Quaternary phosphonium salt-functionalized Cr-MIL-101: A bifunctional and efficient catalyst for CO2 cycloaddition with epoxides

MIL-101(Cr)/aminoclay nanocomposites for conversion of CO2 into cyclic carbonates

We present the use of an amine functionalized two-dimensional clay i.e., aminoclay (AC), in the chemistry of a three-dimensional metal-organic framework (MOF) i.e., MIL-101(Cr), to prepare MIL-101(Cr)/AC composites, which are exploited as catalysts for efficient conversion of CO2 gas into cyclic carbonates under ambient reaction conditions. Three different MOF nanocomposites, denoted as MIL-101(Cr)/AC-1, MIL-101(Cr)/AC-2, and MIL-101(Cr)/AC-3, were synthesized by an in situ process by adding different amounts of AC to the precursor solutions of the MIL-101(Cr). The composites were characterized by various techniques such as FT-IR, PXRD, FESEM, EDX, TGA, N2 adsorption, as well as CO2 and NH3-TPD measurements. The composites were exploited as heterogeneous catalysts for CO2 cycloaddition reactions with different epoxides and the catalytic activity was investigated at atmospheric pressure under solvent-free conditions. Among all the materials, MIL-101(Cr)/AC-2 shows the best catalytic efficiency under the optimized conditions and exhibits enhanced efficacy compared to various MIL-101(Cr)-based MOF catalysts, which typically need either high temperature and pressure or a longer reaction time or a combination of all the parameters. The present protocol using MIL-101(Cr)/AC-2 as the heterogeneous catalyst gives 99.9% conversion for all the substrates into the products at atmospheric pressure.

The post-synthesis modification (PSM) of MOFs for catalysis

While there are myriad ways to construct metal-organic framework (MOF) based catalysts, the introduction of catalytic functionality via covalent post-synthesis functionalization (PSM) offers multiple advantages: (i) a wide range of different catalyst types are generated from a handful of well-known parent MOFs, (ii) MOF catalyst properties can be systematically tuned while changing few variables, and (iii) catalytically active functional groups that would otherwise interfere with MOF assembly can be introduced facilely. This last advantage is particularly crucial for our quest to generate MOF active sites that are decorated with multiple functional groups capable of cooperative activity, analogous to enzyme active sites.

Hydroxyl and amino dual-functionalized core-shell molecular sieves featuring hydrogen bond donor groups for efficient CO2 cycloaddition

In CO2 cycloaddition reactions, hydrogen bond donor (HBD) groups are considered environmentally friendly substitutes for metals to promote epoxide ring-opening through interactions with nucleophilic anions. A core-shell structured ILs-based catalyst (mSiO2@MCM-NH2-OH) with dual hydrogen bond donors (-OH and -NH2) was synthesized by copolymerization strategy. Through in-depth characterization, it has been demonstrated that the catalyst (mSiO2@MCM-NH2-OH) possesses multiple catalytic active sites including -OH, -NH2, Br- groups, and the synergistic effect of double HBD groups (-OH and -NH2) and Lewis base (Br-) significantly improved the catalytic activity. Meanwhile, the core-shell structure of the catalyst effectively prevents the loss of active components, which makes the yield remain at about 94 % after 10 cycles. Based on Density Functional Theory (DFT) calculations, a synergistic catalytic mechanism, which involves dual hydrogen-bond donors (-OH and -NH2) and Lewis bases (Br-) was proposed. The cooperative interaction between -OH/-NH2 and Br- reduced the ring-opening barrier of epoxide from 58.6 to 32.0 kcal mol-1 significantly, and thereby facilitated the CO2 cycloaddition reaction.

Novel porous organic polymers functionalized by metalloporphyrin and phosphonium salts for the efficient synergistic catalysis of CO2 conversion under mild conditions

Metalloporphyrin- and phosphonium-functionalized porous organic polymers (POPs) were fabricated successfully via a post-synthesis modification strategy, which were demonstrated to be efficient heterogeneous catalysts for CO2 conversion.

Integration of polypyridyl-based ionic liquids into MIL-101 for promoting CO2 conversion into cyclic carbonates under cocatalyst-free and solventless conditions

The polypyridyl-based ionic liquid-functionalized MIL-101(Cr) greatly enhanced the epoxide–CO2 cycloaddition reaction under cocatalyst-free and solventless conditions.

A metal-free hydroxyl functionalized quaternary phosphine type ionic liquid polymer for cycloaddition of CO2 and epoxides

Quaternary phosphine type hypercrosslinked polymer catalysts were successfully prepared using the Friedel-Crafts alkylation reactions, which benefit from the synergistic effects between the Brønsted acidity of the hydroxyl group and nucleophilicity of the Br^- group as well as the CO₂ capture of the ionic liquids. The as-obtained metal-free catalysts facilitate the cycloaddition and synthesis of high value-added fine chemicals.

Simple carbonaceous-material-loaded mesoporous SiO2 composite catalyst for epoxide-CO2 cycloaddition reaction

In this paper, a novel arginine-glucose derived carbonaceous-material-loaded SiO₂ composite catalyst (Ar-G-CM/SiO₂) was synthesized from non-toxic and harmless reagents (arginine, glucose and tetraethylorthosilicate) by simple hydrothermal process. Mesoporous SiO₂ with high specific area served as support for carbonaceous material and provided extra hydrogen bond donor (HBD) groups. Ar-G-CM/SiO₂ with acid-base dual functional groups (COOH, NH₂) and HBD group (OH) presented 62% yield and 99% selectivity to product of propylene carbonate in CO₂ cycloaddition reaction with propylene oxide even at 40 °C, 2 MPa under metal-absent and solvent-free conditions. For some less active epoxides with steric hindrance, Ar-G-CM/SiO₂ also showed good yield and selectivity over 90% by raising temperature to 120 °C. Furthermore, the Ar-G-CM/SiO₂ catalyst could be reused for six successive cycles without significant decrease in catalytic activity or structural deterioration, because the carbon deposition was restrained owing to the mesoporous structure of the catalyst.

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

The level of carbon dioxide in the atmosphere is growing rapidly due to fossil fuel combustion processes, heavy oil, coal, oil shelter, and exhausts from automobiles for energy generation, which lead to depletion of the ozone layer and consequently result in global warming. The realization of a carbon-neutral environment is the main focus of science and academic researchers of today. Several processes were employed to minimize carbon dioxide in the air, some of which include the utilization of non-fossil sources of energy like solar, nuclear, and biomass-based fuels. Consequently, these sources were reported to have a relatively high cost of production and maintenance. The applications of both homogeneous and heterogeneous processes in carbon capture and storage were investigated in recent years and the focus now is on the conversion of CO2 into useful chemicals and compounds. It was established that CO2 can undergo cycloaddition reaction with epoxides under the influence of special catalysts to give cyclic carbonates, which can be used as value-added chemicals at a different level of pharmaceutical and industrial applications. Among the various catalysts studied for this reaction, metal-organic frameworks are now on the frontline as a potential catalyst due to their special features and easy synthesis. Several metal-organic framework (MOF)-based catalysts were studied for their application in transforming CO2 to organic carbonates using epoxides. Here, we report some recent studies of porous MOF materials and an in-depth discussion of two repeatedly used metal-organic frameworks as a catalyst in the conversion of CO2 to organic carbonates.

The multifunctional design of metal–organic framework by applying linker desymmetrization strategy: synergistic catalysis for high CO2-epoxide conversion

A novel copper-organic framework was synthesized by a linker desymmetrization strategy. Synergistic catalysis with Lewis and Brønsted acid sites promoted a high catalytic efficiency towards the CO2-propylene oxide cycloaddition reaction.

Aminoethylimidazole ionic liquid-grafted MIL-101-NH2 heterogeneous catalyst for the conversion of CO2 and epoxide without solvent and cocatalyst

An aminoethylimidazole IL-functionalized MIL-101-NHIM-NH₂ catalyst efficiently catalyzes the cycloaddition reaction of CO₂ and epoxide without solvent and cocatalyst, owing to the synergistic effects of Cr, –NH₂ and Br⁻ active sites.

Aliphatic carboxylic acid as a hydrogen-bond donor for converting CO2 and epoxide into cyclic carbonate under mild conditions

The catalytic systems of aliphatic carboxylic acids/quaternary ammonium halides could efficiently convert the coupling of CO₂ and epoxide into cyclic carbonates under mild conditions (80 °C and 4 bar CO₂).

Protic ionic liquids tailored by different cationic structures for efficient chemical fixation of diluted and waste CO2 into cyclic carbonates

Environment-friendly approaches to directly convert atmospheric or flue gas CO₂ to high-value chemicals is of great significance yet challenging.

Pyridinium-Functionalized Ionic Metal-Organic Frameworks Designed as Bifunctional Catalysts for CO2 Fixation into Cyclic Carbonates

Ionic metal-organic frameworks (MOFs) offer a new platform to design and construct complete heterogeneous bifunctional catalytic systems for the chemical fixation of CO₂ with epoxides. Herein, we developed a series of bifunctional pyridinium ionic MOF heterogeneous catalysts (66Pym-RXs and 67BPym-MeI) by the postsynthetic N-alkylation of noncoordinated pyridine sites in porous MOFs. The synergetic catalytic effect of acidic sites with nucleophilic anions in the ionic MOF significantly enhanced the catalytic activity toward the cycloaddition of CO₂ with epoxides to produce cyclic carbonates under cocatalyst-free and solvent-free mild conditions. The catalytic activity of ionic MOFs is easily tuned by the introduction of different alkyl groups into pyridinium cations and halide ions. The 66Pym-iPrI catalyst displayed the highest catalytic performance in terms of the turnover number value for the synthesis of cyclic carbonates. The proposed alternative method provides the means of developing functional N-heterocyclic groups for the new design of bifunctional ionic MOFs as potential heterogeneous catalysts for CO₂ fixation applications.

MIL-101(Cr) for CO2 Conversion into Cyclic Carbonates, Under Solvent and Co-Catalyst Free Mild Reaction Conditions

Mild reaction conditions (nearly room temperature and atmospheric CO2 pressure) for the cycloaddition of CO2 with epoxides to produce cyclic carbonates were investigated applying MIL-101(Cr) as a catalyst. The MIL-101 catalyst contains strong acid sites, which promote the ring-opening of the epoxide substrate. Moreover, the high surface area, enabling the adsorption of more CO2 (substrate), combined with a large pore size of the catalyst is essential for the catalytic performance. Additionally, epoxide substrates bearing electron-withdrawing substituents or having a low boiling point demonstrated an excellent conversion towards the cyclic carbonates. MIL-101(Cr) for the cycloaddition of carbon dioxide with epoxides is demonstrated to be a robust and stable catalyst able to be re-used at least five times without loss in activity.

Metal–organic frameworks for the energy-related conversion of CO2 into cyclic carbonates

MOFs are promising heterogeneous catalysts for chemical fixation of CO₂ and epoxides into cyclic carbonates.