Ethane-Bridged Organosilica Nanotubes Functionalized with Arenesulfonic Acid and Phenyl Groups for the Efficient Conversion of Levulinic Acid or Furfuryl Alcohol to Ethyl Levulinate

A series of ethane-bridged organosilica nanotubes functionalized with arenesulfonic acid and phenyl groups (ArSO3H-Si(Et)Si-Ph-NTs) was fabricated successfully by a P123-directed sol-gel co-condensation route combined with hydrothermal treatment with a carefully adjusted P123-to-bis-silylated organic precursor-to-HCl molar ratio in the starting system. The morphological characteristics, textural properties, BrOnsted acidity, surface hydrophobicity, and structural integrity of the carbon/silica framework were characterized. The ArSO3H-Si(Et)Si-Ph-NTs materials were applied in the synthesis of ethyl levulinate from the esterification of levulinic acid and the ethanolysis of furfuryl alcohol, and the excellent catalytic activity was explained in terms of the strong BrOnsted acidity, unique hollow nanotube morphology, and enhanced surface hydrophobicity. Reusability tests confirmed that ArSO3H-Si(Et)Si-Ph-NTs can be reused for three or five times without a significant loss of activity.