Design of a robust rod-packing scandium–organic framework for C2Hx/CO2 separation, CO2 storage, and catalytic CO2 cycloaddition

Abstract

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 [Sc₃(NTB)₂(CH₃COO)₃] (SNNU-616-Sc, NTB = nitrilotribenzoic acid), was successfully designed and utilized for CO₂ storage and catalytic conversion. The linear [Sc₃(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 Å and 3.8 Å, 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–C₂H_x binary mixtures (C₂H_x = 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%.