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1.
THERMAL AND COMBINED PHOTO-THERMAL DRY REFORMING OF METHANE (DRM) OVER NANOSHAPED Ni/CeO2 CATALYSTS : DISSERTATION
Kristijan Lorber, 2023, doctoral dissertation

Abstract: Dry reforming of methane (DRM) is an attractive reaction for converting the two major greenhouse gases CH4 and CO2 into the product syngas. H2 and CO as synthesis gas are important chemical feedstocks for the further production of valuable products as well as for the production of long-chain hydrocarbons by the Fisher-Tropsch process. High operating temperatures due to the endothermic nature of the DRM process and the occurrence of several side reactions such as Reverse Water Gas Shift, Methane Cracking and Boudoard reaction make the DRM process unattractive for industrial application. For the catalytic application of DRM in thermal mode (thermal energy drives the reaction), different CeO2 morphologies, namely nanorods, nanocubes, and nanospheres, were synthesized by a hydrothermal method. The best catalyst for DRM was found to be 2 wt. % Ni loaded in CeO2 rods morphology (2Ni-R). Characterization techniques (XRD, N2-physisorption, TEM, in-situ XANES/EXAFS TPR and CO2 TPD) were used to investigate the structural and redox properties of the catalysts. The mechanism of CO2 activation on reduced Ni/CeO2-x during DRM was proposed using DFT calculations and in-situ DRIFTS measurements combined with mass spectrometry. The 2Ni-R catalyst, which performed best in thermal DRM reaction, was studied under photo-thermal conditions where it was stimulated by both visible light and thermal energy. The catalytic activity was observed even at low (140 °C) temperatures, and the obtained CH4 and CO2 conversion, as well as H2/CO ratio exceeded thermodynamic limitations. XRD, TEM, and H2-physisorption techniques were used for structural characterization, while in-situ UV-Vis measurements were performed to study the optical properties of the catalyst. By using suitable long-pass filters and with the help of theoretical calculations, we were able to distinguish two photo mechanisms which contribute to photocatalytic activity under photo-thermal mode of the DRM reaction. Shorter wavelengths (< 450 nm) supported the charge transfer and generation mechanism in reduced CeO2-x, while longer wavelengths (> 450 nm) promoted near-field enhancement. However, under full spectrum of visible light (400 - 800 nm), the charge transfer and generation mechanism was dominant and led to 2-3 times higher CH4 activation rates compared to near-field enhancement.
Keywords: DRM, CeO2 nanoshapes, reaction mechanism, photocatalysis
Published in RUNG: 22.09.2023; Views: 706; Downloads: 30
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2.
Antibiotics and their different application strategies in controlling the biofilm forming pathogenic bacteria
Fazlurrahman Khan, Dung T N Pham, Sandra Oloketuyi, Young-Mog Kim, 2020, review article

Abstract: Background: The establishment of a biofilm by most pathogenic bacteria has been known as one of the resistance mechanisms against antibiotics. A biofilm is a structural component where the bacterial community adheres to the biotic or abiotic surfaces by the help of Extracellular Polymeric Substances (EPS) produced by bacterial cells. The biofilm matrix possesses the ability to resist several adverse environmental factors, including the effect of antibiotics. Therefore, the resistance of bacterial biofilm-forming cells could be increased up to 1000 times than the planktonic cells, hence requiring a significantly high concentration of antibiotics for treatment. Methods: Up to the present, several methodologies employing antibiotics as an anti-biofilm, antivirulence or quorum quenching agent have been developed for biofilm inhibition and eradication of a pre-formed mature biofilm. Results: Among the anti-biofilm strategies being tested, the sub-minimal inhibitory concentration of several antibiotics either alone or in combination has been shown to inhibit biofilm formation and down-regulate the production of virulence factors. The combinatorial strategies include (1) combination of multiple antibiotics, (2) combination of antibiotics with non-antibiotic agents and (3) loading of antibiotics onto a carrier. Conclusion: The present review paper describes the role of several antibiotics as biofilm inhibitors and also the alternative strategies adopted for applications in eradicating and inhibiting the formation of biofilm by pathogenic bacteria.
Keywords: Antibiotics, biofilm inhibition, multiple antibiotics, pathogenic bacteria, resistance mechanism, virulence factors
Published in RUNG: 14.01.2021; Views: 2562; Downloads: 0
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3.
Effect of Na, Cs and Ca on propylene epoxidation selectivity over CuOx/SiO2 catalysts studied by catalytic tests, in-situ XAS and DFT
Janvit Teržan, Matej Huš, Iztok Arčon, Blaž Likozar, Petar Djinović, 2020, original scientific article

Abstract: This research focuses on epoxidation of propylene over pristine, Na, Ca and Cs modified CuOx/SiO2 catalysts using O2. The selectivity of the reaction is analyzed using a combination of catalytic tests, in-situ XAS and DFT calculations. The initially present subnanometer CuO clusters are present in all catalysts which re-disperse/flatten during reaction. During catalytic reaction, the Cu1+ becomes the predominant oxidation state. There is no correlation between propylene oxide (PO) selectivity and copper oxidation state. DFT analysis of the propylene reaction pathway revealed that Na, Cs, and Ca addition decreases the bonding strength of propylene to CuO and decreases the O2 activation barrier, while simultaneously increase the exothermicity of O2 dissociation. The Na induced Cu-O bond modification decreases the activation barrier from 0.87 to 0.71 eV for the oxametallacycle (OMC) ring closure (first step in the reaction pathway favoring selectivity towards PO) compared to pristine 5Cu catalyst. At the same time, we observed an increase (from 0.45 to 0.72 eV) of the barrier for the abstraction of allylic hydrogen. The opposite effect is achieved by Ca addition: the activation barrier for OMC ring closure increases to 1.08 eV and that for allylic hydrogen stripping decreases to 0.16 eV.
Keywords: Alkali modification, propylene epoxidation, reaction mechanism, copper oxide, activation barrier.
Published in RUNG: 05.06.2020; Views: 2758; Downloads: 0
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4.
Synthesis of a Cu/ZnO Nanocomposite by Electroless Plating for the Catalytic Conversion of CO2 to Methanol
Maja 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: 3572; Downloads: 0
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5.
Photocatalytic activity of Zr and Mn co-doped TiO2 in aqueous media
Urška Lavrenčič Štangar, O. L. Pliekhov, Nataša Novak Tušar, 2015, published scientific conference contribution abstract

Keywords: mechanism, influence of dopants, Mn scavenger of hydroxyl radicals
Published in RUNG: 01.02.2016; Views: 4953; Downloads: 1
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