Synthesis and metal-exchange of nano-ZIF-67 with Ni(II) and Mn(II) for enhanced catalytic CO2 conversion

Nano-sized Zeolitic imidazolate framework-67 (nZIF-67(Co)) were synthesized in water, and its metal centers partially exchanged with Nickel(II) and Manganese(II) centers to form bimetallic nZIF-67(Co/Ni) (25 % Ni2+) and nZIF-67(Co/Mn) (41 % Mn2+) respectively. This was achieved without altering the structural integrity of the sodalite (SOD) framework of the parent nZIF-67 and the metal oxidation states, as shown by Transmission Electron Microscope (TEM), Powder X-ray diffraction (PXRD) and X-ray photoelectron spectroscopy (XPS). The Co/Ni/Mn atomic composition, determined by XPS, was consistent with values obtained from Inductively Coupled Plasma Optical Emission spectroscopy (ICP-OES) and Energy-dispersive X-ray spectroscopy (EDS). Carbon dioxide (CO2) adsorption studies showed that the uptake of nZIF-67 (39.3 cm3 g-1) was enhanced by metal-exchange to 47.8 cm3 g-1 (nZIF-67(Co/Mn) and 49.4 cm3 g-1 (nZIF-67(Co/Ni), respectively. nZIF-67(Co), nZIF-67(Co/Ni) and nZIF-67(Co/Mn) was employed as catalysts in a solventless and co-catalyst free CO2-epichlorohydrin coupling reaction and yielded cyclic chloropropene carbonate at low pressure (1 bar) and temperature (60 oC). nZIF-67(Co/Ni) performed the best, due to its larger surface area and the presence of nickel. These catalysts can be regenerated and re-used without appreciable loss in activity. [Display omitted]