Acidic ion functionalized N-doped hollow carbon for esterification of levulinic acid
Acidic ion functionalized N-doped hollow carbon (NHC-[C4N][SO3CF3]) has been successfully synthesized by quaternization of N-doped hollow carbon (NHC) with 1,4-butanesultone, followed by ion exchange with trifluoromethanesulonic acid. The catalyst was characterized by fourier transform infrared (FT-IR), scanning electron microscopy (SEM), acid−base titration techniques and other methods. And a hollow spherical catalyst with regular morphology, high acid density (2.72 mmol/g) and good stability was obtained. Various characterizations showed that NHC-[C4N][SO3CF3] possesses abundant nanopores (3.41 nm), large Brunauer–Emmett–Teller (BET) surface areas (154 m2•g-1) and strong and controllable Brønsted acid sites. The as-prepared NHC-[C4N][SO3CF3] was then used for the acid-catalyzed esterification of levulinic acid with ethanol. At the optimum conditions, the highest conversion of levulinic acid reached 94.17% and high conversion was maintained after four recycles. Further investigation of the catalytic activity in the esterification of different aliphatic and aromatic alcohols with levulinate was carried out, showing good results.