Catalytic upgrading of levulinic acid to ethyl levulinate using reusable silica-included Wells-Dawson heteropolyacid as catalyst

In this paper we report, for the first time, the direct incorporation of a heteropolyacid (HPA) with Wells-Dawson structure during the synthesis of silica by the sol–gel technique, in acidic media, using tetraethyl orthosilicate. The catalyst characterization was carried out by 31P MAS-NMR, FT-IR, XRD, N2 adsorption–desorption measurements, and the acidic properties were determined through potentiometric titration with n-butylamine. The synthesized catalysts were used in the esterification of levulinic acid with ethanol, at 78 °C, to obtain ethyl levulinate. The synthesis of silica-included HPAs was satisfactory, and the samples kept their HPA structure intact after synthesis. The catalytic tests for the esterification reaction between levulinic acid and ethanol to produce ethyl levulinate have shown that the silica-included Wells-Dawson HPA is an active and selective catalyst for this reaction. It must be noted that silica-included HPAs also kept their structure and catalytic activity after three consecutive reaction cycles. These results indicated that these solid acids are promissory catalysts for the esterification reaction of levulinic acid and ethanol to ethyl levulinate.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Direct incorporation of Wells-Dawson heteropolyacid in silica by sol-gel. ► Upgrading of levulinic acid using silica included Wells-Dawson structure as catalyst. ► Well-Dawson heteropolyacid as re-usable heterogeneous catalyst in polar media.