Browsing by Subject "Anatase"
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Item Open Access Finding an optimum surface chemistry for [Formula] systems as NOx storage materials(Bilkent University, 2010) Şentürk, Göksu SedaTitania promoted NOx storage materials in the form of BaO/TiO2/Al2O3 were synthesized via two different sol-gel preparation techniques, with varying surface compositions and morphologies [1, 2]. The influence of the TiO2 units on the NOx storage component (8 - 20 wt. % BaO), the nature of the crystallographic phases, thermal stabilities and the dispersion of the surface oxide/nitrate domains were investigated. The structural characterization of the synthesized NOx storage materials were analyzed by means of BET surface area analysis, X-ray diffraction (XRD), ex-situ Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X- ray (EDX) and transmission electron microscopy (TEM). Comparative analysis of the results showed that the TiO2/Al2O3 support material derived by the co-precipitation of the corresponding hydroxides via the sol-gel technique, exhibited distinctively more homogenous distribution of TiO2 domains. The functionality/performance of these materials upon NOx and SOx adsorptions were monitored by temperature programmed desorption (TPD) and insitu Fourier transform infrared (FTIR) spectroscopy. An improved Ba surface dispersion was observed for the BaO/TiO2/Al2O3 materials synthesized via the coprecipitation of alkoxide precursors which was found to originate mostly from the increased fraction of accessible TiO2/TiOx sites on the surface. These TiO2/TiOx sites functioned as strong anchoring sites for surface BaO domains and were tailored to enhance surface dispersion of BaO. The relative stability of the NOx species adsorbed on the BaO/TiO2/Al2O3 system was found to increase in the following order: NO+ /N2O3 on alumina << nitrates on alumina < surface nitrates on BaO < bridged/bidentate nitrates on large/isolated TiO2 clusters < bulk nitrates on BaO on alumina surface and bridged/bidentate nitrates on TiO2 crystallites homogenously distributed on the surface < bulk nitrates on the BaO sites located on the TiO2 domains. The detailed study of the interaction of SOx with BaO/TiO2/Al2O3 ternary oxide materials showed that titania (TiO2) was a promising candidate for improving the sulfur tolerance on these type of surfaces. Adsorption of SOx on both pure Al2O3 and TiO2 showed that Al2O3 formed strongly bound SOx species, that were thermally stable up to T > 1073 K. SOx adsorption directly altered stability of the nitrate species on the Ti/Al (Protocol 1, Protocol 2) samples. SOx uptake properties of the BaO/TiO2/Al2O3 materials were found to be strongly influenced by the morphology of the TiO2/TiOx domains and the BaO loadings (8/20 wt% BaO). Consequently, the presence of titania domains was seen to decrease the SOx desorption temperatures and enhance the sulfur-tolerance of these materials by destabilizing the accumulated sulfate species. SOx exposure on the synthesized materials led to a significant decrease in the NOx adsorption capacities. The results obtained from FT-IR spectra showed that the sulfur deposition on the NOx storage materials promoted by TiItem Open Access SOx uptake and release properties of TiO2/Al2O3 and BaO/TiO2/Al2O3 mixed oxide systems as NOx storage materials(Elsevier, 2012-04-30) Şentürk, G. S.; Vovk, E. I.; Zaikovskii, V. I.; Say, Z.; Soylu, A. M.; Bukhtiyarov, V. I.; Ozensoy, E.Titania was used as a promoter to obtain novel materials in the form of TiO2/Al2O3 (Ti/Al) and BaO/TiO2/Al2O3 (Ba/Ti/Al, containing 8 wt% or 20 wt% BaO) that are relevant to NOx storage reduction (NSR) catalysis. Two different protocols (P1, P2) were utilized in the synthesis. Ti/Al(P1) manifests itself as crystallites of TiO2 on -Al2O3, while Ti/Al(P2) reveals an amorphous AlxTiyOz mixed oxide. The structures of the synthesized materials were investigated via TEM, EDX, BET analysis and XPS while the catalytic functionality/performance of these support materials upon SOx and subsequent NOx adsorption were investigated with TPD and in situ FTIR spectroscopy. Ti/Al(P1, P2) revealed a high affinity towards SOx. Overall thermal stabilities of the adsorbed SOx species and the total SOx uptake of the Ba-free samples increase in the following order: TiO2(anatase) -Al2O3 < Ti/Al(P1) < Ti/Al(P2). The superior SOx uptake of Ti/Al(P1, P2) support materials can be tentatively attributed to the increasing specific surface area upon TiO2 promotion and/or the changes in the surface acidity. Promotion of BaO/Al2O3 with TiO2 leads to the attenuation of the SOx uptake and a significant decrease in the thermal stability of the adsorbed SOx species. The relative SOx adsorption capacities of the investigated materials can be ranked as follows: 8Ba/Ti/Al(P1) < 8Ba/Ti/Al(P2) < 8Ba/Al ∼ 20Ba/Ti/Al(P1) < 20Ba/Al < 20Ba/Ti/Al(P2).