Zr-modified desilicated ZSM-5 catalysts as highly active and recyclable catalysts for production of biodiesel from soybean oil: Insight into improved catalyst properties, acidity and dispersion through desilication

Abstract

Bio-based fuels, such as biodiesel, have recently gained attention due to concern about ever-increasing energy consumption and global warming. Solid catalysts are key materials in the production of green biodiesel. The use of solid catalysts in the production of biodiesel can lower the cost of the separation and thus reduce biodiesel costs. In the present study, zeolite-supported ZrO2 catalyst (ZrO2/ZSM-5) and a series of desilicated zeolite-supported ZrO2 catalyst [ZrO2/ZSM-5(0.1–0.3 M)] were successfully synthesized by impregnation method and used as new catalysts for the production of soybean oil biodiesel through transesterification. Desilication at various sodium hydroxide concentrations enhances the external surface area and mesoporous volume, without jeopardizing crystallinity or microporosity of the catalysts. The synthesized catalysts were characterized via X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), pyridine-FTIR, scanning electron microscopy, TEM, XRF, TGA and nitrogen adsorption-desorption. Nuclear magnetic resonance (NMR) and gas chromatography-mass spectrometry (GC–MS) were used to characterize the biodiesel that was produced. The as-prepared ZrO2/ZSM-5(0.2 M) catalyst exhibited better catalytic activity in the transesterification of soybean oil with methanol, compared to ZrO2/ZSM-5 catalyst, due to large pore volume, high surface area, and high dispersion of ZrO2 on the desilicated zeolite support with improved acidity and high number of active sites. A biodiesel conversion of 90.1% and 97.84% were obtained for zeolite-supported ZrO2 catalyst and desilicated zeolite-supported ZrO2 catalyst, respectively, under optimum reaction conditions of 1.0 wt% catalyst loading, 1:16 soybean oil/methanol molar ratio at 200 °C in 4 h reaction time. Moreover, the desilicated zeolite-supported ZrO2 catalyst exhibited excellent stability and re-usability giving a biodiesel conversion of 93.8% after three cycles of reuse.