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Öğe A Comprehensive Review on Red Mud-Based Catalysts: Modification Methods and Applications in Thermal- and Photocatalysis(Wiley-V C H Verlag Gmbh, 2025) Sekizkardes, Busra; Soyer-Uzun, Sezen; Uzun, Alper; Kuhn, Simon; Kaya-Ozkiper, Kardelen; Kurtoglu-Oztulum, Samira F.Red mud (RM), waste of the Bayer process for aluminum production, is mostly stored in landfill areas, creating serious environmental and economic problems. It offers substantial potential for catalytic applications, primarily because of its cost efficiency and rich chemical composition, including Fe, Si, Al, and Ti oxides. Using RM as a catalyst not only contributes to environmental protection but also offers economic advantages as it can potentially reduce the reliance on expensive noble metals typically used in solid catalyst formulations. RM is predominantly used in thermal- and photocatalysis, serving as a bulk catalyst, support material, promoter, additive, or as a host material for heterojunction catalysts. Before use, RM is generally modified to enhance its textural properties and tailor its composition. This review provides a comprehensive analysis of the utilization of RM in catalytic applications. The structural changes resulting from various pretreatments and their impact on catalytic properties are discussed. Key thermal- and photocatalytic reactions involving RM-based catalysts are presented to highlight their industrial and environmental significance. Potential pathways for further optimization of RM-based catalysts are also proposed, offering a broad perspective on future directions in the field.Öğe Active sites and their individual turnover frequencies for ethylene hydrogenation on reduced graphene aerogel(American Chemical Society, 2024) Kurtoğlu-Öztulum, Samira Fatma; Yalçın, Kaan; Saraç Öztun, F. Eylül; Kanat, Gizem Hasibe; Ünal, Uğur; Uzun, AlperGraphene aerogel (GA) was reduced at various temperatures to prepare a series of reduced graphene aerogels (rGAs) with different surface characteristics. Detailed characterization demonstrated that an increase in the thermal reduction temperature leads to an increase in surface area accompanied by an increase in surface density of defect sites formed by the removal of the oxygen-containing functional groups. rGA samples were then tested for ethylene hydrogenation under identical conditions. A comparison of catalytic performances of each catalyst demonstrated that the rGA sample prepared by reduction in Ar at 900 °C (rGA-900) provides the highest performance compared with others prepared at lower temperatures. Next, we analyzed the per-gram activity of each catalyst as a sum of individual contributions from different defect sites quantified by Raman spectroscopy and CHNS-O analysis to determine the individual turnover frequencies (TOFs) of each active site. This analysis identified polyene-like structures and interstitial defects associated with amorphous sp2 bonded carbon atoms as the dominant active sites responsible for hydrogenation. A comparison of their TOFs further indicated that the polyene-like structures provide approximately ten times higher TOF compared to those associated with the amorphous carbon defects. These results, identifying the dominant active centers and quantifying their corresponding TOFs, provide opportunities toward the rational design of GA-based carbocatalysts.Öğe Atomically dispersed zeolite-supported rhodium complex: Selective and stable catalyst for acetylene semi-hydrogenation(Elsevier, 2024) Kurtoğlu-Öztulum, Samira Fatma; Zhao, Yuxin; Hoffman, Adam S.; Uzun, Alper; Demircan, Oktay; Yordanli, Melisa Su; Hong, Jiyun; Perez-Aguilar, Jorge E.; Saltuk, Aylin; Akgül, Deniz; Ateşin, Tülay A.; Aviyente, Viktorya; Gates, Bruce C.; Bare, Simon R.Supported rhodium catalysts are known to be unselective for semi-hydrogenation reactions. Here, by tuning the electronic structure of supported mononuclear rhodium sites determined by the metal nuclearity and the electron-donor properties of the support, we report that atomically dispersed HY zeolite-supported rhodium with reactive acetylene ligands affords a stable ethylene selectivity > 90 % for acetylene semi-hydrogenation at 373 K and atmospheric pressure, even when ethylene is present in a large excess over acetylene. Infrared and X-ray absorption spectra and measurements of rates of the catalytic reaction complemented with calculations at the level of density functional theory show how the catalyst performance depends on the electronic structure of the rhodium, influenced by the support as a ligand that is a weak electron donor.Öğe Challenges with atomically dispersed supported metal catalysts: Controllingperformance, improving stability, and enhancing metal loading(Elsevier, 2023) Kurtoğlu-Öztulum, Samira Fatma; Uzun, AlperComprehensive Inorganic Chemistry III, a ten-volume reference work, is intended to cover fundamental principles, recent discoveries, and significant applications of elements and their compounds. Authored by renowned experts in the field and edited by a world-class editorial board, each chapter provides a thorough and in-depth overview of the topic covered, featuring resources which will be useful to students, researchers, faculty as well as those in the industry. Comprehensive Inorganic Chemistry III focuses on main group chemistry, biological inorganic chemistry, solid state and materials chemistry, catalysis, and new developments in electrochemistry and photochemistry, as well as NMR and diffraction methods for studying inorganic compounds. The work expands on our 2013 work Comprehensive Inorganic Chemistry II while also adding new volumes on cutting-edge research areas and techniques for studying inorganic compounds. Researchers seeking background information on a specific problem involving the synthesis of inorganic compounds, as well as applications for numerous elements from the periodic table, and their compounds, will be able to rely on and refer to this authoritative scientific resource time and again. This new work complements Comprehensive Coordination Chemistry III (2021) and Comprehensive Organometallic Chemistry IV (2022), constituting a formidable trio of reference resources covering the whole of modern inorganic chemistry.Öğe Reduced graphene aerogel-supported Ir(C2H4)2 complexes at an exceptional Ir loading of 23.8 wt%: Confirming site-isolation by combining XAS and STEM(Turkish Catalysis Society, 2023) Kurtoğlu-Öztulum, Samira Fatma; Yalçın, Kaan; Zhao, Yuxin; Ünal, Uğur; Uzun, AlperAtomically dispersed supported metal catalysts offer significant opportunities when compared to conventional analogues. They provide maximum utilization of expensive noble metals, interesting catalytic properties, and understanding of structure-catalytic activity relationships [1]. These novel catalysts consist of supported single metal atoms bonded to ligands as well as clusters incorporating only a few metal atoms. However, they face certain challenges hindering their industrial use. The main challenges are their limited stability and limited metal loading. Typical metal loadings are limited with <1 wt.%. The support material is crucial in overcoming these challenges. Here, we used reduced graphene aerogel (rGA) as a novel support for Ir(C2H4)2 complexes and assessed the maximum metal loading we can reach. Thanks to the outstanding properties of rGA, such as excellent electronic properties, high porosity and surface area, and multiple bonding sites for Ir atoms, an exceptionally high Ir loading of 23.8 wt% was obtained. Aberration-corrected scanning transmission electron microscopy (STEM) images and X-ray absorption spectroscopy (XAS) data confirmed the site-isolation of Ir atoms at this exceptional loading. Figure 1 shows the STEM images of rGA-supported Ir(C2H4)2 complexes at an Ir loading of 23.8 wt%, a challenging sample because of the three-dimensional multilayer wrinkled-sheet structure of rGA. Besides, these images are one of the first atomic resolution images obtained on a Hitachi HF5000 Cs-corrected cold FEG STEM in Koç University. Results demonstrate the potential of rGA as a superior support material for expensive noble metal complexes to reach exceptional loadings.
