New insights into the catalytic properties of α-MoO3 applied in the biodiesel production from high acidity feedstock

α-MoO 3 has been applied to convert acid oils into biofuel due to the presence of acid sites. Herein, α-MoO 3 was synthesized by the modified Pechini method and applied in methyl catalysis by esterification of oleic acid, transesterification of soybean oil, and simultaneous esterification/transesterification reaction (SET) of acidified soybean oil. Structural characterization confirmed the crystallization of α-MoO 3 in an orthorhombic Pbnm crystal structure, with the presence of Mo 5+ species associated with oxygen vacancies identified by electron paramagnetic resonance (EPR) and confirmed by X-ray absorption near-edge spectroscopy (XANES). Gas chromatography (GC) confirmed a high conversion for the transesterification reaction (99.3 %), while acidity index measurements indicated a conversion of 97.2 % for the esterification reaction at 150 °C for 120 min. This behavior was assigned to Lewis (28.93 μmol g −1 ) and Brønsted (26.10 μmol g −1 ) acid sites. For SET reactions, a higher temperature was necessary to achieve higher activity, with conversions of 95.4 % and 93.6 % for soybean oil acidified with 10 % and 20 % oleic acid, respectively. After three catalyst reuse cycles with higher acidity oil, a small decrease of 5.7 % was observed. After catalysis, weak acid sites increased, following a decrease in the moderate acid sites, indicating molecule adsorption and partial Mo 6+ reduction, changing the local environment surrounding Mo cations, as confirmed by Mo L-edge XANES. Our findings demonstrate the importance of understanding the formation and effect of point defects on the local electronic structural information of Mo sites [MoO 6 ] and [Mo 5+ O 5 ·Vo • ] from EPR and XANES spectroscopy to correlate with the amount of active acid sites quantified by IR spectroscopy after pyridine adsorption/desorption process.