In Situ Approach to Dendritic Fibrous Nitrogen-Doped Carbon Nanospheres Functionalized by Brønsted Acidic Ionic Liquid and Their Excellent Esterification Catalytic Performance

Chemical bonding of Brønsted acidic ionic liquids (BAILs) on suitable supports is one of the promising strategies to develop efficient solid acids for catalytic conversion of biomass/derivatives to fuels and value-added chemicals. For this purpose, a series of dendritic fibrous nitrogen-doped carbon nanospheres functionalized by BAILs are demonstrated for the first time via an in situ silica nanocasting approach followed by chemical modification with 1,3-propanesultone and trifluoromethanesulonic acid successively. The resulting DFNC–[C₃N]­[OTf] (C₃ = PrSO₃H, OTf = SO₃CF₃) serve as the solid acid catalysts for three biomass conversion-concerned esterification reactions, and by the combination of the advantages of superstrong Brønsted acidity, fascinating dendritic fibrous nanostructures, and interesting hierarchical micro-mesoporosity, the DFNC–[C₃N]­[OTf] catalysts exhibit excellent esterification activity. More importantly, the cooperation of chemical bonding the −[C₃]­[OTf^–] sites on the dendritic fibrous nitrogen-doped carbon (DFNC) support and stabilizing the −[C₃]­[OTf^–] sites within the wrinkled fibers of the support result in the DFNC–[C₃N]­[OTf] catalysts’ excellent reusability, and they can be reused at least five times without obvious changes in catalytic activity, nanostructures, porosity properties, and Brønsted acidity.