Synthesis of hierarchical flower-shaped hollow MgO microspheres via ethylene-glycol-mediated process as a base heterogeneous catalyst for transesterification for biodiesel production

Hierarchical flower-shaped hollow MgO (f-MgO) spheres were synthesized through an ethylene-glycol-mediated polyol process via hydrothermal reactions. The structure of f-MgO originates from intermediate flower-shaped Mg glycolate through the Ostwald ripening process. The surface of f-MgO consists of uniform petal-like nanosheets that provide high surface area and excellent accessibility to catalytic sites. Also, the f-MgO microsphere can prevent aggregation and stacking problems of nanosheets and control a surface area for catalytic activity. The morphology and structure of f-MgO were investigated using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The density of basic catalytic sites was derived from CO₂-temperature-programmed desorption measurements. The f-MgO exhibits a basic site density of 0.5134 mmol/g, which is much higher than that of commercial MgO (c-MgO, 0.0288 mmol/g). Experimental results for the fatty acid methyl ester revealed that the catalytic strength of f-MgO as a heterogeneous catalyst for biodiesel production is greater than that of c-MgO. The maximum biodiesel conversion efficiency of f-MgO from canola oil is 93.4%, which is greater than the value of 91.4% for c-MgO.