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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

F-state quenching with CH{sub 4} for buffer-gas cooled {sup 171}Y b{sup +} frequency standard

We report that methane, CH{sub 4}, can be used as an efficient F-state quenching gas for trapped ytterbium ions. The quenching rate coefficient is measured to be (2.8 ± 0.3) × 10{sup 6} s{sup −1} Torr{sup −1}. For applications that use microwave hyperfine transitions of the ground-state {sup 171}Y b ions, the CH{sub 4} induced frequency shift coefficient and the decoherence rate coefficient are measured as δν/ν = (−3.6 ± 0.1) × 10{sup −6} Torr{sup −1} and 1/T{sub 2} = (1.5 ± 0.2) × 10{sup 5} s{sup −1} Torr{sup −1}. In our buffer-gas cooled {sup 171}Y b{sup +} microwave clock system, we find that only ≤10{sup −8} Torr of CH{sub 4} is required under normal operating conditions to efficiently clear the F-state and maintain ≥85% of trapped ions in the ground state with insignificant pressure shift and collisional decoherence of the clock resonance.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Low-Energy, Low-Cost Ethylene Production by Low-Temperature Oxidative Coupling of Methane

Ethylene, one of the highest volume production chemicals in the U.S. and globally, is an essential chemical building block that is used to manufacture countless products, from packaging to antifreeze to tires. Most ethylene is produced via a process called steam cracking, where the feedstock (mostly ethane, sometimes naphtha or propane) is heated to high temperatures over a catalyst. The naphtha feedstock typically comes from petroleum refineries, while ethane is becoming increasingly used as a feedstock in the U.S. due to the rise in domestic natural gas production from shale resources. However, steam cracking is energy intensive and occurs in large- scale facilities. Low-temperature oxidative coupling of methane (LT-OCM) is an alternative ethylene production method that converts methane (natural gas) and optionally ethane to ethylene in a single-step, energy-producing conversion system using an innovative process. While OCM has been studied for over 30 years due to its potential to reduce ethylene production cost, past efforts did not result in a viable catalyst with performance needed for commercialization. These catalysts, while at times achieving promising yield and selectivity, were hampered by very high operating temperatures, low activities, and short lifetimes on the order of hours to days. Recognizing this, Siluria applied a combination of new innovations in catalyst development and a thorough definition and understanding of the problem to develop unique catalysts that enable commercialization of OCM. The OCM catalysts operate at significantly lower temperature (several hundreds of degrees lower) and practical operating pressures (5-10 atmospheres), have high activities and standard lifetimes of years under said conditions. In addition, the simple process provides excellent scalability and flexibility, especially when compared to today’s mega-scale steam crackers, thus enabling small- volume “distributed scale” reactors for on-demand ethylene production for applications such as on-site conversion of ethylene to high value polymer derivatives.

02 PETROLEUM↗
DOE OSTI2014

Techno-Economic Analysis of Bioconversion of Methane into Biofuel and Biochemical (Poster)

In light of the relatively low price of natural gas and increasing demands of liquid transportation fuels and high-value chemicals, attention has begun to turn to novel biocatalyst for conversion of methane (CH4) into biofuels and biochemicals [1]. A techno-economic analysis (TEA) was performed for an integrated biorefinery process using biological conversion of methane, such as carbon yield,process efficiency, productivity (both lipid and acid), natural gas and other raw material prices, etc. This analysis is aimed to identify research challenges as well provide guidance for technology development.

03 NATURAL GAS↗
DOE OSTI2018

Glacial cycles influence marine methane hydrate formation

Methane hydrates in fine-grained continental slope sediments often occupy isolated depth intervals surrounded by hydrate-free sediments. As they are not connected to deep gas sources, these hydrate deposits have been interpreted as sourced by in situ microbial methane. We investigate here the hypothesis that these isolated hydrate accumulations form preferentially in sediments deposited during Pleistocene glacial lowstands that contain relatively large amounts of labile particulate organic carbon, leading to enhanced microbial methanogenesis. To test this hypothesis, we apply an advection-diffusion-reaction model with a time-dependent organic carbon deposition controlled by glacioeustatic sea level variations. In the model, hydrate forms in sediments with greater organic carbon content deposited during the penultimate glacial cycle (~120-240 ka). As a result, the model predictions match hydrate-bearing intervals detected in three sites drilled on the northern Gulf of Mexico continental slope, supporting the hypothesis of hydrate formation driven by enhanced organic carbon burial during glacial lowstands.

58 GEOSCIENCES↗
DOE OSTI2026

MoS 2 Catalysts Selectively Achieve High Yield of Liquid Oxygenate from Direct Conversion of Methane via Hydroxyl Radicals

Directly converting methane (CH 4 ) into liquid oxygenates (e.g., methanol) can circumvent the cost and engineering limits of natural gas transportation and storage. However, oxygenate yields from CH 4 remain low, and sulfur present in natural gas hinders activity in most catalysts. Here, to overcome these barriers, we employ bulk molybdenum disulfide (MoS 2 ), a low-cost, robust catalyst which selectively produces large quantities of liquid oxygenates (>900 µmol/g cat ∙hr) from methane in the presence of hydroxyl (OH • ) radicals produced from dilute hydrogen peroxide (H 2 O 2 ) at 75°C. Under realistic reaction conditions, MoS 2 partially and reversibly adopts a metastable, more electrically conductive phase (1T’) that can only be observed through in situ structural probes. Herein, we elucidate that redox synergy between H 2 O 2 and MoS 2 produces active OH • radical species that selectively transform CH 4 to surface methoxy species at the gas-solid liquid interface, leading to the unitary production of liquid oxygenate at a rate competitive with more costly precious metal catalysts, without additional catalyst preparation steps.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Low-Temperature Transformation of Methane to Methanol on Pd 1 O 4 Single Sites Anchored on the Internal Surface of Microporous Silicate

Direct conversion of methane to chemical feedstocks such as methanol under mild conditions is a challenging but ideal solution for utilization of methane. Pd 1 O 4 single-sites anchored on the internal surface of micropores of a microporous silicate exhibit high selectivity and activity in transforming CH 4 to CH 3 OH at 50–95 °C in aqueous phase through partial oxidation of CH 4 with H 2 O 2 . The selectivity for methanol production remains at 86.4 %, while the activity for methanol production at 95 °C is about 2.78 molecules per Pd 1 O 4 site per second when 2.0 wt % CuO is used as a co-catalyst with the Pd 1 O 4 @ZSM-5. Thermodynamic calculations suggest that the reaction toward methanol production is highly favorable compared to formation of a byproduct, methyl peroxide.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Boosting the Activity of Pd Single Atoms by Tuning Their Local Environment on Ceria for Methane Combustion

Supported Pd single atom catalysts (SACs) have triggered great research interest in methane combustion yet with contradicting views on their activity and stability. Here, in this paper, we show that the Pd SAs can take different electronic structure and atomic geometry on ceria support, resulting in different catalytic properties. By a simple thermal pretreatment to ceria prior to Pd deposition, a unique anchoring site is created. The Pd SA, taking this site, can be activated to Pd δ+ (0<δ<2) that has greatly enhanced activity for methane oxidation: T 50 lowered by up to 130 °C and almost 10 times higher turnover frequency compared to the untreated catalyst. The enhanced activity of Pd δ+ site is related to its oxygen-deficient local structure and elongated interacting distance with ceria, leading to enhanced capability in delivering reactive oxygen species and decomposing reaction intermediates. This work provides insights into designing highly efficient Pd SACs for oxidation reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Impact of Iron Species Dispersion on Fe/ZSM–5 Catalyst Performance for Methane Dehydroaromatization (MDA)

Methane dehydroaromatization (MDA) is one of the most promising technologies for directly transforming methane into aromatics. Unlike the extensively investigated Mo/ZSM-5 catalysts, the structure and, consequently, the catalytic activity of Fe/ZSM-5 are markedly influenced by the method of preparation, as shown here. In this study, we prepared 2 % and 4 % Fe/ZSM-5 catalysts via wet impregnation (WI) and incipient wetness impregnation (IWI). Characterizations (XRD, STEM, UV-Vis, NH 3 -TPD and H 2 -TPR) reveal that 2 %Fe-WI mainly possesses isolated or low-polymerized Fe species within zeolite channels, leading to a rapid activation and a higher benzene yield due to the faster reduction to iron suboxides under MDA conditions. In contrast, 2 %Fe-IWI contains bulk iron oxide aggregates, resulting in a slower activation as these aggregates transform into iron carbide through successive reduction and carbonization. Here, a deactivation kinetic study applied to the 2 % catalysts further demonstrates the quantitative relation between Fe site isolation and catalytic activity. Although both 4 % catalysts inevitably form sizable iron oxide clusters and particles due to the high Fe/Al ratio, similar trends are noted, with the WI catalysts exhibiting a shorter induction/activation period and a higher yield of benzene, paralleling observations made with 2 % catalysts.

03 NATURAL GAS↗
DOE OSTI2023

Genesis of Active Pt/CeO 2 Catalyst for Dry Reforming of Methane by Reduction and Aggregation of Isolated Platinum Atoms into Clusters

Atomically dispersed metal catalysts offer the advantages of efficient metal utilization and high selectivities for reactions of technological importance. Such catalysts have been suggested to be strong candidates for dry reforming of methane (DRM), offering prospects of high selectivity for synthesis gas without coke formation, which requires ensembles of metal sites and is a challenge to overcome in DRM catalysis. However, investigations of the structures of isolated metal sites on metal oxide supports under DRM conditions are lacking, and the catalytically active sites remain undetermined. Data characterizing the DRM reaction-driven structural evolution of a cerium oxide- supported catalyst, initially incorporating atomically dispersed platinum, and the corresponding changes in catalyst performance are reported. X-ray absorption and infrared spectra show that the reduction and agglomeration of isolated cationic platinum atoms to form small platinum clusters/nanoparticles are necessary for DRM activity. Density functional theory calculations of the energy barriers for methane dissociation on atomically dispersed platinum and on platinum clusters support these observations. Here the results emphasize the need for in-operando experiments to assess the active sites in such catalysts. The inferences about the catalytically active species are suggested to pertain to a broad class of catalytic conversions involving the rate-limiting dissociation of light alkanes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

A minor respiratory process with major global implications: is atmospheric methane oxidation in tree stems driven by stem respiration rather than microbial methanotrophy?

Tree stem surfaces are widely recognized as sites of carbon dioxide (CO₂) efflux and oxygen (O₂) influx, reflecting the dynamics of aerobic respiration of photosynthate substrates, such as sugars, delivered via the phloem. Stems are also largely considered passive conduits for methane (CH₄) produced in anoxic soils via microbial methanogenesis, where CH₄ is thought to be transported upward through the transpiration stream and/or diffusion and emitted through stem surfaces and the canopy. However, recent observations from dynamic stem chambers suggest that stems may also act as active sinks for atmospheric CH₄. Despite these findings, the extent and drivers of stem CH₄ consumption remain poorly characterized across biomes, species, and environmental gradients, and its quantitative relationship to stem respiration has not been established. Moreover, previous studies captured only snapshot fluxes, leaving diurnal patterns of CH₄ exchange uncharacterized. Here, we address these limitations by combining real-time measurements of stem CH₄ and O₂ uptake under ambient conditions in a California cherry tree, using a dynamic stem gas exchange system with three chambers receiving a continuous flow of ambient air and automated chamber and reference air sampling every 10 min. Our results confirm that stems of upland trees can actively consume both atmospheric CH₄ and O₂, but with decreasing temperature sensitivity as daily temperatures increase. Early mornings were marked by rapid influxes of both gases, followed by declining uptake as temperatures rose further. Methane uptake was tightly coupled with O₂ influx and represented a minor (0.012% ± 0.002%) fraction of stem respiratory activity, as determined by concurrent O₂ uptake. These findings suggest that while atmospheric CH₄ oxidation is a minor respiratory process in stems, it is strongly linked with stem physiological activity. This challenges the current assumption that terrestrial CH₄ uptake is driven solely by microbial methanotrophy and raises the possibility that living stem tissues may contribute to CH₄ oxidation through an as-yet-unidentified plant-based mechanism.

Atmospheric greenhouse gases↗
DOE OSTI2018

Regimes of Hydrate Formation in the Process of Injection of Carbon Dioxide into a Porous Medium Saturated with Methane and Water

The problem on the formation of the hydrate of carbon dioxide in the process of its injection into a porous medium saturated with methane and water, whose initial temperature does not correspond to the thermodynamic conditions of existence of the carbon-dioxide hydrate, was considered. This problem was solved for the case where the hydrate formation takes place at the front interface not coincident with the boundary of displacement of methane by carbon dioxide. It is shown that, in the case where the initial temperature of the porous medium exceeds the equilibrium temperature of hydrate formation, the carbon-dioxide hydrate can be formed in three regimes. Curves separating these regimes depending on the injection pressure, the initial temperature of the medium, and its permeability have been constructed.

42 ENGINEERING↗
DOE OSTI2022

Investigation of the Mechanisms Underpinning Plasma-Catalyst Interaction for the Conversion of Methane to Oxygenates

Plasma catalysis is a promising approach to further enhance the conversion of methane into value-added products such as methanol. In this work, the mechanisms enabling the conversion of methane to CO, CO 2 and methanol enabled by plasma-enhanced catalysis were investigated. A catalyst reactor was incorporated downstream of the plasma jet to enable the separation between plasma generation and the catalyst bed. An enhancement in CH 3 OH and CO 2 production was observed for the shortest distance between the plasma and catalyst compared to the plasma-only case. Plasma-enabled gas heating was shown not to be responsible for the observed synergy while a gas temperature increase as low as 30-40 K significantly impacted desorption rates of CH 3 OH/C 2 H 5 OH on alumina particles. Correlations between molecular beam mass spectrometry (MBMS) measurements at the inlet and outlet of the catalytic reactor suggest that the observed synergistic effect was caused by radical species most likely the CH 3 O 2 radical. As a result, this study shows that surface reactions induced by radicals such as alkylperoxy radicals might play an important role in surface reactions in plasma-catalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Selective conversion of methane to aromatic hydrocarbons on large crystallite zeolite catalysts with mesoporous structure

Large crystallite mesoporous MFI (ZSM-5) zeolite was synthesized by using carbon nano-powder as a secondary template. The surface properties, morphological and phase composition of the synthesized material and of the commercial ZSM-5 (Zeolyst) zeolite were studied by nitrogen porosimetry, XRD and scanning electron microscopy. The results showed that the volume of mesopores volume increases with development of a secondary mesoporosity in the structure of zeolite. The obtained zeolite supports were used to prepare molybdenum-containing catalysts for the methane aromatization by solid phase preparation technique. Based on the XPS data, molybdenum particles in these catalysts are characterized by more uniform size distribution. The formation of a secondary pore structure restrains the carbon deposit formation as well as increases the methane conversion and the yield of the aromatic compounds.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Spin crossover in homo- and heteroligand iron(II) complexes with tris(pyrazol-1-yl)methane derivatives

The studies concerning coordination compounds of various salts of iron(II) with tris(pyrazol-1-yl)methane derivatives (HC(pz){sub 3}) are discussed. The results of a number of studies on the synthesis and investigation of the homo- and heteroligand iron(II) complexes with tris(3,5- dimethylpyrazol-1-yl)methane (HC(3,5-Me{sub 2}pz){sub 3}) are considered. The study of the temperature dependence μ{sub eff} (T) showed that the spin crossover (SCO) {sup 1}A{sub 1}↔{sup 5}T{sub 2} observed in a series of the compounds discussed is accompanied by thermochromism (color change pink (purple) ↔ colorless). Specific features of the SCO and their dependence on the outer-sphere anion in the iron(II) complexes are discussed. The data of the recently published work devoted to the synthesis of the iron(II) complexes with three N-substituted HC(pz){sub 3} derivatives (general formula {sup x}L, where x = H, CH{sub 2}C{sub 6}H{sub 5} (Bn) and p-SO{sub 3}C{sub 6}H{sub 4}CH{sub 3} (Ts)) are considered.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Optimization of structural and energy characteristics of adsorbents for methane storage

Using numerical and analytical methods, a model for microporous carbon adsorbents with slit-shaped pores of different widths was developed. Such pores are formed during activation procedure by the removal of the hexagonal carbon layers burnt out in a graphite-like crystallites. Dubinin’s theory of volume filling of micropores was used to calculate methane adsorption equilibria on these model adsorbents. Isobaric dependences of methane adsorption on pore width, specific micropore volumes, and the specific surface were plotted in the range of pressures from 1 to 10 MPa. It was found that the isobaric adsorption curves had a maximum the position of which depends on both the structural-energy characteristics of the adsorbent and thermodynamic conditions chosen to operate the adsorption system. As pressure increased, the maximum of adsorption shifts to the porous systems with wider pores and larger micropore volume.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Methane Production by Co-Digesting Vinasse and Whey in an AnSBBR: Effect of Mixture Ratio and Feed Strategy

The most common approach to deal with vinasse (sugarcane stillage) is fertigation, but this technique compromises soil structure and surrounding water bodies. A possible solution is to transport vinasse to local cheese whey producers and perform the co-digestion of these wastewaters together, reducing their organic load and generating bioenergy. Therefore, this study investigated the application of an AnSBBR (anaerobic sequencing batch biofilm reactor) operated in batch and fed-batch mode, co-digesting vinasse and whey at 30 °C. The effect of influent composition and feeding strategy was assessed. In all conditions, the system achieved high organic matter removal (approximately 83%). Increasing the percentage of vinasse from 0 to 100% in the influent resulted in a decrease in methane productivity (76.3 to 51.1 molCH{sub 4} m{sup −3} day{sup −1}) and yield (12.7 to 9.1 molCH{sub 4} kgCOD{sup −1}), but fed-batch mode operation improved reactor performance (73.0 molCH{sub 4} m{sup −3} day{sup −1} and 11.5 molCH{sub 4} kgCOD{sup −1}). From the kinetic metabolic model, it was possible to infer that, at the best condition, methane is produced in a similar way from the acetoclastic and hydrogenotrophic routes. A scheme of four parallel reactors with a volume of 16,950 m{sup 3} each was proposed in the scale-up estimation, with an energy recovery estimated in 28,745 MWh per month.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Hydrometeorological sensitivities of net ecosystem carbon dioxide and methane exchange of an Amazonian palm swamp peatland

Here, we report ecosystem-scale CO 2 and CH 4 flux observations for an Amazonian palm swamp peatland over a two-year period in relation to hydrometeorological forcings. Seasonal and short-term variations in hydrometeorological forcing had a strong effect on carbon dioxide and methane fluxes. High air temperature and vapor pressure deficit exerted an important limitation on photosynthesis during the dry season, while latent heat flux appeared to be insensitive to these climate drivers. Evidence from light-response analyses and flux partitioning support that photosynthetic activity was downregulated during dry conditions, while ecosystem respiration was either inhibited or enhanced depending on water table position. The cumulative net ecosystem carbon dioxide exchange indicated that the peatland was a significant carbon dioxide sink ranging from –465 (–279 to –651) g C m -2 y -1 in 2018 to –462 (–277 to –647) g C m -2 y -1 in 2019. The forest was a methane source of 22 (20 to 24) g C m -2 y -1 , similar in magnitude to other tropical peatlands and larger than boreal and arctic peatlands. Furthermore, the annual carbon budget of this Amazonian palm swamp peatland appears to be a major carbon sink under current hydrometeorological conditions, but evidence indicates that the sink strength is vulnerable to future climate change.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

A re-examination of the catalyst activation and temperature hysteresis in methane combustion on Pt/Al 2 O 3

Methane combustion is an industrially important reaction that has been extensively studied. Supported Pt catalysts on Al 2 O 3 exhibit excellent activity in this reaction owing to their Csingle bondH bond activation capability. Pt/Al 2 O 3 catalyst remains almost inactive until the conversion increases abruptly at the ignition temperature (T ign ). The temperature hysteresis behavior has been reported, where after ignition, as the temperature is lowered below T ign , the catalyst continues to exhibit high activity. The activation has been previously attributed to the removal of adsorbed oxygen on Pt sites at T ign , while the hysteresis has been explained by the local temperature elevation caused by the reaction heat. Here in this work, this behavior was re-examined at a small scale in a fixed-bed flow reactor over a range of pre-treatment and reaction mixture conditions. Low-temperature activation was achieved by pre-treating the catalyst with CH 4 . Carefully designed control experiments yielded observations that cannot be rationalized by the existing theory, suggesting that it is incomplete. Based on these new results, we propose a more comprehensive theory describing the active sites in the oxidation reaction as methane-derived adsorbed carbon active sites, and their formation as the controlling factor in the catalyst activation. The hysteresis can be better explained by the enhanced stability of active sites under reaction conditions. In situ infrared spectroscopy and mass spectrometry studies were conducted in a flow cell, providing strong evidence supporting the theory. The dissociative adsorption of CH 4 was studied under a variety of pre-treatment conditions, and proved to be responsible for the active site formation. The fundamental understanding obtained in this work contributes significant insights to the understanding of reaction mechanism.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗