Title : Noble and base-metal nanoparticles supported on mesoporous metal oxides: Efficient catalysts for the selective hydrogenation of levulinic acid to gamma valerolactone
Abstract:
The selective hydrogenation of levulinic acid, LA to γ-valerolactone, GVL in water and solvent-free systems using metal oxides supported noble and base-metal nanoparticles was investigated. Highly stable and meso- structured TiO2, NiO and MnO2 were synthesized using an inverse surfactant micelle method, and the mesoporous metal oxides supported Ru, Pd, Cu and Cr nanoparticles were synthetized by homogeneous deposition precipitation. The N2-physisorption study showed that all the synthetized materials were mesoporous with type IV isotherms and type I hysteresis loops. The materials have a narrow pore size distribution of uniform size, with the pore diameters of 3.2, 3.7 and 13.3 nm for TiO2, NiO and MnO2, respectively. The diffraction peaks observed in the low angle region of the p-XRD patterns confirm the successful formation of the meso-structured materials, whereas the wide-angle diffraction patterns show that the crystalline structure of the pure nanocatalysts is maintained upon deposition of the metal. The Temperature-Programmed Reduction study showed that the reduced supported nanocatalysts consist of metallic Ru, Pd, Cu and Cr, and the average particle sizes obtained from the high-resolution transmission electron microscopy study were found to be of 2 to 6 nm in diameter. The mesoporous supported noble and base-metal nanocatalysts as synthetized in this study were revealed to be highly stable and efficient for the conversion of biomass-derived LA to GVL, an ideal sustainable liquid fuel. The best performance with complete conversion of LA and >95% GVL selectivity was obtained from the TiO2 and MnO2-based nanocatalysts when water was used as a solvent. The order of reactivity of the supported metal nanoparticles was established as: Pd ≈ Ru > Cu > Cr. With a TOF of up to 277273 the low cost copper-based nanocatalysts as synthetized in this study could be an alternative to the high cost noble metal-based catalysts. The catalysts could be reused several times without substantial loss of activity and selectivity
