A study of ETS-4 molecular sieves and of their adsorption of water and ammonia

Structural and water and ammonia adsorption properties of ETS-4 were studied by means of XRD, FT-IR, Raman, UV-vis and temperature programmed desorption (TPD) techniques. XRD analysis showed that the sample was pure and highly crystalline. Skeletal IR and Raman vibrational spectra are interpreted in agreement with the structure containing chains of corner sharing TiO6 octahedral zig-zag chains, tetrahedral silicate units bridging two TiO6 octahedra (so giving rise to Ti-O-Si-O-Ti structures) and isolated Ti ions with an octahedral coordination involving two short bonds with oxide ions also bonded to extraframework Na+ cations. Electronic spectra agree with the predominance of condensed TiO6 octahedra and the absence of TiO2 impurities. Two forms of molecular adsorbed water were observed from FT-IR and TPD measurements. ETS-4 adsorbed about 2 mole of water per mole of material by coordination to Na+ ions. Ammonia was adsorbed in molecular form both by hydrated and anhydrous ETS-4 through hydrogen bonding with H2O molecules or coordination to Na+ ions, respectively. 0.24 mole of NH3 per mole ETS-4 was adsorbed in both cases.