Steering the Ester and γ‑Valerolactone Selectivities in Levulinic Acid Hydrogenation

Both alkyl esters and γ-valerolactone (GVL) derived from levulinic acid (LA) have applications as renewable transportation fuel/fuel additives. Non-noble metal cobalt supported on La₂O₃ catalyst was developed for efficient cascade LA hydrogenation to GVL via esterification. LA hydrogenation in methanol alone yielded methyl levulinate (MeLA) as a major product along with 43% of GVL. Interestingly, hydrogenation in water gave almost complete selectivity to GVL; nevertheless, it was associated with significant metal leaching. Suppression of metal leaching and enhancement in selectivity to GVL could be achieved by a methanol/water (95:5) solvent system. XRD analysis of La₂O₃-supported catalysts evidenced the characteristic peaks of a mixture of La₂O₃ and La­(OH)₃ phases. Basicity, as well as acidity, of the catalyst as determined by CO₂ and NH₃ TPD was due to these La₂O₃, Co–La, and La­(OH)₃ phases which played an important role in directing the product selectivity in levulinic acid hydrogenation. At the low temperature of 160 °C, almost equal selectivities of MeLA (47%) and GVL (43%) were observed, while higher temperature (200 °C) favored further hydrogenation of MeLA to GVL (75%). Similarly, with an increase in reaction time to 9 h, the GVL selectivity achieved was as high as 80%. The selectivity to MeLA and GVL in LA hydrogenation over Co/La₂O₃ catalyst can be altered by suitably adjusting the reaction conditions