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1.
Catalytic hydro(deoxy)genation of furfural and modelling of its reaction kinetics : dissertation
Rok Šivec, 2024, doktorska disertacija

Opis: In recent decades, there has been a growing interest in producing biofuels and biochemicals from renewable sources. Furfural stands as one of the ligno(hemi)cellulosic biomass derived platform chemical, which can be transformed into numerous value-added products. The goal of this PhD was to systematically study hydrotreatment reactions of furfural under varying operating conditions and to gain insights into the reaction mechanism and kinetics. An extensive experimental and computational study of hydrogenation, hydrodeoxygenation, oligomerisation and etherification of furfural in a three-phase batch reactor was performed. The goals were divided into three consecutive objectives. In the first part, hydrotreatment of furfural over Pd/C catalyst under various reaction conditions, including the solvent selection (solventless conditions, tetrahydrofuran, isopropanol), atmosphere (nitrogen, hydrogen), temperature (100–200 °C), pressure (25–75 bar) and stirring speed, was studied. A reaction pathway network and a micro-kinetic model were developed, incorporating thermodynamics (hydrogen solubility), mass transfer, adsorption, desorption, and surface reactions. These phenomena and their contribution to the surface coverages, TOF’s and global reaction rates were studied. The hydrogen presence on the catalyst surface was found to influence the main reaction pathway, leading to ring, aldehyde group or full hydrogenation. In the second part, various monometallic catalysts (Pd/C, Pt/C, Re/C, Ru/C, Rh/C, Ni/C, Cu/C) were tested at 100 -200 °C with 60 bar of hydrogen and tetrahydrofuran as solvent. A generalized reaction pathway network was developed. H2 temperature-programmed reduction (H2-TPR) and CO temperature-programmed desorption (CO-TPD) were conducted, and a regression analysis of the results was subsequently performed by numerical modelling and optimisation. The obtained adsorption and desorption kinetic parameters for active metallic sites were further used in a generalized micro-kinetic model, applicable to all tested catalysts. Pd/C exhibited high activity and non-selective hydrogenation of furfural, while other catalysts showed selective aldehyde group hydrogenation followed by deoxygenation, consistent with density functional theory (DFT) calculations. Ru/C uniquely produced 2 methyltetrahydrofuran and ring-opening products at 200 °C. In silico optimization of reaction conditions for promising catalysts ((Pd/C, Pt/C, Re/C, Ni/C) aimed to maximize the yield of the target product. In the third part, the influence of support on catalytic activity was studied. Hydrotreatment of furfural over Pd/Al2O3, Pd/SiO2, Ru/Al2O3, Ru/SiO2, Ni/Al2O3, and Ni/SiO2 was performed between 150 - 200 °C, using 60 bar of hydrogen and tetrahydrofuran as solvent. The strength and rate of adsorption and desorption to/from acidic, metallic and interface site structures were determined, using H2-TPR, CO-TPD and NH3-TPD and subsequent regression analysis of the results by numerical modelling and optimisation. The resulting parameters were sequentially used in the generalized micro-kinetic model to quantify the contribution of the active metal (Ni, Pd, or Ru), support (Al2O3 or SiO2), interphase sites and their relationship on catalyst activity and selectivity. Evaluation of morphological and structural characteristics, adsorption/desorption and intrinsic reaction kinetics has indicated that the coverage of acidic sites (on alumina or silica) facilitated yielding ring hydrogenation and inhibited deoxygenation, decarbonylation and cyclic compound opening. The rates for aromatics or aldehyde functional groups were, nonetheless, affected in a different order. The used and developed methods and findings of this PhD offer useful guidelines for transforming furfural into high-value chemicals through catalytic hydrotreatment, with significant implications for future research and industrial applications.
Ključne besede: lignocellulosic biomass, furfural, catalytic hydrogenation, micro-kinetic mass transfer model, reaction kinetics, first-principle methods, furfuryl alcohol, tetrahydrofurfuryl alcoholv, dissertations
Objavljeno v RUNG: 08.11.2024; Ogledov: 292; Prenosov: 4
.pdf Celotno besedilo (9,22 MB)

2.
Structural disorder of AlMg-oxide phase supporting Cu/ZnO catalyst improves efficiency and selectivity for ▫$CO_2$▫ hydrogenation to methanol
Andraž Mavrič, Gregor Žerjav, Blaž Belec, Matevž Roškarič, Matjaž Finšgar, Albin Pintar, Matjaž Valant, 2023, izvirni znanstveni članek

Opis: 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.
Ključne besede: carbon dioxide hydrogenation, heterogenous catalysis, methanol, reducibility
Objavljeno v RUNG: 02.06.2023; Ogledov: 1963; Prenosov: 21
.pdf Celotno besedilo (1,12 MB)

3.
Metal hydroxides for energy conversion and energy storage
Andraž Mavrič, predavanje na tuji univerzi

Opis: Electrocatalysts, electrochromic devices, and pseudo-capacitors based on transition metal (oxy)hydroxides depend on the reversibility of the reduction-oxidation process of metal cations. Rapid switching between different redox states is often involved, particularly in electrocatalysis where redox metal sites act as active centers for electron transfer to the reactant. To ensure long-term durability, the reversibility of the redox metal sites should be robust. Nickel hydroxide is a model catalyst for the oxygen evolution reaction (OER) and the basic representative of the layered double hydroxides. It is frequently combined with other transition metals (e.g. Fe, Co, Mn), forming some of the most active OER electrocatalysts in alkaline media. [1] I will present the use of in-situ spectroscopy to track the reversibility of redox states of the Ni(OH)2 during its lifetime. During the operation at 200 mA cm-2 in 1 M KOH electrolyte, the catalytic activity of Ni(OH)2 gradually degrades until lastly, the catalyst breaks down. During the catalyst lifetime, the reduction-oxidation reversibility of the Ni2+/3+ redox couple is lost and the catalyst converts into an inactive phase. The reversibility of the redox couple is monitored by the in-situ UV/Vis spectroscopy. During the catalyst lifetime, the reversibility of the redox peak is lost. The activity collapse is attributed to the structural amorphization/disordering of the layered Ni(OH)2 catalyst, as confirmed by TEM investigations and in-situ Raman spectroscopy. [2] Similarly, the redox reversibility of metal sites is also important for long cycle life in supercapacitors, based on the pseudo-capacitance mechanism. Contrary to catalysts, for supercapacitors, the water oxidation needs to be suppressed to increase the working voltage range. I will discuss the mechanisms for the deactivation of transition metal hydroxides to serve as capacitors and approaches to increase power density. Finally, I will discuss the use of mixed metal hydroxides to serve as precursors for a copper oxide-based catalytic system for CO2 hydrogenation to methanol. Thermal decomposition of hydrotalcite-based hydroxide precursor is followed by in-situ x-ray diffraction. The conditions to prepare disordered oxide in contact with catalytical active Cu metal are identified and the catalytic performance of catalysts with crystalline and disordered oxide phases are compared. [1] A. Mavrič, C. Cui, (2021), Advances and Challenges in Industrial-Scale Water Oxidation on Layered Double Hydroxides, ACS Appl. Energy Mater., 4, 12032-12055. [2] A. Mavrič, M. Fanetti, Y. Lin, M. Valant, C. Cui, (2020), Spectroelectrochemical Tracking of Nickel Hydroxide Reveals Its Irreversible Redox States upon Operation at High Current Density, ACS Catal., 10, 9451-9457.
Ključne besede: electrochemistry, energy storage, CO2 hydrogenation, methnaol
Objavljeno v RUNG: 13.10.2022; Ogledov: 2024; Prenosov: 0
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4.
Alternative Recovery and Valorization of Metals from Exhausted Catalytic Converters in a New Smart Polymetallic Catalyst
Sebastiano Tieuli, Franco Baldi, Iztok Arčon, Katarina Vogel-Mikuš, Michele Gallo, Laura Sperni, Oreste Piccolo, Stefano Paganelli, 2019, izvirni znanstveni članek

Opis: 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.
Ključne besede: Biogenerated polymetallic exopolysaccharide, biphasic catalysis, hydrogenation, metals-polymeric composite, new catalyst from metallic wastes, EXAFS, XANES
Objavljeno v RUNG: 06.05.2019; Ogledov: 4187; Prenosov: 0
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