Crystal Structure of Ca 2+ -exchanged Zeolite Y Bull. Korean Chem. Soc. 2009, Vol. 30, No. 8 1703 Articles Synthesis and Single-crystal Structure of Fully Dehydrated Fully Ca 2+ -exchanged Zeolite Y (FAU), |Ca 35.5 |[Si 121 Al 71 O 384 ]-FAU Sung Man Seo, Sik Young Choi, Jeong Min Suh, † Ki Jin Jung, ‡ Nam Ho Heo, ‡ and Woo Taik Lim * Department of Applied Chemistry, Andong National University, Andong 760-749, Korea. * E-mail: wtlim@andong.ac.kr † Department of Regional Environmental System Engineering, Pusan National University, Miryang 627-702, Korea ‡ Department of Applied Chemistry, Kyungpook National University, Daegu 702-701, Korea Received May 21, 2009, Accepted June 8, 2009 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 Fd 3 m at 294 K. The large single crystals of zeolite Y (Si/Al = 1.70) were synthesized up to diameters of 200 μm and Ca 2+ -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 F 2 ). About 35.5 Ca 2+ 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 Ca 2+ ions (Ca-O = 2.4194(24) Å and O-Ca-O = 87.00(8) and 93.00(8) o ) are found per unit cell. One Ca 2+ 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 Ca 2+ ions are found at two nonequivalent sites II (in the supercages) with occupancies of 10 and 10 ions, respectively. Each of these Ca 2+ 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. Ca 2+ appears to fit the octahedral site I best. No cations are found at sites III or III’, which are clearly less favorable for Ca 2+ ions in dehydrated zeolite Y. Key Words: Zeolite Y, Ion exchange, Dehydrated, Structure, Calcium Introduction Synthetic faujasite (FAU) with 1.5 ≤ Si / Al ≤ 3.0 is called zeolite Y. It was first synthesized in its sodium form in 1964 by Union Carbide. 1 Zeolite Y has a wide range of industrial applications due primarily to its excellent structural stability and its large and accessible pore volume. The adsorptive properties of zeolites also depend heavily on the size (charge density) of the cations in the lattice and on their distribution among sites. 1 One of the most importantly applied and an informative technique for characterization of cations in zeolite framework is single-crystal X-ray diffraction. So numerous investigations of the positions of the exchangeable cations in zeolite X (Si/Al = 1.09) have been conducted by single-crystal X-ray diffraction technique. 2-4 And the structures of sorption complexes that show how various guest molecules are held on the inner surfaces of zeolites are being obtained crystallographically. 5-11 Smolin et al. 2 determined the crystal structures of Ca-X at various dehydration temperatures. In the partially dehydrated form, Ca 2+ ions were located in sites I, I’, II, and III. They confirmed that the occupancy at site III decreased with increasing dehydration temperature. Using single-crystal X-ray diffraction technique in the cubic space group Fd 3 at 24(1) o C, Seff et al. 3,4 determined the structure of fully dehydrated, fully Ca 2+ -exchanged zeolite X (Si/Al = 1.09) to learn the cation positions and the site selectivity. They also studied the crystal structures of ethylene, 5 acetylene, 5 hydrogen sulfide, 6 benzene, 7 ammonia, 8 cyclopropane, 9 mesitylene, 10 and methylamine 11 complexes of fully dehydrated fully Ca 2+ - exchanged zeolite X (Si/Al = 1.09) to observe the geometry and chemistry of sorption in zeolites (i.e., to determine shifts in cation and framework atomic positions, to observe cation- sorbate interactions, and to detect resultant changes in sorbed molecule geometry). They noted that there were some unusual two kinds of site-II Ca 2+ ions in benzene, 7 mesitylene, 10 and methylamine 11 sorption complexes of Ca 2+ -exchanged zeolite X. They described that the coordination of the sorption com- plexes such as benzene, mesitylene, and methylamine had caused Ca 2+ ions to move along its 3-fold axis more deeply into the supercage from the three O(2) plane, compared to its position in dehydrated Ca46-X. 2-4 Zeolites X and Y are distinct zeolite species with charac- teristic differences, even though they have topologically similar aluminosilicate framework structure. Due to the high thermal stability and the selectivity, zeolite Y is very important catalyst or catalyst supports in various industrial reactions such as cracking, isomerization, and hydrocracking.