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1.
Insight into the interdependence of Ni and Al in bifunctional Ni/ZSM-5 catalysts by Ni K-edge XAS analysis
Iztok Arčon, Hue-Tong Vu, Goran Dražić, Janez Volavšek, Gregor Mali, Nataša Zabukovec Logar, Nataša Novak Tušar, 2023, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: 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.
Ključne besede: Ni/ZSM-5 catalysts, Ni EXAFS, XANES
Objavljeno v RUNG: 19.09.2023; Ogledov: 610; Prenosov: 3
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Winning combination of Cu and Fe oxide clusters with an alumina support for low-temperature catalytic oxidation of volatile organic compounds
Tadej 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: 886; Prenosov: 10
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4.
Insight into the interdependence of Ni and Al in bifunctional Ni/ZSM-5 catalysts at the nanoscale
Hue-Tong Vu, Iztok Arčon, Danilo Oliveira de Souza, Simone Pollastri, Goran Dražić, Janez Volavšek, Gregor Mali, Nataša Zabukovec Logar, Nataša Novak Tušar, 2022, izvirni znanstveni članek

Opis: 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. 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 using Ni K-edge XANES and EXAFS analyses, complemented by XRD and TEM, to resolve 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. Ni species in Ni/ZSM-5 exist as NiO crystals (3–50 nm) 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 ¼ 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.
Ključne besede: Ni/ZSM-5 catalysts, zeolite, Ni XANES, EXAFS
Objavljeno v RUNG: 11.05.2022; Ogledov: 1407; Prenosov: 42
.pdf Celotno besedilo (1,25 MB)
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5.
Removal of copper from aqueous solutions with zeolites and possible treatment of exhaust materials
Nataša Zabukovec Logar, Iztok Arčon, Janez Kovač, Margarita Popova, 2021, izvirni znanstveni članek

Opis: The mechanism of Cu2+ loading into commercially available natural HEU-type and synthetic LTA-type zeolites for their possible use in environmental processes, such as water and air treatment applications, was studied. Elemental analysis, SEM/EDXS, XRD, XAS and XPS analyses revealed 4-fold coordination of Cu2+ cations with oxygen atoms in the pores, a predominant location of copper atoms on the surface of crystallites and retained crystallinity of zeolites throughout the processes. The post-treatment of Cu2+-loaded samples with HCl and/or NaCl solutions confirmed the predominantly reversible sorption of copper on zeolites from aqueous solutions by ion-exchange mechanism and, therefore, excellent regeneration possibilities for both types of zeolites. Furthermore, with the calcination of exhaust metal-loaded zeolites, catalysts for total toluene oxidation reaction, as a model VOC pollutant, were obtained.
Ključne besede: Cu2+ ion exchange, Total toluene oxidation, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, Zeolite
Objavljeno v RUNG: 03.06.2021; Ogledov: 1833; Prenosov: 152
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Study of water adsorption on EDTA dealuminated zeolite Y
O. L. Pliekhov, Olena Pliekhova, Iztok Arčon, Federica Bondino, Elena Magnano, Gregor Mali, Nataša Zabukovec Logar, 2020, izvirni znanstveni članek

Opis: Zeolite Y was synthesized and modified with EDTA dealumination procedure. The modified zeolites were analyzed by X-ray diffraction, X-ray absorption spectroscopy, chemical analysis and water adsorption measurements. We demonstrated that dealumination with bulk organic acid such as EDTA is able to reduce the original intense water affinity. Furthermore, it was found that dealumination with EDTA, in contrast with steaming and HCl dealumination, provides fully controllable, predictable and secure process of Al removal from the zeolites’ frameworks. The shift of the adsorption isotherm in the low partial pressure range represents an interesting result for adsorption-based applications.
Ključne besede: Zeolite Y Water sorption Dealumination Al XANES EDTA treatment
Objavljeno v RUNG: 05.06.2020; Ogledov: 2854; Prenosov: 0
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8.
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, izvirni znanstveni članek

Opis: 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).
Ključne besede: MnS-1 Nanocrystals, Mn XANES, EXAFS, zeolites, microwave-assisted hydrothermal synthesis
Objavljeno v RUNG: 06.05.2019; Ogledov: 3233; Prenosov: 0
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9.
Optimizacija poroznih materialov za zajemanje CO2 : Diplomsko delo
Lara Valentić, 2015, diplomsko delo

Opis: V diplomskem delu sem želela raziskati razlike v sposobnostih za vezavo ogljikovega dioksida v kovinsko-organskih poroznih (MOF) materialih, sintetiziranih z okoljsko manj obremenjujočimi reaktanti, kot so trenutno v uporabi, in oceniti primernost materialov za zajem ogljikovega dioksida iz dimnih plinov v že obstoječih tehnoloških procesih. Pri sintezah sem spreminjala vir Mg in Al ionov, vrsto organskih ligandov in topil, temperaturo in čas sinteze. Večina produktov je bila narejena s solvotermalno sintezo, dva produkta sem poskusila optimizirati z mikrovalovno sintezo. Sintetiziranim produktom sem določala strukturo in/ali poroznost z uporabo rentgenske difrakcije (XRD), elektronske mikroskopije z uporabo elementne analize (SEM in EDX) ter s fizisorpcijo dušika. Najprimernejše produkte sem nato testirala za zajem ogljikovega dioksida. Najboljši produkt za zajemanje ogljikovega dioksida je Al-BPDC, aromatski kovinsko-organski porozni material z BET-specifično površino 1712 m2/g. Alifatski produkti z aluminijem in magnezijem (sukcionat, glutarat in pimelat) imajo opazno stopnjo adsorpcije šele pri visokih tlakih, zato niso primerni za adsorpcijo in zajem ogljikovega dioksida iz dimnih plinov.
Ključne besede: kovinsko-organski porozni materiali, zajem CO2, strukturna karakterizacija, alifatski karboksilati, aromatski karboksilati
Objavljeno v RUNG: 01.09.2015; Ogledov: 6151; Prenosov: 264
.pdf Celotno besedilo (3,63 MB)

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