Heterogeneous supported potassium on promoted CeO2-Al2O3 and La2O3-Al2O3 sol-gel mixed oxides was used as a catalyst for biodiesel production via the transesterification of canola oil with methanol using a batch reactor. These mixed oxides alone do not show any catalytic activity in the transesterification reaction, and the incorporation of potassium increases the catalytic activity, which is greater in the L2O3-promoted catalysts. The improved catalytic activity of the potassium La2O3-promoted catalysts was associated with the partial insertion of lanthanum into alumina with a favorable interaction between the potassium and the oxygenated species of the La2O3-Al2O3 mixed oxide. The larger amount of K2O species in K2O/5La(2)O(3)-Al2O3 and the lower acidity explain their large production of biodiesel. Moreover, the leaching resistance of potassium is remarkable, with the K2O/5La(2)O(3)-Al2O3 catalyst showing < 4% in the first recycle and no more leaching in the four subsequent recycle steps. (C) 2016 Elsevier B.V. All rights reserved.