powder diffraction data were collected on a Bruker D8-ADVANCE Vario-1 using monochromatic Cu Ka1 radiation and modified Debye-Scherrer geometry. Lattice constants and space group were a = 13.9937(10) Å, b = 7.4170(6) Å, c = 22.337(2) Å and Pnnm (No.58). The partial atomic coordinates obtained by the direct method analysis were introduced as a starting model for a Rietveld refinement using the RIETAN-2000 program system.
The framework structure of PLS-3 is a very similar to that of PREFER, but the lattice constant of c-axis was relatively shorten ca. 3 Å. Chemical composition was estimated to be Si36O68(OH)8 2.4(TEAOH) 8(H2O) calculated from refined occupancy factors. Both TEAOH and water molecules were intercalated into an interlayer.
[1]. L. Schreyeck, P. Caullet, J. C. Mougenel, J. L. Guth, B. Marler, Stud. Surf. Sci. Catal., 105, 1949 (1997).