CH4 Generation Research Articles

Single-Atom Pt Anchored Polyoxometalate as Electron-Proton Shuttle for Efficient Photoreduction of CO2 to CH4 Catalyzed by NiCo Layered Doubled Hydroxide.

The crucial role of active hydrogen (H*) in photocatalytic CO2 methanation has long been overlooked, although recently, accelerating proton-coupled electron transfer (PCET) processes to enhance CH4 productivity and selectivity has garnered significant attention. Herein, a single-atom Pt-anchored H3PMo12O40 (Pt1-PMo12) is applied as an efficient proton-electron shuttle to facilitate the photocatalytic performance of NiCo layered double hydroxide (NiCo-LDH). The resultant Pt1-PMo12@NiCo-LDH exhibited superior CH4 productivity (723µmolg-1h-1) with CH4 selectivity of 82.3%, showcasing a 24.9 times productivity enhancement over NiCo-LDH (29µmolg-1h-1). Systematic investigations revealed that abundant H* is generated by the dissociation of H2O on Pt1 sites and stored within Pt1-PMo12. Subsequently, the multiple H* rapidly migrated from Pt1-PMo12 to the catalytic sites on NiCo-LDH by the engineered strong Mo─O─Ni/Co bonds, thereby significantly expediting the PCET process. The in situ DRIFTS and theoretical calculations elucidated that the Pt1-PMo12 decreased the energy barrier for *CO protonation to *CHO (0.38-0.18eV) and optimized the rate-determining step of *CH3 to *CH4 (0.64eV), thus promoting highly active and selective CH4 generation. This work provided novel insights into achieving efficient photocatalytic CO2 methanation by modulating the fast generation and transport of active H*.

Highly Selective Conversion of Carbon Dioxide to Methane by Copper Single Atom Electrocatalysts.

Electrocatalytic carbon dioxide reduction into high-value chemicals is one of the important solutions to the greenhouse effect and energy crisis. However, the slow kinetic process of eight electrons requires the development of efficient catalysts to improve the yields. Single atom catalysts (SACs) with high activity and selectivity have become an emerging research frontier in the field of heterogeneous catalysis. Herein, a catalyst comprised of Cu single atoms loaded on carbon substrate (Cu-NC) is developed for highly selective electrocatalytic reduction of CO2 to methane (CH4). The optimal catalyst (Cu-NC-1-4) exhibits a faradaic efficiency (FE) of over 50 % for CH4 within a wide potential window from -1.3 V to -1.8 V (vs. RHE) and the highest FE of CH4 is up to 67.22 % at -1.6 V (vs. RHE). Meanwhile, the product selectivity of CH4 among all the carbon products reaches 93.00 %, and the activity decay can be negligible via the 70-hour-stability-test. The existence of atomic dispersed Cu-N3 sites was verified by high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption near edge structure (XANES). Density functional theory (DFT) calculations show that the effective adsorption of the key intermediate *CO on Cu-N3 sites prompts the generation of CH4.

Effects of Chitosan-Based Additive on Rumen Fermentation and Microbial Community, Nutrients Digestibility and Lactation Performance in Goats.

Recently, the potential of using chitosan (CHI) as a feed additive to enhance ruminal fermentation and improve animal performance has gained increasing attention in ruminant nutrition. This study was undertaken to investigate the effect of dietary supplementation with increasing doses of CHI on rumen fermentation attributes and microbial composition, digestibility and milk performance in Dhofari goats. Twenty-four lactating goats (27 ± 1.8 kg of initial live body weight) were fed a control diet comprising of Rhodes grass hay plus a concentrate feed mixture. Goats were assigned to one of three experimental treatments (n = 8 per treatment) as: (1) control diet with no supplement (CTRL), (2) control diet with 0.300 g/day CHI (CHI0.3) and (3) control diet supplemented with 0.600 g/day CHI (CHI0.6) for a 45-day experimental period. Dietary supplementation with increasing doses of CHI decreased (p < 0.05) linearly ruminal pH (p = 0.023), total short chain fatty acids concentrations (p = 0.011), acetate (p = 0.013) and butyrate (p = 0.042) proportions, acetate to propionate ratio (p < 0.001), estimated methane (CH4) production (p < 0.001), ammonia nitrogen concentrations (p = 0.003) and protozoa abundance (p = 0.003). However, the ruminal propionate proportion augmented (p = 0.002) linearly with increasing doses of CHI in the diet. Increasing doses of CHI linearly increased the abundance of the ruminal propionate-producing bacteria, while diminished acetate and CH4-producing bacteria (p < 0.05). Serum total protein (p = 0.037) and glucose (p = 0.042) levels linearly increased as CHI doses increased in the diet. However, serum UREA levels decreased linearly (p = 0.002) by 21% with increasing CHI amounts in the diet. The digestibility of organic matter, crude protein and neutral detergent fibre increased linearly with the increasing CHI doses (p < 0.05). Neither linear nor quadratic responses (p > 0.05) were observed in daily milk yield and feed efficiency by supplementing the diet with CHI. In conclusion, supplementing the diet with CHI at a dose of 0.600 g/day as a feed additive for dairy goats reduced estimated CH4 generation and improved fibre and protein digestion, with no influence on feed intake, milk yield or composition.

Combined metabolomic and microbial community analyses reveal that biochar and organic manure alter soil C-N metabolism and greenhouse gas emissions

The use of biochar to reduce the gas emissions from paddy soils is a promising approach. However, the manner in which biochar and soil microbial communities interact to affect CO2, CH4, and N2O emissions is not clearly understood, particularly when compared with other amendments. In this study, high-throughput sequencing, soil metabolomics, and quantitative real-time PCR were utilized to compare the effects of biochar (BC) and organic manure (OM) on soil microbial community structure, metabolomic profiles and functional genes, and ultimately CO2, CH4, and N2O emissions. Results indicated that BC and OM had opposite effects on soil CO2 and N2O emissions, with BC resulting in lower emissions and OM resulting in higher emissions, whereas BC, OM, and their combined amendments increased cumulative CH4 emissions by 19.5 %, 31.6 %, and 49.1 %, respectively. BC amendment increased the abundance of methanogens (Methanobacterium and Methanocella) and denitrifying bacteria (Anaerolinea and Gemmatimonas), resulting in an increase in the abundance of mcrA, amoA, amoB, and nosZ genes and the secretion of a flavonoid (chrysosplenetin), which caused the generation of CH4 and the reduction of N2O to N2, thereby accelerating CH4 emissions while reducing N2O emissions. Simultaneously, OM amendment increased the abundance of the methanogen Caldicoprobacter and denitrifying Acinetobacter, resulting in increased abundance of mcrA, amoA, amoB, nirK, and nirS genes and the catabolism of carbohydrates [maltotriose, D-(+)-melezitose, D-(+)-cellobiose, and maltotetraose], thereby enhancing CH4 and N2O emissions. Moreover, puerarin produced by Bacillus metabolism may contribute to the reduction in CO2 emissions by BC amendment, but increase in CO2 emissions by OM amendment. These findings reveal how BC and OM affect greenhouse gas emissions by modulating soil microbial communities, functional genes, and metabolomic profiles.

Constructing type II heterojunction of 2D/1D Pg-C3N4/Ag3VO4 nanocomposite with high interfacial charge separation for boosting photocatalytic CO2 reduction under solar energy

The well-designed, template-free synthesis of 2D protonated g-C3N4 nanosheets (Pg-C3N4) coupled with novel 1D Ag3VO4 nanorods has been investigated to construct 2D/1D interface heterostructures with strong electrostatic interactions between the positively charged 2D Pg-C3N4 nanosheets and the negatively charged 1D Ag3VO4 nanorods. The coupling of Pg-C3N4 and Ag3VO4 with desirable characteristics resulted in a 2D/1D interface heterojunction with a type II charge carrier transfer mechanism, effectively maintaining and utilizing charge carriers. The 2D/1D Pg-C3N4/Ag3VO4 exhibited remarkable photocatalytic performance for CO2 conversion with H2O, resulting in maximum CH4 and dimethyl ether (DME) production of 352.3 and 130.9 µmol/g-cat, respectively. A quantum yield of 0.23 % for CH4 generation was achieved over the 2D/1D Pg-C3N4/Ag3VO4, which was 2.9 and 1.4 times higher than that of the Pg-C3N4 and Ag3VO4 samples, respectively. The improvement in photocatalytic performance primarily stems from the effective interaction between Pg-C3N4 and ternary Ag3VO4, leading to enhanced transfer and separation of photoinduced charge carriers through the creation of a type II heterojunction. The findings of this study are useful in designing template-free heterojunctions for photocatalytic CO2 conversion and other solar energy applications.

Pyrolysis characteristics and hydrogen production mechanism of biomass impregnated with transition metals

The application of metal impregnation pretreatment to improve the quality of biomass pyrolysis gas production is considered as a promising upgrading technology. Transition metals have been well developed for the unique structural characteristics. After impregnation pretreatment, the product distribution of biomass pyrolysis was changed, and the transfer path of H atoms and the formation mechanism of H2 can be revealed through analysis. The effects of impregnation pretreatment with three different transition metals (iron, cobalt, and nickel) on the pyrolysis characteristics of corn straw were evaluated in this work. Three transition metal solutions with concentrations of 0.5 M, 1 M, and 2 M were used to explore the influence of impregnation concentration on the yield and composition of the pyrolysis products. The results showed that iron promoted the formation of liquid products, whose proportion increased by 37.29% upon increasing the impregnation solution concentration. The addition of cobalt and nickel led to more pyrolysis gas generation. When the impregnation solution concentration was greater than 0.5 M, the gas production rate exceeded 45 wt%. Nickel simultaneously promoted the generation of H2 and CH4 in pyrolysis gas, whose yields were increased by 63% and 20% respectively compared with raw materials. Py-GC/MS analysis showed that Co-CS had strong decarboxylation characteristics during pyrolysis. Metal impregnation decreased the content of aromatic compounds in tar, which increased the stretching vibrations of C-H bonds in char. Ring-opening rearrangements of polycyclic aromatic hydrocarbons were promoted, which formed more -H. Nickel catalyzed the removal of CH3 and H groups and the rearrangement of C-O in volatile products, which formed more H2 and CH4. These findings provide an avenue to optimize the metal impregnation conditions to produce hydrogen via biomass pyrolysis.

Boosting Photocatalytic CO2 Methanation through Interface Fusion over CdS Quantum Dot Aerogels.

In the field of photocatalytic CO2 reduction, quantum dot (QD) assemblies have emerged as promising candidate photocatalysts due to their superior light absorption and better substrate adsorption. However, the poor contacts within QD assemblies lead to low interfacial charge transfer efficiency, making QD assemblies suffer from unsatisfactory photocatalytic performance. Herein, a novel approach is presented involving the construction of strongly interfacial fused CdS QD assemblies (CdS QD gel) for CO2 reduction. The novel CdS QD gel demonstrates outstanding photocatalytic performance for CO2 methanation, achieving a CH4 generation rate of ≈296 µmol g-1 h-1, with a selectivity surpassing 76% and an apparent quantum yield (AQY) of 1.4%. Further investigations reveal that the robust interfacial fusion in these CdS QDs not only boosts their ability to absorb visible light but also significantly promotes charge separation. The present work paves the way for utilizing QD gel photocatalysts in realizing efficient CO2 reduction and highlights the critical role of interfacial engineering in photocatalysts.

Comparative assessment of waste-to-energy scenarios to mitigate GHG emission from MSW in a developing mega city

The search for sustainable municipal solid waste management in urban areas has become a dire need as the generated unprecedented volumes of waste eventually end up in landfills and emits greenhouse gas (GHG). To offer sustainable waste management in Dhaka, Bangladesh, the performance of incineration, anaerobic digestion, and hydrothermal carbonization (HTC) based Waste to Energy (WtE) processes were assessed and compared. The population and the GDP of Dhaka North City Corporation from 2015 to 2023 were used to estimate the MSW generation rate with an empirical multivariable linear regression model. In 2023 around 3600 tons/day of MSW was generated which was 35 % higher than in 2015. The IPCC decay models, ZODM, FODM, and modified triangular model (MTM) yielded 87.3, 41.3, and 38-k tonnes of CH4 generation, respectively. The power generation from incineration-based plants can fall from 30 MW to 3 MW if the moisture content of MSW increases from 70 % to 90 %. Anaerobic digestion produces 34 MW of power. The Optimization of the HTC operating parameters was done and it demonstrates substantial energy potential (up to 65 MW with co-feeding of 420 tons/day of hydrochar with 426 tons/day of plastic from MSW) and GHG emission reduction (221.5 %) compared to landfilling. Additionally, HTC-derived wastewater presents an opportunity for nutrient recovery with 8.16 and 2.66, 0.3 tons/day of K, Na, and P reclamation potential, respectively. A comparison of different scenarios in plastic recycling in incineration and sensitivity analysis for three WtE schemes were conducted. Thus, the study provides a rigorous assessment of different pathways to offer a comprehensive framework for sustainable MSW management that contributes to a cleaner urban environment.

The Potential Significance of Microwave-Assisted Catalytic Pyrolysis for Valuable Bio-Products Driven from Albizia Tree

The objective of this study is to investigate the feasibility of Na2CO3 and ZSM-5 as catalysts in the microwave pyrolysis of Albizia branches. An evaluation was conducted to determine the influence of power applied, experimental time, particle size, and catalysis type and ratio on the quality and quantity of pyrolysis products. Established methods such as GC-MS, FTIR, HHV, SEM, EDX, and BET were used to characterize the properties of bio-oil and biochar produced. The results demonstrated that using both catalyst types led to a substantial enhancement in biogas production. The improvement ranged from 5% to 41% with Na2CO3 and reached 45% with ZSM-5. At a lower power level of 300 W, the bio-oil yield augmented from 28% to 40% and 53% when using ZSM-5 and Na2CO3, respectively. The GC-MS analysis revealed that the utilizing of catalysts enhanced the levels of aromatic compounds, esters, and alcohols in bio-oil, along with an increase in the higher heating value (HHV) from 19.5 MJ/kg to 22 MJ/kg and 24.2 MJ/kg using Na2CO3 and ZSM-5, respectively. Moreover, the biochar's surface area and pore volume experienced a considerable rise, going from 0.5512 m2/g and 0.00011 cm3/g to a higher value of 115.2073 m2/g and 0.0774 cm3/g when treated with Na2CO3. The data indicated that both catalyst types enhanced the generation of CH4, and CO2 was lower with ZSM-5. The utilization of catalysts improves the quality of the biofuel produced and promotes the efficiency of the process in terms of energy consumption and processing time.

Electronic perturbation of Cu nanowire surfaces with functionalized graphdiyne for enhanced CO2 reduction reaction.

Electronic perturbation of the surfaces of Cu catalysts is crucial for optimizing electrochemical CO2 reduction activity, yet still poses great challenges. Herein, nanostructured Cu nanowires (NW) with fine-tuned surface electronic structure are achieved via surface encapsulation with electron-withdrawing (-F) and -donating (-Me) group-functionalized graphdiynes (R-GDY, R = -F and -Me) and the resulting catalysts, denoted as R-GDY/Cu NW, display distinct CO2 reduction performances. In situ electrochemical spectroscopy revealed that the *CO (a key intermediate of the CO2 reduction reaction) binding affinity and consequent *CO coverage positively correlate with the Cu surface oxidation state, leading to favorable C-C coupling on F-GDY/Cu NW over Me-GDY/Cu NW. Electrochemical measurements corroborate the favorable C2H4 production with an optimum C2+ selectivity of 73.15% ± 2.5% observed for F-GDY/Cu NW, while the predominant CH4 production is favored by Me-GDY/Cu NW. Furthermore, by leveraging the *Cu-hydroxyl (OH)/*CO ratio as a descriptor, mechanistic investigation reveals that the protonation of distinct adsorbed *CO facilitated by *Cu-OH is crucial for the selective generation of C2H4 and CH4 on F-GDY/Cu NW and Me-GDY/Cu NW, respectively.

Incorporation anthracene and Cu to NH2-Zr-UiO-67 metal-organic framework: Introducing the simultaneous selectivity and efficiency in photocatalytic CO2 reduction to ethanol

Metal-organic frameworks (MOFs) are considered promising candidates for photocatalytic CO2 reduction (PCR) into valuable organic fuels. However, compared to numerous reports regarding CO, CH4, and CHOOH generation, the explored MOFs have shown limited success in producing alcohols, particularly EtOH, through the PCR strategy. Existing MOFs also suffer from insufficient selectivity and efficiency. This study addresses these limitations by implementing a dual modification strategy on NH2-Zr-UiO-67 MOFs. This strategy involves synthesizing four MOF derivatives with different ratios of redox-active metal sites (Cu) to light absorption antenna (anthracene): 1:1, 2:1, 1:2, and 1:3. The as-synthesized MOFs (denoted as Cu/An (X:X)@NZU67 exhibited a remarkable capability for PCR-to-EtOH, without requiring a photosensitizer. The optimal amount of anthracene plays a crucial role in several aspects: improving light absorption, enhancing CO2 adsorption capacity, and promoting charge transfer/separation. Efficient charge transfer is critical for facilitating the multi-step electron transfer pathway required for ethanol synthesis. Notably, Cu/An (1:2)@NZU67 achieved an ethanol productivity of 624.17 µmolh−1g−1 for EtOH, which is, to the best of our knowledge, the highest efficiency reported for MOFs in PCR-to-EtOH conversion so far. Besides significant performance, the MOF showed 100% selectivity for EtOH production. This work represents a significant milestone in the field of PCR-to-EtOH transformation by providing a new perspective for designing MOF photocatalysts that can simultaneously improve both selectivity and efficiency.

Nanoengineering construction of g-C3N4/Bi2WO6 S-scheme heterojunctions for cooperative enhanced photocatalytic CO2 reduction and pollutant degradation

S-scheme heterojunction photocatalysts featuring efficient charge transport paths provide a promising strategy for cooperative achieving photocatalytic CO2 reduction reaction (CO2RR) and Rhodamine B (RhB) degradation. In this work, S-scheme heterojunctions composed of g-C3N4 nanosheets coated on Bi2WO6 nanosheets were prepared by a one-step hydrothermal method, resulting in broad-spectrum light absorption, high electron–hole separation efficiency, and excellent photocatalytic CO2 reduction and RhB oxidization performance. Mechanistic analysis revealed the formation of a directional charge transport path at the interface of the heterojunction, which maintained a high oxidation and reduction potential and improved the efficiency of photoexcited carrier separation. In particular, the synergistic reaction system showed excellent photoredox activity compared with the two separate half-reactions. The optimal catalyst 15CN/BWO displayed the highest CO2 conversion efficiency, with CO and CH4 generation rates of 4.3 and 2.7 μmol g−1h−1, respectively, and the degradation efficiency of the composite heterojunction was significantly higher than that of its constituent materials. This work provides a new possibility for designing a novel dual-function photocatalytic reaction system.

Experimental and simulation study on the thermal decomposition of Xishan coal and the pyrolysis of coal with Na2SO4

ABSTRACT Based on the Thermal Decomposition of Xishan coal Experiments and ReaxFF MD Simulations, the study investigated the processes and product changes in the thermal decomposition of coal and the pyrolysis of coal with Na2SO4. The results indicate that the initial temperature of thermal decomposition of Xishan coal is around 300 °C in experiments and approximately 1600 K in molecular simulations. The addition of Na2SO4 advances the initial pyrolysis temperature and promotes the generation of total number and types of products. Xishan coal pyrolysis generates a large number of small molecular gases and free radicals, and the addition of Na2SO4 promotes the generation of CO, CH4, and H2S, as well as the accumulation of a significant number of free radicals. Free Na mainly affects the evolution of N elements, promoting the formation of N into amino groups, and Na easily combines with sulfur-containing intermediates. Through the extraction of sulfur-containing intermediates and the analysis of the influence of free radicals, it was found that S elements Xishan coal ultimately forms H2S. This study microscopically confirms that in the coal with Na2SO4 system, H2S originates from the hybridised sulfur atoms in the carbon chain and free SO 4 2 − .

Emissions of CO2 and CH4 from Agricultural Soil with Kitchen Compost at Different Temperatures

Emissions of CO2 from the soil are mainly derived from soil microbial respiration, whereas CH4 emissions originate from anaerobic degradation of organic matter via microbial processes. Kitchen waste compost is used in the agricultural sector to improve soil quality. However, abiotic CO2 and CH4 emissions from soils amended with kitchen waste compost under aerobic conditions remain uncertain. Temperature plays an important role in organic matter decomposition in both biotic and abiotic pathways. This study aimed to evaluate biotic and abiotic emissions of CO2 and CH4 from soils receiving kitchen compost at different temperatures. Ten grams of soil amended with or without 0.1 g kitchen compost (1%) were sterilized or non-sterilized. The mixture and soil-only samples were incubated in 100-mL glass bottles at 20, 30, and 35 °C for 28 d under an aerobic condition. The results showed that CO2 and CH4 emissions increased at higher temperatures and compost application rates (p < 0.05). Emissions of CO2 mainly occurred via biotic pathways. Abiotic processes were potential pathways for CH4 generation, particularly at high temperatures of 35 °C. There was 20–24% of C in kitchen compost changed to CO2 and less than 0.1% to CH4. Our results suggest that global warming enhances abiotic CO2 and CH4 emissions and may contribute to further global warming.

Regulate the adsorption of oxygen-containing intermediates to promote the reduction of CO2 to CH4 on Ni-based catalysts

The introduction of oxophilic metals can enhance the selectivity of CO2 reduction reactions (CO2RR) by modulating the adsorption of oxygen-associated active substances on the catalyst surface. Alloying lanthanide atoms into metals has been shown to improve CH4 selectivity by breaking the linear relationship between the adsorption energies of CO* and HxCO*. In this work, a series of oxophilic transition metals (Fe, Mo, Co, Mn) are introduced to explore the influence on the CO2RR. DFT results demonstrate that the doping of oxophilic metals regulates the adsorption strength between the catalyst surface and intermediates, thereby affecting the CH4 and H3COH pathways. Notably, COOH* formation is enhanced on Ni surfaces, leading to increased H3COH production. Ni-Fe and Ni-Mo exhibit significant H3CO* and CO2* binding energies, which reduces the barrier for H3CO*. Meanwhile, the bond energy of M−O is higher than that of C-O in H3CO*, promoting the generation of CH4. The addition of Co and Mn makes the desorbed of HCOOH smaller than the hydrogenation energy barrier, which accelerates the synthesis of formic acid. This research provides a new pathway for the development of inexpensive and resource-rich catalysts.

Operational effects on aquatic carbon dioxide and methane emissions from the Belo Monte hydropower plant in the Xingu River, eastern Amazonia

Operational demands and the natural inflow of water actively drive biweekly fluctuations in water levels in hydropower reservoirs. These daily to weekly fluctuations could have major effects on methane (CH4) and carbon dioxide (CO2) emissions via release of bubbles from reservoir bottom sediments (ebullition) or organic matter inputs, respectively. The impact of transient fluctuations in water levels on GHG emissions is poorly understood and particularly so in tropical run-of-the-river reservoirs. These reservoirs, characterized by high temperatures and availability of labile organic matter, are usually associated with extensive CH4 generation within bottom sediments. The aim of this study is to determine how water level fluctuations resulting from the operation of the Belo Monte hydropower plant on the Xingu River, eastern Amazon River Basin, affect local CO2 and CH4 emissions. Between February and December 2022, we monitored weekly fluxes and water concentrations of CO2 and CH4 in a site on the margin of the Xingu reservoir. Throughout the study period, fluxes of CO2 and CH4 were 118 ± 137 and 3.62 ± 8.47 mmol m−2 d−1 (average ± 1SD) while concentrations were 59 ± 29.77 and 0.30 ± 0.12 μM, respectively. The fluxes and water concentrations of CO2 were clearly correlated with the upstream discharge, and the variation observed was more closely associated with a seasonal pattern than with biweekly fluctuations in water level. However, CH4 fluxes were significantly correlated with biweekly water level fluctuations. The variations observed in CH4 fluxes occurred especially during the high-water season (February–April), when biweekly water level fluctuations were frequent and had higher amplitude, which increased CH4 ebullition. Reducing water level fluctuations during the high-water season could decrease ebullitive pulses and, consequently, total flux of CH4 (TFCH4) in the reservoir margins. This study underscores the critical role of water level fluctuations in near-shore CH4 emissions within tropical reservoirs and highlights significant temporal variability. However, additional research is necessary to understand how these findings can be applied across different spatial scales.

The effect of silkworms (Bombyx mori) chitosan on rumen fermentation, methanogenesis, and microbial population in vitro.

Ruminant enteric methane (CH4) is one of the largest sources of greenhouse gases that contribute to global warming. To minimize environmental harm caused by ruminants' CH4 production, natural substances can be used to suppress it. Chitosan from crustacean sources had been known to obstruct CH4 generation in the rumen. About 18% of silkworm pupae is chitin, but little is known about the impact of silkworm pupae chitosan on rumen methanogenesis. This study investigated the efficacy of the silkworm chitosan extraction method and its impact on rumen fermentation, methanogenesis, and microbial growth in vitro. This study employed a randomized complete block design featuring five treatments and four batches for rumen incubation as the blocking factor. In this study, five treatments were implemented: Control (CO) (basal diet with no added chitosan), basal diet with 6% chitosan from the Chinese Silkworm strain 804 (CHI804), basal diet with 6% chitosan from the PS 01 Hybrid Silkworm strain (CHIPS01), basal diet with 6% chitosan from the Hybrid F1 Japanese 102 × Chinese 202 races (CHIJC02), and basal diet with 6% commercial shrimp shell chitosan as the positive control (CHICOMM). The in vitro experiments assessed digestibility, pH, total gas generation, CH4 production, ammonia nitrogen (NH3-N), and short-chain fatty acid levels, along with microbial population. Data were analyzed using a general linear model followed by Duncan's test when applicable. A significant effect on dry matter digestibility (DMD), total gas production, CH4, NH3-N, and rumen microbial populations (Methanogens, Ruminoccocus albus, Ruminoccocus flavefaciens, Selonomonas ruminantium, Butyrivibrio fibrisolvens, Streptoccocus bovis, Prevotella spp., and Bacteroides spp.) was observed (p < 0.05). The extracted chitosan (CHIJC02) used in this study exhibited a similar quality to that of commercial chitosan (CHICOMM). CHI804 treatment could reduce gas production, NH3-N production, and B. fibrisolvens population significantly (p < 0.05), while CHIJC02 could reduce CH4 production, methanogen population, acetate (C2) production, and increase propionate (C3) production significantly (p < 0.05). CHIJC02 and CHICOMM treatments could also increase the population of R. flavefaciens, S. ruminantium, and Bacteroides spp. significantly (p < 0.05). Chitosan addition significantly (p < 0.05) reduced DMD but did not impact organic matter digestibility or pH. The extracted chitosan mimics commercial chitosan in physico-chemical properties. Chitosan derived from Japanese and Chinese F1 hybrid silkworm strains demonstrated superior capacity for inhibiting CH4 generation compared to commercial chitosan. The quality and effects on methanogenesis, rumen fermentation, and rumen microbial populations can differ depending on the origin of chitosan.

Coordination-tuned Ru single-atom catalyst for efficient catalysis of CO2 to CH4 on RuBxN4-x@TiN (x=0–4)

Creating useful chemicals or fuels from CO2 is one of the most promising ways to reach carbon neutral. In this work, through the formation of Lewis acid sites, a string of boron-atom-coordinated Ru single-atom catalysts (SACs), namely RuBxN4-x@TiN (x=0–4), were constructed, and their CO2 reduction reaction (CO2RR) was systematically studied. The results show that o-RuB2N2@TiN, p-RuB2N2@TiN, and RuB3N1@TiN are able to efficiently inhibit the competitive hydrogen evolution reaction (HER) and activate CO2, with a potential-determining step lower than 0.7 eV and high selectivity for CH4 generation. This work shows that the synergistic effect of B and Ru atoms are able to effectively improve the catalytic activity, which is expected to offer a possible tactic for the sensible creation of effective CO2RR catalysts.

PH-Optimized Biomethane Production: Evaluating Carrier Materials for Ex-situ Biomethanation

Choosing the appropriate carrier material for ex-situ biomethanation is a critical factor to consider when developing biogas upgrading technologies. The chosen material for biomethanation in a biotrickling filter reactor functions as a substrate that immobilises microorganisms, which act as catalysts in the reaction for producing biomethane. This study conducted experiments on waste-derived materials, including glass foam and vulcanised wood ash material, in addition to polyurethane foam and expanded clay pellets. Pretreratment of wood ash was done to lower the pH of material. The manometric test measured the rate of CH4 generation by quantifying pressure fluctuations. The validity of these results was confirmed by analysing product gas samples using a Shimadzu Nexis GC-2030 gas chromatograph, which was equipped with two parallel lines, a flame ionisation detector (FID) and a thermal conductivity detector (TCD). In order to enhance the biomethane concentration in the end product, two strains of Methanobacterium alcaliphilum were evaluated alongside biogas sludge as the inoculum. These strains of microorganisms are methanogens that utilise hydrogen and can thrive in a high pH environment. Thus, they have the potential to demonstrate improved biomethane production outcomes when a vulcanised wood ash filter is used as the carrier material.

Mathematical Modeling of The Estimate of Methane Gas Generation, of The Organic Fraction Of Msw From The Agreste Alagoano Sanitary Landfill, From Standard Data And Experimental Data

Objective: The objective of this study is to carry out mathematical modeling in the generation of methane gas, through two mathematical models, using standard data and data obtained in the laboratory. Theoretical framework: The emission of methane gas, generated by the decomposition of solid waste in landfills, is one of the serious problems of air pollution and one way to minimize the impacts of methane on the environment is through its use to generate energy. To this end, there are ways to estimate the generation of CH4 during the useful life of the landfill. Method: For modeling, the computer programs of LandGEM and the Intergovernmental Panel on Climate Change (IPCC) were used to carry out the theoretical estimate of CH4 production during the useful life of the Agreste Alagoano landfill in two scenarios: one with standard program values for the local climate region and another with information obtained from experimental data from research by Santana (2022). Results and Discussion: When standard input data was adopted, the LandGEM model presented a 38% higher value in CH4 production compared to the IPCC model. When considering input data obtained experimentally, the IPCC showed CH4 generation 32.66% higher than the LandGEM, this was possible due to the COD value that was high as a result of the L0 of the organic fraction, exceeding the theoretical value of 0.15 to the experimental value of 0.27 in the new scenario. Implications of the research: Determining parameters for modeling methane gas generation will help in managing landfill waste and its energy recovery potential, in addition to the application of mathematical models for estimating biogas production potential as tools essential for both energy and environmental studies. Originality/value: This research presents as originality the determination of experimental parameters applied to the mathematical modeling of methane gas generation in landfills in the rural region, since studies on modeling in landfills with the climatic conditions of the rural region of Brazil are not common in the literature.