Résumé
One of the main challenges in nanoparticle-promoted catalysis is preventing sintering under reaction conditions, while maintaining both stability and high catalytic activity -properties tunable via rational surface ligand design. Although molecular silsesquioxanes offer structural versatility and robustness, their use as stabilizing agents for gold nanoparticles remains underexplored, particularly regarding their influence on nanoparticle properties and catalytic performance. In this work, we report the synthesis of gold nanoparticles functionalized with a series of thiol-decorated molecular silsesquioxanes, and their application as catalysts for the oxidative dehydrogenation of alcohols -a key transformation in organic synthesis and biomass valorization. Five thiolated silsesquioxanes were investigated featuring either three-dimensional (3D) core structures (ladder-type, double-decker, and cubic T8-cage), or a two-dimensional (2D) scaffold based on the quasi-planar all-cis cyclotetrasiloxane (T4) cyclic silanol. We show that the core topology and number of thiol groups affect nanoparticle size and aggregation, which in turn influence catalytic behavior. The tetrathiol-functionalized ladder-type and double-decker silsesquioxanes were the most efficient ligands, affording spherical Au nanoparticles with good yields, predominantly below 2 nm, and with a minor population around 5 nm. Double-decker-stabilized nanoparticles retained high catalytic activity and stability over five cycles in alcohol oxidative dehydrogenation, whereas ladder-type-stabilized NPs showed some sintering.
Conversely, the octathiol-substituted cubic silsesquioxane caused significant nanoparticles aggregation, and the T4-based ligand produced ultra-small Au nanoparticles with low yield and poor catalytic activity. These findings highlight the critical role of the silsesquioxane on nanoparticle stabilization and catalytic performance.