Metal-functionalized carbon nanotubes for biomass conversion: base-free highly efficient and recyclable catalysts for aerobic oxidation of 5-hydroxymethylfurfural

In this study, the oxidative conversion of 5-hydroxymethylfurfural into essential chemicals on recyclable metal (Pt, Pd, Ru, Co, & Ni)- supported catalysts is reported. While most of the catalytic reactions require a base as an additive, this current study provided a base-free environmentally benign heterogeneous catalytic system. The reactions were performed on various M/CNT catalysts. As a support, CNT played an important role in the reaction mechanism. These catalysts showed a high activity for the base free oxidation of HMF under air in aqueous media. The CNT-supported Pt, Pd, and Ru catalysts were found to be more selective towards FDCA (>97%) compared to Ni and Co for DFF (>96%). The conversion and selectivity of the products were determined using NMR and HPLC. The (1 wt%) M/CNT catalysts were prepared via solution processing and were characterized using BET, XRD, TEM, TGA, FTIR, and XPS. A noble and non-noble metal-confined CNT-based catalytic system was developed for the base-free selective oxidation of 5-hydroxymethylfurfural to produce 2,5-furandicarboxylic acid and 2,5-diformylfurane.