Total scattering and spectroscopy reveal the dynamic behaviour of PGM catalysts in the liquid and gas phase designing experiments, following structures

Supported metal nanoparticles (NPs) are a prime example of the advantages of heterogeneous catalysts due to their high surface area and tunable electronic properties. Their catalytic performance is strongly influenced by structural changes undergone in reaction conditions, including hydride formation, oxide reduction, and adsorbate-induced restructuring. Capturing these processes at the nanoscale requires operando multi-technique characterization with simultaneous sensitivity to atomic structure and electronic state. This thesis addresses this challenge by developing a dedicated synchrotron-based experimental platform combining time-resolved high-energy X-ray diffraction (XRD), pair distribution function (PDF) analysis, and X-ray absorption spectroscopy (XAS) to study supported NPs in liquid and gas phases. A systematic approach to data analysis was key to extract kinetic and structural information from complex, synchrotron-sized datasets, enabling unprecedented insight into nanoparticle behavior. The first study investigates the liquid-phase reduction of industrial PdO/Al₂O₃ catalysts with sodium formate and sodium borohydride. Time-resolved XRD, PDF, and XAS reveal distinct reduction pathways and hydride formation modes, demonstrating that the choice of reductant strongly affects nanoparticle size, dispersion, and metal-support interactions. The second study explores the reduction of the same sample in isopropanol, both with and without dissolved H₂ at different temperatures, highlighting the role of the hydrogen donor solvent in controlling hydride content and nanoparticle dispersion. Isopropanol alone yields dispersed Pd NPs with limited bulk hydrides, whereas H₂ accelerates reduction and promotes extensive hydride formation, informing strategies for selective hydrogenation under mild conditions. The third study examines H₂-induced restructuring of Al2O3 supported Pt nanoparticles. Operando XRD and PDF reveal reversible lattice expansion, “breathing,” and partial detachment from the support, confirming theoretical predictions and providing insight into hydride-dependent structural dynamics relevant for catalyst stability. The fourth study investigates CO-induced modifications of Pd nanoparticles in the gas phase. Total scattering analysis shows that CO adsorption partially disorders the surface while relaxing the nanoparticle core, illustrating depth-dependent adsorbate effects. Together, these studies demonstrate that multi-technique operando characterization provides a comprehensive understanding of supported NPs. The experimental setup and analysis framework developed in this work enables real-time monitoring of structural and electronic evolution, offering mechanistic insights critical for rational catalyst design. The findings on Pd and Pt nanoparticles elucidate relationships between reduction conditions, hydride formation, nanoparticle morphology, and metal-support interactions, laying the basement for predictive control of heterogeneous catalysts under industrially relevant conditions.