Facile One-Pot Synthesis of Zn/Mg-MOF-74 with Unsaturated Coordination Metal Centers for Efficient CO₂ Adsorption and Conversion to Cyclic Carbonates

Abstract

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.

One-Pot Method Synthesis of Bimetallic MgCu-MOF-74 and Its CO2 Adsorption under Visible Light

“… 42 Several sharp and clear absorption peaks were observed at 1522, 1420, 890, and 823 cm –1 , which were ascribed to ν(−C=O), ν(−COO−), and ν(C–H) of benzene rings in H 4 dhtp ( Figure S1d ). 28 , 42 The sharp and weak peak at 1240 cm –1 is attributed to the stretching vibration of the C–O band of the phenolate group. Mg 0.2 Cu 0.8 -MOF-74 obtained under various preparation conditions exhibits the aforementioned characteristic peaks (from Figure S1d–f ), 38 which proves that Mg 0.2 Cu 0.8 -MOF-74 was successfully synthesized.…”

“…The synergistic effects originating from two adjacent Mg and Cu metals considerably improved the CO 2 adsorption capacity. 28 …”

Construction of a hierarchical tubular metal–organic framework composed of nanosheet arrays as a photothermal catalyst through phase transformation

“…Moreover, the cocatalyst TBAB played an essential role in the cycloaddition reaction, because the Br À from TBAB could facilitate the opening of the epoxide ring. 39 This was conrmed by a relatively low conversion efficiency of the catalytic reaction in the absence of TBAB, as shown in Fig. 5e.…”

A layered Mn-based coordination polymer as an efficient heterogeneous catalyst for CO2 cycloaddition under mild conditions

“…[18][19][20][21] For instance, Gao et al synthesized a series of bimetallic Zn/Mg-MOF-74 catalysts via a facile onepot method, which exhibit enhanced properties for CO 2 adsorption and catalytic chemical fixation of CO 2 to cyclic carbonates. 22 Isostructural M-MOF-184 reported by Tran et al has accessible mesopore channels and rich Lewis acidity derived from Zn sites, and can be used to efficiently catalyze the cycloaddition of CO 2 . 23 In addition, rigid ligands such as terephthalic acid have been extensively studied to construct robust CPs.…”