Direct synthesis of dimethyl carbonate from CO 2 and methanol by supported bimetallic Cu–Ni/ZIF-8 MOF catalysts

Mechanism and different roles of metal-N sites on ZIF-8 for efficient antibacterial

Bacterial pollution poses a serious threat to human health, making it essential to design and utilize efficient non-antibiotic antibacterial materials. Here, ZIF-8 with different metal-N sites is successfully prepared by introducing divalent metals (Mg2+, Mn2+, Co2+ and Cu2+) directly into the ZIF-8 framework. ZIF-8 with Cu-Nx sites has the best antibacterial activity, with antibacterial rates of 99.8 % and 81.1 % against Escherichia coli and Staphylococcus aureus after 1 h at a concentration of 10 µg/mL, respectively. More importantly, an antibacterial rate of more than 86.7 % can be achieved against multidrug-resistant bacteria MRSA, much higher than Vancomycin. The results show that the introduction of copper could significantly improve the electron transfer, the generation of reactive oxygen species (ROS), the binding affinity with bacteria, and eventually achieve excellent antibacterial activity. DFT calculations show easier oxygen activation at the unsaturated Cu-Nx site. The revealed oxygen activation mechanism sheds light on understanding the high antibacterial activity of the active site of the nanoparticles. Cu-ZIF-8 offers significant advantages in the field of air disinfection.

Uncovering the role of yttrium in a cerium-based binary oxide in the catalytic conversion of carbon dioxide and methanol to dimethyl carbonate

Cerium(IV) oxide (CeO2)-based materials are effective catalysts for the synthesis of dimethyl carbonate (DMC) from carbon dioxide (CO2) and methanol (CH3OH). Herein, 5% Y-CeO2 was synthesized by the co-precipitation method. It forms a solid solution structure, which leads to the highest concentration of oxygen vacancies. The Y-VO-Ce active site created by Y3+ doping enhances the adsorption and activation of CO2 based on moderately passivating CH3OH adsorption. Consequently, 5% Y-CeO2 exhibited the highest CH3OH conversion rate of 0.8% and a DMC yield of 15 mmol⋅(g cat)-1, which is 1.4 times of pure CeO2 (reacting in a stainless-steel autoclave at 140 °C with a stirring speed of 1000 r⋅min-1 and an initial pressure of 3.0 MPa for 2 h). An adsorption test and in situ diffuse reflectance infrared Fourier transform spectroscopy showed that 5% Y-CeO2 could effectively inhibit the formation of triple-bonded methoxy species, and promote the formation of bidentate carbonate and bridged methoxy intermediates, which is conducive to the improvement of reaction activity.

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.

Embedded ionic liquid modified ZIF-8 in CaMgAl hydrotalcites for bio-glycerol transesterification

Novel modified MOF intercalated hydrotalcites was synthesized for catalyzing the conversion of glycerol into high value-added glycerol carbonate in this paper. [APmim]OH/ZIF-8 was prepared by encapsulating aminopropyl hydroxide imidazole ionic liquid in ZIF-8 and inserted in Ca-Mg-Al hydrotalcites with layered structures to prepare [APmim]OH/ZIF-8/LDH with strong basicity and high specific surface area. ZIF-8, [APmim]OH/ZIF-8 and [APmim]OH/ZIF-8/LDH were characterized by XRD, FT-IR, SEM and nitrogen adsorption-desorption. The results showed that the conversion rate of glycerol can reach 98.6% and the glycerol carbonate yield was 96.5% in the transesterification of glycerol with dimethyl carbonate catalyzed by [APmim]OH/ZIF-8/LDH when the molar ratio of DMC and glycerol was 3 : 1, the catalyst dosage was 3 wt%, the reaction temperature was 75 °C and the reaction time was 80 minutes. The glycerol conversion rate can still reach more than 90% after five reaction cycles.

Co3ZnC@NC Material Derived from ZIF-8 for Lithium-Ion Capacitors

Metal-organic framework (MOF)-derived carbon materials were widely reported as the anodes of lithium-ion capacitors (LICs). However, tunning the structure and electrochemical performance of the MOF-derived carbon materials is still challenging. Herein, metal carbide materials of Co3ZnC@NC-8:2 were obtained by the pyrolysis of the MOF materials of Co0.2Zn0.8ZIF-8 (Zn/Co ratio of 8:2). A half-cell assembled with the Co3ZnC@NC-8:2 electrode exhibits a discharge capacity of the electrode material of 598 mAh g-1 at a current density of 0.1 A g-1. After 100 cycles, the retention rate of discharge specific capacity is about 90%. The high performance of Co3ZnC@NC-8:2 is ascribed to its high crystalline degree and well-defined structure, which facilitates the intercalation/deintercalation of lithium ions and buffers the volume change during the charge/discharge process. The high capacitance contribution ratio calculated by cyclic voltammetry (CV) curves at different scanning rates indicates the pseudocapacitance storage mechanism. LICs constructed from the Co3ZnC@NC-8:2 material have a rectangular CV curve, while the charge-discharge curve has a symmetrical triangular shape. This study indicates that MOF-derived carbon is one of the promising materials for high-performance LICs.

Evaluation of Dimethyl Carbonate as Alternative Biofuel. Performance and Smoke Emissions of a Diesel Engine Fueled with Diesel/Dimethyl Carbonate/Straight Vegetable Oil Triple Blends

Dimethyl carbonate (DMC) is an interesting blending component for diesel fuel (D) owing to the high oxygen content (53 wt.%) and the absence of C–C bonds in its structure. Moreover, DMC can be produced from CO2 and methanol, which provides a renewable way to reduce anthropogenic CO2. This research has been addressed to assess the use of DMC as a solvent of sunflower oil (SO) and castor oil (CO), with the purpose of obtaining biofuels that can replace fossil diesel as much as possible. The blending of DMC with straight vegetable oils (SVOs) reduces their high viscosity, allowing their usage as drop-in biofuels without chemical treatments. Based on viscosity requirements of European Standard EN 590, the optimal DMC/SVO double blends have been tested as direct biofuels by themselves or mixed with fossil diesel in D/DMC/SVO triple blends. Relevant physico-chemical properties of fuels have been analyzed. Engine parameters such as power output, brake-specific fuel consumption (BSFC) and soot emissions have been studied to determine the effect of new biofuels on efficiency of a diesel engine. An outstanding engine efficiency is shown by the studied D/DMC/SVO triple blends, either with SO or CO as an SVO. The low calorific value of DMC is the main reason for reduction in power and BSFC, as the amount of diesel in the triple blends is reduced. Experimental results demonstrate that the use of these biofuels allows the replacement of up to 40% of fossil diesel, without compromising the power and BSFC of the engine, and accomplishing optimal cold flow properties and a marked drop in exhaust emissions.

In situ growth of well-aligned Ni-MOF nanosheets on nickel foam for enhanced photocatalytic degradation of typical volatile organic compounds

Exploitation of highly efficient catalysts for photocatalytic degradation of volatile organic compounds (VOCs) under visible light irradiation is highly desirable yet challenging. Herein, well-aligned 2D Ni-MOF nanosheet arrays vertically grown on porous nickel foam (Ni-MOF/NF) without lateral stacking were successfully prepared via a facile in situ solvothermal strategy. In this process, Ni foam could serve as both a skeleton to vertically support the Ni-MOF nanosheets and a self-sacrificial template to afford Ni ions for MOF growth. The Ni-MOF/NF nanosheet arrays with highly exposed active sites and light harvesting centres as well as fast mass and e- transport channels exhibited excellent photocatalytic oxidation activity and mineralization efficiency to typical VOCs emitted from the paint spray industry, which was almost impossible for their three-dimensional (3D) bulk Ni-MOF counterparts. A mineralization efficiency of 86.6% could be achieved at 98.1% of ethyl acetate removal. The related degradation mechanism and possible reaction pathways were also attempted based on the electron paramagnetic resonance (EPR) and online Time-of-Flight Mass Spectrometer (PTR-ToF-MS) results.

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.

Ionic-Liquid-Functionalized UiO-66 Framework: An Experimental and Theoretical Study on the Cycloaddition of CO2 and Epoxides

A facile approach for modifying the UiO-66-NH₂ metal-organic framework by incorporating imidazolium-based ionic liquids (ILs) to form bifunctional heterogeneous catalysts for the cycloaddition of epoxides to CO₂ is reported. Methylimidazolium- and methylbenzimidazolium-based IL units (ILA and ILB, respectively) were introduced into the pore walls of the UiO-66-NH₂ framework through a condensation reaction to generate ILA@U6N and ILB@U6N catalysts, respectively. The resultant heterogeneous catalysts, especially ILA@U6N, exhibited excellent CO₂ adsorption capability, which makes them effective for cycloaddition reactions producing cyclic carbonates under mild reaction conditions in the absence of any cocatalyst or solvent. The significantly enhanced activity of ILA@U6N is attributed to the synergism between the coordinately unsaturated Lewis acidic Zr⁴⁺ centers and Br^- ions in the bifunctional heterogeneous catalysts. The size effect of the ILs on coupling between the epoxide and CO₂ was also studied for ILA@U6N and ILB@U6N. A periodic DFT study was performed to provide evidence of possible intermediates, transition states, and pathways, as well as to gain deeper insight into the mechanism of the ILA@U6N-catalyzed cycloaddition reaction between epichlorohydrin and CO₂ .