Browsing by Author "Ozensoy, Emrah"
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Item Open Access A highly active and stable Ru catalyst for syngas production via glycerol dry reforming: Unraveling the interplay between support material and the active sites(Elsevier, 2022-04-25) Ozden, M.; Say, Zafer; Kocak, Yusuf; Ercan, Kerem Emre; Jalal, Ahsan; Ozensoy, Emrah; Avci, A. K.Glycerol dry reforming (GDR) was studied on Ru/La2O3, Ru/ZrO2, and Ru/La2O3–ZrO2 catalysts. Impacts of the support on morphological, electronic and surface chemical properties of the catalysts were comprehensively characterized by TEM, in–situ DRIFTS, XPS, ATR–IR and XRD. Initial (5 h) CO2 conversion at 750 °C and CO2–to–glycerol ratio of 1–4 was ordered as Ru/La2O3 < Ru/ZrO2 < Ru/La2O3–ZrO2. During 72 h stability tests, Ru/ZrO2 deactivated by ~33% due to Ru sintering, structural deformation of the monoclinic zirconia support, and strong metal–support interaction. Under identical conditions, CO2 conversion on Ru/La2O3 decreased by 27% mainly due to dehydroxylation/carbonation of lanthana and severe coking. Lanthana–stabilized tetragonal zirconia phase of Ru/La2O3–ZrO2 led to finely dispersed small oxidic Ru clusters which deactivated by 15% after 72 h and demonstrated unusually high catalytic performance that was on par with the significantly more expensive Rh–based catalysts, which are known with their exceptional activity and stability in GDR.Item Open Access Influence of La and Si promoters on the anaerobic heterogeneous catalytic decomposition of ammonium dinitramide (ADN) via alumina supported iridium active sites(Elsevier, 2022-02-25) Kurt, Merve; Kap, Zeynep; Senol, Sinem; Ercan, Kerem Emre; Sika-Nartey, Abel Tetteh; Kocak, Yusuf; Koc, A.; Esiyok, H.; Caglayan, B. S.; Aksoylu, A. E.; Ozensoy, EmrahStructural origins of the promotional effects of the La or Si doping of alumina supported Ir catalysts in anaerobic ammonium dinitramide decomposition were investigated. Our findings reveal that Ir/Al2O3 and Ir/La-Al2O3 favorably lower the onset temperature of the ADN decomposition reaction, whereas Si doping boosts the pressure generation during the reaction. Formation of mostly metallic Ir nanoparticles for Ir/Al2O3 and Ir/La-Al2O3 enables the lowering of the activation energy of the reaction. On the other hand, enhancement due to Si promotion is associated to the generation of small oxidic Irnx+ clusters which are strongly interacting with the SiOx-AlOx surface domains of the support material. Fundamental structure-functionality relationships unraveled in the current work may allow design of novel catalytic systems for aerospace monopropellant propulsion systems with higher performance by simultaneous exploitation of Ir active sites with different electronic properties.Item Open Access Two-dimensional bimetallic hydroxide nanostructures for catalyzing low-temperature aerobic C–H bond activation in alkylarene and alcohol partial oxidation(American Chemical Society, 2022-12-08) Sika-Nartey, Abel Tetteh; Sahin, Yesim; Ercan, Kerem Emre; Kap, Zeynep; Kocak, Yusuf; Erdali, Ayşe Dilay; Erdivan, Beyzanur; Türkmen, Yunus Emre; Ozensoy, EmrahTwo-dimensional (2D) bimetallic NixMn1–x(OH)y layered double hydroxide (LDH) nanostructures were synthesized and optimized as a remarkably active catalytic platform for low-temperature aerobic C–H bond activation in alkylarenes and partial oxidation of alcohols using a wide substrate (i.e., reactant) and diverse solvent scope. The NixMn1–x(OH)y structure consists of nonprecious and earth-abundant metals that can effectively operate at low catalyst loadings, requiring only molecular oxygen as the stoichiometric oxidant. Structurally diverse alkylarenes as well as primary and secondary alcohols were shown to be competent substrates where oxidation products were obtained in excellent yields (93–99%). Comprehensive catalyst structural characterization via XRD, ATR-IR, TEM, EDX, XPS, BET, and TGA indicated that the ultimately optimized Ni0.6Mn0.4(OH)y-9S catalyst possessed not only particular rotational faults in its β-Ni0.6Mn0.4(OH)y domains but also distinct α/β-Ni0.6Mn0.4(OH)y interstratification disorders, in addition to a relatively high specific surface area of 125 m2/g, a 2D platelet morphology, and an average Mn oxidation state of +3.5, suggesting the presence of both Mn3+ and Mn4+ species in its structure working in a synergistic fashion with the Ni2+/x+ cations (the latter is justified by the lack of catalytic activity in the monometallic LDH catalysts Ni(OH)2 and Mn(OH)2). Kinetic isotope effect studies carried out in the fluorene oxidation reaction (kH/kD = 5.7) revealed that the rate-determining step of the catalytic oxidation reaction directly involved the scission of a C–H bond. Moreover, the optimized catalyst was demonstrated to be reusable through the application of a regeneration protocol, which can redeem the full initial activity of the carbon-poisoned spent catalyst in the fluorene oxidation reaction.