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

2009년 8월 14일 15시 18분 04초
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목 <발표Ⅱ>
저자 및
서성만, 김경화1, 최식영, 김영훈2, 임우택
안동대학교 응용화학과, Korea
1포항가속기연구소 빔라인부 엑스선운영2팀, Korea
2안동대학교 환경공학과, Korea
The single-crystal structure of |Ca35.5|[Si121Al71O384]-FAU, Ca35.5Si121Al71O384 per unit cell, a = 24.9020(10) Å, dehydrated at 673 K and 2 × 10-6 Torr, has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3-m at 294 K. The large single crystals of zeolite Y (Si/Al = 1.70) were synthesized up to diameters of 200 µm and Ca2+-exchanged zeolite Y were prepared by ion exchange in a batch method of 0.05 M aqueous Ca(NO3)2 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 Fo > 4σ(Fo)) R1 = 0.038 (based on F) and R2 = 0.172 (based on F2). About 35.5 Ca2+ 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 Ca2+ ions (Ca-O = 2.4194(24) Å and O-Ca-O = 87.00(8)o) are found per unit cell. One Ca2+ ion per unit cell is located at site II' in the sodalite cavity and extends 0.50 Å into the sodalite cavity from its 3-oxygen plane (Ca-O = 2.324(13) Å and O-Ca-O = 115.5(10)o). The remaining twenty Ca2+ ions are found at two nonequivalent sites II (in the supercages) with occupancies of 10 and 10 ions, respectively. Each of these Ca2+ ions coordinates to three framework oxygens, either at 2.283(3) or 2.333(5) Å, respectively, and extends either 0.24 or 0.54 Å, 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. Ca2+ appears to fit the octahedral site I best. No cations are found at sites III or III', which are clearly less favorable for Ca2+ ions in dehydrated zeolite Y.