Effect of Capping Ligands for the Synthesis of Gold Nanoparticles and on the Catalytic Performance for the Oxidation of 5-Hydroxymethyl-2-furfural

Different series of Au on carbon catalysts were prepared via sol-immobilization to investigate the role of polymers (polyvinylpyrrolidone PVP, polyethylene glycol PEG and polyvinyl alcohol PVA), employed as gold nanoparticle (NP) stabilizers, on catalyst properties and on catalytic activity. The synthesized materials were widely characterized with several techniques (DLS, XRD, TEM and XPS) and used as catalysts in the 5-hydroxymethylfurfural (HMF) oxidation to produce 2,5-furandicarboxylic acid (FDCA). The obtained results clearly demonstrated the PVA leading to the formation of smaller and more active NPs. On the contrary, polyethylene glycol was shown to affect gold exposure and, as a consequence, to reduce the catalyst activity due to steric effects while PVP-based catalysts presented bigger and more covered Au NPs. The investigation on the reusability of the catalysts demonstrated the presence of a significant deactivation on all prepared materials, but the presence of higher amounts of polymer seems to have a positive effect on catalyst stability even if associated with lower reactivity. Computational studies have provided interesting information on the NP-polymer interactions and consequently on the catalytic activities.