Browsing by Subject "Storage systems"

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • Thumbnail Image
    ItemOpen Access
    Fe promoted NOx storage materials: structural properties and NOx uptake
    (American Chemical Society, 2010) Kayhan, E.; Andonova, S. M.; Şentürk, G. S.; Chusuei, C. C.; Ozensoy, E.
    Fe promoted NOx storage materials were synthesized in the form of FeOx/BaO/Al2O3 ternary oxides with varying BaO (8 and 20 wt %) and Fe (5 and 10 wt %) contents. Synthesized NOx storage materials were investigated via TEM, EELS, BET, FTIR, TPD, XRD, XPS, and Raman spectroscopy, and the results were compared with the conventional BaO/Al2O3 NOx storage system. Our results suggest that the introduction of Fe in the BaO/Al2O3 system leads to the formation of additional NOx storage sites which store NOx mostly in the form of bidentate nitrates. NO2 adsorption experiments at 323 K via FTIR indicate that, particularly in the early stages of the NOx uptake, the NOx storage mechanism is significantly altered in the presence of Fe sites where a set of new surface nitrosyl and nitrite groups were detected on the Fe sites and the surface oxidation of nitrites to nitrates is significantly hindered with respect to the BaO/Al2O3 system. Evidence for the existence of both Fe3+ as well as reduced Fe2+/(3-x)+ sites on the freshly pretreated materials was detected via EELS, FTIR, Raman, and XRD experiments. The influence of the Fe sites on the structural properties of the synthesized materials was also studied by performing ex situ annealing protocols within 323-1273 K followed by XRD and Raman experiments where the temperature dependent changes in the morphology and the composition of the surface domains were analyzed in detail. On the basis of the TPD data, it was found that the relative stability of the stored NOx species is influenced by the morphology of the Ba and Fe containing NOx-storage domains. The relative stabilities of the investigated NOx species were found to increase in the following order: N2O3/NO+ < nitrates on γ-Al2O3 < surface nitrates on BaO < bidentate nitrates on FeOx sites < bulk nitrates on BaO.
  • 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.