Catalytic reduction of biomass-derived furanic compounds with hydrogen

Furfural and 5-hydroxymethylfurfural (HMF) are important platform chemicals in biorefinery. Reduction of furfural or HMF with H₂ over heterogeneous catalysts is the simplest way to convert the oxygen-rich compounds. However, the process can involve many types of reactions such as hydrogenation of the C=O bond, hydrogenation of the furan ring, C-O hydrogenolysis, rearrangement, C-C dissociation, and polymerization. Hydrogenation reactions are most studied in line with hydrogenations of other α,β-unsaturated aldehydes, and it becomes possible to produce each product selectively: furfuryl alcohol, tetrahydrofurfuryl alcohol, 2,5-bis(hydroxymethyl)furan, or 2,5-bis(hydroxymethyl)tetrahydrofuran. Total reduction of side substituents to give 2-methylfuran or 2,5-dimethylfuran is another well-known reaction. Rearrangement and C-O hydrogenolysis reactions have been recently investigated, and they can give useful products such as cyclopentanone, 1,5-pentanediol, and 1,6-hexanediol. Ongoing studies of the reaction mechanisms are also reviewed.