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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: There is increasing interest in using Fe-rich materials in cement, yet the Fe speciation in hydrated cement paste remains poorly understood. This study quantitatively investigates the fate of amorphous Fe in hydrated white Portland cement-fayalitic slag pastes with varying Fe contents cured for 3, 28, and 90 days. The results show that Fe precipitated as ferrihydrite and potentially adsorbed on calcium (alumino)silicate hydrate (C-(A)-S-H) after 3 days of hydration. Afterwards, Fe stabilised in Fe-siliceous hydrogarnet and Fe-adsorbed C-(A)-S-H phases, accounting for ∼15% and ∼ 85% of total reacted Fe, respectively, after hydration for 90 days. The high Fe uptake by C-(A)-S-H was mainly attributed to Fe(III) adsorption rather than Fe(II). Thermodynamic modelling combined with microstructural analysis supported the predominant distribution of Fe on the C-(A)-S-H phase. These findings can advance understanding in using reactive Fe-containing materials in Portland cement pastes and the development of their chemical and physical properties.

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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: Geopolymer wasteforms are a promising alternative to Portland cement for immobilisation of intermediate-level radioactive waste, particularly caesium-137 and strontium-90. Successful implementation relies on ensuring wasteform stability and radionuclide retention under elevated temperatures expected in a geological disposal facility. This study evaluates radionuclide retention and mass transport mechanisms of Cs-and Sr-loaded geopolymers leached at elevated temperatures (35, 50, and 90 °C).Monolithic leach tests confirmed that while Cs consistently exhibits a significantly larger Cumulative Fraction Leached compared with Sr across all temperatures, all geopolymers maintained acceptable leachability indices (Li>6). Increasing the temperature to 90 °C resulted in a pronounced increase in release rates, with Cs release nearly tripling and Sr release increasing by an order of magnitude, primarily due to accelerated kinetics and increased solubility of secondary phases such as SrCO 3 at elevated temperatures. Micro-and nanostructural analysis (XRD, FTIR, NMR) confirmed that the K-A-S-H gel framework remained stable, suggesting that bulk structural integrity is not compromised by these temperatures. Mass transport modelling revealed that Cs and Sr release release is dominated by a complex, multi-parametric combination of diffusion and surface exchange kinetics (DSEM), with diffusion becoming increasingly dominant at higher temperatures. However, the temperature dependency does not conform to the Arrhenius principle, suggesting the process is governed by multiple overlapping mechanisms rather than a single activation energy across the investigated temperature range. Together, these findings show that geopolymers exhibit excellent thermal stability and maintain superior radionuclide retention performance compared to conventional cementitious systems under simulated repository temperature extremes.

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Abstract: Glycerol is an underutilized waste product that is abundantly available from the biodiesel industry. Electrocatalytic oxidation of glycerol (GOR) to formate offers an environmentally friendly and cost-effective approach to valorizing glycerol. In this study, we have developed new types of metal-doped cobalt metal-organic frameworks, which are grown directly on a carbon matrix via a one-pot synthesis as electrocatalyst precursors. In-depth structural analysis has revealed that, in the Ni-doped cobalt MOF, Ni substitutes a fraction of Co sites isomorphically, forming isolated Ni(II) centers, while Cu is present as a mixture of Cu(II) and metallic Cu, with the majority in the oxidized form as highly dispersed species and a small fraction forming nanoparticles. These materials were then subjected to a controlled potential-induced surface reconstruction to produce mixed-metal oxide/oxyhydroxide-like environments interconnected through M-O-M motifs, the extent of the reconstruction depending strongly on the dopant metal. The metal-doped derivatives were tested as electrocatalysts for the alkaline electrooxidation of glycerol using in-house designed electrochemical reactors with different cell configurations and operating modes. We demonstrated that metal-doped derivative phases exhibit improved electrocatalytic activity for GOR compared to the monometallic counterpart. These catalysts yield significant glycerol conversion rates under single-pass operation, with improved Faradaic efficiencies towards formate (up to 70%) and low energy consumption (< 320 kWh kmol−1), while suppressing the complete oxidation of glycerol to carbonate or CO2. This work provides new insight into the rational design of metal-doped MOF derivatives as highly active and selective electrocatalysts for the practical glycerol valorization.