This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/ep.13390 Experimental studies on sodium methoxide supported bentonite catalyst for biodiesel preparation from waste sunflower oil B. Devaraj Naik 1 , M. Udayakumar 2* 1, 2 Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli - 620 015, Tamil Nadu. India. *Corresponding author Email: muday@nitt.edu Abstract Clays are abundantly available support material used for the preparation of green heterogeneous catalysts to produce biodiesel. In the present study, bentonite clay supported on sodium methoxide catalyst was prepared by impregnation process. The catalyst characterization was done by powder X-ray diffraction, brunauer–emmett–teller analysis, thermo-gravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, atomic absorption spectroscopy and Hammett indicator techniques. The study for determination of optimal parameters in biodiesel production was carried out using response surface methodology. A biodiesel yield of 94.33% was achieved with 2 wt.% catalyst amount, 12:1 molar ratio of methanol to oil, 70 minutes reaction time at 55°C. It was observed that the prepared catalyst has good catalytic activity. An additional significance of the synthesized catalyst was that it could be easily recovered and used in consecutive cycles without any substantial loss of catalytic activity. The physical and chemical fuel properties were determined and met the American Society for Testing and Materials Standard. Novelty or Significance This article is protected by copyright. All rights reserved.