Catalysts For Conversion Of CO2 Research Articles

Boosting electrochemical conversion of CO2 to ethanol through the confinement of pyridinic N-B layer on copper nanoparticles

Developing efficient electrocatalysts for CO2 reduction has gained significant attention in the field of sustainable energy, especially the Cu-based catalysts for CO2 conversion to valuable alcohols. In this study, we developed Cu nanoparticles supported on pyridinic N-B doped graphene nanoribbons/amorphous carbon (Cu/BNC-1) as an electrocatalyst for CO2 reduction, exhibiting substantially improved ethanol (EtOH) conversion rate in terms of activity, selectivity, and stability. The Cu/BNC-1 achieved a remarkable 58.64 % Faradaic efficiency (FE) for producing EtOH at −1.0 V vs. RHE with a current density of 20.4 mA cm−2 in 0.5 M KHCO3 electrolyte. In-situ Raman, FT-IR, and density functional theory (DFT) calculations demonstrated that the high C2+ product selectivity of Cu/BNC-1 attributed to the pyridinic N-B modulation, lowering the CO dimerization barrier. Moreover, the synergistic confinement effect of Cu and BNC can stabilize the C-O bond of the *HOCCH intermediate, thereby increasing the yield of EtOH.

A bifunctional catalyst derived from copper metal−organic framework for highly selective photocatalytic CO2 reduction and CO2 cycloaddition reaction

Highly efficient conversion of CO2 into valuable chemicals using green chemical reactions is attractive to the alleviation of global warming. Developing active catalysts with high selectivity remains challenging and is still in pursuit. Herein, a Cu-based metal−organic framework was successfully synthesized by a facile method and denoted as CuTIA. The obtained CuTIA with rich Lewis acid/base sites exhibited enhanced CO2 affinity and served as a bifunctional catalyst for CO2 conversion. To be specific, CuTIA converted CO2 into CH4 (103.78 μmol g−1 h−1) with a selectivity of 100 % under visible light irradiation. Besides, CuTIA drove CO2 cycloaddition reaction with epoxides to produce cyclic carbonates with a yield almost 100 % under mild conditions. This study provides a new perspective in the fabrication of bifunctional catalysts for enhancing CO2 conversion.

Multifunctional g-C3N4-PDI/MOF-545-NH2 photocatalyst for Enhanced CO2 reduction and aniline oxidation

The use of solar energy to convert CO2 into clean energy is one of the ideal strategies for achieving carbon neutrality. However, the rapid recombination of photogenerated electron holes, the complexity of the reduction products and the consumption of sacrificial materials severely limit its development and application. In this work, g-C3N4-PDI (CNP) and MOF-545-NH2 (MNH) were prepared by calcination and hydrothermal methods, respectively, and CNP/MNH photocatalysts were prepared by in situ growth of MNH on CNP surface. The photocatalytic CO2 conversion reaction of CNP/MNH in triethanolamine and aniline solutions was investigated. Experiments show that the prepared CNP/MNH catalyst has excellent photocatalytic performance. When triethanolamine was used as a sacrificial agent, the yield of CH4 reached 192.7 μmol·g−1·h−1 (selectivity 92.94 %). In particular, while the catalyst realizes the conversion of CO2 in the aniline solution, it is surprising to find that part of the CO2 is converted to ethanol. The catalyst’s photochemical properties, CO2 reduction pathway, and aniline oxidation products were characterized by XPS, UV–vis DRS, PL, electrochemistry, zeta potential, ESR, GC–MS and in-situ infrared spectroscopy. The results show that the modification of the catalyst and the formation of heterojunction not only increase the adsorption of CO2, but also accelerate the process of photogenerated electron migration, which plays an important role in the process of carbon dioxide conversion. This study provides a new perspective for the design of photocatalytic CO2 conversion catalysts, and also provides a feasible method for aniline wastewater treatment.

Implanting multi-functional ionic liquids into MOF nodes for boosting CO2 cycloaddition under solventless and cocatalyst-free conditions

It is critical to design an effective catalyst for CO2 conversion into cyclocarbonate to achieve the carbon neutrality. Herein, MIL-101(Cr) tethered by hydrogen bond donors (HBD)-containing ionic liquids (denoted as MIL-101-ILs(R), R = OH, NH2, and COOH) were synthesized through the implantation of 4,4′-bipyridine into MOF nodes via the post-synthetic modification, followed by the decoration with bromoalkanes including bromoethanol, bromoethylamine, and bromoacetic acid. Their catalytic performance were evaluated by the epoxide cycloaddition reaction under 1.0 MPa CO2 and 80 ℃ for 6 h in the absence of solvent and cocatalyst. Compared to MIL-101-ILs without HBD, MIL-101-ILs(OH) and MIL-101-ILs(NH2) demonstrated the more chloropropene carbonate (CPC) yield of 88 % and 83 %, respectively. Notably, MIL-101-ILs(COOH) exhibited an uppermost activity with a CPC yield of 96 %, attributed to the cooperativity of Lewis acidity originating from Cr3O clusters, hydrogen-bond interaction afforded by carboxyl groups, and the strong nucleophilicity offered by Br- ions of ILs. Moreover, MIL-101-ILs(COOH) presented excellent recyclability. A potential catalytic mechanism for epoxide cycloaddition with CO2 into cyclic carbonate has been proposed.

Facet and dual vacancy engineering-boosting BiOBr for enhanced CO2 and epoxide cycloaddition reaction under mild and cocatalyst-free conditions: Double substrate active sites and activated surface bromine ions synergy

Among the many strategies for CO2 resource utilization, the synthetic technology of cyclic carbonates with 100 % atom economy through CO2and epoxide is one of the most industrially viable routes, but its efficiency has been severely hampered by the lack of highly active catalytic sites. Moreover, due to the intrinsic thermodynamic stability and kinetic inertia of CO2 and the higher energy barrier of the ring-opening reaction of epoxides, the heterogeneous catalytic conversion of CO2 highly depends on harsh operating conditions, high temperatures and pressures, and the incorporation of cocatalysts. The development of efficient heterogeneous catalysts for CO2 conversion under cocatalyst-free and mild conditions has always been a challenge. Herein, we have proposed a synergetic strategy of facet and vacancy engineering for the construction of highly efficient heterogeneous catalyst BiO1-xBr1-y-(010) for CO2 cycloaddition, where introducing the OVs-BrVs pairs into typical (010) facets BiOBr with simultaneous surface Lewis acid sites Bi3+ and nucleophilic sites Br−. By combining theoretical calculations and a series of systematic experiments, such as CO2 temperature-programmed desorption, electron paramagnetic resonance and fluorescence probe analysis experiments, the introduced OVs-BrVs pair can not only form Bi3+-Bi(3-x)+ dual active sites on the surface, which activate PO and CO2 respectively to reduce the energy barrier of CO2 insertion, but also activate Br− near BrVs to enhance their nucleophilic attacking ability and reduce the energy barrier of epoxides ring-opening. As a result, the BiO1-xBr1-y-(010) with abundant surface OVs-BrVs pairs showed a high cyclic carbonates conversion of 99 % with 100 % selectivity under cocatalyst-free and mild conditions, far surpassing most heterogeneous catalytic systems. This work provides a completely new strategy to construct high-performance heterogeneous CO2 cycloaddition catalysts through a simple facet and vacancy engineering strategy to overcome the harsh operating conditions limitation and the use of cocatalysts.

Hierarchical Hollow TiO2@Bi2WO6 with Light-Driven Excited Bi(3-x)+ Sites for Efficient Photothermal Catalytic CO2 Reduction.

Converting CO2 into valuable chemicals via sustainable energy sources is indispensable for human development. Photothermal catalysis combines the high selectivity of photocatalysis and the high yield of thermal catalysis, which is promising for CO2 reduction. However, the present photothermal catalysts suffer from low activity due to their poor light absorption ability and fast recombination of photogenerated electrons and holes. Here, a TiO2@Bi2WO6 heterojunction photocatalyst featuring a hierarchical hollow structure was prepared by an in situ growth method. The visible light absorption and photothermal effect of the TiO2@Bi2WO6 photocatalyst is promoted by a hierarchical hollow structure, while the recombination phenomenon is significantly mitigated due to the construction of the heterojunction interface and the existence of excited Bi(3-x)+ sites. Such a catalyst exhibits excellent photothermal performance with a CO yield of 43.7 μmol h-1 g-1, which is 15 and 4.7 times higher than that of pure Bi2WO6 and that of physically mixed TiO2/Bi2WO6, respectively. An in situ study shows that the pathway for the transformation of CO2 into CO over our TiO2@Bi2WO6 proceeds via two important intermediates, including COO- and COOH-. Our work provides a new idea of excited states for the design and synthesis of highly efficient photothermal catalysts for CO2 conversion.

Functionalization of Magnetic UiO-66-NH2 with a Chiral Cu(l-proline)2 Complex as a Hybrid Asymmetric Catalyst for CO2 Conversion into Cyclic Carbonates.

In this study, a chiral [Cu(l-proline)2] complex-modified Fe3O4@SiO2@UiO-66-NH2(Zr) metal-organic framework [Fe3O4@SiO2@UiO-66-NH-Cu(l-proline)2] via multifunctionalization strategies was designed and synthesized. One simple approach to chiralize an achiral MOF-structure that cannot be directly chiralized using a chiral secondary agent like 4-hydroxy-l-proline. Therefore, this chiral catalyst was synthesized with a simple and multistep method. Accordingly, Fe3O4@SiO2@UiO-66-NH2 has been synthesized via Fe3O4 modification with tetraethyl orthosilicate and subsequently with ZrCl4 and 2-aminoterephthalic acid. The presence of the silica layer helps to stabilize the Fe3O4 core, while the bonding between Zr4+ and the -OH groups in the silica layer promotes the development of Zr-MOFs on the Fe3O4 surface, and then the surfaces of the synthesized magnetic MOFs composite are functionalized with 1,2-dichloroethane and Cu(II) complex with 4-hydroxy-l-proline, [Cu(l-proline)2] to afford the magnetically chiral nanocatalyst. Multiple techniques were employed to characterize this magnetically chiral nanocatalyst such as Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDX), powder X-ray diffraction (PXRD), circular dichroism (CD), inductively coupled plasma (ICP), thermogravimetric analysis (TGA), vibrating-sample magnetometry (VSM), and Brunauer-Emmett-Teller (BET) analyses. Moreover, a magnetically chiral nanocatalyst shows the asymmetric CO2 fixation reaction under solvent-free conditions at 80 °C and in ethanol under reflux conditions with up to 99 and 98% ee, respectively. Furthermore, the reaction mechanism was illustrated concerning the total energy of the reactant, intermediates and product, and the structural parameters were analyzed.

1 nm Tin Oxide Cluster for the Electrochemical Conversion of Carbon Dioxide to Formate at Low Overpotential

Due to its cost-effectiveness and high product selectivity, tin oxide has been regarded as a promising catalyst for the electrochemical conversion of CO2 to formate. However, formate production is hindered by the high overpotential; there is a need to reduce the overpotential to enhance energy efficiency and lower electricity cost for the implementation of carbon utilization technology. Here, we report a facile synthesis method for 1 nm-sized SnO2 cluster catalysts, which can be used for CO2-to-formate conversion. SnO2 clusters were prepared through impregnation of porous carbon with a tin precursor solution. The SnO2 clusters showed a low overpotential, generating a current density of 10 mA cm-2 at a potential of -0.34 V vs. RHE in 1 M KOH. They also achieved high Faradaic efficiencies of 90.5% and 81.5% at 200 and 300 mA cm−2, respectively. Their electrocatalytic performance was strongly dependent on the annealing conditions, which affected the particle size, electrochemical active surface area, and metal oxidation state. This paper presents a versatile method for synthesizing metal oxide cluster catalysts, apart from providing insights into the catalytic activity for the electrochemical conversion of CO2 to formate.

Introducing a novel catalyst for efficient conversion of CO2 into syngas through reverse-water-gas-shift (RWGS) reactions based on highly mesoporous structures MCM-41: Influence of the Fe incorporation

The RWGS is the first step in CO2 hydrogenation. This process converts CO2 into valuable compounds, such as methanol, to address the global issue of CO2 emissions. In this research, the performance of a Cu-Fe bimetallic catalyst mounted onto MCM-41 support in RWGS was investigated. Our results demonstrate that MCM-41′s high specific surface area is advantageous for dispersing active metals and preventing their sintering. The Cu-Fe supported on MCM-41 samples are characterized by Scanning Electron Microscopy (SEM), ex situ X-ray Diffraction (XRD), Brunner–Emmet–Teller (BET), and Temperature Programmed Reduction (TPR). In order to investigate the catalytic activity, key variables including a temperature range of 400–600 °C, different H2/CO2 ratios, and various gas hourly space velocities (GHSV) at atmospheric pressure were assessed. In this study, excellent CO2 conversion was attained at a high GHSV (96,000 ml g-1h−1), which is advantageous for the design of smaller reactor volumes. In comparison to industrial Copper-Zinc catalysts and iron-free copper-supported MCM-41 catalysts, which suffer from a high sintering rate at temperatures above 300 °C, adding Iron (Fe) to the copper could increase the catalyst's activity and stability in terms of CO2 conversion and CO selectivity due to the formation of a Cu-Fe alloy. The novelty of this study lies in the assessment of the benefits afforded by bimetallic Cu-Fe catalysts in conjunction with high surface area MCM-41. Also, three different ratios of Cu-Fe (10-1, 7-1, 4-1) were considered for our experiments. The Cu-Fe = 10-1 ratio reached the highest CO2 conversion and CO selectivity value in 600 °C with amounts of 49 % and 99.7 %, respectively.

Noncrystalline Zeolitic Imidazolate Frameworks Tethered with Ionic Liquids as Catalysts for CO2 Conversion into Cyclic Carbonates.

Noncrystalline zeolitic imidazolate frameworks (ZIFs) tethered with ionic liquids (ILs) were successfully employed as catalysts for mild CO2 conversion into cyclic carbonates for the first time. Notably, noncrystalline ZIFs exhibit outstanding catalytic performance in terms of activity, stability, and substrate suitability. Z3 was obtained through the simultaneous incorporation of a boronic acid group and ILs into its ZIF framework and exhibited a superior catalytic activity. A reaction mechanism for the propylene oxide-CO2 cycloaddition has been proposed, which integrates experimental findings with density functional theory calculations. The results indicate that zinc, ILs, and boronic acid play crucial roles in achieving high activity. Zinc and ILs are identified as key contributors to epoxide activation and ring opening, while boronic acid plays a crucial role in stabilizing the turnover frequency-determining transition states. The simplicity of this ZIF synthesis approach, combined with the high activity, stability, and versatility of the products, facilitates practical and efficient conversion of CO2 and epoxides into cyclic carbonates.

Molecular engineering binuclear copper catalysts for selective CO2 reduction to C2 products

Molecular copper catalysts serve as exemplary models for correlating the structure-reaction-mechanism relationship in the electrochemical CO2 reduction (eCO2R), owing to their adaptable environments surrounding the copper metal centres. This investigation, employing density functional theory calculations, focuses on a novel family of binuclear Cu molecular catalysts. The modulation of their coordination configuration through the introduction of organic groups aims to assess their efficacy in converting CO2 to C2 products. Our findings highlight the crucial role of chemical valence state in shaping the characteristics of binuclear Cu catalysts, consequently influencing the eCO2R behaviour. Notably, the Cu(II)Cu(II) macrocycle catalyst exhibits enhanced suppression of the hydrogen evolution reaction (HER), facilitating proton transfer and the eCO2R process. Furthermore, we explore the impact of diverse electron-withdrawing and electron-donating groups coordinated to the macrocycle (R = –F, –H, and –OCH3) on the electron distribution in the molecular catalysts. Strategic placement of –OCH3 groups in the macrocycles leads to a favourable oxidation state of the Cu centres and subsequent C–C coupling to form C2 products. This research provides fundamental insights into the design and optimization of binuclear Cu molecular catalysts for the electrochemical conversion of CO2 to value-added C2 products.

Ionic Liquid Immobilized Fe‐MIL‐101‐NH2 Efficiently Catalyzes the Chemical Fixation of CO2 with Epoxides to Form Cyclic Carbonates

AbstractIn this work, two ionic liquids (ILs) immobilized metal‐organic frameworks (MOFs), Fe‐MIL‐101‐3N(BuBr) and Fe‐MIL‐101‐N(Bnme2)Br, were obtained by modifying amino groups in Fe‐MIL‐101‐NH2 with bromobutane and quaternary ammonium salt. The ionic liquid immobilized MOFs have Lewis acid sites (Fe3+) and nucleophilic sites (Br−), which can synergistically catalyze the cycloaddition reaction of CO2 and epoxides. Various cyclic carbonate derivatives were obtained in excellent yields under the optimal conditions. Additionally, we found that Fe‐MIL‐101‐N(Bnme2)Br exhibited the highest catalytic activity and it can be easily recovered and reused for at least 5 times without loss of catalytic activity. Our method of preparing bifunctional catalysts provides a new approach to design catalysts for the chemical conversion of CO2.

Metal-organic-framework-derived boron and nitrogen dual-doped hollow mesoporous carbon for photo-thermal catalytic conversion of CO2

The facile fabrication of hollow materials with rich defects is highly desired for photothermal conversion of CO2. Herein, we successfully prepared Zn, B, and N co-doped hollow mesoporous carbon (BHNC) by directly pyrolyzing phenylboronic acid/melamine/ZIF-8. The hollow porous structure of the resulting BHNC material can not only achieve high photothermal conversion efficiency but also effectively promote substrate mass transfer. Moreover, the introduction of B extends the light absorption scope of the material, offers active sites for chemical adsorption and further activation of CO2, significantly promoting the cycloaddition reaction. Benefiting from their high specific surface area, hollow mesoporous nanoarchitecture and rich defects, the optimized BHNC can be employed as a high-efficiency catalyst for the CO2 cycloaddition reaction under light irradiation and ambient conditions, affording 3 times higher yield of 4-(chloromethyl)-1,3-dioxolan-2-one (97%) than that of ZIF-8-800. This study provides a new strategy for the design of efficient catalysts for CO2 conversion under mild conditions.

The Effect of Bismuth and Tin on Methane and Acetate Production in a Microbial Electrosynthesis Cell Fed with Carbon Dioxide.

This study investigates the impacts of bismuth and tin on the production of CH4 and volatile fatty acids in a microbial electrosynthesis cell with a continuous CO2 supply. First, the impact of several transition metal ions (Ni2+, Fe2+, Cu2+, Sn2+, Mn2+, MoO42-, and Bi3+) on hydrogenotrophic and acetoclastic methanogenic microbial activity was evaluated in a series of batch bottle tests incubated with anaerobic sludge and a pre-defined concentration of dissolved transition metals. While Cu is considered a promising catalyst for the electrocatalytic conversion of CO2 to short chain fatty acids such as acetate, its presence as a Cu2+ ion was demonstrated to significantly inhibit the microbial production of CH4 and acetate. At the same time, CH4 production increased in the presence of Bi3+ (0.1 g L-1) and remained unchanged at the same concentration of Sn2+. Since Sn is of interest due to its catalytic properties in the electrochemical CO2 conversion, Bi and Sn were added to the cathode compartment of a laboratory-scale microbial electrosynthesis cell (MESC) to achieve an initial concentration of 0.1 g L-1. While an initial increase in CH4 (and acetate for Sn2+) production was observed after the first injection of the metal ions, after the second injection, CH4 production declined. Acetate accumulation was indicative of the reduced activity of acetoclastic methanogens, likely due to the high partial pressure of H2. The modification of a carbon-felt electrode by the electrodeposition of Sn metal on its surface prior to cathode inoculation with anaerobic sludge showed a doubling of CH4 production in the MESC and a lower concentration of acetate, while the electrodeposition of Bi resulted in a decreased CH4 production.

A new Eu(III)-based metal-organic framework: synthesis, characterization, fluorescence detection of nitrobenzene and catalytic conversion of CO2

The employment of metal-organic frameworks (MOFs) as fluorescence sensors for the detection of environmental pollutants and/or heterogeneous catalysts for CO2 conversion is of great importance for protecting human health. For this purpose, we synthesized a new Eu-MOF [Eu2(btpdc)2·(HCOO)2]n (1) (H2btpdc = benzo[b]thiophene-2,5-dicarboxylic acid) with its three-dimensional structure characterized by single-crystal X-ray diffraction. The powder X-ray diffraction (PXRD) and thermal gravimetric analysis (TGA) results indicate that 1 has high chemical durability, good water stability and high thermal stability. Fluorescence sensing investigations demonstrate that 1 is a smart chemical sensor towards nitrobenzene (NB) detection with high sensitivity, high selectivity and good regeneration performance. A high quenching constant (Ksv = 2.33 × 105 M−1) and a low detection limit (LOD = 0.038 μM) are obtained. Combined with experiments and density functional theory calculations, the mechanisms of fluorescence quenching of 1 by NB were also revealed. Furthermore, 1 can serve as a smart catalyst for the cycloaddition reaction of CO2 with epoxides to synthesize cyclic carbonates, displaying high activity, high selectivity, and good generality.

Boosting catalytic performance for CO2 cycloaddition under mild condition via amine grafting on MIL-101-SO3H catalyst

The efforts to achieve sustainable chemical conversion and efficient CO2 utilization are critical to addressing climate change and environmental sustainability, and therefore the development of effective CO2 conversion catalysts is crucial. In this study, novel acid-base bifunctional catalysts, MIL-101-SO3H@Atz and MIL-101-SO3H@DAtz, were successfully synthesized using MIL-101-SO3H as an acid support material through post-synthetic modification with 3-amino-1,2,4-triazole (Atz) and 3,5-diamino-1,2,4-triazole (DAtz) for CO2 conversion reaction. The incorporation of the amine species into MIL-101-SO3H created unique synergistic effects with dual acid-base catalytic sites, facilitating the efficient conversion of CO2 and epoxides into cyclic carbonates. Among the catalysts, MIL-101- SO3H@DAtz demonstrated superior catalytic performance with achieving 100% epichlorohydrin (ECH) conversion with over 99% selectivity to cyclic carbonate with high selectivity of > 99% under the ambient condition of 1 bar CO2 without any co-catalyst or solvent. The elucidated CO2 cycloaddition reaction mechanism highlights the synergistic effects of acid-base functionalities and CO2-philic Lewis bases as well as hydrogen bonding donor groups, providing valuable insights into the factors contributing to superior catalytic performance. The simulated flue gas (15% CO2/85% N2, v/v) was also conducted using MIL-101-SO3H@DAtz catalyst. Additionally, the MIL-101-SO3H@DAtz catalyst exhibited remarkably robust structural stability and recyclability, maintaining its activity over multiple cycles.

Designing bifunctional catalysts for the one-pot conversion of CO2 to sustainable marine transportation fuels

A highly selective bifunctional catalyst for the one-pot conversion of CO2 to DME using CuZnO nanoparticles located on SAPO-34 crystals.

Subnanometric Pt clusters dispersed over Cs-doped TiO2 for CO2 upgrading via low-temperature RWGS: operando mechanistic insights to guide an optimal catalyst design

Cs-doped Pt/TiO2 advanced catalysts for CO2 conversion via low-temperature RWGS: from operando and mechanistic study to real-catalyst design to combat global warming.

Design and Investigation of Superatoms for Redox Applications: First-Principles Studies.

A superatom is a cluster of atoms that acts like a single atom. Two main groups of superatoms are superalkalis and superhalogens, which mimic the chemistry of alkali and halogen atoms, respectively. The ionization energies of superalkalis are smaller than those of alkalis (<3.89 eV for cesium atom), and the electron affinities of superhalogens are larger than that of halogens (>3.61 eV for chlorine atom). Exploring new superalkali/superhalogen aims to provide reliable data and predictions of the use of such compounds as redox agents in the reduction/oxidation of counterpart systems, as well as the role they can play more generally in materials science. The low ionization energies of superalkalis make them candidates for catalysts for CO2 conversion into renewable fuels and value-added chemicals. The large electron affinity of superhalogens makes them strong oxidizing agents for bonding and removing toxic molecules from the environment. By using the superatoms as building blocks of cluster-assembled materials, we can achieve the functional features of atom-based materials (like conductivity or catalytic potential) while having more flexibility to achieve higher performance. This feature paper covers the issues of designing such compounds and demonstrates how modifications of the superatoms (superhalogens and superalkalis) allow for the tuning of the electronic structure and might be used to create unique functional materials. The designed superatoms can form stable perovskites for solar cells, electrolytes for Li-ion batteries of electric vehicles, superatomic solids, and semiconducting materials. The designed superatoms and their redox potential evaluation could help experimentalists create new materials for use in fields such as energy storage and climate change.

A mesoporous ionic metal-organic framework decorated by flexible alkyl imidazolium bromide as heterogeneous catalyst for efficient conversion of CO2 to cyclic carbonates

A mesoporous ionic MOF-based catalyst (Br−)C3H7-Imidazolium-MOF-1 for the cycloaddition of CO2 to epoxides (CCE) was synthesized by template-assisted method, and its composite and structure were determined by FT-IR, PXRD, NMR, SEM, TEM, XPS and N2 adsorption. (Br−)C3H7-Imidazolium-MOF-1, is constructed by Zr6O4(OH)4 clusters and linear dicarboxylic acid ligands covalently modified by flexible alkyl imidazolium groups (1-methylene-3-propyl-imidazolium bromide). By the synergistic effect of Zr4+ Lewis acid sites and Br− nucleophiles, (Br−)C3H7-Imidazolium-MOF-1 shown superior catalytic performance for the cycloaddition of CO2 to epichlorohydrin in the absence of any co-catalyst under mild conditions. Small steric hindrance from the flexible imidazolium groups and rapid mass transport of reactants and products in the mesoporous catalyst acted synergistically to promote this process. A firm bond between the imidazolium bromide and the framework of (Br−)C3H7-Imidazolium-MOF-1 made it a recyclable heterogeneous catalyst. Furthermore, several additional coupling reactions were investigated with other epoxides as substrates.