Adsorption Mechanisms of CO2 on Macroporous Ion-Exchange Resin Organic Amine Composite Materials by the Density Functional Theory

The adsorption mechanisms of CO2 on macroporous cation exchange resin (MCER), D001 ion-exchange resin, and macroporous ion-exchange resin organic amine composite materials (MCER-DEA and D001-PEI) were studied by density functional theory (DFT). The adsorption energies and Mulliken atomic charges in the adsorption process were analyzed, indicating that CO2 on MCER and D001 were physisorbed. The adsorption heat of the adsorption process of MCER-DEA and D001-PEI was calculated by the Monte Carlo method, and it was found that the adsorption process of CO2 by MCER-DEA and D001-PEI was both physical adsorption and chemical adsorption. Besides, the chemical adsorption mechanism of CO2 by MCER-DEA and D001-PEI was investigated by analyzing the free energy barrier and the Gibbs free energy change of the involved chemical reactions and the results showed that the free energy barrier required for MCER-DEA to generate zwitterion was 26.23 kcal/mol, which is 1.74 times that of D001-PEI (15.04 kcal/mol); meanwhile, the free energy barriers of the deprotonation process of zwitterions in MCER-DEA and D001-PEI were 16.23 and 9.89 kcal/mol, respectively, indicating that D001-PEI chemically adsorbs CO2 and requires more energy than MCER-DEA chemical adsorption of CO2. D001-PEI is more conducive to the chemical adsorption of CO2. In addition, H2O molecules were incorporated on the polymer models to study the influence of humidity on the CO2 adsorption mechanism. The analysis revealed that the adsorption of CO2 slowed under humid conditions.

A Novel Molten Salt Mediated Synthesis of Mesoporous Metal Oxides with High Crystallization

The controlled synthesis of mesoporous metal oxides remains a great challenge because the uncontrolled assembly process and high-temperature crystallization can easily destroy the mesostructure. Herein, we develop a facile, versatile, low-cost, and controllable molten salt assisted assembly strategy to synthesize mesoporous metal oxides (e.g., CeO2, ZrO2, SnO2, Li2TiO3) with high surface area (115-155 m2/g) and uniform mesopore size (3.0 nm). We find this molten salt mediated assembly enables the desolvation of the precursors and forms bare metal ions, enhances their coordination interaction with the surfactant, and promotes their assembly into a mesostructure. Furthermore, the molten salt assisted crystallization process can lower the collision probability of the target metal atom, inhibit its further growth into large crystals, and achieve a well-maintained mesostructure with high crystallization. Furthermore, this method can be expanded to synthesize various structured mesoporous metal oxides, including hollow spheres, nanotubes, and nanosheets by introducing the carbon template. The obtained mesoporous CeO2 microspheres loaded with Cu species exhibit excellent antibacterial performance and superior catalytic activity for the hydrogenation of nitrophenol with high conversion and cycling stability.

Treatment of phenolic wastewater by anaerobic fluidized bed microbial fuel cell using carbon brush as anode: microbial community analysis and m-cresol degradation mechanism

Anaerobic fluidized bed microbial fuel cell (AFB-MFC) is a technology that combines fluidized bed reactor and microbial fuel cell to treat organic wastewater and generate electricity. The performance and the mechanism of treating m-cresol wastewater in AFB-MFC using carbon brush as biofilm anode were studied. After 48 h of operation, the m-cresol removal efficiency of AFB-MFC, MAR-AFB (fluidized bed bioreactor with acclimated anaerobic sludge), MAR-FB (ordinary fluidized bed reactor with only macroporous adsorptive resin) and AST (traditional anaerobic sludge treatment) were 95.29 ± 0.67%, 85.78 ± 1.81%, 71.24 ± 1.86% and 70.41 ± 0.32% respectively. The maximum output voltage and the maximum power density of AFB-MFC using carbon brush as biofilm anode were 679.7 mV and 166.6 mW/m2 respectively. The results of high-throughput sequencing analysis indicated the relative abundance of dominant electroactive bacteria, such as Trichococcus, Geobacter, and Pseudomonas, on the anode carbon brushes was higher than that of AST, and also identified such superior m-cresol-degrading bacteria as Bdellovibrio, Thermomonas, Hydrogenophaga, etc. Based on the determination of m-cresol metabolites detected by Gas Chromatography-Mass Spectrometry (GC-MS), the possible biodegradation pathway of m-cresol under anaerobic and aerobic conditions in AFB-MFC was speculated. The results showed that m-cresol was decomposed into formic acid-acetic anhydride and 3-methylpropionic acid under the action of electrochemistry, which is a simple degradation pathway without peripheral metabolism in AFB-MFC.

Tailoring the CO2 Hydrogenation Performance of Fe-Based Catalyst via Unique Confinement Effect of the Carbon Shell

Even though Fe-based catalysts have been widely employed for CO2 hydrogenation into hydrocarbons, oxygenates, liquid fuels, etc., the precise regulation of their physicochemical properties is needed to enhance the catalytic performance. Herein, under the guidance of the traditional concept in heterogeneous catalysis-confinement effect, a core-shell structured catalyst Na-Fe3 O4 @C is constructed to boost the CO2 hydrogenation performance. Benefiting from the carbon-chain growth limitation, tailorable H2 /CO2 ratio on the catalytic interface, and unique electronic property that all endowed by the confinement effect, the selectivity and space-time yield of light olefins (C2 = -C4 = ) are as high as 47.4 % and 15.9 g molFe -1  h-1 , respectively, which are all notably higher than that from the shell-less counterpart. The function mechanism of the confinement effect in Fe-based catalysts are clarified in detail by multiple characterization and density functional theory (DFT). This work may offer a new prospect for the rational design of CO2 hydrogenation catalyst.

Thermal, photonic, and electrocatalysis in lignin depolymerization research

In order to realize a sustainable bio-based future, it is essential to fully harness the potential of biomass, including lignin - a readily available biopolymer that ranks second in abundance and serves as a renewable source of aromatics. While lignin has traditionally been used for lower-value applications like fuel and power generation, unlocking its higher-value potential through diverse conversion and upgrading techniques is of paramount importance. This review focuses on the catalytic conversion of lignin, with a specific emphasis on selective depolymerization, a process that not only supports economically and environmentally sustainable biorefineries but also aligns with Green Chemistry principles, mitigating adverse environmental impacts. Furthermore, we provide a comprehensive discussion of reaction pathways and mechanisms, including C-O and C-C bond cleavage, among different catalysts. Lastly, we analyze and briefly discuss the prospects of rational catalyst design in biomass valorization.

Syngas Production from Biomass Gasification: Influences of Feedstock Properties, Reactor Type, and Reaction Parameters

Syngas from biomass gasification can be used in downstream process industries such as city gas, hydrogen production, etc. In this review, the effects of biomass feedstock properties, and gasification reaction conditions (temperature, gasifier type, etc.) on syngas properties are systematically reviewed. In summary, the cracking and reforming of volatile fractions in the gasification process and the catalytic effect of alkali and alkaline earth metals in the ash on the gasification have a direct impact on the syngas yield. And biomass pretreatment (i.e., terrifying/hydrothermal carbonization) can reduce the moisture content, which can effectively reduce the energy required for gasification and enhance the calorific value and syngas yield further. The fixed-bed gasifiers produce lower amounts of syngas. The concentration of H2 is significantly increased by adding steam as a gasification agent. Additionally higher gasification temperatures produce more syngas, and an equivalence ratio of about 0.2-0.3 is considered suitable for gasification. For the influence of feedstock on syngas, this paper not only reviews the feedstock properties (volatile, ash, moisture) but also compares the influence of two pretreatments on syngas yield and proposes that the combination of torrefaction/hydrothermal carbonization and a multistage air bed gasifier is an important research direction to improve the combustible components of syngas. In addition to the summary of commonly used single gasification agents, two or more gasification agents on the concentration of syngas components are also discussed in the gasification parameters, and it is suggested that further research into the use of more than one gasification agent is also important for future syngas production.

Insight into the Compositional Features of Organic Matter in Xilinguole Lignite through Two Mass Spectrometers

Ethanolysis of lignite is an effective approach for converting organic matter of lignite to liquid coal derivatives. Xilinguole lignite (XL) was reacted with ethanol at 320 °C. Then ethanol and isometric carbon disulfide/acetone mixture were used to extract the reaction mixture in a modified Soxhlet extractor to afford extractable portion 1 (EP₁) and extractable portion 2 (EP₂), respectively. According to analysis of EP₁ with a gas chromatography/mass spectrometer, phenolic compounds made up more than 33% of the compounds detected. This could be ascribed to the ethanolysis of XL; that is, ethanol could selectively break the C_alkyl-O bonds in lignite, producing more phenolic compounds. Furthermore, a quadrupole Orbitrap mass spectrometer equipped with an atmospheric pressure chemical ionization source was used for comprehensive analysis of the compositional features of EP₁. The analysis indicated that O_1-3, N₁O_0-2, and N₂S₁O_3-6 were predominant class species in EP₁. Nitrogen atoms in NO-containing organic compounds may exist in the form of pyridine or amidogen, while oxygen atoms primarily exist in furan, alkoxy, carbonyl, and ester groups. In addition, possible chemical structures of NO-containing organic compounds were speculated.

Development of Low-Cost Porous Carbons through Alkali Activation of Crop Waste for CO2 Capture

To achieve the "double carbon" (carbon peak and carbon neutrality) target, low-cost CO₂ capture at large CO₂ emission points is of great importance, during which the development of low-cost CO₂ sorbents will play a key role. Here, we chose peanut shells (P) from crop waste as the raw material and KOH and K₂CO₃ as activators to prepare porous carbons by a simple one-step activation method. Interestingly, the porous carbon showed a good adsorption capacity of 2.41 mmol/g for 15% CO₂ when the mass ratio of K₂CO₃ to P and the activation time were only 0.5 and 0.5 h, respectively, and the adsorption capacity remained at 98.76% after 10 adsorption-desorption cycle regenerations. The characterization results suggested that the activated peanut shell-based porous carbons were mainly microporous and partly mesoporous, and hydroxyl (O-H), ether (C-O), and pyrrolic nitrogen (N-5) functional groups that promoted CO₂ adsorption were formed during activation. In conclusion, KOH- and K₂CO₃-activated P, especially K₂CO₃-activated P, showed good CO₂ adsorption and regeneration performance. In addition, not only the use of a small amount of the activator but also the raw material of crop waste reduces the sorbent preparation costs and CO₂ capture costs.

Effective Absorption Mechanism of SO2 and NO2 in the Flue Gas by Ammonium-Bromide-Based Deep Eutectic Solvents

Simultaneous capture of SO₂ and NO _x from flue gas is critical for coal-fired power generation. In this study, environmentally friendly and high-performance deep eutectic solvents based on ethylene glycol and ammonium bromide were designed to capture SO₂ and NO₂ simultaneously. The SO₂ and NO₂ absorption performances and absorption mechanisms were systematically investigated by ¹H NMR and Fourier transform infrared (FT-IR) spectroscopy in combination with ab initio calculations using Gaussian software. The results showed that EG-TBAB DESs can absorb low concentrations of SO₂ and NO₂ from the flue gas simultaneously at low temperatures (≤50 °C). ¹H NMR, FT-IR, and simulation results indicate that SO₂ and NO₂ are absorbed by forming EG-TBAB-SO₂-NO₂ complexes, Br^- is the main active site for NO₂ absorption, and NO₂ is more active in an EG-TBAB-NO₂-SO₂ complex than SO₂. EG-TBAB DESs exhibit outstanding regeneration capability, and absorption capacities remain unchanged after five absorption-desorption cycles. The fundamental understanding of simultaneous capture of SO₂ and NO₂ from this study enables DES structures to be rationally designed for efficient and low-cost desulfurization and denitrification reagents.

Synthesis, Crystal Structures, and Density Functional Theory Studies of Two Salt Cocrystals Containing Meldrum's Acid Group

Two salt cocrystals, C₃₁H₃₄N₄O₈ (DDD) and C₁₇H₂₀N₂O₈ (MDD), were synthesized and their structures were determined by single-crystal X-ray diffraction. DDD is made up of one (C₁₃H₁₃O₈)^- anion, one (C₉H₁₁N₂)⁺ cation, and one 5,6-dimethyl-1H-benzo[d]imidazole molecule. MDD consists of one (C₄H₇N₂)⁺ cation and one (C₁₃H₁₃O₈)^- anion. DDD and MDD belong to the monoclinic, P21/c space group and triclinic, P-1 space group, respectively. A 1D-chained structure of DDD was constituted by N-H···N and N-H···O hydrogen bonds. However, a 1D-chained structure of MDD was bridged by N-H···O hydrogen bonds. Their density functional theory-optimized geometric structures with a B3LYP/6-311G(d,p) basis set fit well with those of crystallographic studies. By calculating their thermodynamic properties, the correlation equations of C ⁰ _p,m , S ⁰ _m , H ⁰ _m , and temperature T were obtained. By comparing the experimental electronic spectra with the calculated electronic spectra, it is found that the PBEPBE/6-311G(d,p) method can simulate the UV-Vis spectra of DDD and MDD. In addition, the fluorescence spectra in the EtOH solution analysis show that the yellowish-green emission occurs at 570 nm (λ_ex = 310 nm) for DDD and the purplish-blue emission occurs at 454 nm (λ_ex = 316 nm) for MDD.

N/O Co-doped Porous Carbons Derived from Coal Tar Pitch for Ultra-high Specific Capacitance Supercapacitors

In this paper, a series of N/O co-doped porous carbons (PCs) were designed and used to prepare coal tar pitch-based supercapacitors (SCs). The introduction of N/O species under the intervention of urea effectively improves the pseudocapacitance of PCs. The results show that the specific surface area of synthesized N₃PC_4-700 is 1914 m² g^-1, while the N and O contents are 1.3 and 7.2%, respectively. The unique interconnected pore structure and proper organic N/O co-doping, especially the introduction of pyridine-N and pyrrole-N, are beneficial for improving the electrochemical performance of PCs. In the three-electrode system, the specific capacitance and rate capability of N₃PC_4-700 are 532.5 F g^-1 and 72.5% at the current densities of 0.5 and 20 A g^-1, respectively. In addition, the specific capacitance of N₃PC_4-700 in a coin-type symmetric device is 315.5 F g^-1 at 0.5 A g^-1. The N₃PC_4-700 electrode provides an energy density of 43.8 W h kg^-1 with a power density of 0.5 kW kg^-1 and still maintains a value of 29.7 at 10 kW kg^-1. After 10,000 charge/discharge cycles, the retention rate was as high as 96.7%. In order to obtain high-performance carbon-based SCs, the effective identification and regulation of organic N/O species is necessary.

Oxygen-Induced Elemental Mercury Oxidation in Chemical Looping Combustion of Coal

Mercury emission is an important issue during chemical looping combustion (CLC) of coal. The aim of this work is to explore the effects of different flue gas components (e.g., HCl, NO, SO₂, and CO₂) on mercury transformation in the flue gas cooling process. A two-stage simulation method is used to reveal the reaction mechanism of these gases affecting elemental mercury (Hg⁰) oxidation. Furthermore, using this method, Hg⁰ oxidation by eight oxygen carriers (Co₃O₄, CaSO₄, CeO₂, Fe₂O₃, Al₂O₃, Mn₂O₃, SiO₂, and CuO) commonly used in CLC are investigated and their Hg⁰ oxidation efficiencies were compared with the existing experimental results. The results show that HCl, NO, and CO₂ promote Hg⁰ oxidation during flue gas cooling, while SO₂ inhibits Hg⁰ oxidation. The stronger the oxygen release capacity of oxygen carriers, the higher the oxidation efficiency of Hg⁰ becomes. The order of Hg⁰ removal efficiency from high to low is Co₃O₄, CuO, Mn₂O₃, CaSO₄, Fe₂O₃, CeO₂, Al₂O₃, and SiO₂, and this sequence is in good agreement with the existing experimental results. Different flue gas components directly or indirectly affect the O₂ content, thus affecting the content of gaseous oxidized mercury (Hg²⁺). Different oxygen carriers have different oxygen release capacities and different Hg⁰ oxidation efficiencies. Therefore, O₂ is the core species affecting the mercury transformation in CLC.

Physical and Chemical Properties of Coal Gasification Fine Slag and Its Carbon Products by Hydrophobic-Hydrophilic Separation

Coal gasification fine slag is a kind of solid waste with low resource utilization rate. The complex embedding of residual carbon and inorganic minerals (ash materials) is the main reason restricting the efficient resource separation and utilization of residual carbon or ash materials. Hydrophobic-hydrophilic separation (HHS) is a separation technology in which mineral particles with different surface hydrophobicity values are enriched in the water phase and oil phase under the action of mechanical stirring. The water on the surface of hydrophobic particles is replaced by the oil phase to form flocs, which are enriched in the hydrophobic liquid phase, while hydrophilic particles are dispersed into the aqueous phase. In this study, the HHS process was used to separate the carbon/ash from the fine gasification slag produced by a Shenning gasifier, Texaco gasifier, and GSP gasifier of Ningxia Coal Industry Co., Ltd. The physicochemical properties of the original sample and the residual carbon products obtained by hydrophobic-hydrophilic separation were analyzed. The results show that HHS can separate the carbon/ash in the three kinds of fine slag to varying degrees. The carbon element is enriched into the hydrophobic phase to form the concentrates, while the silicon element, oxygen element, and metal element enter the tailings. The spherical ash with different particle sizes distributed on the surface of residual carbon and the gap of the matrix is basically removed, while the ash in the carbon-ash melt is difficult to remove. The ash contents of the concentrate and tailings of fine slag of the Shenning gasifier are 22.58 and 96.28%, respectively, which reach the best ash index compared with that of the other two gasifiers. From the change of mineral surface properties after HHS, the distribution of oxygen-containing groups, benzene rings, Si-O, and clay minerals or carbonate minerals in the three kinds of fine slag residual carbon products is basically similar. Compared with the other two gasifier products, the GSP gasifier concentrate has a larger specific surface area and less ash material, more amorphous carbon structures (less graphitic), and more active sites, resulting in a stronger combustion activity.

F- Serve as Surface Trapping Sites to Promote the Charge Separation and Transfer of TiO2

Finding an effective strategy to promote the charge transfer and separation of TiO₂ is urgently needed. Herein, a surface fluorination (F^-)-modified TiO₂ (denoted as TO-xF, where x represents the volume of HF added in the solution) catalyst has been prepared by a mild and facile post-treatment method. The changes induced by surface F^- on the morphological, structural, and surface electronic features and the charge separation and transfer efficiency of TiO₂ were specifically examined. Compared with pristine TO, TO-0.4F exhibits enhanced photocatalytic degradation of methyl orange and phenol, production of hydroxyl radicals, and photocurrent response. The enhanced photocatalytic activities of TO-0.4F can be attributed to the role of surface F^- as surface trapping sites in effectively boosting the charge transfer and separation processes, which is verified by the steady-state and time-resolved fluorescence spectroscopy, electrochemical impedance spectroscopy, Bode plot, transient photocurrent response, and open-circuit voltage measurements. This study emphasizes the role of surface F^- in promoting the charge transfer and separation and improving the photocatalytic activity of TiO₂.

Influence of Ni Precursors on the Structure, Performance, and Carbon Deposition of Ni-Al2O3 Catalysts for CO Methanation

Three Ni-Al₂O₃ catalysts were prepared, in planetary ball-milling machine, by the mechanochemical method with Al(NO₃)₃·9H₂O as the aluminum precursor, (NH₄)₂CO₃ as the precipitant, and Ni(NO₃)₂·6H₂O, NiCl₂·6H₂O, and Ni(CH₃COO)₂·4H₂O as nickel precursors (the corresponding catalysts were labeled as Ni-NO, Ni-Cl, and Ni-Ac). The prepared catalysts were characterized by X-ray diffraction (XRD), temperature-programmed reduction (H₂-TPR), and N₂ adsorption-desorption technologies, and CO methanation performance evaluation was carried out for the catalysts. Results showed that the catalyst with Ni(NO₃)₂·6H₂O as the precursor presented good Ni dispersibility and a small Ni grain size of 6.80 nm. CO conversion, CH₄ selectivity, and yield of the catalyst were as high as 78.8, 87.9, and 69.8%, respectively. Carbon deposition analysis from temperature-programmed hydrogenation (TPH) characterization showed that the H₂ consumption peak area of the three samples followed the order: Ni-NO (2886.66 au) < Ni-Cl (4389.97 au) < Ni-Ac (5721.65 au), indicating that the Ni-NO catalyst showed higher resistance to carbon deposition, which might be due to its small Ni grain size.