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[Display omitted] • KI/γ-Al 2 O 3 catalyst for high yield biodiesel production by oil transesterification. • Modified sol–gel synthesis produces catalyst with superior catalytic performances. • Optimal process parameters for transesterification reaction were achieved. • Al-O-K groups take the role as catalytically active centers in transesterification. • Alcoholysis significantly depends on physicochemical properties of catalyst support. The essence of this study is synthesis of a newly developed and efficient heterogeneous catalyst based on aluminum oxide support promoted with potassium iodide (KI) as active dopant responsible for pronounced catalyst activity. Modified sol–gel, reflux and hydrothermal method were used for synthesis of aluminum-oxide support using aluminum isopropoxide as a precursor. The γ-Al 2 O 3 support and KI/γ-Al 2 O 3 catalyst samples were examined by various experimental techniques. Effects of several operational parameters were considered and those are: methanol to sunflower oil molar ratio, catalyst loadings, reaction time and reaction stirring rate. The obtained results indicated that modified sol–gel method for synthesis of γ-Al 2 O 3 catalyst support is the most favorable for obtaining the catalyst with superior catalytic performances in transesterification of sunflower oil. A maximum conversion (triglycerides to methyl esters) of 99.99% was achieved using the SG-KI/γ-Al 2 O 3 -770 catalyst under following optimal process parameters: 15:1 methanol to sunflower oil molar ratio, 2.5 wt% catalysts loading, 600 rpm stirring rate and 4 h of the reaction run. [ABSTRACT FROM AUTHOR]