a b s t r a c tIn this study, we present the activities of Al 2 O 3 supported CaO and MgO catalysts in the transesterification of lipid of yellow green microalgae, Nannochloropsis oculata, as a function of methanol amount and the CaO and MgO loadings at 50°C. We found that pure CaO and MgO were not active and CaO/Al 2 O 3 catalyst among all the mixed oxide catalysts showed the highest activity. Not only the basic site density but also the basic strength is important to achieve the high biodiesel yield. Biodiesel yield over 80 wt.% CaO/ Al 2 O 3 catalyst increased to 97.5% from 23% when methanol/lipid molar ratio was 30.

a b s t r a c tThe activities of single step sol-gel made calcium oxide on alumina catalysts were studied as a function of CaO loading, methanol/oil molar ratio and the amount of the catalyst in the transesterification of sunflower oil at 50°C. Also, the turnover frequency (TOF) of the catalysts was calculated to better understand the relationship between the basicity/basic strength and the catalytic activity. From volcano curve (TOF vs. basic strength), it was found that under 50°C and methanol/oil molar ratio of 9, 60% CaO/Al 2 O 3 had the highest turnover frequency, 0.028 s À1, whereas 85% CaO/Al 2 O 3 showed the highest biodiesel yield, $96.6%, but TOF obtained on it was 0.012 s À1. It seemed that 60% CaO catalyst had the proper basic strength to obtain the highest TOF.

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