Hydrogen Transfer Reaction as an Alternative Reductive Process for the Valorization of Biomass-Derived Building Blocks

In the field of biomass valorization, reductive processes for the sustainable production of bio-fuel additives and chemicals have gained a great deal of interest. Catalytic transfer hydrogenation, which uses alcohols as the hydrogen source, offers an interesting approach that avoids the use of both high H 2 pressure and precious metal catalysts. This H-transfer reaction has been studied in many processes using different type of catalysts (acid, base, and metal-supported materials); recently, reductive upgrading of biomass for chemicals and fuels production through catalytic hydrogen transfer processes, has gained increasing attention. Among the other biomass derived molecules, the H-transfer process can be applied to reduce furfural (FU) and 5-hydroxymethylfurfural (HMF). Reported data demonstrated that in the presence of secondary alcohols and metal-based catalyst, remarkable results were obtained in these reactions, leading to the selective production of furfuryl alcohol (FAL) and 2,5-bis(hydroxymethyl)furan (BHMF). Recent examples demonstrated the possibility to reduce FU and HMF both in liquid and gas phase using inexpensive oxides such as MgO, CaO, SrO, Mg/Fe/O and FeVO 4 , and methanol as hydrogen donor. Compared to the alcohols typically used for carbonyl reductions, methanol showed the advantage of producing gaseous components as the only co-products, which are easily separated from the reaction medium. Moreover, the in situ generation of formaldehyde, due to methanol dehydrogenation, can contribute to the formation of different products. Indeed, in the studied processes, furfuryl alcohol (FAL), bis-hydroxymethylfuran (BHMF) and methyl furan (MF) were produced with high selectivity depending on the reaction conditions and on the chosen catalyst. The obtained results highlight the potential application of the H-transfer reaction over solid basic oxides as an efficient process for the selective de-oxygenation of biomass derived molecules.