Clean synthesis of alkyl levulinates from levulinic acid over one pot synthesized WO3-SBA-16 catalyst

Abstract

The present work highlights the application of solid acid catalyst to produce alkyl levulinate from levulinic acid in continuous mode under vapor phase conditions. In this context, tungsten oxide incorporated SBA-16 catalysts were prepared by one pot direct synthesis method and evaluated for the titled reaction. Under optimized reaction conditions, 3 wt% WO₃-SBA-16 catalyst delivered complete conversion of levulinic acid with 95% selectivity towards ethyl levulinate. The synthesized catalysts were characterized to know the physico-chemical features by various techniques, namely, X-ray diffraction, N₂ physisorption, temperature programmed reduction of hydrogen (H₂-TPR), temperature programmed desorption of ammonia (NH₃-TPD), DR-UV–vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The characterization results suggest that, the superior catalytic activity can be ascribed due to the enhanced acidity of SBA-16 obtained through incorporation of tungsten oxide and easy of accessibility for the dispersed active sites through uniform pore channels. The constant catalytic activity in 10 h time on study shows the sturdiness of the catalyst and the spent catalyst can be regenerated several times. Moreover, various alkyl levulinates (methyl, n-propyl, and n-butyl) were synthesized with more than 90% selectivity over this catalyst.