Adsorption of pyrrole derivatives in alkali metal cation-exchanged faujasites: comparative studies by surface vibrational techniques, X-ray diffraction and temperature-programmed desorption augmented with theoretical studiespart I. Pyrrole as probe molecule

The nature and strength of interaction of pyrrole adsorbed in alkali metal cation-exchanged faujasites have been investigated by the combined use of d ifferent surface vibrational techniques, X-ray diffraction and temperature- programmed desorption accompanied by theoretical studies. The results obtai ned depend on the kind of cation, the degree of ion exchange and the Si/Al ratio of the zeolites, indicating that the effective strength of interactio n depends on both the Lewis acidic properties of the extraframework cations and the Lewis basic properties of the lattice oxygen atoms. It was found t hat pyrrole is adsorbed due to these two different kinds of interactions wh ich occur parallel and influence each other: pyrrole is bound via the NH gr oup to the lattice oxygen atoms by hydrogen bonding and, simultaneously, vi a the aromatic system to the cations, yielding strong host-guest interactio ns. The experimentally obtained results were verified by quantum mechanical calculations and force field simulations.