Design of a robust rod-packing scandium-organic framework for C₂H_x/CO₂ separation, CO₂ storage, and catalytic CO₂ cycloaddition

The exploration of efficient CO2 capture and conversion techniques is of great importance for global sustainable development. Herein, a novel bi-microporous Sc-MOF, named [Sc-3(NTB)(2)(CH3COO)(3)] (SNNU-616-Sc, NTB = nitrilotribenzoic acid), was successfully designed and utilized for CO2 storage and catalytic conversion. The linear [Sc-3(COO)(6)] trinuclear clusters were linked by triple acetate anions into 1D chains, which were further extended by NTB linkers and interleaved to produce the 3D robust rod-packing Sc-MOF with two types of open channels of about 12 angstrom and 3.8 angstrom, respectively. Notably, the bare N atom from NTB ligands can not only act as active sites to adsorb CO2 molecules, but also provide Lewis basic sites for the CO2 fixation reaction. Together with the high framework stability and two types of microporous open channels, SNNU-616-Sc shows high adsorption selectivity to effectively separate CO2 from CO2-C2Hx binary mixtures (C2Hx = acetylene, C2H2; ethylene, C2H4; ethane, C2H6), and a CO2 storage capacity of 30 mmol g(-1) (273 K and 29 bar), which surpasses most MOF adsorbents. Moreover, SNNU-616-Sc can also serve as an efficient recyclable catalyst for CO2 fixation with epoxides in the presence of tetrabutylammonium bromide as a co-catalyst without any organic solvent under mild conditions. Particularly, for the catalytic reaction of CO2 cycloaddition with epoxide bromopropane, the yields of cyclic carbonates can reach up to 97.5% with the selectivity higher than 98% and a conversion of 99%.