Acta Crystallographica Section B

Structural Science

Volume 56, Part 5 (October 2000)

research papers

Acta Cryst. (2000). B56, 766-772 [ doi:10.1107/S0108768100006893 ]

Refinement of framework disorder in dehydrated CaA zeolite from single-crystal synchrotron data

F. Porcher, M. Souhassou, H. Graafsma, A. Puig-Molina, Y. Dusausoy and C. Lecomte

Abstract: An accurate knowledge of zeolite structure is required for understanding their selective sorption capacities and their catalytic properties. In particular, the positions of the exchangeable cations and their interactions with the framework are essential. The present study deals with the accurate crystal structure determination of a fully exchanged and fully dehydrated CaA zeolite (Ca₄₈Al₉₆Si₉₆O₃₈₄, Fm $\bar 3$ c, a = 24.47 Å) using single-crystal high-resolution synchrotron X-ray diffraction [(sin [theta] / [lambda] )_max = 1.4 Å^-1]. It is shown that cation exchange severely distorts the skeleton, especially around the O2 atom. The high-resolution synchrotron data reveal that this latter O atom is disordered and lies out of the mirror plane it occupies in other A-type zeolites. This feature is related to that observed for Ca²⁺ cations.

Keywords: Dehydrated CaA zeolite; Disorder; Cation distribution.