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Abstract: Mitigating climate change is one of the biggest challenges of today's society. The most direct way to achieve this goal is to capture and use CO2 as a source of energy and chemicals. This work, inspired by previous publications focused on homogeneous catalysis, proposes the transformation of the easy-to-prepare CO2 derivatives dialkylureas into C1 chemicals using Ru-MOFs as heterogeneous catalysts. This choice is due to (i) the well-known ability of Ru to catalyze hydrogenation reactions and (ii) that Ru-complexes were the pioneer homogenous catalyst in converting CO2 into an added-value C1 chemical, methanol. Apart from the already reported MOF Ru-HKUST-1, we have prepared a new Ru-MOF material, denoted Ru-BTC, analogous to the semiamorphous Fe-BTC. It has been found by XAS that Ru-BTC and Ru-HKUST-1 have different metal environment and oxidation states: only 3+ in Ru-BTC, a 50:50 mixture of 2+ and 3+ in Ru-HKUST-1. Both Ru-MOFs catalyzed the hydrogenation of N,N’-dimethylurea under relatively mild conditions, giving methane as the main product. Ru-BTC was particularly efficient: 67 % conversion and 96 % selectivity to CH4 at 150 ºC and 30 bars of H2 using a Ru/dimethylurea weight ratio of 1 %. Ru-MOFs were also able to transform CO2 into CH4, again being Ru-BTC the most effective catalyst, but giving much poorer selectivity to CH4. Ru-MOFs, particularly Ru-BTC, were damaged under reaction conditions, but no significant Ru leaching was observed.

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Abstract: This study of manganese (Mn, Z = 25) introduces a novel combination of extended-range high energy resolution fluorescence detection (XR-HERFD), multiple-crystal spectrometers and advanced binary data splicing techniques to address challenges in X-ray emission spectroscopy. XR-HERFD enhances spectral precision by utilizing high-resolution crystal analysers and optimized detector configurations. The systematic application of these methods using multiple Bragg crystal analysers at Diamond Light Source has led to substantial improvements in data quality. Simultaneously, advanced binary data splicing integrates multiple datasets to correct distortions and improve resolution, resulting in sharper spectral features. Our results show a significant increase in peak counts and a notable reduction in full width at half-maximum (FWHM), with peak amplitudes increasing by 83% and resolution improving by 46%. These developments provide greater detail for X-ray absorption or emission spectra, offering valuable insights into complex materials, and permitting advances and breakthroughs in atomic relativistic quantum mechanics, chemical sensitivity of atomic transitions and modelling of solid-state effects.

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Abstract: Operating lithium ion batteries (LIBs) to high charging cut off potentials allows us to accommodate a further push in energy density. However, it requires a thorough understanding of the interplay and temperature dependence of parasitic reactions that aggravate the aging of the electrolyte and the cathode/anode electrodes. In the present study we investigated the interplay of the chemical and the electrochemical electrolyte oxidation, how they are related to the dissolution of transition metal (TM) ions from the cathode active material (CAM), and how they shift or accelerate with temperature. Through an optimized electrochemical protocol an excellent potential dependence of the gas evolution of a LiNi0.80Co0.15Al0.05O2 (NCA) charged against a free standing graphite on a lithium metal electrode in a LP47 electrolyte was achieved. We identified O2 and PF5 gas as suitable proxies for the chemical and electrochemical electrolyte oxidation, respectively. Both processes are separated by at least 300 mV over a temperature range from 10 to 45°C. Through temperature-dependent operando hard X ray absorption spectroscopy measurements and their comparison with the gassing results, it will be shown, that the electrochemical oxidation of the electrolyte is directly linked to the dissolution of TMs, while the chemical electrolyte oxidation mainly leaves the transition metal dissolution unaffected.

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Abstract: Catalytic hydrogenation reactions represent one of the most important transformations in the chemical industry. In the light of the required defossilization of the chemical value chain, the development of new, highly selective hydrogenation catalysts is of utmost importance to deal with renewable resources, such as biomass, recycled feedstock, or CO2. In that regard, this thesis deals with the preparation, characterization and application of metal nanoparticles (NPs) on molecularly modified surfaces for thermo- and electrocatalytic hydrogenation reactions. In the thermocatalytic systems, Mn-based NPs are investigated (monometallic and bimetallic MnRu NPs), as this earth-abundant metal possesses a low environmental impact and generally low toxicity. In addition, the electrocatalytic hydrogenation of alkenes, aldehydes and ketones using a Pickering emulsion-based system is described. Here, Pd NPs on molecularly modified carbon nanotubes are evaluated as catalyst. Firstly, small (1-10 nm) Mn NPs are immobilized on different carbon-based supports, as well as on a supported ionic liquid phase (SILP). Different synthetic methods are developed in order to optimize the properties of the NPs on each respective support, which are investigated using various characterization methods. The materials are evaluated for different catalytic transformations, with the catalytic transfer hydrogenation of aldehydes and ketones using Mn@SILP being found to be best performing. This material is demonstrated to be more active than previously reported Mn NP-based systems. X-ray absorption studies showed that the catalytic activity is highly dependent on the oxidation state of Mn. Followingly, bimetallic MnRu@SILP materials are prepared and characterized. Tuning the metal ratio of Mn:Ru enables the selective targeting of different products for substrates containing multiple reducible moieties. Furthermore, the alloying state of these NPs is investigated in order to assess its importance for the performance of the catalysts. The last part of this thesis deals with electrocatalytic hydrogenation (ECH) reactions, which offer an attractive way for the use of renewable electricity for chemical transformations. As water is used as solvent and hydrogen donor, the application of this reaction type for the conversion of apolar, organic systems is rather limited. In order to overcome this challenge, a Pickering emulsion-based system is developed. Herein, the apolar substrates are located within oil droplets, which are surrounded by an aqueous phase, providing the protons and high conductivity. This emulsion is stabilized by Pd NPs on molecularly modified CNTs. These CNTs additionally conduct electricity to the interface where the reaction is catalyzed by the Pd NPs. The mechanism of the ECH of alkenes is investigated and the reaction rate and Faradaic efficiency surpassed state-of-the-art Pd membrane reactors. The ECH system is further extended to the ECH of aldehydes and ketones to the respective alcohols. Here, the subsequent deoxygenation products can be also be yielded, which was not demonstrated yet in the electrocatalytic application of Pd NPs. Overall, this work contributes towards the development of novel catalytic systems for selective hydrogenation reactions. It can be demonstrated that metal NPs on molecularly modified surfaces represent a class of highly tunable catalysts. Their NP composition, choice of support and molecular modifier are varied to design highly efficient and selective catalysts for thermo- and electrocatalytic hydrogenation reactions.

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Abstract: Regioselective C–H bond functionalization is pivotal in modern scientific exploration, offering solutions for achieving novel synthetic methodologies and pharmaceutical development. In this aspect, achieving exceptional regioselective functionalization, like para-selective products in electron-poor aromatics, diverges from traditional methods. Leveraging the advantages of atomically dispersed photocatalysts, we designed a robust photocatalyst for an unconventional regioselective aromatic C–H bond functionalization. This innovation enabled para-selective trifluoromethylations of electron-deficient meta-directing aromatics (-NO2, -CF3, -CN, etc.), which is entirely orthogonal to the traditional approaches. Mechanistic experiments and DFT analysis confirmed the interaction between Cu-atom and the aromatic substrate, alongside the photocatalyst's molecular arrangement, driving selective exposure of the para-selective functionalization. This strategic approach elucidated pathways for precise molecular transformations, advancing the frontier of regioselective C–H bond functionalization by using atomically dispersed photocatalysts in organic synthesis.