Browsing by Subject "NOx storage capacity"

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    Designing novel DENOx catalysts with a wide thermal operational window
    (2016-06) Tohumeken, Merve
    The main objective of this study is to design novel DeNOx catalyst to widen the operational temperature range of exhaust emission control systems. For this purpose, single and multi NOx-storage domains (e.g. K2O, BaO) were loaded on an Al2O3/ZrO2/TiO2 (AZT) ternary mixed oxide support with various compositions and different catalytic systems were synthesized by utilizing sol-gel and wetness impregnation methods. These materials were characterized by means of XRD, N2 sorption, in-situ FTIR and TPD measurements in comparison to the Pt/20Ba/Al benchmark catalyst. K2O and BaO co-loading on AZT sample reveals better platinum dispersion than that of the single storage domain materials. Particularly, Pt/5.4K-8Ba/AZT system revealed promising NOx storage capacity (NSC) and high sulfur removal performance. NOx/SOx adsorption geometries and stabilities of the generated adsorbates were analyzed using in-situ FTIR and TPD. Although the Pt/20Ba/AZT and Pt/10K/AZT catalysts revealed high NSC, they showed poor sulfur regeneration characteristics. In conclusion, it was demonstrated that K2O and BaO co-impregnated samples can be utilized to design new catalytic architectures to modify the operational temperature window of exhaust emission control catalysts.
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    ItemOpen Access
    Utilization of reducible mixed metal oxides as promoters for the enhancement of sulfur regeneration in nsr catalysts
    (2016-07) Samast, Zehra Aybegüm
    Pt functionalized binary, ternary, and quaternary oxides (e.g. Pt/BaO/CeO2/ZrO2/Al2O3) were synthesized by wetness impregnation method and characterized by X-ray Diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis, in-situ Fourier Transform Infrared (FTIR), and temperature programmed desorption (TPD) techniques. Effect of the synthesis sequence on the NOx storage capacity was investigated by synthesizing subsequently impregnated and co-impregnated ternary oxides. Influence of BaO loading on NOx uptake of quaternary oxides was examined by utilizing two different BaO loadings namely; 8 wt% and 20 wt% on co-impregnated ternary oxide, Pt10-10CeZrAl. Co-presence of CeO2-ZrO2 oxide domains leads to an increase in NOx storage. As BaO loading increases in quaternary oxides, thermal stabilities of nitrates and nitrites increase due to the formation of bulk/ionic nitrates. Although BaO impregnation on co-impregnated ternary oxides leads to a decrease in specific surface area (SSA) values due to sintering, NOx adsorption on BaO-functionalized quaternary oxides was found to be higher than the BaO deficient ternary oxides. Upon sulfur poisoning, formation of strongly bound bulk/ionic sulfate/sulfite functional groups on BaO containing catalysts result in a need for higher temperatures for complete sulfur regeneration. Comparison of the CeO2-ZrO2 promoted systems with that of the Pt/ 20 wt% Ba/Al2O3 conventional NOx Storage Reduction (NSR) catalyst suggests that ceria-zirconia promotion enhances the sulfur tolerance. In conclusion, in this study a new NSR catalyst namely, Pt20Ba10-10CeZrAl, which is promoted with reducible mixed metal oxides, was synthesized and characterized. This novel NSR catalyst formulation revealed favorable sulfur resistance with minor sacrifice in NOx storage ability.