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Abstract: Introduction: Airless planetary bodies with surfaces exposed to the space environment are bombarded by electrons and protons from the solar wind and cosmic rays, as well as micrometeorites, resulting in space weathering [1]. Features of space weathering include partially amorphised grain surface rims, measuring up to ~100 nm thick, containing nanophase Fe metal (npFe0) particles, vesicular blistering, and solar flare tracks [1,2]. Space weathered samples collected by the JAXA Hayabusa spacecraft from asteroid Itokawa have previously been analysed using the I14 X-ray nanoprobe beamline at Diamond Light Source synchrotron, measuring Fe-K X-ray absorption near-edge spectroscopy (XANES), and revealing an increased ferric-ferrous ratio (Fe3+/ΣFe) relative to their respective host grain mineralogy [3]. In this study, we seek to better understand the formation of space weathered lunar surface soil samples collected during the Apollo 17 mission, investigating the Fe-redox variations observed in the dominant silicate phase and the nano-grains of the space weathered rims using Fe-K XANES and EELS, with high-resolution STEM imaging. Methods/Materials: The lunar sample number is 78481,29 - a surface sample collected from the top 1 cm of trench soils at Station 8 of Apollo 17 [4]. Three FIB lift-out sections have been extracted successfully from lunar grains identified to have space weathered surfaces. Two of the lunar grains were augite pyroxene, En81Fs16 and En85Fs12, and one olivine, Fa39. Using the I14 X-ray Nanoprobe Beamline at Diamond, Fe-Kα XAS spectra are obtained from a series of XRF maps over the samples, with energies typically in the range 7000-7300 eV, with a higher energy resolution range over the XANES features (~7100-7150 eV). The XANES maps are processed using Mantis 2.3.02 [5], and isolated spectra normalized in Athena 0.8.056 [6]. By observing increasing shifts in the 1s→3d transition pre- absorption-edge peak centroid energy positions, the Fe-redox variations can be estimated between the sample host mineralogy and the space weathered zone, when compared to reference minerals of known ferric-ferrous ratio (Fe3+/ΣFe). A JEOL ARM200CF and JEOL JEM-ARM300CF instrument was used for EELS analyses and high-resolution STEM imaging respectively, at ePSIC in Diamond. EELS are performed using an accelerating voltage of 200 keV, current 15 μA, and 0.25eV/ch with a 5 mm EELS aperture, measuring linescans from the host to the space weathered zones to provide verification of the Fe-redox variation by observing the shifts in the Fe-Lα peaks. Results: HR-STEM imaging confirmed the expected partial amorphisation and npFe0 particles (Fe0 metal confirmed observing lattice fringe spacings of ~2.06 Å) in the space weathered zones of all three lunar samples. XANES mapping was able to identify the space weathered zone separate from the host grain mineralogy, and analyses of the XANES spectra from each revealed a consistent positive shift in the 1s→3d pre-edge centroid energy positions for the space weathered zone when compared to the host. Increases of up to ~0.23 eV in the space weathered (SW) zone, compared to the substrate host mineralogy of augite or olivine, suggests an increase in ferric content in the space weathered zones up to ΔFe3+/ΣFe ~0.14 ±0.03. Positive shifts in the absorption edge positions for SW zones also support these results. A total of 18 EELS linescans measured, at various locations along the space weathered rims in all three lunar samples, also shows a consistent increased shift in the Fe-L peak energy position. A positive shift in the EELS Fe-L peak position is indicative of increased ferric content, as shown by reference minerals measured including Fe-rich olivine (Fe3+/ΣFe = 0.00) and magnetite (Fe3+/ΣFe = 0.67) with average EELS Fe-L peak positions of ~712.1 eV and ~713.6 eV respectively.

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Abstract: It has only recently been established that doping light elements (lithium, boron, and carbon) into supported transition metals can fill interstitial sites, which can be observed by the expanded unit cell. As an example, interstitial lithium (intLi) can block H filling octahedral interstices of palladium metal lattice, which improves partial hydrogenation of alkynes to alkenes under hydrogen. In contrast, herein, we report intLi is not found in the case of Pt/C. Instead, we observe for the first time a direct ‘substitution’ of Pt with substitutional lithium (subLi) in alternating atomic columns using scanning transmission electron microscopy-annular dark field (STEM-ADF). This ordered substitutional doping results in a contraction of the unit cell as shown by high-quality synchrotron X-ray diffraction (SXRD). The electron donation of d-band of Pt without higher orbital hybridizations by subLi offers an alternative way for ultra-selectivity in catalytic hydrogenation of carbonyl compounds by suppressing the facile CO bond breakage that would form alcohols.

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Abstract: In this Ph.D. project, the effective parameters in the sol-immobilization method which can affect catalytic reactivity including: capping agent, solvent of synthesis, and support were studied. The synthesized catalysts were employed in the liquid phase hydrogenation reactions of two biomass derived molecules namely furfural and vanillin. In this regard, the role of protective agents, which are used to stabilize colloidal nanoparticles (NPs) in solutions, for Pd NPs supported on carbon support in the liquid phase hydrogenation of furfural was explored. The use of Pd as a hydrogenation catalyst is well documented, as hydrogenation reactions can only be performed by metals that can easily chemisorb hydrogen. Pd is one of such metals capable of dissociate hydrogen even at room temperature. The capping agent adsorbed on the surface of the NPs can alter their activity and selectivity, by modifying the particle size, size distribution, morphology, and stability against leaching and agglomeration. Besides, the effect of the amount of protective agent and the synthesis solvents have been investigated, allowing better insight into the metal-support interaction in Pd/TiO2 catalysts for the hydrogenation of furfural. Then, the effect of using different carbonaceous supports with various chemical- physical properties on the activity and selectivity towards the hydrodeoxygenation of vanillin as a lignin model compound was explored.

Open Access

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Abstract: The oxidation of cyclohexane via the in-situ production of H2O2 from molecular H2 and O2 offers an attractive route to the current industrial means of producing cyclohexanone and cyclohexanol (KA oil), key materials in the production of Nylon. The in-situ route has the potential to overcome the significant economic and environmental concerns associated with the use of commercial H2O2, while also allowing for the use of far lower reaction temperatures than those typical of the purely aerobic route to KA oil. Herein we demonstrate the efficacy of a series of bi-functional Pd-based catalysts, which offer appreciable concentrations of KA oil, under conditions where limited activity is observed using O2 alone. In particular the introduction of V into a supported Pd catalyst is seen to improve KA oil concentration by an order of magnitude, compared to the Pd-only analogue. In particular we ascribe this improvement in catalytic performance to the development of Pd domains of mixed oxidation state upon V incorporation as evidenced through X-ray photoelectron spectroscopy.

Open Access

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Abstract: Synchrotron Fe‐K X‐ray absorption spectroscopy and transmission electron microscopy have been used to investigate the mineralogy and Fe‐redox variations in the space‐weathered (SW) rims of asteroidal samples. This study focuses on the FIB lift‐out sections from five Itokawa grains, returned by the Hayabusa spacecraft, including samples RB‐QD04‐0063, RB‐QD04‐0080, RB‐CV‐0011, RB‐CV‐0089, and RB‐CV‐0148. Each of the samples featured partially amorphized SW rims, caused by irradiation damage from implanted low mass solar wind ions, and the impacting of micrometeorites. Using bright‐field and HAADF‐STEM imaging, vesicular blistering and nanophase Fe metal (npFe0) particles were observed within grain rims, and solar flare tracks were observed in the substrate host grain, confirming the presence of SW zones. We use Fe‐K XANES mapping to investigate Fe‐redox changes between the host mineral and the SW zones. All SW zones measured show some increases in the ferric‐ferrous ratio (Fe3+/ΣFe) relative to their respective host grains, likely the result of the implanted solar wind H+ ions reacting with the segregated ferrous Fe in the surface material.