Researcher:
Bozbağ, Selmi Erim

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Selmi Erim

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Bozbağ

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Bozbağ, Selmi Erim

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2011 - 2019192020 - 202314

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    Graphene aerogel supported pt electrocatalysts for oxygen reduction reaction by supercritical deposition
    (Elsevier, 2017) Yu, Haibo; Aindow, Mark; N/A; N/A; N/A; Department of Chemistry; Department of Chemical and Biological Engineering; Öztuna, Feriha Eylül Saraç; Barım, Şansım Bengisu; Bozbağ, Selmi Erim; Ünal, Uğur; Erkey, Can; PhD Student; PhD Student; PhD Student; Faculty Member; Faculty Member; Department of Chemistry; Department of Chemical and Biological Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; N/A; N/A; N/A; 42079; 29633
    Mesoporous graphene aerogel (GA) supported Pt nanoparticles with narrow size distribution were prepared via supercritical deposition (SCD) using supercritical CO2 (scCO(2)). Pt(cod)me(2) precursor was dissolved in scCO(2) and adsorbed onto GA at 35 degrees C and 10.7 MPa. The Pt precursor was converted to its metal form under atmospheric pressure at various temperatures. The effects of precursor conversion temperature (400, 600, and 800 degrees C) on the structural properties of the composites were investigated using Raman Spectroscopy, XRD, XPS, and TEM. The average particle size increased from 1.2 to 2.9 nm when the conversion temperature was increased from 400 to 800 degrees C. The electrocatalytic activity of the samples towards the Oxygen Reduction Reaction were evaluated using cyclic voltammetry (CV) and rotating disc electrode (RDE) measurements. SCD helped to preserve the textural properties of the GA after the Pt nanoparticle deposition, and thus Pt/GA converted at 600 degrees C exhibited an enhanced mass activity of 30.6 mA mg(Pt)(-1), outperforming the mass activities reported in the literature for Pt/GA electrocatalysts prepared using conventional routes. (C) 2017 Elsevier Ltd. All rights reserved.
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    Adsorption of Pt(cod)me(2) onto organic aerogels from supercritical solutions for the synthesis of supported platinum nanoparticles
    (Elsevier Science Bv, 2011) Yasar, N. S.; Zhang, L. C.; Aindow, M.; N/A; Department of Chemical and Biological Engineering; Bozbağ, Selmi Erim; Erkey, Can; Researcher; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; College of Engineering; N/A; 29633
    The thermodynamics and kinetics of adsorption of Pt(cod)me(2) onto resorcinol-formaldehyde aerogel (RFA) from supercritical carbon dioxide (scCO(2)) was investigated by using high performance liquid chromatography (HPLC) to measure Pt(cod)me(2) concentrations in the fluid phase. It was found that the adsorption isotherms of Pt(cod)me(2) at 35 degrees C for different CO2 pressures could be represented by modified Langmuir isotherms. The kinetics of adsorption was determined by following the Pt(cod)me(2) uptake of the RFA spheres; these data correspond closely to the behavior from a mass transfer model based on diffusion within the pore volume with the assumption of local equilibrium at the solid-fluid interface. The adsorbed Pt(cod)me(2) molecules were reduced at atmospheric pressure under flowing hydrogen at 200 degrees C. The resultant Pt nanoparticles were distributed uniformly on the surface and had narrow size distributions. The average particle size of the nanoparticles increased with platinum loading from 2.0 nm at 10 wt.% to 3.3 nm at 34 wt.%. The Pt nanoparticles in an RFA pellet had a uniform radial size distribution, even though the pellet was impregnated with Pt(cod)me(2) for too short a short period of time for the system to reach adsorption equilibrium. The high mobility of the atomic Pt evolved during the reduction process is believed to be responsible for this phenomenon. Performing the adsorption of Pt(cod)me(2) onto RFA at 80 degrees C led to concurrent reduction and Pt nanoparticle growth. (C) 2010 Elsevier B.V. All rights reserved.
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    Mesoporous carbon aerogel supported PtCu bimetallic nanoparticles via supercritical deposition and their dealloying and electrocatalytic behaviour
    (Elsevier Science Bv, 2018) Yu, Haibo; Kızılel, Rıza; Aindow, Mark; N/A; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Barım, Şansım Bengisu; Bozbağ, Selmi Erim; Erkey, Can; Researcher; Researcher; Faculty Member; Department of Chemical and Biological Engineering; N/A; College of Engineering; College of Engineering; N/A; N/A; 29633
    Mesoporous carbon aerogel (CA) supported PtCu bimetallic nanoparticles were prepared via a sequential supercritical deposition (SCD) method using supercritical carbon dioxide (scCO(2)). The effects of deposition order of the metal, annealing temperature and metal composition on the average PtCu particle size, size distribution and dispersion were investigated. Four sets of PtCu/CA samples were prepared with two Pt:Cu molar ratios (1:1 and 1:3) and with two different deposition orders (i.e. either Pt or Cu first). X-ray diffraction and electron microscopy data showed that all of the as-prepared samples formed homogeneously distributed disordered PtCu alloy nanoparticles with narrow particle size distributions on the CA support. Increasing annealing temperature in the range 600-950 degrees C increased the average particle size from 1.8 nm to 4.5 nm and resulted in the elimination of separate Cu nanoparticles on the CA surface. The dealloying of the supported PtCu nanoparticles were carried out by cyclic voltammetry and the activity of the dealloyed nanoparticles (after 300 potential cycles) towards the oxygen reduction reaction (ORR) was investigated using rotating disc electrode (RDE) experiments. During dealloying, peaks associated with bulk dissolution and deposition of Cu and dissolution and re-deposition of Cu from the alloyed PtCu nanoparticles were observed at initial cycles along with peaks associated with creation of new Pt sites. Supported nanoparticles with Pt: Cu molar ratios of 1:1 and 1:3 which were prepared by deposition of Cu first had low activities towards ORR after dealloying. on the contrary, nanoparticles prepared by depositing Pt first exhibited promising electrocatalytic activities after dealloying. Samples with a Pt: Cu molar ratio of 1:3 showed higher activities than those with a molar ratio of 1:1. An enhanced ESA of 137 m(2)/g and dealloying induced enhanced mass activity of 0.123 A/mg(Pt) was obtained using the sample with a Pt: Cu molar ratio of 1:3, which was annealed at 800 degrees C. on the other hand, the same sample annealed at 950 degrees C had the highest specific activity of 0.165 mA/cm(2).
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    Simultaneous supercritical deposition: an alternative route for the preparation of supported bimetallic catalysts for energy conversion technologies
    (Amer Chemical Soc, 2013) Kartal, Ayse Meric; Kurykin, Michael A.; Department of Chemical and Biological Engineering; N/A; Department of Chemical and Biological Engineering; Bozbağ, Selmi Erim; Hossein, Amir; Erkey, Can; Researcher; N/A; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; N/A; College of Engineering; N/A; N/A; 29633
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    Kinetic model comparison and elucidation of mass transfer limitations in Nh3-Scr reactors using Vanadia based washcoats with different thicknesses
    (Elsevier, 2021) N/A; Bozbağ, Selmi Erim; Researcher; N/A; N/A
    Kinetic models of NH3-SCR of NO based on modified redox (MR) and modified Eley-Rideal (ER) mechanisms calibrated using monoliths with Vanadia based washcoats with different thicknesses were cross compared. Both models were satisfactory for the washcoat thicknesses investigated at steady conditions in 120-540 degrees C range. MR mechanism better represented NO transients at 192 degrees C. Dependence of limiting regions on the washcoat thickness was determined via the analysis of washcoat concentration profiles and the concentration ratios of the fluid, fluid-washcoat interface and washcoat. Both models generally agreed with the borders of the limiting regions. During Standard SCR, the limits of the kinetic regime was below 309 and 271 degrees C for thinner and thicker washcoats, respectively. This was followed by mixed limitation regime upto 488 degrees C at the reactor entrance. Above 488 degrees C, transition to kinetically controlled regime was observed at the center of the monolithic reactors. (C) 2021 Elsevier Ltd. All rights reserved.
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    Carbon aerogel supported nickel nanoparticles and nanorods using supercritical deposition
    (Elsevier Science Bv, 2012) Zhang, L. C.; Aindow, M.; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Bozbağ, Selmi Erim; Erkey, Can; Researcher; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; College of Engineering; N/A; 29633
    Carbon aerogel (CA)-nickel nanocomposites were synthesized by impregnating the CAs with nickel(II) acetylacetonate (Ni(acac)(2)) from supercritical carbon dioxide at 30 MPa and 60 degrees C followed by thermal or chemical treatment using H-2 at atmospheric pressure. The CA-Ni(acac)(2)-CO2 adsorption isotherm was measured at the impregnation condition and found to be linear. The decomposition of Ni(acac)(2) on the CA surface was investigated using thermo-gravimetry and mass-spectroscopy. Propane was found in the gaseous decomposition products. CA-Ni composites were characterized using Infrared (IR) Spectroscopy and characteristic Ni(acac)(2) peaks were found to disappear after thermal or chemical treatments. Xray diffraction (XRD) data confirmed that after H-2 treatments nickel nanocrystals were present in the CA. Transmission electron microscopy (TEM) revealed the presence of nickel nanostructures dispersed homogeneously on the surface of the CA. In the samples treated with H-2 at 170 degrees C, the average Ni nanoparticle size increased from 4.9 to 12.9 nm when the Ni loading increased from 3 to 6.5 wt.%. The H-2 treatment at 200 degrees C resulted in Ni nanorods with diameters of 7-11 nm and lengths of 25-50 nm dispersed throughout the CA surface. (c) 2012 Elsevier B.V. All rights reserved.
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    Supercritical fluid reactive deposition: a process intensification technique for synthesis of nanostructured materials
    (Elsevier, 2022) Eriş, Gamze; Uzunlar, Erdal; N/A; N/A; N/A; N/A; N/A; Department of Chemical and Biological Engineering; Yousefzadeh, Hamed; Akgün, Işık Sena; Barım, Şansım Bengisu; Sarı, Tarık Bercan; Bozbağ, Selmi Erim; Erkey, Can; Researcher; Researcher; Researcher; PhD Student; Researcher; Faculty Member; Department of Chemical and Biological Engineering; N/A; N/A; N/A; N/A; N/A; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); N/A; N/A; N/A; Graduate School of Sciences and Engineering; N/A; College of Engineering; N/A; N/A; N/A; N/A; N/A; 29633
    Supercritical fluid reactive deposition (SFRD) is a promising process intensification technique for synthesis of a wide variety of nanostructured materials. The enhanced mass transfer characteristics of supercritical fluids (SCFs) coupled with high solubilities of reducing gases in SCFs provide many advantages related to equipment size and time minimization over conventional techniques. Among SCFs, the emphasis has been placed on supercritical CO2 (scCO(2)) which is non-toxic, cheap and leaves no residue on the treated medium. Moreover, in SFRD, multiple processes such as dissolution, adsorption, reaction, and purification are combined in a single piece of equipment which is an excellent example of process integration for process intensification. In this review, the fundamental thermodynamic and kinetic aspects of the technology are described in detail. The studies in the literature on synthesis of a wide variety of nanostructured materials including supported nanoparticles, films, and ion-exchanged zeolites by SFRD are reviewed and summarized. The applications of these materials as catalysts and sensors are described. The review hopes to lead to further studies on further development of this technology for a wide variety of applications.
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    Synthesis of nanostructured materials using supercritical CO2: Part I. Physical transformations
    (Springer, 2012) N/A; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Şanlı, Deniz; Bozbağ, Selmi Erim; Erkey, Can; Researcher; Researcher; Faculty Member; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; N/A; 29633
    Nanostructured materials have been attracting increased attention for a wide variety of applications due to their superior properties compared to their bulk counterparts. Current methods to synthesize nanostructured materials have various drawbacks such as difficulties in control of the nanostructure and morphology, excessive use of solvents, abundant energy consumption, and costly purification steps. Supercritical fluids especially supercritical carbon dioxide (scCO(2)) is an attractive medium for the synthesis of nanostructured materials due to its favorable properties such as being abundant, inexpensive, non-flammable, non-toxic, and environmentally benign. Furthermore, the thermophysical properties of scCO(2) can be adjusted by changing the processing temperature and pressure. The synthesis of nanostructured materials in scCO(2) can be classified as physical and chemical transformations. In this article, Part I of our review series, synthesis of nanostructured materials using physical transformations is described where scCO(2) functions as a solvent, an anti-solvent or as a solute. The nanostructured materials, which can be synthesized by these techniques include nanoparticles, nanowires, nanofibers, foams, aerogels, and polymer nanocomposites. scCO(2) based processes can also be utilized in the intensification of the conventional processes by elimination of some of the costly purification or separation steps. The fundamental aspects of the processes, which would be beneficial for further development of the technologies, are also reviewed.
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    Origins of Bi-modal NO conversion behavior in NH3-SCR over Cu-chabazite revealed by mass transfer and surface kinetics analysis
    (Elsevier, 2022) Şanlı, Deniz; Özener, Barkın; Hisar, Gökhan; Department of Chemical and Biological Engineering; N/A; N/A; Department of Chemical and Biological Engineering; Bozbağ, Selmi Erim; Sarı, Tarık Bercan; Karadağ, Gülden Hazal; Erkey, Can; Researcher; PhD Student; Master Student; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; 29633
    A multi-site kinetic model for the NH3-SCR (Selective Catalytic Reduction) on a commercial Cu-Chabazite washcoated monolith catalyst was developed and validated using synthetic gas bench data. The model was used to demonstrate the overall controlling regimes in the reactor at temperature and space velocity ranges of 120-550 degrees C and 30,000-80,000 h-1 , respectively. This was performed via characteristic times analysis and via selectively removing external and internal mass transport phenomena from the model. Latter resulted in a bi-modal NO conversion with a conversion trench in 230-430 degrees C range where main mass transfer limitations were found. Bi-modal NO conversion profile was due to the competition between NH3 adsorption/desorption reactions and Standard SCR for surface NH3 species and it can be masked depending on the ratio of Standard SCR rates to the rates of adsorption and desorption in the presence of mass transfer limitations which have positive effects towards NO conversion.(c) 2022 Elsevier Ltd. All rights reserved.
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    Supercritical ion exchange: a new method to synthesize copper exchanged zeolites
    (Elsevier, 2022) Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Yousefzadeh, Hamed; Bozbağ, Selmi Erim; Erkey, Can; Researcher; Researcher; Faculty Member; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); College of Engineering; College of Engineering; College of Engineering; N/A; N/A; 29633
    A new technique termed Supercritical Ion Exchange (SCIE) was developed and used to synthesize Cu-mordenite (Cu-MORS). The ion exchange takes place between the Cu complex (Copper(II)trifluoroacetylacetonate) dissolved in supercritical CO2 (scCO(2)) and the extraframework protons in mordenite zeolite without requiring an aqueous phase. The occurrence of the ion exchange reaction was demonstrated by using H-1 NMR analysis of the high-pressure fluid phase samples and by visual inspection of the fluid phase color change during the synthesis. SCIE resulted in selective ion-exchange inferred by the equilibrium isotherm. The prepared catalysts were used for the stepwise direct methane to methanol (sDMTM) process and results showed that methanol productivity increased linearly with increasing Cu loading up to a certain Cu wt%. Cu-MORS displayed 16% higher methanol productivity as compared to Cu-MORA (prepared by aqueous ion exchange) with the same Cu loading. The results demonstrated the importance of site selective ion-exchange for zeolite catalysis.