Selective Deoxygenation of Biomass Polyols into Diols

The transition to a sustainable chemical industry necessitates efficient valorization of biomass, with polyols serving as versatile, renewable feedstocks. This comprehensive review, focusing on advancements within the last five years, critically analyzes the selective hydrogenolysis of key biomass-derived polyols-including glycerol, erythritol, xylitol, and sorbitol-into valuable diols. Emphasis is placed on the intricate catalytic strategies developed to control C-O bond cleavage, preventing undesired C-C scission and cyclization. The review highlights the design of bifunctional catalysts, often integrating noble metals (e.g., Pt, Ru, Ir) with oxophilic promoters (e.g., Re, W, Sn) on tailored supports (e.g., TiO₂, Nb₂O₅, N-doped carbon), which have led to significant improvements in selectivity towards specific diols such as 1,2-propanediol (1,2-PD), 1,3-propanediol (1,3-PD), and ethylene glycol (EG). While substantial progress in mechanistic understanding and catalyst performance has been achieved, challenges persist regarding catalyst stability under harsh hydrothermal conditions, the economic viability of noble metal systems, and the processing of complex polyol mixtures from lignocellulosic hydrolysates. Future directions for this field underscore the imperative for more robust, cost-effective catalysts, advanced computational tools, and intensified process designs to facilitate industrial-scale production of bio-based diols.