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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only Stepwise conversion of methane to methanol over Cu-mordenite prepared by supercritical and aqueous ion exchange routes and quantification of active Cu species by H2-TPR(Elsevier, 2023) Sushkevich, Vitaly; van Bokhoven, Jeroen A.; Department of Chemical and Biological Engineering; Yousefzadeh, Hamed; Bozbağ, Selmi Erim; Erkey, Can; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); College of EngineeringCopper-exchanged mordenite prepared by supercritical ion exchange (SCIE) and aqueous ion exchange (AIE) were investigated in stepwise conversion of methane to methanol. Increasing the oxygen activation temperature and methane reaction time enhances the methanol yield of copper-exchanged mordenite prepared by SCIE (CuMORS). The reducibility of Cu-MORS was compared with those of Cu-MORA prepared by aqueous ion exchange (AIE) using H-2-TPR. It was demonstrated for the first time that deconvoluted H2-TPR profile coupled with effects of Cu loading and oxygen activation temperature on methanol yield data can be used to distinguish the active Cu sites from inactive ones based on their reduction temperature. The copper species responsible for methane activation were found to be reduced below 150 C by H-2 in both Cu-MORS and Cu-MORA. From the stoichiometry of the reaction of H-2 with Cu2+ species, the average number of copper atoms of active sites were calculated as 2.07 and 2.80 for Cu-MORS and Cu-MORA, respectively. Differences in structure of copper species caused by the synthesis routes were also detected by in-situ FTIR upon NO adsorption indicating a higher susceptibility of CuMORS towards autoreduction. The results demonstrated the potential of TPR based methods to identify copper active sites and suggested the importance of site selective ion exchange in order to controllably synthesize active Cu species in zeolites.Publication Metadata only Supercritical ion exchange: a new player in Cu-zeolite catalyst synthesis towards NH3-SCR of nox(Elsevier B.V., 2024) Department of Chemical and Biological Engineering; Yousefzadeh, Hamed; Sarı, Tarık Bercan; Bozbağ, Selmi Erim; Erkey, Can; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); College of Engineering; Graduate School of Sciences and EngineeringIn this study, the effect of zeolite type, copper loading, and synthesis method/conditions on the performance of a range of Cu/Zeolites in the Standard Selective Catalytic Reduction (SCR) reaction was investigated via utilizing synthesis methods of Supercritical and Aqueous Ion Exchange (SCIE and AIE). Cu/MORS synthesized via SCIE outperformed the conventionally prepared catalyst, Cu-MORA. Cu/MORS and Cu/ZSM-5 exhibited higher NO conversion than Cu/SSZ-13 at low temperatures due to higher Cu loading. However, Cu/SSZ-13 ones surpassed the other catalysts in terms of NO conversion at temperatures above 450 °C. Selective nature of SCIE under different conditions resulted in an obvious difference between the catalyst's performance while the SCIE temperature varied from 40 to 80 °C. The results of this study showed that synthesis method/condition affects directly the Cu speciation and catalyst performance in NH3-SCR, calling for developing new synthesis methods of Cu/Zeolites to modify the catalysts performance in after-treatment systems.Publication Metadata only High-throughput computational screening of MOF adsorbents for efficient propane capture from air and natural gas mixtures(AIP Publishing, 2024) Department of Chemical and Biological Engineering; Erçakır, Göktuğ; Aksu, Gökhan Önder; Keskin, Seda; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of EngineeringIn this study, we used a high-throughput computational screening approach to examine the potential of metal-organic frameworks (MOFs) for capturing propane (C3H8) from different gas mixtures. We focused on Quantum MOF (QMOF) database composed of both synthesized and hypothetical MOFs and performed Grand Canonical Monte Carlo (GCMC) simulations to compute C3H8/N2/O2/Ar and C3H8/C2H6/CH4 mixture adsorption properties of MOFs. The separation of C3H8 from air mixture and the simultaneous separation of C3H8 and C2H6 from CH4 were studied for six different adsorption-based processes at various temperatures and pressures, including vacuum-swing adsorption (VSA), pressure-swing adsorption (PSA), vacuum-temperature swing adsorption (VTSA), and pressure-temperature swing adsorption (PTSA). The results of molecular simulations were used to evaluate the MOF adsorbents and the type of separation processes based on selectivity, working capacity, adsorbent performance score, and regenerability. Our results showed that VTSA is the most effective process since many MOFs offer high regenerability (>90%) combined with high C3H8 selectivity (>7 x 103) and high C2H6 + C3H8 selectivity (>100) for C3H8 capture from air and natural gas mixtures, respectively. Analysis of the top MOFs revealed that materials with narrow pores (<10 angstrom) and low porosities (<0.7), having aromatic ring linkers, alumina or zinc metal nodes, typically exhibit a superior C3H8 separation performance. The top MOFs were shown to outperform commercial zeolite, MFI for C3H8 capture from air, and several well-known MOFs for C3H8 capture from natural gas stream. These results will direct the experimental efforts to the most efficient C3H8 capture processes by providing key molecular insights into selecting the most useful adsorbents.Publication Metadata only Atomically dispersed zeolite-supported rhodium complex: selective and stable catalyst for acetylene semi-hydrogenation(Academic Press Inc., 2024) Su Yordanli, Melisa; Hoffman, Adam S.; Hong, Jiyun; Perez-Aguilar, Jorge E.; Saltuk, Aylin; Akgül, Deniz; Demircan, Oktay; Ateşin, Tülay A.; Aviyente, Viktorya; Gates, Bruce C.; Bare, Simon R.; Department of Chemical and Biological Engineering; Zhao, Yuxin; Bozkurt, Özge Deniz; Öztulum, Samira Fatma Kurtoğlu; Uzun, Alper; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of EngineeringSupported 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.Publication Metadata only Targeting cancer cells via tumor-homing peptide CREKA functional PEG nanoparticles(Elsevier, 2016) N/A; N/A; N/A; Department of Chemical and Biological Engineering; Okur, Aysu Ceren; Erkoç, Pelin; Kızılel, Seda; Master Student; PhD Student; Faculty Member; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 28376Targeting cell microenvironment via nano-particle based therapies holds great promise for treatment of various diseases. One of the main challenges in targeted delivery of nanoparticles for cancer therapy includes reduced localization of delivery vehicles at tumor site. The therapeutic efficacy of drugs can be improved by recruiting delivery vehicles towards specific region of tumorigenesis in the body. Here, we demonstrate an effective approach in creating PEG particles via water-in-water emulsion technique where tumor-homing peptide CREKA was used for functionalization. Simultaneous conjugation of laminin peptide IKVAV into hydrogel network and influence of altered combinations of ligands on intracellular uptake of anticancer drugs by HeLa cells were investigated. CREKA conjugated hydrogel nanoparticles were more effective to improve apoptotic effects of the model drug Doxorubicin (DOX) compared to that of particles conjugated with other peptides. Fluorescence intensity analysis on confocal micrographs suggested significantly higher cellular uptake of CREKA conjugated PEG particles than internalization of nanoparticles in other groups. We observed that fibrin binding ability of PEG particles could be increased up to 94% through CREKA conjugation. Our results suggest the possibility of cancer cell targeting via CREKA-functional PEG nanoparticles.Publication Metadata only Performance of high capacity Li-ion pouch cells over wide range of operating temperatures and discharge rates(Elsevier Science Sa, 2020) N/A; N/A; N/A; Department of Chemical and Biological Engineering; Alipour, Mohammad; Esen, Ekin; Varzeghani, Amir Rahimi; Kızılel, Rıza; PhD Student; PhD Student; PhD Student; Researcher; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; 114475Operating temperature of Lithium-ion batteries (LIBs) significantly affects their electrochemical-thermal performance, cycle life, and cost. This study presents the thermal and electrochemical performance of 20 Ah LiFePO4 cells for 8 current rates (0.2C-5C) at 8 operating temperatures (-20 degrees C to 50 degrees C). Results show that the effects of operating temperature and current rate on cell performance differ above 10 degrees C, between 10 degrees C and 0 degrees C, and at subzero temperatures. Based on the electrochemical impedance spectroscopy (EIS) measurements, significantly higher bulk and charge-transfer resistances in conjunction with the lower diffusion coefficients results in poor battery efficiency at subzero temperatures. Optimum operating condition is 50 degrees C at a rate of 0.2C, in terms of utilized power and capacity, while a considerable power loss and capacity decrease occur below 20 degrees C. Furthermore, increasing the current rate is detrimental above 0 degrees C, whereas it improves cell performance at -10 degrees C, in terms of cell capacity. Moreover, cell temperature reaches an undesirable value at 50 degrees C and 5C rate, thus a thermal management system is necessary for high capacity LiFePO4 cells at higher temperatures and/or at higher C-rates. Additionally, temperature differences on the surface of high capacity cells reach 10 degrees C below room temperature at high current rates which can lead to nonuniform material utilization, and consequently cell failures. Finally, the cycle life of 20 Ah LiFePO4 cells decreases dramatically as discharge current rate increases. (C) 2020 Elsevier B.V. All rights reserved.Publication Metadata only Gas adsorption and diffusion in a highly CO2 selective metal-organic framework: molecular simulations(Taylor and Francis Ltd, 2013) N/A; Department of Chemical and Biological Engineering; Keskin, Seda; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; 40548Grand canonical Monte Carlo and equilibrium molecular dynamics simulations were used to assess the performance of an rht-type metal–organic framework (MOF), Cu-TDPAT, in adsorption-based and membrane-based separation of CH4/H2, CO2/CH4 and CO2/H2 mixtures. Adsorption isotherms and self-diffusivities of pure gases and binary gas mixtures in Cu-TDPAT were computed using detailed molecular simulations. Several properties of Cu-TDPAT such as adsorption selectivity, working capacity, diffusion selectivity, gas permeability and permeation selectivity were computed and compared with well-known zeolites and MOFs. Results showed that Cu-TDPAT is a very promising adsorbent and membrane material especially for separation of CO2 and it can outperform traditional zeolites and MOFs such as DDR, MFI, CuBTC, IRMOF-1 in adsorption-based CO2/CH4 and CO2/H2 separations.Publication Metadata only Structure of mono- and bimetallic heterogeneous catalysts based on noble metals obtained by means of fluid technology and metal-vapor synthesis(Maik Nauka/Interperiodica/Springer, 2012) Said-Galiev, E. E.; Vasil'kov, A. Yu.; Nikolaev, A. Yu.; Lisitsyn, A. I.; Naumkin, A. V.; Volkov, I. O.; Abramchuk, S. S.; Lependina, O. L.; Khokhlov, A. R.; Shtykova, E. V.; Dembo, K. A.; Department of Chemical and Biological Engineering; Erkey, Can; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; 29633Monometallic nanocomposites are obtained with the use of supercritical carbon dioxide (fluid technique) and metal-vapor synthesis (MVS), while bimetallic nanocomposites of Pt and Au noble metals and gamma-Al2O3 oxide matrix are synthesized by a combination of these two methods. The structures, concentrations, and chemical states of metal atoms in composites are studied by means of small-angle X-ray scattering (SAXS), transparent electron microscopy (TEM), X-ray fluorescent analysis (XFA), and X-ray photoelectron spectroscopy (XPS). The neutral state of metal atoms in clusters is shown by XPS and their size distribution is found according to SAXS; as is shown, it is determined by the pore sizes of the oxide matrices and lies in the range of 1 to 50 nm. The obtained composites manifest themselves as effective catalysts in the oxidation of CO to CO2.Publication Metadata only Graphene aerogel-supported ruthenium nanoparticles for COx-free hydrogen production from ammonia(Elsevier, 2021) N/A; N/A; N/A; Department of Chemical and Biological Engineering; Department of Chemistry; Department of Chemistry; Koçer, Tolga; Öztulum, Samira Fatma Kurtoğlu; Uzun, Alper; Ünal, Uğur; Öztuna, Feriha Eylül Saraç; Researcher; PhD Student; Faculty Member; Faculty Member; Researcher; Department of Chemical and Biological Engineering; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; Graduate School of Sciences and Engineering; College of Engineering; College of Sciences; College of Sciences; N/A; 384798; 59917; 42079; N/ARuthenium was highly dispersed on graphene aerogel (GA) at high loadings to achieve high performance in COx-free hydrogen production from ammonia. Catalytic performance measurements on ammonia decomposition showed that the GA-supported catalyst with a Ru loading of 13.6 wt% provides an ammonia conversion of 71.5 % at a space-velocity of 30,000 ml NH3 g(cat)(-1)h(-1) and at 450 degrees C, corresponding to a hydrogen production rate of 21.9 mmol H-2 g(cat)(-1)min(-1). The addition of K increased the ammonia conversion to a record high value of 97.6 % under identical conditions, reaching a hydrogen generation rate of 30.0 mmol H-2 g(cat)(-1) min(-1), demonstrated to be stable for at least 80 h. A comparison of the turnover frequencies of catalysts indicated that this increase in performance upon the addition of K originated from an increase in the number of the active Ru sites and the corresponding electron density available for reaction.Publication Metadata only Transformation of reduced graphene aerogel-supported atomically dispersed iridium into stable clusters approximated as Ir-6 during ethylene hydrogenation catalysis(Elsevier, 2022) Zhao, Yuxin; Hoffman, Adam S.; Gates, Bruce C.; Bare, Simon R.; Department of Chemistry; Department of Chemical and Biological Engineering; N/A; N/A; N/A; Ünal, Uğur; Uzun, Alper; Öztulum, Samira Fatma Kurtoğlu; Yalçın, Kaan; Çağlayan, Hatice Pelin; Faculty Member; Faculty Member; PhD Student; Master Student; Master Student; Department of Chemistry; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); College of Sciences; College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 42079; 59917; 384798; N/A; N/ATransformation of atomically dispersed reduced graphene aerogel (rGA)-supported complexes, Ir-I(C2H4)(2)(+), with an iridium loading of 9.9 wt%, to form low-nuclearity clusters was investigated during ethylene hydrogenation catalysis. Continuous-scan X-ray absorption spectra demonstrate the formation of clusters well approximated as Ir-4 during reaction at 100 degrees C in flowing equimolar ethylene and H-2. The Ir-4 clusters transformed into clusters well approximated as Ir 6 when the feed molar ratio was switched to H-2: C2H4 = 2 and remained stable in pure H-2 at 100 degrees C. Catalyst performance data show that hydrogenation activity increased with metal nuclearity in the order of atomically dispersed iridium/rGA << Ir-4/rGA < Ir-6/ rGA. Continuous scan X-ray absorption data, complemented with aberration-corrected scanning transmission electron microscopy images, demonstrate that the supported clusters approximated as Ir-6 are stable even in H-2 at atmospheric pressure and 100 degrees C. These supported iridium clusters are among the ones having the highest metal loadings reported for a supported metal cluster catalyst.