Ionic Immobilization of Silicotungstic Acid on Amine-Functionalized Zirconia: A Mesoporous Catalyst for Esterification of Maleic Acid

Abstract

Silicotungstic acid (H₄SiW₁₂O₄₀) has been immobilized onto the mesopores of amine-functionalized zirconia by exploitation of electrostatic interactions. The ionic grafting of silicotungstic acid was confirmed by XPS, FTIR, UV/Vis-DRS and TGA analysis. The mesoporosity of the material was confirmed through N₂ adsorption/desorption analysis. The morphology of the material was established by TEM analysis. The immobilized silicotungstate material was found to be an efficient heterogeneous catalyst for selective esterification of maleic acid with butan-1-ol. A 98 % level of conversion of maleic acid and 82 % selectivity for dibutyl maleate within 5 h at 95 °C was achieved. The catalyst could be reused thrice without loss of activity.

Silicotungstic acid was supported on amine-functionalized mesoporous zirconia with the aid of electrostatic interactions. Its catalytic activity in the selective esterification of maleic acid has been established.

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