Selective hydrogenation of levulinic acid to valeric acid and valeric biofuels by a Pt/HMFI catalyst

Abstract

We describe one-pot high-yield catalytic pathways for the conversion of levulinic acid (LA) to valeric acid (VA) or valeric acid esters (so-called valeric biofuels) under relatively mild conditions (2 or 8 bar H₂, 200 °C). A thorough screening study reveals that a HMFI zeolite-supported Pt metal cluster (Pt/HMFI) with an average cluster size of 1.9 nm shows the highest yield of VA (99%) under solvent-free conditions. The use of ethanol or methanol as solvent changes the selectivity, resulting in 81–84% yields of ethyl valerate (EV) or methyl valerate (MV). Pt/HMFI is also effective for selective formation of valeric acid esters from γVL in alcohols under H₂. Kinetics, in situ infrared (IR), and acidity–activity relationship studies show a cooperative mechanism of Pt and Brønsted acid sites of HMFI. VA formation from LA can be driven by Pt-catalyzed hydrogenation of LA to γVL, which undergoes proton-assisted ring-opening by HMFI, followed by Pt-catalyzed hydrogenation. Valeric ester formation from LA is driven by esterification of LA to levulinic ester, which is hydrogenated by Pt.