Characterization of Copper-Modified ZSM-5 with Sorbed Pyridine Using Nuclear Magnetic Resonance Spectroscopy

Solid-state ¹H, ¹³C and ²⁹Si MAS NMR experiments were used to detect sorbed pyridine in hydrated copper-exchanged forms of synthetic zeolite ZSM-5, which is widely used in industry and green chemistry as well. The paper follows on from the previous study of sorption of organic pollutants by copper-modified forms of ZSM-5. Multinuclear MAS NMR experiments performed on hydrated and dehydrated copper-exchanged ZSM-5 samples with sorbed pyridine indicate that dissociation of water molecules in the vicinity of copper cations results in formation of new acid sites in the zeolite channels. Through their reaction with sorbed pyridine molecules, pyridinium ions are formed. ¹³C MAS NMR spectra also confirmed the presence of pyridine molecules not involved in forming pyridinium ions in the copper-modified ZSM-5 samples. From the changes in ²⁹Si NMR spectra, some slight changes in the structure of original copper-modified ZSM-5 after pyridine sorption can be also deduced.