Synthesis of Propylene Carbonate from Alcoholysis of Urea Catalyzed by Modified Hydroxyapatites

Abstract Metal-modified hydroxyapatite (M/HAP) catalysts were prepared by impregnation. Their catalytic activity was tested for urea alcoholysis to propylene carbonate. Hydroxyapatite catalysts modified by alkali metals, alkaline-earth metals, and rare earth metals exhibited higher activity than the hydroxyapatite or corresponding metal oxides. The La-modified hydroxyapatite catalyst (La/HAP) exhibited the highest activity with a 91.5% yield of propylene carbonate. The physicochemical characterization of La/HAP and HAP was performed by X-ray diffraction, scanning electron microscopy, N 2 adsorption, and CO 2 temperature-programmed desorption. The high catalytic activity of La/HAP was attributed to a large number of strong basic sites produced on its surface after HAP was modified by La species.