Pyridinic-nitrogen-dominated nitrogen-doped graphene stabilized Cu for efficient selective oxidation of 5-hydroxymethfurfural

In this work, pyridinic-nitrogen-dominated nitrogen doped graphene with Cu incorporation (Cu/NG) are prepared via a facile and effective process. In prepared nitrogen doped graphene (NG), high nitrogen content up to 13.5 wt% was achieved and pyridinic-nitrogen dopant enriched to 11.9 at.%. Cu nanoparticles can be highly stabilized by NG materials and the stabilized Cu loading is linearly correlated with the pyridinic nitrogen content in NG. With Cu/NG as the catalyst and 2,2,6,6-tetramethyl-piperidin-l-oxyl (TEMPO) as co-catalyst, 5-hydroxymethylfurfural (HMF) was oxidized to 2,5-diformylfuran (DFF) in the new developed catalytic system under relative mild conditions (70 degrees C, 8h) with high HMF conversion (99.8%) and DFF yield (99.2%). By various characterization and experimental data, Cu-N-C nano-centers were speculated to be the actives sites in catalytic oxidation of HMF. Comparison of high-resolution XPS spectra of N 1s between NG and Cu/NG material indicates the existence of strong interaction between Cu nanoparticles and pyridinic N. The developed catalytic system showed high efficiency in HMF oxidation and Cu/NG can be recycled for eight times without any obvious Cu leaching and catalytic activity loss.