Zirconia-coated magnetic Fe2O3 nanoparticles supported 12-tungstophosphoric acid: A novel environmentally friendly catalyst for biodiesel production

A series of solid acid catalysts xHPW/Fe-Z (x represents mass percentage of HPW = 10, 20, 30, and 50%) was synthesized by immobilizing the 12-tungstophosphoric acid (HPW) over magnetic zirconia (Fe-Z) through coprecipitation and impregnation methods. These catalysts were applied as heterogeneous acid catalysts in the esterification of oleic acid with methanol as a model reaction for the preliminary stage of the biodiesel production. The synthesized catalysts were characterized by fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), brunauer-emmet-teller equation (BET), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA),vibrating sample magnetometer (VSM), scanning electron microscope, energy-dispersive X-ray spectroscopy (SEM-EDS), and transmission electron microscopy (TEM), which proved that the catalyst showed excellent thermal and chemical stability and considerable magnetization (9 emu/g). The 30HPW/Fe-Z was identified as the most efficient catalyst because it afforded a high conversion rate of 98.1% and showed a lower loss of activity over successive reaction cycles among all of the samples, and this loss of activity had been analyzed on the basis of the fouling of the materials. Besides, the catalytic conversion of HPW immobilized on magnetic zirconia was even higher than that observed under homogenous conditions due to the positive contribution of the carrier.