Mai, T. T. N., D. T. Chien, T. T. Hong, N. V. Noi, D. T. Tung, N. H. Luong, H. L. Lan, L. T. Son, and G. T. P. Ly. “Preparation and Characterisation of La, Zn/ZrO2-Al2O3-SO4 2- Solid Acid Catalyst for Transesterification of Jatropha Oil for Biodiesel Production”. Petrovietnam Journal, Vol. 8, Aug. 2013, pp. 46-51, http://pvj.vn/index.php/TCDK/article/view/697.