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 studie d by means of XRD, FT-IR, Raman, UV-vis and temperature programmed desorpti on (TPD) techniques. XRD analysis showed that the sample was pure and highl y crystalline. Skeletal IR and Raman vibrational spectra are interpreted in agreement with the structure containing chains of corner sharing TiO6 octa hedral zig-zag chains, tetrahedral silicate units bridging two TiO6 octahed ra (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 b onded to extraframework Na+ cations. Electronic spectra agree with the pred ominance of condensed TiO6 octahedra and the absence of TiO2 impurities. Tw o forms of molecular adsorbed water were observed from FT-IR and TPD measur ements. ETS-4 adsorbed about 2 mole of water per mole of material by coordi nation to Na+ ions. Ammonia was adsorbed in molecular form both by hydrated and anhydrous ETS-4 through hydrogen bonding with H2O molecules or coordin ation to Na+ ions, respectively. 0.24 mole of NH3 per mole ETS-4 was adsorb ed in both cases.