Monoglyceride synthesis by glycerolysis of methyl oleate on MgO: Catalytic and DFT study of the active site

Abstract

The synthesis of monoglycerides by glycerolysis of methyl oleate, a fatty acid methyl ester (FAME), was efficiently promoted on strongly basic MgO. The chemical nature of the base sites responsible for the catalytic activity was investigated, both experimentally and by density functional theory (DFT). MgO catalysts stabilized at different temperatures were used to control the distribution of surface base sites. The nature, density and strength of the catalyst base sites were characterized by TPD and FTIR of CO2. Catalytic results suggested that the synthesis of monoglycerides was promoted mainly on strongly basic low coordination (O2−) surface sites. The molecular modeling of glycerol (Gly) and FAME adsorptions was carried out using terrace, edge and corner sites for representing the MgO surface. Results indicated that Gly was more strongly adsorbed than FAME. Dissociative chemisorption of Gly with O-H bond breaking was favored on low coordination (O2−) surface sites such as those on edges, in agreement with the experimental results. Thus, the proton abstraction from the OH groups of Gly, a necessary step in the reaction mechanism, would take place on unsaturated oxygen anions and the resulting glyceroxides would react with weakly adsorbed FAME molecules.