Browsing by Author "Erdivan, Beyzanur"

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Open Access
Bimetallic hydroxide catalysts for aerobic C-H activation
(2024-01) Erdivan, Beyzanur
The increasing interest in the oxidation of sp3 C-H and O-H bonds has garnered tremendous attention due to its potential for facile production of oxygenated organics. Precious metal-free bimetallic hydroxide-based materials are commonly employed in various applications such as batteries and photocatalysts. However, their prospects in C-H activation reactions have been poorly explored. This research focuses on the development and evaluation of a bimetallic Fe-Mn hydroxide catalyst for aerobic C-H activation and O-H oxidation reactions without the need for an initiator. The Fe-Mn hydroxide catalyst was synthesized and carefully optimized to enhance its catalytic efficiency in the direct oxygenation of a wide scope of alkylarene compounds through C-H functionalization and oxidation of benzylic alcohols. A series of Fe-Mn bimetal hydroxides with different Fe/Mn ratios were synthesized using a customized chemical co-precipitation method. These catalysts were then tested for the catalytic oxidation of fluorene to fluorenone using molecular oxygen as the sole oxidant, with the Fe0.6Mn0.4(OH)y-12S catalyst demonstrating the best performance. Under mild reaction conditions, the catalyst exhibited remarkable performance in activating C-H bonds using molecular oxygen as the oxidant. Various substrates, including alkylarenes and alcohols, were investigated, consistently yielding high yields of oxygenated products with minimal catalyst loadings. XRD, XPS, XANES, ICP-MS, BET, and TGA were employed to gain insights into the structural features of the catalyst. Our findings indicate that the following structural properties of the optimized Fe0.6Mn0.4(OH)y-12S catalyst could be responsible for the currently observed enhanced catalytic reactivity: i) unique Mn oxidation state (ca. Mn2.6+), ii) Fe cationic sites containing a mixture of Fe2+ and Fe3+ species, where Fe3+ species are the dominating species, iii)realtively low specific surface area of 68 m2/g, iv) relatively disordered and defective crystal structure comprised of bimetallic hydroxides as well as additional oxide/oxyhydroxide phases, v) residual Na+ surface species enabling electronic promotion of the cationic active sites via electron donation.
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Gültekin Yazgan’ın hayatı ve Türkiye’de Görme Engelliler Kütüphaneciliği
(Bilkent University, 2017) Erdivan, Beyzanur; Türközü, Ece Büşra; Kerem Boy, Turan; Yıldız, Muhammed Erkan; Kıroğlu, Tarık
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, Emrah
Two-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.