Efficient conversion of levulinic acid or furfuryl alcohol into alkyl levulinates catalyzed by heteropoly acid and ZrO2 bifunctionalized organosilica nanotubes

A series of heteropoly acid and ZrO2 bifunctionalized organosilica nanotubes (PW12/ZrO2-Si(Et)Si-NTs) were fabricated via a P123 single-micelle-templated sol-gel co-condensation route and carefully adjusted Si-to-Zr molar ratio and acidity in the initial gel mixture. The morphological characteristics, textural properties, Bronsted and Lewis acidity, and structural integrity of the incorporated Keggin units, as well as the formation of the carbon/silica framework, were well characterized. The PW12/ZrO2-Si(Et)Si-NTs hybrid nanocatalysts were applied in the synthesis of alkyl levulinates by esterification of levulinic acid and ethanolysis of furfuryl alcohol, and the obtained excellent catalytic activity was explained in terms of the strong Bronsted and Lewis acidity, unique hollow tubular nanostructure, and hydrophobic surface of the hybrid nanocatalysts; additionally, the catalysts could be reused at least three times without significant loss of activity. Finally, the possible reaction mechanism of the PW12/ZrO2-Si(Et)Si-NTs-catalyzed esterification and ethanolysis reactions were put forward. (C) 2015 Elsevier Inc. All rights reserved.