CO2 CH4 Research Articles

Synergy of lacustrine groundwater discharge and algal biomass on CH4 and CO2 pathways and emissions in a large shallow eutrophic lake

Inland lakes are known to be a significant component of the global carbon (C) cycle, with C pathways in these lakes potentially changing alongside their eutrophic states. One factor contributing to eutrophication is lacustrine groundwater discharge (LGD), which is also a key conduit for CH4 and CO2 to enter lakes. However, the regulation of LGD on CH4 and CO2 behavior in these lakes remains unclear. To address this gap, we conducted continuous monitoring of 222Rn, CH4 and CO2, and δ13C at two sites with distinct algal densities in Lake Taihu, a large shallow eutrophic lake in China, and aimed to investigate the synergy of LGD and algal biomass on CH4 and CO2 pathways and emissions. We found that organic matter (OM) degradation is the dominant factor controlling CH4 and CO2 production in the lake, and this process appears to be facilitated by the presence of ample OM and reduced oxygen level at the site with high algal density. In addition, LGD is found to be a significant contributor of CH4 and CO2 to the lake, and the nutrients derived from LGD play a crucial role in regulating the proliferation of algae in the lake. As algal density increases, gas emissions such as CH4 ebullition and CO2 diffusion are amplified, while processes such as CH4 oxidation and atmospheric CO2 exchange within lakes are attenuated. The contribution of LGD to CH4 and CO2 inventories in the lake also decreases as OM degradation becomes a more significant contributor. This study highlights LGD regulation on the C flux and underscores the importance of synergistical studies from both ecological and hydrogeological perspectives in comprehending lacustrine C flux dynamics.

CO2 injection-based enhanced methane recovery from carbonate gas reservoirs via deep learning

CO2 injection is a promising technology for enhancing gas recovery (CO2-EGR) that concomitantly reduces carbon emissions and aids the energy transition, although it has not yet been applied commercially at the field scale. We develop an innovative workflow using raw data to provide an effective approach in evaluating CH4 recovery during CO2-EGR. A well-calibrated three-dimensional geological model is generated and validated using actual field data—achieving a robust alignment between history and simulation. We visualize the spread of the CO2 plume and quantitatively evaluate the dynamic productivity to the single gas well. We use three deep learning algorithms to predict the time histories of CO2 rate and CH4 recovery and provide feedback on production wells across various injection systems. The results indicate that CO2 injection can enhance CH4 recovery in water-bearing gas reservoirs—CH4 recovery increases with injection rate escalating. Specifically, the increased injection rate diminishes CO2 breakthrough time while concurrently expanding the swept area. The increased injection rate reduces CO2 breakthrough time and increases the swept area. Deep learning algorithms exhibit superior predictive performance, with the gated recurrent unit model being the most reliable and fastest among the three algorithms, particularly when accommodating injection and production time series, as evidenced by its smallest values for evaluation metrics. This study provides an efficient method for predicting the dynamic productivity before and after CO2 injection, which exhibits a speedup that is 3–4 orders of magnitudes higher than traditional numerical simulation. Such models show promise in advancing the practical application of CO2-EGR technology in gas reservoir development.

Enhancement of catalytic activity in CO2 methanation in Ni-based catalysts supported on delaminated ITQ-6 zeolite

Ni-based catalysts supported on delaminated ITQ-6 zeolite with different Si/Al ratios, 30 and ∞, were tested in the methanation of CO2 and CO. ITQ-6 supports exhibited high surface areas (> 590 m2/g), and the catalysts based on them presented elevated CO2 and CO conversion values, turnover frequencies (TOF), and CH4 selectivity (> 90 %). Comparing the ITQ-6 catalyst and its precursor ferrierite (FER)-based catalyst, H2-chemisorption results confirmed higher metallic dispersion for the former, which resulted in improved H2 uptake and efficient interaction of reaction intermediates via the associative pathway. Combined kinetic studies indicated that their higher available metallic surface contributed to lower apparent activation energies towards CH4 formation, accounting for the higher selectivity values. A 15 wt% Ni-based catalyst supported on ITQ-6 zeolite (Si/Al = 30) exhibited catalytic results (XCO2 = 79 % y SCH4 = 98 %) comparable or even superior to some of the best zeolite-based catalysts reported so far.

Structural Characterisation of Zeolites Derived from Lithium Extraction: Insights into Channel- and Cage-Type Frameworks

This study investigates the structural and adsorption characteristics of channel- and cage-type zeolites obtained through lithium extraction. Through XRD, FT-IR spectroscopy, and adsorption isotherm analyses, distinct adsorption behaviours of CH4 and CO2 were observed in both zeolite types. Cage-type zeolites exhibited higher adsorption capacities attributed to their structural advantages, highlighting the importance of structural framework selection in determining adsorbent efficacy. The presence of structural defects and an amorphous phase influenced adsorption behaviours, while thermodynamic data underscored the role of adsorbate properties. Kinetics studies revealed the influence of the structural framework on CH4 adsorption and CO2 adsorption kinetics. Analysis of adsorbate–adsorbent interactions demonstrated robust interactions, particularly with LPM16-Y. These findings offer insights into the potential applications of zeolites in gas adsorption processes, emphasising the importance of structural properties and adsorbate characteristics in determining adsorption performance.

H2 promotes the premature replacement of CH4–CO2 hydrate even when the CH4 gas-phase pressure exceeds the phase equilibrium pressure of CH4 hydrate

Submarine CO2 sequestration via solid hydrate has been considered a promising strategy for controlling greenhouse gas emissions. The simultaneous replacement of CH4 from subsea natural gas hydrates through buried CO2 offers a win-win approach. Utilizing H2 as an enhancer to promote CH4–CO2 hydrate replacement, coupled with integrating the replacement products into CH4 steam reforming for cyclic H2 production, presents a potential pathway for CO2 geological storage and eventual H2 recovery. However, the enhancement mechanism of H2 in the hydrate replacement process remains unclear. Focusing on the critical replacement condition, this study investigates the effects of gas-phase partial pressures on hydrate replacement in CH4-rich systems to elucidate the H2 influence mechanism. Remarkably, the results indicate, for the first time, that H2 induces premature CH4 hydrate dissociation under conditions exceeding the corresponding CH4 gas equilibrium pressure in CO2/CH4/H2 ternary gas systems. The critical condition for hydrate replacement depends on the total system pressure, rather than CO2 gas partial pressure. Additionally, in the CH4-rich systems, the driving force for CH4 hydrate decomposition takes precedence over that for hydrate reformation in controlling replacement. The replacement ratio increases from 16.7 % to 24.5 % as the CH4 partial pressure decreases from 2.01 MPa to 1.11 MPa at 274.15 K, despite simultaneous declines in both CO2 partial pressure and total system pressure from 1.70 MPa to 0.97 MPa and from 6.10 MPa to 3.39 MPa, respectively. These findings can provide insights into the improvement of CH4–CO2/H2 hydrate replacement efficiency and the development of oceanic CO2 sequestration.

Study on the performance of photothermal catalyzed carbon dioxide hydrogenation to CH4 over doped sodium tantalate-based perovskite catalysts

NaTaO3 (ABO3)-based catalysts with B-site substituted metals M= (Co, Ni, Fe, Ga, Ti) for photothermal-catalyzed carbon dioxide reduction hydrogenation to C1 products were prepared via a simple one-step hydrothermal method. The B-site metal doping catalysts exhibited excellent performance for the aimed photothermal catalytic reaction. Among them, the NaTa0.9Co0.1O3 was the most eye-catching catalyst with a stable crystal cell, an excellent heterojunction structure, and a bandgap structure for light absorption, The fine structure properties results in a low electron-hole recombination rate and high photoelectron transfer efficiency under light conditions. The suitable alkaline adsorption sites and thermal reduction properties also be the effective assistance for the catalytic process. The CO yield and CH4 yield of the NaTa0.9Co0.1O3 catalyst were 6.6 times and 120 times higher than those of the pure-phase NaTaO3, respectively, and the CH4 selectivity was up to 98% under the illumination condition of 300 ℃. For the photothermal hydrogenation reaction, thermal catalysis dominates the reaction, and light illumination promotes the generation and transfer of photogenerated electrons and improves the catalyst stability. The above studies show that NaTaO3 based perovskite has a great potential in the field of photothermal catalyzed carbon dioxide reduction.

Study of CO2 hydrate formation on the surface of residue shell from dissociated CH4 hydrate

The use of hydrates to store CO2 is considered an effective method that can be implemented. However, the problems of interfacial hydrate film formation and low mass transfer efficiency when forming CO2 hydrate under static conditions still need to be solved. This study compared the growth modes of CH4 hydrate and CO2 hydrate under static conditions and believed that the wall-climbing growth mode of CH4 hydrate can be used to generate CO2 hydrate. It is proposed to use the residual shell of CH4 hydrate as a water-absorbing medium to change the mode in which CO2 hydrate is preferentially generated in the main body of the liquid phase. In this method, CO2 hydrate shows a faster formation rate and almost no induction time, which is attributed to the larger gas-liquid contact area provided by the shell, the residual ring in decomposed water on the surface, and the crystal structure inside the shell. When sodium dodecanoate (SD) is used as a promotor for CH4 hydrate to regenerate CO2 hydrate, the observation of the hydrate growth morphology shows that CO2 hydrate can grow on the CH4 hydrate shell. It does not have the wall climbing height of CH4 hydrate but grows toward the center of the reactor. When SDS is combined with SD to regenerate CO2 hydrate as an accelerator in the CH4 hydrate generation process, filamentous growth of CO2 hydrate can be observed.

Competitive adsorption mechanisms of multicomponent gases in kaolinite under electric fields: A molecular perspective

The investigation of the competitive adsorption mechanisms of gas mixtures within the inorganic nanopores of shale influenced by an electric field holds paramount importance for improving shale gas recovery and enhancing CO2 storage efficiency. This study employs molecular dynamics (MD) simulations to investigate the competitive adsorption mechanisms of gas mixtures on kaolinite surfaces. Subsequently, the engineering parameters governing electric field-enhanced CO2 sequestration and enhanced gas recovery (CS-EGR) are explored and optimized. In the absence of an electric field, the analysis reveals that water molecules exhibit the highest adsorption capacity in a ternary H2O–CO2–CH4 mixture, resulting in the formation of a water film of a specific thickness. CO2 displays a superior adsorption capability over CH4. As the CO2 volume injected into the reservoir increases, CH4 undergoes desorption due to the dominant adsorption effect of CO2. However, the efficiency of CO2 displacing CH4 diminishes significantly. The introduction of an electric field alters the equilibrium state of the gas mixture, leading to a further increase in CO2 adsorption and enhancing its selectivity relative to that of CH4 by 33%. These findings lay the foundation for the practical implementation of electric field-enhanced CS-EGR in shale reservoirs.

Coupling amino acid injection and slow depressurization with hydrate swapping exploitation: An effective strategy to enhance in-situ CO2 storage in hydrate-bearing sediment

Natural gas (mainly methane, CH4) hydrates are a prospective energy resource. CH4-CO2 hydrate swapping has the advantages of producing CH4 gas for clean energy recovery and simultaneously storing CO2 in-situ for carbon emission reduction. Depressurization is the most feasible strategy to recover CH4 from hydrate-bearing sediments. The combination of these two methods has been proved feasible to produce CH4-rich gas and store CO2-rich hydrate. However, the efficiencies of CH4 recovery and CO2 storage decrease significantly when the reservoir is depressurized to the points below CH4/CO2 mixed hydrate equilibrium pressure causing unwanted CO2-rich hydrate dissociation. In this work, amino acid injection (AAI) (L-tryptophan or L-methionine) was employed for CH4/CO2 mixed hydrate formation with enhanced CO2 storage, followed by slow depressurization in various controlled manners, i.e., multistep depressurization, constant-pressure depressurization or multistep constant-pressure depressurization (MCPD) to recover CH4 from the mixed hydrates. In-situ Raman and gas chromatograph (GC) were employed to confirm the compositions of mixed hydrates formed and mixed gases produced. The results showed that AAI decreased CO2 fraction from 30 mol% to 3.1–8.4 mol% in the residual gas, indicating the technique helped regaining reservoir pressure and kinetically promoting further hydrate formation. The pressure recovered by AAI compensated the performance discrepancy caused by different solutions injected. Raman spectra and GC results confirmed CO2-rich hydrate formation, and up to 91.3% CO2 was stored in the sediments. During mixed hydrate dissociation, slow depressurization maintained high CH4-rich gas production (CH4 fraction over 87.5 mol%), with 9.7–30.6% CH4-rich gas recovered and 5.8–17.9% water produced among various trials. The best performance of CO2 storage and CH4 recovery was achieved by AAI of 1000 ppm L-tryptophan at 33.2 bar and MCPD to 20.9 bar, showing a final CO2 storage efficiency of 82.3%, gas recovery percentage of 30.6% and gas/water production ratio of 37.9 STP m3/m3. These findings provided guidance to enhance CO2-rich hydrate storage and CH4-rich gas production by multiple AAI and slow depressurization at controlled depletion pressures after hydrate swapping.

Magnitude of and Hydroclimatic Controls on CO2 and CH4 Emissions in the Subtropical Monsoon Pearl River Basin

AbstractRivers are important ecosystems for carbon emissions and play a crucial role in the global carbon cycle. However, CO2 and CH4 emissions from subtropical rivers are substantially under‐represented in global‐scale estimates. Here, we explored the regional patterns of riverine CO2 and CH4 dynamics in the Pearl River basin with a subtropical monsoon climate. We found that its CO2 and diffusive CH4 emissions showed a decreasing trend with increasing stream order. Seasonality in CO2 and diffusive CH4 emissions was primarily driven by variations in partial pressure of CO2 (pCO2) and CH4 (pCH4) and gas transfer velocities, which were strongly regulated by hydrology and climate. We further estimated the basin‐wide CO2 and diffusive CH4 fluxes at 17.8 ± 7.4 Tg C yr−1 and 191.5 ± 139.9 Gg C yr−1, respectively. When normalized to the water surface, the mean diffusive fluxes were 790.1 and 8.5 mmol m−2 d−1 for CO2 and CH4, respectively, which were 1.3 and 2.5 times higher than the global mean riverine CO2 and CH4 fluxes, respectively. This suggests that the global significance of subtropical rivers is probably underestimated because their substantially higher CH4 fluxes are unaccounted for. Furthermore, compared with measured pCO2, the alkalinity‐based pCO2 could introduce significant errors by 20% at ∼30% of the sampling sites, underscoring the necessity of direct measurements to reduce uncertainty. This study provides the first estimate of basin‐wide CO2 and diffusive CH4 emissions in the PRB through direct pCO2 and pCH4 measurements, and highlights the role of hydrologic and climatic factors in governing riverine carbon emissions.

Biomass-derived sulfur-doped porous carbon for CO2 and CH4 selective adsorption

Series of sulfur-doped porous carbons were prepared by using glucose as carbon source and sodium dodecyl sulfate as sulfur source to synthesize sulfur-based carbon precursor and KOH as activator. Pore structure parameters and sulfur content of the prepared carbon materials could be facility regulated by controlling the ratio of KOH/sulfur-based carbon precursor and activation temperature, and their adsorptive separation properties towards CO2 and CH4 were investigated. Results showed that the higher the ultra-microporous volume and the S content of the prepared sulfur-doped porous carbon were, the larger the CO2 and the CH4 adsorption capacity were. The maximum adsorption capacity of CO2 (6.54 mmol/g, 273.15 K and 101 kPa, hereinafter) and CH4 (2.98 mmol/g), and the excellent selectivity of CO2/N2 (75.7) and CH4/N2 (22.8) were achieved by ACS-700-2 because of its higher ultra-microporous pore volume and the highest S content. Permeation experiment, cycle stability test and adsorption thermodynamics experiment show that the prepared S-doped porous carbon had good application potential in the separation and enrichment of CO2 in flue gas and CH4 in coalbed methane. In addition, the pore formation mechanism of sulfur-doped porous carbon was discussed.

Factor analysis and countermeasures for global warming based on data science methods

In recent years, the frequent and intensifying occurrence of extreme weather events such as heatwaves, floods, and storms worldwide has led scientists and policymakers to be increasingly concerned about the phenomenon of global warming. The global average temperature has steadily risen over the past few decades, and 2015-2022 has been identified as the warmest years on record. Taking global warming as the research object, the main problem is to find out the factors affecting climate change. The article predicts the global average temperature of the future and builds a model to analyse the relationship between global average temperature, time, location and the factors affecting climate change. The prediction models of ARMIA and EEMD-LSTM were built, and the model with the best fit was obtained after several iterations of tuning and trial optimization. The results showed that Flood, Storm, and Extreme temperature, had a high correlation with the global average temperature. The data of greenhouse gas indicators such as CO2, NO, and CH4, and catastrophes such as earthquakes, Volcanic activity, and wildfires have objective effects on global warming. Random forest regression model pairs were developed, and analysis of the importance of each component to the model showed that CO2 concentration and CH4 concentration had significant effects on global average temperature. Propose measures that can curb or slow down global warming.

Solar driven integrated CO2 capture and CH4 dry reforming via FexMny/Ni/CaAl multi-function materials

Integrated CO2 capture and dry reforming of CH4 (ICCU-DRM) holds great promise in mitigating greenhouse gas emissions and producing value-added syngas simultaneously. However, the in-situ conversion is a highly endothermic process, which requires a large amount of energy to drive, making it very difficult for large-scale applications. The combination of solar energy in ICCU-DRM provide a potential solution to tackle the problem, but it needs to construct and evaluate multi-function materials (MFMs) with good features of CO2 adsorption, catalytic conversion and light absorption. Herein, we report a synthesis approach to prepare Fe5Mn5/Ni/CaAl for use in the solar driven ICCU-DRM, which directly utilize the solar energy for syngas production with excellent comprehensive performance. The material prepared demonstrates an average spectral absorbance of 85.81 %, and a CO2 capacity of 8.46 mmol·g−1 with up to 89 % conversion to syngas. We expect the synthesis strategy has good implications on the development of innovative materials for carbon reduction and energy storage applications.

Rationally constructing metastable ZrO2 supported Ni catalysts for highly efficient and stable dry reforming of methane

The metastable Ni/ZrO2 catalysts were rationally constructed via reflux treatment and employed for dry reforming of methane. Reflux could suppress the transformation and improve the stability of the metastable ZrO2, as well as enrich its pore structure. Meanwhile, acidity-basicity, Zr3+ and oxygen vacancies were also promoted. Additionally, Ni dispersion was remarkably improved with increasing reflux time due to the abundant pores and enhanced metal-support interaction. These results illustrated the evaluation that prolonging reflux time could significantly proliferate the performance of Ni/ZrO2. Besides, reflux could strengthen the anti-carbon ability but the widened gap between CH4 dissociation and CO2 activation would cause more carbon deposition. The catalyst with reflux for 240 h showed the robust stability for 9000 min (CH4 conversion: 80 %; CO2 conversion: 88 %) at 750 °C. Furthermore, the mechanisms were discussed to unravel the origin of the accelerated performance by reflux and provide some references for designing efficient Ni-based catalyst.

A critical review on direct catalytic hydrogasification of coal into CH4: catalysis process configurations, evaluations, and prospects

Coal catalytic hydrogasification (CCHG) is a straightforward approach for producing CH4, which shows advantages over the mature coal-to-CH4 technologies from the perspectives of CH4 yield, thermal efficiency, and CO2 emission. The core of CCHG is to make carbon in coal convert into CH4 efficiently with a catalyst. In the past decades, intensive research has been devoted to catalytic hydrogasification of model carbon (pitch coke, activated carbon, coal char). However, the chemical process of CCHG is still not well understood because the coal structure is more complicated, and CCHG is a combination of coal catalytic hydropyrolysis and coal char catalytic hydrogasification. This review seeks to shed light on the catalytic process of raw coal during CCHG. The configuration of suitable catalysts, operating conditions, and feedstocks for tailoring CH4 formation were identified, and the underlying mechanisms were elucidated. Based on these results, the CCHG process was evaluated, emphasizing pollutant emissions, energy efficiency, and reactor design. Furthermore, the opportunities and strategic approaches for CCHG under the restraint of carbon neutrality were highlighted by considering the penetration of “green” H2, biomass, and CO2 into CCHG. Preliminary investigations from our laboratories demonstrated that the integrated CCHG and biomass/CO2 hydrogenation process could perform as an emerging pathway for boosting CH4 production by consuming fewer fossil fuels, fulfilling the context of green manufacturing. This work not only provides systematic knowledge of CCHG but also helps to guide the efficient hydrogenation of other carbonaceous resources such as biomass, CO2, and coal-derived wastes.

Optimizing alkali metal Salt-Induced structural assembly of Ni-MgO dual function materials for enhanced CO2 capture and methanation performance

Alkali metal salts (AMS) promoted Ni-MgO dual function materials (DFMs) show exhibit potential in integrated CO2 capture and methanation. However, the CO2 adsorption and methanation efficiency of these materials is contingent upon their adsorptive and catalytic sites, which are significantly susceptible to the incorporated AMS. Herein, we investigate the effect of assemble configuration of AMS and Ni on the structural properties and integrated CO2 capture and methanation performance of the AMS-promoted Ni-MgO DFMs. By preferentially incorporating AMS to form the Ni-AMS-MgO configuration, AMS is allocated throughout both the internal core and external layer of MgO particles. Given AMS's preferential occupation of specific pore structures, Ni is evenly distributed as smaller particles on the MgO surface, minimally influenced by the carbonate formed during adsorption. The Ni-AMS-MgO configuration demonstrates superior integrated CO2 capture and methanation performance, featuring high CO2 uptake (1.86 mmol/g) and CH4 yield (1.37 mmol/g).

Popping and Locking: Balanced Rigidity and Porosity of Zeolitic Imidazolate Frameworks for High-Productivity Methane Purification.

Zeolitic imidazolate frameworks (ZIFs) hold great promise in carbon capture, owing to their structural designability and functional porosity. However, intrinsic linker dynamics limit their pressure-swing adsorption application to biogas upgrading and methane purification. Recently, a functionality-locking strategy has shown feasibility in suppressing such dynamics. Still, a trade-off between structural rigidity and uptake capacity remains a key challenge for optimizing their high-pressure CO2/CH4 separation performance. Here, we report a sequential structural locking (SSL) strategy for enhancing the CO2 capture capacity and CH4 purification productivity in dynamic ZIFs (dynaZIFs). Specifically, we isolated multiple functionality-locked phases, ZIF-78-lt, -ht1, and -ht2, by activation at 50, 160, and 210 °C, respectively. We observed multiple-level locking through gas adsorption and powder X-ray diffraction. We uncovered an SSL mechanism dominated by linker-linker π-π interactions that transit to C-H···O hydrogen bonds with binding energies increasing from -0.64 to -2.77 and -5.72 kcal mol-1, respectively, as evidenced by single-crystal X-ray diffraction and density functional theory calculations. Among them, ZIF-78-ht1 exhibits the highest CO2 capture capacity (up to 18.6 mmol g-1) and CH4 purification productivity (up to 7.6 mmol g-1) at 298 K and 30 bar. These findings provide molecular and energetic insights into leveraging framework flexibility through the SSL mechanism to optimize porous materials' separation performance.

Interrelationships of CO2, CH4, and N2O fluxes in snow-covered temperate soils, Northern Japan

This study focuses on assessing the concentrations, fluxes, and production rates of greenhouse gases (CO2, CH4, and N2O) in a cold temperate grassland soil underlying snowpack during the winter of 1996/7 in northern Japan. Results included mean ± standard deviation (range) correlation coefficients (R2) for CO2–CH4 concentrations and CO2–N2O concentrations of 0.93 ± 0.07 (0.81–0.99) and 0.96 ± 0.06 (0.83–0.99) for winter, and 0.74 ± 0.17 (0.55–0.92) and 0.96 ± 0.05 (0.88–0.99) for summer, respectively. This suggests close relationships between the mechanisms of CO2 and N2O production and the oxidation of CH4, which are influenced by factors such as oxygen availability, temperature, and moisture in the soil. Furthermore, the study found that winter fluxes of CO2–CH4 and CO2–N2O through the snowpack showed positive linear correlations. Winter CO2 emissions accounted for 96 % of the variability in CH4 oxidation and 77 % of the variability in N2O emissions. This demonstrates that winter CO2 emissions were affected to the magnitude of CH4 oxidations and N2O emissions in the soil. These findings have implications for the modification of terrestrial ecosystem models in temperate regions, particularly in assessing contributions from winter greenhouse gas fluxes to overall annual emissions. Understanding the interrelationships and dynamics of greenhouse gases throughout the year is crucial for accurate modeling and predictions of ecosystem responses to climate change.

Electrochemically coupled CH4 and CO2 consumption driven by microbial processes

The chemical transformations of methane (CH4) and carbon dioxide (CO2) greenhouse gases typically have high energy barriers. Here we present an approach of strategic coupling of CH4 oxidation and CO2 reduction in a switched microbial process governed by redox cycling of iron minerals under temperate conditions. The presence of iron minerals leads to an obvious enhancement of carbon fixation, with the minerals acting as the electron acceptor for CH4 oxidation and the electron donor for CO2 reduction, facilitated by changes in the mineral structure. The electron flow between the two functionally active microbial consortia is tracked through electrochemistry, and the energy metabolism in these consortia is predicted at the genetic level. This study offers a promising strategy for the removal of CH4 and CO2 in the natural environment and proposes an engineering technique for the utilization of major greenhouse gases.

Chemical looping-based catalytic CH4 decomposition and successive coke gasification with CO2 on ordered mesoporous NiMCeOx (M = Co, Zr, La)

Highly ordered mesoporous NiLaCeOx mixed metal oxides were investigated as effective catalysts for the chemical looping-based dry reforming of methane (CH4) with carbon dioxide (CO2) (CL-DRM). This catalyst exhibited an excellent catalytic activity and stability in the decomposition of CH4 to form H2 with surface carbons subsequently activated by CO2 via reverse Boudouard reaction to form CO. Among the NiMCeOx catalysts with various promoter (M = Co, Zr, or La), the optimal NiLaCeOx catalyst preserved its original highly ordered mesoporous structures, leading to the higher dispersion of smaller Ni nanoparticles. This was attributed to the stronger Ni-Ce interactions facilitated by the La2O3 metal oxide promoter. The NiLaCeOx demonstrated a higher rate of H2 formation and successive CO production in the CL-DRM reaction, resulting in a H2/CO ratio above 1.0. Additionally, the NiLaCeOx catalyst exhibited superior structural stability over 5 cyclic CL-DRM reactions for CH4 decomposition (>85 %) and CO2 activation (>45 %), with minimal deposition of cokes.