Green catalytic synthesis of 5-methylfurfural by selective hydrogenolysis of 5-hydroxymethylfurfural over size-controlled Pd nanoparticle catalysts

A green approach for the conversion of 5-(hydroxymethyl) furfural (HMF) to 5-methylfurfural (MF) by using size-controlled palladium catalysts has been developed. Palladium nanoparticles (Pd NPs) with various sizes supported on activated carbon were prepared with polyvinylpyrrolidone (PVP) as the capping agent. The reaction results showed that all the PVP-assisted Pd catalysts achieved high selectivity whilst the hydrogenation ability of Pd NPs could be rationally tuned by varying the mole ratio of Pd/PVP. 2.5% Pd-PVP/C (1 : 2) presented a satisfactory activity with 80% MF yield and 90% selectivity. The reaction kinetics study showed that the transformation of HMF into MF over bifunctional PVP-assisted Pd NPs underwent an acid-catalyzed esterification followed by a Pd-catalyzed hydrogenolysis procedure. The role of formic acid in the transformation is not only as a hydrogen-donating agent but also as a reactant to form the key intermediate. This work provides a novel and environmentally-friendly method for the selective hydrogenation of bio-based HMF to MF.