Role Of CH4 Research Articles

Role of methane in ammonia combustion in air: From microscale to macroscale

Ammonia (NH3) has gained increasing recognition as a carbon-free fuel. To enhance NH3 combustion, reactive gases, like methane (CH4), are usually added to the combustion system. In this work, the role of CH4 in NH3 combustion is systematically studied. A series of reactive force field molecular dynamic (ReaxFF MD) simulations are implemented to investigate effects of CH4 addition on the consumption of NH3 and the yields of nitrogen oxides (NOx) from the atomic perspective: CH4 accelerates the consumption of NH3 by shortening the decomposition time of the first NH3 molecule and increasing the translational kinetic energy of the system; CH4 modifies the yield of NOx by complicating the elementary reactions and introducing additional intermediates. The fuel ratio of CH4 and NH3 between 0.5 and 1 is suggested for a cleaner and enhanced NH3 combustion. By summarising the findings from the latest publications and the present work, the role of CH4 in NH3 combustion is comprehensively analysed from the macroscale and microscale perspectives: CH4 accelerates the progress of NH3 combustion flame, activates chemical reactions, and aggravates NOx emissions at a low CH4 content. Taking the NH3/CH4 combustion as an example, this study provides an exclusive perspective to understand combustion phenomena from the microscale events to macroscale observations.

Determining methane uptake in tropical agroforestry soils: a case for inclusion in REDD+

This study aims to measure possible seasonal methane (CH4) fluxes in tropical agroforestry soils to enhance the case for agroforestry’s inclusion in the Reducing Emissions from Deforestation and Forest Degradation (REDD+) program. The role of CH4 in the REDD+ program is currently uncertain. Air samples and environmental variables from the soil-atmosphere interface of the Maya Mountain Research Farm in southern Belize were collected three times per week throughout April and July of 2019. Samples were analyzed using the static chamber and gas chromatography method. The average CH4 flux for the dry season was − 0.02 mg CH4 m−2 h−1 and − 0.03 mg CH4 m−2 h−1 for the wet season, with negative values indicative of uptake. There was a negative correlation between CH4 flux and rainfall in the dry season and a positive correlation in the wet season, indicating that CH4 uptake occurred during the dry season. However, our results show that there is not a significant pattern of CH4 uptake (at a 95% confidence limit). Given the large discrepancy in the literature regarding CH4 uptake from agroforestry soils, further investigation of CH4 fluxes from agroforestry soils is warranted. Understanding CH4 fluxes in tropical agroforestry soils are of paramount importance for agroforestry utilization as a tool for climate change mitigation through the REDD+ program.

Technological avenues and market mechanisms to accelerate methane and nitrous oxide emissions reductions.

Strategies targeting methane (CH4) and nitrous oxide (N2O) emissions are critical to meeting global climate targets. Existing literature estimates the emissions of these gases from specific sectors, but this knowledge must be synthesized to prioritize and incentivize CH4 and N2O mitigation. Accordingly, we review emissions sources and mitigation strategies in all key sectors (fuel extraction and combustion, landfilling, agriculture, wastewater treatment, and chemical industry) and the role of carbon markets in reducing emissions. The most accessible reduction opportunities are in the hydrocarbon extraction and waste sectors, where half (>3 Gt-CO2e/year) of the emissions in these sectors could be mitigated at no net cost. In total, 60% of CH4 emissions can be mitigated at less than $50/t-CO2. Expanding the scope of carbon markets to include these emissions could provide cost-effective decarbonization through 2050. We provide recommendations for carbon markets to improve emissions reductions and set prices to appropriately incentivize mitigation.

Recent advances on photo-thermo-catalysis for carbon dioxide methanation

The carbon dioxide (CO2) hydrogenation into methane (CH4, Sabatier reaction) has intrigued much research attention considering the role of CH4 in rendering energy for daily life. Photo-thermo-catalysis (PTC) of CO2 methanation integrates both photochemical and thermochemical contributions to drive CH4 generation effectively and selectively. This review critically surveys recent discoveries in PTC-CO2 methanation. After introducing the basics of CO2 methanation, the mechanisms of PTC-CO2 methanation related to electron transfer (non-thermal effect) and photothermal heating are presented. Next, the factors regarding metals, shapes, metal–support interactions and defects are discussed. Moreover, we highlight the emerging catalysts of PTC-CO2 methanation, including plasmonic and non-plasmonic metals, metal oxide semiconductors, metal-organic frameworks, and metal carbides. This review concludes with current challenges and future perspectives in paving the way toward the industrial application of PTC-CO2 methanation.

Wintertime Greenhouse Gas Fluxes in Hemiboreal Drained Peatlands

The aim of this study is to estimate wintertime emissions of greenhouse gases CO2, N2O and CH4 in two abandoned peat extraction areas (APEA), Ess-soo and Laiuse, and in two Oxalis site-type drained peatland forests (DPF) on nitrogen-rich sapric histosol, a Norway spruce and a Downy birch forest, located in eastern Estonia. According to the long-term study using a closed chamber method, the APEAs emitted less CO2 and N2O, and more CH4 than the DPFs. Across the study sites, CO2 flux correlated positively with soil, ground and air temperatures. Continuous snow depth > 5 cm did not influence CO2, but at no snow or a thin snow layer the fluxes varied on a large scale (from −1.1 to 106 mg C m−2 h−1). In all sites, the highest N2O fluxes were observed at a water table depth of −30 to −40 cm. CH4 was consumed in the DPFs and was always emitted from the APEAs, whereas the highest flux appeared at a water table >20 cm above the surface. Considering the global warming potential (GWP) of the greenhouse gas emissions from the DPFs in the wintertime, the flux of N2O was the main component of warming, showing 3–6 times higher radiative forcing values than that of CO2 flux, while the role of CH4 was unimportant. In the APEAs, CO2 and CH4 made up almost equal parts, whereas the impact of N2O on GWP was minor.

Highly conductive, monolayer and large-area reduced graphene oxide films fabricated by electrical connection at the two-dimensional boundaries between the tiled graphene oxide flakes

The demand to fabricate graphene film in large wafer-scale with minimum cost is crucial for device applications, and one of the promising techniques is the reduction of graphene oxide (GO) films. We have investigated morphological changes of large-area, monolayer GO films during methane (CH4)-assisted thermal annealing process and the role of CH4 in the restoration of their electrical conductivity. We have discovered that long reduction process in high CH4 flow rates can contribute to the partial reparation of lattice defects and formation of new multilayer graphene that are stacked at the boundary areas between the reduced GO (rGO) flakes. These multilayer graphene layers with graphitic domains operate as the electrical connection between the separated rGO flakes and create new conduction pathways across the entire films. This phenomenon is more important than the sole reduction process (elimination of oxygen functional groups) in the restoration of electrical conductivity of the continuous rGO films. We have achieved in the fabrication of highly conductive rGO films with a minimum sheet resistance value of 1.01kΩ/sq. This study exhibits a promising reduction method for the mass production of large-area, continuous rGO films for thin film device applications.

Maskless Plasma Etching of Diamond Cones: The Role of CH4 Gas and Enhanced Field Emission Property

Diamond cone arrays were formed by plasma etching of diamond films in a hot filament chemical vapor deposition (HFCVD) system. The role of CH4 in the formation of diamond cone arrays was investigated. It was found that addition of CH4 to H2 plasma could enhance the plasma intensity and hence the etching efficiency to improve the formation of diamond cones with high aspect ratio and controllable density. The microscopic measurement of the as-formed diamond cones shows that they have an inner core of polycrystalline structure and an outer layer of amorphous carbon. These as-formed diamond cones have exhibited field emission current density of 1 μA/cm2 at threshold field of 5 V/μm. For an applied field of 12 V/μm, the emission current density can rapidly reach as high as 560 μA/cm2. The property of high field electron emission is attributed to the high aspect ratio of as-formed diamond cones and the appropriate cone density as well as the outer amorphous carbon layer which acts as a pathway for electron-hopp...

Magnetic and structural transitions in the melt-spun Heusler alloy Ni53Mn25Al22

Diamond cone arrays were formed by plasma etching of diamond films in a hot filament chemical vapor deposition (HFCVD) system. The role of CH4 in the formation of diamond cone arrays was investigated. It was found that addition of CH4 to H-2 plasma could enhance the plasma intensity and hence the etching efficiency to improve the formation of diamond cones with high aspect ratio and controllable density. The microscopic measurement of the as-formed diamond cones shows that they have an inner core of polycrystalline structure and an outer layer of amorphous carbon. These as-formed diamond cones have exhibited field emission current density of 1 mu A/cm(2) at threshold field of 5 V/mu m. For an applied field of 12 V/mu m, the emission current density can rapidly reach as high as 560 mu A/cm(2). The property of high field electron emission is attributed to the high aspect ratio of as-formed diamond cones and the appropriate cone density as well as the outer amorphous carbon layer which acts as a pathway for electron-hopping conduction during field electron emission.

Future atmospheric methane concentrations in the context of the stabilization of greenhouse gas concentrations

Tropospheric CH4 concentration depends, according to modeled tropospheric processes, on many factors, including emissions of CH4 as well as NOx and CO. Illustrative analyses of the relation between emissions and CH4 concentration give some guidance on the role of CH4 in the stabilization of greenhouse gas concentrations. The contribution of CH4 to radiative forcing at the time of stabilization is expected to be modest, provided CH4 and CO emissions do not go far beyond current rates. However, in cases leading to stabilization the potential mitigation of increases in radiative forcing by methane control could be comparable to that of CO2 control over the next century. Whether or not this potential is realized will depend partially on the cost of deep reductions of CH4, NOx, CO, or CO2 emissions over the next century, which is not known.

The role of CH4 and N2O emission reductions in the cost-effective control of the greenhouse gas emissions from Finland

The reduction of carbon dioxide (CO2) emissions may be quite expensive and it is necessary to consider reduction measures for other anthropogenic greenhouse gases, such as methane (CH4) and nitrous oxide (N2O) as well. Their contribution to the total GHG emission from Finland is about 15–20%. In Finland most of the CH4 emissions are due to waste management, agriculture and burning processes. N2O emissions originate from burning processes, agriculture, industry and atmospheric deposition of nitrogen. The cost-effective reduction of the Finnish GHG emissions has been studied with the EFOM-ENV model, which is a quasi-dynamic linear energy system optimisation model. The target function to be minimised is the total discounted cost for the modelled system. In this study the model has been expanded to cover all well-known anthropogenic CO2, CH4 and N2O sources and reduction measures. The results indicate it is economic to reduce the emissions of CO2, CH4 and N2O in Finland. It is profitable to exploit the economic reduction potential of CH4 and N2O, because then the abatement of CO2 emissions does not need to be as extensive as when the reduction is aimed only at CO2 emissions. The inclusion of CH4 and N2O decreases the annual reduction costs about 20% in the year 2010.