MgO nanoparticles confined in ZIF-8 as acid-base bifunctional catalysts for enhanced glycerol carbonate production from transesterification of glycerol and dimethyl carbonate

摘要

MgO-loaded ZIF-8 catalysts (MgO@ZIF-8) with various MgO loadings were prepared and characterized using atomic absorption spectroscopy (AAS), powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FT-IR), N-2 sorption isotherms, field-emission transmission electron microscopy (FE-TEM), and thermogravimetric analysis (TGA). Our results indicate that MgO nanoparticles could deposit onto the ZIF-8 surface with high atom efficiency while maintaining the ZIF-8 structure through a wet-impregnation and calcination process. It is suggested that the surface sites and microporosity of ZIF-8 support provide an adequate environment for the initial deposition of Mg precursor and subsequent growth of MgO nanoparticles through a nanoconfinement effect. MgO@ZIF-8 catalysts were tested for catalytic transesterification of glycerol and dimethyl carbonate to yield glycerol carbonate. It is found that the 50 wt% MgO@ZIF-8 catalyst display an improved catalytic activity than those of MgO and ZIF-8. Furthermore, the MgO@ZIF-8 catalysts showed higher catalytic activities than their physically-mixed counterparts, indicative of a synergistic effect between MgO and ZIF-8, which is explained by a proposed mechanism based on acid-base bifunctional sites on the surface.