The rapid deactivation of zeolite catalysts via coking remains a critical challenge in methane dehydroaromatization (MDA). While the roles of Mo sites and Br & oslash;nsted acid sites (BASs) are well-documented, the contribution of silanol defects remains critically overlooked. Herein, we combine theoretical and experimental approaches to establish that silanol defects are pivotal in accelerating coke deposition. Theoretical calculations identify their strong adsorption affinity (2.87-4.53 eV) toward coke precursors like C6H6 and C8H10. By precisely engineering the concentration and spatial distribution of silanols in MFI zeolites, we demonstrate experimentally that external silanols drive coke accumulation and graphitization more aggressively than internal silanol nests. Building on this insight, we developed an ethylenediamine assisted surface modification strategy that selectively passivates external silanols and BASs while optimizing the intra-channel BAS density. This rational design enhances aromatics yield by 32.2%, reduces total coke deposition by 18.6%, and effectively reduces external coking. This work, for the first time, elucidates the critical and spatially dependent role of silanol defects in MDA coking and provides a targeted surface engineering route to design zeolite catalysts with superior anti-coking stability.

Methane dehydroaromatization (MDA) presents a promising carbon-neutral pathway for benzene, toluene, and xylene (BTX) production, alternative to petroleum-derived routes. Elucidating the regulatory mechanisms of Brønsted acid site (BAS) strength on reaction pathways, alongside the spatial proximity effects between BAS and Mo active sites in bifunctional synergy, remains a critical scientific challenge in catalyst design. This study systematically tunes both BAS strength (via isomorphous metal substitution) and Mo-BAS spatial proximity in zeolites, integrating MDA catalytic evaluations with density functional theory (DFT) calculations to dissect their individual contributions. Strongly acidic BAS catalysts (compared to moderately acidic Fe/Ga-substituted counterparts) exhibit superior performance, evidenced by enhanced aromatic yields. Conversely, weakly acidic B-substituted zeolites demonstrate optimal mono-/bifunctional synergy, outperforming moderate-acid systems. DFT results reveal that acid strength dictates C−H activation mechanisms by modulating the energy barriers of rate-determining steps. While Al-zeolites deliver the highest activity, B-substituted systems display unique potential for mechanistic investigations. Spatial proximity analysis indicates that micrometer-scale Mo-BAS distances hinder effective synergy due to exceeding electron interaction and mass transfer limits, whereas nanometer-scale proximity enhances activity (via accelerated intermediate transport) and suppresses coke formation. These findings establish a theoretical framework for rationalizing zeolite catalyst optimization through BAS property engineering and spatial control of Mo-BAS cooperation, providing actionable guidelines for designing next-generation MDA catalysts.

Achieving carbon neutrality in the power and industrial sectors necessitates the deployment of deep–decarbonization technologies that can retrofit existing fossil fuel infrastructure while ensuring economic viability. Industrial–scale oxy-fuel combustion (OFC) stands out as a promising pathway, producing a high–concentration CO2 flue gas that significantly reduces the energy and cost penalties associated with downstream carbon capture. This paper provides a comprehensive techno-economic assessment of OFC systems, integrating advancements across its core components (oxygen production technologies, combustion system engineering, and oxy-fuel combustion carbon capture). This paper begins by assessing the evolution and performance of oxygen supply systems—from mature cryogenic air separation to emerging adsorption and membrane-based methods—evaluating their energy consumption, capital and operational costs, scalability, and integration economics for industrial–scale OFC applications. It further examines the combustion performance and economic implications of varying oxygen concentrations, comparing OFC with conventional air combustion and alternative clean combustion technologies. A key focus is placed on retrofit economics for existing thermal power plants, analyzing the trade-offs between increased capital expenditure and reduced carbon capture costs. The analysis centres on CO2 separation, identifying the two–stage flash compression and purification unit process as the techno-economically preferred route, alongside emerging direct–desublimation options that gain competitiveness through LNG cold–energy recovery or pressurized OFC operation. This paper offers a systematic techno-economic review for evaluating OFC's potential contributions to carbon neutrality in the combustion sector.

The thermal barrier problem encountered in hypersonic vehicle engines has emerged as a critical bottleneck that directly constrains flight safety, and its effective mitigation remains an urgent challenge. Although regenerative cooling (RC) technologies that employ fuel as the coolant can substantially reduce the thermal load of the engine, their long-term efficiency remains constrained by coke deposition within cooling channels. Consequently, optimizing cooling technologies, enhancing fuel heat sink performance, and suppressing coking have become research priorities in addressing the safety and performance requirements for hypersonic flight. This paper offers a comprehensive review of recent developments in thermal management systems for hypersonic propulsion. First, key cooling technologies in hypersonic propulsion systems are summarized, with particular emphasis on research advances in the most promising RC systems. Secondly, the influence of fuel molecular structures on heat sink performance was analyzed, and recent findings in high-density endothermic hydrocarbon fuels (HDEHFs) for hypersonic applications were reviewed. Finally, based on the framework of radical chain reaction theory, this review highlights the coking mechanism and suppression strategies for hydrocarbon fuels under supercritical conditions. Overall, this review aims to provide theoretical underpinnings and research directions for the comprehensive treatment of hydrocarbon fuel coking issues within the cooling systems of hypersonic vehicles.

Efficient conversion of aromatic compounds in low-temperature coal tar (LTCT) into cycloalkanes is a key step in producing high-density components of coal-based jet fuel. In this study, a combined ReaxFF molecular dynamics and density functional theory approach was employed to construct model systems based on representative LTCT components, with pure naphthalene and 1-naphthol serving as reference systems. The molecular-level hydrogenation network and key reaction mechanisms were systematically elucidated. The results reveal that variations in hydrogenation activity among LTCT components lead to competitive adsorption of H center dot radicals, resulting in significantly higher local H center dot concentrations around naphthalene and 1-naphthol compared with their pure systems, thereby increasing decalin yields at 650 K (20 % and 6.66 %, respectively). In addition, hydrogenation at secondary positions is primarily governed by kinetic control, while the influence of thermodynamic factors becomes more pronounced with increasing H center dot concentration. These findings deepen the understanding of LTCT hydrogenation mechanisms and provide theoretical insights for the design of highly selective hydrogenation catalysts.

Aiming at the great demand of coal rich countries to realize clean and efficient conversion of coal resources, this paper systematically studies the micro mechanism of directional preparation of light aromatics from coal pyrolysis catalyzed by calcium. By constructing a computational chemical system based on coal structure model compounds, combining the multi scale simulation method of reaction molecular dynamics (ReaxFF MD) and density functional theory (DFT), the micro catalytic mechanism of calcium-based catalysts promoting benzene generation was revealed for the first time. The simulation findings reveal that benzene formation during coal pyrolysis is governed by dual reaction channels: (1) direct cleavage of aliphatic side chains within coal derived macromolecular matrices (60% contribution), and (2) bond dissociation of phenolic hydroxyl moieties in micro molecule precursors followed by radical recombination between phenyl radicals and hydrogen radical species (40% contribution). Calcium-based catalytic systems showed pathway-specific catalytic activity: by accurately controlling the concentration of hydrogen radicals, the aliphatic side chain cleavage pathway was selectively enhanced, and the remarkable yield of 47.6% was achieved; formation of dynamic coordination structures with phenolic hydroxyl groups effectively reduces the availability of hydroxyl group in the reaction environment and increases by 57.1% through concentration-dependent optimization. This dual mechanism of "free radical regulation and calcium coordination fixation" provides a theoretical basis for developing efficient alkaline earth metal-based catalysts to realize directional regulation of coal pyrolysis products and has important guiding significance for promoting the development of coal classification conversion technology.

Microwave-enhanced catalyst cracking of waste plastics to produce high concentrations of hydrogen (H2) is a promising method for resource utilization. However, the molecular-level mechanisms by which microwaves reduce reaction temperatures and enhance hydrogen production efficiency remain unclear. In this study, molecular dynamics (MD) simulations were conducted employing the ReaxFF method, with consistent heating rates for both conventional and microwave heating, to investigate the mechanism of microwave enhanced iron-based catalyst cracking of polyethylene (PE). The results indicated that the adsorption amount between Fe and PE increased under the influence of a positive microwave electric field, and the H-C-C bond angle polarization was induced, leading to a reduction in the activation energy (Ea) for C-H bond dissociation from 421 kJ/mol to 65 kJ/mol. By backtracking H2 molecules, we found that among the four H2 generation pathways, the migration and collision of H radicals within the Fe catalyst were the predominant pathways. This study explores the mechanism by which the coupling of microwave and Fe enhances hydrocarbon cracking, clearly demonstrating the distinction between microwave and conventional heating at the same temperature. Furthermore, it provides a theoretical basis for microwave-assisted catalyst cracking of waste plastics to achieve high H2 yields.

The air-staged combustion of ammonia/coal features a unique structure with a main combustion zone and burnout zone, and exhibits a more complex NOX formation mechanism compared to single fuel combustion, making the control of NOX emissions challenging. To reveal detailed reaction mechanisms, based on ReaxFF molecular dynamics (ReaxFF MD), this paper breaks through the limitations of traditional theoretical frameworks and systematically reveals the following three innovative understandings. The ratio of NH2 & sdot; to NH & sdot; is 3:1, generated from initial reactions of NH3 such as oxidation reaction (60.88 %), self-decomposition reaction (19.39 %), and hydrogen-atom abstraction reaction (10.20 %). Overturning the traditional stepwise dehydrogenation theory, it was discovered that the NH3 -> NH & sdot; self-decomposition pathway (accounting for 36.9 %) serves as a significant source of NH & sdot;. It serves as a critical precursor for N2 in the main combustion zone. The dominant reaction pathway (NHi & sdot; -> NNH/N2H2 -> N2) accounts for 70 % of N2 generation in the main combustion zone. In air-staged combustion, N2O formation is primarily controlled by N2 oxidation, mediated by radicals, occurring with a frequency three times that of the NO/NH & sdot; reduction, and exhibiting obvious regional dependence. The study will provide theoretical support for developing air-staged combustion of ammonia/coal from laboratoryscale to industrial application.

Geopolymers have attracted much attention in the field of heavy metal solidification due to their unique chemical and mineralogical properties, especially the ferrochrome slag containing highly toxic chromium (Cr). Herein, we use sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) as complex alkali exciter to prepare aircooled ferrochrome slag (AFCS)-based geopolymers and explore the effects of curing time (7 days, 14 days, or 28 days) and AFCS content (50 %, 60 %, 70 %, and 80 %) on the compressive strength and Cr leaching toxicity of geopolymers. When the AFCS content is 70 % and the curing time is 28 days, the obtained geopolymer (AFCS70-28 days) has the highest compressive strength (36 MPa) and Cr immobilization efficiency (96.74 %), which are higher than other geopolymers. Further characterizations prove that a certain amount of C-S-H-type gel is formed during curing, which is conducive to improving its compressive strength. However, excess calcium oxide (CaO) in AFCS inhibits gel formation, so the compressive strength of AFCS80-28 days is reduced. Furthermore, X-ray photoelectron spectroscopy (XPS) results further demonstrate that the Cr element is immobilized in the gel. This work provides a reference basis for understanding the mechanism of geopolymers in the solidification process of heavy metals.

Global waste management is facing severe challenges, and the resource utilization of acid mine drainage (AMD) has emerged as a promising strategy to address both environmental pollution and resource scarcity In this study, based on the AMD generated from the closure of coal and iron mines in a certain area of Sichuan Province, China, an AMD fuel cell system (AMD-FC) was developed using the principle of electrochemical oxidation, achieving the dual goals of Fe2* removal and energy recovery, while also enabling the recovery of anodic precipitates as valuable resources. A series of batch experiments were conducted to investigate the effects of pH, Fe2* concentration, and ionic strength on system performance. Under optimized conditions, simulated AMD treatment experiments were conducted in three operational modes: batch, recirculation, and continuous flow. Results showed that under optimal conditions, the batch mode achieved a power density of 83.66 mW/m2 and an Fe removal rate of 84.6 %; the recirculation mode maintained power generation for 15 h with a removal rate exceeding 80 %; and the continuous mode exhibited a stable voltage of approximately 100 mV with a removal rate of around 40 %. The main anodic precipitates were identified as Fe(OH)s, FeOOH, and Fe2Os, demonstrating promising potential for resource recovery. This study provides a sustainable approach that integrates pollution control and resource utilization for AMD treatment.

The development of coal-based high-energy-density (HED) aviation fuels is critical for advancing diversified energy strategies in the aviation industry. A core scientific challenge lies in the directional regulation of naphthalene (a key HED precursor) generation during coal pyrolysis. This study integrates experimental methods with Reactive Force Field molecular dynamics (ReaxFF MD) simulations, revealing for the first time the detailed reaction pathway of naphthalene formation and the calcium catalytic enhancement mechanism. By tracking carbon skeleton evolution, we construct a quantitative reaction network for naphthalene generation and identified eight distinct pathways, including a previously unreported route involving the cleavage-recombination of monocyclic aromatic C,3H,8. Experimental results demonstrate that the introduction of calcium significantly accelerates the macromolecular cracking rate, with an increase of up to 75 %; by catalyzing new pathways and promoting naphthol dehydroxylation, the yield of naphthalene derivatives is effectively increased by 56 % under experimental conditions. This study offers critical theoretical guidance and technical support for optimizing coal-based HED fuel precursor production and designing efficient calcium-based catalysts.

Methane dehydroaromatization (MDA) has the potential to be a technology with high environmental efficiency for synthesizing benzene, toluene, and xylenes (BTX) from nonpetroleum feedstocks in a carbon-neutral society. However, a debate presently exists concerning the reaction mechanism of MDA catalysis by the promising Mo/HZSM-5, primarily attributed to the unclear catalytic role of strong Br & oslash;nsted acid sites (BAS), which significantly hampers the development of highly active and anticoking catalysts. This study aims to resolve the controversy surrounding strong BAS in MDA by comparing the silica zeolite with supported molybdenum (Mo/B-sn-S-1) with Mo/HZSM-5. The Mo/B-sn-S-1 featuring internally anchored molybdenum species was prepared to generate a strong metal-support interaction, which resolved the problem, leading to the incomparable catalytic activity of Mo/Silicalite-1 with Mo/HZSM-5, due to the absence of anchoring sites. By physically mixing the Mo/B-sn-S-1 with HZSM-5 and comparing it to bifunctional catalysts, the study reveals that MDA follows a bifunctional mechanism, predominantly through the hydrocarbon pool mechanism, where strong BAS play a facilitating role. This study demonstrates that strong BAS located in spatial proximity to molybdenum species improve the aromatics yield via the autocatalytic reactions of hydrocarbon pool, while those not in spatial proximities catalyze the cyclization and polycondensation of intermediates into polycyclic aromatics and coke. This study provides crucial evidence in clarifying the debate over the role of strong BAS in MDA and lays an important theoretical foundation for the design of catalysts that better utilize BAS to balance catalytic activity and resistance to coking.

NO heterogeneous reduction by char has a great potential in reducing NOx emission. Notably, Na has a considerable effect on heterogeneous reduction. Herein, the Zhundong demineralization coal and the NaCl addition coal were taken as research objects. The char sample structure is characterized by BET surface area analysis, XRD, and XPS. Experimental and density functional theory were used to explore the macroscopic and microscopic effects of the Na contents on NO heterogeneous reduction by nitrogen-containing char in the reduction zone of staged combustion. The results showed that the properties of char are not the key factors, which affect NO heterogeneous by char at high temperature. Na promoted the adsorption and reduction of NO by improving NO chemisorption energy and reducing the largest reduction energy barrier. The catalytic NO heterogeneous activity depended on the contents of Na. While the 0.6 wt.% NaCl addition had the best catalytic effect, the adsorption capacity and reduction rate of NO were 4.96 times and 1.22 times than DC char, respectively. However, a large amount of Na will cover the active centers on char surface to inhibit NO chemisorption and reduction. The reduction of NO to N-2 was accompanied by CO release. According to the simulation results, Na can reduce the largest reaction energy barrier of C(O) complexes desorption to promote the formation of CO.

Understanding the migration and transformation of nitrogen during high-alkali coal pyrolysis and the influence of sodium on the nitrogen-containing components of coal is of great significance for the clean and efficient utilization of coal. In this study, gas chromatography-mass spectrometry (GC-MS), X-ray photoelectron spectroscopy (XPS) and ultraviolet visible spectroscopy (UV-Vis) were used to analyze the conversion of tar-N, char-N and gas-N during coal pyrolysis and the effect of sodium on the nitrogen-containing pyrolysis products of coal. The experimental results were combined with density functional theory (DFT) calculations to investigate the effect of sodium on the internal conversion process of char-N. The results revealed that a large amount of Na (2.5 wt.%, 3.5 wt.%) can reduce the nitrogen content in coal pyrolysis char, promote the formation of amine and amide in tar-N and inhibit the release of gaseous nitrogen. A small amount of Na (0.5 wt.%, 1.5 wt.%) retains nitrogen in char, reducing the total amount of nitrogen-containing species in the gas phase and tar, which is an effective means to inhibit the transformation of nitrogen to volatile matter. In addition, a large amount of Na promotes the conversion of pyrrole nitrogen (N-5) and pyridine nitrogen (N-6) in char to heterocyclic N in tar. A small amount of sodium promotes the hydrogenation and ring opening of heterocyclic-N in tar to HCN. Na promotes the conversion of N-5 and N-6 in char. DFT calculations further confirmed that the addition of Na significantly reduced the energy barrier of the rate determining step by about 36.6 kJ/mol.

Biomass reburning is an efficient and low-cost way to control nitric oxide (NO), and the abundant potassium (K) element in biomass affects the heterogeneous reaction between NO and biochar. Due to the incomplete simulation of the NO heterogeneous reduction reaction pathway at the molecular level and the unclear catalytic effect of K element in biochar, further research is needed on the possible next reaction and the influencing mechanism of the element. After the products of the existing reaction pathways are referenced, two reasonably simplified biochar structural models are selected as the basic reactants to study the microscopic mechanism for further NO heterogeneous reduction on the biochar surface before and after doping with the K atom based on density functional theory. In studying the two further NO heterogeneous reduction reaction pathways, we find that the carbon monoxide (CO) molecule fragment protrudes from the surface of biochar models with the desorption of N2 at the TS4 transition state, and the two edge types of biochar product models obtained by simulation calculation are Klein edge and ac56 edge observed in the experiment. In studying the catalytic effect of potassium in biochar, we find that the presence of K increases the heat release of adsorption of NO molecules, reduces the energy barrier of the rate-determining step in the nitrogen (N2) generation and desorption process (by 50.88 and 69.97%), and hinders the CO molecule from desorbing from the biochar model surface. Thermodynamic and kinetic analyses also confirm its influence. The study proves that the heterogeneous reduction reaction of four NO molecules on the surface of biochar completes the whole reaction process and provides a basic theoretical basis for the emission of nitrogen oxides (NOx) during biomass reburning.

Exploring methane formation is critical for elucidating the catalytic pyrolysis mechanisms and regulating high value-added chemical production. This paper aims to propose a strategy that combines ReaxFF molecular dynamics (ReaxFF MD) with density functional theory (DFT) to systematically tackle the micro -mechanisms of methane generation influenced by Ca -catalyzed coal pyrolysis. This research determines the contribution of three-phase products (char, tar, and gas) and precursors to methanogenesis for the first time, as well as explores the changes in reactivity and micro -path energy barrier of calcium on critical precursors. The results indicate that char serves as the primary product source of methanogenesis, while methoxyl groups are essential structural contributors to its generation. The pivotal factor in calcium impacting methane release is the inhibition of methoxy cleavage. It was found that calcium intensified the difficulty of CH3 & sdot; desorption from the carbonaceous surface by reducing the electron density in the methoxyl region and enhancing the Laplace bond order (LBO) of the methoxyl O -C bond, elevating the energy barrier value of the rate -determining step in the methane generation. This reduced the contribution of methoxy to methane generation from 40% to only 4.34%. The work bridges the inadequacy of the current microscopic insights into metal -influenced product formation and provides a comprehensive and in-depth theoretical basis for the development of coal -catalyzed pyrolysis technology.

Dissolved organic matter (DOM) derived from biochar takes a crucial role in transport and bioavailability toward contaminants; hence, it is undeniable that a thorough analysis of its properties is important. So far, the effect of pyrolysis temperature on the functional groups, components, and evolutionary sequence of manure-based biochar DOM has not been adequately investigated. Here, DOM was released from two typical livestock manures (cow and pig) at five pyrolysis temperatures (300 ~ 700°C), and it was explored in depth with the aid of moving window 2D correlation spectroscopy (MW-2D-COS) and heterogeneous 2D correlation spectroscopy (hetero-2D-COS). The results demonstrated that the concentration, aromaticity, and hydrophobicity of DOM were greater at high temperatures, and more DOM was liberated from cow manure-based biochar at identical temperature. Protein-like compounds dominated at high temperatures. The pyrolysis temperatures of final configuration transformation points of the fulvic acid-like component and the aromatic ring C=C in DOM were 400°C and 500°C, respectively. Moreover, Fourier transform infrared spectroscopy combined with two-dimensional correlation analysis indicated that the functional group evolution of DOM depends on the pyrolysis temperature and feedstock type. The study provides a new perspective on manure management and environmental applications of biochar.

NOx production during coal combustion can be minimized by using the heterogeneous reduction reaction of NO on char. Here, coal-derived char was loaded with different amounts of Fe for heterogeneous reduction of NO at 1300°C in a one-dimensional tube furnace. The effects of Fe loading on the reaction was investigated for the first time. Meanwhile, theoretical calculations based on the wave function theory and density functional theory were carried out to explore the reaction steps at the molecular level. Two reaction pathways were identified involving different chemisorption sites. The catalytic mechanism of Fe in the entire NO reduction process was revealed, and thermodynamic and kinetic analyses were carried out based on the theoretical results. Overall, the NO reduction rate was greatly enhanced when the char contained Fe. At a FeCl3 loading of 0.4 wt%, the NO reduction rate reached the maximum and was 18.8% higher than that of the demineralized char. The catalytic mechanism of Fe could be attributed to the following aspects: creation of more new active sites for the chemisorption of NO by the destruction of conjugated π-bonds, reduction in the energy barrier of the rate-determining step, and facilitation of N–N bond formation and N2 desorption from the char surface. According to the thermodynamic and kinetic calculations, the introduction of Fe increased the upper limit and rate of the heterogeneous reduction reaction of NO.

With the purpose of providing theoretical guidance to assist in regulating NOx emissions, a thorough understanding of the catalytic mechanism of NO2 adsorption reduction on the surface of the carbon material under the impact of K in biochar can be of significance. Through density functional theory (DFT) calculations, two reaction routes including various zigzag and armchair edge biochar models are identified, indicating the changes in the structure of intermediates and the influence mechanism of the K presence. Mayer bond order analysis and wave function analysis is used to investigate a new discovery that the formation process of the pentagon–heptagon reconstruction at zigzag edges (zz-57 edges structure) and the desorption process of CO from the seven-membered ring with an oxygen atom. According to calculation results, the K catalyzes the process in three ways: facilitating the disconnection of N–O bond, the desorption of NO, and the CO2 dissociation, and brings about a decrease in the highest energy barrier for the NO2 reaction path on two char edge models by 48.04% and 39.85%. Thermodynamic and kinetic analysis indicates that the addition of K enhances the upper limit and the maximum reaction rate of the reaction path.