Room temperature oxidative denitrogenation of model esterified bio-oil with remarkable metal-free B and N co-doped carbon-based catalysts

초록

Esterified bio-oil, derived from microalgae, serves as a promising substitute for diminishing fossil fuel resources although improving quality and reducing its high nitrogen content remain key challenges. Here, metal-free B and N co-doped carbon catalysts were used for oxidative denitrogenation of a model esterified bio-oil. The catalysts were prepared by pyrolysis, in two steps, of composites of boric acid (with various contents) and urea-loaded polypyrroles (Ppy). Nearly complete conversion of indole and quinoline could be obtained even at 25 degrees C in 50 min with a selected metal-free catalyst, B(40%)-PpyDC. An extremely low activation energy (26.9 kJ mol-1), which is not far from the energy of a physical process or diffusion, was observed in the indole oxidation. The remarkable performance of the catalyst in oxidative denitrogenation might be due to the ready formation of hydroxyl radicals that was confirmed by electron spin resonance spectroscopy and radical trapping experiments. DFT calculations supported the large charge separations (N delta-and B delta+) on the carbonaceous catalyst where oxidant H2O2 can be effectively adsorbed and activated to produce center dot OH radicals. A potential reaction mechanism could be suggested to follow the experimental and calculation results. B(40%)-PpyDC was recyclable for the oxidative denitrogenation, by simple acetonitrile and ethanol soaking, with comparable performance to the fresh catalyst.

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