PYRIDINE ADSORBED ON NA-FAUJASITE .2. AN FT-RAMAN AND DRIFT SPECTROSCOPIC STUDY

To unravel the nature of the interactions of pyridine with nonacidic Na-faujasites, FT-Raman and DRIFT spectroscopies have been applied. The complementary character of these techniques provides further evidence for the location of pyridine adsorbed in the supercages. It appears that the preferential adsorption sites for pyridine change upon varying the loading of the zeolite. The occupied site of pyridine at low coverage (less than two molecules per supercage) is either in the 12-ring window or through an interaction with both the lone pair and the pi-system of the aromatic. At medium coverage pyridine is adsorbed with its lone pair bonded to one of the four charge-balancing cations present in the supercage, possibly in a tetrahedral conformation. Adsorption of more pyridine molecules results in an enhanced perturbation of the ''breathing'' vibrations, shifting them to higher frequency.