Gas-Phase Catalytic Transfer Hydrogenation of Methyl Levulinate with Ethanol over ZrO2

This paper reports about the gas-phase reduction of methyl levulinate to valerolactone (GVL) via catalytic transfer hydrogenation using ethanol as the H-donor. In particular, high-surface-area, tetragonal zirconia has proven to be a suitable catalyst for the reaction. Under optimized conditions, the reaction is selective toward the formation of GVL (yield 70%). However, both the deposition of heavy oligomeric compounds over the catalytic surface and the progressive conversion from Lewis to Brønsted acidity, due to the reaction with the water formed in situ, led to a progressive change in the chemo-selectivity, promoting side reactions, e.g. the alcoholysis of angelica lactones to ethyl levulinate. However, the in situ regeneration of the catalyst performed by feeding air at 400 °C for 2 h permitted an almost total recovery of the initial catalytic behavior, proving that the deactivation is reversible. The reaction has been tested also using a true bioethanol, derived from agricultural waste.