Zeolites and Related Materials: Trends, Targets and Challenges 709 Proceedings of 4 th International FEZA Conference A. Gedeon, P. Massiani and F. Babboneau (Editors) © 2008 Elsevier B.V. All rights reserved. Cu + , Ag + and Na + Cationic Sites in ZSM-5 Interacting with Benzene: DFT Modeling Joanna Zalucka, a Paweł Kozyra, a Mariusz Mitoraj, a Ewa Broclawik, b Jerzy Datka a a Faculty of Chemistry, Jagiellonian University, ul. Ingardena 3, 30-060 Kraków, Poland b Instytute of Catalysis, Polish Academy of Sciences, Kraków, Poland Abstract The present work is focused on the effect of zeolite framework on the activation of benzene by Cu + , Ag + and Na + ions. DFT calculations have been carried out to obtain geometric structure and electronic properties of both the cluster models of the cationic sites and bare cations interacting with benzene. NOCV (natural orbitals for chemical valence) has been used to elucidate components of differential electron density: donation and back donation. Zeolite framework is shown to intensify the benzene activation for several reasons, e.g. imposing specific adsorption geometry or modifying cation properties. Keywords: benzene, ZSM-5, DFT, TMI sites 1. Introduction High activity of copper sites towards NO or alkenes, promoted by its ability to donate electrons to π antibonding orbitals of the adsorbate is well known [1-5]. Although silver cation is similar in many respects to copper, it activates considered molecules to smaller extent. Thus in this study cations with zeolite playing the role of a ligand as well as bare cations have been compared to capture zeolite function and to discriminate the cations. 2. Methodology Density functional theory (DFT) calculations were carried out by ADF software [6-10]. We have used gradient BP potential with Becke exchange [11] and Perdew correlation [12]. Calculations were carried out in TZP basis set for d-cations, and DZP for other atoms. Inner core orbitals were frozen. This choice was determined by the compromise between computational efficiency and desired accuracy. Population analysis was calculated according to Hirshfeld method [13]. For interpretation of the bonding mechanism the use was made of natural orbitals for chemical valence (NOCV) [14] and Ziegler-Rauk bond energy decomposition analysis [15,16] for the description of the bonding between the cations and benzene ring. In the Ziegler-Rauk bond decomposition scheme the total bonding energy ∆E bon between interacting fragments is divided into three components. The first component ∆E dist , referred to as the distortion term, represents the amount of energy required to promote the separated fragments from their equilibrium geometry to the structure they will take up in the combined molecule. The second term ∆E steric corresponds to the steric interaction between interacting fragments. Finally, the last term ∆E orb represents the interactions between the occupied molecular orbitals on one fragment with the