Acidic ion functionalized N-doped hollow carbon for esterification of levulinic acid

Abstract

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 trifluoromethanesulfonic acid. The catalyst was characterized by Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), acid–base titration techniques and other methods. A hollow spherical catalyst with regular morphology, high acid density (2.72 mmol g⁻¹) and good stability was obtained. Various characterizations showed that NHC-[C₄N][SO₃CF₃] possesses abundant nanopores (3.41 nm), large Brunauer–Emmett–Teller (BET) surface area (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 recycling four times. Further investigation of the catalytic activity in the esterification of different aliphatic and aromatic alcohols with levulinate was carried out, showing good results.