Synthesis and Single-crystal Structure of Fully Dehydrated Fully Ca2+exchanged Zeolite Y (FAU), |Ca35.5|[Si121Al71O384]-FAU

Abstract

Listen

Translate article

The single-crystal structure of |<TEX>$Ca_{35.5}$</TEX>|[<TEX>$Si_{121}Al_{71}O_{384}$</TEX>]-FAU, <TEX>$Ca_{35.5}Si_{121}Al_{71}O_{384}$</TEX> per unit cell, a = 24.9020(10) <TEX>$\AA$</TEX>, dehydrated at 673 K and 2 <TEX>${\times}\;10^{-6}$</TEX>Torr, has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd<TEX>$\overline{3}$</TEX>m at 294 K. The large single crystals of zeolite Y (Si/Al = 1.70) were synthesized up to diameters of <TEX>${\mu}m\;and\;Ca^{2+}$</TEX>-exchanged zeolite Y were prepared by ion exchange in a batch method of 0.05 M aqueous Ca(<TEX>$NO_3)_2$</TEX> for 4 hrs at 294 K. The structure was refined using all intensities to the final error indices (using only the 971 reflections for which <TEX>$F_o\;>\;4{\sigma}(F_o))\;R_1$</TEX> = 0.038 (based on F) and <TEX>$R_2$</TEX> = 0.172 (based on <TEX>$F^2$</TEX>). About 35.5 <TEX>$Ca^{2+}$</TEX> ions per unit cell are found at an unusually large number of crystallographically distinct positions, four. Nearly filling site I (at the centers of the double 6-rings), 14.5 octahedrally coordinated <TEX>$Ca^{2+}$</TEX> ions (Ca-O = 2.4194(24) <TEX>$\AA$</TEX> and O-Ca-O = 87.00(8) and 93.00(<TEX>$8^o$</TEX>) are found per unit cell. One <TEX>$Ca^{2+}$</TEX> ion per unit cell is located at site II’ in the sodalite cavity and extends 0.50 <TEX>$\AA$</TEX> into the sodalite cavity from its 3-oxygen plane (Ca-O = 2.324(13) <TEX>$\AA$</TEX> and O-Ca-O = 115.5(10)o). The remaining twenty <TEX>$Ca^{2+}$</TEX> ions are found at two nonequivalent sites II (in the supercages) with occupancies of 10 and 10 ions, respectively. Each of these <TEX>$Ca^{2+}$</TEX> ions coordinates to three framework oxygens, either at 2.283(3) or 2.333(5) <TEX>$\AA$</TEX>, respectively, and extends either 0.24 or 0.54 <TEX>$\AA$</TEX>, respectively, into the supercage from the three oxygens to which it is bound. In this crystal, site I is the most populated; sites II’ and II are only sparsely occupied.<TEX>$Ca^{2+}$</TEX>+ appears to fit the octahedral site I best. No cations are found at sites III or III’, which are clearly less favorable for <TEX>$Ca^{2+}$</TEX> ions in dehydrated zeolite Y.