1. 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, izvirni znanstveni članek Opis: 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. Ključne besede: selective hydrodechlorination, heterogeneous catalysis, XANES analysis, EXAFS analysis Objavljeno v RUNG: 25.04.2024; Ogledov: 1438; Prenosov: 7 Celotno besedilo (446,63 KB) Gradivo ima več datotek! Več... |
2. Winning combination of Cu and Fe oxide clusters with an alumina support for low-temperature catalytic oxidation of volatile organic compoundsTadej Žumbar, Iztok Arčon, Petar Djinović, Giuliana Aquilanti, Gregor Žerjav, Albin Pintar, Alenka Ristić, Goran Dražić, Janez Volavšek, Gregor Mali, Margarita Popova, Nataša Zabukovec Logar, Nataša Novak Tušar, 2023, izvirni znanstveni članek Opis: A γ-alumina support functionalized with transition metals is one of the most widely used industrial catalysts for the total oxidation of volatile organic compounds (VOCs) as air pollutants at higher temperatures (280−450 °C). By rational design of a
bimetal CuFe-γ-alumina catalyst, synthesized from a dawsonite alumina precursor, the activity in total oxidation of toluene as a model VOC at a lower temperature (200−380
°C) is achieved. A fundamental understanding of the catalyst and the reaction mechanism is elucidated by advanced microscopic and spectroscopic characterizations as well as by temperature-programmed surface techniques. The nature of the metal−support bonding and the optimal abundance between Cu−O−Al and Fe−O−Al species in the catalysts leads to synergistic catalytic activity promoted by small amounts of iron (Fe/Al = 0.005).
The change in the metal oxide−cluster alumina interface is related to the nature of the
surfaces to which the Cu atoms attach. In the most active catalyst, the CuO6 octahedra are
attached to 4 Al atoms, while in the less active catalyst, they are attached to only 3 Al atoms. The oxidation of toluene occurs via the Langmuir−Hinshelwood mechanism. The presented material introduces a prospective family of low-cost and scalable oxidation catalysts with superior efficiency at lower temperatures. Ključne besede: Iron oxide clusters, copper oxide clusters, alumina support, synergistic effect, low-temperature total catalytic oxidation, toluene, Cu, Fe XANES, EXAFS Objavljeno v RUNG: 06.07.2023; Ogledov: 2306; Prenosov: 26 Celotno besedilo (11,05 MB) Gradivo ima več datotek! Več... |
3. Spectroscopic insights into the electrochemical mechanism of rechargeable calcium/sulfur batteriesAntonio Scafuri, Romain Berthelot, Klemen Pirnat, Alen Vižintin, Jan Bitenc, Giuliana Aquilanti, Dominique Foix, Rémi Dedryvère, Iztok Arčon, Robert Dominko, Lorenzo Stievano, 2020, izvirni znanstveni članek Opis: Calcium batteries represent a promising alternative to lithium metal systems. The combination of the low redox potential and low cost and the energy-dense calcium anode (2073 mAh/cm3, similar to 2044 mAh/cm3 for Li) with appropriate low-cost cathode materials such as sulfur could produce a game-changing technology in several fields of applications. In this work, we present the reversible activity of a proof-of-concept Ca/S battery at room temperature, characterized by a surprising medium-term cycling stability with low polarization, promoted by the use of a simple positive electrode made of sulfur supported on an activated carbon cloth scaffold, and a state-of-the-art fluorinated alkoxyborate-based electrolyte. Insights into the electrochemical mechanism governing the chemistry of the Ca/S system were obtained for the first time by combining X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. The mechanism implies the formation of different types of soluble polysulfide species during both charge and discharge at room temperature, and the formation of solid CaS at the end of discharge. The reversible electrochemical activity is proven by the reformation of elemental sulfur at the end of the following charge. These promising results open the way to the comprehension of emerging Ca/S systems, which may represent a valid alternative to Mg/S and Li/S batteries. Ključne besede: Calcium/Sulfur Batteries
EXAFS, XANES Objavljeno v RUNG: 17.10.2020; Ogledov: 3528; Prenosov: 0 Gradivo ima več datotek! Več... |
4. Effects of the molecular potential on coexcitations of valence electrons in the K-shell photoeffect of 3p and 4p elementsRobert Hauko, Jana Padežnik Gomilšek, Alojz Kodre, Iztok Arčon, Giuliana Aquilanti, 2019, izvirni znanstveni članek Opis: Photoabsorption spectra of gaseous hydrides of 3p (PH3, H2S, HCl) and 4p elements (GeH4, AsH3 , H2Se,
HBr) are measured in the energy region within 50 eV above the K edge, to study coexcitations of valence
electrons by photoeffect in the K shell. The analysis of the valence coexcitations is extended to Ar, Kr, and
SiH4. Relative probabilities and energies of states in the individual coexcitation channels are recovered by
modeling the spectral features with a minimal ansatz based on the features in the contiguous noble gas. The
extracted parameters are compared to the results of theoretical calculations for molecules (ORCA code) and
free atoms (Hartree-Fock code). The experimental results confirm that the valence coexcitations in the 3p and
4p hydride molecules can be satisfactorily described by a two-step process, with the shake of the outer electron
following the excitation of the core electron. The total probability—relative to the K-edge jump—of the shake-up
processes shows a steady decrease from 19% in Si to 14% in Cl, and from 15% in Ge to 12% in Br. The
experimental values for Ar (12%) and Kr (10%) are in accord with the trend. The dominant contribution is
the transition to quasiatomic orbitals, in contrast with the deeper coexcitation channels in hydride molecules
where transition to molecular orbitals prevails. Ključne besede: X-ray absorption spectra, gaseous hydrides, 3p K-edge spectra, DFT Objavljeno v RUNG: 05.09.2019; Ogledov: 3487; Prenosov: 0 Gradivo ima več datotek! Več... |
5. K-edge absorption spectra of isoelectronic gaseous hydrides: a combination of atomic and molecular channelsRobert Hauko, Jana Padežnik Gomilšek, Alojz Kodre, Iztok Arčon, Giuliana Aquilanti, 2018, objavljeni povzetek znanstvenega prispevka na konferenci Opis: The fine detail in the x-ray absorption spectra in the energy region of absorption edges
provides the insight into the mechanism of inner-shell photoexcitation: in particular in spectra of
free atoms or simple molecules, the simplest being gaseous hydrides [1-2].
Measured K edge absorption spectra of hydrides of 3p (PH3, H2S in HCl) and 4p (GeH4,
AsH3, H2Se, HBr) elements, and published data of 2p hydrides (CH4, NH3, H2O, HF) as well as
SiH4 [3-6] and the noble gases at the end of the isoelectronic series (Ne, Ar, Kr) are compared to
the respective calculated spectra, obtained by atomic HF86, GRASP codes [7] and molecular
DFT (Density functional theory) ORCA code [8]. For a clearer view of intraatomic processes,
the weak and simple structural (XAFS) signal of the molecule is removed from the spectra.
Among the spectral features below the continuum limit, those with the lowest energy
belong to the transition of the core electron to the lowermost free orbitals with the molecular
character. They are, as a rule, wider than the transitions to the higher orbitals with prevailing
atomic character. The theoretical description with DFT code without specific adaptations is
sufficient for a qualitative picture of the pre-edge structure. The fine structure immediately above
the K edge stems from the coexcitation of valence electrons. We have proved that the
coexcitations can be explained as a two-step process: the inner-shell photoeffect followed by the
shake-up of a valence electron predominantly to a free atomic orbital. This process is markedly
different from coexcitations of more tightly bound electrons [9].
In the collection of consecutive and homologous data, analyzed by a common procedure,
the reaction channels can be identified with better precision and reliability than in analysis of
individual spectra. Our analysis showed that the energies and probabilities of single-electron
transitions into the molecular orbitals are strongly affected by the symmetry of the molecule,
essentially in the same way in 3p and 4p homologues, but not in 2p homologues with a stronger
influence of the core charge. In transitions to atomic orbitals the influence of the molecular field
is negligible. Ključne besede: hidridi, rentgenska spektroskopija, XAFS Objavljeno v RUNG: 12.09.2018; Ogledov: 4613; Prenosov: 0 Gradivo ima več datotek! Več... |
6. K-edge absorption spectra of gaseous hydridesAlojz Kodre, Robert Hauko, Jana Padežnik Gomilšek, Iztok Arčon, Giuliana Aquilanti, 2018, objavljeni povzetek znanstvenega prispevka na konferenci Opis: X-ray absorption spectra in the energy region of absorption edges reveal fine details of the
mechanism of inner-shell photoexcitation: in particular in spectra of free atoms or simple
molecules, the simplest being gaseous hydrides [1-2]. In a collection of data from consecutive
and homologous elements, analyzed by a common procedure, the reaction channels can be
identified with better precision and reliability than in analysis of individual spectra.
Absorption spectra of the hydrides of 3p elements (PH3, H2S in HCl) were measured at the
XAFS beamline of the Elettra synchrotron in Trieste: a new type of adjustable absorption cell
for measurement of noxious gases at room temperature and at low photon energies was
developed for the purpose. For the analysis, data from an earlier experiment on 4p hydrides
(GeH4, AsH3, H2Se, HBr), and published data of 2p hydrides (CH4, NH3, H2O, HF) [3-4] as
well as SiH4 and the noble gases concluding the isoelectronic series (Ne, Ar, Kr) were
adopted. The spectra are compared to respective calculated spectra, obtained by atomic HF86,
GRASP codes and molecular DFT (Density functional theory) ORCA code [5].
Our analysis of the pre-edge structures showed that the energies and probabilities of singleelectron
transitions into the lowermost orbitals with the molecular character were strongly
affected by the symmetry of the molecule, essentially in the same way in 3p and 4p
homologues, but not in 2p homologues with a stronger influence of the core charge. In
transitions to higher orbitals with prevailing atomic character the influence of the molecular
field is negligible.
The fine structure immediately above the K edge stems from the coexcitation of valence
electrons. These coexcitations can be explained as a two-step process: the inner-shell
photoeffect followed by the shake-up of a valence electron predominantly to a free atomic
orbital. The process is markedly different from coexcitations of more tightly bound electrons
[3]. The results of relative shake-up probabilities can be compared to results of emission
spectroscopies, the probabilities of double excitation to bound states show a correlation with
the dissociation probability of the molecule. Ključne besede: večelektronske vzbuditve, hidridi, rentgenska absorpcijska spektroskopija Objavljeno v RUNG: 12.09.2018; Ogledov: 4950; Prenosov: 0 Gradivo ima več datotek! Več... |
7. Fluorinated ether based electrolyte for high-energy lithium-sulfur batteries : Li [sup] + solvation role behind reduced polysulfide solubilitySara Drvarič Talian, Steffen Jeschke, Alen Vižintin, Klemen Pirnat, Iztok Arčon, Giuliana Aquilanti, Patrik Johansson, Robert Dominko, 2018, objavljeni povzetek znanstvenega prispevka na konferenci Ključne besede: Li-žveplive baterije, XANES, polisulfidi Objavljeno v RUNG: 12.09.2018; Ogledov: 3923; Prenosov: 0 Gradivo ima več datotek! Več... |
8. Polysulfides formation in different electrolytes from the perspective of X-ray absorption spectroscopyRobert Dominko, Alen Vižintin, Giuliana Aquilanti, Lorenzo Stievano, Maria Joseph Helen, Anji Reddy Munnangi, Maximilian Fichtner, Iztok Arčon, 2018, izvirni znanstveni članek Opis: Li-S batteries are promising energy storage technology for the future, however there two major problems remained which need to be
solved before successful commercialization. Capacity fading due to polysulfide shuttle and corrosion of lithium metal are directly
connected with the type and quantity of electrolyte used in the cells. Several recent works show dependence of the electrochemical
behavior of Li-S batteries on type of the electrolyte. In this work we compare and discuss a discharge mechanism of sulfur conversion
in three different electrolytes based on measurements with sulfur K-edge XAS. The sulfur conversion mechanism in the ether based
electrolytes, the most studied type of solvents in the Li-S batteries, which are enabling high solubility of polysulfides are compared
with the fluorinated ether based electrolytes with a reduced polysulfide solubility and in carbonate based electrolytes with the sulfur
confined into a ultramicroporous carbon. In all three cases the sulfur reduction proceeds through polysulfide intermediate phases
with a difference on the type polysulfides detected at different steps of discharge. Ključne besede: Li-S batteries, operando sulphur K-edge XANES, EXAFS, Li-polysulphides Objavljeno v RUNG: 01.06.2018; Ogledov: 4184; Prenosov: 0 Gradivo ima več datotek! Več... |
9. A Mechanistic Study of Magnesium Sulfur BatteriesAna Robba, Alen Vižintin, Jan Bitenc, Gregor Mali, Iztok Arčon, Matjaž Kavčič, Matjaž Žitnik, Klemen Bučar, Giuliana Aquilanti, Charlotte Martineau-Corcos, Anna Randon-Vitanova, Robert Dominko, 2017, izvirni znanstveni članek Opis: Magnesium sulfur batteries are considered as attractive energy storage devices due to the
abundance of electrochemically active materials and high theoretical energy density. Here we
report the mechanism of a Mg-S battery operation, which was studied in the presence of
simple and commercially available salts dissolved in a mixture of glymes. The electrolyte
offers high sulfur conversion into MgS in the first discharge with low polarization. The
electrochemical conversion of sulfur with magnesium proceeds through two well-defined
plateaus, which correspond to the equilibrium between sulfur and polysulfides (high-voltage
plateau) and polysulfides and MgS (low-voltage plateau). As shown by XANES, RIXS and
NMR studies, the end discharge phase involves MgS with Mg atoms in a tetrahedral
environment resembling the wurtzite structure, while chemically synthesized MgS crystalizes
in the rock-salt structure with octahedral coordination of magnesium. Ključne besede: magnesium, sulfur, rechargeable batteries, XAS, NMR Objavljeno v RUNG: 19.10.2017; Ogledov: 5120; Prenosov: 0 Gradivo ima več datotek! Več... |
10. Edge profiles in K shell photoabsorption spectra of gaseous hydrides of 3p elements and homologuesRobert Hauko, Jana Padežnik Gomilšek, Alojz Kodre, Iztok Arčon, Giuliana Aquilanti, izvirni znanstveni članek Opis: Photoabsorption spectra of gaseous hydrides of 3p elements (PH3, H2S, HCl) are measured in the energy region of
photoexcitations pertaining to K edge. The analysis of the edge profile is extended to hydrides of 4p series (GeH4,
AsH3, H2Se, HBr) from an earlier experiment, and to published spectra of 2p hydrides (CH4, NH3, H2O, HF) and
noble gases Ar, Kr and Ne and SiH4. The edge profiles are modelled with a linear combination of lorentzian
components, describing excitations to individual bound states and to continuum. Transition energies and
probabilities are also calculated in the non-relativistic molecular model of the ORCA code, in good agreement
with the experiment. Edge profiles in the heavier homologues are closely similar, the symmetry of the molecule
governs the transitions to the lowest unoccupied orbitals. In 2p series the effect of the strong nuclear potential
prevails. Transitions to higher, atomic-like levels remain very much the same as in free atoms. Ključne besede: X-ray absorption spectra, gaseous hydrides, 3p K-edge spectra, DFT Objavljeno v RUNG: 23.08.2017; Ogledov: 4251; Prenosov: 0 Gradivo ima več datotek! Več... |