Effect of Alcaline Cations in Zeolites on their Dielectric Properties Benoît Legras, Isabelle Polaert, Lionel Estel Laboratoire de Sécurité des Procédés Chimiques (LSPC) INSA de Rouen Saint Etienne du Rouvray, France Michel Thomas Direction Catalyse et Séparation IFP Energies Nouvelles - Lyon Solaize, France Received: August 31, 2011 Accepted: November 25, 2011 Journal of Microwave Power and Electromagnetic Energy, 46 (1), 2012, pp. 5-11. A Publication of the International Microwave Power Institute ABSTRACT The effect on dielectric properties of alkaline cations Li + , Na + and K + incorporated in a zeolite Faujasite structure X or Y, has been investigated. Two major phenomena have been proved to occur: ionic conductivity and rotational polarization of the water molecules adsorbed. The polarizability of the cation which is directly linked to its radius, affects ionic conductivity as well as rotational polarization. Li cations are more strongly linked to the framework than K + and Na + and induce a lower ionic conductivity. K + is weakly fixed and induces a ionic conductivity even at low solvation level. At low water content, the cation nature and number mainly control the free rotation of the water molecules and affect the relaxation frequency. Close to saturation, the water molecules are mainly linked together by H bonds: the cation nature and number do not really affect the global dielectric properties anymore. KEYWORDS: Zeolite, alkaline cations, dielectric permittivity, ionic conductivity, rotational polarization. INTRODUCTION Zeolites are microporous crystalline aluminosilicates, composed of SiO 4 and AlO 4 tetrahedra with oxygen atoms bonding neighboring tetrahedra. Zeolites types differ by the way Si, O, and Al atoms are interconnected creating different and well-defined crystalline structures. Faujasite (FAU) is a widely used zeolite in industrial applications as adsorbents, catalysts, and ion exchange supports [Auerbach, 2003]. Their unique layout confers specific pore opening size and void in framework. Selectivity and adsorption capacities strongly depend on specific interactions (electrostatic) as well as on steric interactions. Upon incorporation of Al into a silica framework, the +3 charge on the Al makes the framework negatively charged, and requires the presence of extra framework cations within the structure to keep the overall framework neutral [Yang, 2003]. The general chemical formula of zeolites unit cell (u.c.), with eight super lattices superposed, is M x/n (AlO 2 ) x (SiO 2 ) 192-x 3mH 2 O, where m is the number of water molecules and n is the valence of the exchangeable cation M, as indicated in the Atlas of Zeolite Framework Type [Baerlocher et al., 2007]. In adsorbent applications, extra framework cations are usually of the alkali and alkaline earth metal species (Na + , K + , Li + , Journal of Microwave Power and Electromagnetic Energy, 46 (1), 2012 International Microwave Power Institute 5