Nature and location of organic species in As-synthesized ferrierite probed by near-infrared Fourier transform Raman spectroscopy and multinuclear NMR

Siliceous and aluminosilicate ferrierite samples (Si/Al ratios = 18, 50, and 80) have been prepared in the presence of propylamine and pyridine and characterized by near-infrared Fourier transform Raman spectroscopy and Si-29, Al-27, and C-13 NMR. Incorporation of aluminum into the framework has two main consequences. Firstly, propylammonium cations partially charge compensate for the aluminum substitution in the framework. As a consequence of this, as the Si/Al ratio is lowered and the number of propylammonium cations required for charge neutrality increases, the concentration of pyridine in the main channel decreases because the two molecules compete for space in the zeolite channels. Secondly, two types of pyridine are observed from the splitting of the vl breathing mode. This is proposed to arise from pyridine physically adsorbed in the 8-ring side channel and the main 10-ring channel (nu(1)=991 cm(-1)) and pyridine located in the main channels interacting via hydrogen bonding with propylammonium cations (nu(1) near 1000 cm(-1)). In agreement with this postulate, the proportion of hydrogen-bonded pyridine molecules increases as the aluminum concentration and the number of charge-compensating propylammonium cations increases.