CO Ratio Research Articles

The Inhibition Effect of CO2-N2 Composite Gas on Spontaneous Combustion of Coal and the Law of Competitive Adsorption in Coal

ABSTRACT The purpose of this study is to study the effect of CO2-N2 composite gas on coal spontaneous combustion index gas and the mechanism of inhibiting coal spontaneous combustion through a competitive adsorption process and to provide theoretical guidance for adopting inert injection fire prevention and control technology in goaf to prevent coal spontaneous combustion. The programmed temperature experiment and gas chromatography were used to analyze the indicator gas after injecting different mixed ratios of CO2 and N2 inert gas. In the whole oxidation heating process (25–300 ℃), the generation of indicator gas and the peak point of gas ratio showed an apparent “Hysteresis phenomenon” and the more significant the proportion of CO2 in the composite inert gas, the more pronounced the “Hysteresis phenomenon.” Even in the CO2-dry air environment, the peak point disappears, indicating that with the injection of N2 and CO2, the coal body is in a more complex gas atmosphere, and a variety of gases are in the process of adsorption and desorption on the inner and outer surfaces of the coal body. The characteristics of the evolution of the spontaneous combustion oxidation process of coal are more complex, directly affecting the coal-oxygen interaction, thus affecting the intuitive combustion oxidation process. Molecular simulation studies the characteristics of coal molecules on CO2, N2, and O2. The results show that the adsorption capacity and adsorption energy of coal molecules on CO2 molecules are more significant than O2 and N2, and there is a competitive adsorption relationship between CO2 and N2 molecules and O2 molecules, and the competitive adsorption capacity of CO2 is more significant than N2. It shows that the composite inert gas can inhibit the coal-oxygen adsorption by competitive adsorption to displace oxygen and achieve the combustion inhibition effect. The experimental and theoretical basis for developing and improving inert gas fire extinguishing technology is provided by studying the index gas after CO2-N2 composite inert gas action and the adsorption capacity and energy in the competitive adsorption process.

Decrypting the Controlled Product Selectivity over Tunable Ni─Co Bimetallic Alloy for Photoreduction CO2

AbstractEfficiently regulating reaction pathways for photoreduction CO2 to achieve required products is enormously strenuous. The design of active sites for CO2 adsorption, activation, and tuning of reaction pathways is pivotal to address this grand challenge. Herein, highly selective sites are developed for photoreduction CO2 to HCOOH and CO based on asymmetrically coupling different ratios of Ni and Co loaded on crystalline carbon nitride (CCN) by an alloying synthesis strategy, which is confirmed by high‐resolution transmission electron microscopy (HRTEM) imaging, X‐ray diffraction (XRD) patterns, and X‐ray photoelectron spectroscopy (XPS) spectra. In situ Fourier transform infrared spectra suggest that the key intermediate *OCHO to HCOOH pathway prefers to form on Ni sites, while *COOH to CO pathway tends to generate on Co sites, and the characteristic peaks intensity of the two key intermediates are stronger with the synergistic effects of NiCo bimetallic, further verified by the theory calculations. Accordingly, HCOOH with a selectivity of 98.5% (194.5 µmol g⁻1 h⁻1) or CO with a selectivity of 85.4% (144.8 µmol g−1 h−1) can be achieved on the optimized NixCoy alloy, under sacrificial agent‐free conditions.

Volatile-rich Sub-Neptunes as Hydrothermal Worlds: The Case of K2-18 b

Abstract Temperate exoplanets between the sizes of Earth and Neptune, known as “sub-Neptunes,” have emerged as intriguing targets for astrobiology. It is unknown whether these planets resemble Earth-like terrestrial worlds with a habitable surface, Neptune-like giant planets with deep atmospheres and no habitable surface, or something exotic in between. Recent JWST transmission spectroscopy observations of the canonical sub-Neptune, K2-18 b, revealed ~1% CH4, ~1% CO2, and a nondetection of CO in the atmosphere. While previous studies proposed that the observed atmospheric composition could help constrain the lower atmosphere's conditions and determine the interior structure of sub-Neptunes like K2-18 b, the possible interactions between the atmosphere and a hot, supercritical water ocean at its base remain unexplored. In this work, we investigate whether a global supercritical water ocean, resembling a planetary-scale hydrothermal system, can explain these observations on K2-18 b–like sub-Neptunes through equilibrium aqueous geochemical calculations. We find that the observed atmospheric CH4/CO2 ratio implies a minimum ocean temperature of ~710 K, whereas the corresponding CO/CO2 ratio allows ocean temperatures up to ~1070 K. These results indicate that a global supercritical water ocean on K2-18 b is plausible. While life cannot survive in such an ocean, this work represents the first step toward understanding how a global supercritical water ocean may influence observable atmospheric characteristics on volatile-rich sub-Neptunes. Future observations with better-constrained CO and NH3 mixing ratios could further help distinguish between possible interior compositions of K2-18 b.

Optimizing the Ratio of Metallic and Single-Atom Co in CoNC via Annealing Temperature Modulation for Enhanced Bifunctional Oxygen Evolution Reaction/Oxygen Reduction Reaction Activity.

Developing low-cost, efficient alternatives to catalysts for bifunctional oxygen electrode catalysis in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is critical for advancing the practical applications of alkaline fuel cells. In this study, Co particles and single atoms co-loaded on nitrogen-doped carbon (CoNC) were synthesized via pyrolysis of a C3N4 and cobalt nitrate mixture at varying temperatures (900, 950, and 1000 °C). The pyrolysis temperature and precursor ratios were found to significantly influence the ORR/OER performance of the resulting catalysts. The optimized CoNC-950 catalyst demonstrated exceptional ORR (E1/2 = 0.85 V) and OER (Ej10 = 320 mV) activities, surpassing commercial Pt/C + RuO2-based devices when used in a rechargeable zinc-air battery. This work presents an effective strategy for designing high-performance non-precious metal bifunctional electrocatalysts for alkaline environments.

Co3O4/CuO Hybrid Hollow Microspheres as Long-Cycle-Life Lithium-Ion Battery Anode.

Co3O4/CuO hybrid hollow microspheres have been successfully prepared via thermal decomposition of CoCu glycolates, whose size can be adjusted by varying the molar ratio of Co2+/Cu2+. As lithium-ion battery (LIB) anode, Co3O4/CuO microspheres exhibited excellent electrochemical performance due to synergistic effects and the hollow structural design, the best Co3O4/CuO sample could maintain a high specific capacity of 1170.4 mAh g-1 after 300 cycles at 1 A g-1, and still retain a capacity of 514.5 mAh g-1 after 1000 cycles at 2 A g-1. Thus obtained Co3O4/CuO hybrid hollow microspheres hold great potential as anode materials for high-performance LIBs.

Fabrication of lignin-MOF derived spherical carbon supported NiCo-bimetallic catalysts for selective hydrogenolysis lignin derived ether.

The conversion of abundant lignin was of great significance for the utilization of biomass resources. In this study, lignin sulfonate (LS) was selected as a carbon-based support, which was successfully introduced into the NiCo-MOF structure. A series of lignin and MOF hybrid catalysts (NinCo-MOF-LS) with varying metal ratios of Ni and Co were synthesized via the hydrothermal method. Subsequently, the catalytic hydrogenolysis of lignin-derived dimers was conducted over a range of NinCo-MOF-LS, with the impact of calcination temperature and lignin addition in the catalysts taken into account. The selective conversion of benzyl phenyl ether (BPE) and other lignin dimers was achieved over the NinCo-MOF-LS catalyst with isopropanol serving as the hydrogen donor solvent in a nitrogen atmosphere. The Ni/Co metal ratio and calcination temperature were found to have a significant impact on the catalytic performance. Through a comprehensive investigation of various reaction parameters, including temperature, pressure, reaction time, and reaction solvent, it was determined that the catalyst exhibited excellent catalytic activity in the selective hydrogenolysis of BPE to cycloalkane and cyclohexanol. The optimal reaction conditions (240°C, 4h, 3MPaN2) were found to be conducive to the effective conversion of BPE into methylcyclohexane and cyclohexanol. The combination of lignin and metal-organic framework represented a novel approach to the utilization of lignin resources and the upgrading of biomass-derived chemicals.

Numerical Analysis of Spatial Distribution of Carbon in Methane Dry Reforming over Supported Nickel Catalyst in a Packed Bed Reactor

This study investigates carbon deposition during methane dry reforming over a nickel-based catalyst supported on alumina in a laboratory-scale fixed-bed reactor. Approximately 23.75 grams of catalyst were used, and simulations were performed using COMSOL 6.2 software. The reactor was simulated at isothermal wall conditions at four temperatures (650°C, 750°C, 850°C, and 950°C), with an equimolar CH₄ to CO₂ ratio in the feed. The results showed that while localized carbon deposition density increased with temperature, likely due to a higher local methane decomposition rate, the total amount of carbon deposited was inversely proportional to temperature. This suggests enhanced carbon gasification at higher temperatures. The total carbon deposited was estimated to be around 18 grams after 10,000 seconds of Time on Stream (TOS) at 650°C. As the temperature increased, the total carbon deposition decreased, although this reduction became negligible beyond 850°C. Furthermore, the hydrogen to carbon monoxide (H₂/CO) molar ratio peaked at over 1.1 at 650°C, dropped to approximately 0.76 at 750°C, and then rose back to 0.97 at 950°C. Steady-state operation was not achieved due to continuous carbon deposition and accumulation in the reactor. However, in the absence of carbon deposition, steady-state was reached around 100 seconds after the feed entered, at a velocity of 3 cm/s. Methane conversion reached 97% at 950°C.

Exploring the impact of cobalt and H2 to CO ratios on catalytic performance of FeKAl and FeCoKAl catalysts in CO hydrogenation to light olefins

This study explores the CO hydrogenation to light olefins over FeKAl catalysts, examining how varying H2 to CO ratios (from 1:1 to 7:1) and the introduction of cobalt (Co) influence catalytic performance. Our investigation reveals that Co addition significantly enhances the reducibility of iron oxide species and increases sites favorable for moderate hydrogen adsorption and weak to moderate basicity. We discovered that without Co (FeKAl), increasing the H2 to CO ratio progressively lowers CO2 space–time yield (STY), shifting the reaction’s preference from the water–gas shift reaction towards hydrogenation. The STY of light olefins reaches a peak at an H2 to CO ratio of 3:1, indicating optimal conditions for their production before decreasing at higher ratios. Incorporation of Co (FeCoKAl) maintains this trend but with marked improvements in CO conversion and olefin STY, especially notable at a ratio of 1:1 due to enhanced hydrocarbon product desorption. The findings underscore the critical role of Co and H2 to CO ratios in modulating catalyst stability and activity, with specific ratios significantly reducing catalyst deactivation through diminished wax and carbon fiber formation, and Co presence aiding in the maintenance of steady CO2, hydrocarbon, and light olefin yields by preventing the excessive transformation of iron carbide to Fe3O4.

A method for hydrogen-enriched syngas production from biomass via induction heating

We propose a method for production of syngas with different H2 to CO ratios from biomass via induction heating in a quartz reactor. To transfer heat to the biomass, iron filings or steel balls were added and evenly distributed in the biomass bed. In the case when iron filings were used, the molar ratio of H2 to CO was 2.3:1, while the use of steel balls reduced this ratio to 1:1.4, resulting in a 22 mol.% increase in gas yield. An extra layer of iron filings located in the induction heating area above the mixture of biomass and steel balls facilitated partial decomposition of the heavy tar, increasing the yield of gaseous products by another 20.7 mol.% with the molar ratio of H2 to CO reaching 1.6:1. Secondary reactions of volatile compounds on the surface of iron filings resulted in the formation of p-xylene and o-xylene. The composition of gaseous and liquid pyrolysis products was investigated by GC and GC–MS.

Investigation of the behavior of manganese, iron, cobalt, and nickel at precipitate formation due to oxide addition in molten chlorides

Spent nuclear fuels are generated with the operation of nuclear power generation. The process of recovering nuclear fuel materials from spent nuclear fuels is called reprocessing, and through this reprocessing, nuclear fuel materials are recycled as nuclear fuel. The main reprocessing methods are wet reprocessing and pyro reprocessing. Molten salt electrolysis is used for the pyro reprocessing methods. In pyro reprocessing methods, salt bath is used repeatedly, as a result, ultimately spent salt containing a small amount of nuclear fuel materials is generated. In terms of nuclear material management, the nuclear fuel materials must be isolated and recovered. Therefore, we propose a nuclear fuel material recovery process that combines a precipitation method and a distillation method. However, it has been suggested that spent salt is contaminated by other radioactive materials derived from nuclear reactors, fuel structural materials, and molten salt electrolyzers used in pyro reprocessing. In this study, the behavior of these radioactive substances during precipitate formation was estimated.LiCl–KCl eutectic salt or NaCl–2CsCl salt was placed in a quartz tube in an Ar circulation glove box (GB). 10 wt% of MnCl2 or CoCl2 was added to the salt bath. The precipitant Li2O was added at stoichiometric amounts of 50 %, 100 %, 150 %, and 200 % relative to the amount of Mn(II) or Co(II), respectively. The quartz tube was placed in an electric furnace inside the GB and heated at 700 ℃ in the LiCl–KCl bath and 800 ℃ in the NaCl–2CsCl bath to melt the sample. After the sample was naturally cooled and solidified in the quartz tube, the precipitate and supernatant salt were collected. The precipitate was crushed, washed with pure water, and mixed with BN after drying. The mixture was formed into pellets and subjected to XAFS measurement. XAFS measurements were performed with KEK PF BL-27B, AichiSR BL5S1, and SPring-8 BL22XU. A portion of the supernatant salt was collected, dissolved in pure water, and analyzed using ICP-OES and AAS. The amount of Mn(II) or Co(II) contained and the constituent elements of the salt bath was determined from the analysis results, and the precipitation ratio was calculated. In addition, the reactions assumed in the experiment were evaluated by simulating the precipitation ratio using the thermodynamic database MALT and the multi-element chemical equilibrium calculation software gem.The precipitation ratio is shown in Figure 1 (left). The precipitation ratio of Mn(II) and Co(II) tended to increase as the amount of precipitant added increased. Both Mn(II) and Co(II) tended to increase up to 150 %, but there was no significant difference between 150 and 200 %. It is thought that the chloride produced an oxide precipitate by adding the precipitant. Theoretically, the precipitation ratio would increase to around 100 % if the amount of precipitant added was 100 %, but it was less than 80 % for both Mn(II) and Co(II). There are two possible reasons. One is that O ions derived from Li2O have the property of dissolving in salt bath, so there is a possibility that some of the precipitate will be dissolved in the salt bath. The other reason is that the total amount of Li2O added did not react with Mn(II) and Co(II), and a portion of it was dissolved in the salt bath. Furthermore, between Mn(II) and Co(II), the precipitation ratio of Co(II) tended to be higher. This is thought to be due to the fact that Co(II) reacts more easily with the precipitant than Mn(II). Therefore, in a mixed system, it is assumed that Co(II) precipitates first. Figure 1 (right) is the EXAFS radial structure functions of the Co(II) precipitate and the control sample. In the EXAFS radial structure function, not only the first neighborhood structural peak of the Co-O bond at approximately 1.8 Å coincided with the precipitate, but also the correlations at longer distances showed almost the same behavior. From this, it is assumed that the precipitate is CoO. In the presentation, we also plan to explain Fe(III) and Ni(II).As a result of the experiment, it was found that Mn(II) and Co(II) were recovered as oxides. Since the goal is to recover nuclear fuel materials as oxides, Mn(II) and Co(II) are likely to be entrained in the nuclear fuel materials. Therefore, we believe that it is necessary to add a process to separate Mn(II) and Co(II) from nuclear fuel materials. Figure 1

High stability cubic perovskite Sr0.9Y0.1Co1-xFexO3-δ oxygen evolution by phase control and electrochemical reconstruction

Transition metal oxides are considered ideal electrocatalyst materials due to their low cost and high intrinsic activity. Among them, SrCoO3-δ has received increasing attention due to its multi-phase structure and tunable electronic properties, though its OER reaction kinetics and catalysis stability are unsatisfactory. Herein, based on a simple one-step solid-state reaction method, we use a small amount of rare earth Y ions (10 %) to transform H-SCO2.52 from a hexagonal structure to a stable cubic perovskite Sr0.9Y0.1CoO3−δ. While broadening the atomic ratio of Co and Fe in the B-site under the cubic perovskite Sr0.9Y0.1Co1-xFexO3−δ (x = 0–1), the relationship between the B-site electronic state, oxygen vacancies, and OER performance has been explored. Sr0.9Y0.1Co0.2Fe0.8O3−δ with a high concentration of oxygen vacancies, exhibits the lowest overpotential of 277 mV and maintains stability at 10 mA cm−2 for 88 h. The valence states of Fe and Co atoms in SYC0.2F0.8 O are optimized (Fe2+∼50.81 %, Co2+∼19.39 %), and the oxygen evolution activity is enhanced by electrochemical reconfiguration to form high-valence Fe and Co ions. Selective leaching of Sr ions via electrochemical surface reconstruction activates FeOOH and CoOOH amorphous layer active sites on the catalyst surface, significantly enhancing reaction kinetics.

Synthesis of Co@N-C Porous Electrocatalysts in Alkaline Electrolytes and Their ORR Applications

In recent years, petrochemical-based energy sources have been used for decades, and many researchers have been trying to switch from petrochemical energy sources to clean energy sources to solve the problem of global warming. Among the various green energy sources, fuel cells that use hydrogen and oxygen as raw materials to generate energy from water and electricity have recently gained attention. However, problems such as platinum's small reserves and poor durability have been a major obstacle to the widespread use of fuel cells. In order to solve these problems, we synthesized catalysts in the form of carbon composites doped with inexpensive transition metals and nitrogen with excellent electrical conductivity and evaluated their performance as ORR catalysts in alkaline electrolytes. Depending on the optimal heat treatment synthesis conditions and the ratio of Co and dopamine precursor, we found the best synthesis method in alkaline conditions of 0.1 M KOH, which shows excellent ORR performance due to the synergistic effect of nitrogen-doped carbon and Co. Although the performance is still inferior to that of commercial platinum catalysts, further improvements are expected to improve the performance to that of platinum catalysts.<This research was supported by PEO24016 (KITECH)> Figure 1

Delving into textile fast pyrolysis: A holistic study on the effects of feedstock and temperature variability

Perpetual fast fashion wave, dismal global recycling rate, and poor circularity of textiles urged sustainable textile waste disposal solution in lieu of incineration and landfilling. Herein, textile fast pyrolysis was mooted as a promising solution by dint of its fast disposal rate, mild pollutant emission, and multiple value-added products formation. Following ill-defined thermochemical behaviour of individual textiles, in-depth experimental exploration on textile fast pyrolysis was supplemented by feedstock characterization, product distribution, and product characterization to unravel the effects of feedstock (natural/synthetic) and temperature (500–900oC) variability on pyrolysis products. Textile fast pyrolysis harnessed pyrogas with two variable products, viz. retrievable chars and oils [natural textiles: cotton (C), denim (D), & cashmere/plant fibre (CP)] or non-retrievable chars and waxes [synthetic textiles: polyester (P), P/acrylic (PA), & P/cotton (PC)]. Melting and high aromaticity of polyethylene terephthalate (PET) rendered the synthesis of non-retrievable chars and waxes, separately. Given monotonic char yields (7.31–24.19 wt%) reduction with temperature, the oil/wax (53.19–75.19/60.46–70.52 wt%) and gas (13.44–33.67 wt%) yields were negatively correlated to each other. Twill-woven network of D contributed to exclusively high BET surface area of D chars (132.64–217.10 m2/g). All natural textile chars (28.56–32.88 MJ) exhibited comparable higher heating value (HHV) to commercial coals/coke (14.77–34.39 MJ/kg) and biochars (7.26–33.37 MJ/kg). Compared to the commercial fuels, raw textile oils (incombustible-10.14 MJ/kg) and textile waxes (15.88–23.18 MJ/kg) were inferior fuels with low HHV. Nonetheless, cotton (C & D) oils, CP oils, and P-based textile waxes had respective enriched content of levoglucosan (6.85–34.38 area%), triacetoneamine (6.22–21.09 area%), and benzoic acid (16.37–46.55 area%). Considering noteworthy H2 formation data sets (700–900oC; C700 only), natural textile pyrogas (62.75–79.02%) had greater syngas (H2 & CO) composition than synthetic textile pyrogas (62.48–68.23%). At optimal temperature of 900oC, textile fast pyrolysis generated pyrogas with H2:CO ratios (1.30–3.49 ≈ 2) that nearly ideal for Fischer-Tropsch synthesis. Conversely, textile fast pyrolysis also emitted pollutant gases that differ between natural (NH3, N2O, NO, & SO2) and synthetic [NH3 (excluding P), N2O, & NO2] textiles.

Cu-Doped La0.3Sr1.7Fe1.5Mo0.5O6-σ Decorated with Exsolved Nanoparticles for the Improvement of Syngas Production in Solid Oxide Electrolysers

A major concern within modern society is the need to substitute the fossil fuels with more renewable sources of the energy. Chemical industry is one of major players in the field of the usage of the crude oil to produce more complex chemicals. Despite of being good source of carbon species, a dropping amount of the coal and oil is raising the questions for future solutions. Carbon dioxide can be promising and sustainable source of carbon, but its high C-O bond energy (806 kJmol-1) poses general problems in efficient utilization. The most common feedstock in chemical synthesis is the syngas, a mixture of H2 and CO, which can be simply processed into more complex molecules like e.g., methanol, dimethyl ether, or methane.Highly inert CO2 can be transformed into more valuable CO via, so called, Reverse Water-Gas Shift Reaction (RWGS). Even though there are couple proposed CO2 activation mechanisms, and knowledge on the reaction is quite high, the common issue is still proper selection of the catalyst for the reaction. In the surface redox mechanism Cu metal is being oxidized by CO2 to form Cu2O with the release of CO. After that, Cu+ ions are getting reduced back to metallic copper using surrounding H2. Solid Oxide Cells can become good source of ‘green’ hydrogen and, at the same time, perform direct electrolysis or chemical reduction of CO2. High temperature, at which SOECs are working, is beneficial from the point of Faradaic efficiency and CO2 conversion rate. Steam electrode of SOEC contains copious amount of nickel. It is also a well-known catalyst for many reactions, but in this case the electrodes are struggling under carbon-rich atmosphere. Therefore, an addition of different catalytic materials is needed. Commonly used are mixed catalytic heterogenous systems composed of Cu supported on oxide materials e.g., FexOy, MoO3, La2O3, and many more.In this study a series of catalysts for SOECs were fabricated based on the Cu-doped double perovskite structure able to exsolve intermixed Cu or Cu-Fe nanoparticles supported on the matrix lattice of La0.3Sr1.7Fe1.5Mo0.5O6-σdenoted as LSFM. The usage of LSFM compound as a matrix for Cu exsolution was based on the idea that it already consists of the oxides, which are currently utilized as the catalysts in RWGS. On the other hand, quite high mixed ionic-electronic conductivity may lead to even more enhanced electrochemical activity of the compound.The samples with varying Cu dopant level (5-20 mol.%) were synthesized via modified Pechini method maintaining fixed Fe:Mo ratio. Selected powders were processed into inks and screenprinted onto Ni-YSZ electrode. During the startup procedure of the SOEC, the catalysts were activated and the exsolution of metallic nanoparticles occurred. The powders and catalytic layers were characterized using XRD, SEM, and XPS techniques in both oxidized and reduced states. Doped compounds were able to exsolve metallic nanoparticles with the coverage density and size depending on the initial Cu amount in the lattice and the temperature of the reduction. Additional Temperature-Programmed Reduction and Oxidation (TPR/TPO) tests were performed to better understand the formation mechanism of surficial nanoparticles.SOECs equipped with additional layer of LSFM-Cu on the fuel electrode were examined for the performance in coelectrolysis mode under flowing H2O-CO2 with subsequent measurement of the outlet gases concentration using GC-MS. New layer altered the production of syngas concerning H2:CO ratio, yield, selectivity and conversion rates. The anchoring effect of the exsolution process causes higher integration of the nanoparticles compared to conventional catalysts produced via simple deposition and most likely limits the evaporation and surface diffusion of copper. LSFM-Cu can be promising material for increasing the efficiency of the SOECs. Acknowledgements This work was supported by a project funded by National Science Centre Poland, based on decision UMO-2021/43/B/ST8/01831 (OPUS 22).

Plasma‐Catalytic CO2 Methanation Over Supported Ni–Co Catalysts Prepared by Solution Combustion Synthesis

ABSTRACTIncorporating suitable promoters into nickel‐based catalysts for carbon dioxide methanation proves to be a successful strategy for enhancing catalyst structure, optimizing surface properties, mitigating deactivation, and ultimately boosting catalytic performance. This study focuses on the synthesis of Co‐modified Ni/CaCO3 catalysts using the solution combustion synthesis method. The catalytic activity of the afforded catalysts has been evaluated for CO2 methanation in a dielectric barrier discharge reactor operating at a gaseous hourly space velocity of 11,320 h−1 and an H2:CO2 ratio of 4:1. The catalyst exhibits optimal performance at a Ni:Co ratio of 13:2, achieving a CO2 conversion rate of 57.5% and CH4 selectivity of 92.4%. Characterization techniques such as X‐ray diffraction, transmission electron microscopy, X‐ray photoelectron spectroscopy, programmed temperature‐raising hydrogen reduction, carbon dioxide desorption, and in situ plasma DRIFTS are employed to evaluate the catalysts. The results indicate that the addition of Co to Ni‐based catalysts leads to an increase in moderately basic sites, thereby enhancing the catalytic activity and stability of catalysts for CO2 methanation. Notably, the combination of the plasma and the Ni–Co catalyst offers a novel pathway for CO2 methanation, featuring higher energy efficiency and superior synergistic effects compared to monometallic catalysts.

Improving in-situ biomethanation of sewage sludge under mesophilic conditions: Performance and microbial community analysis

This research investigated the application of in-situ biological hydrogen methanation within a continuous stirred tank reactor (CSTR) system under mesophilic conditions, with sewage sludge used as the substrate. Two CSTRs with an effective capacity of 5 L were installed and loaded with inoculum sludge with a volatile solid (VS) concentration of 1.2–1.5 %. They were fed mixed waste sludge with an organic loading rate (OLR) of 1.5 g VS/L and an average sludge retention time (SRT) of 19 days under mesophilic conditions at 37 °C. One of the reactors operated as a control, while the other was injected with H2 through a microceramic membrane diffuser with a H2:CO2 ratio of 4:1. The results of this study revealed that the addition of H2 and the recirculation of residual hydrogen in biogas led to a substantial increase in the production of methane from 157 L/kg VS to 275 L/kg VS. Increasing the methane content in biogas from 52 % to 78 % yielded an impressive 42.8 % higher methane production rate. Metataxonomic analysis of the microbial community via high-throughput sequencing techniques revealed that the dominant acetoclastic and hydrogenotrophic methanogens were Methanosaeta and Methanoregula, respectively, with greater abundances of both groups in the experimental bioreactor. The dynamics of their activity in both bioreactors were analyzed via qPCR, and the functional genes encoding methyl-coenzyme M reductase (mcrA gene) and hydrogenase Ni-Fe presented comparable changes between RI and RII. By optimizing key operational parameters and closely examining the dynamics of the microbial community, this approach can contribute significantly to sustainable bioenergy solutions while minimizing environmental impact.

Comparison of a Quantum Cascade Laser and an Interband Cascade Laser for the Detection of Stable Carbon Dioxide Isotopes Using Tunable Laser Absorption Spectroscopy.

Quantum cascade lasers (QCLs) and interband cascade lasers (ICLs) are widely used as light sources in tunable laser absorption spectroscopy because they emit in the mid-infrared region where many strong and characteristic absorption bands are present. In this paper, we compare the performance of these lasers emitting at about 2310.1 cm-1 to determine an optimal light source for detecting isotopic ratios of carbon dioxide (CO2). Our results show that the QCL has a higher relative intensity noise of up to 15 dBc/Hz compared to the ICL over the entire measured frequency range. In addition, it has a higher frequency fluctuation. However, the maximum tuning range of the QCL is up to 5.2 cm-1 compared to up to 3.8 cm-1 for the ICL. Both lasers lose more than half of their tuning range when the tuning rate is increased to 10 kHz. When measuring the isotope ratio of CO2, an uncertainty in the value of ‰ was achieved with the ICL and of ‰ with the QCL, both at an integration time of 0.2 s. In summary, the QCL is more appropriate for applications that require a larger spectral tuning range, such as the measurement of a complex gas mixture, while the ICL has an excellent signal-to-noise ratio and is therefore better suited for applications that require higher precision.

Dynamic hydrogen bubble template electrodeposition of a self-supported Co-P electrocatalyst for efficient alkaline oxygen evolution reaction

The development of efficient, inexpensive, and earth-abundant electrocatalysts for the oxygen evolution reaction (OER) represents a significant challenge for the large-scale production of hydrogen. The primary obstacle to the advancement of OER is the necessity for a considerably higher overpotential than the theoretical oxygen evolution potential, due to the sluggish kinetics of the electron transfer reaction, which involves a large amount of thermodynamic energy. In this article, amorphous and cauliflower-like Co-P electrocatalysts were in situ grown on nickel foam by dynamic hydrogen bubble template (DHBT) electrodeposition method. The Co-P electrocatalyst with Co/P ratio optimal presented excellent electrocatalytic activities with a low overpotential of 239 mV for OER at 10 mA·cm−2 and long-term stability in 1.0 M KOH. The outstanding OER performance of the catalyst is mainly attributed the synergistic effect of amorphous and cauliflower-like structure, superhydrophilicity surface, and the electronic regulation by adjusting the atomic ratio of Co to P. This research will bring fresh ideas and strategies for developing novel simple, affordable, and efficient electrocatalysts to boost OER kinetics.

Significant shift of footprint patterns and pollutant source contributions: insights from observations at Shanghuang observatory, East China

Abstract As two of the most important products of the combustion process, carbon dioxide (CO2) and carbon monoxide (CO) are commonly used as tracers for combustion source assignment. Their relationship will help to better understand the regional carbon cycle and assess climate forcing effects. In this study, mixing ratios of CO2 and CO were continuously measured using a Picarro gas concentration analyzer at the Atmospheric Boundary Layer Eco-Environmental Shanghuang Observatory, Chinese Academy of Sciences (ABLECAS) throughout 2022–2023. The variability of the mixing ratio of CO to CO2 (ΔCO/ΔCO2) in a 1 h time interval was calculated based on linear slope analysis after background values were determined and subtracted. The results showed that the mixing ratio of CO had a clear seasonal variability with a moderate increase in the spring (249.1 ± 59.6 part per billion (ppb)) and winter (257.8 ± 90.3 ppb), mostly due to more frequent transport from north of the Yangtze River. ΔCO/ΔCO2 at the ABLECAS varied with air mass origin, with a linear slope 0%–1% on a 1 h basis. Relatively high ΔCO/ΔCO2 values for an air mass from the north in the winter indicate that the emission sources had lower combustion efficiency. In summer, the ΔCO/ΔCO2 ratio mostly reflected the background conditions for air masses from marine areas. The potential source regions and contribution assignments were evaluatedat the ABLECAS according to source–receptor relationship analysis using the FLEXPART model with CO as a pollutant tracer from 2015 to 2023. We found that the footprint of an air mass had a clear transition period between 2018 and 2019, and a synoptic anomaly, related to Arctic Oscillation strength and west Pacific subtropical high position, plays a key role in influencing the pollutant transport patterns. This study provides a scientific basis for the formulation of air quality regulation policy, and helps to implement the national carbon neutralization strategy.

Calibration experiments for dual-comb IPDA XCO2 measurements using a variable pressure absorption cell

Measuring XCO2, the column-averaged dry-air mixing ratio of CO2 in the atmosphere, is essential for monitoring climate change and guiding mitigation efforts. Integrated Path Differential Absorption (IPDA) is a highly effective XCO2 measurement solution for space-borne lidar. However, the limited number of wavelengths limits its capabilities. IPDA, enhanced with Electro-Optical Frequency Comb (EOFC) technology, offers a robust solution. This study validates IPDA measurements using both asymmetric and symmetric Electro-Optic Dual-Comb Spectroscopy (EO-DCS) systems at 1572 nm. This indoor experimental system does not operate in a true lidar mode, but focuses on IPDA measurements of XCO2 through a transmission-style cell. We achieved atmospheric spectral transmittance by a variable pressure CO2 absorption cell, correlating pressures from 425 to 470 mb to XCO2 of 386.81–447.08 ppm. The XCO2 measurements of asymmetric/symmetric systems both exhibit excellent linearity. Their linear fittings yielded the Root Mean Square Error (RMSE) as low as 0.198/0.064 ppm, and the Mean Absolute Percentage Errors (MAPE) was as low as 0.0386%/0.0140%. This level of measurement performance has never been demonstrated in other works. Accuracy was assessed by comparing IPDA results with a pressure gauge, and precision was confirmed through repetitive measurements (1000 times over 10 min) and Allan variance analysis. Notably, our system operates effectively without frequency stabilization, showing tolerance to laser frequency drift—a significant advantage for IPDA applications. The entire experiment was conducted in a comparison between asymmetric and symmetric systems, especially in the analysis of absorption line residuals. We discuss the error transfer from phase to spectral transmittance and its implications and explained why the residuals in the asymmetric system were larger. These results underscore the superior performance of EO-DCS IPDA in measuring XCO2 and its promising potential for applications. To our knowledge, this is the only DCS IPDA calibration demonstration to date.