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      Fe promoted NOx storage materials: structural properties and NOx uptake

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      Author
      Kayhan, E.
      Andonova, S. M.
      Şentürk, G. S.
      Chusuei, C. C.
      Ozensoy, E.
      Date
      2010
      Source Title
      Journal of Physical Chemistry C
      Print ISSN
      1932-7447
      Electronic ISSN
      1932-7455
      Publisher
      American Chemical Society
      Volume
      114
      Issue
      1
      Pages
      357 - 369
      Language
      English
      Type
      Article
      Item Usage Stats
      123
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      103
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      Abstract
      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.
      Keywords
      Adsorption experiment
      Ex-situ annealing
      FTIR
      Raman experiments
      Relative stabilities
      Storage mechanism
      Storage sites
      Storage systems
      Surface domains
      Surface nitrates
      Surface oxidations
      Synthesized materials
      TEM
      Temperature-dependent changes
      Ternary oxides
      XPS
      XRD
      Adsorption
      Barium
      Experiments
      Fourier transform infrared spectroscopy
      Iron oxides
      Materials properties
      Morphology
      Nitrates
      Raman spectroscopy
      Storage (materials)
      Structural properties
      System stability
      X ray diffraction
      Surfaces
      Permalink
      http://hdl.handle.net/11693/22460
      Published Version (Please cite this version)
      http://dx.doi.org/10.1021/jp907982q
      Collections
      • Department of Chemistry 594
      • Institute of Materials Science and Nanotechnology (UNAM) 1775
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