Porous cesium impregnated MgO (Cs–MgO) nanoflakes with excellent catalytic activity for highly selective rapid synthesis of flavanone

Abstract

Magnesium oxide (MgO) is an excellent base catalyst and its performance is well controlled by its morphology, surface area and surface structures. Here, a simple methodology for the synthesis of porous cesium impregnated MgO (Cs–MgO) nano flakes, with enhanced surface area (156 m² g⁻¹), basic properties and improved catalytic activity for flavanone synthesis, is presented. The synthesis of Cs–MgO nano flakes is performed through impregnation of CsNO₃ on a nesquehonite [Mg(HCO₃)OH·2H₂O] rod, followed by calcination. During impregnation the metastable nesquehonite rod rehabilitated to hydromagnesite [4 MgCO₃. Mg(OH)₂·4H₂O] flakes. The flakes were porous, constructed by building blocks of small nanoparticles (10–25 nm) with a large number of edges and corners, step edges and step corners and numerous base sites of various strength (surface hydroxyl groups, low coordinate O²⁻ sites). It is observed that the amount of cesium in the MgO surface has a strong effect on its properties as well as its activity. The synthesized Cs–MgO nanoflakes showed significant improvement in the yield of flavanone through the Claisen–Schmidt condensation. A substantial increase in the reaction rate was also observed when DMF was used as a solvent without catalyst deactivation. As much as ∼90% conversion of 2′-hydroxyacetophenone with ∼81% selectivity of flavanone was observed in just 15–20 min using the synthesized 0.5% Cs loaded MgO nanoflakes as a catalyst and DMF as a solvent. The improved catalytic activity of Cs–MgO as a catalyst and the promotion effect of DMF is discussed by studying the interaction of the substrate and the solvent on the catalyst surface and identification of intermediates formed on the catalyst surface under the reaction conditions using FT-IR.