CHARGE SENSITIVITY ANALYSIS OF THE INTERACTION OF PYRROLE WITH BASIC FAU-TYPE ZEOLITES USING THE ELECTRONEGATIVITY EQUALIZATION METHOD

The interaction of pyrrole with alkali cation exchanged FAU-type zeoli tes is studied using a combination of the electronegativity equalizati on method (EEM) and the Monte Carlo technique. Pyrrole adsorbs at S-II cations, the NH-group pointing to the most basic oxygen O4. The NH-bo nd polarization and the pyrrole framework interaction energy reflect t he fundamental and well established trends of the intrinsic framework basicity: an increasing basicity with an increasing Al-content and, at a given Si:Al-ratio, an increasing basicity with increasing size of t he exchangeable cations. In contrast to a recent interpretation of the IR-spectra of the NH-stretching vibration of pyrrole (D. Murphy, P. M assiani, R. Franck, D. Barthomeuf, J. Phys. Chem., 100 (1996) 6731; D. Murphy, P. Massiani, R. Franck, D. Barthomeuf, Stud. Surf. Sci. Catal ., 105 (1997) 639), our Monte Carlo calculations show that there is on ly one adsorption site for pyrrole in the FAU-structure at low loading s. An alternative explanation for the observed heterogeneity of the IR -spectra of pyrrole is discussed on the basis of our calculations: the orientation of the: pyrrole molecule with respect to the six-ring dep ends on the Si:Al-ratio of the tetrahedra forming the six-rings. (C) 1 997 Elsevier Science B.V.