A New Class of Metal-Cyclam-Based Zirconium Metal–Organic Frameworks for CO2 Adsorption and Chemical Fixation

Hexanuclear 3d-4f complexes as efficient catalysts for converting CO2 into cyclic carbonates

A series of novel hexanuclear 3d-4f complexes formulated as {[Ln2Zn4(μ3-OH)2L4(AcO)2(NO3)2(DMF)2]·2(CH3OH), LnIII = Dy3+ (1), Nd3+ (2), Tb3+ (3)} have been synthesized and characterized. These complexes 1-3 show excellent catalytic performance for the cycloaddition of CO2 and epoxides to obtain cyclic carbonates. The catalytic system has a wide substrate scope with high turnover numbers (9700) and high turnover frequencies (808 h-1) under mild conditions. Additionally, the catalysts could be conveniently prepared on a large scale and recycled.

Ionic-Liquid-Functionalized UiO-66 Framework: An Experimental and Theoretical Study on the Cycloaddition of CO2 and Epoxides

A facile approach for modifying the UiO-66-NH₂ metal-organic framework by incorporating imidazolium-based ionic liquids (ILs) to form bifunctional heterogeneous catalysts for the cycloaddition of epoxides to CO₂ is reported. Methylimidazolium- and methylbenzimidazolium-based IL units (ILA and ILB, respectively) were introduced into the pore walls of the UiO-66-NH₂ framework through a condensation reaction to generate ILA@U6N and ILB@U6N catalysts, respectively. The resultant heterogeneous catalysts, especially ILA@U6N, exhibited excellent CO₂ adsorption capability, which makes them effective for cycloaddition reactions producing cyclic carbonates under mild reaction conditions in the absence of any cocatalyst or solvent. The significantly enhanced activity of ILA@U6N is attributed to the synergism between the coordinately unsaturated Lewis acidic Zr⁴⁺ centers and Br^- ions in the bifunctional heterogeneous catalysts. The size effect of the ILs on coupling between the epoxide and CO₂ was also studied for ILA@U6N and ILB@U6N. A periodic DFT study was performed to provide evidence of possible intermediates, transition states, and pathways, as well as to gain deeper insight into the mechanism of the ILA@U6N-catalyzed cycloaddition reaction between epichlorohydrin and CO₂ .

The Counterion Effect of Imidazolium-Type Poly(ionic liquid) Brushes on Carbon Dioxide Adsorption

Imidazolium-based poly(ionic liquid) brushes were attached to spherical silica nanoparticles bearing various functionalities by using a surface-initiated atom transfer radical polymerization ("grafting from" technique). A temperature-programmed desorption process was applied to evaluate and analyze the carbon dioxide adsorption performance of the synthesized polymer brushes. The confined structure of the surface-attached polymer chains facilitates gas transport and adsorption, leading to an enhanced adsorption capacity of carbon dioxide molecules compared with pure polymer powders. Temperature-programmed desorption profiles of the synthesized polymer brushes after carbon dioxide adsorption reveal that the substituent groups on the nitrogen atom at the 3-position of the imidazole ring, as well as the associated anions significantly affect the adsorption capacity of functionalized poly(ionic liquid) brushes. Of the tested samples, amine-functionalized poly(ionic liquid) brushes associated with hexafluorophosphate ions exhibit the highest carbon dioxide adsorption capacity of 2.56 mmol g^-1 (112.64 mg g^-1 ) at 25 °C under a carbon dioxide partial pressure of 0.2 bar.

Three novel topologically different metal–organic frameworks built from 3-nitro-4-(pyridin-4-yl)benzoic acid

The design and synthesis of metal–organic frameworks (MOFs) have attracted much interest due to the intriguing diversity of their architectures and topologies. However, building MOFs with different topological structures from the same ligand is still a challenge. Using 3-nitro-4-(pyridin-4-yl)benzoic acid (HL) as a new ligand, three novel MOFs, namely poly[[(N,N-dimethylformamide-κO)bis[μ2-3-nitro-4-(pyridin-4-yl)benzoato-κ3 O,O′:N]cadmium(II)] N,N-dimethylformamide monosolvate methanol monosolvate], {[Cd(C12H7N2O4)2(C3H7NO)]·C3H7NO·CH3OH} n , (1), poly[[(μ2-acetato-κ2 O:O′)[μ3-3-nitro-4-(pyridin-4-yl)benzoato-κ3 O:O′:N]bis[μ3-3-nitro-4-(pyridin-4-yl)benzoato-κ4 O,O′:O′:N]dicadmium(II)] N,N-dimethylacetamide disolvate monohydrate], {[Cd2(C12H7N2O4)3(CH3CO2)]·2C4H9NO·H2O} n , (2), and catena-poly[[[diaquanickel(II)]-bis[μ2-3-nitro-4-(pyridin-4-yl)benzoato-κ2 O:N]] N,N-dimethylacetamide disolvate], {[Ni(C12H7N2O4)2(H2O)2]·2C4H9NO} n , (3), have been prepared. Single-crystal structure analysis shows that the CdII atom in MOF (1) has a distorted pentagonal bipyramidal [CdN2O5] coordination geometry. The [CdN2O5] units as 4-connected nodes are interconnected by L − ligands to form a fourfold interpenetrating three-dimensional (3D) framework with a dia topology. In MOF (2), there are two crystallographically different CdII ions showing a distorted pentagonal bipyramidal [CdNO6] and a distorted octahedral [CdN2O4] coordination geometry, respectively. Two CdII ions are connected by three carboxylate groups to form a binuclear [Cd2(COO)3] cluster. Each binuclear cluster as a 6-connected node is further linked by acetate groups and L − ligands to produce a non-interpenetrating 3D framework with a pcu topology. MOF (3) contains two crystallographically distinct NiII ions on special positions. Each NiII ion adopts an elongated octahedral [NiN2O4] geometry. Each NiII ion as a 4-connected node is linked by L − ligands to generate a two-dimensional network with an sql topology, which is further stabilized by two types of intermolecular OW—HW...O hydrogen bonds to form a 3D supramolecular framework. MOFs (1)–(3) were also characterized by powder X-ray diffraction, IR spectroscopy and thermogravimetic analysis. Furthermore, the solid-state photoluminescence of HL and MOFs (1) and (2) have been investigated. The photoluminescence of MOFs (1) and (2) are enhanced and red-shifted with respect to free HL. The gas adsorption investigation of MOF (2) indicates a good separation selectivity (71) of CO2/N2 at 273 K (i.e. the amount of CO2 adsorption is 71 times higher than N2 at the same pressure).

Experimental and theoretical study for CO2 activation and chemical fixation with epoxides

The synthesis of five-membered cyclic carbonates via catalytic cycloaddition reaction of CO₂ with epoxides is considered to be an effective technology for alleviation of the energy crisis and global warming. Various commercial organic bases and ionic salts were used as catalysts, while the relationship of catalytic activity and compound structure has been seldom explored. Herein, a facilely obtained binary catalytic system based on triethylamine/NBu₄Br was developed for CO₂ activation and chemical fixation. The highly efficient catalytic system showed outstanding conversion and above 99% selectivity under metal-free mild reaction conditions (100 °C, 1 atm) in one hour. The detailed process of CO₂ activation and chemical fixation was investigated at the molecular level by a series of experiments and theoretical calculation, which provided a mode for the design and synthesis of a highly efficient catalytic system for conversion of CO₂ under mild conditions.

NEt₃/NBu₄Br works as an excellent metal-free catalyst for CO₂ cycloaddition with epoxides and the detailed process of CO₂ activation by NEt₃ is first studied by theoretical calculation.

Carbon capture and conversion using metal–organic frameworks and MOF-based materials

This review summarizes recent advances and highlights the structure–property relationship on metal–organic framework-based materials for carbon dioxide capture and conversion.

A tri-functional metal–organic framework heterogeneous catalyst for efficient conversion of CO2 under mild and co-catalyst free conditions

A novel tri-functional MOF catalyst was achieved by PSM method. Because of the synergistic effect of Lewis acid, Brønsted acid and Br⁻ anion, MIL-IMAc-Br⁻ displayed an efficient catalytic performance for CO₂ conversion.

An exceptionally stable core–shell MOF/COF bifunctional catalyst for a highly efficient cascade deacetalization–Knoevenagel condensation reaction

A novel strategy has been developed to construct a highly stable core–shell MOF@COF bifunctional catalyst through strong π–π stacking interaction.

New multifunctional 3D porous metal–organic framework with selective gas adsorption, efficient chemical fixation of CO2 and dye adsorption

A new porous Mn(ii)-based MOF was obtained. The studies indicated it exhibits an effective storage capacity for CO₂, highly efficient catalyst behavior for epoxides with different substituents and rapid adsorption behavior of different dyes.

A Core-Shell-Structured Silver Nanowire/Nitrogen-Doped Carbon Catalyst for Enhanced and Multifunctional Electrofixation of CO2

Numerous catalysts have been successfully introduced for CO₂ fixation in aqueous or organic systems. However, a single catalyst showing activity in both solvent types is still rare, to the best of our knowledge. We developed a core-shell-structured AgNW/NC700 composite using a Ag nanowire (NW) core encapsulated by a N-doped carbon (NC) shell at 700 °C. Through control experiments and density functional theory calculations, it was confirmed that Ag nanowires acted as the active sites for CO₂ fixation and the uniformly coating of N-doped carbon created a CO₂ -rich environment around the Ag nanowires, which could significantly improve the catalytic activity of Ag nanowires for electrochemical CO₂ fixation. Under mild conditions, up to 96 % faradaic efficiency of CO, 95 % yield of Ibuprofen and 92 % yield of propylene carbonate could be obtained in the electrochemical CO₂ direct reduction, carboxylation and cycloaddition, respectively, using the same AgNWs/NC700 catalyst. These results might provide an alternative strategy for efficient electrochemical fixation of CO₂ .

A lithium-modified zirconium-based metal organic framework (UiO-66) for efficient CO2 adsorption

The adsorption mechanism of carbon dioxide (CO₂) on Li/UiO-66 was studied by an in situ DRIFTS study.

Solvent-dependent variations of both structure and catalytic performance in three manganese coordination polymers

Three new Mn-based MOFs have been prepared, and a 3D framework can act as an efficient and recycled catalyst in CO₂ cycloaddition with different epoxides.