Breaking the C-C bond of glucose on tungsten oxide-based catalysts in aqueous phase

In chemistry, selective activation of C-C bonds enables the direct production of valuable chemicals from widely available and inexpensive natural materials but remains a fundamental challenge due to their kinetic inertness. The selective cleavage of C-C bond in glucose by tungsten oxide-based catalysts in aqueous phase pioneers a path for converting cellulose biomass into valuable ethylene glycol. However, debates regarding the active phase and how it selectively breaks the C6 into C2 fragments have persisted for over a decade. In this study, we present a comprehensive mechanistic investigation by modeling three potential active phases, i.e. the reduced WO3-x surface, the dissolved tungstic acid, and tungsten bronze, in explicit solvent waters. By constrained molecular dynamics simulations, we have demonstrated that the low-coordinated W center can chelate with glucose, forming a metallacyclic complex with a 5-membered ring after the protonation of carbonyl group. The formation of 5-membered ring serves as the premise for the selectivity to C2 fragments via homolytic cleavage of C-C bond. Furthermore, the reduced W5+ center is suggested to be crucial in facilitating the cleavage process by stabilizing the dissociated C4 intermediates via a redox process. In conclusion, we propose that the surface decoration of reduced and low-coordinated W sites can act as active heterogeneous catalysts for the selective conversion of cellulose in aqueous phase. These recent findings have the potential to provide valuable insights and strategies for C-C bond activation in both biomass conversion and organic synthesis.