Ceria promoted NOx storage and reduction materials
Author(s)
Advisor
Özensoy, EmrahDate
2011Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
In the current work, the effect of CeO2 promotion on the NOx storage
materials and NOx storage-reduction (NSR) catalysts is studied. Synthesized
materials were prepared using different baria and ceria loadings in order to
investigate the influence of the surface composition on the NOx storage process.
Synthesized materials were also thermally treated in the temperature range within
300 - 1273 K to mimic the thermal aging effects on the material structure. Structural
properties of the synthesized materials were investigated via spectroscopic and
diffraction techniques such as Raman spectroscopy, X-ray diffraction (XRD), and
BET (Brunauer, Emmett, ve Teller) surface area analysis. These ex-situ
characterization studies revealed that materials containing Pt showed indications of
sintering after thermal treatment at elevated temperatures where Pt sites grew in size
and were partially covered by BaO domains. Pt addition to the BaO/Al2O3 system
facilitated the formation of the undesired BaAl2O4 phase, particularly at high baria
loadings. Decomposition of the Ba(NO3)2 species took place at lower temperatures
for Pt containing materials. An indication for a strong-metal-support interaction
(SMSI) between Pt and CeO2 sites was observed in Raman spectroscopic data,
resulting in the formation of a new mixed oxide phase on the surface. BET results
indicated that the specific surface area (SSA) of the synthesized materials
monotonically decreased with increasing temperature and increasing BaO and CeO2
loadings. The behavior of the synthesized materials in NOx and SOx adsorption
experiments were also investigated via temperature programmed desorption (TPD)
and in-situ Fourier transform infrared (FTIR) spectroscopy. Ceria promotion had no
significant influence on the nature of the adsorbed nitrate species and the NOx uptake
ability of the alumina support material. On the other hand, addition of Pt to
CeO2/Al2O3 binary and BaO/CeO2/Al2O3 ternary systems was observed to enhance
the NOx storage. For the ternary mixed oxide NOx storage systems
(BaO/CeO2/Al2O3), increasing BaO or CeO2 loadings results in a decrease in the
specific surface area values, which in turn leads to decreasing NOx uptake. SO2 (g) +
O2 (g) interaction with a selected set of samples were also investigated via in-situ
FTIR spectroscopy. These experiments reveal that ceria promotion and platinum
addition assisted the formation of surface sulfate species. Furthermore, the presence
of ceria also resulted in a decrease in the thermal stability of sulfates and enabled
easier regeneration.
Keywords
NSRNOx storage materials
y-Al2O3
Ce/Al
Pt/Ce/Al
Ba/Ce/Al
Ba/Pt/Ce/Al
SOx poisoning
XRD
Raman
BET
FTIR spectroscopy
TPD
XPS