Microwave-assisted synthesis of basic mixed oxides from hydrotalcites

Abstract

Different MgAl mixed oxides with a Mg/Al ratio of 2 were obtained through calcination of the corresponding hydrotalcites at 450 °C and tested for MPV reaction of benzaldehyde with 2-butanol. The influence of several synthetic parameters (such as co-precipitation in the presence of Pluronic P123 or homogeneous precipitation in the presence of urea in the medium) on catalytic performance was studied. The use of urea led to a decrease in surface area as compared to conventional precipitation method (125 m2/g and 201 m2/g, respectively) but an increase in surface basicity (7.3 µmol CO2/m2 and 4.3 µmol CO2/m2, respectively). Utilization of Pluronic 123 increases surface area (183 m2/g) though basicity is hardly affected (4.2 µmol CO2/m2). All the catalysts showed a high conversion and high selective to the desired product, observing a relationship between the density of basic sites and the catalytic activity. All in all, the solid exhibiting the highest benzyl alcohol yield was that synthesized in the presence of urea (labelled as HT-U-450), with a rate of 2.05 mmol benzyl alcohol/gcat × min.