Researcher: Zhao, Yuxin
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Zhao, Yuxin
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Publication Metadata only Acetylene ligands stabilize atomically dispersed supported rhodium complexes under harsh conditions(Elsevier Science Sa, 2024) Hoffman, Adam S.; Hong, Jiyun; Perez-Aguilar, JorgeE.; Bare, Simon R.; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Zhao, Yuxin; Öztulum, Samira Fatma Kurtoğlu; Uzun, Alper; 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 EngineeringFacile sintering of atomically dispersed supported noble metal catalysts at catalytically relevant temperatures, particularly under reducing conditions, poses a challenge for their practical applications. Some ligands, such as carbonyls, aid in improving the stability at the expense of severely suppressing the catalytic activity. Here, we demonstrate that substitution of the carbonyl ligands with reactive acetylene ligands can maintain the atomic dispersion of the supported mononuclear rhodium complex under harsh reducing conditions (>573 K), as confirmed by in -situ X-ray absorption near -edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies. In contrast, the supported rhodium carbonyl complex aggregates into nanoclusters under identical conditions. Furthermore, our results indicate that the acetylene ligands provide this anti -sintering ability while retaining the hydrogenation activity.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; Department of Chemical and Biological Engineering; Zhao, Yuxin; Bozkurt, Özge Deniz; Öztulum, Samira Fatma Kurtoğlu; Uzun, Alper; 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 Interplay between copper nanoparticle size and oxygen vacancy on mg-doped ceria controls partial hydrogenation performance and stability(Amer Chemical Soc, 2021) N/A; N/A; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Zhao, Yuxin; Jalal, Ahsan; Uzun, Alper; PhD Student; PhD Student; Faculty Member; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 59917A series of CunCeMgOx catalysts with various copper nanoparticle sizes and surface defect densities were synthesized and tested for partial hydrogenation of 1,3-butadiene (1,3-BD). The data demonstrated a reaction pathway involving the dissociation of molecular hydrogen on the peripheral oxygen vacancies (O-v-Cu+) before reacting with 1,3-BD adsorbed on the corresponding Cu+ atoms. Analysis of the performance data indicated that the turnover frequency of these Cu+ sites is approximately five times higher than those of the surface Cu-0 sites. Among the catalysts considered, Cu0.5CeMgOx with the smallest copper nanoparticle size provided a stable performance for at least 15 h time-on-stream, while the others were easily deactivating because of carbon deposition. Furthermore, unlike the conventional copper-based catalysts, the Cu0.3CeMgOx catalyst achieved a complete suppression of total hydrogenation even at space velocities offering a complete 1,3-BD conversion. The findings offer a broad potential for the rational design of noble metal-free, highly selective, and stable copper-based partial hydrogenation catalysts for reactions that are prone to coke formation.Publication Metadata only Ionic liquid sheath stabilizes atomically dispersed reduced graphene aerogel-supported iridium complexes during ethylene hydrogenation catalysis(Wiley, 2022) Hoffman, Adam S.; Gates, Bruce C.; Bare, Simon R.; N/A; N/A; N/A; N/A; Department of Chemical and Biological Engineering; Department of Chemistry; Department of Chemical and Biological Engineering; Department of Chemistry; Öztulum, Samira Fatma Kurtoğlu; Yalçın, Kaan; Jalal, Ahsan; Zhao, Yuxin; Uzun, Alper; Ünal, Uğur; PhD Student; Master Student; PhD Student; PhD Student; Faculty Member; Faculty Member; 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; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Sciences; 384798; N/A; N/A; N/A; 59917; 42079An atomically dispersed reduced graphene aerogel (rGA)-supported iridium catalyst having reactive ethylene ligands was synthesized at an iridium loading of 9.9 wt % and coated with an ionic liquid, 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]). Continuous-scan X-ray absorption spectra demonstrated that the iridium remained site-isolated in flowing equimolar C2H4 and H-2 during a temperature ramp to 100 degrees C. The data further showed the lack of detectable iridium aggregation when the feed was H-2-rich or even pure H-2 at 100 degrees C. An Arrhenius plot determined for ethylene hydrogenation catalysis with the sample in flowing equimolar ethylene and hydrogen showed no variation in the apparent activation energy at temperatures up to 100 degrees C, confirming that the active sites remained intact at the higher temperatures. The results point to opportunities for overcoming the stability limitations of atomically dispersed supported noble metal catalysts by choice of electron-donor supports and ionic liquid sheaths.Publication Metadata only Influence of ionic liquids on the electronic environment of atomically dispersed Ir on (MgO)(100)(Royal Society of Chemistry (RSC), 2022) Akgul, Deniz; Findik, Volkan; Monari, Antonio; Aviyente, Viktorya; N/A; N/A; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Öztulum, Samira Fatma Kurtoğlu; Zhao, Yuxin; Uzun, Alper; PhD Student; PhD Student; Faculty Member; 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; Graduate School of Sciences and Engineering; College of Engineering; 384798; N/A; 59917Recently, ionic liquids (ILs) have been used as ligands for single-site Ir(CO)(2) complexes bound to metal-oxide supports because of their electron-donor/acceptor capacities. The combined effects of supports and ILs as ligands may pave the way to the tuning of the surrounding electronic properties to increase electron-donor/acceptor efficiency in metal-oxide supported Ir(CO)(2) complexes. Herein, we have used Density Functional Theory to model Ir(CO)(2) complexes bound to MgO supports with and without the presence of an IL to explain the role of ILs in modifying the electronic structure of the supported complex. Comparison of the nu(CO) band stretching frequencies with experimental results has led to the rationalization of the factors driving the interactions between the IL, the support, and the catalyst as well as the justification of the methodology for further studies.Publication Open Access Pyrolysis temperature tunes the catalytic properties of CuBTC-derived carbon-embedded copper catalysts for partial hydrogenation(American Chemical Society (ACS), 2022) Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Uzun, Alper; Jalal, Ahsan; Zhao, Yuxin; Faculty Member; PhD Student; 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); College of Engineering; 59917; N/A; N/AA family of carbon-embedded copper catalysts was synthesized by pyrolyzing copper benzene-1,3,5-tricarboxylate (Cu-BTC) at various temperatures ranging from 400 to 900 degrees C. Characterization of catalysts demonstrated that the density of defect sites on the carbon support increases with an increase in the pyrolysis temperature leading to an increase in the electron density on the copper sites. Catalytic performance tests on 1,3-butadiene hydrogenation showed that the performance becomes more stable as the pyrolysis temperature increases above 800 degrees C such that the catalyst prepared by pyrolysis at 900 degrees C provided a stable performance for more than 12 h, while the one prepared at 400 degrees C was deactivating by >25%. Data further demonstrated a strong dependence of the turnover frequencies to the defect site density on the carbonaceous layer. These results present a versatile approach for preparing carbon-embedded copper catalysts with tunable electronic structure and consequent catalytic properties.Publication Open Access Composites of porous materials with ionic liquids: synthesis, characterization, applications, and beyond(Elsevier, 2022) Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Durak, Özce; Zeeshan, Muhammad; Habib, Nitasha; Gülbalkan, Hasan Can; Alsuhile, Ala Abdulalem Abdo Moqbel; Çağlayan, Hatice Pelin; Öztulum, Samira Fatma Kurtoğlu; Zhao, Yuxin; Haşlak, Zeynep Pınar; Uzun, Alper; Keskin, Seda; PhD Student; PhD Student; Faculty Member; 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); College of Engineering; Graduate School of Sciences and Engineering; N/A; N/A; N/A; N/A; N/A; N/A; N/A; N/A; N/A; 59917; 40548Modification of the physicochemical properties of porous materials by using ionic liquids (ILs) has been widely studied for various applications. The combined advantages of ILs and porous materials provide great potential in gas adsorption and separation, catalysis, liquid-phase adsorption and separation, and ionic conductivity owing to the superior performances of the hybrid composites. In this review, we aimed to provide a perspective on the evolution of IL/porous material composites as a research field by discussing several different types of porous materials, including metal organic frameworks (MOFs), covalent organic frameworks (COFs), zeolites, and carbonaceous-materials. The main challenges and opportunities in synthesis methods, characterization techniques, applications, and future opportunities of IL/porous materials are discussed in detail to create a road map for the area. Future advances of the field addressed in this review will provide in-depth insights into the design and development of these novel hybrid materials and their replacement with conventional materials.