The Effects of Ammonium Hexafluorosilicate Post-Treatment on the Acidity of H-ZSM-5 Zeolite Studied by Solid-State NMR Spectroscopy

Abstract

In this study, solid-state nuclear magnetic resonance (NMR) spectroscopy was used to probe the changes of acidity of H-ZSM-5 zeolite caused by ammonium hexafluorosilicate (AHFS) washing-related changes of aluminium species. It was observed that the four-coordinate framework aluminum species with Brønsted acidity were partially reduced, while the tri-coordinated framework aluminum with Lewis acidity was slightly decreased after the AHFS treatment. However, AHFS washing was also found to induce mild dealumination and a significant reduction of aluminum species with Lewis acidity containing Al-OH group on zeolites, thus resulting in a remarkable change in the overall acidity of the zeolites.

Keywords

• ammonium hexafluorosilicate (ahfs)
• trimethylphosphine oxide (tmpo) probe molecules
• acidity
• solid-state nuclear magnetic resonance