Showing papers on "Methane published in 2022"

Stabilizing Cu²⁺ Ions by Solid Solutions to Promote CO₂ Electroreduction to Methane

Abstract: Copper is the only metal catalyst that can perform the electrocatalytic CO2 reduction reaction (CRR) to produce hydrocarbons and oxygenates. Its surface oxidation state determines the reaction pathway to various products. However, under the cathodic potential of CRR conditions, the chemical composition of most Cu-based catalysts inevitably undergoes electroreduction from Cu2+ to Cu0 or Cu1+ species, which is generally coupled with phase reconstruction and the formation of new active sites. Since the initial Cu2+ active sites are hard to retain, there have been few studies about Cu2+ catalysts for CRR. Herein we propose a solid-solution strategy to stabilize Cu2+ ions by incorporating them into a CeO2 matrix, which works as a self-sacrificing ingredient to protect Cu2+ active species. In situ spectroscopic characterization and density functional theory calculations reveal that compared with the conventionally derived Cu catalysts with Cu0 or Cu1+ active sites, the Cu2+ species in the solid solution (Cu-Ce-Ox) can significantly strengthen adsorption of the *CO intermediate, facilitating its further hydrogenation to produce CH4 instead of dimerization to give C2 products. As a result, different from most of the other Cu-based catalysts, Cu-Ce-Ox delivered a high Faradaic efficiency of 67.8% for CH4 and a low value of 3.6% for C2H4.

On the climate impacts of blue hydrogen production

Abstract: Natural gas based hydrogen production with carbon capture and storage is referred to as blue hydrogen. If substantial amounts of CO2 from natural gas reforming are captured and permanently stored, such hydrogen could be a low-carbon energy carrier. However, recent research raises questions about the effective climate impacts of blue hydrogen from a life cycle perspective. Our analysis sheds light on the relevant issues and provides a balanced perspective on the impacts on climate change associated with blue hydrogen. We show that such impacts may indeed vary over large ranges and depend on only a few key parameters: the methane emission rate of the natural gas supply chain, the CO2 removal rate at the hydrogen production plant, and the global warming metric applied. State-of-the-art reforming with high CO2 capture rates combined with natural gas supply featuring low methane emissions does indeed allow for substantial reduction of greenhouse gas emissions compared to both conventional natural gas reforming and direct combustion of natural gas. Under such conditions, blue hydrogen is compatible with low-carbon economies and exhibits climate change impacts at the upper end of the range of those caused by hydrogen production from renewable-based electricity. However, neither current blue nor green hydrogen production pathways render fully “net-zero” hydrogen without additional CO2 removal.

Global assessment of oil and gas methane ultra-emitters

Abstract: Methane emissions from oil and gas (O&G) production and transmission represent a considerable contribution to climate change. These emissions comprise sporadic releases of large amounts of methane during maintenance operations or equipment failures not accounted for in current inventory estimates. We collected and analyzed hundreds of very large releases from atmospheric methane images sampled by the TROPOspheric Monitoring Instrument (TROPOMI) between 2019 and 2020. Ultra-emitters are primarily detected over the largest O&G basins throughout the world. With a total contribution equivalent to 8 to 12% (~8 million metric tons of methane per year) of the global O&G production methane emissions, mitigation of ultra-emitters is largely achievable at low costs and would lead to robust net benefits in billions of US dollars for the six major O&G-producing countries when considering societal costs of methane.

Au-ZSM-5 catalyses the selective oxidation of CH4 to CH3OH and CH3COOH using O2

Abstract: The oxidation of methane, the main component of natural gas, to selectively form oxygenated chemical feedstocks using molecular oxygen has been a long-standing grand challenge in catalysis. Here, using gold nanoparticles supported on the zeolite ZSM-5, we introduce a method to oxidize methane to methanol and acetic acid in water at temperatures between 120 and 240 °C using molecular oxygen in the absence of any added coreductant. Electron microscopy reveals that the catalyst does not contain gold atoms or clusters, but rather gold nanoparticles are the active component, while a mechanism involving surface adsorbed species is proposed in which methanol and acetic acid are formed via parallel pathways.

Synergy of Pd atoms and oxygen vacancies on In2O3 for methane conversion under visible light

Abstract: Abstract Methane (CH 4 ) oxidation to high value chemicals under mild conditions through photocatalysis is a sustainable and appealing pathway, nevertheless confronting the critical issues regarding both conversion and selectivity. Herein, under visible irradiation (420 nm), the synergy of palladium (Pd) atom cocatalyst and oxygen vacancies (OVs) on In 2 O 3 nanorods enables superior photocatalytic CH 4 activation by O 2 . The optimized catalyst reaches ca. 100 μmol h −1 of C1 oxygenates, with a selectivity of primary products (CH 3 OH and CH 3 OOH) up to 82.5%. Mechanism investigation elucidates that such superior photocatalysis is induced by the dedicated function of Pd single atoms and oxygen vacancies on boosting hole and electron transfer, respectively. O 2 is proven to be the only oxygen source for CH 3 OH production, while H 2 O acts as the promoter for efficient CH 4 activation through ·OH production and facilitates product desorption as indicated by DFT modeling. This work thus provides new understandings on simultaneous regulation of both activity and selectivity by the synergy of single atom cocatalysts and oxygen vacancies.

Methane transformation by photocatalysis

Abstract: Methane hydrate and shale gas are predicted to have substantial reserves, far beyond the sum of other fossil fuels. Using methane instead of crude oil as a building block is, thus, a very attractive strategy for synthesizing valuable chemicals. Because methane is so inert, its direct conversion needs a high activation energy and typically requires harsh reaction conditions or strong oxidants. Photocatalysis, which employs photons operated under very mild conditions, is a promising technology to reduce the thermodynamic barrier in direct methane conversion and to avoid the common issues of overoxidation and catalyst deactivation. In this Review, we cover the development of photocatalysts and co-catalysts, including the use of inorganic materials and polymeric semiconductors, and explain how the use of batch or flow reaction systems affects the reaction kinetics and product selectivity. We also discuss efforts to understand the underlying reaction mechanisms from both a photophysical and a chemical perspective. Finally, we present our view of the challenges facing this field and suggest potential solutions. Methane, as a replacement for crude oil, can be converted into valuable chemicals through photocatalysis. This Review discusses the design of promising photocatalytic systems and strategies to understand their reaction mechanisms and outlines the most pressing questions still facing the field.

High-performance photocatalytic nonoxidative conversion of methane to ethane and hydrogen by heteroatoms-engineered TiO2

Abstract: Nonoxidative coupling of methane (NOCM) is a highly important process to simultaneously produce multicarbons and hydrogen. Although oxide-based photocatalysis opens opportunities for NOCM at mild condition, it suffers from unsatisfying selectivity and durability, due to overoxidation of CH4 with lattice oxygen. Here, we propose a heteroatom engineering strategy for highly active, selective and durable photocatalytic NOCM. Demonstrated by commonly used TiO2 photocatalyst, construction of Pd-O4 in surface reduces contribution of O sites to valence band, overcoming the limitations. In contrast to state of the art, 94.3% selectivity is achieved for C2H6 production at 0.91 mmol g-1 h-1 along with stoichiometric H2 production, approaching the level of thermocatalysis at relatively mild condition. As a benchmark, apparent quantum efficiency reaches 3.05% at 350 nm. Further elemental doping can elevate durability over 24 h by stabilizing lattice oxygen. This work provides new insights for high-performance photocatalytic NOCM by atomic engineering.

A metal-supported single-atom catalytic site enables carbon dioxide hydrogenation

Abstract: Abstract Nitrogen-doped graphene-supported single atoms convert CO 2 to CO, but fail to provide further hydrogenation to methane – a finding attributable to the weak adsorption of CO intermediates. To regulate the adsorption energy, here we investigate the metal-supported single atoms to enable CO 2 hydrogenation. We find a copper-supported iron-single-atom catalyst producing a high-rate methane. Density functional theory calculations and in-situ Raman spectroscopy show that the iron atoms attract surrounding intermediates and carry out hydrogenation to generate methane. The catalyst is realized by assembling iron phthalocyanine on the copper surface, followed by in-situ formation of single iron atoms during electrocatalysis, identified using operando X-ray absorption spectroscopy. The copper-supported iron-single-atom catalyst exhibits a CO 2 -to-methane Faradaic efficiency of 64% and a partial current density of 128 mA cm −2 , while the nitrogen-doped graphene-supported one produces only CO. The activity is 32 times higher than a pristine copper under the same conditions of electrolyte and bias.

A metal-supported single-atom catalytic site enables carbon dioxide hydrogenation

Abstract: Abstract Nitrogen-doped graphene-supported single atoms convert CO 2 to CO, but fail to provide further hydrogenation to methane – a finding attributable to the weak adsorption of CO intermediates. To regulate the adsorption energy, here we investigate the metal-supported single atoms to enable CO 2 hydrogenation. We find a copper-supported iron-single-atom catalyst producing a high-rate methane. Density functional theory calculations and in-situ Raman spectroscopy show that the iron atoms attract surrounding intermediates and carry out hydrogenation to generate methane. The catalyst is realized by assembling iron phthalocyanine on the copper surface, followed by in-situ formation of single iron atoms during electrocatalysis, identified using operando X-ray absorption spectroscopy. The copper-supported iron-single-atom catalyst exhibits a CO 2 -to-methane Faradaic efficiency of 64% and a partial current density of 128 mA cm −2 , while the nitrogen-doped graphene-supported one produces only CO. The activity is 32 times higher than a pristine copper under the same conditions of electrolyte and bias.

Electronically Engineering Water Resistance in Methane Combustion with an Atomically Dispersed Tungsten on PdO Catalyst.

Abstract: Improving the low-temperature water-resistance of methane combustion catalysts is of vital importance for industrial applications and it is challenging. A stepwise strategy is presented for the preparation of atomically dispersed tungsten species at the catalytically active site (Pd nanoparticles). After an activation process, a Pd-O-W1-like nanocompound is formed on the PdO surface with an atomic scale interface. The resulting supported catalyst possesses much stronger water resistance than the conventional catalysts for methane combustion. The integrated characterization results confirm that catalytic combustion of methane involves water, proceeding via a hydroperoxyl-promoted reaction mechanism on the catalyst surface. The results of density functional theory calculations indicate an upshift of the d-band center of palladium caused by electron transfer from atomically dispersed tungsten, which greatly facilitates the adsorption and activation of oxygen on the catalyst.

Plasma-assisted dry reforming of methane over Mo2C-Ni/Al2O3 catalysts: Effects of β-Mo2C promoter

Abstract: Non-thermal plasma (NTP) coupled with catalysis provides a way to enable the dry reforming of methane (DRM) reaction to occur at low temperatures. While assistance of NTP brings the negative issue of coke deposition due to the faster rate of CH4 dissociation induced by NTP. Herein, β-Mo2C was employed as an effective component to activate CO2 and collaborated with Ni/γ-Al2O3 for the plasma-assisted DRM reaction. Addition of β-Mo2C facilitated the charge deposition, and Ni nanoparticles were found to re-disperse over the β-Mo2C surface due to the strong interaction between Ni and β-Mo2C. Benefiting from the new active interface of Ni-Mo2C, the mechanically mixed Mo2C-Ni/Al2O3 catalyst exhibited much better activity and stability as compared with the undoped Ni/Al2O3 catalyst. The present study reveals the crucial roles of β-Mo2C additives, providing practical solutions to depress carbon deposition, and thereby enhance the catalytic stability in plasma-assisted DRM reaction.

Methane and NOx Emissions from Natural Gas Stoves, Cooktops, and Ovens in Residential Homes.

Abstract: Natural gas stoves in >40 million U.S. residences release methane (CH4)─a potent greenhouse gas─through post-meter leaks and incomplete combustion. We quantified methane released in 53 homes during all phases of stove use: steady-state-off (appliance not in use), steady-state-on (during combustion), and transitory periods of ignition and extinguishment. We estimated that natural gas stoves emit 0.8-1.3% of the gas they use as unburned methane and that total U.S. stove emissions are 28.1 [95% confidence interval: 18.5, 41.2] Gg CH4 year-1. More than three-quarters of methane emissions we measured originated during steady-state-off. Using a 20-year timeframe for methane, annual methane emissions from all gas stoves in U.S. homes have a climate impact comparable to the annual carbon dioxide emissions of 500 000 cars. In addition to methane emissions, co-emitted health-damaging air pollutants such as nitrogen oxides (NOx) are released into home air and can trigger respiratory diseases. In 32 homes, we measured NOx (NO and NO2) emissions and found them to be linearly related to the amount of natural gas burned (r2 = 0.76; p ≪ 0.01). Emissions averaged 21.7 [20.5, 22.9] ng NOx J-1, comprised of 7.8 [7.1, 8.4] ng NO2 J-1 and 14.0 [12.8, 15.1] ng NO J-1. Our data suggest that families who don't use their range hoods or who have poor ventilation can surpass the 1-h national standard of NO2 (100 ppb) within a few minutes of stove usage, particularly in smaller kitchens.

Rapid global phaseout of animal agriculture has the potential to stabilize greenhouse gas levels for 30 years and offset 68 percent of CO2 emissions this century

Abstract: Animal agriculture contributes significantly to global warming through ongoing emissions of the potent greenhouse gases methane and nitrous oxide, and displacement of biomass carbon on the land used to support livestock. However, because estimates of the magnitude of the effect of ending animal agriculture often focus on only one factor, the full potential benefit of a more radical change remains underappreciated. Here we quantify the full “climate opportunity cost” of current global livestock production, by modeling the combined, long-term effects of emission reductions and biomass recovery that would be unlocked by a phaseout of animal agriculture. We show that, even in the absence of any other emission reductions, persistent drops in atmospheric methane and nitrous oxide levels, and slower carbon dioxide accumulation, following a phaseout of livestock production would, through the end of the century, have the same cumulative effect on the warming potential of the atmosphere as a 25 gigaton per year reduction in anthropogenic CO2 emissions, providing half of the net emission reductions necessary to limit warming to 2°C. The magnitude and rapidity of these potential effects should place the reduction or elimination of animal agriculture at the forefront of strategies for averting disastrous climate change.