Fluorinated Mg–Al Hydrotalcites Derived Basic Catalysts for Transesterification of Glycerol with Dimethyl Carbonate

Abstract

A series of fluorinated Mg–Al hydrotalcite-like (HTl) compounds were prepared by introduction of different amount of (AlF6)3− into HTl sheets via co-precipitation method. The fluorine-modified Mg–Al mixed oxides (CHT-F) with mesoporous structure were then acquired by thermal decomposition of as-prepared HTl precursors. The influence of fluorine modifier on the physicochemical properties of CHT-F samples was studied in detail and the results demonstrated that their structure and basicity were strongly related to the fluorine content. Simultaneously, the CHT-F samples were test for the glycerol carbonate (GC) production via transesterification between glycerol and dimethyl carbonate without organic solvent. For these catalysts, the role of basic sites was examined based on reactant conversion and product selectivities in overall reaction as well as in side reaction identified in this work. The catalytic results showed that the activity of CHT-F catalysts depended on the total number of surface basic sites. However, further study demonstrated that the undesired product was catalyzed by strong basic sites, resulting in decrease of GC selectivity. Thus, the introduction of appropriate amount of (AlF6)3− into the HTl structure can promote the production of GC, and the best catalytic performance was obtained over the catalyst with F:Al = 1.0. Besides, various parameters including reaction time, reaction temperature and catalyst amount were investigated to optimize the reaction conditions. Furthermore, these CHT-F catalysts possessed high stability on the basis of reusability test and catalyst characterization.