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 studies part 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 different surface vibrational techniques, X-ray diffraction and temperature-programmed desorption accompanied by theoretical studies. The results obtained 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 interaction depends on both the Lewis acidic properties of the extraframework cations and the Lewis basic properties of the lattice oxygen atoms. It was found that pyrrole is adsorbed due to these two different kinds of interactions which occur parallel and influence each other: pyrrole is bound via the NH group to the lattice oxygen atoms by hydrogen bonding and, simultaneously, via the aromatic system to the cations, yielding strong host-guest interactions. The experimentally obtained results were verified by quantum mechanical calculations and force field simulations.