Characterization of the Structural and Gas Adsorption Properties of ETS-10 Molecular Sieve

Abstract

A sample of ETS-10 was prepared and characterized by spectroscopic (Raman, UV–vis, FT-IR) and TPD techniques. An interpretation of the vibrational spectra was proposed. Absorption in the UV–vis range was typical of charge-transfer transitions involving octahedral Ti. No surface –OH groups were detected on the dehydrated sample. FT-IR measurements showed that water was adsorbed in two different molecular modes while ammonia was adsorbed coordinatively and mostly desorbed below 600 K. These results were confirmed by TPD studies that showed hydrogen-bonded water and water coordinated to Na⁺ and K⁺ cations located in the main channels of ETS-10. Ammonia TPD measurements on the hydrated material provided evidence for two forms of adsorbed NH₃, both bonded to water molecules. On the anhydrous material, NH₃ was probably coordinated only to the more loosely bonded Na⁺ and K⁺ ions in the main channels of ETS-10. The amount of adsorbed NH₃ was markedly reduced after heat treatment that led to a partial loss of crystallinity.