Basic properties of MgLaO mixed oxides as determined by microcalorimetry and kinetics

The surface properties of magnesias and of La oxides supported on MgO and MgAl hydrotalcites were compared, using the adsorption of carbon dioxide followed by microcalorimetry. The differential heat of adsorption of CO2 as a function of coverage is the same for MgO of different surface areas, ranging from 30 to 590 m2/g, showing that the average coordination of Mg does not change, in agreement with the results reported for the structure of these materials. In the case of La catalysts, an effect of the support is noticed on the distribution of basic strengths, with a higher basicity for MgLa mixed oxides. MgAlLaO mixed oxide is also a strong solid base in spite of much lower La content. These catalysts are active for the transesterification of soybean oil with methanol at 338 K, using a ratio methanol/oil = 6, and give a rate comparable to that reported for anchored guanidines, considered as superbases.