Recent advances in cellulose depolymerization: Mechanistic insights, catalytic innovations, and scalable pathways for biomass valorization

Abstract

Cellulose is the most abundant renewable polymer on Earth and a key feedstock for future low-carbon biorefineries. However, its industrial utilization is fundamentally limited by strong structural recalcitrance arising from crystalline domain organization, hierarchical fibrillar architecture, and extensive hydrogen-bonding networks that restrict catalytic accessibility and glycosidic bond cleavage. As a result, efficient cellulose depolymerization remains a central challenge in biomass conversion. This review critically evaluates recent advances in cellulose depolymerization across chemical, enzymatic, thermochemical, mechanochemical, oxidative, and hybrid catalytic systems. Emphasis is placed on mechanistic principles governing bond activation, including hydrolytic, radical-mediated, and energy-assisted pathways, and on how catalyst design, solvent systems, and substrate morphology influence conversion efficiency and selectivity. We further compare key performance metrics relevant to industrial deployment, including product yield, carbon efficiency, energy demand, catalyst stability, solvent recyclability, and lifecycle environmental impact. Mineral-acid processes enable rapid conversion but suffer from corrosion, degradation by-products, and waste handling issues, whereas enzymatic systems offer high selectivity but are limited by slow kinetics and feedstock sensitivity. Finally, we highlight downstream valorization routes and conclude that no single technology satisfies all industrial requirements. Future progress will depend on integrated, circular process designs combining advanced catalysis, process intensification, and digital optimization strategies.