Bimetallic metal–organic frameworks (MOFs) containing two different inorganic metal nodes exhibited enhanced properties in CO2 adsorption and catalytic conversion compared with the corresponding monometallic MOFs. In this work, the novel bimetallic Zn/Mg-MOF-74 with different ratios of Zn/Mg was synthesized successfully by a facile one-pot method. Powder X-ray diffraction, Fourier transform infrared, X-ray photoelectron spectroscopy, scanning electron microscopy/transmission electron microscopy, N2/CO2 adsorption/desorption, and CO2/NH3-temperature-programmed desorption techniques thoroughly characterized the structure, morphology, and physicochemical properties of Zn/Mg-MOF-74. Besides the excellent CO2 adsorption capacity (128.3 cm3/g at 273 K and 1 bar), Zn0.75Mg0.25-MOF-74 also showed efficient catalytic activity for the cycloaddition reaction of CO2 and epoxides to cyclic carbonates with outstanding yield and selectivity all over 99% under solvent-free and mild conditions (60 °C, 0.8 MPa), outperforming the mechanical combination of Zn-MOF-74 and Mg-MOF-74 with the same metal contents, indicating the synergistic effect of two adjacent metals in bimetallic MOF-74. In addition, the Zn0.75Mg0.25-MOF-74 catalyst could be recycled for at least five runs and possess good versatility to various substrates. Finally, a feasible mechanism of the catalytic reaction was proposed. Thanks to the high surface area, affinity toward CO2, and accessibility of multiple active sites of the unsaturated metal centers as active Lewis acid sites and O atoms from Zn–O and Mg–O as Lewis basic sites, efficient chemical fixation of CO2 to cyclic carbonates was obtained over the Zn0.75Mg0.25-MOF-74 catalyst. The present facile synthesis and application of a robust bimetallic MOF catalyst offered a competitive avenue for the integration of CO2 adsorption and CO2 catalytic conversion.

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A novel Lewis acid–base bifunctional Zn­(II)-based MOF-Zn-1 [Zn2L2MA·2DMF] (MA = melamine, H2L = 2,5-thiophenedicarboxylic acid), with abundant micropores and free -NH2 groups was facilely assembled by incorporating zinc­(II) ion with nitrogen-rich melamine and 2,5-thiophenedicarboxylic acid ligands. The constructed MOF-Zn-1 presented an excellent affinity toward CO2 molecules due to the Lewis-base property together with abundant micropores. The Zn active sites could be used for epoxide activation. The acid–base synergistic effects facilitated CO2 conversion into cyclic carbonates under ambient temperature using the porous MOF-Zn-1 as a heterogeneous catalyst. Moreover, the MOF-Zn-1 exhibited satisfied stability and versatility, and it was easy to recycle with no obvious decrease of catalytic activity. Then the feasible synergistic mechanism of MOF-Zn-1/Bu4NBr catalysts for CO2 conversion was proposed.

A new tetratopic bridging ligand 1,1′-(propane-1,3diyl)bis(1H-pyrazole-3,5-dicarboxylic acid) (PDC) with functional pyrazole groups was designed and used for reacting with environmentally friendly zinc centers in mixed solvents; the resulting framework [Zn 3.5 (PDC) 2 (H 2 O) 10 ] (abbreviated as MOF Zn-2PDC) contained numerous organic−inorganic crablike blocks and had high density of zinc sites and coordinated water molecules. Abundant open metal sites (OMSs) were generated after the removal of coordinated water molecules by vacuum drying, which produced exceptionally catalytic performance for CO 2 cycloaddition to bulky styrene oxide, and the produced styrene carbonate yield and selectivity reached up to 86 and 97% under mild conditions of 55 °C, 12 h, and 1 MPa. Moreover, MOF Zn-2PDC also showed general applicability to other bulky epoxides. Meanwhile, the MOF Zn-2PDC catalyst remained with good catalytic performance after six cycles.

An efficient Zn(Bmic)(AT) MOF with available Lewis acid− base blocks was prepared by a solvothermal method combining the mixed ligands 5-aminotetrazole (HAT) and 1-benzimidazole-5-carboxylic acid (H 2 Bmic). The prepared Zn(Bmic)(AT) catalyst is rich in amino groups, uncoordinated oxygen atoms, and multiple open metal sites (OMSs), which contribute to CO 2 adsorption of 79 cm 3 /g at 273 K and 52 cm 3 /g at 298 K, with high adsorption enthalpy (28 kJ mol −1 ). Furthermore, its multiple functional sites facilitate CO 2 cycloaddition to various small-molecule epoxides to give five-ring cyclic carbonates with the assistance of a Bu 4 NBr cocatalyst, achieving a high TON of 170 for propylene carbonates (PC) under solventfree, mild conditions (80 °C, 5 bar). In addition, the Zn(Bmic)(AT) catalyst exhibits good recyclability for six consecutive cycles. Moreover, a feasible synergistic mechanism of Zn(Bmic)(AT)/Bu 4 NBr catalysts for CO 2 conversion into cyclic carbonate is proposed.