Insights into selective hydrogenation of levulinic acid using copper on manganese oxide octahedral molecular sieves

Selective hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) was studied using copper on manganese oxide octahedral molecular sieve (OMS-2) as catalysts. A range of copper supported on OMS-2 catalysts was prepared using the modified wet-impregnation technique and characterized thoroughly using powder X-ray diffraction, inductively coupled plasma optical emission spectroscopy metal analysis, Fourier transform infrared, high-resolution transmission electron microscopy and N₂ sorption analyses. Process parameters for selective hydrogenation of LA to GVL were optimized using the design of experiment (DoE) approach with response surface methodology comprising a central composite design. Using the optimized conditions (190°C reaction temperature, 20 bar H₂ pressure and 20 wt% Cu loading on OMS-2), up to 98% yield of GVL could be achieved in water as a solvent. Based on DoE, H₂ pressure had the most influence on GVL selectivity followed by catalyst loading used for the hydrogenation of LA. The response surface methodology model also showed synergistic effect of reaction temperature and H₂ pressure on the yield of GVL. 20 wt% Cu/OMS-2 catalysts were re-used up to four cycles and showed noticeable loss of activity after the first cycle due to observed leaching of loose Cu species, thereafter the activity loss diminished during subsequent recycles.