​A solid heterogeneous catalyst was derived from oil shale ash by impregnation of the ash with KNO3 followed by

calcination for 4 h. Different preparation conditions were studied (KNO3 concentrations: 0.05 and 0.1 M, and

calcination temperatures: 500 and 700 ◦C). After calcination, the dependence of waste cooking oil to biodiesel

conversion on the reaction variables such as the catalyst loading, the methanol to oil molar ratio, and reaction

time was investigated. The catalyst characterization was conducted using FT-IR, XRD, BET, TEM, and SEM.

Further, the typical unsaturated fatty acids present in common vegetable oils, the oil-to-biodiesel conversion, and

the chemical composition of the produced biodiesel were quantified by (1H NMR). Among the various catalysts

prepared, the ash impregnated with 0.1 M KNO3/and calcined at 700 ◦C (Ash 0.1/700 catalyst) provided the

maximum oil to biodiesel conversion of about 100% at 65 ◦C reaction temperature, methanol to oil molar ratio of

45:1, and 2 h reaction time.