Open Amorphous N-doped Carbon-Coated MoO2 Nanorods for Highly Efficient Synthesis of 2,5-Diformylfuran from 5-Hydroxymethylfurfural/Fructose

Highly efficient synthesis of 2,5-diformylfuran (DFF) from 5-hydroxymethylfurfural (HMF) or fructose has attracted much attention in recent years. Herein, one-dimensional MoO2@a-NCx core–shell nanorods that oxygen vacancy-rich molybdenum dioxide (MoO2) coated with porous amorphous nitrogen-doped carbon layer (a-NC) are synthesized via pyrrole polymerization followed by pyrolysis, using orthorhombic molybdenum trioxide (α-MoO3) nanorods as a precursor. Benefiting from the well-engineered architecture and the strong interfacial interaction between MoO2 and surface carbon, the optimized MoO2@a-NC9 with an a-NC layer thickness of ∼9 nm exhibits considerable catalytic activity and stability in oxidation of HMF/fructose to DFF. Under optimal reaction conditions, MoO2@a-NC9 achieves nearly quantitative DFF yield of 99.1% with complete HMF conversion (100%) in the aerobic oxidation of HMF. A possible reaction mechanism involving a Mo4+/Mo3+ redox cycle is proposed for MoO2@a-NC9-catalyzed oxidation of HMF to DFF, based on experimental and characterization results. Furthermore, MoO2@a-NC9 served as a bifunctional catalyst for direct conversion of fructose to DFF via a “one-pot, two-step” approach, achieving a high DFF yield of 82.5%. Notably, this catalyst exhibits excellent recyclability, maintaining its catalytic performance over at least six reaction cycles without significant activity decay.