Metal-organic frameworks MOF-808-X as highly efficient catalysts for direct synthesis of dimethyl carbonate from CO2 and methanol

Boosting dimethyl carbonate synthesis from CO2 and methanol through oxygen vacancy engineering on CeO2 under thermodynamically favorable conditions

The direct conversion of greenhouse gas CO2 and low-cost CH3OH into valuable dimethyl carbonate (DMC) offers a promising low-carbon synthetic pathway, but the slow CO2 activation kinetics and entropy-decreasing nature of this reaction significantly restrict DMC yield to below 1 %. In this work, 2-cyanopyridine (2-CP) was employed as a dehydrating agent to suppress the reverse reaction between DMC and H2O, shifting the thermodynamic equilibrium in favor of DMC production. Under this thermodynamic unconstrained condition, increasing oxygen vacancies, especially in the form of oxygen vacancy clusters, promotes catalytic activity significantly. We achieve a catalytic activity of 211 mmol/(g·h) at 140 °C on H2-treated, oxygen-vacancy-clusters-rich CeO2 in the presence of 2-CP, a 1.6-fold increase compared to the activity with air-treated CeO2 under identical conditions. The DMC yield reaches 8.54 % in a 20 mL CH3OH solution with 2-CP, surpassing the calculated DMC yield of about 0.66 % from the reaction equilibrium constant under the same conditions and without using the dehydrating agent. This work suggests the importance of using a dehydrating agent and also highlights oxygen vacancy clusters as pivotal active sites to promote DMC synthesis. Achieving sustainable DMC synthesis requires further exploration, encompassing strategies such as methods for regeneration of 2-CP.

Mixed-linker Zr-based metal-organic framework as a highly sensitive probe for ultrafast and selective detection of fluoride ions

The application of mixed-linker strategies in the synthesis of metal-organic frameworks (MOFs) has garnered considerable interest owing to their potential as fluorescent sensors, attributed to their facile synthesis and incorporation of diverse functional ligands. In this study, we designed and synthesized a novel fluorescent Zr-based MOFs, denoted as MOF-808-NH2, through the post-synthetic modification of 2-amino terephthalic acid (BDC-NH2) on coordinatively unsaturated Zr sites, thereby preserving the structural stability of the parent framework. The MOFs exhibited exceptional turn-on fluorescence in aqueous solutions containing fluoride ions (F-). The interaction between the-NH2 groups on MOF-808-NH2 and F- facilitated the formation of hydrogen bonds, significantly enhancing the fluorescence emission intensity of BDC-NH2 at 450 nm and inducing a blue shift in the fluorescence emission peak, enabling the specific recognition of F- even in the presence of various anionic interferences. Notably, MOF-808-NH2 demonstrates an ultrafast response time (within 30 s), a high detection sensitivity with a limit of detection of 1.56 μM, and remarkable selectivity and anti-interference properties with pronounced fluorescence emission against a dark background. Furthermore, MOF-808-NH2 retained outstanding thermal, mechanical, and chemical stabilities, underscoring its potential for practical applications in selective F- detection.

Effective Removal of Tetracycline from Water Using Stable MOF-808: A Comprehensive Investigation on Activation, Stability, and Influencing Parameters

Tetracycline (TC) is a widely utilized antibiotic that raises significant environmental concerns. Therefore, the implementation of effective removal strategies is imperative to mitigate its environmental impacts. This study investigates the adsorption of TC from aqueous solutions using MOF-808, synthesized via a solvothermal method. Two activation techniques, Soxhlet extraction and centrifugation, were applied to optimize the properties of the synthesized MOF-808, resulting in materials designated as S-MOF-808 and C-MOF-808, respectively. Comparative studies have demonstrated that S-MOF-808 shows superior adsorption due to its higher Brunauer-Emmett-Teller (BET) surface area of 1062 m2 g-1, compared to 622 m2 g-1 for C-MOF-808. The experimental adsorption results for both MOF-808s followed the pseudo-second-order kinetic and Langmuir isotherm models. The maximum adsorption capacities for TC were determined to be approximately 333.33 mg g-1 for S-MOF-808 and 312.50 mg g-1 for C-MOF-808, underscoring the optimal performance of S-MOF-808 in adsorption applications. Moreover, chemical stability was assessed over two months, with X-ray diffraction (XRD) analysis showing that S-MOF-808 maintained superior structural integrity compared to C-MOF-808. These findings highlight the potential of S-MOF-808 as a robust and efficient adsorbent for removing TC from complex aqueous environments, featuring its suitability for environmental remediation applications.

Permeable Self-Association of Metal-Organic Framework 808/Ag-Based Fiber Membrane for Broad-Spectrum and Highly Efficient Degradation of Biological and Chemical War Agents

The threat posed by biological and chemical warfare agents (BCWA) to national security, the environment, and personal health underscores the need for innovative chemical protective clothing. To address the limitations of conventional activated carbon materials, which are prone to falling off and adsorption saturation, an efficient self-association approach was introduced. In this study, we proposed the immobilization of metal-organic framework (MOF) 808 and Ag nanoparticles onto a polypropylene (PP) fiber membrane using a rapid self-association method facilitated by chitosan (CS). The MOF 808/Ag-based (PP-CS/808-Ag) fiber membrane demonstrated exceptional degradation efficiency, achieving a remarkable rate of t1/2 within 2 h for the mustard simulant 2-chloroethyl ethyl sulfide (2-CEES) and a rate of t1/2 = 4.12 min for the G-series simulant dimethyl 4-nitrophenylphosphate (DMNP). A theoretical computational model was developed to determine the overall reaction mechanism, and it was verified that MOF 808 and Ag nanoparticles were mainly involved in the hydrolysis process against 2-CEES and DMNP. The PP-CS/808-Ag composite fiber film was prepared as the core layer, and the fracture strength, bending resistance, and moisture permeability were better than those specified by many countries for biochemical protective clothing, showing that it has a broad application prospect in developing a generation of broad-spectrum bioprotective clothing.

Unveiling MOF-808 photocycle and its interaction with luminescent guests

The world of metal-organic frameworks (MOFs) has become a hot topic in recent years due to the extreme variety and tunability of their structures. There is evidence of MOFs that exhibit intrinsic luminescence properties that arise directly from their organic components or from the interaction between them and metallic counterparts. A new perspective is to exploit the porous nature of MOFs by encapsulating luminescent guests, such as organic dyes, in order to explore possible changes in the luminescence activity of the combined systems. This work is focused on the optical study of zirconium-based MOF-808 and its interaction with encapsulated rhodamine B molecules. Using a plethora of different techniques, we were able to unravel its photocycle. MOF-808 displays intrinsic luminescence activity that derives from an energy transfer process from the linker to the metal sites occurring in 300 ps. The emission is a singlet-singlet transition in aqueous solution, and it is a triplet transition in powdered form. After exploring the bare MOF, we combined it with rhodamine B molecules, following an easy post-synthetic process. Rhodamine B molecules were found to be encapsulated in MOF pores and interact with the MOF's matrix through nanosecond energy transfer. We created a totally new dual-emitting system and suggested a way, based on the time-resolved studies, to clearly unravel the photocycle of MOFs from the very first photoexcitation.

Mn-doped CeO2 derived from Ce-MOF porous nanoribbons as highly active catalysts for the synthesis of dimethyl carbonate from CO2 and methanol

It is desirable but challenging to develop highly-efficient catalysts for the direct synthesis of dimethyl carbonate (DMC) from methanol and CO2. The vacancy-mediated incorporation of heteroatom into surface reconstruction is an efficient method of defect engineering for enhancing the catalytic properties. In this work, manganese-doped cerium oxide porous nanoribbons (Mn/CeO2-BTC) were prepared derived from a Ce-BTC by a sacrificial template approach. It is found that the catalytic activity of Mn/CeO2-BTC catalysts can be readily controlled by varying the amount of Mn dopants and the as-synthesized 0.1-Mn/CeO2-BTC exhibited an outstanding activity for the synthesis of DMC from CO2 and methanol, which reached a high DMC yield (6.53 mmolDMC/gcat.) without any dehydrating agents. Based on characterization results, the enhanced performance may be attributed to the defective structures caused by Mn doping and the porous nanoribbons of the CeO2 crystals, which provide more surface oxygen vacancies and acidic-basic sites, favoring adsorption and activation of CO2 and methanol.

A sulfonate ligand-defected Zr-based metal-organic framework for the enhanced selective removal of anionic dyes

In this work, we introduce a novel defective analogue of the representative 6-connected zirconium-based metal-organic framework (MOF-808), by employing 5-sulfoisophthalic acid monosodium salt (H2BTC-SO3Na) as a defect inducer via a mixed-linker approach. The structural integrity and different physicochemical properties were investigated by various characterization techniques, including powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and nitrogen physisorption at 77 K. Additionally, proton nuclear magnetic resonance (1H-NMR), energy-dispersive X-ray (EDX), and inductively coupled plasma optical emission spectroscopy (ICP-OES) were employed to confirm the presence of 6.9 mol% of the 5-sulfoisophthalate ligand within the highly crystalline MOF-808 structure. The defective material exhibited significant enhancements in the removal efficiency of various organic dyes, including approximately 64% and 77% for quinoline yellow and sunset yellow, and 56% and 13% for rhodamine B and malachite green, compared to its pristine counterpart. Importantly, the defective MOF-808 showed a remarkable selectivity toward anionic species in binary-component dyes comprising both anionic and cationic dyes.

Graphene-based versus alumina supports on CO2 methanation using lanthanum-promoted nickel catalysts

The valorization of CO2 as a biofuel, transforming it through methanation as part of the power-to-gas (P2G) process, will allow the reduction of the net emissions of this gas to the atmosphere. Catalysts with 13 wt.% of nickel (Ni) loading incorporated into alumina and graphene derivatives were used, and the effect of the support on the activity was examined at temperatures between 498 and 773 K and 10 bar of pressure. Among the graphene-based catalysts (13Ni/AGO, 13Ni/BGO, 13Ni/rGO, 13Ni-Ol/GO, 13Ni/Ol-GO, and 13Ni/Ol-GO Met), the highest methane yield was found for 13Ni/rGO (78% at 810 K), being the only system comparable to the catalyst supported on alumina 13Ni/Al2O3 (89.5% at 745 K). The incorporation of 14 wt.% of lanthanum (La) into the most promising supports, rGO and alumina, led to nickel-support interactions that enhanced the catalytic activity of 13Ni/Al2O3 (89.5% at lower temperature, 727 K) but was not effective for 13Ni/rGO. The resistance against deactivation by H2S poisoning was also studied for these catalysts, and a fast deactivation was observed. In addition, activity recovery was impossible despite the regeneration treatment carried out over catalysts. The resistance against deactivation by H2S poisoning was also studied for these catalysts, observing that both suffered a rapid/immediate deactivation and which in addition/unfortunately was impossible to solve despite the regeneration treatment carried out over catalysts.

Comparative Study between 2-Furonitrile and 2-Cyanopyridine as Dehydrants in Direct Synthesis of Dialkyl Carbonates from CO2 and Alcohols over Cerium Oxide Catalyst

The shift of equilibrium by removing water with nitrile dehydrants is crucial for CeO2 -catalyzed synthesis of dialkyl carbonates from CO2 and alcohols. Two nitriles - 2-cyanopyridine and 2-furonitrile - were previously found as effective dehydrants, yet their detailed comparison as well as exploration of potential of 2-furonitrile remain insufficient. Herein, the performance of 2-cyanopyridine and 2-furonitrile was compared in the synthesis of various dialkyl carbonates. 2-furonitrile was found to be superior to 2-cyanopyridine in the synthesis of dialkyl carbonates from CO2 and bulky or long-chain (≥C3) alcohols. Namely, the yield of diisopropyl carbonate (up to 50 %) achieved using CeO2 and 2-furonitrile is comparable to or even higher than previously reported ones. Meanwhile, 2-cyanopyridine acted as a better dehydrant than 2-furonitrile in the synthesis of dimethyl carbonate and diethyl carbonate. The adsorption experiments and density functional theory calculations have indicated that the better performance of 2-furonitrile compared to 2-cyanopyridine in the synthesis of dialkyl carbonates from bulky or long-chain alcohols is due to the weaker interaction of 2-furonitrile with the CeO2 surface. Such weak interaction of 2-furonitrile offers a larger reaction field on the catalyst surface for both CO2 and alcohols.

Enhancing catalytic activity and pore structure of metal-organic framework-808 via ligand competition for biodiesel production from microalgal lipids at reduced temperatures

Catalysts with hierarchical porous structures and increased active defects play a crucial role in catalyzing the conversion of microalgae lipids. However, the template methods used for pore expansion and the acidification process employed to enhance activity are cumbersome and prone to deactivation. It is necessary to propose a simple and versatile synthetic approach to overcome these challenges. By modulating N,N-dimethylformamide basicity with formic acid, MOF-808 exhibited enhanced coordination of benzene-1,3,5-tricarboxylic acid to Zr-clusters, creating three types of functional defects. These defects increased pore size from 1.63 nm to 5.34 nm and enhanced catalyst acidity by 22.8%, while maintaining high porosity. The active catalytic sites were confirmed to be defect sites (exposed Zr4+) through density functional theory. Compared to regular MOF-808, catalyst MOF-808-3/1 shows enhanced hierarchical porosity and increased acidity, enabling efficient conversions at reduced reaction temperature (100 °C) and pressure (352 kPa) compared to 200 °C and 4036 kPa, respectively.

Catalytic degradation of CWAs with MOF-808 and PCN-222: Toward practical application

Chemical warfare agents, such as nerve agents (GD and VX) and blister agents (HD), have strong toxicities to mankind. In recent years, zirconium-based metal-organic frameworks have been found to be attractive materials for chemical warfare agent degradation. Among them, metal-organic framework-808 (MOF-808) and porous coordination network-222 (PCN-222) were the best. However, few papers pay attention to their practical application. In this work, we prepared MOF-808 and PCN-222 using water phase and organic solvothermal methods, respectively. Their performance for the catalytic degradation of chemical warfare agents under practical decontamination conditions was studied. The results showed that MOF-808 displayed a high potency for catalytic hydrolysis of VX (10,000 mg L−1) in unbuffered solution. PCN-222 exhibited weaker reactivity with a half-life ( t1/2) of 28.8 min. Their different performances might stem from the different connectivity of the Zr6 nodes and framework structures. The results illustrated that the hydrolysis of high-concentration GD required a strong alkaline buffer to neutralize the hydrolysis product of hydrofluoric acid (HF) to avoid catalyst poisoning. When H2O2 was used as the oxidant instead of O2, both zirconium-based metal-organic frameworks performed with effective catalytic potency for HD degradation without any special lighting and so was suitable for practical application, whereas the products obtained from HD, such as HDO2 and V-HDO2, still possessed vesicant toxicity. Overall, MOF-808 prepared via a water-phase synthesis performed with effective catalysis for the degradation of high-concentration VX, GD, and HD with t1/2 of < 0.5, 3.1 and 2.2 min, respectively, exhibiting its potential for practical applications.

Enhanced transformation of CO2 over microporous Ce-doped Zr metal-organic frameworks

Metal-organic frameworks (MOF) have been studied extensively for the adsorption and catalytic conversion of CO2. However, previous studies mainly focused on the adsorption capabilities of partially or totally Ce substituted UiO-66, there are few studies focusing on transformation of the structure and catalytic activity of these materials. In this work, a series of Zr/Ce-based MOFs with UiO-66 architecture catalysts were prepared for the conversion of CO2 into value-added dimethyl carbonate (DMC). Owing to the different addition order of the two metals, significantly varied shapes and sizes were observed. Accordingly, the catalytic activity is greatly varied by adding a second metal. The different catalytic activities may arise from the different acid-base properties after Ce doping as well as the morphology and shape changes. Besides, the formation of terminal methoxy (t-OCH3) was found to be the rate limiting step. Finally, the reaction mechanism of CO2 transformation in the presence of a dehydrating agent was proposed.

New Strategies on Green Synthesis of Dimethyl Carbonate from Carbon Dioxide and Methanol over Oxide Composites

Dimethyl carbonate is a generally used chemical substance which is environmentally sustainable in nature and used in a range of industrial applications as intermediate. Although various methods, including methanol phosgenation, transesterification and oxidative carbonylation of methanol, have been developed for large-scale industrial production of DMC, they are expensive, unsafe and use noxious raw materials. Green production of DMC from CO2 and methanol is the most appropriate and eco-friendly method. Numerous catalysts were studied and tested in this regard. The issues of low yield and difficulty in tests have not been resolved fundamentally, which is caused by the inherent problems of the synthetic pathway and limitations imposed by thermodynamics. Electron-assisted activation of CO2 and membrane reactors which can separate products in real-time giving a maximum yield of DMC are also being used in the quest to find more effective production method. In this review paper, we deeply addressed green production methods of DMC using Zr/Ce/Cu-based nanocomposites as catalysts. Moreover, the relationship between the structure and activity of catalysts, catalytic mechanisms, molecular activation and active sites identification of catalysts are also discussed.

Single-ion chelation strategy for synthesis of monodisperse Pd nanoparticles anchored in MOF-808 for highly efficient hydrogenation and cascade reactions

Ultrafine Pd nanoparticles are prepared using a single-ion precursor on a MOF-808 carrier. The ligand 2,3-pyrazinedicarboxylic acid (Pza) is dispersed in porous MOF-808 via grafting on formic acid sites, and thus Pd²⁺ ions are chelated by Pza to form a new single-ion precursor Pd@MOF-808-Pza. Then a Pd-nano@MOF-808-Pza catalyst is prepared by direct reduction of this precursor using NaBH₄. Material characterization reveals the homogeneous dispersion of 3-6 nm Pd nanoparticles within the MOF-808 matrix. Pd-nano@MOF-808-Pza exhibits excellent catalytic activity in the hydrogenation of unsaturated nitrogen-containing compounds, and other typical reactions, such as the Knoevenagel condensation, Suzuki/Heck cross-coupling, and hydrogen tandem reactions. In addition, density functional theory (DFT) calculations are carried out to elucidate the chelation of Pd²⁺ ions by Pza on MOF-808 and propose mechanisms of hydrogenation reactions. This work provides an effective reduction catalyst, and more importantly, a single-ion chelation strategy for design and synthesis of metal supported catalysts.

MOF/Polymer Mixed-Matrix Membranes Preparation: Effect of Main Synthesis Parameters on CO2/CH4 Separation Performance

Design and preparation of mixed-matrix membranes (MMMs) with minimum defects and high performance for desired gas separations is still challenging as it depends on a variety of MMM synthesis parameters. In this study, 6FDA-DAM:DABA based MMMs using MOF-808 as filler were prepared to examine the impact of multiple variables on the preparation process of MMMs, including variation in polymer concentration, filler loading, volume of solution cast per membrane area, solvent type used and solvent evaporation rate, and to identify their impact on the CO₂/CH₄ separation performance of these membranes. Solvent evaporation rate proved to be the most critical synthesis parameter, directly influencing the performance and visual appearance of the membranes. Although less dominantly influencing the MMM performance, polymer concentration and solution volume also had an important role via control over the casting solution viscosity, particle agglomeration, and particle settling rate. Among all solvents studied, MMMs prepared with chloroform led to the best performance for this polymer-filler system. Chloroform-based MMMs containing 10 and 30 wt.% MOF-808 showed 73% and 62% increase in CO₂ permeability, respectively, without a decrease in separation factor compared to unfilled membranes. The results indicate that enhanced gas separation performance of MMMs strongly depends on the cumulative effect of various synthesis parameters rather than individual impact, thus requiring a system-specific design and optimization.

The role of urea in regulating the structural properties of Zr–Sn-based oxide catalysts for direct synthesis of dimethyl carbonate from CO2 and methanol

Zr–Sn–O catalysts were prepared with urea as precipitant. It was found that the usage of urea had a crucial effect on the structure properties and the catalytic activity of direct synthesis of DMC from CO2 and methanol.

Fabrication of a novel heteroepitaxial structure from an MOF-on-MOF architecture as a photocatalyst for highly efficient Cr(vi) reduction

Ce-on-Zr-MOF-808, a novel MOF-on-MOF hybrid used for efficient chromium reduction under visible-light irradiation.

Synergetic effect of ZnCo2O4/inorganic salt as a sustainable catalyst system for CO2 utilization

Currently, it is essential to consider the rapidly increasing emission of CO₂ into the atmosphere, causing major environmental issues such as climate change and global warming. In this work, we have developed the binary catalyst system (ZnCo₂O₄/inorganic salt) for chemical fixation of CO₂ with epoxides into cyclic carbonates without solvent, and all reactions were performed on a large scale using a 100 ml batch reactor. Two mesoporous catalysts of ZnCo₂O₄ with different architecture, such as flakes (ZnCo-F) and spheres (ZnCo-S) were synthesized and utilized as a heterogeneous catalyst for cycloaddition reaction. The bifunctional property of catalysts is mainly attributed to strong acidic and basic properties confirmed by TPD (NH₃ & CO₂) analysis. The ZnCo-F catalyst exhibited excellent conversion of propylene oxide (99.9%) with good corresponding selectivity of propylene carbonate (≥99%) in the presence of inorganic salt (KI) at 120 °C, 2 MPa, 3 h. In addition, ZnCo-F catalyst demonstrated good catalytic applicability towards the various substrates scope of the epoxide. Furthermore, the catalytic properties were examined by evaluating the reaction parameter such as catalyst loading, pressure, temperature and time. The proposed catalyst exhibited good reusability for cycloaddition reaction without significant change in its catalytic activity and proposed a possible reaction mechanism for chemical fixation of CO₂ with epoxide into cyclic carbonate over ZnCo-F/KI.

Zr-MOF-808 as Catalyst for Amide Esterification

In this work, zirconium-based metal-organic framework Zr-MOF-808-P has been found to be an efficient and versatile catalyst for amide esterification. Comparing with previously reported homogeneous and heterogeneous catalysts, Zr-MOF-808-P can promote the reaction for a wide range of primary, secondary and tertiary amides with n-butanol as nucleophilic agent. Different alcohols have been employed in amide esterification with quantitative yields. Moreover, the catalyst acts as a heterogeneous catalyst and could be reused for at least five consecutive cycles. The amide esterification mechanism has been studied on the Zr-MOF-808 at molecular level by in situ FTIR spectroscopic technique and kinetic study.

Enhancing the Dispersion of Cu-Ni Metals on the Graphene Aerogel Support for Use as a Catalyst in the Direct Synthesis of Dimethyl Carbonate from Carbon Dioxide and Methanol

Graphene has attracted attention because of its interesting properties in catalyst applications including as a catalyst support; however, it is known that the graphene can be restacked, forming a graphite-like structure that leads to poor specific surface area. Hence, the high-porosity graphene aerogel was used as a Cu-Ni catalyst support to produce dimethyl carbonate (DMC) from carbon dioxide and methanol. In this work, we have introduced a new synthesis route, which can improve the dispersion of metal particles on the graphene aerogel support. Cu-Ni/graphene aerogel catalysts were synthesized by a two-step procedure: forming Cu-Ni/graphene aerogel catalysts via hydrothermal reduction and then Cu-Ni loading by incipient wetness impregnation. It is found that the catalyst prepared by the two-step procedure exhibits higher DMC yield (25%) and MeOH conversion (18.5%) than those of Cu-Ni loading only by an incipient wetness impregnation method. The results prove that this new synthesis route can improve the performance of Cu-Ni/graphene aerogel catalysts for DMC production.

Monolithic ZnxCe1−xO2 catalysts for catalytic synthesis of dimethyl carbonate from CO2 and methanol

The schematic diagram of reactor module comprised of honeycomb ceramic monolith with the catalysts for the synthesis of DMC.

Fe-Containing MOFs as Seeds for the Preparation of Highly Active Fe/Al-SBA-15 Catalysts in the NAlkylation of Aniline

We have successfully incorporated iron species into mesoporous aluminosilicates (Al-SBA-15) using a simple mechanochemical milling method. The catalysts were characterized by nitrogen physisorption, inductively coupled plasma mass spectrometry (ICP-MS), pyridine (PY) and 2,6-dimethylpyridine (DMPY) pulse chromatography titration, powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX). The catalysts were tested in the N-alkylation reaction of aniline with benzyl alcohol for imine production. According to the results, the iron sources, acidity of catalyst and reaction conditions were important factors influencing the reaction. The catalyst showed excellent catalytic performance, achieving 97% of aniline conversion and 96% of imine selectivity under optimized conditions.