Research Project: Grafen Aerojel Destekli Tek Atom Merkezli İridyum Katalizörlerinin Kısmı Hidrojenleme Seçiciliklerinin Yüzey Modifikasyonları İle Kontrol Edilmesi
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Contributors
Funders
ID
TB.00369
Authors
Uzun, Alper
Faculty Member
Publications
Ionic liquid sheath stabilizes atomically dispersed reduced graphene aerogel-supported iridium complexes during ethylene hydrogenation catalysis
(Wiley, 2022) Jalal, Ahsan; Öztulum, Samira Fatma Kurtoğlu; Ünal, Uğur; Uzun, Alper; Yalçın, Kaan; Zhao, Yuxin; Hoffman, Adam S.; Gates, Bruce C.; Bare, Simon R.; Department of Chemistry; Department of Chemical and Biological Engineering; KUTEM (Koç University Tüpraş Energy Center); KUYTAM (Koç University Surface Science and Technology Center); Yes; College of Engineering; College of Sciences; Research Center
An 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.
Atomically dispersed reduced graphene aerogel-supported iridium catalyst with an iridium loading of 14.8 wt %
(American Chemical Society (ACS), 2019) Babucci, Melike; Öztuna, Feriha Eylül Saraç; Ünal, Uğur; Uzun, Alper; Debefve, Louise M.; Boubnov, Alexey; Bare, Simon R.; Gates, Bruce C.; Department of Chemistry; Department of Chemical and Biological Engineering; KUYTAM (Koç University Surface Science and Technology Center); KUTEM (Koç University Tüpraş Energy Center); Yes; College of Engineering; College of Sciences; Research Center
Atomically dispersed iridium complexes were anchored on a reduced graphene aerogel (rGA) by the reaction of Ir(CO)(2)(acac) [acac = acetonylacetonato] with oxygen-containing groups on the rGA. Characterization by X-ray absorption, infrared, and X-ray photoelectron spectroscopies and atomic resolution aberration-corrected scanning transmission electron microscopy demonstrates atomically dispersed iridium, at the remarkably high loading of 14.8 wt %. The rGA support offers sites for metal bonding comparable to those of metal oxides, but with the advantages of high density and a relatively high degree of uniformity, as indicated by the same turnover frequencies for catalytic hydrogenation of ethylene at low and high iridium loadings. The atomic dispersion at a high metal loading- and the high density of catalytic sites per unit of reactor volume, a key criterion for practical catalysts-set this catalyst apart from those reported.
Transformation of reduced graphene aerogel-supported atomically dispersed iridium into stable clusters approximated as Ir6 during ethylene hydrogenation catalysis
(Elsevier, 2022) Öztulum, Samira Fatma Kurtoğlu; Yalçın, Kaan; Zhao, Yuxin; Çağlayan, Hatice Pelin; Ünal, Uğur; Uzun, Alper; Hoffman, Adam S.; Gates, Bruce C.; Bare, Simon R.; Department of Chemistry; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; KUTEM (Koç University Tüpraş Energy Center); Yes; College of Engineering; College of Sciences; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING; Research Center
Transformation of atomically dispersed reduced graphene aerogel (rGA)-supported complexes, IrI(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 Ir4 during reaction at 100 °C in flowing equimolar ethylene and H2. The Ir4 clusters transformed into clusters well approximated as Ir6 when the feed molar ratio was switched to H2:C2H4 = 2 and remained stable in pure H2 at 100 °C. Catalyst performance data show that hydrogenation activity increased with metal nuclearity in the order of atomically dispersed iridium/rGA≪ Ir4/rGA < Ir6/rGA. Continuous scan X-ray absorption data, complemented with aberration-corrected scanning transmission electron microscopy images, demonstrate that the supported clusters approximated as Ir6 are stable even in H2 at atmospheric pressure and 100 °C. These supported iridium clusters are among the ones having the highest metal loadings reported for a supported metal cluster catalyst.
Active sites and their individual turnover frequencies for ethylene hydrogenation on reduced graphene aerogel
(American Chemical Society, 2024) Kanat, Gizem Hasibe; Öztulum, Samira Fatma Kurtoğlu; Öztuna, Feriha Eylül Saraç; Ünal, Uğur; Uzun, Alper; Yalçın, Kaan; Department of Chemistry; Department of Chemical and Biological Engineering; KUTEM (Koç University Tüpraş Energy Center); KUYTAM (Koç University Surface Science and Technology Center); Yes; College of Sciences; College of Engineering; Research Center; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING
Graphene 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 degrees 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 sp(2) 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.
