Structure and Catalytic Properties of Magnesium Stannate in the Acetone Condensation Reaction

The MgSnO3-450 and MgSnO3-750 catalysts of different morphologies, synthesized by calcining magnesium hydroxystannate MgSn(OH)6 at 450 and 750°C, respectively, are studied in the aldol condensation of acetone under supercritical conditions (400°C and a pressure of 12.0 MPa). The structure of the catalysts is characterized via XRD, SEM, TEM, DSC, and BET. The X-ray amorphous MgSnO3-450 sample exhibits high activity (0.42 mol/(h gcat)) and selectivity to isomeric phorones (40%). The MgSnO3-750 catalyst, which has a higher degree of crystallinity, exhibits lower activity (0.33 mol/(h gcat)) and a high selectivity to isomeric mesityl oxides (up to 70%). Comparing the data on the phase composition of the catalysts and the results of the reaction, it can be supposed that the phase responsible for the selective condensation of two acetone molecules into mesityl oxide on the MgSnO3-750 catalyst is magnesium orthostannate Mg2SnO4. The formation of a MgSnO3 magnesium metastannate phase in the X-ray amorphous MgSnO3-450 catalyst contributes to the formation of phorones, which are products of the condensation of three acetone molecules. It is found that the structure of the MgSnO3-450 catalyst is rearranged during the acetone condensation under supercritical conditions.