Showing papers on "Methane published in 2018"

Selective functionalization of methane, ethane, and higher alkanes by cerium photocatalysis

Abstract: With the recent soaring production of natural gas, the use of methane and other light hydrocarbon feedstocks as starting materials in synthetic transformations is becoming increasingly economically attractive, although it remains chemically challenging. We report the development of photocatalytic C-H amination, alkylation, and arylation of methane, ethane, and higher alkanes under visible light irradiation at ambient temperature. High catalytic efficiency (turnover numbers up to 2900 for methane and 9700 for ethane) and selectivity were achieved using abundant, inexpensive cerium salts as photocatalysts. Ligand-to-metal charge transfer excitation generated alkoxy radicals from simple alcohols that in turn acted as hydrogen atom transfer catalysts. The mixed-phase gas/liquid reaction was adapted to continuous flow, enabling the efficient use of gaseous feedstocks in scalable photocatalytic transformations.

Highly selective oxidation of methane to methanol at ambient conditions by titanium dioxide-supported iron species

Abstract: Methane activation under moderate conditions and with good selectivity for value-added chemicals still remains a huge challenge. Here, we present a highly selective catalyst for the transformation of methane to methanol composed of highly dispersed iron species on titanium dioxide. The catalyst operates under moderate light irradiation (close to one Sun) and at ambient conditions. The optimized sample shows a 15% conversion rate for methane with an alcohol selectivity of over 97% (methanol selectivity over 90%) and a yield of 18 moles of alcohol per mole of iron active site in just 3 hours. X-ray photoelectron spectroscopy measurements with and without xenon lamp irradiation, light-intensity-modulated spectroscopies, photoelectrochemical measurements, X-ray absorption near-edge structure and extended X-ray absorption fine structure spectra, as well as isotopic analysis confirm the function of the major iron-containing species—namely, FeOOH and Fe2O3, which enhance charge transfer and separation, decrease the overpotential of the reduction reaction and improve selectivity towards methanol over carbon dioxide production. Methanol synthesis from methane is a promising route to valorize this abundant natural gas, but existing thermal processes require harsh reaction conditions. Now, a photocatalytic approach based on TiO2-supported iron oxide species is described, which affords methanol in high yield and selectivity at ambient conditions.

Production of methane and ethylene from plastic in the environment

Abstract: Mass production of plastics started nearly 70 years ago and the production rate is expected to double over the next two decades. While serving many applications because of their durability, stability and low cost, plastics have deleterious effects on the environment. Plastic is known to release a variety of chemicals during degradation, which has a negative impact on biota. Here, we show that the most commonly used plastics produce two greenhouse gases, methane and ethylene, when exposed to ambient solar radiation. Polyethylene, which is the most produced and discarded synthetic polymer globally, is the most prolific emitter of both gases. We demonstrate that the production of trace gases from virgin low-density polyethylene increase with time, with rates at the end of a 212-day incubation of 5.8 nmol g-1 d-1 of methane, 14.5 nmol g-1 d-1 of ethylene, 3.9 nmol g-1 d-1 of ethane and 9.7 nmol g-1 d-1 of propylene. Environmentally aged plastics incubated in water for at least 152 days also produced hydrocarbon gases. In addition, low-density polyethylene emits these gases when incubated in air at rates ~2 times and ~76 times higher than when incubated in water for methane and ethylene, respectively. Our results show that plastics represent a heretofore unrecognized source of climate-relevant trace gases that are expected to increase as more plastic is produced and accumulated in the environment.

Resources and geology of coalbed methane in China: a review

Abstract: China produced 17.1 billion cubic meters (BCM) of methane sourced from coal seams in 2015, of which 4.43 BCM is from wells drilled from the surface. This level of production is a clear indicator th...

Bioinspired Metal-Organic Framework Catalysts for Selective Methane Oxidation to Methanol.

Abstract: Particulate methane monooxygenase (pMMO) is an enzyme that oxidizes methane to methanol with high activity and selectivity. Limited success has been achieved in incorporating biologically relevant ligands for the formation of such active site in a synthetic system. Here, we report the design and synthesis of metal-organic framework (MOF) catalysts inspired by pMMO for selective methane oxidation to methanol. By judicious selection of a framework with appropriate topology and chemical functionality, MOF-808 was used to postsynthetically install ligands bearing imidazole units for subsequent metalation with Cu(I) in the presence of dioxygen. The catalysts show high selectivity for methane oxidation to methanol under isothermal conditions at 150 °C. Combined spectroscopies and density functional theory calculations suggest bis(μ-oxo) dicopper species as probable active site of the catalysts.

Single rhodium atoms anchored in micropores for efficient transformation of methane under mild conditions.

Abstract: Catalytic transformation of CH4 under a mild condition is significant for efficient utilization of shale gas under the circumstance of switching raw materials of chemical industries to shale gas. Here, we report the transformation of CH4 to acetic acid and methanol through coupling of CH4, CO and O2 on single-site Rh1O5 anchored in microporous aluminosilicates in solution at ≤150 °C. The activity of these singly dispersed precious metal sites for production of organic oxygenates can reach about 0.10 acetic acid molecules on a Rh1O5 site per second at 150 °C with a selectivity of ~70% for production of acetic acid. It is higher than the activity of free Rh cations by >1000 times. Computational studies suggest that the first C–H bond of CH4 is activated by Rh1O5 anchored on the wall of micropores of ZSM-5; the formed CH3 then couples with CO and OH, to produce acetic acid over a low activation barrier. Catalytic transformation of CH4 under mild conditions has implications to shale gas utilization. Here, the authors report the transformation of CH4 to acetic acid through coupling of CH4, CO and O2 on single-site Rh1O5 anchored in microporous aluminosilicates in liquid phase.

A robust fuel cell operated on nearly dry methane at 500 °C enabled by synergistic thermal catalysis and electrocatalysis

Abstract: Solid oxide fuel cells (SOFCs) are potentially the most efficient technology for direct conversion of hydrocarbons to electricity. While their commercial viability is greatest at operating temperatures of 300–500 °C, it is extremely difficult to run SOFCs on methane at these temperatures, where oxygen reduction and C–H activation are notoriously sluggish. Here we report a robust SOFC that enabled direct utilization of nearly dry methane (with ~3.5% H2O) at 500 °C (achieving a peak power density of 0.37 W cm−2) with no evidence of coking after ~550 h operation. The cell consists of a PrBa0.5Sr0.5Co1.5Fe0.5O5+δ nanofibre-based cathode and a BaZr0.1Ce0.7Y0.1Yb0.1O3–δ-based multifunctional anode coated with Ce0.90Ni0.05Ru0.05O2 (CNR) catalyst for reforming of CH4 to H2 and CO. The high activity and coking resistance of the CNR is attributed to a synergistic effect of cationic Ni and Ru sites anchored on the CNR surface, as confirmed by in situ/operando experiments and computations. Solid oxide fuel cells are most commercially viable when run at low temperatures, but this makes it challenging to achieve high performance with hydrocarbon fuels. Here the authors report a fuel cell running at 500 °C on nearly dry methane that incorporates a Ni–Ru–CeO2-based reforming catalyst, achieving high power densities and coking resistance.

Global diffusive fluxes of methane in marine sediments

Abstract: Anaerobic oxidation of methane provides a globally important, yet poorly constrained barrier for the vast amounts of methane produced in the subseafloor. Here we provide a global map and budget of the methane flux and degradation in diffusion-controlled marine sediments in relation to the depth of the methane oxidation barrier. Our new budget suggests that 45–61 Tg of methane are oxidized with sulfate annually, with approximately 80% of this oxidation occurring in continental shelf sediments (<200 m water depth). Using anaerobic oxidation as a nearly quantitative sink for methane in steady-state diffusive sediments, we calculate that ~3–4% of the global organic carbon flux to the seafloor is converted to methane. We further report a global imbalance of diffusive methane and sulfate fluxes into the sulfate–methane transition with no clear trend with respect to the corresponding depth of the methane oxidation barrier. The observed global mean net flux ratio between sulfate and methane of 1.4:1 indicates that, on average, the methane flux to the sulfate–methane transition accounts for only ~70% of the sulfate consumption in the sulfate–methane transition zone of marine sediments.

Direct Methane to Methanol: The Selectivity–Conversion Limit and Design Strategies

Abstract: Currently, methane is transformed into methanol through the two-step syngas process, which requires high temperatures and centralized production. While the slightly exothermic direct partial oxidation of methane to methanol would be preferable, no such process has been established despite over a century of research. Generally, this failure has been attributed to both the high barriers required to activate methane as well as the higher activity of the CH bonds in methanol compared to those in methane. However, a precise and general quantification of the limitations of catalytic direct methane to methanol has yet to be established. Herein, we present a simple kinetic model to explain the selectivity–conversion trade-off that hampers continuous partial oxidation of methane to methanol. For the same kinetic model, we apply two distinct methods, (1) using ab initio calculations and (2) fitting to a large experimental database, to fully define the model parameters. We find that both methods yield strikingly sim...

Stable complete methane oxidation over palladium based zeolite catalysts.

Abstract: Increasing the use of natural gas engines is an important step to reduce the carbon footprint of mobility and power generation sectors. To avoid emissions of unburnt methane and the associated severe greenhouse effect of lean-burn engines, the stability of methane oxidation catalysts against steam-induced sintering at low temperatures (<500 °C) needs to be improved. Here we demonstrate how the combination of catalyst development and improved process control yields a highly efficient solution for complete methane oxidation. We design a material based on palladium and hierarchical zeolite with fully sodium-exchanged acid sites, which improves the support stability and prevents steam-induced palladium sintering under reaction conditions by confining the metal within the zeolite. Repeated short reducing pulses enable the use of a highly active transient state of the catalyst, which in combination with its high stability provides excellent performance without deactivation for over 90 h in the presence of steam.

Toward Global Mapping of Methane With TROPOMI: First Results and Intersatellite Comparison to GOSAT

Abstract: The TROPOspheric Monitoring Instrument (TROPOMI), launched on 13 October 2017, aboard the Sentinel‐5 Precursor satellite, measures reflected sunlight in the ultraviolet, visible, near‐infrared, and shortwave infrared spectral range. It enables daily global mapping of key atmospheric species for monitoring air quality and climate. We present the first methane observations from November and December 2017, using TROPOMI radiance measurements in the shortwave infrared band around 2.3 μm. We compare our results with the methane product obtained from the Greenhouse gases Observing SATellite (GOSAT). Although different spectral ranges and retrieval methods are used, we find excellent agreement between the methane products acquired from the two satellites with a mean difference of 13.6 ppb, standard deviation of 19.6 ppb, and Pearson's correlation coefficient of 0.95. Our preliminary results capture the latitudinal gradient and show expected regional enhancements, for example, in the African Sudd wetlands, with much more detail than has been observed before.

Gold plasmon-induced photocatalytic dehydrogenative coupling of methane to ethane on polar oxide surfaces

Abstract: This work shows the solar-driven dehydrogenative coupling of methane to ethane at room temperature. A solar-to-C2H6 energy conversion efficiency of 0.08% was achieved on the polar surface of Au/ZnO porous nanosheets (NSs), where methane C–H bonds are polarized and dissociated by the local electric field normal to the polar {001} plane, and finally converted into ethane and hydrogen through a radical coupling pathway. Mechanistic studies suggest that the Au-plasmon-induced resonance energy transfer modulates charge carrier energetics to trigger the stoichiometric conversion. Hot electrons reduce protons to H2, which is the rate-determining step of methane coupling.

Tuning the catalytic performance of Ni-catalysed dry reforming of methane and carbon deposition via Ni-CeO2-x interaction

Abstract: The role of tuning metal-support interaction in determining the catalytic activity and carbon formation in dry reforming of methane to syngas was examined over CeO2 supported Ni nanoparticles. The catalysts pre- and post- reaction were subjected to characterisation in terms of N2 physisorption, TPR, XRD, TEM, XPS and TGA-DTG. Reduction of Ni/CeO2 in H2 in the temperature range (773–973 K) generated a strong bonding between Ni and CeO2 that inhibited Ni particle sintering (8.7–9.4 nm). High-temperature (≥873 K) reduction induced decoration/encapsulation of Ni nanoparticles by a thin layer of reduced ceria support with partial coverage of Ni surface. The decoration/encapsulation effect strongly influences the catalytic properties of Ni, which enables to tune the catalytic activity of Ni/CeO2 and carbon deposition in dry reforming of methane.

A review of plasma-assisted catalytic conversion of gaseous carbon dioxide and methane into value-added platform chemicals and fuels

Abstract: CO2 and CH4 contribute to greenhouse gas emissions, while the production of industrial base chemicals from natural gas resources is emerging as well. Such conversion processes, however, are energy-intensive and introducing a renewable and sustainable electric activation seems optimal, at least for intermediate-scale modular operation. The review thus analyses such valorisation by plasma reactor technologies and heterogeneous catalysis application, largely into higher hydrocarbon molecules, that is ethane, ethylene, acetylene, propane, etc., and organic oxygenated compounds, i.e. methanol, formaldehyde, formic acid and dimethyl ether. Focus is given to reaction pathway mechanisms, related to the partial oxidation steps of CH4 with O2, H2O and CO2, CO2 reduction with H2, CH4 or other paraffin species, and to a lesser extent, to mixtures' dry reforming to syngas. Dielectric barrier discharge, corona, spark and gliding arc sources are considered, combined with (noble) metal materials. Carbon (C), silica (SiO2) and alumina (Al2O3) as well as various catalytic supports are examined as precious critical raw materials (e.g. platinum, palladium and rhodium) or transition metal (e.g. manganese, iron, cobalt, nickel and copper) substrates. These are applied for turnover, such as that pertinent to reformer, (reverse) water–gas shift (WGS or RWGS) and CH3OH synthesis. Time-on-stream catalyst deactivation or reactivation is also overviewed from the viewpoint of individual transient moieties and their adsorption or desorption characteristics, as well as reactivity.

Methane production as key to the greenhouse gas budget of thawing permafrost

Abstract: Permafrost thaw liberates frozen organic carbon, which is decomposed into carbon dioxide (CO2) and methane (CH4). The release of these greenhouse gases (GHGs) forms a positive feedback to atmospheric CO2 and CH4 concentrations and accelerates climate change1,2. Current studies report a minor importance of CH4 production in water-saturated (anoxic) permafrost soils3–6 and a stronger permafrost carbon–climate feedback from drained (oxic) soils1,7. Here we show through seven-year laboratory incubations that equal amounts of CO2 and CH4 are formed in thawing permafrost under anoxic conditions after stable CH4-producing microbial communities have established. Less permafrost carbon was mineralized under anoxic conditions but more CO2–carbon equivalents (CO2–Ce) were formed than under oxic conditions when the higher global warming potential (GWP) of CH4 is taken into account 8 . A model of organic carbon decomposition, calibrated with the observed decomposition data, predicts a higher loss of permafrost carbon under oxic conditions (113 ± 58 g CO2–C kgC−1 (kgC, kilograms of carbon)) by 2100, but a twice as high production of CO2–Ce (241 ± 138 g CO2–Ce kgC−1) under anoxic conditions. These findings challenge the view of a stronger permafrost carbon-climate feedback from drained soils1,7 and emphasize the importance of CH4 production in thawing permafrost on climate-relevant timescales. An organic carbon decomposition model, calibrated with laboratory incubations, indicates a greater production rate of CO2-C equivalents from waterlogged (compared to drained) permafrost soils, when the higher global warming potential of methane is factored in.

CO2 reforming with methane over small-sized Ni@SiO2 catalysts with unique features of sintering-free and low carbon

Abstract: Sintering-free and carbon-free Ni catalysts developments are hot topics for high temperature hydrocarbons catalytic reactions. Core-shell is a promising structure to limit sintering, but ineffective towards carbon deposition if big sized Ni nanoparticles are present. In this work, core-shell structured Ni@SiO2 catalysts with small-sized Ni nanoparticles (about 5 nm) were synthesized by microemulsion method, which are featured by both sintering-free and low carbon deposits for high temperature CO2 reforming with methane reaction. The advantages were originated from the silica shell overlay confined moving space of Ni nanoparticles and the small size of Ni nanoparticles guaranteed low carbon diffusion in Ni crystals. The work provides a simple approach to synthesize small-sized Ni nanoparticles in core-shell catalysts for stable performance of CO2 reforming with methane reaction. It is supposed that this type of catalyst could also be applied in many other hydrocarbon catalytic reactions involving sintering and carbon problems.

Ni stabilised on inorganic complex structures: superior catalysts for chemical CO2 recycling via dry reforming of methane

Abstract: CO2 utilisation is becoming an appealing topic in catalysis science due to the urgent need to deal with greenhouse gases (GHG) emissions. Herein, the dry reforming of methane (DRM) represents a viable route to convert CO2 and CH4 (two of the major GHG) into syngas, a highly valuable intermediate in chemical synthesis. Nickel-based catalysts are economically viable materials for this reaction, however they show inevitable signs of deactivation. In this work stabilisation of Ni in a pyrochlore-perovskite structure is reported as a viable method to prevent fast deactivation. Substitution of Zirconium by Ni at various loadings in the lanthanum zirconate pyrochlore La2Zr2O7 is investigated in terms of reactant conversions under various reaction conditions (temperature and space velocity). XRD analysis of the calcined and reduced catalysts showed the formation of crystalline phases corresponding to the pyrochlore structure La2Zr2-xNixO7-δ and an additional La2NiZrO6 perovskite phase at high Ni loadings. Carbon formation is limited using this formulation strategy and, as a consequence, our best catalyst shows excellent activity for DRM at temperatures as low as 600 °C and displays great stability over 350 hours of continuous operation. Exsolution of Ni from the oxide structure, leading to small and well dispersed Ni clusters, could explain the enhanced performance.

Catalytic chemoselective functionalization of methane in a metal−organic framework

Abstract: Methane constitutes the largest fraction of natural gas reserves and is a low-cost abundant starting material for the synthesis of value-added chemicals and fuel. Selective catalytic functionalization of methane remains a vital goal in the chemical sciences due to its low intrinsic reactivity. Borylation has recently emerged as a promising route for the catalytic functionalization of methane. A major challenge in this regard is selective borylation towards the monoborylated product that is more active than methane and can easily lead to over-functionalization. Herein, we report a highly selective microporous metal−organic-framework-supported iridium(iii) catalyst for methane borylation that exhibits a chemoselectivity of >99% (mono versus bis at 19.5% yield; turnover number = 67) for monoborylated methane, with bis(pinacolborane) as the borylation reagent in dodecane, at 150 °C and 34 atm of methane. The preference for the monoborylated product is ascribed to the shape-selective effect of the metal−organic framework pore structures. Methane borylation allows for the functionalization of an otherwise unreactive compound, enabling its use as a one-carbon building block; however, competing diborylation presents a selectivity issue. Now, a metal–organic-framework-based catalyst highly selective for monoborylation is reported. The selectivity is due to the reaction taking place within the catalyst pores, which excludes the formation of the larger diborlyated product.

CO2 reforming of methane over supported LaNiO3 perovskite-type oxides

Abstract: This work investigated the performance of supported LaNiO3 perovskite-type oxides for the CO2 reforming of methane. The methane and CO2 conversion increased at the beginning of reaction for LaNiO3 and LaNiO3/Al2O3 catalysts. On the other hand, conversion remained quite constant for LaNiO3/CeSiO2. in situ XPS experiments under reaction conditions revealed that the metallic Ni particles were oxidized by CO2 from the feed for LaNiO3 and LaNiO3/Al2O3 catalysts. Ceria support was preferentially oxidized, limiting the oxidation of the metallic phase. Raman spectroscopy and thermogravimetric analysis showed that carbon was formed mainly over LaNiO3 and LaNiO3/Al2O3 catalysts. Supporting LaNiO3 over CeSiO2 almost completely suppressed carbon deposition. in situ XPS experiments showed a continuous change of ceria oxidation states between Ce4+ and Ce3+ under reaction conditions. This result in a high oxygen mobility of ceria support that reacts with carbon, inhibiting the formation of nickel carbide and consequently the nucleation and growth of carbon filaments.

State of art and perspectives about the production of methanol, dimethyl ether and syngas by carbon dioxide hydrogenation

Abstract: The conversion of carbon dioxide into feedstock for the chemical and process industry is the most efficient way to rapidly introduce renewable energy in this value chain. Carbon capture and utilization systems are getting the attention from researchers in the last years, also due to the introduction of carbon tax in many States. Through the hydrogenation of carbon dioxide methane, hydrocarbons, ethanol, formic acid, methanol, dimethyl ether and syngas can be produced. However, methanol dimethyl ether and syngas have the lower value of lost hydrogen during the reaction, equal to 0.33, 0.25 and 0, respectively. Then, these compounds are analyzed in this review. Carbon dioxide is an industrial waste, while hydrogen is generally obtained by the electrolysis of water using surplus renewable energies. Processes and reactors reported in literature regarding the production of methanol, dimethyl ether and syngas by hydrogenation of carbon dioxide are analyzed. For the capture of carbon dioxide adsorption, absorption, membranes, cryogenic systems can be developed. An important role will have ionic liquids, under study by many researchers. Future research efforts should focus on dry reforming processes, innovative carbon dioxide capture techniques and hydrogen availability at reduced cost, and wider dissemination of these scientific and technical concepts to enlarge social acceptance.