A Review on the Critical Role of H₂ Donor in the Selective Hydrogenation of 5-Hydroxymethylfurfural

The selective hydrogenation of 5-hydroxymethylfurfural (HMF) has been of great interest to many scientists and researchers. However, conventional hydrogenation inevitably requires the use of gaseous hydrogen as a reducing agent, which is detrimental to its storage and transport. In this regard, other economical and environmentally friendly strategies, such as catalytic transfer hydrogenation/hydrogenolysis without external molecular H₂, become more and more attractive. This Review provides the status and insight into the current research of hydrogenating HMF to high-value chemicals, using formic acid, alcohols, polymethylhydrosiloxane, water, and sodium borohydride as hydrogen donors and explains the hydrogenation mechanisms and the related hydrogenation characteristics of different hydrogen donors in the catalytic systems.