Framework Catalyst Research Articles

Green halogenation of aromatic compounds using environmentally friendly synthesized rod-like metal-organic framework (MIL-88A) catalyst

Metal-organic frameworks (MOFs) have been extensively investigated as catalysts to synthesis of various chemical and eliminate toxic pollutants in water. Herein, MOF was used as an efficient catalyst for the halogenation of aromatic materials (aniline, b-naphthol, and naphthalene). The rod-like MIL-88A as an iron-based MOF was synthesized using Fe3+ with fumaric acid in water as a green solvent. The synthesized catalyst was characterized by FT-IR, XRD, SEM, and Raman. The rod-like MIL-88A is evaluated as the heterogeneous catalyst to activate KBr/I for the halogenation of aromatic compounds. 1HNMR and 13CNMR were used to characterize the halogenated aromatic materials. Halogenation of aromatic rings has been studied using potassium bromide (KBr) and potassium iodide (KI) as brominating and iodinating agents in the presence of rod-like MIL-88A as oxidant under solvent-free reaction (grinding) conditions. The halogenation yield of aromatics materials was 80–99%. The conversion yield of aniline to 4‑bromo aniline using 0, 10, 20, 30, 40, and 50 mg of rod-like MIL-88A at 25 min and room temperature (25 ºC) were 0%, 76%, 85%, 90%, 95%, and 88%, respectively. In addition, the conversion yield of B-naphthol to 1-Bromo-2-naphthol using a green catalyst was 97%. Also, the conversion yield of Naphthalene to 1-Bromonaphthalene using a rod-like catalyst. In most cases, mono-halogen derivatives were obtained in good yield without the aid of strong acids. In addition, the rod-like MIL-88A catalyst shows excellent stability and can be reused after proper washing treatments. It could be concluded that green synthesized rod-like MIL-88A could be used as an environmentally friendly catalyst for the halogenation of aromatics via grinding as a solvent-free reaction at room temperature.

Mechanistic insight into electron orientation by tailoring Ni–Cu atom-pairs for high-performance CO2 electroreduction

The electrochemical CO2 reduction reaction (CO2RR) is a promising solution for addressing global issues related to carbon neutrality and energy shortage. However, it is hindered by the high thermal stability of CO2 and competitive hydrogen evolution reaction, which lead to low efficiency and selectivity. Herein, a Ni–Cu atom-pair catalyst with well-defined electron orientation has been tailored for electrocatalytic CO2RR. In particular, the tailored Ni/Cu0.38–covalent triazine framework catalyst exhibited extremely high catalytic activity with high faradaic efficiency (99.82% at −1.1 V vs. reversible hydrogen electrode, RHE) and turnover frequency (5116 h−1 at −1.1 V vs. RHE). To the best of our knowledge, this is a diatomic catalyst with the lowest reported metal concentration and excellent efficiency and selectivity. Density functional theory calculations and experimental results further revealed that the adsorption of CO2 was enhanced, while the electron orientation from the Cu site to Ni site reduced the antibonding orbital coupling between Ni and C atoms in CO2, thereby breaking the protonation energy barrier and providing high catalytic efficiency. Moreover, the enrichment of electrons from the electrolyte as well as the accumulation of *H at Cu sites was essential for improving CO selectivity.

Bioorthogonal Activation of TLR7 Agonists Provokes Innate Immunity to Reinforce Aptamer-Based Checkpoint Blockade.

Although cancer immunotherapy based on immune checkpoint blockade has shown promising clinical responses, the limited host response rate and systemic side effects still restrict immunotherapy efficacy. To address these challenges, here, we construct an aptamer-functionalized metal-organic framework (MOF) catalyst for bioorthogonal activation of Toll-like receptors (TLR) 7 agonists and programmed death-ligand 1 (PDL1) blockade for enhanced antitumor immunotherapy. The catalyst contains ultrasmall Pd nanoparticles enabling the local activation of TLR7 agonists in native form, which results in the remodeling of the tumor microenvironment (TME). Meanwhile, the loaded PDL1 aptamers release in response to phosphate and block the PD1/PDL1 signaling pathway between T cells and cancer cells. Thus, synergy between TLR7 agonists and PDL1 blockade induces the infiltration and activation of immune cells to initiate a robust immune response, thereby simultaneously inhibiting primary and distant metastatic tumors. The immunotherapeutic effect of our design has been demonstrated in both single and bilateral subcutaneous colorectal cancer (CT26) models. In situ bioorthogonal activation of agonists may offer an alternative approach to improve the therapeutic efficacy of immunotherapy with minimized systemic toxicity. Our work will provide good inspiration for current checkpoint blockade-based immunotherapy.

Designing covalent organic frameworks with Co-O4 atomic sites for efficient CO2 photoreduction

Cobalt coordinated covalent organic frameworks have attracted increasing interest in the field of CO2 photoreduction to CO, owing to their high electron affinity and predesigned structures. However, achieving high conversion efficiency is challenging since most Co related coordination environments facilitate fast recombination of photogenerated electron-hole pairs. Here, we design two kinds of Co-COF catalysts with oxygen coordinated Co atoms and find that after tuning of coordination environment, the reported Co framework catalyst with Co-O4 sites exhibits a high CO production rate of 18000 µmol g−1 h−1 with selectivity as high as 95.7% under visible light irradiation. From in/ex-situ spectral characterizations and theoretical calculations, it is revealed that the predesigned Co-O4 sites significantly facilitate the carrier migration in framework matrixes and inhibit the recombination of photogenerated electron-hole pairs in the photocatalytic process. This work opens a way for the design of high-performance catalysts for CO2 photoreduction.

Ordered CoIII‐MOF@CoII‐MOF Heterojunction for Highly Efficient Photocatalytic Syngas Production

The design of advanced metal–organic framework (MOF) catalysts for solar‐driven conversion of CO2 into syngas (CO/H2 mixture) is beneficial. Herein, the design of a joint MOF heterostructure consisting of orderly assembled CoII‐ and CoIII‐based Prussian blue analogs (PBAs) driven by their spontaneous lattice match in the growth process is reported. As‐prepared H/CoIII‐PBA@CoII‐PBA cage is a mesocrystal and exhibits superior photocatalytic syngas production activity (VCO up to 50.56 mmol g−1 h−1, CO/H2 = 1:1), which is among the best state‐of‐the‐art heterogeneous photocatalysts in the literature. Theoretical calculations and experimental results confirm that CoIII‐PBA exerts a stronger affinity for CO2 molecules than CoII‐PBA, thus serving as the active site. The built‐in electric field in the CoIII‐PBA@CoII‐PBA heterojunction can direct the fast transport of photogenerated electrons from CoII‐PBA to the active CoIII‐PBA. In the present case, the engineering of electronics outweighs morphological engineering to enhance the catalytic properties of CoIII‐MOF@CoII‐MOF for CO2‐to‐syngas conversion.

Sustainable and Highly Reactive Nerve-Agent Simulant Detoxification: Effective Amine Buffers for Metal–Organic Framework Catalysts

The appropriate treatment of chemical warfare agents (CWAs) is essential because of their toxicity and lethality. Metal–organic framework (MOF) catalysts, with the assistance of a volatile small molecule buffer, have been reported to be effective for the destruction of CWAs. However, employing small molecular volatile buffers not only contaminates the catalysts and causes them to lose their activity but also prevents their practical application. In this study, we report a novel polymeric buffer that can enhance the catalytic ability of MOFs without contamination of the catalyst. The macromolecular chain can provide non-flowability to buffer, as well as inhibit catalyst contamination by steric hindrance while maintaining activity as a buffer. The optimized polymer buffer [P(MEMA)43] can effectively degrade nerve-agent simulants (7.7 min of t1/2) in the presence of UiO-66 and preserve its catalytic activity by more than 90% even after three cycles. In addition, the polymeric composite with MOFs coated on a cotton substrate shows excellent detoxification performance in humidified conditions (RH 99%). This fundamental study on a sustainable CWA destruction catalytic system is anticipated to be promising for developing chemical protective textiles against CWAs.

Kinetic Impacts of Defect Sites in Metal–Organic Framework Catalysts under Varied Driving Forces

Defects in metal–organic frameworks (MOFs) primarily manifest as missing linkers or metal nodes induced through synthesis, post-synthetic modification, and/or exposure to reaction conditions. By changing the nature of active site(s) and perturbing crystalline frameworks, defects confer physicochemical alterations to MOF catalysts that may promote or inhibit intrinsic reactivity, electron transfer and excitation, and mass transport. However, the complexity and dynamic character of defects often obfuscate the structure–function relations needed to permit rational catalyst design. Here, highlights of recent studies examining the impact of MOF defects in thermo-, photo-, and electrocatalytic systems pertinent to energy applications demonstrate progress toward identifying defect impacts on MOF catalysis, particularly for widely studied zirconium-based frameworks. Moreover, the combination of ex situ and operando/in situ defect identification and quantification will be paramount in future research to improve the mechanistic understanding of MOF-catalyzed systems for energy conversion but also extends to MOF energy storage, photovoltaics, and gas separations/storage applications.

The influence of Pd4Cr6@(NH2)M-MOF(Cr) catalyst on components of formic acid dehydrogenation gaseous products

ABSTRACT In the dehydrogenation of formic acid, catalyst has a great influence on the composition and formation rate of gaseous products. However, the hydrogen used in fuel cells has strict requirements on the content of carbon monoxide impurities. Therefore, it is very important to study the relationship between catalyst components and their synergistic effects and the composition of gaseous products. The role of Pd-Cr bimetallic nanoparticles supported on amino modified Cr-based metal-organic framework catalyst (Pd4Cr6@(NH2)M-MOF(Cr)) in the formic acid dehydrogenation was explored through comparative experiments and catalyst characterization. Results show that both Cr-based metal-organic framework (MOF(Cr)) and amino-modified Cr-based metal-organic framework ((NH2)M-MOF(Cr)) have no effect on promoting the generation of gaseous products. The presence of Cr and NH2 groups in Pd4Cr6@(NH2)M-MOF(Cr) greatly improves the formation rate of H2 and CO2 products, the gas production rate of Pd4Cr6@(NH2)M-MOF(Cr) is 2.89 times that of Pd4@(NH2)M-MOF(Cr), and the gas production rate of Pd4Cr6@(NH2)M-MOF(Cr) is 6.26 times of Pd4Cr6@MOF(Cr). However, the formation rate of H2 increases more in the presence of Cr. Synergy of Pd-Cr and Pd-NH2 in the Pd4Cr6@(NH2)M-MOF(Cr) catalyst promotes CO formation.

Metal-Organic Framework Materials for Production and Distribution of Ammonia.

The efficient production of ammonia (NH3) from dinitrogen (N2) and water (H2O) using renewable energy is an important step on the roadmap to the ammonia economy. The productivity of this conversion hinges on the design and development of new active catalysts. In the wide scope of materials that have been examined as catalysts for the photo- and electro-driven reduction of N2 to NH3, functional metal-organic framework (MOF) catalysts exhibit unique properties and appealing features. By elucidating their structural and spectroscopic properties and linking this to the observed activity of MOF-based catalysts, valuable information can be gathered to inspire new generations of advanced catalysts to produce green NH3. NH3 is also a surrogate for the hydrogen (H2) economy, and the potential application of MOFs for the practical and effective capture, safe storage, and transport of NH3 is also discussed. This Perspective analyzes the contribution that MOFs can make toward the ammonia economy.

Mechanistic Elucidations of Highly Dispersed Metalloporphyrin Metal‐Organic Framework Catalysts for CO2Electroreduction

AbstractImmobilization of porphyrin complexes into crystalline metal–organic frameworks (MOFs) enables high exposure of porphyrin active sites for CO2electroreduction. Herein, well‐dispersed iron‐porphyrin‐based MOF (PCN‐222(Fe)) on carbon‐based electrodes revealed optimal turnover frequencies for CO2electroreduction to CO at 1 wt.% catalyst loading, beyond which the intrinsic catalyst activity declined due to CO2mass transport limitations. In situ Raman suggested that PCN‐222(Fe) maintained its structure under electrochemical bias, permitting mechanistic investigations. These revealed a stepwise electron transfer‐proton transfer mechanism for CO2electroreduction on PCN‐222(Fe) electrodes, which followed a shift from a rate‐limiting electron transfer to CO2mass transfer as the potential increased from −0.6 V to −1.0 V vs. RHE. Our results demonstrate how intrinsic catalytic investigations and in situ spectroscopy are needed to elucidate CO2electroreduction mechanisms on PCN‐222(Fe) MOFs.

Mechanistic Elucidations of Highly Dispersed Metalloporphyrin Metal-Organic Framework Catalysts for CO2 Electroreduction.

Immobilization of porphyrin complexes into crystalline metal-organic frameworks (MOFs) enables high exposure of porphyrin active sites for CO2 electroreduction. Herein, well-dispersed iron-porphyrin-based MOF (PCN-222(Fe)) on carbon-based electrodes revealed optimal turnover frequencies for CO2 electroreduction to CO at 1 wt.% catalyst loading, beyond which the intrinsic catalyst activity declined due to CO2 mass transport limitations. In situ Raman suggested that PCN-222(Fe) maintained its structure under electrochemical bias, permitting mechanistic investigations. These revealed a stepwise electron transfer-proton transfer mechanism for CO2 electroreduction on PCN-222(Fe) electrodes, which followed a shift from a rate-limiting electron transfer to CO2 mass transfer as the potential increased from -0.6 V to -1.0 V vs. RHE. Our results demonstrate how intrinsic catalytic investigations and in situ spectroscopy are needed to elucidate CO2 electroreduction mechanisms on PCN-222(Fe) MOFs.

Chemistry of iron and copper co-doped zinc oxide: reduction and degradation of pollutants

Porous, ordered framework catalysts, synthesised in a short time and with a low-energy combustion approach, can catalytically reduce pollutants to nontoxic by-products. The approach has a visible future outlook for industrial wastewater treatment.

Single-Site Metal-Organic Framework and Copper Foil Tandem Catalyst for Highly Selective CO2 Electroreduction to C2 H4.

Tandem catalysis is a promising way to break the limitation of linear scaling relationship for enhancing efficiency, and the desired tandem catalysts for electrochemical CO2 reduction reaction (CO2 RR) are urgent to be developed. Here, a tandem electrocatalyst created by combining Cu foil (CF) with a single-site Cu(II) metal-organic framework (MOF), named as Cu-MOF-CF, to realize improved electrochemical CO2 RR performance, is reported. The Cu-MOF-CF shows suppression of CH4 , great increase in C2 H4 selectivity (48.6%), and partial current density of C2 H4 at -1.11V versus reversible hydrogen electrode. The outstanding performance of Cu-MOF-CF for CO2 RR results from the improved microenvironment of the Cu active sites that inhibits CH4 production, more CO intermediate produced by single-site Cu-MOF in situ for CF, and the enlarged active surface area by porous Cu-MOF. This work provides a strategy to combine MOFs with copper-based electrocatalysts to establish high-efficiency electrocatalytic CO2 RR.

Catalytic Application of a Novel Basic Alkane‐sulfonate Metal‐organic Frameworks in the Preparation of Pyrido[2,3‐d]pyrimidines via a Cooperative Vinylogous Anomeric‐based Oxidation

AbstractIn this paper, we have developed and introduced [Zr‐UiO‐66‐PDC‐(CH2)4‐SO3] as a basic alkane‐sulfonate metal‐organic framework (MOF) catalyst. This catalyst was applied in the three‐component reaction for the preparation of (mono, bis, tris and tetrakis) pyrido[2,3‐d]pyrimidines by reaction of various 3‐oxo‐3‐phenylpropanenitrile, 6‐amino‐1,3‐dimethylpyrimidine‐2,4(1H,3H)‐dione and widespread of aldehydes with good to excellent yields under solvent‐free at 110 °C. The last step of the reaction proceeded via a cooperative vinylogous anomeric‐based oxidation (CVABO) as one of the fundamental and basic stereoelectronic concepts.

Sulfite activation for ciprofloxacin rapid degradation using an iron-based metal organic framework derivative in heterogeneous processes: Performance and mechanisms investigation

Owing to its low eco-toxicity and low cost, sulfite is considered a promising precursor for oxysulfur radicals. In this study, we report the rapid degradation of ciprofloxacin in water using a derivative of an iron-based metal–organic framework catalyst (S-MIL-101(Fe)) for the heterogeneous activation of sulfite. S-MIL-101(Fe) possessed a similar structure to the original MIL-101(Fe), and more active sites were exposed. Unlike previous systems used to activate sulfite with Fe-based catalysts, this system exhibited excellent performance under alkaline conditions. Ciprofloxacin (10 mg/L) removal efficiency of 94.7 % was observed at pH 8.7, implying a different activation mechanism. It is suggested that the iron coordinatively unsaturated metal sites (Fe CUSs) on the surface of S-MIL-101(Fe) can effectively complex with SO32− to form Fe(III) CUS-SO3+, followed by the generation of SO3− through single-electron transfer. Quenching and electron paramagnetic resonance experiments demonstrated that SO3−, O2−, SO5− and OH were involved in the degradation of ciprofloxacin, in which SO3− played a significant role. Moreover, HSO5− (peroxymonosulfate ion), an important product produced during the sulfite activation process, also participated in the formation of free radicals. This study complements the mechanism of heterogeneous activation of sulfites by Fe-based materials and reinforces the important role played by SO3− in some cases. The influence of chloride, bicarbonate, nitrate, and humic acid on ciprofloxacin elimination was minimal. In addition, this system could operate efficiently in real water environments.

Zr-Based Metal-Organic Frameworks for Green Biodiesel Synthesis: A Minireview.

Metal-organic frameworks (MOFs) have widespread application prospects in the field of catalysis owing to their functionally adjustable metal sites and adjustable structure. In this minireview, we summarize the current advancements in zirconium-based metal-organic framework (Zr-based MOF) catalysts (including single Zr-based MOFs, modified Zr-based MOFs, and Zr-based MOF derivatives) for green biofuel synthesis. Additionally, the yields, conversions, and reusability of Zr-based MOF catalysts for the production of biodiesel are compared. Finally, the challenges and future prospects regarding Zr-based MOFs and their derivatives for catalytic application in the biorefinery field are highlighted.

MOF-199 as an Efficient Metal Organic Framework Catalyst for the Synthesis of Spiro[Indoline-3,4′-Pyrano[2,3-c]Pyrazole] Derivatives

Metal organic frameworks are frameworks of 1–3 D formed by the interaction between metal ions/clusters and organic molecules. The high specific surface area and large pore volume of these molecules render them as ideal candidates for catalysis applications. A metal-organic framework (MOF-199) has been synthesized by facile chemical method and characterized by infrared (IR) spectroscopy, proton nuclear magnetic resonance (1H NMR), transmission electron microscopy (TEM) and energy dispersive X-ray (EDS) technique. In this study an efficient eco-friendly procedure for the synthesis of spiro[indoline-3,4′-pyrano[2,3-c]pyrazole] derivatives has been developed through a four-component condensation of isatin and its derivatives, hydrazine hydrate, ethyl acetoacetate, and malononitrile/ethyl cyanoacetate, in the presence of catalytic amount of MOF-199 in H2O at room temperature. The advantages of this protocol include mild reaction condition, green, and nontoxic solvent, high yield, easy separation, reusability of the catalyst and operational simplicity.

Cu+-ZrO2 interfacial sites with highly dispersed copper nanoparticles derived from Cu@UiO-67 hybrid for efficient CO2 hydrogenation to methanol

A series of Cu@ZrO2-U framework catalysts derived from Cu@UiO-67 precursors with adjustable copper loadings were constructed by the deposition-precipitation method, and the catalytic activities of methanol synthesis via CO2 hydrogenation were investigated. The optimized 20-Cu@ZrO2-U catalyst showed the best catalytic activity. At 3 MPa and 260 °C, the space-time yield of CH3OH (STYCH3OH) reached 2.28 mmolCH3OH/(gcat·h), which was 3.5 times higher than that of 20-Cu/ZrO2. The catalyst of 20-Cu@ZrO2-U also showed good stability during the 100-h time on stream test. The catalysts were further characterized by XRD, N2 sorption, TEM, XPS, H2-TPR, CO2/H2-TPD and in situ DRIFTS. The characterization results showed that the stable ZrO2 framework derived from UiO-67 is propitious to the confine of copper nanoparticles and formation of Cu+-ZrO2 interfacial sites, which should be responsible for the excellent performance of methanol synthesis. Moreover, in situ DRIFTS was used to probe that the methanol synthesis via CO2 hydrogenation over 20-Cu@ZrO2-U follows a HCOO∗-intermediated reaction pathway.

MXene-Derived Metal-Organic Framework@MXene Heterostructures toward Electrochemical NO Sensing.

The electrochemical sensing of nitric oxide (NO)molecules by metal-organic framework (MOF) catalysts has been impeded, to a large extent, owing to their poor electrical conductivity and weak NO adsorption. In this work, incomplete in situ conversion of V2 CTx (T=terminal atoms) MXene to MOF is adopted, forming MOF@MXene heterostructures, which outperform MXene and MOF monocomponents toward electrochemical NO sensing. Density functional theory (DFT) calculation results indicate metal-like electronic characters for the heterostructure benefiting from the dominating contribution of the V 3d orbitals of the metallic MXene. Moreover, plane-averaged charge density difference shows substantial charge redistribution occurs at the heterointerfaces, producing a built-in field, which facilitates charge transfer. Besides, molecular mechanics-based simulated annealing calculation reveals greatly enhanced adsorption energies of NO molecules on the heterointerfaces than that on separate MOFs and MXenes. Hence, the facilitated charge transfer and preferential NO adsorption are responsible for the dramatically promoted performance toward NO sensing. The prudent design of MOF@MXene heterostructure may spur advanced electrocatalysts for electrochemical sensing.

Cooperative Catalysis between Dual Copper Centers in a Metal-Organic Framework for Efficient Detoxification of Chemical Warfare Agent Simulants.

Chemical warfare agents (CWAs) are among the most lethal chemicals known to humans. Thus, developing multifunctional catalysts for highly efficient detoxification of various CWAs is of great importance. In this work, we developed a robust copper tetrazolate metal-organic framework (MOF) catalyst containing a dicopper unit similar to the coordination geometry of the active sites of natural phosphatase and tyrosinase enzymes. This catalyst aided in phosphate ester bond hydrolysis and hydrogen peroxide decomposition, ultimately achieving high detoxification efficiency against both a nerve agent simulant (diethoxy-phosphoryl cyanide (DECP)) with a half-life of 3.5 min and a sulfur mustard simulant (2-chloroethyl ethyl sulfide (CEES)) with a half-life of 4.5 min, making it competitive with other reported materials. The dicopper sites in ZZU-282 provide versatile binding modes with the substrates, thereby promoting the activation of substrates and enhancing the catalytic efficiency. A combination of postmodified metal exchange control experiments, density functional theory calculations, and catalytic evaluations confirmed that dual Cu sites are the active centers promoting the catalytic reaction. This study offers a new design perspective to achieve advanced catalysts for CWA detoxification.