Ab initio investigation of the adsorption of benzene in mordenite

The adsorption of benzene in pure-silica and acid mordenite has been invest igated using density functional theory, both in the local density approxima tion and including generalized-gradient corrections. Benzene acts as a test molecule for studying the interaction between an aromatic hydrocarbon and a zeolite. Different adsorption modes have been studied for several acid si tes. All configurations have been optimized by minimizing the total energy with respect to all lattice parameters and to the atomic coordinates. The s trength of the adsorption is directly correlated to the local structural di stortion of the zeolitic framework, especially of the acid site. Only if st rong adsorption occurs, the molecule itself is slightly deformed. Furthermo re, an analysis of the differential charges has been performed, indicating substantial polarization effects for the acid site as well as for the molec ule. Finally, the red-shift of the OH-stretching frequencies due to the ads orption has been calculated. (C) 2001 American Institute of Physics.