Direct Methane Research Articles

Aging studies of Dual functional materials for CO2 direct air capture with in situ methanation under simulated ambient conditions: Ru thrifting for cost reduction

Dual function materials (DFMs) comprised of 0.25 %Ru, 6.1 %Na2O/γ-Al2O3//monolith were evaluated for about 250 hours time-on-stream (TOS) at various simulated ambient climate capture conditions followed by temperature swing methanation to 280 °C. This paper focuses on the impact of thrifting Ru to low levels and the impact on performance. Results showed both stable CO2 capture capacity and CH4 production with 0.25 % Ru DFM deposited on a ceramic monolith. The CO2 conversion to CH4 production was decreased slightly by the Ru decrease from 1 % to 0.25 %. The capture capacity decreased since a lower Ru content reduces the complete decomposition of the Na2CO3 precursor producing fewer active adsorption sites (“Na2O”). The deployment of a low Ru DFM monolith would significantly decrease the overall capital cost and give more potential for a large-scale direct air capture and methanation (DACM) application.

Direct methane protonic ceramic fuel cells with self-assembled Ni-Rh bimetallic catalyst

Direct methane protonic ceramic fuel cells are promising electrochemical devices that address the technical and economic challenges of conventional ceramic fuel cells. However, Ni, a catalyst of protonic ceramic fuel cells exhibits sluggish reaction kinetics for CH4 conversion and a low tolerance against carbon-coking, limiting its wider applications. Herein, we introduce a self-assembled Ni-Rh bimetallic catalyst that exhibits a significantly high CH4 conversion and carbon-coking tolerance. It enables direct methane protonic ceramic fuel cells to operate with a high maximum power density of ~0.50 W·cm−2 at 500 °C, surpassing all other previously reported values from direct methane protonic ceramic fuel cells and even solid oxide fuel cells. Moreover, it allows stable operation with a degradation rate of 0.02%·h−1 at 500 °C over 500 h, which is ~20-fold lower than that of conventional protonic ceramic fuel cells (0.4%·h−1). High-resolution in-situ surface characterization techniques reveal that high-water interaction on the Ni-Rh surface facilitates the carbon cleaning process, enabling sustainable long-term operation.

Direct Methane Removal from Air by Aerobic Methanotrophs.

The rapid pace of climate change has created great urgency for short-term mitigation strategies. Appropriately, the long-term target for intervening in global warming is CO2, but experts suggest that methane should be a key short-term target. Methane has a warming impact 34 times greater than CO2 on a 100-year timescale, and 86 times greater on a 20-year timescale, and its short half-life in the atmosphere provides the opportunity for near-term positive climate impacts. One approach to removing methane is the use of bacteria for which methane is their sole carbon and energy source (methanotrophs). Such bacteria convert methane to CO2 and biomass, a potentially value-added product and co-benefit. If air above emissions sites with elevated methane is targeted, technology harnessing the aerobic methanotrophs has the potential to become economically viable and environmentally sound. This article discusses challenges and opportunities for using aerobic methanotrophs for methane removal from air, including the avoidance of increased N2O emissions.

Conditions for higher methanol selectivity for partial CH4 oxidation over Fe-MOR using N2O as the oxidant and comparison to Fe-SSZ-13, Fe-SSZ-39, Fe-FER, and Fe-ZSM-5

Continuous catalytic conversion of methane to methanol was investigated on Fe-MOR at atmospheric pressure and moderate temperatures (270–300 °C) with an emphasis on improving the methanol selectivity. Results showed a relation between the methanol selectivity, iron content and mesopore addition on Fe-MOR as well as H2O concentration in the feed. Decreasing the iron content of Fe-MOR, adding mesopores to MOR or increasing water vapor pressure from 3 to 21 kPa gave higher methanol selectivity. Addition of mesopores suppressed the over-oxidation products (CO and CO2) and coke formation significantly, resulting in an increased catalyst lifetime as well as higher methanol turnover frequency (2.0 vs. 3.9 h−1 at 320 °C). Using DFT methods several active site candidates were analyzed regarding their formation energies, UV–Vis spectra and methanol formation pathways. DFT studies suggest that [Fe2O2]2+ or [HOFe(μ-O)FeOH]2+ sites on the 8 member rings are active for direct methane to methanol conversion.

The base versus tip growth mode of carbon nanotubes by catalytic hydrocarbon cracking: Review, challenges and opportunities

Hydrogen gas production using catalytic hydrocarbon cracking on metal nanoparticles has become a vital bridge technology, as this process, unlike the traditional methane-based reforming process, does not co-produce carbon gasses (e.g., CO, CO2). The major benefit of direct catalytic methane cracking using a nanostructured catalyst is the formation of solid carbon in high-value products, such as carbon nanotubes (CNTs) or filaments. This solid carbon can then be removed physically and valorized. However, it is challenging to design a catalyst capable of sustaining its activity after solid carbon has started to deposit and grow, meanwhile preventing the formation of coke. For CNTs, in particular, the base growth mode of CNTs is the desired pathway, as the catalyst can then be regenerated and re-used. If the CNTs are formed under the tip-growth mode, the catalyst particle will be lifted off the support of the regeneration and reusability is lost. Therefore, the study of CNTs growth modes is a vital topic, both experimentally and theoretically, of designing appropriate catalysts. To date, enormous efforts have been made to investigate conditions where the CNTs base growth mode can be maintained during the carbon deposition process. Several possible correlations and mechanisms regarding the base growth mode have been explored and established. Theoretical calculations and numerical simulations across length scales were conducted to investigate the nucleation mechanism and growth of CNTs. Density functional theory (DFT), classical and quantum-based molecular dynamics (MD) and Monte Carlo (MC) simulations were also carried out to study the initial CNT cap formation and its encapsulation during the catalytic hydrocarbon cracking process. A thermodynamics-based nucleation formula of CNTs for both the base and tip growth modes was also established. However, there is still no consensus on what determines the CNT growth modes and what the roles are of the various influencing factors such as the nanoparticle size, the oxidation state of the catalyst, the mechanical properties of CNT, and the catalyst-support interaction. This paper reviews the current status of CNT's growth mechanism development. The benefits and limitations of theory and modeling approaches concerning CNT growth modes are discussed.

Partial oxidation of methane to methyl oxygenates with enhanced selectivity using a single-atom copper catalyst on amorphous carbon support

In this study, we report a single-atom Cu catalyst on the amorphous carbon support for direct methane partial oxidation. The catalyst was prepared by the carbonization of Cu-doped ZIF-8 to implant single-atom Cu active centers that coordinate with four nitrogen (CuN4) on the amorphous N-doped carbon. Carbonization enhanced the oxidation resistance of the catalyst by preventing the oxidation of Cu-coordinating ligands, leading to a 40% reduction in CO2 production. Our prepared catalyst showed higher methanol selectivity than other single-atom copper catalysts. Mechanistic studies revealed that Cu and the surface carbon atom facilitated the dissociation of H2O2 into OOH and H, which further transformed into Cu–O and led to proton abstraction from methane. We highlight a simple approach to prepare a single-atom catalyst that is supported on amorphous N-doped carbon, derived from a metal-doped ZIF. This catalyst exhibits enhanced selectivity and stability for the partial oxidation of methane.

Computational investigation of methanol pre-chamber combustion in a heavy-duty engine

This work explored the potential of methanol pre-chamber combustion (PCC) for heavy-duty engine applications. An optical engine experiment was conducted to visualize the jet flame development. The measured pressure traces and natural flame luminosity images were also used for the validation of three-dimensional computational fluid dynamics simulations. It was demonstrated that the main chamber (MC) combustion was successfully established by the reactive jet issued from the pre-chamber. Compared to methane PCC in our previous study, the distributed reacting jets were significantly thinner, in particular at the learner condition. The active PCC mode, which comprises enrichment of the mixture in the pre-chamber (PC) by means of direct methane injection, was effective in improving the engine performance. However, excessive PC fueling ratio (PCFR) resulted in lower thermal efficiency due to the higher wall heat transfer and combustion losses. In addition, the effects of various PC and piston geometries on the methanol/methane PC combustion were evaluated. The combination of an optimized PC and a flat piston yielded the highest thermal efficiency owing to the relatively lower combustion and wall heat transfer losses. At engine loads higher than 12.5 bar indicated mean effective pressure, exhaust gas recirculation must be implemented to avoid end-gas autoignition and reduce nitric oxides (NOx) emissions. As expected, the increase in (CR) further promoted engine work because of the higher expansion ratio. With CR of 13 and 14, higher thermal efficiency and lower NOx emission were simultaneously achieved under both intermediate and high loads when the engine was operating at the pure methanol PC combustion mode.

Biomethane production through the power to gas concept: A strategy for increasing the renewable sources exploitation and promoting the green energy transition

Direct catalytic methanation of biogas using hydrogen from electrolysis is a promising pathway to store the electricity from renewable power plants according to the Power to Gas concept. This type of methanation offers technical and economic advantages over the methanation of carbon dioxide separated from biogas, since it eliminates the upgrading step.This work is focused on the sizing and performance analysis of a Power to Biomethane plant based on biogas direct catalytic methanation process. The plant consists of two main sections: i) the Renewable Island, in which an anaerobic digestion plant and a renewable power plant (Photovoltaic plant or Wind farm) supply the biogas and the electricity; ii) the Biomethane Production Island, in which the hydrogenation of the carbon dioxide in the biogas, in presence of methane, occurs.This study, by means of an optimization procedure based on a multi-objective approach, aims to evaluate the optimal size of the Power to Biomethane plant that assures the maximum biomethane production and the maximum exploitation of the renewable electricity. Two case studies, referring to the installation of a Photovoltaic plant and a Wind farm as renewable power plants, have been analyzed.Results have highlighted that, for obtaining an annual biomethane production in the range of 2550–3150 kNm3 and by starting from a biogas availability of 500 Nm3/h, the sizes of the renewable power plants must be in the range 15–20 MW and in the range 19–23 MW for the Wind farm and the Photovoltaic plant, respectively. In terms of performance indicators, even if the PV plant has the highest electricity storage factor (up to 69 %), the Wind-based plant has both the highest plant load factor (up to 81%) and the equivalent full load operating hours (up to 6081), so that it is more favorable for the development of the Power to Biomethane concept.

Continuous direct air capture and methanation using combined system of membrane-based CO2 capture and Ni-Ca based dual functional materials

Direct CO2 capture from the air by membranes (membrane-based DAC, m-DAC) is a promising new technique to achieve CO2 net zero emissions. In addition, a continuous system for CO2 capture and its reduction by hydrogen using coupled reactors has scarcely been investigated. In this study, a new continuous system consisting of a m-DAC and a methanation process (m-DAC-M) was developed. For methanation, Ni nanoparticles supported on Ca-loaded Al2O3 (Ni-Ca/Al2O3; 10 wt% Ni and 6 wt% CaO) were utilized as a dual functional material (DFM). The Ni-Ca/Al2O3 exhibited high CH4 productivity and selectivity, good stability over 100 h, and high humidity resistance properties at a low reaction temperature of 350 °C. The catalytic properties of Ni-Ca/Al2O3 were elucidated using microscopic and spectroscopic techniques. The characterization results indicated that the CaO species not only served as CO2 adsorption sites to trap concentrated CO2 from the m-DAC system but also improved the reducibility of oxidized Ni species in the hydrogenation period, thereby promoting the reduction of surface carbonate species to CH4.

Nonoxidative methane coupling in a micro‐DBD with enhanced secondary electron emission

AbstractThe conversion of methane into transportable and storable materials is crucial in the petrochemical sector. In this study, a specially constructed AC‐driven dielectric barrier discharge (DBD) that has charge injector pyramids on one of the electrodes and runs at ambient temperature and pressure was used to evaluate noncatalytic methane conversion. The obtained result was compared with the traditional flat electrode DBD. It was discovered that the product selectivity in direct nonoxidative methane conversion depended on the discharge conditions. Pyramid electrode plasma sources convert methane up to 50 more than flat electrode plasma due to the appearance of more microdischarges. Pyramid electrode plasma generally has a greater production efficiency than flat electrode plasma, while requiring more operational power. The turnkey solutions offered by the sustainable methane coupling method discussed here may be advantageous for the long‐term small‐scale ethylene exploration scenario.

Effect of the Ni-to-CaO Ratio on Integrated CO2 Capture and Direct Methanation

Direct methanation in an integrated CO2 capture and utilization system has recently gained considerable attention as a promising approach owing to its simplified process and lower requirement of total thermal energy as compared to conventional CO2 capture and utilization techniques. This study formulated macroporous structured Ni/CaO catal-sorbents by controlling the Ni-to-CaO ratio. The influence of this ratio on the CO2 capture (capacity and kinetics) and direct methanation performances (productivity and kinetics) was evaluated at 500 °C. CO2 capture combined with direct methanation experiments revealed that 10Ni/CaO exhibited the best CO2 capture capacity, kinetics, and CH4 productivity with the thermal stability of Ni and CaO species.

Theoretical Perspective of Promoting Direct Methane-to-Methanol Conversion at Complex Metal Oxide-Metal Interfaces.

Direct methane conversion to methanol has been considered as an effective and economic way to address greenhouse effects and the current high demand for methanol in industry. However, the process has long been challenging due to lack of viable catalysts to compromise the activation of methane that typically occurs at high temperatures and retaining of produced methanol that requires mild conditions. This Perspective demonstrates an effective strategy to promote direct methane to methanol conversion by engineering the active sites and chemical environments at complex metal oxide - copper oxide - copper interfaces. Such effort strongly depends on extensive theoretical studies by combining density functional theory (DFT) calculations and kinetic Monte Carlo (KMC) simulations to provide in-depth understanding of reaction mechanism and active sites, which build a strong basis to enable the identification of design principles and advance the catalyst optimization for selective CH4-to-CH3OH conversion.

Enhanced direct methanation of CO2 using Ni-based catalysts supported on ZrO2, CeO2-ZrO2, and La2O3-ZrO2: The effect of support material on the reducible NiO-interacted species and catalytic activity

The lack of reducible NiO-interacted species in ZrO2-supported Ni catalyst at reaction temperature (350 °C) renders it inactive towards CO2 conversion. However, the addition of 2.5 wt.% Ce to the catalyst (Ni/Ce-ZrO2) promotes the formation of reducible NiO-interacted species at around 350 °C, resulting in 23–18.5% CO2 conversion, 60% CH4 selectivity, and 40% CO selectivity during 13 h of time on stream. The lanthana-zirconia support features size-optimized stable Ni sites, the highest population of oxygen vacancy/interacted CO2 species and oxide diminution, leading to constant 38–36% CO2 conversion with 100% CH4 selectivity up to 13 h of time on stream through the direct methanation route (without involving the CO intermediate step). In the longer time on stream (11–13 h), the formate species destabilizes over Ni/CeO2 catalyst, CO2 conversion drops (from 33 to 24%), and CO selectivity increases (from 0.5% to 5.3%) at the expense of CH4 selectivity (from 99.5% to 94.7%).

Elucidation of the CH4 coupling mechanism to C2H4 over GaN catalysts under non-oxidative conditions

The second C−H bond cleavage in methane to form methylene (CH2*) from methyl (CH3*) is the rate-limiting step for the direct non-oxidative methane coupling to ethylene over gallium-nitride catalysts. Herein, we use isotope labelled experiments, in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), 13C solid state-NMR, as well as kinetic modelling to elucidate the reaction mechanism. Our experiments showed that supported GaN/SBA-15 had more aliphatic surface intermediates (CH3* and CH2*) than unsupported GaN catalysts, which had higher amounts of aromatics intermediates and coke deposition. Isotope labelling experiments and the kinetic study confirmed that the most likely pathway is via the fast abstraction of the first H from CH4 to form methyl (CH3*) surface intermediates, followed by the slow second C−H bond cleavage to form methylene (CH2*) and subsequent coupling to ethylene. The intrinsic activation energy predicted by kinetic modelling was rather low at around 20 kJ mol−1.

Direct-methane anode-supported solid oxide fuel cells fabricated by aqueous gel-casting

Direct methane Solid Oxide Fuel Cells (SOFCs) operated under catalytic partial oxidation (CPOX) conditions are investigated, focusing on the processing of the anode support and the anode deactivation caused by carbon deposition. Anode-supported SOFCs based on gadolinium-doped ceria (GDC) electrolyte, and NiO-GDC anode support were fabricated by the gel-casting method. Suitable aqueous slurries formulations of NiO–GDC were prepared, starting NiO-GDC nanocomposite powders, agarose as gelling agent and rice starch as pore former. Electrochemical and mechanical tests evidenced that the support of 550 ± 50 µm thickness and 10 wt% pore former is a good candidate for direct-methane SOFCs. The cells operating under stoichiometric conditions of CPOX reached a performance of 0.64 W·cm−2 at 650 ºC, a very close value to that measured under humidified hydrogen (0.71 W·cm−2). The best electrochemical stability of the cell is achieved at a CH4/O2 ratio of 2.5, showing no evidence of carbon deposition and reducing nickel re-oxidation significantly.

Direct measurement of methane emissions from the upstream oil and gas sector: Review of measurement results and technology advances (2018–2022)

The increasing methane emissions from the upstream oil and gas sector deviates from the goals of the Paris Agreement on sustainable development and climate control. This paper reviews recent direct measurement results and technological advances in the upstream oil and gas sector, based on more than 100 sources published between 2018 and 2022. No consensus was found on the correlation between methane emissions and well data items such as production volume and well age. Aircraft surveys were the most frequently used technology during the study period. Developed countries lead in direct measurement, with only 12.5% of studies conducted in developing countries. The sensing method and the performance of sensor carriers lead to different characterisations of direct measurement techniques. Growing upstream methane emissions accelerate global warming and pose risks to groundwater. Mitigating super-emitters and reported venting and flares could reduce total methane emissions by 20% and 25%, respectively. China, the world's largest methane emitter, emitted approximately 2135 kt methane from its upstream oil and gas sector, mainly through venting (80%). Direct methane measurements and the strength of government management could assist China in prioritising carbon emission reduction and filling the legislative gap.

Experimental investigation of hydrogen-intensified synthetic natural gas production via biomass gasification: a technical comparison of different production pathways

A sustainable and secure energy supply requires alternative concepts for energy generation. Utilizing biomass to produce synthetic natural gas (SNG) allows the synthesis of a currently widely used energy carrier on a renewable basis. The additional integration of hydrogen increases the carbon utilization of the biomass. This study experimentally investigates and compares the production of raw-SNG in three novel process chain configurations combining the advanced dual fluidized bed (DFB) gasification technology, gas cleaning units, and a fluidized bed methanation reactor. The three process chains comprise the direct methanation of DFB product gas, a hybrid route with hydrogen addition to the DFB product gas, and the methanation of a hydrogen-enriched product gas generated through DFB gasification with in situ CO2 removal (SER process). The direct methanation of the DFB product gas yielded a raw-SNG CH4 content of 40 vol.-%db at 360 °C and atmospheric pressure conditions. Through the integration of external hydrogen in a hybrid process, the carbon utilization of the biomass could be increased from 37% to around 70% at an unchanged cold gas efficiency of 58–59%. Via the SER process, a high raw-SNG CH4 content of 70 vol.-%db was achieved at an increased cold gas efficiency of 66% without the need for external hydrogen. Finally, a comparison points out the main advantages of the process configurations and provides a decision basis for novel SNG production pathways.

Highly dispersed Cu-anchored nanoparticles based mordenite zeolite catalyst (Cu-MOR): Influence of the different preparation methods for direct methane oxidation (DMTM) to methanol

Methane is widely recognized as one of the most significant greenhouse gases released into the atmosphere by shale gas and natural gas, contributing to global warming. Developing innovative technology for converting methane into transferable, storable, and useable liquid fuels is essential for long-term sustainability and carbon neutrality. Direct methane oxidation (DMTM) is one of the most efficient and cost-effective methods for producing methanol. The purpose of this research was to develop a highly active Cu-loaded mordenite zeolites (Cu-MOR) catalyst by the hydrothermal and ion exchange processes. Different methods were employed for Cu incorporation via double solvent, physical mixing, wetness impregnation, and incipient wetness impregnation. The synthesized catalysts were characterized by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), N2-adsorption analysis, Fourier Transform Infrared Spectroscopy (FTIR), and Methane Temperature Programmed Desorption (CH4-TPD). The DMTM was performed, and it was found that the Cu-MOR (WI) catalyst that was prepared by wetness impregnation exhibited a higher methanol yield (26.5 μmol gcat−1) compared to other catalysts as a result of the high metal dispersion and high methane adsorption. According to data from TEM and CH4-TPD, this superior performance was strongly related to the particle sizes of copper and the synthesis methods used. Additionally, it was discovered that the longer the methane was in contact with the Cu-MOR (WI), the greater the amount of methanol that was produced (83.3 μmol gcat−1). Based on the finding that the Cu-MOR (WI) catalyst is highly efficient for the DMTM, this study has the potential to significantly decrease methane emissions.

Selective Formation of Acetic Acid and Methanol by Direct Methane Oxidation Using Rhodium Single-Atom Catalysts.

Atomically dispersed catalysts such as single-atom catalysts have been shown to be effective in selectively oxidizing methane, promising a direct synthetic route to value-added oxygenates such as acetic acid or methanol. However, an important challenge of this approach has been that the loading of active sites by single-atom catalysts is low, leading to a low overall yield of the products. Here, we report an approach that can address this issue. It utilizes a metal-organic framework built with porphyrin as the linker, which provides high concentrations of binding sites to support atomically dispersed rhodium. It is shown that up to 5 wt% rhodium loading can be achieved with excellent dispersity. When used for acetic acid synthesis by methane oxidation, a new benchmark performance of 23.62 mmol·gcat-1·h-1 was measured. Furthermore, the catalyst exhibits a unique sensitivity to light, producing acetic acid (under illumination, up to 66.4% selectivity) or methanol (in the dark, up to 65.0% selectivity) under otherwise identical reaction conditions.

Nearly 100% selective and visible-light-driven methane conversion to formaldehyde via. single-atom Cu and Wδ+

Direct solar-driven methane (CH4) reforming is highly desirable but challenging, particularly to achieve a value-added product with high selectivity. Here, we identify a synergistic ensemble effect of atomically dispersed copper (Cu) species and partially reduced tungsten (Wδ+), stabilised over an oxygen-vacancy-rich WO3, which enables exceptional photocatalytic CH4 conversion to formaldehyde (HCHO) under visible light, leading to nearly 100% selectivity, a very high yield of 4979.0 μmol·g−1 within 2 h, and the normalised mass activity of 8.5 × 106 μmol·g-1Cu·h−1 of HCHO at ambient temperature. In-situ EPR and XPS analyses indicate that the Cu species serve as the electron acceptor, promoting the photo-induced electron transfer from the conduction band to O2, generating reactive •OOH radicals. In parallel, the adjacent Wδ+ species act as the hole acceptor and the preferred adsorption and activation site of H2O to produce hydroxyl radicals (•OH), and thus activate CH4 to methyl radicals (•CH3). The synergy of the adjacent dual active sites boosts the overall efficiency and selectivity of the conversion process.