Nanoporous Thulium(III)–Organic Framework for High Catalytic Performance on the CO2-Epoxide Cycloaddition

Considering that the greenhouse effect is the most concerning environmental issue globally, selective capture and resource utilization of CO2 have attracted widespread attention. Herein, we report a highly robust thulium(III)–organic framework of {[Tm2(μ2-OH)(CPPDDA)(H2O)2]·3DMF·2H2O}n (NUC-108), which is obtained from the exquisite combination of undocumented multifunctional clusters of [Tm4(μ2-OH)2(COO)10(H2O)4] and organic ligands of 4,4′-(4-(4-carboxyphenyl)pyridine-2,6-diyl)diisophthalic acid (H5CPPDDA). NUC-108 possesses the following unique merits: (i) the undocumented functional tetranuclear rare-earth clusters of [Tm4(μ2-OH)2(COO)10(H2O)4] serve as the nodes, in which Tm3+ ions can be activated as Lewis acid sites and μ2-OH anions are Lewis base sites; (ii) the high-porosity zeolite architecture contains three kinds of channels: 12.29 × 9.74 Å2 and 8.92 × 4.97 Å2 along the b axis and 12.76 × 8.95 Å2 along the c axis; (iii) uncoordinated pyridine moieties as Lewis base sites further endow the host framework with functionality; and (iv) resistance to weak acidic and alkaline aqueous solutions as well as various organic solvents. Notably, NUC-108a can effectively separate CO2 from a binary CO2/CH4 mixture with high adsorption selectivity, which should be due to the enough Lewis basic sites of pyridine groups and μ2-OH moieties. Furthermore, under mild conditions and without any organic solvent, NUC-108a can also be used as an effective recoverable catalyst to facilitate the cycloaddition of CO2 with epoxides with the aid of tetrabutylammonium bromide. Hence, these findings are beneficial for guiding the development of highly stable and active catalysts for carbon utilization.