Wool-supported Pd and Rh nanoparticles for selective hydrogenation of maleic acid to succinic acid in batch and flow systems

Wool fibers, a renewable and biodegradable waste material, provide an eco-friendly platform for supporting metal nanoparticles, thanks to their unique amino acid composition. This study reports a fast and straightforward synthesis of palladium and rhodium nanoparticles (Pd and Rh NPs) supported on wool fibers (Pd NPs/WF and Rh NPs/WF) derived from low-grade wool. The resulting catalysts, with dispersed spherical nanoparticles (about 5 nm), were characterized by SEM, TEM, XPS, and XRD. They were tested for the selective hydrogenation of maleic acid (MA) to succinic acid (SA) under mild batch and continuous-flow conditions. Both catalysts exhibited excellent activity and full selectivity, achieving complete conversion in 2 h with 3 mol% metal loading in batch, in water solution at room temperature and under H₂ flux. Notably, Rh/WF also performed effectively in a fixed-bed flow reactor using hydrazine sulfate as an alternative hydrogen donor and fully converted MA into SA in 75 minutes, in a water solution at room temperature. The catalysts were robust and recyclable without loss of activity, highlighting wool-supported Pd and Rh NPs as sustainable and efficient catalysts for aqueous hydrogenation reactions.