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Abstract: Carbon dioxide (CO2) hydrogenation represents a central route for sustainable fuel production and carbon recycling, yet its efficiency is critically dependent on the structural and electronic properties of the catalyst. In practical heterogeneous systems prepared by conventional wet-chemical methods, a distribution of active sites, ranging from atomically dispersed species to subnanometric clusters and nanoparticles, typically coexist in the final catalyst. Here, we investigate how support defect engineering governs this distribution in Ru/TiO2 catalysts with varying metal loadings and oxidative pre-treatments. Comprehensive spectroscopic and imaging analyses, including XPS, HR-STEM, and XAS established a clear correlation between Ru structure and catalytic behavior. Critically low Ru loadings (0.2 wt%) induced a transition from metallic nanoparticles to highly dispersed and single atom species, while oxidative pretreatment generated RuO2 like domains. A fraction of isolated Ru atoms persisted, particularly on defect-rich TiO2, where oxygen vacancies act as anchoring sites, improving stability under redox conditions. Catalytic testing revealed that Ru dispersion and oxidation state jointly determine activity and selectivity: extended metallic Ru or oxidized Ru nanoparticles favor complete hydrogenation to CH4, whereas isolated Ru species promote CO formation via the reverse water–gas shift pathway. The coexistence of these Ru configurations is associated with enhanced low temperature activity, while defect engineered supports improve stability against deactivation. Defect engineering of TiO2 provides an effective strategy to stabilize atomically dispersed Ru and to balance nanoparticles and atomic species, offering a versatile strategy to tune CO2 hydrogenation performance and advance the design of Ru based catalysts for sustainable hydrogenation processes.

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Abstract: The development of efficient recycling processes for lithium-ion battery electrode materials is essential for sustainable battery technologies. TiNb2O7 (TNO) is an attractive high-power anode material, but recycling strategies remain largely unexplored. Here, we report a direct recycling approach for TNO anodes recovered from a cycled TNO/LiNi0.6Mn0.2Co0.2O2 cell. We find that residual lithium in recovered TNO promotes the formation of a lithiated rutile impurity phase and Ti2Nb10O29 during thermal processing, which degrades the electrochemical performance of the recovered TNO. Structural and compositional analyses reveal the origin of these phases and guide the development of a recycling route that combines hydrothermal lithium removal with a subsequent heat treatment, preventing impurity formation. Recycled TNO produced by this method delivers high capacity, excellent rate capability, and stable performance at high current densities, achieving 279 (5) and 261 (10) mA h g−1 at 2 and 4 A g−1, respectively, comparable to commercial TNO. These results demonstrate a viable direct recycling strategy for TNO anodes.

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Abstract: Nanoplastic (NPl) particles are increasingly found in aquatic environments due to the long-term degradation of mismanaged plastic waste, and their uptake and accumulation in aquatic organisms are progressively reported. However, their biodistribution and spatial association with biologically relevant elements after ingestion remain poorly understood. In this study, europium-doped polystyrene NPls (Eu-doped NPls) were used as model particles to investigate their spatial distribution in Daphnia magna, a representative freshwater organism, using synchrotron-based nanoprobe X-ray fluorescence (nano-XRF). Daphnia magna neonates (<24 h old) were exposed to 5–20 mg L−1 Eu-doped NPls for 48 h and by using Eu as the tracer, their biodistribution was mapped using nano-XRF at multiple resolutions. No mortality was observed during exposure, although body length was significantly reduced relative to the control under all tested conditions (p < 0.05). Reactive oxygen species (ROS)-associated fluorescence also increased significantly at 10 and 20 mg L−1, indicating an organism-level oxidative-stress response at higher exposure concentrations. Toxicokinetic analysis revealed rapid uptake and efficient depuration, yielding a low bioconcentration factor (BCF = 0.982 L g−1). Two-dimensional nano-XRF maps showed that most Eu-associated signals were localised within gut-associated regions and spatially co-occurred with endogenous elements including Fe, Ca and K. Eu-derived signal metrics increased with external exposure concentration, with broader distribution at lower concentration and more pronounced hotspot formation at higher concentrations. ROI-based co-localisation analysis showed increasing spatial association between Eu and endogenous elements, particularly Fe, suggesting that Eu-associated signals were spatially structured within gut-associated elemental microenvironments rather than uniformly distributed. This study demonstrates that Eu-doped NPls combined with ICP-MS and synchrotron nano-XRF provide a complementary element-specific framework for linking quantitative body-burden analysis with spatially resolved biodistribution in aquatic organisms.

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Abstract: Air pollution is one of the leading global health risks according to the World Health Organization (WHO). Addressing this problem requires a variety of technological solutions such three-way catalysis (TWC), which reduces the tailpipe emissions of gasoline engines. TWC accomplishes this by catalyzing reactions between CO, NO, unburnt hydrocarbons and remaining O2, converting them into less harmful gaseous products. Despite being a long-established technology, continuous innovation is still required to meet the increasingly stringent legislative standards that aim to limit emissions from cars. Since modern three-way catalysts already operate efficiently at elevated temperatures, research efforts have shifted towards improving the low-temperature activity of such catalysts and decreasing emissions slip during the cold-start phase of the engine. Achieving this goal requires a molecular understanding of the underlying catalytic processes, which provides a basis for the rational design and optimization of improved catalyst systems. A typical three-way catalyst consists of a ceramic monolithic substrate onto which a wash coat containing catalytically active material is applied. These typically contain Pd, Pt and Rh as active metals, a ceria-zirconia based oxygen storage component, and a range of catalytic and structural promoters, all supported on alumina which provides stability and a high internal surface area. During operation, the active metals catalyze various reactions in parallel, most notably CO oxidation, NO reduction and hydrocarbon oxidation. The ceria-based component plays a crucial role by storing and releasing oxygen, thereby providing oxygen buffering under fluctuating exhaust gas compositions. Ceria in contact with active metal sites can directly participate in catalytic reactions by supplying oxygen at the metal-ceria interface, which helps mitigate CO poisoning of the metal. Furthermore, ceria can enhance catalyst durability by stabilizing highly dispersed metal species and preventing their agglomeration. The synergy of these functions makes ceria a highly effective promoter in three-way catalysis. Ceria-based catalysts in which the metal is highly or even atomically dispersed have attracted considerable attention due to their unique catalytic properties and high metal utilization. In these catalysts, precise control over both the metal and ceria speciation was found to be key for optimizing catalytic performance. Although substantial progress has been made in identifying catalytically active species and establishing structure-performance relationships, most studies rely on CO oxidation as a model reaction. This work extended this approach by investigating the behavior of ceria-based model three-way catalysts under more realistic operating conditions. These conditions include complex exhaust gas mixtures, fluctuating gas compositions and high temperatures. Particular emphasis is placed on the dynamic nature of metal speciation, which was studied by operando spectroscopy and transient kinetics. Our results reveal that significantly more complex behaviors emerge under realistic conditions than in simplified model reactions. This highlights the critical importance of understanding and controlling dynamic catalyst behavior, as well as identifying the mechanisms of inhibition and deactivation, for the design of effective three-way catalysts. In Chapter 2, Pd-CeO2 and Pt-CeO2 model three-way catalysts containing highly dispersed metal species were investigated under realistic operating conditions. The study included perturbed experiments with oscillating exhaust gas compositions, as well as cold-start tests that mimic the initial phase of rapid catalyst heating. Using quasi-in situ XPS, reducibility was identified as a key parameter determining activity, as it dictates the temperature at which highly active reduced species are formed under reaction conditions.

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Abstract: Nickel-based cathodes are widely used in alkaline water electrolysis, yet the nature and stability of the active surface under operating conditions remains unclear. In particular, the role of metal/oxo–hydroxo interfacial structures in governing hydrogen evolution activity is not well understood. Here, we employ a multimodal, depth-sensitive approach combining operando Ni L-edge X-ray absorption spectroscopy, depth-sensitive X-ray absorption measurements in total electron yield and Auger electron yield modes, X-ray photoelectron spectroscopy, isotopically labeled nano secondary ion mass spectrometry, and online electrochemical mass spectrometry to directly track the evolution of Ni/NiOxHy interfaces during the hydrogen evolution reaction. Using well-defined sputtered Ni thin films as a model system, we show that progressive reduction of near-surface oxide/hydroxide species is accompanied by a gradual loss of hydrogen evolution activity. Depth-resolved measurements reveal a predominantly metallic outermost surface under cathodic bias, while NiOxHy forms on the surface upon relaxation to open-circuit conditions. Importantly, mild anodic pre-conditioning regenerates subsurface NiOxHy species, resulting in a sustained increase in hydrogen evolution activity upon subsequent cathodic polarization. These results establish the crucial role of metal/oxo–hydroxo interfaces as active phases for hydrogen evolution and provide a framework for engineering robust, Earth-abundant HER cathodes capable of operating under dynamic, real-world electrolysis conditions.