Chitosan as a Bio-Based Ligand for the Production of Hydrogenation Catalysts

Bio-based polymers are gaining increasing interest as alternatives to harmful and en-vironmentally concerning non-biodegradable fossil-based products. In particular, bio-based polymers may be employed as ligands for the preparation of metal nanopar-ticles (M(0)NPs). In this study, Chitosan (CS) has been used for the stabilization of Ru(0) and Rh(0) metal nanoparticles (MNPs), prepared by simply mixing RhCl3x3H2O or RuCl3 with an aqueous solution of CS, followed by NaBH4 reduction. The formation of M(0)NPs-CS was confirmed by Fourier Transform Infrared Spectroscopy (FT-IR), Differential Scanning Calorimetry (DSC), Thermal Gravimetric Analysis (TGA), Scan-ning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDX), Transmis-sion Electron Microscopy (TEM) and X-Ray Diffraction (XRD). Their size was estimat-ed to be below 40 nm for Rh(0)-CS and 10nm for Ru(0)-CS by SEM analysis. M(0)NPs-CS were employed for the hydrogenation of (E)-cinnamic aldehyde and le-vulinic acid. Easy recovery by liquid/liquid extraction allowed to separate the catalyst from the reaction products. Recycling experiments demonstrated that M(0)NPs-CS were highly efficient up to four times in best hydrogenation conditions. Data achieved show that CS is an excellent ligand for the stabilization of Rh(0) and Ru(0) nanoparti-cles, allowing to produce among the most efficient, selective, and recyclable hydro-genation catalysts known in the literature.