Natewong, Paweesuda, et al. “Effect of Addition of CaO and ZrO2 on the Performance of MgO AC Catalyst for the Synthesis of New Bio-Diesel (HiBD) from Waste Cooking Oil”. American Scientific Research Journal for Engineering, Technology, and Sciences, vol. 24, no. 1, Aug. 2016, pp. 76-89, https://www.asrjetsjournal.org/American_Scientific_Journal/article/view/2032.