Noble and Base-Metal Nanoparticles Supported on Mesoporous Metal Oxides: Efficient Catalysts for the Selective Hydrogenation of Levulinic Acid to γ-Valerolactone

Abstract: The selective hydrogenation of levulinic acid, LA to γ-valerolactone, GVL in water and solvent-free systems using mesoporous TiO₂, NiO and MnO₂ metal oxides supported noble and base-metal nanoparticles was investigated. BET results showed that all the synthetized materials were mesoporous with type IV isotherms and type I hysteresis. The p-XRD peaks observed in the low angle region 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. TPR results showed that the reduced supported nanocatalysts consist of metallic Ru, Pd, Cu and Cr, and the average particle sizes obtained from HRTEM were found to be of 2 to 6 nm in diameter. The as-synthetized reusable nanocatalysts were revealed to be highly efficient for the conversion of LA to GVL. 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 an activity, TOF of up to 277273 h⁻¹/mol, the low cost copper-based nanocatalysts could be an alternative to the high cost noble metal-based catalysts. Graphical Abstract: [Figure not available: see fulltext.].