Browsing by Subject "Surface acidity"

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • Thumbnail Image
    ItemOpen Access
    Characterization of Zr6Nb2O17 synthesized by a peroxo route as a novel solid acid
    (Elsevier, 2008-03-20) Kantcheva, M.; Budunoğlu, H.; Samarskaya, O.
    The impregnation of hydrated zirconia at pH 0.5 with a solution of peroxoniobium(V) complex, [Nb2(O2)3] 4+, ensuring a ZrO2:Nb2O5 mole ratio of 6:1 followed by calcination at 873 K resulted in the formation of a Zr6Nb2O17 solid solution. The structure of this compound was confirmed by XRD. The surface acidity was investigated by in situ FT-IR spectroscopy using 2,6-dimethylpyridine (lutidine). Zr6Nb2O17 has a sufficient amount of Brønsted acid sites necessary for the stabilization of dispersed Pd(II) species. The potential of the Pd-promoted Zr6Nb2O17 as a catalyst for the reduction of NO with methane was evaluated by studying the reactivity of adsorbed NOx species toward the hydrocarbon. 2007 Elsevier B.V. All rights reserved.
  • Thumbnail Image
    ItemOpen Access
    Nature of the Ti-Ba interactions on the BaO/TiO2/Al 2O3 NOx storage system
    (2009) Andonova, S. M.; Şentürk, G. S.; Kayhan, E.; Ozensoy, E.
    A ternary oxide-based NO* storage material in the form of BaOZTiO2Zy-Al2O3 was synthesized and characterized. Thermally induced structural changes occurring on the surfaces of the TiO2Zy-Al2O3 and BaOZ TiO 2Zy-Al2O3 systems were studied in a comparative manner within 300-1273 K via X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, and BET surface area analysis. The surface acidity of the studied oxide systems was also investigated via pyridine adsorption monitored by in-situ Fourier transform infrared (FTIR) spectroscopy. BaO/TiO2γ-Al 2O3 ternary oxide was synthesized by incorporating different loadings of (8-20 wt %) BaO onto the TiO2/γ Al 2O3 support material, which was originally prepared using the sol-gel method. In the TiO2Zy-Al2O3 binary oxide support material, anatase phase exhibited a relatively high thermal stability at T < 1073 K. The presence of TiO2 domains on the surface of the alumina particles was found to alter the surface acidity of alumina by providing new medium-strength Lewis acid sites. SEMZEDX results indicate that in the BaO/TiO2γ-Al2O3 system, TiO2 domains present a significant affinity toward BaO and/or Ba(NO3) 2 resulting in a strong Ti-Ba interaction and the formation of overlapping domains on the surface. The presence of TiO2 also leads to a decrease in the decomposition temperature of the Ba(N03) 2 phase with respect to the Ti-free Ba(N03) 2ZyAl2O3 system. Such a destabilization is likely to occur due to a weaker interaction between Ba(N03) 2 and y-Al203 domains in the ternary oxide as well as due to the change in the surface acidity in the presence of TiO 2. At relatively high temperatures (e.g., 873-1273 K) formation of complex structures in the form of BaTiO3, Ba1.23Al 2.46Ti5.54O16, BaTiO5, andor Ba x:AlyTizOn., were also observed. © 2009 American Chemical Society.