Dynamic behavior of basic sites of MgO in Tishchenko reaction

Tishchenko reaction of benzaldehyde was carried out over the MgO whose surface O atoms were enriched with 18 O to examine whether the surface O atoms of MgO are incorporated into the product and reactant. The surface lattice 18 O atoms were incorporated in both the product and reactant. The 18 O concentration was significantly higher for the product than for the reactant. In addition, the 18 O in the product ester was located not only in the carbonyl group (C O) but also in the bridging position (C O C); 18 O exchange between benzaldehyde and MgO surface occurred not only in the adsorption–desorption of benzaldehyde, but also in the dimerization process. The oxygen exchange results in the migration of active sites of coordinative unsaturated site (CUS) over the surface of MgO catalyst during the reaction.