1. Structural and chemical analysis of hard carbon negative electrode for Na-ion battery with X-ray Raman scattering and solid-state NMR spectroscopyAva Rajh, Matej Gabrijelčič, Blaž Tratnik, Klemen Bučar, Iztok Arčon, Marko Petric, Robert Dominko, Alen Vižintin, Matjaž Kavčič, original scientific article Abstract: This study explores the structural changes of hard carbon (HC) negative electrodes in sodium-ion batteries induced by insertion of Na ions during sodiation. X-ray Raman spectroscopy (XRS) was used to record both C and Na K-edge absorption spectra from bulk HC anodes carbonized at different temperatures and at several points during sodiation and desodiation. Comparing the [pi]*/[sigma]*
regions in the C K-edge spectra sp2/sp3 hybridization ratio of material was determined. Higher carbonization temperatures led to increased order in graphitic structure and shorter bond lengths. Sodiation caused a decrease in graphitic layer order due to inserted Na ions. Complementary operando solid state 23Na nuclear magnetic resonance (ssNMR) studies confirmed the structural changes, while showing pore filling mechanism, which is not observed in ex situ measurements, primarily at higher carbonization temperatures. XRS analysis of Na K-edge spectra revealed systematic variations in the solid electrolyte interface (SEI) composition during cycling. Changes in XRS spectra were attributed to both SEI composition alterations, accompanied by the insertion/adsorption of Na ions at defect sites within the carbon structure.
Keywords: hard carbon, RIXS, carbon XANES, EXAFS, NMR, Na battery
Published in RUNG: 10.09.2024; Views: 463; Downloads: 0
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2. GasesAlojz Kodre, Iztok Arčon, Jana Padežnik Gomilšek, 2024, scientific entry in dictionary, encyclopaedia or lexicon Abstract: X-ray absorption spectroscopy of gases is seldom used for structural analysis,
except in as much as the extended X-ray absorption fine-structure (EXAFS)
signal is used to monitor some specific molecular process. Gas spectroscopy,
however, has been the main tool in the systematic study of higher-order
photoabsorption processes, multielectron photoexcitations (MEEs), which were
introduced with an experiment at the K edge of argon. Along with noble gases,
where MEEs are studied in the pure form, free of the structural signal,
measurements have been extended to monatomic metal vapours, although at the
cost of considerable experimental difficulties. Several types of absorption cells
have been devised, among them the ceramic double cell and the heat-pipe cell
for experiments in the low-energy region. In a high-temperature oven with
considerable technical refinement, edge profiles of nonvolatile metals were
measured up to 2500 K. Edge profiles and MEEs, which are strongly dependent
on electron correlation, provide sensitive tests of the theory of atomic and
molecular structure.
Keywords: X-ray absorption spectroscopy, absorption cells, gas and vapour samples, multielectron photoexcitation, effects of electron
correlation
Published in RUNG: 05.09.2024; Views: 396; Downloads: 2
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4. XAS analysis of bifunctional Ni/ZSM-5 catalystsIztok Arčon, Hue-Tong Vu, Goran Dražić, Janez Volavšek, Gregor Mali, Nataša Zabukovec Logar, Nataša Novak Tušar, 2024, published scientific conference contribution abstract Abstract: In a bifunctional Ni/ZSM-5 zeolite type catalyst, catalytic properties are usually tuned via varying Al
and Ni contents [1]. Here we present a systematic structural study of the Ni/ZSM-5 materials by Ni
K-edge XANES and EXAFS analyses, to monitor the changes of local structure and chemical state
of Ni species in the catalysts as a function of Al and Ni content. A series of Ni/ZSM-5 type zeolites
with different Al to Si and Ni to Si molar ratios were synthesized by a “green”, template free technique
[2]. With a combination of XAS, XRD and TEM we resolved the changes in the local environment
of Ni species induced by the different Al contents in the
Ni/ZSM-5 catalysts.
Ni species in Ni/ZSM-5 exist as NiO nanocrystals and as
charge compensating Ni2+ cations. The Ni K-edge
XANES and EXAFS results enabled the quantification
of Ni-containing species. At a low Al to Si ratio (nAl/nSi
< 0.04), the NiO nanoparticles predominate in the
samples and account for over 65% of Ni phases.
However, NiO is outnumbered by Ni2+ cations attached
to the zeolite framework in ZSM-5 with a high Al to Si
ratio (nAl/nSi = 0.05) due to a higher number of
framework negative charges imparted by Al. The
obtained results show that the number of highly reducible
and active NiO nanocrystals is strongly correlated with
the framework Al sites present in Ni/ZSM-5 zeolites.
Keywords: Ni EXAFS, XANES Ni/ZSM-5 catalyst
Published in RUNG: 05.07.2024; Views: 693; Downloads: 3
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5. Non-oxidative calcination enhances the methane dry reforming performance of ▫$Ni/CeO_{2−x}$▫ catalysts under thermal and photo-thermal conditionsKristijan Lorber, Vasyl Shvalya, Janez Zavašnik, Damjan Vengust, Iztok Arčon, Matej Huš, Andraž Pavlišič, Janvit Teržan, Uroš Cvelbar, Blaž Likozar, Petar Djinović, 2024, original scientific article Abstract: We analyzed the effect of the calcination atmosphere and visible-light contribution to an accelerated
reaction rate and improved H2 selectivity over 2 wt% Ni/CeO2−x nanorod catalysts. Spectroscopic and
structural characterization was performed by operando DRIFTS, in situ Raman, UV-vis and XAS
techniques, which were complemented by DFT calculations. Calcination in an argon or H2 atmosphere
yields 15% more active catalysts in the thermally driven reaction, which are also more susceptible to
light-induced rate acceleration compared to the catalyst calcined in air. The most active 2Ni/CeO2
catalyst calcined in hydrogen converts methane with a rate of 7.5 mmol (gcat min)−1 and produces a H2/
CO ratio of 0.6 at 460 °C when stimulated by a combination of visible light and thermal energy. In the
absence of visible light illumination and at an identical catalyst temperature, the achieved methane rate
was 4.2 mmol (gcat min)−1 and the H2/CO ratio was 0.49. The non-oxidative calcination improves nickel
dispersion and the formation of subnanometer sized Ni clusters, together with a higher abundance of
surface and bulk oxygen vacancies in ceria nanorods. The Ni–Ov–Ce3+components constitute the
catalytically active sites under visible light illumination, which enable the DRM reaction to proceed with
an Ea value of 20 kJ mol−1. Visible light also induces the following changes in the 2Ni/CeO2−x catalyst
during the DRM reaction: (1) decomposition and desorption of carbonates from the nickel–ceria
interface sites, (2) reduced population of nickel surface with carbonyl species and (3) promoted
adsorption and dissociation of methane.
Keywords: methane dry reforming performance, calcination
Published in RUNG: 05.07.2024; Views: 781; Downloads: 16
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6. Nadzor kakovosti pri izdelavi delilnikov testa : magistrsko deloPrimož Saksida, 2024, master's thesis Abstract: Magistrsko delo obravnava stroj za deljenje testa iz stališča natančnosti deljenja testa. Shematsko so prikazani ključni elementi delilnega stroja, ki vplivajo na natančnost deljenja testa. Opisana je njihova primarna naloga v stroju. Shematsko je prikazano tudi delovanje samega stroja. Opravljene so bile dimenzijske meritve ključnih elementov na populaciji 15 strojev ter izvedena je bila analiza meritev. Dimenzijske meritve posameznih elementov smo izvedli na 3D koordinatnem merilnem sistemu z mikronsko natančnostjo. Analizirali smo tudi elemente, ki so bili že v uporabi v delilnih strojih, pri katerih so bila ugotovljena odstopanja od pričakovanih zahtev za natančnost delitev testa. Z namenom ugotovitve, kako določen element vpliva na natančnost delitve testa, je bil narejen preizkus delovanja stroja z novim, dimenzijsko dobrim elementom in za primerjavo z dimenzijsko slabim elementom. Kot rezultat teh analiz je sledila nadgradnja kontrolnih postopkov ključnih elementov stroja. V ta namen smo določene kontrolne postopke definirali na novo.
Keywords: kontrola kakovosti, delilniki testa, kontrolni postopki, dimenzijske meritve, strojni elementi, magistrske naloge
Published in RUNG: 15.05.2024; Views: 1140; Downloads: 8
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7. Synthesis of helional by hydrodechlorination reaction in the presence of mono- and bimetallic catalysts supported on aluminaOreste Piccolo, Iztok Arčon, Das Gangadhar, Giuliana Aquilanti, Andrea Prai, Stefano Paganelli, Manuela Facchin, Valentina Beghetto, 2024, original scientific article Abstract: Hydrodechlorination reaction of 3-(benzo-1,3-dioxol-5-yl)-3-chloro-2-methylacrylaldehyde in the presence of different low metal content heterogeneous mono- or bimetallic catalysts was tested for the synthesis of the fragrance Helional® (3-[3,4-methylendioxyphenyl]-2-methyl-propionaldehyde). In particular, mono Pd/Al2O3, Rh/Al2O3 or bimetallic Pd-Cu/Al2O3, Rh-Cu/Al2O3 catalysts were tested in different reaction conditions from which it emerged that mono-Rh/Al2O3 was the best performing catalyst, allowing achievement of 100% substrate conversion and 99% selectivity towards Helional® in 24 h at 80 °C, p(H2) 1.0 MPa in the presence of a base. To establish correlations between atomic structure and catalytic activity, catalysts were characterized by Cu, Rh and Pd K-edge XANES, EXAFS analysis. These characterizations allowed verification that the formation of Pd-Cu alloys and the presence of Cu oxide/hydroxide species on the surface of the Al2O3 support are responsible for the very low catalytic efficiency of bimetallic species tested.
Keywords: selective hydrodechlorination, heterogeneous catalysis, XANES analysis, EXAFS analysis
Published in RUNG: 25.04.2024; Views: 1438; Downloads: 7
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8. Resolving a structural issue in cerium-nickel-based oxide : single compound or a two-phase system?Jelena Kojčinović, Dalibor Tatar, Stjepan Šarić, Cora Pravda Bartus, Andraž Mavrič, Iztok Arčon, Zvonko Jagličić, Maximilian Mellin, Marcus Einert, Angela Altomare, Rocco Caliandro, 2023, original scientific article Abstract: CeNiO3 has been reported in the literature in the last few years as a novel LnNiO3 compound with promising applications in different catalytic fields, but its structure has not been correctly reported so far. In this research, CeNiO3 (RB1), CeO2 and NiO have been synthesized in a nanocrystalline form using a modified citrate aqueous sol-gel route. A direct comparison between the equimolar physical mixture (n(CeO2) : n(NiO) = 1:1) and a compound RB1 was made. Their structural differences were investigated by laboratory powder X-ray diffraction (PXRD), selected area electron diffraction (SAED), transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy detector (EDS), and Raman spectroscopy. The surface of the compounds was analyzed by X-ray photoelectron spectroscopy (XPS), while the thermal behaviour was explored by thermogravimetric analysis (TGA). Their magnetic properties were also investigated with the aim of exploring the differences between these two compounds. There were clear differences between the physical mixture of CeO2 + NiO and RB1 presented by all of these employed methods. Synchrotron methods, such as atomic pair distribution function analysis (PDF), X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) were used to explore the structure of RB1 in more detail. Three different models for the structural solution of RB1 were proposed. One structural solution proposes that RB1 is a single-phase pyrochlore compound (Ce2Ni2O7) while the other two solutions suggest that RB1 is a two-phase system of either CeO2 + NiO or Ce1–xNixO2 and NiO.
Keywords: cerium oxide, nickel oxide, crystallography
Published in RUNG: 22.12.2023; Views: 1776; Downloads: 9
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9. Insight into the interdependence of Ni and Al in bifunctional Ni/ZSM-5 catalysts by Ni K-edge XAS analysisIztok Arčon, Hue-Tong Vu, Goran Dražić, Janez Volavšek, Gregor Mali, Nataša Zabukovec Logar, Nataša Novak Tušar, 2023, published scientific conference contribution abstract Abstract: Catalyst design is crucial for improving catalytic activity and product selectivity. In a bifunctional Ni/ZSM-5
zeolite type catalyst, catalytic properties are usually tuned via varying Al and Ni contents [1]. While changes in
acid properties associated with Al sites are usually closely investigated, Ni phases, however, receive inadequate
attention. Herein, we present a systematic structural study of Ni in the Ni/ZSM-5 materials by Ni K-edge
XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure) analyses,
to monitor the local structure and chemical state of Ni species in the catalysts. In combination with XRD and
TEM we resolved the changes in the local environment of Ni species induced by the different Al contents of
the parent ZSM-5 prepared by a “green”, template free technique [2].
Ni species in Ni/ZSM-5 exist as NiO crystals (3–50 nm) and as charge compensating Ni2+ cations. The Ni Kedge
XANES and EXAFS results enabled the quantification of Ni-containing species. At a low Al to Si ratio
(nAl/nSi < 0.04), the NiO nanoparticles predominate in the samples and account for over 65% of Ni phases.
However, NiO is outnumbered by Ni2+ cations attached to the zeolite framework in ZSM-5 with a high Al to Si
ratio (nAl/nSi = 0.05) due to a higher number of framework negative charges imparted by Al. The obtained
results show that the number of highly reducible and active NiO crystals is strongly correlated with the
framework Al sites present in ZSM-5 zeolites, which depend greatly on the synthesis conditions. Therefore,
this kind of study is beneficial for any further investigation of the catalytic activities of Ni/ZSM-5 and other
metal-modified bifunctional catalysts.
Keywords: Ni/ZSM-5 catalysts, Ni EXAFS, XANES
Published in RUNG: 19.09.2023; Views: 1562; Downloads: 5
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10. Periodic anti-phase boundaries and crystal superstructures in ▫$PtCu_3$▫ nanoparticles as fuel cell electrocatalystsAna Rebeka Kamšek, Anton Meden, Iztok Arčon, Primož Jovanovič, Martin Šala, Francisco Ruiz-Zepeda, Goran Dražić, Miran Gaberšček, Marjan Bele, Nejc Hodnik, 2023, original scientific article Published in RUNG: 19.09.2023; Views: 1648; Downloads: 9
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