Nitrogen-Doped Carbon-Based Acidic Ionic Liquid Hollow Nanospheres for Efficient and Selective Conversion of Fructose to 5-Ethoxymethylfurfural and Ethyl Levulinate

Nitrogen-doped carbon-based acidic ionic liquid hollow nanospheres, [C3N][SO3CF3]-HCSs (C-3 = PrSO3H), with different particle sizes (100-900 nm) and shell thicknesses (5-25 nm) as well as interesting morphology-dependent porosity properties were successfully prepared via quaternary ammonization of nitrogen atoms of hollow nitrogen-doped carbon nanospheres by 1,3-propane sultone followed by anion exchange with trifluoromethanesulonic acid. The [C3N][SO3CF3]-HCSs were applied in selective conversion of fructose (FOS) to promising fuel blends, 5-ethoxymethylfurfural (5-EMF) and ethyl levulinate (EL). It showed the [C3N][SO3CF3]-HCSs exhibited high total yields of 5-EMF and EL (higher than 90%), regardless of their particle size and shell thickness, attributed to extremely high selectivity to both compounds, and thereby, very few side products including soluble oligomers and humins were produced. Additionally, the product distribution strongly depended on the morphology and porosity properties of the [C3N] [SO3CF3]-HCSs. [C3N][SO3CF3]-HCSs-1 with the smallest particle size, thinnest shell, and largest Brunauer-Emmett-Teller (BET) surface area possessed the highest EL yield (89.7%), while [C3N][SO3CF3]-HCSs-4 with the smallest particle size, thickest shell, and smallest BET surface area gave rise to the highest 5-EMF yield (67.2%). More importantly, the [C3N] [SO3CF3]-HCSs can be reused five times without changes in catalytic activity, Bronsted acid nature, morphology, and porosity properties.