New methods for ultra sensitive broadband MAS NMR spectroscopy for chemistry ; Nouvelles méthodes de spectroscopie RMN du solide large bande et haute sensibilité pour la chimie

Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy has become an essential tool for probing the atomic-level structure of materials. However, traditional NMR techniques often face significant challenges when applied to samples such as heterogeneous catalysts, inorganic frameworks, or functional materials involving transition metals. These challenges arise due to the broadening of resonances caused by anisotropic interactions or paramagnetism, which can render traditional techniques inefficient for acquiring detailed structural information. This thesis addresses these obstacles by developing and applying new methodologies for ultra-wideline (UW) solid-state magic angle spinning (MAS) NMR spectroscopy, with the aim of enhancing both sensitivity and resolution to provide detailed structural insights. The first part of the thesis delves into the theoretical foundations of UW NMR, explaining the origins of broad NMR signals. Recognizing the inherent difficulties, the second chapter introduces Dynamic Nuclear Polarization (DNP), a technique that offers significant sensitivity gains by several orders of magnitude. This section also explores broadband static and MAS NMR techniques, providing a comprehensive set of tools designed to overcome the challenges presented by UW signals. A significant portion of the manuscript is dedicated to the application of these advanced MAS NMR techniques to the study of platinum-based heterogeneous catalysts, which play a crucial role in various industrial processes. The performance of these catalysts is heavily influenced by the structure of active sites and their interactions with supports. This work presents detailed studies using DNP-enhanced 13C and 195Pt NMR spectroscopy, offering key insights into the local environments of platinum atoms and the structure-function relationships that dictate catalytic activity. Additionally, the thesis extends these techniques to DNP-enhanced surface NMR spectroscopy, particularly through the novel use of natural abundance 13C-195Pt ...