1. Modelling-assisted optimisation of hemicellulose-derived monosaccharide valorization : dissertationAna Jakob, 2025, doctoral dissertation Abstract: Hemicellulose, one of the key components of lignocellulosic biomass, and its sugar monomers offer significant potential as a substrate for producing value-added platform chemicals. With both pentoses (xylose and arabinose) and hexoses (glucose, galactose, and mannose), the conversion of hemicellulose can yield various products including furfural, hydroxymethylfurfural (HMF), and levulinic acid. This doctoral thesis investigates the dehydration of various hemicellulose-derived monosaccharides, utilizing catalyst-free systems, as well as homogeneous and heterogeneous catalysts, in both aqueous and organic solvents. Monosaccharide conversion was evaluated in a catalyst-free aqueous solution at temperatures ranging between 130 – 190 °C. Conducting dehydration reactions under simple, hydrothermal conditions highlighted the differences in the reactivity of individual monosaccharides. Experimental data from extensive activity testing enabled the development of accurate kinetic models. Aiming at the optimization of reaction parameters relevant to the post-Organosolv production of furanics and levulinic acid, sulfuric and formic acid were introduced into the reaction system as homogeneous acid catalysts. Reaction kinetics of acid catalysed conversion using sulfuric and formic acid indicated a significant reduction in the activation energy of ketose dehydration. In addition, the addition of both acids enhanced the dehydration rates and promoted the conversion of HMF towards levulinic acid due to its low activation energies 86 – 91 kJ mol−1 and high reaction rate constants. The established kinetic model for individual saccharides was proven to be robust and able to accurately predict optimal reaction conditions for two distinct industrially relevant hemicellulose streams. In pursuit of a more sustainable and recyclable catalyst, various zeolites, specifically H-BEA, were tested. Although H-BEA exhibited excellent catalytic activity, its selectivity towards furanics remained limited in aqueous media. The low activation energy for HMF rehydration facilitated the formation of levulinic acid even at a moderate reaction temperature of 165 °C. Notably, the addition of THF as an organic solvent in combination with H-BEA, drastically improved the product selectivity towards furanics, particularly furfural. In addition to H-BEA zeolite, various types of zeolites with different Si/Al ratios were studied. Catalyst characterization revealed a strong correlation between catalytic activity and acidity. The addition of THF resulted in 90 mol % of furfural after only 30 min, demonstrating an exponential increase in dehydration rates and a decrease in activation energies. This zeolite-THF system was therefore applied for tandem reactions involving both xylose dehydration and furfural hydrogenation. The addition of metallic active sites via a Ni/H-BEA catalyst, and a hydrogen atmosphere, resulted in the catalytic hydrogenation of xylose to tetrahydrofurfuryl alcohol. Adjusting reaction temperatures allowed the production of secondary hydrogenated (2-methylfuran and 2-methyltetrahydrofuran) and dehydration products (tetrahydropyran), while the addition of water as a co-solvent with THF resulted in the complete inhibition of dehydration reactions and the selective formation of xylitol. Through a systematic study of reaction conditions and the development of comprehensive kinetic models, this work provides an in-depth investigation of monosaccharide dehydration. This doctoral thesis represents a comprehensive study to systematically investigate both catalytic and non-catalytic dehydration of five relevant monosaccharides, providing a methodical kinetic modelling approach that addresses the challenges associated with the complexity related to hemicellulose conversion.
Keywords: hemicellulose, monosaccharides, kinetic modelling, furanics, catalysis, dissertations
Published in RUNG: 19.02.2025; Views: 675; Downloads: 12
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2. Light-Assisted Catalysis and the Dynamic Nature of Surface Species in the Reverse Water Gas Shift Reaction over Cu/γ-Al2O3Kristijan Lorber, Iztok Arčon, Matej Huš, Janez Zavašnik, Jordi Sancho-Parramon, Anže Prašnikar, Blaž Likozar, Nataša Novak Tušar, Petar Djinović, original scientific article Abstract: The reverse water gas shift (RWGS) reaction converts CO2 and H2 into CO and water. We investigated Cu/γ-Al2O3 catalysts in both thermally driven and light-assisted RWGS reactions using visible light. When driven by combined visible light and thermal energy, the CO2 conversion rates were lower than in the dark. Light-assisted reactions showed an increase in the apparent activation energy from 68 to 87 kJ/mol, indicating that light disrupts the energetically favorable pathway active in the dark. A linear correlation between irradiance and decreasing reaction rate suggests a photon-driven phenomenon. In situ diffuse reflectance infrared Fourier transform spectroscopy and TD-DFT analyses revealed that catalyst illumination causes significant, partly irreversible surface dehydroxylation, highlighting the importance of OH groups in the most favorable RWGS pathway. This study offers a novel approach to manipulate surface species and control activity in the RWGS reaction.
Keywords: light-assisted catalysis, reaction mechanism, in situ spectroscopy, hydroxyl, copper, RWGS
Published in RUNG: 07.01.2025; Views: 650; Downloads: 6
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4. Hydrazone-linked covalent organic framework catalyst via efficient Pd recovery from wastewaterMahira Bashri, Sushil Kumar, Pallab Bhandari, Sasi Stephen, Matthew J. O'Connor, Safa Gaber, Tina Škorjanc, Matjaž Finšgar, Gisha Elizabeth Luckachan, Blaž Belec, 2024, original scientific article Abstract: Global consumption and discharge of palladium (Pd) have raised environmental concerns but also present an opportunity for the sustainable recovery and reuse of this precious metal. Adsorption has proven to be an efficient method for the selective recovery of Pd from industrial wastewater. This study investigated a hydrazone-linked covalent organic framework (Tfpa-Od COF) as a potential material for the high-affinity adsorption of Pd2+ ions from wastewater, achieving a Kd value of 3.62 × 106 mL g–1. The electron-rich backbone of the COF contributes to its excellent selective removal efficiency (up to 100%) and adsorption capacity of 372.59 mg g–1. Furthermore, the Pd-adsorbed COF was evaluated as a sustainable catalyst for the Suzuki–Miyaura coupling reaction, demonstrating good catalytic conversion and recyclability. This work attempts to showcase a protocol for reusing waste palladium generated in water to fabricate heterogeneous catalysts and, thereby, promote the circular economy concept.
Keywords: covalent organic frameworks, sustainability, catalysis, palladium adsorption, water purification
Published in RUNG: 22.08.2024; Views: 1349; Downloads: 6
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5. 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: 2551; Downloads: 9
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7. Utilizing structurally disordered AlMg-oxide phase in Cu/ZnO catalyst for efficient ▫$CO_2$▫ hydrogenation to methanolAndraž Mavrič, Gregor Žerjav, Blaž Belec, Matevž Roškarič, Matjaž Finšgar, Albin Pintar, Matjaž Valant, 2023, published scientific conference contribution abstract Keywords: carbon dioxide, methanol, catalysis
Published in RUNG: 15.09.2023; Views: 2834; Downloads: 8
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8. Structural disorder of AlMg-oxide phase supporting Cu/ZnO catalyst improves efficiency and selectivity for ▫$CO_2$▫ hydrogenation to methanolAndraž Mavrič, Gregor Žerjav, Blaž Belec, Matevž Roškarič, Matjaž Finšgar, Albin Pintar, Matjaž Valant, 2023, original scientific article Abstract: The performance of the Cu/ZnO catalyst system with the AlMg-oxide phase is studied for CO2 hydrogenation to methanol. The catalyst is prepared by thermal treatment of the hydrotalcite phase containing intimately mixed metal cations in the hydroxide form. CuO in the presence of ZnO and disordered AlMg-oxide phase gets easily reduced to Cu during the hydrogenation reaction. Its catalytic activity at relatively low Cu metal content (∼14 at.%) remains stable during 100 hours on stream at 260 °C with constant space-time yield for methanol (∼1.8 gMeOH gcat−1 h−1) and high methanol selectivity (>85 %) The improved performance is attributed to the neutralization of surface acidity, increased number of weak basic sites in the disordered phase, and lower tendency for coke formation.
Keywords: carbon dioxide hydrogenation, heterogenous catalysis, methanol, reducibility
Published in RUNG: 02.06.2023; Views: 2560; Downloads: 23
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9. Alternative Recovery and Valorization of Metals from Exhausted Catalytic Converters in a New Smart Polymetallic CatalystSebastiano Tieuli, Franco Baldi, Iztok Arčon, Katarina Vogel-Mikuš, Michele Gallo, Laura Sperni, Oreste Piccolo, 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.
Keywords: Biogenerated polymetallic exopolysaccharide, biphasic catalysis, hydrogenation, metals-polymeric
composite, new catalyst from metallic wastes, EXAFS, XANES
Published in RUNG: 06.05.2019; Views: 4680; Downloads: 0
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10. Synthesis of a Cu/ZnO Nanocomposite by Electroless Plating for the Catalytic Conversion of CO2 to MethanolMaja Pori, Iztok Arčon, Damjan Lašič Jurković, Marjan Marinšek, Goran Dražić, Blaž Likozar, Zorica Crnjak Orel, 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.
Keywords: EXAFS, CuZn alloy, Spillover mechanism, CO2 valorization, Electroless deposition method, Heterogeneous
catalysis
Published in RUNG: 12.04.2019; Views: 5133; Downloads: 0
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