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101.
Effect of Na, Cs and Ca on propylene epoxidation selectivity over CuOx/SiO2 catalysts studied by catalytic tests, in-situ XAS and DFT
Janvit Teržan, Matej Huš, Iztok Arčon, Blaž Likozar, Petar Djinović, 2020, original scientific article

Abstract: This research focuses on epoxidation of propylene over pristine, Na, Ca and Cs modified CuOx/SiO2 catalysts using O2. The selectivity of the reaction is analyzed using a combination of catalytic tests, in-situ XAS and DFT calculations. The initially present subnanometer CuO clusters are present in all catalysts which re-disperse/flatten during reaction. During catalytic reaction, the Cu1+ becomes the predominant oxidation state. There is no correlation between propylene oxide (PO) selectivity and copper oxidation state. DFT analysis of the propylene reaction pathway revealed that Na, Cs, and Ca addition decreases the bonding strength of propylene to CuO and decreases the O2 activation barrier, while simultaneously increase the exothermicity of O2 dissociation. The Na induced Cu-O bond modification decreases the activation barrier from 0.87 to 0.71 eV for the oxametallacycle (OMC) ring closure (first step in the reaction pathway favoring selectivity towards PO) compared to pristine 5Cu catalyst. At the same time, we observed an increase (from 0.45 to 0.72 eV) of the barrier for the abstraction of allylic hydrogen. The opposite effect is achieved by Ca addition: the activation barrier for OMC ring closure increases to 1.08 eV and that for allylic hydrogen stripping decreases to 0.16 eV.
Found in: osebi
Keywords: Alkali modification, propylene epoxidation, reaction mechanism, copper oxide, activation barrier.
Published: 05.06.2020; Views: 450; Downloads: 0
.pdf Fulltext (22,78 MB)

102.
103.
Podobe znanja
Nina Slaček, Iztok Arčon, radio or television broadcast

Abstract: Razvoj novih materialov, nanotehnologije, molekularne biologije in še številnih drugih področij sodobnih znanosti je tesno povezan s podrobnim razumevanjem tega, kaj se dejansko dogaja na molekularnem oziroma atomskem nivoju. Za razvoj denimo novih nanostrukturnih materialov za baterije prihodnosti je nujno videti, kaj se v njih dejansko dogaja med samim delovanjem. To omogoča rentgenska absorpcijska spektroskopija s sinhrotronsko svetlobo. »Ko z rentgenskim žarkom posvetimo na snov, iz atoma izbijemo elektron in ta odleti v okolico, se od nje odbija in nam na ta način sporoči, kaj se v njegovi okolici nahaja,« razlaga osnovni princip te metode prof. dr. Iztok Arčon. Na ta način je mogoče pridobiti številne ključne podatke, ki pogosto na glavo postavijo predhodne domneve raziskovalcev. A za takšne raziskave je nujen sinhrotron. Tovrstnih pospeševalnikov ni veliko in merilni čas na sinhrotronu je potrebno pridobiti z vrhunsko zastavljenimi raziskavami. A tokratni gost Podob znanja, dr. Iztok Arčon, redni profesor na Univerzi v Novi Gorici, ima po zaslugi svojega znanstvenega dela na tem področju na široko odprta vrata, sodeluje pa raziskovalnimi skupinami z zelo različnih področij. Letos je za svoje dosežke prejel tudi Preglovo nagrado. Foto: iz osebnega arhiva Iztoka Arčona
Found in: osebi
Summary of found: ...osnovni princip te metode prof. dr. Iztok Arčon. Na ta način je mogoče pridobiti številne ključne...
Keywords: rentgenska absorpcijska spektroskopija, sinhrotronsko sevanje, raziskave nanomaterialov, Preglova nagrada 2020
Published: 19.10.2020; Views: 204; Downloads: 0
.pdf Fulltext (160,86 KB)

104.
Effect of the Morphology of the High-Surface-Area Support on the Performance of the Oxygen-Evolution Reaction for Iridium Nanoparticles
Leonard Moriau, Marjan Bele, Živa Marinko, Francisco Ruiz-Zepeda, Gorazd Koderman, Martin Šala, Angelija Kjara Šurca, Janez Kovač, Iztok Arčon, Primož Jovanovič, Nejc Hodnik, Luka Suhadolnik, 2021, original scientific article

Abstract: The development of affordable, low-iridium-loading, scalable, active, and stable catalysts for the oxygen-evolution reaction (OER) is a requirement for the commercialization of proton-exchange membrane water electrolyzers (PEMWEs). However, the synthesis of high-performance OER catalysts with minimal use of the rare and expensive element Ir is very challenging and requires the identification of electrically conductive and stable high-surface-area support materials. We developed a synthesis procedure for the production of large quantities of a nanocomposite powder containing titanium oxynitride (TiONx) and Ir. The catalysts were synthesized with an anodic oxidation process followed by detachment, milling, thermal treatment, and the deposition of Ir nanoparticles. The anodization time was varied to grow three different types of nanotubular structures exhibiting different lengths and wall thicknesses and thus a variety of properties. A comparison of milled samples with different degrees of nanotubular clustering and morphology retention, but with identical chemical compositions and Ir nanoparticle size distributions and dispersions, revealed that the nanotubular support morphology is the determining factor governing the catalyst’s OER activity and stability. Our study is supported by various state-of-the-art materials’ characterization techniques, like X-ray photoelectron spectroscopy, scanning and transmission electron microscopies, Xray powder diffraction and absorption spectroscopy, and electrochemical cyclic voltammetry. Anodic oxidation proved to be a very suitable way to produce high-surface-area powder-type catalysts as the produced material greatly outperformed the IrO2 benchmarks as well as the Ir-supported samples on morphologically different TiONx from previous studies. The highest activity was achieved for the sample prepared with 3 h of anodization, which had the most appropriate morphology for the effective removal of oxygen bubbles.
Found in: osebi
Keywords: electrocatalysis, oxygen-evolution reaction, TiONx-Ir powder catalyst, iridium nanoparticles, anodic oxidation, morphology−activity correlation
Published: 04.01.2021; Views: 45; Downloads: 0
.pdf Fulltext (6,36 MB)

105.
Ni več treba tipati v temi!
Iztok Arčon, 2020, other performed works

Abstract: Vidna svetloba, ki jo lahko zaznajo naše oči, predstavlja le droben delček v širokem spektru različnih vrst svetlobe, ki jih ponuja narava. V predavanju si bomo ogledali, kako so velika znanstvena odkritja o nenavadnih lastnostih svetlobe odprla pogled neposredno v čarobni svet atomov, omogočila razvoj sodobnih merskih tehnologij in s tem izjemen preboj v razvoju novih tehnološko zanimivih materialov.
Found in: osebi
Keywords: svetloba, rentgenske spektroskopije, karakterizacija materialov
Published: 21.01.2021; Views: 11; Downloads: 0
.pdf Fulltext (256,81 KB)

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