CH4 Production Research Articles

Diel Greenhouse Gas Emissions Demonstrate a Strong Response to Vegetation Patch Types in a Freshwater Wetland

AbstractWetland methane (CH4) fluxes are highly variable over spatial and temporal scales due to variations in CH4 production, oxidation, and transport. While some aspects of temporal variability in CH4 fluxes are well documented, diel variability is poorly constrained, and studies report conflicting findings, making it difficult to generalize. Topographic, geochemical, hydroclimatic, and vegetative variability can result in characteristically different “patches” that likely influence differences in diel patterns. We investigated diel patterns of CH4 fluxes from a large seasonal‐mineral soil wetland in Maryland (USA) across three functionally unique patches: two with vegetation (emergent and submerged aquatic vegetation) and one without (open water) during the summer of 2021. To explore the relationships between vegetation, environmental conditions, and flux patterns, we also measured physiochemical variables (air and water temperature, pH, relative humidity, PAR, dissolved oxygen, and water depth). To our knowledge, this is the first study comparing diel variability using chambers across such distinct vegetation patch types. We found that diel patterns were strongly linked to patch types: CH4 fluxes from the emergent vegetation did not display a consistent diel pattern, while fluxes from the submerged vegetation and no vegetation patches frequently peaked at 13:00 and 05:00, respectively. These differences could be a direct result of vegetation impact on production, oxidation, and/or transport of CH4 or on conditions covarying with patch type. This study contributes to the growing understanding of how CH4 fluxes vary spatially over diel cycles and emphasizes the importance of considering spatially varying diel patterns when estimating fluxes.

Oxygen vacancies–elusive but common catalytic key defects for thermal upgrading of CO2 to CH4, CO and CH3OH

Single carbon products (C1 compounds) are simple but important chemicals in the road towards energy transition. Catalytic conversion of CO2 with H2 (desirably renewable) can be performed over reducible oxides supporting transition metals to obtain products such as CH4, CO and MeOH. Oxygen vacancies (O-vacancies), which are inherent defects of reducible metal oxides, play an enormous role in driving the catalytic performance (activity, selectivity, stability) for the desired reactions. Yet, the assessment of O-defects at realistic conditions is often complex. Only few techniques can provide direct evidence for their existence and influence in CO2 activation. Among them, electron paramagnetic spectroscopy (EPR), Raman spectroscopy, scanning probe microscopies (SPM) and environmental transmission electron microscopy (ETEM) are nowadays the most informative. In most cases, however, the measurements require reaction conditions far away from CO2 valorization applications. Although great efforts have been fruitful in explaining and demonstrating the huge importance of O-vacancies in CO2 catalysis, still ambiguous or erroneous interpretations about structure-function correlations involving O-vacancies are found in literature, especially, when information is not properly gathered, e.g., by O 1s ex-situ X-ray photon spectroscopy (XPS). Moreover, despite the recognized importance of O-vacancies for CO2 valorization, critical literature compilations about their effects in thermal processes are scarce. Herein, we attempt to contribute in closing this gap by integrally encompassing representative investigations on the thermo-catalytic production of CH4, CO and MeOH. Particularly, we emphasize in the proper selection of assessment tools (direct/indirect) to unambiguously establish structure-function relationships to design optimized O-defective catalysts for the targeted compounds.

New approach to agro-industrial solid and liquid waste management: Performance of an EGSB reactor at different hydraulic retention times for methane production

This study investigated the removal of agro-industrial wastes (5 g COD L⁻1 from coffee and 0.5 g COD L⁻1 from brewery wastewater, plus 1 g L⁻1 of coffee pulp and husk) in a continuous Expanded Granular Sludge Bed (EGSB) reactor at 35 °C. The effect of Hydraulic Retention Times (HRTs) of 72h, 48h, and 24h on CH₄ yield was examined using a mixed culture of cattle manure and granular sludge. Methane yields were 201, 124.5, and 113.8 mL CH₄ g⁻1 COD for the 1st, 2nd, and 3rd phases, respectively. Volatile fatty acids, particularly acetic acid, increased at lower HRTs. Sequencing of the 16S rRNA gene on the Illumina HiSeq platform revealed a syntrophic relationship between Syntrophorhabdus, Syntrophobacter, and Pseudomonas with methanogens Methanomassiliicoccus, Methanospirillum, and Methanobacterium, aiding in the removal of phenolic compounds. The study suggests that an HRT of 72h is optimal for maximizing CH₄ production in the EGSB reactor.

Very low Ru loadings boosting performance of Ni-based dual-function materials during the integrated CO2 capture and methanation process

Herein, the effect of the Ru:Ni bimetallic composition in dual-function materials (DFMs) for the integrated CO2 capture and methanation process (ICCU-Methanation) is systematically evaluated and combined with a thorough material characterization, as well as a mechanistic (in-situ diffuse reflectance infrared fourier-transform spectroscopy (in-situ DRIFTS)) and computational (computational fluid dynamics (CFD) modelling) investigation, in order to improve the performance of Ni-based DFMs. The bimetallic DFMs are comprised of a main Ni active metallic phase (20 wt%) and are modified with low Ru loadings in the 0.1–1 wt% range (to keep the material cost low), supported on Na2O/Al2O3. It is shown that the addition of even a very low Ru loading (0.1–0.2 wt%) can drastically improve the material reducibility, exposing a significantly higher amount of surface-active metallic sites, with Ru being highly dispersed over the support and the Ni phase, while also forming some small Ru particles. This manifests in a significant enhancement in the CH4 yield and the CH4 production kinetics during ICCU–Methanation (which mainly proceeds via formate intermediates), with 0.2 wt% Ru addition leading to the best results. This bimetallic DFM also shows high stability and a relatively good performance under an oxidizing CO2 capture atmosphere. The formation rate of CH4 during hydrogenation is then further validated via CFD modelling and the developed model is subsequently applied in the prediction of the effect of other parameters, including the H2 inlet concentration, inlet flow rate, dual-function material weight, and reactor internal diameter.

The biological mechanism of a lower carbon/nitrogen ratio increases methane emissions during vegetable waste composting

The initial carbon/nitrogen (C/N) ratio is one of the most important factors impacting composting processes, such as methane (CH4) emissions. However, the effects of the C/N ratio on CH4 emissions and the associated biological mechanisms during vegetable waste composting are largely unknown. In this study, a lab-scale experiment was conducted to investigate the effects of different C/N ratios on CH4 emissions and the mechanisms associated with methane-metabolizing microorganisms (methanogens and methanotrophs) during capsicum straw composting. The initial C/N ratios were set to 18, 30 and 50 to simulate the low (L), medium (M) and high (H) C/N ratios, respectively. The results showed that CH4 emissions were mainly concentrated in the thermophilic phase and that the cumulative CH4 emissions were significantly greater in the L treatment than in the M and H treatments by 10.8 and 15.4 times, respectively. During the methanogenic process, the relative abundance of the dominant genus Methanoculleus (47.59 % ∼ 76.92 %) was higher than in the L treatment than in the M and H treatments at the thermophilic and maturation stages, and the Chao1 index and the mcrA gene abundance followed the order of L > M > H at each composting stage. During the methanotrophic process, the dominant genus unclassified_d_bacteria (51.3 % ∼ 91.87 %), Chao1 index, pmoA gene abundance and CO2 emissions were in the order of L > M > H at each composting stage. This pattern suggests that a lower C/N ratio simultaneously enhanced CH4 production and oxidation. A structural equation model further revealed that the methanogenic community, which was driven directly by the relative contents of hemicellulose and cellulose in the substrates, as indicated by the C/N ratio, made greater contributions to CH4 emissions than did the methanotrophic community. In conclusion, a lower C/N ratio increased CH4 emissions mainly by regulating the population and composition of methanogen community.

In vitro ruminant fermentation, degradation, and methane production of four agro-industrial protein-rich co-products, compared with soyabean meal

Soyabean is considered an unsustainable protein source for livestock feeds because of the large quantity of input and energy required to cultivate and process it. Other protein-based agro-industrial co-products that are less input-intensive, can mitigate methane (CH4) production and may therefore be more sustainable options instead soyabean. The objective of this study was to compare the effect of replacing the same amount of protein (40g/kg DM crude protein) as soyabean meal (SBM) with low-carbon local agro-industrial co-products, (brewers’ spent grains, BSG; dried wheat distillers’ grains, WDG; dried corn distillers’ grains, CDG and corn steep liquor CSL), on in vitro rumen degradation, fermentation and gas and methane production. The study used a 72-hour in vitro gas production method with a basal substrate of dried, ground grass silage and wheat. Gas volumes were measured at eleven different specific intervals, and CH4 concentrations were analysed via gas chromatography. After 72hours, in vitro DM degradability (IVDMD) and volatile fatty acid (VFA) concentrations were assessed. Gas and CH4 production curve profiles were fitted to models to determine asymptote production, the extent of degradation in rumen proper (RoP), and the fractional degradation rate (μ) (h-1) in the halfway 50% of the asymptote production. The IVDMD and estimated RoP at 0.04h and 0.025h were lower (P<0.05) for BSG compared to the other treatments, by 4.9 – 6.6%; 5.8 - 9.9%; 5.2 - 9.0%. Gas and CH4 yield (mL/g substrate and mL/g substrate degraded), and pH (SB = 6.77, BSG = 6.80, WDG = 6.74, CDG = 6.84, and CSL = 6.73; P>0.05), were not significantly affected by treatment. Butyrate and valerate were lower (P<0.05) for BSG compared to CSL, and caproate was lower (P<0.001) for BSG compared to the other treatments and in CSL compared to SBM. The results regarding degradability and VFAs concentrations of this study demonstrated that dried wheat distillers’ grains, dried corn distillers’ grains, and corn steep liquor have the potential to replace soyabean meal as protein sources for ruminants, but further reduction of CH4 emissions as a result of such practice may not be expected. Although slightly less degradable, based on their nutrient composition and the fact they did not affect rumen fermentation characteristics, brewers' spent grains can still play a complementary role in ruminant diets, especially in regions where they are locally readily available.

Impact of Side Chains in 1-n-Alkylimidazolium Ionomers on Cu-Catalyzed Electrochemical CO2 Reduction.

This study presents the impact of the side chains in 1-n-alkylimidazolium ionomers with varying side chain lengths (CnH2n+1 where n = 1, 4, 10, 16) on Cu-catalyzed electrochemical CO2 reduction reaction (CO2RR). Longer side chains suppress the H2 and CH4 formation, with the n-hexadecyl ionomer (n = 16) showing the greatest reduction in kinetics by up to 56.5% and 60.0%, respectively. On the other hand, C2H4 production demonstrates optimal Faradaic efficiency with the n-decyl ionomer (n = 10), a substantial increase of 59.9% compared to its methyl analog (n = 1). Through a combination of density functional theory calculations and material characterization, it is revealed that the engineering of the side chains effectively modulates the thermodynamic stability of key intermediates, thus influencing the selectivity of both CO2RR and hydrogen evolution reaction. Moreover, ionomer engineering enables industrially relevant partial current density of -209.5 mA cm-2 and a Faradaic efficiency of 52.4% for C2H4 production at 3.95 V, even with a moderately active Cu catalyst, outperforming previous benchmarks and allowing for further improvement through catalyst engineering. This study underscores the critical role of ionomers in CO2RR, providing insights into their optimal design for sustainable chemicalsynthesis.

Insight into the Pyrolysis Behaviors of Petroleum-Driven Mesophase Pitch via ReaxFF Molecular Dynamics and In Situ TG-FTIR/MS.

Mesophase pitch is regarded as a profoundly promising candidate for the production of advanced carbon-based multifunctional materials such as carbon fibers, carbon microspheres, and carbon foams owing to its excellent intrinsic properties. Consequently, a deeper understanding of pyrolytic chemistry is indispensable for the efficient and environmentally friendly utilization of mesophase pitch. In this study, details about the structure compositions and microscopic morphologies of petroleum-driven mesophase pitch (pMP) were investigated through ultimate, FTIR, XPS, and 13C-NMR analyses. Furthermore, a large-scale molecular model of typical pMP with 11,835 atoms was constructed to unveil the comprehensive pyrolysis behaviors and the underlying reactions. Significantly, the evolution of specific chemical bonds and the decomposition of crucial molecular fragments were elucidated within an amalgamation of experimental TG-FTIR/MS and ReaxFF MD simulation. Accordingly, three fundamental reaction stages were artificially divided, including the low-temperature reaction, rapid thermal decomposition, and the molecular condensation reaction. During the rapid thermal decomposition stage, the cleavages of C-C and C-O bonds cooperatively contributed to the formation of C2H4 and H2O gaseous products. As the temperature escalated to the molecular condensation stage, the pyrolysis process was governed by the dehydrogenation condensation, accompanied by an augmentation of C-C and H-H bonds and a diminution of C-O and C-H bonds. Additionally, the rare graphitization phenomenon was observed, suggesting a remarkable degree of structural organization in pMP. Overall, the results of ReaxFF MD simulations complement experimental observations, successfully reproducing the microstructure of pMP and atomic-scale pyrolysis behavior, thereby providing invaluable insights for the rational guidance of efficient utilization of pMP and other related carbonaceous precursors.

Enhanced Local CO Coverage on Cu Quantum Dots for Boosting Electrocatalytic CO2 Reduction to Ethylene

AbstractEthylene (C2H4) electrosynthesis from the electrocatalytic CO2 reduction process holds enormous potential applications in industrial production. However, the sluggish kinetics of C─C coupling often result in low yield and poor selectivity for C2H4 production. Herein, the performance of Cu catalysts of varying sizes is investigated, prepared via a cryo‐mediated liquid phase exfoliation technique, for the electrochemical CO2 reduction to C2H4. The activity and selectivity of C2H4 gradually increase as the size of the Cu catalysts decreases from tens of nanometers to a few nanometers. Impressively, the 5 nm Cu quantum dots (Cu‐5) achieve a maximum C2H4 Faradaic efficiency (FE) of 81.5% and a half‐cell cathodic energy efficiency (CEE) of 42.2% with a large partial current density of 1.1 A cm−2 at −0.93 V versus the reversible hydrogen electrode. Structural characterization and in situ spectroscopic analysis reveal that the Cu‐5 quantum dots, dominated by the (100) facet, provide an abundance of active sites that enhance CO2 adsorption and activation, promoting the formation of *CO intermediates. The accumulation of *CO intermediates on the Cu active sites facilitates the CO‐CHO coupling reaction, thus enhancing the C2H4 production rate.

CO2 methanation: a bibliometric analysis and review of activated carbon-based materials (2014–24)

Abstract This study highlights the significant potential of activated carbon (AC)-based materials in environmental remediation and energy production, particularly in converting carbon dioxide (CO2) and hydrogen (H2) into methane (CH4) and water (H2O) using transition metal-based catalysts. It emphasizes the role of porous AC in waste reduction and resource utilization, examining various applications of CO2 and evaluating environmental impacts. The research explores commercialization opportunities and specifically investigates CO2 methanation using AC-based materials. Using bibliometric analyses of 4196 articles from the Web of Science database, the study identifies a growing research interest in porous AC-related CO2 methanation from 2014 to 2024. The top three journals in this field are Environment Development and Sustainability, Biomass Conversion and Biorefinery, and Journal of Environment Science and Pollution. However, there is limited inter-institutional collaboration in this field, suggesting room for development towards commercializing sustainable CH4 production pathways. CH4 is highlighted as a crucial intermediate in industrial processes, and research directions are identified through co-occurring author keywords analysis. The study suggests the need for a comprehensive approach integrating AC materials into carbon-neutral energy processes while addressing the potential adverse effects of AC nanoparticles on biological and environmental factors. Ultimately, it clarifies the potential uses and commercialization prospects for porous AC materials, especially in conjunction with carbon capture and utilization technologies, promoting sustainable practices in energy production and environmental management.

Copper Atom Pairs Stabilize *OCCO Dipole Toward Highly Selective CO2 Electroreduction to C2H4

AbstractDeeply electrolytic reduction of carbon dioxide (CO2) to high‐value ethylene (C2H4) is very attractive. However, the sluggish kinetics of C−C coupling seriously results in the low selectivity of CO2 electroreduction to C2H4. Herein, we report a copper‐based polyhedron (Cu2) that features uniformly distributed and atomically precise bi‐Cu units, which can stabilize *OCCO dipole to facilitate the C−C coupling for high selective C2H4 production. The C2H4 faradaic efficiency (FE) reaches 51 % with a current density of 469.4 mA cm−2, much superior to the Cu single site catalyst (Cu SAC) (~0 %). Moreover, the Cu2 catalyst has a higher turnover frequency (TOF, ~520 h−1) compared to Cu nanoparticles (~9.42 h−1) and Cu SAC (~0.87 h−1). In situ characterizations and theoretical calculations revealed that the unique Cu2 structural configuration could optimize the dipole moments and stabilize the *OCCO adsorbate to promote the generation of C2H4.

Fungal Methane Production Under High Hydrostatic Pressure in Deep Subseafloor Sediments

Fungi inhabiting deep subseafloor sediments have been shown to possess anaerobic methane (CH4) production capabilities under atmospheric conditions. However, their ability to produce CH4 under in situ conditions with high hydrostatic pressure (HHP) remains unclear. Here, Schizophyllum commune 20R-7-F01, isolated from ~2 km below the seafloor, was cultured in Seawater Medium (SM) in culture bottles fitted with sterile syringes for pressure equilibration. Subsequently, these culture bottles were transferred into 1 L stainless steel pressure vessels at 30 °C for 5 days to simulate in situ HHP and anaerobic environments. Our comprehensive analysis of bioactivity, biomass, and transcriptomics revealed that the S. commune not only survived but significantly enhanced CH4 production, reaching approximately 2.5 times higher levels under 35 MPa HHP compared to 0.1 MPa standard atmospheric pressure. Pathways associated with carbohydrate metabolism, methylation, hydrolase activity, cysteine and methionine metabolism, and oxidoreductase activity were notably activated under HHP. Specifically, key genes involved in fungal anaerobic CH4 synthesis, including methyltransferase mct1 and dehalogenase dh3, were upregulated 7.9- and 12.5-fold, respectively, under HHP. Enhanced CH4 production under HHP was primarily attributed to oxidative stress induced by pressure, supported by intracellular reactive oxygen species (ROS) levels and comparative treatments with cadmium chloride and hydrogen peroxide. These results may provide a strong theoretical basis and practical guidance for future studies on the contribution of fungi to global CH4 flux.

Mesostructure‐Specific Configuration of *CO Adsorption for Selective CO2 Electroreduction to C2+ Products

AbstractThe multi‐carbon (C2+) alcohols produced by electrochemical CO2 reduction, such as ethanol and n‐propanol, are considered as indispensable liquid energy carriers. In most C−C coupling cases, however, the concomitant gaseous C2H4 product results in the low selectivity of C2+ alcohols. Here, we report rational construction of mesostructured CuO electrocatalysts, specifically mesoporous CuO (m‐CuO) and cylindrical CuO (c‐CuO), enables selective distribution of C2+ products. The m‐CuO and c‐CuO show similar selectivity towards total C2+ products (≥76 %), but the corresponding predominant products are C2+ alcohols (55 %) and C2H4 (52 %), respectively. The ordered mesostructure not only induces the surface hydrophobicity, but selectively tailors the adsorption configuration of *CO intermediate: m‐CuO prefers bridged adsorption, whereas c‐CuO favors top adsorption as revealed by in situ spectroscopies. Computational calculations unravel that bridged *CO adsorbate is prone to deep protonation into *OCH3 intermediate, thus accelerating the coupling of *CO and *OCH3 intermediates to generate C2+ alcohols; by contrast, top *CO adsorbate is apt to undergo conventional C−C coupling process to produce C2H4. This work illustrates selective C2+ products distribution via mesostructure manipulation, and paves a new path into the design of efficient electrocatalysts with tunable adsorption configuration of key intermediates for targeted products.

Assessing the Impact of Climate Change on Methane Emissions from Rice Production Systems in Southern India

The impact of climate change on methane (CH4) emissions from rice production systems in the Coimbatore region (Tamil Nadu, India) was studied by leveraging field experiments across two main treatments and four sub-treatments in a split-plot design. Utilizing the closed-chamber method for gas collection and gas chromatography analysis, this study identified significant differences in CH4 emissions between conventional cultivation methods and the system of rice intensification (henceforth SRI). Over two growing seasons, conventional cultivation methods reported higher CH4 emissions (range: from 36.9 to 59.3 kg CH4 ha−1 season−1) compared with SRI (range: from 2.2 to 12.8 kg CH4 ha−1 season−1). Experimental data were subsequently used to guide parametrization and validation of the DeNitrification–DeComposition (DNDC) model. The validation of the model showed good agreement between the measured and modeled data, as denoted by the statistical tests performed, which included CRM (0.09), D-index (0.99), RMSE (7.16), EF (0.96), and R2 (0.92). The validated model was then used to develop future CH4 emissions projections under various shared socio-economic pathways (henceforth SSPs) for the mid- (2021–2050) and late (2051–2080) century. The analysis revealed a potential increase in CH4 emissions for the simulated scenarios, which was dependent on specific soil and irrigation management practices. Conventional cultivation produced the highest CH4 emissions, but it was shown that they could be reduced if the current practice was replaced by minimal flooding or through irrigation with alternating wetting and drying cycles. Emissions were predicted to rise until SSP 370, with a marginal increase in SSP 585 thereafter. The findings of this work underscored an urgency to develop climate-smart location-specific mitigation strategies focused on simultaneously improving current water and nutrient management practices. The use of methanotrophs to reduce CH4 production from rice systems should be considered in future work. This research also highlighted the critical interaction that exists between agricultural practices and climate change, and emphasized the need to implement adaptive crop management strategies that can sustain productivity and mitigate the environmental impacts of rice-based systems in southern India.

Effects of Oregano on Lactation Performance, Nutrient Digestibility, Ruminal Fermentation Parameters, and Methane Emissions in Dairy Cows: A Meta-Analysis

Growing concerns regarding antibiotic use in livestock, due to antibiotic resistance and potential human transmission, have led to increased interest in herbs and their derivatives, including essential oils, which possess antimicrobial properties that may enhance overall productivity and serve as a strategy for methane mitigation. The objective of this meta-analysis was to investigate the effects of adding oregano to the diet in different forms (essential oils, plant materials, or leaves) on the dry matter intake (DMI), milk yield (MY), milk components, nutrient digestibility, ruminal fermentation parameters, and methane (CH4) emissions of dairy cows. A literature search was conducted to identify papers published from 2000 to 2023. Effect size for all outcomes was reported as a standardized means difference (SMD) and raw means difference with 95% confidence intervals. Heterogeneity was determined using the Q test and I2 statistic. The results of the meta-analysis indicated that adding oregano had no effect on DMI (SMD = 0.081; p = 0.507) and MY (SMD = 0.060; p = 0.665). Milk fat percentage, milk protein percentage, and milk lactose percentage were not affected by oregano. The addition of oregano to the diet significantly decreased dry matter digestibility (SMD = −0.502; p = 0.013), crude protein digestibility (SMD = −0.374; p = 0.040), and neutral detergent fiber digestibility (SMD = −0.505; p = 0.014). Ruminal pH (SMD = −0.122; p = 0.411), total volatile fatty acids concentration (SMD = −0.038; p = 0.798), acetate (SMD = −0.046; p = 0.757), propionate (SMD = 0.007; p = 0.960), and butyrate (SMD = 0.037; p = 0.801) proportion were not affected by oregano. The addition of oregano to the diet tended to decrease CH4/DMI (SMD = −0.275; p = 0.095) but did not affect CH4 production (SMD = −0.156; p = 0.282). Heterogeneity (Q and I2) was non-significant for all parameters. We conclude that the inclusion of oregano in various forms (essential oils, plant materials, or leaves) in the diet of dairy cows reduces nutrient digestibility but does not significantly affect DMI, MY, milk components, ruminal fermentation parameters, or CH4 production. Future research should focus on optimizing the dosage of oregano (both EOs and plant materials) and exploring the impact of its form on lactation, nutrient digestibility, ruminal fermentation, and CH4 emissions in dairy cows.

Intrinsic reactivity of stoichiometric IrO2(1 1 0) surface toward oxidative coupling of methane

This study investigates the oxidative coupling of methane on the IrO2(110) surface using TPRS simulations informed by DFT-derived data. We discover that the efficiency of the IrO2(110) surface in generating ethylene is strongly influenced by methane surface coverage. Our simulations reveal that the presence of surface hydroxyl group enhances the yield of C2+ species from methane oxidation, but this effect is counteracted at high methane coverages due to the accelerated formation of CH2OH. In addition, the study reveals that slight modifications in energy barriers at the branching point (C2H4 formation vs. CH2OH formation) significantly affect C2H4(g) production from the simulation, underscoring the importance of precise energetic data for accurate catalytic reaction predictions. The results have broader implications for reactions and catalysts where branching point selectivity determines high-value product yields. Thus, combining surface science with computational analysis is crucial for accurately determining energy profiles of key steps at the branching points.

Nanostructural evolution by applying various fuels in combustion design of CuZnAl mixed-oxides over HZSM-5 used in one-step production of CH3–O–CH3

The influence of different fuels (urea, ethylene glycol and citric acid) in combustion-based design of nano-structured CuO–ZnO–Al2O3/HZSM-5 catalyst was investigated. The catalytic performance were evaluated in a single step production of dimethyl ether form syngas. The X-ray diffraction, Field emission scanning electron microscopy, Transmission electron microscopy, Energy-dispersive x-ray, Temperature Programmed Reduction-H2, N2 Adsorption and Desorption isotherms and Fourier-transform infrared spectroscopy techniques were used to characterize physico-chemical properties of prepared nanocatalysts. The X-ray diffraction results clarified that application of citric acid increased relative crystallinity of Cu and Zn oxides existed in catalyst structure. The Fourier-transform infrared spectroscopy results demonstrated that the zeolite structure was not destroyed after CuO–ZnO–Al2O3/HZSM-5 introduction. The Field emission scanning electron microscopy and Transmission electron microscopy images illustrated that the nanocatalyst synthesized with citric acid has the highest porosity and less population of particle agglomerations. The highest amount of surface area was obtained when citric acid was used as fuel. According to Temperature Programmed Reduction-H2 profiles, the reducibility of nanocatalyst synthesized with citric acid is higher than other samples. The activity of the fabricated nanocatalysts for syngas to Dimethyl ether process were tested at temperature and pressure range of 225–300 °C and 10–40 bar, respectively. Using citric acid as fuel led to achieve greater amount carbon monoxide conversion and Dimethyl ether yield. Furthermore, stability test represented that the activity of this nanocatalyst remained quite stable during 1060 min.

Plasma-driven non-oxidative coupling of methane to ethylene and hydrogen at mild temperature over CuxO/CeO2 catalyst

We report one-step non-oxidative coupling of methane (CH4) to ethylene (C2H4) at atmospheric pressure and mild temperature (ca. 180–190 °C), by a combination of non-thermal plasma and a CuOx/CeO2 catalyst. The C2H4 selectivity gradually increases during an induction period. The corresponding spent catalysts at different stages were systematically characterized to disclose the evolution of the CuOx/CeO2 catalyst. During the induction period, the CuO/CeO2 catalyst was partially reduced to generate Cu+, Ce3+ and Ov species, which accompany the formation of Cu+-Ov-Ce3+ sites, as proven by XRD, HRTEM, XPS, Raman, EPR and H2-TPR. In addition, the C2H4 selectivity is proportional to the fraction of Cu+, Ce3+, Ov and Cu-O-Ce species, which indicates that Cu+-Ov-Ce3+ is the active site for non-oxidative coupling of CH4 to C2H4. Furthermore, in-situ FTIR results indicate that the Cu+-Ov-Ce3+ interface sites can promote dehydrogenation of CH3* (from CH4 plasma) to produce CH2* on the catalyst surface, which is the basic reason why CuOx/CeO2 acts as a catalyst in speeding up the non-oxidative coupling of CH4 for C2H4 production.

Performance Effects of Different Shutdown Methods on Three Electrode Materials for Electromethanogenesis

AbstractIndustrial applications of microbial electrochemical systems will require regular maintenance shutdowns, involving inspections and component replacements to extend the lifespan of the system. Here, we examined the impact of such shutdowns on the performance of three electrode materials (i. e., platinized titanium, graphite, and nickel) as cathodes in a microbial electrochemical system that would be used for electromethanogenesis in power‐to‐gas applications. We focused on methane (CH4) production from hydrogen (H2) and carbon dioxide (CO2) using Methanothermobacter thermautotrophicus. We showed that the platinized titanium cathode resulted in high volumetric CH4 production rates and Coulombic efficiencies. Using a graphite cathode would be more cost‐effective than using the platinized titanium cathode in microbial electrochemical systems, but showed an inferior performance. The microbial electrochemical system with the nickel cathode showed improvements compared to the graphite cathode. Additionally, this system with a nickel cathode demonstrated the fastest recovery during a shutdown experiment compared to the other two cathodes. Fluctuations in pH and nickel concentrations in the catholyte during power interruptions affected CH4 production recovery in the system with the nickel cathode. This research enhances understanding of the integration of biological and electrochemical processes in microbial electrochemical systems, providing insights into electrode selection and operating strategies for effective and sustainable CH4 production.

A hybrid electro-thermochemical device for methane production from the air

Coupling direct air capture (DAC) with methane (CH4) production is a potential strategy for fuel production from the air. Here, we report a hybrid electro-thermochemical device for direct CH4 production from air. The proposed device features the cogeneration of carbon dioxide (CO2) and hydrogen (H2) in a single compartment via a bipolar membrane electrodialysis module, avoiding a separate water electrolyzer, followed by a thermochemical methanation reaction to produce CH4. H2-induced disturbances lead to efficient CO2 extraction without pumping requirement. The energy consumption and techno-economic analysis predict an energy reduction of 37.8% for DAC and a cost reduction of 36.6% compared with the decoupled route, respectively. Accordingly, CH4 cost is reduced by 12.6%. Our proof-of-concept experiments show that the energy consumption for CO2 release and H2 production is 704.0 kJ mol−1 and 967.4 kJ mol−1, respectively with subsequent methanation achieving a 97.3% conversion of CO2 and a CH4 production energy of 5206.4 kJ mol−1 showing a promising pathway for fuel processing from the air.