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Abstract: Static and in situ nanoscale spectro-microscopy is now routinely performed on the Hard X-ray Nanoprobe beamline at Diamond and the solutions implemented to provide robust energy scanning and experimental operation are described. A software-based scheme for active feedback stabilization of X-ray beam position and monochromatic beam flux across the operating energy range of the beamline is reported, consisting of two linked feedback loops using extremum seeking and position control. Multimodal registration methods have been implemented for active compensation of drift during an experiment to compensate for sample movement during in situ experiments or from beam-induced effects.

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Abstract: Glauconite is an authigenic, iron-rich clay mineral that is abundant in greensands formations worldwide. Evidence from these formations suggests that glauconite is commonly diagenetically converted to carbonate minerals such as siderite, ankerite, and ferroan dolomite. This process represents a natural CO2 sink that may provide an effective mechanism for the engineered mineralization of anthropogenic CO2. To evaluate glauconite carbonation reactions and improve our understanding of glauconite diagenesis, we performed a detailed evaluation of the mechanisms through which carbonate minerals naturally replace glauconite during diagenesis of glauconitic sandstones from the Lower Cretaceous Upper Mannville Group in western Alberta, Canada. Using a combination of optical microscopy and scanning electron imaging, electron microprobe and bulk geochemical analyses, and X-ray fluorescence mapping, we show glauconite carbonation in the Mannville group is an reduction-facilitated, coupled glauconite recrystallization and siderite precipitation reaction. X-ray absorption near-edge spectroscopic mapping and spot analyses demonstrate that this reaction is accompanied by a significant shift in the oxidation state of Fe, from dominantly oxidized in glauconite to reduced in carbonate reaction products. Together, these results suggest that geochemical conditions - most importantly, temperature, partial pressure of CO2, and fluid redox state - were thermodynamically favorable for glauconite carbonation during burial diagenesis of Mannville Group sandstones. Results of thermodynamic models illustrate that, although K-feldspar is favored to precipitate during reductive glauconite dissolution and accompanying Fe-carbonate precipitation, its precipitation is likely kinetically limited, and that an Fe-impoverished glauconite is expected to recrystallize instead. Our findings show that glauconite carbonation is likely a common phenomenon in the subsurface, and thus that glauconite is potentially a significant cation source for mineralizing anthropogenic CO2.

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Abstract: The research for surface active sites with outstanding catalytic activity and selectivity is continuing apace. The rationally designed catalyst with optimised energy level and geometric configuration is key to achieving novel reaction pathways with superior performance. Compared to the conventional supported nanomaterials as catalysts, single atomic site catalysts (SASCs) not only inherit the excellent recyclability but are also featured with ultimate atom efficiency, high structural uniformity and tunable coordination environment. These great advantages of SASCs are due to their unique atomic dispersion nature that preserves features of both heterogeneous and homogeneous catalysts. Especially the homogeneity of SASC enables convincing identification and characterisation of real active sites, making it an ideal platform to establish the definitive structure-activity relationship and to validate reaction mechanisms. Therefore, rational designed SASC has become the most prominent material to fabricate desired active sites with outstanding catalytic activity and selectivity. In this thesis, chemical synthesis strategies and characterisation techniques for SASCs are carefully reviewed. The limitations and future perspectives from a subjective view of the current methodology are discussed in detail as well. As inspired by pioneers’ work, rational designed Ru and Cu SASCs are prepared to investigate their distinct relationships between catalyst structures and reaction behaviours during CO oxidation reaction. With the help of combined in situ characterisation techniques, the structural evolution of active sites for both Ru and Cu catalysts were carefully studied. In the first project, the ultimate rational design of Ru active centre is realised by building surface single-sites to mimic molecular Ru catalysts. Inspired by a homogeneous Ru(II) complex, an air-stable surface -[bipy-Ru(II)(CO)2Cl2] single-site is designed through precise engineering of geometric and electronic structures from -[bipy-Ru(III)Cl4]- site. Such Ru(II) single-site enable oxidation of CO while the Ru(III) site is completely inert, providing an excellent prototype of the synthetic strategy which is generally applicable to transition metals. The second project focuses on the electronic metal-support interactions (EMSI) which describe electron flow between metal sites and a metal oxide support. For CuO-CeO2 catalysts, the electron withdrawing effect on Cu species introduced by electrophilic Ce4+ is maximised for atomically dispersed Cu sites over CeO2 surface. Experiment evidence shows the energy levels of 3d orbitals of isolated Cu(I)/(II) sites are decreased by Ce4+ cations in the support framework. It is demonstrated by in situ study that a [Cu(I)O2]3- site on CeO2 could selectively adsorb molecular O2 and form a rarely reported electrophilic 2-O2 species, leading to ten times higher activity than CuO clusters in CO oxidation. The third project is derived from the previous study of CuO-CeO2 catalysts, in which an unbalanced electron transfer between Cu and Ce is observed for CuO clusters dominant samples. To explain the reaction pathway of CeO2 supported CuO clusters in CO oxidation, an electronic metal-support-carbon interaction (EMSCI) based on EMSI is proposed. In the CuO-CeO2 redox, an additional flow of electron from metallic Cu to surface carbon species is observed by combined in situ studies, providing a complete picture of the mass and electron flow in the catalytic redox cycles.

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Abstract: Joule heating studies on nanoparticle/nanocarbon hybrid aerogels have been reported, but systematic investigations on hydrotalcite-derived catalysts supported onto reduced graphene oxide (rGO) aerogels are rare. In this study, hydrotalcite-derived Cu-Al2O3 nanoparticles were incorporated into a porous and multifunctional rGO aerogel support for fabricating electrically conducting Cu-Al2O3/rGO hybrid aerogels, and their properties were investigated in detail. The hybridization of Cu-Al2O3 with a 3D nanocarbon support network imparts additional functionalities to the widely used functional inorganic nanoparticles, such as direct electrical framework heating and easy regeneration and separation of spent nanoparticles, with well-spaced nanoparticle segregation. 3D variable-range hopping model fitting confirmed that electrons were able to reach the entire aerogel to enable uniform resistive heating. The conductivity of the nanocarbon support framework facilitates uniform and fast heating (up to 636 K/min) of the embedded nanoparticles at very low energy consumption, while the large porosity and high thermal conductivity enable efficient heat dissipation during natural cooling (up to 336 K/min). The thermal stability of the hybrid aerogel was demonstrated by repeated heating/cooling cycling at different temperatures that were relevant to important industrial applications. The facile synthetic approach can be easily adapted to fabricate other types of multifunctional nanoparticle/nanocarbon hybrid aerogels, such as the MgAl-MMO/rGO aerogel and the Ni-Al2O3/rGO aerogel. These findings open up new routes to the functionalization of inorganic nanoparticles and extend their application ranges that involve electrical/thermal heating, temperature-dependent catalysis, sorption, and sensing.

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Abstract: Complex early transition metal oxides have emerged as leading candidates for fast charging lithium- ion battery anode materials. Framework crystal structures with frustrated topologies are good electrode candidates because they may intercalate large quantities of guest ions with minimal structural response. Starting from the empty perovskite (ReO3) framework, shear planes and filled pentagonal columns are examples of motifs that decrease the structural degrees of freedom. As a consequence, many early transition metal oxide shear and bronze structures do not readily undergo the tilts and distortions that lead to phase transitions and/or the clamping of lithium diffusion pathways that occur in a purely corner-shared polyhedral network. In this work, we explore the relationship between composition, crystal structure, and reduction pathway in a variety of mixed transition metal and main group oxides. Operando and ex situ X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data are collected at Ga K-edge, Nb K-edge, W LI,II,III-edges, Bi LIII-edge, and Ti K-edges to track the evolution of electronic and local atomic structure of the complex oxides during lithium insertion and extraction. Early transition metals in their fully oxidized d0 electronic states (Ti4+, Nb5+, W6+) undergo inversion-breaking local distortions. When these oxides are reduced, such as in lithiation in a lithium-ion battery, their local symmetry increases. The symmetry dependence of XANES makes it uniquely sensitive to this phenomenon, known as the second-order Jahn– Teller effect. In mixed metal oxides, XANES and EXAFS differentiate the redox centers and reveal that the transition metals proceed along parallel reduction pathways while the main group elements react in a stepwise conversion-type mechanism. X-ray absorption spectroscopy is complemented by 6/7Li and 23Na solid- state NMR spectroscopy, synchrotron and neutron diffraction, and DFT to gain a comprehensive picture of the charge storage mechanisms. Prospects for tunability and implications for charge rate and structural stability will be discussed.