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 (FeCl3) with a γ-valerolactone (GVL)/H2O co-solvent, revealing the pivotal role of trace water in enhancing furfural production. Under optimized conditions (H2O: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 Fe3+ 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 Fe3+-catalyzed aldose–ketose isomerization and dehydration pathways. Isotopic labeling with [1–13C] and [6–13C] glucose confirmed that Fe3+ 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 FeCl3–GVL/H2O 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 FeCl3–GVL/trace-water system offers superior selectivity and efficiency under optimized conditions for biorefinery of lignocellulosic biomass.