Preparation and structural study of fully dehydrated, highly Mg 2+ -exchanged zeolite Y (FAU, Si/Al 5 1.56) from undried methanol solution Hu Sik Kim • Sang June Choi • Woo Taik Lim Ó Springer Science+Business Media New York 2014 Abstract Single-crystal of fully dehydrated, Mg 2? -exchanged zeolite Y, |Mg 34.5 Na 6 |[Si 117 Al 75 O 384 ]-FAU (Si/ Al = 1.56), was successfully prepared from undried methanol solution (water concentration 0.02 M). A crystal of Na-Y was treated with 0.05 M MgCl 2 Á6H 2 O in the solvent at 333 K, followed by vacuum dehydration at 723 K and 1 9 10 -6 Torr for 2 days. Its structure was determined by single-crystal synchrotron X-ray diffraction techniques, in the cubic space group Fd 3m at 100 K. It was refined to the final error indices R 1 /wR 2 = 0.0587/0.2210 with 1,294 reflections for which F o [ 4r(F o ). In the structure of |Mg 34.5 Na 6 |[Si 117 Al 75 O 384 ]-FAU, 34.5 Mg 2? ions per unit cell are found at four different crystallo- graphic sites: 15 per unit cell are located at site I at the center of the hexagonal prism [Mg–O = 2.216(2) A ˚ ], two are at site I’ in the sodalite cavity near the hexagonal prism [Mg–O = 2.20(3) A ˚ ], only one is located at site II’ in the sodalite cavity [Mg–O = 2.197(23) A ˚ ], and the remaining 16.5 are at site II near single 6-oxygen rings in the super- cage [Mg–O = 2.103(3) A ˚ ]. The residual 6 Na ? ions per unit cell are found at site II [Na–O = 2.218(7) A ˚ ]. No water molecules are found in this structure. Keywords Magnesium Á Zeolite Y Á Methanol Á Ion exchange Á Dehydrated 1 Introduction Faujasite-type zeolites (FAU) have been widely studied and used in many practical applications as adsorbents and catalysts because of the excellent stability of framework structure, a large available pore volume, and surface area [1–5]. Generally, the adsorptive and catalytic properties of zeolites largely depend on the size, charge density, and distribution of cations in the zeolite [1–5]. Water molecules in hydrated zeolite are coordinated to exchangeable cations and/or hydrogen bonded to the zeo- lite framework [6]. Upon dehydration by evacuation and/or heating, zeolite provides a larger working space for sorp- tion and separation [6]. Additionally, the dehydration of zeolite affects the coordination geometry of the cations and their distribution within zeolite [6]. When charge-balancing cations are small in size with high charges such as Li ? and Mg 2? , it often causes critical damage to the framework structure during dehydration at high temperature because of the high hydration energy of cation especially in low silica zeolite [7, 8]. So the con- ditions for the dehydration process should be designed carefully depending on the nature of cations. According to the previous studies [8–10], the preparation of fully dehy- drated Mg 2? -exchanged zeolites without loss of crystalli- ninty is not easy due to the high hydration energy of Mg 2? ion. Mg 2? -exchanged zeolites are especially useful for the adsorption of some guest molecules because Mg 2? ion has a small ionic radius compared to most inorganic cations and high electric field gradient at its surface, which results Electronic supplementary material The online version of this article (doi:10.1007/s10934-014-9812-9) contains supplementary material, which is available to authorized users. H. S. Kim Á W. T. Lim (&) Department of Applied Chemistry, Andong National University, Andong 760-749, Korea e-mail: wtlim@andong.ac.kr S. J. Choi Department of Environmental Engineering, Kyungpook National University, Daegu 702-701, Korea 123 J Porous Mater DOI 10.1007/s10934-014-9812-9