Design of Zeolitic Imidazolate Framework Derived Nitrogen-Doped Nanoporous Carbons Containing Metal Species for Carbon Dioxide Fixation Reactions

Various N-doped nanoporous carbons containing metal species were prepared by direct thermal conversion of zeolitic imidazolate frameworks (ZIFs; ZIF-7, -8, -9, and -67) at different temperatures (600, 800, and 1000 degrees C). These materials were utilized as bifunctional acid-base catalysts to promote the reaction of CO2 with epoxides to form cyclic carbonates under 0.6MPa of CO2 at 80 degrees C. The catalyst generated by thermal conversion of ZIF-9 at 600 degrees C (C600-ZIF-9) was found to exhibit a higher catalytic activity than the other ZIFs, other conventional catalysts, and other metal-organic framework catalysts. The results of various characterization techniques including elemental analysis, X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and transmission electron microscopy show that C600-ZIF-9 contains partly oxidized Co nanoparticles and N species. Temperature-programmed desorption measurements by using CO2 and NH3 as probe molecules revealed that C600-ZIF-9 has both Lewis acid and Lewis base catalytic sites. Finally, the substrate scope was extended to seven other kinds of epoxides.