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Direct ethanol fuel cells (DEFCs) play an indispensable role in the cyclic utilization of carbon resources due to its high volumetric energy density, high efficiency, and environmental benign character. However, owing to the chemically stable carbon-carbon (C─C) bond of ethanol, its incomplete electrooxidation at the anode severely inhibits the energy and power density output of DEFCs. The efficiency of C─C bond cleaving on the state-of-the-art Pt or Pd catalysts is reported as low as 7.5%. Recently, tremendous efforts are devoted to this field, and some effective strategies are put forward to facilitate the cleavage of the C─C bond. It is the right time to summarize the major breakthroughs in ethanol electrooxidation reaction. In this review, some optimization strategies including constructing core-shell nanostructure with alloying effect, doping other metal atoms in Pt and Pd catalysts, engineering composite catalyst with interface synergism, introducing cascade catalytic sites, and so on, are systematically summarized. In addition, the catalytic mechanism as well as the correlations between the catalyst structure and catalytic efficiency are further discussed. Finally, the prevailing limitations and feasible improvement directions for ethanol electrooxidation are proposed.

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The persistent issue of CO2 emissions and their subsequent impact on the Earth's atmosphere can be effectively addressed through the utilization of efficient photocatalysts. Employing a sustainable carbon cycle via photocatalysis presents a promising technology for simultaneously managing the greenhouse effect and the energy dilemma. However, the efficiency of energy conversion encounters limitations due to inadequate carrier utilization and a deficiency of reactive sites. Single-atom catalysts (SACs) have demonstrated exceptional performance in efficiently addressing the aforementioned challenges. This review article commences with an overview of SAC types, structures, fundamentals, synthesis strategies, and characterizations, providing a logical foundation for the design and properties of SACs based on the correlation between their structure and efficiency. Additionally, we delve into the general mechanism and the role of SACs in photocatalytic CO2 reduction. Furthermore, we furnish a comprehensive survey of the latest advancements in SACs concerning their capacity to enhance efficiency, long-term stability, and selectivity in CO2 reduction. Carbon-structured support materials such as covalent organic frameworks (COFs), graphitic carbon nitride (g-C3N4), metal-organic frameworks (MOFs), covalent triazine frameworks (CTFs), and graphene-based photocatalysts have garnered significant attention due to their substantial surface area, superior conductivity, and chemical stability. These carbon-based materials are frequently chosen as support matrices for anchoring single metal atoms, thereby enhancing catalytic activity and selectivity. The motivation behind this review article lies in evaluating recent developments in photocatalytic CO2 reduction employing SACs supported on carbon substrates. In conclusion, we highlight critical issues associated with SACs, potential prospects in photocatalytic CO2 reduction, and existing challenges. This review article is dedicated to providing a comprehensive and organized compilation of recent research findings on carbon support materials for SACs in photocatalytic CO2 reduction, with a specific focus on materials that are environmentally friendly, readily accessible, cost-effective, and exceptionally efficient. This work offers a critical assessment and serves as a systematic reference for the development of SACs supported on MOFs, COFs, g-C3N4, graphene, and CTFs support materials to enhance photocatalytic CO2 conversion.

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Thermal catalytic degradation of formaldehyde (HCHO) over manganese-based catalysts is garnering significant attention. In this study, both theoretical simulations and experimental methods were employed to elucidate the primary reaction pathways of HCHO on the MnO2(110) surface. Specifically, the effects of doping MnO2 with elements such as Fe, Ce, Ni, Co, and Cu on the HCHO oxidation properties were evaluated. Advanced characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), and X-ray photoelectron spectroscopy (XPS), were employed to discern the physical properties and chemical states of the active components on the catalyst surface. The comprehensive oxidation pathway of HCHO on the MnO2(110) surface includes O2 adsorption and dissociation, HCHO adsorption and dehydrogenation, CO2 desorption, H2O formation and desorption, oxygen vacancy supplementation, and other elementary reactions. The pivotal rate-determining step was identified as the hydrogen migration process, characterized by an energy barrier of 234.19 kJ mol-1. Notably, HCHOO and *CHOO emerged as crucial intermediates during the reaction. Among the doped catalysts, Fe-doped MnO2 outperformed its counterparts doped with Ce, Ni, Co, and Cu. The optimal degradation rate and selectivity were achieved at a molar ratio of Fe: Mn = 0.1. The superior performance of the Fe-doped MnO2 can be ascribed to its large specific surface area, conducive pore structure for HCHO molecular transport, rich surface-adsorbed oxygen species, and a significant presence of oxygen vacancies.

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Organic structure-directing agent-free steam-assisted conversion and Cs+ ion exchange were used to transform the faujasite (FAU)-type zeolite to the Cs+-type chabazite/phillipsite (CHA/PHI) composite zeolite. Compared with the pure PHI-type zeolite, the Cs+-type CHA/PHI zeolite showed gate-opening CO2 adsorption behavior and good thermal stability. In situ powder X-ray diffraction (PXRD) of the CO2 adsorption was measured to elucidate the mechanism for the gate-opening adsorption on the CHA/PHI zeolite. The Na+-type CHA/PHI zeolite did not show such adsorption behavior, and the PXRD pattern of the Na+-type CHA/PHI zeolite did not change with increasing CO2 partial pressure, which suggests that this unique adsorption behavior was caused by the PHI framework transition or Cs+ ions moving in both the CHA and PHI frameworks. Furthermore, in situ Fourier-transform infrared spectra of CO2 adsorption and CO2 breakthrough measurement on the Cs+-type CHA/PHI zeolite suggest that the CHA and PHI frameworks in the CHA/PHI zeolite shared eight-membered-ring windows and that CO2 molecules could easily diffuse from a CHA cage to a PHI framework. The ideal adsorbed solution theory was used to calculate the CO2/N2 separation selectivity for the Cs+-type CHA/PHI zeolite. At 298 and 318 K, the Cs+-type CHA/PHI composite zeolite showed a high CO2/N2 separation coefficient of >10,000 compared with other zeolites with high CO2 adsorption capacity. Furthermore, the CO2 working capacity was calculated for the Cs+-type CHA/PHI zeolite in both the pressure- and temperature-swing processes, and the results showed that the CHA/PHI composite zeolite could selectively separate CO2 from the CO2/N2 gas mixtures released from power generation plants operating using these processes.

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Two-dimensional (2D) MXene materials have recently been the focus of membrane research due to their unique properties, such as their single-atomic-layer thickness, flexibility, molecular filtration abilities and microstructural similarities with graphene, which is currently the most efficient precursor material for gas separation applications. In addition, the potential to process nanoscale channels has motivated investigations of parameters which can improve membrane permeability and selectivity. Interlayer spacing and defects, which are still challenging to control, are among the most crucial parameters for membrane performance. Herein, the effect of heat treatment on the d-spacing of MXene nanosheets and the surface functionalization of nanolayers was shown regarding its impact on the gas diffusion mechanism. The distance of the layers was reduced by a factor of over 10 from 0.345 nm to 0.024 nm, the defects were reduced, and the surface functionalization was maintained upon treatment of the Ti3C2 membrane at 500 °C under an Ar/H2 atmosphere as compared to 80 °C under vacuum. This led to a change from Knudsen diffusion to molecular sieving, as demonstrated by single-gas permeation tests at room temperature. Overall, this work shows a simple and promising way to improve H2/CO2 selectivity via temperature treatment under a controlled atmosphere.

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Non-thermal plasma (NTP) is gaining attention as a powerful tool to induce various reactions. The combination of NTP with catalysts has been successfully used to degrade volatile organic compounds (VOCs) for pollution control. In this study, a series of TiO2-C/5A catalysts, synthesized by carbon dots (C-dots) that decorate TiO2 by sol-gel and wetness impregnation methods, were incorporated with a dielectric barrier discharge (DBD) reactor in a single-stage structure to degrade toluene at atmospheric pressure and room temperature. A proton-transfer reaction mass spectrometer and a CO2 analyzer were used to monitor the concentration variations of organic by-products and CO2 online. The effects of input power, mass ratio of C-dots/TiO2 (TiO2/5A (0 wt%), TiO2-C1/5A (2.5 wt%), TiO2-C2/5A (5 wt%), TiO2-C3/5A (10 wt%)), gas flow rate, initial concentration of toluene on the toluene degradation efficiency, and CO2 selectivity were studied. The plasma-catalyst hybrid system could effectively improve the energy efficiency and reaction selectivity, attaining a maximum toluene degradation efficiency of 99.6% and CO2 selectivity of 83.0% compared to 79.5% and 37.5%, respectively, using the conventional plasma alone. Moreover, the generation of organic by-products also declined dramatically, averaging only half as much in plasma alone. The results also indicated that the appropriate amount of C-dot doping could greatly improve the catalyst efficiency in the hybrid plasma system. This is because the interaction between C-dots and TiO2 favors the formation of photoelectron holes and reduces the energy band gap and the recombination rate of photogenerated electron holes, which facilitates the generation of more active species on the catalyst surface, thereby leading to a more effective degradation reaction. These observations will provide guidance for the interaction studies between NTP and catalysts, not only for the exploration of new chemical mechanisms of aromatic compounds, but also for the screening of favorable materials for the desired reactions.

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Post- and precombustion CO2 capture and separation are the vital challenges from industrial viewpoint, as the accessible technologies are not cost-effective and cumbersome. Thus, the development of functional metal-organic frameworks (MOFs) that are found to be promising materials for selective CO2 capture, separation, and conversion is gaining an importance in the scientific world. Based on the strategic design, a new functionalized triazine-based undulated paddle-wheel Cu-MOF (1), {[Cu(MTABA)(H2O)]·4H2O·2EtOH·DMF}n (where, H2MTABA = 4,4'-((6-methoxy-1,3,5-triazine-2,4-diyl)bis(azanediyl))dibenzoic acid), has been synthesized under solvothermal conditions and fully characterized. MOF 1 contains a one-dimensional channel along the a-axis with pore walls decorated with open metal sites, and multifunctional groups (amine, triazine, and methoxy). Unlike other porous materials, activated 1 (1') possesses exceptional increment in CO2/N2 and CO2/CH4 selectivity with increased temperature calculated by the ideal adsorbed solution theory. With an increase in temperature from 298 to 313 K, the selectivity of CO2 rises from 350.3 to 909.5 at zero coverage, which is unprecedented till date. Moreover, 1' behaves as a bifunctional heterogeneous catalyst through Lewis acid (open metal) and Brönsted acid sites to facilitate the chemical fixation of CO2 to cyclic carbonates under ambient conditions. The high selectivity for CO2 by 1' even at higher temperature was further corroborated with configurational bias Monte Carlo molecular simulation that ascertains the multiple CO2-philic sites and epoxide binding sites in 1' to further decipher the mechanistic pathway.

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The Gasification performance of banana peel was examined in a fixed bed reactor. Effect of temperature, steam to carbon ratio (S/C), drying treatment on syngas composition, gas yield, CO2 selectivity and carbon conversion efficiency (CCE) were investigated. The influence of temperature and S/C on hydrogen production was investigated by thermodynamic analysis. The transient characteristics of banana peel steam gasification were investigated by monitoring the evolutionary behavior of syngas production. An increase in S/C can lead to an increase in the selectivity of CO2, but excess steam (S/C > 21.7) causes a decrease in H2 yield and CCE. The increase of temperature is beneficial to the increase of CCE, but which leads to a decrease in CO2 selectivity. When S/C = 27.1, the effect of temperature on H2 yield can be divided into CCE control region and CO2 selectivity control region. At temperature < 1023 K, H2 yield is more sensitive to the changes of CCE. While at temperature > 1023 K, CO2 selectivity has a more significant effect on H2 yield. When S/C = 21.7 and temperature is 1023 K, the yield of H2 produced from the fresh banana peel gasification reaches the maximum value (76.1 ml/g).

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Linear polyimides of intrinsic microporosity have been intensively investigated for gas separation due to their microporous structure and high surface area. The microporous structure in the linear polyimides of intrinsic microporosity comes from their contorted structure. Therefore, most linear polyimides without contorted structure do not have micropores. In this work, the microporous polyimides are constructed through the condensation of a cross-linkable dianhydride monomer with two novel nitrogen-rich diamine monomers and post crosslinking reaction. The linear polyimide precursors without contorted structure have the same main-chain structure. The introduction of crosslinked structure endow the crosslinked polyimides (PI-CLs) with microporous structure. The microporous structure in PI-CLs can be tuned by changing the substituents of the linear polyimide precursors. The PI-CLs have competitive CO2 uptake capacity (7.3-9.4 wt%) at 273 K and 1 bar. Particularly, the crosslinked polyimide containing trifluoromethyl groups (CF3-PI-CL) shows high CO2/N2 and CO2/CH4 selectivity (72 and 22) at 273 K, which are among the best results for reported porous materials. This work reveals that the introduction of crosslinked structure and changing substituents is an efficient method for constructing microporous polyimides with abundant micropores and excellent CO2 selective adsorption capacity. This method also has great potential for fabricating high-performance microporous polymers based on other linear polymers without rigid contorted structure.

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The SO2 solubility in ionic liquids and absorption mechanisms with different functionalities, including ether, halide, carboxylate, dicarboxylate, thiocynate, phenol, amino, azole groups, etc., are presented in this review. Strategies of improving SO2 capture with low binding energy and the separation performance from CO2 are also concluded. Generally, moderate basicity is favourable for enhancing SO2 capacity and the water (below 6 wt%) effect on absorption is indefinite but generally slight. Introducing electron-withdrawing substituents such as nitrile, halogen, aldehyde and carboxylic groups are proposed to decrease the chemical absorption enthalpy between ionic liquid and SO2 in order to reduce regeneration power consumption. Although it is promising, the absorption enthalpy is still much higher than the physisorption performance especially of the ether-functionalized ones. The biocompatible choline-based, betaine-based, and amino acid ionic liquids have clear trends to be applied in SO2 capture due to their biodegradability, nontoxicity and easy accessibility. Generally, comparing to the traditional solvents, ionic liquids have made great improvement in SO2 capacity, however, the high viscosity and desorption energy are two main obstacles for SO2 absorption and separation. Molecular simulations have been applied to reveal the absorption regimes involving the roles of basic functionalities and physical interactions especially the hydrogen bonds, which could be referred for structure designing of the available ionic liquids with readily fluid characteristics and absorption ability.

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Here, we report two novel water-stable amine-functionalized MOFs, namely IISERP-MOF26 ([NH2 (CH3 )2 ][Cu2 O(Ad)(BDC)]⋅(H2 O)2 (DMA), 1) and IISERP-MOF27 ([NH2 (CH3 )2 ]1/2 [Zn4 O(Ad)3 (BDC)2 ]⋅(H2 O)2 (DMF)1/2 , 2), which show selective CO2 capture capabilities. They are made by combining inexpensive and readily available terephthalic acid and N-rich adenine with Cu and Zn, respectively. They possess 1D channels decorated by the free amine group from the adenine and the polarizing oxygen atoms from the terephthalate units. Even more, there are dimethyl ammonium (DMA+ ) cations in the pore rendering an electrostatic environment within the channels. The activated Cu- and Zn-MOFs physisorb about 2.7 and 2.2 mmol g-1 of CO2 , respectively, with high CO2 /N2 and moderate CO2 /CH4 selectivity. The calculated heat of adsorption (HOA=21-23 kJ mol-1 ) for the CO2 in both MOFs suggest optimal physical interactions which corroborate well with their facile on-off cycling of CO2 . Notably, both MOFs retain their crystallinity and porosity even after soaking in water for 24 hours as well as upon exposure to steam over 24 hours. The exceptional thermal and chemical stability, favorable CO2 uptakes and selectivity and low HOA make these MOFs promising sorbents for selective CO2 capture applications. However, the MOF's low heat of adsorption despite having a highly CO2 -loving groups lined walls is quite intriguing.

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The metalloid-centered covalent organic framework has attracted great interest from both its structure and application. Heavier elements have seldomly been incorporated in the covalent organic frameworks, even if they exhibit special structural features and properties. Herein, we reported the first crystalline germanate covalent organic framework with hexacoordinated germanate linked by an anthracene linker. The existence of counterion lithium ions in the framework provides a high CO2 uptake of 88.5 cm3 g-1 at 273 K and a high CO2 /N2 selectivity of 101. A significantly improved lithium ion conductivity of 0.25 mS cm-1 at room temperature was observed due to the soft germanium center.

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Mixed-matrix membranes (MMMs) comprising Matrimid and a microporous azine-linked covalent organic frameworks (ACOF-1) were prepared and tested in the separation of CO2 from an equimolar CO2 /CH4 mixture. The COF-based MMMs show a more than doubling of the CO2 permeability upon 16 wt % ACOF-1 loading together with a slight increase in selectivity compared to the bare polymer. These results show the potential of COFs in the preparation of MMMs.

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In this paper, we describe a new synthesis protocol for the preparation of self-supported hollow fiber membranes composed of porous aromatic framework PAF-56P and PSF. PAF-56P was facilely prepared by the cross-coupling reaction of triangle-shaped cyanuric chloride and linear p-terophenyl monomers. The prepared PAF-56P material possesses an extended conjugated network, the structure of which is confirmed by nuclear magnetic resonance and infrared characterizations, as well as a permanent porosity with a BET surface area of 553.4 m(2) g(-1) and a pore size of 1.2 nm. PAF-56P was subsequently integrated with PSF matrix into PAF-56P/PSF asymmetric hollow fiber membranes via the dry jet-wet quench method employing PAF-56P/PSF suspensions. Scanning electron microscopy studies show that PAF-56P particles are embedded in the PSF matrix to form continuous membranes. Fabricated PAF-56P/PSF membranes were further exploited for CO2 capture, which was exemplified by gas separations of CO2/N2 mixtures. The PAF-56P/PSF membranes show a high selectivity of CO2 over N2 with a separation factor of 38.9 due to the abundant nitrogen groups in the PAF-56P framework. A preferred permeance for CO2 in the binary CO2/N2 gas mixture is obtained in the range of 93-141 GPU due to the large CO2 adsorption capacity and a large pore size of PAF-56P. Additionally, PAF-56P/PSF membranes exhibit excellent thermal and mechanical stabilities, which were examined by thermal analysis and gas separation tests with the dependencies of temperatures and pressures. The merits of high selectivity for CO2, good stability, and easy scale up make PAF-56P/PSF hollow fiber membranes of great interest for the industrial separations of CO2 from the gas exhausts.

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Zeolitic imidazolate frameworks (ZIFs) exhibit enhanced selectivity and increased CO2 uptake due to the incorporation of functional imidazolate units in their structure as well as their extensive porosity and ring flexibility. In situ Raman investigation of a representative host compound, ZIF-69, in practical CO2 pressure and temperature regimes (0-10 bar and 0-64 °C) correlates well with corresponding macroscopic CO2 sorption data and shows clear clear spectroscopic evidence of CO2 uptake. Significant positive shift of the 159 cm(-1) phenyl bending mode of the benzimidazole moiety indicates weak hydrogen bonding with CO2 in the larger cavities of the ZIF matrix. Raman spectroscopy is shown to be an easy and sensitive tool for quantifying CO2 uptake, identifying weak host-guest interactions and elucidating CO2 sorption mechanism in ZIFs.

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The oxidation of toluene in air was investigated using a dielectric barrier discharge (DBD) combined with a Pd/Al2O3 catalyst. When using only plasma, rather low selectivity toward CO2 was obtained: 32-35%. By filling the DBD reactor with Pd/Al2O3 catalyst the CO2 selectivity was significantly enhanced (80-90%), however, a large amount of toluene was desorbed from the catalyst when the discharge was operated. By filling a quarter of the discharge gap with catalyst and placing the rest of the catalyst downstream of the plasma reactor, an important increase of CO2 selectivity (~75%) and a 15% increase in toluene conversion were achieved as compared to the results with plasma alone. The catalyst exhibited a very good stability in this reaction.