Mn-doped BiFe1-xMnxO3 perovskite catalyst for biodiesel preparation: synergistic transesterification and esterification via oxygen vacancy-induced acid-base bifunctionality

The coexistence of free fatty acids (FFAs) and moisture in biodiesel feedstock oils poses major limitations for conventional basic catalytic systems, which motivates the development of heterogeneous catalysts capable of promoting transesterification and esterification. In this work, a Mn-doped perovskite catalyst, BiFe 0.7 Mn 0.3 O 3 , was synthesized using BiFeO 3 as the matrix for biodiesel preparation. Mn doping disrupted the lattice charge balance of BiFeO 3 , which induced lattice distortion and promoted the formation of oxygen vacancies. These structural changes regulated the surface electronic environment and optimized the distribution of acidic-basic active sites. Under optimized reaction conditions of 140 °C, 3.5 h, methanol-to-oil molar ratio of 14:1, and catalyst amount of 3.0 wt%, BiFe 0.7 Mn 0.3 O 3 achieved a biodiesel yield of 95.20%. Even in reaction systems containing 30 wt% FFAs or 8 wt% moisture, the biodiesel yield remained above 80.00%, which confirms its strong resistance to FFAs and moisture-containing feedstocks. Mechanistic analysis reveals that Mn doping-induced oxygen vacancies create an optimized surface acid-base environment that enables the simultaneous promotion of transesterification and esterification reactions. Moreover, BiFe 0.7 Mn 0.3 O 3 exhibits favorable magnetic responsiveness, which enables rapid separation and recovery under an external magnetic field after reaction. Combined with the low synthesis cost and recyclability, this catalyst shows strong potential for sustainable biodiesel preparation from low-quality feedstock oils.