Browsing by Subject "FTIR spectroscopy"

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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
Gold supported on ceria doped by Me3+ (Me = Al and Sm) for water gas shift reaction: Influence of dopant and preparation method
(2010) Andreeva, D.; Kantcheva, M.; Ivanov, I.; Ilieva, L.; Sobczak, J. W.; Lisowski, W.
Gold catalysts supported on ceria doped by Sm and Al were studied. The influence of the preparation method, as well as the nature of dopants on the structure, properties and WGS activity are investigated. The applied methods of preparation cause the modification of ceria in a different extent. In the sample prepared by co-precipitation (CP) and doped by Al, the vacancies are located within the bulk of ceria structure, whereas in the corresponding AuCeSmCP sample the vacancies are located most likely around Sm and the ceria structure seems to be better ordered than the Al doped ceria. There is no distinct correlation between the reducibility and WGS activity of the studied catalysts. The Au 4f XPS spectra of fresh samples reveal higher contribution of dispersed form of Au for Sm doped catalysts than for the corresponding Al doped samples. The Ce 3d XPS spectra disclose also a higher concentration of Ce3+ evaluated before the catalytic operation for Sm doped catalysts as compared with the Al doped fresh samples. The observations by "in situ" FT-IR spectroscopy agree well with the model of active sites and the, mechanism of the WGS reaction proposed recently by some of us. The amount of formate species observed on the AuCeSmCP is higher than that on the AuCeAlCP catalyst and parallels the catalytic activity. The higher concentration of active sites on the surface of the AuCeSmCP catalyst facilitates the dissociation of water.
Open Access
IR and turbidity studies of vitamin E-cholesterol-phospholipid membrane interactions
(Kluwer Academic Publishers-Plenum Publishers, 1995) Severcan, F.; Kazanci, N.; Baykal, Ü.; Süzer, Ş.
Binary and tertiary mixture of α-tocophenol, cholesterol and dimyristoylphosphatidylcholine in the form of multilamellar liposomes were investigated by Fourier Transform Infrared and visible spectroscopy. Results of the FTIR and turbidity experiments indicate that α T decreases or diminishes the effect of cholesterol on the frequency and the bandwidth of the C-H stretching, CH2 scissoring and C=O stretching bands in FTIR spectra and the turbidity measurements (recorded as absorbance values at 440 nm) in phospholipid model membranes. © 1995 Plenum Publishing Corporation.
Open Access
Production and structural characterization of biosurfactant produced by newly isolated staphylococcus xylosus STF1 from petroleum contaminated soil
(Elsevier BV, 2015) Keskin, N. O. S.; Han, D.; Ozkan A.D.; Angun, P.; Umu, O. C. O.; Tekinay, T.
Petroleum-contaminated soil was used to isolate and characterize biosurfactant producing bacteria. The strain could produce higher amount of biosurfactant in medium supplemented with motor oil as sole source of carbon and energy. A new biosurfactant producing bacterium, designated as Staphylococcus xylosus STF1 based on morphological, physiological, biochemical tests and 16S rRNA gene sequencing. The isolated bacterium was first screened for the ability to produce biosurfactant. Partial sequence of STF1 strain of 16S rDNA gene was highly similar to those of various members of the family Staphylococcaceae. Biochemical characterizations including FT-IR, Raman spectroscopy and Mass spectroscopy studies suggested the biosurfactant to be lipopeptide. Study also confirmed that the cell free supernatant exhibited high emulsifying activity against the different hydrocarbons. Moreover, the partially purified biosurfactant exhibited antimicrobial activity by inhibiting the growth of several bacterial species. The strain could be a potential candidate for the production of polypeptide biosurfactant which could be useful in a variety of biotechnological and industrial processes, particularly in the food and oil industry. © 2015 Elsevier B.V.
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.