Fe promoted NOx storage materials: structural properties and NOx uptake
Author
Kayhan, E.
Andonova, S. M.
Şentürk, G. S.
Chusuei, C. C.
Ozensoy, E.
Date
2010Source 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
ArticleItem 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 experimentEx-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/11693/22460Published Version (Please cite this version)
http://dx.doi.org/10.1021/jp907982qCollections
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