Showing papers on "Methane published in 2020"

Light-driven methane dry reforming with single atomic site antenna-reactor plasmonic photocatalysts

Abstract: Syngas, an extremely important chemical feedstock composed of carbon monoxide and hydrogen, can be generated through methane (CH4) dry reforming with CO2. However, traditional thermocatalytic processes require high temperatures and suffer from coke-induced instability. Here, we report a plasmonic photocatalyst consisting of a Cu nanoparticle ‘antenna’ with single-Ru atomic ‘reactor’ sites on the nanoparticle surface, ideal for low-temperature, light-driven methane dry reforming. This catalyst provides high light energy efficiency when illuminated at room temperature. In contrast to thermocatalysis, long-term stability (50 h) and high selectivity (>99%) were achieved in photocatalysis. We propose that light-excited hot carriers, together with single-atom active sites, cause the observed performance. Quantum mechanical modelling suggests that single-atom doping of Ru on the Cu(111) surface, coupled with excited-state activation, results in a substantial reduction in the barrier for CH4 activation. This photocatalyst design could be relevant for future energy-efficient industrial processes. Syngas is a mixture of CO and H2 that can be converted into a variety of fuels. Syngas can be produced thermocatalytically from CH4 and CO2, but this requires high temperatures and coke formation can be a problem. Here the authors demonstrate lower temperature, light-driven production of syngas using a coke-resistant plasmonic photocatalyst.

Hydrophobic zeolite modification for in situ peroxide formation in methane oxidation to methanol

Abstract: Selective partial oxidation of methane to methanol suffers from low efficiency. Here, we report a heterogeneous catalyst system for enhanced methanol productivity in methane oxidation by in situ generated hydrogen peroxide at mild temperature (70°C). The catalyst was synthesized by fixation of AuPd alloy nanoparticles within aluminosilicate zeolite crystals, followed by modification of the external surface of the zeolite with organosilanes. The silanes appear to allow diffusion of hydrogen, oxygen, and methane to the catalyst active sites, while confining the generated peroxide there to enhance its reaction probability. At 17.3% conversion of methane, methanol selectivity reached 92%, corresponding to methanol productivity up to 91.6 millimoles per gram of AuPd per hour.

Dry reforming of methane by stable Ni-Mo nanocatalysts on single-crystalline MgO.

Abstract: Large-scale carbon fixation requires high-volume chemicals production from carbon dioxide. Dry reforming of methane could provide an economically feasible route if coke- and sintering-resistant catalysts were developed. Here, we report a molybdenum-doped nickel nanocatalyst that is stabilized at the edges of a single-crystalline magnesium oxide (MgO) support and show quantitative production of synthesis gas from dry reforming of methane. The catalyst runs more than 850 hours of continuous operation under 60 liters per unit mass of catalyst per hour reactive gas flow with no detectable coking. Synchrotron studies also show no sintering and reveal that during activation, 2.9 nanometers as synthesized crystallites move to combine into stable 17-nanometer grains at the edges of MgO crystals above the Tammann temperature. Our findings enable an industrially and economically viable path for carbon reclamation, and the “Nanocatalysts On Single Crystal Edges” technique could lead to stable catalyst designs for many challenging reactions.

Quantifying methane emissions from the largest oil-producing basin in the United States from space

Abstract: Using new satellite observations and atmospheric inverse modeling, we report methane emissions from the Permian Basin, which is among the world's most prolific oil-producing regions and accounts for >30% of total U.S. oil production. Based on satellite measurements from May 2018 to March 2019, Permian methane emissions from oil and natural gas production are estimated to be 2.7 ± 0.5 Tg a−1, representing the largest methane flux ever reported from a U.S. oil/gas-producing region and are more than two times higher than bottom-up inventory-based estimates. This magnitude of emissions is 3.7% of the gross gas extracted in the Permian, i.e., 60% higher than the national average leakage rate. The high methane leakage rate is likely contributed by extensive venting and flaring, resulting from insufficient infrastructure to process and transport natural gas. This work demonstrates a high-resolution satellite data-based atmospheric inversion framework, providing a robust top-down analytical tool for quantifying and evaluating subregional methane emissions. © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).

Aquatic and terrestrial cyanobacteria produce methane.

Abstract: Evidence is accumulating to challenge the paradigm that biogenic methanogenesis, considered a strictly anaerobic process, is exclusive to archaea. We demonstrate that cyanobacteria living in marine, freshwater, and terrestrial environments produce methane at substantial rates under light, dark, oxic, and anoxic conditions, linking methane production with light-driven primary productivity in a globally relevant and ancient group of photoautotrophs. Methane production, attributed to cyanobacteria using stable isotope labeling techniques, was enhanced during oxygenic photosynthesis. We suggest that the formation of methane by cyanobacteria contributes to methane accumulation in oxygen-saturated marine and limnic surface waters. In these environments, frequent cyanobacterial blooms are predicted to further increase because of global warming potentially having a direct positive feedback on climate change. We conclude that this newly identified source contributes to the current natural methane budget and most likely has been producing methane since cyanobacteria first evolved on Earth.

Water-promoted interfacial pathways in methane oxidation to methanol on a CeO2-Cu2O catalyst

Abstract: Highly selective oxidation of methane to methanol has long been challenging in catalysis. Here, we reveal key steps for the pro-motion of this reaction by water when tuning the selectivity of a well-defined CeO2/Cu2O/Cu(111) catalyst from carbon monoxide and carbon dioxide to methanol under a reaction environment with methane, oxygen, and water. Ambient-pressure x-ray photoelectron spectroscopy showed that water added to methane and oxygen led to surface methoxy groups and accelerated methanol production. These results were consistent with density functional theory calculations and kinetic Monte Carlo simulations, which showed that water preferentially dissociates over the active cerium ions at the CeO2-Cu2O/Cu(111) interface. The adsorbed hydroxyl species blocked O-O bond cleavage that would dehydrogenate methoxy groups to carbon monoxide and carbon dioxide, and it directly converted this species to methanol, while oxygen reoxidized the reduced surface. Water adsorption also displaced the produced methanol into the gas phase.

Hydrochar-Facilitated Anaerobic Digestion: Evidence for Direct Interspecies Electron Transfer Mediated through Surface Oxygen-Containing Functional Groups.

Abstract: Acceleration of the anaerobic digestion (AD) process is crucial to achieving energy-efficient recycling of organic wastes. Hydrochar is produced by hydrothermal liquefaction of biomass, yet its application in the AD process is rarely reported. The present study showed that sewage sludge-derived hydrochar (SH) enhanced the methane production rate of glucose by 37%. SH increased the methane production rate from acetate but did not affect acidification and the methane production rate from H2/CO2. SH enhanced hydrogenotrophic methanogenesis, which could be due to direct interspecies electron transfer (DIET) by converting H+, e-, and CO2 to methane. Trichococcus and Methanosaeta were dominant in the AD process with SH. Label-free proteomic analysis showed Methanosaeta was involved in DIET as reflected by the up-regulation of proteins involved in hydrogenotrophic methanogenesis. Hydrochars derived from corn straw (CH), Enteromorpha algae (EH), and poplar wood (PH), as well as activated carbon (AC), were also tested in the AD process. SH, CH, and EH obviously increased the methane production rates, which were 39%, 15%, and 20% higher than the control experiment, respectively. It was neither electrical conductivity nor the total redox property of hydrochars and AC but the abundances of surface oxygen-containing functional groups that correlated to the methane production rates.

A review on catalytic methane combustion at low temperatures: Catalysts, mechanisms, reaction conditions and reactor designs

Abstract: Natural gas (with methane as its main component) provides an attractive energy source because of its large abundance and its high heat of combustion per mole of carbon dioxide generated. However, the emissions released from the conventional flame combustion (essentially NOx) have harmful impacts on the environment and the human health. Within the scope of rational and clean use of fossil energies, the catalytic combustion of natural gas appears as one of the most promising alternatives to flammable combustion. The presence of catalysts enables complete oxidation of methane at much lower temperatures (typically 500 °C), so that the formation of pollutants can be largely avoided. This work presents a literature review on the catalytic methane combustion. Various aspects are discussed including the catalyst types, the reaction mechanisms and kinetic characteristics, effects of various influencing operational factors and different reactor types proposed and tested. This paper may serve as an essential reference that contributes to the development of well-designed reactors, equipped with appropriate catalysts, and under well-handled operating conditions to realize the favorable (kinetic) performance, for their future applications and propagation in different industrial sectors.

Photocatalytic uphill conversion of natural gas beyond the limitation of thermal reaction systems

Abstract: Dry reforming of methane is one of the key reactions to exploit natural gas feedstocks by their catalytic conversion to synthesis gas (CH4 + CO2 → 2H2 + 2CO), which is used in the production of transportable liquid fuel. However, this reaction suffers from thermodynamic conversion limits and high thermal energy requirements. Herein we report that a SrTiO3-supported rhodium (Rh/STO) catalyst efficiently promotes methane reforming under ultraviolet light irradiation without heat supply at low temperatures, which cannot be achieved by conventional thermal catalysis. The photoexcited holes and electrons are used for CH4 oxidation over STO and CO2 reduction over rhodium, respectively. Isotope analysis clarified that the lattice oxygens (O2−) act as mediator to drive dry reforming of methane. The materials design of Rh/STO can be extended in principle to diverse uphill reactions that utilize photon energy to obtain valued products from different carbon resources. Despite its potential, catalytic dry reforming of methane has not yet reached practical application due to high thermal energy requirements. Now, a photocatalytic method is introduced based on strontium titanate-supported rhodium nanoparticles that afford syngas production solely under light irradiation.

Catalytic Hydrogen Production from Methane: A Review on Recent Progress and Prospect

Abstract: Natural gas (Methane) is currently the primary source of catalytic hydrogen production, accounting for three quarters of the annual global dedicated hydrogen production (about 70 M tons). Steam–methane reforming (SMR) is the currently used industrial process for hydrogen production. However, the SMR process suffers with insufficient catalytic activity, low long-term stability, and excessive energy input, mostly due to the handling of large amount of CO2 coproduced. With the demand for anticipated hydrogen production to reach 122.5 M tons in 2024, novel and upgraded catalytic processes are desired for more effective utilization of precious natural resources. In this review, we summarized the major descriptors of catalyst and reaction engineering of the SMR process and compared the SMR process with its derivative technologies, such as dry reforming with CO2 (DRM), partial oxidation with O2, autothermal reforming with H2O and O2. Finally, we discussed the new progresses of methane conversion: direct decomposition to hydrogen and solid carbon and selective oxidation in mild conditions to hydrogen containing liquid organics (i.e., methanol, formic acid, and acetic acid), which serve as alternative hydrogen carriers. We hope this review will help to achieve a whole picture of catalytic hydrogen production from methane.

A Short Review on Ni Based Catalysts and Related Engineering Issues for Methane Steam Reforming

Abstract: Hydrogen is an important raw material in chemical industries, and the steam reforming of light hydrocarbons (such as methane) is the most used process for its production. In this process, the use of a catalyst is mandatory and, if compared to precious metal-based catalysts, Ni-based catalysts assure an acceptable high activity and a lower cost. The aim of a distributed hydrogen production, for example, through an on-site type hydrogen station, is only reachable if a novel reforming system is developed, with some unique properties that are not present in the large-scale reforming system. These properties include, among the others, (i) daily startup and shutdown (DSS) operation ability, (ii) rapid response to load fluctuation, (iii) compactness of device, and (iv) excellent thermal exchange. In this sense, the catalyst has an important role. There is vast amount of information in the literature regarding the performance of catalysts in methane steam reforming. In this short review, an overview on the most recent advances in Ni based catalysts for methane steam reforming is given, also regarding the use of innovative structured catalysts.

Catalytic Dry Reforming of Methane: Insights from Model Systems

Abstract: Catalytic dry reforming under industrially relevant conditions of high pressures and high temperatures poses severe challenges towards catalyst materials and process engineering. The demanding conditions under which the reaction is performed lead to a coupling of reactions occurring in the gas phase and reactions which are catalyzed by the material employed as catalyst. A profound analysis of the mechanisms occurring in gas phase and resulting products from gas phase reactions is key to understanding part of the challenges that any catalyst material, irrespective of its nature, will have to cope with. The deposition of coke on an active catalyst is as well one of the most limiting factors for catalyst lifetime and catalyst activity in dry reforming. Therefore, an understanding of the thermodynamics behind coke formation and an intricate description of the mechanisms driving the evolution of coke is a vital piece of the picture. Acid‐base properties of the catalyst material and the role and nature of the active metal do also need to be considered. A large part of the review deals with mechanisms which are relevant for coke gasification and insights into materials properties, which are relevant to allow for reaction pathways along these lines. The review article focusses on research results which have been achieved using model systems – typically the analysis of model systems is a more rewarding exercise compared to fully formulated industrial catalyst systems, as here more elucidating structure‐property relationships can be drawn. Additionally the article discusses dry methane reforming in the context of alternative syngas generation technologies and attempts to create an application perspective for the reader in the context of a sustainable approach towards carbon capture and storage.

Efficient Methane Electrosynthesis Enabled by Tuning Local CO2 Availability.

Abstract: The electroreduction of carbon dioxide (CO2RR) to valuable chemicals is a promising avenue for the storage of intermittent renewable electricity. Renewable methane, obtained via CO2RR using renewable electricity as energy input, has the potential to serve as a carbon-neutral fuel or chemical feedstock, and it is of particular interest in view of the well-established infrastructure for its storage, distribution, and utilization. However, CO2RR to methane still suffers from low selectivity at commercially relevant current densities (>100 mA cm-2). Density functional theory calculations herein reveal that lowering *CO2 coverage on the Cu surface decreases the coverage of the *CO intermediate, and then this favors the protonation of *CO to *CHO, a key intermediate for methane generation, compared to the competing step, C-C coupling. We therefore pursue an experimental strategy wherein we control local CO2 availability on a Cu catalyst by tuning the concentration of CO2 in the gas stream and regulate the reaction rate through the current density. We achieve as a result a methane Faradaic efficiency (FE) of (48 ± 2)% with a partial current density of (108 ± 5) mA cm-2 and a methane cathodic energy efficiency of 20% using a dilute CO2 gas stream. We report stable methane electrosynthesis for 22 h. These findings offer routes to produce methane with high FE and high conversion rate in CO2RR and also make direct use of dilute CO2 feedstocks.

Transforming carbon dioxide into jet fuel using an organic combustion-synthesized Fe-Mn-K catalyst

Abstract: With mounting concerns over climate change, the utilisation or conversion of carbon dioxide into sustainable, synthetic hydrocarbons fuels, most notably for transportation purposes, continues to attract worldwide interest. This is particularly true in the search for sustainable or renewable aviation fuels. These offer considerable potential since, instead of consuming fossil crude oil, the fuels are produced from carbon dioxide using sustainable renewable hydrogen and energy. We report here a synthetic protocol to the fixation of carbon dioxide by converting it directly into aviation jet fuel using novel, inexpensive iron-based catalysts. We prepare the Fe-Mn-K catalyst by the so-called Organic Combustion Method, and the catalyst shows a carbon dioxide conversion through hydrogenation to hydrocarbons in the aviation jet fuel range of 38.2%, with a yield of 17.2%, and a selectivity of 47.8%, and with an attendant low carbon monoxide (5.6%) and methane selectivity (10.4%). The conversion reaction also produces light olefins ethylene, propylene, and butenes, totalling a yield of 8.7%, which are important raw materials for the petrochemical industry and are presently also only obtained from fossil crude oil. As this carbon dioxide is extracted from air, and re-emitted from jet fuels when combusted in flight, the overall effect is a carbon-neutral fuel. This contrasts with jet fuels produced from hydrocarbon fossil sources where the combustion process unlocks the fossil carbon and places it into the atmosphere, in longevity, as aerial carbon - carbon dioxide.

Dry reforming of methane catalysed by molten metal alloys

Abstract: Dry reforming of methane usually affords low-quality syngas with equimolar amounts of CO and H2. Here we report the high conversion of CH4 and CO2 to syngas and solid carbon through simultaneous pyrolysis and dry reforming of methane in a bubble column reactor using a molten metal alloy catalyst (65:35 mol% Ni:In). The H2 to CO ratio can be increased above 1:1 using feed ratios of CH4:CO2 greater than 1:1 to produce stoichiometric solid carbon as a co-product that is separable from the molten metal. A coupled reduction–oxidation cycle is carried out in which CO2 is reduced by a liquid metal species (for example, In) and methane is partially oxidized to syngas by the metal oxide intermediate (for example, In2O3), regenerating the native metal. Moreover, the H2:CO product ratio can be easily controlled by adjusting the CH4:CO2 feed ratio, temperature, and residence time in the reactor. Dry reforming of methane can so far afford syngas with equimolar CO and H2, which is suboptimal for Fischer–Tropsch chemistry. Now a process is reported based on a Ni–In molten metal alloy catalyst that is capable of producing syngas with practically relevant H2/CO ratios together with separable carbon.

State of the Art of Hydrogen Production via Pyrolysis of Natural Gas

Abstract: Fossil fuels have to be substituted by climate neutral fuels to contribute to CO2 reduction in the future energy system. Pyrolysis of natural gas is a well‐known technical process applied for production of, e. g., carbon black. In the future it might contribute to carbon dioxide‐free hydrogen production. Production of hydrogen from natural gas pyrolysis has thus gained interest in research and energy technology in the near past. If the carbon by‐product of this process can be used for material production or can be sequestrated, the produced hydrogen has a low carbon footprint. This article reviews literature on the state of the art of methane / natural gas pyrolysis process developments and attempts to assess the technology readiness level (TRL).

Effects of the surface adsorbed oxygen species tuned by rare-earth metal doping on dry reforming of methane over Ni/ZrO2 catalyst

Abstract: During dry reforming of methane, oxygen species over the catalyst surface play an important role in CH4/CO2 reactivity, catalytic performance and carbon deposition. Herein, the effects of the surface adsorbed oxygen species tuned by doping with different rare-metal metals (such as Ce, La, Sm and Y) on the catalytic behavior were elaborated systematically. It was found that Y-doped catalyst exhibited the most amount of surface adsorbed oxygen species, followed by Sm, La, Ce and non-doped catalysts. The results confirmed that the surface adsorbed oxygen species were remarkably beneficial to enhance both CO2 activation and CH4 dissociation. Nevertheless, carbon formation and removal did not keep pace at low temperature due to more promotional effects of the surface adsorbed oxygen species on CH4 dissociation than CO2 activation. The gap between carbon deposition and removal was potential to be ameliorated through the accelerated activation to CO2 at high temperature.

Effects of Oxygen Mobility in La–Fe-Based Perovskites on the Catalytic Activity and Selectivity of Methane Oxidation

Abstract: The mechanism and structure requirements of selective and total oxidation of methane in a chemical looping process are both experimentally and theoretically examined on La1–xSrxFeO3−δ (x = 0, 0.2, ...

Superior catalytic activity of a Pd catalyst in methane combustion by fine-tuning the phase of ceria-zirconia support

Abstract: Methane, one of the greenhouse gases, is controlled by the catalytic combustion that is the most efficient method. Herein, ceria-zirconia solid solutions (CeZrO4) with high specific surface areas and different phases (κappa and tetragonal) were synthesized and then used to construct the supported Pd catalyst for methane combustion. Compared to the tetragonal CeZrO4 support (t-CZ), the smaller particle sizes of PdOx and the higher amount of active PdO species are present on the κappa CeZrO4 support (κ-CZ), leading to a higher ability of the Pd/κ-CZ catalyst for methane activation. More critically, the oxygen mobility of the Pd/κ-CZ catalyst is much higher than that of the Pd/t-CZ catalyst. Consequently, an excellent and stable redox cycle of PdO species is achieved on the Pd/κ-CZ catalyst compared to the Pd/t-CZ catalyst, prompting the oxidation of hydrocarbon fragments. These two factors result into a superior catalytic activity of the Pd/κ-CZ catalyst for methane combustion.

Ultra-rapid uptake and the highly stable storage of methane as combustible ice

Abstract: The continuously increasing trend of natural gas (NG) consumption due to its clean nature and abundant availability indicates an inevitable transition to an NG-dominated economy. Solidified natural gas (SNG) storage via combustible ice or clathrate hydrates presents an economically sound prospect, promising high volume density and long-term storage. Herein, we establish 1,3-dioxolane (DIOX) as a highly efficient dual-action (thermodynamic and kinetic promoter) additive for the formation of clathrate (methane sII) hydrate. By synergistically combining a small concentration (300 ppm) of the kinetic promoter L-tryptophan with DIOX, we further demonstrated the ultra-rapid formation of hydrates with a methane uptake of 83.81 (±0.77) volume of gas/volume of hydrate (v/v) within 15 min. To the best of our knowledge, this is the fastest reaction time reported to date for sII hydrates related to SNG technology and represents a 147% increase in the hydrate formation rate compared to the standard water–DIOX system. Mixed methane–DIOX hydrates in pelletized form also exhibited incredible stability when stored at atmospheric pressure and moderate temperature of 268.15 K, thereby showcasing the potential to be industrially applicable for the development of a large-scale NG storage system.

Embedded Ni nanoparticles in CeZrO2 as stable catalyst for dry reforming of methane

Abstract: Ni nanoparticles embedded in CeO2 (Ni@CeO2) and CeZrO2 (Ni@CeZrO2) were synthesized by sol-gel method and compared with a Ni/CeO2 prepared by support impregnation. The performance of the catalysts was investigated for dry reforming of methane reaction. In situ XRD, XANES and TEM showed that Ni embedded in CeO2 improved the resistance to sintering along the reduction at 800 °C. Doping ceria with zirconia inhibited the growth of Ni particles and increased the oxygen mobility. SEM, TEM, Raman spectroscopy and TGA of the used catalysts after dry reforming of methane showed that carbon formation rate was significantly reduced for the catalysts containing Ni nanoparticles embedded in ceria structure. Carbon deposits were not detected over Ni@CeZrO2 after 24 h of reaction. Therefore, the control of Ni particle size and the high oxygen mobility of Ni@CeZrO2 catalyst inhibited carbon deposition and favored the mechanism of carbon removal, promoting catalyst stability.

Stoichiometric methane conversion to ethane using photochemical looping at ambient temperature

Abstract: Methane activation and utilization are among the major challenges of modern science. Methane is potentially an important feedstock for manufacturing value-added fuels and chemicals. However, most known processes require excessive operating temperatures and exhibit insufficient selectivity. Here, we demonstrate a photochemical looping strategy for highly selective stoichiometric conversion of methane to ethane at ambient temperature over silver–heteropolyacid–titania nanocomposites. The process involves a stoichiometric reaction of methane with highly dispersed cationic silver under illumination, which results in the formation of methyl radicals. Recombination of the generated methyl radicals leads to the selective, and almost quantitative, formation of ethane. Cationic silver species are simultaneously reduced to metallic silver. The silver–heteropolyacid–titania nanocomposites can be reversibly regenerated in air under illumination at ambient temperature. The photochemical looping process achieves a methane coupling selectivity of over 90%, a quantitative yield of ethane of over 9%, high quantum efficiency (3.5% at 362 nm) and excellent stability. Activating methane at ambient temperature is challenging due to its stability, but could ultimately give access to a variety of other fuels and chemicals. Here, the authors present a photochemical looping strategy based on silver chemistry that converts methane to ethane under illumination at room temperature.

Structure Sensitivity in Steam and Dry Methane Reforming over Nickel: Activity and Carbon Formation

Abstract: Hydrogen is currently mainly produced via steam reforming of methane (SMR: CH4 + H2O → CO + 3H2). An alternative to this process, utilizing carbon dioxide and thus potentially mitigating its enviro...

Effects of Zr Doping into Ceria for the Dry Reforming of Methane over Ni/CeZrO2 Catalysts: In Situ Studies with XRD, XAFS, and AP-XPS

Abstract: The methane activation and methane dry reforming reactions were studied and compared over 4 wt % Ni/CeO2 and 4 wt % Ni/CeZrO2 (containing 20 wt % Zr) catalysts. Upon the incorporation of Zr into th...

Highly Selective Carbon Dioxide Electroreduction on Structure-Evolved Copper Perovskite Oxide toward Methane Production

Abstract: Electrochemical carbon dioxide (CO2) conversion is promising to balance the carbon cycle for human society. However, an efficient electrocatalyst is the key to determine the selective conversion of...