Cd/Co-Mofs Containing Lewis Acid-Base Sites is Used for Co 2  Chemical Fixation and Catalysis of Knoevenagel

Abstract

With the continuous increase of CO2 concentration in the atmosphere, many environmental problems and natural disasters have been brought about, so CO2 capture and utilization technology has received extensive attention. Metal-organic frameworks (MOFs) play an important role in the field of CO2 capture due to their high specific surface area, diverse structures and modifiable functions. Herein, two MOFs were designed and synthesized by hydrothermal synthesis: {[Cd2(cjt) (H2O)2]·DMF·2H2O}n (1), {[Co2(cjt)(bpy)(H2O)4]·3.5H2O}n (2) (H4cjt = (3, 5-dicarboxyphenyl) pyridine, 2, 2'-bipyridine = bpy). MOFs 1 is 3D microporous network structure based on a binuclear cadmium unit and (cjt)4- ligand. MOF 2 shows 1D lattice chain, which are linked each other by π···π stacking and hydrogen bonding interactions to form a 3D microporous network. TPD experiments show that there are both Lewis acid sites and Lewis base sites in 1-2, which have high catalytic activity for cycloaddition of epoxides and CO2 under mild solvent-free conditions, and has good recyclability and recyclability. Interestingly, 1-2 showed excellent catalytic CO2 conversion ability, and a strong application potential in the field of industrial waste gas purification. In addition, 1-2 can also be used as a highly efficient catalyst for the Knoevenagel reaction. The thermal filtration experiment has proved its heterogeneity. The cyclic experiments show that 1-2 is an efficient, recyclable and stable heterogeneous catalyst. Finally, the mechanism of CO2 cycloaddition and Knoevenagel condensation catalyzed by 1-2 was discussed.

Keywords: Cd/Co-MOFs, Lewis acid-base active sites, Cycladdition Reaction CO2；Knoevenagel condensation