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31.
Alternative Recovery and Valorization of Metals from Exhausted Catalytic Converters in a New Smart Polymetallic Catalyst
Oreste Piccolo, Laura Sperni, Michele Gallo, Katarina Vogel-Mikuš, Iztok Arčon, Franco Baldi, Sebastiano Tieuli, Stefano Paganelli, 2019, original scientific article

Abstract: A new metals-polymeric composite, Metx-EPS (I), was prepared to be used as catalyst in water or in two-phase aqueous conditions. The metals source was an exhausted catalytic converter that was grinded and treated with an acidic solution at room temperature. After filtration, the solution was concentrated, neutralized and added to a broth of Klebsiella oxytoca DSM 29614 to produce (I) where metals are embedded in a peculiar polysaccharide structure (EPS). The composite was easily recovered from the fermentation broth and purified. The process protocol was verified many times and was shown to be reproducible satisfactorily. The % recovery of metals, originally present in the converter, was good as determined by atomic absorption. The morphology and the chemical state of main metals in (I) were investigated by X-ray absorption spectroscopy methods (XANES and EXAFS). No metallic alloy seems to be evident. The catalytic activity and a possible synergic effect due to the presence of the different metals was valuated in the hydrogenation of some substrates, valuable precursors for theproduction of fine chemicals.
Found in: ključnih besedah
Summary of found: ...investigated by X-ray absorption spectroscopy methods (XANES and EXAFS). No metallic alloy seems to be evident. The...
Keywords: Biogenerated polymetallic exopolysaccharide, biphasic catalysis, hydrogenation, metals-polymeric composite, new catalyst from metallic wastes, EXAFS, XANES
Published: 06.05.2019; Views: 1119; Downloads: 0
.pdf Fulltext (2,87 MB)

32.
Unraveling the arrangement of Al and Fe within the framework explains the magnetism of mixed-metal MIL-100(Al,Fe)
Gregor Mali, Matjaž Mazaj, Iztok Arčon, Darko Hanžel, Denis Arčon, Zvonko Jagličić, 2019, original scientific article

Abstract: Properties of mixed-metal MOFs depend on the distribution of different metals within their frameworks. Determination of this distribution is often very challenging. Using an example of aluminum- and iron-containing MIL-100, we demonstrate that 27Al NMR spectroscopy, when combined with first-principles calculations and magnetic, X-band electron paramagnetic resonance, Fe K-edge extended X-ray absorption fine structure, and Mössbauer measurements, enables one to accurately determine the arrangement of Al and Fe within the metal trimers, which are the basic building units of MIL-100. In this particular material, the incorporation of Fe and Al on the framework metal sites is random. Crucial for deciphering the arrangement is detecting NMR signals, shifted because of the strong hyperfine interaction between the 27Al nuclei and the unpaired electronic spins of Fe3+ ions, assigning the shifted signals aided by first-principles calculations of hyperfine couplings, and quantitatively evaluating the NMR intensities and the measured effective magnetic moment.
Found in: ključnih besedah
Summary of found: ...Fe EXAFS, XANES, MIL100, MOF, magnetizem...
Keywords: Fe EXAFS, XANES, MIL100, MOF, magnetizem
Published: 26.03.2019; Views: 1259; Downloads: 0
.pdf Fulltext (2,57 MB)

33.
Synthesis of a Cu/ZnO Nanocomposite by Electroless Plating for the Catalytic Conversion of CO2 to Methanol
Maja Pori, Iztok Arčon, Marjan Marinšek, Goran Dražić, Blaž Likozar, Zorica Crnjak Orel, Damjan Lašič Jurković, 2019, original scientific article

Abstract: The process of methanol synthesis based on the hydrogenation of CO2 was investigated over binary Cu/ZnO catalyst materials, prepared by applying a novel electroless plating fabrication method. The activity of the produced catalytic samples was determined at temperature range between 200 and 300 °C and the feedstock conversion data were supplemented with a detailed microstructure analysis using high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD) and Cu and Zn K-edge, X-ray absorption near-edge structure (XANES) measurements and extended X-ray absorption fine-structure (EXAFS) measurements. It was confirmed that the disorder in the Cu crystallites created unique geometrical situations, which acted as the additional reactive centres for the adsorption of the reactant molecule species. Copper and zinc structural synergy (spill-over) was also demonstrated as being crucial for the carbon dioxide’s activation. EXAFS and XANES results provide strong evidence for surface alloying between copper and zinc and thus the present results demonstrate new approach applicable for explaining metal–support interactions.
Found in: ključnih besedah
Summary of found: ...structure (XANES) measurements and extended X-ray absorption fine-structure ( EXAFS) measurements. It was confirmed that the disorder...
Keywords: EXAFS, CuZn alloy, Spillover mechanism, CO2 valorization, Electroless deposition method, Heterogeneous catalysis
Published: 12.04.2019; Views: 1399; Downloads: 0
.pdf Fulltext (1,92 MB)

34.
New Insights into Manganese Local Environment in MnS-1Nanocrystals
Alenka Ristić, Matjaž Mazaj, Iztok Arčon, Nina Daneu, Nataša Zabukovec Logar, Roger Glaser, Nataša Novak Tušar, 2019, original scientific article

Abstract: Manganese plays an important role in redox catalysis using zeolites as inorganic support materials, but the formation of the preferred redox manganese species (framework or extraframework) is still not well understood. Herein, the influence of the amount of manganese together with conventional and microwave-assisted hydrothermal synthesis paths on the formation of manganese species within the zeolite silicalite-1 (S-1) with MFI structure was investigated. It was found out that both synthesis procedures led to the formation of framework and extraframework manganese species, but in different molar ratios. However, the conventional synthesis procedure with all Mn/Si molar ratios generates more framework Mn in comparison to the microwave procedure. Additionally, the diminution of the zeolite crystals to nanoscale from 100 to 200 nm was achieved via the conventional procedure for the first time. UV–vis, Raman, and X-ray absorption spectroscopic analyses revealed different local environments of manganese: Mn3+ incorporated into the silicalite-1 framework as “framework manganese” and Mn2+/3+ present as “extraframework manganese” (Mn2O3, Mn3O4). TEM reveals the presence of Mn3O4 nanorods. Both framework manganese and extraframework manganese exhibit good catalytic activity for styrene epoxidation. Catalytic results suggest that, in oxidation reactions of hydrocarbons, framework manganese is more active at lower Mn contents (Mn/Si < 0.015), whereas extraframework manganese is more active at higher loadings (Mn/Si > 0.015).
Found in: ključnih besedah
Summary of found: ...MnS-1 Nanocrystals, Mn XANES, EXAFS, zeolites, microwave-assisted hydrothermal synthesis...
Keywords: MnS-1 Nanocrystals, Mn XANES, EXAFS, zeolites, microwave-assisted hydrothermal synthesis
Published: 06.05.2019; Views: 1288; Downloads: 0
.pdf Fulltext (9,33 MB)

35.
Arabidopsis halleri shows hyperbioindicator behaviour for Pb and leaf Pb accumulation spatially separated from Zn
Stephan Höreth, Paula Pongrac, Marta Debeljak, Katarina Vogel-Mikuš, Matic Pečovnik, Primož Vavpetič, Iztok Arčon, original scientific article

Abstract: Lead (Pb) ranks among the most problematic environmental pollutants. Background contamination of soils is nearly ubiquitous, yet plant Pb accumulation is barely understood. In a survey covering 165 European populations of the metallophyte Arabidopsis halleri, several field samples had indicated Pb hyperaccumulation, offering a chance to dissect plant Pb accumulation. Accumulation of Pb was analysed in A. halleri individuals from contrasting habitats under controlled conditions to rule out aerial deposition as a source of apparent Pb accumulation. Several elemental imaging techniques were employed to study the spatial distribution and ligand environment of Pb. Regardless of genetic background, A. halleri individuals showed higher shoot Pb accumulation than A. thaliana. However, dose–response curves revealed indicator rather than hyperaccumulator behaviour. Xylem sap data and elemental imaging unequivocally demonstrated the in planta mobility of Pb. Highest Pb concentrations were found in epidermal and vascular tissues. Distribution of Pb was distinct from that of the hyperaccumulated metal zinc. Most Pb was bound by oxygen ligands in bidentate coordination. A. halleri accumulates Pb whenever soil conditions render Pb phytoavailable. Considerable Pb accumulation under such circumstances, even in leaves of A. thaliana, strongly suggests that Pb can enter food webs and may pose a food safety risk.
Found in: ključnih besedah
Summary of found: ...Pb accumulation, XANES, EXAFS, Arabidopsis halleri...
Keywords: Pb accumulation, XANES, EXAFS, Arabidopsis halleri
Published: 16.01.2020; Views: 903; Downloads: 0
.pdf Fulltext (4,46 MB)

36.
In-situ XAS study of catalytic N[sub]2O decomposition over CuO/CeO[sub]2 catalysts
Elena Tchernychova, Petar Djinović, Iztok Arčon, Maxim Zabilsky, Albin Pintar, 2021, original scientific article

Abstract: We performed in‐situ XAS study of N 2 O decomposition over CuO/CeO 2 catalysts. The Cu K‐edge and Ce L 3 ‐edge XANES and EXAFS analyses revealed the dynamic and crucial role of Cu 2+ /Cu + and Ce 4+ /Ce 3+ ionic pairs during the catalytic reaction. We observed the initial formation of reduced Cu + and Ce 3+ species during activation in helium atmosphere at 400 °C, while concentration of these species decreased significantly during steady‐state nitrous oxide degradation reaction (2500 ppm N 2 O in He at 400 °C). In‐situ EXAFS analysis further revealed a crucial role of copper‐ceria interface in this catalytic reaction. We observed dynamic changes in average number of Cu‐Ce scatters under reaction conditions, indicating an enlarging the interface between both copper and ceria phases, where electron and oxygen transfer occurs.
Found in: ključnih besedah
Summary of found: ...and Ce L 3 ‐edge XANES and EXAFS analyses revealed the dynamic and crucial role...
Keywords: in-situ XAS, Cu EXAFS, CuO/CeO2 nanorod catalys, N2O decomposition
Published: 29.01.2021; Views: 353; Downloads: 0
.pdf Fulltext (1,31 MB)

37.
Sn-modified TiO[sub]2 thin film photocatalysts prepared by low-temperature sol-gel processing
Ksenija Maver, 2021, doctoral dissertation

Abstract: Due to many advantageous physiochemical properties, titanium dioxide (TiO2) is the most widely used photocatalyst in numerous applications, such as wastewater treatment and air purification, self-cleaning surfaces and energy conversion (H2 generation). However, one of its disadvantages is the high electron-hole recombination rate, and coupling with other semiconductors is one of the strategies to improve it. The objective of this dissertation was to investigate how the photocatalytic activity of pure TiO2 can be improved by tin modification and to explain the mechanism of increased or hindered photoactivity in correlation with the structural properties of the modified TiO2 photocatalysts. A new low-temperature sol-gel synthesis route was developed to prepare Sn- or SnO2-modified TiO2 photocatalysts. In both cases, organic tin and titanium precursors were used. Tin in the form of Sn cations was used to prepare Sn-modified TiO2. In this case, the precursors went through the sol-gel reaction together to form a Sn-TiO2 sol. In the case of SnO2 modification, the SnO2 sol was prepared separately and additionally mixed with the TiO2 sol to form a TiO2/SnO2 bicomponent semiconductor system. Different molar ratios of tin to titanium were prepared to investigate the correlation between the tin concentration and the photocatalytic properties of the photocatalysts in the form of thin films. The results were used to optimize the synthesis conditions to obtain an improved activity of the modified TiO2 photocatalysts under UV-irradiation. The photocatalytic activity of the thin films was determined by measuring the degradation rate of an azo dye. An increase of up to 40 % in the photocatalytic activity of the dried samples (at 150 °C) was achieved when the TiO2 was modified with the Sn or SnO2 in a concentration range of 0.1 to 1 mol.%. At higher Sn or SnO2 loadings and after calcination of the samples at 500 °C, the photocatalytic activity of the photocatalyst was reduced compared to the unmodified TiO2. Different characterization techniques (UV-Vis, XRD, nitrogen physisorption, TEM, SEM and XAS) were employed to clarify the mechanism responsible for the enhanced and hindered photocatalytic performance of the Sn- and SnO2-modified TiO2 photocatalysts. The results showed that a nanocrystalline structure is already achieved in the samples by the low-temperature film treatment (drying at 150 °C) and that the photocatalytic efficiency is mainly influenced by the crystalline phase composition: anatase/rutile in the case of Sn-modified and TiO2/SnO2 in the case of SnO2-modified TiO2. The crystal size and specific surface area differ insignificantly between the equally thermally treated samples and partly explain the differences in photoefficiency of the calcined samples compared to the dried samples. The structural study at the atomic level, using the Sn K-edge EXAFS, revealed that Sn cations act as nucleation sites for the anatase to rutile transformation in the Sn-modified TiO2 photocatalysts, while in the SnO2-modified TiO2 samples the nanocrystalline cassiterite SnO2 is bound to the TiO2 nanocrystallites via the Sn-O-Ti bond. In both cases, the advantage of coupling the two semiconductors was achieved by separating the charge carriers and thus prolonging their lifetime for accessibility to participate in the redox reactions. The maximum activity enhancement was achieved in the low concentration range (0.1–1 mol.%), which means that an optimal ratio and contact of the two phases are obtained for the given physical parameters, such as particle size, shape and specific surface area of the catalyst.
Found in: ključnih besedah
Summary of found: ...the atomic level, using the Sn K-edge EXAFS, revealed that Sn cations act as nucleation...
Keywords: Sn-modified TiO2, SnO2-modified TiO2, low-temperature sol-gel, thin films, photocatalytic activity, anatase/rutile system, Sn K-edge EXAFS, dissertations
Published: 09.06.2021; Views: 50; Downloads: 5
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38.
Photo-Chemically-Deposited and Industrial Cu/ZnO/Al2O3 Catalyst Material Surface Structures During CO2 Hydrogenation to Methanol: EXAFS, XANES and XPS Analyses of Phases After Oxidation, Reduction, and Reaction
Blaž Likozar, Iztok Arčon, Venkata Dasireddy, Maja Pori, 2021, original scientific article

Abstract: Industrial Cu/ZnO/Al2O3 or novel rate catalysts, prepared with a photochemical deposition method, were studied under functional CH3OH synthesis conditions at the set temperature (T) range of 240–350 °C, 20 bar pressure, and stoichiometric carbon dioxide/hydrogen composition. Analytical scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray adsorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) methods were systematically utilized to investigate the interfaces, measured local geometry, and chemical state electronics around the structured active sites of commercially available Cu/ZnO/Al2O3 material or synthesized Cu/ZnO. Processed Cu K-edge EXAFS analysis suggested that various Cu atom species, clusters, metallic fcc Cu, Cu oxides (Cu2O or CuO) and the Cu0.7Zn2 alloy with hexagonal crystalline particles are contained after testing. It was proposed that in addition to the model’s Cu surface area, the amount, ratio and dispersion of the mentioned bonded Cu compounds significantly influenced activity. Additionally, XPS revealed that carbon may be deposited on the commercial Cu/ZnO/Al2O3, forming the inactive carbide coating with Cu or/and Zn, which may be the cause of basicity’s severe deactivation during reactions. The selectivity to methanol decreased with increasing T, whereas more Cu0.7Zn2 inhibited the CO formation through reverse water–gas shift (RWGS) CO2 reduction.
Found in: ključnih besedah
Keywords: CH3OH synthesis, Cu/ZnO-based catalyst, XPS, XANES, EXAFS analyses, Catalyst selectivity and activity
Published: 03.06.2021; Views: 68; Downloads: 0
.pdf Fulltext (3,98 MB)

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