Browsing by Author "Sika-Nartey, Abel Tetteh"
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Item Open Access Catalytic metal hydroxide nanostructures: aerobic C-H activation and catalytic low temperature carbon monoxide oxidation by NixMn(1-x)(OH)2(2021-02) Sika-Nartey, Abel TettehMetal hydroxides and mixed metal hydroxides have been frequently utilized in diverse applications such as battery technologies, electrocatalysis, electrosynthesis, photocatalysis, supercapacitors, electrochromic devices, and electrochemical sensors. Yet, precious metal-free hydroxides have not been utilized to their full potential in the field of catalytic aerobic C-H activation and catalytic low-temperature CO oxidation. In this work, we demonstrate that upon careful optimization of catalyst synthesis protocols, a novel catalytic architecture is achieved in the form of Ni0.6Mn0.4(OH)2 revealing remarkable catalytic performance in the aerobic oxidation of alkylarenes, particularly in the aerobic oxidation of xanthene to xanthone. This optimized catalyst also shows superior catalytic activity in low-temperature CO (g) oxidation. We also present an efficient catalytic regeneration protocol, which can redeem the full initial activity of the carbon-poisoned spent catalyst in xanthene oxidation. Catalytic functionality of this novel nanomaterial architecture is also examined in detail in light of comprehensive characterization experiments including ATR-IR, XRD, BET-SSA, TGA, TEM, EDX and XPS measurements.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 Precious metal-Free LaMnO3 perovskite catalyst with an optimized nanostructure for aerobic C–H bond activation reactions: alkylarene oxidation and naphthol dimerization(American Chemical Society, 2021-02-03) Şahin, Yeşim; Sika-Nartey, Abel Tetteh; Ercan, Kerem Emre; Koçak, Yusuf; Senol, Sinem; Özensoy, Emrah; Türkmen, Yunus EmreIn this article, we describe the development of a new aerobic C–H oxidation methodology catalyzed by a precious metal-free LaMnO3 perovskite catalyst. Molecular oxygen is used as the sole oxidant in this approach, obviating the need for other expensive and/or environmentally hazardous stoichiometric oxidants. The electronic and structural properties of the LaMnO3 catalysts were systematically optimized, and a reductive pretreatment protocol was proved to be essential for acquiring the observed high catalytic activities. It is demonstrated that this newly developed method was extremely effective for the oxidation of alkylarenes to ketones as well as for the oxidative dimerization of 2-naphthol to 1,1-binaphthyl-2,2-diol (BINOL), a particularly important scaffold for asymmetric catalysis. Detailed spectroscopic and mechanistic studies provided valuable insights into the structural aspects of the active catalyst and the reaction mechanism.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.Item Open Access Unraveling molecular fingerprints of catalytic sulfur poisoning at the nanometer scale with near-field infrared spectroscopy(American Chemical Society, 2022-04-29) Say, Zafer; Kaya, Melike; Kaderoǧlu, Çağıl; Koçak, Yusuf; Ercan, Kerem Emre; Sika-Nartey, Abel Tetteh; Jalal, Ahsan; Türk, Ahmet Arda; Langhammer, Christoph; Jahangirzadeh Varjovi, Mirali; Durgun, Engin; Özensoy, EmrahFundamental understanding of catalytic deactivation phenomena such as sulfur poisoning occurring on metal/metal-oxide interfaces is essential for the development of high-performance heterogeneous catalysts with extended lifetimes. Unambiguous identification of catalytic poisoning species requires experimental methods simultaneously delivering accurate information regarding adsorption sites and adsorption geometries of adsorbates with nanometer-scale spatial resolution, as well as their detailed chemical structure and surface functional groups. However, to date, it has not been possible to study catalytic sulfur poisoning of metal/metal-oxide interfaces at the nanometer scale without sacrificing chemical definition. Here, we demonstrate that near-field nano-infrared spectroscopy can effectively identify the chemical nature, adsorption sites, and adsorption geometries of sulfur-based catalytic poisons on a Pd(nanodisk)/Al2O3 (thin-film) planar model catalyst surface at the nanometer scale. The current results reveal striking variations in the nature of sulfate species from one nanoparticle to another, vast alterations of sulfur poisoning on a single Pd nanoparticle as well as at the assortment of sulfate species at the active metal-metal-oxide support interfacial sites. These findings provide critical molecular-level insights crucial for the development of long-lifetime precious metal catalysts resistant toward deactivation by sulfur. ©