Integrated Hydrogen Transfer Reductive Catalytic Fractionation of Lignocellulose in an n -Butanol/Water System

Abstract The reliance on external molecular hydrogen in conventional reductive catalytic fractionation (RCF) compromises the sustainability of lignocellulose valorization. Herein, a hydrogen‑transfer RCF system was developed through coupling a Ru/AC‑400 (activated carbon, 400 mesh) catalyst with an n-butanol (nBuOH)/water solvent mixture, enabling complete biomass conversion with integrated product separation upon cooling of the reaction liquor. Under optimized conditions, this system afforded a lignin monomer yield of 50.7 wt % and a solid residue below 0.5 wt %, with spontaneous phase separation of products upon cooling. This yield was obtained without external hydrogen and is comparable to that reported for nBuOH/water RCF under 30 bar H2, while far exceeding the yield when H2 was replaced by N2. Because the reaction left no solid biomass residue, the catalyst could be recovered by simple filtration, thereby simplifying catalyst recovery compared with conventional RCF processes that require additional separation steps. Mechanistic investigations indicated that nBuOH serves a dual function, acting as both a lignin solvent and, through dehydrogenation on Ru sites, an in situ hydrogen source for selective β−O−4 cleavage, while the aqueous phase promotes polysaccharide hydrolysis and monosaccharide conversion. Recycling experiments traced deactivation primarily to Ru sintering, support degradation, and carbonaceous deposition. Applicable across diverse lignocellulosic feedstocks, the process provides an operationally straightforward strategy for hydrogen‑transfer integrated biorefining.