The basicity of mixed oxides and the influence of alkaline metals: The case of transesterification reactions

Several M(II)/M(III) mixed oxides were prepared and tested in two different transesterification reactions, biodiesel production from sunflower oil and methanol, and the more demanding transesterification of methyl palmitate with isobutanol. The presence of residual alkaline ions after crystallization is the main source for the strong basicity in this kind of solids, as it happened with Mg/Al mixed oxides. The effect of these alkaline traces is more evident with the most demanding reaction, in which the alkaline-free solids did not show any catalytic activity. These results seem to indicate that the strong basicity in mixed oxides is always connected to the presence of alkaline metals, irrespective from the nature of M(II) and M(III). (C) 2010 Elsevier B.V. All rights reserved.