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1.6 Micron Fiber Laser Source for CH <sub/>4</sub> Gas Leak Detection
摘要： We report on the development of a new pulsed fiber laser source at 1645.5 nm, based on stimulated Raman amplification. This laser source is intended to be used in a future lidar system, dedicated to methane gas leak monitoring in the vicinity of industrial facilities. In this paper we discuss reasons for choosing the 1645.5 nm wavelength, and then we present the two-stage amplification architecture of our fiber laser source under development. Recent experimental results and perspectives are drawn.
关键词： Raman amplification,fiber laser,methane gas leak detection,lidar
更新于2025-09-23 15:19:57
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Study on the Simultaneous Measurement of O <sub/>2</sub> and CO Concentrations in the Exhaust Gas of a Methane/Air Flame Using Tunable Diode Laser Absorption Spectroscopy
摘要： Oxygen (O2) and carbon monoxide (CO) are produced in combustion reactions and are important gas species, which are closely related to combustion efficiency and production of air pollutants. O2 generates thermal nitrogen oxide (NOX) by reacting with nitrogen in the air at high temperatures, and the presence of excess O2 also affects the energy efficiency due to increasing exhaust heat energy. CO is generally well known for being a toxic gas, and is a crucial gas species produced by incomplete combustion. However, it is difficult to measure O2 and CO level variations in a huge combustion system, such as used in steel annealing and power plant boilers, because of their harsh environment. Therefore, as a multi-species measurement technique, which is non-intrusive, has a high sensitivity, and high response, tunable diode laser absorption spectroscopy was chosen as the optical method used to measure O2 and CO concentrations in exhaust gases. In this study, experiments were carried out to measure the O2 and CO concentrations in an electrical furnace and a combustion system using direct absorption spectroscopy and wavelength modulation spectroscopy. The measured results were compared with those of a gas analyzer of the electro-chemical (E/C) sensor type. The O2 and CO concentrations were measured in the exhaust gas produced from methane/air flame through adjustment of the equivalence ratio to form both, fuel-lean and rich conditions. In order to measure the O2 and CO concentrations precisely and without interference from other combustion products, visible and near-infrared wavelength regions at 760.8 and 2325.2 nm were selected, respectively.
关键词： Carbon Monoxide,Absorption Spectroscopy,Methane,Oxygen
更新于2025-09-23 15:19:57
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Repeatability and Reproducibility of Measures of Bovine Methane Emissions Recorded using a Laser Detector
摘要： Methane (CH4) emissions represent a worldwide problem due to their direct involvement in atmospheric warming and climate change. Ruminants are among the major players in the global scenario of CH4 emissions, and CH4 emissions are a problem for feed e?ciency since enteric CH4 is eructed to the detriment of milk and meat production. The collection of CH4 phenotypes at the population level is still hampered by costly and time-demanding techniques. In the present study, a laser methane detector was used to assess repeatability and reproducibility of CH4 phenotypes, including mean and aggregate of CH4 records, slope of the linear equation modelling the aggregate function, and mean and number of CH4 peak records. Five repeated measurements were performed in a commercial farm on three Simmental heifers, and the same protocol was repeated over a period of three days. Methane emission phenotypes expressed as parts per million per linear meter (ppm × m) were not normally distributed and, thus, they were log-transformed to reach normality. Repeatability and reproducibility were calculated as the relative standard deviation of ?ve measurements within the same day and 15 measurements across three days, respectively. All phenotypes showed higher repeatability and reproducibility for log-transformed data compared with data expressed as ppm × m. The linear equation modelling the aggregate function highlighted a very high coe?cient of determination (≥0.99), which suggests that daily CH4 emissions might be derived using this approach. The number of CH4 peaks resulted as particularly diverse across animals and therefore it is a potential candidate to discriminate between high and low emitting animals. Results of this study suggest that laser methane detector is a promising tool to measure bovine CH4 emissions in ?eld conditions.
关键词： sustainability,e?ciency,environment,methane emission
更新于2025-09-23 15:19:57
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Phosphorene as H <sub/>2</sub> S and CH <sub/>4</sub> Gas Sensor
摘要： First-principle calculations within density functional theory are carried out to investigate the adsorption of various gas molecules, including hydrogen sulfide and methane on two-dimensional monolayer phosphorene in order to fully exploit the gas sensing capabilities. The adsorption properties of different molecules in the environment on monolayer phosphorene base material is discussed in terms of the Mulliken charge transfer, energy band gap, adsorption energy. The prominent adsorption sites of methane, hydrogen sulfide, water, and oxygen on monolayer phosphorene are investigated at an atomistic level. Based on the results the transport properties of monolayer phosphorene exposed to these gas molecules are investigated both in zigzag and armchair direction using non-equilibrium Green function tuned with density functional theory. The results show that using both directions simultaneously as gas sensing can be an effective technique to distinguish hydrogen sulfide and methane gas molecules from others and demonstrate great selectivity.
关键词： phosphorene,methane,Green function,density functional theory,transport properties,device,hydrogen sulfide,gas sensors
更新于2025-09-23 15:19:57
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Selectively Photocatalytic Oxidation of Low Concentration Methane over Graphitic Carbon Nitride Decorated Tungsten Bronze Cesium
摘要： Although the traditional thermal catalysis is usually used to convert the methane into value-added products, its high reaction temperature results in low performance-price ratio in conversion of low concentration methane. In this regard, we synthesized a series of mace-like g-C3N4 decorated Cs0.33WO3 nanocomposites for photocatalytic conversion of low concentration methane under mild conditions. The optimized g-C3N4@Cs0.33WO3 (weight ratio = 3:7) photocatalyst selectively converted low concentration methane (1000 ppm) into methanol with yield of 4.38 μmol/h/g under light irradiation and at room temperature. Both performance experiments and trapping experiments verified that the methane activation and methyl oxidation involved in photocatalytic conversion process of methane. The ?O2- firstly activated the methane to methyl on the surface of the g-C3N4 in the composite and then the photogenerated electrons from the Cs0.33WO3 in the composite inhibited the peroxidation and increased the generation of methanol. This research provides a new route to design and synthesize photocatalysts for converting methane into value-added chemicals.
关键词： Selective Conversion,Low concentration methane,Tungsten Bronze Cesium,Photocatalytic Methane Conversion,Graphic Carbon Nitride
更新于2025-09-19 17:15:36
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Speed-dependent line mixing in the ν3 band Q branch of methane
摘要： In 1992, we reported high-resolution spectra of the Q branch of the CH4 ν3 band from the Doppler limit to pressures of 500 Torr for various buffer gases recorded with a tunable difference-frequency laser. For P ≤ 100 Torr, the individual transitions were well enough resolved to be fit with simple Dicke-narrowed lineshapes, but at higher pressures, line mixing among the severely blended lines prevented further analysis. Subsequently, using a simultaneous multispectrum analysis, we were able to fit the full range of pressures quite satisfactorily with Dicke-narrowed first-order line-mixing profiles. We also tested scaled model relaxation W-matrix mixing and hypergeometric speed-dependent broadening, but found only minimal improvement not worth the computational complications and increased processing time. Since then, fast quadratic speed-dependence algorithms have been developed, and simplified W-matrix methods involving selected-coupled-doublets have been demonstrated, recently for this same Q branch. Therefore, we have reexamined these newer developments on our higher resolution spectra and found that the improved efficiency is tempered by a strong competition between Dicke narrowing and speed dependence and by a deteriorated fit using only selected-coupled-doublets. A detailed comparative study is reported here, along with some new models proposed and tested for truncating the W-matrix and for a hybrid combination of first-order mixing with selected W-matrix elements.
关键词： Dicke narrowing,Speed-dependent broadening,Non-Voigt effects,Line mixing,Self and foreign-gas-broadened methane
更新于2025-09-19 17:15:36
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Plasmonic photocatalysis applied to solar fuels
摘要： The induction of chemical processes by plasmonic systems is a rapidly growing field with potentially many strategic applications. One of them is the transformation of solar energy into chemical fuel by the association of plasmonic metal nanoparticles (M NPs) and a semi-conductor (SC). When the localized surface plasmon resonance (LSPR) and the SC absorption do not match, one limitation of these systems is the efficiency of hot electron transfer from M NPs to SC through the Schottky barrier formed at the M NPs/SC interfaces. Here we show that high surface area 1wt.%Au/TiO2-UV100, prepared by adsorption of a NaBH4-protected 3 nm gold sol, readily catalyzes the photoreduction of carbon dioxide with water into methane under both solar and visible-only irradiations with a CH4 vs. H2 selectivity of 63%. Tuning Au NPs size and titania surface area, in particular via thermal treatments, highlights the key role of the metal dispersion and of the accessible Au-TiO2 perimeter interface on the direct SC-based solar process. The impact of Au NPs density in turn evidences the dual role of gold as co-catalyst and recombination sites for charge carriers. It is shown that the plasmon-induced process contributes up to 20% of the solar activity. The plasmon-based contribution is enhanced by a large Au NP size and a high degree of crystallinity of the SC support. By minimizing surface hydroxylation while retaining a relatively high surface area of 120 m2 g-1, pre-calcining TiO2-UV100 at 450°C leads to an optimum monometallic system in terms of activity and selectivity under both solar and visible irradiation. A state-of-the-art methane selectivity of 100% is achieved in the hot electron process.
关键词： Methane production,Gold nanoparticles,Titania,Selectivity,CO2 reduction,Hot electrons,Plasmonic photocatalysis,Solar fuels
更新于2025-09-19 17:15:36
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Direct functionalization of methane into ethanol over copper modified polymeric carbon nitride via photocatalysis
摘要： Direct valorization of methane to its alcohol derivative remains a great challenge. Photocatalysis arises as a promising green strategy which could exploit hydroxyl radical (·OH) to accomplish methane activation. However, both the excessive ·OH from direct H2O oxidation and the neglect of methane activation on the material would cause deep mineralization. Here we introduce Cu species into polymeric carbon nitride (PCN), accomplishing photocatalytic anaerobic methane conversion for the first time with an ethanol productivity of 106 μmol gcat?1 h?1. Cu modified PCN could manage generation and in situ decomposition of H2O2 to produce ·OH, of which Cu species are also active sites for methane adsorption and activation. These features avoid excess ·OH for overoxidation and facilitate methane conversion. Moreover, a hypothetic mechanism through a methane-methanol-ethanol pathway is proposed, emphasizing the synergy of Cu species and the adjacent C atom in PCN for obtaining C2 product.
关键词： methane conversion,photocatalysis,polymeric carbon nitride,ethanol production,copper modification
更新于2025-09-19 17:15:36
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Synergy of the catalytic activation on Ni and the CeO <sub/>2</sub> –TiO <sub/>2</sub> /Ce <sub/>2</sub> Ti <sub/>2</sub> O <sub/>7</sub> stoichiometric redox cycle for dramatically enhanced solar fuel production
摘要： Solar thermochemical approaches to CO2 and H2O splitting have emerged as an attractive pathway to solar fuel production. However, efficiently producing solar fuel with high redox kinetics and yields at lower temperature remains a major challenge. In this study, Ni promoted ceria–titanium oxide (CeO2–TiO2) redox catalysts were developed for highly effective thermochemical CO2 and H2O splitting as well as partial oxidation of CH4 at 900 1C. Unprecedented CO and H2 production rates and productivities of about 10–140 and 5–50 times higher than the current state-of-the-art solar thermochemical carbon dioxide splitting and water splitting processes were achieved with simultaneous close to complete CH4 conversions and high selectivities towards syngas. The underlying mechanism for the exceptional reaction performance was investigated by combined experimental characterization and density functional theory (DFT) calculations. It is revealed that the metallic Ni and the Ni/oxide interface manifest catalytic activity for both CH4 activation and CO2 or H2O dissociation, whereas CeO2–TiO2 enhances the lattice oxygen transport via the CeO2–TiO2/Ce2Ti2O7 stoichiometric redox cycle for CH4 partial oxidation and the subsequent CO2 or H2O splitting promoted by catalytically active Ni. Such findings substantiate the significance of the synergy between the reactant activation by catalytic sites and the stoichiometric redox chemistry governing oxygen ion transport, paving the way for designing prospective materials for sustainable solar fuel production.
关键词： thermochemical CO2 splitting,solar fuel production,density functional theory,Ni promoted ceria–titanium oxide,thermochemical H2O splitting,methane partial oxidation,redox catalysts
更新于2025-09-19 17:15:36
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Single Crystal Diamond Deposited by Dual Radio-Frequency Plasma Jet CVD with High Growth Rate
摘要： Single crystal diamonds were deposited on high pressure high temperature (HPHT) substrate with high growth rate, up to 18.5 μm/h, by using dual radio-frequency inductive coupled plasma jet. The methane ?ux was found to in?uence the growth rate of single crystal diamond. The reason for this might be ascribed to the electron temperature increase, raising the ?ux of methane, based on the plasma diagnosis results by optical emission spectra (OES). The results of Raman spectroscopy and the X-ray rocking-curve indicated that as-deposited diamonds are of good quality.
关键词： growth rate,single crystal diamond,methane ?ux,dual radio frequency,chemical vapor deposition (CVD),inductive coupled plasma jet
更新于2025-09-19 17:15:36