LAUSR

Abstract The heterogeneous catalysts used to produce biodiesel include the important group of hybrid silicas that possess basic siloxy sites (≡SiO−). The basicity of these sites varies according to the size of the charge-compensation cation. In this work, hybrid silicas were synthesized in the presence of different cationic surfactants: cetyltrimethylammonium bromide (CTABr), cetylallyldimethylammonium bromide (CADMABr), and cetylpyridinium bromide (CPyBr), in order to determine their effects on the basicity of the silica produced. Characterization of the silicas showed that they presented different particle sizes and shapes, as well as differences in terms of the quantity and quality of the siloxy (≡SiO−) catalytic sites. Catalytic evaluation of the hybrid silicas employed the transesterification of a model monoester (ethyl acetate) and the transesterification of a vegetable oil (soybean oil), with both reactions conducted under mild conditions. The catalytic results for the model transesterification reaction showed the same features as those obtained with the vegetable oil, demonstrating that the use of a simple molecule was sufficient for preliminary evaluation of these catalysts.