Tuning Expanded Pores in Metal-Organic Frameworks for Selective Capture and Catalytic Conversion of Carbon Dioxide

Three Co-based isostructural MOF-74-III materials with expanded pores are synthesized, with varied extent of fused benzene rings onto sidechain of same-length ligands to finely tune the pore sizes to 2.6, 2.4, and 2.2 nm. Gas sorption results for these highly mesoporous materials show that alternately arranged fused benzene rings on one side of the ligand could serve as extra anchoring sites for CO2 molecules with pi-pi interactions, conspicuously enhancing CO2 uptake and CO2/CH4 and CO2/N-2 selectivity; while more steric hindrance effect towards open Co-II sites were imposed by ligands flanked with fused benzene rings on both sides, compromising such extra-sites enhancement. In the catalytic conversion of CO2 with propylene oxide to form propylene carbonate, the as-synthesized MOF-74-III(Co) with desired properties of highly exposed and accessible open Co-II centers, large mesopore apertures and multi-interactive sites, demonstrated higher catalytic activity compared with other two MOFs, with benzene rings fused to ligands hampering the functionality of Co-II centers as Lewis acid sites. Our results highlight the viability of finely tuning the expanded pores of MOF-74 isostructure and the effect of fused benzene rings as functional groups onto selective CO2 capture and conversion.