Study on Selected Metal-Organic Framework-Based Catalysts for Cycloaddition Reaction of CO2 with Epoxides: A Highly Economic Solution for Carbon Capture and Utilization

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

Ionic liquids (ILs) have unique physicochemical properties that make them advantageous for catalysis, such as low vapor pressure, non-flammability, high thermal and chemical stabilities, and the ability to enhance the activity and stability of (bio)catalysts. ILs can improve the efficiency, selectivity, and sustainability of bio(transformations) by acting as activators of enzymes, selectively dissolving substrates and products, and reducing toxicity. They can also be recycled and reused multiple times without losing their effectiveness. ILs based on imidazolium cation are preferred for structural organization aspects, with a semiorganized layer surrounding the catalyst. ILs act as a container, providing a confined space that allows modulation of electronic and geometric effects, miscibility of reactants and products, and residence time of species. ILs can stabilize ionic and radical species and control the catalytic activity of dynamic processes. Supported IL phase (SILP) derivatives and polymeric ILs (PILs) are good options for molecular engineering of greener catalytic processes. The major factors governing metal, photo-, electro-, and biocatalysts in ILs are discussed in detail based on the vast literature available over the past two and a half decades. Catalytic reactions, ranging from hydrogenation and cross-coupling to oxidations, promoted by homogeneous and heterogeneous catalysts in both single and multiphase conditions, are extensively reviewed and discussed considering the knowledge accumulated until now.

SU-101: a Bi(III)-based metal-organic framework as an efficient heterogeneous catalyst for the CO2 cycloaddition reaction

A non-porous version of SU-101 (herein n-SU-101) was evaluated for the CO2 cycloaddition reaction. The findings revealed that open metal sites (Bi3+) are necessary for the reaction. n-SU-101 displays a high styrene oxide conversion of 96.6% under mild conditions (3 bar and 80 °C). The catalytic activity of n-SU-101 demonstrated its potential application for the cycloaddition of CO2 using styrene oxide.

Wet flue gas CO2 capture and utilization using one-dimensional metal-organic chains

Herein, we describe the use of an ultramicroporous metal-organic framework (MOF) with a composition of [Ni₃(pzdc)₂(ade)₂(H₂O)_1.5]·(H₂O)_1.3 (pzdc: 3,5-pyrazole dicarboxylic acid; ade: adenine), for the selective capture of carbon dioxide (CO₂) from wet flue gas followed by its conversion to value-added products. This MOF is comprised of one-dimensional Ni(II)-pyrazole dicarboxylate-adenine chains; through pi-pi stacking and H-bonding interactions, these one-dimensional chains stack into a three-dimensional supramolecular structure with a one-dimensional pore network. Upon heating, our MOF undergoes a color change from light blue to lavender, indicating a change in the coordination geometry of Ni(II). Variable temperature ultraviolet-visible (UV/vis) spectroscopy data revealed a blue shift of the d-d transitions, suggesting a change in the Ni-coordination geometry from octahedral to a mixture of square planar and square pyramidal. The removal of the water molecules coordinated to Ni(II) leads to the generation of a MOF with open Ni(II) sites. Nitrogen isotherms collected at 77 K and 1 bar revealed that this MOF is microporous with a pore volume of 0.130 cm³ g^-1. Carbon dioxide isotherms show a step in the uptake at low pressure, after which the CO₂ uptake is saturated. The step in the CO₂ uptake is likely attributable to the rearrangement of the three-dimensional supramolecular structure to accommodate CO₂ within its pores. The affinity of this MOF for CO₂ is 35.5 kJ mol^-1 at low loadings, and it increases to 41.9 kJ mol^-1 at high loadings. While our MOF is porous to CO₂ and water (H₂O) at 298 K, it is not porous to N₂, and the CO₂/N₂ selectivity increases from 28.5 to 31.5 as a function of pressure. Breakthrough experiments reveal that this MOF can capture CO₂ from dry and wet flue gas with uptake capacities of 1.48 ± 0.01 and 1.14 ± 0.06 mmol g^-1, respectively. The MOF can be regenerated and reused at least three times, demonstrating consistent CO₂ uptake capacities. Upon understanding the sorption behavior of this MOF, catalysis experiments show that the MOF is catalytically active in the fixation of CO₂ into an epoxide ring for the formation of a cyclic carbonate. The turnover frequency for this reaction is 21.95 ± 0.03 h^-1. The MOF showed no catalytic deterioration after two cycles and maintained comparable catalytic activity when dry and wet CO₂/N₂ mixtures were used. This highlights that both N₂ and H₂O do not dramatically affect the catalytic activity of our MOF toward CO₂ fixation.