Browsing by Subject "BaO"

Now showing 1 - 4 of 4

Open Access
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.
Open Access
Finding an optimum surface chemistry for [Formula] systems as NOx storage materials
(2010) Şentürk, Göksu Seda
Titania 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 Ti
Open Access
Influence of ceria on the NOx reduction performance of NOx storage reduction catalysts
(Elsevier, 2013) Say, Z.; Vovk, E. I.; Bukhtiyarov, V. I.; Ozensoy, E.
Influence of ceria on the NOx storage and reduction behavior of NSR catalysts was investigated in a systematic manner over γ-Al2O3, Ba/Al, Ce/Al, Ba/Ce/Al, Pt/Al, Pt/Ce/Al and Ba/Pt/Ce/Al systems using BET, XRD, Raman spectroscopy and in situ FTIR. Although ceria promotion does not seem to have a substantial influence on the overall NOx storage capacity, it does have a clearly positive effect on the NOx reduction via H2(g) during catalytic regeneration under rich conditions which is associated with the enhancement in the total amount of activated hydrogen on the catalyst surface and lowering of the thermal threshold for hydrogen activation. A strong metal support interaction (SMSI) between Pt sites and the BaOx/CeOx domains leads to a complex redox interplay including oxidation of the precious metal sites, reduction of ceria, formation of BaO2 species as well as the formation of Pt-O-Ce interfacial sites on the Ba/Pt/Ce/Al surface. Ceria domains also act as anchoring sites for Pt species, limit their surface diffusion, enhance dispersion and hinder sintering at elevated temperatures. On the Ba/Pt/Ce/Al catalyst surface, reduction of the stored nitrates under relatively mild conditions via H2(g) initially leads to the formation of surface -OH and -NHx species and gas phase N2O, as well as the destruction of surface nitrate species, leaving bulk nitrates mostly intact. Reduction proceeds with the conversion of N2O(g) into N2(g) along with the partial loss of surface -OH and -NHx groups, dehydration and the loss of bulk nitrates.
Open 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.