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- Holm, Alexander, 1983-, et al.
(författare)
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A Water-Promoted Mars-van Krevelen Reaction Dominates Low-Temperature CO Oxidation over Au-Fe2O3 but Not over Au-TiO2
- 2024
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Ingår i: ACS Catalysis. - 2155-5435. ; 14:5, s. 3191-3197
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Tidskriftsartikel (refereegranskat)abstract
- We provide experimental evidence that is inconsistent with often proposed Langmuir−Hinshelwood (LH) mechanistic hypotheses for water-promoted CO oxidation over Au–Fe2O3. Passing CO and H2O, but no O2, over Au-γ-Fe2O3 at 25 °C, we observe significant CO2 production, inconsistent with LH mechanistic hypotheses. Experiments with H218O further show that previous LH mechanistic proposals cannot account for water-promoted CO oxidation over Au-γ-Fe2O3. Guided by density functional theory, we instead postulate a water-promoted Mars–van Krevelen (w-MvK) reaction. Our proposed w-MvK mechanism is consistent both with observed CO2 production in the absence of O2 and with CO oxidation in the presence of H218O and 16O2. In contrast, for Au-TiO2, our data is consistent with previous LH mechanistic hypotheses.
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| 2. |
- Kaya, Kerem, et al.
(författare)
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Nature-Inspired Depolymerization of Soda Lignin : Light-Induced Free Radical Promoted Cleavage of β-O-4 Bonds
- 2024
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Ingår i: Advanced Sustainable Systems. - 2366-7486. ; 8:3
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Tidskriftsartikel (refereegranskat)abstract
- The development of sustainable valorization methods for lignin is a challenging task because the vast majority of the reported studies involve either harsh conditions or expensive transition metal catalysts. Inspired by the sunlight degradation of lignin compounds, known as lignin yellowing, the use of a commercially available cheap organic photoinitiator, namely, phenacyl bromide (PAB) is reported here, for the efficient cleavage of lignin model compound 2-phenoxyacetophenone (2-PAP) and for the depolymerization of soda pulped lignin (SL) under UV-A irradiation and ambient conditions. Real-time NMR investigations of the photoreaction between 2-PAP and PAB shed light on the possible reaction mechanisms involving different radical species, HBr, and molecular oxygen. Interestingly, combined spectral, chromatographic, powder X-ray diffraction, and thermal studies of the photoreaction between PAB and SL indicate the formation of guaiacyl alcohol as the main product. The unprecedented performance of PAB is attributed to the excess generation of phenacyl radicals, the generation of photolabile brominated species, and HBr playing key roles in the cleavage of β-O-4 linkages. This work represents a new edge for sustainable lignin valorization under mild reaction conditions and offers the opportunity for large-scale production of valuable aromatics using technical lignins as feedstock.
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| 3. |
- Ulusoy, Seda, 1989-
(författare)
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Combining operando X-ray scattering and magnetometry to investigate conversion type electrode materials
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The transition towards a society with full electromobility depends heavily on the battery systems, which raises concerns about the environmental friendliness and sustainability of the current products on the market. Magnetite (Fe3O4) from the conversion type electrode family is one of the promising candidates in the search for a sustainable battery technology owing to its high theoretical storage capacity, high abundance, and low toxicity. However, the material suffers severely from capacity degradation in its practical use and hence requires better understanding and adjustments to reach its full potential.Developing nanostructured electrode materials is one of the strategies to enhance its storage capacity, stability, and charging rate. Therefore, this thesis starts with synthesis and chemical lithiation of cubic (ferrimagnetic) Fe3O4 nanoparticles that are used as a model system to establish relationships between structural and magnetic properties upon lithiation. The thesis then explores the relationship between particle size, composition, crystal structure, and electrochemical performance of Fe3O4 electrodes via multi-operando techniques during cycles of lithiation and delithiation reactions. Magnetometry, known for its sensitivity to the chemical, compositional, and agglomeration state of the materials was exploited to measure the magnetic signal of the electrodes under operando conditions as a complement to operando SAXS and WAXS measurements. The results from the operando studies indicated that during electrochemi calcycling; LiFeO2, FeO and metallic iron (Fe) are produced as intermediate compounds, but their stability regions differ greatly when using nanoparticles or bulk materials and also when compared against ex-situ analyzed specimens. In addition, commercial micron- and nanosized (paramagnetic) Co3O4 particles were employed to study evolution of structural and magnetic properties over cycles to shed light on the size-dependent reaction kinetics. The obtained results revealed that nanosizing leads to improved electrochemical performance, variations in surface reaction kinetics, and differences in aging mechanisms. The magnetic measurements were crucial in determining surface capacitance reactions that involve gel-like polymeric layer growth and degradation during Li removal and uptake.Lastly, the magnetic properties of layered NMC-based cathode materials were studied. The differences in their magnetic properties provided important information on the transition metal ordering depending on the choice of synthesis method that is used. Magnetization measurements were used in combination with diffraction data to choose an appropriate structure model to describe actual atomic arrangement in each material. Consequently, the findings in this thesis suggest that (operando) magnetometry can be employed as a complementary tool to elucidate structural details of battery electrodes, potentially revealing insights beyond the detection limits of volume-averaged X-ray scattering techniques.
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