Mn-doped BiFe1-xMnxO3 perovskite catalyst for biodiesel preparation: synergistic transesterification and esterification via oxygen vacancy-induced acid-base bifunctionality - Xin Li; Jisen Liu; Shengli Niu; Yie Hua Tan; Huaji Zhang; Yue Zheng; Xiaobin Sun; Kemeng Li; Yujie Wei (Fuel, 2026)