Preyssler-Structured Tungstophosphoric Acid Catalyst on Functionalized Silica for Esterification of n-Butanol with Acetic Acid

The Preyssler-structured tungstophosphoric acid catalyst supported on functionalized silica (Preyssler/F-silica) was prepared by means of grafting technique with amine group as coupling media, and its catalytic behavior was investigated in the esterification of n-butanol with acetic acid. The catalyst was characterized by infra-red spectroscopy, UV–Vis spectroscopy, Hammett indicator and N2 adsorption techniques. Catalysts prepared directly by impregnating Preyssler acid on silica (Preyssler/silica) were also studied for comparison. The Preyssler/F-silica catalyst with the 14.3% loading of Preyssler acid exhibits a considerable conversion of n-butanol of 46.7% with 100% selectivity for n-butyl acetate in the esterification of n-butanol with acetic acid, which is comparative to the 15%Preyssler/silica catalyst. Moreover, a six-cycle reaction test reveals a good reusability for Preyssler/F-silica due to the water-resistance property of the Preyssler structure on the surface of the functionalized silica, and Preyssler/silica looses its high activity immediately at the second reaction cycle. The active sites on functionalized silica can retain the Preyssler structure before and after reaction. At 120 °C of reaction temperature, 140 min of reaction time, 1:1 molar ratio of acetic acid with n-butanol, and 0.005 g/mL of the catalyst content in reaction media are the suitable reaction conditions over the Preyssler/F-silica catalyst.