Catalytic Properties of Lithium-Doped ZnO Catalysts Used for Biodiesel Preparations

Biodiesel produced by the transesterification of vegetable oils or animal fats with short-chain alcohols (typically methanol) is a promising alternative fuel for diesel engines, because of the limited resources of fossil fuels and environmental concerns. In this work, Li/ZnO catalysts were prepared using an impregnation method followed by calcinations, and then they were tested for soybean oil transesterification. It was determined that Li/ZnO catalysts exhibited good catalytic activities, and the catalytic performance was greatly dependent on (i) the loading amount of lithium and (ii) the calcination temperature. This Li/ZnO catalyst, at an amount of 5 wt %, resulted in a soybean oil conversion of 96.3% in 3 h using a reflux of methanol and a 12:1 molar ratio of methanol to oil. Moreover, the catalyst was characterized using X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), infrared (IR) spectroscopy, thermogravimetry-differental thermal analysis (TG-DTA), and the Hammett titration method. It was shown that the activity of the catalysts for the transesterification reaction is closely related to their basic properties.