Browsing by Subject "SOx poisoning"

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Open Access
Ceria promoted NOx storage and reduction materials
(2011) Say, Zafer
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.
Open Access
Pt-free perovskite based oxidation catalysts for automotive applications
(2013) Doğaç, Merve
Open Access
Sulfur tolerance of Fe promoted BaO/Al2O3 systems as NOx storage materials
(2011) Parmak, Emrah
Ternary mixed oxide systems in the form of BaO/FeOx/Al2O3 were studied with varying compositions as an alternative to the conventional NOx storage materials (i.e. BaO/Al2O3). NOx uptake properties of the freshly prepared samples, sulfur adsorption and NOx storage in the presence of sulfur were investigated in order to elucidate the sulfur tolerance of these advanced NOx storage systems in comparison to their conventional counterparts. The structural characterization of the poisoned NOx storage materials was analyzed by means of scanning electron microscopy (SEM). The performance and sulfur tolerance of these materials upon SOx adsorption were monitored by in-situ Fourier transform infrared (FTIR) spectroscopy, temperature programmed desorption (TPD) and X-Ray Photoelectron Spectroscopy (XPS). Addition of FeOx domains to the conventional BaO/Al2O3 system was observed to introduce additional NOx storage sites and tends to increase the total NOx uptake capacity. SO2+O2 adsorption on the investigated samples was found to lead to the formation of sulfites at low temperatures which are converted into surface and bulk sulfates with increasing temperatures. After annealing at 1173 K in vacuum most of the sulfates can be removed from the surface and the samples can be regenerated. However, for Fe/Ba/Al samples formation of various highly-stable sulfite and sulfate species were also observed which survive on the surface even after annealing at elevated temperatures (1173 K). Sulfur poisoning on 5(10)Fe/8Ba/Al samples leads to preferential poisoning of the FeOx, Al2O3 and surface BaO sites where bulk BaO sites seems to be more tolerant towards sulfur poisoning. In contrast, sulfur poisoning occurs in a rather non-preferential manner on the 5(10)Fe/20Ba/Al samples influencing all of the NOx storage sites. Thermal stability of the sulfate species seem to increase in the following order: surface alumina sulfates < surface Ba sulfates ≈ Fe sulfates < bulk Ba sulfates ≈ bulk alumina sulfates < highly stable sulfates and sulfites on Fe/Ba/Al surfaces. In overall, it can be argued that the Fe promotion has a positive influence on the NOx storage capacity as well as a positive effect on the sulfur tolerance when the Ba loading is equal to 8 wt% (i.e. 5(10)Fe/8Ba/Al). For these samples, even the surface uptakes more SOx than conventional 8Ba/Al system, NOx uptake properties as well as thermal regeneration properties seem slightly improved. On the other hand, for higher Ba loadings (i.e. 5(10)Fe/20Ba/Al) Fe promotion has a minor positive effect on NOx uptake capacity and SOx tolerance for 5 wt% Fe promotion while 10 wt% Fe promotion seems to have no positive influence.