Synergistic role of trace water in FeCl3–γ-valerolactone systems for efficient biomass-to-furfural conversion

Efficient conversion of lignocellulosic biomass into furan-based chemicals is crucial for sustainable biorefineries. This study presents a synergistic catalytic system combining ferric chloride (FeCl 3 ) with a γ-valerolactone (GVL)/H 2 O co-solvent, revealing the pivotal role of trace water in enhancing furfural production. Under optimized conditions (H 2 O:GVL = 2:28, 180 °C), the system achieved an apparent furfural yield of 109.5 %, calculated based on the theoretical furfural yield from the xylan content of corncob. Mechanistic insights elucidated that Fe 3+ disrupts biomass–solvent interactions, thus facilitating hemicellulose and cellulose depolymerization. The significant 5-HMF yield highlights the system capacity to effectively hydrolyze cellulose into glucose and subsequently convert it via Fe 3+ -catalyzed aldose–ketose isomerization and dehydration pathways. Isotopic labeling with [1– 13 C] and [6– 13 C] glucose confirmed that Fe 3+ catalyzes aldose–ketose isomerization, a critical step steering sugar conversion toward furanic compounds. Furthermore, 2D-HSQC NMR and TG-FTIR-GC/MS analyses revealed that the FeCl 3 –GVL/H 2 O system promoted lignin depolymerization into low-molecular-weight aromatics for enhancing lignin valorization. Together, these findings reveal that trace water lowers the activation energy to accelerate sugar release and modulates the hydrogen-bonding network to stabilize furfural, while the GVL-rich phase stabilizes reactive intermediates, suppressing side reactions and improving furfural selectivity. Compared to conventional mineral acid systems, the FeCl 3 –GVL/trace-water system offers superior selectivity and efficiency under optimized conditions for biorefinery of lignocellulosic biomass.